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

Abstract

To provide an electrostatic image developing carrier which is less likely to generate color unevenness in an image.SOLUTION: An electrostatic image developing carrier is provided, comprising a magnetic particle and a coating layer containing a resin and inorganic particles. The magnetic particle have an exposure rate of 50 to 80%, inclusive, on the surface. A roughness curve on the surface has an average length RSm of 0.9 to 1.5 μm, inclusive, and a maximum height of 2.0 to 6.0 μm, inclusive.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a carrier for developing electrostatic images, which comprises magnetic core particles containing 0.05% by mass or more and 1.0% by mass or less of calcium, with a ratio b / a of 5 or more, where the ratio of the calcium content (b) in the surface portion to the calcium content (a) in the interior, and a resin coating layer coating the surface of the magnetic core particles, with a ratio c / b of 0.1 or more and 0.5 or less, where the ratio of the calcium content (c) in the surface portion coated with the resin coating layer to the calcium content (b). Patent Document 2 describes a carrier having magnetic core particles and a coating layer that covers at least a part of the surface of the core particles, in which the BET specific surface area of ​​the core particles is 0.27 m 2 / g~0.31m 2 / g, the exposed core particle ratio is 50% to 80% of the surface area of ​​the carrier, and the exposed core particle height is 0.15 μm to 2.00 μm. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-008987 [Patent Document 2] Patent Publication No. 2021-063895 Summary of the Invention [Problem to be solved by the invention]

[0004] The present disclosure aims to provide an electrostatic charge image developing carrier that is less likely to cause color unevenness in an image, compared to an electrostatic charge image developing carrier in which the exposure rate of magnetic particles is outside the range of 50% or more and 80% or less, the average length RSm of the surface roughness curve is outside the range of 0.9 μm or more and 1.5 μm or less, and the maximum height Rz is outside the range of 2.0 μm or more and 6.0 μm or less.

Means for Solving the Problem

[0005] The means for solving the above problems include the following aspects.

[0006] <1> It has magnetic particles and a coating layer that coats the magnetic particles, The coating layer contains a resin and inorganic particles, The exposure rate of the magnetic particles on the surface is 50% or more and 80% or less, The average length RSm of the surface roughness curve is 0.9 μm or more and 1.5 μm or less and the maximum height Rz is 2.0 μm or more and 6.0 μm or less, An electrostatic charge image developing carrier. <2> The electrostatic charge image developing carrier according to <1>, wherein the exposure rate of the magnetic particles on the surface is 50% or more and 65% or less. <3> The electrostatic charge image developing carrier according to <1> or <2>, wherein the average length RSm of the surface roughness curve is 0.9 μm or more and 1.1 μm or less and the maximum height Rz is 4.0 μm or more and 6.0 μm or less. <4> [[ID=3,3]]When the exposure rate of the magnetic particles on the surface is S% and the amount of the coating layer with respect to 100 parts by mass of the magnetic particles is M parts by mass, the electrostatic charge image developing carrier according to any one of <1> to <3>, which satisfies 22 < S / M <65. <5> When the exposure rate of the magnetic particles on the surface is S% and the amount of the coating layer with respect to 100 parts by mass of the magnetic particles is M parts by mass, the electrostatic charge image developing carrier according to any one of <1> to <4>, which satisfies 22 < S / M <40. <6> The inorganic particles have an average primary particle size of 1 nm or more and 80 nm or less. <1> ~ <5> 10. The carrier for developing electrostatic images according to claim 9. <7> the coating layer contains silica particles, The silicon element concentration on the surface determined by X-ray photoelectron spectroscopy is 0.1 atomic % or more and 1.0 atomic % or less. <1> ~ <6> 10. The carrier for developing electrostatic images according to claim 9. <8> the coating layer contains silica particles, The silicon element concentration on the surface determined by X-ray photoelectron spectroscopy is 0.2 atomic % or more and 0.6 atomic % or less. <1> ~ <7> 10. The carrier for developing electrostatic images according to claim 9. <9> The coating layer further contains resin particles. <1> ~ <8> 10. The carrier for developing electrostatic images according to claim 9. <10> The coating layer further contains conductive particles. <1> ~ <9> 10. The carrier for developing electrostatic images according to claim 9. <11> the magnetic particles are ferrite particles; <1> ~ <10> 10. The carrier for developing electrostatic images according to claim 9. <12> a toner for developing an electrostatic image; <1> ~ <11> and the carrier for developing electrostatic images according to any one of claims 1 to 4. An electrostatic image developer. <13> <12> and a developing means for 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. <14> an image carrier; a charging means for charging the surface of the image carrier; an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier; <12> a developing means for developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer; a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; An image forming apparatus comprising: <15> a charging step of charging the surface of the image carrier; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier; <12> 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 claim 1; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing step of fixing the toner image transferred onto the surface of the recording medium; An image forming method comprising the steps of: <16> <1> A method for producing the carrier for developing electrostatic images according to claim 1, Dry-bonding resin particles and inorganic particles that form the substrate of the coating layer onto the surfaces of the magnetic particles; and stirring the magnetic particles to which the resin particles and the inorganic particles are attached in a rotary kiln while applying a temperature at which the resin particles melt. A method for producing a carrier for developing electrostatic images. [Effects of the Invention]

[0007] <1> , <2> , <3> , <6> , <9> , <10> or <11> According to the invention, there is provided an electrostatic image developing carrier that is less likely to cause color unevenness in images, compared to an electrostatic image developing carrier having an exposure rate of magnetic particles outside the range of 50% or more and 80% or less, an average length RSm of the surface roughness curve outside the range of 0.9 μm or more and 1.5 μm or less, and a maximum height Rz outside the range of 2.0 μm or more and 6.0 μm or less. <4> or <5> According to the invention, 22 <7> or <8> According to the present invention, an electrostatic image developing carrier is provided that is less likely to cause color unevenness in images compared to an electrostatic image developing carrier having a surface silicon element concentration outside the range of 0.1 atomic % or more and 1.0 atomic % or less. <12> According to the invention, an electrostatic image developer is provided that is less likely to cause color unevenness in images compared to an electrostatic image developer using an electrostatic image developing carrier in which the exposure rate of magnetic particles is outside the range of 50% or more and 80% or less, the average length RSm of the surface roughness curve is outside the range of 0.9 μm or more and 1.5 μm or less, and the maximum height Rz is outside the range of 2.0 μm or more and 6.0 μm or less. <13> According to the invention, a process cartridge is provided which is less likely to cause color unevenness in images compared to a process cartridge using an electrostatic image developing carrier in which the exposure rate of magnetic particles is outside the range of 50% or more and 80% or less, the average length RSm of the surface roughness curve is outside the range of 0.9 μm or more and 1.5 μm or less, and the maximum height Rz is outside the range of 2.0 μm or more and 6.0 μm or less. <14> According to the invention, an image forming apparatus is provided that is less likely to produce color unevenness in images than an image forming apparatus that uses an electrostatic image developing carrier in which the exposure rate of magnetic particles is outside the range of 50% or more and 80% or less, the average length RSm of the surface roughness curve is outside the range of 0.9 μm or more and 1.5 μm or less, and the maximum height Rz is outside the range of 2.0 μm or more and 6.0 μm or less. <15> According to the invention, an image forming method is provided which is less likely to cause color unevenness in an image than an image forming method using an electrostatic image developing carrier in which the exposure rate of magnetic particles is outside the range of 50% or more and 80% or less, the average length RSm of the surface roughness curve is outside the range of 0.9 μm or more and 1.5 μm or less, and the maximum height Rz is outside the range of 2.0 μm or more and 6.0 μm or less. <16> According to the invention, there is provided a carrier for developing electrostatic images that is less likely to cause color unevenness in images. [Brief explanation of the drawings]​

[0008] [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

[0009]

[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.

[0010] 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.

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

[0012] 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.

[0013] 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.

[0014] 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.

[0015] 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."

[0016] <Electrostatic image developing carrier> The carrier according to this embodiment has magnetic particles and a coating layer that coats the magnetic particles.

[0017] The coating layer of the carrier according to this embodiment contains a resin and inorganic particles. The resin here refers to a resin that constitutes the substrate of the coating layer. When the coating layer contains resin particles, the resin particles and the resin that constitutes the substrate are separate elements.

[0018] On the surface of the carrier according to this embodiment, the exposure rate of magnetic particles is 50% or more and 80% or less.

[0019] The surface of the carrier according to this embodiment has a roughness curve mean length RSm of 0.9 μm or more and 1.5 μm or less, and a maximum height Rz of 2.0 μm or more and 6.0 μm or less.

[0020] In a carrier having a coating layer containing inorganic particles, the above three characteristics of the carrier surface (i.e., magnetic particle exposure rate of 50% to 80%, RSm of 0.9 μm to 1.5 μm, and Rz of 2.0 μm to 6.0 μm) have not previously been achieved simultaneously. The carrier according to this embodiment not only adjusts the magnetic particle exposure rate when forming the coating layer, but also reflects the unevenness of the magnetic particles on the carrier surface, thereby achieving all three characteristics simultaneously.

[0021] The carrier according to this embodiment is less likely to cause color unevenness in images. This effect is particularly pronounced when combined with a toner exposed to high temperature and high humidity (for example, a temperature of 50°C and a relative humidity of 60%). The mechanism behind this effect is presumed to be as follows.

[0022] When toner is stirred in the developing unit, external additives gradually become embedded. Toner exposed to high temperatures and humidity is particularly susceptible to external additives being embedded. Toner with embedded external additives adheres to the carrier, causing developer aggregates. When developer aggregates adhere to the stirring means of the developing unit, the developer is not stirred enough or the toner transport from the toner cartridge is delayed, resulting in color unevenness in the image. The carrier according to this embodiment contains inorganic particles in the coating layer, and it is presumed that the non-electrostatic attraction to the toner is relatively weak, making it difficult for the developer to form aggregates. Furthermore, it is presumed that the carrier according to this embodiment has a relatively high exposure rate of magnetic particles, making it difficult for toner to adhere to it and difficult for developer aggregates to form. In addition, the carrier according to this embodiment has a moderate unevenness on the carrier surface (the unevenness is specified by RSm and Rz), and it is presumed that the contact area between the carrier and the toner is relatively small, making it difficult for developer aggregates to form. Therefore, with the carrier according to this embodiment, developer aggregates are less likely to occur in the developing device, and color unevenness is less likely to occur in the image.

[0023] On the surface of the carrier according to this embodiment, the exposure rate of magnetic particles is 50% or more and 80% or less. If the exposure rate of the magnetic particles on the carrier surface is less than 50%, the formation of a coating layer on the protrusions of the magnetic particles becomes large, the exposure of the protrusions is suppressed, and the toner is more likely to adhere to the carrier surface than when the protrusions are moderately exposed. From this perspective, the exposure rate of the magnetic particles is 50% or more, preferably 55% or more, and more preferably 60% or more. If the exposure rate of the magnetic particles on the carrier surface exceeds 80%, the protrusions of the magnetic particles will be insufficiently covered or completely exposed, making it easier for toner to adhere to the protrusions of the magnetic particles compared to when the protrusions of the magnetic particles are adequately covered. Furthermore, insufficient coverage on the carrier surface will result in insufficient triboelectric charging between the toner and carrier, resulting in unstable image formation. From this perspective, the exposure rate of the magnetic particles is 80% or less, preferably 70% or less, and more preferably 65% ​​or less.

[0024] The surface of the carrier according to this embodiment has a mean length RSm of the roughness curve of 0.9 μm or more and 1.5 μm or less. If RSm is less than 0.9 μm, the convex portions derived from the magnetic particles are small, making it difficult for a fine coating layer to form on the convex portion surfaces, and therefore, compared to when RSm is appropriate, the toner is more likely to adhere to the carrier surface and form aggregates. From this perspective, RSm is 0.9 μm or more, and preferably 1.0 μm or more. If RSm exceeds 1.5 μm, the convex portions derived from the magnetic particles become too large, resulting in a large contact area between the toner and the carrier, and the toner is more likely to adhere to the carrier surface and form aggregates than when RSm is appropriate. From this viewpoint, RSm is 1.5 μm or less, preferably 1.3 μm or less, and more preferably 1.1 μm or less.

[0025] The surface of the carrier according to this embodiment has a maximum height Rz of the roughness curve of 2.0 μm or more and 6.0 μm or less. If Rz is less than 2.0 μm, the convex portions of the magnetic particles are likely to be covered with the coating layer, and the particles become closer to a spherical shape, resulting in a larger contact area between the toner and carrier, making it easier for them to form aggregates. From this perspective, Rz is 2.0 μm or more, preferably 3.0 μm or more, and more preferably 4.0 μm or more. If Rz exceeds 6.0 μm, the convex portions of the magnetic particles are too large, and the toner is easily deformed and adhered when the carrier convex portions collide with the toner. From this viewpoint, Rz is 6.0 μm or less, preferably 5.5 μm or less, and more preferably 5.0 μm or less.

[0026] In this embodiment, the exposure rate of the magnetic particles is determined by X-ray photoelectron spectroscopy (XPS) in the following manner. The elemental composition is analyzed using a JPS-9000MX (manufactured by JEOL Ltd.) with an X-ray intensity of 10 kV / 30 mA and an analysis depth in normal mode. The percentage (%) of the Fe peak area in the total peak area of ​​the main elements that make up a typical carrier, C, O, N, Fe, Mn, Mg, and Sr, is calculated and used as the magnetic particle exposure rate (%).

[0027] In this embodiment, the roughness curve, average length RSm and maximum height Rz of the carrier surface are determined in accordance with JIS B0601:2013. The roughness curve, RSm, and Rz are determined by observing the carrier at an appropriate magnification (for example, 1000x) using a surface profile measuring device (for example, Keyence Corporation's "Ultra-Deep Color 3D Profile Measuring Microscope VK-9500"). The reference length is 10 μm, and the cutoff value is 0.08 mm. 100 carriers are measured, and the RSm and Rz are each calculated as an arithmetic average.

[0028] The carrier according to this embodiment has a magnetic particle exposure rate of S% on the carrier surface, and a coating layer amount of M parts by mass per 100 parts by mass of magnetic particles. An S / M ratio of more than 22 indicates that the coating layer components do not coat the magnetic particles, that is, that the coating layer components are not uniform but are distributed ubiquitously over the entire carrier surface. The partial distribution of the coating components indicates that the carrier surface is uneven, and that the contact area between the toner and the carrier is small. From this perspective, an S / M ratio of more than 22 is preferable, more preferably more than 23, and even more preferably more than 40. ​If the S / M ratio is less than 65, the coating layer is not formed only on the recesses, but tends to adhere partially to the protrusions of the magnetic particles, which is advantageous for the formation of aggregates between the toner and carrier, and also tends to result in uniform triboelectric charging between the toner and carrier, making it possible to obtain stable images. From this perspective, the S / M ratio is preferably less than 65, more preferably less than 50, and even more preferably less than 40.

[0029] The volume average particle size of the carrier is preferably 15 μm to 120 μm, more preferably 20 μm to 100 μm, and even more preferably 30 μm to 80 μm. The volume average particle size refers to the particle size that is 50% cumulative from the smallest diameter side in the volume-based particle size distribution.

[0030] The configuration of the carrier according to this embodiment will be described in detail below.

[0031] [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.

[0032] In this embodiment, ferrite particles are preferred as the magnetic particles from the viewpoint of chargeability.

[0033] The volume average particle size of the magnetic particles is preferably 15 μm to 100 μm, more preferably 20 μm to 80 μm, and even more preferably 30 μm to 60 μm, where the volume average particle size refers to the particle size that is 50% cumulative from the smallest diameter side in the volume-based particle size distribution.

[0034] 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.

[0035] 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 )

[0036] [Coating layer] The average thickness of the coating layer is preferably 0.05 μm or more and 1.0 μm or less, more preferably 0.1 μm or more and 0.8 μm or less, and even more preferably 0.1 μm or more and 0.5 μm or less. The average thickness of the coating layer is determined by analyzing cross-sectional images of 100 carrier particles using image analysis software.

[0037] Resins that make up the substrate of the coating layer 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 resin constituting the substrate portion of the coating layer, 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 styrene acrylic resin in the total resin constituting the substrate portion of the coating layer is preferably 80% by mass or more, more preferably 90% by mass or more, and even more preferably substantially all of the resin is styrene acrylic resin.

[0041] The coating layer contains inorganic particles. The inorganic particles are separate from the conductive particles described below. Examples of the inorganic particles include silica particles. As the inorganic particles, silica particles are preferred from the viewpoint of good adhesion to the resin (particularly styrene acrylic resin) that constitutes the substrate portion of the coating layer.

[0042] The content of the inorganic particles in the coating layer is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the resin. The content of inorganic particles in the coating layer is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less, per 100 parts by mass of the resin.

[0043] The content of silica particles in the coating layer is preferably 20 parts by mass or more, more preferably 25 parts by mass or more, and even more preferably 30 parts by mass or more, per 100 parts by mass of the resin. The content of silica particles in the coating layer is preferably 70 parts by mass or less, more preferably 60 parts by mass or less, and even more preferably 50 parts by mass or less, per 100 parts by mass of the resin.

[0044] The average primary particle size of the inorganic particles is preferably 1 nm or more and 80 nm or less, more preferably 5 nm or more and 50 nm or less, and even more preferably 5 nm or more and 30 nm or less, from the viewpoint of good adhesion to the resin constituting the substrate portion of the coating layer. The average primary particle size of the inorganic particles is determined by analyzing the inorganic particles contained in the cross-sectional images of 100 carrier particles using image analysis software.

[0045] From the viewpoint of good adhesion to the resin constituting the substrate of the coating layer, the average primary particle size of the silica particles is preferably 1 nm or more and 80 nm or less, more preferably 5 nm or more and 50 nm or less, and even more preferably 5 nm or more and 30 nm or less.

[0046] In the carrier according to this embodiment, the coating layer preferably contains silica particles, and the silicon element concentration on the carrier surface determined by X-ray photoelectron spectroscopy is preferably 0.1 atomic % or more and 1.0 atomic % or less. When the silicon element concentration on the carrier surface is 0.1 atomic % or more, there are many silica particles on the coating layer surface, and it is thought that the non-electrostatic adhesion force is weaker than when the silicon element concentration is 0.1 atomic % or less, making it difficult for the toner and carrier to form aggregates. From this perspective, the silicon element concentration on the carrier surface is preferably 0.1 atomic % or more, more preferably 0.15 atomic % or more, and even more preferably 0.2 atomic % or more. When the silicon element concentration on the carrier surface is 1.0 atomic % or less, the carrier structure is more likely to be maintained even under the agitation stress of a developer during continuous printing due to the binding action of the resin, which is determined by the ratio of silica particles to resin components on the coating layer surface, compared to when the silicon element concentration is 1.0 atomic % or more, and aggregates of toner and carrier are less likely to form. From this perspective, the silicon element concentration on the carrier surface is preferably 1.0 atomic % or less, more preferably 0.8 atomic % or less, and even more preferably 0.6 atomic % or less.

[0047] The silicon element concentration (atomic %) on the carrier surface is analyzed by X-ray photoelectron spectroscopy (XPS) using the carrier as a sample under the following conditions: Carbon, oxygen, and silicon are analyzed, and the percentage of silicon in the total amount of these three elements is defined as the silicon element concentration (atomic %). XPS equipment: JEOL Ltd. JPS-9000MX ·X-ray source: MgKα Acceleration voltage: 20 kV Emission current: 10mA Etching gun: Argon gas cluster ion gun ·Vacuum degree: (3±1)×10-2Pa Measurement intensity: 400 eV, 6 mA ·Sweep area: 6mm x 6mm

[0048] The coating layer may contain resin particles for the purpose of increasing the mechanical strength of the coating layer. The resin particles are a separate element from the resin constituting the substrate of the coating layer. The resin particles are observed as particles in the coating layer in an image of the cross section of the carrier.

[0049] 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.

[0050] When resin particles are contained in the coating layer, the content of the resin particles contained in the coating layer is preferably 3 parts by mass or more and 30 parts by mass or less, more preferably 4 parts by mass or more and 25 parts by mass or less, and even more preferably 5 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the resin.

[0051] The coating layer may contain 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 a metal.

[0052] When the coating layer contains conductive particles, the content of the conductive particles in the coating layer is preferably 1 part by mass or more and 30 parts by mass or less, more preferably 2 parts by mass or more and 25 parts by mass or less, and even more preferably 3 parts by mass or more and 20 parts by mass or less, per 100 parts by mass of the resin.

[0053] The amount of the coating layer is preferably 1 to 10 parts by mass, more preferably 1.2 to 5 parts by mass, and even more preferably 1.3 to 3 parts by mass, per 100 parts by mass of the magnetic particles.

[0054] <Method of manufacturing electrostatic image developing carrier> The method for producing the carrier according to this embodiment is not particularly limited, but a production method using a rotary kiln is preferred.

[0055] A manufacturing method using a rotary kiln includes dry-adhering resin particles, which form the substrate of the coating layer, and inorganic particles to the surface of magnetic particles (adhering step), and stirring the magnetic particles with the resin particles and inorganic particles attached in a rotary kiln while applying a temperature at which the resin particles melt (rotary kiln treatment step). This manufacturing method can achieve three carrier surface characteristics (i.e., magnetic particle exposure rate of 50% to 80%, RSm of 0.9 μm to 1.5 μm, and Rz of 2.0 μm to 6.0 μm) in a carrier having a coating layer containing inorganic particles. The mechanism behind this is explained below, along with details of each step.

[0056] [Attachment process] The adhesion process is a process in which resin particles (referred to as "first resin particles") that form the substrate of the coating layer and inorganic particles are adhered to the surfaces of the magnetic particles in a dry manner. "Dry" means that no solvent is used to dissolve or disperse the resin.

[0057] The first resin particles melt during the rotary kiln treatment process and become the substrate of the 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 with thermal properties that prevent them from maintaining their particle shape during the rotary kiln treatment process.

[0058] When the carrier coating layer contains resin particles, which are 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 and maintain their particle shape during the rotary kiln treatment step.

[0059] When conductive particles are contained in the coating layer of the carrier, the conductive particles are also attached to the magnetic particles in the attachment step.

[0060] 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 impact force. Specific examples of the process include a process of placing the materials in an agitation mixer and agitating them. The temperature inside the agitation mixer 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).

[0061] In the adhesion process, a coating containing at least first resin particles and inorganic particles is formed on the surface of the magnetic particles, following the irregularities of the magnetic particles. Due to the difference in specific gravity between the first resin particles and the inorganic particles, the inorganic particles are unevenly distributed on the magnetic particle side of the coating, and the first resin particles are unevenly distributed on the surface side of the coating. This coating is melted in the rotary kiln treatment process to form a coating layer.

[0062] [Rotary kiln processing process] The rotary kiln treatment step is a step of stirring at least the first resin particles and the magnetic particles having the inorganic particles attached thereto in a rotary kiln while applying a temperature at which the first resin particles melt, where "melting" means that the first resin particles melt together without maintaining their particle shape.

[0063] A rotary kiln is a device that applies heat to the material to be treated while rotating and stirring it. Because the shear force applied to the material in a rotary kiln is weaker than that of other devices (e.g., a Henschel mixer, kneader, or extruder), the position and internal state of the coating formed on the surface of the magnetic particles during the adhesion process are less likely to change. Therefore, it is believed that the resin is less likely to migrate to the recesses of the magnetic particles, and that the coating layer is formed with inorganic particles unevenly distributed on the magnetic particle side. As a result, three characteristics of the carrier surface (i.e., magnetic particle exposure rate of 50% to 80%, RSm of 0.9 μm to 1.5 μm, and Rz of 2.0 μm to 6.0 μm) are achieved. When equipment other than a rotary kiln is used, the resin tends to migrate from the convex portions of the magnetic particles to the concave portions and accumulate in the concave portions, resulting in a small value for RSm and / or Rz.

[0064] The structure of a rotary kiln is generally divided into a material inlet, a rotating drum, and a discharge port. The rotary kiln is preferably an externally heated rotary kiln in which the rotating drum is heated from the outside. The rotary kiln may be either a batch type or a continuous type, with the batch type being preferred.

[0065] The temperature inside the rotary kiln is such that the first resin particles can fuse together. The temperature inside the rotary kiln is preferably the glass transition temperature of the first resin particles, 105°C or higher and 300°C or lower, more preferably 105°C or higher and 280°C or lower, and even more preferably 105°C or higher and 250°C or lower.

[0066] The rotational stirring time for the object to be treated is preferably from 1 minute to 60 minutes, more preferably from 2 minutes to 45 minutes, and even more preferably from 3 minutes to 30 minutes.

[0067] [Crushing cooling process] Following the rotary kiln treatment step, it is preferable to carry out a crushing and cooling step in which the material to be treated in the rotary kiln is cooled while being crushed. This step is a step in which the material to be treated in the rotary kiln is cooled while being crushed into primary particles.

[0068] 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.

[0069] The crushing and cooling step is preferably followed by a classification step or a sieving step. There are no limitations on the means for classification or sieving, and known means can be used.

[0070] <Electrostatic image developer> The developer according to this embodiment contains the toner and the carrier according to this embodiment.

[0071] 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.

[0072] [Electrostatic image developing toner] 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.

[0073] -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.

[0074] The binder resin is preferably a polyester resin, and examples of the polyester resin include known polyester resins.

[0075] 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."

[0076] 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.

[0077] 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.

[0078] -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.

[0079] 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.

[0080] 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.

[0081] -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.

[0082] 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."

[0083] 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.

[0084] -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.

[0085] -Characteristics of toner particles, etc.- The toner particles may be toner particles of a single layer structure, or may be toner particles of a so-called core-shell structure composed of a core (core particle) and a coating layer (shell layer) that coats the core. The toner particles of the core-shell structure may be composed of, for example, a core composed of a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer composed of a binder resin.

[0086] 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.

[0087] -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.

[0088] 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.

[0089] 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).

[0090] 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.

[0091] -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.

[0092] <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.

[0093] 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.

[0094] 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.

[0095] 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.

[0096] 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.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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).

[0101] 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.

[0102] 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.

[0103] 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.

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] <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.

[0111] 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.

[0112] 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.

[0113] 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]

[0114] 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.

[0115] <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.

[0116] [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).

[0117] 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%.

[0118] [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).

[0119] [Preparation of colorant particle dispersion (K1)] Carbon black (Cabot, Regal 330): 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 (K1) with a solid content of 20%.

[0120] [Preparation of Colorant Particle Dispersion (C1)] Cyan pigment (Pigment Blue 15:3, Dainichi Seika Color & Chemicals): 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 (C1) with a solid content of 20%.

[0121] [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%.

[0122] [Preparation of Colorant Particle Dispersion (Y1)] Yellow pigment (Pigment Yellow 74, Dainichi Seika Color & Chemicals): 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 (Y1) with a solid content of 20%.

[0123] [Preparation of black toner particles (K1)] 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 (K1): 15 parts Anionic surfactant (TaycaPower): 2.8 parts The above materials were placed in a reaction vessel, and 0.1 N 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 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 N aqueous sodium hydroxide solution. Next, 1 part of anionic surfactant (TaycaPower) was added, and the mixture was heated to 85°C while continuing to stir, 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 black toner particles (K1) with a volume average particle size of 5.7 μm and an average circularity of 0.971.

[0124] [Preparation of cyan toner particles (C1)] Cyan toner particles (C1) were obtained in the same manner as in the preparation of black toner particles (K1), except that the colorant particle dispersion liquid (K1) was changed to the colorant particle dispersion liquid (C1).

[0125] [Preparation of magenta toner particles (M1)] Magenta toner particles (M1) were obtained in the same manner as in the preparation of black toner particles (K1), except that the colorant particle dispersion liquid (K1) 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 black toner particles (K1), except that the colorant particle dispersion liquid (K1) was changed to the colorant particle dispersion liquid (Y1).

[0127] [Preparation of black toner (K1)] 100 parts by mass of black toner particles (K1) 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 for 30 seconds at a rotation speed of 10,000 rpm. The mixture was then sieved through a vibrating sieve with 45 μm openings to obtain black toner (K1) with a volume average particle size of 5.7 μm.

[0128] [Preparation of cyan toner (C1)] Cyan toner (C1) was obtained in the same manner as in the preparation of black toner (K1), except that the black toner particles (K1) were changed to cyan toner particles (C1).

[0129] [Preparation of magenta toner (M1)] A magenta toner (M1) was obtained in the same manner as in the preparation of the black toner (K1), except that the black toner particles (K1) were changed to magenta toner particles (M1).

[0130] [Preparation of Yellow Toner (Y1)] Yellow toner (Y1) was obtained in the same manner as in the preparation of black toner (K1), except that the black toner particles (K1) were changed to yellow toner particles (Y1).

[0131] Example 1 MnMg ferrite particles (volume average particle size 35 μm): 100 parts First resin particles: styrene-methyl methacrylate copolymer resin particles (polymerization ratio by mass 2:8, weight average molecular weight 500,000): 1.5 parts Silica particles (HM30S, manufactured by Tokuyama Corporation, average primary particle size 8 nm): 0.6 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 to cause the resin particles and silica particles to adhere to the MnMg ferrite particles. The MnMg ferrite particles with resin particles and silica particles attached were placed in a rotary kiln (manufactured by Chuo Kakoki Co., Ltd.) and subjected to rotational agitation at a temperature of 220°C for 30 minutes. The treated material was recovered from the rotary kiln and continuously fed to a Comil crusher (punched metal diameter 1 mm) where it was cooled while being crushed into primary particles, yielding crushed material at a temperature of 60°C or less. The crushed material was sieved through a mesh with 75 μm openings to remove coarse particles, yielding a carrier.

[0132] 100 parts of the carrier and 20 parts of the black toner (K1) were charged into a V-blender and stirred for 20 minutes, and then sieved through a sieve with 212 μm openings to obtain a black developer. 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.

[0133] <Examples 2 to 4> Carriers of Examples 2 to 4 were manufactured in the same manner as in Example 1, except that the amounts of first resin particles (styrene-methyl methacrylate copolymer resin particles) and silica particles used were increased or decreased, and second resin particles and conductive particles were used. In the same manner as in Example 1, developers of Examples 2 to 4 were produced from the carriers of Examples 2 to 4 and the toners of each color, respectively. The second resin particles and conductive particles used in Examples 2 and 3 are as follows. Second resin particles: melamine resin particles (Eposter FS, manufactured by Nippon Shokubai Co., Ltd., average primary particle size 200 nm) Conductive particles: Carbon black (VXC72, manufactured by Cabot Corporation, average primary particle size 30 nm)

[0134] <Comparative Example 1> MnMg ferrite particles (volume average particle size 35 μm): 100 parts First resin particles: styrene-methyl methacrylate copolymer resin particles (polymerization ratio by mass 2:8, weight average molecular weight 500,000): 1.4 parts Second resin particles: melamine resin particles (Eposter FS, manufactured by Nippon Shokubai Co., Ltd., average primary particle size 200 nm): 0.14 parts Conductive particles: Carbon black (VXC72, manufactured by Cabot Corporation, average primary particle size 30 nm): 0.14 parts Using the above materials, a carrier of Comparative Example 1 was produced in the same manner as in Example 1. In the same manner as in Example 1, a developer of Comparative Example 1 was produced from the carrier of Comparative Example 1 and the toner of each color.

[0135] <Comparative Example 2> MnMg ferrite particles (volume average particle size 35 μm): 100 parts Styrene-methyl methacrylate copolymer (polymerization ratio by mass 2:8, weight average molecular weight 500,000): 1.5 parts Silica particles (HM30S, manufactured by Tokuyama Corporation, average primary particle size 8 nm): 0.6 parts Toluene: 5 parts Styrene-methyl methacrylate copolymer, silica particles, toluene, and glass beads (1 mm diameter, same amount as toluene) were placed in a sand mill and stirred at a rotation speed of 1200 rpm for 30 minutes to obtain a solution for forming a coating layer. The MnMg ferrite particles were placed in a vacuum degassing kneader, followed by the coating layer forming solution, and the mixture was heated and decompressed for 30 minutes while stirring at 40 rpm to distill off the toluene. The contents were removed from the kneader and sieved through a 75 μm mesh to remove coarse particles, thereby obtaining a carrier.

[0136] In the same manner as in Example 1, a developer of Comparative Example 2 was produced from the carrier of Comparative Example 2 and the toners of each color.

[0137] <Comparative Example 3> MnMg ferrite particles (volume average particle size 35 μm): 100 parts Styrene-methyl methacrylate copolymer (polymerization ratio by mass 2:8, weight average molecular weight 500,000): 1.5 parts Silica particles (HM30S, manufactured by Tokuyama Corporation, average primary particle size 8 nm): 0.6 parts Toluene: 10 parts Styrene-methyl methacrylate copolymer, silica particles, toluene, and glass beads (1 mm diameter, same amount as toluene) were placed in a sand mill and stirred at a rotation speed of 1200 rpm for 30 minutes to obtain a solution for forming a coating layer. Using a Spiracoater (manufactured by Okada Seiko), the coating layer forming solution was applied to the surfaces of MnMg ferrite particles at a rate of 30 g / min in an atmosphere at 70°C so that the coating layer components were 2.1 parts per 100 parts of MnMg ferrite particles, and then dried. The dried powder was removed from the Spiracoater and sieved through a 75 μm mesh to remove coarse powder, yielding a carrier.

[0138] In the same manner as in Example 1, a developer of Comparative Example 3 was produced from the carrier of Comparative Example 3 and the toners of each color.

[0139] <Comparative Example 4> MnMg ferrite particles (volume average particle size 35 μm): 100 parts First resin particles: styrene-methyl methacrylate copolymer resin particles (polymerization ratio by mass 2:8, weight average molecular weight 500,000): 1.5 parts Silica particles (HM30S, manufactured by Tokuyama Corporation, average primary particle size 8 nm): 0.6 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 to cause the resin particles and silica particles to adhere to the MnMg ferrite particles. 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. The powder was removed from the stirring mixer and sieved through a mesh with 75 µm openings to remove coarse powder, thereby obtaining a carrier.

[0140] In the same manner as in Example 1, a developer of Comparative Example 4 was produced from the carrier of Comparative Example 4 and the toners of each color.

[0141] <Comparative Example 5> MnMg ferrite particles (volume average particle size 35 μm): 100 parts First resin particles: styrene-methyl methacrylate copolymer resin particles (polymerization ratio by mass 2:8, weight average molecular weight 500,000): 1.5 parts Silica particles (HM30S, manufactured by Tokuyama Corporation, average primary particle size 8 nm): 0.6 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 to cause the resin particles and silica particles to adhere to the MnMg ferrite particles. An extruder (continuous twin-screw extrusion mixer TEM50, manufactured by Toshiba Machine Co., Ltd.) was used, the extruder casing heating temperature was set to 250°C, MnMg ferrite particles with resin particles and silica particles attached were continuously fed from the raw material inlet, and the treated material (approximately 190°C) was collected from the outlet. The recovered material was continuously fed to a Comil crusher (punched metal diameter 1 mm) and cooled while being crushed to primary particles, obtaining crushed material at a temperature of 60°C or less. The crushed material was sieved through a mesh with 75 μm openings to remove coarse particles and obtain a carrier.

[0142] In the same manner as in Example 1, a developer of Comparative Example 5 was produced from the carrier of Comparative Example 5 and the toner of each color.

[0143] <Comparative Example 6> MnMg ferrite particles (volume average particle size 35 μm): 100 parts First resin particles: styrene-methyl methacrylate copolymer resin particles (polymerization ratio by mass 2:8, weight average molecular weight 500,000): 1.5 parts Silica particles (HM30S, manufactured by Tokuyama Corporation, average primary particle size 8 nm): 0.6 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 to cause the resin particles and silica particles to adhere to the MnMg ferrite particles. 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 5.0 m / s. Next, the temperature inside the stirring mixer was raised to 20°C, and the mixture was stirred and mixed for 15 minutes at a peripheral speed of 10.0 m / sec. The powder was removed from the stirring mixer and sieved through a 75 μm mesh to remove coarse powder, thereby obtaining a carrier.

[0144] In the same manner as in Example 1, a developer of Comparative Example 6 was produced from the carrier of Comparative Example 6 and the toners of each color.

[0145] <Performance evaluation> [Image color unevenness] The toner of each color was placed in a toner cartridge and placed in an environment of 50°C and 60% relative humidity to control the temperature and humidity. An image forming apparatus DocuCenterColor400 (manufactured by Fujifilm Business Innovation Co., Ltd.) was prepared, and the developer of each example or comparative example was placed in the developing unit, and the above toner cartridge was installed. In an environment of a temperature of 28.5° C. and a relative humidity of 85%, the following steps (1) to (5) were carried out using the image forming apparatus and A4 size paper (J paper manufactured by Fuji Xerox Co., Ltd.). (1) Continuously output 5,000 images with an image density of 1%. (2) Following (1), 2000 images with an image density of 30% are output continuously. (3) Following (2), the toner amount is 9.8 g / cm on the entire surface of the paper. 2 Ten 3D color images (process black images) with 100% image density are output consecutively. (4) Following (3), remove the upper cover of the developing unit, take out 50 g of the developer, sieve it through a 106 μm mesh, and visually count the number of agglomerates. Then, return the sieved developer to the developing unit. (5) Visually observe the color unevenness of the 10 tertiary color images. The above steps (1) to (5) were repeated once a day for 10 days (i.e., a total of 10 cycles). The number of aggregates and color unevenness were classified as follows. The results are shown in Table 1. Grades up to C are within the practically acceptable range.

[0146] A: 0 aggregates. No color unevenness. B: There are 1 to 3 aggregates. No color unevenness. C: There are 4 or more aggregates. There are some areas where slight color unevenness is felt. D: There are 4 or more aggregates. Color unevenness is observed. E: There are 4 or more aggregates. Clear color unevenness is observed.

[0147] [Table 1] [Explanation of symbols]

[0148] 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 coating layer that coats the magnetic particles, the coating layer contains a non-particulate resin and silica particles, the exposure rate of the magnetic particles on the surface is 50% or more and 80% or less, The average length RSm of the roughness curve on the surface is 0.9 μm or more and 1.5 μm or less, and the maximum height Rz is 2.0 μm or more and 6.0 μm or less. Carrier for developing electrostatic images.

2. 2. The carrier for developing electrostatic images according to claim 1, wherein the exposed ratio of the magnetic particles on the surface is 50% or more and 65% or less.

3. 3. The carrier for developing electrostatic images according to claim 1, wherein the average length RSm of the roughness curve on the surface is from 0.9 μm to 1.1 μm and the maximum height Rz is from 4.0 μm to 6.0 μm.

4. 4. The carrier for developing electrostatic images according to claim 1, wherein, when an exposure rate of the magnetic particles on the surface is S %, and the amount of the coating layer per 100 parts by mass of the magnetic particles is M parts by mass, the relationship 22<S / M<65 is satisfied.

5. 5. The carrier for developing electrostatic images according to claim 1, wherein, when an exposure rate of the magnetic particles on the surface is S %, and the amount of the coating layer per 100 parts by mass of the magnetic particles is M parts by mass, the carrier satisfies 22<S / M<40.

6. 6. The carrier for developing electrostatic images according to claim 1, wherein the silica particles have an average primary particle size of 1 nm or more and 80 nm or less.

7. 7. The carrier for developing electrostatic images according to claim 1, wherein the silicon element concentration on the surface determined by X-ray photoelectron spectroscopy is 0.1 atomic % or more and 1.0 atomic % or less.

8. 8. The carrier for developing electrostatic images according to claim 1, wherein the silicon element concentration on the surface determined by X-ray photoelectron spectroscopy is 0.2 atomic % or more and 0.6 atomic % or less.

9. 9. The carrier for developing electrostatic images according to claim 1, wherein the coating layer further contains at least one type of resin particles selected from the group consisting of crosslinkable resin particles and thermosetting resin particles.

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

11. 11. The carrier for developing electrostatic images according to claim 1, wherein the magnetic particles are ferrite particles.

12. 12. An electrostatic image developer comprising a toner for developing electrostatic images and the carrier for developing electrostatic images according to claim 1.

13. a developing unit containing the electrostatic image developer according to claim 12 and developing an electrostatic image formed on a 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.

14. an image carrier; a charging means for charging the surface of the image carrier; an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier; a developing unit containing the electrostatic image developer according to claim 12 and developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer; a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; An image forming apparatus comprising:

15. a charging step of charging the surface of the image carrier; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier; a developing step of developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer according to claim 12; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing step of fixing the toner image transferred onto the surface of the recording medium; An image forming method comprising the steps of:

16. 2. A method for producing the carrier for developing electrostatic images according to claim 1, comprising the steps of: Dry-bonding resin particles, which will be the substrate of the coating layer, i.e., the non-particulate resin, and silica particles to the surfaces of the magnetic particles; and stirring the magnetic particles to which the resin particles and the silica particles are attached in a rotary kiln while applying a temperature at which the resin particles melt. A method for producing a carrier for developing electrostatic images.

Images