Two-component developer

Abstract

With respect to a two-component developer according to the present invention, external additive particles in toner particles contain resin particles. The resin particles contain a crosslinked resin that has a repeating unit derived from a crosslinking agent. Each carrier particle comprises a carrier core and a coat layer that covers the surface of the carrier core. The coat layer contains a coat resin and barium titanate particles. The coat resin contains a silicone resin. The number average primary particle diameter of the barium titanate particles is 100 nm to 500 nm. The content of the barium titanate particles is 5 parts by mass to 45 parts by mass relative to 100 parts by mass of the coat resin. The ratio of the mass of the coat layer to the mass of the carrier core is more than 0.0% by mass but not more than 4.9% by mass. The shape factor of the carrier particles is 34.0 to 85.0.

Description

[Technical Field]

[0001] The present invention relates to a two-component developer. [Background technology]

[0002] An image forming apparatus that forms an image using a toner is required to charge the toner to a desired charge amount and form an image with little fog. For example, the resin-coated carrier described in Patent Document 1 has a resin coating layer of 0.01 to 2.0% by mass relative to the mass of the carrier core. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-330342 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the present inventors have found through their investigations that the resin-coated carrier described in Patent Document 1 is insufficient in terms of fogging resistance, stable formation of images with a desired image density, reduction of image density differences within the formed image, and suppression of image defects due to poor cleaning.

[0005] The present invention has been made in view of the above-mentioned problems, and an object of the present invention is to provide a two-component developer that has excellent fogging resistance, can stably form images of a desired image density, has little image density difference within the formed image, and is less likely to cause image defects due to poor cleaning. [Means for solving the problem]

[0006] The two-component developer according to the present invention includes a toner containing toner particles and a carrier containing carrier particles. The toner particles include toner base particles and external additive particles provided on the surfaces of the toner base particles. The external additive particles include resin particles. The resin particles include a crosslinked resin having repeating units derived from a crosslinking agent. The carrier particles include a carrier core and a coating layer covering the surface of the carrier core. The coating layer includes a coating resin and barium titanate particles. The coating resin includes a silicone resin. The number-average primary particle diameter of the barium titanate particles is 100 nm or more and 500 nm or less. The content of the barium titanate particles is 5 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the coating resin. The ratio of the mass of the coating layer to the mass of the carrier core is more than 0.0 mass% and 4.9 mass% or less. The shape factor of the carrier particles is 34.0 or more and 85.0 or less. [Effects of the Invention]

[0007] The two-component developer according to the present invention has excellent fogging resistance, can stably form images of desired image density, has small image density differences within the formed image, and is less likely to produce image defects due to poor cleaning. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram illustrating a two-component developer according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0009] First, the meanings of the terms used in this specification and measurement methods will be explained. A toner is an aggregate (e.g., powder) of toner particles. An external additive is an aggregate (e.g., powder) of external additive particles. A carrier is an aggregate (e.g., powder) of carrier particles. Unless otherwise specified, evaluation results (values ​​indicating shape, physical properties, etc.) for powders (more specifically, toner particle powder, external additive particle powder, carrier particle powder, etc.) are the number averages of values ​​measured for a considerable number of particles of the powder. Unless otherwise specified, the "main component" of a material refers to the component that is most abundant in the material by mass. The strength of hydrophobicity (or hydrophilicity) can be expressed, for example, by the contact angle of a water droplet (ease of wetting with water). The larger the contact angle of the water droplet, the stronger the hydrophobicity. The term "system" may be added after the name of a compound to collectively refer to the compound and its derivatives. When the name of a polymer is expressed by adding "based" after the name of a compound, it means that the repeating units of the polymer are derived from the compound or its derivatives. Acrylic and methacrylic may be collectively referred to as "(meth)acrylic." Acrylonitrile and methacrylonitrile may be collectively referred to as "(meth)acrylonitrile." Each component described in this specification may be used alone or in combination of two or more.

[0010] Volume median diameter (D 50Unless otherwise specified, the measured value of (Tm) is the volume-based median diameter measured using a laser diffraction / scattering particle size analyzer (LA-950, manufactured by Horiba, Ltd.). Unless otherwise specified, the number-average primary particle diameter is the number-average value of the equivalent circle diameters of primary particles (Heywood diameter: the diameter of a circle having the same area as the projected area of ​​a primary particle) measured using a scanning electron microscope. The number-average primary particle diameter is, for example, the number-average value of the equivalent circle diameters of 100 primary particles. Unless otherwise specified, the softening point (Tm) is a value measured using a high-speed flow tester (CFT-500D, manufactured by Shimadzu Corporation). In the S-shaped curve (horizontal axis: temperature, vertical axis: stroke) measured using the high-speed flow tester, the temperature at which "(baseline stroke value + maximum stroke value) / 2" occurs corresponds to the softening point. Unless otherwise specified, the measured value of the melting point (Mp) is the temperature of the maximum endothermic peak in the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured using a differential scanning calorimeter (Seiko Instruments Inc., "DSC-6220"). This endothermic peak appears due to melting of the crystallized portion. Unless otherwise specified, the measured value of the glass transition point (Tg) is a value measured using a differential scanning calorimeter (Seiko Instruments Inc., "DSC-6220") in accordance with "JIS (Japanese Industrial Standards) K7121-2012." In the endothermic curve measured using the differential scanning calorimeter (vertical axis: heat flow (DSC signal), horizontal axis: temperature), the temperature of the inflection point due to the glass transition (specifically, the temperature at the intersection of the extrapolated line of the baseline and the extrapolated line of the falling line) corresponds to the glass transition point. Unless otherwise specified, the measured values ​​of the acid value and hydroxyl value are values ​​measured in accordance with JIS (Japanese Industrial Standards) K0070-1992. Unless otherwise specified, the measured values ​​of the mass average molecular weight (Mw) are values ​​measured using gel permeation chromatography. Unless otherwise specified, the charge amount (unit: μC / g) is a value measured using a small suction-type charge amount measuring device (Trek Model 212HS) under an environment of 25°C and 50% RH. Unless otherwise specified, the charge strength is the ease of triboelectric charging against a standard carrier provided by the Imaging Society of Japan.For example, the object to be measured is stirred with a standard carrier (anionic: N-01, cationic: P-01) provided by the Imaging Society of Japan, causing the object to be triboelectrically charged. For example, a Q / m meter (Trek Model 212HS) is used to measure the amount of charge per unit mass of the object to be measured before and after triboelectric charging, and the greater the change in the amount of charge per unit mass before and after triboelectric charging, the stronger the chargeability of the object to be measured. The above explains the meanings of the terms used in this specification and the measurement method.

[0011] [Two-component developer] A two-component developer (hereinafter, sometimes referred to as developer) 1 according to an embodiment of the present invention will be described below with reference to Fig. 1. Fig. 1 shows developer 1 according to this embodiment. In Fig. 1, multiple identical elements are indicated by the same hatching, and one of these identical elements is assigned a reference number, with the remaining reference numbers omitted.

[0012] The developer 1 includes a toner and a carrier. The toner includes toner particles 10. The carrier includes carrier particles 20. The toner particles 10 include toner base particles 11 and external additive particles 12. The external additive particles 12 are provided on the surfaces of the toner base particles 11. The external additive particles 12 include resin particles 13. The resin particles 13 include a crosslinked resin having repeating units derived from a crosslinking agent. The carrier particles 20 include a carrier core 21 and a coating layer 22. The coating layer 22 covers the surface of the carrier core 21. The coating layer 22 includes a coating resin and barium titanate particles 23. The coating resin includes a silicone resin. The number-average primary particle diameter of the barium titanate particles 23 is 100 nm or more and 500 nm or less. The content of the barium titanate particles 23 is 5 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the coating resin. The ratio of the mass of the coating layer 22 to the mass of the carrier core 21 is more than 0.0 mass % and not more than 4.9 mass %. The shape factor of the carrier particle 20 is not less than 34.0 and not more than 85.0.

[0013] Hereinafter, the "ratio of the mass of the coating layer 22 to the mass of the carrier core 21" may be referred to as the "coating layer / core ratio."

[0014] By virtue of the above-described constitution, developer 1 according to the present embodiment has excellent fogging resistance, can stably form images of desired image density, has small image density differences within the formed image, and is less likely to produce image defects due to poor cleaning. The reasons for this are presumed to be as follows.

[0015] In the developer 1 according to this embodiment, the coating layer 22 of the carrier particles 20 contains barium titanate particles 23. Because the barium titanate particles 23 are ferroelectric and have a high dielectric constant, the carrier particles 20 containing the barium titanate particles 23 in the coating layer 22 have a high charge retention capability. The carrier particles 20 with high charge retention capability can impart a sufficient amount of charge to the toner particles 10 upon contact with the toner particles 10. When printing multiple images using an image forming apparatus, the toner concentration in the developer 1 contained in the developing device may fluctuate during printing. However, the carrier particles 20 with high charge retention capability can impart a sufficient amount of charge to the toner particles 10 up to the saturated charge amount, even if the toner concentration in the developer 1 contained in the developing device increases during printing and the number of toner particles 10 to be charged increases. As a result, even if the toner concentration in the developer 1 changes, the fluctuation in the toner charge amount can be minimized, enabling the stable formation of images with the desired image density. Furthermore, since the carrier particles 20 can impart a sufficient amount of charge to the toner particles 10, the number of toner particles 10 whose charge amount is less than the desired value and the number of toner particles 10 that are oppositely charged are reduced, and an image with less fog can be formed.

[0016] In the developer 1 according to this embodiment, the number-average primary particle diameter of the barium titanate particles 23 is 100 nm or more and 500 nm or less. When the number-average primary particle diameter of the barium titanate particles 23 is less than 100 nm, the relative dielectric constant of the barium titanate particles 23 tends to decrease. When the number-average primary particle diameter of the barium titanate particles 23 is 100 nm or more, the relative dielectric constant of the barium titanate particles 23 is sufficiently high. By providing the coating layer 22 containing the barium titanate particles 23 with a high relative dielectric constant, the carrier particles 20 can impart a sufficient amount of charge to the toner particles 10. As a result, the number of toner particles 10 with a charge amount less than the desired value and the number of oppositely charged toner particles 10 are reduced, resulting in the formation of images with less fog. On the other hand, when the number-average primary particle diameter of the barium titanate particles 23 is 500 nm or less, the barium titanate particles 23 are incorporated into the coating layer 22 and are less likely to be detached from the coating layer 22. This prevents the barium titanate particles 23 from being detached and carried into the gap between the photosensitive drum and the cleaning blade, thereby reducing the likelihood of poor cleaning and resulting image defects.

[0017] In the developer 1 according to this embodiment, the content of the barium titanate particles 23 is 5 parts by weight or more and 45 parts by weight or less per 100 parts by weight of the coating resin. When the content of the barium titanate particles 23 is 5 parts by weight or more per 100 parts by weight of the coating resin, the amount of the barium titanate particles 23 in the coating layer 22 increases, enhancing the charge retention capability of the carrier particles 20. Carrier particles 20 with high charge retention capability can impart a sufficient amount of charge to the toner particles 10 upon contact with the toner particles 10. Therefore, even when the toner concentration in the developer 1 changes, fluctuations in the toner charge can be minimized, enabling stable formation of images with the desired image density. Furthermore, because the carrier particles 20 can impart a sufficient amount of charge to the toner particles 10, fewer toner particles 10 with a charge amount less than the desired value and fewer oppositely charged toner particles 10 are present, resulting in the formation of images with less fog. On the other hand, when the content of the barium titanate particles 23 is 45 parts by mass or less per 100 parts by mass of the coating resin, the barium titanate particles 23 are incorporated into the coating layer 22 and are less likely to detach from the coating layer 22. Therefore, the detached barium titanate particles 23 are less likely to inhibit contact between the toner particles 10 and the carrier particles 20. Therefore, a sufficient amount of charge can be imparted from the carrier particles 20 to the toner particles 10. As a result, the number of toner particles 10 whose charge amount is less than the desired value and the number of oppositely charged toner particles 10 are reduced, and an image with less fog can be formed.

[0018] In the developer 1 according to this embodiment, the coat layer / core ratio of the carrier particles 20 is greater than 0.0% by mass and equal to or less than 4.9% by mass. A coat layer / core ratio of 4.9% by mass or less allows the coat layer 22 to be appropriately thin. The coat resin contained in the coat layer 22 is hygroscopic. A moderately thin coat layer 22 reduces the amount of coat resin, thereby reducing the influence of moisture-absorbed coat resin on triboelectric charging (e.g., the influence of a decrease in the triboelectric charge of the toner particles 10). Furthermore, a coat layer / core ratio of 4.9% by mass or less can suppress aggregation of the carrier particles 20 when forming the coat layer 22 in the carrier formation process described below. Since the non-aggregated or less-aggregated carrier particles 20 are suitably triboelectrically charged, the toner particles 10 can be charged to the desired charge amount. As a result, the number of toner particles 10 with a charge amount less than the desired value and the number of oppositely charged toner particles 10 are reduced, allowing for the formation of images with less fog. On the other hand, when the coating layer / core ratio is 0.0% by mass, the carrier particles 20 do not have the coating layer 22, and the coating layer 22 cannot come into contact with the toner particles 10. As a result, the toner particles 10 cannot be sufficiently triboelectrically charged. When the coating layer / core ratio is higher than 0.0% by mass, the coating layer 22 comes into contact with the toner particles 10, the toner particles 10 are triboelectrically charged to a desired charge amount, and the toner particles 10 are suitably developed.

[0019] In the developer 1 according to this embodiment, the shape factor of the carrier particles 20 is 34.0 or more and 85.0 or less. The shape factor of the carrier particles 20 is calculated from the formula "shape factor of the carrier particles 20 = measured carrier particle diameter / calculated carrier particle diameter." The calculated carrier particle diameter in the above formula is calculated from the formula "calculated carrier particle diameter = 6 / (true specific gravity of the carrier particles 20 × BET specific surface area of ​​the carrier particles 20)." As the shape factor of the carrier particles 20 approaches 1.0, the shape of the carrier particles 20 approaches a perfect sphere, and the surface irregularities of the carrier particles 20 become smaller. When the shape factor of the carrier particles 20 is 34.0 or more, the surface irregularities of the carrier particles 20 become appropriately large, and the recesses on the surface of the carrier particles 20 capture the external additive particles 12 detached from the toner particles 10. This reduces the influence of the detached external additive particles 12, and the carrier particles 20 charge the toner particles 10 to the desired charge amount in a short time. As a result, images with less fog are formed. Furthermore, when the shape factor of the carrier particles 20 is 34.0 or more, the fluidity of the carrier particles 20 is improved. This allows the developer 1 to be transported with good fluidity through the stirring chamber of the developing device. This prevents temporary stagnation of the transport of the developer 1 within the stirring chamber, which in turn prevents a temporary decrease in the amount of developer 1 supplied from the developing device to the photosensitive drum. As a result, the image density difference within the formed image is reduced. On the other hand, when the shape factor of the carrier particles 20 is 85.0 or less, the surface irregularities of the carrier particles 20 are not too large, allowing the toner particles 10 to be charged to the desired charge amount. As a result, the number of toner particles 10 with a charge amount less than the desired value and the number of oppositely charged toner particles 10 are reduced, resulting in the formation of an image with less fog.

[0020] In the developer 1 according to this embodiment, the external additive particles 12 of the toner particles 10 contain resin particles 13, which contain a crosslinked resin. Because the coating layer 22 contains hard barium titanate particles 23, the carrier particles 20 are relatively hard. The resin particles 13 of the toner particles 10 function as spacers when the toner particles 10 and the carrier particles 20 come into contact with each other. Therefore, even if the carrier particles 20 are relatively hard, the external additive particles 12 (e.g., other external additive particles 14, particularly silica particles that contribute to charging) are buried in the surface of the toner base particles 11 upon contact with the carrier particles 20, preventing the charge amount of the toner particles 10 from becoming lower than the desired value. Furthermore, during high-speed printing, the temperature inside the image forming apparatus may rise. The resin particles 13, which contain a crosslinked resin, have relatively high heat resistance. Therefore, even during high-speed printing, the resin particles 13 maintain their spacer function, allowing the toner particles 10 to be triboelectrically charged to the desired charge amount. As a result, the number of toner particles 10 whose charge amount is less than the desired value and the number of oppositely charged toner particles 10 are reduced, and an image with less fog can be formed. Note that the developer 1 of this embodiment exhibits excellent fog resistance not only during high-speed printing but also during normal-speed printing.

[0021] The above explains why the developer 1 according to this embodiment has excellent fogging resistance, can stably form images of the desired image density, has small image density differences within the formed image, and is less likely to produce image defects due to poor cleaning.

[0022] In addition to the above effects, according to the developer 1 of this embodiment, the coating layer 22 contains hard barium titanate particles 23, so that the coating layer 22 is less abraded. Also, because the shape factor of the carrier particles 20 is 85.0 or less, even when a large number of sheets are printed, the coating layer 22 is less abraded and the shape of the carrier particles 20 is less likely to change. For these reasons, the life of the carrier particles 20 can be extended. Next, the toner and carrier contained in the developer 1 will be described in more detail.

[0023] [toner] The toner includes toner particles 10. The toner particles 10 have toner base particles 11 and external additive particles 12. The external additive particles 12 are provided on the surfaces of the toner base particles 11. The external additive particles 12 and the toner base particles 11 will be described below.

[0024] <External additive particles> The external additive particles 12 include resin particles 13. The external additive particles 12 further include external additive particles 14 other than the resin particles 13 (hereinafter, may be referred to as other external additive particles) as needed. The resin particles 13 and the other external additive particles 14 will be described below.

[0025] (resin particles) The resin particles 13 contain a crosslinked resin. The crosslinked resin has a repeating unit derived from a crosslinking agent. The main chains of the crosslinked resin are crosslinked to each other via the repeating unit derived from the crosslinking agent. The repeating unit derived from the crosslinking agent causes the main chain of the crosslinked resin to branch into a branched chain. Examples of the repeating unit derived from the crosslinking agent include a repeating unit derived from a compound having two or more vinyl groups, a repeating unit derived from a trivalent or higher carboxylic acid monomer, and a repeating unit derived from a trivalent or higher alcohol monomer. As the repeating unit derived from the crosslinking agent, a repeating unit derived from a compound having two or more vinyl groups is preferred, a repeating unit derived from a compound having two vinyl groups (divinyl compound) is more preferred, and a repeating unit derived from divinylbenzene is particularly preferred.

[0026] Examples of the crosslinked resin contained in the resin particles 13 include polyester resins, styrene resins, acrylic ester resins (more specifically, acrylic ester polymers, methacrylic ester polymers, etc.), olefin resins (more specifically, polyethylene resins, polypropylene resins, etc.), vinyl resins (more specifically, vinyl chloride resins, polyvinyl alcohol, vinyl ether resins, N-vinyl resins, etc.), polyamide resins, and urethane resins. Copolymers of these resins, i.e., copolymers in which any repeating unit is introduced into the above resins (more specifically, styrene-acrylic resins, styrene-butadiene resins, etc.), can also be used as the crosslinked resin contained in the resin particles 13.

[0027] In order to ensure good fixation of the toner particles 10 to a recording medium, the crosslinked resin contained in the resin particles 13 is preferably a styrene-acrylic resin having a repeating unit derived from a crosslinking agent (hereinafter, sometimes referred to as a crosslinked styrene-acrylic resin). The crosslinked styrene-acrylic resin is a copolymer of at least one styrene-based monomer, at least one acrylic acid-based monomer, and at least one crosslinking agent. That is, the crosslinked styrene-acrylic resin has at least one repeating unit derived from a styrene-based monomer, at least one repeating unit derived from an acrylic acid-based monomer, and at least one repeating unit derived from a crosslinking agent.

[0028] Examples of styrene-based monomers include styrene, α-methylstyrene, p-hydroxystyrene, m-hydroxystyrene, vinyltoluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-ethylstyrene. Of the styrene-based monomers, styrene is preferred.

[0029] Examples of acrylic acid monomers include (meth)acrylic acid, (meth)acrylonitrile, (meth)acrylic acid alkyl esters, and (meth)acrylic acid hydroxyalkyl esters. Examples of (meth)acrylic acid alkyl esters include alkyl esters of (meth)acrylic acid having 1 to 8 carbon atoms, more specifically methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of (meth)acrylic acid hydroxyalkyl esters include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. The acrylic acid monomer is preferably a (meth)acrylic acid alkyl ester, more preferably an alkyl ester of (meth)acrylic acid having 1 to 8 carbon atoms, still more preferably butyl (meth)acrylate, and even more preferably n-butyl (meth)acrylate or isobutyl (meth)acrylate.

[0030] As the crosslinking agent, a compound having two or more vinyl groups is preferred, a compound having two vinyl groups (divinyl compound) is more preferred, and divinylbenzene is even more preferred.

[0031] In order to enhance the heat resistance of the resin particles 13, the crosslinked resin contained in the resin particles 13 is preferably a crosslinked styrene-acrylic resin, more preferably a styrene-acrylic resin having a repeating unit derived from a compound having two or more vinyl groups, even more preferably a copolymer of styrene, an alkyl (meth)acrylate ester, and a divinyl compound, even more preferably a copolymer of styrene, an alkyl ester of (meth)acrylic acid having 1 to 8 carbon atoms, and a divinyl compound having 10 to 20 carbon atoms, even more preferably a copolymer of styrene, butyl (meth)acrylate, and divinylbenzene, and particularly preferably a copolymer of styrene, butyl methacrylate, and divinylbenzene.

[0032] The greater the amount (blending ratio) of crosslinking agent relative to the total amount of styrene-based monomer, acrylic acid-based monomer, and crosslinking agent, the higher the heat resistance of the crosslinked styrene-acrylic resin. Furthermore, the greater the amount (blending ratio) of acrylic acid-based monomer relative to the amount of styrene-based monomer, the lower the glass transition temperature of the crosslinked styrene-acrylic resin. To achieve a balance between the heat resistance of the resin particles 13 and the fixability of the toner particles 10 to a recording medium, the ratio of the amount of repeating units derived from the crosslinking agent relative to the total amount of repeating units derived from the styrene-based monomer, repeating units derived from the acrylic acid-based monomer, and repeating units derived from the crosslinking agent is preferably 40 mol% to 80 mol%, more preferably 50 mol% to 70 mol%, and even more preferably 50 mol% to 60 mol%. For the same reason, the ratio of the amount of repeating units derived from styrene-based monomers to the total amount of repeating units derived from styrene-based monomers, repeating units derived from acrylic acid-based monomers, and repeating units derived from crosslinking agents is preferably 4 mol% to 12 mol%, more preferably 6 mol% to 10 mol%, and even more preferably 8 mol% to 10 mol%. For the same reason, the ratio of the amount of repeating units derived from acrylic acid-based monomers to the total amount of repeating units derived from styrene-based monomers, repeating units derived from acrylic acid-based monomers, and repeating units derived from crosslinking agents is preferably 16 mol% to 48 mol%, more preferably 24 mol% to 40 mol%, and even more preferably 32 mol% to 40 mol%. Resin particles 13 may contain only a crosslinked resin, or may contain a resin other than the crosslinked resin in addition to the crosslinked resin.

[0033] In order to obtain a toner having excellent heat-resistant storage stability while enhancing the spacer function, the number-average primary particle diameter of the resin particles 13 is preferably 30 nm or more and 120 nm or less, more preferably 40 nm or more and 100 nm or less, and even more preferably 60 nm or more and 80 nm or less. The number-average primary particle diameter of the resin particles 13 can be measured using, for example, a scanning electron microscope.

[0034] The number-average primary particle diameter of the resin particles 13 can be adjusted, for example, by changing the reaction time and stirring speed in the polymerization reaction of the monomer. The longer the reaction time, the larger the number-average primary particle diameter of the resin particles 13 tends to be. Furthermore, the slower the stirring speed, the larger the number-average primary particle diameter of the resin particles 13 tends to be. Reaction Examples A to E of the polymerization reaction of the monomer are shown in Table 1. Reaction Examples A to E show the relationship between the reaction temperature, reaction time, and stirring speed in the polymerization reaction of the monomer and the number-average primary particle diameter of the resin particles 13 obtained by the polymerization reaction. In Table 1, "diameter" refers to the number-average primary particle diameter of the resin particles 13.

[0035] [Table 1]

[0036] The amount of resin particles 13 is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, more preferably 0.3 parts by mass or more and 1.0 parts by mass or less, and even more preferably 0.4 parts by mass or more and 1.0 parts by mass or less, relative to 100.0 parts by mass of toner base particles 11.

[0037] (Other external additive particles) Examples of the other external additive particles 14 include silica particles, alumina particles, magnesium oxide particles, and zinc oxide particles. The other external additive particles 14 may be surface-treated. For example, when silica particles are used as the other external additive particles 14, the surfaces of the silica particles may be rendered hydrophobic and / or positively chargeable by a surface treatment agent. The number-average primary particle diameter of the other external additive particles 14 is preferably 1 nm or more and 60 nm or less, and more preferably 5 nm or more and 25 nm or less. The amount of the other external additive particles 14 is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, and more preferably 1.0 parts by mass or more and 2.0 parts by mass or less, relative to 100.0 parts by mass of the toner base particles 11.

[0038] <Toner base particles> The toner base particles 11 contain, for example, at least one selected from the group consisting of a binder resin, a colorant, a charge control agent, and a release agent. The binder resin, the colorant, the charge control agent, and the release agent will be described below.

[0039] (binder resin) To obtain a toner with excellent low-temperature fixability, the toner base particles 11 preferably contain a thermoplastic resin as a binder resin, and more preferably contain a thermoplastic resin in a proportion of 85% by mass or more of the total binder resin. Examples of thermoplastic resins include polyester resins, styrene-based resins, acrylic ester-based resins (more specifically, acrylic ester polymers, methacrylic ester polymers, etc.), olefin-based resins (more specifically, polyethylene resins, polypropylene resins, etc.), vinyl resins (more specifically, vinyl chloride resins, polyvinyl alcohol, vinyl ether resins, N-vinyl resins, etc.), polyamide resins, and urethane resins. Copolymers of these resins, i.e., copolymers in which any repeating unit is introduced into the above resins (more specifically, styrene-acrylic resins, styrene-butadiene-based resins, etc.), can also be used as binder resins.

[0040] The binder resin is preferably a polyester resin. The polyester resin is a polymer of one or more polyhydric alcohol monomers and one or more polycarboxylic acid monomers. Instead of the polycarboxylic acid monomers, polycarboxylic acid derivatives (more specifically, polycarboxylic acid anhydrides, polycarboxylic acid halides, etc.) may be used.

[0041] Examples of polyhydric alcohol monomers include diol monomers, bisphenol monomers, and trihydric or higher alcohol monomers.

[0042] Examples of diol monomers include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-butene-1,4-diol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, 1,4-benzenediol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol.

[0043] Examples of bisphenol monomers include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adducts, and bisphenol A propylene oxide adducts.

[0044] Examples of trihydric or higher alcohol monomers include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

[0045] Examples of polycarboxylic acid monomers include dicarboxylic acid monomers and tricarboxylic or higher carboxylic acid monomers.

[0046] Examples of dicarboxylic acid monomers include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, 5-sulfoisophthalic acid, sodium 5-sulfoisophthalate, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, succinic acid, alkylsuccinic acid, and alkenylsuccinic acid. Examples of alkylsuccinic acid include n-butylsuccinic acid, isobutylsuccinic acid, n-octylsuccinic acid, n-dodecylsuccinic acid, and isododecylsuccinic acid. Examples of alkenylsuccinic acid include n-butenylsuccinic acid, isobutenylsuccinic acid, n-octenylsuccinic acid, n-dodecenylsuccinic acid, and isododecenylsuccinic acid.

[0047] Examples of trivalent or higher carboxylic acid monomers include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empol trimer acid.

[0048] The polyester resin is preferably a polymer of a bisphenol monomer, a dicarboxylic acid monomer, and a tricarboxylic acid monomer. The polyester resin is more preferably a polymer of a bisphenol A alkylene oxide adduct, a dicarboxylic acid having 3 to 6 carbon atoms, and an aryl tricarboxylic acid. The polyester resin is further preferably a polymer of a bisphenol A ethylene oxide adduct, a bisphenol A propylene oxide adduct, fumaric acid, and trimellitic acid.

[0049] The polyester resin is preferably an amorphous polyester resin. It is often impossible to measure a clear melting point for an amorphous polyester resin. Therefore, a polyester resin that cannot be determined to have a clear endothermic peak in an endothermic curve measured using a differential scanning calorimeter can be considered an amorphous polyester resin.

[0050] The softening point of the polyester resin is preferably 50° C. or higher and 200° C. or lower, and more preferably 80° C. or higher and 120° C. or lower. The glass transition point of the polyester resin is preferably 40° C. or higher and 100° C. or lower, and more preferably 40° C. or higher and 60° C. or lower.

[0051] The weight average molecular weight of the polyester resin is preferably 10,000 or more and 50,000 or less, and more preferably 20,000 or more and 40,000 or less.

[0052] The polyester resin preferably has an acid value of 1 mgKOH / g or more and 30 mgKOH / g or less, more preferably 10 mgKOH / g or more and 20 mgKOH / g or less, and a hydroxyl value of 1 mgKOH / g or more and 50 mgKOH / g or less, more preferably 20 mgKOH / g or more and 40 mgKOH / g or less.

[0053] The amount of the binder resin is preferably 85 parts by mass or more and 95 parts by mass or less with respect to 100 parts by mass of the toner base particles 11 .

[0054] (coloring agent) As the colorant, known pigments or dyes can be used in accordance with the color of the toner, and examples of the colorant include black colorants, yellow colorants, magenta colorants, and cyan colorants.

[0055] An example of the black colorant is carbon black. The black colorant may also be a colorant that is toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

[0056] The yellow colorant may be, for example, one or more compounds selected from the group consisting of condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds. Examples of the yellow colorant include CI Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155, 168, 174, 175, 176, 180, 181, 191, and 194), Naphthol Yellow S, Hansa Yellow G, and CI Vat Yellow.

[0057] Examples of magenta colorants that can be used include one or more compounds selected from the group consisting of condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. Examples of magenta colorants include CI Pigment Red (2, 3, 5, 6, 7, 19, 23, 48:2, 48:3, 48:4, 57:1, 81:1, 122, 144, 146, 150, 166, 169, 177, 184, 185, 202, 206, 220, 221, and 254).

[0058] The cyan colorant may be, for example, one or more compounds selected from the group consisting of copper phthalocyanine compounds, anthraquinone compounds, and basic dye lake compounds, including, for example, CI Pigment Blue (1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, and 66), phthalocyanine blue, CI Vat Blue, and CI Acid Blue.

[0059] The amount of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

[0060] (charge control agent) Charge control agents are used, for example, to obtain toner with excellent charge stability and charge buildup characteristics. The charge buildup characteristics of a toner are an indicator of whether the toner can be charged to a predetermined charge level in a short period of time. Examples of charge control agents include positive charge control agents and negative charge control agents. The inclusion of a positive charge control agent in the toner base particles 11 can strengthen the cationic (positively charged) nature of the toner, while the inclusion of a negative charge control agent in the toner base particles 11 can strengthen the anionic (negatively charged) nature of the toner. Examples of positive charge control agents include pyridine, nigrosine, and quaternary ammonium salts. Examples of negative charge control agents include metal-containing azo dyes, sulfogroup-containing resins, oil-soluble dyes, naphthenic acid metal salts, acetylacetone metal complexes, salicylic acid metal complexes, boron compounds, fatty acid soaps, and long-chain alkyl carboxylate salts. However, if sufficient chargeability is ensured in the toner, it is not necessary to include a charge control agent in the toner base particles 11. The amount of the charge control agent is preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the binder resin.

[0061] (mold release agent) Releasing agents are used, for example, to obtain toners with excellent hot offset resistance. Examples of releasing agents include aliphatic hydrocarbon waxes, oxides of aliphatic hydrocarbon waxes, plant-derived waxes, animal-derived waxes, mineral-derived waxes, ester waxes primarily composed of fatty acid esters, and waxes in which fatty acid esters are partially or completely deoxidized. Examples of aliphatic hydrocarbon waxes include polyethylene waxes (e.g., low-molecular-weight polyethylene), polypropylene waxes (e.g., low-molecular-weight polypropylene), polyolefin copolymers, polyolefin waxes, microcrystalline waxes, paraffin waxes, and Fischer-Tropsch waxes. Examples of oxides of aliphatic hydrocarbon waxes include oxidized polyethylene waxes and block copolymers of oxidized polyethylene waxes. Examples of plant-derived waxes include candelilla wax, carnauba wax, Japan wax, jojoba wax, and rice wax. Examples of animal-derived waxes include beeswax, lanolin, and spermaceti. Examples of mineral-derived waxes include ozokerite, ceresin, and petrolatum. Examples of ester waxes containing fatty acid ester as a main component include Montan acid ester wax and castor wax. Examples of waxes in which the fatty acid ester is partially or completely deoxidized include deoxidized carnauba wax. The amount of the release agent is preferably 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the binder resin.

[0062] The toner particles 10 may contain known additives as needed. The volume median diameter of the toner particles 10 is preferably 4 μm or more and 12 μm or less. The volume median diameter of the toner base particles 11 is preferably 4 μm or more and 12 μm or less, and more preferably 5 μm or more and 9 μm or less. The toner particles 10 may be magnetic toner or non-magnetic toner. When the toner particles 10 are magnetic toner, the toner base particles 11 further contain magnetic powder. In the developer 1, the amount of toner is preferably 1 part by mass or more and 15 parts by mass or less, and more preferably 3 parts by mass or more and 10 parts by mass or less, per 100 parts by mass of carrier. For ease of explanation, FIG. 1 shows non-encapsulated toner base particles 11. However, the toner base particles 11 shown in FIG. 1 may be encapsulated toner base particles having a toner core and a shell layer covering the toner core. This concludes the description of the toner.

[0063] [Career] The carrier includes carrier particles 20. The carrier particles 20 have a carrier core 21 and a coating layer 22. The coating layer 22 is provided on the surface of the carrier core 21. The coating layer 22 covers the surface of the carrier core 21. The coating layer 22 may cover the entire surface of the carrier core 21, or may cover only a portion of the surface of the carrier core 21.

[0064] As already mentioned, the coating layer / core ratio is greater than 0.0% by mass and equal to or less than 4.9% by mass. The coating layer / core ratio is preferably equal to or greater than 0.1% by mass, and more preferably equal to or greater than 0.4% by mass. The coating layer / core ratio is preferably equal to or less than 4.6% by mass, more preferably equal to or less than 4.4% by mass, even more preferably equal to or less than 4.0% by mass, even more preferably equal to or less than 3.0% by mass, even more preferably equal to or less than 2.0% by mass, even more preferably equal to or less than 1.4% by mass, even more preferably equal to or less than 1.0% by mass, especially preferably equal to or less than 0.9% by mass, and especially especially preferably equal to or less than 0.5% by mass. In another embodiment, the coating layer / core ratio may be equal to or greater than 2.1% by mass.

[0065] The ratio of the mass of the coating resin to the mass of the carrier core 21 is preferably greater than 0.0% by mass and less than 4.0% by mass. Hereinafter, the "ratio of the mass of the coating resin to the mass of the carrier core 21" may be referred to as the "resin / core ratio." The resin / core ratio is more preferably 3.0% by mass or less, even more preferably 2.0% by mass or less, even more preferably 1.4% by mass or less, still more preferably 1.0% by mass or less, especially preferably 0.9% by mass or less, and even more preferably 0.5% by mass or less. The resin / core ratio is more preferably 0.3% by mass or more.

[0066] The mass of the coating layer 22 is 0.10 g / m per unit surface area of ​​the carrier core 21 when the carrier core 21 is assumed to be a perfect sphere. 2 More than 1.80g / m 2 It is preferable that the mass of the coating layer 22 per unit area on the surface of the carrier core 21 when the carrier core 21 is assumed to be a perfect sphere is hereinafter referred to as the "unit area film mass." 2If the film mass per unit area is 1.80 g / m, the carrier particles 20 are less likely to adhere to the photosensitive drum (carrier development). This makes it possible to prevent the carrier particles 20 adhering to the photosensitive drum from migrating from the photosensitive drum to the transfer section, thereby preventing image defects such as transfer defects. 2 If the coating resin amount is less than 0.20 g / m, the amount of the coating resin is appropriately reduced, and the influence on triboelectric charging caused by the coating resin that easily absorbs moisture (for example, the influence of a decrease in the amount of triboelectric charge of the toner particles 10) can be reduced. As a result, the number of toner particles 10 whose charge amount is less than the desired value and the number of toner particles 10 that are oppositely charged are reduced, and an image with less fog can be formed. In order to suppress carrier development, the unit area film mass is 0.20 g / m 2 It is preferable that the content is 0.30 g / m or more. 2 More preferably, it is 0.40 g / m or more. 2 More preferably, it is 0.50 g / m or more. 2 It is even more preferable that the value is 0.70 g / m or more. 2 In order to form an image with little fog, the unit area film mass is preferably 1.50 g / m or more. 2 Preferably, it is 1.00 g / m or less. 2 More preferably, it is 0.90 g / m or less. 2 More preferably, it is 0.85 g / m or less. 2 It is more preferable that the film mass per unit area is equal to or less than 10 ...

[0067] The calculation method of the membrane mass per unit area will be explained below. The membrane mass per unit area is calculated according to the following formulas (2) to (6), (7A), (7B), (8), (9A), and (9B). Formula (7B) is obtained by rewriting formula (7A) using formulas (3), (6), (5), and (4). Formula (9B) is obtained by rewriting formula (9A) using formulas (8) and (7B).

[0068] r = (volume median diameter × 10 -6 ) / twenty two) A=4πr 2 ···(3) B=4 / 3πr 3 ···(4) C=B×s1=B×s2×10 6 ···(5) X=W / C (6) Y = A × X (7A) Y=A×X=(4πr 2 )×(W / C)=4πr 2 ×W / (B×s2×10 6 )=4πr 2 ×W / (4 / 3πr 3 ×s2×10 6 )=3W×10 -6 / (r×s2) (7B) Z = W × (coat layer / core ratio) / 100 (8) E=Z / Y= (9A) E = Z / Y = [W × (coat layer / core ratio) / 100] / [3W × 10 -6 / (r × s2)] = (coat layer / core ratio) × r × s2 × 10 4 / 3 (9B)

[0069] The symbols in the formulas (2) to (6), (7A), (7B), (8), (9A), and (9B) are as follows: r: radius of one carrier core (unit: m) Volume median diameter: Volume median diameter of the carrier core (unit: μm) A: Surface area of ​​one carrier core (unit: m 2 ) B: Volume of one carrier core (unit: m 3 ) C: Mass of one carrier core (unit: g) s1: True specific gravity of carrier core (unit: g / m 3 ) s2: True specific gravity of carrier core (unit: g / cm 3 ) W: Mass of the carrier core to be measured (unit: g) X: Number of carrier cores contained in a carrier core of mass Wg (unit: pieces) Y: Total surface area of ​​carrier cores contained in carrier cores of mass Wg (unit: m 2 ) Z: Mass of the coating layer relative to the carrier core mass Wg (unit: g) E: membrane mass per unit area (unit: g / m 2 ) Coat layer / core ratio: Coat layer / core ratio of the carrier particles (unit: mass%)

[0070] The specific method for calculating the membrane mass per unit area is as follows. First, the volume median diameter of the carrier cores 21 is measured using a laser diffraction / scattering particle size distribution analyzer (LA-950 manufactured by Horiba, Ltd.). The true specific gravity s2 of the carrier cores 21 is measured using a dry automatic density meter (AccuPyc II 1340 Series manufactured by Micromeritics). Next, the radius r of one carrier core 21 is calculated from the measured volume median diameter of the carrier cores 21 according to formula (2). Next, the membrane mass per unit area E is calculated from the calculated radius r of one carrier core 21, the measured true specific gravity s2 of the carrier core 21, and the coating layer / core ratio of the carrier particles 20 according to formula (9B). The method for calculating the membrane mass per unit area has been described above.

[0071] In order to charge the toner to a desired charge amount in a short time and form an image with little fog, the BET specific surface area of ​​the carrier particles 20 is 0.3 m 2 / g or more, and 0.5m 2 / g or more is more preferable, and 0.6m 2 / g or more is more preferable, and 0.7m 2 / g or more is more preferable, and 1.0m 2 / g or more is more preferable, and 1.5m 2 For the same reason, the BET specific surface area of ​​the carrier particles 20 is particularly preferably 5.0 m / g or more. 2 / g or less, and 2 / g or less is more preferable, and 4.5m 2 / g or less is more preferable, and 4.0m 2 / g or less is even more preferable, 2 / g or less is particularly preferred. The BET specific surface area of ​​the carrier particles 20 is determined from the amount of liquid nitrogen adsorbed on the surface of the carrier particles 20 using an automatic specific surface area measuring device based on the BET method (nitrogen adsorption specific surface area method).

[0072] As already mentioned, the shape factor of the carrier particles 20 is 34.0 or more and 85.0 or less. In order to form an image with little fog and small image density difference, the shape factor of the carrier particles 20 is preferably 35.0 or more. In order to form an image with little fog, the shape factor of the carrier particles 20 is preferably 80.0 or less, more preferably 70.0 or less, even more preferably 60.0 or less, and particularly preferably 55.0 or less. The shape factor of the carrier particles 20 is measured, for example, by the method described in the Examples. A method for adjusting the shape factor of the carrier particles 20 will be described later in the <Carrier Formation Step> section.

[0073] The flowability (FR, unit: seconds / 50 g) of the carrier particles 20 is measured in accordance with JIS (Japanese Industrial Standards) Z 2502:2012 "Metal Powders - Flowability Measurement Method." The flowability of the carrier particles 20 corresponds to the time required to discharge 50 g of the carrier particles 20 from a funnel. The flowability of the carrier particles 20 is preferably 25.0 seconds / 50 g or more and 35.0 seconds / 50 g or less, and more preferably 26.0 seconds / 50 g or more and 29.0 seconds / 50 g or less.

[0074] The apparent density (AD, unit: g / cm) of the carrier particles 20 3 ) is measured in accordance with JIS (Japanese Industrial Standards) Z 2504:2012 "Metal Powders - Apparent Density Measurement Method." The apparent density of the carrier particles 20 is 1.0 g / cm 3 More than 5.0g / cm 3 Preferably, it is 2.0 g / cm or less. 3 More than 2.6g / cm 3 More preferably, it is 2.3 g / cm or less. 3 More than 2.4g / cm3 It is more preferable that:

[0075] The product of the fluidity and apparent density of the carrier particles 20 (hereinafter sometimes referred to as (FR×AD)) is preferably 50.0 or more and 80.0 or less, more preferably 52.0 or more and 77.0 or less, even more preferably 55.5 or more and 71.0 or less, and even more preferably 55.5 or more and 62.0 or less. Here, the stirring chamber of the developing device of the image forming apparatus is equipped with, for example, a stirring screw that stirs and transports the toner and carrier. The fluidity of the carrier particles 20 is an index indicating the speed at which the carrier particles 20 are transported per unit mass by the stirring screw. The apparent density of the carrier particles 20 indicates the mass of the carrier particles 20 per unit volume. Therefore, the value (FR×AD), which is the product of the fluidity and apparent density of the carrier particles 20, is an index indicating the speed at which the carrier particles 20 are transported per unit volume by the stirring screw. When the value (FR×AD) is 50.0 or more, the carrier particles 20 are transported by the stirring screw at an appropriate speed, thereby favorably forming an image with little density difference. When the value (FR×AD) is 80.0 or less, the carrier particles 20 are not transported too fast, ensuring sufficient time for the toner particles 10 to be frictionally charged by contact with the carrier particles 20. As a result, there are fewer toner particles 10 with a charge amount less than the desired value and fewer toner particles 10 that are oppositely charged, thereby forming an image with little fog.

[0076] The developer 1 of this embodiment can be particularly suitably used in an image forming apparatus having a developing device equipped with an agitating screw. The number of agitating screws provided in the developing device is preferably 1 to 3, and more preferably 2.

[0077] The carrier particles 20 preferably satisfy formula (1): In formula (1), FR represents the fluidity of the carrier particles 20, AD represents the apparent density of the carrier particles 20, and X represents the shape factor of the carrier particles 20. 0.73≦FR×AD / X≦2.10 (1)

[0078] Hereinafter, the "value calculated from the formula "FR×AD / X"" in formula (1) may be referred to as "value (FR×AD / X)." As already mentioned, the value (FR×AD) is an index indicating the speed at which the carrier particles 20 are transported per unit volume by the stirring screw. Also, as already mentioned, the shape factor of the carrier particles 20 indicates the degree of surface roughness of the carrier particles 20, and affects the ability of the carrier particles 20 to charge the toner to a desired charge amount in a short period of time (charge imparting ability) and the fluidity of the carrier particles 20 (and thus the transport speed of the carrier particles 20). For these reasons, the "value (FR×AD / X)" is an index indicating the balance between the transport speed and charge imparting ability of the carrier particles 20. In order to improve the transport speed and charge imparting ability of the carrier particles 20 in a balanced manner and form an image with little density difference, the value (FR×AD / X) is preferably 0.73 or more, as shown in formula (1), and more preferably 0.95 or more. In order to improve the transport speed and charge imparting ability of the carrier particles 20 in a balanced manner and form an image with little fog, the value (FR×AD / X) is preferably 2.10 or less, as shown in formula (1), and more preferably 2.00 or less.

[0079] Next, the carrier core 21 and the coating layer 22 of the carrier particle 20 will be described.

[0080] <Career Core> The carrier core 21 contains, for example, a magnetic material. Examples of magnetic materials contained in the carrier core 21 include metal oxides, more specifically, magnetite, maghemite, and ferrite. Ferrite tends to have high fluidity and be chemically stable. Therefore, from the viewpoint of forming high-quality images over a long period of time, it is preferable that the carrier core 21 contains ferrite. Examples of ferrite include barium ferrite, manganese ferrite (Mn-ferrite), Mn-Zn ferrite, Ni-Zn ferrite, Mn-Mg ferrite, Ca-Mg ferrite, Li ferrite, and Cu-Zn ferrite. The shape of the carrier core 21 is not particularly limited and may be irregular or spherical. Commercially available carrier cores 21 may be used. Alternatively, the carrier cores 21 may be prepared by pulverizing and firing a magnetic material.

[0081] The volume median diameter of the carrier core 21 is preferably 20.0 μm or more and 80.0 μm or less, more preferably 20.0 μm or more and 65.0 μm or less, even more preferably 20.0 μm or more and 60.0 μm or less, even more preferably 20.0 μm or more and 50.0 μm or less, even more preferably 20.0 μm or more and less than 40.0 μm, even more preferably 20.0 μm or more and 35.0 μm or less, and particularly preferably 25.0 μm or more and 35.0 μm or less. When the volume median diameter of the carrier core 21 is 20.0 μm or more, carrier development is less likely to occur, and carrier particles 20 attached to the photosensitive drum can be prevented from migrating from the photosensitive drum to the transfer section, thereby preventing image defects such as transfer defects. On the other hand, when the volume median diameter of the carrier core 21 is 80.0 μm or less, the magnetic brush of the developer 1 formed on the peripheral surface of the developing roller during image formation becomes fine, allowing for the formation of a fine-textured image. The volume median diameter of the carrier core 21 is measured, for example, by the method described in the Examples.

[0082] The saturation magnetization of the carrier core 21 is preferably 65 emu / g or more and 90 emu / g or less, and more preferably 70 emu / g or more and 85 emu / g or less. When the saturation magnetization of the carrier core 21 is 65 emu / g or more, carrier development is less likely to occur. When the saturation magnetization of the carrier core 21 is 90 emu / g or less, the magnetic brush of the developer 1 formed on the circumferential surface of the developing roller during image formation becomes finer, allowing for the formation of fine-textured images. When the carrier core 21 contains Mn-ferrite, the saturation magnetization of the carrier core 21 tends to decrease as the Mn content increases. Furthermore, when the carrier core 21 contains Mn-Mg ferrite, the saturation magnetization of the carrier core 21 tends to decrease as the Mg content increases. The saturation magnetization of the carrier core 21 is measured, for example, by the method described in the Examples.

[0083] The apparent density of the carrier core 21 is 1.20 x 10 3 kg / m 3 Over 2.80 x 10 3 kg / m 3 The carrier core 21 preferably has a flowability of 21 seconds / 50 g or more and 50 seconds / 50 g or less. The carrier core 21 preferably has an electrical resistivity of 1×10 2 Ω m or more 1×10 7 It is preferable that the resistance is Ω·m or less.

[0084] The residual magnetization of the carrier core 21 is 0.4 Am 2 / kg or more 10.0Am 2 The holding power of the carrier core 21 is preferably 5 A / m·10 3 / 4π or more 10A / m·10 3 It is preferable that the coercive force of the carrier core 21 is 10 A / m 10 3 When the axial distance is 0.05π or less, the fluidity of the developer 1 in the developing device is improved, and the toner particles 10 are suitably charged to a desired charge amount, thereby forming an image with less fog. The residual magnetization and the coercive force are measured, for example, by applying an external magnetic field of 0 A / m or more to 79.58×10 using a room temperature vibration sample magnetometer (VSM) ("VSM-P7" manufactured by Toei Kogyo Co., Ltd.).4 Measurement can be performed by applying a continuous current of 10000 oersteds or less for one cycle.

[0085] <Coating layer> The coating layer 22 includes a coating resin and barium titanate particles 23. The coating layer 22 preferably further includes carbon black particles 24. However, the coating layer 22 does not necessarily include carbon black particles 24. The coating resin, barium titanate particles 23, and carbon black particles 24 will be described below.

[0086] (coating resin) The coating resin contains a silicone resin. When the coating resin contains a silicone resin, the toner can be triboelectrically charged to a desired charge amount. Furthermore, by using a silicone resin as the coating resin, a thinner coating layer 22 can be formed compared to resins other than silicone resin (e.g., fluororesin). This allows the amount of coating resin contained in the coating layer 22 to be reduced, and the effect on triboelectric charging caused by moisture-absorbing coating resin (e.g., the effect of reducing the triboelectric charge amount of the toner particles 10) can be reduced.

[0087] Suitable examples of silicone resins include silicone resins having methyl groups and epoxy resin-modified silicone resins. One example of a silicone resin having methyl groups is a silicone resin having methyl groups but not a phenyl group. Another example of a silicone resin having methyl groups is a silicone resin having methyl groups and phenyl groups (hereinafter sometimes referred to as "methylphenylsilicone resin"). The coating layer 22 may contain only a silicone resin as the coating resin, or may further contain a resin other than a silicone resin.

[0088] (barium titanate particles) As already mentioned, the number average primary particle diameter of the barium titanate particles 23 is 100 nm or more and 500 nm or less. In order to form an image with little fog, the number average primary particle diameter of the barium titanate particles 23 is preferably 200 nm or more. In order to suppress the occurrence of image defects due to poor cleaning, the number average primary particle diameter of the barium titanate particles 23 is preferably 400 nm or less. The number average primary particle diameter of the barium titanate particles 23 is measured, for example, by the method described in the Examples.

[0089] As already mentioned, the content of the barium titanate particles 23 is 5 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the coating resin. The content of the barium titanate particles 23 is preferably 25 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the coating resin. When the coating resin contains two or more resins, 100 parts by mass of the coating resin means that the total mass of the two or more resins is 100 parts by mass.

[0090] The method for producing the barium titanate particles 23 is not particularly limited, but examples include hydrothermal synthesis and the oxalate method. The method for producing the barium titanate particles 23 is preferably hydrothermal synthesis. That is, the barium titanate particles 23 are preferably a hydrothermal synthesis product. The true specific gravity of the barium titanate particles 23 produced by the hydrothermal synthesis method is lower than that of the barium titanate particles 23 produced by the oxalate method due to the presence of voids therein. Furthermore, the particle size distribution of the barium titanate particles 23 produced by the hydrothermal synthesis method is sharp. For these reasons, the barium titanate particles 23 produced by the hydrothermal synthesis method are easily dispersed uniformly in the coating resin, making it easy to obtain a carrier with high charge-imparting ability. As a result, the toner is rapidly charged due to friction with the carrier, resulting in images with less fog.

[0091] The hydrothermal synthesis method includes, for example, a hydrothermal reaction step and a heat treatment step. In the hydrothermal reaction step, a water-soluble barium salt is added to a titanium oxide dispersion liquid in which titanium oxide particles are dispersed, and the mixture is heated to cause a hydrothermal reaction. In this manner, barium titanate hydrothermally synthesized particles are obtained. In the heat treatment step, the barium titanate hydrothermally synthesized particles are heat-treated to obtain barium titanate particles 23. The heating temperature in the hydrothermal reaction step is preferably 80°C or higher. The heat treatment temperature in the heat treatment step is preferably 650°C or higher and 850°C or lower. The number-average primary particle diameter of the barium titanate particles 23 can be adjusted, for example, by changing the heating temperature and the hydrothermal reaction time in the hydrothermal reaction step. For example, the higher the heating temperature in the hydrothermal reaction step, the larger the number-average primary particle diameter of the barium titanate particles 23. Furthermore, the longer the hydrothermal reaction time, the larger the number-average primary particle diameter of the barium titanate particles 23.

[0092] (carbon black particles) The carbon black particles 24 are conductive. Therefore, when the coating layer 22 contains the carbon black particles 24, charge transfers smoothly from the carrier particles 20 to the toner particles 10. As a result, the toner particles 10 can be charged to the desired charge amount, and images with less fog can be formed. Furthermore, even if the toner concentration in the developer 1 changes, the fluctuation in the toner charge amount can be reduced, and images with the desired image density can be stably formed.

[0093] The number average primary particle diameter of the carbon black particles 24 is preferably 10 nm or more and 50 nm or less, and more preferably 20 nm or more and 40 nm or less. The DBP oil absorption of the carbon black particles 24 is 50 cm 3 / 100g or more 700cm 3 / 100g or less is preferable, and 100cm 3 / 100g or more 600cm 3 The BET specific surface area of ​​the carbon black particles 24 is preferably 100 m / 100 g or less. 2 / g or more 2000m 2 / g or less, and 100m2 / g or more 200m 2 / g or less, or 1200m 2 / g or more 1500m 2 It is more preferable that the saturation coefficient is 1 / g or less.

[0094] The inclusion of barium titanate particles 23 in coating layer 22 moderately reduces the electrical resistance of carrier particles 20. Therefore, even if the amount of carbon black particles 24, which are conductive, is small, the electrical resistance of carrier particles 20 moderately reduces. Because the amount of carbon black particles 24 can be reduced, it is possible to prevent color turbidity from occurring in images formed using developer 1 containing carrier particles 20. The amount of carbon black particles 24 is preferably 1 part by mass or more and 10 parts by mass or less, more preferably 3 parts by mass or more and 9 parts by mass or less, and even more preferably 3 parts by mass or more and 6 parts by mass or less, or 6 parts by mass or more and 9 parts by mass or less, relative to 100 parts by mass of coating resin.

[0095] The carrier particles 20 may contain known additives as needed. The volume median diameter of the carrier particles 20 is preferably 25 μm or more and 100 μm or less. The carrier has been described above.

[0096] [Manufacturing method of developer] An example of a method for producing the developer 1 according to this embodiment will be described below. The method for producing the developer 1 according to this embodiment includes, for example, a toner forming step, a carrier forming step, and a toner and carrier mixing step.

[0097] <Toner formation process> In the toner formation process, for example, a binder resin, a colorant, a charge control agent, and a release agent are mixed to obtain a mixture. The mixture is melted and kneaded to obtain a molten and kneaded product. The molten and kneaded product is pulverized to obtain a pulverized product. The pulverized product is classified to obtain toner base particles 11. The toner base particles 11 are mixed with external additive particles 12 (resin particles 13 and other external additive particles 14) using a mixer. By mixing, the external additive particles 12 adhere to the surfaces of the toner base particles 11, thereby obtaining a toner containing toner particles 10. Mixing with the external additive particles 12 is preferably carried out under conditions such that the external additive particles 12 are not completely embedded in the toner base particles 11. The external additive particles 12 adhere to the surfaces of the toner base particles 11 by physical bonds (physical forces) rather than chemical bonds.

[0098] <Carrier formation process> In the carrier formation process, a coating layer 22 is formed on the surface of the carrier core 21 to obtain a carrier containing carrier particles 20. For example, a coating liquid containing a coating resin, barium titanate particles 23, and optional carbon black particles 24 is sprayed onto the carrier cores 21 in a fluidized bed. Next, the carrier cores 21 onto which the coating liquid has been sprayed are heated at a first predetermined temperature (hereinafter sometimes referred to as the predetermined drying temperature) to dry the coating liquid adhered to the surface of the carrier core 21, thereby obtaining a dried product. Next, the dried product is heated at a second predetermined temperature (hereinafter sometimes referred to as the predetermined baking temperature) using an electric furnace to harden the coating resin contained in the coating liquid on the surface of the carrier core 21. In this way, a coating layer 22 is formed on the surface of the carrier core 21. The predetermined drying temperature is preferably 70°C or higher and 80°C or lower. The predetermined baking temperature is preferably 200°C or higher and 300°C or lower.

[0099] The shape factor of the carrier particles 20 can be adjusted, for example, by changing the predetermined drying temperature. The higher the predetermined drying temperature, the more the coating liquid dries before it spreads over the entire surface of the carrier core 21. Therefore, the higher the predetermined drying temperature, the more likely it is that the coating layer 22 will be formed on only part of the surface of the carrier core 21 rather than on the entire surface, and the larger the shape factor of the carrier particles 20 will tend to be.

[0100] <Toner and carrier mixing process> In the toner and carrier mixing step, the developer 1 is obtained by mixing the toner and carrier using a mixer. [Example]

[0101] The present invention will be described in more detail below using examples, but the present invention is not limited to the scope of the examples.

[0102] <Preparation of carrier> Carriers (CA-1) to (CA-23) and (CB-1) to (CB-9) were prepared. The compositions of these carriers are shown in Tables 2 to 4 below. Carriers (CA-1) to (CA-23) and (CB-1) to (CB-9) were used to prepare developers (A-1) to (A-23) and (B-1) to (B-9), respectively. To facilitate understanding, in Tables 2 to 4, carriers having the same composition are shown with different carrier numbers corresponding to the developer numbers.

[0103] (Preparation of Carrier (CA-1)) A coating liquid was obtained by mixing 361.2 g of a silicone resin solution ("KR-255" manufactured by Shin-Etsu Chemical Co., Ltd., solid concentration: 50 mass%, solid content: 180.6 g), 9.0 g of barium titanate ("BT-01" manufactured by Sakai Chemical Industry Co., Ltd., barium titanate produced by hydrothermal synthesis, number average primary particle diameter: 102 nm), 5.4 g of carbon black ("Ketjenblack EC-300J" manufactured by Lion Specialty Chemicals Co., Ltd.), and 1444.8 g of toluene using a homomixer.

[0104] Using a fluidized bed coating device (Powrex Corporation, "FD-MP-01 D type"), 5000 g of carrier cores were fluidized while spraying the coating liquid onto the carrier cores. In this way, carrier cores coated with the coating liquid were obtained. The coating conditions were an inlet air temperature (corresponding to the predetermined drying temperature described in the embodiment) of 75°C, an inlet air volume of 0.3 m3, and a coating temperature of 75°C. 3The conditions were a rotation speed of 1000 rpm / min and a rotor rotation speed of 400 rpm. Manganese ferrite cores (manufactured by DOWA IP Creation Co., Ltd., volume median diameter: 20.3 μm, saturation magnetization: 67 emu / g) were used as carrier cores. The carrier cores coated with the coating liquid were fired in an electric furnace at a temperature of 200°C (corresponding to the predetermined firing temperature described in the embodiment) for 1 hour. In this way, a coating layer was formed on the surface of the carrier core, and a carrier (CA-1) was obtained.

[0105] (Preparation of Carriers (CA-2) to (CA-23) and (CB-1) to (CB-9)) Carriers (CA-2) to (CA-23) and (CB-1) to (CB-8) were each prepared by the same method as carrier (CA-1), except for the following changes. Specifically, the types of coating resin solutions shown in Tables 2 to 4 were used in amounts that would result in the solid contents shown in Tables 2 to 4. Barium titanate produced by the methods shown in Tables 2 to 4 and having the number-average primary particle diameters shown in Tables 2 to 4 was used in the amounts shown in Tables 2 to 4. The types of carbon black shown in Tables 2 to 4 were used in the amounts shown in Tables 2 to 4. Carrier cores having the volume median diameter and saturation magnetization shown in Tables 2 to 4 were used. For carrier (CB-9), no coating layer was formed, and carrier cores having the volume median diameter and saturation magnetization shown in Table 4 were used as carrier particles.

[0106] Details of the coating resin solutions and carbon black shown in Tables 2 to 4 will be described later in the explanation of the terms in Tables 2 to 4. The barium titanates used were those shown below, which were produced by the methods shown in Tables 2 to 4 and had the number-average primary particle diameters shown in Tables 2 to 4. The carrier cores having the volume median diameters and saturation magnetizations shown in Tables 2 to 4 were all manganese ferrite cores manufactured by DOWA IP Creation Co., Ltd. The carrier cores used to prepare carriers (CA-1) to (CA-23) and (CB-1) to (CB-9) all had a retentivity of 8 (unit: Oe, i.e., A / m 10 3 / 4π). Barium titanate (manufacturing method: hydrothermal synthesis, number-average primary particle size: 102 nm): "BT-01" manufactured by Sakai Chemical Industry Co., Ltd. Barium titanate (manufacturing method: hydrothermal synthesis, number-average primary particle size: 304 nm): "BT-03" manufactured by Sakai Chemical Industry Co., Ltd. Barium titanate (manufacturing method: hydrothermal synthesis, number-average primary particle size: 495 nm): "BT-05" manufactured by Sakai Chemical Industry Co., Ltd. Barium titanate (manufacturing method: hydrothermal synthesis, number average primary particle size: 76 nm): particle size adjusted product manufactured by Sakai Chemical Industry Co., Ltd. Barium titanate (manufacturing method: hydrothermal synthesis, number-average primary particle size: 687 nm): "BT-07" manufactured by Sakai Chemical Industry Co., Ltd. Barium titanate (manufacturing method: oxalate method, number average primary particle size: 304 nm): 0.3 μm product of "Palceram BT" manufactured by Nippon Chemical Industry Co., Ltd.

[0107] <Preparation of resin particles> Resin particles (R1) to (R6) to be used as external additives for toner were synthesized by the following method.

[0108] (Synthesis of resin particles (R1)) A glass reaction vessel equipped with a thermometer (thermocouple), a stirrer, a reflux condenser, and a nitrogen gas inlet tube was placed in an 80°C water bath. 300 parts by mass of ion-exchanged water and 1 part by mass of di-tert-butyl peroxide were added to the reaction vessel to obtain a solution. While maintaining the resulting solution at 80°C and stirring, 0.2 parts by mass of ammonium persulfate and 60 parts by mass of a monomer mixture were added dropwise to the solution over 1 hour under a nitrogen gas atmosphere. The monomer mixture was a mixture of 10 mol% styrene, 40 mol% butyl methacrylate, and 50 mol% divinylbenzene. The contents of the reaction vessel were then polymerized while stirring. The polymerization reaction conditions were a reaction temperature of 100°C, a reaction time of 3 hours, and a stirring speed of 1400 rpm. The emulsion solution obtained by the reaction was dried to obtain resin particles (R1). The number-average primary particle diameter of the resin particles (R1) was 30 nm.

[0109] (Synthesis of resin particles (R2) to (R6)) Resin particles (R2) to (R6) were synthesized by the same method as for synthesizing resin particles (R1), except that the reaction time and stirring speed of the polymerization reaction were changed to change the number average primary particle diameter from 30 nm to the values ​​shown in Tables 8 to 10. The reaction time and stirring speed were set with reference to the method for adjusting the number average primary particle diameter of resin particles described in the embodiment.

[0110] <Synthesis of amorphous polyester resin (PS1)> An amorphous polyester resin (PS1) for use as a binder resin for toner base particles was synthesized by the following method. First, a reaction vessel equipped with a thermometer (thermocouple), a dehydration tube, a nitrogen inlet tube, and a stirring device (stirring blade) was placed in an oil bath. 1575 g of BPA-PO (bisphenol A propylene oxide adduct), 163 g of BPA-EO (bisphenol A ethylene oxide adduct), 377 g of fumaric acid, and 4 g of catalyst (dibutyltin oxide) were added to the reaction vessel. A nitrogen atmosphere was then created inside the reaction vessel, and the temperature inside the reaction vessel was raised to 220°C using an oil bath while stirring the contents. Under the nitrogen atmosphere and at 220°C, the contents of the reaction vessel were polymerized for 8 hours while distilling off by-product water. The pressure inside the reaction vessel was then reduced, and the contents of the reaction solution were polymerized for an additional hour under a reduced pressure (pressure: 60 mmHg) at 220°C. Next, the temperature inside the reaction vessel was lowered to 210°C, and then 336 g of trimellitic anhydride was added to the reaction vessel. The contents of the reaction vessel were then reacted under reduced pressure (pressure: 60 mmHg) at a temperature of 210°C. The reaction time was adjusted so that the physical properties of the reaction product, amorphous polyester resin (PS1), would be as follows. The reaction product was then removed from the reaction vessel and cooled, yielding an amorphous polyester resin (PS1) with the following physical properties. Note that the obtained polyester resin (PS1) was determined to be amorphous because no clear endothermic peak was observed in the endothermic curve measured using a differential scanning calorimeter, and a clear melting point could not be measured.

[0111] (Physical properties of amorphous polyester resin (PS1)) Softening point (Tm): 100℃ Glass transition temperature (Tg): 50℃ Mass average molecular weight (Mw): 30,000 Acid value: 15mgKOH / g Hydroxyl value: 30 mg KOH / g

[0112] <Toner Preparation> Toners (TA-1) to (TA-23) and (TB-1) to (TB-9) were prepared. The compositions of these toners are shown in Tables 8 to 10 described below. The toners (TA-1) to (TA-23) and (TB-1) to (TB-9) were used to prepare developers (A-1) to (A-23) and (B-1) to (B-9), respectively. To facilitate understanding, toners having the same composition are shown with different toner numbers corresponding to the developer numbers in Tables 8 to 10.

[0113] (Preparation of Toner (TA-1)) Using an FM mixer ("FM-10B" manufactured by Nippon Coke and Engineering Co., Ltd.), 100 parts by mass of binder resin, 4 parts by mass of colorant, 1 part by mass of charge control agent, and 5 parts by mass of release agent were mixed to obtain a mixture. The amorphous polyester resin (PS1) obtained in the above "Synthesis of Amorphous Polyester Resin (PS1)" was used as the binder resin. Copper phthalocyanine blue pigment (CI Pigment Blue 15:3) was used as the colorant. A quaternary ammonium salt ("BONTRON (registered trademark) P-51" manufactured by Orient Chemical Industries Co., Ltd.) was used as the charge control agent. Carnauba wax ("Special Carnauba Wax No. 1" manufactured by Kato Yoko Co., Ltd.) was used as the release agent. The obtained mixture was melt-kneaded using a twin-screw extruder ("PCM-30" manufactured by Ikegai Corporation) to obtain a melt-kneaded product. The melt-kneading was carried out at a set temperature of 120°C, a rotation speed of 150 rpm, and a throughput of 5 kg / hour. The melt-kneaded mixture was pulverized using a mechanical pulverizer (Turbo Mill, manufactured by Freund Turbo Corporation) to obtain a pulverized product. The pulverized product was then classified using a classifier (Elbow Jet, manufactured by Nittetsu Mining Co., Ltd.). This resulted in powdered toner base particles with a volume median diameter of 6.8 μm.

[0114] 100.0 parts by mass of toner base particles, 1.5 parts by mass of silica particles, and 0.4 parts by mass of resin particles (R1) were mixed for 5 minutes at 4,000 rpm using an FM mixer ("FM-10B" manufactured by Nippon Coke & Engineering Co., Ltd.). The silica particles used were "AEROSIL (registered trademark) REA90" manufactured by Nippon Aerosil Co., Ltd. (dry silica particles with a surface treatment to impart positive charging properties, number-average primary particle diameter of 20 nm). The resulting mixture was sieved using a 200-mesh sieve (openings of 75 μm) to obtain toner (TA-1).

[0115] (Preparation of Toners (TA-2) to (TA-23) and (TB-1) to (TB-9)) Toners (TA-2) to (TA-23), (TB-1) to (TB-6), and (TB-8) to (TB-9) were each prepared by the same method as for preparing toner (TA-1), except that the types of resin particles shown in Tables 8 to 10 were used in the amounts shown in Tables 8 to 10. Toner (TB-7) was prepared by the same method as for preparing toner (TA-1), except that no resin particles were used.

[0116] <Preparation of Developer> Using a shaker mixer (Turbler (registered trademark) Mixer T2F manufactured by Willy & Bachofen (WAB)), 6 parts by mass of toner and 100 parts by mass of carrier were mixed for 30 minutes to obtain a developer with a toner concentration of 6% by mass. The toners and carriers shown in Tables 8 to 10 were used to prepare the developers. For example, the toner (TA-1) and carrier (CA-1) shown in the "Developer (A-1)" column of Table 8 were used to prepare developer (A-1).

[0117] <Measurement of saturation magnetization> The saturation magnetization of the carrier core was measured using a high-sensitivity vibrating sample magnetometer ("VSM-P7" manufactured by Toei Kogyo Co., Ltd.) under the condition of an external magnetic field of 3000 (unit: Oe). The measurement results are shown in Tables 2 to 4.

[0118] <Volume Median Diameter Measurement> The volume median diameter (ie, median diameter) of the carrier core was measured using a laser diffraction / scattering particle size distribution analyzer (LA-950 manufactured by Horiba, Ltd.) The measurement results are shown in Tables 2 to 4.

[0119] <Measurement of number average primary particle size> The number-average primary particle diameters of barium titanate particles, silica particles, and resin particles were measured using a scanning electron microscope (field-emission scanning electron microscope, "JSM-7600F" manufactured by JEOL Ltd.). In measuring the number-average primary particle diameter, the circle-equivalent diameters (Heywood diameter: the diameter of a circle having the same area as the projected area of ​​a primary particle) of 100 primary particles were measured, and the number-average value was calculated. The measurement results of the number-average primary particle diameter of barium titanate particles are shown in Tables 2 to 4. The measurement results of the number-average primary particle diameters of silica particles and resin particles are shown in Tables 8 to 10.

[0120] <Measurement of membrane mass per unit area> First, the true specific gravity of the carrier core (unit: g / cm 3 ) was measured using a dry automatic density meter (Micromeritics' "AccuPyc II 1340 Series," accessories: multi-volume kit, measurement principle: dry density measurement by constant volume expansion method). From the true specific gravity of the carrier core measured in this manner, the volume median diameter of the carrier core measured in the above <Measurement of volume median diameter>, and the coating layer / core ratios shown in Tables 2 to 4, the membrane mass per unit area was calculated according to formulas (2) and (9B) described in the embodiment. The calculated membrane mass per unit area is shown in Tables 5 to 7.

[0121] For example, the method for calculating the unit area film mass of carrier (CA-1) was as follows. As shown in Table 2, the volume median diameter of the carrier core of carrier (CA-1) was 20.3 μm, and the coating layer / core ratio was 3.9 mass %. The true specific gravity s2 of the carrier core measured by the above method was 5 g / cm. 3 From equation (2), r = (volume median diameter × 10 -6 ) / 2=(20.3×10 -6 ) / 2=10.15×10 -6and calculated. Next, from Equation (9B), E = (coat layer / core ratio) × r × s2 × 10 4 / 3 = 3.9 × (10.15 × 10 -6 ) × 5 × 10 4 / 3 ≈ 0.66 was calculated. The calculation result was rounded to the third decimal place. Thus, the mass per unit area of the carrier (CA-1) was 0.66.

[0122] <Measurement of the mobility (FR) of carrier particles> In accordance with JIS (Japanese Industrial Standards) Z 2502:2012 "Metal powder - Method for measuring flowability", the flowability of the carrier particles was measured. The measurement environment was a temperature of 22°C and a relative humidity of 50%RH. Specifically, a metal funnel (cone angle: 60°, orifice diameter: 2.5 mm, orifice length: 3.2 mm) was prepared. With the orifice of the funnel blocked, 50 g of the sample (carrier particles) was placed in the funnel. Subsequently, when the orifice of the funnel was opened, the stopwatch was started simultaneously (measurement start), and the stopwatch was stopped at the moment when the last carrier particle left the orifice (measurement end). The time measured by the stopwatch from the start of measurement to the end of measurement (the discharge time of the carrier particles) was taken as the flowability of the carrier particles (unit: seconds / 50 g). The measurement results are shown in Tables 5 to 7.

[0123] <Measurement of the apparent density (AD) of carrier particles> In accordance with JIS (Japanese Industrial Standards) Z 2504:2012 "Metal powder - Method for measuring apparent density", the apparent density of the carrier particles (unit: g / cm 3 ) was measured. The measurement environment was a temperature of 22°C and a relative humidity of 50%RH.

[0124] <Measurement of BET specific surface area> Using an automatic specific surface area measuring device ("Macsorb model 1208" manufactured by Mount Tech Co., Ltd.), nitrogen was adsorbed onto the surface of the samples (each carrier), and the BET specific surface area of the samples was measured by the flow method (BET one-point method). Specifically, the mass of the empty cell was measured. Next, 9 g of the sample was filled into the cell so as not to adhere to the inner wall surface of the cell. While adjusting the nitrogen flow rate to 25 mL / min using a flow meter, nitrogen was passed through the cell filled with the sample at a temperature of 45°C for 30 minutes. In this way, the sample was degassed. Then, after cooling the cell for 2 minutes, measurement was started using an automatic specific surface area measuring device. After the start of measurement, the cell was immersed in the liquid nitrogen in the Dewar flask to perform the adsorption process, and then the cell was returned from the Dewar flask to the atmosphere to perform the desorption process. The actual surface area of the sample was measured by automatic measurement during the desorption process. Based on the measured value, from the formula "specific surface area = actual surface area of the sample / mass of the sample", the BET specific surface area of the sample (unit: m 2 / g) was determined. The measurement results are shown in Tables 5 to 7.

[0125] <Measurement of shape factor> First, the volume median diameter of the carrier particles was measured using a laser diffraction / scattering particle size distribution measuring device ("LA-950" manufactured by Horiba, Ltd.), and the measured value was taken as the actually measured carrier particle diameter (unit: μm).

[0126] Next, the true specific gravity of the carrier particles (unit: g / cm 3 ) was measured using a dry automatic densitometer ("AccuPyc II 1340 series" manufactured by Micromeritics, accessory: multi-bore kit, measurement principle: dry density measurement by constant volume expansion method). From the measured true specific gravity of the carrier particles and the BET specific surface area of the carrier particles measured in the above <Measurement of BET specific surface area>, according to the formula "calculated carrier particle diameter = 6 / (true specific gravity of the carrier particles × BET specific surface area of the carrier particles)", the calculated carrier particle diameter (unit: μm) was determined.

[0127] Next, the shape factor of the carrier particles was calculated from the formula: "Shape factor of carrier particle = measured carrier particle diameter / calculated carrier particle diameter." The calculated shape factors of the carrier particles are shown in Tables 5 to 7.

[0128] <Calculation of value (FR × AD) and value (FR × AD / shape factor)> The value (FR×AD) was calculated from the flowability measured in the above <Measurement of Carrier Particle Flowability (FR)>, the apparent density measured in the above <Measurement of Carrier Particle Apparent Density (AD)>, and the shape factor measured in the above <Measurement of Shape Factor> according to the formula "FR×AD", and the value (FR×AD / Shape Factor) was calculated according to the formula "FR×AD / Shape Factor". The calculation results are shown in Tables 5 to 7.

[0129] <Evaluation> For the evaluation of each developer, an evaluation machine (prototype machine manufactured by Kyocera Document Solutions Inc.) having the following configuration was used: The developer was placed in the cyan developing device of the evaluation machine, and replenishment toner was placed in the cyan toner container.

[0130] (Configuration of evaluation machine) Paper feed speed: 55 sheets / min Surface shape of developer carrier: Knurled shape Outer diameter of developer carrier: 20mm Developer carrier recesses: 80 rows of recesses in the circumferential direction Regulating blade: Magnetic blade made of SUS430 Regulator blade thickness: 1.5mm Developer transport volume: 345g / m 2 Developing roller speed / drum speed: 1.8 (trail at opposing position) Distance between photoconductor and developing roller: 0.375mm Photoconductor: Amorphous silicon photoconductor Bias applied to developing roller: AC bias, duty 50%, square wave, Vpp 1125v, frequency 10KHz Toner charging polarity: positive charging

[0131] Using the evaluation machine, durability printing was carried out by printing A4 size images on 100,000 sheets of paper under the printing conditions shown in Table 11 (more specifically, conditions of printing environment, printing mode, and image printing rate).

[0132] The printing environment shown in Table 11 was as follows: LL environment: Temperature 10°C and relative humidity 15%RH NN environment: Temperature 22°C and relative humidity 50%RH HH environment: Temperature 32.5℃ and relative humidity 80%RH

[0133] The printing modes shown in Table 11 were as follows: Continuous mode: A mode in which printing is performed continuously on paper. 5-sheet intermittent mode: This mode repeats a printing pattern of printing on 5 sheets of paper and then pausing for 12 seconds.

[0134] The images with the printing rates shown in Table 11 were as follows: 2%: Character image with 2% coverage 5%: 5% print rate of text image 20%: Band image with 20% print rate 50%: Band image with 50% print rate

[0135] In Table 11, "Start" indicates the number of sheets of 100,000 sheets from which printing under the corresponding printing conditions began. Furthermore, "Timing of image evaluation" indicates the number of sheets of 100,000 sheets from which printing was completed before image evaluation. When changing the printing environment, the evaluation machine was left undisturbed in the new printing environment for 24 hours before endurance printing was resumed. The evaluation results for each developer are shown in Tables 8 to 10.

[0136] (Method for evaluating image density) First, a solid image (A4 size) was printed on one sheet of paper using the evaluation machine in an NN environment, and the printed paper was designated as the first evaluation paper. Next, the above-mentioned durability printing was performed. During the durability printing, a solid image (A4 size) was printed on one sheet of paper using the evaluation machine at the image evaluation timing shown in Table 11, and the printed paper was designated as the second evaluation paper. The image densities of the solid images printed on the first and second evaluation papers were measured using a reflection densitometer (X-Rite "RD-19I"). The image density reduction was then calculated using the formula "image density reduction = image density of solid image printed on first evaluation paper - image density of solid image printed on second evaluation paper." The image density reduction was calculated for all second evaluation papers, and the maximum of the calculated image density reductions was designated as the evaluation value. The evaluation value was evaluated according to the following criteria. A smaller image density reduction indicates that an image with the desired image density can be stably formed. A grade of A, B, or C was judged as a pass, and a grade of D was judged as a fail.

[0137] (Image density evaluation criteria) A: The decrease in image density is less than 0.2. B: The reduction in image density is 0.2 or more and less than 0.3. C: The reduction in image density is 0.3 or more and less than 0.4. D (poor): The reduction in image density is 0.4 or more.

[0138] (Method for evaluating image density differences within a formed image) The above-described durability printing was performed. During the durability printing, a solid image (A4 size) was printed on one sheet of paper using the evaluation machine at the image evaluation timing shown in Table 11, and the printed paper was used as the evaluation paper. Using a reflection densitometer (X-Rite "RD-19I"), the image density of each of the top, bottom, left, and right edge regions of the solid image printed on the evaluation paper was measured. The highest and lowest image densities (maximum and minimum image densities) among the four measured image densities were used to calculate the image density difference within one formed image according to the formula "image density difference = maximum image density - minimum image density." The image density difference was calculated for all evaluation papers, and the maximum of the calculated image density differences was used as the evaluation value. The evaluation values ​​were evaluated according to the following criteria. Grades A and B were considered acceptable, and grades C were considered unacceptable.

[0139] (Evaluation criteria for image density difference within a formed image) A: The image density difference is 0.00 or more and less than 0.20. B: The image density difference is 0.20 or more and less than 0.40. C (poor): The image density difference is 0.40 or more.

[0140] (Method for evaluating fogging resistance) The above-mentioned durability printing was performed. During the durability printing, a blank image (A4 size) was printed on one sheet of paper using the evaluation machine at the timing of image evaluation shown in Table 11, and the printed paper was used as the evaluation paper. The reflection density of the blank area of ​​the evaluation paper was measured using a white light meter (Tokyo Denshoku Co., Ltd., "TC-6DS"). The fog density was then calculated based on the formula "Fog density = Reflection density of blank area - Reflection density of unprinted paper." The fog density was calculated for all evaluation papers, and the maximum value of the calculated fog densities was used as the evaluation value. The evaluation values ​​were evaluated according to the following criteria. A rating of A or B was determined as passing, and a rating of C was determined as failing.

[0141] (Evaluation Criteria for Fog Resistance) A: The fog density is less than 0.010. B: The fog density is 0.010 or more and less than 0.020. C (poor): The fog density is 0.020 or more.

[0142] (Method for evaluating suppression of carrier development) The above-mentioned durability printing was carried out. During the durability printing, a blank image (A4 size) was printed on one sheet of paper using the evaluation machine at the timing of image evaluation shown in Table 11, and the printed paper was used as the evaluation paper. The blank image printed on the evaluation paper was observed using a 25x magnification loupe. The area of ​​the blank image was 10 cm 2 The number of carrier particles present in the area was counted and defined as the number of carrier particles per unit area. For a blank image printed on one evaluation paper, the number of carrier particles present in each of 10 areas (specifically, 3 areas on the upstream side in the paper feed direction, 4 areas near the center, and 3 areas on the downstream side) was counted. Then, the number of developed carrier particles (unit: particles / cm) was calculated from the formula "Number of developed carrier particles = total number of carrier particles present in 10 areas / total area of ​​10 areas = total number of carrier particles present in 10 areas / 100". 2 ) was obtained. The number of developed carrier particles was calculated for all evaluation papers, and the maximum value of the calculated number of developed carrier particles was used as the evaluation value. The evaluation values ​​were evaluated according to the following criteria. A, B, and C were judged as passing, and D was judged as failing.

[0143] (Evaluation criteria for suppression of carrier development) A: The number of carrier particles developed is 0.1 particles / cm 2 is less than. B: Number of carrier development particles is 0.1 particles / cm 2 More than 0.3 pieces / cm 2 is less than. C: Number of carrier development particles is 0.3 particles / cm 2 More than 1.0 pieces / cm 2 is less than. D (Poor): The number of carrier particles developed is 1.0 particles / cm 2 That's all.

[0144] (Method for evaluating inhibition of skin texture deterioration) First, in an NN environment, a halftone image (a band image with a printing rate of 50%) was printed on one sheet of paper using the evaluation machine, and the printed paper was designated as the first evaluation paper. Next, the above-mentioned durability printing was performed. During the durability printing, a halftone image (a band image with a printing rate of 50%) was printed on one sheet of paper using the evaluation machine at the timing of the image evaluation shown in Table 11, and the printed paper was designated as the second evaluation paper. The texture of the halftone images printed on the first and second evaluation papers was observed with the naked eye. The degree of deterioration of the texture of the halftone image printed on the second evaluation paper was then confirmed compared to the texture of the halftone image printed on the first evaluation paper. Of all the second evaluation papers, the evaluation paper with the worst deterioration in the texture of the halftone image was evaluated according to the following criteria. Grades A, B, and C were determined as passing, and grade D was determined as failing.

[0145] (Evaluation criteria for suppression of skin texture deterioration) A: There is absolutely no deterioration in texture. B: There is some deterioration in texture. C: Texture has deteriorated, but the deterioration is not serious enough to cause any problems in practical use. D (poor): The texture has deteriorated, and the deterioration is so noticeable that it is problematic for practical use.

[0146] (Method for evaluating suppression of image defects caused by cleaning defects) The above-mentioned durability printing was carried out. During the durability printing, a character image with a printing rate of 5% was printed on one sheet of paper using the evaluation machine at the timing of image evaluation shown in Table 11, and the printed paper was used as the evaluation paper. The character image printed on the evaluation paper was observed with the naked eye to confirm whether or not there was any image defect due to poor cleaning. Note that image defect due to poor cleaning is an image defect in which thin streaks parallel to the paper feed direction appear. Of all the evaluation papers, the evaluation paper that had the most image defects due to poor cleaning was evaluated according to the following criteria. Grades A, B, and C were judged as passing, and grade D was judged as failing.

[0147] (Evaluation criteria for suppressing image defects caused by cleaning defects) A: No image defects caused by poor cleaning occurred. B: A small amount of image defects due to poor cleaning occurred. C: Image defects due to poor cleaning have occurred, but the image defects are not serious enough to cause problems in practical use. D (poor): Image defects have occurred due to poor cleaning, and the image defects are so noticeable that they cause problems in practical use.

[0148] Next, the meanings of the terms used in the following Tables 2 to 10 will be explained. The meanings of the terms in Tables 2 to 10 are as follows. Core: Carrier core D 50 :Volume median diameter Solid content: The solid content of the coating resin. The solid content of the coating resin is calculated using the formula: [Solid content of coating resin (unit: parts by mass)] = [Amount of silicone resin solution (unit: parts by mass)] x [Solid content concentration of silicone resin solution (unit: mass %)] / 100. Resin / Core: Resin / Core ratio (unit: mass %). The resin / core ratio is calculated from the formula: [Resin / Core ratio (unit: mass %)] = 100 × [mass of coating resin (unit: parts by mass)] / [mass of carrier core (unit: parts by mass)] = 100 × [solid content of silicone resin solution (unit: parts by mass)] / [mass of carrier core (unit: parts by mass)]. ·wt%: mass% ·Part: Mass part BT: Barium titanate particles Manufacturing method: Manufacturing method of barium titanate particles ·Hydrothermal: Hydrothermal synthesis method Oxalate: Oxalate method Quantity ratio in the "BT" column: The content of barium titanate particles per 100 parts by mass of coating resin Diameter: Number average primary particle diameter CB: Carbon black particles Quantity ratio in the "CB" column: The amount of carbon black particles per 100 parts by mass of coating resin Coat layer / core: Coat layer / core ratio. The coat layer / core ratio is calculated from the formula: "[Coat layer / core ratio (unit: mass %)] = 100 × [mass of coat layer (unit: parts by mass)] / [mass of carrier core (unit: parts by mass)]] = 100 × [mass of solids in coating solution (unit: parts by mass)] / [mass of carrier core (unit: parts by mass)]] = 100 × {[solids content of silicone resin solution (unit: parts by mass)] + [mass of barium titanate (unit: parts by mass)] + [mass of carbon black (unit: parts by mass)]} / [mass of carrier core (unit: parts by mass)]." KR-255: Silicone resin solution ("KR-255" manufactured by Shin-Etsu Chemical Co., Ltd., solid content: methylphenyl silicone resin, solid content concentration: 50% by mass) KR-301: Silicone resin solution ("KR-301" manufactured by Shin-Etsu Chemical Co., Ltd., solid content: methylphenyl silicone resin, solid content concentration: 40% by mass) ES-1001N: Silicone resin solution ("ES-1001N" manufactured by Shin-Etsu Chemical Co., Ltd., solid content: epoxy resin-modified silicone resin, solid content concentration: 45% by mass) EC: Carbon black (Lion Specialty Chemicals Corporation "Ketjenblack EC-300J", conductive carbon black, DBP oil absorption: 360 cm 3 / 100g, BET specific surface area: 1270m 2 / g, number average primary particle size: 39.5 nm) MA: Carbon black (Mitsubishi Chemical Corporation "Mitsubishi (registered trademark) Carbon Black MA100"), DBP oil absorption: 100 cm 3 / 100g, BET specific surface area: 110m 2 / g, number average primary particle size: 24 nm) RE: Carbon black (Cabot Corporation "REGAL (registered trademark) 400") FR: Flow rate of carrier particles AD: Apparent density of carrier particles BET: BET specific surface area of ​​carrier particles FR×AD: Value (FR×AD) FR×AD / shape factor: value (FR×AD / shape factor) FD:Fog density Fog: Evaluation of fog resistance Carrier development: Evaluation of carrier development suppression Texture: Evaluation of suppression of skin texture deterioration Image density: Evaluation of image density Cleaning: Evaluation of suppression of image defects caused by cleaning defects Density difference: Evaluation of image density difference within the formed image Not measured: An attempt was made to form an image on a recording medium using a developer, but the toner contained in the developer did not allow an image worthy of evaluation to be formed, so the physical properties of the carrier contained in the developer were not measured. Image formation impossible: An attempt was made to form an image on a recording medium using a developer, but the developer was not developed sufficiently and an image could not be formed, making it impossible to carry out the evaluation. -: The relevant ingredient is not used or there is no relevant value

[0149] [Table 2]

[0150] [Table 3]

[0151] [Table 4]

[0152] [Table 5]

[0153] [Table 6]

[0154] [Table 7]

[0155] [Table 8]

[0156] [Table 9]

[0157] [Table 10]

[0158] [Table 11]

[0159] As shown in Table 3, the content of barium titanate particles in the carrier particles contained in the carrier (CB-1) of developer (B-1) was less than 5 parts by mass per 100 parts by mass of the coating resin. As shown in Table 9, the evaluation results of the fogging resistance and the image density of developer (B-1) were both poor, and it was determined to be unacceptable.

[0160] As shown in Table 3, the content of barium titanate particles in the carrier particles contained in the carrier (CB-2) of developer (B-2) exceeded 45 parts by mass per 100 parts by mass of the coating resin. As shown in Table 9, the evaluation results for the fogging resistance of developer (B-2) were poor, and it was determined to be unacceptable.

[0161] As shown in Table 4, the number average primary particle diameter of the barium titanate particles contained in the carrier (CB-3) of developer (B-3) was less than 100 nm. As shown in Table 10, the evaluation result of the fogging resistance of developer (B-3) was poor and it was judged to be unacceptable.

[0162] As shown in Table 4, the number average primary particle diameter of the barium titanate particles contained in the carrier (CB-4) of developer (B-4) exceeded 500 nm. As shown in Table 10, the evaluation results for developer (B-4) in terms of suppressing the occurrence of image defects due to poor cleaning were poor, and it was determined to be unacceptable.

[0163] As shown in Table 7, the shape factor of the carrier particles contained in the carrier (CB-5) of developer (B-5) exceeded 85.0. As shown in Table 10, the evaluation result of the fogging resistance of developer (B-5) was poor and it was judged to be unacceptable.

[0164] As shown in Table 7, the shape factor of the carrier particles contained in the carrier (CB-6) of developer (B-6) was less than 34.0. As shown in Table 10, the evaluation results of the fogging resistance of developer (B-6) and the evaluation results of the image density difference in the formed image were both poor, and developer (B-6) was judged to be unacceptable.

[0165] As shown in Table 10, the external additive particles contained in the toner particles contained in the toner (TB-7) of developer (B-7) did not contain resin particles containing a crosslinked resin. As shown in Table 10, the evaluation result of the fogging resistance of developer (B-7) was poor and it was judged to be unacceptable.

[0166] As shown in Table 4, the coating layer / core ratio of the carrier particles contained in the carrier (CB-8) of developer (B-8) exceeded 4.9% by mass. As shown in Table 10, the evaluation results for the fogging resistance of developer (B-8) were poor, and it was determined to be unacceptable.

[0167] As shown in Table 4, the carrier particles contained in the carrier (CB-9) of developer (B-9) did not have a coating layer, and the coating layer / core ratio was 0.0 mass%. As shown in Table 10, an attempt was made to form an image on a recording medium using developer (B-9), but the toner contained in developer (B-9) prevented the formation of an image worthy of evaluation. Therefore, evaluation of developer (B-9) was not possible.

[0168] As shown in Tables 2 to 10, developers (A-1) to (A-23) had the following configurations. Specifically, the external additive particles of the toner particles contained resin particles, and the resin particles contained a crosslinked resin. The coating layer of the carrier particles contained a coating resin and barium titanate particles, and the coating resin contained a silicone resin. The number-average primary particle diameter of the barium titanate particles was 100 nm or more and 500 nm or less. The content of the barium titanate particles was 5 parts by mass or more and 45 parts by mass or less per 100 parts by mass of the coating resin. The coating layer / core ratio was more than 0.0 mass% and 4.9 mass% or less. The shape factor of the carrier particles was 34.0 or more and 85.0% or less. As shown in Tables 8 to 10, the evaluation results of developers (A-1) to (A-23) for fogging resistance, image density, image density difference within the formed image, and suppression of image defects due to poor cleaning were all judged to be acceptable. In addition to these evaluation results, as shown in Tables 8 to 10, the evaluation results for developers (A-1) to (A-23) in terms of suppressing deterioration in texture and suppressing occurrence of carrier development were also judged to be acceptable.

[0169] From the above, it has been shown that the developers of the present invention, including developers (A-1) to (A-23), have excellent fogging resistance, can stably form images of desired image density, have small image density differences within the formed images, and are less likely to cause image defects due to poor cleaning. [Industrial Applicability]

[0170] The developer according to the present invention can be used to form images in, for example, a copier, a printer, or a multifunction machine.

Claims

1. a toner including toner particles and a carrier including carrier particles; the toner particles have toner base particles and external additive particles provided on the surfaces of the toner base particles, the external additive particles include resin particles, the resin particles contain a crosslinked resin having a repeating unit derived from a crosslinking agent, The carrier particles have a carrier core and a coating layer that covers the surface of the carrier core, the coating layer contains a coating resin, barium titanate particles, and carbon black particles; the coating resin includes a silicone resin, The barium titanate particles have a number average primary particle diameter of 100 nm or more and 500 nm or less, The content of the barium titanate particles is 5 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coating resin, the content of the carbon black particles is 1 part by mass or more and 10 parts by mass or less relative to 100 parts by mass of the coating resin, a ratio of the mass of the coating layer to the mass of the carrier core is 0.1% by mass or more and 4.9% by mass or less; The two-component developer, wherein the shape factor of the carrier particles is 34.0 or more and 85.0 or less.

2. The two-component developer according to claim 1 , wherein the carrier particles satisfy formula (1). 0.73≦FR×AD / X≦2.10 (1) (In the formula (1), FR represents the fluidity of the carrier particles, AD represents the apparent density of the carrier particles, and X represents the shape factor of the carrier particles.)

3. The mass of the coating layer is 0.10 g / m per unit area of ​​the surface of the carrier core when the carrier core is assumed to be a perfect sphere. 2 1.80g / m or more 2 2. The two-component developer of claim 1, wherein:

4. 2. The two-component developer according to claim 1, wherein the toner base particles contain at least one selected from the group consisting of a binder resin, a colorant, a charge control agent, and a release agent, and further contain carbon black particles, the two-component developer being free of a nonionic surfactant.

5. 2. The two-component developer according to claim 1, wherein the content of the barium titanate particles is 25 parts by mass or more and 45 parts by mass or less with respect to 100 parts by mass of the coating resin.

6. 2. The two-component developer according to claim 1, wherein the saturation magnetization of the carrier core is 65 emu / g or more and 90 emu / g or less.

7. 2. The two-component developer according to claim 1, wherein the volume median diameter of the carrier core is 20.0 μm or more and 60.0 μm or less.

8. 2. The two-component developer according to claim 1, wherein a ratio of the mass of the coating resin to the mass of the carrier core is 0.1% by mass or more and 4.0% by mass or less.

9. The BET specific surface area of ​​the carrier particles is 0.6 m 2 / g or more 4.7m 2 The two-component developer according to claim 1 , wherein the average particle size is 1 / g or less.

10. 2. The two-component developer according to claim 1, wherein the resin particles have a number average primary particle diameter of 30 nm or more and 120 nm or less.

11. 2. The two-component developer according to claim 1, wherein the crosslinked resin contained in the resin particles is a styrene-acrylic resin, and the repeating unit derived from the crosslinking agent is a repeating unit derived from a compound having two or more vinyl groups.

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