Toner for developing electrostatic images, electrostatic image developer, toner cartridge, process cartridge, and image forming apparatus

Abstract

To provide a toner for electrostatic charge image development that can prevent the occurrence of a phenomenon (fogging) in which toner is attached to a non-image part and fixed when images are continuously formed in a high temperature and high humidity environment.SOLUTION: A toner for electrostatic charge image development has toner particles having an average circularity Cc of 0.98 or more, and an external additive including monodisperse silica particles having an average primary particle diameter of 20 nm or more and 70 nm or less and titanic acid compound particles having an average primary particle diameter of 20 nm or more and 70 or less. The absolute value of the difference in the average primary particle diameter between the monodisperse silica particles and the titanic acid compound particles is 25 nm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a toner for developing an electrostatic image, an electrostatic image developer, a toner cartridge, a process cartridge, and an image forming apparatus. [Background technology]

[0002] Patent Document 1 describes a toner containing toner particles and an external additive, the external additive containing inorganic fine particles A and silica fine particles B, the inorganic fine particles A being fine particles of titanate containing a Group 2 element, the number average particle diameter (D1) of the primary particles of the titanate fine particles being DA, the DA being 10 nm or more and 60 nm or less, the number average particle diameter (D1) of the primary particles of the silica fine particles B being DB, the DB being 40 nm or more and 300 nm or less, the compaction density of the silica fine particles B being 0.75 or more and 0.93 or less, the ratio of the number average particle diameter of the primary particles of the titanate fine particles to the silica fine particles being DA, the number average particle diameter (D1) of the primary particles of the silica fine particles being DB, the compaction density of the silica fine particles being 0.75 or more and 0.93 or less, A toner characterized in that the ratio of the number average particle diameter of the primary particles of B (DB / DA) is 1.0 or more and 20.0 or less, and the effective Ti ratio calculated by the following formula is 0.20 or more and 0.60 or less, where Tie is the value of the Ti element derived from the titanate fine particles measured by observing the surface of the toner by X-ray photoelectron spectroscopy (ESCA), Sie is the value of the Si element derived from the silica fine particles B, Tix is ​​the value of the Ti element derived from the titanate fine particles measured by observing the toner by X-ray fluorescence elemental analysis (XRF), and Six is ​​the value of the Si element derived from the silica fine particles B. The effective Ti ratio is proposed as (Tie / (Sie+Tie)) / (Tix / (Six+Tix)). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-109416 Summary of the Invention [Problem to be solved by the invention]

[0004] The object of the present invention is to provide a toner for developing electrostatic images, which comprises toner particles having an average circularity Cc of 0.98 or more and an external additive containing monodispersed silica particles and titanic acid compound particles, and which can suppress the occurrence of a phenomenon in which toner adheres to and is fixed in non-image areas (fog) when continuously forming images in a high-temperature, high-humidity environment, compared to when the average primary particle size of the monodispersed silica particles is less than 20 nm or more than 70 nm, when the average primary particle size of the titanic acid compound particles is less than 20 nm or more than 70 nm, or when the absolute value of the difference in average primary particle size between the monodispersed silica particles and the titanic acid compound particles exceeds 25 nm. [Means for solving the problem]

[0005] The above problems are solved by the following means: <1> toner particles having an average circularity Cc of 0.98 or more; and an external additive containing monodispersed silica particles having an average primary particle size of 20 nm or more and 70 nm or less and titanic acid compound particles having an average primary particle size of 20 nm or more and 70 nm or less, The toner for developing electrostatic images, wherein the absolute value of the difference in average primary particle size between the monodisperse silica particles and the titanic acid compound particles is 25 nm or less. <2> the average circularity Ca of the monodispersed silica particles is more than 0.86 but less than 0.94; The titanate compound particles have an average circularity Cb of more than 0.78 and less than 0.94. <1> 2. The toner for developing electrostatic images according to claim 1. <3> The average circularity Ca of the monodispersed silica particles is greater than the average circularity Cb of the titanate compound particles. <2> 2. The toner for developing electrostatic images according to claim 1. <4> The monodisperse silica particles have a specific gravity Da of 1.1 or more and 1.3 or less, The specific gravity Db of the titanic acid compound particles is greater than the specific gravity Da of the monodispersed silica particles. <1> ~ <3> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <5> The specific gravity Db of the titanic acid compound particles is 4.0 or more and 6.5 or less. <4> 2. The toner for developing electrostatic images according to claim 1. <6> The titanic acid compound particles are alkaline earth metal titanate particles. <1> ~ <5> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <7> The titanate compound particles contain a dopant. <1> ~ <6> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <8> The dopant is at least one of lanthanum and silica. <7> 2. The toner for developing electrostatic images according to claim 1. <9> The content of the titanic acid compound particles relative to the content of the monodispersed silica particles is in a mass ratio of 0.1 to 10. <1> ~ <8> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <10> The aforementioned <1> ~ <9> 10. An electrostatic image developer comprising the toner for developing electrostatic images according to any one of claims 1 to 9. <11> The aforementioned <1> ~ <9> The toner for developing electrostatic images according to any one of the above items is contained in the container. A toner cartridge that is detachably attached to an image forming device. <12> The aforementioned <10> and a developing means for developing an electrostatic image formed on the surface of an image carrier into a toner image by using the electrostatic image developer, A process cartridge is detachably mounted in an image forming apparatus. <13> an image carrier; a charging means for charging the surface of the image carrier; an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier; The aforementioned <10> a developing means for developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer; a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; An image forming apparatus comprising: [Effects of the Invention]

[0006] <1> According to the invention, there is provided a toner for developing electrostatic images, which comprises toner particles having an average circularity Cc of 0.98 or more and an external additive containing monodisperse silica particles and titanate compound particles, and which can suppress the occurrence of a phenomenon in which toner adheres to and is fixed in non-image areas (fog) when images are continuously formed in a high-temperature, high-humidity environment, compared to when the average primary particle size of the monodisperse silica particles is less than 20 nm or more than 70 nm, when the average primary particle size of the titanate compound particles is less than 20 nm or more than 70 nm, or when the absolute value of the difference in average primary particle size between the monodisperse silica particles and the titanate compound particles exceeds 25 nm. <2> According to the invention, there is provided a toner for developing electrostatic images that can suppress the occurrence of a phenomenon (fog) in which toner adheres to and is fixed in non-image areas when images are continuously formed under a high-temperature, high-humidity environment, compared to when the average circularity Ca of the monodispersed silica particles is 0.86 or less or 0.94 or more, or when the average circularity Cb of the titanate compound particles is 0.78 or less or 0.94 or more. <3> According to the invention, there is provided a toner for developing electrostatic images that can suppress the occurrence of a phenomenon (fog) in which toner adheres to and is fixed in non-image areas when images are continuously formed under a high-temperature, high-humidity environment, compared to when the average circularity Ca of the monodispersed silica particles is smaller than the average circularity Cb of the titanate compound particles. <4> According to the invention, there is provided a toner for developing electrostatic images that can suppress the occurrence of a phenomenon (fog) in which toner adheres to and is fixed in non-image areas when images are continuously formed under a high-temperature, high-humidity environment, compared to when the specific gravity Da of the monodispersed silica particles is less than 1.1 or exceeds 1.3, or when the specific gravity Db of the titanate compound particles is smaller than the specific gravity Da of the monodispersed silica particles. <5> According to the present invention, there is provided a toner for developing electrostatic images that can suppress the occurrence of a phenomenon (fog) in which toner adheres to and fixes to non-image areas when images are continuously formed in a high-temperature, high-humidity environment, compared to when the specific gravity Db of the titanate compound particles is less than 4.0 or more than 6.5.

[0007] <6> According to the present invention, a toner for developing electrostatic images is provided that can suppress the occurrence of a phenomenon (fog) in which toner adheres to and is fixed in non-image areas when images are continuously formed in a high-temperature, high-humidity environment, compared to when the titanate compound particles are not alkaline earth metal titanate particles (e.g., alkali metal titanate particles). <7> According to the present invention, there is provided a toner for developing electrostatic images that can suppress the occurrence of a phenomenon (fog) in which toner adheres to and is fixed in non-image areas when images are continuously formed in a high-temperature, high-humidity environment, compared to when the titanate compound particles do not contain a dopant. <8> According to the invention, there is provided a toner for developing electrostatic images that can suppress the occurrence of a phenomenon (fog) in which toner adheres to and fixes to non-image areas when images are continuously formed in a high-temperature, high-humidity environment, compared to when the dopant is not contained. <9> According to the invention, there is provided a toner for developing electrostatic images that can suppress the occurrence of a phenomenon (fog) in which toner adheres to and is fixed in non-image areas when images are continuously formed under a high-temperature, high-humidity environment, compared to when the content of the titanate compound particles relative to the content of the monodispersed silica particles is less than 0.1 or more than 10 in mass ratio. <10> , <11> , <12> , or <13> According to the invention, there is provided an electrostatic image developer, a toner cartridge, a process cartridge, or an image forming apparatus including an electrostatic image developing toner that can suppress the occurrence of a phenomenon in which toner adheres to and is fixed in non-image areas (fog) when continuously forming images in a high-temperature, high-humidity environment, compared to when the average primary particle size of the monodispersed silica particles is less than 20 nm or more than 70 nm, when the average primary particle size of the titanic acid compound particles is less than 20 nm or more than 70 nm, or when the absolute value of the difference in average primary particle size between the monodispersed silica particles and the titanic acid compound particles exceeds 25 nm. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a process cartridge according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0010] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[0011] <Toner for developing electrostatic images> The electrostatic image developing toner according to this embodiment (hereinafter, the electrostatic image developing toner may also be referred to as "toner") contains toner particles having an average circularity Cc of 0.98 or more, and an external additive containing monodispersed silica particles having an average primary particle size of 20 nm or more and 70 nm or less and titanic acid compound particles having an average primary particle size of 20 nm or more and 70 nm or less. The absolute value of the difference in average primary particle size between the monodispersed silica particles and the titanic acid compound particles is 25 nm or less.

[0012] The toner according to the present embodiment, due to the above-described configuration, suppresses the occurrence of the phenomenon (fog) in which toner adheres to and fixes to non-image areas when images are continuously formed under a high-temperature and high-humidity environment. The reason for this is presumed to be as follows.

[0013] In recent years, there has been an increasing demand for energy saving, high image quality, etc. in electrophotographic image formation. In order to meet these demands, toners for developing electrostatic images having toner particles with a high average circularity (for example, toner particles with an average circularity of more than 0.98; hereinafter, also referred to as spherical toner particles) have been developed. For example, spherical toner particles containing titanate compound particles such as strontium titanate as an external additive are characterized by being less susceptible to changes in humidity, temperature, and the like during image formation. However, titanate compound particles can easily become positively charged by frictional charging, which can make it difficult for the toner to be charged in the developing unit. Therefore, when forming an image in a high-temperature, high-humidity environment, the toner tends to adhere to non-image areas of the image carrier (e.g., photoreceptor) during the development process, which can cause image defects such as fogging. Therefore, spherical toner particles containing titanate compound particles and silica particles as external additives have been developed. Silica particles can easily become negatively charged due to triboelectric charging. Therefore, even if the titanate compound particles become positively charged due to triboelectric charging, the silica particles are negatively charged, so the triboelectric charging of the external additives is reduced throughout the toner. As a result, the toner is easily charged in the developing unit. However, when forming images under high-temperature, high-humidity environments, the toner can cause the silica particles of the external additive to become embedded, the external additive to become liberated, or the external additive to aggregate. As a result, image defects such as fogging cannot be suppressed when forming images under high-temperature, high-humidity environments.

[0014] The toner according to this embodiment contains an external additive containing monodispersed silica particles having an average primary particle size of 20 to 70 nm and titanic acid compound particles having an average primary particle size of 20 to 70 nm. By setting the average primary particle size of the monodispersed silica particles and titanic acid compound particles to 20 nm or more, the external additive is prevented from being embedded in the toner particles. Furthermore, by setting the average primary particle size of the monodispersed silica particles and titanic acid compound particles to 70 nm or less, the external additive is prevented from being released from the toner particles. Furthermore, in the toner according to this embodiment, the absolute value of the difference in average primary particle size between the monodispersed silica particles and the titanic acid compound particles is 25 nm or less. By setting the particle size of the external additive within this range, the monodispersed silica particles and the titanic acid compound particles are easily dispersed uniformly on the surface of the toner particles. This is because, macroscopically, the particles are positively and negatively charged and have similar particle sizes, so there is no repulsion or attraction between the particles, resulting in an appropriate charge balance. As a result, aggregation of the external additive is suppressed.

[0015] From the above, it is presumed that the toner according to this embodiment suppresses the occurrence of the phenomenon (fog) in which toner adheres to and fixes to non-image areas when images are continuously formed in a high-temperature, high-humidity environment.

[0016] (toner particles) The toner particles are composed of, for example, a binder resin, and, if necessary, a colorant, a release agent, and other additives.

[0017] -Binder resin- As the binder resin, a vinyl resin is used. Examples of the vinyl resin include styrene polymerizable monomers (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic polymerizable monomers (e.g., (meth)acrylic acid, methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated Examples of the vinyl resin include a homopolymer of a polymerizable monomer such as a nitrile polymerizable monomer (e.g., acrylonitrile, methacrylonitrile, etc.), a vinyl ether polymerizable monomer (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), a vinyl ketone polymerizable monomer (vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), or an olefin polymerizable monomer (e.g., ethylene, propylene, butadiene, etc.), or a copolymer of two or more of these polymerizable monomers. As the binder resin, in addition to vinyl resins, for example, non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosins, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these may also be used in combination. However, the vinyl resin should account for 50% by mass or more (preferably 80% by mass or more, more preferably 90% by mass or more) of the total binder resins. These binder resins may be used alone or in combination of two or more.

[0018] Among these, a suitable vinyl resin is styrene (meth)acrylic resin. Styrene (meth)acrylic resin is a copolymer obtained by copolymerizing at least a styrene-based polymerizable monomer (a polymerizable monomer having a styrene skeleton) and a (meth)acrylic-based polymerizable monomer (a polymerizable monomer having a (meth)acryloyl skeleton). The term "(meth)acrylic" includes both "acrylic" and "methacrylic."

[0019] Examples of styrene-based polymerizable monomers include styrene, alkyl-substituted styrenes (e.g., α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), halogen-substituted styrenes (e.g., 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), vinylnaphthalene, etc. The styrene-based polymerizable monomers may be used alone or in combination of two or more. Of these, styrene is preferred as the styrene-based monomer in terms of ease of reaction, ease of reaction control, and availability.

[0020] Examples of (meth)acrylic polymerizable monomers include (meth)acrylic acid and (meth)acrylic acid esters. Examples of (meth)acrylic acid esters include (meth)acrylic acid alkyl esters (e.g., methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-lauryl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate, n-octadecyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, amyl (meth)acrylate, and (meth) Examples of the (meth)acrylic acid polymerizable monomer include neopentyl acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, etc.), aryl (meth)acrylate esters (e.g., phenyl (meth)acrylate, biphenyl (meth)acrylate, diphenylethyl (meth)acrylate, t-butylphenyl (meth)acrylate, terphenyl (meth)acrylate, etc.), dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, β-carboxyethyl (meth)acrylate, and (meth)acrylamide. The (meth)acrylic acid polymerizable monomer may be used alone or in combination of two or more.

[0021] The copolymerization ratio of the styrene polymerizable monomer to the (meth)acrylic polymerizable monomer (mass basis, styrene polymerizable monomer / (meth)acrylic polymerizable monomer) is preferably, for example, 85 / 15 to 70 / 30.

[0022] The styrene (meth)acrylic resin may have a crosslinked structure. Examples of the styrene (meth)acrylic resin having a crosslinked structure include a crosslinked product obtained by copolymerizing at least a styrene-based polymerizable monomer, a (meth)acrylic acid-based polymerizable monomer, and a crosslinkable monomer.

[0023] Examples of the crosslinkable monomer include bifunctional or higher functional crosslinking agents. Examples of bifunctional crosslinking agents include divinylbenzene, divinylnaphthalene, di(meth)acrylate compounds (e.g., diethylene glycol di(meth)acrylate, methylene bis(meth)acrylamide, decanediol diacrylate, glycidyl (meth)acrylate, etc.), polyester-type di(meth)acrylate, 2-([1'-methylpropylideneamino]carboxyamino)ethyl methacrylate, etc. Examples of polyfunctional crosslinking agents include tri(meth)acrylate compounds (e.g., pentaerythritol tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, etc.), tetra(meth)acrylate compounds (e.g., tetramethylolmethane tetra(meth)acrylate, oligoester (meth)acrylate, etc.), 2,2-bis(4-methacryloxy, polyethoxyphenyl)propane, diallyl phthalate, triallyl cyanurate, triallyl isocyanurate, triallyl trimellitate, diaryl chlorendate, etc.

[0024] The copolymerization ratio of the crosslinkable monomer to the total monomers (based on mass, crosslinkable monomer / total monomers) may be, for example, 2 / 1000 to 30 / 1000.

[0025] The glass transition temperature (Tg) of the styrene (meth)acrylic resin is, for example, from 50°C to 75°C, preferably from 55°C to 65°C, and more preferably from 57°C to 60°C, from the viewpoint of fixability. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), more specifically, from the "extrapolated glass transition onset temperature" described in JIS K 7121-1987 "Method for measuring transition temperatures of plastics."

[0026] The weight average molecular weight of the styrene (meth)acrylic resin is, for example, 30,000 or more and 200,000 or less, preferably 40,000 or more and 100,000 or less, and more preferably 50,000 or more and 80,000 or less, from the viewpoint of storage stability. The weight-average molecular weight is measured by gel permeation chromatography (GPC). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC measuring device, a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent. The weight-average molecular weight is calculated from the measurement results using a molecular weight calibration curve created with monodisperse polystyrene standard samples.

[0027] The content of the binder resin is, for example, preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass, based on the total mass of the toner particles.

[0028] -Coloring agent- Examples of colorants include carbon black, chrome yellow, Hansa Yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Balkan orange, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, ultramarine blue, and the like. Examples of the dye include various pigments such as phosphorus blue, chalco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate, and various dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, and thiazole-based dyes. The colorant may be used alone or in combination of two or more kinds.

[0029] The colorant may be surface-treated as needed, or may be used in combination with a dispersant. Furthermore, a plurality of colorants may be used in combination.

[0030] The content of the colorant is, for example, preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 15% by mass or less, based on the total mass of the toner particles.

[0031] -Mold release agent- Examples of release agents include hydrocarbon waxes, natural waxes such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral / petroleum waxes such as montan wax, and ester waxes such as fatty acid esters and montanic acid esters, but are not limited thereto.

[0032] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) by using the "melting peak temperature" as described in the method for determining the melting temperature in JIS K 7121-1987 "Method for measuring transition temperatures of plastics."

[0033] The content of the release agent is, for example, preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less, based on the total mass of the toner particles.

[0034] -Other additives- Examples of other additives include well-known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

[0035] -Characteristics of toner particles, etc.- The toner particles may be toner particles of a single layer structure, or may be toner particles of a so-called core-shell structure composed of a core part (core particle) and a coating layer (shell layer) that coats the core part. Here, the toner particles having a core-shell structure may be composed of, for example, a core containing a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer containing the binder resin.

[0036] The volume average particle size (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less.

[0037] The various average particle sizes and particle size distribution indices of the toner particles are measured using a Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolyte is measured using an ISOTON-II (manufactured by Beckman Coulter). For the measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5% aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant, and this is then added to 100 ml to 150 ml of the electrolyte. The electrolyte solution containing the suspended sample is dispersed for 1 minute using an ultrasonic disperser, and the particle size distribution of particles with a particle size range of 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. The number of particles sampled is 50,000. Based on the particle size distribution measured, cumulative distributions of volume and number are drawn for each divided particle size range (channel) from the smallest diameter side, and the particle size at 16% of the cumulative total is defined as the volume particle size D16v, the number particle size D16p, the particle size at 50% of the cumulative total as the volume average particle size D50v, the cumulative number average particle size D50p, and the particle size at 84% of the cumulative total as the volume particle size D84v and the number particle size D84p. Using these, the volumetric particle size distribution index (GSDv) is (D84v / D16v) 1 / 2 , the number particle size distribution index (GSDp) is (D84p / D16p) 1 / 2 It is calculated as:

[0038] The average circularity Cc of the toner particles is 0.98 or more. The average circularity Cc of toner particles is calculated by (circular equivalent perimeter) / (perimeter) [(perimeter of a circle having the same projected area as the particle image) / (perimeter of the particle projected image)]. Specifically, this value is measured by the following method. First, the toner particles to be measured are sucked and collected, forming a flat flow, and a still image of the particles is captured by instantaneously activating a strobe light, and the particle image is analyzed using a flow-type particle image analyzer (FPIA-3000 manufactured by Sysmex Corporation).The number of samples to be sampled when calculating the average circularity is 3,500. When the toner contains external additives, the toner (developer) to be measured is dispersed in water containing a surfactant, and then ultrasonic treatment is performed to obtain toner particles from which the external additives have been removed.

[0039] (external additives) The external additive contains monodisperse silica particles having an average primary particle size of 20 nm or more and 70 nm or less, and titanic acid compound particles having an average primary particle size of 20 nm or more and 70 nm or less.

[0040] -Monodispersed silica particles- The monodisperse silica particles may be particles containing silica, i.e., SiO2, as the main component. In this specification, the term "main component" refers to a component that accounts for 50% by mass or more of the total mass of a mixture of multiple components. In this specification, the term "monodisperse" refers to a particle size distribution index shown below of 1.25 or less.

[0041] The monodisperse silica particles have an average primary particle size of 20 nm or more and 70 nm or less. From the viewpoint of further suppressing the occurrence of fogging when images are continuously formed under a high-temperature and high-humidity environment by further suppressing the embedding of the monodispersed silica particles in the toner particles and the liberation of the monodispersed silica particles from the toner particles, the average primary particle size of the monodispersed silica particles is preferably 25 nm or more and 70 nm or less, more preferably 30 nm or more and 65 nm or less, and even more preferably 35 nm or more and 65 nm or less.

[0042] Monodisperse silica particles have a particle size distribution index of 1.25 or less. From the viewpoint of further suppressing aggregation of the monodisperse silica particles and further suppressing the occurrence of fogging when images are continuously formed under a high-temperature and high-humidity environment, the particle size distribution index of the monodisperse silica particles is preferably 1.05 or more and 1.25 or less, more preferably 1.05 or more and 1.2 or less, and even more preferably 1.05 or more and 1.15 or less.

[0043] Here, the average primary particle size and particle size distribution index of the monodisperse silica particles are measured by the following method. The silica particles to be measured are dispersed in resin particles (e.g., polyester resin, weight-average molecular weight Mw = 500,000) with a volume average particle size of 100 μm. The resulting primary particles are observed using a scanning electron microscope (SEM) (S-4100, manufactured by Hitachi, Ltd.) and images are taken (40,000 magnification). 200 silica particles to be measured are randomly selected, and the image information is imported into an image analyzer (Winroof). The area of ​​each particle is measured by image analysis, and the equivalent circle diameter is calculated from this area value. The 50% diameter of the volume-based cumulative frequency of the obtained equivalent circle diameter is taken as the average primary particle size. Then, the 16% diameter (D16) and 84% diameter (D84) in the cumulative frequency of the obtained circle equivalent diameter on a volume basis are calculated. The square root of the calculated 84% diameter (D84) divided by the 16% diameter (D16) is used as the particle size distribution index (= (D84 / D16) 1 / 2 The magnification of the electron microscope is adjusted so that 10 to 50 silica particles to be measured are visible in one field of view, and the circle-equivalent diameter of the primary particle is determined by combining the observations of multiple fields of view.

[0044] The surfaces of the monodisperse silica particles are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the monodisperse silica particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, but examples thereof include known organosilicon compounds having an alkyl group (e.g., a methyl group, an ethyl group, a propyl group, a butyl group, etc.). Specific examples thereof include silane-based coupling agents such as silazane compounds (e.g., silane compounds such as methyltrimethoxysilane, dimethyldimethoxysilane, trimethylchlorosilane, and trimethylmethoxysilane; hexamethyldisilazane; tetramethyldisilazane, etc.). Other examples of the hydrophobic treatment agent include silicone oil, titanate-based coupling agents, and aluminum-based coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is, for example, 1 part by mass or more and 200 parts by mass or less per 100 parts by mass of the monodisperse silica particles.

[0045] The content of the monodisperse silica particles is preferably from 0.01 to 10% by mass, more preferably from 0.05 to 5% by mass, and even more preferably from 0.1 to 2.5% by mass, based on the mass of the toner particles.

[0046] -Production of monodispersed silica particles- The monodisperse silica particles are preferably produced by a wet method. In this embodiment, the "wet method" is distinguished from the gas phase method, and is a production method in which sodium silicate is neutralized with a mineral acid or an alkoxysilane is hydrolyzed. Among the wet methods, it is preferable to produce monodisperse silica particles by a sol-gel method.

[0047] Hereinafter, the method for producing monodisperse silica particles used in this embodiment will be described using the sol-gel method as an example. However, the method for producing monodisperse silica particles is not limited to the sol-gel method. The particle size of the monodispersed silica particles can be freely controlled by the weight ratio of alkoxysilane, ammonia, alcohol and water in the hydrolysis and polycondensation steps of the sol-gel method, the reaction temperature, the stirring speed and the supply speed.

[0048] The method for producing monodisperse silica particles by the sol-gel method will be specifically described below. That is, tetramethoxysilane is added dropwise to the mixture in the presence of water and alcohol, using aqueous ammonia as a catalyst, while heating and stirring. Next, the solvent is removed from the silica sol suspension obtained by the reaction, and the mixture is dried to obtain the desired monodisperse silica particles. Thereafter, the obtained monodisperse silica particles are subjected to a hydrophobic treatment, if necessary.

[0049] When monodisperse silica particles are produced by the sol-gel method, the surfaces of the silica particles may be simultaneously subjected to a hydrophobic treatment. In this case, as described above, the silica sol suspension obtained by the reaction is centrifuged to separate it into wet silica gel, alcohol, and ammonia water, and then a solvent is added to the wet silica gel to make it into a silica sol again, and a hydrophobic treatment agent is added to hydrophobize the surfaces of the silica particles. Next, the solvent is removed from this hydrophobic treated silica sol and it is dried to obtain the desired monodisperse silica particles. The monodisperse silica particles thus obtained may be subjected to a hydrophobic treatment again.

[0050] The hydrophobization treatment for the silica particle surfaces may be carried out by a dry method such as a spray-drying method in which a hydrophobization treatment agent or a solution containing a hydrophobization treatment agent is sprayed onto silica particles suspended in a gas phase, a wet method in which silica particles are immersed in a solution containing a hydrophobization treatment agent and then dried, or a mixing method in which a hydrophobization treatment agent and silica particles are mixed in a mixer. After the hydrophobic treatment of the silica particle surfaces, a step of washing the silica particles with a solvent to remove the remaining hydrophobic treatment agent and low-boiling point residues may be added.

[0051] -Titanium oxide compound particles- The titanate compound particles may be particles containing a titanate compound as a main component. Titanate compounds are called metatitanates and are salts formed from, for example, titanium oxide and other metal oxides or other metal carbonates.

[0052] The titanic acid compound particles are preferably alkaline earth metal titanate particles. Here, the alkaline earth metal titanate is a salt represented by the general formula RTiO3 (wherein R is one or more alkaline earth metals).

[0053] By using alkaline earth metal titanate particles as titanate compound particles, the speed at which saturated charge is reached is high, and therefore the occurrence of fogging when images are continuously formed in a high-temperature, high-humidity environment is further suppressed. Specific examples of titanate compound particles include particles of strontium titanate (SrTiO3), calcium titanate (CaTiO3), magnesium titanate (MgTiO3), barium titanate (BaTiO3), zinc titanate (PbTiO3), and the like. From the viewpoint of further suppressing the occurrence of fogging when continuously forming images under a high-temperature, high-humidity environment, it is preferable that the titanate compound particles are at least one type selected from the group consisting of strontium titanate particles, calcium titanate particles, and magnesium titanate particles. These titanic acid compound particles may be used alone or in combination of two or more kinds.

[0054] The titanate compound particles have an average primary particle size of 20 nm or more and 70 nm or less. In order to further suppress the occurrence of fogging when continuously forming images in a high-temperature, high-humidity environment by further suppressing the embedding of the titanate compound particles in the toner particles and their liberation from the toner particles, the average primary particle size of the titanate compound particles is preferably 25 nm or more and 70 nm or less, more preferably 30 nm or more and 65 nm or less, and even more preferably 35 nm or more and 55 nm or less.

[0055] Here, the calculation of the average primary particle size of the titanate compound particles is the same as the calculation of the average primary particle size of the monodisperse silica particles.

[0056] The titanate compound particles preferably contain a dopant. By incorporating a dopant, the titanate compound particles have a reduced crystallinity and a moderately angular shape. This, for example, makes it easier for the titanate compound particles to have an average circularity Cb in the range of more than 0.78 and less than 0.94. This makes it easier for the titanate compound particles to be fixed to the toner particle surface. This further reduces the liberation of the titanate compound particles from the toner particles. From the above, it is presumed that the occurrence of fogging is further reduced when continuously forming images in a high-temperature, high-humidity environment.

[0057] The dopant for the titanate compound particles is preferably a metal element that, when ionized, has an ionic radius that can be incorporated into the crystal structure that constitutes the titanate compound particles. From this perspective, the dopant for the titanate compound particles is preferably a metal element that, when ionized, has an ionic radius of 40 pm or more and 200 pm or less, more preferably a metal element that has an ionic radius of 60 pm or more and 150 pm or less.

[0058] Specific examples of dopants for titanate compound particles include lanthanoids, silica, aluminum, magnesium, calcium, barium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, niobium, molybdenum, ruthenium, palladium, indium, antimony, tantalum, tungsten, rhenium, iridium, platinum, bismuth, yttrium, zirconium, niobium, silver, and tin. Lanthanoids are preferably lanthanum and cerium. Among these, at least one of lanthanum and silica is preferred, from the viewpoint of having an ionic radius that is easily incorporated into the crystal structure constituting the strontium titanate particles and from the viewpoint of easily forming the titanate compound into a moderately angular shape.

[0059] In order to give the titanate compound a moderately angular shape, the amount of dopant in the titanate compound particles is preferably in the range of 0.1 mol % to 20 mol % relative to the alkaline earth metal atoms contained in the titanate compound particles, more preferably in the range of 0.1 mol % to 15 mol %, and even more preferably in the range of 0.1 mol % to 10 mol %.

[0060] The surface of the particles A may be subjected to a hydrophobic treatment. Examples of the hydrophobic treatment agent include known surface treatment agents, and specific examples include silane coupling agents and silicone oils. Examples of silane coupling agents include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, benzyldimethylchlorosilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-butyltrimethoxysilane, n-hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltriacetoxysilane. Examples of silicone oils include dimethylpolysiloxane, methylhydrogenpolysiloxane, and methylphenylpolysiloxane.

[0061] The mass ratio of the content of titanate compound particles to the content of monodispersed silica particles is preferably 0.1 or more and 10 or less, more preferably 0.3 or more and 8 or less, and even more preferably 0.4 or more and 5 or less.

[0062] The content of the titanic acid compound particles is preferably from 0.01 to 5% by mass, more preferably from 0.05 to 3% by mass, and even more preferably from 0.1 to 2% by mass, based on the mass of the toner particles.

[0063] -Production of titanic acid compound particles- The method for producing the titanic acid compound particles is not particularly limited, but from the viewpoint of controlling the particle size and shape, a wet production method is preferred. The wet method for producing titanate compound particles is, for example, a method of reacting a mixture of metal element sources contained in a titanate compound while adding an alkaline aqueous solution, followed by acid treatment. In this production method, the particle size of the titanate compound particles can be controlled by the mixing ratio of the metal element sources, the concentration of the metal element sources at the beginning of the reaction, the temperature and addition rate of the alkaline aqueous solution, etc.

[0064] Here, examples of the source of the metal element contained in the titanic acid compound include mineral acid peptized products of hydrolyzed titanium compounds, and nitrates and chlorides containing metal elements other than titanium. Specifically, when the titanic acid compound particles are alkaline earth metal titanate particles, examples of the suitable materials include mineral acid peptized products of hydrolyzed titanium compounds and nitrates and chlorides containing alkaline earth metal elements. More specifically, when the titanate compound particles are strontium titanate particles, examples of the source include a mineral acid peptized product of a hydrolyzed titanium compound (hereinafter also referred to as a titanium source), strontium nitrate, strontium chloride, etc. (hereinafter also referred to as a strontium source).

[0065] Hereinafter, a method for producing strontium titanate particles will be described as an example of a method for producing titanate compound particles, but the present invention is not limited to this. The mixing ratio of the titanium oxide source to the strontium source is preferably an SrO / TiO molar ratio of 0.9 to 1.4, more preferably 1.05 to 1.20. The concentration of the titanium oxide source in terms of TiO at the start of the reaction is preferably 0.05 to 1.3 mol / L, more preferably 0.5 to 1.0 mol / L.

[0066] It is preferable to add a dopant source to a mixed solution of a titanium oxide source and a strontium source. Examples of the dopant source include oxides of metals other than titanium and strontium. The metal oxide as the dopant source is added as a solution dissolved in, for example, nitric acid, hydrochloric acid, sulfuric acid, or the like. The amount of the dopant source added is preferably an amount such that the amount of the dopant metal is 0.1 mol or more and 10 mol or less, and more preferably an amount such that the amount is 0.5 mol or more and 10 mol or less, per 100 mol of strontium.

[0067] The dopant source may be added when the alkaline aqueous solution is added to the mixed solution of the titanium oxide source and the strontium source. In this case, the metal oxide of the dopant source may be added as a solution dissolved in nitric acid, hydrochloric acid, or sulfuric acid.

[0068] The alkaline aqueous solution is preferably a sodium hydroxide aqueous solution. The higher the temperature at which the alkaline aqueous solution is added, the more likely it is that strontium titanate particles with good crystallinity will be obtained. In this embodiment, the temperature is preferably in the range of 60°C or higher and 100°C or lower. The slower the addition rate of the alkaline aqueous solution, the larger the particle size of the resulting strontium titanate particles, and the faster the addition rate, the smaller the particle size of the resulting strontium titanate particles. The addition rate of the alkaline aqueous solution is, for example, from 0.001 equivalents / h to 1.2 equivalents / h, and preferably from 0.002 equivalents / h to 1.1 equivalents / h, relative to the amount of the raw material.

[0069] After the addition of the alkaline aqueous solution, an acid treatment is carried out to remove unreacted strontium source, for example, by adjusting the pH of the reaction solution to 2.5 to 7.0, more preferably 4.5 to 6.0, using hydrochloric acid. After the acid treatment, the reaction liquid is subjected to solid-liquid separation, and the solid content is dried to obtain strontium titanate particles. By adjusting the conditions for drying the solid content, the moisture content of the strontium titanate particles can be controlled. To be controlled. When the surfaces of the strontium titanate particles are subjected to a hydrophobic treatment, the moisture content may be controlled by adjusting the conditions of the drying treatment after the hydrophobic treatment. Here, preferred drying conditions for controlling the moisture content are, for example, a drying temperature of 90°C or higher and 300°C or lower (preferably 100°C or higher and 150°C or lower) and a drying time of 1 hour or higher and 15 hours or lower (preferably 5 hours or higher and 10 hours or lower).

[0070] Hydrophobic treatment The hydrophobic treatment of the surfaces of strontium titanate particles is carried out, for example, by preparing a treatment liquid by mixing a hydrophobic treatment agent with a solvent, mixing the strontium titanate particles with the treatment liquid under stirring, and continuing to stir. After the surface treatment, a drying treatment is carried out in order to remove the solvent from the treatment solution.

[0071] Examples of the hydrophobic treatment agent include those already mentioned above. The solvent used to prepare the treatment liquid is preferably an alcohol (for example, methanol, ethanol, propanol, or butanol), or a hydrocarbon (for example, benzene, toluene, normal hexane, or normal heptane).

[0072] In the treatment liquid, the concentration of the hydrophobic treatment agent is preferably from 1% to 50% by mass, more preferably from 5% to 40% by mass, and even more preferably from 10% to 30% by mass.

[0073] As described above, the amount of the hydrophobic treatment agent used in the hydrophobic treatment is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, even more preferably 5% by mass or more and 30% by mass or less, and particularly preferably 10% by mass or more and 25% by mass or less, relative to the mass of the strontium titanate particles.

[0074] -Other external additives- The toner used in this embodiment may contain other particles other than the monodisperse silica particles and titanic acid compound particles described above as other external additives. The other particles include inorganic particles other than silica particles and titanic acid compound particles. Examples of inorganic particles include Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, K2O·(TiO2)n, Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, and MgSO4.

[0075] The surfaces of inorganic particles as other external additives are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment 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 inorganic particles.

[0076] Other examples of particles include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning agents (for example, particles of fluorine-based high molecular weight materials), and the like.

[0077] When other external additives are contained, the content of the other external additives is preferably 1% by mass or more and 99% by mass or less, more preferably 10% by mass or more and 90% by mass or less, and even more preferably 20% by mass or more and 85% by mass or less, relative to the total content of the external additives.

[0078] (Physical properties of external additives) -Absolute value of difference in average primary particle size- The absolute value of the difference in average primary particle size between the monodispersed silica particles and the titanic acid compound particles is 25 nm or less. From the viewpoint of further suppressing the occurrence of fogging when continuously forming images under a high-temperature, high-humidity environment, the absolute value of the difference in average primary particle size between the monodispersed silica particles and the titanate compound particles is preferably 0 nm or more and 18 nm or less, more preferably 2 nm or more and 16 nm or less, and even more preferably 4 nm or more and 14 nm or less.

[0079] -Average circularity Ca and average circularity Cb- It is preferred that the average circularity Ca of the monodispersed silica particles is more than 0.86 and less than 0.94, and the average circularity Cb of the titanate compound particles is more than 0.78 and less than 0.94.

[0080] By adjusting the average circularity of the monodispersed silica particles and titanate compound particles to fall within the above range, the occurrence of fogging can be further suppressed when images are continuously formed under a high-temperature, high-humidity environment. The reason for this is presumed to be as follows. By setting the numerical ranges of the average circularity Ca of the monodispersed silica particles and the average circularity Cb of the titanate compound particles within the above ranges, both the monodispersed silica particles and the titanate compound particles tend to have moderately irregular shapes. As a result, the monodispersed silica particles and the titanate compound particles are less likely to roll on the toner particles, further suppressing the aggregation of the external additives. From the above, it is presumed that by setting the numerical ranges of the average circularity Ca of the monodispersed silica particles and the average circularity Cb of the titanate compound particles within the above ranges, the occurrence of fogging when continuously forming images under a high-temperature, high-humidity environment is further suppressed.

[0081] From the viewpoint of further suppressing the occurrence of fogging when images are continuously formed under a high-temperature and high-humidity environment, the average circularity Ca of the monodispersed silica particles is more preferably 0.87 or more and 0.93 or less, and even more preferably 0.88 or more and 0.92 or less. From the viewpoint of further suppressing the occurrence of fogging when continuously forming images under a high-temperature, high-humidity environment, the average circularity Cb of the titanate compound particles is more preferably 0.79 or more and 0.93 or less, and even more preferably 0.80 or more and 0.92 or less.

[0082] The average circularity Ca of the monodispersed silica particles is preferably greater than the average circularity Cb of the titanate compound particles. By satisfying the above relationship between the average circularity Ca of the monodispersed silica particles and the average circularity Cb of the titanate compound particles, the titanate compound particles tend to have a more angular shape than the monodispersed silica particles. As a result, the titanate compound particles are more easily fixed to the toner particle surface than the monodispersed silica particles. On the other hand, the monodispersed silica particles tend to have a more rounded shape than the titanate compound particles. As a result, the monodispersed silica particles roll more easily on the toner particle surface than the titanate compound particles, and are more likely to adhere to areas of the toner particle surface where no titanate compound particles are present. Therefore, the monodispersed silica particles and titanate compound particles are less likely to be liberated from the toner particles, and the aggregation of external additives is more suppressed. Based on the above, it is presumed that by making the average circularity Ca of the monodispersed silica particles greater than the average circularity Cb of the titanate compound particles, the occurrence of fogging during continuous image formation under high-temperature, high-humidity environments is more suppressed.

[0083] Here, the average circularity of the monodispersed silica particles and titanic acid compound particles is measured by the following method. The particles to be measured (monodispersed silica particles or titanic acid compound particles) are dispersed in resin particles (e.g., polyester resin, weight-average molecular weight Mw=500,000) with a volume average particle size of 100 μm, and the resulting primary particles are observed with a scanning electron microscope (SEM) (S-4100, manufactured by Hitachi, Ltd.) and images are taken (40,000 magnification). 200 silica particles to be measured are randomly selected, and their image information is imported into an image analyzer (Winroof). The particle size is calculated from the planar image analysis of the obtained primary particles using the following formula: Formula: Circularity = (4π × A) / I 2 [In the formula, I represents the perimeter of the primary particle on the image, and A represents the projected area of ​​the primary particle.] The average circularity of the particles to be measured (monodispersed silica particles or titanic acid compound particles) is obtained as the 50% circularity in the cumulative frequency of the circularities of 200 primary particles obtained by the planar image analysis.

[0084] -Specific gravity of monodispersed silica particles Da and specific gravity of titanate compound particles Db- It is preferable that the specific gravity Da of the monodispersed silica particles is 1.1 or more and 1.3 or less, and the specific gravity Db of the titanate compound particles is greater than the specific gravity Da of the monodispersed silica particles.

[0085] When the specific gravity Da of the monodisperse silica particles and the specific gravity Db of the titanate compound particles satisfy the above relationship, the occurrence of fogging is further suppressed when images are continuously formed under a high-temperature, high-humidity environment. The reason for this is presumed to be as follows. When the specific gravity Db of the titanate compound particles is greater than the specific gravity Da of the monodispersed silica particles, the titanate compound particles tend to preferentially adhere to the toner particle surface when the monodispersed silica particles and titanate compound particles are externally added to the toner particles. As a result, the monodispersed silica particles tend to adhere to areas of the toner particle surface where no titanate compound particles are present. Therefore, aggregation of the monodispersed silica particles and titanate compound particles is further suppressed. Based on the above, it is presumed that by setting the specific gravity of the monodispersed silica particles and titanate compound particles within the above range, the occurrence of fogging during continuous image formation under high-temperature, high-humidity environments can be further suppressed.

[0086] The specific gravity Db of the titanate compound particles is preferably 4.0 or more and 6.5 or less, more preferably 4.1 or more and 5.5 or less, and even more preferably 4.2 or more and 5.0 or less.

[0087] By setting the specific gravity Db of the titanate compound particles within the above range, the adhesion of the titanate compound particles to the toner particle surface is more likely to be improved. As a result, the monodisperse silica particles and titanate compound particles are less likely to be liberated from the toner particles, and the aggregation of external additives is more suppressed. This is thought to further suppress the occurrence of fogging when continuously forming images under a high-temperature, high-humidity environment.

[0088] The specific gravity Da of the monodisperse silica particles and the specific gravity Db of the titanic acid compound particles are measured using a Le Chatelier pycnometer in accordance with JIS K 0061 (2001) as follows. (1) Pour approximately 250 ml of ethyl alcohol into the Le Chatelier pycnometer and adjust so that the meniscus is at the scale. (2) Immerse the pycnometer in a thermostatic water bath, and when the liquid temperature reaches 20.0±0.2°C, accurately read the meniscus position on the pycnometer's scale (with an accuracy of 0.025 ml). (3) Weigh out approximately 100 g of the sample and let its mass be W (g). (4) Place the weighed sample in a density bottle and remove any bubbles. (5) Immerse the pycnometer in a thermostatic water bath, and when the liquid temperature reaches 20.0±0.2°C, accurately read the meniscus position on the pycnometer's scale (with an accuracy of 0.025 ml). (6) Calculate the specific gravity using the following formula. D=W / (L2-L1) ρ=D / 0.9982 In the formula, D is the density of the sample (20°C) (g / cm 3 ), ρ is the specific gravity of the sample (20°C), W is the apparent mass of the sample (g), L1 is the meniscus reading (20°C) (ml) before the sample is placed in the pycnometer, L2 is the meniscus reading (20°C) (ml) after the sample is placed in the pycnometer, and 0.9982 is the density of water at 20°C (g / cm 3 )

[0089] (Toner manufacturing method) Next, a method for producing the toner according to this embodiment will be described. The toner according to this exemplary embodiment is obtained by producing toner particles and then externally adding an external additive to the toner particles.

[0090] The toner particles may be produced by any of a dry production method (for example, a kneading and pulverization method) and a wet production method (for example, an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). The method for producing the toner particles is not particularly limited, and any well-known production method may be used.

[0091] Among these, it is preferable to obtain toner particles by the suspension polymerization method in order to obtain toner particles having an average circularity Cc of 0.98 or more.

[0092] Specifically, for example, when toner particles are produced by a suspension polymerization method, Toner particles are manufactured through a process including a step of preparing a polymerizable monomer composition containing at least a polymerizable monomer that becomes a binder resin by polymerization (polymerizable monomer composition preparation process), a step of mixing the polymerizable monomer composition with an aqueous dispersion medium to prepare a suspension (suspension preparation process), and a step of polymerizing the polymerizable monomer in the suspension to form toner particles (polymerization process).

[0093] Each step will be described in detail below. In the following description, a method for obtaining toner particles containing a colorant and a release agent will be described, but the colorant and the release agent are used as needed. Of course, additives other than the colorant and the release agent may also be used.

[0094] -Polymerizable monomer composition preparation step- In the polymerizable monomer composition preparation step, for example, a polymerizable monomer (a polymerizable monomer containing a crosslinkable monomer as needed) that becomes a binder resin by polymerization, a colorant, and a release agent are mixed, dissolved, or dispersed to prepare a polymerizable monomer composition. In addition to the other additives described above, well-known additives such as an organic solvent and a polymerization initiator may also be mixed, dissolved, or dispersed in the polymerizable monomer composition.

[0095] For preparing the polymerizable monomer composition, a mixer such as a homogenizer, a ball mill, or an ultrasonic disperser is used.

[0096] Examples of the polymerization initiator include well-known polymerization initiators such as organic peroxides (di-t-butyl peroxide, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-hexylperoxy-2-ethylhexanoate, t-butylperoxypivalate, diisopropyl peroxydicarbonate, di-t-butylperoxyisophthalate, and t-butylperoxyisobutyrate), inorganic persulfates (potassium persulfate and ammonium persulfate), and azo compounds (4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide, 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobisisobutyronitrile). The content of the polymerization initiator is preferably 0.1 to 20 parts by mass, more preferably 0.3 to 15 parts by mass, and even more preferably 1.0 to 10 parts by mass, relative to 100 parts by weight of the polymerizable monomer. The polymerization initiator may be added to the polymerizable monomer composition, or may be added to the aqueous medium before suspending the polymerizable monomer composition in the suspension preparation step described below.

[0097] -Suspension preparation process- In the suspension preparation step, for example, the polymerizable monomer composition is mixed with an aqueous medium, and the polymerizable monomer composition is suspended in the aqueous medium to prepare a suspension. That is, droplets of the polymerizable monomer composition are formed in the aqueous medium.

[0098] The suspension is prepared using a mixer such as a homogenizer, a ball mill, or an ultrasonic disperser.

[0099] Here, examples of the aqueous medium include water alone and mixed solvents containing water and an aqueous solvent (for example, lower alcohol, lower ketone, etc.).

[0100] The aqueous medium may contain a dispersion stabilizer. Examples of dispersion stabilizers include organic dispersion stabilizers and inorganic dispersion stabilizers. Examples of organic dispersion stabilizers include surfactants (anionic surfactants, nonionic surfactants, amphoteric surfactants, etc.), aqueous polymer compounds (polyvinyl alcohol, methyl cellulose, gelatin, etc.), and sulfates. Examples of inorganic dispersion stabilizers include phosphates, sulfates (barium sulfate, calcium sulfate, etc.), carbonates (barium carbonate, calcium carbonate, magnesium carbonate, etc.), phosphates (calcium phosphate, etc.), metal oxides (aluminum oxide, titanium oxide, etc.), and metal hydroxides (aluminum hydroxide, magnesium hydroxide, ferric hydroxide, etc.). One type of dispersion stabilizer may be used alone, or two or more types may be used in combination. The content of the dispersion stabilizer is preferably 0.1 parts by mass or more and 20 parts by mass or less, and more preferably 0.2 parts by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the polymerizable monomer.

[0101] -Polymerization process- In the polymerization step, for example, the suspension is heated to polymerize the polymerizable monomer to form toner particles. That is, in the polymerization step, a binder resin is produced by polymerization of the polymerizable monomer in droplets of the polymerizable monomer composition dispersed in the suspension, and toner particles containing the binder resin, a colorant, and a release agent are formed.

[0102] Here, the polymerization temperature of the polymerizable monomer is preferably 50°C or higher, more preferably 60°C or higher and 98°C or higher. The polymerization time of the polymerizable monomer is preferably 1 hour or higher and 20 hours or lower, more preferably 2 hours or higher and 15 hours or lower. The polymerization of the polymerizable monomer is preferably carried out while stirring the suspension.

[0103] Through the above steps, toner particles are obtained. Note that the toner particles formed in the above polymerization step may be used as core particles (cores) to form a shell layer using known methods such as insitu polymerization or phase separation, thereby producing toner particles with a core-shell structure. For example, when forming a shell layer using insitu polymerization, a polymerizable monomer that becomes a binder resin through polymerization (a polymerizable monomer that becomes a resin for forming the shell layer) is added (and a polymerization initiator is added, if necessary) to the aqueous medium in which the core particles obtained through the above polymerization step are dispersed, and polymerized to produce a resin that coats the surface of the core particles, thereby forming a shell layer. This produces toner particles with a core-shell structure in which a shell layer is formed on the surface of the core particles (cores). When a shell layer is formed on the surface of a core particle (core portion), the shell layer may be formed after removing the dispersion stabilizer contained in the aqueous medium in which the core particles are dispersed, or the shell layer may be formed without removing the dispersion stabilizer contained in the aqueous medium in which the core particles are dispersed.

[0104] After the polymerization step is completed, the toner particles formed in the aqueous medium are subjected to a known washing step, a solid-liquid separation step, and a drying step to obtain dried toner particles. In the washing step, in order to remove the dispersion stabilizer, it is preferable to add an acid or an alkali to the aqueous medium in which the toner particles are dispersed. Specifically, for example, if the dispersion stabilizer used is an acid-soluble compound, a known acid is added, and if the dispersion stabilizer used is an alkali-soluble compound, a known alkali is added. The solid-liquid separation step is not particularly limited, but from the viewpoint of productivity, it is preferable to carry out suction filtration, pressure filtration, or the like. There is no particular limitation on the method for the drying step either, but from the viewpoint of productivity, freeze drying, flash drying, fluidized bed drying, vibration-type fluidized bed drying, etc. are preferably used.

[0105] The toner according to the present embodiment is produced by, for example, adding an external additive to the obtained dry toner particles and mixing them. The mixing can be carried out using, for example, a V blender, a Henschel mixer, a Loedige mixer, or the like. Furthermore, if necessary, coarse particles may be removed from the toner using a vibrating sieve, an air sieve, or the like.

[0106] <Electrostatic image developer> The electrostatic image developer according to this embodiment contains at least the toner according to this embodiment. The electrostatic image developer according to this embodiment may be a one-component developer containing only the toner according to this embodiment, or may be a two-component developer containing the toner mixed with a carrier.

[0107] The carrier is not particularly limited, and examples thereof include known carriers, such as coated carriers in which the surface of a core material made of magnetic powder is coated with a coating resin, magnetic powder dispersion carriers in which magnetic powder is dispersed and blended in a matrix resin, and resin-impregnated carriers in which porous magnetic powder is impregnated with a resin. The magnetic powder dispersion type carrier and the resin impregnated type carrier may be a carrier in which the constituent particles of the carrier are used as a core material and are coated with a coating resin.

[0108] Examples of magnetic powder include magnetic metals such as iron, nickel, and cobalt, and magnetic oxides such as ferrite and magnetite.

[0109] Examples of coating resins and matrix resins include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene-acrylic acid ester copolymer, straight silicone resins containing organosiloxane bonds or modified products thereof, fluororesins, polyesters, polycarbonates, phenolic resins, and epoxy resins. The coating resin and the matrix resin may contain other additives such as conductive particles. Examples of conductive particles include particles of metals such as gold, silver, and copper, carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, and potassium titanate.

[0110] Here, the method of coating the surface of the core material with a coating resin includes a method of coating with a solution for forming a coating layer in which the coating resin and, if necessary, various additives are dissolved in an appropriate solvent. The solvent is not particularly limited and may be selected taking into consideration the coating resin to be used, its applicability, etc. Specific resin coating methods include an immersion method in which the core material is immersed in a solution for forming a coating layer, a spray method in which the solution for forming a coating layer is sprayed onto the surface of the core material, a fluidized bed method in which the solution for forming a coating layer is sprayed onto the core material while it is suspended in flowing air, and a kneader coater method in which the core material of the carrier and the solution for forming a coating layer are mixed in a kneader coater and the solvent is removed.

[0111] In the two-component developer, the mixing ratio (mass ratio) of toner to carrier is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100.

[0112] <Image forming device / image forming method> An image forming apparatus and an image forming method according to this embodiment will be described. The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, a developing unit that contains an electrostatic image developer and develops the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, a transfer unit that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing unit that fixes the toner image transferred to the surface of the recording medium. The electrostatic image developer according to the present embodiment is used as the electrostatic image developer.

[0113] The image forming apparatus according to this embodiment carries out an image forming method (the image forming method according to this embodiment) that includes a charging step of charging the surface of an image carrier, an electrostatic image forming step of forming an electrostatic image on the surface of the charged image carrier, a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer according to this embodiment, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium.

[0114] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a cleaning means that cleans the surface of the image carrier after the transfer of the toner image but before charging; and an apparatus equipped with a discharging means that irradiates the surface of the image carrier with discharging light to discharge it after the transfer of the toner image but before charging. In the case of an intermediate transfer type device, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means which primarily transfers the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means which secondarily transfers the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0115] In the image forming apparatus according to the present embodiment, for example, a portion including the developing means may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge equipped with developing means that accommodates the electrostatic image developer according to the present embodiment is preferably used.

[0116] An example of an image forming apparatus according to the present embodiment will be described below, but the present invention is not limited to this. Note that only the main parts shown in the drawings will be described, and descriptions of other parts will be omitted.

[0117] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to this embodiment. The image forming apparatus shown in Figure 1 includes first through fourth electrophotographic image forming units 10Y, 10M, 10C, and 10K (image forming means) that output images in the colors yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side horizontally spaced a predetermined distance apart from one another. Note that these units 10Y, 10M, 10C, and 10K may also be process cartridges that are detachable from the image forming apparatus.

[0118] Above each of the units 10Y, 10M, 10C, and 10K in the drawing, an intermediate transfer belt 20 serving as an intermediate transfer body extends through each unit. The intermediate transfer belt 20 is wound around a drive roll 22 and a support roll 24 that are spaced apart from each other and arranged from left to right in the drawing, and is configured to run in a direction from the first unit 10Y to the fourth unit 10K. A force is applied to the support roll 24 in a direction away from the drive roll 22 by a spring or the like (not shown), thereby applying tension to the intermediate transfer belt 20 wound around them. In addition, an intermediate transfer body cleaning device 30 is provided on the image carrier side of the intermediate transfer belt 20, facing the drive roll 22. In addition, the developing devices (developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K are supplied with toner including four colors of toner, yellow, magenta, cyan, and black, contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0119] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration, the first unit 10Y, which forms a yellow image and is disposed upstream in the direction of travel of the intermediate transfer belt, will be described here as a representative. Note that parts equivalent to those of the first unit 10Y are given reference numerals with magenta (M), cyan (C), and black (K) instead of yellow (Y), and descriptions of the second to fourth units 10M, 10C, and 10K will be omitted.

[0120] The first unit 10Y has a photoreceptor 1Y that acts as an image carrier. Around the photoreceptor 1Y, there are arranged in this order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential; an exposure device (an example of an electrostatic image forming means) 3 that exposes the charged surface to a laser beam 3Y based on a color-separated image signal to form an electrostatic image; a developing device (an example of a developing means) 4Y that supplies charged toner to the electrostatic image to develop it; a primary transfer roll 5Y (an example of a primary transfer means) that transfers the developed toner image onto an intermediate transfer belt 20; and a photoreceptor cleaning device (an example of a cleaning means) 6Y that removes toner remaining on the surface of the photoreceptor 1Y after the primary transfer. The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is positioned opposite the photoreceptor 1Y. Furthermore, a bias power supply (not shown) that applies a primary transfer bias is connected to each of the primary transfer rolls 5Y, 5M, 5C, and 5K. Each bias power supply varies the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

[0121] The operation of forming a yellow image in first unit 10Y will be described below. First, prior to operation, the surface of the photosensitive member 1Y is charged to a potential of −600V to −800V by the charging roll 2Y. The photoconductor 1Y has conductivity (for example, volume resistivity at 20°C: 1×10 -6The photosensitive layer is formed by laminating a photosensitive layer on a substrate with a resistivity of Ωcm or less. This photosensitive layer normally has a high resistance (the resistance of ordinary resins), but when irradiated with a laser beam 3Y, the resistivity of the irradiated portion changes. Therefore, a laser beam 3Y is output to the charged surface of the photosensitive element 1Y via an exposure device 3 in accordance with image data for yellow sent from a control unit (not shown). The laser beam 3Y is irradiated onto the photosensitive layer on the surface of the photosensitive element 1Y, thereby forming an electrostatic charge image of a yellow image pattern on the surface of the photosensitive element 1Y.

[0122] An electrostatic image is an image formed on the surface of the photosensitive element 1Y by charging it; the laser beam 3Y reduces the resistivity of the irradiated portion of the photosensitive layer, causing the charged charges on the surface of the photosensitive element 1Y to flow, while the charges remain in the portions not irradiated by the laser beam 3Y, forming a so-called negative latent image. The electrostatic image formed on the photoreceptor 1Y is rotated to a predetermined development position as the photoreceptor 1Y travels. At this development position, the electrostatic image on the photoreceptor 1Y is made visible as a toner image (developed image) by the developing device 4Y.

[0123] The developing device 4Y contains an electrostatic image developer containing, for example, at least yellow toner and a carrier. The yellow toner is frictionally charged by being stirred inside the developing device 4Y, and is held on a developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the charge on the photoreceptor 1Y. As the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed with the yellow toner. The photoreceptor 1Y on which the yellow toner image has been formed continues to travel at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transported to a predetermined primary transfer position.

[0124] When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y to the primary transfer roll 5Y acts on the toner image, causing the toner image on the photoreceptor 1Y to be transferred onto the intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the (-) polarity of the toner, and in the first unit 10Y, for example, it is controlled to +10 μA by a control unit (not shown). On the other hand, the toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

[0125] Furthermore, the primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K of the second unit 10M and subsequent units is also controlled in accordance with the first unit. In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is conveyed sequentially through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are transferred onto the intermediate transfer belt 20 in a superimposed manner.

[0126] The intermediate transfer belt 20, onto which the four-color toner images have been multiplex-transferred through the first to fourth units, reaches a secondary transfer section composed of the intermediate transfer belt 20, a support roll 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 arranged on the image bearing surface side of the intermediate transfer belt 20. Meanwhile, recording paper (an example of a recording medium) P is fed via a supply mechanism into the gap between the secondary transfer roll 26 and the intermediate transfer belt 20 at a predetermined timing, and a secondary transfer bias is applied to the support roll 24. The transfer bias applied at this time has a negative polarity, the same as the negative polarity of the toner. Electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined according to resistance detected by resistance detection means (not shown) that detects resistance in the secondary transfer section, and is voltage-controlled.

[0127] Thereafter, the recording paper P is sent to the pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image.

[0128] Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copying machines, printers, etc. In addition to the recording paper P, examples of the recording medium include overhead projector sheets and the like. To further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper in which the surface of plain paper is coated with resin or the like, or art paper for printing, is preferably used.

[0129] The recording paper P on which the color image has been fixed is conveyed toward the discharge section, and the series of color image forming operations is completed.

[0130] <Process cartridges / toner cartridges> The process cartridge according to this embodiment will be described. The process cartridge according to this embodiment is a process cartridge that is detachably attached to an image forming apparatus and that contains the electrostatic image developer according to this embodiment and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image.

[0131] The process cartridge according to this embodiment is not limited to the above configuration, but may also be configured to include a developing device and, if necessary, at least one other means selected from an image carrier, a charging means, an electrostatic image forming means, and a transfer means.

[0132] An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this. Note that only the main parts shown in the drawings will be described, and descriptions of other parts will be omitted.

[0133] FIG. 2 is a schematic diagram showing the configuration of the process cartridge according to the present embodiment. The process cartridge 200 shown in FIG. 2 is configured to integrally combine and hold a photosensitive member 107 (an example of an image carrier), a charging roll 108 (an example of a charging means) provided around the photosensitive member 107, a developing device 111 (an example of a developing means), and a photosensitive member cleaning device 113 (an example of a cleaning means), which are held by a housing 117 provided with, for example, mounting rails 116 and an opening 118 for exposure, and is made into a cartridge. In FIG. 2, 109 denotes an exposure device (an example of an electrostatic image forming means), 112 denotes a transfer device (an example of a transfer means), 115 denotes a fixing device (an example of a fixing means), and 300 denotes recording paper (an example of a recording medium).

[0134] Next, the toner cartridge according to this embodiment will be described. The toner cartridge according to the present embodiment is a toner cartridge that contains the toner according to the present embodiment and is detachably attached to an image forming apparatus. The toner cartridge contains replenishment toner to be supplied to a developing unit provided in the image forming apparatus.

[0135] 1 is an image forming apparatus having a configuration in which toner cartridges 8Y, 8M, 8C, and 8K can be attached and detached, and developing devices 4Y, 4M, 4C, and 4K are connected to the toner cartridges corresponding to each developing device (color) by toner supply pipes (not shown). When the toner stored in a toner cartridge runs low, the toner cartridge is replaced. [Example]

[0136] Examples will be described below, but the present invention is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are based on mass.

[0137] <Preparation of Toner Particles (A)> (Preparation of Core Particle Dispersion (A)) Styrene (Fujifilm Wako Pure Chemical Industries): 80 parts n Butyl acrylate (Fujifilm Wako Pure Chemical Industries, Ltd.): 20 parts Divinylbenzene (Fujifilm Wako Pure Chemical Industries, Ltd.): 0.65 parts Dodecanethiol (Fujifilm Wako Pure Chemical Industries, Ltd.): 2 parts Cyan pigment (Pigment Blue 15:3, manufactured by Dainichi Seika Color & Chemicals Mfg. Co., Ltd.): 8 parts The above materials were placed in a stainless steel container and premixed by stirring, and then thoroughly dispersed using a media-type disperser (paint shaker) to obtain a polymerizable monomer composition.

[0138] The following ingredients were placed in a round-bottom stainless steel flask and heated to 58°C. Ion-exchanged water: 80 parts ·0.1mol / L Na3PO4 aqueous solution: 100 parts ·1N HCl aqueous solution: 2.8 parts

[0139] Next, the mixture was dispersed and stirred at 13,000 rpm using a homogenizer (Clearmix, manufactured by M Technique Co., Ltd.). 10 parts of a 1.0 mol / L CaCl2 aqueous solution was gradually added to the mixture to prepare an aqueous medium containing Ca3(PO4)2. While maintaining the temperature at 58°C, the dispersed polymerizable monomer composition was added to the Ca3(PO4)2 dispersion and stirred until homogenized. While dispersing with the homogenizer, 6 parts of tetramethylbutyl-peroxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perocta O) was gradually added to the suspension to form droplets of the polymerizable monomer composition.

[0140] The suspension containing dispersed droplets was heated to 90° C. by external heating while stirring in a refluxable reaction vessel, thereby allowing the polymerization reaction to proceed. After the reaction was sufficiently carried out while maintaining the temperature, the suspension was cooled to room temperature, and ion-exchanged water was added thereto so that the concentration of the polymerizable monomer composition relative to the total dispersion was 20% by mass, thereby preparing a core particle dispersion (A).

[0141] (Preparation of Resin Particle Dispersion (A) for Forming Shell Layer) -Preparation of polyester resin A- Bisphenol A-ethylene oxide 2 mole adduct: 49.2 parts Ethylene glycol: 8.9 parts Terephthalic acid: 14.4 parts Isophthalic acid: 5.8 parts The above monomers were placed in a well-dried, N-purged three-necked flask, heated to 185°C while blowing in N2 to dissolve, and then thoroughly mixed. After adding 0.03 parts of tetrabutoxy titanate, the temperature in the system was raised to 220°C and the reaction was carried out for 5 hours while maintaining that temperature, to obtain polyester resin A.

[0142] -Preparation of resin particle dispersion (A) for forming shell layer- Polyester resin A: 100.0 parts by mass Methyl ethyl ketone: 45.0 parts by mass Tetrahydrofuran: 45.0 parts by mass The above raw materials were placed in a well-dried, N-purged three-neck flask, heated to 80°C while blowing in N2, dissolved, and thoroughly mixed. Next, 300.0 parts by mass of 80°C ion-exchanged water was added, thoroughly mixed, and the resulting solution was transferred to a distillation apparatus. Distillation was continued until the distillate temperature reached 100°C, and after cooling, ion-exchanged water was added to the resulting solution, adjusting the concentration of polyester resin A to 20% by mass relative to the total dispersion. This was used as shell layer-forming resin particle dispersion (A).

[0143] (Preparation of Toner Particles (A)) To 500.0 parts by mass of the core particle dispersion (A), 15.0 parts by mass of the shell layer-forming resin particle dispersion (A) was added dropwise at a rate of 1.0 part by mass / min. The resulting mixed solution was stirred at 200 rpm (rotations per minute). The mixed solution was then heated to 55°C, and dilute hydrochloric acid was added dropwise to dissolve and remove Ca3(PO4)2. The mixed solution was further stirred at 55°C for 2 hours, then heated to 65°C and stirred for 1 hour. The mixed solution was then cooled to room temperature, thoroughly washed with ion-exchanged water, and subjected to solid-liquid separation using Nutsche suction filtration. Next, the mixture was redispersed in ion-exchanged water at 40°C and washed with stirring for 15 minutes. This washing procedure was repeated several times, followed by solid-liquid separation using Nutsche suction filtration and freeze-drying under vacuum to obtain toner particles (A) (volume average particle size (D50v): 6.6 μm, average circularity Cc: 0.98).

[0144] <Preparation of monodispersed silica particles> (Preparation of Silica Particle Dispersion (1)) 300 parts of methanol and 70 parts of 10% aqueous ammonia were added to a glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer and mixed to obtain an alkaline catalyst solution. This alkaline catalyst solution was adjusted to 30°C (dropping start temperature), and then 185 parts of tetramethoxysilane and 50 parts of 8% aqueous ammonia were simultaneously dropped into the solution while stirring to obtain a hydrophilic silica particle dispersion (solid content 12%). The dropping time was 30 minutes. The obtained silica particle dispersion was then concentrated to a solid content of 40% using a rotary filter R-Fine (manufactured by Kotobuki Industries Co., Ltd.). This concentrated solution was designated silica particle dispersion (1).

[0145] (Preparation of Silica Particle Dispersions (2) to (12)) Silica particle dispersions (2) to (12) were prepared in the same manner as silica particle dispersion (1), except that the conditions of the alkaline catalyst solution (amount of methanol, concentration and amount of aqueous ammonia) and the conditions for producing silica particles (amount of tetramethoxysilane (TMOS) in the alkaline catalyst solution, concentration and total amount of aqueous ammonia added, dropwise addition time and dropwise start temperature of TMOS and aqueous ammonia) were changed according to Table 1 in the preparation of silica particle dispersion (1).

[0146] [Table 1]

[0147] (Preparation of monodisperse silica particles (S1)) Using silica particle dispersion (1), silica particles were surface treated with a siloxane compound in a supercritical carbon dioxide atmosphere as follows: For the surface treatment, an apparatus equipped with a carbon dioxide cylinder, a carbon dioxide pump, an entrainer pump, an autoclave (500 ml capacity) equipped with a stirrer, and a pressure valve was used.

[0148] First, 300 parts of silica particle dispersion (1) was placed in an autoclave (volume 500 ml) equipped with a stirrer, and the stirrer was rotated at 100 rpm. Subsequently, liquefied carbon dioxide was injected into the autoclave, and the temperature was increased with a heater while the pressure was increased with a carbon dioxide pump, bringing the autoclave into a supercritical state of 150°C and 15 MPa. While maintaining the pressure inside the autoclave at 15 MPa with a pressure valve, supercritical carbon dioxide was circulated from the carbon dioxide pump, and methanol and water were removed from the silica particle dispersion (1) (solvent removal step), yielding silica particles (untreated silica particles).

[0149] Next, when the amount of supercritical carbon dioxide circulated (cumulative amount: measured as the amount of carbon dioxide circulated under standard conditions) reached 900 parts, the circulation of the supercritical carbon dioxide was stopped. Thereafter, the temperature was maintained at 150 ° C. using a heater, and the pressure was maintained at 15 MPa using a carbon dioxide pump. While maintaining the supercritical state of carbon dioxide in the autoclave, a treatment solution was prepared by dissolving 20 parts of hexamethyldisilazane (HMDS: manufactured by Yuki Gosei Yakuhin Kogyo Co., Ltd.) as a hydrophobic treatment agent and 0.3 parts of dimethylsilicone oil (DSO: trade name "KF-96 (manufactured by Shin-Etsu Chemical Co., Ltd.)") with a viscosity of 10,000 cSt per 100 parts of the silica particles (untreated silica particles). The treatment solution was then injected into the autoclave using an entrainer pump, and the mixture was allowed to react at 180 ° C. for 20 minutes while stirring. Then, supercritical carbon dioxide was again circulated, and the excess treatment solution was removed. Then, the stirring was stopped, the pressure valve was opened, and the pressure in the autoclave was released to atmospheric pressure, and the temperature was lowered to room temperature (25 ° C.). In this way, the solvent removal step and the surface treatment with HMDS and DSO were carried out in sequence to obtain monodisperse silica particles (S1).

[0150] (Preparation of monodisperse silica particles (S2) to (12)) Monodispersed silica particles (S2) to (12) were obtained in the same manner as in the preparation of monodispersed silica particles (S1).

[0151] <Preparation of titanic acid compound particles (T1)> 0.7 moles of desulfurized and peptized metatitanic acid, the titanium source, was collected as TiO2 and placed in a reaction vessel. Next, 0.77 moles of an aqueous solution containing strontium chloride as another metal oxide source was added to the reaction vessel so that the SrO / TiO2 molar ratio was 1.1. Next, a solution containing lanthanum oxide dissolved in nitric acid as a dopant source was added to the reaction vessel in an amount equivalent to 1 mole of lanthanum dopant per 100 moles of strontium. The initial TiO2 concentration in the mixture of the three materials was adjusted to 0.75 mole / L. The mixture was then stirred and heated to 90°C. While maintaining the temperature at 90°C and stirring, 153 mL of 10 N (mol / L) aqueous sodium hydroxide solution was added over 2 hours. Stirring was continued for another hour while maintaining the temperature at 90°C. The reaction mixture was then cooled to 40°C, and hydrochloric acid was added until the pH reached 5.5, followed by stirring for 1 hour. The precipitate was then washed by repeated decantation and redispersion in water. Hydrochloric acid was added to the slurry containing the washed precipitate to adjust the pH to 6.5, and the solids were filtered off and dried. An ethanol solution of i-butyltrimethoxysilane (i-BTMS) was added to the dried solids in an amount of 20 parts i-BTMS per 100 parts solids, and the mixture was stirred for 1 hour. The solids were filtered off and dried in air at 130°C for 7 hours to obtain titanic acid compound particles (T1).

[0152] <Preparation of titanate compound particles (T2) to (T15)> Titanate compound particles were obtained in the same manner as in the preparation of titanate compound particles (T1), except that the type of other metal oxide source, the amount of other metal oxide source added, the type of dopant source, the amount of dopant source added, and the addition time of 153 mL of 10 N (mol / L) sodium hydroxide aqueous solution were changed as shown in Table 2. The amount of the other metal oxide source added was adjusted so that the mole number of the other metal oxide source relative to the mole number of TiO2 was the value shown in Table 2. The amount of dopant source added was adjusted so that the number of moles of the dopant element per 100 moles of strontium was the value shown in Table 2.

[0153] [Table 2]

[0154] Example 1: Preparation of toner and developer To 100 parts of the toner particles (A), 0.4 parts of surface-treated monodisperse silica particles (S1) and 0.5 parts of titanic acid compound particles (T1) were added as external additives, and the mixture was mixed in a Henschel mixer at a stirring peripheral speed of 30 m / sec for 15 minutes to obtain a toner.

[0155] Each of the obtained toners and the following resin-coated carrier were placed in a V blender at a toner:carrier ratio of 8:92 (mass ratio), and stirred for 20 minutes to obtain a developer.

[0156] -Career- Mn-Mg-Sr ferrite particles (average particle size 40 μm): 100 parts Toluene: 14 parts Polymethyl methacrylate: 2 parts Carbon black (VXC72: manufactured by Cabot): 0.12 parts The above materials except for the ferrite particles were mixed with glass beads (1 mm diameter, same amount as toluene) and stirred for 30 minutes at a rotation speed of 1200 rpm using a sand mill manufactured by Kansai Paint Co., Ltd. to obtain a dispersion liquid. This dispersion liquid and the ferrite particles were placed in a vacuum degassing kneader and dried under reduced pressure while stirring to obtain a resin-coated carrier.

[0157] <Examples 2 to 25 and Comparative Examples 1 to 4> The toner and developer were obtained in the same manner as in Example 1, except that the type of toner particles added during toner production, and the type and amount of external additives (surface-treated monodisperse silica particles and titanic acid compound particles) added were changed as shown in Table 3.

[0158] <Evaluation> Each developer was placed in the developing device of a modified image forming apparatus "Apeos PortIVC5575 (manufactured by Fuji Xerox Co., Ltd.)" (a modified apparatus in which the automatic density control sensor for environmental fluctuations was turned off). Using this modified image forming apparatus, evaluation of fogging and evaluation of image density stability were carried out.

[0159] (Fog evaluation) Images with an image density of 40% were continuously printed on 300,000 sheets of A4 paper in a high temperature and humidity environment (28°C, 85% RH), and the fogging of the last 30 sheets was evaluated. [Fog evaluation index] G1: No overlapping is observed on any of the 30 sheets. G2: There is a slight amount of fogging on one sheet, but it is within the practically acceptable range. G3: Slight fogging is observed on several sheets, but is within the practically acceptable range. G4: Obvious fogging is observed on multiple sheets, making it unsuitable for practical use. G5: There is complete overlap on all 30 sheets.

[0160] (Image density stability evaluation) In a high temperature and humidity environment (28°C, 85% RH), 100,000 A4 size images with 1% image density were printed continuously, and the difference in image density between the 500th and 100,000th images was measured. Image density was measured using an X-Rite color reflection densitometer. [Image density stability evaluation index] G1: The density difference between the 100,000th sheet and the 100th sheet is less than 0.03 G2: The difference in density between the 100,000th sheet and the 100th sheet is 0.03 or more and less than 0.05 G3: The difference in density between the 100,000th sheet and the 100th sheet is 0.05 or more and less than 0.07 G4: The density difference between the 100,000th sheet and the 100th sheet is 0.07 or more and less than 0.09 G5: The density difference between the 100,000th sheet and the 100th sheet is 0.09 or more

[0161] [Table 3]

[0162] The abbreviations in the table are explained below. Particle size difference (Si particles - Ti particles, nm): Absolute value of the difference in average primary particle size between monodispersed silica particles and titanic acid compound particles Particle size ratio (Ti particles / Si particles): Ratio of the average primary particle size of titanate compound particles to the average primary particle size of monodispersed silica particles Content ratio (Ti particles / Si particles): The content of titanate compound particles relative to the content of monodispersed silica particles Circularity ratio (Cb / Cc): The value of the average circularity Cb of titanate compound particles relative to the average circularity Cc of toner particles (Cb / Cc)

[0163] From the above results, it is understood that the toner of this example can suppress the occurrence of the phenomenon (fog) in which toner adheres to and is fixed in non-image areas when images are continuously formed in a high-temperature, high-humidity environment. [Explanation of symbols]

[0164] 1Y, 1M, 1C, 1K Photoconductor (an example of an image carrier) 2Y, 2M, 2C, 2K Charging roll (an example of charging means) 3. Exposure device (an example of an electrostatic image forming means) 3Y, 3M, 3C, 3K laser beam 4Y, 4M, 4C, 4K developing device (an example of developing means) 5Y, 5M, 5C, 5K Primary transfer roll (an example of a primary transfer means) 6Y, 6M, 6C, 6K: Photoconductor cleaning device (an example of a cleaning means) 8Y, 8M, 8C, 8K toner cartridges 10Y, 10M, 10C, 10K image forming units 20 Intermediate transfer belt (an example of an intermediate transfer body) 22 Drive Roll 24 Support Roll 26 Secondary transfer roll (an example of a secondary transfer means) 30 Intermediate transfer body cleaning device 107 Photosensitive body (an example of an image carrier) 108 Charging roll (an example of charging means) 109 Exposure device (an example of electrostatic image forming means) 111 Developing device (an example of developing means) 112 Transfer device (an example of transfer means) 113 Photosensitive drum cleaning device (an example of cleaning means) 115 Fixing device (an example of fixing means) 116 Mounting Rail 118 Exposure opening 117 Cabinet 200 Process Cartridge 300 Recording paper (an example of a recording medium) P Recording paper (an example of a recording medium)

Claims

1. toner particles having an average circularity Cc of 0.98 or more; an external additive containing monodispersed silica particles having an average primary particle size of 20 nm or more and 70 nm or less and titanic acid compound particles having an average primary particle size of 20 nm or more and 70 nm or less; the absolute value of the difference in average primary particle size between the monodispersed silica particles and the titanic acid compound particles is 25 nm or less; the specific gravity Da of the monodisperse silica particles is 1.1 or more and 1.3 or less, the specific gravity Db of the titanate compound particles is greater than the specific gravity Da of the monodisperse silica particles, The toner for developing electrostatic images, wherein the specific gravity Db of the titanic acid compound particles is 4.2 or more and 5.0 or less.

2. the average circularity Ca of the monodispersed silica particles is more than 0.86 and less than 0.94; 2. The toner for developing electrostatic images according to claim 1, wherein the titanic acid compound particles have an average circularity Cb of more than 0.78 but less than 0.

94.

3. 3. The toner for developing electrostatic images according to claim 2, wherein the average circularity Ca of the monodisperse silica particles is greater than the average circularity Cb of the titanic acid compound particles.

4. 4. The toner for developing electrostatic images according to claim 1, wherein the titanic acid compound particles are alkaline earth metal titanate particles.

5. 5. The toner for developing electrostatic images according to claim 1, wherein the titanic acid compound particles contain a dopant.

6. 6. The toner for developing electrostatic images according to claim 5, wherein said dopant is at least one of lanthanum and silica.

7. 7. The toner for developing electrostatic images according to claim 1, wherein the content of the titanic acid compound particles relative to the content of the monodisperse silica particles is 0.1 or more and 10 or less in mass ratio.

8. An electrostatic image developer comprising the toner for developing electrostatic images according to any one of claims 1 to 7.

9. A toner for developing electrostatic images according to any one of claims 1 to 7 is contained therein, A toner cartridge that is detachably attached to an image forming device.

10. a developing unit containing the electrostatic image developer according to claim 8 and developing an electrostatic image formed on the surface of an image carrier into a toner image by using the electrostatic image developer, A process cartridge is detachably mounted in an image forming apparatus.

11. an image carrier; a charging means for charging the surface of the image carrier; an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier; a developing unit containing the electrostatic image developer according to claim 8 and developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer; a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; An image forming apparatus comprising:

Images