Electrophotographic image forming carrier, electrophotographic image forming developer, electrophotographic image forming method, electrophotographic image forming apparatus, and process cartridge

Abstract

To provide a carrier for electrophotographic image formation that achieves high durability, can control electrical characteristics in a low resistance region, reduces variation in a resistance value of the carrier in long-term printing, and prevents carrier adhesion.SOLUTION: A carrier for electrophotographic image formation has a core material particle and a coating layer coating the core material particle. The coating layer includes at least antimony-containing particles and an anionic dispersant. The antimony-containing particles include inorganic fine particles as base particles. The above-mentioned problem is solved by the carrier for electrophotographic image formation.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] In image formation by an electrophotographic method, an electrostatic latent image is formed on an electrostatic latent image carrier such as a photoconductive substance. Then, charged toner is attached to the electrostatic latent image to form a toner image, and the toner image is transferred to a recording medium and fixed to obtain an output image. In recent years, along with the increase in printing speed, there is a strong demand for the ability of the carrier to quickly impart charge to the toner. Under such circumstances, during long-term printing, the charge of the carrier may vary due to toner spent in which deteriorated toner adheres to the carrier surface. Therefore, the toner replenished to the developer is not sufficiently triboelectrically charged with the carrier and does not become charged, resulting in problems such as toner scattering where toner accumulates outside the developing device and ground contamination where toner is developed on blank paper portions. In addition, due to the demand for further higher image quality in recent years, the carrier is subjected to strong stress inside the developing machine for high-speed development, and the core material is exposed due to shaving or peeling of the carrier coating resin, and the carrier adhesion occurs where the carrier transfers onto the electrostatic latent image carrier due to the change in the electrical resistance of the carrier. For this reason, a defect occurs in which white spots appear at the image edges or the center, and the requirements for this problem are becoming more severe in recent years.

[0003] Therefore, various attempts have been made so far to maintain the electrical resistance of the carrier. For example, Patent Documents 1 and 2 disclose methods of improving the adhesion and durability with the core material by coating with an appropriate resin material. Patent Documents 3 and 4 disclose methods of improving the durability of the carrier coating layer by adding inorganic fine particles to the coating resin. Patent Document 5 describes a method for increasing durability under long-term printing conditions by using a highly durable resin for the coating and further incorporating a large amount of inorganic fine particles near the surface of the coating layer. Patent Document 6 describes how conductive fine particles are added to the carrier coating layer to adjust the carrier's resistance and improve its durability. [Overview of the project] [Problems that the invention aims to solve]

[0004] The object of the present invention is to provide an electrophotographic image forming carrier that achieves high durability, enables control of electrical characteristics in the low-resistance region, exhibits minimal fluctuation in carrier resistance under long-term printing conditions, and suppresses carrier adhesion. [Means for solving the problem]

[0005] The above problem is solved by the following configuration 1). 1) An electrophotographic image forming carrier having core material particles and a coating layer covering the core material particles, The coating layer contains at least antimony-containing particles and an anionic dispersant, The antimony-containing particles use inorganic fine particles as base particles. The substrate particles are surface-treated with antimond-doped tin oxide. The inorganic fine particles that constitute the substrate are aluminum oxide or titanium oxide. A carrier for forming electrophotographic images, characterized by the above features. [Effects of the Invention]

[0006] According to the present invention, it is possible to provide an electrophotographic image forming carrier that achieves high durability, enables control of electrical characteristics in the low-resistance region, minimizes fluctuations in carrier resistance under long-term printing conditions, and suppresses carrier adhesion. [Brief explanation of the drawing]

[0007] [Figure 1] This is a diagram illustrating an example of the process cartridge of the present invention. [Figure 2] This figure shows a normal image and a problematic ghost image in a vertical band chart. [Modes for carrying out the invention]

[0008] The embodiments of the present invention will be described in more detail below. The electrophotographic image forming carrier of the present invention is as shown in configuration 1) above, but the present invention also preferably includes the following forms 2) to 12).

[0009] 2) The electrophotographic image forming carrier according to 1) above, characterized in that the antimony-containing particles contain antimony-doped tin oxide. 3) The electrophotographic image forming carrier according to 1) or 2) above, characterized in that the antimony-containing particles contain diantimony pentoxide. 4) The electrophotographic image forming carrier according to any one of 1) to 3) above, characterized in that the inorganic fine particles that are the substrate particles are aluminum oxide. 5) The electrophotographic image forming carrier according to any one of 1) to 4) above, characterized in that the anionic dispersant is a phosphate ester surfactant. 6) An electrophotographic image forming carrier according to any one of 1) to 5) above, characterized in that it contains an antifoaming agent in the coating layer. 7) The electrophotographic image forming carrier according to 6) above, characterized in that the defoaming agent is a silicone-based defoaming agent. 8) An electrophotographic image forming carrier according to any one of 1) to 7) above, characterized in that the coating layer contains inorganic fine particles in addition to the antimony-containing particles. 9) The electrophotographic image forming carrier according to 8) above, characterized in that the inorganic fine particles other than the antimony-containing particles are white. 10) The electrophotographic image forming carrier according to 8) or 9) above, characterized in that the inorganic fine particles other than the antimony-containing particles contain barium sulfate. 11) An electrophotographic image forming carrier according to any one of 8) to 10) above, characterized in that the inorganic fine particles other than the antimony-containing particles are barium sulfate alone. 12) An electrophotographic image forming agent characterized by containing an electrophotographic image forming carrier as described in any of 1) to 8) above. 13) An electrophotographic image forming method characterized by forming an image using the electrophotographic image forming developer described in 12) above. 14) An electrophotographic image forming apparatus characterized by comprising the electrophotographic image forming agent described in 12) above. 15) A process cartridge characterized by comprising the electrophotographic image forming developer described in 12) above.

[0010] The above-mentioned conventional technology has the following problems. Patent documents 1 and 2 describe a method for improving adhesion and durability to the core material by coating it with a suitable resin material. However, in recent years, due to increased printing speeds and lower toner fixing temperatures, wear on the carrier toner residue and the resin material has become more likely, making it insufficient to simply change the resin material. Patent documents 3 and 4 describe a method for improving the durability of the carrier coating layer by adding inorganic fine particles to the coating resin. However, simply adding inorganic fine particles to the coating resin improves the durability of the carrier, but problems arise when inorganic fine particles that are not sufficiently fixed to the coating resin detach, causing changes in the electrical properties of the carrier and leading to carrier adhesion. Patent Document 5 describes a method for increasing durability under long-term printing by using a highly durable resin for the coating and further incorporating a large amount of inorganic fine particles near the surface of the coating layer. However, as the amount of inorganic fine particles added increases, there is a risk of desorption occurring, particularly from areas where the inorganic fine particles are abundant due to uneven distribution. Additionally, the increased exposure of inorganic fine particles due to abrasion of the coating resin can alter the electrical properties of the carriers. In Patent Document 6, by adding conductive fine particles to the carrier coating layer, the resistance of the carrier is adjusted and the durability of the carrier is obtained. The resulting resistance value is determined by the conductivity of the conductive fine particles and their addition amount. However, in the case of particles with high conductivity, in order to obtain a low resistance value, it is necessary to increase the addition amount. While durability is obtained, this leads to an increase in the risk of detachment and a large resistance decrease due to an increase in the exposure of the fine particles when the coating resin is scraped off. Also, in the case of particles with low conductivity, it is easy to obtain the intended resistance value with a small addition amount, but there is a problem that the durability of the film decreases.

[0011] The carrier for electrophotographic image formation of the present invention enables control of electrical characteristics in a low resistance region while exhibiting high durability with the addition of a small amount of conductive fine particles, has little variation in the resistance value of the carrier under long-term printing, and can suppress carrier adhesion in non-image areas.

[0012] As shown in the above Configuration 1), the carrier for electrophotographic image formation of the present invention has core material particles and a coating layer that coats the core material particles, and the coating layer contains at least antimony-containing particles and an anionic dispersant, and the antimony-containing particles have inorganic fine particles as base particles.

[0013] In the case of enabling control of electrical characteristics in a low resistance region while exhibiting high durability with the addition of a small amount of conductive fine particles in a carrier for electrophotographic image formation, the following two points can be cited as important points of the present invention.

[0014] First, the coating layer contains antimony-containing particles with inorganic fine particles as matrix particles. Antimony has excellent conductivity and can impart high conductivity to carriers with a small amount of addition. Since the addition amount is small, it is possible to suppress the exfoliation of fine particles and the exposure of fine particles when they are scraped off. Antimony can be contained in the particles or used as particles themselves. In particular, by doping antimony into tin oxide, a very high resistance regulator can be obtained. Also, by using inorganic fine particles as the matrix, it is possible to prevent the antimony-containing particles from collapsing in the coating layer and becoming fragments and detaching from the coating layer, thereby losing the resistance adjustment ability.

[0015] The inorganic fine particles used as the matrix can be conventional or novel materials. In particular, the use of aluminum oxide is preferable because the resistance adjustment ability becomes remarkable. This is considered to be because it has good compatibility with the conductive treatment on the surface of the matrix particles and the treatment effect functions efficiently.

[0016] The antimony-containing particles preferably have an equivalent circle diameter of 500 nm or more and 1000 nm or less. When it is 500 nm or more, the particle diameter is not too small, and the carrier resistance can be efficiently reduced. Also, when it is 1000 nm or less, it becomes difficult for exfoliation from the coating layer surface to occur.

[0017] The antimony-containing particles are preferably contained in an amount of 40 to 120 parts by mass, more preferably 60 to 100 parts by mass, based on 100 parts by mass of the resin used in the coating layer.

[0018] Here, the antimony-containing particles preferably contain antimony pentoxide. Generally, antimony trioxide, which is antimony used for the purpose of resistance adjustment, has been pointed out to be harmful to the human body and is not a preferably used material. By using particles containing antimony pentoxide, a carrier with low harm to the human body and an efficient resistance adjustment ability can be obtained.

[0019] The second feature is the inclusion of an anionic dispersant in the coating layer. In a coating solution that forms a coating layer consisting of resin, inorganic fine particles including antimony-containing particles, and a diluent, by formulating an anionic dispersant, 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, such as those that are not sufficiently embedded in the resin and are weakly fixed to the carrier surface. While antimony-containing particles provide high conductivity with only a small amount added, there is a risk of reduced durability of the coating layer if the amount added is small. However, by adding a dispersant, the fine particles are uniformly distributed within the coating layer, thus maintaining the durability of the film. Furthermore, since the dispersant has both groups that are compatible with the resin and groups that are compatible with the inorganic fine particles, 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 the stress of long-term printing. This suppresses the occurrence of carrier adhesion to solid image areas over time.

[0020] As mentioned above, it is important that the dispersant is an anionic dispersant. Anionic dispersants have excellent dispersibility properties, and by adding an anionic dispersant, the particle size distribution of inorganic fine particles can be narrowed and uniformly arranged in the coating liquid. Anionic dispersants are 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 preferable. Phosphate ester surfactants enable good dispersion of inorganic fine particles contained in the coating layer 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. In addition, as a result of the inventors' studies, it has been found that adding an anionic dispersant having a phosphate ester structure further improves the margin against toner scattering. This is because the structural portion of the phosphate ester becomes positively charged with negatively charged toner, and when an anionic dispersant containing a phosphate ester surfactant is added, the charging properties with the toner are improved compared to when it is not added. In particular, the charging properties immediately after mixing and stirring with toner, or the so-called charge rise, are excellent, which is highly effective in suppressing toner scattering during replenishment, as toner may scatter because it is not sufficiently charged.

[0021] The anionic dispersant preferably contains a phosphate ester surfactant as its main component. In this embodiment, for it to be considered a "main component," the dispersant preferably contains 50% by mass or more of the phosphate ester surfactant. It is even more preferable that it contains 90% by mass or more. Furthermore, the amount of anionic dispersant added is preferably 0.5 parts by mass or more and 10.0 parts by weight or less per 100 parts by mass of the total amount of antimony-containing particles and other inorganic fine particles. By adding 0.5 parts by mass or more of anionic dispersant, all inorganic fine particles can be dispersed down to the primary particle size, and aggregated inorganic fine particles are less likely to remain. If aggregated particles are present, they are not sufficiently fixed to the coating layer and detach due to stress at the beginning of printing, reducing resistance and causing carrier adhesion. In addition, the amount of dispersant present on the outermost surface of the coating layer is small, resulting in poor charge rise and a lack of advantage against toner scattering. Moreover, by adding 10.0 parts by weight or less of anionic dispersant, the amount of dispersant components in the coating layer that cannot be adsorbed by inorganic fine particles is reduced, the proportion of resin in the coating layer becomes appropriate, the durability of the coating layer is improved, and the detachment of inorganic fine particles during printing is suppressed, preventing carrier adhesion to solid image areas and toner scattering during printing. The amount of the anionic dispersant added is more preferably 1.0 part by mass or more and 3.0 parts by mass or less.

[0022] Furthermore, in the present invention, it is even more desirable to add an antifoaming agent to the coating layer. When an anionic dispersant is formulated in a coating liquid that forms a coating layer consisting of resin, inorganic fine particles including antimony-containing particles, a diluting solvent, etc., while the anionic dispersant has excellent dispersibility, the coating liquid tends to foam easily. When coating is performed with this foamed coating liquid, the coating layer is formed with incorporated foam, and voids caused by the incorporated foam may occur in the coating layer. These voids in the coating layer reduce the durability of the film, and film abrasion progresses over time during printing. Therefore, by formulating an antifoaming agent in addition to the dispersant, foaming of the coating liquid can be suppressed, and the occurrence of voids in the coating layer can be eliminated. This reduces film abrasion over time during printing due to voids formed in the coating layer, making it possible to obtain a carrier with higher durability and further suppression of carrier adhesion.

[0023] While not particularly limited, examples of defoaming agents include silicone-based, acrylic-based, and vinyl-based agents. Among these, silicone-based agents are preferable. Generally, a balance between compatibility and incompatibility with the solvent is important for exhibiting defoaming effects. Silicone-based defoaming agents have a good balance of compatibility and incompatibility, allowing for high defoaming effects even with small amounts added, and suppressing the generation of voids in the coating layer.

[0024] Commercially available defoaming agents 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.).

[0025] Furthermore, 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 forming the coating layer. Adding 1.0 part by mass or more of the defoaming agent provides a sufficient defoaming effect and prevents the formation of voids in the coating layer. Adding 10.0 part by mass or less of the defoaming agent prevents surface defects of the coating film called "repellency," suppresses embrittlement of the coating layer on the carrier surface and detachment of inorganic fine particles, and improves carrier adhesion to the solid image area. It is even more preferable that the amount of defoaming agent added is 2.0 parts by mass or more and 7.0 parts by mass or less.

[0026] The coating layer preferably contains inorganic fine particles in addition to the antimony-containing particles. The inclusion of these inorganic fine particles improves the coating layer's resistance to abrasion and suppresses deterioration due to wear and abrasion. While the presence of antimony-containing particles also improves the coating layer's durability, the amount of antimony-containing particles affects the carrier's electrical resistance, making it impossible to adjust the amount in the coating layer for the purpose of improving durability. Therefore, it is preferable to ensure the coating layer's durability through these inorganic fine particles.

[0027] Furthermore, it is preferable that the inorganic fine particles other than the antimony-containing particles are white. Using white inorganic fine particles is preferable because it minimizes the impact on the toner's color even when they detach from the coating layer. The inorganic fine particles are not limited in their material, but when negatively charged toner is used, using a material with positive charge properties for the inorganic fine particles ensures stable long-term charge imparting ability. Examples of inorganic fine particles include metal fine particles such as gold, silver, copper, silica, and aluminum, as well as titanium oxide, tin oxide, zinc oxide, zirconium oxide, indium oxide, antimony oxide, calcium oxide, ITO, silicone oxide, colloidal silica, aluminum oxide, yttrium oxide, cobalt oxide, copper oxide, iron oxide, manganese oxide, niobium oxide, vanadium oxide, selenium oxide, barium sulfate, magnesium oxide, magnesium hydroxide, silicon dioxide, boron nitride, silicon nitride, potassium titanate, hydrotalcite, tin oxide doped with antimony or tungsten, and indium oxide doped with tin. Particularly preferred materials include barium sulfate, magnesium oxide, magnesium hydroxide, and hydrotalcite, with barium sulfate being the most suitable due to its white color and high charging ability for negatively charged toner.

[0028] When barium sulfate is used as an inorganic fine particle other than the antimony-containing particles, it is preferable that the barium sulfate be in its pure form. Barium sulfate exerts a charge imparting effect by being present on the surface of the coating layer and coming into contact with the toner. When barium sulfate is in its pure form, the probability of contact with the toner increases, and the charge imparting effect can be maximized. "Pure barium sulfate" refers to particles used as "inorganic fine particles other than antimony-containing particles" that are composed solely of barium sulfate.

[0029] Furthermore, it is desirable that inorganic fine particles other than antimony-containing particles have an equivalent circular diameter of 400 nm to 900 nm. Within this range, the inorganic fine particles can be present in a convex state relative to the surface of the coating layer, ensuring charging with the toner. To ensure stable charging and developing capabilities, it is more preferable that the equivalent circular diameter of the inorganic fine particles be 600 nm or more. Also, it is preferable that the equivalent circular diameter of the inorganic fine particles be 900 nm or less, because the particle size of the inorganic fine particles is not too large relative to the thickness of the coating layer, so they are sufficiently retained by the resin and less likely to detach from the coating layer.

[0030] The inorganic fine particles other than the antimony-containing particles are preferably present in an amount of 30 to 100 parts by mass, and more preferably in an amount of 50 to 80 parts by mass, per 100 parts by mass of the resin used in the coating layer.

[0031] The equivalent circle diameter as used in this invention can be confirmed by conventionally known methods. For example, before carrier formation, it can be measured using, for instance, the NanoTrac UPA series (manufactured by Nikkiso Co., Ltd.). After carrier formation, it can be confirmed by, for example, cutting the coating layer on the carrier surface with FIB and observing the cross-section with SEM and EDX. Examples are given below. The carrier was mixed with embedding resin (Devcon, two-component, 30-minute curing epoxy resin), allowed to cure overnight or longer, and a rough cross-sectional sample was prepared by mechanical polishing. The cross-section was then finished using a cross-section polisher (JEOL SM-09010) with an acceleration voltage of 5.0kV and a beam current of 120μA. This was then imaged using a scanning electron microscope (Carl Zeiss Merlin) with an acceleration voltage of 0.8kV and a magnification of 30,000x. The captured images were imported into TIFF format, and the equivalent circle diameter of 100 particles was measured using Media Cybernetics Image-Pro Plus, with the average value being used. It should be noted that this is not the only method of verification. Similarly, the thickness of the coating layer can also be measured from the captured images. However, since there are individual differences in particles and variations in the thickness of the coating layer depending on the location, measurements should not be limited to just one particle / one location, but rather a statistically sound number of measurements (n) should be taken.

[0032] In the present invention, the coating layer may contain a resin and, if necessary, other components. Such resins may include silicone resin, acrylic resin, or a combination thereof. While acrylic resin has excellent abrasion resistance due to its strong adhesion and low brittleness, its high surface energy can lead to problems such as reduced charge due to the accumulation of toner components when combined with easily spent toners. In such cases, this problem can be resolved by using a silicone resin in combination, which 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. However, silicone resin has weak 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, which makes it possible to obtain a coating film that is both difficult to spend and highly abrasion-resistant. This is because silicone resin has a low surface energy, making it difficult for toner components to spend and reducing the accumulation of spent components that cause film abrasion.

[0033] As used herein, silicone resins refer to all commonly known silicone resins, including but not limited to straight silicones consisting only of organosilosane bonds, and silicone resins modified with alkyds, polyesters, epoxys, acrylics, urethanes, etc. For example, commercially available 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. Furthermore, 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.

[0034] 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.

[0035] When using silicone resin, acrylic resin, or a combination thereof as the aforementioned resin, the film strength can be increased by crosslinking the silanol groups through condensation polymerization catalyst. Examples of condensation polymerization catalysts include titanium-based catalysts, tin-based catalysts, zirconium-based catalysts, and aluminum-based catalysts. However, in this invention, among these various catalysts, titanium-based catalysts that yield excellent results are most preferred, with titanium diisopropoxybis(ethyl acetate) being 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.

[0036] The carrier of the present invention preferably has a volume-average particle size of 20 μm or more and 100 μm or less. When the volume-average particle size of the carrier particles is 20 μm or more, carrier adhesion is reduced, and when it is 100 μm or less, the reproducibility of image details does not decrease, and it is not impossible to form a fine image. In particular, using a size of 20 to 60 μm can more effectively meet the demands for high image quality in recent years. The volume-average particle size can be measured using, for example, the Microtrac particle size distribution analyzer model HRA9320-X100 or the SRA type (Nikkiso Co., Ltd.).

[0037] In the present invention, it is preferable that the coating liquid forming the coating layer contains a silane coupling agent. This allows for the stable dispersion of inorganic fine particles. Silane coupling agents are not particularly limited, but include γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride, γ-glycidoxypropyltrimethoxysilane, γ-mercaptopropyltrimethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, vinyltriacetoxysilane, γ-chloropropyltrimethoxysilane, hexamethyldisilazane, and γ-anilinol. Examples include propyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, γ-chloropropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, allyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, dimethyldiethoxysilane, 1,3-divinyltetramethyldisilazane, methacrylateoxyethyldimethyl(3-trimethoxysilylpropyl)ammonium chloride, and two or more may be used in combination.

[0038] 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, and Z-6 Examples include 187, 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.

[0039] The amount of silane coupling agent added is preferably 0.1 to 10% by mass relative to the silicone resin. Adding 0.1% by mass or more of the silane coupling agent improves the adhesion between the core material particles or conductive fine particles and the silicone resin, preventing the coating layer from peeling off during long-term use, while adding 10% by mass or less prevents toner filming during long-term use.

[0040] In the present invention, 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.

[0041] Furthermore, it is desirable that the coating layer has an average film thickness of 0.50 μm or more. An average film thickness of 0.50 μm or more allows for the formation of a coating film that has no defects and can adequately retain fine particles. A more preferable average film thickness for the coating layer is 0.50 μm or more and 1.00 μm or less.

[0042] The carrier of the present invention can be manufactured, for example, by preparing a coating liquid to form the coating layer, uniformly applying the coating liquid to the surface of the core material particles using a known coating method, drying, and then baking. Examples of such coating methods include immersion, spraying, and brush application. The aforementioned solvent is not particularly limited and can be appropriately selected depending on the purpose. Examples include toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, cellosolve, butyl acetate, and synthetic isoparaffinic hydrocarbons. There are no particular restrictions on the baking method, and it can be appropriately selected according to the purpose. For example, it may be an external heating method or an internal heating method. There are no particular restrictions on the baking apparatus, and it can be appropriately selected according to the purpose. Examples include fixed electric furnaces, fluidized bed electric furnaces, rotary electric furnaces, burner furnaces, and apparatus equipped with microwaves.

[0043] The developer of the present invention contains the carrier of the present invention and may further contain toner. The toner may contain a binder resin, colorant, charge control agent, external additive, etc., and may be either a monochrome toner or a color toner. Furthermore, for application in an oil-less system where oil to prevent toner adhesion is not applied to the fixing roller, the toner may contain a release agent. Such toners are generally prone to filming, but the carrier of the present invention can suppress filming, so the developer of the present invention can maintain good quality over a long period of time. In addition, color toners, especially yellow toners, generally have the problem of color staining due to abrasion of the carrier coating layer, but the developer of the present invention can suppress the occurrence of color staining.

[0044] 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. 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.).

[0045] 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. 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.

[0046] The binder resin is not particularly limited, but examples include styrene and its substituted homopolymers such as polystyrene, poly-p-styrene, and polyvinyltoluene; styrene-p-chlorostyrene copolymer, styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-methacrylic acid copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-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, but 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.

[0047] The colorants (pigments or dyes) are not particularly limited, but include yellow pigments such as cadmium yellow, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, and tartrazine lake; orange pigments such as molybdenum orange, permanent orange GTR, pyrazolone orange, balkan orange, indanthrene brilliant orange RK, benzidine orange G, and 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, and rhodamine red. Examples of pigments include red pigments such as Ki 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; black pigments such as azine dyes such as Carbon Black, Oil Furnace Black, Channel Black, Lamp Black, Acetylene Black, and Aniline Black, metal salt azo dyes, metal oxides, and composite metal oxides; and white pigments such as Titanium Dioxide. Two or more pigments may be used in combination, and they may not be used in the case of transparent toner.

[0048] While not particularly limited, examples of release agents include polyethylene, polypropylene and other polyolefins, fatty acid metal salts, fatty acid esters, paraffin wax, amide wax, polyhydric alcohol wax, silicone varnish, carnauba wax, ester wax, and more than one of these may be used in combination.

[0049] Furthermore, the toner may further contain a charge control agent. The antistatic agent is not particularly limited, but may include nigrosine; azine dyes having alkyl groups with 2 to 16 carbon atoms; CIBasic Yello 2 (CI41000), CIBasic Yello 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 of suitable materials 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; 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.

[0050] External additives are not particularly limited, but 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 are hydrophobically treated, 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.

[0051] 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 consisting of 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 carrier charge degradation due to toner deposition on the carrier, but by using this method, the amount of carrier replenishment is also large 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. The mixing ratio of the replenishment developer is preferably 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 excess carrier supply, and the carrier concentration in the developing device does not become too high, so the charge of the developer does not increase easily. An increase in the charge of the developer reduces the developing ability and lowers the image density. When the toner is 50 parts by mass or less, the proportion of carriers in the replenishment developer does not decrease, so there is more carrier turnover in the image forming device, and an effect against carrier degradation can be expected.

[0052] The electrophotographic image forming developer of the present invention is characterized by containing the carrier of the present invention described above. Furthermore, it is preferable that the developer contains toner in a 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.

[0053] (Image forming method) The image forming method of the present invention is characterized by forming an image using the developer of the present invention, and specifically comprises the following steps: 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 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.

[0054] (Process cartridge) The process cartridge of the present invention is characterized by comprising the developer of the present invention, and more specifically comprises 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 developer of the present invention, and a cleaning member for cleaning the electrostatic latent image carrier.

[0055] Figure 1 shows an example of a process cartridge of the present invention. The process cartridge (10) integrally supports a photoreceptor (11) which is an electrostatic latent image carrier, a charging device (12) which is a charging member that charges the photoreceptor (11), a developing device (13) which 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, and a cleaning device (14) which 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. The process cartridge (10) is detachable from the main body of an image forming apparatus such as a copier or printer.

[0056] 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 a 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 a 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 a transfer device from a paper feeding unit (not shown), synchronized with the rotation of the photoreceptor (11). Furthermore, the transfer paper onto which the toner image has been transferred is separated from the surface of the photoreceptor (11), introduced into a fuser, and fixed, and then printed out as a copy to the outside of the image forming apparatus. Meanwhile, the surface of the photoreceptor (11) after the toner image has been transferred is cleaned by a cleaning device (14) to remove any remaining toner, then static electricity is removed by a static eliminator, and it is used repeatedly for image forming.

[0057] (Image forming apparatus) The image forming apparatus of the present invention is characterized by including the developer of the present invention, and specifically comprises an electrostatic latent image carrier, a charging means for charging the electrostatic latent image carrier, an exposure means for forming an electrostatic latent image on the electrostatic latent image carrier, a developing means for developing the electrostatic latent image formed on the electrostatic latent image carrier 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, and further comprises other means as appropriate as needed, such as a static elimination means, a cleaning means, a recycling means, a control means, etc., and uses the developer of the present invention as the developer. [Examples]

[0058] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these. Unless otherwise specified, "parts" in the following description refers to "parts by mass," and "%" refers to "mass%."

[0059] (Carrier 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%) 35 parts • Antimond pentoxide-doped tin oxide surface-treated aluminum oxide (equivalent circle diameter = 0.55 μm) 700 units Barium sulfate (equivalent circle diameter = 0.60 μm) 570 units • Toluene 6000 copies • Dispersant (phosphate ester-based surfactant) 25 parts • Antifoaming agent (silicone-based, silicone content: 1%) 430 units

[0060] In resin liquid 1, the above materials were dispersed in a homomixer for 10 minutes to prepare a coating layer forming solution. Mn-Mg-Sr ferrite with a volume-average particle size of 36 μm was used as the carrier core material, and the above 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 a 60°C atmosphere to a thickness of 0.50 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 T from the core material surface to the coating layer surface was 0.50 μm. 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 thickness T (μm) from the core material surface to the coating layer surface was determined by observing the carrier cross-section using a transmission electron microscope (TEM). The thickness T from the core material surface to the coating layer surface was measured at 50 points at 0.2 μm intervals along the carrier surface, and the obtained measurements were averaged.

[0061] (Carrier manufacturing example 2) Carrier 2 was obtained in the same manner as in carrier manufacturing example 1, except that aluminum oxide surface-treated with antimond oxide dioxide was changed to aluminum oxide surface-treated with antimond oxide trioxide.

[0062] (Carrier manufacturing example 3) Carrier 3 was obtained in the same manner as in carrier production example 1, except that the phosphate ester surfactant was changed to a sulfate ester surfactant.

[0063] (Carrier manufacturing example 4) Carrier 4 was obtained in the same manner as in carrier production example 1, except that the phosphate ester surfactant was changed to a carboxylic acid surfactant.

[0064] (Carrier manufacturing example 5) Carrier 5 was obtained in the same manner as in carrier manufacturing example 1, except that aluminum oxide surface-treated with antimond oxide pentoxide and tin oxide was replaced with titanium oxide surface-treated with antimond oxide pentoxide and tin oxide.

[0065] (Carrier manufacturing example 6) <Resin liquid 6> • Acrylic resin solution (solid content concentration: 20%) 200 units • Silicone resin solution (solid content concentration: 40%) 2000 units • Aminosilane (solid content concentration: 100%) 35 parts • Antimond pentoxide-doped tin oxide surface-treated aluminum oxide (equivalent circle diameter = 0.55 nm) 700 units • Toluene 6000 copies • Dispersant (phosphate ester surfactant) 14 parts • Antifoaming agent (silicone-based, silicone content: 1%) 400 units Carrier 6 was obtained in the same manner as in carrier manufacturing example 1, except that resin liquid 1 was changed to resin liquid 6.

[0066] (Carrier manufacturing example 7) Carrier 7 was obtained in the same manner as in carrier production example 1, except that barium sulfate was replaced with magnesium oxide.

[0067] (Carrier manufacturing example 8) Carrier 8 was obtained in the same manner as in carrier manufacturing example 1, except that barium sulfate was replaced with hydrotalcite.

[0068] (Carrier manufacturing example 9) Carrier 9 was obtained in the same manner as in carrier production example 1, except that barium sulfate was replaced with magnesium hydroxide.

[0069] (Carrier manufacturing example 10) Carrier 10 was obtained in the same manner as in carrier production example 1, except that barium sulfate was replaced with aluminum oxide.

[0070] (Carrier manufacturing example 11) Carrier 11 was obtained in the same manner as in carrier manufacturing example 1, except that the silicone-based defoaming agent was changed to an acrylic-based defoaming agent.

[0071] (Carrier manufacturing example 12) Carrier 12 was obtained in the same manner as in carrier manufacturing example 1, except that the silicone-based defoaming agent was changed to a vinyl-based defoaming agent.

[0072] (Carrier manufacturing example 13) Carrier 13 was obtained in the same manner as in carrier production example 1, except that aluminum oxide surface-treated with antimond oxide pentoxide was replaced with tin oxide surface-treated with antimond oxide pentoxide.

[0073] (Carrier manufacturing example 14) Carrier 14 was obtained in the same manner as in carrier production example 1, except that the phosphate ester surfactant was changed to a dialkylamine salt surfactant.

[0074] <Example of toner manufacturing> -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 at 230°C for 15 hours. Next, the reaction was carried out under reduced pressure of 5-10 mmHg for 6 hours to synthesize a polyester resin. The resulting 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.

[0075] —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 the mixture was 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.

[0076] -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 a ketimine compound (the active hydrogen group-containing compound). The amine value of the obtained ketimine compound (the active hydrogen group-containing compound) was 423.

[0077] -Masterbatch creation- 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.

[0078] -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.

[0079] -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%.

[0080] —Preparation of toner material solution— 70 parts polyester resin A, 10 parts prepolymer, and 100 parts ethyl acetate were placed in a beaker and stirred until dissolved. 5 parts paraffin wax (HNP-9, manufactured by Nippon Seiro Co., Ltd., melting point 75°C), 2 parts MEK-ST (manufactured by Nissan Chemical Industries, Ltd.), and 10 parts 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% volume of zirconia beads with a particle size of 0.5 mm packed inside. Then, 2.7 parts of the aforementioned ketimine were added and dissolved to prepare the toner material solution.

[0081] —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).

[0082] —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.

[0083] —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.

[0084] -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.

[0085] —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. The toner dispersion was then 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.

[0086] —Drying— The resulting final filtered cake was dried in a circulating air dryer at 45°C for 48 hours, and then sieved with a 75 μm mesh to obtain toner matrix particles 1.

[0087] —External additive treatment— 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.

[0088] [Example 1] Developer 1 was prepared by mixing 7 parts by mass of toner 1 obtained in toner manufacturing example and 93 parts by mass of carrier 1 obtained in carrier manufacturing example 1 in a mixer for 3 minutes.

[0089] [Examples 2-12] As shown in Table 2, developers 2 to 12 were prepared in the same manner as in Example 1, except that carrier 1 was changed to carriers 2 to 12.

[0090] [Comparative Example 1] Developer 13 was prepared in the same manner as in Example 1, except that carrier 1 was changed to carrier 13.

[0091] [Comparative Example 2] Developer 14 was prepared in the same manner as in Example 1, except that carrier 1 was changed to carrier 14.

[0092] Table 1 shows the composition of the coating layer for each carrier in the obtained developer.

[0093] [Table 1]

[0094] <Developer Characteristics Evaluation> The following evaluations were performed using the obtained [Developer 1] to [Developer 14]. To evaluate carrier wear, charging, and resistance fluctuations during long-term printing, we evaluated edge carrier adhesion and solid carrier adhesion. To evaluate charging stability during long-term printing, we evaluated toner scattering, ID, charging rise time, charging stability over time, and ghost images.

[0095] The resulting developer was used in a commercially available digital full-color multifunction printer (Ricoh Pro C9100), and image evaluation was performed.

[0096] (Toner scattering) After running 1 million pages, the amount of toner accumulated at the bottom of the developer carrier was suctioned and collected, and the toner weight was measured. The evaluation criteria are as follows: ◎, ○, and △ ratings indicate a passing grade. 0mg 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)

[0097] (Edge carrier attachment) After running 1 million images, the machine was placed in an environmental evaluation room (low temperature and low humidity environment of 10°C and 15%) and left for a day. Edge carrier adhesion was then evaluated using each developer. Under development conditions (charging potential (Vd): -630V, development bias: DC-500V), an image was printed on A3 size paper with 170μm x 170μm squares, alternating between solid areas and white areas vertically and horizontally. The number of white areas in the image due to carrier adhesion at the boundaries of each square was counted. The evaluation criteria are shown below. ◎, ○, and △ ratings indicate a pass. 0 items: ◎ (Excellent) 1~3 pieces: ○(good) 4~10 pieces: △(Available) 11 or more: × (defective)

[0098] (Adhered to a beta carrier) After running 1 million prints, the machine was subjected to laboratory conditions (25°C, 60% humidity) and the adhesion of beta carriers was evaluated using each developer. A solid image was processed under specified development conditions (charging potential (Vd): -600V, potential after exposure in the image area (solid original): -100V, development bias: DC-500V). Image development was interrupted by methods such as turning off the power, and the number of carrier deposits on the photoreceptor after transfer was counted for evaluation. The evaluation area was a 10mm x 100mm area on the photoreceptor. The evaluation criteria are shown below. ◎, ○, and △ ratings indicate a pass. 0 items: ◎ (Excellent) 1~3 pieces: ○(good) 4~10 pieces: △(Available) 11 or more: × (defective)

[0099] (ID) After placing the machine in an environmental evaluation room (low temperature and low humidity environment of 10°C and 15%) and running 100,000 sheets (100,000 sheets), three copies each of solid white and solid black images on A3 paper (brand: RICOH MyPaper) were printed, and the image density (visual evaluation) on the image samples was assessed. The above evaluation results were ranked on the following four-point scale. ◎, ○, and △ ratings indicate a passing grade. ◎: Excellent, ○: Good, △: Usable, ×: Poor

[0100] (Static charge rise) A sample was prepared by mixing 93% carrier by mass with 7% toner by mass, and then triboelectrically charging it. The sample was then measured using a blow-off valve TB-200 (manufactured by Toshiba Chemical Co., Ltd.). At this time, the charge level at 15 seconds after the start of mixing of carrier and toner was defined as Q1, and the charge level at 600 seconds after the start of mixing was defined as Q2. The charge rise time was defined as the absolute value of (Q1-Q2) / (Q1)×100. The evaluation criteria are shown below. ◎, ○, and △ ratings indicate a pass. 15 or higher: ◎ (Excellent) 10 or more but less than 15: ○ (Good) 5 or more but less than 10: △ (Usable) 0 or greater but less than 5: × (Poor)

[0101] (Static stability over time) The Ricoh Pro C9100 (Ricoh digital color copier / printer) was evaluated using developers 1-14 from the examples and comparative examples, along with their replenishment developers, on a carrier after 1 million runs at an image area ratio of 40%. First, the initial charge level of the carriers (Q1) was measured using a TB-200 blow-off device (manufactured by Toshiba Chemical Co., Ltd.) on a sample prepared by mixing carriers 1-14 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. ◎, ○, and △ ratings indicate a pass. 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)

[0102] (Ghost image) Ghost images were created by printing a vertical band chart, as shown in Figure 2, an A4-sized image chart with an image area ratio of 8%. The density difference between one full rotation of the sleeve (a) and the area after one rotation (b) was measured using an X-Rite938 (manufactured by X-Rite Corporation), and the average density difference measured at three locations (center, rear, and front) was defined as ΔID, which was then ranked as follows. In Figure 2, the upper figure shows a normal image in the vertical band chart, and the lower figure shows problematic ghost images (b1), (b2), and (b3) for image sections (a1), (a2), and (a3), respectively. ◎: Excellent, ○: Good, △: Acceptable, ×: Not usable for practical purposes ◎, ○, and △ were marked as passing grades, while × was marked as a failing grade. ◎: 0.01≧ΔID ○: 0.01 < ΔID ≤ 0.03 △: 0.03 < ΔID ≤ 0.06 ×: 0.06 < ΔID

[0103] The results of the image evaluation are shown in Table 2.

[0104] [Table 2] [Explanation of symbols]

[0105] 10 Process Cartridges 11 Photoreceptor 12 Charging device 13. Developing device 14 Cleaning device [Prior art documents] [Patent Documents]

[0106] [Patent Document 1] Japanese Patent Application Publication No. 8-305090 [Patent Document 2] Japanese Patent Publication No. 2001-117288 [Patent Document 3] Japanese Patent Application Publication No. 06-202381 [Patent Document 4] Japanese Patent Publication No. 2017-167387 [Patent Document 5] Japanese Patent Publication No. 2012-58448 [Patent Document 6] Japanese Patent Publication No. 2014-029464

Claims

1. In an electrophotographic image forming carrier having core material particles and a coating layer covering the core material particles, The coating layer contains at least antimony-containing particles and an anionic dispersant, The antimony-containing particles are particles in which inorganic fine particles are used as substrate particles, and the substrate particles are surface-treated with antimony-doped tin oxide. The inorganic fine particles that constitute the substrate are aluminum oxide or titanium oxide. A carrier for forming electrophotographic images, characterized by the above features.

2. The electrophotographic image forming carrier according to claim 1, characterized in that the antimony-containing particles contain diantimony pentoxide.

3. The electrophotographic image forming carrier according to claim 1, characterized in that the inorganic fine particles that are the substrate particles are aluminum oxide.

4. The electrophotographic image forming carrier according to claim 1, characterized in that the anionic dispersant is a phosphate ester surfactant.

5. The electrophotographic image forming carrier according to claim 1, characterized in that the coating layer contains an antifoaming agent.

6. The carrier for forming electrophotographic images according to claim 5, characterized in that the defoaming agent is a silicone-based defoaming agent.

7. The electrophotographic image forming carrier according to claim 1, characterized in that the coating layer contains inorganic fine particles in addition to the antimony-containing particles.

8. The electrophotographic image forming carrier according to claim 7, characterized in that the inorganic fine particles other than the antimony-containing particles are white.

9. The electrophotographic image forming carrier according to claim 7, characterized in that the inorganic fine particles other than the antimony-containing particles contain barium sulfate.

10. The electrophotographic image forming carrier according to claim 9, characterized in that the inorganic fine particles other than the antimony-containing particles are barium sulfate in elemental form.

11. An electrophotographic image forming developer characterized by comprising the electrophotographic image forming carrier described in claim 1.

12. An electrophotographic image forming method characterized by forming an image using the electrophotographic image forming developer described in claim 11.

13. An electrophotographic image forming apparatus characterized by comprising the electrophotographic image forming agent described in claim 11.

14. A process cartridge characterized by comprising the electrophotographic image forming developer described in claim 11.

Images