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

Abstract

To provide a toner and a developer that can maintain stable electrification characteristics.SOLUTION: A toner for electrostatic charge image development includes toner particles, silica particles externally added to the toner particle, and titanic acid compound particles externally added to the toner particle and having an average circularity of 0.890 or more and 0.950 or less. The silica particles include particles having a primary particle diameter of 80 nm or less, and the particles having a primary particle diameter of 80 nm or less have at least one peak within a range of 20 nm or more and less than 80 nm in the number primary particle diameter distribution curve (hereinafter, silica particles having the peak are referred to as "specific silica particles"). The titanic acid compound particles have at least one peak within a range of 20 nm or more and less than 80 nm in the number primary particle diameter distribution curve. The difference between the average circularity of the specific silica particles and the average circularity of the titanic acid compound particles is 0.05 or less. The difference between the coverage of the toner by the specific silica particles and the coverage of the toner with the titanic acid compound particles is 20% points 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, an image forming apparatus, and an image forming method. [Background technology]

[0002] Patent Document 1 discloses a toner for developing electrostatic images, which includes toner particles having an average circularity of 0.91 or more and 0.98 or less, silica particles externally added to the toner particles, and strontium titanate particles externally added to the toner particles, the strontium titanate particles having an average primary particle size of 10 nm or more and 100 nm or less, an average circularity of the primary particles of 0.82 or more and 0.94 or less, and a circularity of more than 0.92, which accounts for 84% of the cumulative total of the primary particles. Patent Document 2 discloses a positively charged electrophotographic toner characterized in that silica particles that have been surface-treated with a quaternary ammonium salt compound that is substantially insoluble or poorly soluble in water are added to the toner particles. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2019-28235 [Patent Document 2] Japanese Patent Application Publication No. 4-101162 Summary of the Invention [Problem to be solved by the invention]

[0004] Toners using silica particles and titanic acid compound particles have sometimes had poor charging characteristics under low temperature and low humidity conditions, resulting in contamination inside the machine and fogging in non-image areas. The object of the present invention is to provide a toner / developer that can maintain stable charging characteristics even when silica particles and titanic acid compound particles are used as external additives. [Means for solving the problem]

[0005] The invention described in claim 1 comprises toner particles, silica particles externally added to the toner particles, and titanic acid compound particles externally added to the toner particles and having an average circularity of 0.890 or more and 0.950 or less, wherein the silica particles have a primary particle size of 80 nm or less, and the particles with a primary particle size of 80 nm or less have at least one peak in a range of 20 nm or more and less than 80 nm in a number primary particle size distribution curve (hereinafter, silica particles having this peak will be referred to as "specific silica particles"). The titanic acid compound particles have at least one peak in a range of 20 nm or more and less than 80 nm in a number primary particle size distribution curve, the difference between the average circularity of the specific silica particles and the average circularity of the titanic acid compound particles is 0.05 or less, and the difference between the toner coverage rate of the specific silica particles and the toner coverage rate of the titanic acid compound particles is 20 percentage points or less. The specific silica particles and the titanic acid compound particles are present as primary particles on the toner particles at a rate of 10% or more. The toner for developing electrostatic images is characterized in that:

[0006] The invention described in claim 2 is the toner for developing electrostatic images described in claim 1, wherein the titanate compound particles have at least one peak in the range of 30 nm or more and less than 80 nm in a number primary particle size distribution curve, and the particle size difference between the titanate compound particles and the specific silica particles, each of which has a maximum peak in the range of 20 nm or more and less than 80 nm, is 20 nm or less. A third aspect of the present invention is the toner for developing electrostatic images, wherein the particle size difference at which the maximum peak is reached is 15 nm or less. A fourth aspect of the present invention is the toner for developing electrostatic images according to the first aspect, wherein the difference between the toner coverage of the specific silica particles and the coverage of the titanic acid compound particles is 15% points or less. A fifth aspect of the present invention is the toner for developing electrostatic images according to the first aspect, wherein the difference between the average circularity of the specific silica particles and the average circularity of the titanic acid compound particles is 0.03 or less. The invention described in claim 6 is the toner for developing electrostatic images according to claim 1, wherein the difference between the half-value width of the peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve of the specific silica particles and the half-value width of the peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve of the titanate compound particles is 20 nm or less. The invention described in claim 7 is the toner for developing electrostatic images according to claim 1, wherein the titanate compound particles are at least one selected from the group consisting of strontium titanate particles, magnesium titanate particles, and calcium titanate particles.

[0007] An eighth aspect of the present invention provides the toner for developing electrostatic images according to the seventh aspect, wherein the titanate compound particles are strontium titanate particles. A ninth aspect of the present invention is the toner for developing electrostatic images according to the eighth aspect, wherein the strontium titanate particles are lanthanum-doped strontium titanate particles. A tenth aspect of the present invention provides the toner for developing electrostatic images according to the eighth aspect, wherein the strontium titanate particles have surfaces that have been subjected to a hydrophobic treatment. The invention described in claim 11 is The toner for developing electrostatic images according to claim 1, wherein a maximum exposed area, which is the area of ​​the largest region where there is no external additive and where the toner particles are exposed, is determined for each of the toner particles before and after output from the actual machine, and the area ratio calculated by the following formula is 1.36 or less. Area ratio = Maximum exposed area of ​​toner particles after output / Maximum exposed area of ​​toner particles before output The invention described in claim 12 is an electrostatic image developer containing the toner for developing electrostatic images described in any one of claims 1 to 11. The invention described in claim 13 is a toner cartridge that contains the electrostatic image developing toner described in any one of claims 1 to 11 and is detachably mountable on an image forming apparatus. The invention described in claim 14 is a process cartridge that contains the electrostatic image developer described in claim 12, has 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, and is detachably attached to an image forming apparatus. The invention described in claim 15 is an image forming apparatus comprising 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 means that contains the electrostatic image developer described in claim 12 and develops the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, a transfer means that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing means that fixes the toner image transferred to the surface of the recording medium. The invention described in claim 16 is an image forming method having a charging step of charging the surface of an image carrier, an electrostatic image forming step of forming an electrostatic image on the charged surface of the 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 described in claim 12, 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. [Effects of the Invention]

[0008] According to the first aspect of the present invention, it is possible to provide a toner for developing electrostatic images that can maintain stable charging characteristics. According to the invention of claim 2, a toner for developing electrostatic images can be provided that has no peak in the number primary particle size distribution curve between 30 nm and 80 nm, and that can maintain stable charging characteristics compared to a case in which the difference in particle size between the titanate compound particles and the specific silica particles at the maximum peak position in the range between 20 nm and 80 nm is greater than 20 nm. According to the invention of claim 3, a toner for developing electrostatic images can be provided that can maintain stable charging characteristics compared to when the particle size difference between the titanate compound particles and the specific silica particles at the maximum peak position in the range of 20 nm or more and less than 80 nm is greater than 15 nm. According to the invention of claim 4, a toner for developing electrostatic images can be provided that can maintain stable charging characteristics compared to when the difference between the toner coverage rate of the specific silica particles and the coverage rate of the titanate compound particles is greater than 15% points. According to the invention of claim 5, a toner for developing electrostatic images can be provided that can maintain stable charging characteristics compared to when the difference between the average circularity of the specific silica particles and the average circularity of the titanate compound particles is greater than 0.03. According to the invention of claim 6, a toner for developing electrostatic images can be provided in which mutual charging is suppressed compared to when the difference between the half-value width of the peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve of the specific silica particles and the half-value width of the peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve of the titanate compound particles is greater than 20 nm. According to the invention of claim 7, a toner for developing electrostatic images can be provided that has stable charging properties compared to when the titanate compound particles are not strontium titanate particles, magnesium titanate particles, or calcium titanate particles.

[0009] According to the eighth aspect of the present invention, it is possible to provide a toner for developing electrostatic images that has stable chargeability compared to when the titanate compound particles are not strontium titanate particles. According to the ninth aspect of the present invention, it is possible to provide a toner for developing electrostatic images that can maintain favorable charging characteristics compared to when strontium titanate particles that are not doped with lanthanum are used. According to the invention of claim 10, it is possible to provide a toner for developing electrostatic images that has controlled and stable charging characteristics compared to strontium titanate particles having surfaces that have not been hydrophobized. According to the invention of claim 11, a toner for developing electrostatic images can be provided that can maintain stable charging characteristics compared to when the proportion of the specific silica particles and the titanate compound particles present as primary particles on the toner particles is less than 10%. According to the twelfth aspect of the present invention, it is possible to provide an electrostatic image developer containing a toner for developing electrostatic images that can maintain stable charging characteristics. According to the invention of claim 13, it is possible to provide a toner cartridge containing a toner for developing electrostatic images that can maintain stable charging characteristics. According to the invention of claim 14, 15 or 16, it is possible to provide a process cartridge, an image forming apparatus or an image forming method that uses an electrostatic image developer containing a toner for developing electrostatic images that can maintain stable charging characteristics. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating an example of a process cartridge that is detachably mounted to an image forming apparatus according to an exemplary embodiment of the present invention. [Figure 3] FIG. 10 is a schematic diagram showing how toner particle exposed regions are selected in order to determine the uneven distribution degree of an external additive on the toner. DETAILED DESCRIPTION OF THE INVENTION

[0011] The following describes embodiments of the present invention. These descriptions and examples are merely illustrative of the embodiments and do not limit the scope of the invention.

[0012] In this disclosure, the expressions "from XX to XX" or "XX to XX" that represent a numerical range mean a numerical range including the stated upper and lower limits, unless otherwise specified. Furthermore, in this disclosure, when referring to the amount of each component in a composition, if the composition contains multiple substances corresponding to each component, the expression means the total amount of the multiple substances present in the composition, unless otherwise specified. In the present disclosure, "toner for developing electrostatic images" may be simply referred to as "toner," and "electrostatic image developer" may be simply referred to as "developer."

[0013] <Toner for developing electrostatic images> The toner according to this embodiment comprises toner particles, silica particles externally added to the toner particles, and titanic acid compound particles externally added to the toner particles and having an average circularity of 0.890 or more and 0.950 or less, wherein the silica particles have a primary particle size of 80 nm or less, and the particles having a primary particle size of 80 nm or less have at least one peak in the range of 20 nm or more and less than 80 nm in a number primary particle size distribution curve (hereinafter, silica particles having this peak will be referred to as "specific silica particles"). The titanic acid compound particles have at least one peak in the range of 20 nm or more and less than 80 nm in a number primary particle size distribution curve, the difference between the average circularity of the specific silica particles and the average circularity of the titanic acid compound particles is 0.05 or less, and the difference between the toner coverage of the specific silica particles and the toner coverage of the titanic acid compound particles is 20 percentage points or less. As described above, particles having at least one peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve are referred to as "specific silica particles" in the present invention.

[0014] The toner according to this embodiment is capable of maintaining stable charging characteristics, and the mechanism by which this is achieved is presumed to be as follows. To improve the fluidity of toner, external additives (such as silica particles) with a particle size of about 20 nm to 80 nm are often used. These silica particles can increase the charge level under low humidity conditions, resulting in low image density. To solve the problem of low image density, it is known to suppress the charge level by using titanate compound particles such as strontium titanate in combination (see, for example, Patent Document 1). When silica particles and titanic acid compound particles are used together as external additives to toner, intermittent printing of low-density images one at a time over a long period of time in a low-temperature, low-humidity environment can sometimes result in toner contamination within the device and image fogging. Intermittent printing places a much greater stress on the toner than continuous printing because the developer is idle during setup. The cause of the contamination and fogging under these conditions is the mutual charging that occurs between the silica particles and titanic acid compound particles, the external additives, on the toner surface, resulting in a wider range of toner charge levels. In this embodiment, for silica particles and titanic acid compound particles, the following conditions of (a) particle size distribution peak position, (b) average circularity, and (c) toner coverage have made it possible to prevent toner contamination within the device and maintain stable charging characteristics without the occurrence of image fogging. It is presumed that by bringing the particle size distribution peak positions closer together and bringing the shape represented by the average circularity and the coverage closer together for the silica particles and titanic acid compound particles, mutual charging between the external additives, i.e., the silica particles and the titanic acid compound particles, on the toner surface has been suppressed. (a) Particle size distribution peak position: Both the silica particles and the titanic acid compound particles have at least one peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve. (b) Average circularity: The titanate compound particles have a rounded shape with an average circularity of 0.890 or more and 0.950 or less (details will be described later), and the difference between the average circularity of the specific silica particles and the average circularity of the titanate compound particles is 0.05 or less. (c) Toner coverage: The difference between the toner coverage of the specific silica particles and the toner coverage of the titanic acid compound particles is 20% points or less.

[0015] The configuration of the toner according to this embodiment will be described in detail below. [Toner particles] The toner particles contain, for example, a binder resin, and, if necessary, a colorant, a release agent, and other additives. -Binder resin- Examples of binder resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., 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 nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), and vinyl resins made of copolymers of two or more of these monomers. Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these. These binder resins may be used alone or in combination of two or more.

[0016] The binder resin is preferably a polyester resin, such as a condensation polymer of a polycarboxylic acid and a polyhydric alcohol.

[0017] Examples of polycarboxylic acids include aliphatic dicarboxylic acids (such as oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenylsuccinic acid, adipic acid, and sebacic acid), alicyclic dicarboxylic acids (such as cyclohexanedicarboxylic acid), aromatic dicarboxylic acids (such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). Among these, aromatic dicarboxylic acids are preferred as polycarboxylic acids. As the polycarboxylic acid, a trivalent or higher carboxylic acid having a crosslinked or branched structure may be used in combination with a dicarboxylic acid. Examples of the trivalent or higher carboxylic acid include trimellitic acid, pyromellitic acid, anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polycarboxylic acids may be used singly or in combination of two or more kinds.

[0018] Examples of polyhydric alcohols include aliphatic diols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, etc.), alicyclic diols (e.g., cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, etc.), and aromatic diols (e.g., ethylene oxide adducts of bisphenol A, propylene oxide adducts of bisphenol A, etc.). Among these, preferred polyhydric alcohols are aromatic diols and alicyclic diols, and more preferred are aromatic diols. As the polyhydric alcohol, a trihydric or higher polyhydric alcohol having a crosslinked or branched structure may be used in combination with the diol. Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, and pentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more.

[0019] The glass transition temperature (Tg) of the polyester resin is preferably 50°C or higher and 80°C or lower, and more preferably 50°C or higher and 65°C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, is determined from the "extrapolated glass transition onset temperature" described in the method for determining glass transition temperature in JIS K7121-1987 "Method for measuring transition temperature of plastics."

[0020] The weight average molecular weight (Mw) of the polyester resin is preferably 5,000 to 1,000,000, more preferably 7,000 to 500,000. The number average molecular weight (Mn) of the polyester resin is preferably 2,000 to 100,000. The molecular weight distribution (Mw / Mn) of the polyester resin is preferably 1.5 to 100, more preferably 2 to 60. The weight-average molecular weight and number-average molecular weight of polyester resins are measured by gel permeation chromatography (GPC). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC measuring device and a Tosoh TSKgel Super HM-M (15 cm) column in THF solvent. The weight-average molecular weight and number-average molecular weight are calculated from the measurement results using a molecular weight calibration curve created with monodisperse polystyrene standard samples.

[0021] The polyester resin can be obtained by a known production method, for example, by carrying out the reaction at a polymerization temperature of 180°C or higher and 230°C or lower, reducing the pressure in the reaction system as necessary, and removing water and alcohol generated during the condensation. If the raw material monomer is not soluble or compatible at the reaction temperature, a high-boiling solvent may be added as a solubilizer to dissolve it. In this case, the polycondensation reaction is carried out while distilling off the solubilizer. If a monomer with poor compatibility is present, it is advisable to first condense the poorly compatible monomer with the acid or alcohol to be polycondensed, and then polycondense it with the main component.

[0022] The content of the binder resin is 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.

[0023] -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, Examples of suitable dyes include pigments such as ultramarine blue, chalco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate; and 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.

[0024] 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. The content of the colorant is preferably from 1% by mass to 30% by mass, and more preferably from 3% by mass to 15% by mass, based on the total mass of the toner particles.

[0025] -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.

[0026] 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" described in the method for determining the melting temperature in JIS K7121-1987 "Method for measuring transition temperatures of plastics."

[0027] The content of the release agent is preferably from 1% by mass to 20% by mass, and more preferably from 5% by mass to 15% by mass, based on the total mass of the toner particles.

[0028] -Other additives- Examples of other additives include known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

[0029] [Characteristics of toner particles] 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 (core particle) and a coating layer (shell layer) that covers the core. The toner particles of the core-shell structure are composed of, for example, a core containing a binder resin and, if necessary, a colorant and a release agent, and the like, and a coating layer containing a binder resin.

[0030] 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.

[0031] The volume-average particle size of toner particles is measured using a Coulter Multisizer II (manufactured by Beckman Coulter) and an ISOTON-II (manufactured by Beckman Coulter). For measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5% by weight aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is then added to 100 ml to 150 ml of electrolyte. The electrolyte containing the suspended sample is dispersed in an ultrasonic disperser for 1 minute, and the particle sizes of particles ranging from 2 μm to 60 μm are measured using a Coulter Multisizer II with an aperture diameter of 100 μm. 50,000 particles are sampled. The volume-average particle size D50v is the particle size that represents the 50% cumulative size from the smallest diameter in the volume-based particle size distribution of the measured particle sizes.

[0032] In this embodiment, the average circularity of the toner particles is preferably 0.91 to 0.98, more preferably 0.94 to 0.98, and even more preferably 0.95 to 0.97, from the viewpoint of improving the cleaning property of the toner from the image carrier.

[0033] In this embodiment, the circularity of a toner particle is (the perimeter of a circle having the same area as the projected image of the particle) divided by (the perimeter of the projected image of the particle), and the average circularity of a toner particle is the cumulative circularity that is 50% from the smallest side in the circularity distribution. The average circularity of a toner particle is determined by analyzing at least 3,000 toner particles using a flow-type particle image analyzer.

[0034] When toner particles are produced by an aggregation-coalescence method, the average circularity of the toner particles can be controlled by adjusting the stirring speed of the dispersion, the temperature of the dispersion, or the retention time in the fusion-coalescence step.

[0035] [Silica particles] The silica particles used as an external additive to the toner in this embodiment include particles having a primary particle size of 80 nm or less. In this embodiment, the silica particles used as an external additive to the toner may have a particle size distribution that is monodisperse or polydisperse, or may be polydisperse silica particles obtained by mixing monodisperse silica particles. The "specific silica particles" in this embodiment have at least one peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve, the difference in average circularity between the specific silica particles and the titanate compound particles is 0.05 or less, and the difference in toner coverage between the specific silica particles and the titanate compound particles is 20 percentage points or less. The specific silica particles preferably have one peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve, but may have multiple peaks. When multiple peaks exist, the peak with the largest number of particles is defined as the "specific silica particles" in this embodiment. From the viewpoint of improving the fluidity of the toner, the specific silica particles have at least one peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve, preferably in the range of 30 nm or more and less than 80 nm, and more preferably in the range of 40 nm or more and less than 80 nm. In order to maintain stable charging characteristics of the toner, it is preferable that the specific silica particles and the titanic acid compound particles have similar shapes and coverage in the toner. From the above viewpoints, the difference in average circularity between the specific silica particles and the titanic acid compound particles is 0.05 or less. The difference in average circularity is preferably 0.03 or less, and particularly preferably 0.01 or less. Furthermore, the difference in toner coverage between the specific silica particles and the titanic acid compound particles is 20% or less. The difference in coverage is preferably 15% or less, particularly preferably 10% or less, and more preferably 5% or less. When the difference in average circularity is greater than the above value, or when the difference in coverage is greater than the above value, mutual charging tends to occur between the specific silica particles and the titanate compound particles. In order to maintain stable charging characteristics of the toner, it is preferable that the particle size and peak shape of the specific silica particles and the titanic acid compound particles are similar to each other. From the above viewpoints, the difference in particle size between the specific silica particles and the titanate compound particles, each with a maximum peak in the range of 20 nm to less than 80 nm, is preferably 20 nm or less, more preferably 15 nm or less, and particularly preferably 10 nm or less.Furthermore, the difference in half width of the peak in the range of 20 nm to less than 80 nm on the number primary particle size distribution curve of the specific silica particles and the peak in the range of 20 nm to less than 80 nm on the number primary particle size distribution curve of the titanate compound particles is preferably 20 nm or less, more preferably 10 nm or less. When the difference in particle size is larger than the above value, or when the half-value width is larger than the above value, mutual charging tends to occur between the specific silica particles and the titanic acid compound particles. It is preferable that the particle size of the specific silica particles having the maximum peak in the range of 20 nm or more and less than 80 nm is larger, because the larger the particle size, the greater the contribution to charging the toner, and in order to maintain the charge level of the negatively chargeable toner, it is preferable to increase the size of the silica having a high negative chargeability.

[0036] (Characteristics of specific silica particles) - Hydrophobicity - The hydrophobicity of the specific silica particles according to this embodiment is preferably 10% to 60%, more preferably 10% to 50%, and even more preferably 20% to 50% from the viewpoint of narrowing the charge distribution. If the hydrophobicity of the silica particles is 10% or less, the amount of coating on the structure due to the reaction product of the silane coupling agent is low, and the content of the nitrogen-containing compound tends to decrease, which makes the charge distribution more likely to spread. On the other hand, when the hydrophobicity of silica particles exceeds 60%, the density of the structure increases due to the reaction of the silane coupling agent, the pores become smaller, and the content of nitrogen-containing compounds tends to decrease, which makes the charge distribution more likely to spread. The hydrophobic treatment is carried out, for example, by immersing the silica particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, but 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, for example, 1 to 10 parts by mass per 100 parts by mass of the silica particles.

[0037] The hydrophobicity of silica particles is measured as follows. 0.2% by mass of sample silica particles is placed in 50 ml of ion-exchanged water, and methanol is added dropwise from a burette while stirring with a magnetic stirrer. The mass fraction of methanol in the methanol-water mixed solution at the end point when the entire sample has sunk is determined as the degree of hydrophobicity.

[0038] -Number primary particle size distribution curve and average primary particle size- The average primary particle size of the specific silica particles according to this embodiment is preferably 10 nm or more and 200 nm or less, more preferably 10 nm or more and 80 nm or less, and even more preferably 10 nm or more and 60 nm or less. When the average primary particle diameter of the specific silica particles is within the above range, the specific surface area is large and excessive charging is likely to occur. However, the silica particles according to this embodiment achieve a narrow charge distribution even when the average primary particle diameter is within the above range.

[0039] Here, the number primary particle size distribution curve and average primary particle size of the specific silica particles are measured as follows. Toner particles with externally added silica particles are observed under a scanning electron microscope (SEM) at 40,000x magnification, and the images of the silica particles on the observed toner particles are analyzed using image processing analysis software WinRoof (manufactured by Mitani Corporation) to determine the circle-equivalent diameters of at least 300 particles. A distribution curve is then drawn for the number of individual particles, starting from the smallest diameter, to obtain a number primary particle size distribution curve. The silica particles of this embodiment have at least one peak in the range of 20 nm to 80 nm. Furthermore, a cumulative distribution of the number of individual particles is drawn starting from the smallest diameter side, and the particle size at 50% of the cumulative total from the smallest diameter side, the average primary particle size, is determined. The number primary particle size distribution curve and average primary particle size of titanic acid compound particles, which will be described later, are also measured in the same manner.

[0040] -Circularity- The average circularity of the specific silica particles according to this embodiment is preferably 0.85 or more and 1.00 or less, more preferably 0.88 or more and 0.96 or less, and even more preferably 0.90 or more and 0.95 or less. When the average circularity of the specific silica particles is within the above range, the specific surface area is large and excessive charging is likely to occur. However, the silica particles according to this embodiment achieve a narrow charge distribution even when the average circularity is within the above range.

[0041] Here, the average circularity of the silica particles is measured as follows. The toner with externally added silica particles was observed at 40,000x magnification using a scanning electron microscope (SEM), and the images of the silica particles on the observed toner particles were analyzed using image processing analysis software WinRoof (manufactured by Mitani Shoji Co., Ltd.) to determine the circularity of 300 or more particles, and the average circularity was calculated by arithmetic averaging. The circularity is calculated by the following formula: A specific measurement method will be described in the Examples below. Circularity = (perimeter of a circle with the same area as a particle) ÷ (perimeter of the particle image) = 4π × (area of ​​particle) ÷ (perimeter of particle image) 2 The average circularity of titanate compound particles, which will be described later, is also measured in the same manner.

[0042] -Coverage rate- The coverage of the toner particles with the specific silica particles is preferably 5% to 40%, more preferably 8% to 35%. The coverage is proportional to the amount of silica particles added, and if the coverage is too low, the toner fluidity tends to deteriorate, while if the coverage is too high, low image density problems tend to occur under low humidity conditions. The coverage can be adjusted mainly by the amount of external additives such as silica particles added to the toner. The amount of specific silica particles added (external addition amount) is preferably 0.1 parts by mass or more and 10 parts by mass or less, more preferably 0.5 parts by mass or more and 7.0 parts by mass or less, and even more preferably 1.0 parts by mass or more and 5.0 parts by mass or less, relative to 100 parts by mass of toner particles.

[0043] Here, the coverage of the toner particles with the silica particles is measured as follows. Toner with externally added silica particles is observed at 40,000x magnification using a scanning electron microscope (SEM). The image of the observed toner is then binarized into each external additive particle and the toner base particle. The ratio of the area of ​​silica particles to the other areas in a specific region is calculated using the image processing analysis software WinRoof (Mitani Shoji Co., Ltd.), and the toner coverage rate by silica is calculated as the arithmetic average of 300 or more particles. In practice, analysis is performed on toner particles to which both silica particles and titanic acid compound particles are externally added. Images of each external additive, such as silica particles and titanic acid compound particles, are distinguished from the toner base particles using low-acceleration SEM conditions or an energy dispersive X-ray analyzer (EDX analyzer), and the areas of the silica particles or titanic acid compound particles and other particles are determined to determine the coverage. Specific measurement methods are described in the Examples below. The coverage of the toner particles with the titanic acid compound particles is also measured in a similar manner.

[0044] -Ratio of primary particles- It is believed that the specific silica particles and titanic acid compound particles will be mutually charged if they are unevenly distributed on the toner, and therefore it is considered preferable that they are in a dispersed state on the toner. Therefore, the proportion of the external additive (the total of the specific silica particles and titanic acid compound particles) present as primary particles is preferably 10% or more, and more preferably 15% or more. The proportion of primary particles is measured by the following method. A toner containing silica particles and an external additive containing a titanic acid compound is observed at 40,000x magnification using a scanning electron microscope (SEM). The number of external additive particles (Y) present in aggregate with the external additive (X) present as primary particles within a specific area on the obtained SEM image is counted, and the proportion of primary particles is calculated using the following formula. The specific measurement method is described in the Examples section below. Primary particle abundance (%) = X ÷ (X + Y) × 100

[0045] (Method of manufacturing specific silica particles) The specific silica particles are preferably silica particles produced by a wet process from the viewpoint of controlling the primary particle size and obtaining silica particles having a monodisperse particle size distribution. A preferred wet method for producing specific silica particles is a sol-gel method using tetraalkoxysilane as a material. The sol-gel method for producing silica particles is well known. The sol-gel method includes, for example, adding ammonia water dropwise to a mixture of tetraalkoxysilane, water, and alcohol to prepare a silica sol suspension, centrifuging wet silica gel from the silica sol suspension, and drying the wet silica gel to obtain silica particles. Examples of tetraalkoxysilane include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane.

[0046] [Titanium oxide compound particles] As described above, the titanate compound particles of this embodiment have at least one peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve, the difference between the average circularity of the specific silica particles and the average circularity of the titanate compound particles is 0.05 or less, and the difference between the toner coverage rate of the specific silica particles and the toner coverage rate of the titanate compound particles is 20 percentage points or less.

[0047] The titanate compound particles preferably have one peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve, but may have multiple peaks.If multiple peaks exist, the peak with the largest number of particles is the titanate compound particle of this embodiment. From the viewpoint of improving the fluidity of the toner, the titanate compound particles have at least one peak in the range of 20 nm or more and less than 80 nm in the number primary particle size distribution curve, preferably in the range of 20 nm or more and less than 60 nm, and more preferably in the range of 30 nm or more and less than 60 nm. From the viewpoint of excellent transfer retention, the shape of the titanate compound particles is preferably rounded rather than cubic or rectangular. Titanate compound particles have a perovskite crystal structure and are usually cubic or rectangular parallelepiped in shape. However, in cubic or rectangular parallelepiped titanate compound particles, i.e., titanate compound particles with corners, electric charges are concentrated at the corners, which creates a large electrostatic repulsion force locally between the corners and the silica particles, which is thought to easily cause uneven distribution of the silica particles. In order to maintain transfer efficiency for a long period of time under low-temperature and low-humidity environments, it is preferable that the shape of the titanate compound particles be a shape with few corners, i.e., a rounded shape.

[0048] The titanate compound particles have an average primary particle circularity of 0.890 or more and 0.950 or less, preferably 0.890 or more and 0.940 or less, more preferably 0.895 or more and 0.935 or less, and even more preferably 0.885 or more and 0.930 or less, from the viewpoint of maintaining the transferability of the toner through the particles and from the viewpoint of making the difference in average circularity from the specific silica particles 0.05 or less in order to approximate the shape of the specific silica particles. In this embodiment, the circularity of the primary particle of the titanate compound particle is expressed as 4π × (area of ​​the primary particle image) ÷ (perimeter of the primary particle image). 2The average circularity of primary particles is the cumulative circularity of the smallest 50% in the circularity distribution. The circularity of titanic acid compound particles is determined by taking an electron microscope image of a toner to which titanic acid compound particles have been externally added and analyzing the image of at least 300 titanic acid compound particles on the toner particles. A specific measurement method is described in the Examples below.

[0049] From the viewpoint of improving the fluidity of the toner, the titanate compound particles preferably have an average primary particle size of 10 nm or more and 100 nm or less. If the average primary particle size of the titanate compound particles is too small, they tend to be easily embedded in the toner particles, and the effect of improving the fluidity of the toner tends to be difficult to achieve. If the average primary particle size of the titanate compound particles is too large, they tend to roll on the surface of the toner particles and be unevenly distributed in the recesses of the irregularly shaped toner particles, and the effect of improving the fluidity of the toner tends to be difficult to achieve. From the above viewpoint, the average primary particle size of the titanate compound particles is preferably 10 nm or more and 100 nm or less, more preferably 20 nm or more and 80 nm or less, even more preferably 20 nm or more and 60 nm or less, and even more preferably 30 nm or more and 60 nm or less.

[0050] In this embodiment, the primary particle size of titanate compound particles is the diameter of a circle having the same area as the primary particle image (so-called circle equivalent diameter), and the average primary particle size of titanate compound particles is the particle size that is the cumulative 50% from the smallest diameter side in the number-based distribution of primary particle sizes. The primary particle size of titanate compound particles is determined by taking an electron microscope image of a toner to which titanate compound particles have been externally added and analyzing the image of at least 300 titanate compound particles on the toner particle. Specific measurement methods are described in the Examples below. The circularity, peak position and average primary particle size of the titanate compound particles can be controlled, for example, by varying the various conditions used when producing the titanate compound particles by a wet process.

[0051] The coverage of the toner particles with the titanate compound particles is preferably 5% to 40%, more preferably 8% to 35%. The coverage is proportional to the amount of silica particles added, and if the coverage is too low, the toner fluidity tends to deteriorate, while if the coverage is too high, low image density problems tend to occur under low humidity conditions.

[0052] Preferred examples of titanate compound particles include metal titanate particles. From the viewpoint of stable chargeability under various environments, strontium titanate particles, magnesium titanate particles, and calcium titanate particles are preferred, and strontium titanate particles are more preferred.

[0053] The titanate compound particles are preferably doped with a metal element (hereinafter also referred to as a dopant) other than titanium and the metals constituting the titanate compound. By including the dopant, the crystallinity of the perovskite structure of the titanate compound particles decreases, resulting in a rounded shape.

[0054] The dopant of the titanate compound particles is not particularly limited as long as it is a metal element other than titanium and the metals constituting the titanate compound. A metal element having an ionic radius that can be incorporated into the crystalline structure constituting the titanate compound particles when ionized is preferred. From this perspective, the dopant of the titanate compound particles is preferably a metal element having an ionic radius of 40 pm or more and 200 pm or less when ionized, more preferably a metal element having an ionic radius of 60 pm or more and 150 pm or less.

[0055] When the titanate compound is strontium titanate, the dopant for the titanate compound particles may specifically include lanthanoids, silica, aluminum, magnesium, calcium, barium, phosphorus, sulfur, calcium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, gallium, yttrium, zinc, niobium, molybdenum, ruthenium, rhodium, palladium, silver, indium, tin, antimony, barium, tantalum, tungsten, rhenium, osmium, iridium, platinum, and bismuth. Preferred lanthanoids are lanthanum and cerium. Among these, lanthanum is preferred from the viewpoint of ease of doping and easy shape control of the titanate compound particles.

[0056] Furthermore, in order to prevent the titanate compound particles from being excessively negatively charged, when the titanate compound is strontium titanate, the dopant for the titanate compound particles is preferably a metal element having an electronegativity of 2.0 or less, more preferably a metal element having an electronegativity of 1.3 or less. In this embodiment, the electronegativity is the Allred-Rochow electronegativity. Examples of metal elements with an electronegativity of 2.0 or less include lanthanum (electronegativity 1.08), magnesium (1.23), aluminum (1.47), silica (1.74), calcium (1.04), vanadium (1.45), chromium (1.56), manganese (1.60), iron (1.64), cobalt (1.70), nickel (1.75), copper (1.75), zinc (1.66), gallium (1.82), yttrium (1.11), zirconium (1.22), niobium (1.23), silver (1.42), indium (1.49), tin (1.72), barium (0.97), tantalum (1.33), rhenium (1.46), and cerium (1.06). Among these, lanthanum is preferred.

[0057] In order to achieve a rounded shape while maintaining a perovskite-type crystal structure, the amount of dopant in the titanate compound particles is preferably in the range of 0.1 mol % to 20 mol % relative to the metal element such as strontium, 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 %.

[0058] The titanate compound particles preferably have a water content of 1.5% by mass or more and 10% by mass or less. When the water content is 1.5% by mass or more and 10% by mass or less (more preferably 2% by mass or more and 5% by mass or less), the resistance of the titanate compound particles is controlled within an appropriate range, and uneven distribution due to electrostatic repulsion between titanate compound particles is effectively suppressed. The water content of the titanate compound particles can be controlled, for example, by producing the titanate compound particles by a wet method and adjusting the temperature and time of a drying treatment. When the titanate compound particles are subjected to a hydrophobic treatment, the water content of the titanate compound particles can be controlled by adjusting the temperature and time of a drying treatment after the hydrophobic treatment.

[0059] The water content of the titanate compound particles is measured as follows. 20 mg of the measurement sample is left to stand in a chamber at a temperature of 22°C and a relative humidity of 55% for 17 hours to condition the humidity, and then heated from 30°C to 250°C at a temperature increase rate of 30°C / min in a nitrogen gas atmosphere using a thermobalance (Shimadzu TGA-50 model) in a room at a temperature of 22°C and a relative humidity of 55%, and the loss on heating (mass lost by heating) is measured. Then, the moisture content is calculated based on the measured heat loss using the following formula. Moisture content (mass%) = (heat loss from 30°C to 250°C) ÷ (mass after humidity control before heating) × 100

[0060] From the viewpoint of improving the function of the titanate compound particles, the titanate compound particles are preferably titanate compound particles having a hydrophobized surface, and more preferably titanate compound particles having a hydrophobized surface with a silicon-containing organic compound.

[0061] -Method of manufacturing titanate compound particles- The titanate compound particles may be titanate compound particles themselves, or may be titanate compound particles whose surfaces have been subjected to hydrophobic treatment. The method for producing the titanate compound particles is not particularly limited, but a wet method is preferred from the viewpoint of controlling the particle size and shape.

[0062] -Production of titanate compound particles The wet method for producing titanate compound particles is, for example, a method in which a mixture of a titanium oxide source and a metal source such as strontium is reacted with an aqueous alkaline solution, followed by an acid treatment. In this production method, the particle size of the titanate compound particles can be controlled by the mixing ratio of the titanium oxide source and the metal source, the concentration of the titanium oxide source at the start of the reaction, the temperature and rate of addition of the aqueous alkaline solution, etc.

[0063] The titanium oxide source is preferably a mineral acid peptized product of a hydrolyzed titanium compound. The metal source includes nitrates, chlorides, etc. When the metal is strontium, the strontium source includes strontium nitrate, strontium chloride, etc.

[0064] The mixing ratio of the titanium oxide source and the metal source, where the metal is expressed as MO, is preferably an MO / TiO2 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 TiO2 at the initial stage of the reaction is preferably 0.05 to 1.3 mol / L, more preferably 0.5 to 1.0 mol / L.

[0065] In order to obtain titanate compound particles with a rounded shape rather than a cube or a rectangular parallelepiped, it is preferable to add a dopant source to a mixture of a titanium oxide source and a metal source. Examples of dopant sources include oxides of metals other than titanium and strontium. The metal oxide used as the dopant source is added as a solution dissolved in, for example, nitric acid, hydrochloric acid, or sulfuric acid. The amount of dopant source added is preferably such that the amount of metal contained in the dopant source is 0.1 to 20 moles, more preferably 0.5 to 10 moles, per 100 moles of metal contained in the metal source, such as strontium.

[0066] The alkaline aqueous solution is preferably a sodium hydroxide aqueous solution. The higher the temperature of the reaction solution when the alkaline aqueous solution is added, the better the crystallinity of the resulting titanate compound particles. The temperature of the reaction solution when the alkaline aqueous solution is added is preferably in the range of 60°C to 100°C, in order to obtain titanate compound particles with a rounded shape while maintaining a perovskite-type crystal structure. The slower the addition rate of the alkaline aqueous solution, the larger the particle size of the resulting titanate compound particles, and the faster the addition rate, the smaller the particle size of the resulting titanate compound 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 charged raw material.

[0067] After the addition of the alkaline aqueous solution, an acid treatment is carried out to remove unreacted metal sources. The acid treatment involves adjusting the pH of the reaction solution to 2.5 to 7.0, preferably 4.5 to 6.0, using, for example, hydrochloric acid. After the acid treatment, the reaction solution is subjected to solid-liquid separation, and the solid content is dried to obtain titanate compound particles.

[0068] Surface treatment The surface treatment of the titanic acid compound particles is carried out, for example, by preparing a treatment liquid by mixing a silicon-containing organic compound, which is a hydrophobic treatment agent, with a solvent, and mixing the titanic acid compound particles with the treatment liquid under stirring, and further continuing stirring. After the surface treatment, a drying treatment is carried out to remove the solvent from the treatment liquid.

[0069] Examples of the silicon-containing organic compound used for the surface treatment of the titanic acid compound particles include alkoxysilane compounds, silazane compounds, and silicone oils.

[0070] Examples of alkoxysilane compounds used for the surface treatment of titanic acid compound particles include tetramethoxysilane, tetraethoxysilane, methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, and hexyltriethoxysilane. Examples of suitable silanes include dimethylsilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane, trimethylmethoxysilane, and trimethylethoxysilane.

[0071] Examples of the silazane compound used for the surface treatment of the titanic acid compound particles include dimethyldisilazane, trimethyldisilazane, tetramethyldisilazane, pentamethyldisilazane, and hexamethyldisilazane.

[0072] Examples of silicone oils used for the surface treatment of titanic acid compound particles include silicone oils such as dimethylpolysiloxane, diphenylpolysiloxane, and phenylmethylpolysiloxane; and reactive silicone oils such as amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, carbinol-modified polysiloxane, fluorine-modified polysiloxane, methacryl-modified polysiloxane, mercapto-modified polysiloxane, and phenol-modified polysiloxane.

[0073] As the solvent used in preparing the treatment liquid, when the silicon-containing organic compound is an alkoxysilane compound or a silazane compound, an alcohol (e.g., methanol, ethanol, propanol, butanol) is preferred, and when the silicon-containing organic compound is a silicone oil, a hydrocarbon (e.g., benzene, toluene, normal hexane, normal heptane) is preferred.

[0074] In the treatment liquid, the concentration of the silicon-containing organic compound is preferably 1% by mass to 50% by mass, more preferably 5% by mass to 40% by mass, and even more preferably 10% by mass to 30% by mass.

[0075] The amount of the silicon-containing organic compound used for surface treatment is preferably 1 part by mass or more and 50 parts by mass or less, more preferably 5 parts by mass or more and 40 parts by mass or less, and even more preferably 5 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the titanate compound particles.

[0076] The amount of titanic acid compound particles added externally is preferably 0.2 to 4 parts by mass, more preferably 0.4 to 3 parts by mass, and even more preferably 0.6 to 2 parts by mass, per 100 parts by mass of toner particles.

[0077] The amount of titanic acid compound particles added externally is preferably 10 to 100 parts by mass, more preferably 20 to 90 parts by mass, and even more preferably 30 to 80 parts by mass, per 100 parts by mass of silica particles.

[0078] [Other external additives] The toner according to the present embodiment may contain external additives other than silica particles and titanic acid compound particles, as long as the effects of the present embodiment can be obtained. Examples of the external additives include the following inorganic particles and resin particles.

[0079] Other external additives include, for example, inorganic particles such as TiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, K2O·(TiO2)n, Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, and MgSO4.

[0080] The surfaces of inorganic particles as 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 usually 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles.

[0081] Other external additives 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.

[0082] The amount of other external additives added is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, based on the toner particles.

[0083] [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.

[0084] 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). There are no particular limitations on these production methods, and any known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0085] Specifically, for example, when toner particles are produced by the aggregation-coalescence method, the toner particles are produced through the following steps: a step of preparing a resin particle dispersion in which resin particles to be a binder resin are dispersed (resin particle dispersion preparation step); a step of aggregating the resin particles (and other particles, if necessary) in the resin particle dispersion (in a dispersion after mixing other particle dispersions, if necessary) to form aggregated particles (aggregated particle formation step); and a step of heating the aggregated particle dispersion in which the aggregated particles are dispersed to fuse and coalesce the aggregated particles to form toner particles (fusion and coalescence step).

[0086] 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, other additives than the colorant and the release agent may also be used.

[0087] -Resin particle dispersion preparation process- Along with a resin particle dispersion in which resin particles serving as a binder resin are dispersed, for example, a colorant particle dispersion in which colorant particles are dispersed and a release agent particle dispersion in which release agent particles are dispersed are prepared.

[0088] The resin particle dispersion is prepared, for example, by dispersing resin particles in a dispersion medium using a surfactant. Examples of the dispersion medium used in the resin particle dispersion include aqueous media. Examples of aqueous media include water such as distilled water and ion-exchanged water, alcohols, etc. These may be used alone or in combination of two or more.

[0089] Examples of surfactants include anionic surfactants such as sulfate ester salts, sulfonate salts, phosphate esters, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; and nonionic surfactants such as polyethylene glycols, alkylphenol ethylene oxide adducts, and polyhydric alcohols. Among these, anionic surfactants and cationic surfactants are particularly preferred. Nonionic surfactants may be used in combination with anionic surfactants or cationic surfactants. The surfactants may be used alone or in combination of two or more.

[0090] In a resin particle dispersion, resin particles can be dispersed in a dispersion medium by common dispersion methods such as a rotary shear homogenizer, a ball mill with media, a sand mill, or a Dynomill. Depending on the type of resin particles, the resin particles may be dispersed in a dispersion medium by a phase inversion emulsification method. The phase inversion emulsification method involves dissolving the resin to be dispersed in a hydrophobic organic solvent in which the resin is soluble, neutralizing the organic continuous phase (O phase) by adding a base, and then introducing an aqueous medium (W phase) to invert the phase from W / O to O / W, thereby dispersing the resin in particulate form in the aqueous medium.

[0091] The volume average particle size of the resin particles dispersed in the resin particle dispersion is, for example, preferably from 0.01 μm to 1 μm, more preferably from 0.08 μm to 0.8 μm, and even more preferably from 0.1 μm to 0.6 μm. The volume average particle size of resin particles is measured using a particle size distribution obtained by measurement with a laser diffraction particle size distribution analyzer (e.g., LA-700 manufactured by Horiba, Ltd.), and the cumulative distribution for the volume of the divided particle size range (channel) is subtracted from the small particle size side, and the particle size at which the cumulative 50% of all particles is measured is taken as the volume average particle size D50v. The volume average particle sizes of particles in other dispersions are measured in the same way.

[0092] The content of resin particles contained in the resin particle dispersion is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less.

[0093] In the same manner as in the resin particle dispersion, for example, a colorant particle dispersion and a release agent particle dispersion are also prepared. That is, the volume average particle size, dispersion medium, dispersion method, and particle content of the particles in the resin particle dispersion are the same for the colorant particles dispersed in the colorant particle dispersion and the release agent particles dispersed in the release agent particle dispersion.

[0094] -Agglomerated particle formation process- Next, the resin particle dispersion, the colorant particle dispersion, and the release agent particle dispersion are mixed together, and the resin particles, the colorant particles, and the release agent particles are hetero-aggregated in the mixed dispersion to form aggregated particles containing the resin particles, the colorant particles, and the release agent particles and having a diameter close to that of the target toner particles.

[0095] Specifically, for example, an aggregating agent is added to the mixed dispersion, and the pH of the mixed dispersion is adjusted to be acidic (for example, pH 2 or higher and 5 or lower), and a dispersion stabilizer is added as necessary. After that, the mixed dispersion is heated to a temperature close to the glass transition temperature of the resin particles (specifically, for example, the glass transition temperature of the resin particles -30°C or higher and the glass transition temperature -10°C or lower), causing the particles dispersed in the mixed dispersion to aggregate and form aggregated particles. In the aggregate particle formation step, for example, the mixed dispersion may be stirred with a rotary shear homogenizer, an aggregating agent may be added at room temperature (e.g., 25°C), the pH of the mixed dispersion may be adjusted to an acidic value (e.g., pH 2 or more and 5 or less), a dispersion stabilizer may be added as needed, and then the mixture may be heated.

[0096] Examples of the flocculant include a surfactant having a polarity opposite to that of the surfactant contained in the mixed dispersion, an inorganic metal salt, and a divalent or higher metal complex. When a metal complex is used as the flocculant, the amount of surfactant used can be reduced, and the charging characteristics can be improved. If necessary, an additive that forms a complex or a similar bond with the metal ions of the flocculant may be used together with the flocculant, and a chelating agent is preferably used as this additive.

[0097] Examples of inorganic metal salts include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate; and inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, and calcium polysulfide. The chelating agent may be a water-soluble chelating agent, for example, hydroxycarboxylic acids such as tartaric acid, citric acid, and gluconic acid; aminocarboxylic acids such as iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), and ethylenediaminetetraacetic acid (EDTA); and the like. The amount of the chelating agent added is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.1 parts by mass or more and less than 3.0 parts by mass, relative to 100 parts by mass of the resin particles.

[0098] -Fusion / coalescence process- Next, the aggregated particle dispersion liquid in which the aggregated particles are dispersed is heated, for example, to a temperature equal to or higher than the glass transition temperature of the resin particles (for example, a temperature 10°C to 30°C higher than the glass transition temperature of the resin particles), to fuse and coalesce the aggregated particles and form toner particles.

[0099] Through the above steps, toner particles are obtained. After obtaining the aggregated particle dispersion liquid in which the aggregated particles are dispersed, the toner particles may be produced through the following steps: a step of further mixing the aggregated particle dispersion liquid with a resin particle dispersion liquid in which resin particles are dispersed, and aggregating the aggregated particles so that further resin particles adhere to the surfaces of the aggregated particles to form second aggregated particles; and a step of heating the second aggregated particle dispersion liquid in which the second aggregated particles are dispersed, and fusing and coalescing the second aggregated particles to form toner particles having a core-shell structure.

[0100] After the fusion and coalescence process is completed, the toner particles formed in the solution are subjected to a known washing process, solid-liquid separation process, and drying process to obtain dried toner particles. In the washing process, from the viewpoint of chargeability, it is preferable to perform sufficient substitution washing with ion-exchanged water. In the solid-liquid separation process, from the viewpoint of productivity, it is preferable to perform suction filtration, pressure filtration, etc. In the drying process, from the viewpoint of productivity, it is preferable to perform freeze drying, flash drying, fluidized drying, vibration-type fluidized drying, etc.

[0101] The toner according to this 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.

[0102] <Electrostatic image developer> The electrostatic image developer according to the present embodiment contains at least the toner according to the present embodiment. The electrostatic image developer according to the present embodiment may be a one-component developer containing only the toner according to the present embodiment, or may be a two-component developer in which the toner is mixed with a carrier.

[0103] The carrier is not particularly limited, and known carriers can be used. Examples of the carrier include coated carriers in which the surface of a core material made of magnetic powder is coated with a resin; magnetic powder dispersion carriers in which magnetic powder is dispersed in a matrix resin; and resin-impregnated carriers in which porous magnetic powder is impregnated with a resin. The magnetic powder dispersion carrier and the resin-impregnated carrier may be carriers in which the constituent particles of the carrier are used as a core material and the surface of the core material is coated with a resin.

[0104] Examples of magnetic powder include magnetic metals such as iron, nickel, and cobalt; and magnetic oxides such as ferrite and magnetite.

[0105] 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, fluororesin, polyester, polycarbonate, phenolic resin, and epoxy resin. The coating resin and matrix resin may contain 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.

[0106] Examples of methods for coating the surface of a core material with a resin include coating with a coating layer-forming solution prepared by dissolving the coating resin and various additives (used as needed) in an appropriate solvent. The solvent is not particularly limited and may be selected taking into consideration the type of resin used, its applicability, and other factors. Specific resin coating methods include an immersion method in which the core material is immersed in the coating layer-forming solution; a spray method in which the coating layer-forming solution is sprayed onto the surface of the core material; a fluidized bed method in which the coating layer-forming solution is sprayed onto the core material while suspended in flowing air; and a kneader coater method in which the carrier core material and the coating layer-forming solution are mixed in a kneader coater and then the solvent is removed.

[0107] The mixing ratio (mass ratio) of the toner and the carrier in the two-component developer is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100.

[0108] <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.

[0109] 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.

[0110] 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. When the image forming apparatus according to the present embodiment is an apparatus of the intermediate transfer type, 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 for primarily transferring the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means for secondarily transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0111] 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.

[0112] 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. In the following description, the main parts shown in the drawings will be described, and descriptions of other parts will be omitted.

[0113] 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. These units 10Y, 10M, 10C, and 10K may be process cartridges that are detachably attached to the image forming apparatus.

[0114] An intermediate transfer belt (an example of an intermediate transfer body) 20 extends above each of the units 10Y, 10M, 10C, and 10K and passes through each unit. The intermediate transfer belt 20 is wound around a drive roll 22 and a support roll 24, which are in contact with the inner surface of the intermediate transfer belt 20, and runs in a direction from the first unit 10Y to the fourth unit 10K. A force is applied to the support roll 24 by a spring or the like (not shown) in a direction away from the drive roll 22, and tension is applied to the intermediate transfer belt 20 wound around them. An intermediate transfer belt cleaning device 30 is provided on the image bearing surface side of the intermediate transfer belt 20, facing the drive roll 22.

[0115] The developing devices (examples of developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K are supplied with yellow, magenta, cyan, and black toner contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0116] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, we will explain here the first unit 10Y, which forms a yellow image and is arranged upstream in the direction of travel of the intermediate transfer belt.

[0117] The first unit 10Y has a photoconductor 1Y that acts as an image carrier. Around the photoconductor 1Y, there are arranged in this order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoconductor 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 (an example of a primary transfer means) 5Y that transfers the developed toner image onto the intermediate transfer belt 20; and a photoconductor cleaning device (an example of an image carrier cleaning means) 6Y that removes toner remaining on the surface of the photoconductor 1Y after the primary transfer.

[0118] The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is provided at a position facing the photoreceptor 1Y. A bias power supply (not shown) that applies a primary transfer bias is connected to the primary transfer rolls 5Y, 5M, 5C, and 5K of each unit. Each bias power supply changes the value of the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

[0119] The operation of forming a yellow image in the 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, a volume resistivity of 1×10 at 20°C).-6 The 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, the resistivity of the irradiated portion changes. Therefore, the exposed surface of the photosensitive element 1Y is irradiated with a laser beam 3Y from the exposure device 3 in accordance with image data for yellow sent from a control unit (not shown). This forms an electrostatic charge image of a yellow image pattern on the surface of the photosensitive element 1Y.

[0120] 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 rotates to a predetermined development position as the photoreceptor 1Y moves, and at this development position, the electrostatic image on the photoreceptor 1Y is developed into a toner image by the developing device 4Y and made visible.

[0121] 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 stirring 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.

[0122] When the yellow toner image on photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to primary transfer roll 5Y, and electrostatic force from photoreceptor 1Y to primary transfer roll 5Y acts on the toner image, causing the toner image on photoreceptor 1Y to be transferred onto intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the (-) polarity of the toner, and is controlled to, for example, +10 μA by a control unit (not shown) in first unit 10Y. Any toner remaining on photoreceptor 1Y is removed and collected by photoreceptor cleaning device 6Y.

[0123] 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 superimposed and transferred.

[0124] 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 feed 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.

[0125] The recording paper P onto which the toner image has been transferred is sent to the pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of a fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image. After the color image has been fixed, the recording paper P is conveyed toward the discharge portion, and the series of color image forming operations is completed.

[0126] Examples of recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copiers, printers, etc. Examples of recording media include overhead projector sheets and the like in addition to recording paper P. 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, and for example, coated paper in which the surface of plain paper is coated with a resin or the like, art paper for printing, etc. are preferably used.

[0127] <Process cartridges, toner cartridges> 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.

[0128] The process cartridge according to this embodiment may be configured to include a developing means 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.

[0129] An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0130] FIG. 2 is a schematic diagram showing an example 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).

[0131] 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.

[0132] 1 is an image forming apparatus having a configuration in which toner cartridges 8Y, 8M, 8C, and 8K are detachably attached, and developing devices 4Y, 4M, 4C, and 4K are connected to toner cartridges corresponding to the respective colors by toner supply pipes (not shown). When the toner contained in a toner cartridge runs low, the toner cartridge is replaced. [Example]

[0133] Hereinafter, embodiments of the present invention will be described in detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" are by mass.

[0134] <Production of toner particles> -Preparation of resin particle dispersion- Terephthalic acid: 30 parts by mole Fumaric acid: 70 parts by mole Bisphenol A ethylene oxide adduct: 5 parts by mole Bisphenol A propylene oxide adduct: 95 parts by mole The above materials were placed in a flask equipped with a stirrer, nitrogen inlet tube, temperature sensor, and distillation column, and the temperature was raised to 220°C over 1 hour. Then, 1 part of titanium tetraethoxide was added per 100 parts of the above materials. The temperature was raised to 230°C over 30 minutes while distilling off the resulting water. The dehydration condensation reaction was continued at that temperature for 1 hour, and the reaction mixture was then cooled. This yielded a polyester resin with a weight-average molecular weight of 18,000 and a glass transition temperature of 60°C.

[0135] A vessel equipped with a temperature control device and a nitrogen purge device was charged with 40 parts of ethyl acetate and 25 parts of 2-butanol to form a mixed solvent. 100 parts of polyester resin was then gradually added and dissolved. A 10% by mass aqueous ammonia solution (equivalent to three times the molar amount of the resin's acid value) was then added and stirred for 30 minutes. The atmosphere inside the vessel was then purged with dry nitrogen, the temperature was maintained at 40°C, and 400 parts of ion-exchanged water was added dropwise at a rate of 2 parts / min while stirring the mixture. After the addition, the temperature was returned to room temperature (20°C to 25°C), and dry nitrogen was bubbled through the mixture for 48 hours while stirring to obtain a resin particle dispersion in which the ethyl acetate and 2-butanol concentrations were reduced to 1000 ppm or less. Ion-exchanged water was added to the resin particle dispersion to adjust the solids content to 20% by mass, yielding a resin particle dispersion.

[0136] -Preparation of colorant particle dispersion- ·CIPigment Blue 15:3 (Dainichiseika Industries): 70 copies Anionic surfactant (Daiichi Kogyo Seiyaku, Neogen RK): 5 parts Ion-exchanged water: 200 parts The above materials were mixed and dispersed for 10 minutes using a homogenizer (IKA, product name Ultra Turrax T50). Ion-exchanged water was added so that the solid content of the dispersion was 20% by mass, and a colorant particle dispersion containing colorant particles with a volume average particle size of 170 nm was obtained.

[0137] -Preparation of release agent particle dispersion- Paraffin wax (Nippon Seiro, HNP-9): 100 parts Anionic surfactant (Dai-ichi Kogyo Seiyaku, Neogen RK): 1 part Ion-exchanged water: 350 parts The above materials were mixed and heated to 100°C, dispersed using a homogenizer (IKA, trade name Ultra Turrax T50), and then dispersed using a Manton-Gaulin high-pressure homogenizer (Gaulin) to obtain a release agent particle dispersion (solid content 20% by mass) in which release agent particles with a volume average particle size of 200 nm were dispersed.

[0138] -Production of toner particles- ·Resin particle dispersion: 403 parts Colorant particle dispersion: 12 parts Release agent particle dispersion: 50 parts Anionic surfactant (TaycaPower): 2 parts The above materials were placed in a round stainless steel flask and adjusted to pH 3.5 with the addition of 0.1 N nitric acid. Then, 30 parts of a 10% by weight nitric acid aqueous solution containing polyaluminum chloride were added. The mixture was then dispersed at 30°C using a homogenizer (IKA, Ultra Turrax T50). The mixture was then heated to 45°C in a heating oil bath and held for 30 minutes. 100 parts of the resin particle dispersion was then added and held for 1 hour. The pH was adjusted to 8.5 with the addition of 0.1 N aqueous sodium hydroxide, and the mixture was then heated to 84°C and held for 2.5 hours. The mixture was then cooled to 20°C at a rate of 20°C / min, filtered, thoroughly washed with ion-exchanged water, and dried to obtain toner particles. The volume average particle size of the toner particles was 5.7 μm.

[0139] <Production of Silica Particles> -Preparation of silica particle dispersion (1)- Into a 1.5 L glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer, 320 parts of methanol and 73 parts of 10% aqueous ammonia were added and mixed to obtain an alkaline catalyst solution. After adjusting this alkali catalyst solution to 30°C, 47 parts of tetramethoxysilane (TMOS) and 9 parts of 8.0% aqueous ammonia were simultaneously added dropwise over 11 minutes while stirring to obtain a hydrophilic silica particle dispersion. The obtained silica particle dispersion was then concentrated to a solids concentration of 40% using a rotary filter R-Fine (manufactured by Kotobuki Industries Co., Ltd.). This concentrated dispersion was designated silica particle dispersion (1).

[0140] -Preparation of silica particle dispersions (2) and (4)- Silica particle dispersions (2) and (4) were prepared in the same manner as for silica particle dispersion (1), except that in the preparation process for silica particle dispersion (1), the amount of 10% ammonia water in the alkaline catalyst solution, the amount of tetramethoxysilane added to the alkaline catalyst solution, the amount of 8% ammonia water dropped, and the dropping time were changed to the conditions shown in Table 1.

[0141] [Table 1]

[0142] -Hydrophobic surface treatment (1), (2) and (4)- Silica particle dispersions (1), (2), and (4) were each centrifuged and dried at 120°C for 2 hours to obtain silica. 100 parts of silica and 500 parts of ethanol were placed in an evaporator and stirred for 15 minutes while maintaining the temperature at 40°C. Next, 10 parts of dimethyldimethoxysilane per 100 parts of silica was added as a hydrophobic treatment agent and stirred for an additional 15 minutes. The temperature in the system was then raised to 90°C to remove the ethanol, and the surface-treated silica was removed and vacuum-dried at 120°C for 30 minutes. The dried silica was pulverized to obtain silica particles (1), (2), and (4).

[0143] -Hydrophobic surface treatment (3)- To 250 parts of the silica particle dispersion (1), 20 parts of hexamethyldisilazane (HMDS) was added as a hydrophobic treatment agent, and the mixture was reacted at 120°C for 2 hours. After cooling, the mixture was dried by spray drying to obtain hydrophobic silica particles (3) whose surfaces had been hydrophobized.

[0144] <Production of strontium titanate particles> [Strontium titanate particles (1)] 0.7 moles of desulfurized and peptized metatitanic acid, the titanium source, was collected and placed in a reaction vessel. Next, 0.77 moles of strontium chloride aqueous solution was added to the reaction vessel to achieve a SrO / TiO molar ratio of 1.1. Next, a solution of lanthanum oxide dissolved in nitric acid was added to the reaction vessel in an amount equivalent to 2.5 moles of lanthanum per 100 moles of strontium. The initial TiO concentration in the mixture of the three materials was adjusted to 0.75 moles / L. The mixture was then stirred and heated to 90°C. While maintaining the temperature at 90°C, 153 mL of 10N aqueous sodium hydroxide solution was added dropwise over 4.2 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. The mixture was then stirred for one 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, followed by solid-liquid separation by filtration and drying of the solid. An ethanol solution of i-butyltrimethoxysilane was added to the dried solid in an amount of 20 parts i-butyltrimethoxysilane per 100 parts solid, and the mixture was stirred for 1 hour. Solid-liquid separation was performed by filtration, and the solid was dried in air at 130°C for 7 hours to obtain strontium titanate particles (1).

[0145] [Strontium titanate particles (2)] Strontium titanate particles (2) were prepared in the same manner as for the preparation of strontium titanate particles (1), except that the time for dropping the 10N aqueous sodium hydroxide solution was changed to 5.5 hours.

[0146] [Strontium titanate particles (3)] Strontium titanate particles (3) were prepared in the same manner as for the preparation of strontium titanate particles (1), except that the time for dropping the 10N aqueous sodium hydroxide solution was changed to 6.5 hours.

[0147] <Creating the carrier> Ferrite particles (average particle size 35 μm): 100 parts Toluene: 14 parts Styrene / methyl methacrylate copolymer (copolymerization ratio 15 / 85): 2 parts Carbon black: 0.2 parts The above materials except for the ferrite particles were dispersed in a sand mill to prepare a dispersion liquid, and this dispersion liquid was placed in a vacuum degassing kneader together with the ferrite particles, and the mixture was stirred under reduced pressure and dried to obtain a carrier.

[0148] <Preparation of Toner and Developer: Examples 1 to 7, Comparative Examples 1 to 4> Silica particles and strontium titanate particles were added to 100 parts of toner particles in the combinations and amounts shown in Table 2, and mixed for 15 minutes using a Henschel mixer at a stirring peripheral speed of 30 m / sec. The mixture was then sieved using a vibrating sieve with 45 μm openings to obtain an externally added toner.

[0149] 10 parts of the externally added toner and 100 parts of the carrier were placed in a V-blender and stirred for 20 minutes, after which the mixture was sieved through a sieve with 212 μm openings to obtain a developer.

[0150] <Analysis of toner and external additives> [Silica particle and strontium titanate particle shape characteristics (average primary particle size, peak position, average circularity)] The toner to which external additives containing silica particles and strontium titanate particles were added was analyzed using an energy dispersive X-ray analyzer (EDX device) (Horiba, Ltd., EMAX Evolution X-Max 80mm 2 Images were taken at 40,000x magnification using a scanning electron microscope (SEM) (Hitachi High-Technologies, S-4800) equipped with a ion beam splitter. EDX analysis identified more than 300 primary silica particles within a single field of view based on the presence of Si, and more than 300 primary strontium titanate particles within a single field of view based on the presence of Ti. SEM observations were performed at an accelerating voltage of 15 kV, an emission current of 20 μA, and a working distance of 15 mm. EDX analysis was performed under the same conditions for a detection time of 60 minutes. The identified silica particles and strontium titanate particles were analyzed using image processing analysis software WinRoof (Mitani Corporation) to determine the circle-equivalent diameter, area, and perimeter of each primary particle image. Furthermore, the circularity was calculated using the formula: 2 asked for. A distribution curve was drawn for the number of individual particles, starting from the smallest diameter side of the equivalent circle diameter, to obtain a number primary particle size distribution curve. The equivalent circle diameter at 50% cumulative from the smallest diameter side was defined as the average primary particle size, and the position of the particle size at the maximum peak in the range of 20 nm to less than 80 nm on the distribution curve was determined. In addition, the circularity at 50% cumulative from the smallest side in the circularity distribution was defined as the average circularity. In all Examples, the particle size distributions of the silica particles and strontium titanate particles were monodisperse. The half-width of the peak in the range of 20 nm to less than 80 nm for each particle was 15 nm to 35 nm, and the difference between the half-width of the peak for the silica particles and that of the strontium titanate particles in each Example was 20 nm or less.

[0151] [External additive coverage] Toner containing external additives including silica particles and strontium titanate particles was photographed at a magnification of 40,000x under low-acceleration SEM conditions using a scanning electron microscope equipped with the EDX device described above. After binarization of each external additive particle and toner base particle, the silica particles were white and the strontium titanate particles were gray, which could be visually distinguished due to the low-acceleration SEM conditions. The following coverage rates were then calculated for each particle. Silica particle coverage: The ratio of the area occupied by silica particles to the total area of ​​the toner Strontium titanate particle coverage: The ratio of the area occupied by strontium titanate particles to the total area of ​​the toner. (In this example, it was possible to distinguish between silica particles and strontium titanate particles, but if this is difficult, the elements Si and Ti can be separated by EDX.) In the present invention, the coverage rate is a ratio determined by image analysis as described above. On the other hand, the coverage rate of an external additive can be calculated from the toner particle size, toner specific gravity, particle size of the external additive, and specific gravity of the external additive using the following equation 1. The results calculated using equation 1 are also shown in Table 2, and the numerical differences between the image analysis values ​​and the calculated values ​​were all less than 1% points, confirming that the analytical values ​​from the image analysis also had good reproducibility.

[0152]

number

[0153] In Equation 1, Dt represents the average primary particle size of the toner, ρt represents the specific gravity of the toner, Da represents the average primary particle size of the external additive, and ρa represents the specific gravity of the external additive. The average primary particle size of the toner base particles (before adding the external additive) was determined using the method described above and was 5.7 nm. The specific gravity of each substance was determined by actual measurement using a pycnometer and used the following values. Toner specific gravity: 1.1 Silica particle density: 1.2 Strontium titanate particle density: 3.6 The true specific gravity of silica is 2.2, and the true specific gravity of strontium titanate is 5.1, and both measured specific gravity values ​​are small. This is presumably due to the presence of voids in the compound and internal water content that are present when the external additive is produced by a wet method. Since calculation using Equation 1 requires the specific gravity of the external additive, which varies depending on the production method, the coverage of the external additive in the present invention is the coverage determined by the image analysis described above.

[0154] [External additive primary particle content] The toner to which the external additives containing silica particles and strontium titanate particles were added was photographed at a magnification of 40,000 times using the above scanning electron microscope. A relatively smooth portion of the toner surface, 1 μm x 1 μm in size, was selected above, and the number of primary particles (X) and aggregated particles (Y) of the external additive was counted (counting without distinguishing between silica particles and strontium titanate particles), and the average of 20 fields of view was calculated using the following formula to determine the proportion (%) of primary particles present. Primary particle abundance (%) = X ÷ (X + Y) × 100

[0155] The analysis results of the toner and developer are shown in Table 2. [Table 2]

[0156] [Water content of strontium titanate particles] The moisture content of the strontium titanate particles before being added to the toner particles was measured by the above-mentioned method. The moisture content of the strontium titanate particles (1) to (3) was in the range of 2% by mass or more and 5% by mass or less.

[0157] <Evaluation of toner and developer> [Image output conditions on actual device] The developer was loaded into a digital multifunction printer (Apeos C7070 modified model manufactured by Fujifilm Business Innovation Co., Ltd.). The toner amount on the photoconductor was 5 g / m. 2 The developing potential was adjusted so that the image area ratio was 1%, and images with an image area ratio of 1% were continuously printed on 100,000 sheets of A4-sized plain paper under low temperature and low humidity (temperature 10°C / relative humidity 20%).

[0158] [Developer soiling (toner cloud evaluation)] To evaluate the toner cloud (toner floating in the multifunction printer), the level of contamination of the developing machine was observed after the 100,000 sheets were output, and the developer was graded A to D according to the following evaluation criteria. A and B were considered acceptable. The results are shown in Table 3. A: There is almost no dirt. B: The cover of the developing machine looks the same color as the toner. C: Toner is accumulated on the developing machine. D: Toner is spilling from the developing machine.

[0159] [Toner charge distribution] The charge distribution of the toner was evaluated by measuring the amount of reverse polarity toner in the developer after the actual machine output using a charge distribution measuring device (Espart Analyzer, manufactured by Hosokawa Micron Co., Ltd.) according to the following charge evaluation criteria. A rating of A or B was considered acceptable. The results are shown in Table 3. A: The amount of reverse polarity toner is less than 5%. B: The amount of reverse polarity toner is 5% or more and less than 10%. C: The amount of reverse polarity toner is 10% or more and less than 20%. D: The amount of reverse polarity toner is 20% or more.

[0160] [Uneven distribution of external additives] For each toner in the examples and comparative examples, images were taken at 40,000x magnification using an SEM (Hitachi High-Technologies Corporation, S-4800) of the toner in the developer before and after output from the actual machine. Within a 1 μm x 1 μm area of ​​a toner particle, the largest area surrounded by external additives, where the toner particles were exposed and free of external additives, was selected, and the area was calculated. (Figure 3 shows a schematic diagram of the method for selecting the exposed toner particle area, although it is not the largest area.) The average of the maximum exposed area of ​​toner particles was determined for 300 locations (1 μm×1 μm) before and after actual machine output, and the area ratio was calculated using the following formula. Area ratio = Maximum exposed area of ​​toner particles after output / Maximum exposed area of ​​toner base particles before output The smaller the obtained area ratio, the less uneven distribution of the external additive. The area ratio was evaluated according to the following criteria. The evaluation criteria, A and B, are within the acceptable range. The results are shown in Table 3. A: The ratio of the maximum exposed area of ​​toner particles before and after output is less than 1.15. B: The ratio of the maximum exposed area of ​​toner particles before and after output is 1.15 or more and less than 1.30. C: The ratio of the maximum exposed area of ​​toner particles before and after output is 1.30 or more and less than 1.50. D: The ratio of the maximum exposed area of ​​toner particles before and after output is 1.50 or more.

[0161] [Cover] Using the above digital multifunction printer, an image with an image density of 20% was printed on 100,000 sheets of A4 paper, and then an image with an image density of 1% was printed on one sheet of A4 paper. The fog (fog in the background) of the printed image was measured using an X-Rite 938 image densitometer (manufactured by X-Rite Corporation), and the measured fog density was evaluated according to the following evaluation criteria. Visual images are also shown in parentheses for reference. In the evaluation criteria, A and B are within the acceptable range. The results are shown in Table 3. A: Fog density is less than 0.1 (no fog visible with a magnifying glass) B: Fog density is 0.1 or more but less than 0.2 (fog can be seen with a magnifying glass, but not visible to the naked eye) C: Fog density is 0.2 or more and less than 0.3 (partial fog is visible to the naked eye). D: Fog density is 0.3 or more (fog is visible on the entire surface) [comprehensive evaluation] The above evaluation results were combined and an overall evaluation was made according to the following criteria, which are shown in Table 3. In the evaluation criteria, A and B are within the acceptable range. A: When replacing each individual rating with 1 for A, 2 for B, 3 for C, and 4 for D, and calculating the average of the individual ratings (same criteria as below), the average rating is 1.5 or less. (Example: If each individual rating is only A and B, there must be 2 or less Bs.) B: The average of the individual ratings is above 1.5 and below 2.5. C: The average of the individual ratings is above 2.5 and below 3.5. D: The average of the individual ratings is greater than 3.5. (Example: All Ds, or no more than one C when the grade is C.)

[0162] [Table 3] [Explanation of symbols]

[0163] 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 an image carrier 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) 28 Fixing device (an example of fixing means) 30 Intermediate transfer belt cleaning device (an example of an intermediate transfer body cleaning means) P Recording paper (an example of a recording medium)

[0164] 107 Photoconductor (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 member cleaning device (an example of an image carrier cleaning means) 115 Fixing device (an example of fixing means) 116 Mounting Rail 117 Cabinet 118 Exposure opening 200 Process Cartridge 300 Recording paper (an example of a recording medium)

Claims

1. toner particles; silica particles externally added to the toner particles; titanic acid compound particles having an average circularity of 0.890 or more and 0.950 or less, which are externally added to the toner particles; Including, The silica particles include particles having a primary particle size of 80 nm or less, and the particles having a primary particle size of 80 nm or less have at least one peak in a range of 20 nm or more and less than 80 nm in a number primary particle size distribution curve (hereinafter, the silica particles having this peak are referred to as "specific silica particles"). the titanate compound particles have at least one peak in a range of 20 nm or more and less than 80 nm in a number primary particle size distribution curve, the difference between the average circularity of the specific silica particles and the average circularity of the titanate compound particles is 0.05 or less; a difference between the toner coverage of the specific silica particles and the toner coverage of the titanic acid compound particles is 20 percentage points or less; The specific silica particles and the titanic acid compound particles are present as primary particles on the toner particles at a rate of 10% or more.

1. A toner for developing electrostatic images, comprising:

2. 2. The toner for developing electrostatic images according to claim 1, wherein the titanate compound particles have at least one peak in a range of 30 nm or more and less than 80 nm in a number primary particle size distribution curve, and the difference in particle size between the titanate compound particles and the specific silica particles, each of which has a maximum peak in a range of 20 nm or more and less than 80 nm, is 20 nm or less.

3. 3. The toner for developing electrostatic images according to claim 2, wherein the particle size difference at the maximum peak is 15 nm or less.

4. 2. The toner for developing electrostatic images according to claim 1, wherein the difference between the toner coverage of said specific silica particles and the coverage of said titanic acid compound particles is 15% points or less.

5. 2. The toner for developing electrostatic images according to claim 1, wherein the difference between the average circularity of said specific silica particles and the average circularity of said titanic acid compound particles is 0.03 or less.

6. 2. The toner for developing electrostatic images according to claim 1, wherein a difference between a half-value width of a peak in the range of 20 nm or more and less than 80 nm in a number primary particle size distribution curve of the specific silica particles and a half-value width of a peak in the range of 20 nm or more and less than 80 nm in a number primary particle size distribution curve of the titanic acid compound particles is 20 nm or less.

7. 2. The toner for developing electrostatic images according to claim 1, wherein the titanate compound particles are at least one selected from the group consisting of strontium titanate particles, magnesium titanate particles, and calcium titanate particles.

8. 8. The toner for developing electrostatic images according to claim 7, wherein said titanate compound particles are strontium titanate particles.

9. 9. The toner for developing electrostatic images according to claim 8, wherein said strontium titanate particles are lanthanum-doped strontium titanate particles.

10. 9. The toner for developing electrostatic images according to claim 8, wherein said strontium titanate particles have surfaces that have been subjected to a hydrophobic treatment.

11. A toner for developing electrostatic images as described in claim 1, wherein a maximum exposed area, which is the area of ​​the largest region in which there are no external additives and in which the toner particles are exposed, is determined for each of the toner particles before and after output from the actual machine, and the area ratio calculated by the following formula is 1.36 or less. Area ratio = Maximum exposed area of ​​toner particles after output / Maximum exposed area of ​​toner particles before output

12. An electrostatic image developer comprising the toner for developing electrostatic images according to any one of claims 1 to 11.

13. A toner for developing electrostatic images according to any one of claims 1 to 11 is contained therein, A toner cartridge that is detachably attached to an image forming device.

14. a developing unit containing the electrostatic image developer according to claim 12 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.

15. 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 12 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:

16. a charging step of charging the surface of the image carrier; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier; a developing step of developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer according to claim 12; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing step of fixing the toner image transferred onto the surface of the recording medium; An image forming method comprising the steps of:

Images