JP7841334B2 - Carrier, developer, image forming method, image forming apparatus, and process cartridge - Google Patents

Description

This invention relates to a carrier, a developer, an image forming method, an image forming apparatus, and a process cartridge.

In electrophotographic image formation, an electrostatic latent image is formed on an electrostatic latent image carrier such as a photoconductive material. Charged toner is then applied to this electrostatic latent image to form a toner image. This toner image is then transferred to a recording medium, fixed, and becomes the output image. In recent years, the technology for multifunction devices and printers using electrophotography has been rapidly expanding from monochrome to full color, and the full-color market is trending upward.

In full-color image formation, generally, three color toners—yellow, magenta, and cyan—or four color toners (yellow, magenta, and cyan plus black) are layered to reproduce all colors. Therefore, to obtain a sharp full-color image with excellent color reproduction, it is necessary to smooth the surface of the fixed toner image to reduce light scattering. For this reason, many conventional full-color copiers and other electrostatic latent image machines achieved high gloss by increasing the amount of toner deposited on the electrostatic latent image to achieve smoothness. Consequently, toner splatter, where degraded toner adheres to the carrier surface, has become a problem during long-term printing. The main problems associated with carrier degradation due to toner splatter are increased carrier resistance and decreased carrier charging capacity. When the carrier's charging capacity decreases, so-called toner scattering occurs, contaminating the machine and causing malfunctions such as sensor misdetection.

Various attempts are being made to resolve the aforementioned problem.
Patent documents 1 and 2 disclose carriers containing barium sulfate in a coating resin, in which the Ba/Si ratio relative to all elements, as measured by XPS, is 0.01 to 0.08. These have shown a certain effect in suppressing toner emission.
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.

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.

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.

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.

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, contains voids, 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, when the cross-sectional area of the voids is S1 and 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% , and the core material particles contain Mnferrat .
Porosity [%]=S1/S2×100

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.

This is a schematic diagram to explain porosity. This is a schematic diagram illustrating the average film thickness. This diagram shows a cell used to measure the volume resistivity of a carrier. This figure shows an example of a process cartridge of the present invention.

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 effects of the present invention is included within the scope of the present invention.

(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

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.

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

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, including electrostatically charged inorganic microparticles in the coating layer can suppress the occurrence of abnormalities such as toner scattering and background staining due to a decrease in electrostatic charge.

In conventional technology, a thick coating layer suppresses carrier abrasion, causing toner components to be spent on the carrier surface, resulting in a decrease in charge over time. Conversely, while a thinner coating layer might suppress spending, it weakens the film's durability, making it easier for charged inorganic particles to detach. This, in turn, leads to a decrease in charge over time.

The inventors conducted thorough research and found that it is important that the coating layer contains resin and electrostatically charged inorganic fine particles, and that the average film thickness of the resin portion (sometimes referred to as the resin portion or coating resin) is between 0.10 μm and 0.45 μm. If the average film thickness of the resin portion is 0.45 μm or more, the coating layer becomes thick, suppressing carrier abrasion. This leads to a problem where toner components are spent on the carrier surface, causing a decrease in charge over time. Furthermore, if the average film thickness of the resin portion is less than 0.10 μm, the coating layer becomes thin, weakening the durability of the carrier film. This makes it easier for the electrostatically charged inorganic fine particles to detach over time, potentially causing a decrease in charge over time even in the case of a thin film. For these reasons, the average film thickness of the resin portion must be between 0.10 μm and 0.45 μm.

Furthermore, the inventors conducted further studies and found that the inclusion of voids within the coating layer is also crucial to solving the conventional problems. The presence of voids in the coating layer allows the electrostatically charged inorganic fine particles to be exposed to the surface over time, enabling stable charging over time.

On the other hand, it is important that the voids contained within the coating layer meet certain conditions.
In the cross-section of the coating layer, if the cross-sectional area of the voids is S1 and 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, then the porosity must be 0.1% or more and less than 2.8%.
Porosity [%]=S1/S2×100

A porosity of 0.1% to less than 2.8% allows the charged inorganic fine particles to be appropriately exposed to the surface over time, resulting in stable charging over time. If the porosity is less than 0.1%, toner components will be spent, leading to a decrease in charge. If the porosity is 2.8% or higher, the resin layer (coating layer) becomes brittle, and fillers detach, resulting in a decrease in charge.

Our investigations revealed that good results can be obtained by specifying 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 poor durability of the carrier film. When the coating layer is thin, it is thought that lowering the porosity can increase the film's durability and suppress the desorption of charged inorganic fine particles. However, even with a thin coating layer, eliminating the voids within the coating layer will cause spending to proceed similarly to a thick film, resulting in poor chargeability.

Therefore, we discovered that good results can be obtained by setting the average film thickness of the resin portion containing electrostatically charged inorganic fine particles within the above range, and by 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, 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.

Furthermore, this invention yields excellent results even when a dispersant is included in the coating layer, and also when the carrier exhibits high adhesion between the resin and the electrostatically charged inorganic fine particles. Moreover, even when a dispersant is included in the coating layer or when the carrier exhibits high adhesion between the resin and the electrostatically charged inorganic fine particles, toner scattering can be suppressed over the long term when using low-temperature fixing toner.

Methods for maintaining the porosity within the above range include, for example, the use of defoaming agents or controlling the amount of defoaming agent added.

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 portion 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 portion 32 is S2, the porosity [%] can be calculated by S1/S2 × 100.

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 this diagram of the coating layer, 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.

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

<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.

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.

Furthermore, a circular equivalent diameter of the charged inorganic fine particles of 900 nm or less is preferable because the particle size of the charged inorganic fine particles is not too large relative to the thickness of the coating layer, allowing them to be sufficiently retained by the binder resin and making them less likely to detach from the coating layer. A circular equivalent diameter of 600 nm or more is more preferable. In this case, more stable charging and developing capabilities can be ensured. The circular equivalent diameter of the charged inorganic fine particles can be calculated by cutting the carrier using ion milling and observing it with cross-sectional SEM and EDX.

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 occurs on the surface of the coating layer, in carriers where the exposure of barium sulfate to the surface of the coating layer is extremely low, 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, 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, which is preferable.

<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.

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.

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.

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 coating layer surface.

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 solution (which may also be called a coating solution, carrier coating solution, etc.), and conductivity can be imparted after coating the carrier. Additionally, even if the toner detaches from the coating layer, discoloration of the toner does not occur, suppressing the deterioration of image quality due to color staining.

While there are no particular restrictions on the conductive polymer particles, 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.

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, and sulfoisophthalic acid esters. Other examples include high molecular weight strongly acidic substances.

When the desorption of the conductive component responsible for resistance adjustment is reduced, fluctuations in carrier resistance become less likely, leading to improved image quality stability.

<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.

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 this 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, allowing for the formation of a stronger film, and making it more difficult for the inorganic fine particles to detach from the coating layer even under stress during printing. This suppresses the occurrence of carrier adhesion to solid image areas over time. In addition, since the detachment of inorganic fine particles 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.

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, homogenizing the inorganic fine particles within the coating layer and increasing the affinity between the resin and the inorganic fine particles.

Furthermore, our researchers found 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; therefore, 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—are excellent, which significantly reduces the problem of toner scattering during replenishment, where the toner is not sufficiently charged before scattering.

When using a phosphate ester-based surfactant as a dispersant, it is preferable that the 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.

Examples of 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 Bic Chemie), and Floren DOPA-158, 22, 17, G-700, TG-720W, 730W (manufactured by Kyoeisha Chemical Co.).

<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.

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 crucial for achieving defoaming effects, and silicone-based materials exhibit a good balance of these properties. Therefore, a high defoaming effect can be obtained even with small amounts of additive, and the formation of pores in the coating layer can be suppressed.

Examples of commercially available products include 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), BYK-065, BYK-066N, BYK-070, BYK-088, BYK-141 (manufactured by Bic Chemie Co., Ltd.), Disparon 1930N, Disparon 1933, Disparon 1934 (manufactured by Kusumoto Chemical Co., Ltd.), etc., but are not limited to these.

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 form in the coating resin. If the amount of defoaming agent added exceeds 10.0 parts by mass, surface defects called "repellency" will appear in the coating film, 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.

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.

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

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 accumulating toner components, 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 accumulate. This reduces the accumulation of accumulating components that cause film abrasion, thus resolving this problem.

However, since silicone resin has weak adhesion and high brittleness, it also has the weakness of 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 good abrasion resistance, and the improvement effect is significant. This is because, due to the low surface energy of silicone resin, toner components are less likely to spend, and the accumulation of spent components that cause film abrasion is less likely to occur.

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

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 Silicon. In this case, it is possible to use the silicone resin alone, but it is also possible to use other components that undergo crosslinking reactions, charge adjustment components, etc., simultaneously.

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.

In this specification, "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 crosslinking reactions include, but are not limited to, amino resins and acidic catalysts. "Amino resin" here refers to, but is not limited to, guanamine resins, melamine resins, etc. Furthermore, "acidic catalyst" here refers to any catalyst with catalytic activity. For example, it includes, but is not limited to, catalysts with reactive groups such as fully alkylated, methylol-type, imino-type, and methylol/imino-type catalysts.

The carrier of this invention preferably has a volume-average particle size of 28 μm or more and 40 μm or less. A volume-average particle size of 28 μm or more suppresses carrier adhesion, while a size of 40 μm or less suppresses a decrease in the reproducibility of image details and prevents the formation of fine images.

Furthermore, 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.).

The carrier of this invention preferably has a volume resistivity of 8 to 16 Log Ω·cm. If the volume resistivity is 8 Log Ω·cm or higher, carrier adhesion will not occur in non-image areas, and if it is 16 Log Ω·cm or lower, the edge effect will not reach an unacceptable level.

Furthermore, 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. Ten 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.

r×(2.5×4)/0.2... Formula 1

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 catalysts.

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 for their superior results, and titanium diisopropoxybis(ethyl acetate) is particularly preferred. This is because it significantly promotes the condensation reaction of silanol groups and is less prone to catalyst deactivation.

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.

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.

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 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 shedding of the coating layer during long-term use. Furthermore, if the amount is 10% by mass or less, it is possible to suppress the occurrence of toner filming during long-term use.

<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.

The volume-average particle size of the core material 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 thus 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 more effectively meet the demands for high image quality in recent years.

(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.

The toner contains a binder resin and a colorant, and may be either a monochrome or 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 abrasion of the carrier coating layer, but the developer of the present invention can suppress the occurrence of color staining.

Toner can be manufactured using known methods such as grinding and polymerization. For example, when manufacturing toner using the grinding method, the molten mixture obtained by kneading the toner materials is first 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 the toner.

At this time, 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 (manufactured by Kobe Steel, Ltd.), TEM type (manufactured by Toshiba Machine Co., Ltd.), twin-screw extruders (manufactured by KCK Corporation), PCM type (manufactured by Ikegai Iron Works Co., Ltd.), and KEX type (manufactured by Kurimoto Iron Works Co., Ltd.); and continuous single-screw kneaders such as the Co-Kneader (manufactured by Buss Co., Ltd.).

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 to an average particle size of 3 to 15 μm.

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.

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 may be used in combination.

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 resins, polyesters, styrene-butadiene copolymers, polyvinylpyrrolidone, methyl vinyl ether-maleic anhydride copolymer, maleic acid-modified phenol resins, and phenol-modified terpene resins; two or more of these may be used in combination.

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, 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 like 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 pigments may be used in combination.

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., and two or more may be used in combination.

Furthermore, the toner may further contain a charge control agent. The charge control agent is not particularly limited and can be appropriately selected. For example, nigrosine; azine dyes having an alkyl group with 2 to 16 carbon atoms; C.I. Basic Yellow 2 (C.I. 41000), C.I. Basic Yellow 3, C.I. Basic Red 1 (C.I. 45160), C.I. Basic Red 9 (C.I. 42500), C.I. Basic Violet 1 (C.I. 42535), C.I. Basic Violet 3 (C.I. 42555), C.I. Basic Violet 10 (C.I. 45170), C.I. Basic Violet 14 (C.I.42510), C.I. I. Basic Blue 1 (C.I.42025), C.I. I. Basic Blue 3 (C.I.51005), C.I. I. Basic Blue 5 (C.I.42140), C.I. I. Basic Blue 7 (C.I.42595), C.I. I. Basic Blue 9 (C.I.52015), C.I. I. Basic Blue 24 (C.I.52030), C.I. I. Basic Blue25 (C.I.52025), C.I. I. Basic dyes such as Basic Blue 26 (C.I. 44045), C.I. Basic Green 1 (C.I. 42040), C.I. Basic Green 4 (C.I. 42000); lake pigments of these basic dyes; C.I. Examples include Solvent Black 8 (C.I. 26150), quaternary ammonium salts such as 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; organoboron 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.

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 with hydrophobicly treated surfaces are preferred.

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.

By applying the carrier of this invention to an image forming apparatus that performs image formation while discharging excess developer from the developing unit, 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 unit is replaced with the undegraded carrier in the replenishment developer, maintaining a stable charge level over a long period and resulting in a stable image. This method is particularly effective for high-image-area printing. During high-image-area printing, carrier degradation is primarily caused by carrier charge degradation due to toner deposition. However, by using this method, the amount of carrier replenishment increases during high-image-area printing, thus increasing the frequency of replacement of deteriorated carriers. This allows for the acquisition of extremely stable images over a very long period.

The preferred mixing ratio for the replenishment developer is, for example, 2 to 50 parts by mass of toner per 1 part by mass of carrier. When the toner is 2 parts by mass or more, there is no risk of excessive carrier supply, and the carrier concentration in the developing device does not become too high, thus making it difficult to increase the charge level of the developer. An increase in the developer's charge level can reduce developing ability and decrease image density. Furthermore, when the toner is 50 parts by mass or less, the carrier proportion in the replenishment developer does not decrease, leading to increased carrier turnover in the image forming device, which is expected to have an effect against carrier degradation.

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.

(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.

(Process 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.

Figure 4 shows an example of the 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.

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 an exposure device that performs scanning exposure with 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.

(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.

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 descriptions refers to "parts by mass," and "%" refers to "mass percent."

(Manufacturing Example 1)
<Resin Liquid 1>
200 parts of acrylic resin solution (solids concentration: 20%), 2000 parts of silicone resin solution (solids concentration: 40%), 20 parts of aminosilane (solids concentration: 100%), and 1160 parts of tungsten oxide-doped tin oxide (WTO) surface-treated alumina (powder resistivity: 40 [Ω・cm]).
Barium sulfate 880 parts (equivalent circle diameter: 0.60 [μm])
• Toluene 6800 parts • Dispersant (phosphate ester surfactant) 40 parts • Antifoaming agent (silicone-based) 290 parts

The above materials were 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 for the carrier. [Resin Liquid 1] was applied to the core material surface at a rate of 30 g/min using a Spira Coater SP-40 (manufactured by Okada Seikou Co., Ltd.) at 60°C 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%.

Let me explain the measurement process.
The volume-average particle size of the core material 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.

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 4.5 kV and a processing time of 5 hours. This was then imaged using a scanning electron microscope (Carl Zeiss Merlin) at an acceleration voltage of 2.0 kV and a magnification of 10 kx. 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.

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

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

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 electrostatic inorganic fine particles contained in the resin layer.
S2=S3-S1-S4

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, a two-part epoxy resin that cures in 12 hours), 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 4.5 kV and a processing time of 5 hours. This was then imaged using a scanning electron microscope (Carl Zeiss Merlin) at an acceleration voltage of 0.8 kV and a magnification of 10 kx. 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.

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 0-10 nm, detecting information near the surface of the carriers. The specific measurement method is as follows: Measurement mode: Al: 1486.6 eV, Excitation source: Monochrome (Al), Detection method: Spectral mode, Magnet 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. Afterward, the atomic percentage of barium for all detected elements is calculated using the included peak analysis software.

(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.

(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.

(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).

(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).

(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).

(Manufacturing Example 7)
<Resin Liquid 7>
200 parts of acrylic resin solution (solids concentration: 20%), 2000 parts of silicone resin solution (solids concentration: 40%), 20 parts of aminosilane (solids concentration: 100%), and 1160 parts of tungsten oxide-doped tin oxide (WTO) surface-treated alumina (powder resistivity: 40 [Ω・cm]).
• Barium sulfate 220 parts (equivalent circle diameter: 0.60 [μm])
• Toluene 6800 parts • Dispersant (phosphate ester surfactant) 30 parts • Antifoaming agent (silicone-based) 270 parts

Except for changing [Resin Liquid 1] to [Resin Liquid 7], [Carrier 7] was obtained in the same manner as in Manufacturing Example 1.

(Manufacturing Example 8)
<Resin Liquid 8>
200 parts of acrylic resin solution (solids concentration: 20%), 2000 parts of silicone resin solution (solids concentration: 40%), 20 parts of aminosilane (solids concentration: 100%), and 1160 parts of tungsten oxide-doped tin oxide (WTO) surface-treated alumina (powder resistivity: 40 [Ω・cm]).
• Barium sulfate 220 parts (equivalent circle diameter: 0.60 [μm])
• Toluene 6800 parts • Dispersant (phosphate ester surfactant) 30 parts • Antifoaming agent (silicone-based) 580 parts

Except for changing [Resin Liquid 1] to [Resin Liquid 8], [Carrier 8] was obtained in the same manner as in Manufacturing Example 1. The porosity of the coating layer of [Carrier 8] was 0.3%.

(Manufacturing Example 9)
<Resin liquid 9>
200 parts of acrylic resin solution (solids concentration: 20%), 2000 parts of silicone resin solution (solids concentration: 40%), 20 parts of aminosilane (solids concentration: 100%), and 1160 parts of tungsten oxide-doped tin oxide (WTO) surface-treated alumina (powder resistivity: 40 [Ω・cm]).
• Barium sulfate 220 parts (equivalent circle diameter: 0.60 [μm])
• Toluene 6800 parts • Dispersant (phosphate ester surfactant) 30 parts • Antifoaming agent (silicone-based) 110 parts

Except for changing [Resin Liquid 1] to [Resin Liquid 9], [Carrier 9] was obtained in the same manner as in Manufacturing Example 1. The porosity of the coating layer of [Carrier 9] was 2.7%.

(Comparative example 1 of manufacturing)
A 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.

(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.

(Manufacturing Comparison Example 3)
<Resin liquid 12>
200 parts of acrylic resin solution (solids concentration: 20%), 2000 parts of silicone resin solution (solids concentration: 40%), 20 parts of aminosilane (solids concentration: 100%), and 1160 parts of tungsten oxide-doped tin oxide (WTO) surface-treated alumina (powder resistivity: 40 [Ω・cm]).
• Toluene 6800 parts • Dispersant (phosphate ester surfactant) 30 parts • Antifoaming agent (silicone-based) 110 parts

Except for changing [Resin Liquid 1] to [Resin Liquid 12], [Carrier 12] was obtained in the same manner as in Manufacturing Example 1.

(Manufacturing Comparison Example 4)
<Resin liquid 13>
200 parts of acrylic resin solution (solids concentration: 20%), 2000 parts of silicone resin solution (solids concentration: 40%), 20 parts of aminosilane (solids concentration: 100%), and 1160 parts of tungsten oxide-doped tin oxide (WTO) surface-treated alumina (powder resistivity: 40 [Ω・cm]).
• Barium sulfate 220 parts (equivalent circle diameter: 0.60 [μm])
• Toluene 6800 parts • Dispersant (phosphate ester surfactant) 30 parts • Antifoaming agent (silicone-based) 580 parts

The above materials were 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 for the carrier. [Resin Liquid 13] was applied to the core material surface at a rate of 30 g/min using a Spira Coater SP-40 (manufactured by Okada Seikou Co., Ltd.) at 60°C to a thickness of 0.35 μm, 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%.

(Comparative example 5 of manufacturing)
<Resin liquid 14>
200 parts of acrylic resin solution (solids concentration: 20%), 2000 parts of silicone resin solution (solids concentration: 40%), 20 parts of aminosilane (solids concentration: 100%), and 1160 parts of tungsten oxide-doped tin oxide (WTO) surface-treated alumina (powder resistivity: 40 [Ω・cm]).
• Barium sulfate 220 parts (equivalent circle diameter: 0.60 [μm])
• Toluene 6800 parts • Dispersant (phosphate ester surfactant) 30 parts

Except for changing [Resin Liquid 1] to [Resin Liquid 14], [Carrier 14] was obtained in the same manner as in Manufacturing Example 1. The porosity of the coating layer of [Carrier 14] was 7.0%.

The obtained carrier characteristics are shown in Table 1.

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

<Synthesis of polyester resin A>
In a reaction vessel equipped with a condenser, a stirrer, and a 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 and 230°C for 15 hours. Next, the mixture was reacted 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.

<Synthesis of prepolymers (polymers that can react with active hydrogen group-containing compounds)>
In a reaction vessel equipped with a condenser, a stirrer, and a nitrogen inlet tube, 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. Then, the mixture was reacted 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 the solid content concentration of the [prepolymer] (after standing at 150°C for 45 minutes) was 50% by mass.

<Synthesis of Ketimine (the active hydrogen group-containing compound)>
In a reaction vessel equipped with a stirring rod and a thermometer, 30 parts of isophoronediamine 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.

<Masterbatch Preparation>
1,000 parts water, 540 parts Printex 35 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.

<Preparation of water-based 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.

<Measurement of critical micelle concentration>
The critical micelle concentration of surfactants was measured using the following method. Analysis was performed using a Sigma surface tension meter (KSV Instruments) and an analysis program within the Sigma system. Surfactants were added dropwise to an aqueous medium at a rate of 0.01%, and the interfacial tension was measured after stirring and standing. From the obtained surface tension curve, the surfactant concentration at which the interfacial 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%.

<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 until dissolved. 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.

<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).

<Removal of organic solvents>
A 100-part emulsified slurry was placed in a container 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.

<Washing>
After 100 parts of the dispersion slurry was 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 then 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% by mass hydrochloric acid were added to the obtained filtration cake, and the mixture was mixed in a TK homomixer (at a rotation speed of 12,000 rpm for 10 minutes) and then filtered.

<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 a rotation speed of 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 surfactant concentration calibration curve. Based on this value, deionized water was added until the surfactant concentration reached the target surfactant concentration of 0.05%, thereby obtaining the toner dispersion.

<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.

<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].

<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.

(Preparation of the developing agent)
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 developers 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%.

(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.

<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.

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

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

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

The evaluation results are shown in Table 2.

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 carrier according to <1>, characterized in that the electrostatically 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 <1> or <2>, characterized in that the amount of barium exposed on the surface of the coating layer is 0.1 atomic% or more.
<4> The carrier according to any one of <1> to <3>, characterized in that it contains an antifoaming agent in the coating layer.
A developer characterized by containing any of the carriers described in <5>, <1>, to <4>.
An image forming method characterized by using the developer described in <6> and <5>.
An image forming apparatus characterized by comprising the developer described in <7> and <5>.
A process cartridge characterized by comprising the developer described in <8> and <5>.

1a Electrode 1b Electrode 2 Container 3 Carrier 10 Process cartridge 11 Photoreceptor 12 Charging device 13 Developing device 14 Cleaning device 20 Core material particles 30 Coating layer 31 Void 32 Resin 33 Chargeable fine particles 34 Conductive component

Patent No. 5534409 Japanese Patent Publication No. 2011-209678 Japanese Patent Publication No. 2016-212254 Japanese Patent Publication No. 2017-167387 Japanese Patent Publication No. 2021-076820

Claims (8)

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 The carrier according to claim 1, characterized in that the electrostatically charged inorganic fine particles are one or more selected from barium sulfate, magnesium oxide, magnesium hydroxide, and hydrotalcite. 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. The carrier according to claim 1 or 2, characterized in that it contains an antifoaming agent in the coating layer. A developer characterized by containing the carrier described in claim 1 or 2. An image forming method characterized by using the developer described in claim 5 . An image forming apparatus characterized by comprising the developer described in claim 5 . A process cartridge characterized by comprising the developer described in claim 5 .