Carrier, developer, image forming method, image forming apparatus, and process cartridge

Abstract

To provide a carrier that is capable of sufficient electrification control for image quality required in the field of electronic photography, can prevent scattering of toner for a long period, and can prevent scattering of toner for a long period even when a low temperature fixing toner is used.SOLUTION: A carrier includes a core material particle 20 and a coating layer 30 coating the core material particle. The coating layer includes resin 32 and a charged inorganic fine particle 33, and the coating layer includes a void 31. A part of the resin has an average film thickness of 0.10 μm or more and less than 0.45 μm. On a cross section of the coating layer, when the cross-sectional area of the void is defined as S1, the cross-sectional area of the part of the resin as S2, and the cross-sectional area ratio of the void represented by the following formula as a void ratio, the void ratio is 0.1% or more and less than 2.8%. The void ratio[%]=S1 / S2×100.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a carrier, a developer, an image forming method, an image forming apparatus, and a process cartridge.

Background Art

[0002] In electrophotographic image formation, an electrostatic latent image is formed on an electrostatic latent image carrier such as a photoconductive substance, and a charged toner is attached to the electrostatic latent image to form a toner image. Thereafter, the toner image is transferred to a recording medium and fixed to obtain an output image. In recent years, the technology of multifunctional devices and printers using the electrophotographic method is rapidly evolving from monochrome to full color, and the full-color market tends to expand.

[0003] In full-color image formation, generally, three-color color toners of yellow, magenta, and cyan or four-color color toners obtained by adding black thereto are laminated to reproduce all colors. Therefore, in order to obtain a full-color image with excellent color reproducibility and sharpness, it is necessary to smooth the surface of the fixed toner image to reduce light scattering. For such reasons, in electrostatic latent image images of conventional full-color copiers and the like, many are those that increase the toner adhesion amount of the electrostatic latent image to achieve high gloss in order to achieve the smoothness of the toner image. Therefore, toner spent in which deteriorated toner adheres to the carrier surface has been a problem during long-term printing. Among the carrier deteriorations caused by toner spent, problems are the increase in carrier resistance and the decrease in carrier charging ability. When the charging ability of the carrier decreases, so-called toner scattering occurs, which causes malfunctions such as sensor misdetection by contaminating the inside of the machine.

[0004] In order to solve the above problems, various attempts have been made. Patent Document 1 and Patent Document 2 disclose carriers containing barium sulfate in a coating resin and having a Ba / Si ratio of 0.01 to 0.08 with respect to all elements measured by XPS. These have achieved a certain effect in suppressing toner spent. However, in recent years, toner has tended to be fixed at lower temperatures to reduce power consumption, and coupled with faster print speeds, toner deposition on the carrier has become even more likely. Furthermore, due to the demand for higher image quality, toners tend to contain many additives, and these are deposited on the carrier, resulting in a decrease in toner charge, toner scattering, and reduced margin for protecting the background surface.

[0005] Furthermore, because the amount of charged microparticles is reduced to enable low-temperature fixing of the toner, problems have arisen where the toner does not mix sufficiently with the developer during replenishment, resulting in it not becoming charged and scattering. To address these new problems, Patent Documents 3 and 4 describe carriers containing barium sulfate or magnesium oxide as charged microparticles on the outermost surface of the coating resin. However, it is difficult to ensure uniform presence within the coating resin, and as the number of copies increases, the material detaches from the coating resin, making it difficult to maintain stable charge control over the long term.

[0006] Furthermore, Patent Document 5 describes a carrier characterized by containing at least two types of inorganic fine particles in the coating resin, and also containing a dispersant and an antifoaming agent. The formulation of the dispersant and antifoaming agent makes it difficult for the inorganic fine particles to detach from the coating resin, and thus the decrease in charge over time due to detachment can be suppressed. However, the increased adhesion between the resin and inorganic fine particles in the coating layer creates a stronger film, making toner deposition on the carrier more likely. [Overview of the project] [Problems that the invention aims to solve]

[0007] While the above techniques can achieve a certain level of effectiveness, they do not meet the standards required in the field of electrophotography. Therefore, in view of the above-mentioned technical problems, the present invention aims to provide a carrier that enables sufficient charge control for the image quality required in the field of electrophotography, enables long-term suppression of toner scattering, and enables long-term suppression of toner scattering even when low-temperature fixing toner is used. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides a carrier comprising core material particles and a coating layer covering the core material particles, wherein the coating layer comprises a resin and electrostatically charged inorganic fine particles, and the coating layer contains voids. It contains conductive inorganic fine particles with a powder resistivity of 200 Ω·cm or less. The average film thickness of the resin portion is 0.10 μm or more and less than 0.45 μm, and in the cross-section of the coating layer, if the cross-sectional area of ​​the void is S1 and the cross-sectional area of ​​the resin portion is S2, and the ratio of the cross-sectional areas of the void expressed by the following formula is defined as the porosity, then the porosity is 0.1% or more and less than 2.8%. Furthermore, the core material particles contain Mnferrat. It is characterized by the following: Porosity [%]=S1 / S2×100 [Effects of the Invention]

[0009] According to the present invention, it is possible to provide a carrier that enables sufficient charge control for the image quality required in the field of electrophotography, and that suppresses toner scattering over the long term, even when using low-temperature fixing toner. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram to explain porosity. [Figure 2] This is a schematic diagram illustrating the average film thickness. [Figure 3] This diagram shows a cell used to measure the volume resistivity of a carrier. [Figure 4] This figure shows an example of a process cartridge of the present invention. [Modes for carrying out the invention]

[0011] The carrier, developer, image forming method, image forming apparatus, and process cartridge according to the present invention will be described below with reference to the drawings. It should be noted that the present invention is not limited to the embodiments shown below, and other embodiments, additions, modifications, and deletions may be made within the scope of what a person skilled in the art can conceive. Any embodiment that achieves the function and effect of the present invention is included within the scope of the present invention.

[0012] (Career) The carrier of the present invention is a carrier comprising core material particles and a coating layer covering the core material particles, wherein the coating layer comprises a resin and electrostatically charged inorganic fine particles, and contains voids, the average film thickness of the resin portion is 0.10 μm or more and less than 0.45 μm, and in the cross-section of the coating layer, when the cross-sectional area of ​​the voids is S1, the cross-sectional area of ​​the resin portion is S2, and the ratio of the cross-sectional areas of the voids expressed by the following formula is defined as the porosity, the porosity is 0.1% or more and less than 2.8%. Porosity [%]=S1 / S2×100

[0013] The coating layer may also be referred to as a film layer, carrier coating layer, coating layer, resin layer, coating film, coating film, coating resin, etc.

[0014] The carrier of the present invention can be used for electrophotographic image formation, and the present invention can provide a developer, an image forming method, an image forming apparatus, and a process cartridge for electrophotographic systems.

[0015] The electrostatically charged inorganic microparticles (sometimes referred to as electrostatic fillers) contained in the coating layer can increase the electrostatic properties of the toner, and the electrostatically charged inorganic microparticles on the surface can maintain their electrostatic properties even after long-term output at high image area. Therefore, by including electrostatically charged inorganic microparticles in the coating layer, it is possible to suppress the occurrence of abnormalities such as toner scattering and background staining that occur due to a decrease in charge.

[0016] When the film thickness of the coating layer is large as in the prior art, there is a problem that chipping of carriers is suppressed, toner components are spent on the carrier surface layer, and charging over time decreases. On the other hand, if the film thickness of the coating layer is reduced, it is considered that spending is suppressed, but the durability of the film becomes weak and the chargeable inorganic fine particles are likely to desorb. For this reason, charging over time decreases.

[0017] The inventors of the present invention have conducted intensive studies and found that it is important that the coating layer contains a resin and chargeable inorganic fine particles, and the average film thickness of the resin portion (which may also be referred to as a resin portion, a coating resin, etc.) is 0.10 μm or more and less than 0.45 μm. When the average film thickness of the resin portion is 0.45 μm or more, the coating layer becomes a thick film, and chipping of carriers is suppressed. For this reason, there is a problem that charging over time decreases due to toner components being spent on the carrier surface layer. Further, when the average film thickness of the resin portion is less than 0.10 μm, the coating layer becomes a thin film, and the durability of the carrier film becomes weak. For this reason, chargeable inorganic fine particles are likely to desorb over time, and even in the case of a thin film, charging over time may decrease. For these reasons, it is necessary that the average film thickness of the resin portion is 0.10 μm or more and less than 0.45 μm.

[0018] Further, the inventors of the present invention have conducted further studies and found that it is also very important that voids are contained in the coating layer in order to solve conventional problems. By containing voids in the coating layer, chargeable inorganic fine particles are exposed on the surface over time, and stable charging over time can be obtained.

[0019] On the other hand, it is important that the voids contained in the coating layer satisfy predetermined conditions. In the cross-section of the coating layer, when the cross-sectional area of the voids is S1, the cross-sectional area of the resin portion is S2, and the cross-sectional area ratio of the voids represented by the following formula is defined as the porosity, the porosity needs to be 0.1% or more and less than 2.8%. Porosity [%] = S1 / S2 × 100

[0020] When the porosity is 0.1% or more and less than 2.8%, the charged inorganic fine particles are moderately exposed on the surface over time, and stable charging over time can be obtained. When the porosity is less than 0.1%, spent of the toner components occurs, resulting in a decrease in charging. When the porosity is 2.8% or more, the resin layer (coating layer) becomes brittle and the fillers are detached, leading to a decrease in charging.

[0021] As a result of the study by the present inventors, it was found that good results can be obtained by defining the film thickness of the resin portion and the porosity of the voids contained in the coating layer within an appropriate range. The presence of voids in the coating layer is cited as a cause of the deterioration of the durability of the carrier film. When the coating layer is a thin film, it is considered that by reducing the porosity, the durability of the film can be increased and the detachment of the charged inorganic fine particles can be suppressed. However, even if the coating layer is a thin film, if the voids in the coating layer are eliminated, spent progresses as in the case of a thick film, and good charging properties cannot be obtained.

[0022] Therefore, the present inventors have found that good results can be obtained by setting the average film thickness of the resin portion containing the charged inorganic fine particles within the above range and setting the porosity of the voids contained in the coating layer within the above range, leading to the present invention. According to the present invention, sufficient charge control can be achieved for the image quality required in the field of electrophotography, and suppression of toner scattering can be achieved in the long term, and a carrier capable of suppressing toner scattering in the long term even when a low-temperature fixing toner is used can be provided.

[0023] In addition, in the present invention, good results can be obtained even when a dispersant is contained in the coating layer, and good results can also be obtained in a carrier having high adhesion between the resin and the charged inorganic fine particles. Furthermore, even when a dispersant is contained in the coating layer or in a carrier having high adhesion between the resin and the charged inorganic fine particles, toner scattering when using a low-temperature fixing toner can be suppressed in the long term.

[0024] Examples of the method for setting the porosity within the above range include using an antifoaming agent and controlling the addition amount of the antifoaming agent.

[0025] Figure 1 shows a schematic diagram illustrating porosity. Figure 1 schematically shows core material particles 20 and a coating layer 30 covering the core material particles 20. Only a part is shown here. In the illustrated example, the coating layer 30 has voids 31, resin 32, electrostatically charged inorganic fine particles 33, and conductive components 34. When the cross-sectional area of ​​the voids 31 is S1 and the cross-sectional area of ​​the resin 32 is S2, the porosity [%] can be calculated by S1 / S2 × 100.

[0026] Figure 2 shows a schematic diagram illustrating the average film thickness of the resin portion. Figure 2 schematically shows the core material particles 20 and the coating layer covering the core material particles 20. In the coating layer shown here, voids, charged fine particles, etc., are omitted from the illustration. When the outer circumference length of the carrier is L and the cross-sectional area of ​​the resin portion 32 is S2, the average film thickness [μm] of the resin portion can be calculated by S2 / L.

[0027] The cross-sectional area S2 of the resin portion may also be calculated by subtracting the cross-sectional areas of voids, electrostatically charged fine particles, and conductive components from the cross-sectional area of ​​the entire coating layer. For example, if the cross-section of the coating layer is S3 for the entire coating layer and S4 for the sum of the cross-sectional areas of the conductive components and electrostatically charged inorganic fine particles contained in the coating layer, the cross-sectional area S2 of the resin portion may be calculated as follows. S2 = S3 - S1 - S4

[0028] <Electrostatically charged inorganic microparticles> The coating layer in the present invention contains electrostatically charged inorganic fine particles and optionally contains other components. The electrostatically charged inorganic fine particles can be selected as appropriate, and are preferably inorganic fine particles selected from, for example, barium sulfate, magnesium oxide, magnesium hydroxide, and hydrotalcite. For example, since these materials can be positively charged, the ability to impart charge over a long period of time is stable when negatively charged toner is used. Barium sulfate, in particular, is well used because it has a high charging ability for negatively charged toner, is white, and has little impact on the color of the toner even when it detaches from the coating resin.

[0029] The electrostatically charged inorganic fine particles preferably have an equivalent circular diameter of 400 nm to 900 nm (0.4 μm to 0.9 μm). Within this range, the electrostatically charged inorganic fine particles can be present in a convex state on the surface of the coating layer, improving the electrostatic properties with the toner.

[0030] Furthermore, it is preferable that the equivalent circle diameter of the charged inorganic fine particles is 900 nm or less, because the particle size of the charged inorganic fine particles is not too large relative to the thickness of the coating layer, so they are sufficiently retained by the binder resin and are less likely to detach from the coating layer. It is more preferable that the equivalent circle diameter of the charged inorganic fine particles is 600 nm or more. In this case, more stable charging and developing capabilities can be ensured. The equivalent circle diameter of the charged inorganic fine particles can be calculated by cutting the carrier with ion milling and observing it with cross-sectional SEM and EDX.

[0031] When barium sulfate is used as the electrostatically charged inorganic fine particles, it is preferable that the amount of barium exposed on the surface of the coating layer be 0.1 atomic% or more. Since charge exchange for charging the toner takes place on the surface of the coating layer, in carriers where the exposure of barium sulfate on the surface of the coating layer is extremely small, the charge-imparting ability of barium sulfate is only exhibited when the coating layer is significantly worn away due to long-term carrier use. On the other hand, when the amount of barium exposed on the surface of the coating layer is 0.1 atomic% or more, it is preferable because the charge-imparting ability can be exhibited not only when the coating layer is worn away, but also when toner components adhere to the carrier surface (so-called spent) due to long-term use.

[0032] <Conductive components> The carrier of the present invention preferably contains a conductive component in the coating layer. In the present invention, the conductive component is a component present in the coating layer that enhances the conductivity of a coating resin with low conductivity. The conductive component can be appropriately selected, and in the case of inorganic fine particles, conventional existing materials and new materials can be used as long as the powder resistivity is 200 Ω·cm or less.

[0033] Furthermore, considering that the coating layer will gradually wear away with long-term use, it is preferable that the conductive component be as white or nearly colorless as possible. In this case, even if the coating layer gradually wears away with long-term use and the conductive component, which can function as a resistance modifier, detaches from the carrier surface, color contamination of the toner can be suppressed.

[0034] Examples of materials used as conductive components that exhibit good color and conductivity include compounds obtained by doping tin oxide with tungsten, indium, or phosphorus, or any of their oxides. These can be used as individual elements or as fine particles on the surface of substrate particles. As substrate particles, conventional or novel materials can be used, such as aluminum oxide and titanium oxide.

[0035] The inorganic fine particles used as conductive components preferably have an equivalent circular diameter of 600 nm to 1000 nm. A diameter of 600 nm or more prevents the particle size from being too small, allowing for efficient reduction of carrier resistance. A diameter of 1000 nm or less reduces the likelihood of desorption from the surface of the coating layer.

[0036] Furthermore, conductive polymer particles may be used as the conductive component. Conductive polymer particles are fine particles composed of a conductive polymer and dopant ions, which exhibit conductivity when dispersed in a solution or coating resin in a fine particle state. Because the conductive polymer exists in a fine particle state with dopant ions, it can be dispersed in the coating layer forming liquid (which may also be called a coating liquid, carrier coating liquid, etc.), and conductivity can be imparted after coating the carrier. In addition, even if it detaches from the coating layer, discoloration of the toner does not occur, and the deterioration of image quality due to color staining can be suppressed.

[0037] There are no particular restrictions on the conductive polymer particles, but it is preferable to use PEDOT (polyethylenedioxythiophene) as the conductive polymer. Furthermore, it is preferable to use PEDOT / PSS with polystyrene sulfonic acid as the dopant ion. Other examples of conductive polymers include polythiophene, polythiophene derivatives, polypyrrole, polypyrrole derivatives, polyaniline, and polyaniline derivatives.

[0038] Examples of dopant ions include β-naphthalenesulfonic acid, dodecylsulfonic acid, p-dodecylbenzenesulfonic acid, 10-camphorsulfonic acid, 1,2-benzenedicarboxylic acid-4-sulfonic acid-1,2-di(2-ethylhexyl) ester, sulfisophthalic acid esters, and other high molecular weight strongly acidic substances.

[0039] When the desorption of the conductive component responsible for resistance adjustment is less likely to occur, fluctuations in carrier resistance become less likely, and the stability of image quality improves.

[0040] <Dispersant> It is preferable to formulate the carrier of the present invention with a dispersant. By formulating a dispersant in a coating layer forming liquid containing a resin (binding resin), inorganic fine particles, a diluent solvent, etc., the inorganic fine particles can be dispersed down to the primary particle size and the particle size distribution can be narrowed. This eliminates coarse particles, which are not sufficiently embedded in the binding resin and are weakly fixed to the carrier surface. The aforementioned fine particles are prone to detachment due to stress in the initial stages of printing, which reduces carrier resistance and causes carrier adhesion to solid image areas, but this can be suppressed by formulating a dispersant. Note that the inorganic fine particles described here are common to both electrostatically charged inorganic fine particles and inorganic fine particles used as conductive components.

[0041] Furthermore, it is preferable that the dispersant has both a group that is compatible with the resin and a group that is compatible with the inorganic fine particles, in which case it has the effect of improving the affinity between the resin and the inorganic fine particles. As a result, the adhesion between the resin and the inorganic fine particles in the coating layer is increased, a stronger film can be formed, and the inorganic fine particles are less likely to detach from the coating layer even under stress during printing. This makes it possible to suppress the occurrence of carrier adhesion to solid image areas over time. In addition, since the detachment of inorganic fine particles that are responsible for charging with the toner is suppressed, it is possible to maintain the charging ability with the toner over time, and toner scattering becomes less likely.

[0042] The dispersant is not particularly limited, but examples include phosphate ester surfactants, sulfate ester surfactants, sulfonic acid surfactants, and carboxylic acid surfactants. Among these, phosphate ester surfactants are preferred. In this case, it becomes possible to disperse the inorganic fine particles well down to the primary particle size, homogenize the inorganic fine particles in the coating layer, and increase the affinity between the resin and the inorganic fine particles.

[0043] Furthermore, the inventors' studies have shown that adding a dispersant having a phosphate ester structure further improves the margin of safety against toner scattering. This is because the phosphate ester structure becomes positively charged relative to the negatively charged toner, and when a dispersant containing phosphate ester is added, the charging properties with the toner improve compared to when it is not added. In particular, the charging properties immediately after mixing and stirring with the toner, the so-called charge rise properties, are improved, which has a significant effect on the problem of toner scattering during replenishment, where the toner scatters because it is not sufficiently charged during replenishment.

[0044] When a phosphate ester surfactant is used as a dispersant, it is preferable that the phosphate ester surfactant contains a phosphate ester as its main component. In this embodiment, for it to be considered a "main component," it is preferable that the dispersant contains 50% by mass or more of the phosphate ester, and more preferably 90% by mass or more.

[0045] Commercially available products include, but are not limited to, Solspers 2000, 2400, 2600, 2700, 2800 (manufactured by Zeneca), Ajipar PB711, PA111, PB811, PW911 (manufactured by Ajinomoto Co.), EFKA-46, 47, 48, 49 (manufactured by EFKA Chemical Co.), Disperbic 160, 162, 163, 166, 170, 180, 182, 184, 190 (manufactured by Big Chemie Co.), Floren DOPA-158, 22, 17, G-700, TG-720W, 730W (manufactured by Kyoeisha Chemical Co.).

[0046] <Antifoaming agent> The carrier of the present invention preferably contains an antifoaming agent. By containing an antifoaming agent, foaming of the coating liquid can be suppressed, the generation of holes (voids) in the coating layer can be suppressed, and the void ratio can be controlled within the range mentioned above.

[0047] While not particularly limited, examples of defoaming agents include silicone-based, acrylic-based, and vinyl-based materials. Among these, silicone-based materials are preferred. A balance between compatibility and incompatibility with the solvent is important for exhibiting defoaming effects, and silicone-based materials have a good balance of compatibility and incompatibility. Therefore, a high defoaming effect can be obtained even with a small amount of additive, and the formation of pores in the coating layer can be suppressed.

[0048] Commercially available products include, but are not limited to, KS-530, KF-96, KS-7708, KS-66, KS-69 (manufactured by Shin-Etsu Silicone Co., Ltd.), TSF451, THF450, TSA720, YSA02, TSA750, TSA750S (manufactured by Momentive Performance Materials Inc.), BYK-065, BYK-066N, BYK-070, BYK-088, BYK-141 (manufactured by Bic Chemie Inc.), Disparon 1930N, Disparon 1933, Disparon 1934 (manufactured by Kusumoto Chemical Co., Ltd.).

[0049] The amount of defoaming agent to be added can be selected as appropriate, but it is preferable that it be between 1.0 part by mass and 10.0 parts by mass per 100 parts by mass of the total amount of coating liquid (coating layer forming liquid) that forms the coating layer. If the amount of defoaming agent added is less than 1.0 part by mass, the defoaming effect will not be sufficiently obtained, and holes will be formed in the coating resin. If the amount of defoaming agent added exceeds 10.0 parts by mass, surface defects called "repellency" will appear, the coating layer on the carrier surface will become brittle, inorganic fine particles will easily detach, and carrier adhesion to the solid image area will deteriorate.

[0050] Based on these considerations, the amount of defoaming agent added is preferably 1.0 part by mass or more and 10.0 parts by mass or less per 100 parts by mass of the total amount of coating liquid, and more preferably 2.0 parts by mass or more and 7.0 parts by mass or less.

[0051] <Resin> The resin included in the coating layer (also referred to as coating resin, etc.) can be selected as appropriate, and examples include silicone resin, acrylic resin, etc., and these may be used in combination. In particular, the use of silicone resin and acrylic resin in combination is preferred.

[0052] Acrylic resin has excellent abrasion resistance due to its strong adhesion and low brittleness. However, its high surface energy can lead to problems when combined with toners that are prone to smudging, such as a decrease in charge due to the accumulation of toner components. Silicone resin, on the other hand, has a low surface energy, making it difficult for toner components to smudge. This reduces the accumulation of smudging components that can cause film abrasion, thus resolving this problem.

[0053] However, silicone resin has weaknesses such as poor adhesion and high brittleness, resulting in poor abrasion resistance. Therefore, it is important to achieve a good balance between the properties of these two types of resins. In this case, it is possible to obtain a coating layer that is resistant to spending and also has abrasion resistance, and the improvement effect is significant. This is because silicone resin has a low surface energy, making it difficult for toner components to spend, and thus reducing the accumulation of spent components that cause film abrasion.

[0054] As used herein, "silicone resin" refers to all commonly known silicone resins, including, for example, straight silicone consisting only of organosilosane bonds, and silicone resins modified with alkyds, polyesters, epoxy, acrylics, urethanes, etc. However, it is not limited to these.

[0055] As commercially available products, they can be selected as appropriate. Examples of straight silicone resins include KR271, KR255, and KR152 from Shin-Etsu Chemical, and SR2400, SR2406, and SR2410 from Toray Dow Corning Silicone. In this case, it is possible to use the silicone resin alone, but it is also possible to use other components that undergo cross-linking reactions, charge adjustment components, etc., simultaneously.

[0056] Furthermore, examples of modified silicone resins include KR206 (alkyd modified), KR5208 (acrylic modified), ES1001N (epoxy modified), and KR305 (urethane modified) from Shin-Etsu Chemical, and SR2115 (epoxy modified) and SR2110 (alkyd modified) from Toray Dow Corning Silicone.

[0057] As used herein, "acrylic resin" refers to all resins containing acrylic components and is not particularly limited. While acrylic resin can be used alone, it is also possible to use at least one other component that undergoes a crosslinking reaction simultaneously. Examples of other components that undergo a crosslinking reaction include, but are not limited to, amino resins and acidic catalysts. Examples of amino resins include, but are not limited to, guanamine and melamine resins. Furthermore, any acidic catalyst exhibiting catalytic activity can be used. Examples include, but are not limited to, fully alkylated, methylol-type, imino-type, and methylol / imino-type catalysts with reactive groups.

[0058] The carrier of the present invention preferably has a volume-average particle size of 28 μm or more and 40 μm or less. If the volume-average particle size of the carrier particles is 28 μm or more, carrier adhesion can be suppressed, and if it is 40 μm or less, a decrease in the reproducibility of image details can be suppressed, and the inability to form a fine image can be suppressed.

[0059] The volume-average particle size can be measured, for example, using a microtrac particle size distribution analyzer model HRA9320-X100 (manufactured by Nikkiso Co., Ltd.).

[0060] The carriers of the present invention preferably have a volume resistivity of 8 to 16 LogΩ·cm. If the volume resistivity is 8 LogΩ·cm or higher, carrier adhesion will not occur in non-image areas, and if it is 16 LogΩ·cm or lower, the edge effect will not reach an unacceptable level.

[0061] The volume resistivity can be measured using the cell shown in Figure 3. Specifically, first, a carrier (3) is filled into a cell consisting of a fluororesin container (2) containing electrodes (1a) and (1b) with a surface area of ​​2.5 cm × 4 cm, separated by a distance of 0.2 cm. Then, 10 taps are performed with a drop height of 1 cm and a tapping speed of 30 taps / minute. Next, a DC voltage of 1000 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). The volume resistivity [Ω·cm] can then be calculated from the following formula 1.

[0062] r×(2.5×4) / 0.2 ··· Formula 1

[0063] When using silicone resin, acrylic resin, or a combination thereof as the coating resin, the film strength can be increased by crosslinking the silanol groups through condensation polymerization catalyst.

[0064] Examples of condensation catalysts include titanium-based catalysts, tin-based catalysts, zirconium-based catalysts, and aluminum-based catalysts. Among these various catalysts, titanium-based catalysts are preferred as they yield excellent results, and titanium diisopropoxybis(ethyl acetate) is particularly preferred. This is because it has a strong effect in promoting the condensation reaction of silanol groups and is less prone to catalyst deactivation.

[0065] A silane coupling agent may be used in the coating layer. By using a silane coupling agent, the charged inorganic fine particles can be stably dispersed. Silane coupling agents are not particularly limited, but examples include r-(2-aminoethyl)aminopropyltrimethoxysilane, r-(2-aminoethyl)aminopropylmethyldimethoxysilane, r-methacryloxypropyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-r-aminopropyltrimethoxysilane hydrochloride, r-glycidoxypropyltrimethoxysilane, r-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane, r-chloropropyltrimethoxysilane, and hexamethyldisilazane. Examples include r-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, r-chloropropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, allyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, dimethyldiethoxysilane, 1,3-divinyltetramethyldisilazane, methacrylateoxyethyldimethyl(3-trimethoxysilylpropyl)ammonium chloride, etc. Two or more may be used in combination.

[0066] Examples of commercially available silane coupling agents include 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, Z Examples include -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.), etc.

[0067] The amount of silane coupling agent added is preferably 0.1 to 10% by mass relative to the silicone resin. If the amount of silane coupling agent added is 0.1% by mass or more, it is possible to suppress a decrease in the adhesion between the core material particles or conductive fine particles and the silicone resin, and to suppress the peeling off of the coating layer during long-term use. If the amount is 10% by mass or less, it is possible to suppress the occurrence of toner filming during long-term use.

[0068] <Core material particles> The core material particles are not particularly limited as long as they are magnetic materials, but examples 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 a resin. Among these, Mn-based ferrite, Mn-Mg-based ferrite, and Mn-Mg-Sr ferrite are preferred from an environmental perspective.

[0069] The volume-average particle size of the core material particles is not particularly limited and can be selected as appropriate. From the viewpoint of preventing carrier adhesion and carrier scattering, a volume-average particle size of 20 μm or more is preferred. From the viewpoint of preventing the occurrence of abnormal images such as carrier streaks and preventing a decrease in image quality, a size of 100 μm or less is preferred. In particular, using particles of 28 to 40 μm can better meet the demands for high image quality in recent years.

[0070] (Developer) The developer of the present invention has the carrier of the present invention. The developer of the present invention can be used for electrophotographic image formation, and the two-component developer of the present invention has the carrier and toner of the present invention. The toner is preferably a negatively charged toner.

[0071] The toner contains a binder resin and a colorant, and may be either a monochrome toner or a color toner. Furthermore, for application in oil-less systems where toner-adhesion prevention oil is not applied to the fuser roller, the toner particles may contain a release agent. Such toners are generally prone to filming, but the carrier of the present invention can suppress filming, allowing the developer of the present invention to maintain good quality over a long period. Moreover, color toners, particularly yellow toners, generally suffer from color staining due to wear of the carrier coating layer, but the developer of the present invention can suppress the occurrence of color staining.

[0072] Toner can be manufactured using known methods such as grinding and polymerization. For example, when manufacturing toner using the grinding method, first, the molten mixture obtained by kneading the toner material is cooled, then ground and classified to produce matrix particles. Next, to further improve transferability and durability, an external additive is added to the matrix particles to produce toner.

[0073] In this case, the equipment used to knead the toner material is not particularly limited, but examples include batch-type two-roll extruders; Banbury mixers; continuous twin-screw extruders such as the KTK type twin-screw extruder (manufactured by Kobe Steel, Ltd.), TEM type twin-screw extruder (manufactured by Toshiba Machine Co., Ltd.), twin-screw extruder (manufactured by KCK Co., Ltd.), PCM type twin-screw extruder (manufactured by Ikegai Iron Works Co., Ltd.), and KEX type twin-screw extruder (manufactured by Kurimoto Iron Works Co., Ltd.); and continuous single-screw kneaders such as the Co-Kneader (manufactured by Buss Co., Ltd.).

[0074] Furthermore, when grinding the cooled molten mixture, it can be coarsely ground using a hammer mill, Rotoplex, etc., and then finely ground using a jet-stream pulverizer, mechanical pulverizer, etc. It is preferable to grind it so that the average particle size is 3 to 15 μm.

[0075] Furthermore, when classifying the crushed molten mixture, a wind-powered classifier or the like can be used. It is preferable to classify the material so that the average particle size of the parent particles is 5 to 20 μm. Furthermore, when adding external additives to the parent particles, mixing and stirring with mixers causes the external additives to break down and adhere to the surface of the parent particles.

[0076] The binder resin is not particularly limited and can be selected as appropriate. Examples include homopolymers of styrene and its substituted products such as polystyrene, poly-p-styrene, and polyvinyltoluene; styrene-based copolymers such as 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-chloromethacrylate 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; 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, aromatic petroleum resin, etc. Two or more of these may be used in combination.

[0077] The binder resin for pressure fixing is not particularly limited and can be selected as appropriate. Examples 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 phenol resin, and phenol-modified terpene resin, and two or more may be used in combination.

[0078] The coloring agent (pigment or dye) is not particularly limited and can be selected as appropriate. For example, 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, tartrazine lake; orange pigments such as molybdenum orange, permanent orange GTR, pyrazolone orange, balkan orange, indanthrene brilliant orange RK, benzidine orange G, indanthrene brilliant orange GK; red iron oxide, cadmium red, permanent red 4R, lysol red, pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodochrosite Examples of pigments include red pigments such as Min 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, Metalless 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 such as Carbon Black, Oil Furnace Black, Channel Black, Lamp Black, Acetylene Black, and Aniline Black, as well as metal salt azo dyes, metal oxides, and composite metal oxides. Two or more types may be used in combination.

[0079] The mold release agent is not particularly limited and can be selected as appropriate. Examples 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. Two or more types may be used in combination.

[0080] Furthermore, the toner may further contain a charge control agent. The charge control agent is not particularly limited and can be selected as appropriate. For example, nigrosine; an azine dye having an alkyl group with 2 to 16 carbon atoms; CIBasic Yellow 2 (CI41000), CIBasic Yellow 3, CIBasic Red 1 (CI45160), CIBasic Red 9 (CI42500), CIBasic Violet 1 (CI42535), CIBasic Violet 3 (CI42555), CIBasic Violet 10 (CI45170), CIBasic Violet 14 (CI42510), CIBasic Blue 1 (CI42025), CIBasic Blue 3 (CI51005), CIBasic Blue 5 (CI42140), CIBasic Blue 7 (CI42595), CIBasic Blue 9 (CI52015), CIBasic Blue 24 (CI52030), CIBasic Blue 25 (CI52025), CIBasic Blue Examples include basic dyes such as 26 (CI44045), CIBasic Green 1 (CI42040), and CIBasic Green 4 (CI42000); lake pigments of these basic dyes; quaternary ammonium salts such as CISolvent Black 8 (CI26150), benzoylmethylhexadecylammonium chloride, and decyltrimethyl chloride; dialkyltin compounds such as dibutyl and dioctyl; dialkyltin borate compounds; guanidine derivatives; polyamine resins such as vinyl polymers and condensation polymers having amino groups; metal complex salts of monoazo dyes; salicylic acid; metal complexes of dialkylsalicylic acid, naphthoic acid, and dicarboxylic acids such as Zn, Al, Co, Cr, and Fe; sulfonated copper phthalocyanine pigments; organoboro salts; fluorine-containing quaternary ammonium salts; and calixalene compounds, although two or more may be used in combination. For color toners other than black, metal salts of white salicylic acid derivatives are preferred.

[0081] The external additives are not particularly limited and can be selected as appropriate. Examples include inorganic particles such as silica, titanium dioxide, alumina, silicon carbide, silicon nitride, and boron nitride; and resin particles such as polymethyl methacrylate particles and polystyrene particles with an average particle size of 0.05 to 1 μm obtained by soap-free emulsion polymerization. Two or more types may be used in combination. Among these, metal oxide particles such as silica and titanium dioxide, whose surfaces have been hydrophobized, are preferred.

[0082] Furthermore, by using hydrophobically treated silica and hydrophobically treated titanium dioxide in combination, and by adding a larger amount of hydrophobically treated titanium dioxide than hydrophobically treated silica, a toner with excellent charge stability against humidity can be obtained.

[0083] By applying the carrier of the present invention to an image forming apparatus that performs image formation while discharging excess developer from the developing apparatus, using a replenishment developer containing carrier and toner, extremely stable image quality can be obtained over a very long period. In other words, the deteriorated carrier in the developing apparatus is replaced with the undegraded carrier in the replenishment developer, maintaining a stable charge level over a long period and obtaining a stable image. This method is particularly effective when printing high image area. When printing high image area, the main carrier degradation is due to carrier charge degradation caused by toner deposition on the carrier. However, by using this method, the amount of carrier replenishment increases when printing high image area, so the frequency of replacement of deteriorated carriers increases. As a result, an extremely stable image can be obtained over a very long period.

[0084] As for the mixing ratio of the replenishment developer, it is preferable to use a ratio of 2 to 50 parts by mass of toner per 1 part by mass of carrier. When the amount of toner is 2 parts by mass or more, there is no excess carrier supply, and the carrier concentration in the developing device does not become too high, making it difficult to increase the charge amount of the developer. When the charge amount of the developer increases, the developing ability decreases and the image density may decrease. Also, when the amount is 50 parts by mass or less, the proportion of carriers in the replenishment developer does not decrease, so there is a greater exchange of carriers in the image forming device, and an effect against carrier degradation can be expected.

[0085] Furthermore, it is preferable that the toner concentration in the two-component developer is in the range of 4% by mass or more and 9% by mass or less. A concentration of 4% by mass or more results in a large amount of toner, allowing for appropriate image density. A concentration of 9% by mass or less makes it easier for the carrier toner to be retained, reducing the likelihood of toner scattering.

[0086] (Image forming method) The image forming method of the present invention uses the developer of the present invention. The image forming method of the present invention includes, for example, the steps of: forming an electrostatic latent image on an electrostatic latent image carrier; developing the electrostatic latent image formed on the electrostatic latent image carrier using the two-component developer of the present invention to form a toner image; transferring the toner image formed on the electrostatic latent image carrier to a recording medium; and fixing the toner image transferred to the recording medium. The developer used is the developer of the present invention, for example, a two-component developer.

[0087] (Processing cartridge) The process cartridge of the present invention comprises the developer of the present invention. The process cartridge of the present invention includes, for example, an electrostatic latent image carrier, a charging member for charging the surface of the electrostatic latent image carrier, a developing member for developing the electrostatic latent image formed on the electrostatic latent image carrier using the two-component developer of the present invention, and a cleaning member for cleaning the electrostatic latent image carrier. The developer of the present invention, for example, a two-component developer, is used as the developer.

[0088] Figure 4 shows an example of a process cartridge of the present invention. The process cartridge 10 is supported integrally by a photoreceptor 11, a charging device 12, a developing device 13, and a cleaning device 14. The photoreceptor 11 is an electrostatic latent image carrier. The charging device 12 is a charging member that charges the photoreceptor 11. The developing device 13 is a developing member that develops the electrostatic latent image formed on the photoreceptor 11 using the developer of the present invention to form a toner image. The cleaning device 14 is a cleaning member that removes the toner remaining on the photoreceptor 11 after transferring the toner image formed on the photoreceptor 11 to a recording medium. Furthermore, the process cartridge 10 is detachable from the main body of an image forming device such as a copier or printer.

[0089] The following describes a method for forming an image using an image forming apparatus equipped with a process cartridge 10. First, the photoreceptor 11 is driven to rotate at a predetermined peripheral speed, and the peripheral surface of the photoreceptor 11 is uniformly charged to a predetermined positive or negative potential by the charging device 12. Next, exposure light is irradiated onto the peripheral surface of the photoreceptor 11 from an exposure device such as a slit exposure device or a scanning exposure device using a laser beam, and electrostatic latent images are sequentially formed. Furthermore, the electrostatic latent images formed on the peripheral surface of the photoreceptor 11 are developed by the developing device 13 using the developer of the present invention, and a toner image is formed. Next, the toner image formed on the peripheral surface of the photoreceptor 11 is sequentially transferred to transfer paper fed between the photoreceptor 11 and the transfer device from the paper feeding unit (not shown), synchronized with the rotation of the photoreceptor 11. Furthermore, the transfer paper on which the toner image has been transferred is separated from the peripheral surface of the photoreceptor 11, introduced into a fixing device, and fixed, and then printed out as a copy to the outside of the image forming apparatus. On the other hand, after the toner image is transferred, the surface of the photoreceptor 11 is cleaned by the cleaning device 14 to remove any remaining toner, then static electricity is removed by the static elimination device, and it is used repeatedly for image formation.

[0090] (Image forming apparatus) The image forming apparatus of the present invention is equipped with the developer of the present invention. The image forming apparatus of the present invention includes, for example, 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 using the developer 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. Furthermore, it includes other means as appropriate as needed, such as a static elimination means, a cleaning means, a recycling means, a control means, etc. The developer of the present invention, for example a two-component developer, is used as the developer. [Examples]

[0091] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" in the following description refers to "parts by mass," and "%" refers to "percent mass."

[0092] (Manufacturing Example 1) <Resin liquid 1> • Acrylic resin solution (solid content concentration: 20%) 200 units • Silicone resin solution (solid content concentration: 40%) 2000 units • Aminosilane (solid content concentration: 100%) 20 parts Tungsten oxide-doped tin oxide (WTO) surface-treated alumina, 1160 parts (Powder specific resistance: 40 [Ω cm]) Barium sulfate 880 units (Equivalent diameter of circle: 0.60 [μm]) • Toluene 6800 copies • Dispersant (phosphate ester-based surfactant) 40 parts • Antifoaming agent (silicone-based) 290 units

[0093] Each of the above materials was dispersed in a homomixer for 10 minutes to prepare [Resin Liquid 1] as a coating layer forming liquid (resin layer forming liquid). Mn ferrite with a volume average particle size of 36.5 μm was used as the core material particle of the carrier, and [Resin Liquid 1] was applied to the surface of the core material at a rate of 30 g / min in a 60°C atmosphere using a Spira Coater SP-40 (manufactured by Okada Seikou Co., Ltd.) to a thickness of 0.35 μm, and then dried. The obtained carrier was fired in an electric furnace at 230°C for 1 hour, and after cooling, it was crushed using a sieve with a mesh size of 100 μm to obtain [Carrier 1]. The average thickness (average film thickness) T of the coating resin (resin portion) of [Carrier 1] was 0.35 μm. The porosity of the coating layer was 1.3%.

[0094] Let me explain the measurement process. The volume-average particle size of the core material particles was measured using a Microtrac particle size analyzer (SRA type, Nikkiso Co., Ltd.) with a range setting of 0.7 μm or more and 125 μm or less. The porosity of the coating layer and the average thickness of the coating resin (average film thickness) were confirmed by cutting the carrier using ion milling and observing the cross-section with SEM.

[0095] The details are as follows: The carrier was mixed with embedding resin (Struers EpoFix, two-component, 12-hour curing epoxy resin), allowed to cure overnight or longer, and a rough cross-sectional sample was prepared using a cutter. The cross-section was then finished using ion milling (Hitachi High-Technologies IM4000PLUS) at an acceleration voltage of 4.5kV and a processing time of 5 hours. This was then imaged using a scanning electron microscope (Carl Zeiss Merlin) at an acceleration voltage of 2.0kV and a magnification of 10kx. The captured images were imported into TIFF format, and the porosity of the coating layer and the average thickness of the coating resin (average film thickness) were calculated using Media Cybernetics Image-Pro Plus.

[0096] The void ratio was calculated by taking a cross-section of the coating layer, where S1 was the cross-sectional area of ​​the voids and S2 was the cross-sectional area of ​​the resin portion, and calculating it using the following formula. Porosity [%]=S1 / S2×100

[0097] The average thickness (average film thickness) was calculated using the following formula, where S2 is the cross-sectional area of ​​the resin portion and L is the outer circumference of the carrier in the cross-section of the coating layer. Average film thickness [μm]=S2 / L

[0098] The cross-sectional area S2 of the resin portion was calculated as follows, with S3 being the total cross-sectional area of ​​the coating layer and S4 being the sum of the cross-sectional areas of the conductive components and electrostatically charged inorganic fine particles contained in the resin layer. S2 = S3 - S1 - S4

[0099] Furthermore, the equivalent circular diameter of charged inorganic nanoparticles can be confirmed by slicing the carriers using ion milling and observing them with cross-sectional SEM and EDX. The details are as follows: The carrier was mixed with embedding resin (Struers EpoFix, two-component epoxy resin, 12-hour curing type), allowed to cure overnight or longer, and a rough cross-sectional sample was prepared using a cutter. The cross-section was then finished using ion milling (Hitachi High-Technologies IM4000PLUS) under conditions of acceleration voltage 4.5kV and processing time 5 hours. This was then imaged using a scanning electron microscope (Carl Zeiss Merlin) under conditions of acceleration voltage 0.8kV and magnification 10kx. The captured images were imported into TIFF format, and the equivalent circle diameter of 100 charged inorganic microparticles was measured using Media Cybernetics Image-Pro Plus, and the average value was used.

[0100] Furthermore, the amount of barium exposed on the surface of the coating layer can be detected by the atomic percentage of barium calculated using peak analysis with AXIS / ULTRA (Shimadzu / KRATOS). The beam irradiation area of ​​this device is approximately 900 μm × 600 μm, and detection is performed within a range of 25 carriers × 17. The penetration depth is 0 to 10 nm, and information near the surface of the carriers is detected. The specific measurement method is as follows: Measurement mode: Al: 1486.6 eV, Excitation source: Monochrome (Al), Detection method: Spectral mode, Magnetic lens: OFF. First, the detected elements are identified by a wide-area scan, and then peaks are detected for each detected element using a narrow scan. After that, the atomic percentage of barium for all detected elements is calculated using the attached peak analysis software.

[0101] (Manufacturing Example 2) Carrier 2 was obtained in the same manner as in Manufacturing Example 1, except that the above-mentioned resin liquid 1 was applied to the core material surface with a Spira Coater SP-40 to a thickness of 0.12 μm.

[0102] (Manufacturing Example 3) A carrier (carrier 3) was obtained in the same manner as in Manufacturing Example 1, except that the above-mentioned resin liquid (1) was applied to the core material surface with a Spira Coater SP-40 to a thickness of 0.44 μm.

[0103] (Manufacturing Example 4) Carrier 4 was obtained in the same manner as in Manufacturing Example 1, except that barium sulfate was replaced with magnesium oxide (equivalent circle diameter: 0.55 μm).

[0104] (Manufacturing Example 5) Carrier 5 was obtained in the same manner as in Manufacturing Example 1, except that barium sulfate was replaced with magnesium hydroxide (equivalent circle diameter: 0.61 μm).

[0105] (Manufacturing Example 6) Carrier 6 was obtained in the same manner as in Manufacturing Example 1, except that barium sulfate was replaced with hydrotalcite (equivalent circle diameter: 0.58 μm).

[0106] (Manufacturing Example 7) <Resin liquid 7> • Acrylic resin solution (solid content concentration: 20%) 200 units • Silicone resin solution (solid content concentration: 40%) 2000 units • Aminosilane (solid content concentration: 100%) 20 parts Tungsten oxide-doped tin oxide (WTO) surface-treated alumina, 1160 parts (Powder specific resistance: 40 [Ω cm]) Barium sulfate 220 units (Equivalent diameter of circle: 0.60 [μm]) • Toluene 6800 copies • Dispersant (phosphate ester-based surfactant) 30 parts • Antifoaming agent (silicone-based) 270 units

[0107] Carrier 7 was obtained in the same manner as in Manufacturing Example 1, except that resin liquid 1 was changed to resin liquid 7.

[0108] (Manufacturing Example 8) <Resin liquid 8> • Acrylic resin solution (solid content concentration: 20%) 200 units • Silicone resin solution (solid content concentration: 40%) 2000 units • Aminosilane (solid content concentration: 100%) 20 parts Tungsten oxide-doped tin oxide (WTO) surface-treated alumina, 1160 parts (Powder specific resistance: 40 [Ω cm]) Barium sulfate 220 units (Equivalent diameter of circle: 0.60 [μm]) • Toluene 6800 copies • Dispersant (phosphate ester-based surfactant) 30 parts • Antifoaming agent (silicone-based) 580 units

[0109] Carrier 8 was obtained in the same manner as in Manufacturing Example 1, except that [Resin Liquid 1] was changed to [Resin Liquid 8]. The porosity of the coating layer of Carrier 8 was 0.3%.

[0110] (Manufacturing Example 9) <Resin liquid 9> • Acrylic resin solution (solid content concentration: 20%) 200 units • Silicone resin solution (solid content concentration: 40%) 2000 units • Aminosilane (solid content concentration: 100%) 20 parts Tungsten oxide-doped tin oxide (WTO) surface-treated alumina, 1160 parts (Powder specific resistance: 40 [Ω cm]) Barium sulfate 220 units (Equivalent diameter of circle: 0.60 [μm]) • Toluene 6800 copies • Dispersant (phosphate ester-based surfactant) 30 parts • Antifoaming agent (silicone-based) 110 units

[0111] Carrier 9 was obtained in the same manner as in Manufacturing Example 1, except that resin liquid 1 was replaced with resin liquid 9. The porosity of the coating layer of carrier 9 was 2.7%.

[0112] (Comparative example 1 of manufacturing) A carrier (carrier 10) was obtained in the same manner as in Manufacturing Example 1, except that the above-mentioned resin liquid (1) was applied to the core material surface with a Spira Coater SP-40 to a thickness of 0.50 μm.

[0113] (Manufacturing Comparison Example 2) A carrier (carrier 11) was obtained in the same manner as in Manufacturing Example 1, except that the above-mentioned resin liquid (1) was applied to the core material surface with a Spira Coater SP-40 to a thickness of 0.08 μm.

[0114] (Manufacturing Comparison Example 3) <Resin liquid 12> • Acrylic resin solution (solid content concentration: 20%) 200 units • Silicone resin solution (solid content concentration: 40%) 2000 units • Aminosilane (solid content concentration: 100%) 20 parts Tungsten oxide-doped tin oxide (WTO) surface-treated alumina, 1160 parts (Powder specific resistance: 40 [Ω cm]) • Toluene 6800 copies • Dispersant (phosphate ester-based surfactant) 30 parts • Antifoaming agent (silicone-based) 110 units

[0115] The carrier 12 was obtained in the same manner as in Manufacturing Example 1, except that resin liquid 1 was changed to resin liquid 12.

[0116] (Manufacturing Comparison Example 4) <Resin liquid 13> • Acrylic resin solution (solid content concentration: 20%) 200 units • Silicone resin solution (solid content concentration: 40%) 2000 units • Aminosilane (solid content concentration: 100%) 20 parts Tungsten oxide-doped tin oxide (WTO) surface-treated alumina, 1160 parts (Powder specific resistance: 40 [Ω cm]) Barium sulfate 220 units (Equivalent diameter of circle: 0.60 [μm]) • Toluene 6800 copies • Dispersant (phosphate ester-based surfactant) 30 parts • Antifoaming agent (silicone-based) 580 units

[0117] Each of the above materials was dispersed in a homomixer for 10 minutes to prepare [resin liquid 13] as a coating layer forming liquid. [Resin liquid 13] was degassed to remove dissolved gases. Mn ferrite with a volume average particle size of 36.5 μm was used as the core material particle of the carrier, and [resin liquid 13] was applied to the core material surface to a thickness of 0.35 μm at a rate of 30 g / min using a Spira Coater SP-40 (manufactured by Okada Seikou Co., Ltd.) in a 60°C atmosphere, and then dried. [Carrier 13] was obtained in the same manner as in Manufacturing Example 1 except for the above. The porosity of the coating layer of [carrier 13] was 0.05%.

[0118] (Comparative Example 5) <Resin liquid 14> • Acrylic resin solution (solid content concentration: 20%) 200 units • Silicone resin solution (solid content concentration: 40%) 2000 units • Aminosilane (solid content concentration: 100%) 20 parts Tungsten oxide-doped tin oxide (WTO) surface-treated alumina, 1160 parts (Powder specific resistance: 40 [Ω cm]) Barium sulfate 220 units (Equivalent diameter of circle: 0.60 [μm]) • Toluene 6800 copies • Dispersant (phosphate ester-based surfactant) 30 parts

[0119] Carrier 14 was obtained in the same manner as in Manufacturing Example 1, except that resin liquid 1 was replaced with resin liquid 14. The porosity of the coating layer of carrier 14 was 7.0%.

[0120] The obtained carrier characteristics are shown in Table 1.

[0121] [Table 1]

[0122] (Example of toner manufacturing) The toner was manufactured as follows:

[0123] <Synthesis of polyester resin A> In a reaction vessel equipped with a condenser, stirrer, and nitrogen inlet, 65 parts of a 2-mol ethylene oxide adduct of bisphenol A, 86 parts of a 3-mol propion oxide adduct of bisphenol A, 274 parts of terephthalic acid, and 2 parts of dibutyltin oxide were added and reacted at atmospheric pressure at 230°C for 15 hours. Next, the reaction was carried out under reduced pressure of 5-10 mmHg for 6 hours to synthesize [Polyester Resin A]. The obtained [Polyester Resin A] had a number-average molecular weight (Mn) of 2,300, a weight-average molecular weight (Mw) of 8,000, a glass transition temperature (Tg) of 58°C, an acid value of 25 mgKOH / g, and a hydroxyl value of 35 mgKOH / g.

[0124] <Synthesis of prepolymers (polymers that can react with active hydrogen group-containing compounds)> In a reaction vessel equipped with a condenser, stirrer, and nitrogen inlet, 682 parts of bisphenol A ethylene oxide 2 molar adduct, 81 parts of bisphenol A propylene oxide 2 molar adduct, 283 parts of terephthalic acid, 22 parts of trimellitic anhydride, and 2 parts of dibutyltin oxide were charged and reacted at atmospheric pressure at 230°C for 8 hours. Subsequently, the reaction was carried out under reduced pressure of 10-15 mHg for 5 hours to synthesize the intermediate polyester. The obtained intermediate polyester had a number-average molecular weight (Mn) of 2,100, a weight-average molecular weight (Mw) of 9,600, a glass transition temperature (Tg) of 55°C, an acid value of 0.5, and a hydroxyl value of 49. Next, 411 parts of the [intermediate polyester], 89 parts of isophorone diisocyanate, and 500 parts of ethyl acetate were charged into a reaction vessel equipped with a condenser, a stirrer, and a nitrogen inlet tube, and reacted at 100°C for 5 hours to synthesize a [prepolymer] (a polymer capable of reacting with the active hydrogen group-containing compound). The obtained prepolymer had a free isocyanate content of 1.60% by mass, and its solid content (after standing at 150°C for 45 minutes) was 50% by mass.

[0125] <Synthesis of Ketimine (the active hydrogen group-containing compound)> In a reaction vessel equipped with a stirring rod and a thermometer, 30 parts of isophorone diamine and 70 parts of methyl ethyl ketone were charged, and the reaction was carried out at 50°C for 5 hours to synthesize [ketimine] (the active hydrogen group-containing compound). The amine value of the obtained [ketimine] (the active hydrogen group-containing compound) was 423.

[0126] <Masterbatch Preparation> 1,000 parts water, 540 parts Printex35 carbon black (manufactured by Degussa) with a DBP oil absorption of 42 mL / 100 g and a pH of 9.5, and 1,200 parts polyester resin A were mixed using a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.). Next, the resulting mixture was kneaded at 150°C for 30 minutes using a double roll mill, then rolled and cooled, and pulverized in a pulperizer (manufactured by Hosokawa Micron Corporation) to prepare a masterbatch.

[0127] <Preparation of aqueous media> A water-based medium was prepared by mixing and stirring 306 parts of deionized water, 265 parts of a 10% by mass suspension of tricalcium phosphate, and 1.0 part of sodium dodecylbenzenesulfonate until uniformly dissolved.

[0128] <Measurement of critical micelle concentration> The critical micelle concentration of surfactants was measured using the following method. Analysis was performed using an analysis program within the Sigma system with a Sigma surface tension meter (KSV Instruments). Surfactants were added dropwise to an aqueous medium in 0.01% increments, and the surface tension was measured after stirring and standing. From the obtained surface tension curve, the surfactant concentration at which the surface tension no longer decreased with further addition of surfactant was calculated as the critical micelle concentration. The critical micelle concentration of sodium dodecylbenzenesulfonate relative to the mass of the aqueous medium was measured using a Sigma surface tension meter and found to be 0.05%.

[0129] <Preparation of toner material solution> 70 parts of [polyester resin A], 10 parts of [prepolymer], and 100 parts of ethyl acetate were placed in a beaker and stirred to dissolve. 5 parts of paraffin wax (HNP-9, manufactured by Nippon Seiro Co., Ltd., melting point 75°C), 2 parts of MEK-ST (manufactured by Nissan Chemical Industries, Ltd.), and 10 parts of [masterbatch] were added as release agents. Using an UltraViscomill bead mill (manufactured by AIMEX Corporation), the mixture was passed through three passes at a liquid delivery rate of 1 kg / hour and a disk peripheral speed of 6 m / sec, with 80% by volume of zirconia beads with a particle size of 0.5 mm packed inside. Then, 2.7 parts of [ketimine] were added and dissolved to prepare the toner material solution.

[0130] <Preparation of emulsified or dispersed liquids> 150 parts of the aqueous media phase were placed in a container and stirred at a rotation speed of 12,000 rpm using a TK-type homomixer (manufactured by Tokushu Kika Kogyo Co., Ltd.). 100 parts of the toner material liquid were added to this mixture and mixed for 10 minutes to prepare an emulsified or dispersed liquid (emulsified slurry).

[0131] <Removal of organic solvents> A 100-part emulsified slurry was placed in a corve equipped with a stirrer and thermometer, and the solvent was removed at 30°C for 12 hours while stirring at a peripheral speed of 20 m / min to prepare a dispersed slurry.

[0132] <Cleaning> After 100 parts of the dispersion slurry were filtered under reduced pressure, 100 parts of deionized water were added to the filter cake, and the mixture was mixed in a TK homomixer (at a rotation speed of 12,000 rpm for 10 minutes) and then filtered. The process of adding 300 parts of deionized water to the obtained filter cake, mixing in a TK homomixer (at a rotation speed of 12,000 rpm for 10 minutes), and filtering was repeated twice. 20 parts of a 10% by mass sodium hydroxide aqueous solution were added to the obtained filter cake, and the mixture was mixed in a TK homomixer (at a rotation speed of 12,000 rpm for 30 minutes), and then filtered under reduced pressure. 300 parts of deionized water were added to the obtained filter cake, and the mixture was mixed in a TK homomixer (at a rotation speed of 12,000 rpm for 10 minutes), and then filtered. The process of adding 300 parts of deionized water to the obtained filter cake, mixing in a TK homomixer (at a rotation speed of 12,000 rpm for 10 minutes), and then filtering was repeated twice. Furthermore, 20 parts of 10% hydrochloric acid were added to the resulting filtration cake, and the mixture was mixed using a TK homomixer (at a rotation speed of 12,000 rpm for 10 minutes) before being filtered.

[0133] <Surfactant amount adjustment> The filtration cake obtained by the above washing process was mixed with 300 parts of deionized water using a TK homomixer (at 12,000 rpm for 10 minutes). The electrical conductivity of the resulting toner dispersion was measured, and the surfactant concentration of the toner dispersion was calculated from a previously prepared calibration curve. Based on this value, deionized water was added until the surfactant concentration reached the target concentration of 0.05%, thereby obtaining the toner dispersion.

[0134] <Surface treatment process> The toner dispersion, adjusted to the predetermined surfactant concentration, was heated in a water bath at a heating temperature T1 = 55°C for 10 hours while being mixed at 5000 rpm using a TK homomixer. After that, the toner dispersion was cooled to 25°C and filtered. Furthermore, 300 parts of deionized water were added to the resulting filter cake, mixed in a TK homomixer (at a rotation speed of 12,000 rpm for 10 minutes), and then filtered.

[0135] <Drying> The resulting final filtered cake was dried in a circulating air dryer at 45°C for 48 hours and sieved with a 75 μm mesh to obtain [toner matrix particles 1].

[0136] <External processing> Furthermore, to obtain [Toner 1], 100 parts of [Toner matrix particles 1] were mixed in a Henschel mixer with 3.0 parts of hydrophobic silica with an average particle size of 100 nm, 1.0 part of titanium dioxide with an average particle size of 20 nm, and 1.5 parts of hydrophobic silica fine powder with an average particle size of 15 nm.

[0137] (Preparation of developer) The carriers [1] to

[14] (93 parts) and toner 1 (7 parts) obtained in the examples and comparative examples were mixed and stirred at 81 rpm for 3 minutes using a turbulent mixer to prepare the developer [1] to

[14] for evaluation. In addition, replenishment developers for these developers were prepared using the carriers and toner so that the toner concentration was 95%.

[0138] (evaluation) The following evaluations were performed using the obtained [Developer 1] to [Developer 14]. To evaluate the ability to impart charge to the toner, we evaluated the stability of charge over time and the scattering of toner. The digital full-color multifunction printer (Ricoh Pro C9100) used for the evaluation is a color production printer, and the continuous paper feeding at low image area density was evaluated even in a high-speed machine using low-temperature fixing toner, as described below.

[0139] <Static stability over time> The Ricoh Pro C9100 (Ricoh digital color copier / printer) was evaluated using the [Developer 1] to [Developer 14] from the examples and comparative examples, along with their replenishment developers, on a carrier after running 1 million images at an image area ratio of 40%. First, the initial charge level of the carriers (Q1) was measured using a blow-off device TB-200 (manufactured by Toshiba Chemical Co., Ltd.) on a sample prepared by mixing [Carrier 1] to [Carrier 14] and [Toner 1] in a mass ratio of 93:7 and triboelectrically charging it. The charge level of the carriers after 1 million runs (Q2) was measured in the same manner as above, except that the carriers used were those from which the toners of each color had been removed from the developer after running using the blow-off device. The rate of change in charge level was defined as the absolute value of (Q1-Q2) / (Q1)×100. The evaluation criteria are shown below.

[0140] [Evaluation Criteria] 0 or more but less than 5: ◎ (Excellent) 5 or higher but less than 10: ○ (Good) 10 or more but less than 20: △ (Usable) 20 or more: × (defective)

[0141] <Toner scattering> Using a Ricoh Pro C9100 (Ricoh digital color copier / printer), the amount of toner accumulated at the bottom of the developer carrier after running 1 million images at an image area ratio of 40% with [Developer 1] to [Developer 14] from the examples and comparative examples, along with their replenishment developers, was collected and the toner mass was measured. The evaluation criteria are shown below.

[0142] [Evaluation Criteria] 0mg or more to less than 50mg: ◎ (Excellent) 50mg or more but less than 100mg: ○ (Good) 100mg or more but less than 250mg: △ (Usable) 250mg or more: × (Poor)

[0143] The evaluation results are shown in Table 2.

[0144] [Table 2]

[0145] Examples of the present invention are as follows: <1> A carrier comprising core material particles and a coating layer covering the core material particles, The coating layer comprises a resin and electrostatically charged inorganic fine particles, and contains voids within the coating layer. The average film thickness of the aforementioned resin portion is 0.10 μm or more and less than 0.45 μm. A carrier characterized in that, in the cross-section of the coating layer, S1 is the cross-sectional area of ​​the voids, S2 is the cross-sectional area of ​​the resin portion, and the void ratio is expressed by the following formula, the void ratio is 0.1% or more and less than 2.8%. Porosity [%]=S1 / S2×100 <2> The electrostatically charged inorganic fine particles are characterized by being one or more selected from barium sulfate, magnesium oxide, magnesium hydroxide, and hydrotalcite. <1> The careers listed. <3> The electrostatically charged inorganic fine particles contain barium sulfate, The coating layer is characterized in that the amount of barium exposed on its surface is 0.1 atomic% or more. <1> or <2> The careers listed. <4> The coating layer is characterized by containing an antifoaming agent. <1> from <3> A carrier listed in any of the above. <5> <1> from <4> A developer characterized by containing a carrier as described in any of the following. <6> <5> An image forming method characterized by using the developer described above. <7> <5> An image forming apparatus characterized by comprising the developer described above. <8> <5> A process cartridge characterized by comprising the developer described above. [Explanation of Symbols]

[0146] 1a electrode 1b electrode 2 containers 3 carriers 10 Process Cartridges 11 Photoreceptor 12 Charging device 13. Developing device 14 Cleaning device 20 Core material particles 30 Covering layer 31 void 32 resin 33 Charged particles 34 Conductive components [Prior art documents] [Patent Documents]

[0147] [Patent Document 1] Patent No. 5534409 [Patent Document 2] Japanese Patent Publication No. 2011-209678 [Patent Document 3] Japanese Patent Publication No. 2016-212254 [Patent Document 4] Japanese Patent Publication No. 2017-167387 [Patent Document 5] Japanese Patent Publication No. 2021-076820

Claims

1. A carrier comprising core material particles and a coating layer covering the core material particles, The coating layer comprises a resin and electrostatically charged inorganic fine particles, and contains voids within the coating layer, and includes conductive inorganic fine particles with a powder resistivity of 200 Ω·cm or less. The average film thickness of the aforementioned resin portion is 0.10 μm or more and less than 0.45 μm. In the cross-section of the coating layer, let S1 be the cross-sectional area of ​​the voids and S2 be the cross-sectional area of ​​the resin portion, and let the ratio of the cross-sectional areas of the voids, expressed by the following formula, be the porosity, such that the porosity is 0.1% or more and less than 2.8%. A carrier characterized by containing Mnferrat in the core material particles. Porosity [%]=S1 / S2×100

2. The carrier according to claim 1, characterized in that the charged inorganic fine particles are one or more selected from barium sulfate, magnesium oxide, magnesium hydroxide, and hydrotalcite.

3. The electrostatically charged inorganic fine particles contain barium sulfate, The carrier according to claim 1 or 2, characterized in that the amount of barium exposed on the surface of the coating layer is 0.1 atomic% or more and 0.7 atomic% or less.

4. The carrier according to claim 1 or 2, characterized in that it contains an antifoaming agent in the coating layer.

5. A developer characterized by containing the carrier described in claim 1 or 2.

6. An image forming method characterized by using the developer described in claim 5.

7. An image forming apparatus characterized by comprising the developer described in claim 5.

8. A process cartridge characterized by comprising the developer described in claim 5.

Images