Carrier for electrostatic charge image development, method for manufacturing the carrier for electrostatic charge image development, electrostatic charge image developer, image forming method, and image forming apparatus

Abstract

To provide an electrostatic image developing carrier capable of suppressing image density unevenness when a high-density image is formed in a high-temperature high-humidity environment after successively forming low-density images in the high-temperature high-humidity environment.SOLUTION: An electrostatic image developing carrier comprises magnetic particles and resin layers covering the magnetic particles, where aggregates having a volume-average particle diameter of 20 μm or more and 50 μm or less, major axes of 75 μm or more, and aspect ratios of 1.4 or more and 4.0 or less, are 2.0 mass% or less to the entire electrostatic image developing carrier.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a carrier for electrostatic charge image development, a method for manufacturing the carrier for electrostatic charge image development, an electrostatic charge image developer, an image forming method, and an image forming apparatus.

Background Art

[0002] Patent Document 1 discloses a carrier for electrostatic charge image development formed by forming a resin coating layer on the surface of core material particles by a dry coating method, wherein the volume average particle diameter D 50 is in the range of 40 to 80 μm, 50 particles of *1.20 μm or more are 5% by weight or less, and D 50 particles of *0.7 μm or less are 5% by weight or less. The core material particles are coated with resin fine particle aggregates having a volume average particle diameter D 50 in the range of 0.5 to 20 μm, and the ratio D 25 of D 50 to D 25 / D 50 is 0.5 to 1.0, and the ratio D 75 of D 50 to D 75 / D 50 is 1.0 to 1.8. A carrier for electrostatic charge image development characterized by being formed. Patent Document 2 discloses a carrier for electrostatic charge image development formed by fixing resin fine particles on the surface of magnetic particles using mechanical pressure to form a resin coating layer. The resin fine particles are composed of aggregates of primary particles, and the volume average particle diameter D 50 of the aggregates is 0.5 to 20 μm, and the ratio D 25 / D 50 of the D50 of the volume 25% particle diameter D25 to the D50 is 0.5 to 1.0, and the ratio D 75 of the D50 of the volume 75% particle diameter D 75 / D 50 is 1.0 to 1.8. A carrier for electrostatic charge image development characterized by being formed.

Prior Art Documents

Patent Documents

[0003] Patent Document 1 Japanese Patent Laid-Open No. 7-152208 Patent Document 2 Japanese Patent Laid-Open No. 5-211807 Summary of the Invention Problems to be Solved by the Invention

[0004] The problem of the present invention is that in an electrostatic charge image developing carrier having magnetic particles and a resin layer covering the magnetic particles, when the volume average particle diameter is less than 20 μm or exceeds 50 μm, or when the major axis is 75 μm or more and the aspect ratio is 1.4 or more and 4.0 or less, the aggregates are compared with those exceeding 2.0% by mass with respect to the entire electrostatic charge image developing carrier, and after continuously forming a low-density image in a high-temperature and high-humidity environment, it is to provide an electrostatic charge image developing carrier that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. Means for Solving the Problems

[0005] The above problems are solved by the following means. That is <1> Magnetic particles and a resin layer covering the magnetic particles, and having a volume average particle diameter of 20 μm or more and 50 μm or less, and an aggregate having a major axis of 75 μm or more and an aspect ratio of 1.4 or more and 4.0 or less is 2.0% by mass or less with respect to the entire electrostatic charge image developing carrier. An electrostatic charge image developing carrier. <2> The electrostatic charge image developing carrier according to <1> above, wherein the volume average particle diameter of the magnetic particles is 18 μm or more and 48 μm or less. <3> The electrostatic charge image developing carrier according to <1> or <2> above, wherein the film thickness of the resin layer is 0.5 μm or more and 2.0 μm or less. <4> The electrostatic charge image developing carrier according to any one of <1> to <3> above, wherein the aggregate is 1.0% by mass or less with respect to the entire electrostatic charge image developing carrier. <5> The electrostatic charge image developing carrier according to any one of <1> to <4> above, wherein the resin layer contains resin particles. <6> The electrostatic charge image developing carrier according to <5> above, wherein the content of the resin particles is 5% by mass or more and 20% by mass or less with respect to the entire resin layer. <7> A first step of adding magnetic particles and a solution containing a resin and a solvent constituting the resin layer to a mixer equipped with a stirring blade, and mixing the magnetic particles and the solution to obtain a mixture; A second step of kneading the mixture under reduced pressure while drying the solvent to form a resin coating layer on the magnetic particles; A third step of cooling while crushing the resin-coated magnetic particles by stirring, and then taking out the carrier from the mixer, wherein the ratio (clearance / diameter D of the stirring blade) of the clearance (m) between the inner wall of the casing of the mixer and the outer periphery of the stirring blade and the diameter D (m) of the stirring blade is 1.0% or more and 5% or less; In the second step, the rotational speed of the stirring blade is N 2 (rps), the diameter of the stirring blade is D (m), the pi is π, and the time of the second step is t 2 (s), and the manufacturing method of the electrostatic charge image developing carrier according to any one of <1> to <6> above, which satisfies the following formulas 1 and 2. Formula 1: 0.2 ≦ the peripheral speed πDN of the stirring blade 2 (m / s) ≦ 1.6 Formula 2: 100 < t 2 (πDN 2 ) 2 <6000 <8> In the second step, the temperature of the mixture is in a region of 25 ° C or higher and lower than the glass transition temperature Tg (° C) of the resin constituting the resin layer, and the pressure in the mixer containing the mixture is in a region of 1 kPa-abs or higher and 101 kPa-abs or lower. The manufacturing method of the electrostatic charge image developing carrier according to <7> above, which is dried. <9> The manufacturing method of the electrostatic charge image developing carrier according to <7> or <8> above, wherein in the second step, the pressure in the mixer is increased from the vacuum pressure side to the atmospheric pressure side. <10>In the second step, the load power value of the stirring blade is continuously monitored, and the pressure in the mixer is controlled so as to reach an arbitrary value, the method for manufacturing a carrier for electrostatic charge image development according to any one of <7> to <9> above. <11>In the third step, the rotation speed of the stirring blade is N 3 (rps), the diameter of the stirring blade is D (m), and when the stirring time in the third step is t 3 (s), the method for manufacturing a carrier for electrostatic charge image development according to any one of <7> to <10> above, which satisfies the following formula 2 and the following formula 3. Formula 3: 0.2 ≤ the peripheral speed πDN of the stirring blade 3 (m / s) ≤ 2.0 Formula 4: 1×10 3 ≤ stirring work amount (peripheral speed × stirring time t 3 ) ≤ 4×10 3 <12>The method for manufacturing a carrier for electrostatic charge image development according to any one of <7> to <11> above, including a fourth step of removing coarse particles after the third step. <13>An electrostatic charge image developer containing the carrier for electrostatic charge image development and the toner for electrostatic charge image development according to any one of <1> to <6> above. <14>At least a charging step of charging an image carrier, An exposure step of forming an electrostatic latent image on the surface of the image carrier, A developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic charge image developer to form a toner image, A transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a transfer body, A fixing step of fixing the toner image, and including The electrostatic charge image developer is the electrostatic charge image developer described in <13> above An image forming method. <15>An image carrier, Charging means for charging the image carrier, Exposure means for exposing the charged image carrier to form an electrostatic latent image on the image carrier, Developing means for developing the electrostatic latent image with an electrostatic charge image developer to form a toner image, transfer means for transferring the toner image from the image holding member to a transfer target; fixing means for fixing the toner image, and the electrostatic charge image developer is the electrostatic charge image developer according to <13>. An image forming apparatus.

Advantages of the Invention

[0006] <1>, in an electrostatic charge image developing carrier having magnetic particles and a resin layer covering the magnetic particles, when the volume average particle diameter is less than 20 μm or exceeds 50 μm, or when the major axis is 75 μm or more and the aspect ratio is 1.4 or more and 4.0 or less, aggregates are present in the electrostatic charge image developing carrier as a whole. Compared with the case where it exceeds 2.0% by mass, an electrostatic charge image developing carrier is provided that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment. <2>, compared with the case where the volume average particle diameter of the magnetic particles is less than 18 μm or exceeds 48 μm, after continuously forming a low-density image in a high-temperature and high-humidity environment, an electrostatic charge image developing carrier is provided that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. <3>, even when the film thickness of the resin layer is 0.5 μm or more and 2.0 μm or less, after continuously forming a low-density image in a high-temperature and high-humidity environment, an electrostatic charge image developing carrier is provided that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. <4>, compared with the case where aggregates exceed 1.0% by mass with respect to the entire electrostatic charge image developing carrier, after continuously forming a low-density image in a high-temperature and high-humidity environment, an electrostatic charge image developing carrier is provided that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. According to the invention according to <5>, a resin layer contains resin fine particles, and when the content of the resin fine particles is less than 5% by mass or exceeds 20% by mass with respect to the entire electrostatic charge image developing carrier, after continuously forming a low-density image in a high-temperature and high-humidity environment, an electrostatic charge image developing carrier is provided that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. According to the invention according to <6>, when the resin fine particles are fine particles made of a melamine-formaldehyde condensate, compared with the case where no resin fine particles are added, after continuously forming a low-density image in a high-temperature and high-humidity environment, an electrostatic charge image developing carrier is provided that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. According to the invention according to <7>, a magnetic particle and a solution containing a resin and a solvent constituting a resin layer are added to a mixer equipped with a stirring blade, and a first step of mixing the magnetic particle and the solution to obtain a mixed solution, a second step of kneading the mixed solution under reduced pressure conditions to obtain a mixture, and a third step of taking out a carrier from the mixer after crushing the mixture by stirring are included, and the ratio (clearance / diameter D of the stirring blade) of the clearance (m) between the inner wall of the casing of the mixer and the outer periphery of the stirring blade and the diameter D (m) of the stirring blade is 1.0 or more and 5% or less. In the manufacturing method of the electrostatic charge image developing carrier, in the second step, the rotation speed of the stirring blade is N 2 (rps), the diameter of the stirring blade is D (m), and the time of the second step is t 2 (s), compared with the case where the following formulas C1 and C2 are satisfied, after continuously forming a low-density image in a high-temperature and high-humidity environment, an electrostatic charge image developing carrier is obtained that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. A manufacturing method of an electrostatic charge image developing carrier is provided. Formula C1: 0.2 ≧ circumferential speed πDN of the stirring blade 2 (m / s) or circumferential speed πDN of the stirring blade 2 (m / s) ≧ 1.6 Formula C2: 100 ≧ t 2 (πN 2 D) 2 or t 2 (πN 2 D) 2 ≧ 6000 According to the invention according to <8>, in the second step, when drying the mixture at a temperature lower than 25°C or in a region exceeding the glass transition temperature Tg (°C) of the resin constituting the resin layer, or when drying the mixture in a region where the pressure in the mixer containing the mixture is less than 1 kPa-abs or exceeds 101 kPa-abs, compared with the case of continuously forming a low-density image in a high-temperature and high-humidity environment and then forming a high-density image in a high-temperature and high-humidity environment, a method for manufacturing an electrostatic charge image developing carrier is provided, which can obtain an electrostatic charge image developing carrier that suppresses the occurrence of image density unevenness. According to the invention according to <9>, in the second step, compared with the case where the pressure in the mixer is not increased gradually from the vacuum pressure side to the atmospheric pressure side, after continuously forming a low-density image in a high-temperature and high-humidity environment, a method for manufacturing an electrostatic charge image developing carrier is provided, which can obtain an electrostatic charge image developing carrier that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. According to the invention according to <10>, in the second step, compared with the case where the load power value of the stirring blade is continuously monitored and not set to an arbitrary value, after continuously forming a low-density image in a high-temperature and high-humidity environment, a method for manufacturing an electrostatic charge image developing carrier is provided, which can obtain an electrostatic charge image developing carrier that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. According to the invention according to <11>, in the third step, the rotational speed of the stirring blade is N 3 (rps), the diameter of the stirring blade is D (m), and the stirring time of the third step is t 3 (s), compared with the case where the following formula C2 and the following formula C3 are satisfied, after continuously forming a low-density image in a high-temperature and high-humidity environment, a method for manufacturing an electrostatic charge image developing carrier is provided, which can obtain an electrostatic charge image developing carrier that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment. Formula C3: 0.2 > the peripheral speed πDN of the stirring blade 3 (m / s) or the peripheral speed πDN of the stirring blade 3 (m / s) > 2.0 Formula C4: 1×10 3 > the stirring work amount (peripheral speed × stirring time t 3) or stirring work amount (peripheral speed × stirring time t 3 ) > 4 × 10 3 According to the invention according to <12>, after the third step, compared with the case where the fourth step of removing coarse particles is not included, after continuously forming a low-density image in a high-temperature and high-humidity environment, when forming a high-density image in a high-temperature and high-humidity environment, a method for manufacturing an electrostatic charge image developing carrier capable of suppressing the occurrence of image density unevenness is provided. According to the invention according to <13>, <14>, or <15>, in an electrostatic charge image developing carrier having magnetic particles and a resin layer covering the magnetic particles, when the volume average particle diameter is less than 20 μm or exceeds 50 μm, or when the aggregate having a major axis of 75 μm or more and an aspect ratio of 1.4 or more and 4.0 or less exceeds 2.0% by mass based on the entire electrostatic charge image developing carrier, compared with the case, after continuously forming a low-density image in a high-temperature and high-humidity environment, an electrostatic charge image developing agent, an image forming method, or an image forming apparatus including an electrostatic charge image developing carrier capable of suppressing the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment is provided.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0008] Hereinafter, an embodiment which is an example of the present invention will be described. These descriptions and examples are illustrative of the embodiments and do not limit the scope of the invention. In the numerical ranges described step by step in this specification, the upper limit value or the lower limit value described in one numerical range may be replaced with the upper limit value or the lower limit value of the numerical range described in other step-by-step descriptions. Also, in the numerical ranges described in this specification, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples.

[0009] Each component may contain a plurality of corresponding substances. When referring to the amount of each component in the composition, when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the plurality of substances present in the composition. The term "step" includes not only independent steps but also cases where it cannot be clearly distinguished from other steps, as long as the intended action of the step is achieved.

[0010] <Carrier for Electrostatic Charge Image Development> The carrier for electrostatic charge image development according to this embodiment (hereinafter, the "carrier for electrostatic charge image development" is also simply referred to as "carrier") has magnetic particles and a resin layer covering the magnetic particles. Moreover, the volume average particle diameter of the carrier is 20 μm or more and 50 μm or less. And aggregates with a major axis of 75 μm or more and an aspect ratio of 1.4 or more and 4.0 or less are 2.0 mass% or less with respect to the entire electrostatic charge image developing carrier. Here, the "aggregate" refers to a product in which primary particles of a plurality of carriers are aggregated.

[0011] Due to the above configuration, the carrier according to the present embodiment suppresses the occurrence of image density unevenness when forming a high-density image (for example, an image with an image density of 30% or less) in a high-temperature and high-humidity environment (for example, in an environment of 28.5°C and 85% RH) after continuously forming a low-density image (for example, an image with an image density of 1% or less) in a high-temperature and high-humidity environment (for example, in an environment of 28.5°C and 85% RH). The reason is speculated as follows.

[0012] In the manufacturing method of an electrostatic charge image developing carrier having magnetic particles and a resin layer covering the magnetic particles, for example, when there is a step of drying after mixing magnetic particles and a solution containing a resin and a solvent constituting the resin layer, in the drying, for example, aggregates with a major axis of 75 μm or more and an aspect ratio of 1.4 or more and 4.0 or less may be likely to occur. Since the aggregates cannot pass through a layer regulating member that regulates the amount of developer on the developing sleeve and stay in front of the layer regulating member in the developing device, when the carrier contains a certain amount or more of the aggregates, the structure of the developing brush to which the developer composed of the carrier and toner adheres and is formed on the developing sleeve is likely to become irregular. This phenomenon is likely to become prominent after continuously forming low-density images in a high-temperature and high-humidity environment. And when forming a high-density image in a high-temperature and high-humidity environment in a state where the layer structure of the carrier and toner formed on the developing sleeve becomes irregular after continuously forming low-density images in a high-temperature and high-humidity environment, image density unevenness may be likely to occur.

[0013] The carrier according to this embodiment reduces the content of aggregates having a major axis of 75 μm or more and an aspect ratio of 1.4 or more and 4.0 or less to 2.0 mass% or less with respect to the entire electrostatic charge image developing carrier among carriers having a volume average particle diameter of 20 μm or more and 50 μm or less. Therefore, even when a low-density image is continuously formed in a high-temperature and high-humidity environment, the structure of the developing brush formed on the developing sleeve is less likely to become irregular. When the volume average particle diameter of the carrier is 20 μm or less, the magnetic force per particle decreases, so the structure of the developing brush due to the magnetic restraint force is likely to become irregular. When it is 50 μm or more, the structure of the developing brush due to the magnetic restraint force becomes stronger, so it is more likely to be affected by layer regulation by aggregates.

[0014] From the above, it is presumed that the carrier according to this embodiment suppresses the occurrence of image density unevenness when a high-density image is formed in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment.

[0015] (Magnetic particles) The magnetic particles are not particularly limited, and known magnetic particles used as the core material of the carrier are applicable. Specifically, 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 obtained by impregnating porous magnetic powder with resin; magnetic powder-dispersed resin particles in which magnetic powder is dispersed and blended in resin; and the like. In this embodiment, ferrite particles are preferable as the magnetic particles.

[0016] The volume average particle diameter of the magnetic particles is preferably 10 μm or more and 100 μm or less, more preferably 15 μm or more and 80 μm or less, and still more preferably 20 μm or more and 60 μm or less. Here, the volume average particle diameter is measured using a laser diffraction / scattering type particle size distribution measuring device (LS Particle Size Analyzer: LS13 320, manufactured by BECKMAN COULTER). In the measured volume-based particle size distribution, the particle diameter D50v at which the cumulative value becomes 50% from the small-diameter side is defined as the volume average particle diameter.

[0017] The arithmetic mean height Ra (JIS B0601:2001) of the roughness curve of the magnetic particles is preferably 0.1 μm or more and 1 μm or less, more preferably 0.2 μm or more and 0.8 μm or less. The arithmetic mean height Ra of the roughness curve of the magnetic particles is obtained by observing the magnetic particles at an appropriate magnification (for example, magnification of 1000 times) using a surface shape measuring device (for example, "Ultra Depth Color 3D Shape Measuring Microscope VK-9700" manufactured by Keyence Corporation), obtaining a roughness curve with a cut-off value of 0.08 mm, and extracting a reference length of 10 μm in the direction of the mean line from the roughness curve. The Ra of 100 magnetic particles is arithmetically averaged.

[0018] The magnetic force of the magnetic particles is preferably such that the saturation magnetization in a magnetic field of 3000 oersted is 50 emu / g or more, more preferably 60 emu / g or more. The measurement of the saturation magnetization is performed using a vibrating sample type magnetic measurement device VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.). The measurement sample is packed in a cell with an inner diameter of 7 mm and a height of 5 mm and set in the device. The measurement is performed by applying a magnetic field and sweeping up to a maximum of 3000 oersted. Then, the applied magnetic field is decreased to create a hysteresis curve on a recording paper. The saturation magnetization, residual magnetization, and coercive force are obtained from the curve data.

[0019] The volume electrical resistance (volume resistivity) of the magnetic particles is 1×10 5 Ω·cm or more and 1×10 9 Ω·cm or less is preferable, and 1×10 7 Ω·cm or more and 1×10 9 Ω·cm or less is more preferable. The volume electrical resistance (Ω·cm) of the magnetic particles is measured as follows. On the surface of a circular jig with electrode plates of 20 cm 2 , the object to be measured is placed flat so as to have a thickness of 1 mm or more and 3 mm or less to form a layer. On this, the 20 cm 2Place the electrode plates on top and sandwich the layer. To eliminate the gap between the objects to be measured, apply a load of 4 kg on the electrode plates placed on the layer, and then measure the thickness (cm) of the layer. Both the upper and lower electrodes of the layer are connected to an electrometer and a high-voltage power supply generator. Apply a high voltage so that the electric field between the two electrodes becomes 103.8 V / cm, and read the current value (A) that flowed at this time. The measurement environment shall be a temperature of 20°C and a relative humidity of 50%. The calculation formula for the volume electrical resistance (Ω·cm) of the object to be measured is as shown in the following formula. R = E × 20 / (I - I 0 ) / L In the above formula, R is the volume electrical resistance (Ω·cm) of the object to be measured, E is the applied voltage (V), I is the current value (A), I 0 is the current value (A) at an applied voltage of 0 V, and L is the thickness (cm) of the layer, respectively. The coefficient 20 represents the area (cm 2 ) of the electrode plate.

[0020] (Resin layer) The resin layer contains the resin that constitutes the resin layer. Examples of the resin that constitutes the resin layer include styrene-acrylic acid copolymer; 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 copolymer; straight silicone resin composed of organosiloxane bonds or its modified products; fluorine resins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyester; polyurethane; polycarbonate; amino resins such as urea-formaldehyde resin; epoxy resin; and the like.

[0021] The resin layer preferably contains an acrylic resin having an alicyclic structure. As the polymerization component of the acrylic resin having an alicyclic structure, a lower alkyl ester of (meth)acrylic acid (for example, an alkyl (meth)acrylate having 1 to 9 carbon atoms in the alkyl group) is preferable. Specifically, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc. can be mentioned. These monomers may be used alone or in combination of two or more. The acrylic resin having an alicyclic structure preferably contains cyclohexyl (meth)acrylate as a polymerization component. The content of the monomer unit derived from cyclohexyl (meth)acrylate contained in the acrylic resin having an alicyclic structure is preferably 75% by mass or more and 100% by mass or less, more preferably 85% by mass or more and 100% by mass or less, and still more preferably 95% by mass or more and 100% by mass or less with respect to the total mass of the acrylic resin having an alicyclic structure.

[0022] The film thickness of the resin layer is preferably 0.5 μm or more and 2.0 μm or less, more preferably 0.8 μm or more and 1.7 μm or less, and still more preferably 1.0 μm or more and 1.5 μm or less.

[0023] When the film thickness of the resin layer is 0.4 μm or more and 2.0 μm or less, aggregates tend to be more likely to occur during the production of the carrier. Therefore, carriers with a resin layer film thickness within this range tend to contain a large amount of aggregates. Even when the carrier according to this embodiment has a film thickness of 0.4 μm or more and 2.0 μm or less, since the content of aggregates is small, after continuously forming a low-density image in a high-temperature and high-humidity environment and then forming a high-density image in a high-temperature and high-humidity environment, the occurrence of image density unevenness can be suppressed.

[0024] The film thickness of the resin layer is determined by the following method. Embed the carrier in an epoxy resin, cut it with a microtome, and prepare a cross-section of the carrier. Take an SEM image of the cross-section of the carrier using a Scanning Electron Microscope (SEM) and import it into an image processing and analysis device for image analysis. Randomly select 10 locations per carrier particle to measure the thickness (μm) of the resin layer. Further measure 100 carriers and calculate the arithmetic mean of all of them, which is defined as the film thickness (μm) of the resin layer.

[0025] The content of the resin constituting the resin layer is preferably 50% by mass or more and 100% by mass or less, more preferably 52% by mass or more and 98% by mass or less, and even more preferably 55% by mass or more and 95% by mass or less, based on the entire resin layer.

[0026] -Internal additive- The resin layer preferably contains an internal additive. Here, the internal additive refers to components other than the resin constituting the resin layer among the components contained in the resin layer. Examples of the internal additive include conductive materials, inorganic particles other than conductive materials, resin particles, etc.

[0027] ·Conductive material Examples of the conductive material include carbon black, metals such as gold, silver, and copper, and titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, potassium titanate, tin-doped indium oxide, antimony-doped tin oxide, aluminum-doped zinc oxide, resin particles coated with a metal, etc.

[0028] The content of the conductive material is preferably 0% by mass or more and 10% by mass or less, more preferably 0.05% by mass or more and 5% by mass or less, based on the entire resin layer.

[0029] ·Inorganic particles other than conductive materials Examples of the inorganic particles other than conductive materials include silica particles, alumina particles, etc. The content of the conductive material is preferably 0% by mass or more and 60% by mass or less, more preferably 0.05% by mass or more and 50% by mass or less, based on the entire resin layer.

[0030] ·Resin particles The resin layer preferably contains resin particles. By including resin particles in the resin layer, the resin fine particles on the surface of the resin layer serve as spacers, suppressing the peeling of the carrier resin layer due to stirring in the developing device and making it difficult to generate aggregates with resin peeling as the core in the developing device. Therefore, it is more likely to become an electrostatic charge image developer that suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment. If it is too little, the spacer effect cannot be obtained, and if it is too much, the adhesion and binding property between the resin and the magnetic particles deteriorate and resin peeling progresses.

[0031] Examples of the resin particles include thermosetting resin particles and crosslinked resin particles. The thermosetting resin particles are not particularly limited as long as they are particles formed of a thermosetting resin, but particles formed of a resin containing a nitrogen element are preferred. Among them, melamine resin, urea resin, urethane resin, guanamine resin, and amide resin are preferred because they have a high positive chargeability and a high resin hardness, so a decrease in the charge amount due to peeling of the resin coating layer is suppressed.

[0032] Commercially available products can also be used as the thermosetting resin particles. For example, Eposta S (manufactured by Nippon Shokubai Co., Ltd., melamine-formaldehyde condensation resin), Eposta MS (manufactured by Nippon Shokubai Co., Ltd., benzoguanamine-formaldehyde condensation resin), etc.

[0033] The crosslinked resin particles are not particularly limited as long as they are polymers of polymerizable monomers. For example, a resin using at least one selected from styrene compounds, (meth)acrylate compounds, and polyvinyl compounds, which have good charge control properties, is preferred. Examples of the styrene compound include styrene and α-methylstyrene. Examples of the (meth)acrylate compound include (meth)acrylic acid and alkyl (meth)acrylate compounds. Examples of the alkyl (meth)acrylate compound include alicyclic alkyl (meth)acrylate compounds such as methyl (meth)acrylate, ethyl (meth)acrylate, and cyclohexyl (meth)acrylate. Among these, a homopolymer or copolymer of an alicyclic (meth)acrylate compound having low hygroscopicity is more preferable. Examples of the alicyclic (meth)acrylate compound include cyclohexyl methacrylate.

[0034] The crosslinked resin particles may contain a nitrogen-containing monomer to impart a charge-giving effect. Examples include dialkylaminoalkyl (meth)acrylates such as diethylaminoethyl (meth)acrylate and dimethylaminoethyl (meth)acrylate, alkylaminoalkyl (meth)acrylates such as ethylaminoethyl (meth)acrylate and methylaminoethyl (meth)acrylate, aminoalkyl (meth)acrylates such as aminoethyl (meth)acrylate, 1,2,2,6,6-pentamethyl-4-piperidyl methacrylate, and 2,2,6,6-tetramethyl-4-piperidyl methacrylate.

[0035] When producing the crosslinked resin particles, the means for forming the crosslinked structure is not particularly limited, and examples include a method of using a crosslinking agent such as a crosslinkable monomer.

[0036] Specific examples of the crosslinking agent include, for example, aromatic polyvinyl compounds such as divinylbenzene and divinylnaphthalene; polyvinyl esters of aromatic polyvalent carboxylic acids such as divinyl phthalate, divinyl isophthalate, divinyl terephthalate, divinyl homophthalate, trivinyl trimesate, divinyl naphthalenedicarboxylate, and divinyl biphenylcarboxylate; divinyl esters of nitrogen-containing aromatic compounds such as divinyl pyridinedicarboxylate; vinyl esters of unsaturated heterocyclic compound carboxylic acids such as vinyl pyromucate, vinyl furancarboxylate, vinyl pyrrole-2-carboxylate, and vinyl thiophenecarboxylate; (meth)acrylic acid esters of linear polyhydric alcohols such as butanediol methacrylate, hexanediol acrylate, octanediol methacrylate, decanediol acrylate, and dodecanediol methacrylate; (meth)acrylic acid esters of branched and substituted polyhydric alcohols such as neopentyl glycol dimethacrylate and 2-hydroxy-1,3-diacryloxypropane; polyethylene glycol di(meth)acrylate, polypropylene polyethylene glycol di(meth)acrylates; polyvinyl esters of polyvalent carboxylic acids such as divinyl succinate, divinyl fumarate, vinyl / maleic acid divinyl, divinyl diglycolate, vinyl / itaconic acid divinyl, divinyl acetonedicarboxylate, divinyl glutarate, divinyl 3,3'-thiodipropionate, vinyl / trans-aconitic acid divinyl / trivinyl, divinyl adipate, divinyl pimelate, divinyl suberate, divinyl azelate, divinyl sebacate, divinyl dodecanedioate, and divinyl brassylate; and the like.

[0037] In this embodiment, these crosslinking agents may be used alone or in combination of two or more. Among the above crosslinking agents, acrylate-based ones are desirable in order not to impair the chargeability of the coating resin. (Meth)acrylic acid esters of linear polyhydric alcohols such as butanediol methacrylate, hexanediol acrylate, octanediol methacrylate, decanediol acrylate, dodecanediol methacrylate; (meth)acrylic acid esters of branched and substituted polyhydric alcohols such as neopentyl glycol dimethacrylate, 2-hydroxy-1,3-diacryloxypropane; polyethylene glycol di(meth)acrylate, polypropylene polyethylene glycol di(meth)acrylates, etc. are preferably used.

[0038] As methods for producing the thermosetting resin particles and the crosslinked resin particles, there are methods of synthesizing resin particles by an emulsion polymerization method, a suspension polymerization method, etc., and methods of obtaining the synthesized resin by pulverizing and classifying or emulsifying and dispersing in water. In this embodiment, it is preferable to use resin particles produced by polymerizing and drying by an emulsion polymerization method using a polymerization initiator and a surfactant.

[0039] The average particle diameter of the resin particles is preferably 50 nm or more and 1000 nm or less, more preferably 70 nm or more and 500 nm or less, and still more preferably 90 nm or more and 300 nm or less. The measurement of the average particle diameter of the resin particles is carried out as follows. Embed the carrier with an epoxy resin, cut it with a microtome to prepare a cross-section of the carrier. Take a SEM image of the cross-section of the carrier by a Scanning Electron Microscope (SEM) and import it into an image processing and analysis device for image analysis. Randomly select 100 resin particles (primary particles) in the resin layer, obtain the equivalent circle diameter (nm) of each, and calculate the arithmetic mean, which is taken as the average particle diameter (nm) of the resin particles.

[0040] From the perspective of using a carrier for electrostatic charge image development that further suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in the same environment, the resin particle content is preferably 5% by mass or more and 20% by mass or less, more preferably 7% by mass or more and 18% by mass or less, and even more preferably 8% by mass or more and 15% by mass or less with respect to the entire resin layer.

[0041] (Properties of the carrier) -Volume average particle diameter- The volume average particle diameter of the carrier is 20 μm or more and 50 μm or less. From the perspective of further suppressing the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in the same environment, the volume average particle diameter of the carrier is preferably 23 μm or more and 49 μm or less, more preferably 25 μm or more and 48 μm or less, and even more preferably 27 μm or more and 47 μm or less.

[0042] The volume average particle diameter of the carrier is measured as follows. Using a Coulter Multisizer II (manufactured by Beckman Coulter) as the measuring device and ISOTON-II (manufactured by Beckman Coulter) as the electrolyte, first, add 0.5 mg or more and 50 mg or less of the measurement sample to 2 ml of a 5% by mass aqueous solution of a surfactant, preferably sodium alkylbenzene sulfonate, as a dispersant, and add this to 100 ml or more and 150 ml or less of the above electrolyte. The electrolyte in which the measurement sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for about 1 minute, and the particle size distribution of particles in the range of 2.0 μm or more and 60 μm or less in particle size is measured using an aperture with an aperture diameter of 100 μm by the Coulter Multisizer II. The number of particles to be measured is 50,000. For the measured particle size distribution, draw a cumulative distribution with respect to the divided particle size ranges (channels) in terms of volume from the small particle size side, and define the particle size at which the cumulative value reaches 50% as the volume average particle diameter (D 50v ).

[0043] -Content of aggregates- Aggregates with a major axis of 75 μm or more and an aspect ratio of 1.4 or more and 4.0 or less (hereinafter also referred to as specific aggregates) are 2.0 mass% or less with respect to the entire electrostatic charge image developing carrier.

[0044] Here, the content of the specific aggregates is measured as follows. Using a powder tester (manufactured by Hosokawa Micron Corporation), a sieve with an aperture of 75 μm is placed. 2 g of the accurately weighed carrier is put on the sieve, and vibration is applied at an amplitude of 1 mm for 90 seconds, leaving the aggregates contained in the carrier on the sieve after vibration. The mass of the aggregates on the sieve after vibration is measured, and the "mass % of the aggregates on the sieve after vibration with respect to the entire carrier" is calculated. Subsequently, the aggregates on the sieve after vibration are observed with a SEM (Scanning Electron Microscope) at a magnification of 350 times to take an image, and this image is imported into an image analysis device (LUZEXIII, manufactured by Nireco Corporation). By image analysis of the aggregates, the length in the major axis direction and the length in the minor axis direction of the aggregates are calculated. Here, the length in the major axis direction of the aggregates refers to the longest length among the line segments connecting two points on the contour of the aggregates in the said image. Also, the length in the minor axis direction of the aggregates refers to the shortest length among the line segments connecting two points on the contour of the aggregates in the image and perpendicular to the straight line parallel to the length in the major axis direction of the aggregates. The calculation of the length in the major axis direction and the length in the minor axis direction of these aggregates is performed for 500 aggregates. Then, from the obtained values, the average length in the major axis direction and the average length in the minor axis direction of the aggregates are calculated. The average length in the major axis direction of the aggregates is defined as the "major axis diameter" of the aggregates. The average length in the major axis direction of the aggregates when the average length in the minor axis direction of the aggregates is set to 1 is defined as the "aspect ratio" of the aggregates. When the "major axis diameter" of the aggregates measured by the above procedure is 75 μm or more and the "aspect ratio" of the aggregates is 1.4 or more and 4.0 or less, the "content (mass%) of the aggregates on the sieve after vibration with respect to the entire carrier" is defined as the content (mass%) of the specific aggregates with respect to the entire carrier.

[0045] The content of the specific aggregates is preferably 1.0% by mass or less, more preferably 0.7% by mass or less, and still more preferably 0.5% by mass or less with respect to the entire electrostatic charge image developing carrier.

[0046] By setting the content of the specific aggregates within the above numerical range, the amount of the specific aggregates contained in the carrier becomes less. Therefore, it becomes a carrier that can further suppress the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment.

[0047] <Method for manufacturing a carrier> The method for manufacturing a carrier includes the following steps. A first step of adding magnetic particles and a solution containing a resin and a solvent constituting a resin layer to a mixer equipped with a stirring blade, and mixing the magnetic particles and the solution to obtain a mixture. A second step of kneading the mixture under reduced pressure while drying the solvent to form a resin coating layer on the magnetic particles. A third step of cooling while crushing the resin-coated magnetic particles by stirring, and then taking out the carrier from the mixer. And the ratio of the clearance (m) between the inner wall of the casing of the mixer and the outer periphery of the stirring blade to the diameter D (m) of the stirring blade is such that (clearance / diameter D of the stirring blade) is 1.0% or more and 5% or less, In the second step, the rotational speed of the stirring blade is N 2 (rps), the diameter of the stirring blade is D (m), the pi is π, and the time of the second step is t 2 (s), the following formulas 1 and 2 are satisfied. Formula 1: 0.5 ≦ the peripheral speed πDN of the stirring blade 2 (m / s) ≦ 1.6 Formula 2: 100 < t 2 (πDN 2 ) 2 <6000

[0048] In the second step, 0.2 (m / s) ≦ πDN 2 And, t 2 (πDN 2 ) 2By setting the value to a number greater than 100, in the second step, the dispersion state of the magnetic particles in the mixed solution is likely to be good. Therefore, the mixture obtained in the second step is less likely to aggregate, and the generation of aggregates of the carrier is also suppressed. On the other hand, in the second step, πDN 2 When ≦ 1.6 (m / s), a uniform kneading state is maintained, but when it exceeds 1.6 (m / s), only the stirring blade rotates idly with respect to the mixture in a high-viscosity state, and a uniform kneading state cannot be maintained, so a uniform resin coating layer is not formed. Furthermore, t 2 (πN 2 D) 2 By setting it to less than 6000, too much force is not applied to the mixture obtained in the second step, and the resin coating layer of the magnetic particles is less likely to peel off. When the coating resin of the magnetic particles peels off, aggregates of the carrier are likely to occur. Therefore, t 2 (πDN 2 ) 2 By setting it to less than 6000, aggregates of the carrier are less likely to occur.

[0049] From the above, the method for manufacturing a carrier according to this embodiment is likely to result in a state where the amount of specific aggregates contained in the carrier is small without performing sieving. Therefore, the method for manufacturing a carrier according to this embodiment can more effectively suppress the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment, and is a manufacturing method that can obtain a carrier with a good yield.

[0050] (First step) The first step is a step of adding a solution containing a resin and a solvent constituting the resin layer to a mixer equipped with a stirring blade, and mixing the magnetic particles and the solution to obtain a mixture.

[0051] As the first step, after adding a mixer equipped with a stirring blade to uniformly mix the magnetic particles and a solution containing a resin and a solvent constituting the resin layer, the magnetic particles and the solution are stirred at a rotational speed of the stirring blade of 0.2 ≦ the peripheral speed πDN of the stirring blade 1It is preferable to mix for 5 minutes or more and 60 minutes or less under the condition that (m / s) ≤ 2.0 rpm or higher. In addition, when the shape and diameter D of the stirring blade are continuously carried out in the same apparatus until the second or third step described later, the stirring blades used are the same, but this is not the case when each step is taken out to a separate apparatus.

[0052] As the magnetic particles and the resin constituting the resin layer, those described are applicable. As the solvent used in the solution containing the resin and the solvent constituting the resin layer, it is preferable that the resin constituting the resin layer is dissolved in 50 parts by mass or more with respect to 100 parts by mass of the solvent. The solvent is appropriately changed depending on the type of resin constituting the resin layer to be used.

[0053] The amount of the solution containing the resin and the solvent constituting the resin layer added to the mixer equipped with the stirring blade is such that the solid content of the solution containing the resin and the solvent constituting the resin layer with respect to 100 parts by mass of the magnetic particles is 1.0 part by mass or more and 40.0 parts by mass or less, more preferably 1.5 parts by mass or more and 35.0 parts by mass or less, and still more preferably 2.0 parts by mass or more and 30.0 parts by mass or less. In addition, the solid content of the coating liquid containing the resin and the solvent constituting the resin layer is preferably 5 parts by mass or more and 50 parts by mass or less, more preferably 10 parts by mass or more and 40 parts by mass or less, and still more preferably 15 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the solution.

[0054] - Mixer equipped with stirring blade - The mixer equipped with the stirring blade is not particularly limited as long as it is a mixer capable of "stirring, heating, and cooling substances in the mixer", "measuring the temperature of substances in the mixer, the pressure in the mixer, and the load power value of the stirring blade", and "reducing the pressure in the mixer", and a known mixer is applicable. In addition, the mixer used in the present embodiment is preferably a batch mixer, and more preferably a batch vacuum mixer. Furthermore, as the batch mixer, a blade type kneader is preferable, and the axial direction of the blade may be vertical or horizontal. Among them, a kneader is more preferable, and a twin-screw horizontal kneader is particularly preferable. Also, it is preferable that the mixer has a temperature control structure capable of heating and cooling under reduced pressure of the pressure inside the mixing tank, and a mechanism capable of detecting the load power value of the stirring blade. Although there is no particular limitation on the temperature control structure, a jacket structure is preferable.

[0055] The ratio of the clearance (m) between the inner wall of the casing and the outer periphery of the stirring blade of the mixer equipped with the stirring blade to the diameter D (m) of the stirring blade is (clearance / diameter D of the stirring blade) is 1.0% or more and 5% or less. Here, the inner wall of the casing of the mixer refers to the narrowest part with the stirring blade of the mixer. Also, the diameter of the stirring blade is the maximum diameter of the rotation locus of the stirring blade when viewed from the axial direction of the rotation axis of the stirring blade. Although there is no particular limitation on the shape of the stirring blade, examples thereof include shapes such as a Banbury type, a sigma type, a zet type, a spiral type, and a fish tail type.

[0056] (Second step) The second step is a step of kneading the mixture obtained in the first step under reduced pressure conditions while drying the solvent to form a resin coating layer on the magnetic particles. And in the second step, the rotation speed of the stirring blade is N 2 (rps), the diameter of the stirring blade is D (m), and the time of the second step is t 2 When (s), the following formula 1 and the following formula 2 are satisfied. Formula 1: 0.5 ≦ the peripheral speed πDN of the stirring blade 2 (m / s) ≦ 1.6 Formula 2: 100 < t 2 (πDN 2 ) 2 <6000

[0057] From the perspective of providing a method for manufacturing a carrier for electrostatic charge image development that further suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment, in the second step, it is preferable to satisfy the following formula 1-2, and further preferably to satisfy the following formula 2-2, more preferably to satisfy the following formula 2-3, and even more preferably to satisfy the following formula 2-4. Formula 1-2; 0.5 < πDN 2 (m / s) < 1.1 Formula 2-2: 120 < t 2 (πDN 2 ) 2 < 5000 Formula 2-3: 200 < t 2 (πDN 2 ) 2 < 3000 Formula 2-4: 300 < t 2 (πDN 2 ) 2 < 2000

[0058] The time t of the second step 2 is the time (unit: sec) from the start point to the end point of the second step defined by the load power value of the stirring blade as follows.

[0059] First, the transition of the load power value of the stirring blade in the first step to the third step will be described. In the first step to the third step, for example, it is considered that the load power value of the stirring blade shown in FIG. 3 fluctuates. FIG. 3 is a schematic graph showing the variation of the load power value of the stirring blade and the variation of the temperature inside the mixer with the passage of time in an example of the method for manufacturing a carrier for electrostatic charge image development according to the present embodiment. The left vertical axis in FIG. 3 represents the load power value (kW) of the stirring blade, the right vertical axis represents the temperature inside the mixer (°C), and the horizontal axis represents the elapsed time (min).

[0060] At T0 shown in FIG. 3, magnetic particles and a solution containing a resin and a solvent that constitute a resin layer (hereinafter also referred to as a coating solution) are put into a mixer. From T0 to T1, the coating solution and the magnetic particles are in a state of being mixed, which is the first step. From T1 to T2, while reducing the pressure, the solvent contained in the coating solution is evaporated, and it is a state until the drying of the carrier is completed, which is the second step. From T2 to T3, the dried carrier is crushed and, if necessary, cooled, which is a part of the third step. Note that T3 indicates the point in time when the rotation of the stirring blade is stopped.

[0061] Regarding the variation of the load power value of the stirring blade shown in FIG. 3, it is as follows. From T0 to T1 (the first step), the load power value of the stirring blade is almost constant. From T1 to T2 (the second step), as the solvent evaporates, the viscosity of the mixed solution of the coating solution and the magnetic particles in the mixer increases, and the load power value of the stirring blade continues to rise until the drying of the carrier is completed. When the drying of the carrier is completed and a mixture is obtained, the load power value of the stirring blade suddenly decreases and decreases to a value almost the same as the load power value of the stirring blade from T0 to T1. From T2 to T3 (the third step), again, the load power value of the stirring blade becomes almost constant.

[0062] Regarding the variation of the temperature inside the mixer shown in FIG. 3, it is as follows. From T0 to T1, it gradually rises to the set temperature (for example, jacket temperature). From T1 to T2, due to the heat of vaporization of the solvent, the temperature does not rise stably, but as the drying of the mixed solution progresses as a whole, the temperature gradually rises. From T2 to T3, it gradually rises according to the temperature set during drying, and at the same time, cooling is started and the temperature gradually decreases according to the set cooling temperature (for example, jacket temperature).

[0063] The start point and the end point of the second step are defined as follows. The start point (T1 in FIGS. 3 to 6) when the decompression and stirring of the mixture are started is defined as the start point of the second step. Then, the point in time (T2 in FIGS. 3 to 6) when the load power value of the stirring blade, which has decreased due to further evaporation of the solvent contained in the mixed solution, becomes 1.3 times or less the load power value of the stirring blade at the start point of the second step (see p1 in FIGS. 3 to 6) is defined as the end point of the second step. Here, the load power value of the stirring blade is a value measured by a mixer.

[0064] The time t of the second step 2 From the viewpoint of adjusting to a more suitable time and suppressing the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment, in the second step, the temperature of the mixture is changed in the range of 25°C or higher and lower than the glass transition temperature Tg (°C) of the resin constituting the resin layer, and the pressure in the mixer containing the mixed solution is preferably changed in the range of 1 kPa-abs or higher and 101 kPa-abs or lower. Also, it is preferable to increase the pressure in the mixer from the vacuum pressure side to the atmospheric pressure side.

[0065] In the second step, the temperature of the mixture is set to 50°C to 90°C at the start point of the second step, preferably 60°C to 85°C, and more preferably 70°C to 80°C. In the second step, the pressure in the mixer is in the range of 80 kPa-abs to 1 kPa-abs, preferably in the range of 60 kPa-abs to 5 kPa-abs, and more preferably in the range of 20 kPa-abs to 5 kPa-abs, from the time when 1 minute has elapsed from the start point of the second step to the time when 10 minutes have elapsed. At the start point of the second step, after the temperature in the mixer containing the mixture reaches the above temperature, the pressure in the mixer is reduced to the above-mentioned pressure, and then the pressure in the mixer is fixed at that pressure until the end of the second step or until the end of the third step. By combining the temperature at the start point and the pressure in the mixer, the drying rate is made variable to control the second step time t 2 to control. For example, with reference to schematic graphs 3 and 4 showing the set value of the pressure inside the tank over time, the variation in the load power value of the stirring blade, and the variation in the temperature inside the mixer in an example of the method for manufacturing a carrier for electrostatic charge image development according to the present embodiment, an explanation will be given. After reaching an arbitrary temperature, the pressure inside the tank is reduced to 10 kPa-abs in FIG. 3, and the pressure inside the mixer is fixed until the end of the third step. On the other hand, as shown in FIG. 4, the pressure is reduced to 30 kPa-abs and the pressure inside the mixer is fixed until the end of the third step. By doing so, the drying rate (time) can be controlled according to the magnitude of the deviation between the boiling point of the solvent determined by the pressure inside the tank and the temperature inside the tank.

[0066] As another pressure control inside the mixer in the second step, after reducing the pressure inside the mixer containing the mixture to the aforementioned pressure, the pressure is gradually released to atmospheric pressure. By doing so, the drying rate can be slowed down, and the second step time t 2 can be extended. For example, with reference to schematic graph 5 showing the set value of the pressure inside the tank over time, the variation in the load power value of the stirring blade, and the variation in the temperature inside the mixer in an example of the method for manufacturing a carrier for electrostatic charge image development according to the present embodiment, an explanation will be given. After reducing the pressure to 10 kPa-abs, the pressure is released to 60 kPa-abs over an arbitrary time. After drying is completed, the pressure is reduced to 10 kPa-abs again.

[0067] From the perspective of providing a method for manufacturing a carrier for electrostatic charge image development that further suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in the same environment, as another pressure control, the load power value of the stirring blade of the mixer containing the mixture is continuously monitored, and the pressure inside the mixer is varied so as to reach a preset load power value. By doing so, the kneading state of the mixture can be kept constant for an arbitrary time, and a more uniform coating layer can be formed. For example, with reference to FIG. 6, which is a schematic graph showing the set value of the pressure in the tank, the variation of the load power value of the stirring blade, and the variation of the temperature inside the mixer over time in an example of the method for manufacturing an electrostatic charge image developing carrier according to the present embodiment, the explanation will be given. After the pressure is reduced to 10 kPa-abs, as drying progresses, the load current value increases. However, when it exceeds the preset load power value p2 of the stirring blade, the pressure inside the tank and the machine is decreased with a certain deviation to reduce the load power value to p2. Conversely, when it is lower than p2, the pressure inside the tank is increased with a certain deviation to make the load power constant.

[0068] (Step 3) The third step is a step of taking out the carrier from the mixer after cooling while crushing the resin-coated magnetic particles obtained in the second step by stirring. In the second step, resin-coated magnetic particles close to powder are obtained. Since the resin-coated magnetic particles contain many aggregates of the carrier, in the third step, the mixture is further stirred to crush the aggregates and reduce the amount of aggregates.

[0069] In the third step, the rotation speed of the stirring blade is N 3 (rps), the diameter of the stirring blade is D (m), and the stirring time of the third step is t 3 (s), it is preferable to satisfy the following formula 3 and the following formula 4. Formula 3: 0.2 ≦ (πDN 3 ) ≦ 2.0 Formula 4: 1×10 3 ≦ t 3 (πDN 3 ) ≦ 4×10 3

[0070] Here, the stirring time t 3 of the third step is the time (unit: second) from the end point of the second step (for example, T2 in FIG. 3) to the point when the rotation of the stirring blade stops (for example, T3 in FIG. 3).

[0071] In the third step, by satisfying the above conditions, peeling of the resin layer of the carrier during crushing is suppressed, and generation of aggregates is suppressed. Therefore, it becomes a method for manufacturing a carrier for electrostatic charge image development that further suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment.

[0072] From the viewpoint of further suppressing the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment, in the third step, it is more preferable to satisfy the following formula 3-2 and the following formula 4-2, and it is even more preferable to satisfy the following formula 3-3 and the following formula 4-3.

[0073] Formula 3-2: 0.5 ≦ (πDN 3 ) ≦ 2.0 Formula 4-2: 1.1×10 3 ≦ Stirring work amount (peripheral speed × stirring time t 3 ) ≦ 3.5×10 3

[0074] Formula 3-3: 0.7 ≦ (πDN 3 ) ≦ 1.5 Formula 4-3: 1.4×10 3 ≦ t 3 (πDN 3 ) Stirring work amount (peripheral speed × stirring time t 3 ) ≦ 2.5×10 3

[0075] The rotation speed N of the stirring blade 3 is preferably 10 rpm or more and 200 rpm or less, more preferably 15 rpm or more and 160 rpm or less, and particularly preferably 50 rpm or more and 160 rpm or less from the viewpoint of easily satisfying Formula 3 and Formula 4.

[0076] The stirring time t in the third step 3 is preferably 5 minutes or more and 280 minutes or less, more preferably 10 minutes or more and 80 minutes or less, and particularly preferably 20 minutes or more and 70 minutes or less from the viewpoint of easily satisfying Formula 2 and Formula 3. That is, the stirring time t of the third step 3 is preferably 300 seconds or more and 16,800 seconds or less, more preferably 600 seconds or more and 4,800 seconds or less, and particularly preferably 1,200 seconds or more and 4,200 seconds or less.

[0077] The temperature of the carrier when taking out the carrier from the mixer is preferably equal to or lower than the glass transition temperature Tg - 20°C of the resin contained in the resin layer.

[0078] (Fourth step) As the fourth step, it is preferable to include a fourth step of removing coarse particles. By including this step, the content of specific aggregates is more likely to be reduced. Therefore, it becomes a method for manufacturing a carrier for electrostatic charge image development that further suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment.

[0079] As the fourth step, for example, a step of removing coarse particles using a vibrating sieve equipped with a screen having a mesh size of 45 μm or more and 500 μm or less can be mentioned.

[0080] The mesh size of the screen used in the fourth step is more preferably 45 μm or more and 106 μm or less, and even more preferably 60 μm or more and 75 μm or less.

[0081] The fourth step is not limited to the above method, and a method using a gyro sifter, an ultrasonic sieve, a pneumatic sieve, etc. may also be used.

[0082] Through the above steps, the carrier according to this embodiment is manufactured. It should be noted that during the first step, the second step, and the third step, it is preferable to continue stirring with the stirring blade.

[0083] <Electrostatic charge image developer> The electrostatic charge image developer according to this embodiment is configured as a two-component developer containing the carrier according to this embodiment and toner for electrostatic charge image development (hereinafter also simply referred to as "toner"). In the two-component developer, the mixing ratio (mass ratio) of toner to carrier is preferably toner:carrier = 1:100 to 30:100, more preferably 3:100 to 20:100. Hereinafter, the toner used in the electrostatic charge image developer according to this embodiment will be described.

[0084] (Toner for Electrostatic Charge Image Development) The toner for electrostatic charge image development according to this embodiment (hereinafter also simply referred to as toner) is composed of toner particles and, if necessary, external additives. The toner particles are composed of, for example, a binder resin, and, if necessary, a colorant, a release agent, and other additives. The binder resin, colorant, release agent, and other additives contained in the toner particles, as well as the external additives, are not particularly limited, and examples include those conventionally known for use in toners.

[0085] (Properties of Toner Particles, etc.) The toner particles may be single-layer toner particles, or may be so-called core-shell structured toner particles composed of a core part (core particles) and a coating layer (shell layer) covering the core part. Here, the core-shell structured toner particles are preferably composed of a core part containing a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer containing a binder resin.

[0086] The volume average particle diameter (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, more preferably 4 μm or more and 8 μm or less.

[0087] In addition, various average particle diameters and various particle size distribution indices of the toner particles are measured using a Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolyte used is ISOTON-II (manufactured by Beckman Coulter). In the measurement, 0.5 mg or more and 50 mg or less of a measurement sample is added to 2 ml of a 5% aqueous solution of a surfactant (sodium alkylbenzene sulfonate is preferred) as a dispersant. This is added to 100 ml or more and 150 ml or less of an electrolytic solution. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment with an ultrasonic disperser for 1 minute, and the particle size distribution of particles having a particle size in the range of 2 μm or more and 60 μm or less is measured using an aperture with an aperture diameter of 100 μm by a Coulter Multisizer II. The number of particles to be sampled is 50,000. Based on the measured particle size distribution, cumulative distributions of volume and number are drawn for the particle size ranges (channels) divided, and the particle size at which the cumulative value becomes 16% is defined as the volume particle size D16v, the number particle size D16p, the particle size at which the cumulative value becomes 50% is defined as the volume average particle size D50v, the cumulative number average particle size D50p, and the particle size at which the cumulative value becomes 84% is defined as the volume particle size D84v and the number particle size D84p. Using these, the volume particle size distribution index (GSDv) is (D84v / D16v) 1 / 2 , and the number particle size distribution index (GSDp) is (D84p / D16p) 1 / 2 and is calculated as such.

[0088] As the average circularity of the toner particles, 0.94 or more and 1.00 or less is preferred, and 0.95 or more and 0.98 or less is more preferred.

[0089] The average circularity of the toner particles is obtained by (circumference equivalent to a circle) / (circumference) [(circumference of a circle having the same projected area as the particle image) / (circumference of the particle projection image)]. Specifically, it is a value measured by the following method. First, the toner particles to be measured are aspirated and collected, a flat flow is formed, and a stroboscopic light emission is instantaneously performed to capture the particle image as a still image, and it is obtained by a flow type particle image analyzer (FPIA-3000 manufactured by Sysmex Corporation) that analyzes the particle image. The number of samplings when obtaining the average circularity is 3,500. When the toner has an external additive, after dispersing the toner (developer) to be measured in water containing a surfactant, ultrasonic treatment is performed to obtain toner particles from which the external additive has been removed.

[0090] (Method for manufacturing toner) Next, the method for manufacturing the toner according to this embodiment will be described. The toner according to this embodiment is obtained by externally adding an external additive to toner particles after manufacturing the toner particles.

[0091] The toner particles may be manufactured by either a dry method (for example, kneading and pulverizing method, etc.) or a wet method (for example, aggregation and coalescence method, suspension polymerization method, dissolution and suspension method, etc.). The manufacturing method of the toner particles is not particularly limited to these methods, and well-known manufacturing methods are adopted. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0092] Specifically, for example, when manufacturing toner particles by the aggregation and coalescence method, a step of preparing a resin particle dispersion liquid in which resin particles serving as a binder resin are dispersed (resin particle dispersion liquid preparation step), and in the resin particle dispersion liquid (in the dispersion liquid after mixing other particle dispersion liquids as necessary), aggregating the resin particles (and other particles as necessary) to form aggregated particles (aggregated particle formation step), and heating the aggregated particle dispersion liquid in which the aggregated particles are dispersed to fuse and coalesce the aggregated particles to form toner particles (fusion and coalescence step), and through these steps, toner particles are manufactured.

[0093] And the toner according to this embodiment is manufactured, for example, by adding and mixing an external additive to the obtained dry toner particles. The mixing is preferably performed by, for example, a V blender, a Henschel mixer, a Lodige mixer, etc. Further, if necessary, coarse particles of the toner may be removed using a vibrating sieve, an air classifier, etc.

[0094] (Image forming apparatus / Image forming method) The image forming apparatus / image forming method according to this embodiment will be described. The image forming apparatus according to this embodiment includes an image carrier, a charging unit that charges the image carrier, an exposure unit that exposes the charged image carrier to form an electrostatic latent image on the image carrier, a developing unit that develops the electrostatic latent image with an electrostatic charge image developer to form a toner image, a transfer unit that transfers the toner image from the image carrier to a transfer medium, and a fixing unit that fixes the toner image. And, as the electrostatic charge image developer, the electrostatic charge image developer according to this embodiment is applied.

[0095] In the image forming apparatus according to this embodiment, a charging step of charging the surface of the image carrier, an electrostatic charge image forming step of forming an electrostatic charge image on the surface of the charged image carrier, and the electrostatic charge image developer according to this embodiment are used to develop the electrostatic charge image formed on the surface of the image carrier as a toner image, and an image forming method (image forming method according to this embodiment) including 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 is implemented.

[0096] The image forming apparatus according to this embodiment is an apparatus of a direct transfer type that directly transfers the toner image formed on the surface of the image carrier to a recording medium; an apparatus of an intermediate transfer type that first transfers the toner image formed on the surface of the image carrier to the surface of an intermediate transfer member and then secondarily transfers the toner image transferred to the surface of the intermediate transfer member to the surface of a recording medium; an apparatus provided with a cleaning unit that cleans the surface of the image carrier before charging after the transfer of the toner image; a well-known image forming apparatus such as an apparatus provided with a discharging unit that irradiates the surface of the image carrier with a discharging light to discharge the charge before charging after the transfer of the toner image is applied. In the case of an apparatus of the intermediate transfer type, the transfer unit has a configuration including, for example, an intermediate transfer member on which a toner image is transferred to the surface, a primary transfer unit that primarily transfers the toner image formed on the surface of the image carrier to the surface of the intermediate transfer member, and a secondary transfer unit that secondarily transfers the toner image transferred to the surface of the intermediate transfer member to the surface of a recording medium.

[0097] In the image forming apparatus according to the present embodiment, for example, a portion including developing means may be a cartridge structure (process cartridge) that is detachable from the image forming apparatus. As the process cartridge, for example, a process cartridge including developing means that houses the electrostatic charge image developer according to the present embodiment is preferably used.

[0098] Hereinafter, an example of the image forming apparatus according to the present embodiment will be shown, but it is not necessarily limited thereto. Note that the main parts shown in the drawings will be described, and the description of the others will be omitted.

[0099] FIG. 1 is a schematic configuration diagram showing an image forming apparatus according to the present embodiment. The image forming apparatus shown in FIG. 1 includes first to fourth image forming units 10Y, 10M, 10C, and 10K (image forming means) of an electrophotographic system that output images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter, may be simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side at a predetermined distance from each other in the horizontal direction. Note that these units 10Y, 10M, 10C, and 10K may be process cartridges that are detachable from the image forming apparatus.

[0100] Above each of the units 10Y, 10M, 10C, and 10K in the drawing, an intermediate transfer belt 20 as an intermediate transfer member extends through each unit. The intermediate transfer belt 20 is provided by being wound around a driving roll 22 and a support roll 24 that is in contact with the inner surface of the intermediate transfer belt 20 and is arranged at a distance from each other in the left-to-right direction in the drawing, and is configured to travel in the direction from the first unit 10Y to the fourth unit 10K. Note that a force is applied to the support roll 24 in a direction away from the driving roll 22 by a spring or the like (not shown), and tension is applied to the intermediate transfer belt 20 wound around both of them. Further, an intermediate transfer member cleaning device 30 is provided on the side surface of the image holding body of the intermediate transfer belt 20 so as to face the driving roll 22. In addition, each of the developing devices (developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K is supplied with toner including four colors of toner, i.e., yellow, magenta, cyan, and black, stored in the toner cartridges 8Y, 8M, 8C, and 8K.

[0101] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration, here, the first unit 10Y that forms a yellow image disposed on the upstream side in the intermediate transfer belt running direction will be described as a representative. Note that the second to fourth units 10M, 10C, and 10K will be omitted from the description by attaching reference numerals with magenta (M), cyan (C), and black (K) instead of yellow (Y) to the parts equivalent to the first unit 10Y.

[0102] The first unit 10Y has a photoreceptor 1Y that acts as an image holding member. Around the photoreceptor 1Y, there are a charging roll (an example of charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential, an exposure device (an example of electrostatic charge image forming means) 3 that exposes the charged surface with a laser beam 3Y based on a color-separated image signal to form an electrostatic charge image, a developing device (an example of developing means) 4Y that supplies charged toner to the electrostatic charge image to develop the electrostatic charge image, a primary transfer roll 5Y (an example of primary transfer means) that transfers the developed toner image onto the intermediate transfer belt 20, and a photoreceptor cleaning device (an example of cleaning means) 6Y that removes the toner remaining on the surface of the photoreceptor 1Y after primary transfer, which are arranged in this order. Note that the primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is provided at a position facing the photoreceptor 1Y. Further, each of the primary transfer rolls 5Y, 5M, 5C, and 5K is connected to a bias power source (not shown) that applies a primary transfer bias. Each bias power source varies the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

[0103] Hereinafter, the operation of forming a yellow image in the first unit 10Y will be described. First, prior to the operation, the surface of the photoreceptor 1Y is charged to a potential of -600 V to -800 V by the charging roll 2Y. The photoreceptor 1Y is formed by laminating a photosensitive layer on a conductive substrate (for example, volume resistivity at 20°C: 1×10 -6 Ωcm or less). This photosensitive layer is usually of high resistance (resistance of a general resin), but has the property that when irradiated with the laser beam 3Y, the specific resistance of the irradiated portion of the laser beam changes. Therefore, on the surface of the charged photoreceptor 1Y, according to the yellow image data sent from a control unit (not shown), the laser beam 3Y is output via the exposure device 3. The laser beam 3Y is irradiated onto the photosensitive layer on the surface of the photoreceptor 1Y, thereby forming an electrostatic charge image of the yellow image pattern on the surface of the photoreceptor 1Y.

[0104] The electrostatic charge image is an image formed on the surface of the photoreceptor 1Y by charging. By the laser beam 3Y, the specific resistance of the irradiated portion of the photosensitive layer decreases, and the charged charges on the surface of the photoreceptor 1Y flow, while the charges in the portion not irradiated with the laser beam 3Y remain, thereby forming a so-called negative latent image. The electrostatic charge image formed on the photoreceptor 1Y is rotated to a predetermined development position as the photoreceptor 1Y travels. And at this development position, the electrostatic charge image on the photoreceptor 1Y is visualized as a toner image (developed image) by the developing device 4Y.

[0105] Inside the developing device 4Y, for example, an electrostatic charge image developer containing at least yellow toner and carrier is accommodated. The yellow toner is triboelectrically charged by being agitated inside the developing device 4Y and has the same polarity (negative polarity) charge as the charged charges on the photoreceptor 1Y and is held on the developer roll (an example of a developer holding body). And 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 by the yellow toner. The photoreceptor 1Y on which the yellow toner image is formed continues to travel at a predetermined speed, and the toner image developed on the photoreceptor 1Y is conveyed to a predetermined primary transfer position.

[0106] When the yellow toner image on the photoreceptor 1Y is conveyed to primary transfer, a primary transfer bias is applied to the primary transfer roll 5Y, and the electrostatic force from the photoreceptor 1Y toward the primary transfer roll 5Y acts on the toner image, transferring the toner image on the photoreceptor 1Y onto the intermediate transfer belt 20. The transfer bias applied at this time has a polarity (+) opposite to the polarity (-) of the toner. For example, in the first unit 10Y, it is controlled to +10 μA by a control unit (not shown). On the other hand, the toner remaining on the photoreceptor 1Y is removed and recovered by the photoreceptor cleaning device 6Y.

[0107] Also, the primary transfer biases applied to the primary transfer rolls 5M, 5C, and 5K after the second unit 10M are also controlled according to the first unit. In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred in the first unit 10Y is sequentially conveyed through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are overlapped and multi-transferred.

[0108] The intermediate transfer belt 20 onto which the four-color toner images have been multi-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 secondary transfer means) 26 arranged on the image holding surface side of the intermediate transfer belt 20. On the other hand, the recording paper (an example of a recording medium) P is fed at a predetermined timing into the gap where the secondary transfer roll 26 and the intermediate transfer belt 20 are in contact via a feeding mechanism, and a secondary transfer bias is applied to the support roll 24. The transfer bias applied at this time has the same polarity (-) as the polarity (-) of the toner, and the 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. Note that the secondary transfer bias at this time is determined according to the resistance detected by resistance detection means (not shown) for detecting the resistance of the secondary transfer section and is voltage-controlled.

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

[0110] Examples of the recording paper P for transferring the toner image include plain paper used in electrophotographic copiers, printers, etc. Recording media other than the recording paper P also include OHP sheets and the like. In order to further improve the smoothness of the image surface after fixing, the surface of the recording paper P is preferably smooth. For example, coated paper with the surface of plain paper coated with resin or the like, art paper for printing, etc. are preferably used.

[0111] The recording paper P on which the fixing of the color image is completed is carried out toward the discharge portion, and a series of color image forming operations are terminated.

[0112] <Process cartridge / Toner cartridge> The process cartridge according to this embodiment will be described. The process cartridge according to this embodiment contains the electrostatic charge image developer according to this embodiment, and includes developing means for developing the electrostatic charge image formed on the surface of the image carrier as a toner image with the electrostatic charge image developer, and is a process cartridge that is detachable from the image forming apparatus.

[0113] Note that the process cartridge according to this embodiment is not limited to the above configuration, and may be a configuration including a developing device and at least one selected from other means such as an image carrier, charging means, electrostatic charge image forming means, and transfer means as necessary.

[0114] Hereinafter, an example of the process cartridge according to this embodiment is shown, but it is not limited thereto. Note that the main parts shown in the figure are described, and the others are omitted from the description.

[0115] FIG. 2 is a schematic configuration diagram showing the process cartridge according to this embodiment. The process cartridge 200 shown in FIG. 2 is configured by integrally combining and holding, for example, a photoreceptor 107 (an example of an image holding member), a charging roll 108 (an example of charging means) provided around the photoreceptor 107, a developing device 111 (an example of developing means), and a photoreceptor cleaning device 113 (an example of cleaning means) with a housing 117 provided with an attachment rail 116 and an opening 118 for exposure, and is cartridgeized. In FIG. 2, 109 indicates an exposure device (an example of electrostatic charge image forming means), 112 indicates a transfer device (an example of transfer means), 115 indicates a fixing device (an example of fixing means), and 300 indicates recording paper (an example of a recording medium).

[0116] Next, the toner cartridge according to the present embodiment will be described. The toner cartridge according to the present embodiment is a toner cartridge that houses the toner according to the present embodiment and is detachable from the image forming apparatus. The toner cartridge houses replenishing toner for supplying to developing means provided in the image forming apparatus.

[0117] The image forming apparatus shown in FIG. 1 is an image forming apparatus having a configuration in which toner cartridges 8Y, 8M, 8C, and 8K are detachable, and developing devices 4Y, 4M, 4C, and 4K are connected by toner supply pipes corresponding to the respective developing devices (colors) and toner cartridges (not shown). Further, when the toner housed in the toner cartridge runs low, the toner cartridge is replaced.

Example

[0118] Examples will be described below, but the present invention is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are based on mass.

[0119] 〔Preparation of Coating Liquid 1〕 · Cyclohexyl methacrylate / methyl methacrylate copolymer (copolymerization ratio 95 mol: 5 mol): 3 parts · Toluene: 15 parts · Carbon black (average particle size 0.2 μm): 0.2 parts · Resin fine particles (melamine formaldehyde condensate, Epostar FS, average particle size: 0.2 μm, manufactured by Nippon Shokubai Co., Ltd.): 0.3 parts The above materials were put into a sand mill and dispersed for 30 minutes to obtain Coating Liquid 1. The above materials were put into a disperser to obtain a coating liquid with a solid content of 17%.

[0120] 〔Preparation of Coating Liquid 2〕 Coating Liquid 2 was prepared in the same procedure as the preparation procedure of Coating Liquid 1, except that the addition amount of the resin fine particles was 0.12 parts.

[0121] 〔Preparation of Coating Liquid 3〕 Coating Liquid 3 was prepared in the same procedure as the preparation procedure of Coating Liquid 1, except that the addition amount of the resin fine particles was 0.15 parts.

[0122] 〔Preparation of Coating Liquid 4〕 Coating Liquid 4 was prepared in the same procedure as the preparation procedure of Coating Liquid 1, except that the addition amount of the resin fine particles was 0.57 parts.

[0123] 〔Preparation of Coating Liquid 5〕 Coating Liquid 5 was prepared in the same procedure as the preparation procedure of Coating Liquid 1, except that the addition amount of the resin fine particles was 0.63 parts.

[0124] (Preparation of Ferrite Particles (1)) Fe 2 O 3 1318 parts, Mn(OH) 2 587 parts, and Mg(OH) 2 96 parts were mixed and calcined at a temperature of 900 °C for 4 hours. In water, the calcined product, 6.6 parts of polyvinyl alcohol, 0.5 part of polycarboxylic acid as a dispersant, and zirconia beads with a media diameter of 1 mm were put in, and pulverized and mixed with a sand mill for 30 minutes to obtain a dispersion liquid. The volume average particle diameter of the particles in the dispersion liquid was 1.5 μm. Granulation and drying were carried out using a spray dryer with a dispersion as a raw material to obtain particulate matter with a volume average particle diameter of 35 μm. Next, under an oxygen-nitrogen mixed atmosphere with an oxygen partial pressure of 1%, firing was performed using an electric furnace at a temperature of 1350 °C for 4 hours, and then heating was carried out in the atmosphere at a temperature of 900 °C for 3 hours to obtain fired particles. The fired particles were crushed and classified to obtain ferrite particles (1) with a volume average particle diameter of 34 μm.

[0125] (Preparation of ferrite particles (2)) Ferrite particles (2) with a volume average particle diameter of 29 μm were obtained by classifying ferrite particles (1) using an elbow jet classifier (manufactured by Nippon Steel Mining Co., Ltd.).

[0126] (Preparation of ferrite particles (3)) Ferrite particles (3) with a volume average particle diameter of 49 μm were obtained by sieving ferrite particles (1) with a 20-μm mesh.

[0127] (Preparation of ferrite particles (4)) Ferrite particles (4) with a volume average particle diameter of 19 μm were obtained by classifying ferrite particles (1) using an elbow jet classifier (manufactured by Nippon Steel Mining Co., Ltd.).

[0128] (Preparation of ferrite particles (5)) Ferrite particles (5) with a volume average particle diameter of 17 μm were obtained by classifying ferrite particles (1) using an elbow jet classifier (manufactured by Nippon Steel Mining Co., Ltd.).

[0129] (Preparation of ferrite particles (6)) Ferrite particles (6) with a volume average particle diameter of 47 μm were obtained by sieving ferrite particles (1) with a 25-μm mesh.

[0130] The manufacturing conditions of the carrier are the following Manufacturing Condition Examples 1 to 15 and Comparative Condition Examples 1 to 6. The Examples and Comparative Examples described later were manufactured according to any one of the manufacturing conditions of any one of the following condition examples using ferrite particles as any one of ferrite particles (1) to (6). <Manufacturing Condition Example 1> -First step- Ferrite particles (volume average particle size 35 μm): 100 parts Coating liquid 1: An amount such that the solid content is 3 parts with respect to 100 parts of ferrite particles The above components were charged into a batch stirring type vacuum mixer (50 L kneader manufactured by Inoue Manufacturing Co., Ltd., stirring blade diameter D = 0.25 m, clearance between the inner wall of the casing and the outer periphery of the stirring blade / D = 3.5%) with the jacket temperature heated to 90°C, and preheated to 70°C while stirring and mixing at 60 rpm.

[0131] - Second step - Next, the internal pressure of the mixer was reduced from atmospheric pressure to 10 kPa - abs in 5 minutes and fixed at 10 kPa - abs until the solvent dried. When the stirring power in the mixer decreased to 1.3 times the stirring power value before the start of drying, 20°C cold water was injected into the jacket of the mixer. In the second step, the rotational speed N 2 (rps) of the stirring blade, the diameter D of the stirring blade, and the time t 2 (s) of the second step were adjusted so that the relationship "peripheral speed of the stirring blade (πDN 2 ), t 2 (πDN 2 ) 2 " and the temperature of the mixture at the start of drying and the pressure inside the mixer became the values described in Table 1. Note that the "temperature of the mixture" described in Table 1 indicates the temperature inside the tank at the start of the second step. Also, in order to understand the outline of the change in the pressure inside the tank over time, one of the schematic diagrams from Figure 3 to Figure 6 was described in Table 1. - Third step - Stirring was stopped 45 minutes after injecting 20°C cold water into the mixer ( = end point of the second step), and the mixture was discharged from the mixer into a container to prepare a carrier. In the third step, the rotational speed N 3 (rps) of the stirring blade, the diameter D (m) of the stirring blade, and the stirring time t 3 (s) of the third step were adjusted so that the relationship "(πDN 3 ), t 3 (πDN 3 )" became the values described in Table 1. - Fourth step - The carrier taken out from the mixer was sieved with a 75-μm opening to produce a carrier.

[0132] <Manufacturing Condition Examples 2 to 14, Comparative Condition Examples 1 to 6> A carrier was obtained in the same manner as in Manufacturing Condition Example 1, except that the second and third steps were changed as shown in Table 1.

[0133] <Examples 1 to 8, 17 to 27, Comparative Examples 1 to 6> Carriers for each example were obtained with the types of ferrite particles and manufacturing conditions as shown in Table 2.

[0134] <Example 9> A carrier was obtained in the same manner as in Example 1, except that the addition amount of Coating Liquid 1 was set to an amount such that the solid content was 1.2 parts with respect to 100 parts of ferrite particles.

[0135] <Example 10> A carrier was obtained in the same manner as in Example 1, except that the addition amount of Coating Liquid 1 was set to an amount such that the solid content was 1.5 parts with respect to 100 parts of ferrite cores.

[0136] <Example 11> A carrier was obtained in the same manner as in Example 1, except that the addition amount of Coating Liquid 1 was set to an amount such that the solid content was 6 parts with respect to 100 parts of ferrite cores.

[0137] <Example 12> A carrier was obtained in the same manner as in Example 1, except that the addition amount of Coating Liquid 1 was set to an amount such that the solid content was 6.3 parts with respect to 100 parts of ferrite cores.

[0138] <Example 13> A carrier was obtained in the same manner as in Example 1, except that Coating Liquid 2 was used instead of Coating Liquid 1.

[0139] <Example 14> A carrier was obtained in the same manner as in Example 1, except that Coating Liquid 3 was used instead of Coating Liquid 1.

[0140] <Example 15> A carrier was obtained in the same manner as in Example 1, except that Coating Liquid 4 was used instead of Coating Liquid 1.

[0141] <Example 16> A developer was obtained in the same manner as in Example 1, except that Coating Liquid 5 was used instead of Coating Liquid 1.

[0142] <Image density unevenness evaluation> Using the carriers obtained in each example, a developer for DocuCeNterColor400 (manufactured by Fuji Xerox Co., Ltd.) was prepared. The obtained developer was filled into the developing unit of DocuCeNterColor400 (manufactured by Fuji Xerox Co., Ltd.). Using DocuCeNterColor400 in an environment of 28.5°C and 85% RH, a test was conducted to output 10,000 images with a chart having an image density of 1% on A4-sized J paper (manufactured by Fuji Xerox Co., Ltd.) over 10 days. After a total of 10,000 images were output, 500 images with an image density of 30% were printed, and then 45 sheets of A4-sized paper (Ricoh Co., Ltd., basis weight 52 gsm) were used. For the solid image of the tertiary color (process black) with a toner loading of 9.8 g / cm 2 and the image sample with patches of the secondary color with a toner loading of 6.5 g / cm 2 10 image samples were printed. For the solid image of the tertiary color and the second image sample of the image sample with patches of the secondary color (hereinafter simply referred to as the image sample), the white point evaluation was visually confirmed based on the following evaluation criteria. Hereinafter, up to C was defined as the allowable range. A: There is no problem with the image quality. B: Slight unevenness is observed around the solid image of the tertiary color, but there is no problem with the image quality. C: In addition to the solid image of the tertiary color, slight unevenness is observed around the patches of the secondary color, but there is no problem with the image quality. D: Unevenness is observed in the solid image of the tertiary color E: In addition to the solid image of the tertiary color, unevenness is also observed around the patches of the secondary color

[0143]

Table 1

[0144]

Table 2

[0145] The "clearance rate (%)" described in Table 1 indicates the ratio (clearance / diameter D of the stirring blade) between the clearance (m) between the inner wall of the casing of the mixer and the outer periphery of the stirring blade and the diameter D (m) of the stirring blade. The "amount of aggregates (mass%)" described in Table 2 indicates the amount of aggregates having a major axis of 75 μm or more and an aspect ratio of 1.4 or more and 4.0 or less with respect to the entire carrier.

[0146] From the above results, it can be seen that the carrier of this example suppresses the occurrence of image density unevenness when forming a high-density image in a high-temperature and high-humidity environment after continuously forming a low-density image in a high-temperature and high-humidity environment.

Explanation of Signs

[0147] 1Y, 1M, 1C, 1K Photoreceptor (an example of an image holding member) 2Y, 2M, 2C, 2K Charging roll (an example of a charging means) 3 Exposure device (an example of an electrostatic charge image forming means) 3Y, 3M, 3C, 3K Laser beam 4Y, 4M, 4C, 4K Developing device (an example of a developing means) 5Y, 5M, 5C, 5K Primary transfer roll (an example of a primary transfer means) 6Y, 6M, 6C, 6K Photoreceptor cleaning device (an example of a cleaning means) 8Y, 8M, 8C, 8K Toner cartridge 10Y, 10M, 10C, 10K Image forming unit 20 Intermediate transfer belt (an example of an intermediate transfer member) 22 Driving roll 24 Support roll 26 Secondary transfer roll (an example of secondary transfer means) 30 Intermediate transfer member cleaning device 107 Photoconductor (an example of an image holding member) 108 Charging roll (an example of charging means) 109 Exposure device (an example of electrostatic charge image forming means) 111 Developing device (an example of developing means) 112 Transfer device (an example of transfer means) 113 Photoconductor cleaning device (an example of cleaning means) 115 Fixing device (an example of fixing means) 116 Mounting rail 118 Opening for exposure 117 Housing 200 Process cartridge 300 Recording paper (an example of a recording medium) P Recording paper (an example of a recording medium)

Claims

1. A first step of adding magnetic particles and a solution containing a resin and a solvent constituting a resin layer to a mixer equipped with a stirring blade, and mixing the magnetic particles and the solution to obtain a mixture; A second step of kneading the mixture under reduced pressure while drying the solvent to form a resin coating layer on the magnetic particles; A third step of cooling while crushing by stirring the resin-coated magnetic particles, and then taking out the carrier from the mixer, and The ratio (clearance / diameter D of the stirring blade) of the clearance (m) between the inner wall of the casing of the mixer and the outer periphery of the stirring blade and the diameter D (m) of the stirring blade is 1.0% or more and 5% or less; In the second step, the rotation speed of the stirring blade is N ２ (rps), the diameter of the stirring blade is D (m), the pi is π, and the time of the second step is t ２ (s), the following formulas 1 and 2 are satisfied, The magnetic particles; And the resin coating layer that coats the magnetic particles, The volume average particle size is 20 μm or more and 50 μm or less, A method for producing an electrostatic charge image developing carrier, wherein aggregates having a major axis of 75 μm or more and an aspect ratio of 1.4 or more and 4.0 or less are 2.0% by mass or less based on the entire electrostatic charge image developing carrier. Formula 1: 0.2 ≤ the peripheral speed πDN of the stirring blade ２ (m / s) ≤ 1.6 Formula 2: 100 < t ２ (πDN ２ ) ２ < 6000

2. The method for producing an electrostatic charge image developing carrier according to claim 1, wherein the volume average particle size of the magnetic particles is 18 μm or more and 48 μm or less.

3. The method for producing an electrostatic charge image developing carrier according to claim 1 or claim 2, wherein the film thickness of the resin coating layer is 0.5 μm or more and 2.0 μm or less.

4. The method for producing an electrostatic charge image developing carrier according to any one of claims 1 to 3, wherein the aggregates are 1.0% by mass or less based on the entire electrostatic charge image developing carrier.

5. The method for producing an electrostatic charge image developing carrier according to any one of claims 1 to 4, wherein the resin coating layer contains resin particles.

6. The method for producing an electrostatic charge image developing carrier according to claim 5, wherein the content of the resin particles is 5% by mass or more and 20% by mass or less based on the entire resin coating layer.

7. In the second step, the temperature of the mixture is in a region of 25 ° C or higher and lower than the glass transition temperature Tg (° C) of the resin constituting the resin coating layer, and the pressure in the mixer containing the mixture is 1 kPa-abs or more and 101 kPa-abs or less. The method for producing an electrostatic charge image developing carrier according to any one of claims 1 to 6, which is dried in the following region.

8. The method for producing an electrostatic charge image developing carrier according to any one of claims 1 to 7, wherein in the second step, the pressure in the mixer is increased from the vacuum pressure side to the atmospheric pressure side.

9. The method for manufacturing an electrostatic charge image developing carrier according to any one of claims 1 to 8, wherein in the second step, the load power value of the stirring blade is continuously monitored, and the pressure in the mixer is controlled so as to obtain an arbitrary value.

10. In the third step, the rotational speed of the stirring blade is N ３ (rps), the diameter of the stirring blade is D (m), and the stirring time of the third step is t ３ (s), the method for manufacturing a carrier for electrostatic charge image development according to any one of claims 1 to 9, which satisfies the following formula 2 and the following formula 3. Formula 3: 0.2 ≤ the peripheral speed πDN of the stirring blade ３ (m / s) ≤ 2.0 Formula 4: 1×10 ３ ≤Mixing work amount (peripheral speed × mixing time t ３ ) ≤ 4×10 ３

11. The method for manufacturing an electrostatic charge image developing carrier according to any one of claims 1 to 10, including a fourth step of removing coarse particles after the third step.

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