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

Abstract

To provide an electro-photographic image formation carrier which includes the carrier adhesion preventing property and ghost preventing property while maintaining the stable electrifying capability in long-term use.SOLUTION: The above-mentioned problem is solved by an electro-photographic image formation carrier which comprises: a core material particle; and a coating layer which covers the core material particle, in which the apparent density of the carrier is equal to or greater than 2.0 [g / cm3] and less than 2.5 [g / cm3], and contains an electrified particle and a dispersing agent in the coating layer.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] Generally, in image forming methods such as the electrophotographic method and the electrostatic photographic method, a developer obtained by stirring and mixing toner and a carrier is used to develop an electrostatic latent image formed on a latent image carrier. This developer is required to be a properly charged mixture. Generally, as a method for developing an electrostatic latent image, a method using a two-component developer obtained by mixing toner and a carrier and a method using a one-component developer not containing a carrier are known. The two-component developing system uses a carrier, so the frictional charging area with respect to the toner is wide, the charging characteristics are more stable than the one-component system, and it is advantageous for maintaining high image quality over a long period. In addition, since the toner supply ability to the development area is high, it is particularly widely adopted in high-speed machines. Also, in a digital electrophotographic system in which an electrostatic latent image is formed on a photoreceptor with a laser beam or the like and this latent image is visualized, the two-component developing system is widely adopted because the above-described characteristics are useful.

[0003] Carriers used in such a two-component development system are being studied to improve their durability by coating them with a suitable resin material for purposes such as preventing toner spent on the carrier surface, forming a uniform carrier surface, preventing surface oxidation, preventing a decrease in moisture sensitivity, extending the life of the developer, protecting the photoreceptor from scratches or wear caused by the carrier, controlling the charging polarity, or adjusting the charge amount. For example, those coated with a specific resin material (Patent Document 1), those in which various additives are added to the coating layer (Patent Documents 2 to 8), and those using carriers with additives attached to the carrier surface (Patent Document 9) are disclosed. Patent Document 10 discloses a carrier coating material composed of a guanamine resin and a thermosetting resin capable of crosslinking with the guanamine resin, and Patent Document 11 discloses using a crosslinked product of a melamine resin and an acrylic resin as a carrier coating material.

[0004] For example, in Patent Documents 12 to 15, resin-coated carriers in which conductive carbon or conductive fillers are dispersed as conductive agents in the coating layer of the carrier have been proposed.

[0005] Patent Document 16 also discloses a carrier having a coating layer containing first conductive particles that are metal oxide conductive particles and second conductive particles whose surfaces of metal oxide particles and / or metal salt particles are electrically conductive treated. Patent Documents 17 and 18 disclose carriers containing barium sulfate in the coating film and having a Ba / Si ratio of 0.01 to 0.08 with respect to all elements measured by XPS. Patent Document 19 also describes an example using barium sulfate as a base material.

[0006] Patent Document 20 speculates that the cause of ghost images is an increase in the development potential due to toner (so-called "sleeve contamination") adhering to the developer carrier (development sleeve) when the developer carrier passes through the development region facing the non-image portion on the latent image carrier. Patent Document 20 proposes a developing apparatus that suppresses the occurrence of sleeve contamination and avoids the occurrence of ghost images by reducing the friction coefficient of the surface layer of the developer carrier and adjusting the AC component of the voltage applied to the developer carrier.

Summary of the Invention

Problems to be Solved by the Invention

[0007] An object of the present invention is to provide an electrophotographic image forming carrier having charge imparting ability that is stable even during long-term use and having carrier adhesion resistance and ghost resistance.

Means for Solving the Problems

[0008] The above problems are solved by the following configuration 1). 1) In an electrophotographic image forming carrier having core material particles and a coating layer covering the core material particles, the apparent density of the carrier is 2.0 [g / cm 3 or more and less than 2.5 [g / cm 3 , the coating layer contains chargeable particles and a dispersant, the dispersant is any one of a phosphate ester surfactant, a sulfate ester surfactant, a sulfonic acid surfactant, or a carboxylic acid surfactant, the apparent density of the carrier is measured according to JIS-Z2504:2000, the magnetization in a magnetic field of 1000 [Oe] (79.58 kA / m) is 56 [Am 2 / kg] or more and less than 73 [Am 2 / kg], and contains at least one kind of particles selected from barium sulfate, zinc oxide, magnesium oxide, magnesium hydroxide, and hydrotalcite as the charged particles, the core particles are formed using Mn ferrite or Mn-Mg-Sr ferrite An electrophotographic image forming carrier, characterized by the above.

Effects of the Invention

[0009] According to the present invention, it is possible to provide an electrophotographic image forming carrier having charge imparting ability that is stable even during long-term use and having carrier adhesion resistance and ghost resistance.

Brief Description of the Drawings

[0010] [Fig. 1] This is a diagram for explaining an example of the process cartridge of the present invention.

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in more detail. The gist of the present invention is as described in the above configuration 1), but also includes the following embodiments 2) to 16).

[0012] 2) The electrophotographic image forming carrier according to 1), characterized in that an antifoaming agent is contained in the coating layer. 3) The electrophotographic image forming carrier according to 1) or 2), characterized in that the internal porosity of the core material particles is 0.0 [%] or more and less than 2.0 [%]. 4) The electrophotographic image forming carrier according to any one of 1) to 3), characterized in that the surface roughness Rz of the core material particles is 2.0 [μm] or more and less than 3.0 [μm]. 5) The electrophotographic image forming carrier according to any one of 1) to 4), characterized in that at least one kind of particles selected from barium sulfate, zinc oxide, magnesium oxide, magnesium hydroxide and hydrotalcite is contained as the chargeable particles. 6) The electrophotographic image forming carrier according to any one of 1) to 5), characterized in that barium sulfate is contained as the chargeable particles and the barium exposure amount on the surface of the coating layer is 0.1 [atomic%] or more. 7) The electrophotographic image forming carrier according to any one of 1) to 6), characterized in that the coating layer contains inorganic particles in addition to the chargeable particles. 8) The inorganic particles are tin oxide doped with any one of tungsten, indium, phosphorus, or their oxides, or particles obtained by providing tin oxide doped with any one of tungsten, indium, phosphorus, or their oxides on the substrate surface, and the carrier for electrophotographic image formation according to any one of 1) to 7). 9) The carrier for electrophotographic image formation according to any one of 1) to 8), wherein the core particles are formed using Mn ferrite. 10) The magnetization in a magnetic field of 1000 [Oe] (79.58 kA / m) is 56 [Am 2 / kg] or more and less than 73 [Am 2 / kg], and the carrier for electrophotographic image formation according to any one of 1) to 9). 11) The carrier for electrophotographic image formation according to any one of 1) to 10), wherein the dispersant is a phosphate ester surfactant. 12) The carrier for electrophotographic image formation according to 2), wherein the defoaming agent is silicone-based. 13) A developer for electrophotographic image formation, comprising the carrier for electrophotographic image formation according to any one of 1) to 12). 14) An electrophotographic image forming method, characterized by forming an image using the developer for electrophotographic image formation according to 13). 15) An electrophotographic image forming apparatus, comprising the developer for electrophotographic image formation according to 13). 16) A process cartridge, characterized by comprising the developer for electrophotographic image formation according to 13).

[0013] As described above, carriers with coated surfaces are known in the prior art. However, carriers with coated surfaces tend to have lower magnetization than the so-called core material particles before coating. This is because the resin used as the coating material does not have magnetization. Furthermore, when non-magnetic inorganic fine particles such as barium sulfate are contained in the coating layer (coat layer), this decrease in magnetization becomes more significant. When the magnetization of the carrier becomes low, the magnetic binding force from the developer carrier becomes weak, so the risk of carrier adhesion due to the aforementioned counter charge or injection charging from the developer carrier increases.

[0014] In recent years, the demand for high image quality in the market has been increasing steadily, and among them, "ghost", which is one of the abnormal images, has been cited as a major issue. Patent Document 20 speculates that the cause of the ghost image is an increase in the development potential due to toner (so-called "sleeve contamination") adhering to the developer carrier (development sleeve) when the developer carrier passes through the development region facing the non-image portion on the latent image carrier. In Patent Document 20, a developing device has been proposed that suppresses the occurrence of sleeve contamination and avoids the occurrence of ghost images by reducing the friction coefficient of the surface layer of the developer carrier and adjusting the AC component of the voltage applied to the developer carrier. However, due to long-term use, when the surface of the developer carrier deteriorates and changes in the direction of increasing the friction coefficient, its effectiveness decreases and ghost images are generated.

[0015] Also, as described above, in maintaining high image quality over a long period, it is important that the charging characteristics are stable. One of the factors that hinders the charging stability over time is the accumulation of the adhesion (spent) of toner components on the carrier surface. Spent often starts from the concave portions on the carrier surface and accumulates with the inside of the concave portions as nests. The recesses on the carrier surface are often formed along the shape of the core material particles, but are somewhat alleviated by being coated with a resin layer. However, during coating, air may enter and become trapped between the recessed grooves on the surface of the core material particles and the coating layer. Particularly for core material particles with many irregularities on the surface, and furthermore, for core material particles with prominent irregularities in the vertical direction (the direction in which the shape index Rz indicating surface roughness increases), the probability of air being trapped in the recesses becomes very high. When air is trapped inside the coating layer, in the case of the carrier manufacturing process that undergoes a firing process after coating, the air in the coating layer expands due to the heat of firing and bulges, forming crater-like recesses on the surface of the coating layer, which can become spent accumulation nests or the starting point of spent accumulation.

[0016] Also, as described above, by incorporating charged particles (hereinafter referred to as "charged particles") into the carrier coating layer, the charging ability of the carrier when balancing toner at a high image area can be suppressed by the charge imparting function of the charged particles. However, since the magnetic moment of a single carrier particle becomes small, the magnetic binding force received from the developer carrier becomes low, resulting in the drawback of low carrier adhesion resistance. Most of the magnetic moment of the carrier is borne by the magnetization of the core material particles. Since magnetization itself is determined by the composition of the core material particles, in order to increase the magnetic moment per core material particle and compensate for the decrease in magnetic moment caused by the charged particles, it is effective to make the mass of each core material particle as high as possible. On the one hand, as described above, ghosting is caused by the increase in the development potential due to sleeve contamination. However, even if sleeve contamination occurs equally, carriers with a lower apparent density can suppress the degree of ghosting to a lower level. This is because the lower the apparent density of the carriers, the higher the space occupancy rate of the carriers between the latent image carrier, which is the development region, and the developing sleeve, and the lower the electrical resistance of the bulk carriers. When the electrical resistance of the bulk carriers is low, the mirror charges can easily move through the carriers in the direction of canceling out the potential raised by the sleeve contamination. Therefore, it is considered that the increase in potential is alleviated and the occurrence of ghosting is suppressed. Conversely, increasing the apparent density of the carriers tends to worsen ghosting.

[0017] One of the factors that determines the apparent density of the bulk carriers is the mass of one carrier particle. Increasing the mass of one carrier particle tends to increase the apparent density of the bulk carriers. Therefore, it is difficult to lower the apparent density of the bulk carriers while increasing the mass of one carrier particle. For this reason, the carrier adhesion resistance and the ghosting resistance are in a trade-off relationship, and it has been difficult to achieve both high levels of carrier adhesion resistance and ghosting resistance until now.

[0018] The inventors of the present invention have intensively studied to solve the above problems. As a result, it has been found that the above problems can be solved by an electrophotographic image forming carrier having an apparent density of 2.0 [g / cm 3 or more and less than 2.5 [g / cm 3 and containing charged particles and a dispersant in the coating layer.

[0019] In addition, according to the study by the inventors of the present invention, even for carriers in which the magnetic moment tends to decrease by containing charged particles in the coating layer, in order to minimize the increase in the apparent density and maximize the mass of one carrier particle, and efficiently increase the magnetic moment per carrier particle, it is found that it is preferable to make the internal voids of the core particles less than 2.0 [%].

[0020] However, reducing the apparent density of the carrier to 2.0 [g / cm 3 or more and less than 2.5 [g / cm 3 and suppressing the internal porosity of the core material particles to less than 2.0 [%] are in an antinomic relationship. To solve this problem, for example, adjusting the surface roughness of the carrier can be mentioned. For example, when the surface roughness of the carrier is increased, the above-mentioned apparent density and internal porosity can be achieved without sacrificing the mass per carrier particle, and anti-carrier adhesion and anti-ghosting can be achieved at a high level.

[0021] The surface roughness of the carrier is also affected by the surface roughness of the core material particles. As a result of the study by the present inventors, it has been found that by setting the Rz (maximum height) of the core material particles to 2.0 [μm] or more, the apparent density after carrier formation can be more efficiently reduced. Further, by setting Rz to less than 3.0 [μm], the unevenness on the surface of the core material particles is reduced, and even when the carrier is used for a long time, the convex portions of the core material particles are less likely to be exposed on the carrier surface, and the life of the carrier can be extended.

[0022] The Rz of the core material particles means the maximum height Rz of the surface shape (roughness curve) defined in JIS B0601:2001 (ISO1365-1).

[0023] However, when the surface roughness of the core material particles is increased to reduce the apparent density, particularly when the surface roughness is increased in the direction of increasing the value of Rz, air is likely to be trapped in the coating layer as described above. When the trapped air expands due to thermal expansion or the like, crater-shaped recesses are formed, which causes spent accumulation. The present inventors have intensively studied this problem and found that by incorporating a dispersant in the coating layer, the resin layer fills the recesses on the surface of the core material particles, air is not trapped in the coating layer, and crater-shaped recesses generated by the expansion of the trapped air are not generated, so that a decrease in charging stability due to spent can be suppressed.

[0024] Dispersants are often used for the purpose of promoting the dispersion of fine particles in the coating layer. The reason for the promoted dispersion is that the surfactant improves the wettability of the coating liquid (coating liquid for forming the coating layer) with respect to the surface of the inorganic fine particles, and the aggregation of the inorganic fine particles that have been secondary-particleized is released. That is, the original function of the dispersant is to enhance the wettability between the coating liquid and the inorganic material, and this has the same effect not only on inorganic fine particles but also on the surface of the core material particles. When the wettability of the coating liquid with respect to the core material particles increases, the coating liquid easily enters the recesses on the surface of the core material particles, and the internal air can be pushed out. As a result, it becomes difficult for air to be trapped in the recesses of the core material particles. Consequently, the crater-shaped recesses formed by the air escaping are reduced, and the accumulation of spent is decreased.

[0025] Since the dispersant also loses its effect as a surfactant on the inorganic fine particles in the coating liquid, it is preferable to determine the addition amount based on the amount of the inorganic fine particles. Specifically, it is preferably 0.5 parts by mass or more and 10.0 parts by mass or less with respect to 100 parts by mass of the total amount of the inorganic fine particles in the coating liquid. When the addition amount of the dispersant is 0.5 parts by mass or more, the action of improving the wettability with respect to the surface of the core material particles becomes sufficient, and it becomes difficult for air to remain in the grooves of the recesses of the core material particles. On the other hand, when the addition amount of the dispersant is 10.0 parts by mass or less, the ratio of the resin in the solid content of the coating layer becomes appropriate, the strength of the coating layer is improved, the abrasion of the coating layer and the detachment of the inorganic fine particles during long-term use are suppressed, and stable image quality can be obtained.

[0026] The dispersant referred to in the present invention generally refers to surfactants having a function of promoting the dispersion of inorganic fine particles into the coating liquid, and the material thereof is not particularly limited. Examples include phosphate ester surfactants, sulfate ester surfactants, sulfonic acid surfactants, and carboxylic acid surfactants. In particular, it is preferable to be a phosphate ester surfactant for efficient function expression. As phosphate ester-based dispersants, commercially available products include Solsperse 2000, 2400, 2600, 2700, 2800 (manufactured by Zeneca), Adiper PB711, PA111, PB811, PW911 (manufactured by Ajinomoto), EFKA-46, 47, 48, 49 (manufactured by EFKA Chemicals), Disperbyk 160, 162, 163, 166, 170, 180, 182, 184, 190 (manufactured by BYK-Chemie), Florentine DOPA-158, 22, 17, G-700, TG-720W, 730W (manufactured by Kyoeisha Chemical Co., Ltd.), etc., but are not limited thereto.

[0027] In addition, in fields such as painting, defoamers are often used in combination with dispersants. The reason is that since the dispersant mainly contains a surfactant, bubbles are often generated in the liquid, and the purpose is to make the painted surface smooth after drying by eliminating the bubbles before the paint dries. The inventors of the present invention have found that even when the air in the concave portion of the core material particles is extruded using a dispersant, the crater-shaped concave portion can be more suppressed by using a defoamer in combination. Due to the effect of the dispersant, when air is extruded from the concave portion on the surface of the core material particles, if the viscosity of the coating liquid is high, the extruded air will stay in the coating liquid layer and become bubbles, so the formation of crater-shaped concave portions cannot be completely suppressed. However, by using a defoamer in combination, it is possible to eliminate the bubbles caused by the air that has stayed in the coating layer although it has been extruded from the concave portion of the core material particles by the dispersant, and the formation of crater-shaped concave portions can be more effectively suppressed. As defoamers, generally commercially available ones can be used, and any of those having a foam-breaking action, a foam-suppressing action, or a degassing action can be used. Examples of materials that can be used include silicone-based, acrylic-based, vinyl-based, etc. Among them, silicone-based defoamers are particularly effective. In order for the defoamer to exhibit its effect, the balance between compatibility and incompatibility with the solvent is important. In particular, silicone-based has a good balance between this compatibility and incompatibility, and can exhibit a high effect even with a small addition amount. The addition amount of the defoaming agent should be adjusted according to the ability of the defoaming agent used. Generally, the range of 1.0 part by mass or more and 10.0 parts by mass or less with respect to 100 parts by mass of the total amount of the coating liquid forming the coating layer is a guide.

[0028] Examples of commercially available silicone-based defoaming agents 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 Inc.), BYK-065, BYK-066N, BYK-070, BYK-088, BYK-141 (manufactured by BYK-Chemie GmbH), Disparlon 1930N, Disparlon 1933, Disparlon 1934 (manufactured by Enomoto Kasei Co., Ltd.), etc., but are not limited thereto.

[0029] By containing chargeable particles in the coating layer, the electrophotographic image forming carrier of the present invention can suppress a decrease in the charging ability of the carrier when the toner is balanced at a high image area due to its charge imparting function, and can suppress the occurrence of abnormalities such as toner scattering and background contamination accompanying the decrease in charging.

[0030] The chargeable particles referred to here mean particles having a relatively low ionization potential, and more specifically, particles having an ionization potential lower than that of alumina particles (AA-03 manufactured by Sumitomo Chemical Co., Ltd.). Examples of preferable materials include barium sulfate, zinc oxide, magnesium oxide, magnesium hydroxide, and hydrotalcite, and particularly preferable material is barium sulfate. The ionization potential was measured using PYS-202 manufactured by Sumitomo Heavy Industries, Ltd.

[0031] The proportion of the chargeable particles in the coating layer is preferably, for example, 3 to 50% by mass, and more preferably 6 to 27% by mass.

[0032] When using barium sulfate as the charged particle, the barium exposure amount on the surface of the coating layer is preferably 0.1 [atomic%] or more. Since the charge exchange for charging the toner is carried out on the surface layer of the coating layer, in a carrier with an appropriate exposure of barium sulfate on the surface of the coating layer, the charge imparting ability of barium sulfate can be exhibited even if the coating layer is not significantly worn during long-term use of the carrier. When the barium exposure amount on the surface of the coating layer is 0.1 [atomic%] or more, it is preferable because the charge imparting ability can be exhibited not only when the coating layer is worn but also when toner components adhere (so-called spent) to the surface layer of the carrier during long-term use.

[0033] More preferably, the barium exposure amount on the surface of the coating layer is 0.1 to 0.2 [atomic%].

[0034] The exposure of barium sulfate on the surface layer of the carrier can be detected by the atomic% of barium calculated by peak analysis with AXIS / ULTRA (manufactured by Shimadzu / KRATOS). The beam irradiation area of this apparatus is approximately 900 μm × 600 μm, and detection is performed in the range of 25 carriers × 17. Also, the penetration depth is 0 to 10 nm, and information near the surface layer of the carrier is detected. The specific measurement method is carried out with the measurement mode: Al: 1486.6 eV, excitation source: monochromatic (Al), detection method: spectrum mode, and magnet lens: OFF. First, the detection elements are identified by wide-area scanning, and then the peaks are detected by narrow scanning for each detection element. After that, the atomic% of barium for all detected elements is calculated using the attached peak analysis software.

[0035] There is no particular limitation on the particle size of the charged particle, but when the total average thickness of the coating layer is T, it is preferable that the particle size h satisfies the following formula. h / 2 ≦ T ≦ h By making the particle size of the charged particles larger than the thickness of the coating layer, the probability that the charged particles protrude from the surface of the resin coating layer increases. When the top of the charged particle protrudes from the resin coating layer, it functions as a spacer between the rubbing objects and the resin of the coating layer when carriers rub against each other, or when the carrier rubs against the wall surface of the storage container or the transfer jig, and the life of the coating layer can be extended. In addition, since the contact probability of the charged particles with the toner increases, it is also preferable from the viewpoint of the charge imparting function. Further, when the thickness T of the coating layer is larger than half of the particle size of the charged particles, the charged particles can be firmly captured by the coating layer, so that the charged particles are less likely to detach from the resin coating layer.

[0036] The particle size of the charged particles can be confirmed by a conventionally known method. For example, before carrier formation, it can be measured using, for example, the NanoTrack UPA series (manufactured by Nikkiso Co., Ltd.). After carrier formation, for example, the coating layer on the carrier surface can be cut with FIB, and the cross section can be observed with SEM and EDX for confirmation. An example is given below. The carrier is mixed into an embedding resin (Devcon, two-component mixture, 30-minute curing type epoxy resin), left overnight to cure, and a rough cross-sectional sample is prepared by mechanical polishing. Using a cross-section polisher (SM-09010 manufactured by JEOL), the cross section was finished under the conditions of an acceleration voltage of 5.0 kV and a beam current of 120 μA. This was photographed using a scanning electron microscope (Merlin manufactured by Carl Zeiss) under the conditions of an acceleration voltage of 0.8 kV and a magnification of 30,000 times. The photographed image was imported into a TIFF image, and the equivalent circle diameter of 100 barium sulfate particles was measured using Image-Pro Plus manufactured by Media Cybernetics, and the average value was used. Note that the confirmation method is not limited to this. Also, the thickness of the coating layer can be measured in the same way from the photographed image. However, since there are individual differences for each particle and thickness variations depending on the location for the coating layer thickness, not only the measurement of only 1 particle / 1 location is performed, but statistical measurement of n number without problems is performed.

[0037] As described above, the carrier for image formation of the present invention preferably has an internal porosity of 0.0 [%] or more and less than 2.0 [ %]. As described above, when the internal porosity becomes 2.0 [ %] or more, the loss of the magnetic moment in one particle increases, and the carrier adhesion resistance decreases. The measurement of the internal porosity of the carrier can be performed using the following method. First, the carrier is cut and the cross-section is photographed. For cross-section photography, a conventionally known method such as SEM can be used. Next, using a conventionally known image analysis software (for example, Image Pro Premier manufactured by Media Cybernetics), the area S of the contour of one particle is obtained from the cross-sectional photograph of the particle. Similarly, the area s of the void portion inside one particle is obtained, and the porosity of one particle is obtained from the following formula. Porosity of one particle [%] = (s / S) × 100 This is performed on 60 particles randomly selected, and the average value is taken as the internal porosity.

[0038] The carrier of the present invention has an apparent density of 2.0 [g / cm 3 or more and less than 2.5 [g / cm 3 . As described above, when the apparent density of the carrier becomes 2.5 [g / cm 3 or more, the space occupancy rate of the carrier particles present in the development region when developing from the development roller to the image carrier becomes low. Therefore, the movement of charges via the carrier in the development region becomes difficult, and it becomes difficult to relax the potential increase due to the toner adhering to the development sleeve, and ghosting is likely to occur. Also, when the apparent density is less than 2.0 [g / cm 3 , a sufficient magnetic moment cannot be obtained, and carrier adhesion deteriorates. The apparent density of the carrier was measured according to JIS-Z2504:2000.

[0039] In addition, the present inventors formulated charged particles like the carrier of the present invention in the coating layer, while making the internal porosity less than 2.0 [ %], and the apparent density was 2.5 [g / cm 3When the surface of the core material particles is roughened so as to be less than a certain value, a new finding has been made that the ability to impart charge during long-term use functions more effectively.

[0040] Although the detailed reason why the above effects are achieved by this preferred form has not been elucidated, it is presumed to occur by the following mechanism. As described above, the spent toner components deposited on the surface of the carrier due to long-term use contribute to the reduction of the charging ability. However, although the internal porosity is low, the apparent density is less than 2.5 [g / cm 3 In carriers with large surface irregularities such that the apparent density is less than a certain value, when the carrier particles rub against and collide with each other in the developing machine, the convex portions of the carrier serve as claws for scraping off the spent substances on the surface of the resin coating layer. However, at this time, if the weight of one carrier particle is small, the energy applied during the rubbing and collision of the carrier particles is small, so the effect of the convex portion of the carrier scraping off the spent substances is low. Therefore, when the internal porosity is lowered to less than 2.0 [%] and the weight per particle is increased like the carrier of the present invention, a large amount of energy is applied to the scraping, so that the spent substances can be effectively scraped off by the convex portion of the carrier, the deposition of the spent substances is suppressed, and the reduction of the charging ability of the carrier can be effectively suppressed. In addition, the carrier of the present invention contains chargeable particles in the resin coating layer. However, in order for the chargeable particles to exhibit the charge-imparting ability, it is necessary to come into contact with the toner particles. However, since the chargeable particles are also covered with the resin in the coating layer, in order to exhibit the charge-imparting ability, it is necessary to damage the resin covering the chargeable particles and expose the chargeable particles. The scraping by the convex portion of the carrier and the weight per carrier particle serves to expose the chargeable particles and early express the charge-imparting ability, while continuously exhibiting that ability over a long period of time.

[0041] The core material particles used in the carrier of the present invention can be appropriately selected from those known for two-component carriers for electrophotography according to the purpose. In particular, Mn ferrite is a material with relatively high magnetization, so from the viewpoint of resistance to carrier adhesion, it is suitable because it is easy to set the magnetic moment per carrier particle within an appropriate range.

[0042] The magnetization of the carrier in a magnetic field of 1000 [Oe] (79.58 kA / m) is 56 [Am 2 / kg] or more and less than 73 [Am 2 / kg], preferably 56 [Am 2 / kg] or more and 63 [Am 2 / kg] or less is more preferable. Even if the internal porosity is reduced and the mass of one particle is increased, if the magnetization is 56 [Am 2 / kg] or more, the magnetic moment per particle does not decrease, and carrier adhesion is less likely to occur. Also, when the magnetization is 56 [Am 2 / kg] or more, not only is carrier adhesion less likely to occur, but also carriers on the developer carrier are rubbed against each other with a strong force, so the scraping of the spent material described above is promoted, which is also preferable from the viewpoint of maintaining the charging ability of the carrier. When the magnetization of the carrier is less than 73 [Am 2 / kg], the magnetization is not too high, and the developer with a low toner concentration after development does not leave the development roller and enter the development region again as it is, the image density in the second and subsequent passes of the development roller for solid images does not decrease, and vertical stripe abnormal images are less likely to occur. To make the magnetization of the carrier within the above range, the magnetization of the core material particles in a magnetic field of 1000 [Oe] is preferably 66 [Am 2 / kg] or more and less than 75 [Am 2 / kg].

[0043] The magnetization of the carrier core material particles was measured using a room-temperature dedicated vibrating sample magnetometer (VSM) (manufactured by Toei Industry Co., Ltd., VSM-P7). An external magnetic field of 0 to 1000 [Oe] was continuously applied in one cycle, and the magnetization σ1000 at an external magnetic field of 1000 [Oe] was measured.

[0044] The coating layer can contain inorganic particles in addition to the charged particles. As such inorganic particles, it is preferable to contain a conductive material for the purpose of resistance adjustment. Conventionally, carbon black has been widely used as the conductive material. However, when used for a long time as a developer, due to friction or collision between carriers or between toner and carriers, carbon black or resin pieces containing carbon black detach from the carrier coating layer and adhere to the toner particles or are developed as they are. Particularly, in a developer combined with yellow toner, white toner, or transparent toner, it appears prominently as a problem of color turbidity (color stain). Therefore, it is preferable that the conductive material is as close to white or colorless as possible. Particularly, as a material having good color and conductive functions, compounds in which tin oxide is doped with any one of tungsten, indium, phosphorus, or their oxides can be mentioned, and they can be used as single substances or as particles provided on the surface of the substrate particles. As the substrate particles, known materials can be used, and examples thereof include aluminum oxide and titanium oxide.

[0045] The coating layer can contain resin and other components as required. As the resin used for the coating layer, silicone resin, acrylic resin, or a combination thereof can be used. This is because acrylic resin has strong adhesiveness and low brittleness, so it has very excellent wear resistance properties. However, on the other hand, since its surface energy is high, in combination with toner that is easily spent, problems such as a decrease in charge amount due to the accumulation of spent toner components may occur. In that case, by using in combination a silicone resin that has a low surface energy, making it difficult for toner components to be spent and having the effect of making it difficult for the accumulation of spent components leading to film peeling to progress, this problem can be solved. However, since silicone resin has weak adhesiveness and high brittleness, it also has the weakness of poor wear resistance. Therefore, it is important to balance the properties of these two resins, thereby making it possible to obtain a coating film that is difficult to be spent and has wear resistance. This is because silicone resin has a low surface energy, making it difficult for toner components to be spent and having the effect of making it difficult for the accumulation of spent components leading to film peeling to progress.

[0046] The silicone resin referred to in this specification refers to all generally known silicone resins, including straight silicone consisting only of organosiloxane bonds, and silicone resins modified with alkyd, polyester, epoxy, acrylic, urethane, etc., but is not limited thereto. For example, as commercially available straight silicone resins, KR271, KR255, KR152 manufactured by Shin-Etsu Chemical Co., Ltd., SR2400, SR2406, SR2410 manufactured by Toray Dow Corning Silicone Co., Ltd., etc. can be mentioned. In this case, it is possible to use the silicone resin alone, but it is also possible to simultaneously use other components that undergo a crosslinking reaction, charge amount adjustment components, etc. Furthermore, as modified silicone resins, KR206 (alkyd modified), KR5208 (acrylic modified), ES1001N (epoxy modified), KR305 (urethane modified) manufactured by Shin-Etsu Chemical Co., Ltd., SR2115 (epoxy modified), SR2110 (alkyd modified) manufactured by Toray Dow Corning Silicone Co., Ltd., etc. can be mentioned.

[0047] Examples of the polycondensation catalyst include titanium-based catalysts, tin-based catalysts, zirconium-based catalysts, and aluminum-based catalysts. In the present invention, among these various catalysts, among the titanium-based catalysts that give excellent results, titanium diisopropoxybis(ethylacetoacetate) is most preferred as the catalyst. This is presumably because it has a great effect of promoting the condensation reaction of the silanol group and the catalyst is less likely to be deactivated.

[0048] As used herein, the acrylic resin refers to all resins having an acrylic component and is not particularly limited. Further, it is possible to use the acrylic resin alone, but it is also possible to use at least one or more other components that undergo a crosslinking reaction simultaneously. Examples of the other components that undergo a crosslinking reaction as used herein include, but are not limited to, amino resins, acidic catalysts, etc. The amino resin as used herein refers to, but is not limited to, guanamine, melamine resin, etc. Further, as the acidic catalyst as used herein, any substance having a catalytic action can be used. For example, those having reactive groups such as fully alkylated type, methylol group type, imino group type, methylol / imino group type, etc., but are not limited thereto.

[0049] Furthermore, it is more preferable that the coating layer contains a crosslinked product of an acrylic resin and an amino resin. Thereby, it is possible to suppress the fusion of the coating layers while maintaining appropriate elasticity. The amino resin is not particularly limited, but melamine resin and benzoguanamine resin are preferred because they can improve the charge imparting ability of the carrier. Further, when it is necessary to appropriately control the charge imparting ability of the carrier, melamine resin and / or benzoguanamine resin may be used in combination with other amino resins. As the acrylic resin capable of crosslinking with the amino resin, those having a hydroxyl group and / or a carboxyl group are preferable, and those having a hydroxyl group are more preferable. Thereby, the adhesion to the core material particles and the conductive fine particles can be further improved, and the dispersion stability of the conductive fine particles can also be improved. At this time, the acrylic resin preferably has a hydroxyl value of 10 mgKOH / g or more, and more preferably 20 mgKOH / g or more.

[0050] In the present invention, the composition for forming the coating layer preferably contains a silane coupling agent. Thereby, the conductive fine particles can be stably dispersed. The silane coupling agent is 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, hexamethyldisilazane, r-anilinopropyltrimethoxysilane, vinyltrimethoxysilane, octadecyldimethyl[3-(trimethoxysilyl)propyl]ammonium chloride, r-chloropropylmethyldimethoxysilane, methyltrichlorosilane, dimethyldichlorosilane, trimethylchlorosilane, allyltriethoxysilane, 3-aminopropylmethyldiethoxysilane, 3-aminopropyltrimethoxysilane, dimethyldiethoxysilane, 1,3-divinyltetramethyldisilazane, methacryloxyethyldimethyl(3-trimethoxysilylpropyl)ammonium chloride, etc. Two or more kinds may be used in combination.

[0051] 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-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.

[0052] The addition amount of the silane coupling agent is preferably 0.1 to 10% by mass based on the silicone resin. When the addition amount of the silane coupling agent is 0.1% by mass or more, the adhesiveness between the core material particles or conductive fine particles and the silicone resin is improved, and the peeling of the coating layer during long-term use can be prevented. When it is 10% by mass or less, filming of the toner during long-term use can be prevented.

[0053] The volume average particle diameter of the core material particles of the carrier used in the present invention is not particularly limited. However, from the viewpoints of preventing carrier adhesion and carrier scattering, those having a volume average particle diameter of 20 μm or more are preferable. From the viewpoint of preventing the occurrence of abnormal images such as carrier streaks and preventing the deterioration of image quality, those having a volume average particle diameter of 100 μm or less are preferable. In particular, by using those having a volume average particle diameter of 20 to 60 μm, it is possible to more suitably respond to the recent high image quality requirements. The volume average particle diameter can be measured, for example, using a Microtrac particle size distribution analyzer model HRA9320-X100 (manufactured by Nikkiso Co., Ltd.).

[0054] The carrier of the present invention can be manufactured, for example, by dissolving the resin or the like in a solvent to prepare a coating solution, uniformly coating the coating solution on the surface of the core material particles by a known coating method, drying, and then baking. Examples of the coating method include dipping method, spraying method, brush coating method, etc. There is no particular limitation on the solvent, and it can be appropriately selected according to the purpose. For example, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, cellosolve, butyl acetate, etc. can be mentioned. There is no particular limitation on the baking method, and it can be appropriately selected according to the purpose. For example, an external heating method or an internal heating method may be used. There is no particular limitation on the baking apparatus, and it can be appropriately selected according to the purpose. For example, a stationary electric furnace, a fluidized electric furnace, a rotary electric furnace, a burner furnace, an apparatus equipped with a microwave, etc. can be mentioned. The average thickness of the coating layer is preferably 0.2 μm or more and 1.0 μm or less, and more preferably 0.4 μm or more and 0.8 μm or less. Here, the average thickness of the coating layer can be measured, for example, by observing the cross section of the carrier using a transmission electron microscope (TEM).

[0055] The developer of the present invention contains the carrier of the present invention and can further contain toner. The toner can contain a binder resin, a colorant, a release agent, a charge control agent, an external additive, etc., and can be any of monochromatic toner, color toner, white toner, transparent toner, toner having a metallic luster. Its manufacturing method can also be a conventionally known method such as a pulverization method or a polymerization method, or other manufacturing methods.

[0056] For example, when manufacturing toner using the pulverization method, first, the melt-kneaded product obtained by kneading the toner material is cooled, then pulverized and classified to produce mother particles. Next, in order to further improve transferability and durability, an external additive is added to the mother particles to produce toner. At this time, the apparatus for kneading the toner material is not particularly limited, but examples include batch-type two-rolls; Banbury mixers; continuous twin-screw extruders such as KTK type twin-screw extruders (manufactured by Kobe Steel, Ltd.), TEM type twin-screw extruders (manufactured by Toshiba Machine Co., Ltd.), twin-screw extruders (manufactured by KCK), PCM type twin-screw extruders (manufactured by Ikegai Iron Works Co., Ltd.), KEX type twin-screw extruders (manufactured by Kurimoto Iron Works Co., Ltd.); continuous single-screw kneaders such as co-kneaders (manufactured by Buss).

[0057] Also, when pulverizing the cooled melt-kneaded product, it can be roughly pulverized using a hammer mill, rotorplex, etc., and then finely pulverized using a fine pulverizer using jet air flow, a mechanical fine pulverizer, etc. Note that it is preferable to pulverize so that the average particle size becomes 3 to 15 μm. Furthermore, when classifying the pulverized melt-kneaded product, an air classifier or the like can be used. Note that it is preferable to classify so that the average particle size of the matrix particles becomes 5 to 20 μm. Also, when adding an external additive to the matrix particles, the external additive adheres to the surface of the matrix particles while being disintegrated by mixing and stirring using mixers.

[0058] The binder resin is not particularly limited, and examples thereof include homopolymers of styrene and its substituents such as polystyrene, poly-p-styrene, and polyvinyltoluene; styrene 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-methyl 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, and aromatic petroleum resin. Two or more of them may be used in combination. The binder resin for pressure fixing is not particularly limited, and examples thereof include polyolefins such as low molecular weight polyethylene and low molecular weight polypropylene; olefin copolymers such as ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-vinyl chloride copolymer, ethylene-vinyl acetate copolymer, and ionomer resin; epoxy resin, polyester, styrene-butadiene copolymer, polyvinyl pyrrolidone, methyl vinyl ether-maleic anhydride copolymer, maleic acid-modified phenolic resin, and phenol-modified terpene resin. Two or more of them may be used in combination.

[0059] The coloring agent (pigment or dye) is not particularly limited, and examples include yellow pigments such as cadmium yellow, mineral fast yellow, nickel titanium yellow, Naples 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 pigments such as red iron oxide, cadmium red, permanent red 4R, rhodamine red, pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B; purple pigments such as fast violet B, methyl violet lake; blue pigments such as cobalt blue, alkali blue, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, fast sky blue, indanthrene blue BC; green pigments such as chromium green, chromium oxide, pigment green B, malachite green lake; black pigments such as carbon black, oil furnace black, channel black, lamp black, acetylene black, aniline black, azine dyes, metal salt azo dyes, metal oxides, composite metal oxides, and white pigments such as titanium oxide. Two or more of them may be used in combination, and they may not be used in the case of transparent toners.

[0060] The release agent is not particularly limited, and examples include polyolefins such as polyethylene and polypropylene, fatty acid metal salts, fatty acid esters, paraffin wax, amide wax, polyhydric alcohol wax, silicone varnish, carnauba wax, ester wax, etc. Two or more of them may be used in combination.

[0061] Further, the toner may further contain a charge control agent. The charge control agent is not particularly limited, but nigrosine; azine dyes having an alkyl group with 2 to 16 carbon atoms; C.I. Basic Yello 2 (C.I. 41000), C.I. Basic Yello 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. Basic Blue 1 (C.I. 42025), C.I. Basic Blue 3 (C.I. 51005), C.I. Basic Blue 5 (C.I. 42140), C.I. Basic Blue 7 (C.I. 42595), C.I. Basic Blue 9 (C.I. 52015), C.I. Basic Blue 24 (C.I. 52030), C.I. Basic Blue25 (C.I. 52025), C.I. Basic Blue 26 (C.I. 44045), C.I. Basic Green 1 (C.I. 42040), C.I. Basic Green 4 (C.I. 42000) and other basic dyes; lake pigments of these basic dyes; quaternary ammonium salts such as C.I. Solvent Black 8 (C.I. 26150), benzoylmethylhexadecylammonium chloride, decyltrimethyl chloride; dialkyltin compounds such as dibutyl and dioctyl; dialkyltin borate compounds; guanidine derivatives; polyamine resins such as vinyl polymers having an amino group and condensed polymers having an amino group; metal complexes of monoazo dyes; salicylic acid; metal complexes of dialkylsalicylic acid, naphthoic acid, dicarboxylic acid with metals such as Zn, Al, Co, Cr, Fe; sulfonated copper phthalocyanine pigments; organic boron salts; fluorine-containing quaternary ammonium salts; calixarene compounds, etc. may be mentioned, and two or more kinds may be used in combination. In addition, in color toners other than black, metal salts of white salicylic acid derivatives and the like are preferable.

[0062] The external additives are not particularly limited, and examples thereof include inorganic particles such as silica, titanium oxide, alumina, silicon carbide, silicon nitride, and boron nitride; resin particles such as polymethyl methacrylate particles and polystyrene particles having an average particle size of 0.05 to 1 μm obtained by a soap-free emulsion polymerization method, and two or more of them may be used in combination. Among them, metal oxide particles such as silica and titanium oxide whose surfaces are hydrophobically treated are preferable. Further, hydrophobically treated silica and hydrophobically treated titanium oxide are used in combination, and by increasing the addition amount of hydrophobically treated titanium oxide compared to hydrophobically treated silica, a toner excellent in charging stability against humidity can be obtained.

[0063] The electrophotographic image forming method of the present invention is characterized by forming an image using the developer of the present invention, and the electrophotographic image forming apparatus of the present invention is characterized by including the developer of the present invention. Specifically, the electrophotographic image forming method of the present invention includes a step of forming an electrostatic latent image on an electrostatic latent image carrier (including a charging step of charging the electrostatic latent image carrier and an exposure step of forming an electrostatic latent image on the electrostatic latent image carrier), a step of developing the electrostatic latent image formed on the electrostatic latent image carrier using the developer of the present invention to form a toner image, a step of transferring the toner image formed on the electrostatic latent image carrier to a recording medium, and a step of fixing the toner image transferred to the recording medium, and further includes other steps as necessary. The electrophotographic image forming apparatus of the present invention includes an electrostatic latent image carrier, a charging means for charging the latent image carrier, an exposure means for forming an electrostatic latent image on the latent image carrier, a developing means for developing the electrostatic latent image formed on the electrostatic latent image carrier using the developer of the present invention to form a toner image, a transfer means for transferring the toner image formed on the electrostatic latent image carrier to a recording medium, and a fixing means for fixing the toner image transferred to the recording medium, and further includes other means appropriately selected as necessary, such as a discharging means, a cleaning means, a recycling means, a control means, and the like.

[0064] Figure 1 shows an example of the process cartridge of the present invention. This process cartridge integrally supports a photoreceptor (20), a proximity type brush-like charging means (32), a developing device (40) for storing the developer of the present invention, and a cleaning device having at least a cleaning blade (61), and is detachable from the main body of the image forming apparatus. In the present invention, each of the above-described components can be integrally combined as a process cartridge, and this process cartridge can be configured to be detachable from the main body of an image forming apparatus such as a copying machine or a printer.

Example

[0065] Hereinafter, the present invention will be described with reference to examples and comparative examples. Note that the present invention is not limited to the examples illustrated herein. In the following, "parts" represents parts by mass, and "%" represents mass %. In addition, Examples 20 and 21 are regarded as Reference Examples 20 and 21 that are not included in the present invention.

[0066] [Preparation of Toner] (Binder Resin Synthesis Example 1) Into a reaction vessel equipped with a cooling pipe, a stirrer, and a nitrogen introduction pipe, 724 parts of bisphenol A ethylene oxide 2 mol adduct, 276 parts of isophthalic acid, and 2 parts of dibutyltin oxide were placed, and reacted at 230 ° C for 8 hours under normal pressure, and further reacted at a reduced pressure of 10 to 15 mmHg for 5 hours. After that, it was cooled to 160 ° C, and 32 parts of phthalic anhydride was added thereto and reacted for 2 hours. Next, it was cooled to 80 ° C and reacted with 188 parts of isophorone diisocyanate in ethyl acetate for 2 hours to obtain an isocyanate-containing prepolymer (P1). Next, 267 parts of prepolymer (P1) and 14 parts of isophorone diamine were reacted at 50 ° C for 2 hours to obtain a urea-modified polyester (U1) having a weight average molecular weight of 64000. In the same manner as above, 724 parts of bisphenol A ethylene oxide 2 mol adduct and 276 parts of terephthalic acid were polycondensed at 230 ° C for 8 hours under normal pressure, and then reacted at a reduced pressure of 10 to 15 mmHg for 5 hours to obtain an unmodified polyester (E1) having a peak molecular weight of 5000. 200 parts of urea-modified polyester (U1) and 800 parts of unmodified polyester (E1) were dissolved and mixed in 2000 parts of an ethyl acetate / MEK (1 / 1) mixed solvent to obtain an ethyl acetate / MEK solution of the binder resin (B1). It was dried under partial vacuum to isolate the binder resin (B1).

[0067] (Masterbatch Preparation Example 1) Pigment: C.I.Pigment Yellow 155: 40 parts Binder resin: Polyester resin A: 60 parts Water: 30 parts

[0068] (Synthesis Example of Polyester Resin A) Terephthalic acid: 60 parts Dodecenyl succinic anhydride: 25 parts Trimellitic anhydride: 15 parts Bisphenol A (2,2) propylene oxide: 70 parts Bisphenol A (2,2) ethylene oxide: 50 parts The above composition was placed in a 1 L four-necked round-bottom flask equipped with a thermometer, a stirrer, a condenser, and a nitrogen gas inlet tube. The flask was set on a mantle heater, and nitrogen gas was introduced through the nitrogen gas inlet tube to keep the inside of the flask under an inert atmosphere. Then, the temperature was raised, and 0.05 g of dibutyltin oxide was added to keep the temperature at 200 °C for reaction to obtain polyester resin A.

[0069] The above raw materials were mixed in a Henschel mixer to obtain a mixture in which water had penetrated into the pigment aggregates. This was kneaded for 45 minutes with two rolls set at a roll surface temperature of 130 °C, and then pulverized to a size of 1 mmφ with a pulverizer to obtain masterbatch (M1).

[0070] (Toner Production Example A) 240 parts of an ethyl acetate / MEK solution of the above binder resin (B1), 20 parts of pentaerythritol tetrabehenate (melting point 81°C, melt viscosity 25 cps), and 8 parts of masterbatch (M1) were placed in a beaker, and stirred at 12,000 rpm with a TK type homomixer at 60°C to uniformly dissolve and disperse them, preparing a toner material solution. 700 parts of ion-exchanged water, 300 parts of a 10% suspension of hydroxyapatite (Superapatite 10 manufactured by Nippon Chemical Industry Co., Ltd.), and 0.2 part of sodium dodecylbenzenesulfonate were placed in a beaker and uniformly dissolved. Next, the temperature was raised to 60°C, and while stirring at 12,000 rpm with a TK type homomixer, the above toner material solution was added and stirred for 10 minutes. Then, this mixed solution was transferred to a corvette equipped with a stirring rod and a thermometer, heated to 98°C to remove the solvent, filtered, washed, dried, and then classified by air classification to obtain mother toner particles A. 1.2 parts of hydrophobic silica and 1.0 part of hydrophobized titanium oxide were mixed with 100 parts of mother toner particles A using a Henschel mixer to obtain toner A. When the toner particle size was measured using a particle size analyzer "Coulter Counter TA2" manufactured by Coulter Electronics, Inc. with an aperture diameter of 100 μm, toner A had a volume average particle diameter (Dv) = 6.2 μm and a number average particle diameter (Dn) = 5.1 μm.

[0071] [Preparation of Carrier] (Carrier Production Example 1) <Core Material Particles A> · Mn-Mg-Sr ferrite Internal porosity: 1.9 [%], apparent density: 2.0 [g / cm 3 , surface roughness Rz: 2.5 [μm], σ1000: 63 [Am 2 / kg], average particle diameter: 36 μm

[0072] <Resin Solution 1> · 200 parts by mass of an acrylic resin solution (solid content concentration: 20 [mass%]) · 2000 parts by mass of a silicone resin solution (solid content 40 [mass%]) · Amino silane (solid content concentration: 100 [mass%]) 30 parts by mass · Tungsten-doped tin oxide 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Barium sulfate 650 parts by mass (Average particle size: 0.4 [μm]) · Toluene 6000 parts by mass · Dispersant (phosphate ester surfactant) 10 parts by mass

[0073] Each material of Resin Liquid 1 was dispersed with a homomixer for 10 minutes to prepare a coating layer forming liquid. The coating layer forming liquid of Resin Liquid 1 was applied to Core Particle A at a rate of 30 g / min in an atmosphere of 55°C with a spiral coater (manufactured by Okada Seiko Co., Ltd.) so that the thickness would be 0.6 μm on the surface of the core particle, and then dried. The adjustment of the layer thickness was performed by the liquid volume. The obtained carrier was left in an electric furnace at 150°C for 1 hour for baking, and after cooling, it was crushed using a sieve with an opening of 100 μm to obtain Carrier 1.

[0074] (Carrier Production Example 2) <Core Particle B> · Mn-Mg-Sr ferrite Internal porosity: 1.6 [%], apparent density: 2.3 [g / cm 3 , surface roughness Rz: 2.0 [μm], σ1000: 63 [Am 2 / kg], average particle size: 36 μm <Resin Liquid 2> · Acrylic resin solution (solid content concentration: 20 [mass%]) 200 parts by mass · Silicone resin solution (solid content 40 [mass%]) 2000 parts by mass · Amino silane (solid content concentration: 100 [mass%]) 30 parts by mass · Tungsten-doped tin oxide 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Barium sulfate 650 parts by mass (Average particle size: 0.4 [μm]) · Toluene 6000 parts by mass · Dispersant (phosphate ester surfactant): 180 parts by mass Carrier 2 was obtained in the same manner as in Production Example 1, except that the core particles were changed to core particles B and the resin solution was changed to resin solution 2.

[0075] (Carrier Production Example 3) <Core particles C> · Mn-Mg-Sr ferrite Internal porosity: 1.9 [%], apparent density: 1.8 [g / cm 3 , surface roughness Rz: 2.8 [μm], σ1000: 63 [Am 2 / kg], average particle size: 36 μm Carrier 3 was obtained in the same manner as in Production Example 1, except that the core particles were changed to core particles C.

[0076] (Carrier Production Example 4) <Core particles D> · Mn-Mg-Sr ferrite Internal porosity: 0.7 [%], apparent density: 2.5 [g / cm 3 , surface roughness Rz: 1.6 [μm], σ1000: 63 [Am2 / kg], average particle size: 36 μm Carrier 4 was obtained in the same manner as in Production Example 2, except that the core particles were changed to core particles D.

[0077] (Carrier Production Example 5) <Core particles E> · Mn-Mg-Sr ferrite Internal porosity: 1.4 [%], apparent density: 2.2 [g / cm 3 , surface roughness Rz: 2.4 [μm], σ1000: 63 [Am 2 / kg], average particle size: 36 μm <Resin solution 3> · Acrylic resin solution (solid content concentration: 20 [mass%]): 200 parts by mass · Silicone resin solution (solid content 40 [mass%]): 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]): 35 parts by mass · Tungsten-doped tin oxide: 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · 6,000 parts by mass of toluene · 24 parts by mass of dispersant (phosphate ester surfactant) Carrier 5 was obtained in the same manner as in Production Example 1, except that the core material particles were changed to core material particles E and the resin liquid was changed to resin liquid 3.

[0078] (Carrier Production Example 6) <Resin Liquid 4> · 200 parts by mass of acrylic resin solution (solid content concentration: 20 [mass%]) · 2,000 parts by mass of silicone resin solution (solid content 40 [mass%]) · 30 parts by mass of aminosilane (solid content concentration: 100 [mass%]) · 1,200 parts by mass of tungsten-doped tin oxide (Powder specific resistance: 40 [Ω·cm]) · 650 parts by mass of barium sulfate (Average particle diameter: 0.4 [μm]) · 6,000 parts by mass of toluene Carrier 6 was obtained in the same manner as in Production Example 5, except that the resin liquid was changed to resin liquid 4.

[0079] (Carrier Production Example 7) <Resin Liquid 5> · 200 parts by mass of acrylic resin solution (solid content concentration: 20 [mass%]) · 2,000 parts by mass of silicone resin solution (solid content 40 [mass%]) · 30 parts by mass of aminosilane (solid content concentration: 100 [mass%]) · 1,200 parts by mass of tungsten-doped tin oxide (Powder specific resistance: 40 [Ω·cm]) · 650 parts by mass of barium sulfate (Average particle diameter: 0.4 [μm]) · 6,000 parts by mass of toluene · 40 parts by mass of dispersant (phosphate ester surfactant) · 500 parts by mass of antifoaming agent (silicone-based) Carrier 7 was obtained in the same manner as in Production Example 5, except that the resin liquid was changed to resin liquid 5.

[0080] (Carrier Production Example 8) <Core Particle F> ·Mn-Mg-Sr ferrite Internal porosity: 2.1 [%], apparent density: 2.2 [g / cm 3 , surface roughness Rz: 1.8 [μm], σ1000: 63 [Am 2 / kg], average particle size: 36 μm Carrier 8 was obtained in the same manner as in Production Example 7 except that the core particles were changed to core particles F.

[0081] (Carrier Production Example 9) <Core Particle G> ·Mn-Mg-Sr ferrite Internal porosity: 1.8 [%], apparent density: 2.3 [g / cm 3 , surface roughness Rz: 1.9 [μm], σ1000: 63 [Am 2 / kg], average particle size: 36 μm Carrier 9 was obtained in the same manner as in Production Example 7 except that the core particles were changed to core particles G.

[0082] (Carrier Production Example 10) <Core Particle H> ·Mn-Mg-Sr ferrite Internal porosity: 1.7 [%], apparent density: 2.2 [g / cm 3 , surface roughness Rz: 2.1 [μm], σ1000: 63 [Am 2 / kg], average particle size: 36 μm Carrier 10 was obtained in the same manner as in Production Example 7 except that the core particles were changed to core particles H.

[0083] (Carrier Production Example 11) <Core Particle I> ·Mn-Mg-Sr ferrite Internal porosity: 0.4 [%], apparent density: 2.0 [g / cm 3 , surface roughness Rz: 2.9 [μm], σ1000: 63 [Am 2 / kg], average particle size: 36 μm Carrier 11 was obtained in the same manner as in Production Example 7 except that the core particles were changed to core particles I.

[0084] (Carrier Production Example 12) <Core Material Particle J> ·Mn-Mg-Sr ferrite Internal porosity: 0.3 [%], apparent density: 2.0 [g / cm3], surface roughness Rz: 3.1 [μm], σ1000: 63 [Am 2 / kg], average particle size: 36 μm Carrier 12 was obtained in the same manner as in Production Example 7, except that the core material particles were changed to core material particles J.

[0085] (Carrier Production Example 13) <Resin Liquid 6> · Acrylic resin solution (solid content concentration: 20 [mass%]) 200 parts by mass · Silicone resin solution (solid content 40 [mass%]) 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]) 30 parts by mass · Tungsten-doped tin oxide 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Magnesium oxide 650 parts by mass (Average particle size: 0.05 [μm]) · Toluene 6000 parts by mass · Dispersant (phosphate ester surfactant) 40 parts by mass · Defoaming agent (silicone-based) 500 parts by mass Carrier 13 was obtained in the same manner as in Production Example 7, except that the resin liquid was changed to resin liquid 6.

[0086] (Carrier Production Example 14) <Resin Liquid 7> · Acrylic resin solution (solid content concentration: 20 [mass%]) 200 parts by mass · Silicone resin solution (solid content 40 [mass%]) 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]) 30 parts by mass · Tungsten-doped tin oxide 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · 650 parts by mass of magnesium hydroxide (Average particle size: 0.1 [μm]) · 6000 parts by mass of toluene · 40 parts by mass of dispersant (phosphate ester surfactant) · 500 parts by mass of antifoaming agent (silicone-based) Carrier 14 was obtained in the same manner as in Production Example 7, except that the resin solution was changed to Resin Solution 7.

[0087] (Carrier Production Example 15) <Resin Solution 8> · 200 parts by mass of acrylic resin solution (solid content concentration: 20 [mass%]) · 2000 parts by mass of silicone resin solution (solid content 40 [mass%]) · 30 parts by mass of aminosilane (solid content concentration: 100 [mass%]) · 1200 parts by mass of tungsten-doped tin oxide (Powder specific resistance: 40 [Ω·cm]) · 650 parts by mass of hydrotalcite (Average particle size: 0.5 [μm]) · 6000 parts by mass of toluene · 40 parts by mass of dispersant (phosphate ester surfactant) · 500 parts by mass of antifoaming agent (silicone-based) Carrier 15 was obtained in the same manner as in Production Example 7, except that the resin solution was changed to Resin Solution 8.

[0088] (Carrier Production Example 16) <Resin Solution 9> · 200 parts by mass of acrylic resin solution (solid content concentration: 20 [mass%]) · 2000 parts by mass of silicone resin solution (solid content 40 [mass%]) · 30 parts by mass of aminosilane (solid content concentration: 100 [mass%]) · 1200 parts by mass of tungsten-doped tin oxide (Powder specific resistance: 40 [Ω·cm]) · 650 parts by mass of alumina (Average particle size: 0.4 [μm]) · 6000 parts by mass of toluene · Dispersant (phosphate ester surfactant): 40 parts by mass · Antifoaming agent (silicone-based): 500 parts by mass A carrier 16 was obtained in the same manner as in Production Example 7, except that the resin solution was changed to resin solution 9.

[0089] (Carrier Production Example 17) <Resin solution 10> · Acrylic resin solution (solid content concentration: 20 [mass%]): 200 parts by mass · Silicone resin solution (solid content 40 [mass%]): 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]): 30 parts by mass · Tungsten-doped tin oxide: 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Barium sulfate: 150 parts by mass (Average particle size: 0.4 [μm]) · Toluene: 6000 parts by mass · Dispersant (phosphate ester surfactant): 40 parts by mass · Antifoaming agent (silicone-based): 500 parts by mass A carrier 17 was obtained in the same manner as in Production Example 7, except that the resin solution was changed to resin solution 10.

[0090] (Carrier Production Example 18) <Resin solution 11> · Acrylic resin solution (solid content concentration: 20 [mass%]): 200 parts by mass · Silicone resin solution (solid content 40 [mass%]): 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]): 30 parts by mass · Carbon (Ketjen black): 900 parts by mass · Barium sulfate: 650 parts by mass (Average particle size: 0.4 [μm]) · Toluene: 6000 parts by mass · Dispersant (phosphate ester surfactant): 40 parts by mass · Antifoaming agent (silicone-based): 500 parts by mass A carrier 18 was obtained in the same manner as in Production Example 7, except that the resin solution was changed to resin solution 11.

[0091] (Carrier Production Example 19) <Resin Solution 12> · Acrylic resin solution (solid content concentration: 20 [mass%]) 200 parts by mass · Silicone resin solution (solid content 40 [mass%]) 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]) 30 parts by mass · Indium oxide-doped tin oxide 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Barium sulfate 650 parts by mass (Average particle size: 0.4 [μm]) · Toluene 6000 parts by mass · Dispersant (phosphate ester-based surfactant) 40 parts by mass · Antifoaming agent (silicone-based) 500 parts by mass A carrier 19 was obtained in the same manner as in Production Example 7, except that the resin solution was changed to resin solution 12.

[0092] (Carrier Production Example 20) <Resin Solution 13> · Acrylic resin solution (solid content concentration: 20 [mass%]) 200 parts by mass · Silicone resin solution (solid content 40 [mass%]) 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]) 30 parts by mass · Phosphorus pentoxide-doped tin oxide 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Barium sulfate 650 parts by mass (Average particle size: 0.4 [μm]) · Toluene 6000 parts by mass · Dispersant (phosphate ester-based surfactant) 40 parts by mass · Antifoaming agent (silicone-based) 500 parts by mass A carrier 20 was obtained in the same manner as in Production Example 7, except that the resin solution was changed to resin solution 13.

[0093] (Carrier Production Example 21) <Core Material Particles K> ·Mn ferrite Internal porosity: 0.5 [%], Apparent density: 2.2 [g / cm 3 , Surface roughness Rz: 2.3 [μm], σ1000: 70 [Am 2 / kg], Average particle size: 36 μm Carrier 21 was obtained in the same manner as in Production Example 7, except that the core material particles were changed to core material particles K.

[0094] (Carrier Production Example 22) <Core Material Particles L> ·Mn ferrite Internal porosity: 0.5 [%], Apparent density: 2.2 [g / cm 3 , Surface roughness Rz: 2.3 [μm], σ1000: 65 [Am 2 / kg], Average particle size: 36 μm Carrier 22 was obtained in the same manner as in Production Example 7, except that the core material particles were changed to core material particles L.

[0095] (Carrier Production Example 23) <Core Material Particles M> ·Mn ferrite Internal porosity: 0.5 [%], Apparent density: 2.2 [g / cm3], Surface roughness Rz: 2.3 [μm], σ1000: 67 [Am 2 / kg], Average particle size: 36 μm Carrier 23 was obtained in the same manner as in Production Example 7, except that the core material particles were changed to core material particles M.

[0096] (Carrier Production Example 24) <Core Material Particles N> ·Mn ferrite Internal porosity: 0.5 [%], Apparent density: 2.2 [g / cm 3 , Surface roughness Rz: 2.3 [μm], σ1000: 74 [Am 2 / kg], Average particle size: 36 μm Carrier 24 was obtained in the same manner as in Production Example 7, except that the core material particles were changed to core material particles N.

[0097] (Carrier Production Example 25) <Core particle O> · Mn ferrite Internal porosity: 0.5 [%], apparent density: 2.2 [g / cm 3 , surface roughness Rz: 2.3 [μm], σ1000: 76 [Am 2 / kg], average particle size: 36 μm Carrier 25 was obtained in the same manner as in Production Example 7, except that the core particles were changed to core particle O.

[0098] (Carrier Production Example 26) <Resin solution 14> · Acrylic resin solution (solid content concentration: 20 [mass%]) 200 parts by mass · Silicone resin solution (solid content 40 [mass%]) 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]) 30 parts by mass · Tungsten-doped tin oxide 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Barium sulfate 650 parts by mass (Average particle size: 0.4 [μm]) · Toluene 6000 parts by mass · Dispersant (carboxylic acid-based surfactant) 40 parts by mass · Defoaming agent (silicone-based) 500 parts by mass Carrier 26 was obtained in the same manner as in Production Example 21, except that the resin solution was changed to resin solution 14.

[0099] (Carrier Production Example 27) <Resin solution 15> · Acrylic resin solution (solid content concentration: 20 [mass%]) 200 parts by mass · Silicone resin solution (solid content 40 [mass%]) 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]) 30 parts by mass · Tungsten-doped tin oxide 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Barium sulfate 650 parts by mass (Average particle size: 0.4 [μm]) · 6,000 parts by mass of toluene · 40 parts by mass of a dispersant (sulfone-based surfactant) · 500 parts by mass of an antifoaming agent (silicone-based) A carrier 27 was obtained in the same manner as in Production Example 21 except that the resin solution was changed to Resin Solution 15.

[0100] (Carrier Production Example 28) <Resin Solution 16> · 200 parts by mass of an acrylic resin solution (solid content concentration: 20 [mass%]) · 2,000 parts by mass of a silicone resin solution (solid content 40 [mass%]) · 30 parts by mass of an aminosilane (solid content concentration: 100 [mass%]) · 1,200 parts by mass of tungsten-doped tin oxide (Powder specific resistance: 40 [Ω·cm]) · 650 parts by mass of barium sulfate (Average particle diameter: 0.4 [μm]) · 6,000 parts by mass of toluene · 40 parts by mass of a dispersant (sulfate ester-based surfactant) · 500 parts by mass of an antifoaming agent (silicone-based) A carrier 28 was obtained in the same manner as in Production Example 21 except that the resin solution was changed to Resin Solution 16.

[0101] (Carrier Production Example 29) <Resin Solution 17> · 200 parts by mass of an acrylic resin solution (solid content concentration: 20 [mass%]) · 2,000 parts by mass of a silicone resin solution (solid content 40 [mass%]) · 30 parts by mass of an aminosilane (solid content concentration: 100 [mass%]) · 1,200 parts by mass of tungsten-doped tin oxide (Powder specific resistance: 40 [Ω·cm]) · 650 parts by mass of barium sulfate (Average particle diameter: 0.4 [μm]) · 6,000 parts by mass of toluene · 40 parts by mass of a dispersant (phosphate ester-based surfactant) · Defoaming agent (acrylic-based): 500 parts by mass A carrier 29 was obtained in the same manner as in Production Example 21, except that the resin solution was changed to Resin Solution 17.

[0102] (Carrier Production Example 30) <Resin Solution 18> · Acrylic resin solution (solid content concentration: 20 [mass%]): 200 parts by mass · Silicone resin solution (solid content: 40 [mass%]): 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]): 30 parts by mass · Tungsten-doped tin oxide: 1200 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Barium sulfate: 650 parts by mass (Average particle size: 0.4 [μm]) · Toluene: 6000 parts by mass · Dispersant (phosphate ester-based surfactant): 40 parts by mass · Defoaming agent (vinyl-based): 500 parts by mass A carrier 30 was obtained in the same manner as in Production Example 21, except that the resin solution was changed to Resin Solution 18.

[0103] (Carrier Production Example 31) <Resin Solution 19> · Acrylic resin solution (solid content concentration: 20 [mass%]): 200 parts by mass · Silicone resin solution (solid content: 40 [mass%]): 2000 parts by mass · Aminosilane (solid content concentration: 100 [mass%]): 30 parts by mass · Tungsten-doped tin oxide surface-treated alumina: 1400 parts by mass (Powder specific resistance: 40 [Ω·cm]) · Barium sulfate: 650 parts by mass (Average particle size: 0.4 [μm]) · Toluene: 6000 parts by mass · Dispersant (phosphate ester-based surfactant): 40 parts by mass · Defoaming agent (silicone-based): 500 parts by mass A carrier 31 was obtained in the same manner as in Production Example 21, except that the resin liquid was changed to resin liquid 19.

[0104] Table 1 shows the physical properties of the carriers obtained in Carrier Production Examples 1 to 31.

[0105]

Table 1

[0106] (Example) [Example 1] 7 parts by mass of toner A obtained in Toner Production Example and 93 parts by mass of carrier 1 obtained in Carrier Production Example 1 were used, and they were stirred for 10 minutes with a mixer to prepare developer 1. The developer was set in a commercially available digital full-color printer (manufactured by Ricoh Company, Ltd., imagio MP C6004SP), and evaluation with an initial agent was carried out. Also, a total of 100,000 images, including 50,000 character charts with an image area ratio of 5% and 50,000 image charts with an image area ratio of 20%, were output, and evaluation with an agent over time was performed.

[0107] <Charge decrease amount> Evaluation of the charge decrease amount before and after outputting 100,000 images was carried out. First, a sample mixed at a ratio of 7% by mass of toner to 93% by mass of the initial carrier and triboelectrically charged was measured by a general blow-off method (manufactured by Toshiba Chemical Corporation, TB-200), and this value was taken as the initial charge amount. Next, the toner was removed from the developer after image output using the blow-off device, and toner A was newly mixed at a ratio of 7% by mass with respect to 93% by mass of the obtained carrier, and a sample triboelectrically charged in the same manner as the initial carrier was measured for the charge amount in the same manner as the initial carrier, and the difference from the initial charge amount was taken as the charge decrease amount. The target value of the charge decrease amount is less than 10 μC / g.

[0108] <Ghost> In the initial agent, a solid image was output, and the difference in image density between the tip of the image and the image one circumference behind the developing roller was visually observed for rank evaluation. ◎: Very good, ○: Good, △: Acceptable, ×: Unacceptable level in practical use

[0109] <White spots (carrier adhesion)> In each of the initial agent and the agent over time, a solid image and an image of an image pattern of 2-dot lines (100 lpi / inch) in the sub-scanning direction were output on A3 paper, and the number of white spots generated by the carrier attached between the solid image and the lines of the 2-dot lines was visually observed and evaluated in ranks. ◎: Very good, ○: Good, △: Acceptable, ×: Unacceptable level in practical use

[0110] <Vertical band abnormal image> The printer was tilted 1° forward, a solid image was output in the initial agent, and the vertical band-shaped abnormal image was visually observed and ranked. ○: Good, △: Acceptable, ×: Unacceptable level in practical use

[0111] <Color stain> A solid image was output with the initial agent and the 100,000-image output agent and measured by X-Rite. Specifically, using the values (L0*, a0*, b0*, ID) measured by X-Rite (X-Rite 938 D50 manufactured by Amtech Co., Ltd.) for the solid image output with the initial agent and the values (L1*, a1*, b1*, ID’) measured by X-Rite for the solid image output after 100,000 images were output, ΔE was obtained by the following formula and ranked as follows. Color difference ΔE = {(L0* - L1*) 2 + (a0* - a1*) 2 + (b0* - b1*) 2} 1 / 2 L0*, a0*, and b0*: Initial agent measurement values L1*, a1*, and b1*: Measurement values after 100,000 images were output 〇: ΔE ≤ 2 △: 2 < ΔE ≤ 6 ×: 6 < ΔE 〇 and △ are passes.

[0112] [Examples 2 to 27, Comparative Examples 1 to 4] Evaluation was carried out in the same manner as in Example 1, except that Carriers 2 to 31 were used as carriers and Developers 2 to 31 were used as developers. Table 2 shows the carriers of the developers used in each example and comparative example and the evaluation results.

[0113]

Table 2

[0114] From Table 2, since each example shows practically sufficient or excellent results in terms of charge decay amount, ghosting, carrier adhesion, longitudinal stripe abnormal image, and color stain, it was found that the carrier of the present invention has charge imparting ability that is stable even during long-term use, and has carrier adhesion resistance and ghosting resistance.

Explanation of Signs

[0115] 20 Photoconductor 32 Charging means 40 Developing means 61 Cleaning means

Prior Art Documents

Patent Documents

[0116]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Patent Document 6

Patent Document 7

Patent Document 8

Claims

1. In an electrophotographic image forming carrier having core material particles and a coating layer covering the core material particles, The apparent density of the carrier is 2.0 [g / cm 3 or more and less than 2.5 [g / cm 3 , and the coating layer contains charged particles and a dispersant. the dispersant is any one of a phosphate ester surfactant, a sulfate ester surfactant, a sulfonic acid surfactant, or a carboxylic acid surfactant, the apparent density of the carrier is measured according to JIS-Z2504:2000, The magnetization in a magnetic field of 1000 [Oe] (79.58 kA / m) is 56 [Am 2 / kg] or more and less than 73 [Am 2 / kg], and as the charged particles, contains at least one kind of particles selected from barium sulfate, zinc oxide, magnesium oxide, magnesium hydroxide, and hydrotalcite, An electrophotographic image forming carrier, characterized in that the core material particles are formed using Mn ferrite or Mn-Mg-Sr ferrite.

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

3. The electrophotographic image forming carrier according to claim 1 or 2, characterized in that the internal porosity of the core material particles is 0.0 [%] or more and less than 2.0 [%].

4. The electrophotographic image forming carrier according to any one of claims 1 to 3, characterized in that the surface roughness Rz of the core material particles is 2.0 [μm] or more and less than 3.0 [μm].

5. The electrophotographic image forming carrier according to any one of claims 1 to 4, characterized in that it contains barium sulfate as the charged particles and the barium exposure amount on the surface of the coating layer is 0.1 [atomic%] or more.

6. The electrophotographic image forming carrier according to any one of claims 1 to 5, characterized in that the coating layer contains inorganic particles in addition to the charged particles.

7. The electrophotographic image forming carrier according to claim 6, characterized in that the inorganic particles are tin oxide doped with any one of tungsten, indium, phosphorus, or their oxides, or particles provided on the substrate surface with tin oxide doped with any one of tungsten, indium, phosphorus, or their oxides.

8. The electrophotographic image forming carrier according to any one of claims 1 to 7, characterized in that the dispersant is a phosphate ester surfactant.

9. The electrophotographic image forming carrier according to claim 2, characterized in that the antifoaming agent is silicone-based.

10. An electrophotographic image forming developer, characterized by containing the electrophotographic image forming carrier according to any one of claims 1 to 9.

11. An electrophotographic image forming method, characterized by forming an image using the electrophotographic image forming developer according to claim 10.

12. An electrophotographic image forming apparatus, characterized by including the electrophotographic image forming developer according to claim 10.

13. A process cartridge, characterized by comprising the electrophotographic image forming developer according to claim 10.

Images