Electrostatic image developer, process cartridge, image forming apparatus and image forming method

Abstract

To provide an electrostatic charge image developer which is excellent in density change suppression even when high density printing is performed after printing with a small image amount has been continuously performed.SOLUTION: An electrostatic charge image developer has: a toner which contains a binder resin and a release agent, and has toner particles having an exposure rate of the release agent of 15% or more and 30% or less; and a carrier which has magnetic particles, and a resin coating layer coating the magnetic particles and containing inorganic particles, has an arithmetic average particle diameter of the inorganic particles of 5 nm or more and 90 nm or less and average thickness of the resin coating layer of 0.6 μm or more and 1.4 μm or less, and has a ratio B / A of an uneven surface area B to a planar view area A of an analysis region when fine uneven structure surface roughness of the carrier surface is three-dimensionally analyzed of 1.020 or more and 1.100 or less.SELECTED DRAWING: None

Description

[Technical field]

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

[0002] Patent Document 1 discloses a two-component developer comprising a toner and a carrier, the toner comprising colored resin particles having a volume average particle size of 4 to 9 μm and including a hydrocarbon wax having a melting point of 64 to 77°C, and an external additive having a number average particle size of 80 to 300 nm, the carrier comprising coated core particles having a volume average particle size of 25 to 60 μm and including core particles made of a ferrite component and a coating layer of a thermosetting straight silicone resin provided on the surface of the core particles, the intensity ratio Si / Fe between the X-ray intensity of Si and the X-ray intensity of Fe measured by fluorescent X-ray analysis of the coated core particles being 0.01 or more and 0.03 or less. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2009-069502 A Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present invention is to provide an electrostatic image developer which comprises a toner having toner particles with an exposure rate of a release agent of 15% or more and 30% or less, and a carrier having magnetic particles and a resin coating layer which coats the magnetic particles and contains inorganic particles, the inorganic particles having an average particle size of 5 nm or more and 90 nm or less, and the resin coating layer having an average thickness of 0.6 μm or more and 1.4 μm or less, and which, when the surface roughness of the fine uneven structure of the carrier surface is analyzed in three dimensions, suppresses a decrease in image density which occurs when images of low image density are continuously formed, compared to when the ratio B / A of the planar view area A of the analyzed region to the uneven surface area B is less than 1.020 or exceeds 1.100. [Means for solving the problem]

[0005] Means for solving the above problems include the following aspects. <1> An electrostatic image developer comprising: a toner having toner particles which contain a binder resin and a release agent, and in which an exposure rate of the release agent is 15% or more and 30% or less; and a carrier which has magnetic particles and a resin coating layer which coats the magnetic particles and contains inorganic particles, wherein the inorganic particles have an arithmetic average particle size of 5 nm or more and 90 nm or less, and the resin coating layer has an average thickness of 0.6 μm or more and 1.4 μm or less, and when a surface roughness of a fine uneven structure of the carrier surface is analyzed in three dimensions, a ratio B / A of a planar view area A of an analyzed region to an uneven surface area B is 1.020 or more and 1.100 or less. <2> The ratio B / A is 1.040 or more and 1.080 or less. <1> Electrostatic image developer according to claim 1. <3> The inorganic particles have an arithmetic mean particle size of 5 nm or more and 70 nm or less. <1> or <2> Electrostatic image developer according to claim 1. <4> The average thickness of the resin coating layer is 0.8 μm or more and 1.2 μm or less. <1> ~ <3> 13. The electrostatic image developer according to claim 12, <5> The toner contains an external additive, and the inorganic particles have the same charge polarity as the external additive. <1> ~ <4> 13. The electrostatic image developer according to claim 12, <6> The inorganic particles are inorganic oxide particles. <1> ~ <5> 13. The electrostatic image developer according to claim 12, <7> The inorganic particles are silica particles, and the silicon element concentration on the surface of the carrier determined by X-ray photoelectron spectroscopy is more than 2 atomic % and less than 20 atomic %. <1> ~ <6> 13. The electrostatic image developer according to claim 12, <8> The silicon element concentration is more than 5 atomic % and less than 20 atomic %. <7> Electrostatic image developer according to claim 1. <9> The content of the inorganic particles is 10% by mass or more and 60% by mass or less with respect to the total mass of the resin coating layer. <1> ~ <8> 13. The electrostatic image developer according to claim 12, <10> The weight average molecular weight of the resin contained in the resin coating layer is less than 300,000. <1> ~ <9> 13. The electrostatic image developer according to claim 12, <11> The weight average molecular weight of the resin contained in the resin coating layer is less than 250,000. <10> Electrostatic image developer according to claim 1. <12> The arithmetic mean height Ra of the roughness curve of the magnetic particles is 0.3 μm or more and 1.2 μm or less. <1> ~ <11> 13. The electrostatic image developer according to claim 12, <13> <1> ~ <12> 1. A process cartridge detachably mounted to an image forming apparatus, comprising: a developing unit that contains the electrostatic image developer according to any one of claims 1 to 9; and that develops an electrostatic image formed on a surface of an image carrier into a toner image by the electrostatic image developer. <14> an image carrier; a charging means for charging a surface of the image carrier; and an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier; <1> ~ <12> and a developing unit that uses the electrostatic image developer to develop an electrostatic image formed on the surface of the image carrier into a toner image; a transfer unit that transfers the toner image formed on the surface of the image carrier to a surface of a recording medium; and a fixing unit that fixes the toner image transferred to the surface of the recording medium. <15> a charging step of charging a surface of an image carrier; and an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier. <1> ~ <12> a developing step of developing an electrostatic image formed on the surface of the image carrier as a toner image by using the electrostatic image developer according to any one of the above items 1 to 5; a transferring step of transferring the toner image formed on the surface of the image carrier to a surface of a recording medium; and a fixing step of fixing the toner image transferred to the surface of the recording medium. Effect of the Invention

[0006] <1> or <6> According to the invention, an electrostatic image developer is provided which includes a toner having toner particles with an exposure rate of a release agent of 15% or more and 30% or less, and a carrier having magnetic particles and a resin coating layer that coats the magnetic particles and contains inorganic particles, the inorganic particles having an arithmetic average particle size of 5 nm or more and 90 nm or less, and an average thickness of the resin coating layer of 0.6 μm or more and 1.4 μm or less, and which, when the surface roughness of the fine uneven structure of the carrier surface is analyzed in three dimensions, suppresses a decrease in image density that occurs when low-density images are continuously formed, compared to when the ratio B / A of the planar view area A of the analyzed region to the uneven surface area B is less than 1.020 or exceeds 1.100. <2> According to the present invention, there is provided an electrostatic image developer which more effectively suppresses the decrease in image density that occurs when images of low image density are continuously formed, as compared with the case where the ratio B / A is less than 1.040 or exceeds 1.080. <3> According to the present invention, there is provided an electrostatic image developer which more effectively suppresses the decrease in image density that occurs when images of low image density are continuously formed, compared to when the arithmetic mean particle size of the inorganic particles is less than 5 nm or exceeds 70 nm. <4> According to the present invention, there is provided an electrostatic image developer which more effectively suppresses the decrease in image density that occurs when images of low image density are continuously formed, compared to when the average thickness of the resin coating layer is less than 0.8 μm or exceeds 1.2 μm. <5> According to the present invention, there is provided an electrostatic image developer which more effectively suppresses the decrease in image density that occurs when images of low image density are continuously formed, compared to when the inorganic particles are particles having a different charging polarity from the external additive. <7> According to the invention, there is provided an electrostatic image developer which further suppresses the decrease in image density that occurs when images of low image density are continuously formed, compared to when the inorganic particles are silica particles and the silicon element concentration on the carrier surface determined by X-ray photoelectron spectroscopy is 2 atomic% or less or 20 atomic% or more. <8> According to the present invention, there is provided an electrostatic image developer which more effectively suppresses the decrease in image density that occurs when images of low image density are continuously formed, compared to when the silicon element concentration is 5 atomic % or less or 20 atomic % or more. <9> According to the present invention, there is provided an electrostatic image developer which more effectively suppresses a decrease in image density that occurs when images of low image density are continuously formed, compared to when the content of the inorganic particles is less than 10 mass % or more than 60 mass % relative to the total mass of the resin coating layer. <10> According to the present invention, there is provided an electrostatic image developer which more effectively suppresses the decrease in image density that occurs when images of low image density are continuously formed, compared to when the weight average molecular weight of the resin contained in the resin coating layer is 300,000 or more. <11> According to the present invention, there is provided an electrostatic image developer which more effectively suppresses the decrease in image density that occurs when images of low image density are continuously formed, compared to when the weight average molecular weight of the resin contained in the resin coating layer is 250,000 or more. <12> According to the present invention, there is provided an electrostatic image developer which more effectively suppresses the decrease in image density that occurs when low-density images are continuously formed, compared to when the arithmetic mean height Ra of the roughness curve of the magnetic particles is less than 0.3 μm or exceeds 1.2 μm. <13> ~ <15> According to the invention, in an electrostatic image developer having a toner having toner particles with an exposure rate of a release agent of 15% or more and 30% or less, and a carrier having magnetic particles and a resin coating layer that coats the magnetic particles and contains inorganic particles, the inorganic particles having an arithmetic average particle size of 5 nm or more and 90 nm or less, and an average thickness of the resin coating layer of 0.6 μm or more and 1.4 μm or less, when the surface roughness of the fine uneven structure of the carrier surface is analyzed in three dimensions, the ratio B / A of the planar view area A of the analyzed region to the uneven surface area B of the analyzed region is less than 1.020 or exceeds 1.100, and a process cartridge, image forming apparatus, or image forming method is provided that suppresses a decrease in image density that occurs when images of low image density are formed continuously. [Brief description of the drawings]

[0007] [Figure 1]1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Diagram 2] FIG. 2 is a schematic diagram illustrating an example of a process cartridge that is detachably mounted to the image forming apparatus according to the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0008] Hereinafter, embodiments of the present disclosure will be described. These descriptions and examples are merely illustrative of the embodiments, and are not intended to limit the scope of the embodiments.

[0009] In the present disclosure, a numerical range indicated using "~" indicates a range that includes the numerical values ​​before and after "~" as the minimum and maximum values, respectively.

[0010] In the numerical ranges described in the present disclosure in stages, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in the present disclosure, the upper or lower limit value of the numerical range may be replaced with a value shown in the examples.

[0011] In the present disclosure, the term "step" includes not only an independent step, but also a step that cannot be clearly distinguished from other steps, as long as the intended purpose of the step is achieved.

[0012] When an embodiment of the present disclosure is described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. In addition, the size of the members in each drawing is conceptual, and the relative relationship between the sizes of the members is not limited to this.

[0013] In the present disclosure, each component may contain multiple types of corresponding substances. When referring to the amount of each component in a composition in the present disclosure, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified.

[0014] In the present disclosure, the particles corresponding to each component may include multiple types. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0015] In the present disclosure, "(meth)acrylic" means at least one of acrylic and methacrylic, and "(meth)acrylate" means at least one of acrylate and methacrylate.

[0016] In this disclosure, "toner for developing electrostatic images" is also referred to as "toner", "carrier for developing electrostatic images" is also referred to as "carrier", and "electrostatic image developer" is also referred to as "developer".

[0017] (Electrostatic image developer) The electrostatic image developer according to the present embodiment comprises a toner having toner particles that contain a binder resin and a release agent, and an exposure rate of the release agent being 15% or more and 30% or less, and a carrier having magnetic particles and a resin coating layer that coats the magnetic particles and contains inorganic particles, wherein the inorganic particles have an arithmetic average particle size of 5 nm or more and 90 nm or less, and the resin coating layer has an average thickness of 0.6 μm or more and 1.4 μm or less, and when the surface roughness of the fine uneven structure of the carrier surface is analyzed in three dimensions, the ratio B / A of the planar view area A of the analyzed region to the uneven surface area B is 1.020 or more and 1.100 or less.

[0018] In this embodiment, carbon black is not considered to be an inorganic particle.

[0019] The electrostatic image developer according to the present embodiment suppresses the decrease in image density that occurs when low-density images are continuously formed. The mechanism by which this occurs is presumed to be as follows.

[0020] In order to prevent offset during fixing, a toner is used in which the amount of exposed release agent on the toner surface is controlled. In the continuous output of high-density images in which a large amount of toner is developed, the free external additives adhere to the exposed part of the release agent on the toner surface, which makes it easier to suppress the release agent from contaminating the carrier surface. However, the present inventors have found that when continuous output of low image density continues (for example, when 50,000 sheets of A4 paper with an area coverage of 5%), the free external additives become embedded in the release agent exposed on the toner surface, causing the release agent on the toner surface to adhere to the carrier surface, impairing triboelectric charging, making it difficult to obtain a stable image density, and causing a decrease in image density. When the electrostatic image developer according to the present embodiment is used, due to the above-mentioned aspect, the toner and carrier come into contact with each other mostly at points, making it possible to reduce the area where the release agent on the toner surface adheres to the carrier surface. It is therefore presumed that even a toner having a large amount of exposed release agent on its surface can be imparted with an appropriate triboelectric charge, thereby suppressing the decrease in image density that occurs when low-density images are continuously formed (hereinafter also referred to as "image density change suppression").

[0021] The configuration of the electrostatic image developer according to this embodiment will be described in detail below.

[0022] <Career> The electrostatic image developer according to this embodiment has magnetic particles and a resin coating layer that coats the magnetic particles and contains inorganic particles, the inorganic particles having an arithmetic mean particle size of 5 nm or more and 90 nm or less, the resin coating layer having an average thickness of 0.6 μm or more and 1.4 μm or less, and when the surface roughness of the fine uneven structure of the carrier surface is analyzed in three dimensions, the ratio B / A of the planar area A of the analyzed region to the uneven surface area B is 1.020 or more and 1.100 or less.

[0023] <<The ratio B / A, where A is the planar area and B is the surface area, when the carrier surface is analyzed in three dimensions>> The carrier used in this embodiment has a ratio B / A of the planar area A to the surface area B when the carrier surface is analyzed in three dimensions, which is 1.020 or more and 1.100 or less, and from the viewpoint of suppressing image density change, is preferably 1.040 or more and 1.080 or less, and more preferably 1.040 or more and 1.070 or less.

[0024] In this embodiment, the ratio B / A is an index for evaluating the surface roughness. As an example, the ratio B / A can be determined by the following method. As a device for three-dimensionally analyzing the carrier surface, a scanning electron microscope having four secondary electron detectors (for example, ERA-8900FE, electron beam three-dimensional roughness analyzer manufactured by Elionix Co., Ltd.) is used, and the analysis is performed as follows. The surface of one carrier particle is magnified 5,000 times. The measurement points are spaced 0.06 μm apart, 400 points are measured along the long side and 300 points along the short side, and an area of ​​24 μm x 18 μm is measured to obtain 3D image data. For the three-dimensional image data, the limit wavelength of a spline filter (a frequency-selective filter that uses a spline function) is set to 12 μm to remove wavelengths with a period of 12 μm or more, thereby removing the waviness components of the carrier surface, extracting the roughness components, and obtaining a roughness curve. Furthermore, the cutoff value of a Gaussian high-pass filter (a frequency-selective filter using a Gaussian function) is set to 2.0 μm to remove wavelengths with a period of 2.0 μm or more, thereby removing wavelengths corresponding to the convex parts of the magnetic particles exposed on the carrier surface from the roughness curve after spline filter processing, thereby obtaining a roughness curve from which wavelength components with a period of 2.0 μm or more have been removed. From the 3D roughness curve data after filtering, the central 12 μm × 12 μm area (planar area A = 144 μm 2 ) surface area B (μm 2 ) and calculate the ratio B / A. Calculate the ratio B / A for each of 100 carriers and take the arithmetic average.

[0025] <<Magnetic particles>> The carrier used in this embodiment has magnetic particles and a resin coating layer that coats the magnetic particles.

[0026] As the material of the magnetic particles, a known material used as the core material of the carrier is applied. Specific examples of 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. In this embodiment, ferrite particles are preferred as the magnetic particles.

[0027] From the viewpoint of suppressing a change in image density, the volume average particle size of the magnetic particles is preferably from 15 μm to 100 μm, more preferably from 20 μm to 80 μm, and even more preferably from 30 μm to 60 μm. The volume average particle diameter of the magnetic particles and carrier in this embodiment is a value measured by a laser diffraction particle size distribution measuring device LA-700 (manufactured by Horiba, Ltd.) Specifically, for a particle size range (channel) into which the particle size distribution obtained by the measuring device is divided, the particle diameter at which the cumulative volume distribution is subtracted from the small particle size side and the cumulative 50% is defined as the volume average particle diameter. A suitable method for separating the magnetic particles from the carrier is to dissolve the resin coating layer with an organic solvent and separate the magnetic particles. Another suitable method is the method described below for measuring the BET specific surface area.

[0028] The arithmetic mean height Ra (JIS B0601:2001) of the roughness curve of the magnetic particles is preferably from 0.1 μm to 1.5 μm, more preferably from 0.2 μm to 1.3 μm, and particularly preferably from 0.3 μm to 1.2 μm. The arithmetic mean height Ra of the roughness curve of a magnetic particle is determined by observing the magnetic particle at an appropriate magnification (for example, 1000x magnification) using a surface shape measuring device (for example, Keyence Corporation's "Ultra-Deep Color 3D Shape Measuring Microscope VK-9700"), obtaining a roughness curve at a cutoff value of 0.08 mm, and extracting a reference length of 10 μm from the roughness curve in the direction of the average line. The Ra of 100 magnetic particles is calculated as the arithmetic mean.

[0029] The magnetic force of the magnetic particles is preferably 50 emu / g or more, more preferably 60 emu / g or more, in terms of saturation magnetization in a magnetic field of 3,000 oersteds. The saturation magnetization is measured using a vibrating sample magnetic measuring device VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.). The measurement sample is packed in a cell with an inner diameter of 7 mm and a height of 5 mm and set in the device. The measurement is performed by applying a magnetic field and sweeping up to a maximum of 3,000 oersteds. The applied magnetic field is then reduced, and a hysteresis curve is prepared on a recording paper. The saturation magnetization, residual magnetization, and retentivity are determined from the curve data.

[0030] The volume resistivity of magnetic particles is 1×10 5 Ω cm or more 1×10 9 Ω cm or less is preferable, and 1×10 7 Ω cm or more 1×10 9 Ω·cm or less is more preferable. The volume resistivity (Ω·cm) of magnetic particles is measured as follows: 2 The 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. In order to eliminate any gaps between the objects being measured, a 4 kg load is placed on the electrode plate placed on the layer, and then the thickness of the layer (cm) is measured. Both the top and bottom electrodes of 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 is 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 relative humidity of 50%. The formula for calculating the volumetric electrical resistivity (Ω·cm) of the object being measured is as shown below. R=E×20 / (I-I0) / L In the above formula, R is the volume resistivity (Ω cm) of the object to be measured, E is the applied voltage (V), I is the current value (A), I0 is the current value (A) at an applied voltage of 0 V, and L is the layer thickness (cm). The coefficient 20 is the area of ​​the electrode plate (cm 2 )

[0031] <<Resin coating layer>> The carrier used in this embodiment has magnetic particles and a resin coating layer that coats the magnetic particles and contains inorganic particles, the inorganic particles having an arithmetic mean particle size of 5 nm or more and 90 nm or less, and the resin coating layer having an average thickness of 0.6 μm or more and 1.4 μm or less.

[0032] The average thickness of the resin coating layer in this embodiment is from 0.6 μm to 1.4 μm, and from the viewpoint of suppressing image density change, is preferably from 0.8 μm to 1.2 μm, and more preferably from 0.8 μm to 1.1 μm.

[0033] The arithmetic average particle size of the inorganic particles in the resin coating layer is 5 nm or more and 90 nm or less, and from the viewpoint of suppressing image density change, it is preferably 8 nm or more and 70 nm or less, more preferably 5 nm or more and 50 nm or less, and particularly preferably 10 nm or more and 50 nm or less.

[0034] In this embodiment, the average particle size of the inorganic particles contained in the resin coating layer and the average thickness of the resin coating layer are determined by the following method. The carrier is embedded in epoxy resin and cut with a microtome to prepare a carrier cross section. The SEM image of the carrier cross section taken with a scanning electron microscope (SEM) is imported into an image processing analyzer for image analysis. 100 inorganic particles (primary particles) in the resin coating layer are randomly selected, and the circle equivalent diameter (nm) of each is determined and the arithmetic average is taken, which is the average particle size (nm) of the inorganic particles. In addition, 10 locations per carrier particle are randomly selected to measure the thickness (μm) of the resin coating layer, and further measurements are taken for 100 carriers, and all the values ​​are arithmetically averaged, which is the average thickness (μm) of the resin coating layer.

[0035] Examples of inorganic particles contained in the resin coating layer include metal oxide particles such as silica, titanium oxide, zinc oxide, and tin oxide; metal compound particles such as barium sulfate, aluminum borate, and potassium titanate; and metal particles such as gold, silver, and copper. Among these, from the viewpoint of suppressing a change in image density, inorganic oxide particles are preferable, and silica particles are more preferable.

[0036] In addition, when the toner contains an external additive, from the viewpoint of suppressing a change in image density, it is preferable that the inorganic particles are particles having the same charge polarity as the external additive.

[0037] The surface of the inorganic particles may be subjected to hydrophobic treatment. Examples of the hydrophobic treatment agent include known organosilicon compounds having an alkyl group (e.g., methyl group, ethyl group, propyl group, butyl group, etc.), and specific examples include alkoxysilane compounds, siloxane compounds, and silazane compounds. Among these, the hydrophobic treatment agent is preferably a silazane compound, and hexamethyldisilazane is preferable. The hydrophobic treatment agent may be used alone or in combination of two or more kinds.

[0038] Examples of methods for hydrophobizing inorganic particles with a hydrophobizing agent include a method in which supercritical carbon dioxide is used to dissolve the hydrophobizing agent in supercritical carbon dioxide and adhere the hydrophobizing agent to the surfaces of the inorganic particles; a method in which a solution containing a hydrophobizing agent and a solvent that dissolves the hydrophobizing agent is applied (e.g., sprayed or coated) to the surfaces of inorganic particles in the atmosphere to adhere the hydrophobizing agent to the surfaces of the inorganic particles; and a method in which a solution containing a hydrophobizing agent and a solvent that dissolves the hydrophobizing agent is added to an inorganic particle dispersion in the atmosphere, the solution is maintained, and then the mixed solution of the inorganic particle dispersion and the solution is dried.

[0039] From the viewpoint of suppressing image density change, the content of inorganic particles contained in the resin coating layer is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 55% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less, relative to the total mass of the resin coating layer. From the viewpoint of suppressing image density change, the content of silica particles contained in the resin coating layer is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 55% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less, relative to the total mass of the resin coating layer.

[0040] The silicon element concentration on the carrier surface of the carrier used in this embodiment, determined by X-ray photoelectron spectroscopy, is preferably more than 2 atomic% and less than 20 atomic%, more preferably more than 5 atomic% and less than 20 atomic%, and particularly preferably more than 6 atomic% and less than 19 atomic%, from the viewpoints of long-term image quality stability and suppression of image density change.

[0041] In this embodiment, the silicon element concentration on the carrier surface is measured by the following method. The carrier is used as a sample and analyzed by X-ray Photoelectron Spectroscopy (XPS) under the following conditions, and the silicon element concentration (atomic %) is calculated from the peak intensity of each element. XPS equipment: ULVAC-PHI, VersaProbe II Etching gun: Argon gun Acceleration voltage: 5kV Emission current: 20mA Sputtering area: 2mm x 2mm Sputtering rate: 3nm / min (SiO2 equivalent)

[0042] Examples of resins that make up 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 products thereof 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. In particular, from the viewpoints of electrostatic charge, control of external additive adhesion, and suppression of image density change, it is preferable that the resin constituting the resin coating layer contains an acrylic resin, it is more preferable that the acrylic resin is contained in an amount of 50 mass% or more based on the total mass of the resin in the resin coating layer, and it is particularly preferable that the acrylic resin is contained in an amount of 80 mass% or more based on the total mass of the resin in the resin coating layer.

[0043] From the viewpoint of suppressing image density change, the resin coating layer preferably contains an acrylic resin having an alicyclic structure. As a polymerization component of the acrylic resin having an alicyclic structure, a lower alkyl ester of (meth)acrylic acid (for example, an alkyl (meth)acrylic acid ester having 1 to 9 carbon atoms in the alkyl group) is preferable, and specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. These monomers may be used alone or in combination of two or more. The acrylic resin having an alicyclic structure preferably contains cyclohexyl (meth)acrylate as a polymerization component. The content of the monomer unit derived from cyclohexyl (meth)acrylate contained in the acrylic resin having an alicyclic structure is preferably 75% by mass or more and 100% by mass or less, more preferably 85% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on the total mass of the acrylic resin having an alicyclic structure.

[0044] The weight average molecular weight of the resin contained in the resin coating layer is preferably less than 300,000, more preferably less than 250,000, even more preferably from 5,000 to less than 250,000, and particularly preferably from 10,000 to 200,000. When in the above range, the abrasion resistance of the resin coating layer is improved, and appropriate triboelectric charging can be imparted over a long period of time, resulting in superior suppression of image density change.

[0045] The resin coating layer may contain conductive particles for the purpose of controlling electrostatic charge and resistance. Examples of the conductive particles include carbon black and the above-mentioned inorganic particles having electrical conductivity.

[0046] 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 above solvent.

[0047] 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 surfaces of magnetic particles, a fluidized bed method in which magnetic particles are fluidized in a fluidized bed and then sprayed with a resin liquid for forming a resin coating layer, and a kneader coater method in which magnetic particles are mixed with a resin liquid for forming a resin coating layer in a kneader coater and the solvent is removed. These manufacturing methods may be repeated or combined. The resin liquid for forming the resin coating layer used in the wet manufacturing method is prepared by dissolving or dispersing the resin, inorganic particles, and other components in a solvent. The solvent is not particularly limited, 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.

[0048] An example of the 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.

[0049] The ratio B / A can be controlled by the manufacturing conditions. For example, in a manufacturing method in which the kneader-coater method is repeated multiple times (e.g., twice) to form a resin coating layer in stages, the mixing time of the particles to be coated and the resin liquid for forming the resin coating layer in the final kneader-coater process is adjusted to control the ratio B / A. The longer the mixing time in the final kneader-coater process, the smaller the ratio B / A tends to be. In another example, in a production method in which a liquid composition containing inorganic particles (which may or may not contain resin) is applied by a spray method to the surface of a resin-coated carrier produced by a kneader coater method, the particle size and content of the inorganic particles contained in the liquid composition, or the amount of the liquid composition applied to the resin-coated carrier, is adjusted to control the ratio B / A.

[0050] The exposed area ratio of the magnetic particles on the carrier surface is preferably 5% to 30%, more preferably 7% to 25%, and even more preferably 10% to 25%. The exposed area ratio of the magnetic particles on the carrier can be controlled by the amount of resin used to form the resin coating layer, and the greater the amount of resin relative to the amount of magnetic particles, the smaller the exposed area ratio.

[0051] The exposed area ratio of the magnetic particles on the carrier surface is a value determined by the following method. A target carrier and magnetic particles from which the resin coating layer has been removed from the target carrier are prepared. Methods for removing the resin coating layer from the carrier include, for example, a method for removing the resin coating layer by dissolving the resin component with an organic solvent, and a method for removing the resin coating layer by eliminating the resin component by heating at about 800°C. The carrier and magnetic particles are each used as measurement samples, and the Fe concentration (atomic%) on the sample surface is quantified by XPS, and the exposed area ratio (%) of the magnetic particles is calculated by (Fe concentration of the carrier)÷(Fe concentration of the magnetic particles)×100.

[0052] From the viewpoint of suppressing concentration change, the volume average particle size of the carrier is preferably from 25 μm to 36 μm, more preferably from 26 μm to 35 μm, and particularly preferably from 28 μm to 34 μm.

[0053] The mixture ratio (mass ratio) of the carrier to the toner in the developer is preferably from 100:1 to 100:30, more preferably from 100:3 to 100:20.

[0054] <Toner> The toner used in the present embodiment contains a binder resin and a release agent, and has toner particles in which the exposure rate of the release agent is 15% or more and 30% or less. The toner used in the present embodiment preferably contains toner particles and an external additive.

[0055] <<Toner particles>> The toner particles are configured to contain, for example, a binder resin, a release agent, and, if necessary, a colorant and other additives.

[0056] -Binding resin- Examples of the binder resin include vinyl resins made of 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.), or 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 coexistence of these. These binder resins may be used alone or in combination of two or more kinds.

[0057] The binder resin is preferably a polyester resin. The polyester resin may be, for example, a known amorphous polyester resin. The polyester resin may be used in combination with a crystalline polyester resin together with the amorphous polyester resin. However, the content of the crystalline polyester resin is preferably in the range of 2% by mass to 40% by mass (preferably 2% by mass to 20% by mass) based on the total binder resin.

[0058] The "crystallinity" of a resin refers to the presence of a clear endothermic peak rather than a stepwise change in the amount of endothermic heat in differential scanning calorimetry (DSC); specifically, it refers to the half-width of the endothermic peak being within 10°C when measured at a heating rate of 10 (°C / min). On the other hand, the term "amorphous" for a resin refers to a half-width exceeding 10° C., a stepwise change in endothermic heat quantity, or no clear endothermic peak being observed.

[0059] Amorphous polyester resin The amorphous polyester resin may be, for example, a condensation polymer of a polyvalent carboxylic acid and a polyhydric alcohol. As the amorphous polyester resin, a commercially available product or a synthesized product may be used.

[0060] Examples of polyvalent carboxylic acids include aliphatic dicarboxylic acids (e.g., oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenylsuccinic acid, adipic acid, sebacic acid, etc.), alicyclic dicarboxylic acids (e.g., cyclohexanedicarboxylic acid, etc.), aromatic dicarboxylic acids (e.g., terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, etc.), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). Among these, aromatic dicarboxylic acids are preferable as polyvalent carboxylic acids. The polyvalent carboxylic acid may be a trivalent or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the trivalent or higher carboxylic acid include trimellitic acid, pyromellitic acid, anhydrides thereof, and lower (e.g., carbon number 1 to 5) alkyl esters thereof. The polyvalent carboxylic acids may be used alone or in combination of two or more kinds.

[0061] Examples of polyhydric alcohols include aliphatic diols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, etc.), alicyclic diols (e.g., cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, etc.), and aromatic diols (e.g., ethylene oxide adducts of bisphenol A, propylene oxide adducts of bisphenol A, etc.). Among these, examples of polyhydric alcohols include aromatic diols and alicyclic diols, and more preferably aromatic diols. As the polyhydric alcohol, a polyhydric alcohol having a crosslinked or branched structure of three or more may be used in combination with the diol. Examples of the polyhydric alcohol having a trihydric or higher valence include glycerin, trimethylolpropane, and pentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more kinds.

[0062] The glass transition temperature (Tg) of the amorphous 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, it 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."

[0063] The weight average molecular weight (Mw) of the amorphous polyester resin is preferably 5,000 or more and 1,000,000 or less, and more preferably 7,000 or more and 500,000 or less. The number average molecular weight (Mn) of the amorphous polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the amorphous polyester resin is preferably 1.5 or more and 100 or less, and more preferably 2 or more and 60 or less. The weight average molecular weight and number average molecular weight are measured by gel permeation chromatography (GPC). The molecular weight measurement by GPC is performed using a Tosoh GPC HLC-8120GPC as the measuring device, a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent. The weight average molecular weight and number average molecular weight are calculated from the measurement results using a molecular weight calibration curve created with a monodisperse polystyrene standard sample.

[0064] The amorphous polyester resin can be obtained by a known production method, for example, by carrying out the reaction while removing water and alcohol generated during condensation by setting the polymerization temperature to 180° C. or higher and 230° C. or lower, and reducing the pressure in the reaction system as necessary. If the raw material monomer is not soluble or compatible at the reaction temperature, a high boiling point solvent may be added as a solubilizing agent to dissolve it. In this case, the polycondensation reaction is carried out while distilling off the solubilizing agent. If a monomer with poor compatibility is present in the copolymerization reaction, it is recommended that the monomer with poor compatibility is condensed in advance with the acid or alcohol to be polycondensed, and then polycondensed with the main component.

[0065] Crystalline polyester resin The crystalline polyester resin may be, for example, a polycondensate of a polyvalent carboxylic acid and a polyhydric alcohol. As the crystalline polyester resin, a commercially available product or a synthesized product may be used. Here, the crystalline polyester resin is preferably a polycondensate using a straight-chain aliphatic polymerizable monomer rather than a polymerizable monomer having an aromatic ring, since it easily forms a crystalline structure.

[0066] Examples of polyvalent carboxylic acids include aliphatic dicarboxylic acids (e.g., oxalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, etc.), aromatic dicarboxylic acids (e.g., dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, naphthalene-2,6-dicarboxylic acid, etc.), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polyvalent carboxylic acid may be a trivalent or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the trivalent carboxylic acid include aromatic carboxylic acids (e.g., 1,2,3-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, etc.), their anhydrides, and their lower alkyl esters (e.g., carbon number 1 to 5). As the polyvalent carboxylic acid, a dicarboxylic acid having a sulfonic acid group and a dicarboxylic acid having an ethylenic double bond may be used in combination with these dicarboxylic acids. The polyvalent carboxylic acids may be used alone or in combination of two or more kinds.

[0067] Examples of polyhydric alcohols include aliphatic diols (for example, straight-chain aliphatic diols having 7 to 20 carbon atoms in the main chain). Examples of aliphatic diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,14-eicosanedecanediol. Among these, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol are preferred as aliphatic diols. The polyhydric alcohol may be a trihydric or higher alcohol having a crosslinked or branched structure in combination with the diol. Examples of the trihydric or higher alcohol include glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more kinds.

[0068] Here, the polyhydric alcohol has an aliphatic diol content of 80 mol % or more, preferably 90 mol % or more.

[0069] The melting temperature of the crystalline polyester resin is preferably 50°C or higher and 100°C or lower, more preferably 55°C or higher and 90°C or lower, and even more preferably 60°C or higher and 85°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) based on the "peak melting temperature" described in the method for determining melting temperature in JIS K7121:1987 "Method for measuring transition temperature of plastics."

[0070] The weight average molecular weight (Mw) of the crystalline polyester resin is preferably 6,000 or more and 35,000 or less.

[0071] The crystalline polyester resin can be obtained, for example, by a known production method, like the amorphous polyester.

[0072] The content of the binder resin is preferably from 40% by mass to 95% by mass, more preferably from 50% by mass to 90% by mass, and even more preferably from 60% by mass to 85% by mass, based on the total mass of the toner particles.

[0073] -Release agent- The toner particles used in this embodiment contain a binder resin and a release agent, and the exposure rate of the release agent is 15% or more and 30% or less. The exposure rate of the release agent (the exposure rate of the release agent on the surface of the toner particles) is 15% or more and 30% or less, and from the viewpoint of suppressing changes in image density, it is preferably 18% or more and 30% or less, more preferably 20% or more and 28% or less, and particularly preferably 21% or more and 27% or less.

[0074] The exposure rate of the release agent in this embodiment is a value determined by XPS (X-ray photoelectron spectroscopy) measurement. The XPS measurement device used is a JPS-9000MX manufactured by JEOL Ltd., and the measurement is performed using MgKα radiation as the X-ray source, with an acceleration voltage of 10 kV and an emission current of 30 mA. Here, the amount of release agent on the toner surface is quantified by the peak separation method of the C1s spectrum. In the peak separation method, the measured C1s spectrum is separated into each component using curve fitting by the least squares method. The exposure rate is calculated from the peak area and composition ratio of the separated peaks originating from the release agent. For the component spectrum that serves as the basis for separation, the C1s spectrum obtained by measuring the release agent and binder resin used in the preparation of the toner particles separately is used. When the toner particles to be measured are toners containing external additives, the toner particles are ultrasonically treated with a mixed solution of ion-exchanged water and a surfactant for 20 minutes to remove the external additives, and the measurement is performed after removing the surfactant and drying and recovering the toner particles. The external additive removal process can be repeated until the external additives are removed.

[0075] As a method for adjusting the amount of exposed release agent on the toner particle surface, from the viewpoints of dispersibility between the binder resin and the release agent and controllability of the amount of exposed release agent, a method in which the coating layer (shell layer) that covers the core part of the core-shell structured toner obtained by the aggregation-coalescence method is made to contain the binder resin and the release agent to obtain toner particles.

[0076] Examples of the release agent 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 montan acid esters. The release agent is not limited to these.

[0077] 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) based on the "peak melting temperature" described in the method for determining melting temperature in JIS K7121:1987 "Method for measuring transition temperature of plastics."

[0078] 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.

[0079] -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 the dyes include pigments such as ultramarine blue, chalcoil 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.

[0080] The colorant may be surface-treated as necessary, or may be used in combination with a dispersant. In addition, a plurality of types of colorants may be used in combination.

[0081] 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.

[0082] -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.

[0083] -Characteristics of toner particles, etc.- The toner particles may be toner particles having a single layer structure, or may be toner particles having a so-called core-shell structure composed of a core portion (core particle) and a coating layer (shell layer) that coats the core portion. The toner particles having a core-shell structure may be composed of, for example, a core containing a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer containing the binder resin.

[0084] The volume average particle size (D50v) of the toner particles is preferably from 2 μm to 10 μm, and more preferably from 4 μm to 8 μm. The volume average particle size (D50v) of the toner particles is measured using a Coulter Multisizer II (manufactured by Beckman Coulter, Inc.), and the electrolyte is measured using an ISOTON-II (manufactured by Beckman Coulter, Inc.). For the measurement, 0.5 mg to 50 mg of the measurement sample is added to 2 ml of a 5 mass % aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant, and this is then added to 100 ml to 150 ml of the electrolyte. The electrolyte with the sample suspended in it is dispersed for 1 minute using an ultrasonic disperser, and the particle size distribution of particles with diameters in the range of 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. The number of particles sampled is 50,000. The particle size distribution based on volume is plotted from the smallest diameter side, and the particle size at which the cumulative 50% is reached is defined as the volume average particle size D50v.

[0085] The average circularity of the toner particles is preferably 0.90 or more and 1.00 or less, and more preferably 0.92 or more and 0.98 or less. The average circularity of toner particles is calculated by (circular equivalent perimeter) / (perimeter) [(perimeter of a circle having the same projected area as the particle image) / (perimeter of the particle projected image)]. Specifically, it is a value measured by the following method. First, the toner particles to be measured are sucked and collected, flattened, and a still image of the particles is captured by instantaneous strobe light emission, and the particle image is analyzed by a flow-type particle image analyzer (FPIA-3000 manufactured by Sysmex Corporation). The number of samples to be taken in order to calculate the average circularity is 3,500. When the toner contains an external additive, the toner (developer) to be measured is dispersed in water containing a surfactant, and then ultrasonic treatment is performed to obtain toner particles from which the external additive has been removed.

[0086] -Method of manufacturing toner particles- The toner particles may be produced by any of a dry production method (e.g., a kneading and grinding method, etc.) and a wet production method (e.g., an aggregation and coalescence method, a suspension polymerization method, a dissolution suspension method, etc.). There are no particular limitations on these production methods, and any known production method may be used.

[0087] Specifically, for example, when toner particles are produced by the aggregation and coalescence method, the toner particles are produced through a step of preparing a resin particle dispersion in which resin particles to be a binder resin are dispersed (resin particle dispersion preparation step), a step of aggregating resin particles (other particles, if necessary) in the resin particle dispersion (in a dispersion after mixing other particle dispersions, if necessary) to form aggregated particles (aggregated particle formation step), and a step of heating the aggregated particle dispersion in which the aggregated particles are dispersed, to fuse and coalesce the aggregated particles, thereby forming toner particles (fusion and coalescence step).

[0088] Each step will be described in detail below. In the following description, a method for obtaining toner particles containing a colorant and a release agent will be described, but the colorant and the release agent are used as necessary. Of course, additives other than the colorant and the release agent may be used.

[0089] -Resin particle dispersion preparation process- Along with a resin particle dispersion in which resin particles serving as a binder resin are dispersed, for example, a colorant particle dispersion in which colorant particles are dispersed, and a release agent particle dispersion in which release agent particles are dispersed are prepared.

[0090] The resin particle dispersion liquid is prepared, for example, by dispersing resin particles in a dispersion medium with the aid of a surfactant.

[0091] The dispersion medium used in the resin particle dispersion liquid is, for example, an aqueous medium. Examples of the aqueous medium include water such as distilled water and ion-exchanged water, alcohols, etc. These may be used alone or in combination of two or more kinds.

[0092] Examples of the surfactant include anionic surfactants such as sulfate salts, sulfonates, phosphates, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; and nonionic surfactants such as polyethylene glycols, alkylphenol ethylene oxide adducts, and polyhydric alcohols. Among these, anionic surfactants and cationic surfactants are particularly preferred. The nonionic surfactants may be used in combination with anionic surfactants or cationic surfactants. The surfactant may be used alone or in combination of two or more kinds.

[0093] In the resin particle dispersion, the resin particles are dispersed in the dispersion medium by a general dispersion method such as a rotary shear type homogenizer, a ball mill having a media, a sand mill, or a dyno mill. Depending on the type of resin particles, the resin particles may be dispersed in the dispersion medium by a phase inversion emulsification method. The phase inversion emulsification method is a method in which the resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, a base is added to the organic continuous phase (O phase) to neutralize it, and then an aqueous medium (W phase) is added to invert the phase from W / O to O / W, thereby dispersing the resin in the aqueous medium in the form of particles.

[0094] The volume average particle size of the resin particles dispersed in the resin particle dispersion is, for example, preferably from 0.01 μm to 1 μm, more preferably from 0.08 μm to 0.8 μm, and even more preferably from 0.1 μm to 0.6 μm. The volume average particle size of the resin particles is measured by using a particle size distribution obtained by measurement using a laser diffraction particle size distribution measuring device (for example, LA-700 manufactured by Horiba, Ltd.), subtracting the cumulative distribution from the small particle size side for the volume of the divided particle size range (channel), and measuring the particle size at which the cumulative distribution is 50% of all particles as the volume average particle size D50v. The volume average particle sizes of particles in other dispersions are measured in the same manner.

[0095] The content of the resin particles in the resin particle dispersion is preferably from 5% by mass to 50% by mass, and more preferably from 10% by mass to 40% by mass.

[0096] In the same manner as the resin particle dispersion liquid, for example, a colorant particle dispersion liquid and a release agent particle dispersion liquid are also prepared. That is, the volume average particle size, dispersion medium, dispersion method, and particle content of the particles in the resin particle dispersion liquid are the same for the colorant particles dispersed in the colorant particle dispersion liquid and the release agent particles dispersed in the release agent particle dispersion liquid.

[0097] -Agglomerated particle formation process- Next, the resin particle dispersion liquid, the colorant particle dispersion liquid, and the release agent particle dispersion liquid are mixed together. Then, in the mixed dispersion, the resin particles, the colorant particles, and the release agent particles are hetero-aggregated to form aggregated particles containing the resin particles, the colorant particles, and the release agent particles and having a diameter close to that of the target toner particles.

[0098] Specifically, for example, an aggregating agent is added to the mixed dispersion, the pH of the mixed dispersion is adjusted to be acidic (e.g., pH 2 or more and 5 or less), a dispersion stabilizer is added as necessary, and then the mixed dispersion is heated to a temperature close to the glass transition temperature of the resin particles (specifically, for example, glass transition temperature of the resin particles -30°C or more and glass transition temperature -10°C or less), and the particles dispersed in the mixed dispersion are aggregated to form aggregated particles. In the aggregated particle formation process, for example, the mixed dispersion may be stirred with a rotary shear homogenizer, an aggregating agent may be added at room temperature (e.g., 25°C), the pH of the mixed dispersion may be adjusted to an acidic state (e.g., pH 2 or more and 5 or less), a dispersion stabilizer may be added as necessary, and then the mixture may be heated.

[0099] Examples of the flocculant include a surfactant having a polarity opposite to that of the surfactant contained in the mixed dispersion, an inorganic metal salt, and a divalent or higher metal complex. When a metal complex is used as the flocculant, the amount of the surfactant used is reduced, and the charging characteristics are improved. If necessary, an additive that forms a complex or a similar bond with the metal ion of the flocculant may be used together with the flocculant. As this additive, a chelating agent is preferably used.

[0100] Examples of inorganic metal salts include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate; and inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, and calcium polysulfide. The chelating agent may be a water-soluble chelating agent, for example, oxycarboxylic acid such as tartaric acid, citric acid, gluconic acid, etc., aminocarboxylic acid such as iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), ethylenediaminetetraacetic acid (EDTA), etc. The amount of the chelating agent added is preferably from 0.01 to 5.0 parts by mass, and more preferably from 0.1 to less than 3.0 parts by mass, relative to 100 parts by mass of the resin particles.

[0101] -Fusion / unification process- Next, the aggregated particle dispersion liquid in which the aggregated particles are dispersed is heated, for example, to a temperature equal to or higher than the glass transition temperature of the resin particles (for example, a temperature 10° C. to 30° C. higher than the glass transition temperature of the resin particles) to fuse and coalesce the aggregated particles to form toner particles.

[0102] Through the above steps, toner particles are obtained. After obtaining the aggregated particle dispersion in which the aggregated particles are dispersed, the aggregated particle dispersion is further mixed with a resin particle dispersion in which resin particles and a release agent particle dispersion are dispersed, and the aggregated particles are aggregated so that the resin particles are further attached to the surfaces of the aggregated particles to form second aggregated particles, and the second aggregated particle dispersion in which the second aggregated particles are dispersed is heated to fuse and coalesce the second aggregated particles to form toner particles having a core-shell structure, thereby producing toner particles.

[0103] After the fusion and coalescence process is completed, the toner particles formed in the solution are subjected to a known washing process, solid-liquid separation process, and drying process to obtain dried toner particles. From the viewpoint of chargeability, the washing process is preferably performed by sufficient substitution washing with ion-exchanged water. From the viewpoint of productivity, the solid-liquid separation process is preferably performed by suction filtration, pressure filtration, etc. From the viewpoint of productivity, the drying process is preferably performed by freeze drying, air flow drying, fluidized drying, vibration type fluidized drying, etc.

[0104] The toner used in the present embodiment is produced, for example, by adding an external additive to the obtained toner particles in a dry state and mixing them. The mixing may be performed, for example, by using a V blender, a Henschel mixer, a Loedige mixer, etc. Furthermore, if necessary, coarse particles of the toner may be removed using a vibration sieve, an air sieve, etc.

[0105] <<External additives>> The toner used in this embodiment preferably contains an external additive. Examples of the external additive include inorganic particles. Examples of the inorganic particles include 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. Among these, it is preferable to contain silica particles from the viewpoint of suppressing a change in image density.

[0106] The surface of the inorganic particles as an external additive may be subjected to a hydrophobic treatment. The hydrophobic treatment may be performed, 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 hydrophobizing agent is usually, 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.

[0107] 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 fluorine-based polymer particles), and the like.

[0108] The amount of the external additive is preferably from 0.01% by mass to 5% by mass, and more preferably from 0.01% by mass to 2.0% by mass, based on the toner particles.

[0109] <Image forming device, image forming method> The image forming apparatus according to the present embodiment includes 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 developing the electrostatic image formed on the surface of the image carrier as a toner image with the electrostatic image developer, 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. The electrostatic image developer according to the present embodiment is used as the electrostatic image developer.

[0110] In the image forming apparatus according to this embodiment, an image forming method (the image forming method according to this embodiment) is carried out, which 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 the electrostatic image developer according to this embodiment, 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.

[0111] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus in which a toner image formed on the surface of an image holder is directly transferred to a recording medium; an intermediate transfer type apparatus in which a toner image formed on the surface of an image holder is primarily transferred to the surface of an intermediate transfer body, and the toner image transferred to the surface of the intermediate transfer body is secondarily transferred to the surface of a recording medium; an apparatus equipped with a cleaning means for cleaning the surface of the image holder after the transfer of the toner image and before charging; and an apparatus equipped with a discharging means for irradiating the surface of the image holder with discharging light to discharge it after the transfer of the toner image and before charging it. When the image forming apparatus according to the present embodiment is an intermediate transfer type apparatus, the transfer means has, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means which primarily transfers the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means which secondarily transfers the toner image transferred onto the surface of the intermediate transfer body onto the surface of a recording medium.

[0112] In the image forming apparatus according to the present embodiment, for example, a portion including the developing means may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge that contains the electrostatic charge image developer according to the present embodiment and has the developing means is preferably used.

[0113] 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 example. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0114] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to the present embodiment. The image forming apparatus shown in Fig. 1 includes first to fourth image forming units 10Y, 10M, 10C, and 10K (image forming means) of an electrophotographic type that output images of each color of yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged in parallel at predetermined distances from each other in the horizontal direction. These units 10Y, 10M, 10C, and 10K may be process cartridges that are detachably attached to the image forming apparatus.

[0115] Above each of the units 10Y, 10M, 10C, and 10K, an intermediate transfer belt (one example of an intermediate transfer body) 20 is provided, which extends through each unit. The intermediate transfer belt 20 is provided wrapped around a drive roll 22 and a support roll 24, and runs in a direction from the first unit 10Y toward the fourth unit 10K. A force is applied to the support roll 24 by a spring (not shown) or the like in a direction away from the drive roll 22, and tension is applied to the intermediate transfer belt 20 wrapped around them. An intermediate transfer body cleaning device 30 is provided on the image carrier side of the intermediate transfer belt 20, facing the drive roll 22. The developing devices (an example of developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K are supplied with yellow, magenta, cyan, and black toners contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0116] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, the first unit 10Y that forms a yellow image and is disposed upstream in the direction in which the intermediate transfer belt travels will be described here as a representative.

[0117] The first unit 10Y has a photoconductor 1Y that acts as an image carrier. Around the photoconductor 1Y, a charging roll (an example of a charging means) 2Y that charges the surface of the photoconductor 1Y to a predetermined potential, an exposure device (an example of an electrostatic image forming means) 3 that exposes the charged surface to a laser beam 3Y based on a color-separated image signal to form an electrostatic image, a developing device (an example of a developing means) 4Y that supplies charged toner to the electrostatic image to develop it, a primary transfer roll 5Y (an example of a primary transfer means) that transfers the developed toner image onto an intermediate transfer belt 20, and a photoconductor cleaning device (an example of a cleaning means) 6Y that removes toner remaining on the surface of the photoconductor 1Y after the primary transfer are arranged in this order. The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20, and is provided at a position facing the photoconductor 1Y. A bias power supply (not shown) that applies a primary transfer bias is connected to the primary transfer rolls 5Y, 5M, 5C, and 5K of each unit. Each bias power supply changes the value of the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

[0118] Hereinafter, the operation of forming a yellow image in the first unit 10Y will be described. First, prior to operation, the surface of the photoconductor 1Y is charged to a potential of −600V to −800V by the charging roll 2Y. The photoconductor 1Y has a conductivity (for example, a volume resistivity of 1×10 at 20° C. -6The photosensitive layer is formed by laminating a photosensitive layer on a substrate having a resistivity of Ωcm or less. This photosensitive layer is usually highly resistive (the resistance of ordinary resins), but when irradiated with a laser beam, the resistivity of the portion irradiated with the laser beam changes. Therefore, the exposed surface of the charged photoreceptor 1Y is irradiated with a laser beam 3Y from the exposure device 3 in accordance with image data for yellow sent from a control unit (not shown). As a result, an electrostatic charge image of a yellow image pattern is formed on the surface of the photoreceptor 1Y.

[0119] An electrostatic image is an image formed on the surface of the photoconductor 1Y by electrostatic charging. The laser beam 3Y reduces the resistivity of the irradiated parts of the photosensitive layer, causing the charged charges on the surface of the photoconductor 1Y to flow, while the charges remain in the parts not irradiated by the laser beam 3Y. This is a so-called negative latent image. The electrostatic image formed on the photoconductor 1Y rotates to a predetermined developing position as the photoconductor 1Y travels. At this developing position, the electrostatic image on the photoconductor 1Y is developed into a toner image by the developing device 4Y and made visible.

[0120] The developing device 4Y contains an electrostatic image developer including at least yellow toner and a carrier, for example. The yellow toner is triboelectrically charged by being stirred inside the developing device 4Y, and is held on a developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the charge on the photoconductor 1Y. As the surface of the photoconductor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image portion on the surface of the photoconductor 1Y, and the latent image is developed with the yellow toner. The photoconductor 1Y on which the yellow toner image has been formed continues to travel at a predetermined speed, and the toner image developed on the photoconductor 1Y is transported to a predetermined primary transfer position.

[0121] When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y toward the primary transfer roll 5Y acts on the toner image, and the toner image on the photoreceptor 1Y is transferred onto the intermediate transfer belt 20. The transfer bias applied at this time has a polarity (+) opposite to the polarity (-) of the toner, and is controlled to, for example, +10 μA by a control unit (not shown) in the first unit 10Y. On the other hand, the toner remaining on the photoconductor 1Y is removed and collected by the photoconductor cleaning device 6Y.

[0122] The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K subsequent to the second unit 10M is also controlled in accordance with the first unit. In this manner, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is conveyed successively through the second to fourth units 10M, 10C, and 10K, where the toner images of each color are transferred and superimposed.

[0123] The intermediate transfer belt 20 onto which the four color toner images have been transferred in multiple layers through the first to fourth units reaches a secondary transfer section that is composed of the intermediate transfer belt 20, a support roll 24 that contacts the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 arranged on the image bearing surface side of the intermediate transfer belt 20. Meanwhile, a recording paper (an example of a recording medium) P is fed at a predetermined timing into the gap between the secondary transfer roll 26 and the intermediate transfer belt 20 via a supply mechanism, and a secondary transfer bias is applied to the support roll 24. The transfer bias applied at this time has a (-) polarity that is the same as the (-) polarity of the toner, and an electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, and the toner image on the intermediate transfer belt 20 is transferred onto the recording paper P. The secondary transfer bias at this time is determined according to the resistance detected by a resistance detection means (not shown) that detects the resistance of the secondary transfer section, and is voltage-controlled.

[0124] Thereafter, the recording paper P is sent to a pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (one example of a fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image.

[0125] The recording paper P onto which the toner image is transferred can be, for example, plain paper used in electrophotographic copying machines, printers, etc. In addition to the recording paper P, other examples of the recording medium include overhead projector sheets and the like. To further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper in which the surface of ordinary paper is coated with a resin or the like, art paper for printing, etc. are preferably used.

[0126] After the color image has been fixed, the recording paper P is conveyed toward the discharge section, and the series of color image forming operations is completed.

[0127] <Process cartridge> The process cartridge according to this embodiment is a process cartridge that contains the electrostatic image developer according to this embodiment, is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image, and is detachably attached to an image forming apparatus.

[0128] The process cartridge according to this embodiment is not limited to the above configuration, and may be configured to include a developing means and, as necessary, at least one other means selected from an image carrier, a charging means, an electrostatic image forming means, and a transfer means.

[0129] An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this example. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0130] FIG. 2 is a schematic diagram showing the process cartridge according to the present embodiment. The process cartridge 200 shown in FIG. 2 is configured by, for example, a housing 117 having a mounting rail 116 and an opening 118 for exposure, and integrally combining and holding a photoconductor 107 (an example of an image carrier), a charging roll 108 (an example of a charging means) provided around the photoconductor 107, a developing device 111 (an example of a developing means), and a photoconductor cleaning device 113 (an example of a cleaning means), which are assembled into a cartridge. In FIG. 2, 109 denotes an exposure device (an example of an electrostatic image forming means), 112 denotes a transfer device (an example of a transfer means), 115 denotes a fixing device (an example of a fixing means), and 300 denotes a recording paper (an example of a recording medium). EXAMPLES

[0131] Hereinafter, the embodiments of the present invention will be described in detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" are based on mass.

[0132] In the following description, the volume average particle size refers to a particle size D50v that is 50% cumulative from the small diameter side in a volume-based particle size distribution.

[0133] <Toner Production> -Preparation of colorant particle dispersion 1- Cyan pigment (copper phthalocyanine B15:3 (manufactured by Dainichi Seika Chemicals Co., Ltd.)): 50 parts by mass Anionic surfactant: Neogen SC (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 5 parts by mass Ion-exchanged water: 200 parts by weight The above was mixed and dispersed for 5 minutes using an Ultra Turrax manufactured by IKA Corporation, and further dispersed for 10 minutes using an ultrasonic bath to obtain a colorant particle dispersion liquid 1 with a solid content of 21%. The volume average particle size was measured using a particle size measuring instrument LA-700 manufactured by Horiba Ltd. and found to be 160 nm.

[0134] -Preparation of release agent particle dispersion 1- Paraffin wax: HNP-9 (manufactured by Nippon Seiro Co., Ltd.): 19 parts by weight Anionic surfactant: Neogen SC (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 1 part by weight Ion-exchanged water: 80 parts by weight The above was mixed in a heat-resistant container, heated to 90°C, and stirred for 30 minutes. Next, the molten liquid was passed through the bottom of the container into a Gaulin homogenizer, and circulated for three passes under a pressure condition of 5 MPa, after which the pressure was increased to 35 MPa and circulated for another three passes. The emulsion thus obtained was cooled to 40°C or less in the heat-resistant solution, to obtain a release agent particle dispersion 1. The volume average particle size was measured using a particle size measuring instrument LA-700 manufactured by Horiba Ltd. and found to be 240 nm.

[0135] -Resin particle dispersion 1- [Oil layer] Styrene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 30 parts by weight n-Butyl acrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 10 parts by mass β-Carboxyethyl acrylate (manufactured by Rhodia Nikka Co., Ltd.): 1.3 parts by mass Dodecanethiol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 0.4 parts by mass

[0136] [Water layer 1] Ion-exchanged water: 17 parts by weight Anionic surfactant (Dowfax, manufactured by Dow Chemical Company): 0.4 parts by mass

[0137] [Water layer 2] Ion-exchanged water: 40 parts by weight Anionic surfactant (Dowfax, manufactured by Dow Chemical Company): 0.05 parts by mass Ammonium peroxodisulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 0.4 parts by mass

[0138] The oil layer components and the aqueous layer 1 components were placed in a flask and mixed with stirring to obtain a monomer emulsion dispersion. The aqueous layer 2 components were placed in a reaction vessel, the atmosphere in the vessel was fully replaced with nitrogen, and the reaction system was heated in an oil bath with stirring until the temperature inside the reaction system reached 75°C. The monomer emulsion dispersion was gradually added dropwise to the reaction vessel over a period of 3 hours to carry out emulsion polymerization. After the end of the addition, the polymerization was continued at 75°C and terminated after 3 hours. The volume average particle diameter D50v of the obtained resin particles was measured to be 250 nm using a laser diffraction particle size distribution measuring device LA-700 (manufactured by Horiba, Ltd.), the glass transition point of the resin was measured to be 53°C at a heating rate of 10°C / min using a differential scanning calorimeter (DSC-50, manufactured by Shimadzu Corporation), and the number average molecular weight (polystyrene equivalent) was measured to be 13,000 using a molecular weight measuring device (HLC-8020, manufactured by Tosoh Corporation) using THF as a solvent. As a result, a resin particle dispersion liquid with a volume average particle diameter of 250 nm, solid content of 42%, glass transition point of 52°C, and number average molecular weight Mn of 13,000 was obtained.

[0139] - Preparation of Toner 1 - Resin particle dispersion: 150 parts by mass Colorant particle dispersion: 30 parts by weight Release agent particle dispersion: 40 parts by weight Polyaluminum chloride: 0.4 parts by weight The above components were thoroughly mixed and dispersed in a stainless steel flask using an Ultra Turrax manufactured by IKE Corporation, and then the flask was heated to 48° C. with stirring in a heating oil bath. After maintaining at 48° C. for 80 minutes, 50 parts by mass of the same resin particle dispersion liquid as above and 20 parts by mass of the release agent particle dispersion liquid were slowly added thereto. After that, the pH of the system was adjusted to 6.0 using a 0.5 mol / L aqueous solution of sodium hydroxide, and the stainless steel flask was sealed, the seal of the stirring shaft was magnetically sealed, and the mixture was heated to 97°C while continuing to stir, and maintained for 3 hours. After the reaction was completed, the mixture was cooled at a temperature drop rate of 1°C / min, filtered, thoroughly washed with ion-exchanged water, and then subjected to solid-liquid separation by Nutsche suction filtration. The mixture was further dispersed in 3,000 parts by mass of ion-exchanged water at 40°C, and stirred and washed at 300 rpm for 15 minutes. This washing operation was repeated five more times, and when the pH of the filtrate reached 6.54 and the electrical conductivity reached 6.5 μS / cm, solid-liquid separation was performed using No. 5A filter paper by Nutsche suction filtration. Next, vacuum drying was continued for 12 hours to obtain toner base particles. The volume average particle diameter D50v of the toner base particles was measured by a Coulter counter and found to be 6.2 μm, and the volume average particle size distribution index GSDv was 1.20. When the shape was observed by a Luzex image analyzer manufactured by Luzex Corporation, it was observed that the particle shape factor SF1 was 135 and that the particle was potato-shaped. The glass transition point of the toner was 52°C. Furthermore, silica (SiO2) particles with an average primary particle diameter of 40 nm that had been surface-hydrophobized with hexamethyldisilazane (hereinafter sometimes abbreviated as "HMDS") and metatitanic acid compound particles with an average primary particle diameter of 20 nm, which are the reaction product of metatitanic acid and isobutyltrimethoxysilane, were added to this toner so that the coverage rate of the surface of the toner particles was 40%, and mixed in a Henschel mixer to produce toner 1.

[0140] <Preparation of Toners 2 to 5> Toners 2 to 6 were each produced in the same manner as Toner 1, except that the amounts of resin particle dispersion and release agent particle dispersion added after maintaining at 48° C. for 80 minutes were changed as follows: Toner 2: 45 parts by weight of resin particle dispersion, 25 parts by weight of release agent particle dispersion Toner 3: 55 parts by weight of resin particle dispersion, 15 parts by weight of release agent particle dispersion Toner 4: 60 parts by weight of resin particle dispersion, 10 parts by weight of release agent particle dispersion Toner 5: 35 parts by weight of resin particle dispersion, 35 parts by weight of release agent particle dispersion

[0141] <Preparation of Toner 6> 850 parts of polyester resin powder obtained by drying the resin particle dispersion used in the preparation of toner 1, 75 parts of cyan pigment (copper phthalocyanine, CI Pigment Blue 15:3, manufactured by Dainichi Seikagaku Kogyo Co., Ltd.), and 80 parts of paraffin wax: HNP-9 (manufactured by Nippon Seiro Co., Ltd.) were thoroughly mixed and stirred in a 5L Henschel mixer (manufactured by Mitsui Miike Machine Co., Ltd.), and the resulting kneaded product was melt-kneaded in a TEM18 screw extruder (manufactured by Toshiba Machine Co., Ltd.), rolled and cooled, and then pulverized in a fluidized bed pulverizer AFG200 (manufactured by Hosokawa Micron Corporation). Next, the product was classified using an inertial classifier ELB3 (manufactured by Matsubo Co., Ltd.) to prepare toner 7.

[0142] <Preparation of magnetic particles 1> 1,318 parts by mass of Fe2O3, 586 parts by mass of Mn(OH)2, 96 parts by mass of Mg(OH)2, and 1 part by mass of SrCO3 were mixed, and a dispersant, water, and zirconia beads with a media diameter of 1 mm were added, and the mixture was crushed and mixed in a sand mill. The zirconia beads were filtered and dried, and then further mixed in a rotary kiln at 20 rpm and 900 ° C to obtain a mixed oxide. Next, a dispersant and water were added, and 6.6 parts by mass of polyvinyl alcohol were added, and the mixture was pulverized in a wet ball mill until the volume average particle size was 1.2 μm. Next, the mixture was granulated and dried in a spray dryer so that the dry particle size was 32 μm. Furthermore, the mixture was fired in an electric furnace at a temperature of 1220 ° C in an oxygen-nitrogen mixed atmosphere with an oxygen concentration of 1% for 5 hours. The obtained particles were subjected to a crushing process and a classification process, and then heated in a rotary kiln at 15 rpm and 900 ° C for 2 hours, and similarly subjected to a classification process to obtain magnetic particles 1. The volume average particle size of magnetic particle 1 is 30 μm and the BET specific surface area is 0.20 m 2 / g.

[0143] <Preparation of inorganic particles to be added to carrier resin coating layer> [Inorganic particles 1] Commercially available hydrophilic silica particles (fumed silica particles, no surface treatment, volume average particle size 40 nm) were prepared and designated as inorganic particles 1.

[0144] [Inorganic particles 2] 890 parts of methanol and 210 parts of 9.8% aqueous ammonia were added and mixed in a glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer to obtain an alkaline catalyst solution. After adjusting the alkaline catalyst solution to 45°C, 550 parts of tetramethoxysilane and 140 parts of 7.6% aqueous ammonia were dropped simultaneously over a period of 450 minutes while stirring to obtain a silica particle dispersion (A). The silica particles in the silica particle dispersion (A) have a volume average particle size of 4 nm, a volume particle size distribution index (the square root of the ratio of the particle size D16v at 16% cumulative from the small diameter side in the volume-based particle size distribution to the particle size D84v at 84% cumulative (D84v / D16v) 1 / 2 )1.2. 300 parts of the silica particle dispersion (A) were put into an autoclave equipped with a stirrer, and the stirrer was rotated at a rotation speed of 100 rpm. While continuing to rotate the stirrer, liquefied carbon dioxide was injected into the autoclave from a carbon dioxide cylinder via a pump, and the inside of the autoclave was heated with a heater while the inside of the autoclave was pressurized with a pump, so that the inside of the autoclave was in a supercritical state of 150°C and 15 MPa. The pressure valve was operated to keep the inside of the autoclave at 15 MPa, and supercritical carbon dioxide was circulated to remove methanol and water from the silica particle dispersion (A). When the amount of carbon dioxide supplied to the autoclave reached 900 parts, the supply of carbon dioxide was stopped, and a powder of silica particles was obtained. The inside of the autoclave was kept at 150°C and 15MPa by a heater and a pump to maintain the supercritical state of carbon dioxide, and while continuing to rotate the stirrer of the autoclave, 50 parts of hexamethyldisilazane per 100 parts of silica particles was injected into the autoclave by an entrainer pump, and the temperature inside the autoclave was raised to 180°C and reacted for 20 minutes. Next, supercritical carbon dioxide was again circulated in the autoclave to remove excess hexamethyldisilazane. Next, the stirring was stopped, the pressure valve was opened to release the pressure inside the autoclave to atmospheric pressure, and the temperature was lowered to room temperature (25°C). In this way, inorganic particles 2 surface-treated with hexamethyldisilazane were obtained. The inorganic particles 2 had a volume average particle size of 4 nm.

[0145] [Inorganic particles 3] In the same manner as in the preparation of inorganic particles 2, however, the amount of tetramethoxysilane and 7.6% aqueous ammonia added when preparing silica particle dispersion (A) was increased to change the volume average particle size of the silica particles in the silica particle dispersion to 6 nm, and inorganic particles 3 surface-treated with hexamethyldisilazane were obtained. Inorganic particles 3 had a volume average particle size of 7 nm.

[0146] [Inorganic particles 4] Commercially available hydrophobic silica particles (fumed silica particles surface-treated with hexamethyldisilazane, volume average particle size 12 nm) were prepared and used as inorganic particles 4.

[0147] [Inorganic particles 5] Commercially available hydrophilic silica particles (fumed silica particles, no surface treatment, volume average particle size 62 nm) were prepared and used as inorganic particles 5.

[0148] [Inorganic particles 6] Commercially available hydrophobic silica particles (fumed silica particles surface-treated with hexamethyldisilazane, volume average particle size 88 nm) were prepared and used as inorganic particles 6.

[0149] [Inorganic particles 7] Commercially available hydrophobic silica particles (fumed silica particles surface-treated with hexamethyldisilazane, volume average particle size 93 nm) were prepared and used as inorganic particles 7.

[0150] [Inorganic particles 8] Commercially available calcium carbonate particles (volume average particle size: 20 nm) were prepared and used as inorganic particles 8.

[0151] [Inorganic particles 9] Commercially available barium carbonate particles (volume average particle size: 20 nm) were prepared and used as inorganic particles 9.

[0152] [Inorganic particles 10] Commercially available barium sulfate particles (volume average particle size: 30 nm) were prepared and used as inorganic particles 10.

[0153] <Preparation of Coating Agent for Forming Carrier Resin Coating Layer> [Coating agent (1)] Perfluoropropylethyl methacrylate-methyl methacrylate copolymer (polymerization ratio by mass: 30:70, weight average molecular weight: 19,000): 9.0 parts Polycyclohexyl methacrylate (weight average molecular weight 200,000): 9 parts Carbon black (Cabot Corporation, VXC72): 0.5 parts ·Inorganic particles 1:20 parts Toluene: 250 parts Isopropyl alcohol: 50 parts The above materials and glass beads (diameter 1 mm, same amount as toluene) were put into a sand mill and stirred at a rotation speed of 190 rpm for 30 minutes to obtain a coating agent (1) with a solid content of 11%.

[0154] [Coating agents (2) to (7)] Coating agents (2) to (7) were obtained in the same manner as in the preparation of coating agent (1), except that inorganic particles 1 were replaced with any of inorganic particles 2 to 7, respectively.

[0155] [Coating agents (8) to (11)] Coating agents (8) to (11) were obtained in the same manner as in the preparation of coating agent (1), except that the amount of inorganic particles 1 added was changed as follows: Coating agent (8): 10 parts of inorganic particles Coating agent (9): 12 parts of inorganic particles Coating agent (10): 30 parts of inorganic particles 1 Coating agent (11): 40 parts of inorganic particles 1

[0156] [Coating agents (12) to (14)] Coating agents (12) to (14) were obtained in the same manner as in the preparation of coating agent (1), except that inorganic particle 1 was changed to any one of inorganic particles 8 to 10, respectively.

[0157] [Coating agents (15) to (17)] Coating agents (15) to (17) were prepared in the same manner as coating agent (1), except that the amounts of perfluoropropylethyl methacrylate-methyl methacrylate copolymer and polycyclohexyl methacrylate added were changed as follows. Coating agent (15): 11 parts of perfluoropropylethyl methacrylate-methyl methacrylate copolymer, 5 parts of polycyclohexyl methacrylate Coating agent (16): 6 parts of perfluoropropylethyl methacrylate-methyl methacrylate copolymer, 14 parts of polycyclohexyl methacrylate Coating agent (17): 1.5 parts of perfluoropropylethyl methacrylate-methyl methacrylate copolymer, 19 parts of polycyclohexyl methacrylate

[0158] (Examples 1 to 30 and Comparative Examples 1 to 6) <Preparation of Resin-Coated Carrier> -Creating Carrier 1- 1,000 parts of the magnetic particles and 125 parts of the coating agent (1) 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 the coating agent (1) was added and mixed at room temperature (25° C.) for 20 minutes. Then, the mixture was heated to 70° C. and dried 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 1.

[0159] -Production of Carriers 2 to 31- Carriers 2 to 31 were obtained in the same manner as carrier 1, except that the coating agent, the amount thereof, and the mixing time were changed to those shown in Table 1.

[0160] <Preparation of developer> The carrier and the toner shown in Table 1 were mixed in a V blender at a mixing ratio of carrier:toner=100:10 (mass ratio) and stirred for 20 minutes to obtain developers 1 to 26, respectively.

[0161] <Exposure rate of release agent> The exposure rate of the release agent was determined by XPS (X-ray photoelectron spectroscopy). Specifically, JPS-9000MX manufactured by JEOL Ltd. was used as the XPS measurement device, and the measurement was performed using MgKα radiation as the X-ray source, with an acceleration voltage of 10 kV and an emission current of 30 mA. Here, the amount of release agent on the toner surface was quantified by the peak separation method of the C1s spectrum. In the peak separation method, the measured C1s spectrum was separated into each component using curve fitting by the least squares method. The exposure rate was calculated from the peak area and composition ratio of the release agent among the separated peaks. For the component spectrum that is the basis of the separation, the C1s spectrum obtained by measuring the release agent and binder resin used in the preparation of the toner particles separately was used. When the toner particles to be measured were toners containing external additives, the toner particles were subjected to ultrasonic treatment for 20 minutes together with a mixed solution of ion-exchanged water and a surfactant to remove the external additives, and the measurement was performed after removing the surfactant and drying and recovering the toner particles. The external additive removal treatment can be repeated until the external additives are removed.

[0162] <Measurement of the average particle size of inorganic particles in the resin coating layer> The carrier was embedded in epoxy resin and cut with a microtome to prepare a carrier cross section. SEM images of the carrier cross section taken with a scanning transmission electron microscope (Hitachi, S-4100) were imported into an image processing analyzer (Nireco, Luzex AP) for image analysis. 100 inorganic particles (primary particles) were randomly selected from the resin coating layer, and the circle equivalent diameter (nm) of each was calculated and the arithmetic average was calculated to obtain the average particle diameter (nm) of the inorganic particles.

[0163] <Measurement of the average thickness of the resin coating layer> The SEM image was imported into an image processing analyzer (Luzex AP, manufactured by Nireco Corporation) and image analysis was performed. The thickness (μm) of the resin coating layer was measured at 10 randomly selected points per carrier particle, and then measurements were taken for 100 carrier particles, and the arithmetic average of all measurements was calculated to determine the average thickness (μm) of the resin coating layer.

[0164] <Carrier surface analysis> As a device for three-dimensionally analyzing the carrier surface, an electron beam three-dimensional roughness analyzer ERA-8900FE manufactured by Elionix Co., Ltd. The carrier surface analysis using the ERA-8900FE was specifically carried out as follows. The surface of one carrier particle was enlarged 5,000 times, and 300 measurement points were taken along the long side and short side, respectively, to perform 3D measurements, obtaining 3D image data for an area of ​​24μm x 18μm. For the 3D image data, the limit wavelength of the spline filter was set to 12μm to remove wavelengths with a period of 12μm or more, and further, the cutoff value of the Gaussian high-pass filter was set to 2.0μm to remove wavelengths with a period of 2.0μm or more, obtaining 3D roughness curve data. From the 3D roughness curve data, the central 12μm x 12μm area (plan view area A = 144μm) 2 ) surface area B (μm 2 ) was calculated to obtain the ratio B / A. The ratio B / A was calculated for each of 100 carriers and the arithmetic average was calculated.

[0165] <Measurement of silicon element concentration> The carrier was used as a sample and analyzed by X-ray photoelectron spectroscopy (XPS) under the following conditions, and the silicon element concentration (atomic %) was calculated from the peak intensity of each element. XPS equipment: ULVAC-PHI, VersaProbe II Etching gun: Argon gun Acceleration voltage: 5kV Emission current: 20mA Sputtering area: 2mm x 2mm Sputtering rate: 3nm / min (SiO2 equivalent)

[0166] <Collection of magnetic particles from developer> The carrier was separated from the developer using a 16m mesh. The coating layer of the separated carrier was dissolved using, for example, toluene to extract the magnetic particles. The solvent was changed arbitrarily according to the coating resin. The difference in dissolution was achieved by heating, applying ultrasonic waves, etc. according to the solvent.

[0167] <Volume average particle size of magnetic particles> The volume average particle size of the magnetic particles was measured using a laser diffraction particle size distribution measuring device LA-700 (manufactured by Horiba, Ltd.).

[0168] <Image density change suppression> The concentration difference of the obtained developer was determined. The smaller the concentration difference, the better the concentration change suppression ability. A modified Fuji Xerox DocuCenter Color400 machine was used to print 50,000 sheets of a test chart with an area coverage of 5% on A4-sized embossed paper (Tokushu Tokai Paper Co., Ltd., Lezac 66) in a low-temperature, low-humidity environment with an indoor temperature of 10°C and a relative humidity of 15%. The image density difference between the 1,000th sheet and the 50,000th sheet was measured using a spectrophotometer (X-Rite Ci62, manufactured by X-Rite) at three arbitrary points in the image. * Value, a * value and b * The values ​​were measured, and the color difference ΔE was calculated based on the following formula. The color difference ΔE was classified and evaluated as follows. A: Color difference ΔE is 1 or less, no problem. B: Color difference ΔE is greater than 1 and less than 2. There is little color difference and no problem. C: Color difference ΔE is more than 2 and less than 3. There is a density difference, but it is acceptable. D: Color difference ΔE is more than 3 and not more than 5. There is a density difference, but it is acceptable. E: Color difference ΔE exceeds 5. Problematic.

[0169]

number

[0170] [Table 1]

[0171] From the above results, it can be seen that the present embodiment is superior in suppressing density change compared to the comparative example, even when high-density printing is performed after successive printing with a small image amount. [Explanation of symbols]

[0172] 1Y, 1M, 1C, 1K Photoconductor (an example of an image carrier) 2Y, 2M, 2C, 2K Charging roll (an example of a charging means) 3 Exposure device (an example of an electrostatic image forming means) 3Y, 3M, 3C, 3K laser beam 4Y, 4M, 4C, 4K developing device (an example of developing means) 5Y, 5M, 5C, 5K Primary transfer roll (an example of a primary transfer means) 6Y, 6M, 6C, 6K Photoconductor cleaning device (an example of a cleaning means) 8Y, 8M, 8C, 8K toner cartridges 10Y, 10M, 10C, 10K Image forming units 20 Intermediate transfer belt (an example of an intermediate transfer body) 22 Driving Roll 24 Support roll 26 Secondary transfer roll (an example of a secondary transfer means) 28 Fixing device (an example of fixing means) 30 Intermediate transfer body cleaning device P Recording paper (an example of a recording medium) 107 Photoconductor (an example of an image carrier) 108 Charging roll (an example of charging means) 109 Exposure device (an example of electrostatic image forming means) 111 Developing device (an example of developing means) 112 Transfer device (an example of a transfer means) 113 Photoconductor cleaning device (an example of a cleaning means) 115 Fixing device (an example of fixing means) 116 Mounting Rail 117 Cabinet 118 Exposure Aperture 200 Process Cartridge 300 Recording paper (an example of a recording medium)

Claims

1. a toner including toner particles containing a binder resin and a release agent, the toner particles having an exposure rate of the release agent of 15% or more and 30% or less; a carrier having magnetic particles and a resin coating layer that coats the magnetic particles and contains inorganic particles, the inorganic particles having an arithmetic average particle size of 5 nm or more and 90 nm or less, the resin coating layer having an average thickness of 0.6 μm or more and 1.4 μm or less, and when a surface roughness of a fine uneven structure on the carrier surface is three-dimensionally analyzed, a ratio B / A of a planar view area A of an analyzed region to an uneven surface area B is 1.020 or more and 1.100 or less, The inorganic particles are silica particles. Electrostatic image developer.

2. 2. The electrostatic image developer according to claim 1, wherein the ratio B / A is 1.040 or more and 1.080 or less.

3. 3. The electrostatic image developer according to claim 1, wherein the inorganic particles have an arithmetic mean particle size of 5 nm or more and 70 nm or less.

4. 4. The electrostatic image developer according to claim 1, wherein the resin coating layer has an average thickness of 0.8 [mu]m or more and 1.2 [mu]m or less.

5. the toner contains an external additive, 5. The electrostatic image developer according to claim 1, wherein the inorganic particles have the same charge polarity as the external additive.

6. An electrostatic image developer according to claim 1, wherein the silicon element concentration on the carrier surface determined by X-ray photoelectron spectroscopy is greater than 2 atomic % and less than 20 atomic %.

7. 7. The electrostatic image developer according to claim 6, wherein the silicon element concentration is more than 5 atomic % and less than 20 atomic %.

8. 8. The electrostatic image developer according to claim 1, wherein the content of the inorganic particles is from 10% by mass to 60% by mass with respect to the total mass of the resin coating layer.

9. 9. The electrostatic image developer according to claim 1, wherein the weight average molecular weight of the resin contained in the resin coating layer is less than 300,000.

10. 10. The electrostatic image developer according to claim 9, wherein the weight average molecular weight of the resin contained in the resin coating layer is less than 250,000.

11. 11. The electrostatic image developer according to claim 1, wherein the magnetic particles have an arithmetic mean height Ra of a roughness curve of 0.3 [mu]m or more and 1.2 [mu]m or less.

12. a developing unit that contains the electrostatic image developer according to any one of claims 1 to 11 and develops an electrostatic image formed on a surface of an image carrier into a toner image by the electrostatic image developer, A process cartridge that is detachably attached to an image forming apparatus.

13. 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 charged surface of the image carrier; a developing unit that contains the electrostatic image developer according to any one of claims 1 to 11 and develops the electrostatic image formed on the surface of the image carrier into a toner image by the electrostatic image developer; a transfer means for transferring the toner image formed on the surface of the image carrier to a surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; An image forming apparatus comprising:

14. a charging step of charging a surface of an image carrier; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier; a developing step of developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer according to any one of claims 1 to 11; a transfer step of transferring the toner image formed on the surface of the image carrier onto a surface of a recording medium; a fixing step of fixing the toner image transferred onto the surface of the recording medium; The image forming method according to claim 1,

Images