Method for manufacturing electrostatic image developing carrier, method for manufacturing electrostatic image developer, image forming method, and electrostatic image developing carrier

Abstract

To provide a manufacturing method of a carrier for electrostatic charge image development which is excellent in the color dullness suppression property of an image to be obtained.SOLUTION: A manufacturing method of a carrier for electrostatic charge image development comprises a coating step of forming a resin coating layer on a surface of a magnetic particle by adding coating liquid containing resin and solvent and the magnetic particle to a mixer having a blade and taking out a carrier having the resin coating layer from the mixer. The agitation condition until taking out from the mixer after vaporizing and drying the solvent with heating in the mixer in the coating step satisfies 0.2≤the peripheral velocity πDN(m / s) of the blade≤2.0 and 1×103≤the peripheral velocity×the agitation time T≤4×103. D represents the diameter of the blade, N represents the rotation speed of the blade and T represents the time from the point when drying is terminated and the previous load force value is lowered to 1.3 times or less of the value before drying to the point when agitation is terminated in the mixer.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] Patent Document 1 discloses an electrophotographic carrier characterized in that, in a carrier having a resin coating film layer mainly composed of a thermosetting resin on the entire surface of the carrier particle, the convex resin film portion is formed as a thin film, and the occupancy ratio of the convex resin film is 55% to 90% of the total carrier area.

[0003] Patent Document 2 describes a carrier for electrophotography obtained by coating a core material made of a magnetic material with a resin, in which the content concentration of free resin powder particles in the carrier is 5×10 3 An electrophotographic carrier characterized by having a density of particles / ml or less is disclosed.

[0004] Patent Document 3 discloses a method for manufacturing an electrophotographic carrier comprising a carrier core material and a resin that coats the surface of the carrier core material, characterized in that the carrier is homogenized using an air classifier.

[0005] Furthermore, Patent Document 4 discloses a method for producing an electrophotographic developer carrier, which comprises subjecting a developer carrier to resin coating, curing and loosening processes, and then subjecting the resulting developer carrier to a free resin removal process to remove the free resin from the developer carrier surface. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Publication No. 10-097104 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-256858 [Patent Document 3] Japanese Patent Application Publication No. 8-234499 [Patent Document 4] Japanese Patent Application Publication No. 6-059519 Summary of the Invention [Problem to be solved by the invention]

[0007] The object of the present invention is to provide a carrier having a coating step in which a coating liquid containing a resin and a solvent and magnetic particles are added to a mixer having a stirring blade to form a resin coating layer on the surface of the magnetic particles, and the carrier having the resin coating layer is taken out from the mixer, wherein, in the coating step, under stirring conditions from when the solvent is evaporated by heating in the mixer to when the carrier is taken out from the mixer, the peripheral speed of the stirring blade is less than 0.2 m / s or more than 2.0 m / s, or the value of peripheral speed x stirring time is 1 x 10 3 Less than m or 4×10 3 The present invention provides a method for producing a carrier for developing electrostatic images, which is superior in suppressing dullness of the resulting image compared to when the carrier is more than m. [Means for solving the problem]

[0008] Means for solving the above problems include the following aspects. <1> A method for producing a carrier for developing electrostatic images, comprising a coating step of adding a coating liquid containing a resin and a solvent and magnetic particles to a mixer having stirring blades to form a resin coating layer on the surfaces of the magnetic particles, and then removing the carrier having the resin coating layer from the mixer, wherein the stirring conditions from when the carrier is heated in the mixer to evaporate the solvent and dry it until the carrier is removed from the mixer in the coating step satisfy the conditions of the following formulas 1 and 2: 0.2≦the peripheral speed of the stirring blade πDN (m / s)≦2.0 Equation 1 1×10 3 ≦Mixing work load (peripheral speed × mixing time T)≦4×10 3 formula 2 In Equation 1 and Equation 2, D represents the diameter (m) of the stirring blade, N represents the rotation speed (rps) of the stirring blade, and T represents the time (s) from the point at which the load power value of the stirring blade before drying of the solvent increases as drying progresses and the previous load power value decreases to 1.3 times or less the value before drying after drying is completed, to the point at which stirring in the mixer is completed. <2> The method further includes a cooling step of continuously cooling the carrier in a fluidized bed apparatus after the coating step to a glass transition temperature (Tg) of the resin contained in the resin coating layer −20° C. or lower. <1> 10. A method for producing the carrier for developing electrostatic images according to claim 9. <3> The superficial velocity v (m / s) of the fluidizing gas during cooling in the cooling step is 2 to 10 times the minimum fluidizing velocity Umf. <2> 10. A method for producing the carrier for developing electrostatic images according to claim 9. <4> The mixer is a batch vacuum mixer, and the clearance between the outer periphery of the mixing blade and the inner wall of the casing satisfies the condition of the following formula 3: <1> ~ <3> 10. A method for producing the carrier for developing electrostatic images according to any one of the above items. Clearance / Agitator impeller diameter≦5% Equation 3 <5> The amount of free resin contained in the resulting electrostatic image developing carrier is 200 ppm or less. <1> ~ <4> 10. A method for producing the carrier for developing electrostatic images according to any one of the above items. <6> The amount of free resin contained in the resulting electrostatic image developing carrier is 100 ppm or less. <5> 10. A method for producing the carrier for developing electrostatic images according to claim 9. <7> <1> ~ <6> 10. A method for producing an electrostatic image developer, comprising the method for producing the carrier for electrostatic image development according to any one of the above items. <8> <1> ~ <6> 10. An image forming method using a carrier for developing electrostatic images manufactured by the manufacturing method of a carrier for developing electrostatic images according to any one of 8. to 10. <9> <1> ~ <6> 10. A carrier for developing electrostatic images, which is produced by the method for producing a carrier for developing electrostatic images according to any one of 1 to 9. [Effects of the Invention]

[0009] <1> According to the invention of the present invention, the method includes a coating step of adding a coating liquid containing a resin and a solvent and magnetic particles to a mixer having stirring blades to form a resin coating layer on the surface of the magnetic particles, and then removing the carrier having the resin coating layer from the mixer, and the stirring conditions in the coating step from when the solvent is evaporated and dried by heating in the mixer to when the carrier is removed from the mixer are such that the peripheral speed of the stirring blade is less than 0.2 m / s or more than 2.0 m / s, or the value of peripheral speed x stirring time is 1 x 10 3 Less than m or 4×10 3 The present invention provides a method for producing a carrier for developing electrostatic images that is superior in suppressing dull color in the resulting image compared to when the carrier is more than m. <2> According to the present invention, there is provided a method for producing a carrier for developing electrostatic images, which is superior in suppressing dullness of the resulting image compared to a case where the cooling step is not carried out. <3> According to the invention, there is provided a method for producing a carrier for developing electrostatic images, which is superior in suppressing dullness of the obtained image compared to when the superficial velocity v (m / s) of the fluidizing gas during cooling in the cooling step is less than 2 times or more than 10 times the minimum fluidizing velocity Umf. <4> According to the invention, a method for producing a carrier for developing electrostatic images is provided, which is superior in suppressing dullness of the resulting image compared to a batch vacuum mixer in which the clearance between the outer periphery of the stirring blade and the casing is such that the value of clearance / stirring blade diameter exceeds 5%. <5> According to the present invention, a method for producing an electrostatic image developing carrier is provided, which is superior in suppressing color dullness of the resulting image compared to when the amount of free resin contained in the resulting electrostatic image developing carrier is more than 200 ppm. <6> According to the present invention, a method for producing an electrostatic image developing carrier is provided, which is superior in suppressing color dullness of the resulting image compared to when the amount of free resin contained in the resulting electrostatic image developing carrier is more than 100 ppm. <7> ~ <9> According to the invention, in a method for producing a carrier for developing electrostatic images, the method includes a coating step of adding a coating liquid containing a resin and a solvent and magnetic particles to a mixer having an agitating blade to form a resin coating layer on the surface of the magnetic particles, and then removing the carrier having the resin coating layer from the mixer, the agitating conditions in the coating step from when the solvent is evaporated and dried by heating in the mixer until the carrier is removed from the mixer are such that the peripheral speed of the agitating blade is less than 0.2 m / s or more than 2.0 m / s, or the value of peripheral speed x agitation time is 1 x 10 3 Less than m or 4×10 3 The present invention provides a method for producing an electrostatic image developer, an image forming method, and an electrostatic image developing carrier that are superior in suppressing dullness of the resulting image compared to when the average molecular weight is more than m. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating an example of a process cartridge that is detachably mounted to an image forming apparatus according to an exemplary embodiment of the present invention. [Figure 3] 4 is a schematic graph showing the fluctuation of the load power value of the stirring blade and the fluctuation of the temperature inside the mixer over time in an example of a method for producing an electrostatic image developing carrier according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011]

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

[0012] In the present disclosure, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively.

[0013] In the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. Furthermore, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0014] In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

[0015] When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited to these.

[0016] In the present disclosure, each component may contain multiple corresponding substances. When referring to the amount of each component in a composition in the present disclosure, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified.

[0017] In the present disclosure, the composition may contain multiple types of particles corresponding to each component. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0018] In the present disclosure, "(meth)acrylic" means at least one of acrylic and methacrylic, and "(meth)acrylate" means at least one of acrylate and methacrylate.

[0019] For purposes of this disclosure, carbon black is not considered to be an inorganic particle.

[0020] In this disclosure, "toner for developing electrostatic images" is also referred to as "toner," "carrier for developing electrostatic images" is also referred to as "carrier," and "electrostatic image developer" is also referred to as "developer."

[0021] (Method of manufacturing carrier for developing electrostatic images) The method for producing a carrier for developing electrostatic images according to this embodiment includes a coating step in which a coating liquid containing a resin and a solvent and magnetic particles are added to a mixer having stirring blades to form a resin coating layer on the surfaces of the magnetic particles, and the carrier having the resin coating layer is removed from the mixer, and the stirring conditions in the coating step from when the carrier is heated in the mixer to evaporate the solvent and dry it until when the carrier is removed from the mixer satisfy the conditions of the following formula 1 and formula 2. 0.2≦the peripheral speed of the stirring blade πDN (m / s)≦2.0 Equation 1 1×10 3 ≦Mixing work load (peripheral speed × mixing time T)≦4×10 3 formula 2 In Equation 1 and Equation 2, D represents the diameter (m) of the stirring blade, N represents the rotation speed (rps) of the stirring blade, and T represents the time (s) from the point at which the load power value of the stirring blade before drying of the solvent increases as drying progresses and the previous load power value decreases to 1.3 times or less the value before drying after drying is completed, to the point at which stirring in the mixer is completed. The electrostatic image developing carrier according to this embodiment is manufactured by the method for manufacturing an electrostatic image developing carrier according to this embodiment.

[0022] In the dip-coating method for producing a carrier, the solvent is dried using an agitation vacuum mixer, and then the agglomerated powder is crushed, cooled, and removed. However, after drying, shear force is applied to the carrier by agitation, which causes the resin coating layer to peel off, exposing the surface of the core (magnetic particle) and increasing the amount of free resin powder from the resin component of the resin coating layer. The exposed core surface and the coating residue components, such as resin fragments and free resin powder, resulting from the peeling, are developed together with the toner, and this can cause discoloration due to the coating residue components, particularly with yellow toner and clear toner. After the solvent dries, the agglomerates formed during the drying process are broken down by the shear force (proportional to the peripheral speed) and the agitation workload (proportional to the peripheral speed x time) applied by the rotation of the agitator blade. If the peripheral speed is too slow, or if the peripheral speed is fast but the agitation workload is small, the finished carrier will not be broken down into primary particles, resulting in a decrease in the yield of carrier particles smaller than the desired particle size. Conversely, if the peripheral speed is too fast, or if the peripheral speed is slow but the agitation workload is large, the shear force and frictional forces acting on the carrier will cause the resin coating layer to peel off, resulting in an increase in coating residue. This can even progress to the point where the core surface is exposed. These problems become more pronounced when the carrier has a large amount of coating resin or when conductive particles such as carbon black are added to the resin coating layer. In addition, in the case of a carrier in which conductive particles are added to the resin coating layer, applying a certain amount of stirring work or more can fix the conductive particles to the coating resin, thereby suppressing the amount of free conductive particles. In the method for producing a carrier for developing electrostatic images according to this embodiment, the stirring conditions in the coating step, from when the carrier is heated in the mixer to evaporate the solvent and dry it, until when the carrier is removed from the mixer, satisfy the conditions of the formula 1 and the formula 2. This allows the finished carrier to be crushed into primary particles, and by suppressing the shear force (peripheral speed) in a state in which the resin coating layer after drying is not completely fixed, not only is core exposure due to peeling of the resin coating layer suppressed, but the strength of the resin coating layer is also ensured, and the generation of free resin powder is suppressed even when printing is performed for a long period of time, resulting in excellent suppression of dull color in the resulting images.

[0023] The method for producing the carrier for developing electrostatic images according to this embodiment will be described in detail below.

[0024] <Coating process> The method for producing a carrier for developing electrostatic images according to this embodiment includes a coating step of adding a coating liquid containing a resin and a solvent and magnetic particles to a mixer having an agitating blade to form a resin coating layer on the surface of the magnetic particles, and then removing the carrier having the resin coating layer from the mixer. In the coating step, the stirring conditions from when the solvent is evaporated by heating in the mixer to when the mixture is dried to when the mixture is removed from the mixer satisfy the conditions of the following formula 1 and formula 2. 0.2≦the peripheral speed of the stirring blade πDN (m / s)≦2.0 Equation 1 1×10 3 ≦Mixing work load (peripheral speed × mixing time T)≦4×10 3 formula 2 In Equation 1 and Equation 2, D represents the diameter (m) of the stirring blade, N represents the rotation speed (rps) of the stirring blade, and T represents the time (s) from the point at which the load power value of the stirring blade before drying of the solvent increases as drying progresses and the previous load power value decreases to 1.3 times or less the value before drying after drying is completed, to the point at which stirring in the mixer is completed. Moreover, the π represents the ratio of the circumference of a circle to its diameter.

[0025] In the coating step, for example, fluctuations in the load power value of the stirring blades shown in FIG. 3 are thought to occur. FIG. 3 is a schematic graph showing the fluctuation of the load power value of the stirring blade and the fluctuation of the temperature inside the mixer over time in an example of the method for producing an electrostatic image developing carrier according to the present embodiment. The vertical axis on the left side of FIG. 3 represents the load power value (kW) of the stirring blade, the vertical axis on the right side represents the temperature inside the mixer (° C.), and the horizontal axis represents the elapsed time (miN).

[0026] 3, the coating liquid and magnetic particles are put into a mixer at T0, and the coating liquid and magnetic particles are mixed from T0 to T1, the solvent contained in the coating liquid is evaporated under reduced pressure from T1 to T2 until the carrier is completely dried, and the dried carrier is crushed and cooled as necessary from T2 to T3. Furthermore, at T3, mixing in the mixer is completed and the carrier is removed from the mixer.

[0027] The fluctuations in the load power value of the stirring impeller shown in FIG. 3 are as follows. From T0 to T1, the load power value of the stirring impeller is 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 value of the agitator blade continues to rise until the carrier is completely dried. Once the carrier is completely dried, the load power value of the agitator blade suddenly decreases to a value less than 1.3 times the load power value of the agitator blade from T0 to T1. From T2 to T3, the load power value of the stirring impeller again becomes almost constant. The T is the time from T2 to T3.

[0028] The temperature fluctuations in the mixer shown in Figure 3 are as follows: From T0 to T1, the temperature is gradually increased to a set temperature (for example, 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 rises gradually as the drying of the carrier progresses. From T2 to T3, the temperature gradually rises according to the temperature set during drying, and as cooling begins, the temperature gradually drops according to the set cooling temperature (for example, jacket temperature).

[0029] The mixer used in this embodiment may be any mixer having stirring blades, and any known mixer may be used, but from the viewpoint of drying properties, a vacuum mixer is preferred. Furthermore, the mixer used in this embodiment is preferably a batch batch mixer, more preferably a batch batch vacuum mixer, from the viewpoints of mixing performance and suppressing color dullness in the resulting image. Furthermore, the batch mixer is preferably a blade-type kneader, and the direction of the rotation axis of the blade may be vertical or horizontal. Vertical types include a spiral mixer (manufactured by Aikosha Seisakusho Co., Ltd.) and a planetary mixer (manufactured by Inoue Seisakusho Co., Ltd.), and horizontal types include a kneader (manufactured by Inoue Seisakusho Co., Ltd.). Among them, a biaxial horizontal kneader is particularly preferred from the viewpoints of mixing ability and suppression of color dullness in the resulting image. The mixer preferably has a temperature control structure capable of heating and cooling the mixing vessel while reducing the pressure therein, and a mechanism capable of detecting the stirring power value of the stirring blades. The temperature control structure is not particularly limited, but a jacket structure is preferred.

[0030] The shape of the stirring blade is not particularly limited, and examples thereof include Banbury type, Sigma type, Z type, spiral type, and fishtail type. The diameter D of the impeller is not particularly limited as long as it is a size that matches the mixer to be used. In addition, the diameter D of the impeller in this embodiment is the maximum outer diameter of the part that the impeller passes through as it rotates in a plane perpendicular to the rotation axis. The rotation speed N of the stirring blade is preferably 10 rpm or more and 200 rpm or less, more preferably 15 rpm or more and 160 rpm or less, and particularly preferably 20 rpm or more and 160 rpm or less, from the viewpoint of the carrier production speed and the suppression of color dullness of the obtained image. The clearance (gap) between the stirring vessel and the stirring blade in the mixer is not particularly limited and is determined according to the size of the mixer used, but if the clearance is too large, not only will the carrier accumulated at the bottom not be completely crushed, but the shear force of the crushing will be determined not only by the peripheral speed and stirring work of the stirring blade but also by the clearance. Therefore, the narrower the clearance, the better, but there is a limit to the clearance due to constraints on the manufacture of the device, so the clearance between the outer periphery of the stirring blade and the stirring vessel is preferably 5% or less, and more preferably 3.5% or less, in terms of the value of clearance / stirring blade diameter.

[0031] The time T from the point at which the load power value of the stirring blade drops to the value before drying after the start of drying the solvent until the carrier is removed from the mixer is preferably 5 minutes or more and 280 minutes or less, more preferably 10 minutes or more and 80 minutes or less, and particularly preferably 20 minutes or more and 70 minutes or less, from the viewpoint of suppressing color dullness of the resulting image. That is, from the viewpoint of suppressing color dullness of the obtained image, T is preferably 300 seconds or more and 16,800 seconds or less, more preferably 600 seconds or more and 4,800 seconds or less, and particularly preferably 1,200 seconds or more and 4,200 seconds or less. It is also preferable to continue stirring with the stirring blades during the coating step.

[0032] In the coating step, the stirring conditions from the time when the solvent is evaporated by heating in the mixer to the time when the mixture is removed from the mixer preferably satisfy the following formula 1-1, and more preferably satisfy the following formula 1-2, from the viewpoint of suppressing color dullness in the resulting image. 0.2≦the peripheral speed of the stirring blade πDN (m / s)≦2.0 Equation 1-1 0.7≦the peripheral speed of the stirring blade πDN (m / s)≦2.0 Equation 1-2

[0033] In addition, in the coating step, the stirring conditions from the time when the solvent is evaporated by heating in the mixer and the mixture is dried until the mixture is removed from the mixer preferably satisfy the following formula 2-1, and more preferably satisfy the following formula 2-2, from the viewpoint of suppressing color dullness in the obtained image. 1.1×10 3 ≦Mixing work load (peripheral speed × mixing time T)≦3.5×10 3 Formula 2-1 1.4×10 3 ≦Mixing work load (peripheral speed × mixing time T)≦2.5×10 3 Formula 2-2

[0034] From the viewpoint of the coating property of the resin coating layer and the suppression of color dullness of the resulting image, the maximum temperature of the carrier in the coating step is preferably at least the glass transition temperature (Tg) of the resin contained in the resin coating layer minus 20° C. and at most the glass transition temperature (Tg) of the resin contained in the resin coating layer. This is because by raising the temperature to the vicinity of Tg, the resin becomes soft and a uniform resin coating layer can be formed. When the resin coating layer contains two or more types of resins, the glass transition temperature Tg of the resin contained in the resin coating layer is the Tg of the resin with the lower glass transition temperature among the two or more types of resin contained in the resin coating layer.

[0035] In the coating step, the solvent may be evaporated by heating under normal pressure, under reduced pressure, or by heating under reduced pressure. However, heating under reduced pressure is preferred because it allows drying without causing the temperature to rise above the boiling point of the solvent and the glass transition temperature Tg of the resin. The pressure in the coating step is not particularly limited and may be appropriately selected depending on the glass transition temperature of the resin and the solvent used. From the viewpoints of the evaporation rate of the solvent and suppression of color dullness in the resulting image, the pressure is preferably from 0.1 kPa-a to 80 kPa-a, and more preferably from 5 kPa-a to 60 kPa-a. Note that kPa-a represents atmospheric pressure (kPa) based on absolute pressure. The pressure reducing means in the mixer is not particularly limited, and known pressure reducing means such as a vacuum pump can be used. The evaporated solvent may be recovered by a solvent recovery means such as a cold trap.

[0036] The temperature of the carrier when removed from the mixer is preferably the glass transition temperature Tg of the resin contained in the resin coating layer minus 20° C. or less, from the viewpoint of suppressing color dullness of the resulting image. Furthermore, when a cooling step described below is performed after the coating step, the temperature of the carrier when it is removed from the mixer is preferably equal to or lower than the glass transition temperature Tg of the resin contained in the resin coating layer, and more preferably equal to or lower than the glass transition temperature Tg-10°C of the resin contained in the resin coating layer. The carrier crushed in the mixer is collected in a container and stored in the container until sieved through an arbitrary mesh opening, but the closer the storage temperature is to the glass transition temperature Tg of the carrier coating resin, the less the coating resin is fixed, and therefore the weight of the carrier in the tank causes the state of the resin coating layer to become uneven depending on the storage location in the tank, and the amount of free resin may not be stabilized. Therefore, when performing the cooling step described below, it is preferable to cool the carrier in a cooling device continuously after the coating step in order to suppress the generation of coating residue.

[0037] The amounts of the coating liquid and magnetic particles used in the coating step are not particularly limited, and may be appropriately selected depending on the disperser used, etc. The ratio of the amounts of the coating liquid and the magnetic particles may be appropriately selected depending on the concentration of the coating liquid and the thickness of the resin coating layer to be formed. Furthermore, in the coating step, other components to be contained in the resin coating layer, such as particles, may be added to the mixer in addition to the coating liquid and the magnetic particles. The coating liquid containing the resin and solvent, the magnetic particles, and other components used in the coating step will be described in detail below.

[0038] <Cooling process> From the viewpoint of suppressing color dullness of the resulting image, the method for producing a carrier for developing electrostatic images according to the present embodiment preferably further includes, following the coating step, a cooling step of cooling the carrier in a cooling device to a glass transition temperature (Tg) of the resin contained in the resin coating layer or lower (Tg-20°C). Examples of the cooling device include a fluidized bed device, a paddle mixer, a screw mixer, etc., but a fluidized bed device is preferred from the viewpoint of suppressing color dullness of the resulting image. By cooling using a fluidized bed device that can mix without stirring, the generation of free resin is further suppressed, and a carrier with more stable quality can be obtained. The fluidized bed device is not particularly limited, and may be a fluidized bed device that uses only fluidized air or a vibration fluidized bed that assists fluidization by vibration.

[0039] The fluidized bed apparatus may be any apparatus capable of discharging dehumidified gas from the bottom of the apparatus at a temperature below the target cooling 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 have a jacket structure through which cooling water is circulated. The fluidized bed apparatus is not particularly limited, and any known fluidized bed apparatus can be used. Furthermore, "continuously after the coating step" means that the carrier removed from the mixer in the coating step is directly introduced into the fluidized bed apparatus, and it is preferable to introduce the carrier into the fluidized bed apparatus directly from the mixer in the coating step.

[0040] The cooling rate in a fluidizer depends on the 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 superficial velocity based on the minimum fluidization velocity Umf (described below). Therefore, the lower the fluidizing gas temperature and the faster the fluidization velocity, the shorter the cooling time. However, the faster the fluidization velocity, the greater the friction between the carriers in the device, resulting in the generation of coating residue. From the viewpoints of the cooling rate and suppression of color dullness in the resulting image, the superficial velocity v (m / s) of the fluidizing gas during cooling in the cooling step is preferably from 2 to 10 times the minimum fluidizing velocity Umf, more preferably from 3 to 8 times the minimum fluidizing velocity Umf, and particularly preferably from 3 to 5 times the minimum fluidizing velocity Umf. The minimum fluidization velocity Umf can be experimentally determined using the following formula from the flow rate at the point where the pressure of the fluidizing gas begins to stabilize after increasing. Minimum fluidization velocity Umf (m / s) = flow rate at the change point (m 3 / s) ÷ cross-sectional area of ​​fluidizer (m 2 ) 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 more, and more preferably 20 mm / s or more and 50 mm / s or more.

[0041] The fluidizing gas in the fluidizer is not particularly limited, and air, nitrogen, argon, etc. can be used, with air being preferred. Furthermore, 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.

[0042] In the cooling step, from the viewpoint of suppressing color dullness of the resulting image, it is preferable to cool to a glass transition temperature (Tg) of the resin contained in the resin coating layer −20°C or less, more preferably to a glass transition temperature (Tg) of the resin contained in the resin coating layer −25°C or less, and particularly preferable to cool to 25°C or more to a glass transition temperature (Tg) of the resin contained in the resin coating layer −30°C or less.

[0043] The cooling time in the cooling step is not particularly limited, but from the viewpoint of the carrier production speed and the suppression of color dullness of the resulting image, 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.

[0044] The method for producing the electrostatic image developing carrier according to this embodiment may include other steps in addition to the coating step and the cooling step. The other steps are not particularly limited and may include known steps. The method for producing the carrier for developing electrostatic images according to this embodiment preferably further includes a step of preparing magnetic particles and a step of preparing a coating liquid containing a resin and a solvent.

[0045] <Carrier properties> The volume average particle size of the carrier for developing electrostatic images obtained by the method for producing a carrier for developing electrostatic images 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. The volume average particle diameters of the magnetic particles and carrier in this embodiment are values ​​measured using a laser diffraction particle size distribution analyzer LA-700 (manufactured by Horiba, Ltd.) Specifically, the particle size distribution obtained by the analyzer is divided into particle size ranges (channels), and the particle diameter at which the cumulative volume distribution is subtracted from the small particle size side and cumulative 50% is defined as the volume average particle diameter.

[0046] The amount of the resin coating layer in the electrostatic image developing carrier obtained by the method for producing an electrostatic image developing carrier according to this embodiment is preferably from 0.5% by mass to 10% by mass, and more preferably from 1% by mass to 5% by mass, relative to the total mass of the carrier, from the viewpoints of thickness stability of the resin coating layer and chargeability.

[0047] The amount of free resin in the electrostatic image developing carrier obtained by the method for producing an electrostatic image developing carrier according to this embodiment is preferably 200 ppm or less, more preferably 100 ppm or less, even more preferably 75 ppm or less, and particularly preferably 50 ppm or less, from the viewpoint of suppressing color dullness in the resulting image.

[0048] In this embodiment, the method for measuring the amount of free resin in the carrier for developing an electrostatic image is as follows. A certain amount of carrier was weighed and dispersed in water, and the dispersion was filtered while the carrier was fixed with a magnet. The filter paper was dried, and the amount of free resin was calculated using the following formula from the difference in mass before and after the filter paper and the weighed amount of carrier. Amount of free resin (ppm) = Increase in filter paper (g) ÷ Carrier (g)

[0049] The proportion of aggregates after sieving through a 75 μm sieve in the electrostatic image developing carrier obtained by the method for producing an electrostatic image developing carrier according to this embodiment is preferably 5% by number or less, more preferably 1% by number or less, even more preferably 0.1% by number or less, and particularly preferably 0.01% by number or less, from the viewpoint of suppressing color dullness in the resulting image.

[0050] In this embodiment, the method for measuring the proportion of aggregates in the carrier for developing electrostatic images after sieving through a 75 μm sieve is as follows. The carrier is sieved using a sieve with 75 μm openings, and the sieved carrier is spread out so as not to overlap as much as possible. A scanning electron microscope (SEM) photograph is taken at 350x magnification, and the ratio of the number of carriers that have not been broken down to primary particles to the number of carriers in one field of view is measured.

[0051] In this embodiment, the fluidity of the carrier for developing electrostatic images is preferably 20 sec / 50 g or more and 50 sec / 50 g or less, more preferably 22 sec / 50 g or more and 35 sec / 50 g or less, and particularly preferably 25 sec / 50 g or more and 30 sec / 50 g or less, from the viewpoint of suppressing density changes in the resulting image. The fluidity of the carrier for developing electrostatic images in this embodiment is a value measured at 25° C. and 50% RH in accordance with JIS Z2502 (2020).

[0052] <Magnetic particles> The magnetic particles used in this embodiment are known magnetic particles. Known materials are used as the magnetic particles, and examples thereof include magnetic metals such as iron, nickel, and cobalt, alloys of these magnetic metals with manganese, chromium, and rare earth elements, magnetic oxides such as iron oxide, ferrite, and magnetite, and resin-dispersed magnetic particles in which a conductive material is dispersed in a matrix resin. Examples of resins used in the 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 containing organosiloxane bonds or modified products thereof, fluororesin, polyester, polycarbonate, phenolic resin, and epoxy resin. Among these, the magnetic particles are preferably magnetic oxide particles, and more preferably ferrite particles.

[0053] -Ferrite particles- Ferrite is generally (MO) X (Fe2O3) Y In the formula, M is mainly MN, but it is also possible to combine at least one or several elements selected from the group consisting of Li, Ca, Sr, SN, Cu, ZN, Ba, Fe, Ti, Ni, Al, Co, and Mo. Furthermore, X and Y represent molar ratios and satisfy the condition X+Y=100. In general, the properties of ferrite particles change depending on their composition and structure.

[0054] The ferrite particles used in this embodiment are not particularly limited, but can be prepared, for example, as follows. Powders of metal oxides or metal salts as raw materials are mixed and calcined using a rotary kiln or the like to obtain a calcined product. Examples of the metal oxides or metal salts used as raw materials include Fe2O3, MNO2, SrCO3, and Mg(OH)2. For example, the amount of SrCO3 is adjusted to a strontium content of 0.1% by mass to 1.0% by mass in the ferrite particles. The calcination temperature can be 800°C to 1,000°C, and the calcination time can be 6 hours to 10 hours. The calcination temperature can be 800°C to 1,000°C, and the calcination time can be 6 hours to 10 hours. The resulting calcined product is then pulverized using a known milling method, specifically, by adding polyvinyl alcohol, water, a surfactant, and an antifoaming agent, using a mortar, ball mill, jet mill, or the like. The calcined product is pulverized, for example, until the average particle size is 4 μm to 10 μm. The pulverized pre-calcined product is then granulated and dried using a spray dryer. This dried pre-calcined product is then calcined again (re-calcined) to remove any contained organic matter, yielding a re-calcined product. The re-calcined product can be calcined at a temperature of 800°C to 1,000°C for a period of 5 to 10 hours. Polyvinyl alcohol, water, a surfactant, and an antifoaming agent are added to the resulting re-calcined product, which is then pulverized using a mortar, ball mill, jet mill, or the like. The re-calcined product is pulverized until the average particle size is, for example, 4 μm to 8 μm. The pulverized re-calcined product is then granulated and dried using a spray dryer. The dried granulated product is then calcined (main calcined) using a rotary kiln or the like to yield a main calcined product. The main calcined temperature can be 1,000°C to 1,400°C for a period of 3 to 6 hours. The fired product is subsequently subjected to a crushing step and a classification step to obtain ferrite particles.

[0055] 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 fired product or ferrite particles is a 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, and the particle size at which the cumulative 50% is reached is defined as the volume-average 50% particle size.

[0056] The BET specific surface area of ​​the magnetic particles is set to 0.10 m from the viewpoint of long-term image quality stability and suppression of density change. 2 / g or more 0.35m 2 / g or less, and 2 / g or more 0.28m 2 / g or less is more preferable, and 0.12m 2 / g or more 0.24m 2 In addition, within the above range, an appropriate amount of the coating resin can penetrate into the gaps between the magnetic particles, preventing deterioration of the resin coating layer due to an anchoring effect, and providing excellent long-term image quality stability and density change suppression.

[0057] The BET specific surface area of ​​the magnetic particles is measured using a SA3100 specific surface area analyzer (manufactured by Beckman Coulter) with nitrogen substitution and a three-point method. Specifically, 5 g of magnetic particles are placed in a cell, degassed at 60°C for 120 minutes, and then measured using a mixed gas of nitrogen and helium (30:70). More specifically, a method for separating magnetic particles from carriers involves placing 20 g of resin-coated carrier in 100 mL of toluene. Apply ultrasound at 40 kHz for 30 seconds. Separate the magnetic particles from the resin solution using any filter paper appropriate for the particle size. Wash the magnetic particles remaining on the filter paper by pouring 20 mL of toluene over them. Next, collect the magnetic particles remaining on the filter paper. Place the collected magnetic particles in 100 mL of toluene in the same way and apply ultrasound at 40 kHz for 30 seconds. Filter in the same way, wash with 20 mL of toluene, and then collect the particles. Repeat this process 10 times in total. Finally, dry the collected magnetic particles, and measure the BET specific surface area under the same conditions.

[0058] 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 a magnetic particle is determined by observing the magnetic particles at an appropriate magnification (for example, 1000x magnification) using a surface profile measuring device (for example, Keyence Corporation's "Ultra-Deep Color 3D Profile Measuring Microscope VK-9700"), 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 Ra of 100 magnetic particles is then arithmetically averaged.

[0059] The magnetic force of the magnetic particles is preferably 50 emu / g or more, more preferably 60 emu / g or more, in terms of saturation magnetization in a magnetic field of 3,000 oersteds. The saturation magnetization is measured using a vibrating sample magnetometer VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.). The measurement sample is placed in a cell with an inner diameter of 7 mm and a height of 5 mm and set in the instrument. The measurement is performed by applying a magnetic field and sweeping up to a maximum of 3,000 oersteds. The applied magnetic field is then reduced, and a hysteresis curve is created on recording paper. The saturation magnetization, remanent magnetization, and coercive force are determined from the curve data.

[0060] The volume electrical resistance (volume resistivity) of magnetic particles is 1×10 5 Ω cm or more 1×10 9 Ω·cm or less is preferable, and 1×10 7 Ω cm or more 1×10 9 Ω·cm or less is more preferable. The volume resistivity (Ω·cm) of magnetic particles is measured as follows: 2 The object to be measured is placed flat on the surface of the circular jig on which the electrode plate is arranged, with a thickness of 1 mm to 3 mm, to form a layer. 2The layer is sandwiched between two electrode plates. To eliminate any gaps between the objects being measured, a 4 kg load is placed on the electrode plates placed on the layer, and then the layer thickness (cm) is measured. The electrodes above and below the layer are connected to an electrometer and a high-voltage power supply generator. A high voltage is applied to both electrodes so that the electric field becomes 103.8 V / cm, and the current value (A) that flows at this time is read. The measurement environment is a temperature of 20°C and a relative humidity of 50%. The formula for calculating the volume electrical resistivity (Ω·cm) of the object being measured is as shown below. R=E×20 / (I-I0) / L In the above formula, R represents the volume electrical resistance (Ω·cm) of the object to be measured, E represents the applied voltage (V), I represents the current value (A), I0 represents the current value (A) at an applied voltage of 0 V, and L represents the layer thickness (cm). The coefficient 20 is the area of ​​the electrode plate (cm 2 )

[0061] <Resin coating layer> The electrostatic image developing carrier produced by the method for producing an electrostatic image developing carrier according to this embodiment has a resin coating layer that coats the magnetic particles.

[0062] Resins that can be used to form the resin coating layer include styrene-acrylic acid copolymers; polyolefin resins such as polyethylene and polypropylene; polyvinyl or polyvinylidene resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymers; straight silicone resins or modified silicone resins consisting of organosiloxane bonds; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyesters; polyurethanes; polycarbonates; amino resins such as urea-formaldehyde resins; and epoxy resins. In particular, from the viewpoints of electrostatic chargeability, control of external additive adhesion, and suppression of concentration change, it is preferable that the resin constituting the resin coating layer contains an acrylic resin, and it is more preferable that the acrylic resin accounts for 50% by mass or more of the total mass of the resin in the resin coating layer, and it is particularly preferable that the acrylic resin accounts for 80% by mass or more of the total mass of the resin in the resin coating layer.

[0063] From the viewpoint of suppressing concentration change, the resin coating layer preferably contains an acrylic resin having an alicyclic structure. The polymerization component of the acrylic resin having an alicyclic structure is preferably a lower alkyl ester of (meth)acrylic acid (for example, a (meth)acrylic acid alkyl ester having an alkyl group with 1 to 9 carbon atoms), and specific examples thereof include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, hexyl (meth)acrylate, cyclohexyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. These monomers may be used alone or in combination of two or more. The acrylic resin having an alicyclic structure preferably contains cyclohexyl(meth)acrylate as a polymerization component. The content of the monomer unit derived from cyclohexyl(meth)acrylate contained in the acrylic resin having an alicyclic structure is preferably 75% by mass or more and 100% by mass or less, more preferably 85% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on the total mass of the acrylic resin having an alicyclic structure.

[0064] The weight-average molecular weight of the resin contained in the resin coating layer is preferably less than 300,000, more preferably less than 250,000, even more preferably from 5,000 to less than 250,000, and particularly preferably from 10,000 to 200,000. Within the above range, the smoothness of the resin-coated surface of the carrier is improved, thereby reducing the amount of external additives attached to the carrier and providing better suppression of concentration change.

[0065] The resin coating layer may contain conductive particles for the purpose of controlling charging and resistance. Examples of conductive particles include carbon black and conductive inorganic particles described below. Among these, carbon black is preferred. From the viewpoint of charging properties, the content of the conductive particles contained in the resin coating layer is preferably 0.1% by mass or more and 30% by mass or less, more preferably 0.5% by mass or more and 20% by mass or less, and even more preferably 1% by mass or more and 10% by mass or less, relative to the total mass of the resin coating layer.

[0066] The resin coating layer may also contain inorganic particles. Examples of inorganic particles contained in the resin coating layer include metal oxide particles such as silica, titanium oxide, zinc oxide, and tin oxide; metal compound particles such as barium sulfate, aluminum borate, and potassium titanate; and metal particles such as gold, silver, and copper. Among these, silica particles are preferred from the viewpoint of suppressing concentration changes.

[0067] From the viewpoint of suppressing concentration changes, the arithmetic mean particle size of the inorganic particles in the resin coating layer is preferably 5 Nm or more and 90 Nm or less, more preferably 5 Nm or more and 70 Nm or less, even more preferably 5 Nm or more and 50 Nm or less, and particularly preferably 8 Nm or more and 50 Nm or less.

[0068] In this embodiment, the average particle size of the inorganic particles contained in the resin coating layer and the average thickness of the resin coating layer are determined by the following method. The carrier is embedded in epoxy resin and cut with a microtome to prepare a carrier cross section. SEM images of the carrier cross section taken with a scanning electron microscope (ScaNNiNg ElectroN Microscope, SEM) are imported into an image processing analyzer for image analysis. One hundred inorganic particles (primary particles) in the resin coating layer are randomly selected, and their equivalent circle diameters (Nm) are calculated and arithmetically averaged to obtain the average particle size (Nm) of the inorganic particles. Additionally, the thickness (μm) of the resin coating layer is measured at 10 random locations per carrier particle. Further measurements are taken for 100 carriers, and the arithmetic average of all measurements is obtained to obtain the average thickness (μm) of the resin coating layer.

[0069] The surfaces of the inorganic particles may be subjected to a hydrophobic treatment. Examples of the hydrophobic treatment agent include known organosilicon compounds having an alkyl group (e.g., a methyl group, an ethyl group, a propyl group, a butyl group, etc.), and specific examples include alkoxysilane compounds, siloxane compounds, and silazane compounds. Among these, the hydrophobic treatment agent is preferably a silazane compound, and hexamethyldisilazane is preferred. The hydrophobic treatment agent may be used alone or in combination of two or more types.

[0070] Examples of methods for hydrophobizing inorganic particles with a hydrophobizing agent include a method using supercritical carbon dioxide to dissolve the hydrophobizing agent in supercritical carbon dioxide and adhere the hydrophobizing agent to the surfaces of the inorganic particles; a method in which a solution containing the hydrophobizing agent and a solvent that dissolves the hydrophobizing agent is applied (e.g., sprayed or painted) to the surfaces of inorganic particles in the atmosphere to adhere the hydrophobizing agent to the surfaces of the inorganic particles; and a method in which a solution containing the hydrophobizing agent and a solvent that dissolves the hydrophobizing agent is added to an inorganic particle dispersion in the atmosphere, the mixture is maintained, and then the inorganic particle dispersion and the mixed solution are dried.

[0071] From the viewpoint of suppressing concentration change, the content of inorganic particles contained in the resin coating layer is preferably 10% by mass or more and 60% by mass or less, more preferably 15% by mass or more and 55% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less, relative to the total mass of the resin coating layer.

[0072] The exposed area ratio of the magnetic particles on the carrier surface is preferably 3% to 30%, more preferably 4% to 25%, and even more preferably 5% to 20%. The exposed area ratio of the magnetic particles on the carrier can be controlled by the amount of resin used to form the resin coating layer, and the greater the amount of resin relative to the amount of magnetic particles, the smaller the exposed area ratio. That is, the coverage of the resin coating layer on the carrier surface is preferably 70% or more and 97% or less, more preferably 75% or more and 96% or less, and even more preferably 80% or more and 95% or less.

[0073] The exposed area ratio of the magnetic particles on the carrier surface and the coverage ratio of the resin coating layer are values ​​determined by the following method. The target carrier and magnetic particles from which the resin coating layer has been removed are prepared. Methods for removing the resin coating layer from the carrier include, for example, dissolving the resin component in 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. The carrier and magnetic particles are each used as measurement samples, and the ratios (atomic %) of Fe, C, and O on the sample surfaces are quantified using XPS, and the exposed area ratio (%) of the magnetic particles is calculated as (Fe ratio of the carrier) ÷ (Fe ratio of the magnetic particles) × 100. The coverage (%) of the resin coating layer is calculated by (100-exposed area ratio of magnetic particles).

[0074] The solvent used to form the coating resin layer is not particularly limited as long as it dissolves or disperses the resin, and examples thereof include aromatic hydrocarbons such as toluene and xylene; ketones such as acetone and methyl ethyl ketone; and ethers such as tetrahydrofuran and dioxane. Of these, toluene is preferred.

[0075] The solid content of the coating liquid used to form the coating resin layer is not particularly limited, but is preferably 5% by mass to 50% by mass, and more preferably 10% by mass to 30% by mass.

[0076] Furthermore, the coating liquid may contain the conductive particles or the inorganic particles, or the conductive particles or the inorganic particles may be added separately from the coating agent in the coating step.

[0077] 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.

[0078] The average thickness of the resin coating layer is measured by the following method. The carrier is embedded in an epoxy resin or the like, and then cut with a diamond knife or the like to prepare a thin section. This thin section is observed with a transmission electron microscope (TEM) or the like, and cross-sectional images of multiple carrier particles are taken. The thickness of the resin coating layer is measured at 20 points from the cross-sectional images of the carrier particles, and the average value is used.

[0079] (Electrostatic image developer) The developer according to the present embodiment is a two-component developer containing a toner and a carrier for developing electrostatic images manufactured by the method for manufacturing a carrier for developing electrostatic images according to the present embodiment. The toner contains toner particles and, if necessary, an external additive. The method for producing a developer according to this embodiment preferably includes the method for producing a carrier for developing electrostatic images according to this embodiment.

[0080] The mixture ratio (mass ratio) of the carrier to the toner in the developer is preferably from 100:1 to 100:30, more preferably from 100:3 to 100:20.

[0081] <Toner particles> The toner particles are composed of, for example, a binder resin, and, if necessary, a colorant, a release agent, and other additives.

[0082] -Binder resin- Examples of binder resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, N-propyl acrylate, N-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, N-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), and vinyl resins made of copolymers of two or more of these monomers. Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these. These binder resins may be used alone or in combination of two or more.

[0083] As the binder resin, a polyester resin is preferable. Examples of polyester resins include known amorphous polyester resins. The polyester resin may be used in combination with a crystalline polyester resin. However, the content of the crystalline polyester resin is preferably in the range of 2% by mass to 40% by mass (preferably 2% by mass to 20% by mass) relative to the total binder resin.

[0084] The "crystalline" nature of a resin refers to the presence of a clear endothermic peak rather than a stepwise change in endothermic heat in differential scanning calorimetry (DSC). Specifically, this refers to the half-width of the endothermic peak being within 10°C when measured at a heating rate of 10°C / min. On the other hand, the term "amorphous" for a resin means that the half-width exceeds 10°C, that the endothermic amount exhibits a stepwise change, or that no clear endothermic peak is observed.

[0085] Amorphous polyester resin The amorphous polyester resin may be, for example, a condensation polymer of a polycarboxylic acid and a polyhydric alcohol. As the amorphous polyester resin, a commercially available product or a synthesized product may be used.

[0086] Examples of polycarboxylic acids include aliphatic dicarboxylic acids (such as oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenylsuccinic acid, adipic acid, and sebacic acid), alicyclic dicarboxylic acids (such as cyclohexanedicarboxylic acid), aromatic dicarboxylic acids (such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). Among these, aromatic dicarboxylic acids are preferred as polycarboxylic acids. The polycarboxylic acid may be a trivalent or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the trivalent or higher carboxylic acid include trimellitic acid, pyromellitic acid, anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polycarboxylic acids may be used alone or in combination of two or more.

[0087] 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, preferred polyhydric alcohols are aromatic diols and alicyclic diols, and more preferred are aromatic diols. As the polyhydric alcohol, a trihydric or higher polyhydric alcohol having a crosslinked or branched structure may be used in combination with the diol. Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, and pentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more.

[0088] The glass transition temperature (Tg) of the amorphous polyester resin is preferably 50°C or higher and 80°C or lower, and more preferably 50°C or higher and 65°C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, is determined from the "extrapolated glass transition onset temperature" described in the method for determining glass transition temperature in JIS K7121:1987 "Method for measuring transition temperature of plastics."

[0089] The weight average molecular weight (Mw) of the amorphous polyester resin is preferably 5,000 or more and 1,000,000 or less, and more preferably 7,000 or more and 500,000 or less. The number average molecular weight (MN) of the amorphous polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / MN of the amorphous polyester resin is preferably 1.5 or more and 100 or less, and more preferably 2 or more and 60 or less. The weight average molecular weight and number average molecular weight are measured by gel permeation chromatography (GPC). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC measuring device, a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent. The weight average molecular weight and number average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.

[0090] The amorphous polyester resin can be obtained by a known production method, for example, by carrying out the reaction at a polymerization temperature of 180°C or higher and 230°C or lower, reducing the pressure in the reaction system as necessary, and removing water and alcohol generated during the condensation. If the raw material monomers are not soluble or compatible at the reaction temperature, a high-boiling solvent may be added as a solubilizer to dissolve them. In this case, the polycondensation reaction is carried out while distilling off the solubilizer. If a monomer with poor compatibility is present in the copolymerization reaction, it is advisable to first condense the poorly compatible monomer with the acid or alcohol to be polycondensed, and then polycondense it with the main component.

[0091] Crystalline polyester resin Examples of the crystalline polyester resin include a polycondensate of a polycarboxylic acid and a polyhydric alcohol. As the crystalline polyester resin, a commercially available product or a synthesized product may be used. Here, the crystalline polyester resin is preferably a polycondensate using a linear aliphatic polymerizable monomer rather than a polymerizable monomer having an aromatic ring, since it easily forms a crystalline structure.

[0092] 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., dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalene-2,6-dicarboxylic acid), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polycarboxylic acid may be a tricarboxylic or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the tricarboxylic acid include aromatic carboxylic acids (e.g., 1,2,3-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, etc.), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). As the polycarboxylic acid, a dicarboxylic acid having a sulfonic acid group and a dicarboxylic acid having an ethylenic double bond may be used in combination with these dicarboxylic acids. The polycarboxylic acids may be used alone or in combination of two or more.

[0093] Examples of polyhydric alcohols include aliphatic diols (for example, straight-chain aliphatic diols having 7 to 20 carbon atoms in the main chain). Examples of aliphatic diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,14-eicosanedecanediol. Among these, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol are preferred as aliphatic diols. The polyhydric alcohol may be a trihydric or higher alcohol having a crosslinked or branched structure, such as glycerin, trimethylolethane, trimethylolpropane, or pentaerythritol, in combination with the diol. The polyhydric alcohols may be used alone or in combination of two or more.

[0094] Here, the polyhydric alcohol has an aliphatic diol content of 80 mol % or more, preferably 90 mol % or more.

[0095] The melting temperature of the crystalline polyester resin is preferably 50°C or higher and 100°C or lower, more preferably 55°C or higher and 90°C or lower, and even more preferably 60°C or higher and 85°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) by using the "melting peak temperature" described in the method for determining the melting temperature in JIS K7121:1987 "Method for measuring transition temperatures of plastics."

[0096] The weight average molecular weight (Mw) of the crystalline polyester resin is preferably 6,000 or more and 35,000 or less.

[0097] The crystalline polyester resin can be obtained by a known production method, for example, in the same manner as the amorphous polyester.

[0098] The content of the binder resin is preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass, based on the total mass of the toner particles.

[0099] -Coloring agent- Examples of colorants include carbon black, chrome yellow, Hansa Yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Balkan orange, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, Examples of suitable dyes include pigments such as ultramarine blue, chalco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate; and dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, and thiazole-based dyes. The colorant may be used alone or in combination of two or more kinds.

[0100] The colorant may be surface-treated as needed, or may be used in combination with a dispersant. Furthermore, a plurality of colorants may be used in combination.

[0101] The content of the colorant is preferably from 1% by mass to 30% by mass, and more preferably from 3% by mass to 15% by mass, based on the total mass of the toner particles.

[0102] -Mold release agent- Examples of release agents include hydrocarbon waxes, natural waxes such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral / petroleum waxes such as montan wax, and ester waxes such as fatty acid esters and montanic acid esters, but are not limited thereto.

[0103] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) by using the "melting peak temperature" described in the method for determining the melting temperature in JIS K7121:1987 "Method for measuring transition temperatures of plastics."

[0104] The content of the release agent is preferably from 1% by mass to 20% by mass, and more preferably from 5% by mass to 15% by mass, based on the total mass of the toner particles.

[0105] -Other additives- Examples of other additives include known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

[0106] -Characteristics of toner particles, etc.- The toner particles may be toner particles of a single layer structure, or may be toner particles of a so-called core-shell structure composed of a core part (core particle) and a coating layer (shell layer) that coats the core part. The toner particles having a core-shell structure may be composed of, for example, a core containing a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer containing the binder resin.

[0107] 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 the toner particles is measured using a Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolyte is measured using an ISOTON-II (manufactured by Beckman Coulter). For the measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5 mass % aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant, and this is then added to 100 ml to 150 ml of the electrolyte. The electrolyte solution containing the suspended sample is dispersed in an ultrasonic disperser for 1 minute, and the particle size distribution of particles with a particle size range of 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. 50,000 particles are sampled. The volume-based particle size distribution is plotted from the smallest diameter side, and the particle size at which the cumulative 50% is reached is defined as the volume average particle size D50v.

[0108] The average circularity of the toner particles is preferably 0.94 or more and 1.00 or less, and more preferably 0.95 or more and 0.98 or less. The average circularity of toner particles is calculated by (circular equivalent perimeter) / (perimeter) [(perimeter of a circle having the same projected area as the particle image) / (perimeter of the particle projected image)]. Specifically, this value is measured by the following method. First, the toner particles to be measured are sucked and collected, forming a flat flow, and a still image of the particles is captured by instantaneously activating a strobe light, and the particle image is analyzed using a flow-type particle image analyzer (FPIA-3000 manufactured by Sysmex Corporation).The number of samples to be sampled when calculating the average circularity is 3,500. When 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.

[0109] -Method of manufacturing toner particles- The toner particles may be produced by any of a dry production method (for example, a kneading and pulverization method) and a wet production method (for example, an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). There are no particular limitations on these production methods, and any known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0110] Specifically, for example, when toner particles are produced by the aggregation and coalescence method, the toner particles are produced through the following steps: a step of preparing a resin particle dispersion in which resin particles to be a binder resin are dispersed (resin particle dispersion preparation step); a step of aggregating resin particles (and other particles, as needed) in the resin particle dispersion (in a dispersion after mixing other particle dispersions, as needed) to form aggregated particles (aggregated particle formation step); and a step of heating the aggregated particle dispersion in which the aggregated particles are dispersed, fusing and coalescing the aggregated particles to form toner particles (fusion and coalescence step).

[0111] Each step will be described in detail below. In the following description, a method for obtaining toner particles containing a colorant and a release agent will be described, but the colorant and the release agent are used as needed. Of course, other additives than the colorant and the release agent may also be used.

[0112] -Resin particle dispersion preparation process- Along with a resin particle dispersion in which resin particles serving as a binder resin are dispersed, for example, a colorant particle dispersion in which colorant particles are dispersed and a release agent particle dispersion in which release agent particles are dispersed are prepared.

[0113] The resin particle dispersion is prepared, for example, by dispersing resin particles in a dispersion medium using a surfactant.

[0114] Examples of the dispersion medium used in the resin particle dispersion include aqueous media. Examples of aqueous media include water such as distilled water and ion-exchanged water, alcohols, etc. These may be used alone or in combination of two or more.

[0115] Examples of surfactants include anionic surfactants such as sulfate ester salts, sulfonate salts, phosphate esters, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; and nonionic surfactants such as polyethylene glycols, alkylphenol ethylene oxide adducts, and polyhydric alcohols. Among these, anionic surfactants and cationic surfactants are particularly preferred. Nonionic surfactants may be used in combination with anionic surfactants or cationic surfactants. The surfactants may be used alone or in combination of two or more.

[0116] In a resin particle dispersion, resin particles can be dispersed in a dispersion medium by common dispersion methods such as a rotary shear homogenizer, a ball mill with media, a sand mill, or a Dynomill. Depending on the type of resin particles, the resin particles may be dispersed in a dispersion medium by a phase inversion emulsification method. The phase inversion emulsification method involves dissolving the resin to be dispersed in a hydrophobic organic solvent in which the resin is soluble, neutralizing the organic continuous phase (O phase) by adding a base, and then introducing an aqueous medium (W phase) to invert the phase from W / O to O / W, thereby dispersing the resin in particulate form in the aqueous medium.

[0117] The volume average particle size of the resin particles dispersed in the resin particle dispersion is, for example, preferably from 0.01 μm to 1 μm, more preferably from 0.08 μm to 0.8 μm, and even more preferably from 0.1 μm to 0.6 μm. The volume average particle size of resin particles is measured using a particle size distribution obtained by measurement with a laser diffraction particle size distribution analyzer (for example, LA-700 manufactured by Horiba, Ltd.), and the cumulative distribution for the volume of the divided particle size range (channel) is subtracted from the small particle size side, and the particle size at which the cumulative 50% of all particles is measured is taken as the volume average particle size D50v. The volume average particle sizes of particles in other dispersions are measured in the same way.

[0118] The content of resin particles contained 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.

[0119] In the same manner as in the resin particle dispersion, for example, a colorant particle dispersion and a release agent particle dispersion are also prepared. That is, the volume average particle size, dispersion medium, dispersion method, and particle content of the particles in the resin particle dispersion are the same for the colorant particles dispersed in the colorant particle dispersion and the release agent particles dispersed in the release agent particle dispersion.

[0120] -Agglomerated particle formation process- Next, the resin particle dispersion, the colorant particle dispersion, and the release agent particle dispersion are mixed together. Then, in the mixed dispersion, the resin particles, colorant particles, and release agent particles are hetero-aggregated to form aggregated particles containing the resin particles, colorant particles, and release agent particles and having a diameter close to that of the target toner particles.

[0121] Specifically, for example, an aggregating agent is added to the mixed dispersion, and the pH of the mixed dispersion is adjusted to be acidic (for example, pH 2 or higher and 5 or lower), and a dispersion stabilizer is added as necessary. After that, the mixed dispersion is heated to a temperature close to the glass transition temperature of the resin particles (specifically, for example, the glass transition temperature of the resin particles -30°C or higher and the glass transition temperature -10°C or lower), causing the particles dispersed in the mixed dispersion to aggregate and form aggregated particles. In the aggregate particle formation step, for example, the mixed dispersion may be stirred with a rotary shear homogenizer, an aggregating agent may be added at room temperature (e.g., 25°C), the pH of the mixed dispersion may be adjusted to an acidic value (e.g., pH 2 or more and 5 or less), a dispersion stabilizer may be added as needed, and then the mixture may be heated.

[0122] Examples of the flocculant include a surfactant having a polarity opposite to that of the surfactant contained in the mixed dispersion, an inorganic metal salt, and a divalent or higher metal complex. When a metal complex is used as the flocculant, the amount of surfactant used can be reduced, and the charging characteristics can be improved. If necessary, an additive that forms a complex or a similar bond with the metal ions of the flocculant may be used together with the flocculant, and a chelating agent is preferably used as this additive.

[0123] Examples of inorganic metal salts include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate; and inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, and calcium polysulfide. The chelating agent may be a water-soluble chelating agent, such as hydroxycarboxylic acid (e.g., tartaric acid, citric acid, gluconic acid), or aminocarboxylic acid (e.g., iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), or ethylenediaminetetraacetic acid (EDTA). The amount of the chelating agent added is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.1 parts by mass or more and less than 3.0 parts by mass, relative to 100 parts by mass of the resin particles.

[0124] -Fusion / coalescence process- Next, the aggregated particle dispersion liquid in which the aggregated particles are dispersed is heated, for example, to a temperature equal to or higher than the glass transition temperature of the resin particles (for example, a temperature 10°C to 30°C higher than the glass transition temperature of the resin particles), to fuse and coalesce the aggregated particles and form toner particles.

[0125] Through the above steps, toner particles are obtained. After obtaining the aggregated particle dispersion liquid in which the aggregated particles are dispersed, the toner particles may be produced through the following steps: a step of further mixing the aggregated particle dispersion liquid with a resin particle dispersion liquid in which resin particles are dispersed, and aggregating the aggregated particles so that further resin particles adhere to the surfaces of the aggregated particles to form second aggregated particles; and a step of heating the second aggregated particle dispersion liquid in which the second aggregated particles are dispersed, and fusing and coalescing the second aggregated particles to form toner particles having a core-shell structure.

[0126] After the fusion and coalescence process is completed, the toner particles formed in the solution are subjected to a known washing process, solid-liquid separation process, and drying process to obtain dried toner particles. In the washing process, from the viewpoint of chargeability, it is preferable to perform sufficient substitution washing with ion-exchanged water. In the solid-liquid separation process, from the viewpoint of productivity, it is preferable to perform suction filtration, pressure filtration, etc. In the drying process, from the viewpoint of productivity, it is preferable to perform freeze drying, flash drying, fluidized drying, vibration-type fluidized drying, etc.

[0127] The toner according to this embodiment is produced by, for example, adding an external additive to the obtained dry toner particles and mixing them. The mixing can be carried out using, for example, a V blender, a Henschel mixer, a Loedige mixer, or the like. Furthermore, if necessary, coarse particles may be removed from the toner using a vibrating sieve, an air sieve, or the like.

[0128] -External additives- Examples of external additives include inorganic particles, such as SiO2, TiO2, Al2O3, CuO, ZnO, SNO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, and K2O·(TiO2). N , Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, MgSO4, etc.

[0129] The surfaces of inorganic particles as external additives are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is usually, for example, 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the inorganic particles.

[0130] Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning agents (for example, metal salts of higher fatty acids such as zinc stearate, and particles of fluorine-based polymers).

[0131] The amount of the external additive added is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, based on the toner particles.

[0132] <Image forming device, image forming method> The image forming apparatus according to the present embodiment includes an image carrier, a charging unit for charging the surface of the image carrier, an electrostatic image forming unit for forming an electrostatic image on the charged image carrier, a developing unit containing an electrostatic image developer and developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, a transfer unit for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing unit 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 developing carrier manufactured by the method for manufacturing an electrostatic image developing carrier according to the present embodiment.

[0133] The image forming apparatus according to this embodiment carries out an image forming method (the image forming method according to this embodiment) that includes a charging step of charging the surface of an image carrier, an electrostatic image forming step of forming an electrostatic image on the surface of the charged image carrier, a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer according to this embodiment, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium. The image forming method according to this embodiment uses the electrostatic image developing carrier manufactured by the method for manufacturing the electrostatic image developing carrier according to this embodiment.

[0134] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a cleaning means that cleans the surface of the image carrier after the transfer of the toner image but before charging; and an apparatus equipped with a discharging means that irradiates the surface of the image carrier with discharging light to discharge it after the transfer of the toner image but before charging. When the image forming apparatus according to the present embodiment is an apparatus of the intermediate transfer type, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means for primarily transferring the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means for secondarily transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0135] In the image forming apparatus according to the present embodiment, for example, the portion including the developing means may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge that contains the electrostatic image developer according to the present embodiment and is equipped with the developing means is preferably used.

[0136] An example of an image forming apparatus according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0137] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to this embodiment. The image forming apparatus shown in Figure 1 includes first through fourth electrophotographic image forming units 10Y, 10M, 10C, and 10K (image forming means) that output images in the colors yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side horizontally spaced apart by predetermined distances. These units 10Y, 10M, 10C, and 10K may be process cartridges that are detachably attached to the image forming apparatus.

[0138] An intermediate transfer belt (an example of an intermediate transfer body) 20 is provided above each of the units 10Y, 10M, 10C, and 10K and extends through each unit. The intermediate transfer belt 20 is provided wrapped around a drive roll 22 and a support roll 24, and runs in a direction from the first unit 10Y to the fourth unit 10K. A force is applied to the support roll 24 by a spring or the like (not shown) in a direction away from the drive roll 22, and tension is applied to the intermediate transfer belt 20 wrapped around them. An intermediate transfer body cleaning device 30 is provided on the image carrier side of the intermediate transfer belt 20, facing the drive roll 22. The developing devices (examples of developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K are supplied with yellow, magenta, cyan, and black toner contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0139] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, we will explain here the first unit 10Y, which forms a yellow image and is arranged upstream in the direction of travel of the intermediate transfer belt.

[0140] The first unit 10Y has a photoreceptor 1Y that acts as an image carrier. Around the photoreceptor 1Y, there are arranged in this order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential; an exposure device (an example of an electrostatic image forming means) 3 that exposes the charged surface to a laser beam 3Y based on a color-separated image signal to form an electrostatic image; a developing device (an example of a developing means) 4Y that supplies charged toner to the electrostatic image to develop it; a primary transfer roll 5Y (an example of a primary transfer means) that transfers the developed toner image onto an intermediate transfer belt 20; and a photoreceptor cleaning device (an example of a cleaning means) 6Y that removes toner remaining on the surface of the photoreceptor 1Y after the primary transfer. The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is provided at a position facing the photoreceptor 1Y. A bias power supply (not shown) that applies a primary transfer bias is connected to the primary transfer rolls 5Y, 5M, 5C, and 5K of each unit. Each bias power supply changes the value of the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

[0141] The operation of forming a yellow image in the first unit 10Y will be described below. First, prior to operation, the surface of the photosensitive member 1Y is charged to a potential of −600V to −800V by the charging roll 2Y. The photoconductor 1Y has conductivity (for example, a volume resistivity of 1×10 at 20°C). -6 The photosensitive layer is formed by laminating a photosensitive layer on a substrate with a resistivity of Ωcm or less. This photosensitive layer normally has a high resistance (the resistance of ordinary resins), but when irradiated with a laser beam, the resistivity of the irradiated portion changes. Therefore, the exposed surface of the photosensitive element 1Y is irradiated with a laser beam 3Y from the exposure device 3 in accordance with image data for yellow sent from a control unit (not shown). This forms an electrostatic charge image of a yellow image pattern on the surface of the photosensitive element 1Y.

[0142] An electrostatic image is an image formed on the surface of the photosensitive element 1Y by charging it; the laser beam 3Y reduces the resistivity of the irradiated portion of the photosensitive layer, causing the charged charges on the surface of the photosensitive element 1Y to flow, while the charges remain in the portions not irradiated by the laser beam 3Y, forming a so-called negative latent image. The electrostatic image formed on the photoreceptor 1Y rotates to a predetermined development position as the photoreceptor 1Y moves, and at this development position, the electrostatic image on the photoreceptor 1Y is developed into a toner image by the developing device 4Y and made visible.

[0143] The developing device 4Y contains an electrostatic image developer containing, for example, at least yellow toner and a carrier. The yellow toner is frictionally charged by being stirred inside the developing device 4Y, and is held on a developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the charge on the photoreceptor 1Y. As the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed with the yellow toner. The photoreceptor 1Y on which the yellow toner image has been formed continues to travel at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transported to a predetermined primary transfer position.

[0144] When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y to the primary transfer roll 5Y acts on the toner image, causing the toner image on the photoreceptor 1Y to be transferred onto the intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the (-) polarity of the toner, and is controlled to, for example, +10 μA by a control unit (not shown) in the first unit 10Y. On the other hand, the toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

[0145] The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K of the second unit 10M and subsequent units is also controlled in accordance with the first unit. In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is conveyed sequentially through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are superimposed and transferred.

[0146] The intermediate transfer belt 20, onto which the four-color toner images have been multiplex-transferred through the first to fourth units, reaches a secondary transfer section composed of the intermediate transfer belt 20, a support roll 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 arranged on the image bearing surface side of the intermediate transfer belt 20. Meanwhile, recording paper (an example of a recording medium) P is fed via a feed mechanism into the gap between the secondary transfer roll 26 and the intermediate transfer belt 20 at a predetermined timing, and a secondary transfer bias is applied to the support roll 24. The transfer bias applied at this time has a negative polarity, the same as the negative polarity of the toner. Electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined according to resistance detected by resistance detection means (not shown) that detects resistance in the secondary transfer section, and is voltage-controlled.

[0147] Thereafter, the recording paper P is sent to the pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image.

[0148] Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copiers, printers, etc. In addition to the recording paper P, examples of the recording medium include overhead projector sheets and the like. To further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper in which the surface of plain paper is coated with resin or the like, or art paper for printing, etc., is preferably used.

[0149] The recording paper P on which the color image has been fixed is conveyed toward the discharge section, and the series of color image forming operations is completed.

[0150] <Process cartridge> The process cartridge according to this embodiment is a process cartridge that is detachably attached to an image forming apparatus and that contains the electrostatic image developer according to this embodiment and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image.

[0151] The process cartridge according to this embodiment is not limited to the above configuration, but may also be configured to include a developing means and, if necessary, at least one other means selected from an image carrier, a charging means, an electrostatic image forming means, and a transfer means.

[0152] An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0153] FIG. 2 is a schematic diagram showing the configuration of the process cartridge according to the present embodiment. The process cartridge 200 shown in FIG. 2 is configured to integrally combine and hold a photosensitive member 107 (an example of an image carrier), a charging roll 108 (an example of a charging means) provided around the photosensitive member 107, a developing device 111 (an example of a developing means), and a photosensitive member cleaning device 113 (an example of a cleaning means), which are held by a housing 117 provided with, for example, mounting rails 116 and an opening 118 for exposure, and is made into a cartridge. In FIG. 2, 109 denotes an exposure device (an example of an electrostatic image forming means), 112 denotes a transfer device (an example of a transfer means), 115 denotes a fixing device (an example of a fixing means), and 300 denotes recording paper (an example of a recording medium). [Example]

[0154] Hereinafter, embodiments of the present invention will be described in detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" are based on mass.

[0155] <Toner Production> -Preparation of colorant particle dispersion- Cyan pigment (copper phthalocyanine B15:3 (manufactured by Dainichi Seika Color & Chemicals Mfg. 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 ingredients were mixed and dispersed for 5 minutes using an Ultra Turrax manufactured by IKA, and then for 10 minutes using an ultrasonic bath to obtain a colorant particle dispersion with a solid content of 21%. The volume average particle size was measured using a particle size analyzer LA-700 manufactured by Horiba, Ltd., and was found to be 160 Nm.

[0156] -Preparation of release agent particle dispersion- Paraffin wax: HNP-9 (manufactured by Nippon Seiro Co., Ltd.): 19 parts by weight Anionic surfactant: Neogen SC (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 1 part by mass Ion-exchanged water: 80 parts by weight The above ingredients were mixed in a heat-resistant container, heated to 90°C, and stirred for 30 minutes. The melt was then passed through a Gaulin homogenizer from the bottom of the container, and after three passes of circulation under a pressure of 5 MPa, the pressure was increased to 35 MPa and another three passes of circulation were performed. The resulting emulsion was cooled to 40°C or below in the heat-resistant solution, yielding a release agent particle dispersion. The volume average particle size was measured using a particle size analyzer LA-700 manufactured by Horiba, Ltd., and found to be 240 Nm.

[0157] -Resin particle dispersion- [Oil layer] Styrene (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 (Fujifilm Wako Pure Chemical Industries, Ltd.): 0.4 parts by mass

[0158] [Water layer 1] Ion-exchanged water: 17 parts by mass Anionic surfactant (Dowfax, manufactured by The Dow Chemical Company): 0.4 parts by mass

[0159] [Water layer 2] Ion-exchanged water: 40 parts by mass Anionic surfactant (Dowfax, manufactured by The Dow Chemical Company): 0.05 parts by mass Ammonium peroxodisulfate (Fujifilm Wako Pure Chemical Industries, Ltd.): 0.4 parts by mass

[0160] The oil layer components and aqueous layer 1 components were placed in a flask and mixed with stirring to form a monomer emulsion dispersion. The aqueous layer 2 components were placed in a reaction vessel, the atmosphere in the vessel was thoroughly purged with nitrogen, and the reaction system was heated in an oil bath with 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. After the dropwise addition was completed, polymerization was continued at 75°C and terminated after 3 hours. The volume average particle diameter D50v of the resulting resin particles was measured using a laser diffraction particle size analyzer LA-700 (Horiba, Ltd.) and found to be 250 Nm. The glass transition temperature of the resin was measured using a differential scanning calorimeter (DSC-50, Shimadzu Corporation) at a heating rate of 10°C / min and found to be 53°C. The number average molecular weight (polystyrene equivalent) was measured using a molecular weight analyzer (HLC-8020, Tosoh Corporation) and THF as the solvent and found to be 13,000. This resulted in a resin particle dispersion with a volume average particle diameter of 250 Nm, a solids content of 42%, a glass transition temperature of 52°C, and a number average molecular weight MN of 13,000.

[0161] -Preparation of Toner 1- Resin particle dispersion: 150 parts by mass Colorant 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 an Ultra Turrax manufactured by IKE Corporation, and then the flask was heated to 48°C while stirring in a heating oil bath. After maintaining at 48°C for 80 minutes, 70 parts by mass of the same resin particle dispersion liquid as above was slowly added thereto. The pH of the system was then adjusted to 6.0 using a 0.5 mol / L aqueous solution of sodium hydroxide. The stainless steel flask was then sealed, the stirring shaft was magnetically sealed, and the mixture was heated to 97°C and maintained at this temperature 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 ion-exchanged water, and then subjected to solid-liquid separation using Nutsche suction filtration. The mixture was then redispersed in 3,000 parts by weight of ion-exchanged water at 40°C, stirred and washed for 15 minutes at 300 rpm. This washing procedure was repeated five more times. When the filtrate reached a pH of 6.54 and an electrical conductivity of 6.5 μS / cm, it was subjected to solid-liquid separation using Nutsche suction filtration using No. 5A filter paper. Vacuum drying was then continued for 12 hours to obtain toner particles. The volume average particle diameter D50v of the toner particles was measured using a Coulter counter and found to be 6.2 μm, and the volume average particle size distribution index GSDv was 1.20. Shape observation using a Luzex image analyzer manufactured by Luzex Corporation revealed that the particle shape factor SF1 was 135 and that the particles were potato-shaped. The glass transition temperature of the toner was 52°C. Furthermore, silica (SiO2) particles with an average primary particle diameter of 40 nm that had been surface-hydrophobized with hexamethyldisilazane (hereinafter sometimes abbreviated as "HMDS") and metatitanic acid compound particles with an average primary particle diameter of 20 nm, which are the reaction product of metatitanic acid and isobutyltrimethoxysilane, were added to this toner so that the surface coverage of the toner particles was 40%, and the mixture was mixed using a Henschel mixer to produce Toner 1.

[0162] [Preparation of Coating Liquid 1] Lacquer (a solution of 20 parts of polycyclohexyl methacrylate (weight average molecular weight: 65,000, glass transition temperature: 105 ° C.) mixed with 80 parts of toluene): 100 parts Carbon black (average particle size 0.2 μm): 0.2 parts The above materials were charged into a sand mill and dispersed for 30 minutes, after which coating liquid 1 was obtained.

[0163] Example 1 Ferrite core (volume average particle size 35 μm): 100 parts Coating liquid 1: Amount that results in 3.0 parts of resin solid content per 100 parts of ferrite core The above components were charged into a batch-type agitator vacuum mixer (50 L kneader manufactured by Inoue Seisakusho Co., Ltd., with an agitator blade diameter D of 0.25 m and a clearance between the outer periphery of the blade and the inner wall of the casing of 3.5%), whose jacket temperature had been warmed to 90°C. The mixture was preheated to 70°C while being agitated and mixed at 60 rpm. The internal pressure of the mixer was then reduced to 5 kPa-a to dry the solvent. The agitator power in the mixer increased with drying and then decreased as drying was completed. When the agitator power had fallen to 1.3 times the agitator power before drying began, 20°C cold water was injected into the jacket. 45 minutes after the cold water was injected (i.e., when the agitator blade load power value after the start of solvent drying had fallen to 1.3 times the value before drying), agitation was stopped and the mixture was discharged from the mixer into a container to produce Carrier 1.

[0164] Example 2 Carrier 2 was produced in the same manner as in Example 1, except that when the stirring power in the mixer had decreased to 1.3 times or less the stirring power before the start of drying, cold water at 20°C was injected into the jacket, and stirring was stopped 30 minutes after the cold water was injected (= the point at which the load power value of the stirring blades had decreased to the value before drying after the start of drying the solvent), and the mixture was discharged from the mixer into a container.

[0165] Example 3 Carrier 3 was produced in the same manner as in Example 1, except that when the stirring power in the mixer had decreased to 1.3 times or less the stirring power before the start of drying, cold water at 20°C was injected into the jacket, and stirring was stopped 80 minutes after the cold water was injected (= the point at which the load power value of the stirring blades had decreased to the value before drying after the start of drying the solvent), and the mixture was discharged from the mixer into a container.

[0166] Example 4 Carrier 4 was produced in the same manner as in Example 1, except that when the stirring power in the mixer had decreased to 1.3 times or less the stirring power before drying began, the rotation speed was changed from 60 rpm to 20 rpm, cold water at 20°C was poured into the jacket, and stirring was stopped 65 minutes after the cold water was poured (= the point at which the load power value of the stirring blades had decreased to the value before drying after drying of the solvent began), and the mixture was discharged from the mixer into a container.

[0167] Example 5 Carrier 5 was produced in the same manner as in Example 1, except that when the stirring power in the mixer decreased to 1.3 times or less the stirring power before the start of drying, the rotation speed was changed from 60 rpm to 20 rpm, cold water at 20°C was injected into the jacket, and stirring was stopped 240 minutes after the cold water was injected (= the point at which the load power value of the stirring blade decreased to the value before drying after the start of drying the solvent), and the mixture was discharged from the mixer into a container.

[0168] Example 6 Carrier 6 was produced in the same manner as in Example 1, except that when the stirring power in the mixer had decreased to 1.3 times or less the stirring power before the start of drying, the rotation speed was changed from 60 rpm to 80 rpm, cold water at 20°C was poured into the jacket, and stirring was stopped 30 minutes after the cold water was poured (= the point at which the load power value of the stirring blades had decreased to the value before drying after the solvent started drying), and the mixture was discharged from the mixer into a container.

[0169] Example 7 Carrier 7 was produced in the same manner as in Example 1, except that when the stirring power in the mixer decreased to 1.3 times or less the stirring power before the start of drying, the rotation speed was changed from 60 rpm to 150 rpm, cold water at 20°C was injected into the jacket, and stirring was stopped 30 minutes after the cold water was injected (= the point at which the load power value of the stirring blade decreased to the value before drying after the start of drying the solvent), and the mixture was discharged from the mixer into a container.

[0170] Example 8 Carrier 8 was produced in the same manner as in Example 1, except that when the stirring power in the mixer (50 L kneader, stirring blade diameter D = 0.25 m, clearance / D between the outer periphery of the blade and the inner wall of the casing = 5.0%) decreased to 1.3 times or less the stirring power before the start of drying, cold water at 20°C was injected into the jacket while maintaining the rotation speed at 60 rpm, and stirring was stopped 45 minutes after the cold water was injected (= the time when the load power value of the stirring blade decreased to the value before drying after the start of drying the solvent), and the mixture was discharged from the mixer into a container.

[0171] Example 9 Carrier 9 was produced in the same manner as in Example 1, except that when the stirring power in the mixer (50 L kneader, stirring blade diameter D = 0.25 m, clearance / D between the outer periphery of the blade and the inner wall of the casing = 7.5%) decreased to 1.3 times or less the stirring power before the start of drying, cold water at 20°C was injected into the jacket while maintaining the rotation speed at 60 rpm, and stirring was stopped 45 minutes after the cold water was injected (= the time when the load power value of the stirring blade decreased to the value before drying after the start of drying the solvent), and the mixture was discharged from the mixer into a container.

[0172] Example 10 Carrier 2 prepared in Example 2 with a recovery temperature of 90°C was continuously fed into a fluidized bed cooler Slit Flow (manufactured by Okawara Manufacturing Co., Ltd.), and was fluidized with air at 20°C at a superficial velocity of 20 mm / s (twice the minimum fluidization velocity) for 115 minutes, and cooled to 70°C to produce carrier 10.

[0173] Example 11 As in Example 10, carrier 2 was continuously fed into a fluidized bed cooling device, slit flow, and fluidized with air at 20°C at a superficial velocity of 50 mm / s (five times the minimum fluidization velocity) for 100 minutes, and cooled to 70°C to produce carrier 11.

[0174] Example 12 As in Example 10, carrier 2 was continuously fed into a slit flow fluidized bed cooling device, and was fluidized with air at 20°C at a superficial velocity of 100 mm / s (10 times the minimum fluidization velocity) for 80 minutes, and cooled to 70°C to produce carrier 12.

[0175] Example 13 As in Example 10, Carrier 2 was continuously fed into a fluidized bed cooling device, Slit Flow, and fluidized with air at 20°C at a superficial velocity of 150 mm / s (15 times the minimum fluidization velocity) for 60 minutes, and cooled to 70°C to produce Carrier 13.

[0176] Example 14 Water at 20°C was circulated through the jacket of a paddle dryer NPD-1.5W-1 / 2L (manufactured by Nara Machinery Manufacturing Co., Ltd.), and 50 kg of carrier 2 with a recovery temperature of 90°C prepared in Example 2 was added, cooled at 45 rpm for 50 minutes, and cooled to 70°C to produce carrier 14.

[0177] Example 15 Ferrite core (volume average particle size 35 μm): 100 parts Coating liquid 1: Amount that results in 5.0 parts of resin solid content per 100 parts of ferrite core Carrier 15 was prepared in the same manner as in Example 1, except that the above components were changed.

[0178] Example 16 [Preparation of Coating Liquid 2] Lacquer (a solution of 20 parts of polycyclohexyl methacrylate (weight average molecular weight: 65,000, glass transition temperature: 105 ° C.) mixed with 80 parts of toluene): 100 parts Carbon black (average particle size 0.2 μm): 0.4 parts The above materials were charged into a sand mill and dispersed for 30 minutes, after which coating liquid 2 was obtained. A carrier 16 was produced in the same manner as in Example 1, except that the coating liquid 1 in Example 1 was changed to the coating liquid 2.

[0179] Example 17 Ferrite core (volume average particle size 25 μm): 100 parts Coating liquid 1: Amount that results in 3.0 parts of resin solid content per 100 parts of ferrite core Carrier 17 was produced in the same manner as in Example 1, except that the particle size of the ferrite core was changed to 25 μm.

[0180] Example 18 Carrier 18 was produced in the same manner as in Example 1, except that coating liquid 2 and the particle size of the ferrite core were changed to 25 μm.

[0181] (Comparative Example 1) Carrier 19 was produced in the same manner as in Example 1, except that when the stirring power in the mixer had decreased to 1.3 times or less the stirring power before drying began, the rotation speed was changed from 60 rpm to 10 rpm, cold water at 20°C was injected into the jacket, and stirring was stopped 100 minutes after the cold water was injected (= the point at which the load power value of the stirring blades had decreased to the value before drying after drying of the solvent began), and the mixture was discharged from the mixer into a container.

[0182] (Comparative Example 2) Carrier 20 was produced in the same manner as in Example 1, except that when the stirring power in the mixer decreased to 1.3 times or less the stirring power before drying began, the rotation speed was changed from 60 rpm to 10 rpm, cold water at 20°C was injected into the jacket, and stirring was stopped 300 minutes after the cold water was injected (= the point at which the load power value of the stirring blade decreased to the value before drying after drying of the solvent began), and the mixture was discharged from the mixer into a container.

[0183] (Comparative Example 3) Carrier 21 was produced in the same manner as in Example 1, except that when the stirring power in the mixer had decreased to 1.3 times or less the stirring power before drying began, cold water at 20°C was injected into the jacket, and stirring was stopped at 60 rpm 15 minutes after the cold water was injected (= the point at which the load power value of the stirring blades had decreased to the value before drying after drying of the solvent began), and the mixture was discharged from the mixer into a container.

[0184] Comparative Example 4 Carrier 22 was produced in the same manner as in Example 1, except that when the stirring power in the mixer had decreased to 1.3 times or less the stirring power before the start of drying, cold water at 20°C was injected into the jacket, and stirring was stopped at 60 rpm 90 minutes after the point at which the cold water was injected (= the point at which the load power value of the stirring blades had decreased to the value before drying after the start of drying the solvent), and the mixture was discharged from the mixer into a container.

[0185] (Comparative Example 5) Carrier 23 was produced in the same manner as in Example 1, except that when the stirring power in the mixer had decreased to 1.3 times or less the stirring power before drying began, the rotation speed was changed from 60 rpm to 175 rpm, cold water at 20°C was injected into the jacket, and stirring was stopped 10 minutes after the cold water was injected (= the point at which the load power value of the stirring blades had decreased to the value before drying after drying of the solvent began), and the mixture was discharged from the mixer into a container.

[0186] (Comparative Example 6) Carrier 24 was produced in the same manner as in Example 1, except that when the stirring power in the mixer had decreased to 1.3 times or less the stirring power before the start of drying, the rotation speed was changed from 60 rpm to 175 rpm, cold water at 20°C was poured into the jacket, and stirring was stopped 30 minutes after the cold water was poured (= the point at which the load power value of the stirring blades had decreased to the value before drying after the solvent started drying), and the mixture was discharged from the mixer into a container.

[0187] <Preparation of developer> Any one of Carriers 1 to 15 and Toner 1 were placed in a V blender at a mixing ratio of carrier:toner=100:10 (mass ratio) and stirred for 20 minutes to obtain Developers 1 to 15, respectively.

[0188] -Measurement of the coverage rate of the resin coating layer on the carrier- The coverage of the resin coating layer on the surface of the carrier was determined by X-ray photoelectron spectroscopy (XPS) using the following method. The target carrier and magnetic particles with the resin coating layer removed from the target carrier were prepared. The resin coating layer was removed from the carrier by dissolving the resin component with toluene. The carrier and the magnetic particles with the resin coating layer removed were each used as measurement samples, and the Fe, C, and O (atomic%) were quantified using XPS. The exposed percentage (%) of the magnetic particles was calculated by (Fe in the carrier) ÷ (Fe in the magnetic particles) × 100, and the coverage rate (%) of the resin coating layer was determined as (100 - exposed percentage of the magnetic particles).

[0189] -Measurement of free resin amount in carrier- A certain amount of carrier was weighed and dispersed in water, and the dispersion was filtered while the carrier was fixed with a magnet. The filter paper was dried, and the amount of free resin was calculated from the difference in mass before and after the filter paper and the weighed amount of carrier.

[0190] -Measurement of the percentage of aggregates in the carrier after sieving through a 75 μm sieve- The carrier was sieved using a sieve with 75 μm openings, and the sieved carrier was spread out so as not to overlap as much as possible. Scanning electron microscope (SEM) photographs were taken at 350x magnification, and the ratio of the number of carriers that had not been broken down to primary particles to the number of carriers in one field of view was measured.

[0191] -Evaluation of color dullness suppression- The evaluation of color dullness was carried out as follows. Using the 700 Digital Color Press (manufactured by Fuji Xerox Co., Ltd.) filled with the obtained developer, one 5 cm x 5 cm solid image patch was output (Sample 1), and after outputting 100,000 images with an area coverage of 5%, one 5 cm x 5 cm solid image patch was output again (Sample 2). Then, the color gamuts (L * , a * , b * The color gamut was measured using an image densitometer X-RITE938 (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 this was used as an index for evaluating color dullness. ΔE=〔(ΔL * ) 2 +(Δa * ) 2 +(Δb * ) 2 〕 1 / 2 Here, ΔL * =(Sample 2 L * -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: -Evaluation criteria- G1:ΔE≦3.0 G2:3.0<ΔE≦6.0 G3:6.0<ΔE≦10 G4:10<ΔE

[0192] The evaluation results are shown in Tables 1 and 2.

[0193] [Table 1]

[0194] [Table 2]

[0195] From the above results, it can be seen that the present example is superior to the comparative example in suppressing dullness of the obtained image. [Explanation of symbols]

[0196] 1Y, 1M, 1C, 1K Photoconductor (an example of an image carrier) 2Y, 2M, 2C, 2K Charging roll (an example of charging means) 3. Exposure device (an example of an electrostatic image forming means) 3Y, 3M, 3C, 3K laser beam 4Y, 4M, 4C, 4K developing device (an example of developing means) 5Y, 5M, 5C, 5K Primary transfer roll (an example of a primary transfer means) 6Y, 6M, 6C, 6K: Photoconductor cleaning device (an example of a cleaning means) 8Y, 8M, 8C, 8K toner cartridges 10Y, 10M, 10C, 10K image forming units 20 Intermediate transfer belt (an example of an intermediate transfer body) 22 Drive Roll 24 Support Roll 26 Secondary transfer roll (an example of a secondary transfer means) 28 Fixing device (an example of fixing means) 30 Intermediate transfer body cleaning device P Recording paper (an example of a recording medium) 107 Photoconductor (an example of an image carrier) 108 Charging roll (an example of charging means) 109 Exposure device (an example of electrostatic image forming means) 111 Developing device (an example of developing means) 112 Transfer device (an example of transfer means) 113 Photosensitive drum cleaning device (an example of cleaning means) 115 Fixing device (an example of fixing means) 116 Mounting Rail 117 Cabinet 118 Exposure opening 200 Process Cartridge 300 Recording paper (an example of a recording medium)

Claims

1. a coating step of adding a coating liquid containing a resin and a solvent and magnetic particles to a mixer having an agitating blade to form a resin coating layer on the surface of the magnetic particles, and then removing the carrier having the resin coating layer from the mixer; In the coating step, stirring conditions from the time when the solvent is evaporated by heating in the mixer and the mixture is dried to the time when the mixture is removed from the mixer satisfy the conditions of the following formula 1 and the following formula 2, The mixer has an agitator blade, The shape of the stirring blade is a Banbury type, a sigma type, a Z type, a spiral type, or a fishtail type, The rotation speed N of the stirring blade is 10 rpm or more and 200 rpm or less, The clearance between the stirring vessel and the stirring blade in the mixer satisfies the condition of the following formula 3, The load power value of the stirring blade increases as the drying of the solvent progresses, and the time T from the point at which the drying is completed and the load power value has decreased to 1.3 times or less the value before drying to the point at which stirring in the mixer is completed is 5 minutes or more and 280 minutes or less. A method for producing a carrier for developing electrostatic images. 0.2≦the peripheral speed πDN (m / s) of the stirring blade≦2.0 Formula 1 1 x 10 ３ ≦Mixing work load (peripheral speed×mixing time T)≦4×10 ３ Formula 2 In Equation 1 and Equation 2, D represents the diameter (m) of the stirring blade, N represents the rotation speed (rps) of the stirring blade, and T represents the time (s) from the point at which the load power value of the stirring blade before drying of the solvent increases as drying progresses and the previous load power value decreases to 1.3 times or less the value before drying after drying is completed, to the point at which stirring in the mixer is completed. Clearance / Agitator impeller diameter≦5% Formula 3

2. 2. The method for producing a carrier for developing electrostatic images according to claim 1, further comprising, continuously after the coating step, a cooling step of cooling the carrier in a fluidized bed apparatus to a glass transition temperature (Tg) of the resin contained in the resin coating layer −20° C. or lower.

3. 3. The method for producing a carrier for developing an electrostatic image according to claim 2, wherein the superficial velocity v (m / s) of the fluidizing gas during cooling in the cooling step is from 2 to 10 times the minimum fluidizing velocity Umf.

4. 4. The method for producing a carrier for developing an electrostatic image according to claim 1, wherein the mixer is a batch type vacuum mixer.

5. 5. The method for producing an electrostatic image developing carrier according to claim 1, wherein the amount of free resin contained in the resulting electrostatic image developing carrier is 200 ppm or less.

6. 6. The method for producing an electrostatic image developing carrier according to claim 5, wherein the amount of free resin contained in the resulting electrostatic image developing carrier is 100 ppm or less.

7. A method for producing an electrostatic image developer, comprising the method for producing the electrostatic image developing carrier according to any one of claims 1 to 6.

8. 7. An image forming method using an electrostatic image developing carrier produced by the method for producing an electrostatic image developing carrier according to claim 1.

Images