Electrostatic image developing carrier and manufacturing method thereof, electrostatic image developer, process cartridge, image forming apparatus, and image forming method

Abstract

To provide a carrier for electrostatic charge image development with which uneven glossiness is prevented in an image to be obtained.SOLUTION: A carrier for electrostatic charge image development has a magnetic particle and a resin coating layer covering the magnetic particle. The resin coating layer includes aggregates of inorganic particles. An arithmetic average particle diameter of the aggregates of inorganic particles present on a surface of the carrier is 30 nm or more and 150 nm or less. A surface exposure ratio of the magnetic particles is 0 area% or more and 5 area% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an electrostatic image developing carrier and a method for producing the same, an electrostatic image developer, a process cartridge, an image forming apparatus, and an image forming method. [Background technology]

[0002] Patent Document 1 discloses a magnetic carrier comprising magnetic carrier particles having magnetic carrier core particles and a resin coating layer formed on the surface of the magnetic carrier core particles, and inorganic fine particles A present on the surface of the magnetic carrier particles, wherein the inorganic fine particles A have a rectangular parallelepiped particle shape, the inorganic fine particles A have a number average particle size (D1) of 10 nm to 60 nm, and the inorganic fine particles A have been surface-treated with a surface treatment agent, the solubility parameter (SP1) (J / mol)1 / 2 of the resin coating layer and the solubility parameter (SP2) (J / mol)1 / 2 of the surface treatment agent satisfy formula (1), and the coverage of the magnetic carrier surface with the inorganic fine particles A measured by ESCA is 5.0 atom % to 20.0 atom %. SP1-SP2≦14.00 (1) Patent Document 2 discloses a developing device that contains a developer containing a carrier and a toner and develops an electrostatic latent image formed on an electrostatic latent image carrier using the developer, the device comprising: a developer carrier that faces the electrostatic latent image carrier and transports the developer; and a developer regulating member that regulates the amount of the developer carried on the developer carrier; the carrier contains core particles and a resin coating layer that coats the core particles; the resin coating layer contains resin, carbon black, and two types of inorganic particles, inorganic particles A and inorganic particles B; and the inorganic particles, The developing device is characterized in that inorganic fine particles A and the carbon black exist with a concentration gradient in the thickness direction of the resin coating layer, the concentration of the inorganic fine particles A increases and the concentration of the carbon black decreases toward the surface side of the carrier, the volume content of the carbon black in the resin coating layer on the surface side of the carrier in a range of 0.0 μm to 0.1 μm deep from the surface of the resin coating layer is 0% or more and 30% or less, and a developing bias in which an AC component with a frequency of 5 kHz or more is superimposed on a DC component is applied to the developer carrier. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2020-091471 [Patent Document 2] Japanese Patent Application Publication No. 2018-155970 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a carrier for developing electrostatic images that has magnetic particles and a resin coating layer that coats the magnetic particles, and that suppresses uneven gloss in the resulting image compared to a carrier for developing electrostatic images in which the arithmetic mean particle size of aggregates of inorganic particles present on the carrier surface is less than 30 nm or more than 150 nm, or the surface exposure rate of the magnetic particles exceeds 5 area %. [Means for solving the problem]

[0005] The means for solving the above problems include the following aspects. <1> A carrier for developing electrostatic images, comprising magnetic particles and a resin coating layer covering the magnetic particles, the resin coating layer containing aggregates of inorganic particles, the aggregates of inorganic particles present on the carrier surface having an arithmetic mean particle size of 30 nm or more and 150 nm or less, and the surface exposure rate of the magnetic particles being 0 area % or more and 5 area % or less. <2> A gap is present at least partially between the resin coating layer and the surface of the magnetic particles. <1> 10. The carrier for developing electrostatic images according to claim 19. <3> The average width of the voids in the thickness direction of the resin coating layer is 50 nm or more and 300 nm or less. <2> 10. The carrier for developing electrostatic images according to claim 19. <4> The Si / C ratio of the carrier surface measured by X-ray photoelectron spectroscopy is 0.05 or more and 1.5 or less. <1> ~ <3> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <5> The Si / C ratio of the carrier surface measured by X-ray photoelectron spectroscopy is 0.05 or more and 1.0 or less. <4> 10. The carrier for developing electrostatic images according to claim 19. <6> The resin coating layer further contains conductive particles. <1> ~ <5> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <7> The resin coating layer further contains a binder polymer and resin particles. <1> ~ <6> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <8> The content of the inorganic particles including the aggregates of the inorganic particles is 15% by mass or more and 60% by mass or less with respect to the total mass of the resin coating layer. <1> ~ <7> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <9> The content of the inorganic particles including the aggregates of the inorganic particles is 20% by mass or more and 45% by mass or less with respect to the total mass of the resin coating layer. <8> 10. The carrier for developing electrostatic images according to claim 19. <10> The average primary particle size of the inorganic particles in the aggregate of inorganic particles is 5 nm or more and 50 nm or less. <1> ~ <9> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <11> The value of the arithmetic mean particle size of the aggregates of the inorganic particles / the mean thickness of the resin coating layer is 0.01 or more and 0.3 or less. <1> ~ <10> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <12> The value of the arithmetic mean particle diameter of the aggregates of the inorganic particles / the volume mean particle diameter of the carrier is 0.003 or more and 0.01 or less. <1> ~ <11> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <13> The content of aggregates of the inorganic particles relative to all inorganic particles contained in the resin coating layer is 50% by number or more and 90% by number or less. <1> ~ <12> 10. The electrostatic image developing carrier according to claim 9, wherein the carrier is a fluororesin. <14> The process includes mixing magnetic particles, inorganic particles, and a binder polymer in a stirring and mixing device and forming a resin coating layer by a dry method. <1> ~ <13> 10. A method for producing the carrier for developing electrostatic images according to any one of the above items. <15> <1> ~ <13> 1. An electrostatic image developer comprising the electrostatic image developing carrier according to any one of 1 to 8 above and a toner for electrostatic image development. <16> <15> and a developing means for developing an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image, the process cartridge being detachably mountable to an image forming apparatus. <17> The method includes at least a charging step of charging an image carrier, an exposure step of forming an electrostatic latent image on the surface of the image carrier, a developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic image developer to form a toner image, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a transfer receiving material, and a fixing step of fixing the toner image, wherein the electrostatic image developer is <15> 2. An image forming method using the electrostatic image developer according to claim 1. <18> an image carrier; a charging unit for charging the image carrier; an exposure unit for exposing the charged image carrier to light to form an electrostatic latent image on the image carrier; a developing unit for developing the electrostatic latent image with an electrostatic image developer to form a toner image; a transfer unit for transferring the toner image from the image carrier to a transfer receiving member; and a fixing unit for fixing the toner image, wherein the electrostatic image developer is <15> 2. An image forming apparatus, wherein the electrostatic image developer is the electrostatic image developer described in 1. [Effects of the Invention]

[0006] <1> , <2> , <6> , <7> or <14> According to the invention, there is provided a carrier for developing electrostatic images, which has magnetic particles and a resin coating layer covering the magnetic particles, and in which the arithmetic mean particle size of the aggregates of inorganic particles present on the carrier surface is less than 30 nm or more than 150 nm, or in which the surface exposure rate of the magnetic particles exceeds 5 area %, and in which gloss unevenness in the obtained image is suppressed compared to a carrier for developing electrostatic images. <3> According to the present invention, there is provided a carrier for developing electrostatic images in which gloss unevenness in the obtained image is more suppressed than in a carrier for developing electrostatic images in which the average width of the voids in the thickness direction of the resin coating layer is less than 50 nm or more than 300 nm. <4> According to the present invention, there is provided a carrier for developing electrostatic images in which gloss unevenness in the obtained image is more suppressed than in a carrier for developing electrostatic images in which the Si / C ratio, measured on the carrier surface by X-ray photoelectron spectroscopy, is less than 0.05 or more than 1.5. <5> According to the invention, there is provided a carrier for developing electrostatic images in which gloss unevenness in the obtained image is more suppressed than in a carrier for developing electrostatic images in which the Si / C ratio, measured on the carrier surface by X-ray photoelectron spectroscopy, is less than 0.05 or more than 1.0. <8> According to the invention, there is provided a carrier for developing electrostatic images in which gloss unevenness in the obtained image is more suppressed than in a carrier for developing electrostatic images in which the content of inorganic particles including aggregates of inorganic particles is less than 15 mass % or more than 60 mass % relative to the total mass of the resin coating layer. <9> According to the invention, there is provided a carrier for developing electrostatic images in which gloss unevenness in the obtained image is more suppressed than in a carrier for developing electrostatic images in which the content of inorganic particles including aggregates of inorganic particles is less than 20 mass % or more than 45 mass % relative to the total mass of the resin coating layer. <10> According to the invention, there is provided a carrier for developing electrostatic images in which gloss unevenness in the obtained image is more suppressed than in a carrier for developing electrostatic images in which the average primary particle size of the inorganic particles in the aggregate of the inorganic particles is less than 5 nm or more than 50 nm. <11> According to the invention, there is provided a carrier for developing electrostatic images in which gloss unevenness in the obtained image is more suppressed than in a carrier for developing electrostatic images in which the value of the arithmetic mean particle size of the aggregates of the inorganic particles / the average thickness of the resin coating layer is less than 0.01 or more than 0.3. <12> According to the invention, there is provided a carrier for developing electrostatic images in which gloss unevenness in the obtained image is more suppressed than in a carrier for developing electrostatic images in which the value of the arithmetic mean particle diameter of the aggregates of the inorganic particles / the volume mean particle diameter of the carrier is less than 0.003 or more than 0.01. <13> According to the invention, there is provided an electrostatic image developing carrier in which gloss unevenness in the obtained image is more suppressed than in an electrostatic image developing carrier in which the content of inorganic particle aggregates relative to all inorganic particles contained in the resin coating layer is less than 50% by number or more than 90% by number. <14> ~ <18> According to the invention, when a carrier having magnetic particles and a resin coating layer that coats the magnetic particles is used, an electrostatic image developer, process cartridge, image forming method, or image forming apparatus is provided in which uneven gloss in the resulting image is suppressed compared to an electrostatic image developing carrier in which the arithmetic mean particle size of the aggregates of inorganic particles present on the carrier surface is less than 30 nm or more than 150 nm, or the surface exposure rate of the magnetic particles exceeds 5 area %. [Brief explanation 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. [Figure 2] 1 is a schematic diagram illustrating an example of a process cartridge that is detachably mounted to an image forming apparatus according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0008]

[0023] The following describes embodiments of the present disclosure. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

[0009] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In the numerical ranges described in stages in this disclosure, 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. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0010] 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 purpose of the step is achieved.

[0011] When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited to these.

[0012] In the present disclosure, each component may contain multiple 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. In the present disclosure, the composition may contain multiple types of particles corresponding to each component. 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.

[0013] 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.

[0014] 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."

[0015] <Electrostatic image developing carrier> The carrier for developing electrostatic images according to this embodiment has magnetic particles and a resin coating layer that coats the magnetic particles, the resin coating layer contains aggregates of inorganic particles, the arithmetic mean particle size of the aggregates of inorganic particles present on the carrier surface is 30 nm or more and 150 nm or less, and the surface exposure rate of the magnetic particles is 0 area % or more and 5 area % or less.

[0016] When an image is printed, the resin coating layer of the carrier peels off, and the peeled pieces of resin coating layer adhere to the toner for development and transfer, and the peeled pieces of resin coating layer are fixed while remaining attached to the toner. The peeled pieces of resin coating layer melt due to the heat during fixing, but do not peel off from the fixing member, and because of poor releasability, uneven gloss often occurs, especially on coated paper with a small basis weight. In the carrier for developing electrostatic images according to this embodiment, the resin coating layer contains aggregates of inorganic particles, and the arithmetic mean particle size of the aggregates of inorganic particles present on the carrier surface is 30 nm or more and 150 nm or less, and the surface exposure rate of the magnetic particles is 0 area % or more and 5 area % or less. This allows the aggregates of inorganic particles present on the carrier surface to act as spacers and reduce stress on the carrier within the developing unit. Furthermore, the high coverage of the resin coating layer makes the resin coating layer less likely to peel off due to stress within the developing unit, and therefore an electrostatic image developing carrier can be obtained in which uneven gloss in the resulting image caused by peeling of the resin coating layer during fixing is suppressed.

[0017] On the surface of the carrier according to this embodiment, the exposure rate of magnetic particles is 0% or more and 5% or less. If the exposure rate of the magnetic particles on the carrier surface exceeds 5%, the resin coating layer is likely to peel off due to stress in the developing means, and the resulting image will have increased gloss unevenness due to peeling of the resin coating layer during fixing. From the viewpoint of further suppressing gloss unevenness in the resulting image (hereinafter also referred to as "gloss unevenness suppression"), the surface exposure rate of the magnetic particles on the carrier surface is preferably 0% or more and 4% or less, more preferably 0% or more and 3% or less, and particularly preferably 0% or more and 0.5% or less.

[0018] In this embodiment, the surface exposure rate of the magnetic particles on the carrier surface is determined by the following method. The SEM image of the carrier surface taken with a scanning electron microscope (SEM) at 1,500x magnification is binarized. The ratio of the area of ​​exposed magnetic particles to the area of ​​the entire carrier is the surface exposure rate (%) of magnetic particles.

[0019] Furthermore, the Si / C ratio of the carrier surface measured by X-ray photoelectron spectroscopy is preferably 0.05 or more and 1.5 or less, more preferably 0.05 or more and 1.0 or less, and particularly preferably 0.2 or more and 0.9 or less, from the viewpoint of suppressing gloss unevenness. Furthermore, in the above embodiment, the resin coating layer preferably contains an aggregate of silica particles as the aggregate of inorganic particles.

[0020] The Si / C ratio on the carrier surface is determined by X-ray photoelectron spectroscopy (XPS) using the following method. The elemental composition is analyzed using a JPS-9000MX (manufactured by JEOL Ltd.) as an analytical device, with an X-ray intensity of 10 kV / 30 mA and an analysis depth in Normal mode, and the peak area of ​​Si and the peak area of ​​C are measured and calculated.

[0021] The carrier according to this embodiment preferably has a gap at least partially between the resin coating layer and the surface of the magnetic particle. For example, when the resin coating layer is formed by a dry method as described below, the average width of the voids in the thickness direction of the resin coating layer is often 50 nm or more. From the viewpoint of suppressing gloss unevenness, the average width of the voids in the thickness direction of the resin coating layer is preferably 50 nm or more, more preferably 50 nm or more and 500 nm or less, even more preferably 50 nm or more and 300 nm or less, and particularly preferably 100 nm or more and 250 nm or less.

[0022] In the carrier according to this embodiment, from the viewpoint of suppressing uneven gloss, the area ratio of voids to the entire area of ​​the carrier is preferably 0% or more and 5% or less. The lower the area ratio of the voids, the better. From the viewpoint of suppressing uneven gloss, the area ratio of the voids to the entire carrier is preferably 4% or less, and more preferably 3% or less. The area ratio of voids to the entire area of ​​the carrier is preferably 0.05% or more, more preferably 0.1% or more, and even more preferably 0.2% or more, from the viewpoint of suppressing uneven gloss.

[0023] In this embodiment, the method for observing the cross section of the carrier and the method for measuring the average width and area ratio of the voids present at the boundary between the magnetic particles and the resin coating layer are as follows. The carrier is mixed with the epoxy resin, and the epoxy resin is solidified. The resulting solidified material is cut using an ultramicrotome to prepare a thin section sample with a thickness of 100 nm to 200 nm. The thin section sample is observed at 5000x magnification using a field emission scanning electron microscope (FE-SEM, e.g., Hitachi High-Technologies Corporation S-4800), and a cross-section is imaged. The cross-sectional image is analyzed using image analysis software (WinROOF2015, Mitani Corporation) to measure the maximum width of voids in the thickness direction of the resin coating layer that exist at the boundary between the magnetic particles and the resin coating layer. Furthermore, the maximum width of voids in the thickness direction of the resin coating layer for 100 carrier particles is arithmetically averaged, and the average width of the voids in the thickness direction of the resin coating layer is calculated. The void area ratio is calculated by determining the cross-sectional area of ​​one carrier particle (the area consisting of the magnetic particle, the resin coating layer, and the void) and the area of ​​the voids present at the boundary between the magnetic particle and the resin coating layer, and then calculating the void area ratio (%) of the cross-sectional area of ​​one carrier particle.The void area ratios (%) of 100 carrier particles are then arithmetically averaged.

[0024] The configuration of the carrier according to this embodiment will be described in detail below.

[0025] [Resin coating layer] The carrier for developing electrostatic images according to this embodiment has a resin coating layer that coats the magnetic particles, the resin coating layer contains aggregates of inorganic particles, and the arithmetic mean particle size of the aggregates of inorganic particles present on the carrier surface is 30 nm or more and 150 nm or less. The "aggregate of inorganic particles" in this embodiment may be any particle formed by aggregating two or more inorganic particles.

[0026] The arithmetic mean particle size of the inorganic particle aggregates in the resin coating layer is 30 nm or more and 150 nm or less, and from the viewpoint of suppressing gloss unevenness, it is preferably 50 nm or more and 150 nm or less, more preferably 80 nm or more and 150 nm or less, and particularly preferably 90 nm or more and 140 nm or less.

[0027] From the viewpoint of suppressing gloss unevenness, the average primary particle size of the inorganic particles in the resin coating layer is preferably 5 nm or more and 90 nm or less, more preferably 5 nm or more and 70 nm or less, even more preferably 5 nm or more and 50 nm or less, and particularly preferably 8 nm or more and 50 nm or less.

[0028] The average thickness of the resin coating layer is preferably 0.2 μm or more and 3.0 μm or less, more preferably 0.3 μm or more and 2.0 μm or less, and even more preferably 0.4 μm or more and 1.5 μm or less.

[0029] In this embodiment, the arithmetic mean particle size of the aggregates of inorganic particles contained in the resin coating layer, the average primary particle size of the inorganic particles, and the average thickness of the resin coating layer are determined by the following methods. 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 and analysis device and subjected to image analysis. One hundred aggregates of inorganic particles in the resin coating layer are randomly selected, and the maximum length (nm) of each is determined and the arithmetic average is calculated, which is defined as the arithmetic average particle size (nm) of the aggregates of inorganic particles. In addition, 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 mean is taken, which is the average particle diameter (nm) of the inorganic particles. Furthermore, the thickness (μm) of the resin coating layer is measured at 10 randomly selected locations per carrier particle, and then measurements are taken for 100 carrier particles, and the arithmetic average of all measurements is taken, which is the average thickness (μm) of the resin coating layer.

[0030] 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, silica particles are preferred from the viewpoint of suppressing uneven gloss.

[0031] The surfaces of the inorganic particles and aggregates of inorganic particles may be subjected to a hydrophobic treatment. Examples of hydrophobic treatment agents include known organosilicon compounds having an alkyl group (e.g., a methyl group, an ethyl group, a propyl group, a 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 preferred. The hydrophobic treatment agent may be used alone or in combination of two or more types.

[0032] Examples of methods for hydrophobizing inorganic particles and aggregates of inorganic particles with a hydrophobizing agent include a method using supercritical carbon dioxide 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 the hydrophobizing agent and a solvent that dissolves the hydrophobizing agent is applied (e.g., sprayed or painted) 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 the hydrophobizing agent and a solvent that dissolves the hydrophobizing agent is added to an inorganic particle dispersion in the atmosphere, the mixture is maintained, and then the inorganic particle dispersion and the mixed solution are dried.

[0033] From the viewpoint of suppressing gloss unevenness, the content of inorganic particles, including aggregates of inorganic particles, in the resin coating layer is preferably 10% by mass or more and 65% by mass or less, more preferably 15% by mass or more and 60% by mass or less, even more preferably 20% by mass or more and 45% by mass or less, and particularly preferably 20% by mass or more and 35% by mass or less, relative to the total mass of the resin coating layer.

[0034] From the viewpoint of suppressing gloss unevenness, the value of the arithmetic mean particle size of the inorganic particle aggregates / the mean thickness of the resin coating layer is preferably 0.005 or more and 0.5 or less, more preferably 0.01 or more and 0.3 or less, and particularly preferably 0.05 or more and 0.2 or less.

[0035] From the viewpoint of suppressing gloss unevenness, the value of the arithmetic mean particle diameter of the inorganic particle aggregates / volume mean particle diameter of the carrier is preferably 0.001 or more and 0.05 or less, more preferably 0.002 or more and 0.03 or less, and particularly preferably 0.003 or more and 0.01 or less.

[0036] From the viewpoint of suppressing gloss unevenness, the content of the inorganic particle aggregates relative to the total inorganic particles contained in the resin coating layer is preferably 50% by number or more and 99% by number or less, more preferably 50% by number or more and 90% by number or less, and particularly preferably 70% by number or more and 90% by number or less.

[0037] From the viewpoints of mechanical strength and suppression of uneven gloss, the resin coating layer preferably contains a binder polymer, and more preferably contains a binder polymer and resin particles. Examples of binder polymers include styrene-acrylic resins; polyolefin resins such as polyethylene and polypropylene; polyvinyl or polyvinylidene resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymers; straight silicone resins or modified silicone resins consisting of organosiloxane bonds; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyesters; polyurethanes; polycarbonates; amino resins such as urea-formaldehyde resins; and epoxy resins.

[0038] As the binder polymer, a styrene acrylic resin is preferred from the viewpoint of adhesiveness to magnetic particles (particularly ferrite particles).

[0039] As a polymerization component of the styrene-acrylic resin, a lower alkyl ester of (meth)acrylic acid (for example, a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 9 carbon atoms) is preferred, and specific examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc. These monomers may be used alone or in combination of two or more.

[0040] The proportion of the styrene acrylic resin in the total binder polymer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably the total binder polymer is substantially styrene acrylic resin.

[0041] The resin coating layer may contain resin particles for the purpose of increasing the mechanical strength of the resin coating layer. The resin particles are a separate element from the binder polymer of the resin coating layer. The resin particles are observed as particles in the resin coating layer in an image of a cross section of the carrier.

[0042] Examples of resin particles include particles of crosslinkable resins and particles of thermosetting resins. Examples of cross-linkable resins include cross-linked styrene acrylic resins. Examples of the thermosetting resin include melamine resin, urea resin, urethane resin, guanamine resin, and amide resin.

[0043] Furthermore, from the viewpoint of mechanical strength, the content of resin particles in the resin coating layer is preferably 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.05 parts by mass or more and 5 parts by mass or less, even more preferably 0.1% by mass or more and 3% by mass or less, and particularly preferably 0.1% by mass or more and 1% by mass or less, relative to 100 parts by mass of the magnetic particles.

[0044] The resin coating layer preferably contains conductive particles for the purpose of controlling the charge or resistance of the carrier. Examples of conductive particles include carbon black; metals such as gold, silver, and copper; metal compounds such as barium sulfate, aluminum borate, potassium titanate, titanium oxide, zinc oxide, tin oxide, antimony-doped tin oxide, tin-doped indium oxide, and aluminum-doped zinc oxide; and resin particles coated with metals.

[0045] Furthermore, from the viewpoint of charging properties, the amount of conductive particles added to the resin coating layer is preferably 0.01 parts by mass or more and 10 parts by mass or less, more preferably 0.05 parts by mass or more and 5 parts by mass or less, even more preferably 0.1% by mass or more and 3% by mass or less, and particularly preferably 0.1% by mass or more and 1% by mass or less, relative to 100 parts by mass of the magnetic particles.

[0046] From the viewpoint of suppressing uneven gloss, the amount of the resin coating layer is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 1.5 parts by mass or more and 8 parts by mass or less, and even more preferably 2 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of magnetic particles.

[0047] [Magnetic particles] The magnetic particles are not particularly limited, and known magnetic particles used as a core material of a carrier can be used. Specific examples of the magnetic particles include particles of magnetic metals such as iron, nickel, and cobalt; particles of magnetic oxides such as ferrite and magnetite; resin-impregnated magnetic particles in which porous magnetic powder is impregnated with resin; and magnetic powder-dispersed resin particles in which magnetic powder is dispersed in resin.

[0048] In this embodiment, ferrite particles are preferred as the magnetic particles from the viewpoint of chargeability.

[0049] The volume average particle size of the magnetic particles is preferably 15 μm or more and 100 μm or less, more preferably 20 μm or more and 80 μm or less, and even more preferably 30 μm or more and 60 μm or less.

[0050] The magnetic force of the magnetic particles is, for example, 50 emu / g or more, preferably 60 emu / g or more, in terms of saturation magnetization in a magnetic field of 3000 oersteds. The saturation magnetization is measured using a vibrating sample magnetometer VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.). The measurement sample is placed in a cell with an inner diameter of 7 mm and a height of 5 mm and set in the instrument. The measurement is performed by applying a magnetic field and sweeping up to a maximum of 3000 oersteds. The applied magnetic field is then reduced, and a hysteresis curve is created on recording paper. The saturation magnetization, remanent magnetization, and coercive force are determined from the curve data.

[0051] The volume electrical resistance (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 a circular jig on which the electrode plate is arranged, with a thickness of 1 mm to 3 mm, forming a layer. 2 The layer is sandwiched between two electrode plates. To eliminate any gaps between the objects being measured, a 4 kg load is placed on the electrode plates placed on the layer, and the layer thickness (cm) is then measured. 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 becomes 103.8 V / cm, and the current value (A) that flows at this time is read. The measurement environment is a temperature of 20°C and a relative humidity of 50%. The formula for calculating the volume electrical resistivity (Ω·cm) of the object being measured is as shown below. R=E×20 / (I-I0) / L In the above formula, R represents the volume electrical resistance (Ω·cm) of the object to be measured, E represents the applied voltage (V), I represents the current value (A), I0 represents the current value (A) at an applied voltage of 0 V, and L represents the layer thickness (cm). The coefficient 20 is the area of ​​the electrode plate (cm 2 )

[0052] [Carrier Properties] The volume average particle size of the carrier for developing electrostatic images according to this embodiment is preferably 15 μm or more and 120 μm or less, more preferably 20 μm or more and 100 μm or less, and even more preferably 30 μm or more and 80 μm or less. The volume average particle diameters of the magnetic particles and carrier in this embodiment are values ​​measured using a laser diffraction particle size distribution analyzer LA-700 (manufactured by Horiba, Ltd.) Specifically, the particle size distribution obtained by the analyzer is divided into particle size ranges (channels), and the particle diameter at which the cumulative volume distribution is subtracted from the small particle size side and cumulative 50% is defined as the volume average particle diameter.

[0053] The amount of free resin in the carrier for developing electrostatic images according to this embodiment is preferably 200 ppm or less, more preferably 100 ppm or less, and particularly preferably 75 ppm or less, from the viewpoint of suppressing color dullness.

[0054] In this embodiment, the method for measuring the amount of free resin in the carrier for developing an electrostatic image is as follows. A certain amount of carrier was weighed and dispersed in water, and the dispersion was filtered while the carrier was fixed with a magnet. The filter paper was dried, and the amount of free resin was calculated using the following formula from the difference in mass before and after the filter paper and the weighed amount of carrier. Amount of free resin (ppm) = Increase in filter paper (g) ÷ Carrier (g)

[0055] From the viewpoint of suppressing color dullness, the proportion of aggregates in the carrier for developing electrostatic images according to this embodiment after sieving through a 75 μm sieve is preferably 5% by number or less, more preferably 1% by number or less, even more preferably 0.1% by number or less, and particularly preferably 0.01% by number or less.

[0056] In this embodiment, the method for measuring the proportion of aggregates in the carrier for developing electrostatic images after sieving through a 75 μm sieve is as follows. The carrier is sieved using a sieve with 75 μm openings, and the sieved carrier is spread out so as not to overlap as much as possible. A scanning electron microscope (SEM) photograph is taken at 350x magnification, and the ratio of the number of carriers that have not been broken down to primary particles to the number of carriers in one field of view is measured.

[0057] In this embodiment, the fluidity of the carrier for developing electrostatic images is preferably 20 sec / 50 g or more and 50 sec / 50 g or less, more preferably 22 sec / 50 g or more and 35 sec / 50 g or less, and particularly preferably 25 sec / 50 g or more and 30 sec / 50 g or less, from the viewpoint of suppressing density changes in the resulting image. The fluidity of the carrier for developing electrostatic images in this embodiment is a value measured at 25° C. and 50% RH in accordance with JIS Z2502 (2020).

[0058] <Method of manufacturing electrostatic image developing carrier> The method for producing the carrier for developing electrostatic images according to the present embodiment is not particularly limited, but is preferably a production method including a step of mixing magnetic particles, inorganic particles, and a binder polymer in a stirring and mixing device and forming a resin coating layer by a dry method. As the stirring and mixing device, a known stirring and mixing device can be used, among which a Henschel mixer is preferred. By using a Henschel mixer, it is easy to set the arithmetic mean particle size of the inorganic particle aggregates in the resin coating layer to 30 nm or more and 150 nm or less, and to set the exposed rate of the magnetic particles to 5% or less.

[0059] Furthermore, a preferred example of a method for manufacturing a carrier for developing electrostatic images according to this embodiment is a manufacturing method using an agitation mixer, which includes dry-adhering resin particles that will become the binder polymer of the resin coating layer and inorganic particles to the surfaces of magnetic particles in the agitation mixer (adhering step), and mixing the magnetic particles to which the resin particles and inorganic particles are adhered while heating them in the agitation mixer to a temperature at which the resin particles melt (heating and mixing step). The manufacturing method will be described in detail below.

[0060] -Attachment process- The adhesion step is a step in which resin particles (referred to as "first resin particles") that will become the binder polymer of the resin coating layer and inorganic particles are dry-adhered to the surfaces of the magnetic particles in a stirring and mixing device. "Dry" means that no solvent is used to dissolve or disperse the resin. In the adhesion step, it is preferable to stir and mix in a stirring and mixing device.

[0061] The first resin particles melt during the heating and mixing process to become the binder polymer of the resin coating layer. Here, "melting" means that the first resin particles melt together without maintaining their particle shape. Therefore, the first resin particles are resin particles having thermal properties that prevent them from maintaining their particle shape during the heating and mixing process. In addition, the addition of the first resin particles and the like to the stirring and mixing device in the adhesion step may be carried out only once, or may be carried out in two or more separate steps.

[0062] When the resin coating layer of the carrier contains resin particles, which are an element separate from the substrate, the resin particles (referred to as "second resin particles") are also attached to the magnetic particles in the attachment step. The second resin particles are resin particles that do not melt during the heating and mixing step and maintain their particle shape.

[0063] When conductive particles are contained in the resin coating layer of the carrier, the conductive particles are also attached to the magnetic particles in the attachment step.

[0064] The adhering step is preferably a step of adhering the first resin particles or the like to the surface of the magnetic particles by mechanical stirring. A specific example of the process is a process of placing the materials in a stirring and mixing device and stirring them. The temperature inside the stirring and mixing device is a temperature at which the first resin particles do not melt (i.e., a temperature at which the particle shape of the first resin particles is maintained).

[0065] The mixing temperature in the adhesion step is preferably lower than the mixing temperature in the heating and mixing step, and although it depends on the melting temperature of the resin particles used, it is preferably 0°C or higher and 80°C or lower, more preferably 10°C or higher and 50°C or lower. The mixing time in the adhesion step is not particularly limited, but is preferably from 0.1 to 120 minutes, more preferably from 1 to 60 minutes.

[0066] -Heating mixing process- The heating and mixing step is a step of mixing magnetic particles with at least first resin particles and inorganic particles attached thereto in the stirring and mixing device while heating them to a temperature at which the first resin particles melt. Here, "melting" means that the first resin particles melt and fuse together without maintaining their particle shape. The heating and mixing step melts the first resin particles and kneads them into the fine irregularities on the magnetic particle surfaces together with the inorganic particles, forming a highly adhesive resin coating layer.

[0067] The stirring and mixing device preferably has a temperature control structure capable of heating and cooling, and stirring blades. The temperature control structure is not particularly limited, but a jacket structure is preferred. The shape of the stirring blade is not particularly limited, and examples thereof include Banbury type, Sigma type, Z type, spiral type, and fishtail type. The diameter D of the impeller is not particularly limited as long as it is a size that matches the stirring and mixing device to be used. In addition, the diameter D of the impeller in this embodiment is the maximum outer diameter of the part that the impeller passes through as it rotates in a plane perpendicular to the rotation axis. From the viewpoint of the carrier production speed and the suppression of gloss unevenness, the peripheral speed of the stirring blade is preferably 0.1 m / sec or more and 100 m / sec or less, more preferably 1 m / sec or more and 50 m / sec or less, and particularly preferably 2 m / sec or more and 30 m / sec or less. The clearance between the stirring vessel and the impeller in the stirring and mixing apparatus is not limited and should be adjusted to suit the mixer used. However, if the clearance is too large, not only will the carrier accumulated at the bottom not be completely crushed, but the shear force of the crushing process will depend not only on the peripheral speed and stirring workload of the impeller but also on the clearance itself. Therefore, the narrower the clearance, the better. However, due to limitations in the manufacture of the apparatus, there is a limit to the clearance. Therefore, the clearance between the outer periphery of the impeller and the stirring vessel is preferably 5% or less, and more preferably 3.5% or less, in terms of the value of clearance / impeller diameter. It is also preferable to continue stirring with the stirring blades during the mixing step.

[0068] The heating temperature in the heating and mixing step is preferably equal to or higher than the melting temperature of the first resin particles, and more preferably 20°C or more higher than the melting temperature of the first resin particles. Depending on the melting temperature of the resin particles used, the heating temperature is preferably 80°C or higher and 200°C or lower, more preferably 100°C or higher and 180°C or lower, and particularly preferably 120°C or higher and 180°C or lower. The mixing time in the heating and mixing step is not particularly limited, but is preferably from 0.1 to 120 minutes, more preferably from 1 to 60 minutes.

[0069] -Crushing cooling process- In the method for producing an electrostatic image developing carrier according to this embodiment, it is preferable to carry out a crushing and cooling step, following the heating and mixing step, in which the material obtained in the heating and mixing step is cooled while being crushed. This step is a step in which the material obtained in the heating and mixing step is cooled while being crushed into primary particles of the carrier.

[0070] The crushing and cooling step does not require active cooling, but simply involves crushing at room temperature (for example, in an atmosphere of 5° C. to 35° C.) There are no limitations on the crushing means, and a known mixer or mill can be used.

[0071] In the method for producing the electrostatic image developing carrier according to the present embodiment, it is preferable to carry out a classification step or a sieving step after the mixing step or the crushing and cooling step. There are no limitations on the means for classification or sieving, and known means can be used. The method for producing the electrostatic image developing carrier according to this embodiment may also include other steps, such as a step of preparing resin particles.

[0072] <Electrostatic image developer> The developer according to this embodiment contains the toner and the carrier according to this embodiment.

[0073] The developer according to this embodiment is prepared by mixing the toner and the carrier according to this embodiment in an appropriate ratio. The mixing ratio (mass ratio) of the toner to the carrier is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100.

[0074] [Toner for developing electrostatic images] The toner is not particularly limited, and known toners can be used. For example, a colored toner containing toner particles containing a binder resin and a colorant can be used, and an infrared absorbing toner using an infrared absorbing agent instead of a colorant can also be used. The toner may contain a release agent, various internal additives, external additives, etc.

[0075] -Binder resin- Examples of binder resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), and vinyl resins made of copolymers of two or more of these monomers. Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these. These binder resins may be used alone or in combination of two or more.

[0076] The binder resin is preferably a polyester resin, and examples of the polyester resin include known polyester resins.

[0077] The glass transition temperature (Tg) of the polyester resin is preferably 50°C or higher and 80°C or lower, and more preferably 50°C or higher and 65°C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, is determined from the "extrapolated glass transition onset temperature" described in the method for determining glass transition temperature in JIS K7121-1987 "Method for measuring transition temperature of plastics."

[0078] The weight average molecular weight (Mw) of the 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 polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the 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). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC 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 prepared with monodisperse polystyrene standard samples.

[0079] The content of the binder resin is preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass, based on the total mass of the toner particles.

[0080] -Coloring agent- Examples of colorants include carbon black, chrome yellow, Hansa Yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Balkan orange, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, Examples of suitable dyes include pigments such as ultramarine blue, chalco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate; and dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, and thiazole-based dyes. The colorant may be used alone or in combination of two or more kinds.

[0081] The colorant may be surface-treated as needed, or may be used in combination with a dispersant. Furthermore, a plurality of colorants may be used in combination.

[0082] 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.

[0083] -Mold release agent- Examples of release agents include hydrocarbon waxes, natural waxes such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral / petroleum waxes such as montan wax, and ester waxes such as fatty acid esters and montanic acid esters, but are not limited thereto.

[0084] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) by using the "melting peak temperature" described in the method for determining the melting temperature in JIS K7121-1987 "Method for measuring transition temperatures of plastics."

[0085] 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.

[0086] -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.

[0087] -Characteristics of toner particles, etc.- The toner particles may be toner particles of a single layer structure, or may be toner particles of a so-called core-shell structure composed of a core (core particle) and a resin coating layer (shell layer) that coats the core. The toner particles of the core-shell structure may be composed of, for example, a core composed of a binder resin and, if necessary, other additives such as a colorant and a release agent, and a resin coating layer composed of a binder resin.

[0088] The volume average particle size (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less. The volume average particle size (D50v) of toner particles is measured using a Coulter Multisizer II (manufactured by Beckman Coulter) and an ISOTON-II (manufactured by Beckman Coulter). For measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5% by weight aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is then added to 100 ml to 150 ml of electrolyte. The electrolyte containing the suspended sample is dispersed in an ultrasonic disperser for 1 minute, and the particle size distribution of particles ranging from 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. 50,000 particles are sampled.

[0089] -External additives- Examples of external additives include inorganic particles such as SiO2, TiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, KO, Na2O, ZrO2, CaO·SiO2, KO·(TiO2)n, Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, and MgSO4.

[0090] The surfaces of inorganic particles as external additives are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is usually, for example, 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the inorganic particles.

[0091] Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning agents (for example, metal salts of higher fatty acids such as zinc stearate, and particles of fluorine-based polymers).

[0092] The amount of the external additive added is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, based on the toner particles.

[0093] -Toner manufacturing method- The toner is obtained by producing toner particles and then externally adding an external additive to the toner particles. The toner particles may be produced by either a dry production method (e.g., a kneading and pulverization method) or a wet production method (e.g., an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). There are no particular restrictions on these production methods, and any known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0094] <Image forming device, image forming method> The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, a developing unit that contains an electrostatic image developer and develops the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, a transfer unit that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing unit that fixes 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.

[0095] The image forming apparatus according to this embodiment carries out an image forming method (the image forming method according to this embodiment) that 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.

[0096] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a cleaning means that cleans the surface of the image carrier after the transfer of the toner image but before charging; and an apparatus equipped with a discharging means that irradiates the surface of the image carrier with discharging light to discharge it after the transfer of the toner image but before charging. When the image forming apparatus according to the present embodiment is an apparatus of the intermediate transfer type, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means for primarily transferring the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means for secondarily transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0097] In the image forming apparatus according to the present embodiment, for example, the 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 image developer according to the present embodiment and is equipped with the developing means is preferably used.

[0098] 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. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0099] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to this embodiment. The image forming apparatus shown in Figure 1 includes first through fourth electrophotographic image forming units 10Y, 10M, 10C, and 10K (image forming means) that output images in the colors 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 side by side horizontally spaced apart by predetermined distances. These units 10Y, 10M, 10C, and 10K may be process cartridges that are detachably attached to the image forming apparatus.

[0100] An intermediate transfer belt (an example of an intermediate transfer body) 20 is provided above each of the units 10Y, 10M, 10C, and 10K and 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 to the fourth unit 10K. A force is applied to the support roll 24 by a spring or the like (not shown) 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 (examples of developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K are supplied with yellow, magenta, cyan, and black toner contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0101] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, we will explain here the first unit 10Y, which forms a yellow image and is arranged upstream in the direction of travel of the intermediate transfer belt.

[0102] The first unit 10Y has a photoreceptor 1Y that acts as an image carrier. Around the photoreceptor 1Y, there are arranged in this order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoreceptor 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 photoreceptor cleaning device (an example of a cleaning means) 6Y that removes toner remaining on the surface of the photoreceptor 1Y after the primary transfer. The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is provided at a position facing the photoreceptor 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).

[0103] The operation of forming a yellow image in the first unit 10Y will be described below. First, prior to operation, the surface of the photosensitive member 1Y is charged to a potential of −600V to −800V by the charging roll 2Y. The photoconductor 1Y has 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 with a resistivity of Ωcm or less. This photosensitive layer normally has a high resistance (the resistance of ordinary resins), but when irradiated with a laser beam, the resistivity of the irradiated portion changes. Therefore, the exposed surface of the photosensitive element 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). This forms an electrostatic charge image of a yellow image pattern on the surface of the photosensitive element 1Y.

[0104] An electrostatic image is an image formed on the surface of the photosensitive element 1Y by charging it; the laser beam 3Y reduces the resistivity of the irradiated portion of the photosensitive layer, causing the charged charges on the surface of the photosensitive element 1Y to flow, while the charges remain in the portions not irradiated by the laser beam 3Y, forming a so-called negative latent image. The electrostatic image formed on the photoreceptor 1Y rotates to a predetermined development position as the photoreceptor 1Y moves, and at this development position, the electrostatic image on the photoreceptor 1Y is developed into a toner image by the developing device 4Y and made visible.

[0105] The developing device 4Y contains an electrostatic image developer containing, for example, at least yellow toner and a carrier. The yellow toner is frictionally 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 photoreceptor 1Y. As the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed with the yellow toner. The photoreceptor 1Y on which the yellow toner image has been formed continues to travel at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transported to a predetermined primary transfer position.

[0106] 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 to the primary transfer roll 5Y acts on the toner image, causing the toner image on the photoreceptor 1Y to be 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 photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

[0107] The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K of the second unit 10M and subsequent units is also controlled in accordance with the first unit. In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is conveyed sequentially through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are superimposed and transferred.

[0108] The intermediate transfer belt 20, onto which the four-color toner images have been multiplex-transferred through the first to fourth units, reaches a secondary transfer section composed of the intermediate transfer belt 20, a support roll 24 in contact with 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, recording paper (an example of a recording medium) P is fed via a feed mechanism into the gap between the secondary transfer roll 26 and the intermediate transfer belt 20 at a predetermined timing, and a secondary transfer bias is applied to the support roll 24. The transfer bias applied at this time has a negative polarity, the same as the negative polarity of the toner. Electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined according to resistance detected by resistance detection means (not shown) that detects resistance in the secondary transfer section, and is voltage-controlled.

[0109] Thereafter, the recording paper P is sent to the pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image.

[0110] Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copiers, printers, etc. In addition to the recording paper P, 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 plain paper is coated with resin or the like, or art paper for printing, etc., is preferably used.

[0111] The recording paper P on which the color image has been fixed is conveyed toward the discharge section, and the series of color image forming operations is completed.

[0112] <Process cartridge> The process cartridge according to this embodiment is a process cartridge that is detachably attached to an image forming apparatus and that contains the electrostatic image developer according to this embodiment and 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.

[0113] The process cartridge according to this embodiment is not limited to the above configuration, but may also be configured to include a developing means and, if necessary, at least one other means selected from an image carrier, a charging means, an electrostatic image forming means, and a transfer means.

[0114] An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0115] FIG. 2 is a schematic diagram showing the configuration of the process cartridge according to the present embodiment. The process cartridge 200 shown in FIG. 2 is configured to integrally combine and hold a photosensitive member 107 (an example of an image carrier), a charging roll 108 (an example of a charging means) provided around the photosensitive member 107, a developing device 111 (an example of a developing means), and a photosensitive member cleaning device 113 (an example of a cleaning means), which are held by a housing 117 provided with, for example, mounting rails 116 and an opening 118 for exposure, and is made 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 recording paper (an example of a recording medium). [Example]

[0116] The present embodiment will be described in more detail below by way of examples, but the present embodiment is not limited to the following examples. Synthesis, processing, production, etc. were carried out at room temperature (25°C ± 3°C) unless otherwise specified. In the following description, all "parts" and "%" are by mass unless otherwise specified.

[0117] <Toner Production> [Preparation of amorphous polyester resin dispersion (A1)] Ethylene glycol: 37 parts Neopentyl glycol: 65 parts 1,9-nonanediol: 32 parts Terephthalic acid: 96 parts The above materials were placed in a reaction vessel, the temperature was raised to 200°C over 1 hour, and after confirming uniform stirring within the reaction system, 1.2 parts of dibutyltin oxide was added. The temperature was raised to 240°C over 6 hours while distilling off the resulting water. Stirring was continued at 240°C for 4 hours to obtain an amorphous polyester resin (acid value 9.4 mgKOH / g, weight-average molecular weight 13,000, glass transition temperature 62°C). The amorphous polyester resin was transferred in its molten state to an emulsifier / disperser (Cavitron CD1010, Eurotech) at a rate of 100 g / min. Separately, dilute ammonia water (0.37% concentration) prepared by diluting reagent ammonia water with ion-exchanged water was placed in a tank and heated to 120°C in a heat exchanger. This was then transferred to the emulsifier / disperser at a rate of 0.1 L / min simultaneously with the amorphous polyester resin. The emulsifier / disperser was operated at a rotor speed of 60 Hz and a pressure of 5 kg / cm. 2 The operation was carried out under the conditions of the above, and an amorphous polyester resin dispersion (A1) having a volume average particle size of 160 nm and a solid content of 20% was obtained.

[0118] [Preparation of Crystalline Polyester Resin Dispersion (C1)] Decanedioic acid: 81 parts Hexanediol: 47 parts The above materials were placed in a reaction vessel, and the temperature was raised to 160°C over 1 hour. After confirming that the reaction system was uniformly stirred, 0.03 parts of dibutyltin oxide was added. The temperature was raised to 200°C over 6 hours while distilling off the produced water, and stirring was continued at 200°C for 4 hours. The reaction liquid was then cooled, solid-liquid separation was performed, and the solid was dried at 40°C under reduced pressure to obtain crystalline polyester resin (C1) (melting point 64°C, weight average molecular weight 15,000).

[0119] Crystalline polyester resin (C1): 50 parts Anionic surfactant (Dai-ichi Kogyo Seiyaku Co., Ltd., Neogen RK): 2 parts Ion-exchanged water: 200 parts The above materials were heated to 120°C and thoroughly dispersed using a homogenizer (Ultra Turrax T50, IKA), and then dispersed using a pressure discharge homogenizer. When the volume average particle size reached 180 nm, the particles were collected to obtain a crystalline polyester resin dispersion (C1) with a solid content of 20%.

[0120] [Preparation of release agent particle dispersion (W1)] Paraffin wax (HNP-9 manufactured by Nippon Seiro Co., Ltd.): 100 parts Anionic surfactant (Dai-ichi Kogyo Seiyaku Co., Ltd., Neogen RK): 1 part Ion-exchanged water: 350 parts The above materials were mixed and heated to 100°C, dispersed using a homogenizer (IKA Ultra Turrax T50), and then dispersed using a pressure discharge Gaulin homogenizer to obtain a release agent particle dispersion liquid in which release agent particles with a volume average particle size of 200 nm were dispersed. Ion-exchange water was added to this release agent particle dispersion liquid to adjust the solid content to 20%, and this was used as release agent particle dispersion liquid (W1).

[0121] [Preparation of Colorant Particle Dispersion (C1)] Cyan pigment (Pigment Blue 15:3, manufactured by Dainichi Seika Color & Chemicals Co., Ltd.): 50 parts Anionic surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Neogen RK): 5 parts Ion-exchanged water: 195 parts The above materials were mixed and dispersed for 60 minutes using a high-pressure impact disperser (Ultimizer HJP30006, Sugino Machine Co., Ltd.) to obtain a colorant particle dispersion (C1) with a solid content of 20%.

[0122] [Preparation of Colorant Particle Dispersion (M1)] Magenta pigment (Pigment Red 122, DIC): 50 parts Anionic surfactant (Dai-ichi Kogyo Seiyaku Co., Ltd., Neogen RK): 5 parts Ion-exchanged water: 195 parts The above materials were mixed and dispersed for 60 minutes using a high-pressure impact disperser (Ultimizer HJP30006, Sugino Machine Co., Ltd.) to obtain a colorant particle dispersion (M1) with a solid content of 20%.

[0123] [Preparation of Colorant Particle Dispersion (Y1)] Yellow pigment (Pigment Yellow 74, manufactured by Dainichi Seika Color & Chemicals Co., Ltd.): 50 parts Anionic surfactant (manufactured by Daiichi Kogyo Seiyaku Co., Ltd., Neogen RK): 5 parts Ion-exchanged water: 195 parts The above materials were mixed and dispersed for 60 minutes using a high-pressure impact disperser (Ultimizer HJP30006, Sugino Machine Co., Ltd.) to obtain a colorant particle dispersion (Y1) with a solid content of 20%.

[0124] [Preparation of cyan toner particles (C1)] Ion-exchanged water: 200 parts Amorphous polyester resin dispersion (A1): 150 parts Crystalline polyester resin dispersion (C1): 10 parts Release agent particle dispersion (W1): 10 parts Colorant particle dispersion (C1): 15 parts Anionic surfactant (TaycaPower): 2.8 parts The above materials were placed in a reaction vessel, and 0.1 mol / L nitric acid was added to adjust the pH to 3.5. An aqueous polyaluminum chloride solution prepared by dissolving 2 parts of polyaluminum chloride (Oji Paper Co., Ltd., 30% powder product) in 30 parts of ion-exchange water was then added. The mixture was dispersed at 30°C using a homogenizer (IKA Ultra Turrax T50), then heated to 45°C in a heating oil bath and maintained at that temperature until the volume average particle size reached 4.9 μm. Next, 60 parts of amorphous polyester resin dispersion (A1) were added and maintained for 30 minutes. When the volume average particle size reached 5.2 μm, another 60 parts of amorphous polyester resin dispersion (A1) were added and maintained for 30 minutes. Next, 20 parts of a 10% NTA (nitrilotriacetic acid) metal salt aqueous solution (Chilest 70, Chelest Co., Ltd.) was added, and the pH was adjusted to 9.0 by adding 1 mol / L aqueous sodium hydroxide solution. Next, 1 part of anionic surfactant (TaycaPower) was added, and the mixture was heated to 85°C with continued stirring and maintained at that temperature for 5 hours. The mixture was then cooled to 20°C at a rate of 20°C / min. The mixture was then filtered, thoroughly washed with ion-exchanged water, and dried to obtain cyan toner particles (C1) with a volume average particle size of 5.7 μm.

[0125] [Preparation of magenta toner particles (M1)] Magenta toner particles (M1) were obtained in the same manner as in the preparation of cyan toner particles (C1), except that the colorant particle dispersion liquid (C1) was changed to the colorant particle dispersion liquid (M1).

[0126] [Preparation of Yellow Toner Particles (Y1)] Yellow toner particles (Y1) were obtained in the same manner as in the preparation of cyan toner particles (C1), except that the colorant particle dispersion liquid (C1) was changed to the colorant particle dispersion liquid (Y1).

[0127] [Preparation of Cyan Toner (C1)] 100 parts by mass of cyan toner particles (C1) and 1.5 parts by mass of hydrophobic silica particles (RY50, manufactured by Nippon Aerosil Co., Ltd.) were placed in a sample mill and mixed at a rotation speed of 10,000 rpm for 30 seconds. The mixture was then sieved through a vibrating sieve with 45 μm openings to obtain cyan toner (C1) with a volume average particle size of 5.7 μm.

[0128] [Preparation of magenta toner (M1)] A magenta toner (M1) was obtained in the same manner as in the preparation of the cyan toner (C1), except that the cyan toner particles (C1) were changed to magenta toner particles (M1).

[0129] [Preparation of Yellow Toner (Y1)] A yellow toner (Y1) was obtained in the same manner as in the preparation of the cyan toner (C1), except that the cyan toner particles (C1) were changed to yellow toner particles (Y1).

[0130] [Silica particles (1)] HM20S (fumed silica particles, manufactured by Tokuyama Corporation, volume average particle size 12 nm) was prepared and used as silica particles (1).

[0131] Example 1 MnMg ferrite core material (volume average particle size 30 μm): 100 parts Styrene / methyl methacrylate copolymer resin particles (polymerization ratio by mass 2 / 8, weight average molecular weight 500,000): 2.0 parts Silica particles (1): 1.0 parts The above materials were placed in a stirring mixer with stirring blades, the temperature inside the stirring mixer was set to 20°C, and the materials were stirred and mixed for 15 minutes at a peripheral speed of the stirring blades of 10.0 m / sec (adhesion process), causing the resin particles and silica particles to adhere to the core material. Next, the temperature inside the stirring mixer was raised to 140°C, and the mixture was stirred and mixed for 15 minutes at a peripheral speed of the stirring blade of 5.0 m / s (heating and mixing step). The powder was taken out of the stirring mixer and sieved through a mesh with 75 μm openings to remove coarse powder, thereby obtaining a carrier (carrier for developing electrostatic images).

[0132] [Silica particles (2)] Commercially available hydrophobic silica particles (fumed silica particles surface-treated with hexamethyldisilazane, volume average particle size 40 nm) were prepared and designated as silica particles (2).

[0133] [Silica particles (3)] Commercially available hydrophobic silica particles (fumed silica particles surface-treated with hexamethyldisilazane, volume average particle size 90 nm) were prepared and designated as silica particles (3).

[0134] [Inorganic particles (1)] Commercially available barium sulfate particles (BARIFINE BF-20, manufactured by Sakai Chemical Industry Co., Ltd., volume average particle size 30 nm) were prepared and used as inorganic particles (1).

[0135] [Second Resin Particles] Melamine resin particles Eposter FS (manufactured by Nippon Shokubai Co., Ltd., average primary particle size 200 nm) were prepared and used as second resin particles.

[0136] [Conductive particles] Carbon black VXC72 (manufactured by Cabot Corporation, average primary particle size 30 nm) was prepared and used as the conductive particles.

[0137] <Examples 2, 3, 5 and 6, and Comparative Examples 4 and 5> As shown in Table 1, carriers were produced in the same manner as in Example 1, except that the composition of the resin coating layer was changed.

[0138] Example 4 MnMg ferrite core material (volume average particle size 30 μm): 100 parts Styrene / methyl methacrylate copolymer resin particles (polymerization ratio by mass 2 / 8, weight average molecular weight 500,000): 1.0 parts The above materials were placed in a stirring mixer with stirring blades, the temperature inside the stirring mixer was set to 20°C, and the materials were stirred and mixed for 15 minutes at a peripheral speed of the stirring blades of 10.0 m / sec (adhesion step) to adhere the resin particles to the core material.

[0139] Styrene / methyl methacrylate copolymer resin particles (polymerization ratio by mass 2 / 8, weight average molecular weight 500,000): 1.0 parts Silica particles (1): 1.0 parts The above materials were further added to the stirring mixer with stirring blades, the temperature inside the stirring mixer was raised to 20°C, and the materials were stirred and mixed for 15 minutes at a peripheral speed of the stirring blades of 10.0 m / sec (second adhesion process), causing the resin particles and silica particles to adhere to the core material. Next, the temperature inside the stirring mixer was raised to 140°C, and the mixture was stirred and mixed for 15 minutes at a peripheral speed of the stirring blade of 5.0 m / s (heating and mixing step). The powder was taken out of the stirring mixer and sieved through a mesh with 75 μm openings to remove coarse powder, thereby obtaining a carrier (carrier for developing electrostatic images).

[0140] Example 7 MnMg ferrite core material (volume average particle size 30 μm): 100 parts Styrene / methyl methacrylate copolymer resin particles (polymerization ratio by mass 2 / 8, weight average molecular weight 500,000): 2.0 parts Silica particles (1): 1.0 parts The above materials were placed in a stirring mixer with stirring blades, the temperature inside the stirring mixer was set to 20°C, and the materials were stirred and mixed for 15 minutes at a peripheral speed of the stirring blades of 10.0 m / sec (adhesion process), causing the resin particles and silica particles to adhere to the core material. Next, the temperature inside the stirring mixer was raised to 160°C, and the mixture was stirred and mixed for 60 minutes at a peripheral speed of the stirring blade of 5.0 m / s (heating and mixing step). The powder was taken out of the stirring mixer and sieved through a mesh with 75 μm openings to remove coarse powder, thereby obtaining a carrier (carrier for developing electrostatic images).

[0141] Example 8 MnMg ferrite core material (volume average particle size 50 μm): 100 parts Styrene / methyl methacrylate copolymer resin particles (polymerization ratio by mass 2 / 8, weight average molecular weight 500,000): 2.0 parts Silica particles (1): 1.0 parts The above materials were placed in a stirring mixer with stirring blades, the temperature inside the stirring mixer was set to 20°C, and the materials were stirred and mixed for 15 minutes at a peripheral speed of the stirring blades of 10.0 m / sec (adhesion process), causing the resin particles and silica particles to adhere to the core material. Next, the temperature inside the stirring mixer was raised to 140°C, and the mixture was stirred and mixed for 15 minutes at a peripheral speed of the stirring blade of 5.0 m / s (heating and mixing step). The powder was taken out of the stirring mixer and sieved through a mesh with 75 μm openings to remove coarse powder, thereby obtaining a carrier (carrier for developing electrostatic images).

[0142] <Comparative Example 1: Kneader> MnMg ferrite core material (volume average particle size 30 μm): 100 parts Styrene / methyl methacrylate copolymer resin particles (polymerization ratio by mass 2 / 8, weight average molecular weight 500,000): 2.0 parts Silica particles (1): 1.0 parts Toluene: 5 parts Among the above materials, cyclohexyl methacrylate / methyl methacrylate copolymer, silica particles (1), and glass beads (1 mm diameter, equal amount of toluene) were placed in a sand mill and stirred at 1,200 rpm for 30 minutes to prepare a resin coating layer forming solution. The ferrite core material was placed in a vacuum degassing kneader, and the resin coating layer forming solution was then added. The temperature was increased and the pressure was reduced over 30 minutes while stirring at 40 rpm, and the toluene was distilled off to coat the ferrite core material with resin. The mixture was then removed from the kneader and sieved through a 75 μm mesh to remove coarse particles, yielding the carrier of Comparative Example 1.

[0143] <Comparative Example 2: Spray Dryer> MnMg ferrite core material (volume average particle size 30 μm): 100 parts Styrene / methyl methacrylate copolymer resin particles (polymerization ratio by mass 2 / 8, weight average molecular weight 500,000): 2.0 parts Silica particles (1): 1.0 parts Toluene: 10 parts Of the above materials, the cyclohexyl methacrylate / methyl methacrylate copolymer, silica particles (1), and glass beads (diameter 1 mm, same amount as toluene) were put into a sand mill to prepare a solution for forming a resin coating layer. Using a Spira Coater (a coating device using a spray dryer, manufactured by Okada Seiko Co., Ltd.), the resin coating layer forming solution was sprayed onto the surface of the ferrite core material at a rate of 30 g / min in an atmosphere of 70°C so that the components of the resin coating layer were 2.8 parts relative to the ferrite core material, and then dried. The dried powder was removed from the Spira Coater and crushed using a sieve with 75 μm openings to obtain a carrier of Comparative Example 2.

[0144] <Comparative Example 3: Extruder> MnMg ferrite core material (volume average particle size 30 μm): 100 parts Styrene / methyl methacrylate copolymer resin particles (polymerization ratio by mass 2 / 8, weight average molecular weight 500,000): 2.0 parts Silica particles (1): 1.0 parts The above materials were placed in a stirring mixer with stirring blades, the temperature inside the stirring mixer was raised to 20°C, and the materials were stirred and mixed for 15 minutes at a peripheral speed of the stirring blades of 10.0 m / sec to adhere the resin particles and silica particles to the core material. A continuous heat treatment device (continuous twin-screw extrusion kneader TEM50, manufactured by Toshiba Machine Co., Ltd.) was used, the casing heating temperature of the continuous heat treatment device was set to 250°C, the core material to which the resin particles and silica particles had been attached was continuously fed from the raw material inlet, and the heated and molten product (approximately 190°C) was recovered from the outlet. The recovered heated and melted product was continuously fed to a Comil crusher (punched metal φ1 mm), where it was cooled while being crushed to primary particles, and after obtaining a crushed product at a temperature of 60°C or less, it was sieved through a mesh with 75 μm openings to remove coarse powder, and the carrier of Comparative Example 3 was obtained.

[0145] <Preparation of Electrostatic Image Developer> Using the obtained carrier, cyan, magenta, and yellow developers (electrostatic image developers) were prepared as follows. 100 parts of the carrier and 20 parts of the cyan toner (C1) were charged into a V-blender and stirred for 20 minutes, and then sieved through a sieve with 212 μm openings to obtain a cyan developer. 100 parts of the carrier and 20 parts of the magenta toner (M1) were charged into a V-blender and stirred for 20 minutes, after which the mixture was sieved through a sieve with 212 μm openings to obtain a magenta developer. 100 parts of the carrier and 20 parts of the yellow toner (Y1) were charged into a V-blender and stirred for 20 minutes, and then sieved through a sieve with 212 μm openings to obtain a yellow developer.

[0146] <Arithmetic mean particle size of inorganic particle aggregates> The carrier was embedded in epoxy resin and cut with a microtome to prepare a carrier cross section. The size (maximum diameter) of the aggregates was measured from SEM images of the carrier cross section taken at 10,000x magnification using a scanning electron microscope (SEM). 100 randomly selected cross-sectional photographs of the carrier particles were measured, and the arithmetic average was taken as the arithmetic mean particle size of the aggregates.

[0147] <Surface exposure rate of magnetic particles> The carrier surface was photographed using a scanning electron microscope (SEM) at a magnification of 1,500x and binarized. The ratio of the area of ​​the exposed magnetic particles in the SEM image to the area of ​​the entire carrier was determined as the surface exposure rate of the magnetic particles.

[0148] <Gap width> The carrier is embedded in epoxy resin and cut with a microtome to prepare a carrier cross section. The carrier cross section is photographed with a scanning electron microscope (SEM) at 10,000x magnification, and the maximum gap width at the interface between the carrier core material and the coating layer is measured from SEM images. 100 randomly selected cross-sectional photographs of the carrier particles are measured, and the arithmetic average is taken as the gap width.

[0149] <Si / C ratio on carrier surface> In this embodiment, the Si / C ratio on the carrier surface was determined by X-ray photoelectron spectroscopy (XPS) using the following method. The elemental composition was analyzed using a JPS-9000MX (manufactured by JEOL Ltd.) as an analyzer with an X-ray intensity of 10 kV / 30 mA and an analysis depth in normal mode, and the peak areas of Si and C were measured and calculated.

[0150] <Evaluation of gloss unevenness suppression> In an environment of 28.5°C and 85% RH, an "Iridesse Production Press" (manufactured by Fujifilm Business Innovation Co., Ltd.) was used to continuously print 100,000 sheets of an image sample with a chart at an image density of 1% using A4 size J paper (manufactured by Fujifilm Business Innovation Co., Ltd.). After printing 100,000 sheets, A4 size 45 paper (manufactured by Ricoh Co., Ltd., basis weight 52 gsm) was used to print an image sample with a toner coverage (TMA) of 9.8 g / cm. 2 A full-solid image sample was printed in the tertiary colors (process black, cyan toner: magenta toner: yellow toner = 1:1:1 (mass ratio)). The gloss was measured at two points (75-degree gloss meter), and the difference was judged as gloss unevenness. The evaluation criteria are as follows. A to C are preferable. A: The difference in gloss is 3% or less B: The difference in gloss is more than 3% and 10% or less C: The difference in gloss is more than 10% and 20% or less D: The difference in gloss is more than 20% and less than 40% E: The difference in the gross is more than 40%

[0151] [Table 1]

[0152] From the above results, it can be seen that the present example is superior to the comparative example in suppressing uneven gloss in the obtained image. [Explanation of symbols]

[0153] 1Y, 1M, 1C, 1K Photoconductor (an example of an image carrier) 2Y, 2M, 2C, 2K Charging roll (an example of 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 Drive 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 Photosensitive body (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 transfer means) 113 Photosensitive drum cleaning device (an example of cleaning means) 115 Fixing device (an example of fixing means) 116 Mounting Rail 117 Cabinet 118 Exposure opening 200 Process Cartridge 300 Recording paper (an example of a recording medium)

Claims

1. The magnetic material has magnetic particles and a resin coating layer that coats the magnetic particles, the resin coating layer contains an aggregate of inorganic particles, a binder polymer, and resin particles; the arithmetic mean particle size of the aggregates of the inorganic particles present on the carrier surface is 30 nm or more and 150 nm or less; The surface exposure rate of the magnetic particles is 0% by area or more and 5% by area or less. Carrier for developing electrostatic images.

2. 2. The carrier for developing electrostatic images according to claim 1, wherein a void is present at least partially between the resin coating layer and the surface of the magnetic particles.

3. 3. The carrier for developing electrostatic images according to claim 2, wherein the average width of the voids in the thickness direction of the resin coating layer is 50 nm or more and 300 nm or less.

4. 4. The carrier for developing electrostatic images according to claim 1, wherein the Si / C ratio of the carrier surface measured by X-ray photoelectron spectroscopy is 0.05 or more and 1.5 or less.

5. 5. The carrier for developing electrostatic images according to claim 4, wherein the Si / C ratio of the carrier surface as measured by X-ray photoelectron spectroscopy is 0.05 or more and 1.0 or less.

6. 6. The carrier for developing electrostatic images according to claim 1, wherein the resin coating layer further contains conductive particles.

7. 7. The carrier for developing electrostatic images according to claim 1, wherein the content of the inorganic particles including the aggregates of inorganic particles is 15% by mass or more and 60% by mass or less with respect to the total mass of the resin coating layer.

8. 8. The carrier for developing electrostatic images according to claim 7, wherein the content of the inorganic particles including the aggregates of inorganic particles is 20% by mass or more and 45% by mass or less with respect to the total mass of the resin coating layer.

9. 9. The carrier for developing electrostatic images according to claim 1, wherein the inorganic particles in the aggregate have an average primary particle size of 5 nm or more and 50 nm or less.

10. 10. The carrier for developing electrostatic images according to claim 1, wherein a value of the arithmetic mean particle size of the aggregates of the inorganic particles divided by the mean thickness of the resin coating layer is 0.01 or more and 0.3 or less.

11. 11. The carrier for developing electrostatic images according to claim 1, wherein a value of the arithmetic mean particle size of the aggregates of the inorganic particles / the volume mean particle size of the carrier is 0.003 or more and 0.01 or less.

12. 12. The carrier for developing electrostatic images according to claim 1, wherein the content of aggregates of the inorganic particles relative to all inorganic particles contained in the resin coating layer is 50% by number or more and 90% by number or less.

13. 13. The method for producing the carrier for developing electrostatic images according to claim 1, further comprising the step of mixing magnetic particles, inorganic particles and a binder polymer in a stirring and mixing device, and forming a resin coating layer by a dry method.

14. 13. An electrostatic image developer comprising the electrostatic image developing carrier according to claim 1 and a toner for developing an electrostatic image.

15. a developing unit containing the electrostatic image developer according to claim 14 and developing an electrostatic image formed on the surface of an image carrier into a toner image by using the electrostatic image developer, A process cartridge is detachably mounted in an image forming apparatus.

16. a charging step of charging at least an image carrier; an exposure step of forming an electrostatic latent image on the surface of the image carrier; a developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic image developer to form a toner image; a transfer step of transferring the toner image formed on the surface of the image carrier onto a surface of a transfer receiving material; a fixing step of fixing the toner image, The electrostatic image developer is the electrostatic image developer according to claim 14. Image forming method.

17. an image carrier; a charging means for charging the image carrier; an exposure unit that exposes the charged image carrier to light to form an electrostatic latent image on the image carrier; a developing means for developing the electrostatic latent image with an electrostatic image developer to form a toner image; a transfer means for transferring the toner image from the image carrier to a transfer receiving member; a fixing means for fixing the toner image, The electrostatic image developer is the electrostatic image developer according to claim 14. Image forming device.

Images