Carrier for electrostatic latent image developer, two-component developer, image forming apparatus, process cartridge, and image forming method

Abstract

To provide a carrier for electrostatic latent image developer that can maintain electrification stability, resistance stability, and high image quality for a long period.SOLUTION: A carrier for electrostatic latent image developer has a core material particle and a coating layer coating the core material particle. The coating layer includes electrified fine particles in a flat shape. The apparent density of the carrier is 2.0 g / cm3 or more and 2.5 g / cm3 or less. The internal porosity of the core material particle is 0.0% or more and 2.0% or less. The flat shape of the electrified fine particles is such that the ratio of the major axis R1 nm to the thickness R2 nm satisfies the relationship of 1.0≤R1 / R2≤3.0.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[0002] In recent years, electrophotographic image formation methods have come to require high image quality on a par with that of printed images, and various improvements and developments have been made to meet this demand. Among these, maintaining high image quality over a long period of time has been an issue, and improvements have been made to toner, carrier, and developing means. Regarding the carrier, for example, in order to produce a toner with little change in carrier resistance value and little spent, a carrier for electrostatic latent image developer has been proposed in which, when viewed in cross section of the carrier, the shape factor SF2 of the core particles is in the range of 120 to 160, the area ratio of the filler is 30 to 85% of the entire resin coating layer, and the ratio of the average domain diameter of the core particles to the number-average particle diameter of the filler is in the range of 1:1 to 1:0.003 (see Patent Document 1).

[0003] Furthermore, as a carrier that can ensure durability while maintaining image quality over time, a carrier for electrostatic latent image developers has been proposed that consists of magnetic core particles and a resin layer covering the surface of the core particles, with conductive fine particles contained in the resin layer, wherein the conductive fine particles are conductive fine particles formed by coating a white inorganic pigment with phosphorus-doped tin or tungsten-doped tin as a conductive material, and the ratio of the phosphorus or tungsten doped to the tin in the conductive material is 0.010 to 0.100 (see Patent Document 2).

[0004] Furthermore, in order to suppress an increase in fluidity even when the toner concentration in the developing means decreases, a carrier for developing electrostatic images has been proposed, which includes, as carrier particles, single particles each having a core material and a coating layer covering the core material, and associated particles in which two or more single particles are bound together via the coating layer, wherein the average particle size D1 of the single particles is smaller than the average particle size D2 of the associated particles, and the ratio of the number of associated particles N2 to the sum of the number of particles N1 of the single particles and the number of particles N2 of the associated particles is 5% or more by number (see Patent Document 3). Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present invention is to provide a carrier for an electrostatic latent image developer that can maintain charge stability, resistance stability, and high image quality for a long period of time. [Means for solving the problem]

[0006] The above problem is solved by the following configuration 1). 1) A carrier for an electrostatic latent image developer having core particles and a coating layer that coats the core particles, the coating layer contains flat-shaped electrostatically charged fine particles, the electrostatically charged fine particles are contained in an amount of 10 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the resin contained in the coating layer, and the conductive fine particles are contained in an amount of 10 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the resin contained in the coating layer; The apparent density of the carrier is 2.0 [g / cm 3 ] or more than 2.5[g / cm 3 ] or less, The internal porosity of the core particles is 0.0% or more and 2.0% or less, and The carrier for electrostatic latent image developer is characterized in that the flat shape of the chargeable fine particles has a ratio of a major axis R1 [nm] to a thickness R2 [nm] that satisfies the relationship of the following formula 1. 1.2 ≦R1 / R2≦3.0 Formula 1 [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a carrier for an electrostatic latent image developer that can maintain charge stability, resistance stability, and high image quality for a long period of time. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram showing an example of a cell for measuring volume resistivity. [Figure 2] FIG. 2 is a schematic view illustrating an example of a process cartridge of the present invention. [Figure 3] 1A and 1B are diagrams illustrating the flat shape of charged fine particles in the present invention. [Figure 4] FIG. 10 is a diagram for explaining a vertical band chart employed in the examples. [Figure 5] 1 is a schematic diagram illustrating an example of an image forming apparatus of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the embodiments of the present invention will be described in more detail. The carrier for an electrostatic latent image developer of the present invention has core particles and a coating layer that coats the core particles, the coating layer containing flat-shaped chargeable fine particles, and an apparent density of the carrier of 2.0 [g / cm 3 ] or more than 2.5[g / cm 3 ] or less, the internal porosity of the core particles is 0.0% or more and 2.0% or less, and the flat shape of the charged microparticles is characterized in that the ratio of the major axis R1 [nm] to the thickness R2 [nm] satisfies the relationship of the following formula 1. 1.0≦R1 / R2≦3.0 Equation 1

[0010] After extensive research, the inventors discovered that specifying the apparent density of the carrier for electrostatic latent image developer, the internal porosity of the core particles, and the flat shape of the chargeable fine particles are important for maintaining long-term charge and resistance stability. This is believed to be because the specific flat shape of the chargeable fine particles in the coating layer, which affects charge, prevents the chargeable fine particles from detaching over time, thereby maintaining charge and resistance over a long period of time. This effect is particularly pronounced when the surface roughness Rz of the core particles, as described below, is 2.0 μm or greater but less than 3.0 μm. In this configuration, the chargeable fine particles in the coating layer near the core protrusions cover the core protrusions, further preventing the chargeable fine particles from detaching over time, thereby maintaining charge and resistance over a long period of time. Furthermore, it was unexpectedly found that the use of the carrier for electrostatic latent image developer of the present invention (hereinafter sometimes referred to as the carrier of the present invention) improves the phenomenon of ghost images, which are differences in print density within an image. Although the exact mechanism is not clear, it is thought that the fact that the charged fine particles are less likely to separate from the coating layer of the carrier suppresses the contamination of the developing sleeve, which is the cause of ghost images. Therefore, the carrier of the present invention can maintain charge stability, resistance stability, and high image quality for a long period of time.

[0011] <Coating layer> The coating layer contains flat, chargeable fine particles, and preferably contains a resin, and may further contain other components as required.

[0012] -resin- The resin can be a silicone resin, an acrylic resin, or a combination of these. Silicone resins or a combination of silicone and acrylic resins are preferred. Acrylic resins have strong adhesion and low brittleness, resulting in excellent abrasion resistance. However, due to their high surface energy, when combined with toners that are prone to toner waste, problems such as a decrease in charge due to the accumulation of spent toner components can occur. In this case, this problem can be solved by using a silicone resin, which has low surface energy and therefore is less prone to toner waste and less likely to accumulate spent components that would otherwise cause the coating layer to wear away. However, silicone resins have poor adhesion and high brittleness, resulting in poor abrasion resistance. Therefore, it is important to balance the properties of these two resins, which allows for the production of a coating layer that is both less prone to toner waste and more abrasion-resistant. This is because silicone resins have low surface energy and therefore are less prone to toner waste and less likely to accumulate spent components that would otherwise cause the coating layer to wear away.

[0013] The silicone resin referred to in this specification refers to all commonly known silicone resins, including straight silicones consisting only of organosiloxane bonds, and silicone resins modified with alkyd, polyester, epoxy, acrylic, urethane, etc. Commercially available silicone resins can be used. Examples of commercially available straight silicone resins include KR271, KR255, and KR152 manufactured by Shin-Etsu Chemical Co., Ltd., and SR2400, SR2406, and SR2410 manufactured by Toray Dow Corning Silicone Co., Ltd. In this case, the silicone resin can be used alone, or other crosslinkable components, charge-adjusting components, etc. can also be used simultaneously. Further, examples of modified silicone resins include KR206 (alkyd-modified), KR5208 (acrylic-modified), ES1001N (epoxy-modified), and KR305 (urethane-modified) manufactured by Shin-Etsu Chemical Co., Ltd., and SR2115 (epoxy-modified) and SR2110 (alkyd-modified) manufactured by Toray Dow Corning Silicone Co., Ltd.

[0014] As used herein, acrylic resin refers to any resin containing an acrylic component and is not particularly limited. Acrylic resins can be used alone, but they can also be used in combination with at least one other component that undergoes a crosslinking reaction. Examples of other components that undergo a crosslinking reaction include, but are not limited to, amino resins and acid catalysts. Amino resins include, but are not limited to, guanamine and melamine resins. Acid catalysts can include any catalysts that have catalytic properties. Examples include, but are not limited to, fully alkylated, methylol, imino, and methylol / imino reactive groups. Furthermore, the coating layer more preferably contains a crosslinked product of an acrylic resin and an amino resin. This makes it possible to prevent the coating layers from fusing together while maintaining appropriate elasticity. The amino resin is not particularly limited, but melamine resin and benzoguanamine resin are preferred because they can improve the charge-imparting ability of the carrier. Furthermore, when it is necessary to appropriately control the charge-imparting ability of the carrier, the melamine resin and / or benzoguanamine resin may be used in combination with other amino resins. The acrylic resin capable of crosslinking with the amino resin preferably has a hydroxyl group and / or a carboxyl group, more preferably a hydroxyl group. This can further improve adhesion to the core particles and the chargeable fine particles, and can also improve the dispersion stability of the chargeable fine particles. In this case, the acrylic resin preferably has a hydroxyl value of 10 mgKOH / g or more, more preferably 20 mgKOH / g or more.

[0015] The resin may be an acrylic copolymer composed of the following monomer components A, B, and C. When such an acrylic copolymer is used, the coating layer is extremely strong and resistant to abrasion, and high durability can be achieved. Even if the coating layer is thin, the core particles are unlikely to become exposed during use.

[0016] [Chemistry]

[0017] [Chemistry]

[0018] [Chemistry]

[0019] In the general formulas (1) to (3) above, R 1 , m, R 2 , R 3 , X, Y, and Z represent the following. R 1 represents a hydrogen atom or a methyl group. m represents an integer from ₁ to ₈. Therefore, (CH₂) m represents an alkylene group such as a methylene group, ethylene group, propylene group, or butylene group having ₁ to ₈ carbon atoms. R 2 represents an alkyl group such as a methyl group, ethyl group, propyl group, isopropyl group, or butyl group having ₁ to ₄ carbon atoms. R 3 represents an alkyl group such as a methyl group, ethyl group, propyl group, isopropyl group, or butyl group having ₁ to ₈ carbon atoms, or an alkoxy group such as a methoxy group, ethoxy group, propoxy group, or butoxy group having ₁ to ₄ carbon atoms. X = 10 mol% to 40 mol%, Y = 10 mol% to 40 mol%, Z = 30 mol% to 80 mol%, and it is preferable that 60 mol% < Y + Z < 90 mol%.

[0020] Component A, represented by general formula (1), has the atomic group tris(trimethylsiloxy)silane, which has many methyl groups in its side chain. As the ratio of component A to the total resin increases, the surface energy decreases, reducing adhesion of the toner's resin and wax components. A content of component A of 10 mol % or more provides sufficient effectiveness, preventing a sudden increase in adhesion of toner components. Furthermore, a content of 40 mol % or less prevents problems such as insufficient crosslinking, insufficient toughness, and reduced adhesion between the core material and the coating layer, resulting in poor durability of the carrier coating. R 2 is an alkyl group having 1 to 4 carbon atoms, and examples of such component A include tris(trialkylsiloxy)silane compounds represented by the following formula: In the formula below, Me is a methyl group, Et is an ethyl group, and Pr is a propyl group. CH2=CMe-COO-C3H6-Si(OSiMe3)3 CH2=CH-COO-C3H6-Si(OSiMe3)3 CH2=CMe-COO-C4H8-Si(OSiMe3)3 CH2=CMe-COO-C3H6-Si(OSiEt3)3 CH2=CH-COO-C3H6-Si(OSiEt3)3CH2=CMe-COO-C4H8-Si(OSiEt3)3CH2=CMe-COO-C3H6-Si(OSiPr3)3CH2=CH-COO-C3H6-Si(OSiPr3)3CH2=CMe-COO-C4H8-Si(OSiPr3)3

[0021] The component B represented by the general formula (2) is a radically polymerizable bifunctional (R 3 is an alkyl group), or trifunctional (R 3The silane compound is a compound of the formula (B) (in the case of an alkoxy group), and if the component B is 10 mol % or more, sufficient toughness can be obtained. On the other hand, if the component B is 40 mol % or less, the coating becomes hard and brittle, preventing the problem of film abrasion. It also prevents deterioration of environmental properties. This is because if a large number of hydrolyzed crosslinking components remain as silanol groups, it is thought that this could worsen environmental properties (humidity dependency). Examples of the component B include 3-methacryloxypropyltrimethoxysilane, 3-acryloxypropyltrimethoxysilane, 3-methacryloxypropyltriethoxysilane, 3-acryloxypropyltriethoxysilane, 3-methacryloxypropylmethyldimethoxysilane, 3-methacryloxypropylmethyldiethoxysilane, 3-methacryloxypropyltri(isopropoxy)silane, 3-acryloxypropyltri(isopropoxy)silane, etc. These may be used alone or in combination of two or more.

[0022] The component C represented by the general formula (3) imparts flexibility to the coating layer and improves the adhesion between the core particles and the coating layer. If the component C is 30 mol % or more, sufficient adhesion is obtained, and if it is 80 mol % or less, it is possible to prevent either the component A or the component B from becoming 10 mol % or less, and it is possible to achieve both water repellency, hardness, and flexibility (film abrasion) of the carrier coating. The acrylic compound (monomer) of the component C is preferably, for example, an acrylic acid ester or a methacrylic acid ester, and specific examples thereof include methyl methacrylate, methyl acrylate, ethyl methacrylate, ethyl acrylate, butyl methacrylate, butyl acrylate, 2-(dimethylamino)ethyl methacrylate, 2-(dimethylamino)ethyl acrylate, 3-(dimethylamino)propyl methacrylate, and 3-(dimethylamino)propyl acrylate. These may be used alone or in combination of two or more. Among these, alkyl methacrylate is preferred, and methyl methacrylate is more preferred.

[0023] In a preferred embodiment, the acrylic copolymer obtained by radical copolymerization of the above-mentioned monomer A component, the above-mentioned monomer B component, and the above-mentioned monomer C component is hydrolyzed to generate silanol groups, and the crosslinked product obtained by condensing the crosslinked product using a catalyst is coated on core particles, and then heat-treated to form a coating layer.Examples of catalysts used in this condensation polymerization include titanium-based catalysts, tin-based catalysts, zirconium-based catalysts, and aluminum-based catalysts. Among these, titanium-based catalysts are preferred. Titanium diisopropoxybis(ethylacetoacetate) is particularly preferred as the titanium-based catalyst. This is thought to be because it has a significant effect of promoting the condensation reaction of silanol groups and the catalyst is less likely to be deactivated.

[0024] -Charged fine particles- In the present invention, flat charged fine particles are used. To maintain charging function over a long period of time, it is important that the charged fine particles in the coating layer of the carrier do not come off even when subjected to stress from within the developing machine over time. For this reason, it is important that the flat shape of the charged fine particles has a ratio of the major axis R1 [nm] to the thickness R2 [nm] satisfying the relationship of the following formula 1, and preferably the relationship of the following formula 10. 1.0≦R1 / R2≦3.0 Equation 1 1.2≦R1 / R2≦2.0 Equation 10 By setting R1 / R2 within the specified range, the charged particles will have a moderately elongated particle shape, making them less likely to fall off even when subjected to stress over time in the coating layer. If R1 / R2 is less than 1, the charged particles will have a shape that makes them more likely to fall off over time. On the other hand, if R1 / R2 is greater than 3.0, the edges of the charged particles will protrude from the coating layer as protrusions, and these protrusions will collide with each other over time, causing the coating layer to wear away.

[0025] Fig. 3 is a diagram illustrating the flat shape of the charged fine particles of the present invention. In Fig. 3, (a) is a plan view of the charged fine particles P, and (b) is a side view of the charged fine particles P. The flat shape referred to in the present invention means that the charged fine particles P have a major axis R1 and a minor axis R10 in the plan view (a), and as shown in (b), the thickness R2 is shorter than the major axis R1 and the minor axis R10. The major axis R1 refers to the maximum diameter in the area where the projected area of ​​the charged fine particles P is greatest (= "maximum projected area"), and the thickness R2 refers to the longest point on the perpendicular line drawn from the major axis R1 to the maximum projected area. R1 and R2 in the flat shape are measured by the method described in the Examples.

[0026] Furthermore, the chargeable fine particles should be relatively large to provide the carrier with charging functionality, and the major axis R1 is preferably 300 nm or more and 600 nm or less. It is more preferably 400 nm or more and 500 nm or less. By having R1 of 300 nm or more, sufficient charging properties can be achieved. On the other hand, by having R1 of 600 nm or less, separation of the chargeable fine particles from the coating layer can be further prevented.

[0027] The amount of chargeable fine particles added to the coating layer is preferably 10 to 25 parts by weight per 100 parts by weight of the resin contained in the coating layer, and more preferably 15 to 20 parts by weight per 100 parts by weight of the resin. By adding 10 parts by weight or more, the charging ability and strength of the coating layer are further improved. On the other hand, by adding 25 parts by weight or less, the chargeable fine particles are properly exposed on the carrier surface, the carrier is less susceptible to spent external additives, and charge retention is improved.

[0028] Examples of chargeable fine particles include titanium oxide, tin oxide, zinc oxide, alumina, barium sulfate, magnesium oxide, magnesium hydroxide, and hydrotalcite. These may be used alone or in combination of two or more. Among these, barium sulfate is preferred from the viewpoint of maintaining chargeability for a long period of time. The charged fine particles used in the present invention may be commercially available, for example, barium sulfate BF-10 manufactured by Sakai Chemical Industry Co., Ltd.

[0029] --Conductive particles-- Conductive particles may be used to adjust the resistance of the carrier. In terms of durability, conductive particles made of inorganic pigments coated with a conductive material are preferred. Conductive materials include indium-doped tin oxide, tungsten-doped tin oxide, phosphorus-doped tin oxide, niobium-doped tin oxide, tantalum-doped tin oxide, antimony-doped tin oxide, and fluorine-doped tin oxide. Considering overall productivity, safety, cost, and other factors, tungsten-doped tin oxide or tungsten-doped tin oxide is preferred. As the inorganic pigment that serves as the base particle of the fine particles, any of commercially available titanium dioxide, aluminum oxide, silicon dioxide, zinc oxide, barium sulfate, zirconium oxide, alkali metal titanate, muscovite, etc. To explain in more detail using titanium dioxide as an example, there is no limitation on the particle size, and shapes such as spherical and acicular shapes, as well as anatase, rutile, and amorphous crystal forms, can be used. The secondary particle size of the conductive fine particles is preferably 0.20 μm or more and 0.80 μm or less, and more preferably 0.30 μm or more and 0.60 μm or less. The secondary particle size of the conductive fine particles can be measured using a dynamic light scattering particle size distribution analyzer.

[0030] The amount of conductive fine particles added to the coating layer is preferably 10 to 25 parts by mass, more preferably 15 to 20 parts by mass, per 100 parts by mass of the resin contained in the coating layer. When the amount is 10 parts by mass or more, the effect of lowering the carrier resistance is sufficiently achieved, while when the amount is 25 parts by mass or less, the exposure of the conductive fine particles on the carrier surface is suppressed, making it difficult for the toner to be spent with external additives, and enabling the resistance to be maintained.

[0031] Conductive fine particles can be produced by various methods, for example, by uniformly depositing a tin salt hydrate layer containing a hydrate of a phosphorus or tungsten salt on the surface of inorganic pigment particles and then firing the resulting coating layer. To uniformly deposit a tin salt hydrate layer containing a hydrate of a phosphorus or tungsten salt on the surface of inorganic pigment particles, for example, an acidic aqueous solution containing dissolved therein a phosphorus salt (e.g., phosphorus pentoxide or POCl3, etc.) or a tungsten salt (e.g., tungsten chloride, tungsten oxychloride, sodium tungstate, tungstic acid, etc.), and a tin salt (e.g., tin salts such as tin chloride, tin sulfate, and tin nitrate, stannates such as sodium stannate and potassium stannate, and organic tin compounds such as tin alkoxides) is added dropwise to a solution containing phosphorus or tungsten and tin in the form of hydrates, which are then precipitated and deposited on the surface of the pigment particles. This can be accomplished by simultaneously dripping a pH adjuster (e.g., an aqueous base) into an aqueous solution in which inorganic pigment particles have been dispersed, preventing dissolution or surface alteration of the inorganic pigment particles due to acid or alkali, and by adjusting the amounts of phosphorus or tungsten and tin chloride solution added, the doping ratio of phosphorus or tungsten on the inorganic pigment particle surface can be adjusted (however, it is important to note that the isoelectric point of tin hydrate, i.e., tin hydroxide or stannic acid, is not necessarily the same as the isoelectric point of the phosphorus or tungsten component, and that there is a difference in their solubilities at a specific pH). Furthermore, a water-soluble organic solvent, such as methanol or methyl ethyl ketone, can be mixed in order to mitigate attack on inorganic pigment particles during the dripping operation and the aggressive hydration reaction of phosphorus or tungsten and tin, thereby homogenizing the coating layer. The obtained hydrate can be preferably fired at 300 to 850°C in a non-oxidizing atmosphere, which makes it possible to keep the volume resistivity of the powder very low compared to that of a powder that has been heat-treated in air. The conductive fine particles may be subjected to a surface treatment. By performing such a treatment, the upper conductive layer can be uniformly and firmly fixed to the particle surface, thereby enabling the resistance adjustment effect to be fully exerted. Amino-based silane coupling agents, methacryloxy-based silane coupling agents, vinyl-based silane coupling agents, and mercapto-based silane coupling agents can be used.

[0032] -Other ingredients- The other components are not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include a silane coupling agent.

[0033] --Silane coupling agent-- The silane coupling agent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane, r-chloropropyltrimethoxysilane, hexamethyldisilazane, r-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, r-chloropropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, allyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, dimethyldiethoxysilane, 1,3-divinyltetramethyldisilazane, and methacryloxyethyldimethyl(3-trimethoxysilylpropyl)ammonium chloride. These may be used alone or in combination of two or more. As the silane coupling agent, commercially available products can be used, such as AY43-059, SR6020, SZ6023, SH6026, SZ6032, SZ6050, AY43-310M, SZ6030, SH6040, AY43-026, AY43-031, sh6062, Z-6911, sz6300, sz6075, sz6079, sz6083, sz6070, sz6072, Z-6721, AY43-004, and Z-6187. , AY43-021, AY43-043, AY43-040, AY43-047, Z-6265, AY43-204M, AY43-048, Z-6403, AY43-206M, AY43-206E, Z6341, AY43-210MC, AY43-083, AY43-101, AY43-013, AY43-158E, Z-6920, Z-6940 (manufactured by Toray Silicone Co., Ltd.), and the like. The content of the silane coupling agent is preferably 0.1% by mass or more and 10% by mass or less relative to 100 parts by mass of the resin contained in the coating layer. If the content of the silane coupling agent is less than 0.1% by mass, the adhesion between the core particles or conductive fine particles and the silicone resin may decrease, causing the coating layer to fall off during long-term use. If the content of the silane coupling agent is more than 10% by mass, toner filming may occur during long-term use.

[0034] <Core particles> The core particles are not particularly limited as long as they are magnetic, and examples thereof include ferromagnetic metals such as iron and cobalt; iron oxides such as magnetite, hematite, and ferrite; various alloys and compounds; and resin particles in which these magnetic materials are dispersed in resin. Among these, Mn-based ferrite, Mn-Mg-based ferrite, and Mn-Mg-Sr ferrite are preferred from the viewpoint of environmental friendliness.

[0035] It is important to set a range for the internal porosity of core particles, and it is also preferable to set a range for the surface roughness Rz. Internal porosity represents the ratio of the sum of the areas of internal voids to the total area of ​​the cross section of a core particle. The smaller the value, the fewer internal voids there are, and the more dense the core particle. Such dense core particles can increase magnetization, which is desirable from the perspective of suppressing carrier adhesion. An internal porosity of 0.0% or more and 2.0% or less is preferable. If the internal porosity exceeds 2.0%, the magnetization of the core particles will decrease due to the large number of internal voids, resulting in poor carrier adhesion. Internal porosity can be calculated, for example, by analyzing SEM images of the core particle cross section.

[0036] On the other hand, surface roughness Rz refers to the maximum height roughness. A reference length is cut from the roughness curve in the direction of the mean line. The distance between the peak and valley lines of this cut section is measured in the longitudinal direction of the roughness curve, and this value is expressed in micrometers (μm). A high Rz value results in significant surface irregularities, which also affects the packing of core particles. Rz is preferably 2.0 μm or more but less than 3.0 μm, and more preferably 2.3 μm or more but less than 2.7 μm. By specifying the Rz of the core particles, the appropriate packing can be maintained even after conversion into a carrier, improving image quality. An Rz of 2.0 μm or more ensures the core particles have adequate surface smoothness and packing, suppressing the apparent density when converted into a carrier and preventing image quality degradation such as ghost images. On the other hand, by keeping Rz less than 3.0 μm, the degree of surface roughness of the core particle becomes appropriate, and the convex parts of the core particle can be well covered with a resin layer during carrier formation, preventing solid carrier adhesion. Rz can be calculated from surface observation data using a confocal microscope.

[0037] <Carrier manufacturing method> The carrier can be produced, for example, by dissolving the resin or the like in a solvent to prepare a coating solution, then uniformly coating the coating solution on the surfaces of the core particles by a known coating method, drying, and then baking. Examples of the coating method include a dipping method, a spraying method, and a brush coating method. The solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples of the solvent include toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, cellosolve, and butyl acetate. The baking method is not particularly limited and can be appropriately selected depending on the purpose. For example, it may be an external heating method or an internal heating method. The baking equipment is not particularly limited and can be appropriately selected depending on the purpose. Examples include a fixed type electric furnace, a fluidized type electric furnace, a rotary type electric furnace, a burner furnace, and an apparatus equipped with a microwave.

[0038] The average thickness of the coating layer is preferably 0.50 μm or more and 1.10 μm or less, and more preferably 0.60 μm or more and 1.00 μm or less. Having an average thickness of 0.50 μm or more prevents the film from being scraped off due to collisions between carrier particles over time. Having an average thickness of 1.10 μm or less suppresses the migration of external toner additives to the carrier surface over time, thereby maintaining the carrier's charging ability. The average thickness of the coating layer can be calculated, for example, by image measurement of a cross-sectional SEM image. In the coating layer of the present invention, the chargeable fine particles tend to be aligned in a direction parallel to the plane of the core particles, and it is presumed that this configuration is advantageous for achieving the effects of the present invention.

[0039] <Career characteristics> The apparent density of the carrier of the present invention is 2.0 [g / cm 3 ] or more than 2.5[g / cm 3 ] or less, and 2.1 [g / cm 3 ] or more than 2.4[g / cm 3It is more preferable that the apparent density is 2.0 [g / cm 3 ] or less. The apparent density affects the degree of spent toner that the carrier receives from the external additives of the toner when the carrier and the toner are rubbed in the developing machine. 3 On the other hand, if the apparent density is less than 2.5 [g / cm 3 ], the carrier is light and scattering of the carrier is likely to occur. 3 If the apparent density is greater than [0.01], the external additives will be spent and the carrier will not be able to maintain its charging ability for a long period of time. The apparent density of the carrier can be measured by the method described in JIS Z 2504, for example.

[0040] Furthermore, the carrier of the present invention preferably has a volume resistivity of 10 Log Ω·cm or more and 14 Log Ω·cm or less. A volume resistivity of 10 Log Ω·cm or more prevents carrier adhesion in non-image areas, and a volume resistivity of 14 Log Ω·cm or less brings the edge effect to an acceptable level.

[0041] The volume resistivity of the carrier can be measured using the cell shown in Figure 1. Specifically, a cell consisting of a fluororesin container 2 containing electrodes 1a and 1b, each with a surface area of ​​2.5 cm x 4 cm, spaced 0.2 cm apart, is filled with carrier 3, and the cell is subjected to 10 taps at a drop height of 1 cm and a tapping speed of 30 taps per minute. Next, a DC voltage of 1,000 V is applied between electrodes 1a and 1b, and the resistance value r [Ω] after 30 seconds is measured using a High Resistance Meter 4329A (manufactured by Yokogawa Hewlett-Packard Co., Ltd.). The volume resistivity [Ω·cm] can then be calculated using the following formula:

[0042]

number

[0043] The volume resistivity (Log Ω·cm) of the carrier is the common logarithm of the volume resistivity [Ω·cm] obtained by the above measurement.

[0044] (two-component developer) The two-component developer of the present invention comprises the carrier and toner of the present invention. The mixing ratio of the toner and carrier in the two-component developer is preferably 2.0 to 12.0 parts by mass of the toner, more preferably 2.5 to 10.0 parts by mass, per 100 parts by mass of the carrier.

[0045] <Toner> The toner contains a binder resin and a colorant, and may be either a monochrome toner or a color toner. Furthermore, the toner may contain a release agent so as to be applicable to an oil-less system in which oil for preventing toner adhesion is not applied to the fixing roller. While such toners are generally prone to filming, the carrier of the present invention can suppress filming, allowing the developer of the present invention to maintain good quality over a long period of time. Furthermore, color toners, particularly yellow toners, generally have the problem of color staining due to scraping of the carrier coating layer, but the developer of the present invention can suppress the occurrence of color staining.

[0046] The toner can be produced by known methods such as a pulverization method or a polymerization method. For example, when producing the toner by a pulverization method, first, a molten mixture obtained by kneading toner materials is cooled, and then pulverized and classified to produce base particles. Next, in order to further improve transferability and durability, an external additive is added to the base particles to produce the toner.

[0047] In this case, the device for kneading the toner materials is not particularly limited and can be appropriately selected depending on the purpose. Examples include batch-type two-roll mixers; Banbury mixers; continuous twin-screw extruders such as a KTK type twin-screw extruder (manufactured by Kobe Steel, Ltd.), a TEM type twin-screw extruder (manufactured by Toshiba Machine Co., Ltd.), a twin-screw extruder (manufactured by KCK Corporation), a PCM type twin-screw extruder (manufactured by Ikegai Corporation), and a KEX type twin-screw extruder (manufactured by Kurimoto Iron Works, Ltd.); and continuous single-screw kneaders such as a Ko-Kneader (manufactured by Buss). Furthermore, when pulverizing the cooled molten kneaded product, it can be roughly pulverized using a hammer mill, a rotoplex, etc., and then finely pulverized using a fine pulverizer using a jet stream, a mechanical fine pulverizer, etc. It is preferable to pulverize the product so that the volume average particle size is 3 μm or more and 15 μm or less. Furthermore, when classifying the pulverized melt-kneaded product, an air classifier or the like can be used. It is preferable to classify the base particles so that the volume average particle size is 5 μm or more and 20 μm or less. When adding external additives to the base particles, the external additives are mixed and stirred using a mixer, so that the external additives are adhering to the surfaces of the base particles while being crushed.

[0048] -Binder resin- The binder resin is not particularly limited and can be appropriately selected depending on the purpose. Examples of the binder resin include homopolymers of styrene and its substituted derivatives, such as polystyrene, poly-p-styrene, and polyvinyltoluene; styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, and styrene-maleic acid ester copolymer; and polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polyester, polyurethane, epoxy resin, polyvinyl butyral, polyacrylic acid, rosin, modified rosin, terpene resin, phenolic resin, aliphatic or aromatic hydrocarbon resin, and aromatic petroleum resin. These may be used alone or in combination of two or more.

[0049] The binder resin for pressure fixing is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polyolefins such as low-molecular-weight polyethylene and low-molecular-weight polypropylene; olefin copolymers such as ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, and ionomer resin; epoxy resin, polyester, styrene-butadiene copolymer, polyvinylpyrrolidone, methyl vinyl ether-maleic anhydride copolymer, maleic acid-modified phenolic resin, and phenol-modified terpene resin. These may be used alone or in combination of two or more.

[0050] -Coloring agent- The colorant (pigment or dye) is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include yellow pigments such as cadmium yellow, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, and tartrazine lake; orange pigments such as molybdenum orange, permanent orange GTR, pyrazolone orange, vulcan orange, indanthrene brilliant orange RK, benzidine orange G, and indanthrene brilliant orange GK; red iron oxide, cadmium red, permanent red 4R, lithol red, pyrazolone red, watching red calcium salt, and lake red. Examples of pigments include red pigments such as rhodamine D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, and brilliant carmine 3B; purple pigments such as fast violet B and methyl violet lake; blue pigments such as cobalt blue, alkali blue, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, fast sky blue, and indanthrene blue BC; green pigments such as chrome green, chromium oxide, pigment green B, and malachite green lake; and black pigments such as azine dyes, metal salt azo dyes, metal oxides, and composite metal oxides, including carbon black, oil furnace black, channel black, lamp black, acetylene black, and aniline black. These pigments may be used alone or in combination of two or more.

[0051] -Mold release agent- The release agent is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include polyolefins such as polyethylene and polypropylene, fatty acid metal salts, fatty acid esters, paraffin wax, amide wax, polyhydric alcohol wax, silicone varnish, carnauba wax, ester wax, etc. These may be used alone or in combination of two or more.

[0052] -Charge control agent-The toner may further contain a charge control agent. The charge control agent is not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include nigrosine; azine dyes having an alkyl group having 2 to 16 carbon atoms; CI Basic Yellow 2 (CI41000), CI Basic Yellow 3, CI Basic Red 1 (CI45160), CI Basic Red 9 (CI42500), CI Basic Violet 1 (CI42535), CI Basic Violet 3 (CI42555), CI Basic Violet 10 (CI45170), CI Basic Violet 14 (CI42510), CI Basic Blue 1 (CI42025), CI Basic Blue 3 (CI51005), CI Basic Blue 5 (CI42140), CI Basic Blue 7 (CI42595), CI Basic Blue 9 (CI52015), CI Basic Blue 24 (CI52030), CI Basic Examples of suitable dyes include basic dyes such as Blue 25 (CI 52025), CI Basic Blue 26 (CI 44045), CI Basic Green 1 (CI 42040), and CI Basic Green 4 (CI 42000); lake pigments of these basic dyes; quaternary ammonium salts such as CI Solvent Black 8 (CI 26150), benzoylmethylhexadecylammonium chloride, and decyltrimethylchloride; dialkyltin compounds such as dibutyl and dioctyl; dialkyltin borate compounds; guanidine derivatives; polyamine resins such as vinyl polymers containing amino groups and condensation polymers containing amino groups; metal complex salts of monoazo dyes; salicylic acid; complexes of dialkylsalicylic acid, naphthoic acid, and dicarboxylic acids with Zn, Al, Co, Cr, Fe, and the like; sulfonated copper phthalocyanine pigments; organic boron salts; fluorine-containing quaternary ammonium salts; and calixarene compounds. These may be used alone or in combination. For color toners other than black, white metal salts of salicylic acid derivatives are preferred.

[0053] -External additives- The external additive is not particularly limited and can be appropriately selected depending on the purpose. Examples include inorganic particles such as silica, titanium oxide, alumina, strontium titanate, silicon carbide, silicon nitride, and boron nitride; and resin particles such as polymethyl methacrylate particles and polystyrene particles having an average particle size of 0.05 μm to 1 μm obtained by soap-free emulsion polymerization. These may be used alone or in combination of two or more. Among these, silica whose surface has been hydrophobized is preferred. Furthermore, it is more preferable to use two or more types of silica with different particle sizes in combination. Specifically, it is recommended to use a combination of silica with a secondary particle size of 100 nm or more and one less than 100 nm. Large silica particles of 100 nm or more act as spacers for the toner base particles, allowing the highly adhesive base particles to be separated. Adding small silica particles of less than 100 nm to the toner base particles can impart fluidity to the toner. This results in a highly fluid toner with individual particles separated, contributing to higher image quality. The secondary particle size can be measured using, for example, Zetasizer Pro (manufactured by Spectris Inc.).

[0054] The total number of large particle size silica and small particle size silica is preferably 1.5 to 5 parts by weight, more preferably 2 to 3 parts by weight, per 100 parts by weight of the base toner. A total number of 1.5 parts by weight or more provides high toner fluidity and prevents toner transfer defects during the transfer process. A total number of 5 parts by weight or less prevents silica from adhering to the electrostatic latent image carrier, suppressing the occurrence of abnormal images.

[0055] The color of the toner is not particularly limited and can be appropriately selected depending on the purpose, and can be at least one selected from black toner, cyan toner, magenta toner, and yellow toner. Each color toner can be obtained by appropriately selecting the type of colorant, but color toner is preferred.

[0056] (Process cartridge) The process cartridge of the present invention comprises an electrostatic latent image carrier, charging means for charging the surface of the electrostatic latent image carrier, developing means for developing an electrostatic latent image formed on the electrostatic latent image carrier using the developer of the present invention, and cleaning means for cleaning toner remaining on the surface of the electrostatic latent image carrier, and may further comprise other means as necessary. The process cartridge can be detachably mounted in various electrophotographic image forming apparatuses, and is preferably detachably mounted in the image forming apparatus of the present invention, which will be described later.

[0057] (Image forming apparatus and image forming method) The image forming apparatus of the present invention comprises an electrostatic latent image carrier, a charging means for charging the electrostatic latent image carrier, an exposure means for forming an electrostatic latent image on the electrostatic latent image carrier, a developing means for developing the electrostatic latent image formed on the electrostatic latent image carrier with the developer of the present invention to form a toner image, a transfer means for transferring the toner image formed on the electrostatic latent image carrier to a recording medium, and a fixing means for fixing the toner image transferred to the recording medium, and may further comprise other means as necessary. The image forming method of the present invention includes a step of forming an electrostatic latent image on an electrostatic latent image carrier, a step of developing the electrostatic latent image formed on the electrostatic latent image carrier with the developer of the present invention to form a toner image, a step of transferring the toner image formed on the electrostatic latent image carrier to a recording medium, and a step of fixing the toner image transferred to the recording medium, and may further include other steps as necessary.

[0058] <Electrostatic latent image carrier> The electrostatic latent image bearing member is not particularly limited in terms of material, shape, structure, size, etc., and can be appropriately selected depending on the purpose. The shape may be, for example, a drum shape. Examples of the material include inorganic photoconductors such as amorphous silicon and selenium, and organic photoconductors such as polysilane and phthalopolymethine, etc. Among these, amorphous silicon is preferred in terms of long life. The amorphous silicon photoreceptor may be, for example, a photoreceptor having a photoconductive layer made of a-Si formed on a support by heating the support to 50°C to 400°C and forming the photoconductive layer on the support by a film formation method such as vacuum deposition, sputtering, ion plating, thermal CVD, photo-CVD, or plasma CVD (hereinafter, sometimes referred to as an "a-Si-based photoreceptor"). Among these, plasma CVD, i.e., a method in which a raw material gas is decomposed by direct current, high frequency, or microwave glow discharge to form an a-Si deposited film on the support, is preferred.

[0059] <Charging Process and Charging Means> The charging step can be carried out, for example, by applying a voltage to the surface of the electrostatic latent image bearing member using the charging means. The charging means is not particularly limited and can be appropriately selected depending on the purpose. Examples include a known contact charger equipped with a conductive or semiconductive roller, brush, film, rubber blade, etc., and a non-contact charger utilizing corona discharge such as a corotron or scorotron. The charging means may take any form, such as a roller, a magnetic brush, a fur brush, or the like, and can be selected according to the specifications and configuration of the electrophotographic device. When a magnetic brush is used, the magnetic brush uses various ferrite particles, such as Zn-Cu ferrite, as the charging member, and is composed of a non-magnetic conductive sleeve for supporting the magnetic brush and a magnet roller enclosed within the sleeve. When a brush is used, for example, the fur brush is made of fur treated with conductivity, such as carbon, copper sulfide, metal, or metal oxide, and is wound or attached to a metal or other conductive core to form a charger. The charging means is not limited to the contact type charger described above, but it is preferable to use a contact type charger because this will result in an image forming apparatus in which the amount of ozone generated from the charger is reduced.

[0060] <Exposure Process and Exposure Means> The exposure step can be carried out, for example, by exposing the surface of the electrostatic latent image bearing member to light in an imagewise manner using the exposure unit. The exposure means is not particularly limited as long as it can expose the surface of the electrostatic latent image carrier charged by the charging means in the form of an image to be formed, and can be appropriately selected depending on the purpose. Examples of the exposure means include various exposure devices such as a copying optical system, a rod lens array system, a laser optical system, and a liquid crystal shutter optical system. In the present invention, a backlight system may be employed in which exposure is performed imagewise from the back side of the electrostatic latent image bearing member.

[0061] <Developing step and developing means> The developing unit is a unit that develops the electrostatic latent image with the toner or the two-component developer to form a visible image. The visible image can be formed, for example, by developing the electrostatic latent image with the toner or the two-component developer of the present invention. The developing means is not particularly limited as long as it can develop using the toner or the two-component developer, and can be appropriately selected depending on the purpose. However, it is preferable that the developing means has at least a developing device that stores the toner or the two-component developer and can apply the toner or the two-component developer to the electrostatic latent image in a contact or non-contact manner, and a developing device equipped with a toner container is more preferable. The developing means may be of a dry developing type or a wet developing type, and may be a single-color developing device or a multi-color developing device. For example, a suitable example is one having an agitator that frictionally agitates and charges the toner or the two-component developer, and a rotatable magnetic roller. In the developing unit, for example, the toner and the carrier are mixed and stirred, and the toner is charged by friction during this process and held in a standing state on the surface of a rotating magnet roller, forming a magnetic brush. Because the magnet roller is located near the electrostatic latent image carrier (photosensitive member), a portion of the toner constituting the magnetic brush formed on the surface of the magnet roller moves to the surface of the electrostatic latent image carrier (photosensitive member) by electrical attraction. As a result, the electrostatic latent image is developed with the toner, and a visible toner image is formed on the surface of the electrostatic latent image carrier (photosensitive member). The developer contained in the developing unit is a developer containing the toner, and the developer may be a one-component developer or a two-component developer. The toner contained in the developer is the toner.

[0062] <Transfer process and transfer means> The transfer means is not particularly limited as long as it is a means for transferring the visible image onto a recording medium, and can be appropriately selected depending on the purpose. However, a means is preferred which uses an intermediate transfer body, performs primary transfer of a visible image onto the intermediate transfer body, and then performs secondary transfer of the visible image onto the recording medium, and it is preferred that the toner used is two or more colors, preferably full-color toner, and that the transfer means has a primary transfer means which transfers the visible image onto the intermediate transfer body to form a composite transfer image, and a secondary transfer means which transfers the composite transfer image onto the recording medium. The transfer can be performed by, for example, charging the electrostatic latent image carrier (photosensitive member) using a transfer charger, and can be performed by the transfer unit. The transfer unit preferably has a primary transfer unit that transfers the visible image onto an intermediate transfer member to form a composite transfer image, and a secondary transfer unit that transfers the composite transfer image onto a recording medium. The intermediate transfer body is not particularly limited and can be appropriately selected from known transfer bodies depending on the purpose, and a suitable example is a transfer belt. The transfer means (the primary transfer means, the secondary transfer means) preferably has at least a transfer device that peels and charges the visible image formed on the electrostatic latent image carrier (photosensitive member) onto the recording medium. The number of transfer devices may be one or more. Examples of the transfer device include a corona transfer device that uses corona discharge, a transfer belt, a transfer roller, a pressure transfer roller, and an adhesive transfer device. The recording medium is typically plain paper, but there are no particular restrictions as long as it is capable of transferring the unfixed image after development, and it can be selected appropriately depending on the purpose. PET base for overhead projectors can also be used.

[0063] <Fixing Process and Fixing Means> The fixing means is a means for fixing the transferred image transferred onto the recording medium using a fixing member, and may be a means for fixing each color of toner each time it is transferred onto the recording medium, or may be a means for fixing each color of toner simultaneously at once while they are stacked. The fixing member is not particularly limited and can be appropriately selected depending on the purpose, but is preferably a known heating and pressing member, such as a combination of a heating roller and a pressure roller, or a combination of a heating roller, a pressure roller, and an endless belt. The heating temperature in the heating and pressing member is usually preferably 80°C to 200°C.

[0064] <Other processes and other means> The other steps are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a static elimination step, a cleaning step, a recycling step, and a control step. The other means are not particularly limited and can be appropriately selected depending on the purpose. Examples thereof include a static elimination means, a cleaning means, a recycling means, and a control means.

[0065] -Static elimination process and static elimination means- The discharging means is not particularly limited as long as it is a means capable of applying a discharging bias to the electrostatic latent image bearing member, and can be appropriately selected depending on the purpose, and examples thereof include a discharging lamp.

[0066] -Cleaning process and cleaning means- The cleaning means is not particularly limited as long as it is a means capable of removing the electrophotographic toner remaining on the electrostatic latent image carrier, and can be appropriately selected depending on the purpose. Examples of the cleaning means include a magnetic brush cleaner, an electrostatic brush cleaner, a magnetic roller cleaner, a blade cleaner, a brush cleaner, and a web cleaner.

[0067] -Recycling process and means- The recycling means is not particularly limited and can be appropriately selected depending on the purpose, and examples thereof include known transport means.

[0068] -Control process and control means- The control means is not particularly limited as long as it is a means capable of controlling the movement of each of the means, and can be appropriately selected depending on the purpose. For example, devices such as a sequencer and a computer can be mentioned.

[0069] An example of the process cartridge of the present invention is shown in Fig. 2. The process cartridge 10 in Fig. 2 integrally supports an electrostatic latent image carrier 11, charging means 12 for charging the electrostatic latent image carrier 11, developing means 13 for forming a toner image by developing the electrostatic latent image formed on the electrostatic latent image carrier 11 with the developer of the present invention, and cleaning means 14 for removing toner remaining on the electrostatic latent image carrier 11 after the toner image formed on the electrostatic latent image carrier 11 is transferred to a recording medium, and the process cartridge 10 is detachable from the main body of an image forming apparatus such as a copier or printer.

[0070] Next, a method for forming an image using an image forming apparatus equipped with the process cartridge 10 will be described. First, the electrostatic latent image carrier 11 is rotated at a predetermined peripheral speed, and the peripheral surface of the electrostatic latent image carrier 11 is uniformly charged to a predetermined positive or negative potential by the charging means 12. Next, exposure light is irradiated onto the peripheral surface of the electrostatic latent image carrier 11 from an exposure means (not shown), such as a slit exposure type exposure means or an exposure means that scans and exposes with a laser beam, and electrostatic latent images are sequentially formed. Furthermore, the electrostatic latent images formed on the peripheral surface of the electrostatic latent image carrier 11 are developed by the developing means 13 using the developer of the present invention, and toner images are formed. Next, the toner images formed on the peripheral surface of the electrostatic latent image carrier 11 are sequentially transferred, in synchronization with the rotation of the electrostatic latent image carrier 11, to transfer paper fed from a paper feed unit (not shown) between the electrostatic latent image carrier 11 and the transfer means (not shown). Furthermore, the recording medium onto which the toner image has been transferred is separated from the peripheral surface of the electrostatic latent image carrier 11 and introduced into a fixing means (not shown) where the toner image is fixed, and then printed out as a duplicate (copy) to the outside of the image forming apparatus. Meanwhile, the surface of the electrostatic latent image carrier 11 onto which the toner image has been transferred is cleaned by cleaning means 14 to remove any remaining toner, and then is neutralized by neutralization means (not shown) and is used repeatedly for image formation.

[0071] 5 is a schematic diagram showing an example of an image forming apparatus equipped with the above-described process cartridge. In the image forming apparatus of the above configuration, process cartridges 2A, 2B, 2C, and 2D are detachably installed in the image forming apparatus main body. Process cartridges 2A, 2B, 2C, and 2D are equipped with photosensitive elements 1A, 1B, 1C, and 1D, respectively. Each of the process cartridges 2A, 2B, 2C, and 2D further includes a charging means 33, a developing means 34, a cleaning means 35, an image exposure means 36, a paper feed unit 37, an intermediate transfer body 38, an image fixing means 39, a primary transfer means 110, a transfer material 120, a tray 53, and a secondary transfer means 54. Explaining operation, the toner image formed as described above is intermediately transferred onto the belt-shaped intermediate transfer body 38 by the primary transfer means 110, and then sequentially transferred by the secondary transfer means 54 onto a transfer material 120 fed from the paper feed unit 37 between the intermediate transfer body 38 and the secondary transfer means 54 in synchronization with the rotation of the photoreceptors 1A, 1B, 1C, and 1D. The transfer material 120 having received the transferred image is separated from the surface of the intermediate transfer body 38 and introduced into the image fixing means 39, where the image is fixed, and then printed out as a duplicate (copy) onto a tray 53 outside the apparatus. After the image transfer, the surfaces of the photoreceptors 1A, 1B, 1C, and 1D are cleaned by cleaning means 35 to remove any remaining toner, and are then discharged before being used repeatedly for image formation. [Example]

[0072] Examples of the present invention will be described below, but the present invention is not limited to these examples in any way.

[0073] (Core particle manufacturing example 1) As raw materials, 21.5 kg of Fe2O3 (average particle size: 0.3 μm, SiO2 content: 0.02 mass%), 10.4 kg of Mn3O4 (average particle size: 0.5 μm, SiO2 content: 0.01 mass%), and 0.28 kg of SrCO3 (average particle size: 0.6 μm) were dispersed in 10.0 kg of pure water, and 120 g of carbon black as a reducing agent and 180 g of a polycarboxylate ammonium dispersant (Cerna D305, manufactured by Chukyo Yushi Co., Ltd.) as a dispersant were added to prepare a mixture. This mixture was pulverized in a wet ball mill (media diameter: 2 mm) to obtain a mixed slurry. This mixed slurry was sprayed into hot air at about 130°C using a spray dryer to obtain dried granules with particle sizes of 10 μm to 75 μm. From this granule, fine particles with a particle size of 25 μm or less were removed using a sieve. The granulated material was placed in an electric furnace and heated to 1,200°C over 4.5 hours. Thereafter, firing was carried out by holding at 1,200°C for 8 hours. Then, the mixture was cooled to room temperature over 10 hours. At this time, the oxygen concentration in the electric furnace was set to 5,000 ppm during firing and 1,200 ppm during cooling. The obtained fired material was pulverized using a hammer mill ("Hammer Crusher NH-34S", manufactured by Sansho Industry Co., Ltd., screen opening: 0.3 mm) and classified using a vibrating sieve. The fired material was then subjected to an oxidation treatment (high resistance treatment) by holding it at 450°C for 1.5 hours in an air atmosphere, and core particles C1 with an internal porosity of 0% and Rz of 2.5 μm were obtained.

[0074] <Internal porosity> The internal porosity of core particles was measured using the following method. First, a core particle was cut and a cross-section was photographed. A conventionally known method, such as SEM, could be used to photograph the cross-section. Next, using conventionally known image analysis software (Image Pro Premier, manufactured by Media Cybernetics), the area S of the outline of a single particle was obtained from the cross-sectional photograph of the particle. Similarly, the area s of the void space inside a single particle was obtained, and the porosity of a single particle was calculated using the following formula: Porosity of 1 particle [%] = (s / S) × 100 This was carried out on 50 randomly selected grains, and the average value was taken as the internal porosity.

[0075] <rz> Rz was measured using a confocal microscope, OPTELICS C130 (Lasertec Corporation), by observing the carrier surface with an eyepiece at 50x magnification, a resolution of 0.44 μm, and Imaging Mode: Max Peak, to obtain a 3D image. The Rz values ​​were analyzed within a 12 μm square area of ​​the obtained carrier image. 50 samples were analyzed, and the average value of the 50 samples was used.

[0076] (Core particle manufacturing example 2) The raw materials were 21.5 kg of Fe2O3 (average particle size: 0.9 μm, SiO2 content: 0.02 mass%) and 10.4 kg of Mn3O4 (average particle size: 1.2 μm, SiO2 content: 0.01 mass%), and the firing temperature was changed to 1,000°C. Except for this, core particles C2 with an internal porosity of 2% and Rz of 2.5 μm were obtained in exactly the same manner as in Production Example 1.

[0077] (Core particle manufacturing example 3) Core particles C3 with an internal porosity of 0% and Rz of 2.5 μm were obtained in exactly the same manner as in Production Example 1, except that the raw materials used were 21.5 kg of Fe2O3 (average particle size: 0.6 μm, SiO2 content: 0.02 mass%) and 10.4 kg of Mn3O4 (average particle size: 0.9 μm, SiO2 content: 0.01 mass%).

[0078] (Core particle manufacturing example 4) Core particles C4 having an internal porosity of 0% and Rz of 1.8 μm were obtained in the same manner as in Production Example 3, except that the firing temperature was changed to 1,080° C.

[0079] (Core Particle Manufacturing Example 5) Core particles C5 having an internal porosity of 0% and Rz of 2.0 μm were obtained in the same manner as in Production Example 3, except that the firing temperature was changed to 1,100° C.

[0080] (Core particle manufacturing example 6) Core particles C6 having an internal porosity of 0% and Rz of 3.0 μm were obtained in the same manner as in Production Example 3, except that the firing temperature was changed to 1,300° C.

[0081] (Core particle manufacturing example 7) Core particles C7 having an internal porosity of 0% and Rz of 3.2 μm were obtained in the same manner as in Production Example 3, except that the firing temperature was changed to 1,320° C.

[0082] (Core material manufacturing example 8) Core particles C8 having an internal porosity of 2.2% and Rz of 2.5 μm were obtained in the same manner as in Production Example 2, except that the firing temperature was set to 950° C.

[0083] (Core particle manufacturing example 9) Core particles C9 having an internal porosity of 0% and Rz of 2.5 μm were obtained in the same manner as in Production Example 1, except that the firing temperature was set to 1,220° C.

[0084] (Example of manufacturing conductive particles) 100 g of alumina (AKP-50 manufactured by Sumitomo Chemical) was dispersed in 1 L of water to form a suspension, which was then heated to 65°C. A solution of 600 g of stannic chloride and 18.0 g of sodium tungstate dissolved in 1.7 L of 2N hydrochloric acid and 12 wt% aqueous ammonia were added dropwise to the suspension over a period of 2 hours so that the pH of the suspension was between 7 and 8. After the addition, the suspension was filtered and washed, and the resulting cake was dried at 110°C. Next, this dried powder was treated in a nitrogen stream at 500°C for 1 hour to obtain conductive microparticles.

[0085] (Carrier manufacturing example 1) -Creating a carrier- The following composition was dispersed in a homomixer for 10 minutes to obtain a coating layer forming solution. Using 5,000 parts by mass of C1 as core particles, the coating layer forming solution was applied to the surfaces of the core particles using a Spira Coater (manufactured by Okada Seiko Co., Ltd.) at an internal temperature of 55°C and then dried. The resulting carrier was then fired in an electric furnace at 200°C for 1 hour. After cooling, the ferrite powder bulk was crushed using a sieve with 63 μm openings to obtain Carrier 1.

[0086] [composition] ·Silicone resin solution (solid content: 20% by mass, SR2410, manufactured by Toray Dow Corning Silicone Co., Ltd.): 510 parts by mass ·Titanium catalyst (solid content: 60% by mass, TC-750, manufactured by Matsumoto Fine Chemical Co., Ltd.): 4 parts by mass ·Aminosilane (solid content: 100% by mass, SH6020, manufactured by Toray Dow Corning Silicone Co., Ltd.): 3.2 parts by mass ·Chargeable fine particles P1 (titanium oxide, particle size: 450 nm): 18 parts by mass ·Conductive fine particles: 18 parts by mass ·Toluene: 1,000 parts by mass

[0087] Next, regarding the obtained carrier 1, when R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were measured by the method shown below, they were 450, 450, 1.0, 0.85, 2.5, and 13.3, respectively.

[0088] <R1, R2, R1 / R2, average thickness> Mix the carrier into an embedding resin (Devcon, two-component mixture, 30-minute curing type epoxy resin, manufactured by ITW Performance Polymers & Fruitz Japan), leave it overnight or longer to cure, and prepare a rough cross-section sample by mechanical polishing. Using a cross-section polisher (SM-09010 manufactured by JEOL), finish the cross-section under the conditions of an acceleration voltage of 5.0 kV and a beam current of 120 μA. Photograph this under the conditions of an acceleration voltage of 0.8 kV and a magnification of 30,000 times using a scanning electron microscope (Merlin manufactured by Carl Zeiss). Import the photographed image into a TIFF image, select 50 particles using Image-Pro Plus manufactured by Media Cybernetics, measure them as the long axis R1 [nm] and thickness R2 [nm], calculate R1, R2, and R1 / R2 for 50 particles, and use the average value. The average thickness [μm] was obtained by selecting 50 cross-sectional views of the carrier, measuring the thickness of the coating layer in the normal direction from 4 locations on the surface of the core material particles for each carrier, and using the average value of a total of 200 thickness measurements.

[0089] <Apparent density [g / cm 3 > Measurement was carried out according to the method described in JIS Z 2504.

[0090] <Volume resistivity> Using the cell shown in Figure 1, a cell consisting of a fluororesin container 2 containing electrodes 1a and 1b with a surface area of ​​2.5 cm × 4 cm, spaced 0.2 cm apart, was filled with a carrier 3, and tapped 10 times at a drop height of 1 cm and a tapping speed of 30 times / min. After applying a DC voltage of 1,000 V between electrodes 1a and 1b for 30 seconds, the resistance value r [Ω] was measured using a High Resistance Meter 4329A (manufactured by Yokogawa Hewlett-Packard Co., Ltd.), and the volume resistivity [Ω cm] was calculated using the following formula (2).

[0091]

number

[0092] (Carrier manufacturing example 2) Carrier 2 was obtained in the same manner as in Carrier Production Example 1, except that the charged fine particles were changed to P2 (titanium oxide, particle size 450 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 150, 3.0, 0.85, 2.5, and 13.4, respectively.

[0093] (Carrier manufacturing example 3) Carrier 3 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C2. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 450, 1.0, 0.85, 2.0, and 13.1, respectively.

[0094] (Carrier Manufacturing Example 4) Carrier 4 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C2 and the charged fine particles were changed to P2 (titanium oxide, particle size 450 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 150, 3.0, 0.85, 2.0, and 13.2, respectively.

[0095] (Carrier Manufacturing Example 5) Carrier 5 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3 and the charged fine particles were changed to P3 (titanium oxide, particle size 280 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 280, 190, 1.5, 0.85, 2.3, and 13.3, respectively.

[0096] (Carrier Manufacturing Example 6) Carrier 6 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3 and the charged fine particles were changed to P4 (titanium oxide, particle size 300 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 300, 200, 1.5, 0.85, 2.3, and 13.1, respectively.

[0097] (Carrier Manufacturing Example 7) Carrier 7 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3 and the charged fine particles were changed to P5 (titanium oxide, particle size 600 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 600, 400, 1.5, 0.85, 2.3, and 13.2, respectively.

[0098] (Carrier Manufacturing Example 8) Carrier 8 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3 and the charged fine particles were changed to P6 (titanium oxide, particle size 620 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 620, 420, 1.5, 0.85, 2.3, and 13.1, respectively.

[0099] (Carrier Manufacturing Example 9) Carrier 9 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C4 and the charged fine particles were changed to P7 (titanium oxide, particle size 450 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.85, 2.4, and 13.2, respectively.

[0100] (Carrier Manufacturing Example 10) Carrier 10 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C5 and the charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.85, 2.4, and 13.1, respectively.

[0101] (Carrier Manufacturing Example 11) Carrier 11 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C6 and the charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.85, 2.2, and 13.4, respectively.

[0102] (Carrier Manufacturing Example 12) Carrier 12 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C7 and the charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.85, 2.2, and 13.3, respectively.

[0103] (Carrier Manufacturing Example 13) Carrier 13 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3, the silicone resin solution was changed to 270 parts, and the charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.45, 2.3, and 13.2, respectively.

[0104] (Carrier Manufacturing Example 14) Carrier 14 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3, the silicone resin solution was changed to 300 parts, and the electrostatically charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.50, 2.3, and 13.2, respectively.

[0105] (Carrier Manufacturing Example 15) Carrier 15 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3 and the charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.85, 2.3, and 13.1, respectively.

[0106] (Carrier Manufacturing Example 16) Carrier 16 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3, the silicone resin solution was changed to 660 parts, and the electrostatically charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 1.10, 2.3, and 13.1, respectively.

[0107] (Carrier Manufacturing Example 17) Carrier 17 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3, 690 parts of silicone resin solution, and the charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 1.15, 2.3, and 13.3, respectively.

[0108] (Carrier Manufacturing Example 18) Carrier 18 was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3 and the charged fine particles were changed to P8 (barium sulfate, particle size 450 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.85, 2.3, and 13.1, respectively.

[0109] (Comparative Carrier Manufacturing Example 1) Carrier 1' was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C8 and the charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.85, 1.9, and 13.3, respectively.

[0110] (Carrier Manufacturing Comparative Example 2) Carrier 2' was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C9 and the charged fine particles were changed to P7. The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 300, 1.5, 0.85, 2.6, and 13.3, respectively.

[0111] (Carrier Manufacturing Comparative Example 3) Carrier 3' was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3 and the charged fine particles were changed to P9 (titanium oxide, particle size 450 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 500, 0.9, 0.85, 2.3, and 13.1, respectively.

[0112] (Carrier Manufacturing Comparative Example 4) Carrier 4' was obtained in the same manner as in Carrier Production Example 1, except that the core particles were changed to C3 and the charged fine particles were changed to P10 (titanium oxide, particle size 450 nm). The R1, R2, R1 / R2, average thickness, apparent density, and volume resistivity were 450, 140, 3.2, 0.85, 2.3, and 13.2, respectively.

[0113] The properties of the resulting carriers 1 to 18 and carriers 1′ to 4′ are shown in Table 1.

[0114] [Table 1]

[0115] (Toner Production Example 1) <Preparation of Toner 1> -Synthesis of polyester resin A- Into a reaction vessel equipped with a thermometer, a stirrer, a condenser, and a nitrogen inlet tube, 443 parts by mass of a bisphenol A-PO adduct (hydroxyl value: 320 mgKOH / g), 135 parts by mass of diethylene glycol, 422 parts by mass of terephthalic acid, and 2.5 parts by mass of dibutyltin oxide were placed and reacted at 200°C until the acid value reached 10 mgKOH / g, yielding polyester resin A. The resulting polyester resin A had a glass transition temperature (Tg) of 63°C and a peak number-average molecular weight of 6,000.

[0116] -Synthesis example of polyester resin B- Into a reaction vessel equipped with a thermometer, a stirrer, a condenser, and a nitrogen inlet tube, 443 parts by mass of a bisphenol A-PO adduct (hydroxyl value: 320 mgKOH / g), 135 parts by mass of diethylene glycol, 422 parts by mass of terephthalic acid, and 2.5 parts by mass of dibutyltin oxide were placed and reacted at 230°C until the acid value reached 7 mgKOH / g, yielding polyester resin B. The resulting polyester resin B had a glass transition temperature (Tg) of 65°C and a peak number-average molecular weight of 16,000.

[0117] -Manufacturing of parent toner particles- The following toner constituent materials were mixed in a Henschel mixer (a Henschel 20B manufactured by Nippon Coke & Engineering Co., Ltd., at 1,500 rpm for 3 minutes), and then kneaded in a single-screw kneader (a small Buss-Co kneader manufactured by Buss) under the following conditions (set temperatures: inlet 100°C, outlet 50°C, feed rate: 2 kg / hr) to obtain a base toner. [Composition of parent toner particles] Polyester resin A: 40 parts by weight Polyester resin B: 60 parts by weight Carnauba wax (WA-05, manufactured by Cerarica Noda Co., Ltd.): 1 part by weight Carbon black (#44, manufactured by Mitsubishi Chemical Corporation): 15 parts by mass Next, the [base toner] is kneaded, rolled and cooled, and pulverized in a pulverizer. The mixture is then milled in an I-type mill (IDS-2 model manufactured by Nippon Pneumatic Co., Ltd.) using a flat-type collision plate and an air pressure of 6.8 atm / cm. 2 The mixture was finely pulverized under the conditions of 0.5 kg / hr (feed rate: 0.5 kg / hr) and further classified using a classifier (132MP, manufactured by Alpine Co., Ltd.) to obtain [base toner particles].

[0118] -External additive treatment- Next, 0.5 parts by mass of large particle size silica (MSP-009, manufactured by Teika Corporation, secondary particle diameter 160 nm) and 1.0 part by mass of small particle size silica (MSP-015, manufactured by Teika Corporation, secondary particle diameter 40 nm) were added as external additives to 100 parts by mass of the "parent toner particles," and mixed in a Henschel mixer to obtain toner particles. In this way, "Toner 1" was produced. The volume average particle size of Toner 1 was 7.2 μm.

[0119] (Developer Production Examples 1 to 18 and Comparative Developer Production Examples 1 to 4) -Preparation of Developers 1 to 18 and Developers 1' to 4'- Two-component developers 1 to 18 and 1' to 4' were prepared by adding 7.0 parts by mass of toner 1 obtained in the toner production example to 93 parts by mass of each of carriers 1 to 18 and carriers 1' to 4' obtained in the carrier production examples and stirring the mixture in a ball mill for 20 minutes.

[0120] <Developer characteristics> Using each of the two-component developers obtained, image evaluations were carried out in a digital color copier / printer all-in-one (Ricoh Co., Ltd., Ricoh Pro C901) under an environment of 23°C temperature and 55% relative humidity. Specifically, first, using developers 1 to 14 and 1' to 4' of the examples and comparative examples and toner 1, printing was carried out up to 1 million sheets at an image area ratio of 2%, and various evaluations were carried out. The results are shown in Table 2.

[0121] <<Image density>> The center of a 30mm x 30mm solid area (Note 1) was measured at five points using a spectrophotometric densitometer (X-Rite 938, manufactured by X-Rite), and the average value was calculated. The ID difference between the initial state and after printing 1 million sheets was evaluated according to the following criteria. Note 1: Location equivalent to 400V development potential = (exposed area potential - development bias DC) = -100V - (-500V) [Evaluation criteria] ◎: ID difference is 0 or more and less than 0.2, very good ○: ID difference is 0.2 or more and less than 0.3, good △: ID difference is 0.3 or more and less than 0.4, usable ×: ID difference is 0.4 or more, defective

[0122] <<Carrier adhesion (solid area)>> Carrier adhesion can cause scratches on the photoreceptor and fixing roller, resulting in a decrease in image quality. Even if carrier adhesion occurs on the photoreceptor, only a portion of the carrier is transferred to the paper, so it was evaluated using the following method. The number of carrier particles adhering to a solid image (30 mm x 30 mm) under the development conditions (charging potential (Vd): -600 V, potential after exposure of the image area (solid original): -100 V, development bias: DC -500 V) was counted on the photoreceptor to evaluate carrier adhesion (solid area). [Evaluation criteria] ◎: Very good (no carrier adhesion) ○: Good (there is some carrier adhesion, but it does not affect the image) △: Usable (there is carrier adhesion, which is visible in the image, but it is at an acceptable level) ×: (Carrier adhesion is present and is visible in the image, at an unacceptable level)

[0123] <<Edge carrier adhesion>> A two-dot line (100 lpi / inch) image was formed in the sub-scanning direction on the photoreceptor under the development conditions of a charging potential (Vd) of -600 V, an exposed area potential of -100 V, and a development bias (Vb) of DC -400 V, i.e., a background potential of 200 V. Next, the two-dot line developed on the photoreceptor was attached to an adhesive tape (area 100 cm). 2 The number of particles was counted to evaluate the carrier adhesion. [Evaluation criteria] ◎: Very good (no carrier adhesion) ○: Good (there is some carrier adhesion, but it does not affect the image) △: Usable (there is carrier adhesion, which is visible in the image, but it is at an acceptable level) ×: (Carrier adhesion is present and is visible in the image, at an unacceptable level)

[0124] <<Ghost image>> Regarding ghosting, a character chart with an 8% image area (size of each character: approximately 2mm x 2mm) was output at 100K, and then the vertical band chart shown in Figure 4 was printed. The density difference between one revolution of the sleeve (a) and one revolution later (b) was measured using an X-Rite938 (manufactured by X-Rite). The average density difference measured at three locations (center, rear, and front) was taken as ΔID and ranked as follows: ◎: Very good, ○: Good, △: Usable, ×: Unusable for practical use ◎, ○, and △ were considered to be pass marks, and × was considered to be fail marks. ◎: 0.01 ≥ ΔID ○: 0.01<ΔID≦0.03 △:0.03<ΔID≦0.06 ×:0.06<ΔID The results after 1 million sheets are shown in Table 2.

[0125] [Table 2]

[0126] From the results in Table 2, the developers of each Example showed practically sufficient or excellent results in the evaluations of image density, solid carrier adhesion, edge carrier adhesion, and ghost images. [Explanation of symbols]

[0127] 1a, 1b electrode 1A, 1B, 1C, 1D photoreceptor 2. Fluorine resin containers 2A, 2B, 2C, 2D, 10 process cartridges 3. Career 11 Electrostatic latent image carrier 12 Charging means 13 Developing means 14 Cleaning means 33 Charging means 34 Developing means 35 Cleaning means 36 Image exposure means 37 Paper feed section 38 Intermediate transfer body 39 Image fixing means 110 Primary transfer means 120 Transfer material [Prior art documents] [Patent documents]

[0128] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-170131 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-029464 [Patent Document 3] Japanese Patent Application Laid-Open No. 2009-103787< / rz>

Claims

1. A carrier for an electrostatic latent image developer having core particles and a coating layer that coats the core particles, the coating layer contains flat-shaped electrostatically charged particles, the electrostatically charged particles being contained in an amount of 10 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the resin contained in the coating layer, and the conductive particles being contained in an amount of 10 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the resin contained in the coating layer; The apparent density of the carrier is 2.0 [g / cm 3 ] or more 2.5 [g / cm 3 ] or less, The internal porosity of the core particles is 0.0% or more and 2.0% or less, and The carrier for electrostatic latent image developer is characterized in that the flat shape of the chargeable fine particles has a ratio of a major axis R1 [nm] to a thickness R2 [nm] that satisfies the relationship of the following formula 1. 1.2≦R1 / R2≦3.0 Formula 1

2. 2. The carrier for an electrostatic latent image developer according to claim 1, wherein the length of the major axis R1 of the chargeable fine particles is 300 nm or more and 600 nm or less.

3. 3. The carrier for an electrostatic latent image developer according to claim 1, wherein the surface roughness Rz of the core particles is 2.0 [μm] or more and less than 3.0 [μm].

4. 4. The carrier for an electrostatic latent image developer according to claim 1, wherein the coating layer has an average thickness of 0.50 μm or more and 1.10 μm or less.

5. 5. The carrier for an electrostatic latent image developer according to claim 1, wherein the chargeable fine particles are barium sulfate.

6. A two-component developer comprising the carrier for electrostatic latent image developer according to any one of claims 1 to 5 and a toner.

7. 10. An image forming apparatus comprising: an electrostatic latent image carrier; charging means for charging the latent image carrier; exposure means for forming an electrostatic latent image on the latent image carrier; developing means for developing the electrostatic latent image formed on the electrostatic latent image carrier with the developer according to claim 6 to form a toner image; transfer means for transferring the toner image formed on the electrostatic latent image carrier to a recording medium; and fixing means for fixing the toner image transferred to the recording medium.

8. 7. A process cartridge comprising: an electrostatic latent image carrier; a charging member for charging the surface of the electrostatic latent image carrier; a developing unit for developing an electrostatic latent image formed on the electrostatic latent image carrier using the developer according to claim 6; and a cleaning member for cleaning the electrostatic latent image carrier.

9. 10. An image forming method comprising: a step of forming an electrostatic latent image on an electrostatic latent image carrier; a step of developing the electrostatic latent image formed on the electrostatic latent image carrier with the developer according to claim 6 to form a toner image; a step of transferring the toner image formed on the electrostatic latent image carrier to a recording medium; and a step of fixing the toner image transferred to the recording medium.

Images