Method for manufacturing a carrier for electrostatic image development, electrostatic image developer, image forming method, and image forming apparatus

Abstract

To provide a method for manufacturing a carrier for electrostatic charge image development that is excellent in preventing darkening of the color of an obtained image.SOLUTION: A method for manufacturing a carrier for electrostatic charge image development includes: a mixing step of adding magnetic particles and a coat liquid including resin, conductive particles, and solvent into a mixer having a stirring blade and mixing them to obtain a mixture; and a drying step of evaporating and drying the solvent from the mixture to manufacture a carrier having a resin coating layer on the surface of the magnetic particles. The viscosity μ of the coat liquid at the addition into the mixer is more than 60 mPa s and 1,000 mPa s or less. The value of the ratio μ / W of the viscosity μ (mPa s) to the amount W (pts.mass) of the resin coating layer based on 100 pts.mass of the magnetic particles in the carrier is 20 or more and 500 or less.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a color developer containing a color toner and a carrier having at least non-magnetic colorant-containing resin particles and an external additive, characterized in that (1) the toner contains titanium dioxide fine particles as an external additive, with a particle size in the range of 0.01 to 0.2 μm and a degree of hydrophobicity of 40 to 80%, and (2) the carrier is a carrier with a weight-average particle size of 17 to 200 μm coated with a resin in an amount of 0.05 to 10.0% by weight relative to the weight of the carrier core material, and the carrier core material is coated with a resin having a number-average molecular weight (Mn) in the range of 10,000 to 200,000 and a glass transition temperature (Tg) of 55 to 140°C, and the carrier is resin-coated under conditions of a resin solution with a solution viscosity of 6 to 60 cP when introduced into the resin coating apparatus as the coating resin, and the temperature inside the apparatus is 60 to 140°C.

[0003] Patent Document 2 discloses an electrophotographic carrier having a resin coating layer mainly composed of a thermosetting resin on the entire surface of the carrier particles, characterized in that the protruding resin film portion is formed as a thin film, and the occupancy ratio of the protruding resin film is 55% to 90% of the total carrier area. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 5-181321 [Patent Document 2] Japanese Patent Application Publication No. 10-97104 [Overview of the initiative] [Problems that the invention aims to solve]

[0005] An object of the present invention is to provide a method for producing a carrier for electrostatic charge image development that is superior in suppressing color fading of an obtained image as compared with cases where the viscosity μ at the time of adding a coating liquid to a mixer is 60 mPa·s or less or exceeds 1,000 mPa·s, or where the value of the ratio μ / W of the viscosity μ (mPa·s) to the amount W (parts by mass) of a resin coating layer with respect to 100 parts by mass of magnetic particles in a carrier is less than 20 or exceeds 500.

Means for Solving the Problems

[0006] The means for solving the above problems include the following aspects. <1> A mixing step of adding a coating liquid containing a resin, conductive particles, and a solvent and magnetic particles to a mixer having a stirring blade and mixing them to obtain a mixture, and a drying step of evaporating and drying the solvent from the mixture to produce a carrier having a resin coating layer on the surface of the magnetic particles, wherein the viscosity μ at the time of adding the coating liquid to the mixer is more than 60 mPa·s and 1,000 mPa·s or less, and the value of the ratio μ / W of the viscosity μ (mPa·s) to the amount W (parts by mass) of the resin coating layer with respect to 100 parts by mass of the magnetic particles in the carrier is 20 or more and 500 or less. A method for producing a carrier for electrostatic charge image development. <2> The method for producing a carrier for electrostatic charge image development according to <1>, wherein the amount W of the resin coating layer is 1 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the magnetic particles. <3> The method for producing a carrier for electrostatic charge image development according to <2>, wherein the amount W of the resin coating layer is 2 parts by mass or more and 4 parts by mass or less with respect to 100 parts by mass of the magnetic particles. <4> The method for producing a carrier for electrostatic charge image development according to any one of <1> to <3>, wherein the viscosity μ is 80 mPa·s or more and 800 mPa·s or less. <5> The method for producing a carrier for electrostatic charge image development according to <4>, wherein the viscosity μ is 100 mPa·s or more and 500 mPa·s or less. <6> The method for producing a carrier for electrostatic charge image development according to any one of <1> to <5>, wherein the value of μ / W is 30 or more and 150 or less. <7> The method for producing a carrier for electrostatic charge image development according to any one of <1> to <6>, wherein the solid content concentration S of the mixture excluding the magnetic particles in the mixture is 10% by mass or more and 30% by mass or less. <8> The method for producing a carrier for electrostatic charge image development according to any one of <1> to <7>, wherein the stirring conditions in the mixing step satisfy the following formula 1. 1×10 4 ≦Stirring work amount (= circumferential speed πDN × stirring time T) × the viscosity μ (mPa·s) ≦ 5×10 5 ····Formula 1 In formula 1, D represents the diameter (m) of the stirring blade, N represents the rotational speed (rps) of the stirring blade, and T represents the stirring time (s) from the addition of the coating liquid until the evaporation and drying of the solvent starts. <9> The method for producing a carrier for electrostatic charge image development according to any one of <1> to <8>, wherein the temperature inside the mixer in the mixing step is -50°C or more and -20°C or less than the boiling point of the solvent according to the pressure inside the mixer. <10> The method for producing a carrier for electrostatic charge image development according to any one of <1> to <9>, wherein the addition amount of the conductive particles in the mixing step is 0.1 part by mass or more and 1.0 part by mass or less with respect to 100 parts by mass of the magnetic particles. <11> A carrier for electrostatic charge image development produced by the method for producing a carrier for electrostatic charge image development according to any one of <1> to <10>, and an electrostatic charge image developer containing the toner for electrostatic charge image development. <12> An image forming method including 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, and a fixing step of fixing the toner image, wherein the electrostatic charge image developer is the electrostatic charge image developer according to <11>. <13> The device comprises an image holder, a charging means for charging the image holder, an exposure means for exposing the charged image holder to form an electrostatic latent image on the image holder, a developing means for developing the electrostatic latent image with an electrostatic image developer to form a toner image, a transfer means for transferring the toner image from the image holder to a transfer target, and a fixing means for fixing the toner image, wherein the electrostatic image developer is <11> An image forming apparatus that uses the electrostatic image developer described above. [Effects of the Invention]

[0007] <1> According to the present invention, a method for manufacturing an electrostatic image developing carrier is provided that exhibits superior suppression of color dullness in the resulting image compared to cases where the viscosity μ when the coating solution is added to the mixer is 60 mPa·s or less or greater than 1,000 mPa·s, or where the ratio μ / W of the viscosity μ (mPa·s) to the amount W (parts by mass) of the resin coating layer per 100 parts by mass of magnetic particles in the carrier is less than 20 or greater than 500. <2> According to the invention, a method for manufacturing an electrostatic image developing carrier is provided that is superior in suppressing color dullness of the resulting image compared to cases where the amount W of the resin coating layer is less than 1 part by mass or more than 5 parts by mass per 100 parts by mass of the magnetic particles. <3> According to the invention, a method for manufacturing an electrostatic image developing carrier is provided that is superior in suppressing color dullness of the resulting image compared to cases where the amount W of the resin coating layer is less than 2 parts by mass or more than 4 parts by mass per 100 parts by mass of the magnetic particles. <4> According to the invention, a method for manufacturing an electrostatic image developing carrier is provided that is superior in suppressing color dullness of the resulting image compared to cases where the viscosity μ is less than 80 mPa·s or greater than 800 mPa·s. <5> According to the invention, a method for manufacturing an electrostatic image developing carrier is provided that is superior in suppressing color dullness of the resulting image compared to cases where the viscosity μ is less than 100 mPa·s or greater than 500 mPa·s. <6> According to the invention, a method for manufacturing an electrostatic image developing carrier is provided that is superior in suppressing color dullness of the resulting image compared to cases where the μ / W value is less than 30 or greater than 150. <7> According to the invention, a method for manufacturing an electrostatic image developing carrier is provided that is superior in suppressing color dullness of the resulting image compared to cases where the solid content concentration S of the mixture excluding the magnetic particles is less than 10% by mass or greater than 30% by mass. <8> According to the invention, the value of stirring work (= peripheral speed πDN × stirring time T) × viscosity μ (mPa·s) is 1 × 10 4 Less than, or 5 x 10 5 A method for manufacturing electrostatic image developing carriers is provided that exhibits superior suppression of color dullness in the resulting image compared to the case where the method is used. <9> According to the invention, a method for manufacturing an electrostatic image developing carrier is provided that is superior in suppressing color dullness of the resulting image compared to a case where the temperature inside the mixer in the mixing step is below -50°C or above -20°C, depending on the pressure inside the mixer. <10> According to the invention, a method for manufacturing an electrostatic image developing carrier is provided that is superior in suppressing color dullness of the resulting image compared to cases where the amount of conductive particles added in the mixing step is less than 1 part by mass or more than 10 parts by mass per 100 parts by mass of magnetic particles. <11> ~ <13> According to the present invention, when the viscosity μ of the coating solution added to the mixer during the production of the carrier is 60 mPa·s or less or greater than 1,000 mPa·s, or the ratio μ / W of the viscosity μ (mPa·s) to the amount W (parts by mass) of the resin coating layer per 100 parts by mass of magnetic particles in the carrier is less than 20 or greater than 500, an electrostatic image developer, an image forming method, or an image forming apparatus is provided that exhibits superior suppression of color dullness in the resulting image. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic diagram showing an example of an image forming apparatus according to this embodiment. [Figure 2]This is a schematic diagram showing an example of a process cartridge that can be attached to and detached from the image forming apparatus according to this embodiment. [Figure 3] This is a schematic graph showing the fluctuations in the load power value of the stirring blade and the temperature inside the mixer over time in an example of a method for manufacturing a carrier for developing electrostatic images according to this embodiment. [Modes for carrying out the invention]

[0009] The embodiments of this disclosure are described below. These descriptions and embodiments are illustrative and do not limit the scope of the embodiments.

[0010] In this disclosure, the numerical range indicated using "~" represents a range that includes the numbers before and after "~" as the minimum and maximum values, respectively.

[0011] In numerical ranges described in stages within this disclosure, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range described in stages. Furthermore, in numerical ranges described within this disclosure, the upper or lower limit of that range may be replaced with the values ​​shown in the examples.

[0012] In this disclosure, the term "process" includes not only independent processes but also any process that cannot be clearly distinguished from other processes, provided that its intended purpose is achieved.

[0013] When embodiments are described in this disclosure with reference to the drawings, the configuration of such embodiments is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each figure are conceptual, and the relative relationships between the components are not limited thereto.

[0014] In this disclosure, each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition in this disclosure, if there are multiple types of the substance corresponding to each component in the composition, it means the total amount of those multiple types of substances present in the composition unless otherwise specified.

[0015] In this disclosure, each component may contain multiple types of particles. If multiple types of particles corresponding to each component are present in the composition, the particle size of each component refers to the value for a mixture of such multiple types of particles present in the composition, unless otherwise specified.

[0016] In this disclosure, "(meth)acrylic" means at least one of acrylic and methacrylic, and "(meth)acrylate" means at least one of acrylate and methacrylate.

[0017] In this disclosure, carbon black is defined as not being inorganic particles.

[0018] In this disclosure, "electrostatic image developing toner" is also referred to as "toner," "electrostatic image developing carrier" is also referred to as "carrier," and "electrostatic image developer" is also referred to as "developer."

[0019] (Method for manufacturing carriers for developing electrostatic images) The method for manufacturing a carrier for electrostatic image development according to this embodiment includes a mixing step of preparing a coating solution containing a resin, conductive particles, and a solvent, adding the coating solution and magnetic particles to a mixer having a stirring blade and mixing to obtain a mixture, and a drying step of evaporating and drying the solvent from the mixture to produce a carrier having a resin coating layer on the surface of the magnetic particles, wherein the viscosity μ of the coating solution when added to the mixer is greater than 60 mPa·s and less than or equal to 1,000 mPa·s, and the ratio μ / W of the viscosity μ (mPa·s) to the amount W (parts by mass) of the resin coating layer per 100 parts by mass of the magnetic particles in the carrier is between 20 and 500. Furthermore, the electrostatic image developing carrier according to this embodiment is an electrostatic image developing carrier manufactured by the method for manufacturing the electrostatic image developing carrier according to this embodiment.

[0020] In the preliminary stage of preparing the coating solution to be added to the mixer, the aggregated structure of the conductive particles cannot be sufficiently broken, or even if broken, they re-aggregate. Therefore, it is necessary to disperse the conductive particles during the process of forming a resin coating layer on the magnetic particles after adding the coating solution and magnetic particles to the mixer, and stirring and mixing until drying begins. In the process of adding the coating liquid and magnetic particles to a mixer and then stirring and mixing to form a resin coating layer on the magnetic particles before drying begins, if the coating liquid has low viscosity, the coating performance is high, but because there is no stirring power to mix the magnetic particles and the coating liquid, the dispersion power of the conductive particles is weak. Conversely, if the coating liquid has high viscosity, the coating performance is low, but because stirring power is applied, the dispersion power of the conductive particles is strong. This is because the magnetic particles act as a dispersion medium, dispersing the conductive particles in the coating liquid. Specifically, when forming a high-coverage resin coating layer using a low-viscosity coating liquid, while a high coverage rate is achieved, if the viscosity is too low, the conductive particles in the resin coating layer will not disperse properly, resulting in many aggregates of conductive particles existing on the carrier surface. After solvent drying, a large amount of free conductive particle powder will be released. However, if the coating liquid is too viscous, the coverage rate will be low even when forming a high-volume resin coating layer, so an appropriate viscosity is necessary. In the method for manufacturing an electrostatic image developing carrier according to this embodiment, the viscosity μ of the coating solution is set within the range, and the ratio μ / W of the amount W (parts by mass) of the resin coating layer to 100 parts by mass of the magnetic particles is set within the range according to the viscosity μ, thereby obtaining an electrostatic image developing carrier with a high coverage rate of the resin coating layer, suppression of exposure of conductive particles on the surface of the resulting carrier, and excellent suppression of color dullness in the resulting image.

[0021] The method for manufacturing the electrostatic charge image developing carrier according to this embodiment will be described in detail below.

[0022] The dispersion process for preparing the coating solution used in this embodiment can be any liquid-based disperser. From the viewpoint of uniform dispersion, it is preferable that the device is one in which a dispersion medium such as glass beads is agitated together with the dispersion liquid in an agitator, generating collision and shear forces, and dispersing aggregates with these forces. These dispersion chambers come in vertical and horizontal types, and the shape of the agitator can be disc type, pin type, single rotor type, etc. The smaller the particle size of the dispersion medium, the better the dispersion, but the smaller the particle size, the worse the separation from the dispersion liquid becomes, so it is necessary to select an appropriate particle size. The particle sizes currently on the market range from 2 mm to 0.05 mm, but due to the effect of viscosity increase in the dispersion liquid, around 1 mm is preferable. As a result, the magnetic particles in the mixer are smaller in diameter than the dispersion medium, and therefore the dispersion process proceeds more smoothly.

[0023] In the method for manufacturing a carrier for developing electrostatic images according to this embodiment, for example, fluctuations in the load power value of the stirring blade shown in Figure 3 are expected to occur. Figure 3 is a schematic graph showing the fluctuations in the load power value of the stirring blade and the temperature inside the mixer over time in an example of a method for manufacturing a carrier for developing an electrostatic image according to this embodiment. In Figure 3, the left vertical axis 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).

[0024] As shown in Figure 3, at T0, the coating liquid and magnetic particles are introduced into the mixer. From T0 to T1, the coating liquid and magnetic particles are mixed. From T1 to T2, the solvent contained in the coating liquid is evaporated under reduced pressure until the carrier is completely dry. From T2 to T3, the dried carrier is crushed and cooled as needed. At T3, stirring in the mixer ends, and the carrier is removed from the mixer.

[0025] The fluctuations in the load power value of the impeller shown in Figure 3 are as follows: From T0 to T1, the load power value of the impeller remains almost constant. From T1 to T2, as the solvent evaporates, the viscosity of the mixture of coating liquid and magnetic particles in the mixer increases, and the load power of the impeller continues to rise until the carrier is completely dry. Once the carrier is completely dry, the load power of the impeller rapidly decreases to a value less than 1.3 times the load power of the impeller from T0 to T1. From T2 to T3, the load power value of the impeller becomes almost constant again. The aforementioned T is the time from T2 to T3.

[0026] Furthermore, the temperature fluctuations inside the mixer shown in Figure 3 are as follows: From T0 to T1, the temperature gradually rises to the set temperature (for example, the jacket temperature). From T1 to T2, the temperature does not rise steadily due to the heat of vaporization of the solvent, but overall, the temperature gradually rises as the carrier dries. From T2 to T3, the temperature gradually increases according to the temperature set during drying, and as cooling begins, the temperature gradually decreases according to the set cooling temperature (e.g., jacket temperature).

[0027] <μ / W value> In the method for manufacturing a carrier for electrostatic image development according to this embodiment, the ratio μ / W of the viscosity μ (mPa·s) of the coating solution when it is added to the mixer in the mixing step to the amount W (parts by mass) of the resin coating layer in the manufactured carrier to 100 parts by mass of the magnetic particles is 20 or more and 500 or less. From the viewpoint of suppressing color dullness in the resulting image (hereinafter also simply referred to as "color dullness suppression"), it is preferably 25 or more and 300 or less, more preferably 30 or more and 150 or less, and particularly preferably 30 or more and 100 or less.

[0028] Furthermore, from the viewpoint of suppressing discoloration, the amount W of the resin coating layer per 100 parts by mass of the magnetic particles in the manufactured carrier is preferably 0.5 parts by mass or more and 7 parts by mass or less, more preferably 1 part by mass or more and 5 parts by mass or less, even more preferably 2 parts by mass or more and 4 parts by mass or less, and particularly preferably 2.5 parts by mass or more and 3.5 parts by mass or less. Furthermore, from the viewpoint of suppressing discoloration, the amount of the resin coating layer in the manufactured carrier is preferably 0.5% by mass or more and 5% by mass or less, more preferably 1.5% by mass or more and 4% by mass or less, and particularly preferably 2.5% by mass or more and 3.5% by mass or less, relative to the total mass of the carrier.

[0029] In this embodiment, the viscosity μ (mPa·s) of the coating liquid when it is added to the mixer in the mixing step shall be measured using a vibrating viscometer (Viscomate VM-10A, manufactured by Sekonic Corporation) at the temperature at which the coating liquid is added to the mixture.

[0030] In this embodiment, there are no particular limitations on the method for measuring the amount W (parts by mass) of the resin coating layer relative to 100 parts by mass of magnetic particles in the manufactured carrier. For example, the resin coating layer may be removed by dissolving at least the resin component with a solvent or the like, the magnetic particles may be dried, and W may be determined from the weight before removal and after drying.

[0031] <Mixing process> The method for manufacturing a carrier for electrostatic image development according to this embodiment includes a mixing step of adding a coating solution containing a resin, conductive particles, and a solvent to a mixer having stirring blades and mixing to obtain a mixture, wherein the viscosity μ of the coating solution when added to the mixer is greater than 60 mPa·s and less than or equal to 1,000 mPa·s.

[0032] The viscosity μ of the coating liquid when added to the mixer in the mixing step is greater than 60 mPa·s and less than or equal to 1,000 mPa·s at the temperature of the coating liquid at the time of addition. From the viewpoint of suppressing discoloration, it is preferably 80 mPa·s or more and 800 mPa·s or less, more preferably 100 mPa·s or more and 600 mPa·s or less, and particularly preferably 100 mPa·s or more and 300 mPa·s or less.

[0033] The mixer used in this embodiment can be any mixer having a stirring blade, and any known mixer can be used, but from the viewpoint of drying performance, a vacuum mixer is preferable. Furthermore, the mixer used in this embodiment is preferably a batch mixer, and more preferably a batch vacuum mixer, from the viewpoint of mixing performance and suppression of color dullness. Furthermore, a blade-type kneader is preferred as the batch mixer, and the orientation of the blade's rotation axis may be vertical or horizontal. Examples of vertical mixers include spiral mixers (manufactured by Aikousha Seisakusho Co., Ltd.) and planetary mixers (manufactured by Inoue Seisakusho Co., Ltd.), while examples of horizontal mixers include kneaders (manufactured by Inoue Seisakusho Co., Ltd.). Among these, a twin-screw horizontal kneader is particularly preferred from the viewpoint of mixing performance and suppression of discoloration. Furthermore, it is preferable that the mixer has a temperature control structure that allows heating and cooling under reduced pressure in the mixing tank, and a mechanism that can detect the stirring power value of the stirring blades. There are no particular limitations on the temperature control structure, but a jacket structure is preferred.

[0034] There are no particular restrictions on the shape of the aforementioned stirring blade, but examples include Banbury type, Sigma type, Z type, spiral type, and fishtail type. The diameter D of the stirring blade is not particularly limited and can be any size appropriate for the mixer used. In this embodiment, the diameter D of the stirring blade is the maximum outer diameter of the portion that the stirring blade passes through as it rotates in a plane perpendicular to the axis of rotation. The rotation speed N of the stirring blade is preferably 10 rpm to 200 rpm, more preferably 15 rpm to 100 rpm, and particularly preferably 20 rpm to 60 rpm, from the viewpoint of carrier production speed and suppression of discoloration. There are no restrictions on the clearance between the mixing tank and the stirring blade in the aforementioned mixer, and the size will be determined according to the mixer used. However, if the clearance is too wide, not only will the carrier accumulated at the bottom not be completely broken down, but the shear force for breaking down is determined not only by the peripheral speed and mixing work of the stirring blade, but also by the clearance. Therefore, a narrower clearance is preferable, but due to manufacturing constraints of the device, there are limits to the clearance. For this reason, the clearance / diameter of the stirring blade between the outer circumference of the stirring blade and the mixing tank is preferably 5% or less, and more preferably 3.5% or less. Furthermore, it is preferable to continue stirring with the stirring blade during the mixing process.

[0035] From the viewpoint of suppressing discoloration, the stirring conditions in the mixing step are preferably satisfied by the following formula 1, and more preferably by the following formula 1-1. 1 x 10 4 ≤ Agitation work (= Peripheral speed πDN × Agitation time T) × Viscosity μ (mPa·s) ≤ 5 × 10 5 ...Formula 1 2 x 10 4 ≤ Work done by stirring (= Peripheral speed πDN × Stirring time T) × Viscosity μ (mPa·s) ≤ 4 × 10 5 ...Equation 1-1 In Equations 1 and 1-1, D represents the diameter (m) of the stirring blade, N represents the rotational speed (rps) of the stirring blade, and T represents the stirring time (s) from the time the coating liquid is added until the solvent begins to evaporate.

[0036] Preferably, the temperature inside the mixer during the mixing step is between -50°C and -20°C, depending on the pressure inside the mixer. Furthermore, if the coating liquid contains two or more of the solvents, the boiling point of the solvent contained in the resin coating layer shall be the boiling point of the solvent with the lower boiling point among the two or more solvents contained in the coating liquid.

[0037] The solid content concentration S of the mixture excluding the magnetic particles in the above mixture is preferably 10% by mass or more and 30% by mass or less, and more preferably 15% by mass or more and 25% by mass or less, from the viewpoint of suppressing discoloration.

[0038] There are no particular restrictions on the amount of coating liquid and magnetic particles used in the mixing step, and they can be appropriately selected depending on the disperser used. Furthermore, the ratio of the coating solution to the magnetic particles can be appropriately selected depending on the concentration of the coating solution and the thickness of the resin coating layer to be formed. Furthermore, in the mixing step, other components to be included in the resin coating layer, such as particles, may be added to the mixer in addition to the coating liquid and magnetic particles. Details of the coating liquid containing the resin and solvent used in the mixing process, magnetic particles, and other components will be described later.

[0039] <Drying process> The method for manufacturing a carrier for electrostatic image development according to this embodiment includes a drying step of evaporating and drying the solvent from the mixture to obtain a carrier having a resin coating layer on the surface of the magnetic particles.

[0040] In the drying process, the evaporation of the solvent may be carried out by heating under normal pressure, under reduced pressure, or by heating under reduced pressure. However, heating under reduced pressure is preferable because it allows drying without raising the temperature from the boiling point of the solvent above the glass transition temperature Tg of the resin. The atmospheric pressure in the drying process is not particularly limited and can be appropriately selected depending on the glass transition temperature of the resin and the solvent used. However, from the viewpoint of solvent evaporation rate and suppression of color dullness, it is preferably 0.1 kPa-a to 95 kPa-a, and more preferably 5 kPa-a to 80 kPa-a. Note that kPa-a represents atmospheric pressure (kPa) based on absolute pressure. Furthermore, the drying process is preferably carried out in the mixer, from the viewpoint of suppressing discoloration and ease of use. There are no particular restrictions on the pressure reduction means in the aforementioned mixer, and known pressure reduction means such as a pressure pump can be used. Furthermore, the evaporated solvent may be recovered using solvent recovery means such as a cooling trap.

[0041] In the drying process, the temperature of the carrier when it is removed from the mixer is preferably below the glass transition temperature Tg -10°C of the resin contained in the resin coating layer, from the viewpoint of suppressing discoloration. Furthermore, if a cooling process described later is performed after the drying process, the temperature of the carrier when it is removed from the mixer is preferably below the glass transition temperature Tg of the resin contained in the resin coating layer, and more preferably below the glass transition temperature Tg - 20°C of the resin contained in the resin coating layer. In this process, the carrier crushed by the mixer is collected in a container and stored in the container until it is sieved with a desired mesh size. However, if the storage temperature is close to the glass transition temperature (Tg) of the carrier's coating resin, the coating resin may not be fully fixed. As a result, the weight of the carrier within the tank can cause uneven distribution of the resin coating layer depending on the storage location within the tank, and the amount of free resin may not stabilize. Therefore, when performing the cooling process described later, it is preferable to cool the material using a cooling device immediately after the drying process to suppress the generation of coating residue.

[0042] <Cooling process> In this embodiment, the method for manufacturing a carrier for electrostatic image development preferably further includes a cooling step, which is performed immediately after the drying step, in which the carrier is cooled by a cooling device to a temperature Tg of the resin contained in the resin coating layer, or below, from the viewpoint of suppressing color dullness. Examples of the cooling device include a fluidized bed device, a paddle-type mixer, and a screw mixer, but a fluidized bed device is preferred from the viewpoint of suppressing discoloration. Cooling with a fluidized bed device that allows mixing without stirring further suppresses the generation of free resins and provides a carrier with more stable quality. Fluidized bed devices include fluidized bed devices that use only fluidized air and vibrating fluidized beds that assist in fluidization by vibration, and are not particularly limited.

[0043] A fluidized bed apparatus is any apparatus capable of discharging a dehumidified gas from the bottom of the apparatus at a temperature below the cooling target temperature of the object to be cooled. Depending on the required cooling capacity, the gas may be cooled to below room temperature, or the body of the fluidized bed apparatus may be made into a jacket structure and cooling water may be circulated. There are no particular restrictions on the fluidized bed apparatus, and any known fluidized bed apparatus can be used. Furthermore, "continuously after the drying process" means that the carrier removed from the mixer in the drying process can be directly fed into the fluidized bed apparatus, and it is preferable to directly feed the carrier from the mixer in the drying process into the fluidized bed apparatus.

[0044] The cooling rate by a fluidizing device depends on the conduction heat transfer efficiency, which is determined by the temperature of the fluidizing gas, the flow rate of the fluidizing gas per unit weight of the carrier, and the stirring state in the tank, which is determined by the empty tower velocity based on the minimum fluidization rate Umf described later. Therefore, the lower the temperature of the fluidizing gas and the faster the fluidization rate, the shorter the cooling time. However, the faster the fluidization rate, the greater the frictional force between carriers in the device, which causes coating residue to be generated. Based on these considerations, the empty column velocity v (m / s) of the fluidized gas during cooling in the cooling process is preferably 2 to 10 times the minimum fluidization velocity Umf, more preferably 3 to 8 times the minimum fluidization velocity Umf, and particularly preferably 3 to 5 times the minimum fluidization velocity Umf, from the viewpoint of cooling rate and suppression of discoloration. The minimum fluidization rate Umf can be experimentally determined from the flow rate at the point where the fluidized gas pressure begins to stabilize after increasing, using the following formula. Minimum fluidization velocity Umf (m / s) = Flow rate (m 3 / s) at the change point ÷ Cross-sectional area of the fluidization device (m 2 ) Also, the superficial velocity v of the fluidizing gas during cooling in the cooling step is not particularly limited, but is preferably 10 mm / s or more and 100 mm / s or less, and more preferably 20 mm / s or more and 50 mm / s or less.

[0045] The fluidizing gas in the fluidization device is not particularly limited, and air, nitrogen, argon, etc. can be used. Among them, air is preferred. Also, the fluidizing gas is preferably a dehumidified gas, preferably a gas with a relative humidity of 30% or less, more preferably a gas with a relative humidity of 20% or less, and particularly preferably a gas with a relative humidity of 10% or less.

[0046] In the cooling step, from the viewpoint of suppressing color fading, it is preferable to cool to 20°C or lower than the glass transition temperature Tg of the resin contained in the resin coating layer, more preferably to 25°C or lower than the glass transition temperature Tg of the resin contained in the resin coating layer, and particularly preferably to 30°C or lower than the glass transition temperature Tg of the resin contained in the resin coating layer.

[0047] The cooling time in the cooling step is not particularly limited, but from the viewpoint of the production speed of the carrier and suppressing color fading, it is preferably 10 minutes or more and 360 minutes or less, more preferably 30 minutes or more and 240 minutes or less, and particularly preferably 60 minutes or more and 150 minutes or less.

[0048] The method for producing an electrostatic charge image developing carrier according to this embodiment may include other steps other than the mixing step, the drying step, and the cooling step. The other steps are not particularly limited and may include known steps. Furthermore, the method for manufacturing a carrier for electrostatic image development according to this embodiment preferably further includes a step of preparing magnetic particles and a step of preparing a coating solution containing a resin and a solvent. Furthermore, the method for manufacturing a carrier for electrostatic image development according to this embodiment preferably further includes a coarse powder removal step in which the manufactured carrier is sieved and coarse powder is removed.

[0049] <Properties of the carrier> The volume-average particle size of the electrostatic image developing carrier obtained by the method for manufacturing electrostatic image developing carriers according to this embodiment is preferably 10 μm or more and 500 μm or less, more preferably 15 μm or more and 100 μm or less, and particularly preferably 20 μm or more and 60 μm or less. In this embodiment, the volume-average particle size of the magnetic particles and carriers is determined by a laser diffraction particle size distribution analyzer LA-700 (manufactured by Horiba, Ltd.). Specifically, the particle size distribution obtained by the analyzer is divided into particle size ranges (channels), and the volume-average particle size is determined by subtracting the cumulative volume distribution from the small particle size side, resulting in a cumulative total of 50%.

[0050] From the viewpoint of suppressing color dullness, the amount of free resin in the electrostatic image developing carrier obtained by the method for manufacturing electrostatic image developing carriers according to this embodiment is preferably 200 ppm or less, more preferably 100 ppm or less, and particularly preferably 75 ppm or less.

[0051] The method for measuring the amount of free resin in the electrostatic image developing carrier in this embodiment is as follows. A fixed amount of carrier was weighed and dispersed in water. The dispersion was then filtered while the carrier was held in place with a magnet. The filter paper was dried, and the amount of free resin was calculated from the mass difference before and after the filter paper and the amount of carrier weighed using the following formula. Free resin content (ppm) = Increase in filter paper volume (g) ÷ Carrier volume (g)

[0052] From the viewpoint of suppressing color dullness, the proportion of aggregates in the electrostatic image developing carrier obtained by the method for producing electrostatic image developing carriers according to this embodiment after sieving at 75 μm is preferably 5 percent or less, more preferably 1 percent or less, even more preferably 0.1 percent or less, and particularly preferably 0.01 percent or less.

[0053] The method for measuring the proportion of aggregates in the electrostatic image developing carrier after 75 μm sieving in this embodiment is as follows. The carriers are sieved using a sieve with a mesh size of 75 μm. The sieved carriers are spread out so that they do not overlap as much as possible, and scanning electron microscope (SEM) images are taken at 350x magnification. The ratio of the number of carriers that have not been broken down to primary particles to the total number of carriers in one field of view is then measured.

[0054] In this embodiment, the fluidity of the electrostatic image developing carrier is preferably 20 seconds / 50g or more and 50 seconds / 50g or less, more preferably 22 seconds / 50g or more and 35 seconds / 50g or less, and particularly preferably 25 seconds / 50g or more and 30 seconds / 50g or less, from the viewpoint of suppressing density changes in the resulting image. In this embodiment, the fluidity of the electrostatic image developing carrier shall be a value measured in accordance with JIS Z2502(2020) at 25°C and 50%RH.

[0055] <Magnetic particles> Known magnetic particles are used as the magnetic particles in this embodiment. Known materials can be used as the magnetic particles. Examples include magnetic metals such as iron, nickel, and cobalt; alloys of these magnetic metals with manganese, chromium, rare earth elements, etc.; magnetic oxides such as iron oxide, ferrite, and magnetite; and resin-dispersed magnetic particles in which conductive materials are dispersed in a matrix resin. Examples of resins used in the aforementioned resin-dispersed magnetic particles include, but are not limited to, polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene-acrylic acid copolymer, straight silicone resin or modified thereof composed of organosiloxane bonds, fluororesin, polyester, polycarbonate, phenolic resin, epoxy resin, etc. In particular, the magnetic particles are preferably magnetic oxide particles, and more preferably ferrite particles.

[0056] -Ferrite particles- Ferrite is generally (MO) X (Fe2O3) Y It is expressed as follows: In the formula, M mainly consists of MN, but it is also possible to combine at least one or more elements selected from the group consisting of Li, Ca, Sr, SN, Cu, Zn, Ba, Fe, Ti, Ni, Al, Co, and Mo. Also, X and Y represent the molar ratio and satisfy the condition X + Y = 100. In general, the properties of ferrite particles change depending on their composition and structure.

[0057] The ferrite particles used in this embodiment are not particularly limited, but can be produced, for example, as follows. The raw material is a mixture of metal oxide or metal salt powders, which are then calcined using a rotary kiln or the like to obtain a calcined product. Examples of raw material metal oxides or metal salts include Fe2O3, MNO2, SrCO3, and Mg(OH)2. For example, the amount of SrCO3 is adjusted to control the strontium content in the ferrite particles from 0.1% by mass to 1.0% by mass. The calcination temperature is typically between 800°C and 1,000°C, and the calcination time is typically between 6 and 10 hours. The obtained calcined product is then crushed using a known crushing method, specifically by adding polyvinyl alcohol, water, a surfactant, and an antifoaming agent, and crushing it using a mortar, ball mill, jet mill, or the like. The crushing of the calcined product is carried out, for example, until the average particle size is between 4 μm and 10 μm. Next, the crushed calcined material is granulated in a spray dryer and dried. This dried calcined material is calcined again (re-calcined) to remove the contained organic matter and obtain a re-calcined material. The re-calcination temperature is typically between 800°C and 1,000°C, and the re-calcination time is typically between 5 hours and 10 hours. The obtained re-calcined material is then crushed using a mortar and pestle, ball mill, jet mill, etc., with polyvinyl alcohol, water, surfactant, and defoamer added. The re-calcined material is crushed until, for example, the average particle size is between 4 μm and 8 μm. Next, the crushed re-calcined material is granulated in a spray dryer and dried. The dried granules are then calcined (final calcination) using a rotary kiln, etc., to obtain a final calcined material. Here, the final calcination temperature is typically between 1,000°C and 1,400°C, and the final calcination time is typically between 3 hours and 6 hours. The calcined material then undergoes a crushing process and a classification process to obtain ferrite particles.

[0058] The volume-average particle size of the magnetic particles used in this embodiment is preferably 10 μm or more and 500 μm or less, more preferably 15 μm or more and 100 μm or less, and particularly preferably 20 μm or more and 60 μm or less. The average particle size of the calcined material or ferrite particles is the value measured using a laser diffraction / scattering particle size distribution analyzer (LS Particle Size ANalyzer: LS13 320, manufactured by BECKMAN COULTER, Inc.). The obtained particle size distribution is divided into particle size ranges (channels), and the cumulative distribution is subtracted from the small particle size side. The particle size at which the cumulative distribution reaches 50% is defined as the volume-average 50% particle size.

[0059] The BET specific surface area of ​​the magnetic particles is set to 0.10 m² from the viewpoint of long-term image quality stability and density change suppression. 2 / g or more 0.35m 2 It is preferable that it be less than or equal to / g, and 0.11m 2 / g or more 0.28m 2 It is more preferable that it be less than or equal to / g, and 0.12m 2 / g or more 0.24m 2 It is particularly preferable that the value be less than or equal to / g. Furthermore, within the above range, an appropriate amount of coating resin can penetrate into the gaps between magnetic particles, suppressing deterioration of the resin coating layer due to the anchoring effect, resulting in excellent long-term image quality stability and suppression of density changes.

[0060] The BET specific surface area of ​​magnetic particles is measured using a SA3100 specific surface area analyzer (manufactured by Beckman Coulter) with nitrogen purging and the three-point method. Specifically, 5g of magnetic particles is placed in a cell, degassed at 60°C for 120 minutes, and measured using a mixed gas of nitrogen and helium (30:70). More specifically, as a method for separating magnetic particles from a carrier, for example, 20g of resin-coated carrier is placed in 100mL of toluene. Ultrasound is applied for 30 seconds at 40kHz. The magnetic particles and resin solution are separated using filter paper of appropriate particle size. 20mL of toluene is poured over the magnetic particles remaining on the filter paper to wash them. Next, the magnetic particles remaining on the filter paper are collected. The collected magnetic particles are similarly placed in 100mL of toluene and subjected to 30 seconds of ultrasound at 40kHz. They are similarly filtered, washed with 20mL of toluene, and collected. This process is repeated a total of 10 times. Finally, the collected magnetic particles are dried, and the BET specific surface area is measured under the above conditions.

[0061] 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, and more preferably 0.2 μm or more and 0.8 μm or less. The arithmetic mean height Ra of the roughness curve of magnetic particles is determined by observing the magnetic particles at an appropriate magnification (e.g., 1000x) using a surface shape measuring device (e.g., Keyence Corporation's "VK-9700 ultra-deep color 3D shape measuring microscope"), obtaining a roughness curve with a cutoff value of 0.08 mm, and extracting a reference length of 10 μm from the roughness curve in the direction of the mean line. The arithmetic mean of the Ra values ​​of 100 magnetic particles is then calculated.

[0062] The magnetic force of the magnetic particles is preferably such that the saturation magnetization in a 3,000 oorsted magnetic field is 50 emu / g or higher, and more preferably 60 emu / g or higher. The above saturation magnetization is measured using a vibrating sample type magnetic measuring device VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.). The measurement sample is packed into a cell with an inner diameter of 7 mm and a height of 5 mm and set in the device. The measurement is performed by applying a magnetic field and sweeping up to a maximum of 3,000 oorsted. Then, the applied magnetic field is reduced and a hysteresis curve is created on recording paper. From the curve data, the saturation magnetization, remanent magnetization, and coercivity are determined.

[0063] The volume electrical resistance (volume resistivity) of magnetic particles is 1 × 10⁻⁶ 5 Ω cm or more 1×10 9 Preferably less than Ω·cm, and 1 × 10 7 Ω cm or more 1×10 9 A value of Ω·cm or less is preferable. The volume electrical resistance (Ω·cm) of magnetic particles is measured as follows: 20cm 2 The object to be measured is placed flat on the surface of a circular jig on which electrode plates are arranged, so as to be between 1 mm and 3 mm in thickness, forming a layer. The aforementioned 20 cm 2The electrode plates are placed on top of the layer, sandwiching it between them. To eliminate any gaps between the objects to be measured, a 4kg load is applied to the electrode plates placed on the layer before measuring the thickness of the layer (cm). Both electrodes on the top and bottom of the layer are connected to an electrometer and a high-voltage power generator. A high voltage is applied to both electrodes so that the electric field is 103.8V / cm, and the current value (A) that flows at this time is read. The measurement environment is set to a temperature of 20°C and a relative humidity of 50%. The formula for calculating the volumetric electrical resistance (Ω·cm) of the object to be measured is as shown in the formula below. R = E × 20 / (I - I0) / L In the above formula, R represents the volume electrical resistance of the object being measured (Ω·cm), E represents the applied voltage (V), I represents the current value (A), I0 represents the current value at an applied voltage of 0V (A), and L represents the thickness of the layer (cm). The coefficient 20 represents the area of ​​the electrode plate (cm²). 2 ) represents.

[0064] <Resin coating layer> The electrostatic image developing carrier manufactured by the method for manufacturing electrostatic image developing carriers according to this embodiment has a resin coating layer that covers the magnetic particles.

[0065] Examples of resins that make up the resin coating layer include styrene-acrylic acid copolymers; polyolefin resins such as polyethylene and polypropylene; polyvinyl or polyvinylidene resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinylcarbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymers; straight silicone resins or modified products thereof consisting of organosiloxane bonds; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyester; polyurethane; polycarbonate; amino resins such as urea-formaldehyde resin; epoxy resins; and others. In particular, the resin constituting the resin coating layer preferably contains acrylic resin from the viewpoint of electrostatic properties, controllability of external additive adhesion, and suppression of concentration changes. It is more preferable that the acrylic resin is present in an amount of 50% by mass or more of the total mass of resin in the resin coating layer, and it is especially preferable that the acrylic resin is present in an amount of 80% by mass or more of the total mass of resin in the resin coating layer.

[0066] From the viewpoint of suppressing concentration changes, the resin coating 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 ester of (meth)acrylate with an alkyl group having 1 to 9 carbon atoms) is preferred, and specifically, examples include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, etc. One of these monomers may be used, or two or more may be used in combination. Acrylic resins having an alicyclic structure preferably contain cyclohexyl (meth)acrylate as a polymerization component. The content of monomer units derived from cyclohexyl (meth)acrylate in the alicyclic acrylic resin is preferably 75% to 100% by mass, more preferably 85% to 100% by mass, and even more preferably 95% to 100% by mass, based on the total mass of the alicyclic acrylic resin.

[0067] The weight-average molecular weight of the resin contained in the resin coating layer is preferably less than 300,000, more preferably less than 250,000, even more preferably between 5,000 and 250,000, and particularly preferably between 10,000 and 200,000. Within this range, the smoothness of the resin coating surface of the carrier is improved, reducing the amount of external additive adhering to the carrier and resulting in superior suppression of concentration changes.

[0068] The resin coating layer may contain conductive particles for the purpose of controlling static charge and resistance. Examples of conductive particles include carbon black and conductive inorganic particles, which will be discussed later. Carbon black is preferred among these. From the viewpoint of suppressing discoloration and electrostatic properties, the content of conductive particles in the resin coating layer is preferably 0.1% to 30% by mass, more preferably 0.5% to 20% by mass, and even more preferably 1% to 10% by mass, relative to the total mass of the resin coating layer. Furthermore, from the viewpoint of suppressing discoloration and chargeability, the amount of conductive particles added in the mixing step is preferably 0.1 parts by mass or more and 1 part by mass or less, more preferably 0.1 parts by mass or more and 0.5 parts by mass or less, even more preferably 0.1% by mass or more and 0.3% by mass or less, and particularly preferably 0.1% by mass or more and 0.2% by mass or less, per 100 parts by mass of magnetic particles.

[0069] Furthermore, the resin coating layer may contain inorganic particles. Inorganic particles contained in the resin coating layer include metal oxide particles such as silica, titanium oxide, zinc oxide, and tin oxide; metal compound particles such as barium sulfate, aluminum borate, and potassium titanate; and metal particles such as gold, silver, and copper. Among these, silica particles are preferred from the viewpoint of suppressing changes in concentration.

[0070] From the viewpoint of suppressing concentration changes, the arithmetic mean particle size of inorganic particles in the resin coating layer is preferably 5 nm to 90 nm, more preferably 5 nm to 70 nm, even more preferably 5 nm to 50 nm, and particularly preferably 10 nm to 30 nm.

[0071] In this embodiment, the average particle size of the inorganic particles contained in the resin coating layer and the average thickness of the resin coating layer are determined by the following method. Carriers are embedded in epoxy resin and cut with a microtome to create carrier cross-sections. SEM images of the carrier cross-sections are captured using a scanning electron microscope (SEM) and imported into an image processing and analysis system for image analysis. 100 inorganic particles (primary particles) are randomly selected from the resin coating layer, their equivalent circle diameter (nm) is determined, and the arithmetic mean is taken to obtain the average particle size (nm) of the inorganic particles. In addition, the thickness (μm) of the resin coating layer is measured at 10 random locations per carrier particle, and this measurement is repeated for all 100 carriers. The arithmetic mean of all measurements is taken to obtain the average thickness (μm) of the resin coating layer.

[0072] The surface of the inorganic particles may be subjected to a hydrophobic treatment. Examples of hydrophobic agents include known organosilicon compounds having alkyl groups (e.g., methyl, ethyl, propyl, butyl groups, etc.), and specific examples include alkoxysilane compounds, siloxane compounds, and silazane compounds. Among these, silazane compounds are preferred as the hydrophobic agent, and hexamethyldisilazane is preferred. The hydrophobic agent may be used alone or in combination of two or more.

[0073] Methods for hydrophobizing inorganic particles with a hydrophobicizing agent include, for example, a method of using supercritical carbon dioxide to dissolve the hydrophobicizing agent in supercritical carbon dioxide and adhering the hydrophobicizing agent to the surface of the inorganic particles; a method of applying (e.g., by spraying or coating) a solution containing the hydrophobicizing agent and a solvent that dissolves the hydrophobicizing agent to the surface of the inorganic particles in the atmosphere and adhering the hydrophobicizing agent to the surface of the inorganic particles; and a method of adding a solution containing the hydrophobicizing agent and a solvent that dissolves the hydrophobicizing agent to an inorganic particle dispersion in the atmosphere, holding it, and then drying the mixed solution of the inorganic particle dispersion and the solution.

[0074] From the viewpoint of suppressing concentration changes, the inorganic particle content in the resin coating layer is preferably 10% to 60% by mass, more preferably 15% to 55% by mass, and even more preferably 20% to 50% by mass, relative to the total mass of the resin coating layer.

[0075] The exposure area ratio of magnetic particles on the carrier surface is preferably 3% to 30%, more preferably 4% to 25%, and even more preferably 5% to 20%. The exposure area ratio of magnetic particles on the carrier can be controlled by the amount of resin used to form the resin coating layer; the greater the amount of resin relative to the amount of magnetic particles, the smaller the exposure area ratio. In other words, the coverage rate of the resin coating layer on the carrier surface is preferably 70% to 97%, more preferably 75% to 96%, even more preferably 80% to 95%, and particularly preferably 85% to 95%.

[0076] The percentage of exposed magnetic particles on the carrier surface and the coverage rate of the resin coating layer are determined by the following method. Prepare the target carrier and magnetic particles from which the resin coating layer has been removed. Methods for removing the resin coating layer from the carrier include, for example, dissolving the resin component with an organic solvent to remove the resin coating layer, or heating to about 800°C to eliminate the resin component and remove the resin coating layer. Prepare the carrier and magnetic particles as measurement samples, quantify the ratio of Fe, C, and O (atomic%) on the sample surface by XPS, and calculate the exposed area ratio (%) of the magnetic particles by (Fe ratio of carrier) ÷ (Fe ratio of magnetic particles) × 100. Furthermore, the coverage rate (%) of the resin coating layer can be calculated from (100 - percentage of exposed magnetic particles).

[0077] The solvent used to form the coating resin layer is not particularly limited as long as it dissolves or disperses the resin, and examples of such solvents include aromatic hydrocarbons such as toluene and xylene; ketones such as acetone and methyl ethyl ketone; ethers such as tetrahydrofuran and dioxane; and alcohols such as methanol. Among them, toluene is a preferred choice.

[0078] Furthermore, there are no particular restrictions on the solid content of the coating liquid used to form the coating resin layer, but it is preferably 5% by mass or more and 50% by mass or less, more preferably 10% by mass or more and 30% by mass or less, and particularly preferably 15% by mass or more and 30% by mass or less.

[0079] Furthermore, the coating liquid may contain the conductive particles or inorganic particles, etc., and the conductive particles or inorganic particles, etc. may be added separately from the coating agent during the mixing step.

[0080] The average thickness of the resin coating layer is preferably 0.1 μm or more and 10 μm or less, more preferably 0.2 μm or more and 5 μm or less, and even more preferably 0.3 μm or more and 3 μm or less.

[0081] The average thickness of the resin coating layer is measured by the following method: The carrier is embedded in epoxy resin or the like, and thin sections are prepared by cutting with a diamond knife or similar tool. These thin sections are observed with a transmission electron microscope (TEM), and cross-sectional images of multiple carrier particles are taken. The thickness of the resin coating layer is measured at 20 locations from the cross-sectional images of the carrier particles, and the average value is adopted.

[0082] (Electrostatic image developer) The developer according to this embodiment is a two-component developer comprising an electrostatic image developing carrier manufactured by the method for manufacturing electrostatic image developing carriers according to this embodiment, and a toner. The toner comprises toner particles and, optionally, an external additive. Furthermore, the method for producing the developer according to this embodiment preferably includes a method for producing the electrostatic image developing carrier according to this embodiment.

[0083] The mixing ratio (mass ratio) of carrier and toner in the developer is preferably carrier:toner = 100:1 to 100:30, and more preferably 100:3 to 100:20.

[0084] <Toner particles> Toner particles are composed of, for example, a binder resin, and optionally, a colorant, a release agent, and other additives.

[0085] -Binding resin- Examples of binder resins include vinyl resins consisting of homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, N-propyl acrylate, N-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, N-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), or copolymers of two or more of these monomers. Examples of binder resins include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin; mixtures of these with the aforementioned vinyl resins; and graft polymers obtained by polymerizing vinyl monomers in the presence of these. These binding resins may be used individually or in combination of two or more types.

[0086] Polyester resin is preferred as the binder resin. Examples of polyester resins include known amorphous polyester resins. In addition to amorphous polyester resins, crystalline polyester resins may also be used in combination. However, the crystalline polyester resin should be used in an amount of 2% to 40% by mass (preferably 2% to 20% by mass) relative to the total binding resin.

[0087] The "crystallinity" of a resin refers to the presence of a clear endothermic peak rather than a stepwise change in endothermic heat absorption in differential scanning calorimetry (DSC). Specifically, it means that the full width at half maximum of the endothermic peak measured at a heating rate of 10°C / miN is within 10°C. On the other hand, "amorphous" resins refer to those with a full width at half maximum exceeding 10°C, exhibiting a stepwise change in endothermic capacity, or lacking a clear endothermic peak.

[0088] Amorphous polyester resin Examples of amorphous polyester resins include condensation polymers of polycarboxylic acids and polyhydric alcohols. Commercially available amorphous polyester resins may be used, or synthesized ones may be used.

[0089] Examples of polycarboxylic acids include aliphatic dicarboxylic acids (e.g., oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenylsuccinic acid, adipic acid, sebacic acid, etc.), alicyclic dicarboxylic acids (e.g., cyclohexanedicarboxylic acid, etc.), aromatic dicarboxylic acids (e.g., terephthalic acid, isophthalic acid, phthalic acid, naphthalenedicarboxylic acid, etc.), their anhydrides, or their lower alkyl esters (e.g., with 1 to 5 carbon atoms). Among these, aromatic dicarboxylic acids are preferred as polycarboxylic acids. Polycarboxylic acids may be used in combination with dicarboxylic acids, or with trivalent or higher carboxylic acids that have a cross-linked or branched structure. Examples of trivalent or higher carboxylic acids include trimellitic acid, pyromellitic acid, their anhydrides, or their lower alkyl esters (e.g., having 1 to 5 carbon atoms). Polycarboxylic acids may be used individually or in combination of two or more.

[0090] Examples of polyhydric alcohols include aliphatic diols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, etc.), alicyclic diols (e.g., cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, etc.), and aromatic diols (e.g., ethylene oxide adducts of bisphenol A, propylene oxide adducts of bisphenol A, etc.). Among these, aromatic diols and alicyclic diols are preferred as polyhydric alcohols, and aromatic diols are more preferred. As for the polyhydric alcohol, a trihydric or higher polyhydric alcohol with a cross-linked or branched structure may be used in combination with the diol. Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, and pentaerythritol. Polyhydric alcohols may be used individually or in combination of two or more types.

[0091] The glass transition temperature (Tg) of amorphous polyester resin is preferably 50°C to 80°C, and more preferably 50°C to 65°C. The glass transition temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, it is determined by the "extracorporeal glass transition onset temperature" described in JIS K7121:1987 "Method for Measuring Transition Temperatures of Plastics".

[0092] The weight-average molecular weight (Mw) of the amorphous polyester resin is preferably 5,000 to 1,000,000, and more preferably 7,000 to 500,000. The number-average molecular weight (MN) of the amorphous polyester resin is preferably between 2,000 and 100,000. The molecular weight distribution (Mw / MN) of the amorphous polyester resin is preferably 1.5 to 100, and more preferably 2 to 60. Weight-average molecular weight and number-average molecular weight are measured by gel permeation chromatography (GPC). GPC molecular weight measurement is performed using a Tosoh GPC-HLC-8120GPC analyzer, a Tosoh TSKgel SuperHM-M (15cm) column, and THF solvent. The weight-average molecular weight and number-average molecular weight are calculated from these measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.

[0093] Amorphous polyester resins can be obtained by known manufacturing methods. Specifically, for example, they can be obtained by a method in which the polymerization temperature is set to 180°C or higher and 230°C or lower, and the reaction system is subjected to reduced pressure as needed, while removing water and alcohol generated during condensation. If the monomers of the raw materials do not dissolve or miscible at the reaction temperature, a high-boiling point solvent may be added as a solubilizer to dissolve them. In this case, the polycondensation reaction should be carried out while distilling off the solubilizer. If there are monomers with poor miscibility in the copolymerization reaction, it is advisable to condense the poorly miscible monomers with the acid or alcohol to be polycondensed with them beforehand, and then polycondense them with the main component.

[0094] • Crystalline polyester resin Examples of crystalline polyester resins include polycondensates of polycarboxylic acids and polyhydric alcohols. Commercially available crystalline polyester resins may be used, or synthesized resins may be used. Here, a polycondensate using linear aliphatic polymerizable monomers is preferred over polymerizable monomers having aromatic rings, because the crystalline polyester resin readily forms a crystalline structure.

[0095] Examples of polycarboxylic acids include aliphatic dicarboxylic acids (e.g., oxalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, etc.), aromatic dicarboxylic acids (e.g., phthalic acid, isophthalic acid, terephthalic acid, dibasic acids such as naphthalene-2,6-dicarboxylic acid, etc.), their anhydrides, or their lower alkyl esters (e.g., having 1 to 5 carbon atoms). Polycarboxylic acids may be used in combination with dicarboxylic acids, or with trivalent or higher carboxylic acids that have a crosslinked or branched structure. Examples of trivalent carboxylic acids include aromatic carboxylic acids (e.g., 1,2,3-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4-naphthalentricarboxylic acid, etc.), their anhydrides, or their lower alkyl esters (e.g., having 1 to 5 carbon atoms). In addition to these dicarboxylic acids, polycarboxylic acids with sulfonic acid groups and dicarboxylic acids with ethylenic double bonds may also be used in combination. Polycarboxylic acids may be used individually or in combination of two or more.

[0096] Examples of polyhydric alcohols include aliphatic diols (for example, linear aliphatic diols with 7 to 20 carbon atoms in the main chain). Examples of aliphatic diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,14-eicosandecanediol. Among these, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol are preferred as aliphatic diols. Polyhydric alcohols may be used in combination with diols, including trihydric or higher alcohols that have a cross-linked or branched structure. Examples of trihydric or higher alcohols include glycerin, trimethylolethane, trimethylolpropane, and pentaerythritol. Polyhydric alcohols may be used individually or in combination of two or more types.

[0097] Here, the polyhydric alcohol is preferably composed of 80 mol% or more of aliphatic diols, and more preferably 90 mol% or more.

[0098] The melting temperature of the crystalline polyester resin is preferably 50°C to 100°C, more preferably 55°C to 90°C, and even more preferably 60°C to 85°C. The melting temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC) using the "melting peak temperature" described in JIS K7121:1987 "Method for determining the transition temperature of plastics".

[0099] The weight-average molecular weight (Mw) of the crystalline polyester resin is preferably between 6,000 and 35,000.

[0100] Crystalline polyester resins can be obtained, for example, by known manufacturing methods, similar to amorphous polyesters.

[0101] The binder resin content is preferably 40% to 95% by mass, more preferably 50% to 90% by mass, and even more preferably 60% to 85% by mass, relative to the total toner particles.

[0102] -Coloring agent- Examples of colorants include carbon black, chrome yellow, Hansa yellow, benzidine yellow, surene yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, balkan orange, Watch Young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, risole red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, Pigments such as ultramarine blue, chalcioyl blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate; dyes such as acridine, xanthene, azo, benzoquinone, azine, anthraquinone, thioindico, dioxazine, thiazine, azomethine, indico, phthalocyanine, aniline black, polymethine, triphenylmethane, diphenylmethane, and thiazole; are examples. The coloring agent may be used alone or in combination of two or more types.

[0103] The coloring agent may be a surface-treated coloring agent as needed, and may be used in combination with a dispersant. Furthermore, multiple types of coloring agents may be used in combination.

[0104] The colorant content is preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 15% by mass or less, relative to the total toner particles.

[0105] -Release agent- Examples of release agents include hydrocarbon waxes; natural waxes such as carnauba wax, rice wax, and candelilla wax; synthetic or mineral / petroleum-based waxes such as montan wax; and ester waxes such as fatty acid esters and montanic acid esters. However, the release agents are not limited to these.

[0106] The melting temperature of the release agent is preferably 50°C to 110°C, and more preferably 60°C to 100°C. The melting temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC) using the "melting peak temperature" described in JIS K7121:1987 "Method for determining the transition temperature of plastics".

[0107] The release agent content is preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less, relative to the total toner particles.

[0108] -Other additives- Other known additives include, for example, magnetic materials, charge control agents, and inorganic powders. These additives are included in the toner particles as internal additives.

[0109] -Characteristics of toner particles, etc.- The toner particles may be single-layer toner particles, or they may be toner particles with a so-called core-shell structure, consisting of a core (core particle) and a coating layer (shell layer) that covers the core. The core-shell structure of the toner particles may consist of, for example, a core made up of a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer made up of a binder resin.

[0110] The volume-average particle size (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less. The volume-average particle size (D50v) of toner particles is measured using a Coulter Multisizer II (Beckman Coulter), and the electrolyte is measured using an ISOTON-II (Beckman Coulter). For measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5% aqueous solution of a surfactant (preferably sodium alkylbenzenesulfonate) as a dispersant. This is then added to 100 ml to 150 ml of electrolyte. The electrolyte containing the suspended sample is dispersed in an ultrasonic disperser for 1 minute. The particle size distribution of particles with a diameter of 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. The number of particles sampled is 50,000. The volume-based particle size distribution is plotted from the smallest diameter side, and the particle size at which the cumulative distribution reaches 50% is defined as the volume-average particle size D50v.

[0111] The average circularity of the toner particles is preferably 0.94 to 1.00, and more preferably 0.95 to 0.98. The average circularity of toner particles is determined by (circular equivalent perimeter) / (perimeter) [(perimeter of a circle with the same projected area as the particle image) / (perimeter of the particle projection image)]. Specifically, it is a value measured by the following method. First, the toner particles to be measured are collected by suction, a flattened flow is formed, and a still image of the particles is captured by instantaneous strobe flashing. This particle image is then analyzed using a flow-type particle image analyzer (FPIA-3000 manufactured by Sysmex Corporation). The number of samples used to determine the average circularity is 3500. If the toner contains external additives, the toner (developer) to be measured is dispersed in water containing a surfactant, and then ultrasonic treatment is performed to obtain toner particles from which the external additives have been removed.

[0112] -Manufacturing method for toner particles- Toner particles may be manufactured by either a dry process (e.g., kneading and grinding) or a wet process (e.g., agglomeration, suspension polymerization, dissolution and suspension). There are no particular restrictions on these methods, and known methods can be used. Among these, obtaining toner particles by agglomeration is preferable.

[0113] Specifically, for example, when manufacturing toner particles by the agglomeration and coalescence method, the process involves: preparing a resin particle dispersion in which resin particles that will serve as the binder are dispersed (resin particle dispersion preparation step); agglomerating the resin particles (and other particles as needed) in the resin particle dispersion (or in a dispersion after mixing in other particle dispersions as needed) to form aggregated particles (aggregated particle formation step); and heating the aggregated particle dispersion in which the aggregated particles are dispersed to fuse and coalesce the aggregated particles to form toner particles (fusion and coalescence step).

[0114] The details of each step are explained below. The following description explains a method for obtaining toner particles containing a colorant and a release agent, but the colorant and release agent are used as needed. Of course, other additives besides colorants and release agents may also be used.

[0115] -Resin particle dispersion preparation process- Along with a resin particle dispersion containing resin particles that will act as a binder, a colorant particle dispersion containing colorant particles and a release agent particle dispersion containing release agent particles are prepared.

[0116] A resin particle dispersion is prepared, for example, by dispersing resin particles in a dispersion medium using a surfactant.

[0117] Examples of dispersion media used in resin particle dispersions include aqueous media. Examples of aqueous media include water such as distilled water and deionized water, and alcohols. These may be used individually or in combination of two or more.

[0118] Examples of surfactants include anionic surfactants such as sulfate esters, sulfonates, phosphates, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; and nonionic surfactants such as polyethylene glycol, alkylphenol ethylene oxide adducts, and polyhydric alcohols. Among these, anionic surfactants and cationic surfactants are particularly noteworthy. Nonionic surfactants may be used in combination with anionic or cationic surfactants. Surfactants may be used individually or in combination of two or more types.

[0119] In resin particle dispersions, common dispersion methods for dispersing resin particles in a dispersion medium include, for example, rotary shear homogenizers, ball mills with media, sand mills, and dyno mills. Depending on the type of resin particles, the resin particles may also be dispersed in the dispersion medium by phase inversion emulsification. Phase inversion emulsification is a method in which the resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, a base is added to neutralize the organic continuous phase (O phase), and then an aqueous medium (W phase) is added to perform a phase inversion from W / O to O / W, thereby dispersing the resin in particulate form in the aqueous medium.

[0120] The volume-average particle size of the resin particles dispersed in the resin particle dispersion is preferably 0.01 μm or more and 1 μm or less, more preferably 0.08 μm or more and 0.8 μm or less, and even more preferably 0.1 μm or more and 0.6 μm or less. The volume-average particle size of resin particles is measured using a laser diffraction particle size distribution analyzer (e.g., LA-700 manufactured by Horiba). The particle size distribution is obtained by subtracting the cumulative distribution from the smallest particle size side for each divided particle size range (channel). The particle size at which the cumulative distribution reaches 50% of all particles is measured as the volume-average particle size D50v. The volume-average particle size of particles in other dispersions is measured in the same manner.

[0121] The resin particle content in the resin particle dispersion is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less.

[0122] Similarly to the resin particle dispersion, for example, colorant particle dispersions and mold release agent particle dispersions are prepared. In other words, the volume-average particle size, dispersion medium, dispersion method, and particle content of the resin particle dispersion are the same for colorant particles dispersed in the colorant particle dispersion and mold release agent particles dispersed in the mold release agent particle dispersion.

[0123] -Agglomerated particle formation process- Next, the resin particle dispersion, the colorant particle dispersion, and the mold release agent particle dispersion are mixed together. Then, in the mixed dispersion, the resin particles, colorant particles, and release agent particles are heteroaggregated to form aggregated particles containing the resin particles, colorant particles, and release agent particles, which have a diameter close to the diameter of the target toner particles.

[0124] Specifically, for example, a coagulant is added to a mixed dispersion, the pH of the mixed dispersion is adjusted to be acidic (for example, pH 2 to 5), a dispersion stabilizer is added as needed, and then the mixture is heated to a temperature close to the glass transition temperature of the resin particles (specifically, for example, above -30°C or below -10°C), causing the particles dispersed in the mixed dispersion to coagulate and form coagulated particles. In the agglomerated particle formation process, for example, the mixed dispersion may be stirred in a rotary shear homogenizer, a flocculant may be added at room temperature (e.g., 25°C), the pH of the mixed dispersion may be adjusted to acidic (e.g., pH 2 to 5), a dispersion stabilizer may be added as needed, and then heating may be performed.

[0125] Examples of flocculants include surfactants with opposite polarity to the surfactant contained in the mixed dispersion, inorganic metal salts, and metal complexes with a valency of 2 or higher. When a metal complex is used as a flocculant, the amount of surfactant used is reduced and the electrostatic properties are improved. Along with the flocculant, an additive that forms a complex or similar bond with the metal ions of the flocculant may be used as needed. A chelating agent is preferably used as this additive.

[0126] Examples of inorganic metal salts include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate; and inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, and calcium polysulfide. As a chelating agent, a water-soluble chelating agent may be used. Examples of chelating agents include oxycarboxylic acids such as tartaric acid, citric acid, and gluconic acid; and aminocarboxylic acids such as iminodiacid acetic acid (IDA), nitrilotriacetic acid (NTA), and ethylenediaminetetraacetic acid (EDTA). The amount of chelating agent added is preferably 0.01 parts by mass or more and 5.0 parts by mass or less per 100 parts by mass of resin particles, and more preferably 0.1 parts by mass or more and less than 3.0 parts by mass.

[0127] -Fusion / coalescence process- Next, the dispersion of aggregated particles is heated to a temperature above the glass transition temperature of the resin particles (for example, 10°C to 30°C higher than the glass transition temperature of the resin particles) to fuse and combine the aggregated particles and form toner particles.

[0128] Toner particles are obtained through the above process. Toner particles may be manufactured by first obtaining an aggregate particle dispersion in which aggregate particles are dispersed, then further mixing the aggregate particle dispersion with a resin particle dispersion in which resin particles are dispersed, and agglomerating the aggregate particles so that the resin particles adhere to the surface of the aggregate particles to form second aggregate particles, and then heating the second aggregate particle dispersion in which the second aggregate particles are dispersed to fuse and combine the second aggregate particles to form toner particles with a core-shell structure.

[0129] After the fusion and combination process is completed, the toner particles formed in the solution are subjected to known washing, solid-liquid separation, and drying processes to obtain dried toner particles. From the viewpoint of electrostatic properties, the washing process should be performed thoroughly by displacement washing with deionized water. From the viewpoint of productivity, the solid-liquid separation process should be performed by suction filtration, pressure filtration, etc. From the viewpoint of productivity, the drying process should be performed by freeze-drying, air-flow drying, fluidized bed drying, vibratory fluidized bed drying, etc.

[0130] The toner according to this embodiment is manufactured, for example, by adding an external additive to the obtained dried toner particles and mixing them. Mixing can be performed using, for example, a V-blender, a Henschel mixer, a Redigge mixer, etc. Furthermore, if necessary, coarse particles of the toner may be removed using a vibrating screen separator, a wind screen separator, etc.

[0131] -External additives- Examples of external additives include inorganic particles. These inorganic particles include SiO2, TiO2, Al2O3, CuO, ZNO, SNO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, and K2O·(TiO2). N Examples include Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, and MgSO4.

[0132] The surface of the inorganic particles used as an external additive should preferably be hydrophobic. Hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic agent. The hydrophobic agent is not particularly limited, but examples include silane-based coupling agents, silicone oil, titanate-based coupling agents, and aluminum-based coupling agents. These may be used individually or in combination of two or more. The amount of hydrophobic treatment agent is typically, for example, 1 to 10 parts by mass per 100 parts by mass of inorganic particles.

[0133] Examples of external additives include resin particles (such as polystyrene, polymethyl methacrylate, and melamine resin) and cleaning activators (for example, metal salts of higher fatty acids represented by zinc stearate, and fluorine-based high molecular weight particles).

[0134] The amount of external additive added is preferably 0.01% by mass or more and 5% by mass or less relative to the toner particles, and more preferably 0.01% by mass or more and 2.0% by mass or less.

[0135] <Image forming device, image forming method> The image forming apparatus according to this embodiment comprises an image holder, a charging means for charging the surface of the image holder, an electrostatic image forming means for forming an electrostatic image on the charged surface of the image holder, a developing means for containing an electrostatic image developer and developing the electrostatic image formed on the surface of the image holder as a toner image using the electrostatic image developer, a transfer means for transferring the toner image formed on the surface of the image holder to the surface of a recording medium, and a fixing means for fixing the toner image transferred to the surface of the recording medium. The electrostatic image developer used is an electrostatic image developer containing an electrostatic image developer carrier manufactured by the method for manufacturing an electrostatic image developer carrier according to this embodiment.

[0136] The image forming apparatus according to this embodiment implements an image forming method (image forming method according to this embodiment) comprising: a charging step of charging the surface of an image holder; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image holder; a developing step of developing the electrostatic image formed on the surface of the image holder as a toner image using an electrostatic image developer according to this embodiment; a transfer step of transferring the toner image formed on the surface of the image holder to the surface of a recording medium; and a fixing step of fixing the toner image transferred to the surface of the recording medium. Furthermore, the image forming method according to this embodiment uses an electrostatic image developing carrier manufactured by the method for manufacturing an electrostatic image developing carrier according to this embodiment.

[0137] The image forming apparatus according to this embodiment may be any known image forming apparatus such as: a direct transfer apparatus that directly transfers a toner image formed on the surface of an image holder to a recording medium; an intermediate transfer apparatus that first transfers a toner image formed on the surface of an intermediate transfer body to the surface of an intermediate transfer body, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer body to the surface of a recording medium; an apparatus equipped with cleaning means for cleaning the surface of the image holder before charging after the transfer of the toner image; or an apparatus equipped with static elimination means for irradiating the surface of the image holder with static elimination light before charging after the transfer of the toner image. In the case of an image forming apparatus of the present embodiment, if the image forming apparatus is an intermediate transfer type apparatus, the transfer means may include, for example, an intermediate transfer body on which a toner image is transferred; a primary transfer means for primaryly transferring the toner image formed on the surface of the image holder to the surface of the intermediate transfer body; and a secondary transfer means for secondary transferring the toner image transferred to the surface of the intermediate transfer body to the surface of the recording medium.

[0138] In the image forming apparatus according to this embodiment, for example, the part including the developing means may be a cartridge structure (process cartridge) that can be attached to and detached from the image forming apparatus. As the process cartridge, for example, a process cartridge containing the electrostatic image developer according to this embodiment and equipped with a developing means is preferably used.

[0139] The following describes an example of an image forming apparatus according to this embodiment, but is not limited to this example. In the following description, only the main parts shown in the figures will be described, and other parts will be omitted.

[0140] Figure 1 is a schematic diagram showing the image forming apparatus according to this embodiment. The image forming apparatus shown in Figure 1 is equipped with first to fourth electrophotographic image forming units 10Y, 10M, 10C, and 10K (image forming means) that output images of yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side at predetermined distances from each other in the horizontal direction. These units 10Y, 10M, 10C, and 10K may also be process cartridges that can be attached to and detached from the image forming apparatus.

[0141] An intermediate transfer belt (an example of an intermediate transfer body) 20 extends above each unit 10Y, 10M, 10C, and 10K, passing through each unit. The intermediate transfer belt 20 is wrapped around a drive roll 22 and a support roll 24, and is configured to travel in the direction from the first unit 10Y to the fourth unit 10K. The support roll 24 is subjected to a force moving away from the drive roll 22 by a spring or the like (not shown), and tension is applied to the intermediate transfer belt 20 wrapped around both. An intermediate transfer body cleaning device 30 is provided on the image holder side of the intermediate transfer belt 20, facing the drive roll 22. Each of the developing devices (examples of developing means) for each unit 10Y, 10M, 10C, and 10K, 4Y, 4M, 4C, and 4K, is supplied with yellow, magenta, cyan, and black toner contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0142] Since the first to fourth units 10Y, 10M, 10C, and 10K have equivalent configurations and operations, the first unit 10Y, which forms the yellow image and is located upstream of the intermediate transfer belt's travel direction, will be described as a representative example.

[0143] The first unit 10Y has a photoreceptor 1Y that acts as an image holder. Around the photoreceptor 1Y are, in order, a charging roll (an example of a charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential, an exposure device (an example of a charge image forming means) 3 that exposes the charged surface with a laser beam 3Y based on a color-separated image signal to form a charge image, a developing device (an example of a developing means) 4Y that supplies charged toner to the charge image to develop the charge image, a primary transfer roll 5Y (an example of a primary transfer means) that transfers the developed toner image onto an intermediate transfer belt 20, and a photoreceptor cleaning device (an example of a cleaning means) 6Y that removes toner remaining on the surface of the photoreceptor 1Y after primary transfer. The primary transfer roll 5Y is positioned inside the intermediate transfer belt 20, facing the photoreceptor 1Y. Each primary transfer roll 5Y, 5M, 5C, and 5K of each unit is connected to a bias power supply (not shown) that applies the primary transfer bias. Each bias power supply changes the value of the transfer bias applied to each primary transfer roll through control by a control unit (not shown).

[0144] The following describes the process of forming the yellow image in the first unit 10Y. First, prior to operation, the surface of the photoreceptor 1Y is charged to a potential of -600V to -800V by the charging roll 2Y. The photoreceptor 1Y is conductive (for example, has a volume resistivity of 1 × 10 at 20°C). -6 The photosensitive layer is formed by laminating a photosensitive layer on a substrate (less than Ωcm). This photosensitive layer normally has high resistance (resistance of general resin), but when irradiated with a laser beam, the resistivity of the irradiated area changes. Therefore, a laser beam 3Y is irradiated from the exposure device 3 onto the surface of the charged photoreceptor 1Y according to image data for yellow sent from a control unit (not shown). As a result, an electrostatic charge image of the yellow image pattern is formed on the surface of the photoreceptor 1Y.

[0145] A static charge image is an image formed on the surface of a photoreceptor 1Y due to charging. It is a so-called negative latent image formed when the resistivity of the irradiated portion of the photoreceptor layer decreases due to the laser beam 3Y, causing the charged material on the surface of the photoreceptor 1Y to flow, while the charge remains in the portion not irradiated by the laser beam 3Y. The electrostatic charge image formed on the photoreceptor 1Y rotates to a predetermined development position as the photoreceptor 1Y moves. At this development position, the electrostatic charge image on the photoreceptor 1Y is developed as a toner image by the developing device 4Y and made visible.

[0146] The developing unit 4Y contains, for example, an electrostatic image developer including at least yellow toner and a carrier. The yellow toner is triboelectrically charged by being agitated inside the developing unit 4Y and is held on the developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the static charge on the photoreceptor 1Y. As the surface of the photoreceptor 1Y passes through the developing unit 4Y, the yellow toner electrostatically adheres to the discharged latent image 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 has been formed, continues to move at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transported to a predetermined primary transfer position.

[0147] When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force acts on the toner image from the photoreceptor 1Y to the primary transfer roll 5Y, 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 toner's polarity (-) (+), and in the first unit 10Y, it is controlled by a control unit (not shown) to, for example, +10 μA. Meanwhile, any toner remaining on the photoreceptor 1Y is removed and recovered by the photoreceptor cleaning device 6Y.

[0148] The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K from the second unit 10M onward is also controlled in accordance with the first unit. Thus, the intermediate transfer belt 20, on which the yellow toner image has been transferred in the first unit 10Y, is sequentially transported through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are superimposed and multiple times transferred.

[0149] The intermediate transfer belt 20, on which four-color toner images have been multiplexed through the first to fourth units, proceeds to a secondary transfer section consisting of the intermediate transfer belt 20, a support roll 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 positioned on the image-holding surface side of the intermediate transfer belt 20. Meanwhile, recording paper (an example of a recording medium) P is fed via a supply mechanism into the gap where the secondary transfer roll 26 and the intermediate transfer belt 20 are in contact at a predetermined timing, 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 toner's polarity (-), and an electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined according to the resistance detected by a resistance detection means (not shown) that detects the resistance of the secondary transfer section, and is voltage-controlled.

[0150] After this, the recording paper P is fed to the contact area (nip area) of a pair of fixing rolls in a fixing device (an example of fixing means) 28, where the toner image is fixed onto the recording paper P, and a fixed image is formed.

[0151] Examples of recording paper P used to transfer toner images include plain paper used in electrophotographic photocopiers and printers. Other recording media besides recording paper P include OHP sheets. To further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper, which is plain paper coated with resin or the like, or art paper for printing are preferably used.

[0152] Once the color image has been fixed onto the recording paper P, it is discharged towards the output section, and the series of color image formation operations is completed.

[0153] <Processing Cartridge> The process cartridge according to this embodiment contains the electrostatic image developer according to this embodiment and includes a developing means for developing the electrostatic image formed on the surface of the image holder as a toner image using the electrostatic image developer, and is a process cartridge that can be attached to and detached from an image forming apparatus.

[0154] The process cartridge according to this embodiment is not limited to the above configuration, and may also include a developing means and, as necessary, at least one other means selected from, for example, an image holder, a charging means, an electrostatic image forming means, and a transfer means.

[0155] An example of a process cartridge according to this embodiment is shown below, but it is not limited to this example. In the following description, only the main parts shown in the figure will be described, and other parts will be omitted from the description.

[0156] Figure 2 is a schematic diagram showing the process cartridge according to this embodiment. The process cartridge 200 shown in Figure 2 is constructed by integrally holding a photoreceptor 107 (an example of an image holder), a charging roll 108 (an example of a charging means) provided around the photoreceptor 107, a developing device 111 (an example of a developing means), and a photoreceptor cleaning device 113 (an example of a cleaning means) within a housing 117 equipped with a mounting rail 116 and an opening 118 for exposure, and is then formed into a cartridge. In Figure 2, 109 is an exposure apparatus (an example of electrostatic image formation means), 112 is a transfer apparatus (an example of a transfer means), 115 is a fixing apparatus (an example of a fixing means), and 300 is recording paper (an example of a recording medium). [Examples]

[0157] The embodiments of the invention will be described in detail below with reference to examples, but the embodiments of the invention are not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" are based on mass.

[0158] <Toner production> -Preparation of a dispersion of coloring agent particles- Cyanide pigment (copper phthalocyanine B15:3 (manufactured by Dainichi Seika Kogyo Co., Ltd.)): 50 parts by mass Anionic surfactant: Neogen SC (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 5 parts by mass Ion-exchanged water: 200 parts by mass The above mixture was dispersed for 5 minutes using an IKA Ultra-Turrax and then for 10 minutes using an ultrasonic bath to obtain a dispersion of colorant particles with a solid content of 21%. The volume-average particle size was measured using a Horiba LA-700 particle size analyzer and found to be 160 Nm.

[0159] -Preparation of a mold release agent particle dispersion- Paraffin wax: HNP-9 (manufactured by Nippon Seiro Co., Ltd.): 19 parts by mass Anionic surfactant: Neogen SC (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 1 part by mass Ion-exchanged water: 80 parts by mass The above ingredients were mixed in a heat-resistant container and stirred for 30 minutes at a temperature of 90°C. Next, the molten liquid was passed from the bottom of the container to a Gorin homogenizer and circulated for three passes under a pressure of 5 MPa. Then the pressure was increased to 35 MPa and circulated for another three passes. The resulting emulsion was cooled in the aforementioned heat-resistant solution to below 40°C to obtain a release agent particle dispersion. The volume-average particle size was measured using a Horiba LA-700 particle size analyzer and found to be 240 Nm.

[0160] -Resin particle dispersion- [Oil layer] Styrene (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 30 parts by mass N-butyl acrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 10 parts by mass β-Carboxyethyl acrylate (manufactured by Rhodia Nikka Co., Ltd.): 1.3 parts by mass Dodecanethiol (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 0.4 parts by mass

[0161] [Water layer 1] Ion-exchanged water: 17 parts by mass Anionic surfactant (Dowfax, manufactured by Dow Chemical): 0.4 parts by mass

[0162] [Water layer 2] Deionized water: 40 parts by mass Anionic surfactant (Dowfax, manufactured by Dow Chemical): 0.05 parts by mass Ammonium peroxodisulfate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.): 0.4 parts by mass

[0163] The oil layer components and the aqueous layer 1 components were placed in a flask and stirred to mix and obtain a monomer emulsion dispersion. The aqueous layer 2 components were added to the reaction vessel, the vessel was thoroughly purged with nitrogen, and the reaction system was heated in an oil bath while stirring until the temperature reached 75°C. The monomer emulsion dispersion was gradually added dropwise to the reaction vessel over 3 hours to carry out emulsion polymerization. Polymerization was continued at 75°C after the dropwise addition was complete, and the polymerization was terminated after 3 hours. The obtained resin particles had their volume-average particle size D50v measured at 250 Nm using a laser diffraction particle size distribution analyzer LA-700 (manufactured by Horiba, Ltd.). The glass transition temperature of the resin was measured at 53°C using a differential scanning calorimeter (DSC-50, manufactured by Shimadzu Corporation) at a heating rate of 10°C / min. The number-average molecular weight (polystyrene equivalent) was measured at 13,000 using a molecular weight analyzer (HLC-8020, manufactured by Tosoh Corporation) with THF as the solvent. Thus, a resin particle dispersion with a volume-average particle size of 250 Nm, a solid content of 42%, a glass transition temperature of 52°C, and a number-average molecular weight MN of 13,000 was obtained.

[0164] - Toner 1 creation - Resin particle dispersion: 150 parts by mass Coloring agent particle dispersion: 30 parts by mass Release agent particle dispersion: 40 parts by mass Polyaluminum chloride: 0.4 parts by mass The above components were thoroughly mixed and dispersed in a stainless steel flask using IKE Ultra-Turrax, and then heated to 48°C in a heating oil bath while stirring the flask. After holding at 48°C for 80 minutes, 70 parts by mass of the same resin particle dispersion were slowly added. Subsequently, the pH of the system was adjusted to 6.0 using a 0.5 mol / L sodium hydroxide aqueous solution. The stainless steel flask was then sealed, the stirring shaft seal was magnetically sealed, and the mixture was heated to 97°C and held for 3 hours while continuing to stir. After the reaction was complete, the mixture was cooled at a rate of 1°C / min, filtered, thoroughly washed with deionized water, and then solid-liquid separation was performed by Nutsche suction filtration. This was then redispersed with 3,000 parts by mass of deionized water at 40°C, and stirred and washed at 300 rpm for 15 minutes. This washing operation was repeated 5 more times until the filtrate's pH reached 6.54 and its electrical conductivity reached 6.5 μS / cm. Solid-liquid separation was then performed using No. 5A filter paper by Nutsche suction filtration. Next, vacuum drying was continued for 12 hours to obtain toner particles. The volume-average particle size D50v of the toner particles was measured using a Coulter counter and found to be 6.2 μm, with a volume-average particle size distribution index GSDv of 1.20. Shape observation using a Luzex image analyzer from Luzex revealed that the particle shape coefficient SF1 was 135, indicating a potato shape. The glass transition temperature of the toner was 52°C. Furthermore, silica (SiO2) particles with an average primary particle size of 40 Nm, surface-hydrophobized with hexamethyldisilazane (hereinafter sometimes abbreviated as "HMDS"), and metatitanic acid compound particles with an average primary particle size of 20 Nm, which are reaction products of metatitanic acid and isobutyltrimethoxysilane, were added to this toner so that the coverage of the toner particles was 40%, and the mixture was prepared using a Henschel mixer.

[0165] [Preparation of coating solution 1] 100 parts of lacquer (a solution prepared by mixing 20 parts of cyclohexyl methacrylate / methyl methacrylate copolymer (copolymerization ratio 95 mol% / 5 mol%) (weight-average molecular weight: 65,000, glass transition temperature 105°C) with 80 parts of toluene) Carbon black (average particle size 0.2 μm): 0.22 parts per 100 parts of magnetic particles Glass beads with a diameter of φ1 mm were packed into a disperser (sand mill), the above material was added, and after dispersion at a disk peripheral speed of 10 m / s for 30 minutes, coating solution 1 was obtained.

[0166] (Example 1) -1st process (mixing process)- Ferrite particles (volume-average particle size 35 μm): 100 parts Coating solution 1: A quantity such that the solid content is 3 parts per 100 parts of ferrite particles. 50 kg of the above ingredients were placed into a batch-type agitator vacuum mixer (50L kneader manufactured by Inoue Seisakusho Co., Ltd., with a stirring blade diameter D=0.25 m and a clearance between the inner wall of the casing and the outer circumference of the stirring blade / D=3.5%) whose jacket temperature was warmed to 90°C. The mixture was stirred and mixed at 60 rpm with an internal pressure of 80 kPa-abs until the internal temperature of the tank reached 70°C. Furthermore, the relationship between the rotational speed N1 (rps) of the stirring blade, the diameter D of the stirring blade, and the time t1 (s) of the first process, "peripheral speed of the stirring blade (πDN1) × t1 (πDN1) × viscosity μ of the dispersion," as well as the pressure inside the mixer and the temperature reached by the mixture at the start of drying, were prepared to match the values ​​listed in Table 1. Note that the "temperature of the mixture" listed in Table 1 refers to the temperature inside the tank at the start of the second process.

[0167] -2nd process (drying process)- Next, the internal pressure of the mixer was reduced to 10 kPa-abs over 5 minutes and then fixed at 10 kPa-abs at 60 rpm 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.

[0168] -3rd process (cooling process)- From the point when 20°C cold water was injected into the mixer (the end of the second process), stirring was stopped at 60 rpm for 45 minutes, and the mixture was discharged from the mixer into a container to create a carrier.

[0169] -4th process (coarse powder removal process)- The carrier extracted from the aforementioned mixer was sieved using a sieve with a mesh size of 75 μm to produce carrier 1.

[0170] (Examples 2-10) Carriers 2 to 10, which are carriers for Examples 2 to 10, were prepared in the same manner as in Example 1, except that they were modified to satisfy the conditions listed in Table 1.

[0171] (Example 11) [Preparation of coating solution 2] Carrier 11 was prepared under the conditions listed in Table 1, except that a lacquer; styrene / methyl methacrylate copolymer (copolymerization ratio 30% by mass / 70% by mass) was used.

[0172] (Example 12) Carrier 12 was prepared under the conditions listed in Table 1, except for the use of 100 parts of ferrite particles (volume-average particle size 25 μm).

[0173] (Comparative Example 1) [Preparation of coating solution C1] 100 parts of lacquer (a solution prepared by mixing 5 parts of cyclohexyl methacrylate / methyl methacrylate copolymer (copolymerization ratio 95 mol:5 mol) (weight-average molecular weight: 65,000, glass transition temperature 105°C) with 95 parts of toluene) Carbon black (average particle size 0.2 μm): 0.6 parts per 100 parts of coating solution C1 Glass beads with a diameter of φ1 mm were packed into a disperser (sand mill), the above material was added, and after dispersion at a disk peripheral speed of 10 m / s for 30 minutes, coating solution C1 was obtained.

[0174] Carrier C1, which is the carrier for Comparative Example 1, was prepared in the same manner as in Example 1, except that coating solution 1 was changed to coating solution C1 in Table 1.

[0175] (Comparative Examples 2-4) Carriers C2 to C4, which are the carriers for Comparative Examples 2 to 4, were prepared in the same manner as in Example 1, except that they were modified to satisfy the conditions listed in Table 1.

[0176] <Preparation of developer> Carrier 1-12 and C1-C4 were mixed with Toner 1 in a carrier:toner ratio of 100:10 (mass ratio) in a V-blender and stirred for 20 minutes to obtain Developer 1-12 and C1-C4, respectively.

[0177] -Measurement of coating fluid viscosity (μ)- A vibrating viscometer (Viscomate VM-10A, manufactured by Sekonic Corporation) was used to measure the viscosity (mPa·s) of the coating solution at the temperature during the first step (mixing step) when the solution was added.

[0178] -Measurement of the coverage rate of the resin coating layer on the carrier- The coverage rate of the resin coating layer on the carrier surface was determined by X-ray photoelectron spectroscopy (XPS) using the following method. The target carrier and magnetic particles obtained by removing the resin coating layer from the target carrier were prepared. To remove the resin coating layer from the carrier, a method was used in which the resin component was dissolved with toluene to remove the resin coating layer. The carrier and the magnetic particles with the resin coating layer removed were used as measurement samples, and Fe, C, and O (atomic%) were quantified by XPS. The exposure rate of the magnetic particles (%) was calculated as (Fe of the carrier) ÷ (Fe of the magnetic particles) × 100, and (100 - exposure rate of the magnetic particles) was taken as the coverage rate of the resin coating layer (%).

[0179] -Measurement of free resin content in carrier- A fixed amount of carrier was weighed and dispersed in water. The dispersion was then filtered while the carrier was held in place with a magnet. The filter paper was dried, and the amount of free resin was calculated from the mass difference before and after the filter paper and the amount of carrier weighed.

[0180] -Evaluation of color dullness suppression- The evaluation of color dullness was carried out as follows: Using a DocuColor 7171 P (manufactured by Fujifilm Business Innovation Co., Ltd.) filled with the obtained developer, one 5cm x 5cm solid image patch was printed (Sample 1). Subsequently, 100,000 images with 5% area coverage were printed, and then another 5cm x 5cm solid image patch was printed (Sample 2). The color gamut (L) of Sample 1 and Sample 2 was then analyzed. * a * , b * The following measurements were taken. The color gamut was measured using an X-RITE938 image densitometer (manufactured by X-RITE Corporation). From the difference between the color gamut of Sample 2 and the color gamut of Sample 1, ΔE was calculated using the following formula and used as an index for evaluating color dullness. ΔE = [(ΔL * ) 2 +(Δa * ) 2 +(Δb * ) 2 ] 1 / 2 Here, ΔL * =(L of sample 2) * - L of sample 1 * ), Δa * =(a of sample 2) * - Sample 1 a * ), Δb * =(b of sample 2) * - Sample 1 b * ) The evaluation criteria are as follows: G1 or G2 is preferred, and G1 is more preferred. -Evaluation Criteria- G1:ΔE≦3.0 G2: 3.0 < ΔE ≤ 6.0 G3: 6.0 < ΔE ≤ 10 G4:10<ΔE

[0181] The evaluation results are summarized in Table 1.

[0182] [Table 1]

[0183] In addition, the asterisk (*) in Table 1, as well as A and B in the resin type column, represent the following. *: Amount relative to 100 parts by mass of magnetic particles Material type A: cyclohexyl methacrylate / methyl methacrylate copolymer (copolymerization ratio 95 mol% / 5 mol%) Material type B: styrene / methyl methacrylate copolymer (copolymerization ratio 30 mass% / 70 mass%) Also, the description "E+0n" (n = 3, 4, or 5) in the μ×work amount column in Table 1 represents "×10 n ". That is, the description "1.1E+05" in the μ×work amount column of Example 1 represents "1.1×10 5 ".

[0184] From the above results, it can be seen that this example is superior to the comparative example in terms of suppressing color fading of the obtained image.

Description of reference numerals

[0185] 1Y, 1M, 1C, 1K Photoconductor (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 Photoconductor 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 a secondary transfer means) 28 Fixing device (an example of a fixing means) 30 Intermediate transfer member cleaning device P recording paper (an example of a recording medium) 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 117 Housing 118 Opening for exposure 200 Process cartridge 300 Recording paper (an example of a recording medium)

Claims

1. A mixing step in which a coating liquid containing resin, conductive particles, and solvent is added to a mixer having stirring blades to obtain a mixture, and The process includes a drying step of evaporating and drying the solvent from the mixture to produce a carrier having a resin coating layer on the surface of the magnetic particles, The viscosity μ of the coating liquid when added to the mixer is greater than 60 mPa·s and less than or equal to 600 mPa·s. The ratio μ / W of the viscosity μ (mPa·s) to the amount W (parts by mass) of the resin coating layer relative to 100 parts by mass of the magnetic particles in the carrier is 20 or more and 500 or less. The resin is an alicyclic (meth)acrylic resin having an alicyclic structure, wherein the content of monomer units derived from a polymer component having an alicyclic structure is 75% by mass or more and 100% by mass or less of the total mass of the resin; the conductive particles are carbon black; the solvent is aromatic hydrocarbons; and the magnetic particles are magnetic oxide particles. A method for manufacturing carriers for developing electrostatic images.

2. The method for manufacturing a carrier for developing an electrostatic image according to claim 1, wherein the amount W of the resin coating layer is 1 part by mass or more and 5 parts by mass or less per 100 parts by mass of the magnetic particles.

3. The method for manufacturing a carrier for developing an electrostatic image according to claim 2, wherein the amount W of the resin coating layer is 2 parts by mass or more and 4 parts by mass or less with respect to 100 parts by mass of the magnetic particles.

4. A method for manufacturing a carrier for developing an electrostatic image according to any one of claims 1 to 3, wherein the viscosity μ is 80 mPa·s or more and 600 mPa·s or less.

5. The method for manufacturing a carrier for developing an electrostatic image according to claim 4, wherein the viscosity μ is 100 mPa·s or more and 500 mPa·s or less.

6. A method for manufacturing a carrier for electrostatic image development according to any one of claims 1 to 5, wherein the μ / W value is 30 or more and 150 or less.

7. A method for producing a carrier for electrostatic image development according to any one of claims 1 to 6, wherein the solid content concentration S of the mixture excluding the magnetic particles in the mixture is 10% by mass or more and 30% by mass or less.

8. A method for manufacturing a carrier for electrostatic image development according to any one of claims 1 to 7, wherein the stirring conditions in the mixing step satisfy the following formula 1. 1 x 10 ４ ≤ Agitation work (= Peripheral speed πDN × Agitation time T) × Viscosity μ (mPa·s) ≤ 5 × 10 ５ ...Formula 1 In Equation 1, D represents the diameter (m) of the stirring blade, N represents the rotational speed (rps) of the stirring blade, and T represents the stirring time (s) from the time the coating liquid is added until the solvent begins to evaporate and dry.

9. A method for manufacturing a carrier for electrostatic image developing according to any one of claims 1 to 8, wherein the temperature inside the mixer in the mixing step is, depending on the pressure inside the mixer, at or above the boiling point of the solvent minus 50°C and at or below the boiling point of the solvent minus 20°C.

10. A method for manufacturing a carrier for developing electrostatic images according to any one of claims 1 to 9, wherein the amount of conductive particles added in the mixing step is 0.1 parts by mass or more and 1.0 part by mass or less per 100 parts by mass of magnetic particles.

11. The method for producing a carrier for electrostatic image development according to any one of claims 1 to 10, wherein the polymerization component having an alicyclic structure is cyclohexyl (meth)acrylate.

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