Toner for electrostatic charge image development, electrostatic charge image developer, toner cartridge, process cartridge, image forming apparatus, and image forming method

Abstract

To prevent concentration of silica particles in a toner for electrostatic charge image development or the like.SOLUTION: A toner for electrostatic charge image development includes: toner particles; titanic acid compound particles having a peak present within a range of 20 nm or more and less than 80 nm in the number primary particle diameter distribution curve, and having an average circularity of 0.88 or more and 0.94 or less; and silica particles having a small-diameter side peak present within a range of 20 nm or more and less than 80 nm in the number primary particle diameter distribution curve, a large-diameter side peak present within a range of 80 nm or more and less than 130 nm, and a valley present between the small-diameter side peak and the large-diameter side peak. The difference in the particle diameter between the peak in the number primary particle diameter distribution curve of the titanic acid compound particles and the small-diameter side peak in the number primary particle diameter distribution curve of the silica particles is 20 nm or less. In the number primary particle diameter distribution curve of the silica particles, when silica particles having a particle diameter less than that of the valley is defined as small-diameter silica particles, the average circularity of the small-diameter silica particles is 0.88 or more and 0.94 or less.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a toner for electrostatic charge image development, an electrostatic charge image developer, a toner cartridge, a process cartridge, an image forming apparatus, and an image forming method.

Background Art

[0002] Patent Document 1 discloses a toner to which a single type of inorganic fine particle having a maximum value of the number ratio for each of a primary particle diameter x [nm] (where x is in the range of 20 to 50 nm) and a primary particle diameter y [nm] (where y is in the range of 3x to 6x [nm]) in a number-based primary particle diameter distribution curve is externally added. Patent Document 2 discloses a toner to which fine particles of titanate having an average primary particle diameter of 10 nm or more and 60 nm or less and silica fine particles having an average primary particle diameter of 40 nm or more and 300 nm or less are externally added.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a toner to which titanate compound particles and silica particles having a larger diameter than the titanate compound particles are externally added, for example, when the developer is operated under conditions where the toner is replaced less frequently, the silica particles are electrostatically attracted to the titanate compound particles and the silica particles are concentrated, and fogging may occur in the non-image portion. The present invention aims to suppress the concentration of silica particles in an electrostatic charge image developing toner in which titanate compound particles and silica particles are externally added to toner particles, as compared with a case where the number-based primary particle size distribution curve of the silica particles does not have a peak with a particle size difference of 20 nm or less from the peak in the number-based primary particle size distribution curve of the titanate compound particles.

Means for Solving the Problems

[0005] The invention according to claim 1 includes toner particles, titanate compound particles externally added to the toner particles, having a peak in the range of 20 nm or more and less than 80 nm in the number-based primary particle size distribution curve and an average circularity of 0.88 or more and 0.94 or less, and silica particles externally added to the toner particles, having a small-diameter side peak in the range of 20 nm or more and less than 80 nm, a large-diameter side peak in the range of 80 nm or more and less than 130 nm, and a valley existing between the small-diameter side peak and the large-diameter side peak in the number-based primary particle size distribution curve. The particle size difference between the peak in the number-based primary particle size distribution curve of the titanate compound particles and the small-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 20 nm or less. When the silica particles having a particle size less than the valley are defined as small-diameter silica particles and the silica particles having a particle size greater than or equal to the valley are defined as large-diameter silica particles, it is an electrostatic charge image developing toner in which the average circularity of the small-diameter silica particles is 0.88 or more and 0.94 or less. The invention according to claim 2 is the electrostatic charge image developing toner according to claim 1, characterized in that in the number-based primary particle size distribution curve of the particles obtained by combining the titanate compound particles and the silica particles, it has a maximum value in the range of 20 nm or more and less than 80 nm, and has a first peak composed of the titanate compound particles and the small-diameter silica particles and a second peak existing in the range of 80 nm or more and 130 nm or less and composed of the large-diameter silica particles. The invention according to claim 3 is the electrostatic charge image developing toner according to claim 1, characterized in that the coating rate A (%) of the titanate compound particles with respect to the toner particles and the coating rate B (%) of the small-diameter silica particles with respect to the toner particles satisfy the following formula (1). 0.2 ≦ A / (A + B) ≦ 0.8 …(1) The invention according to claim 4 is an electrostatic charge image developing toner according to claim 3, characterized in that the coating rate A (%) of the titanate compound particles with respect to the toner particles and the coating rate B (%) of the small-diameter silica particles with respect to the toner particles satisfy the following formula (2). 10 ≦ A + B ≦ 50 …(2) The invention according to claim 5 is an electrostatic charge image developing toner according to claim 4, characterized in that the coating rate of the large-diameter silica particles with respect to the toner particles is 20% or more and 40% or less. The invention according to claim 6 is an electrostatic charge image developing toner according to claim 1, characterized in that the particle size difference between the small-diameter side peak and the large-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 20 nm or more and 70 nm or less. The invention according to claim 7 is an electrostatic charge image developing toner according to claim 1, characterized in that the particle size difference between the peak in the number-based primary particle size distribution curve of the titanate compound particles and the large-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 20 nm or more and 70 nm or less. The invention according to claim 8 is an electrostatic charge image developing toner according to claim 1, characterized in that the difference between the average circularity of the titanate compound particles and the average circularity of the small-diameter silica particles is 0.08 or less. The invention according to claim 9 is an electrostatic charge image developing toner according to claim 1, characterized in that the half-value width of the small-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 25 nm or less. The invention according to claim 10 is an electrostatic charge image developing toner according to claim 1, characterized in that the titanate compound particles are strontium titanate particles. The invention according to claim 11 is an electrostatic charge image developing toner according to claim 10, characterized in that the strontium titanate particles are strontium titanate particles doped with lanthanum. The invention according to claim 12 is an electrostatic charge image developer containing the electrostatic charge image developing toner according to any one of claims 1 to 11. The invention according to claim 13 is a toner cartridge that houses the toner for electrostatic charge image development according to any one of claims 1 to 11 and is detachable from an image forming apparatus. The invention according to claim 14 is a process cartridge that houses the electrostatic charge image developer according to claim 12, includes developing means for developing an electrostatic charge image formed on the surface of an image carrier as a toner image with the electrostatic charge image developer, and is detachable from an image forming apparatus. The invention according to claim 15 is an image forming apparatus including an image carrier, charging means for charging the surface of the image carrier, electrostatic charge image forming means for forming an electrostatic charge image on the charged surface of the image carrier, developing means for housing the electrostatic charge image developer according to claim 12 and developing the electrostatic charge image formed on the surface of the image carrier as a toner image with the electrostatic charge image developer, transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and fixing means for fixing the toner image transferred to the surface of the recording medium. The invention according to claim 16 is an image forming method including a charging step of charging the surface of an image carrier, an electrostatic charge image forming step of forming an electrostatic charge image on the charged surface of the image carrier, a developing step of developing the electrostatic charge image formed on the surface of the image carrier as a toner image with the electrostatic charge 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, and a fixing step of fixing the toner image transferred to the surface of the recording medium.

Advantages of the Invention

[0006] According to the invention of claim 1, in the toner for electrostatic charge image development in which titanium compound particles and silica particles are externally added to toner particles, the concentration of silica particles can be suppressed as compared with the case where the number-based primary particle size distribution curve of the silica particles does not have a peak with a particle size difference of 20 nm or less from the peak in the number-based primary particle size distribution curve of the titanium compound particles. According to the invention of claim 2, the concentration of silica particles can be further suppressed as compared with the case where the first peak is not composed of titanium compound particles and small-diameter silica particles. According to the invention of claim 3, the charging characteristics can be improved as compared with the case where the coating rate A of the titanate compound particles and the coating rate B of the small-diameter silica particles do not satisfy formula (1). According to the invention of claim 4, the charging characteristics can be improved as compared with the case where the coating rate A of the titanate compound particles and the coating rate B of the small-diameter silica particles do not satisfy formula (2). According to the invention of claim 5, the concentration of silica particles can be more suppressed as compared with the case where the coating rate of the large-diameter silica particles exceeds 40%. According to the invention of claim 6, the concentration of silica particles can be more suppressed as compared with the case where the difference between the small-diameter peak and the large-diameter peak in the number-based primary particle size distribution curve of silica particles exceeds 70 nm. According to the invention of claim 7, the concentration of silica particles can be more suppressed as compared with the case where the difference between the peak in the number-based primary particle size distribution curve of the titanate compound particles and the large-diameter peak in the number-based primary particle size distribution curve of silica particles exceeds 70 nm. According to the invention of claim 8, the concentration of silica particles can be more suppressed as compared with the case where the difference between the average circularity of the titanate compound particles and the average circularity of the small-diameter silica particles exceeds 0.08. According to the invention of claim 9, the concentration of silica particles can be more suppressed as compared with the case where the half-value width of the small-diameter peak in the number-based primary particle size distribution curve of silica particles exceeds 25 nm. According to the invention of claim 10, the charging characteristics can be improved as compared with the case where the titanate compound particles are not strontium titanate particles. According to the invention of claim 11, the charging characteristics can be improved as compared with the case of using strontium titanate particles not doped with lanthanum. According to the invention of claim 12, an electrostatic charge image developer including an electrostatic charge image developing toner in which the concentration of silica particles is suppressed can be provided as compared with the case where the number-based primary particle size distribution curve of silica particles does not have a peak with a particle size difference of 20 nm or less from the peak in the number-based primary particle size distribution curve of the titanate compound particles. According to the invention of claim 13, it is possible to provide a toner cartridge containing an electrostatic charge image developing toner in which the concentration of silica particles is suppressed as compared with the case where the number-based primary particle size distribution curve of the silica particles does not have a peak with a particle size difference of 20 nm or less from the peak in the number-based primary particle size distribution curve of the titanate compound particles. According to the inventions of claims 14, 15, or 16, it is possible to provide a process cartridge, an image forming apparatus, or an image forming method to which an electrostatic charge image developer containing an electrostatic charge image developing toner in which the concentration of silica particles is suppressed as compared with the case where the number-based primary particle size distribution curve of the silica particles does not have a peak with a particle size difference of 20 nm or less from the peak in the number-based primary particle size distribution curve of the titanate compound particles is applied.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Figure 4

Embodiments for Carrying Out the Invention

[0008] Hereinafter, embodiments of the invention will be described. These descriptions and examples etc. are illustrative of the embodiments and do not limit the scope of the invention.

[0009] In the present disclosure, unless otherwise specified, the description of "XX or more and XX or less" or "XX to XX" representing a numerical range means a numerical range including the described upper and lower limits. Further, in the present disclosure, when referring to the amount of each component in a composition, if there are multiple types of substances corresponding to each component in the composition, unless otherwise specified, it means the total amount of the multiple types of substances present in the composition. In the present disclosure, "toner for electrostatic charge image development" may sometimes be simply described as "toner", and "electrostatic charge image developer" may sometimes be simply described as "developer".

[0010] <Toner for electrostatic charge image development> The toner according to this embodiment includes toner particles, titanate compound particles externally added to the toner particles, having a peak in the range of 20 nm or more and less than 80 nm in the number-based primary particle size distribution curve, and having an average circularity of 0.88 or more and 0.94 or less, and silica particles externally added to the toner particles, having a small-diameter side peak in the range of 20 nm or more and less than 80 nm and a large-diameter side peak in the range of 80 nm or more and less than 130 nm in the number-based primary particle size distribution curve, and having a valley between the small-diameter side peak and the large-diameter side peak. The particle size difference between the peak in the number-based primary particle size distribution curve of the titanate compound particles and the small-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 20 nm or less. When the silica particles having a particle size less than the valley are defined as small-diameter silica particles and the silica particles having a particle size of the valley or more are defined as large-diameter silica particles, the average circularity of the small-diameter silica particles is 0.88 or more and 0.94 or less.

[0011] In the toner for electrostatic charge image development in which titanate compound particles and silica particles are externally added to toner particles according to this embodiment, the concentration of silica particles is suppressed as compared with the case where the number-based primary particle size distribution curve of the silica particles does not have a peak with a particle size difference of 20 nm or less from the peak in the number-based primary particle size distribution curve of the titanate compound particles. The following is presumed as the mechanism.

[0012] Conventionally, in order to improve the charging characteristics of toner, as an external additive for toner, titanate compound particles such as strontium titanate particles and silica particles having a larger diameter than the titanate compound particles have been used. By externally adding silica particles having a larger diameter than the titanate compound particles to the toner, the burial of the titanate compound particles in the toner particles is suppressed, and the charging characteristics by the titanate compound particles are maintained.

[0013] Here, when forming an image for a long period of time under conditions where the replacement of the toner in the developing device is less (for example, under high temperature and high humidity, low image density, intermittent operation) using a toner to which titanate compound particles and silica particles having a larger diameter than the titanate compound particles are externally added, fogging may occur in the image. This is presumed to be due to the following reasons. That is, due to the mechanical load applied to the toner in the developing device during long-term image formation, the silica particles having a larger diameter are released from the toner. Then, the negatively charged silica particles having a large diameter released from the toner and the titanate compound particles having a weak negative polarity externally added to the toner are electrostatically attracted to each other (mutual charging), and the toner in which the silica particles having a large diameter are concentrated accumulates in the developing device. Since the toner in which the silica particles having a large diameter are concentrated has a strong negative polarity, a charging potential difference occurs between the toner and the toner replenished to the developing device, and mutual charging occurs between the toners, resulting in fogging in the image.

[0014] The toner of the present embodiment suppresses the concentration of silica particles in the toner and suppresses the occurrence of image fogging during image formation according to the following (a) and (b). (a) The titanium compound particles have a peak in the range of 20 nm or more and less than 80 nm in the number-based primary particle size distribution curve, and the silica particles have a small-diameter side peak in the range of 20 nm or more and less than 80 nm in the number-based primary particle size distribution curve. And the particle size difference between the peak in the number-based primary particle size distribution curve of the titanate compound particles and the small-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 20 nm or less. As a result, among the silica particles externally added to the toner, there are many small-diameter silica particles having a particle size close to that of the titanate compound particles, and it becomes difficult for the titanate compound particles and the large-diameter silica particles to be mutually charged. (b) The average circularity of the titanate compound particles and the average circularity of the small-diameter silica particles are both 0.88 or more and 0.94 or less. As a result, the surfaces of the toner particles can be uniformly coated with the titanate compound particles and the small-diameter silica particles, and the release of the large-diameter silica particles from the toner particles is suppressed.

[0015] Hereinafter, the configuration of the toner according to the present embodiment will be described in detail. [Toner particles] The toner particles contain, for example, a binder resin, and optionally, a colorant, a release agent, and other additives. -Binder resin- Examples of the binder resin 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.), olefins (e.g., ethylene, propylene, butadiene, etc.), or vinyl resins composed of copolymers obtained by combining two or more of these monomers. Examples of the binding resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, modified rosin, mixtures of these and the vinyl resins, or graft polymers obtained by polymerizing vinyl monomers in the coexistence of these. These binding resins may be used alone or in combination of two or more.

[0016] As the binding resin, a polyester resin is preferred. Examples of the polyester resin include condensation polymers of polyvalent carboxylic acids and polyhydric alcohols.

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

[0018] Examples of the polyhydric alcohol include aliphatic diols (such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, etc.), alicyclic diols (such as cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, etc.), and aromatic diols (such as ethylene oxide adducts of bisphenol A, propylene oxide adducts of bisphenol A, etc.). Among these, as the polyhydric alcohol, for example, aromatic diols and alicyclic diols are preferred, and aromatic diols are more preferred. As the polyhydric alcohol, a polyhydric alcohol having a crosslinked structure or a branched structure with a valence of 3 or more may be used in combination with the diol. Examples of the polyhydric alcohol having a valence of 3 or more include glycerin, trimethylolpropane, and pentaerythritol. The polyhydric alcohol 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, more preferably 50°C or higher and 65°C or lower. The glass transition temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC). More specifically, it is determined by the "extrapolated glass transition start temperature" described in the method for determining the glass transition temperature in JIS K7121-1987 "Method for Measuring the Transition Temperature of Plastics".

[0020] The weight average molecular weight (Mw) of the polyester resin is preferably 5,000 or more and 1,000,000 or less, more preferably 7,000 or more and 500,000 or less. The number average molecular weight (Mn) of the polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the polyester resin is preferably 1.5 or more and 100 or less, more preferably 2 or more and 60 or less. The weight average molecular weight and number average molecular weight of the polyester resin are measured by gel permeation chromatography (GPC). The molecular weight measurement by GPC is carried out using GPC·HLC-8120GPC manufactured by Tosoh as the measuring device, using a column·TSKgel SuperHM-M (15 cm) manufactured by Tosoh, and in a THF solvent. The weight average molecular weight and number average molecular weight are calculated using a molecular weight calibration curve prepared with a monodisperse polystyrene standard sample from this measurement result.

[0021] The polyester resin is obtained by a known production method. Specifically, for example, it can be obtained by a method in which the polymerization temperature is set to 180°C or higher and 230°C or lower, the inside of the reaction system is depressurized as necessary, and the reaction is carried out while removing water or alcohol generated during condensation. When the raw material monomers do not dissolve or are not compatible at the reaction temperature, a high-boiling solvent may be added as a dissolution aid to dissolve them. In this case, the polycondensation reaction is carried out while distilling off the dissolution aid. When monomers with poor compatibility are present, it is advisable to first condense the monomers with poor compatibility with the acid or alcohol to be polycondensed with that monomer and then carry out polycondensation with the main component.

[0022] The content of the binder resin is preferably 40% by mass or more and 95% by mass or less, more preferably 50% by mass or more and 90% by mass or less, and still more preferably 60% by mass or more and 85% by mass or less, based on the total toner particles.

[0023] -Colorant- Examples of the colorant include pigments such as carbon black, chrome yellow, Hansa yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Vulcan orange, Watchung red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, resorcin red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, ultramarine blue, calco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, malachite green oxalate; 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, thiazole-based dyes; etc. The colorant may be used alone or in combination of two or more.

[0024] As the colorant, a surface-treated colorant may be used as necessary, and it may be used in combination with a dispersant. Also, a plurality of types of colorants may be used in combination. The content of the colorant is preferably 1% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 15% by mass or less, based on the total toner particles.

[0025] - Release agent - Examples of the release agent include hydrocarbon waxes; natural waxes such as carnauba wax, rice wax, candelilla wax; synthetic or mineral / oil-based waxes such as montan wax; ester waxes such as fatty acid esters, montanic acid esters; etc. The release agent is not limited thereto.

[0026] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, more preferably 60°C or higher and 100°C or lower. The melting temperature is determined by the "melting peak temperature" described in the method for determining the melting temperature of JIS K7121-1987 "Method for Measuring Transition Temperature of Plastics" from the DSC curve obtained by differential scanning calorimetry (DSC).

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

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

[0029] [Properties of Toner Particles] The toner particles may be single-layered toner particles or so-called core-shell structured toner particles composed of a core part (core particles) and a coating layer (shell layer) covering the core part. The core-shell structured toner particles are composed of, for example, a core part containing a binder resin and, if necessary, a colorant and a release agent, etc., and a coating layer containing a binder resin.

[0030] The volume average particle diameter (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, more preferably 4 μm or more and 8 μm or less.

[0031] The volume average particle diameter of the toner particles is measured using a Coulter Multisizer II (manufactured by Beckman Coulter, Inc.), and the electrolyte used is ISOTON-II (manufactured by Beckman Coulter, Inc.). When measuring, as a dispersant, 0.5 mg or more and 50 mg or less of the measurement sample is added to 2 ml of a 5 mass% aqueous solution of a surfactant (sodium alkylbenzene sulfonate is preferred). This is added to 100 ml or more and 150 ml or less of the electrolyte. The electrolyte in which the sample is suspended is subjected to a dispersion treatment for 1 minute with an ultrasonic disperser, and the particle diameter of particles in the range of 2 μm or more and 60 μm or less is measured using an aperture with an aperture diameter of 100 μm by the Coulter Multisizer II. The number of particles to be sampled is 50,000. In the volume-based particle size distribution of the measured particle diameters, the particle diameter at which the cumulative value from the small diameter side reaches 50% is defined as the volume average particle diameter D50v.

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

[0033] In the present embodiment, the circularity of the toner particles is (circumference of a circle having the same area as the particle projection image)÷(circumference of the particle projection image), and the average circularity of the toner particles is the circularity at which the cumulative value from the smaller side in the circularity distribution reaches 50%. The average circularity of the toner particles is determined by analyzing at least 3,000 toner particles with a flow-type particle image analyzer.

[0034] The average circularity of the toner particles can be controlled, for example, when the toner particles are manufactured by the aggregation-unification method, by adjusting the stirring speed, the temperature of the dispersion liquid, or the holding time in the fusion-unification step.

[0035] [Silica particles] In the present embodiment, the silica particles used as an external additive for toner have, in the number-based primary particle size distribution curve, a peak existing in the range of 20 nm or more and less than 80 nm (hereinafter referred to as the small-diameter side peak), a peak existing in the range of 80 nm or more and less than 130 nm (hereinafter referred to as the large-diameter side peak), and a valley existing between the small-diameter side peak and the large-diameter side peak and having a minimum value in the number ratio. Further, the silica particles have, in the number-based primary particle size distribution curve, when the silica particles having a particle size less than the valley are defined as small-diameter silica particles and the silica particles having a particle size greater than or equal to the valley are defined as large-diameter silica particles, an average circularity of the small-diameter silica particles of 0.88 or more and 0.94 or less.

[0036] (Number-based primary particle size distribution curve) FIG. 1 is a diagram showing an example of the number-based primary particle size distribution curve of the silica particles used as an external additive for toner in the present embodiment. In FIG. 1, the vertical axis represents the number ratio of primary particles, and the horizontal axis represents the particle size. Note that the number-based primary particle size distribution curve of the silica particles shown in FIG. 1 is an example for explanation and is not necessarily accurate. As shown in FIG. 1, the silica particles according to the present embodiment have, in the number-based primary particle size distribution curve, a peak existing in the range of 20 nm or more and less than 80 nm (small-diameter side peak, indicated by reference sign PS1 in FIG. 1) and a peak existing in the range of 80 nm or more and less than 130 nm (large-diameter side peak, indicated by reference sign PS2 in FIG. 1). Further, the silica particles according to the present embodiment have, in the number-based primary particle size distribution curve, a valley (indicated by reference sign VS in FIG. 1) existing between the small-diameter side peak and the large-diameter side peak.

[0037] Here, in the present embodiment, the peak in the number-based primary particle size distribution curve is a point at which the slope of the number-based primary distribution curve changes from positive to negative as the particle size increases. Further, the valley in the number-based primary particle size distribution curve is a point at which the number ratio takes a minimum value and at which the slope of the number-based primary particle size distribution curve changes from negative to positive as the particle size increases.

[0038] In the silica particles of this embodiment, in the number-based primary particle size distribution curve, the number of peaks in the range of 20 nm or more and less than 80 nm and the number of peaks in the range of 80 nm or more and less than 130 nm are each preferably 1, but they may be plural. For example, when there are a plurality of peaks in the range of 20 nm or more and less than 80 nm, the peak with the largest proportion of the number of primary particles among the plurality of peaks is defined as the small-diameter side peak of this embodiment. Similarly, when there are a plurality of peaks in the range of 80 nm or more and less than 130 nm, the peak with the largest proportion of the number of primary particles among the plurality of peaks is defined as the large-diameter side peak of this embodiment. Also, in the silica particles of this embodiment, in the number-based primary particle size distribution curve, it is preferable that there are no peaks in the range less than 20 nm and the range of 130 nm or more, but there may be peaks in the range less than 20 nm or the range of 130 nm or more.

[0039] In this embodiment, since the silica particles have a large-diameter side peak in the range of 80 nm or more and less than 130 nm in the number-based primary particle size distribution curve, the burial of the toner particles of the silica particles and the titanate compound particles having a primary particle size of 20 nm or more and less than 80 nm is suppressed, and the charging characteristics by the titanate compound particles are likely to be maintained.

[0040] Here, in a toner to which titanate compound particles and silica particles having a primary particle size of 80 nm or more and less than 130 nm are externally added, when a mechanical load is applied to the toner for a long time, the titanate compound particles and the silica particles having a primary particle size of 80 nm or more and less than 130 nm may be mutually charged and the silica particles may be concentrated. In this embodiment, since the silica particles have a small-diameter side peak in the range of 20 nm or more and less than 80 nm in the number-based primary particle size distribution curve, the generation of electrostatic mutual charging between the titanate compound particles and the silica particles having a primary particle size of 80 nm or more and less than 130 nm can be suppressed by the small-diameter silica particles having a primary particle size of 20 nm or more and less than 80 nm, and the concentration of the silica particles is suppressed.

[0041] In the number-based primary particle size distribution curve of the silica particles, the particle size difference between the small-diameter side peak and the large-diameter side peak is preferably 20 nm or more and 70 nm or less from the viewpoint of suppressing the release of the large-diameter silica particles described later and suppressing the burial of the small-diameter silica particles and titanate compound particles described later by the large-diameter silica particles. When the particle size difference between the small-diameter side peak and the large-diameter side peak is too small, the effect of suppressing the burial of the small-diameter silica particles and titanate compound particles by the large-diameter silica particles tends to be difficult to obtain. Also, when the particle size difference between the small-diameter side peak and the large-diameter side peak is too large, the large-diameter silica particles tend to be easily released from the toner particles.

[0042] In the number-based primary particle size distribution curve of the silica particles, the full width at half maximum of the small-diameter side peak is preferably 25 nm or less, and more preferably 20 nm or less. Compared with the case where the full width at half maximum of the small-diameter side peak is larger than 25 nm, the variation in the particle size of the small-diameter silica particles becomes smaller, and it becomes easier to suppress the concentration of the large-diameter silica particles by the small-diameter silica particles.

[0043] Here, the number-based primary particle size distribution curve of the silica particles is measured as follows. Toner particles externally added with silica particles are observed at 40,000 times with a scanning electron microscope (SEM), and the images of the silica particles on the observed toner particles are analyzed with image processing analysis software WinRoof (manufactured by Mitani Corporation), and the equivalent circle diameters of at least 300 particles are obtained. Then, a distribution curve is drawn from the small-diameter side for the number of each particle, and a number-based primary particle size distribution curve is obtained. The number-based primary particle size distribution curve of the titanate compound particles described later is also measured by the same method.

[0044] (Average circularity) Here, in the silica particles according to the present embodiment, in the above-described number-based primary particle size distribution curve, the silica particles having a particle size less than the valley existing between the small-diameter side peak and the large-diameter side peak are defined as small-diameter silica particles, and the silica particles having a particle size of the valley or more are defined as large-diameter silica particles. The small-diameter silica particles preferably have an average circularity of 0.88 or more and 0.94 or less, more preferably 0.89 or more and 0.93 or less, and even more preferably 0.90 or more and 0.92 or less, from the viewpoints of approaching the average circularity of the titanate compound particles and uniformly coating the surface of the toner particles.

[0045] The average circularity of the large-diameter silica particles is not particularly limited. For example, it is 0.85 or more and 1.00 or less, preferably 0.88 or more and 0.96 or less, and more preferably 0.90 or more and 0.95 or less.

[0046] Here, the average circularity of the silica particles (small-diameter silica particles, large-diameter silica particles) is measured as follows. The toner with silica particles externally added is observed at 40,000 times magnification with a scanning electron microscope (SEM). The images of the silica particles on the observed toner particles are analyzed using image processing analysis software WinRoof (manufactured by Mitani Corporation). The circularity of 300 or more particles is determined, and the average circularity is calculated by arithmetic averaging. The circularity is calculated by the following formula. A specific measurement method is described in [Examples] below. Circularity = (circumference of a circle having the same area as the particle) ÷ (circumference of the particle image) = 4π × (area of the particle) ÷ (circumference of the particle image) 2 The average circularity of the titanate compound particles described below is also measured by the same method.

[0047] (Coating rate) For the silica particles according to this embodiment, the coating rate of the toner particles with the small-diameter silica particles is preferably 1% or more and 30% or less, and more preferably 10% or more and 25% or less. The coating rate of the toner particles with the small-diameter silica particles will be described in detail later in relation to the coating rate of the toner particles with the titanate compound particles and the like.

[0048] In addition, from the viewpoint of suppressing the release of large-diameter silica particles and suppressing the burial of small-diameter silica particles and titanate compound particles by the large-diameter silica particles, the coating rate of the toner particles by the large-diameter silica particles is 10% or more and 50% or less, and preferably 20% or more and 40% or less. When the coating rate of the toner particles by the large-diameter silica particles is too small, it tends to be difficult to obtain the effect of suppressing the burial of the small-diameter silica particles and the titanate compound particles by the large-diameter silica particles. Further, when the coating rate of the toner particles by the large-diameter silica particles is too large, the large-diameter silica particles tend to be easily released from the toner particles.

[0049] Here, the coating rates of the toner particles by the small-diameter silica particles and the large-diameter silica particles are measured as follows. Using a scanning electron microscope (SEM), toner externally added with silica particles including small-diameter silica particles and large-diameter silica particles is observed at 40,000 times, and the observed toner image is subjected to binarization processing between each externally added agent particle and the toner mother particle. Then, using image processing analysis software WinRoof (manufactured by Mitani Corporation), the ratio of the area of the small-diameter silica particles to the other area among the silica particles, and the ratio of the area of the large-diameter silica particles to the other area among the silica particles are obtained, and the coating rates of the toner particles by the small-diameter silica particles and the large-diameter silica particles are respectively analyzed by the arithmetic mean for 300 or more toner particles. In actuality, analysis is performed on toner particles externally added with both silica particles and titanate compound particles. Using low-acceleration SEM conditions or an energy-dispersive X-ray analyzer (EDX device), etc., the images of each externally added agent such as each silica particle and titanate compound particle are distinguished from the toner mother particle, the area of the silica particle or titanate compound particle and the other area are obtained, and the coating rate is obtained. A specific measurement method will be described in [Examples] below.

[0050] (Method for manufacturing silica particles) The silica particles to which the present embodiment is applied are obtained, for example, by mixing small-diameter silica particles having a monodisperse particle size distribution and an average primary particle diameter of 20 nm or more and less than 80 nm, and large-diameter silica particles having a monodisperse particle size distribution and an average primary particle diameter of 80 nm or more and less than 130 nm. Among the small-diameter silica particles and large-diameter silica particles to be mixed, at least the small-diameter silica particles are preferably silica particles produced by a wet process from the viewpoint of narrowing the peak width of the peak on the small-diameter side in the number-based primary particle size distribution curve of the silica particles.

[0051] As the wet process for silica particles, a sol-gel method using tetraalkoxysilane as a material is preferable. The sol-gel method for producing silica particles is known. The sol-gel method includes, for example, dropping aqueous ammonia into a mixed solution 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, tetrabutoxysilane, and the like.

[0052] The surface of the silica particles is preferably hydrophobized. The hydrophobization treatment is performed, for example, by immersing the silica particles in a hydrophobizing agent. The hydrophobizing agent is not particularly limited, and examples thereof include silane-based coupling agents, silicone oils, titanate-based coupling agents, and aluminum-based coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobizing agent is, for example, 1 part by mass or more and 70 parts by mass or less with respect to 100 parts by mass of the silica particles.

[0053] (External addition amount) The external addition amount of the silica particles obtained by combining small-diameter silica particles and large-diameter silica particles is preferably 0.1 part by mass or more and 10 parts by mass or less, more preferably 0.5 part by mass or more and 7.0 parts by mass or less, and even more preferably 1.0 part by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the toner particles.

[0054] [Titanate compound particles] In this embodiment, the titanate compound particles used as an external additive for the toner have a peak in the number-based primary particle size distribution curve in the range of 20 nm or more and less than 80 nm, and have a peak with a particle size difference of 20 nm or less from the peak on the smaller diameter side in the number-based primary particle size distribution curve of the silica particles. Further, the titanate compound particles have an average circularity of 0.88 or more and 0.94 or less.

[0055] In this embodiment, the titanate compound particles used as an external additive for the toner have a peak in the number-based primary distribution curve in the range of 20 nm or more and less than 80 nm from the viewpoint of improving the fluidity of the toner. When the particle size of the peak that the titanate compound particles have in the number-based primary particle size distribution curve is less than 20 nm, the titanate compound particles are likely to be buried in the toner particles, so that the effect of improving the fluidity of the toner tends to be difficult to obtain. Further, when the particle size of the peak that the titanate compound particles have in the number-based primary particle size distribution curve is 80 nm or more, the titanate compound particles tend to roll on the surface of the toner particles and are unevenly distributed in the concave portions of the irregularly shaped toner particles, and the effect of improving the fluidity of the toner tends to be difficult to obtain.

[0056] Further, from the viewpoint of suppressing the mutual charging between the titanate compound particles and the large-diameter silica particles and suppressing the concentration of the large-diameter silica particles with respect to the titanate compound particles, the particle size difference between the peak existing in the range of 20 nm or more and less than 80 nm in the number-based primary particle size distribution curve and the peak on the smaller diameter side in the number-based primary particle size distribution curve of the above-described silica particles is 20 nm or less. If the particle size difference between the peak in the number-based primary particle size distribution curve of the titanate compound particles and the peak on the smaller diameter side in the number-based primary particle size distribution curve of the silica particles is too large, the effect of suppressing the concentration of the large-diameter silica particles with respect to the titanate compound particles tends to be difficult to obtain.

[0057] In this embodiment, from the viewpoint of suppressing the burial of the titanate compound particles by the large-diameter silica particles, it is preferable that the particle size difference between the peak existing in the range of 20 nm or more and less than 80 nm in the number-based primary particle size distribution curve of the titanate compound particles and the peak on the larger diameter side in the number-based primary particle size distribution curve of the silica particles is 20 nm or more and 70 nm or less.

[0058] From the viewpoint of excellent transfer retention property, the shape of the titanate compound particles is preferably a rounded shape rather than a cube or a rectangular parallelepiped. The titanate compound particles have a perovskite crystal structure and usually have a cube or rectangular parallelepiped particle shape. However, in the case of cubic or rectangular parallelepiped titanate compound particles, that is, titanate compound particles having corners, charges are concentrated at the corners, and a large local electrostatic repulsive force acts between the corners and the silica particles, which is considered to easily cause uneven distribution of the silica particles. In order to maintain the transfer efficiency in a low-temperature and low-humidity environment for a longer period, the shape of the titanate compound particles is preferably a shape with few corners, that is, a rounded shape.

[0059] From the viewpoint of maintaining the transferability of the toner by the particles and reducing the difference from the average circularity of the small-diameter silica particles in order to approximate the shape of the small-diameter silica particles, the average circularity of the primary particles of the titanate compound particles is 0.88 or more and 0.94 or less, preferably 0.89 or more and 0.93 or less, and more preferably 0.90 or more and 0.92 or less. Also, from the viewpoint of suppressing the release of the large-diameter silica particles, the difference between the average circularity of the titanate compound particles and the average circularity of the above-mentioned small-diameter silica particles is preferably 0.08 or less, and more preferably 0.05 or less. When the difference between the average circularity of the titanate compound particles and the average circularity of the small-diameter silica particles is too large, it becomes difficult to uniformly coat the toner particles with the titanate compound particles and the small-diameter silica particles, and the large-diameter silica particles tend to be easily released from the toner particles.

[0060] In this embodiment, the circularity of the primary particles of the specific titanate compound particles is 4π×(area of the primary particle image)÷(perimeter of the primary particle image) 2 The average circularity of the primary particles is the circularity at which the cumulative value becomes 50% from the smaller side in the circularity distribution. The circularity of the titanate compound particles is obtained by taking an electron microscope image of the toner to which the titanate compound particles are externally added and analyzing at least 300 titanate compound particles on the toner particles. A specific measurement method will be described in [Examples] below.

[0061] The titanate compound particles are a preferred example of metal titanate particles. From the viewpoint of the charge property being stable in various environments, strontium titanate particles, magnesium titanate particles, and calcium titanate particles are preferred, and strontium titanate particles are more preferred.

[0062] The titanate compound particles are preferably doped with a metal element other than titanium and the metal constituting the titanate compound (hereinafter also referred to as a dopant). By including a dopant, the titanate compound particles have a reduced crystallinity of the perovskite structure and a rounded shape.

[0063] The dopant of the titanate compound particles is not particularly limited as long as it is a metal element other than titanium and the metal constituting the titanate compound. A metal element having an ionic radius that can enter the crystal structure constituting the titanate compound particles when ionized is preferred. From this viewpoint, 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, and more preferably a metal element having an ionic radius of 60 pm or more and 150 pm or less.

[0064] When the titanate compound is strontium titanate, specific examples of the dopant of the titanate compound particles 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. As the lanthanoid, lanthanum and cerium are preferred. Among these, lanthanum is preferred from the viewpoints of being easy to dope and easy to control the shape of the titanate compound particles.

[0065] In addition, as the dopant of the titanate compound particles, from the viewpoint of not excessively negatively charging the titanate compound particles, when the titanate compound is strontium titanate, a metal element with an electronegativity of 2.0 or less is preferable, and a metal element with an electronegativity of 1.3 or less is more preferable. In this embodiment, the electronegativity is the electronegativity of Allred-Rochow. Examples of the metal element 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), cerium (1.06), etc. Among these, lanthanum is preferable.

[0066] From the viewpoints of having a rounded shape while having a perovskite-type crystal structure and productivity, the amount of the dopant in the titanate compound particles is preferably in the range of 0.1 mol% or more and 15 mol% or less, more preferably in the range of 0.1 mol% or more and 10 mol% or less, and still more preferably in the range of 0.1 mol% or more and 5 mol% or less with respect to a metal element such as strontium.

[0067] The water content of the titanate compound particles is preferably 1.5 mass% or more and 10 mass% or less. When the water content is 1.5 mass% or more and 10 mass% or less (more preferably 2 mass% or more and 5 mass% or less), the resistance of the titanate compound particles is controlled within an appropriate range, and it is excellent in suppressing uneven distribution due to electrostatic repulsion between the titanate compound particles. 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 the drying treatment. When the titanate compound particles are subjected to a hydrophobization treatment, the water content of the titanate compound particles can be controlled by adjusting the temperature and time of the drying treatment after the hydrophobization treatment.

[0068] The water content of the titanate compound particles is measured as follows. After allowing 20 mg of the measurement sample to stand in a chamber at a temperature of 22°C and a relative humidity of 55% for 17 hours for humidity conditioning, in a room at a temperature of 22°C and a relative humidity of 55%, it is heated from 30°C to 250°C at a temperature increase rate of 30°C / min in a nitrogen gas atmosphere using a thermobalance (TGA-50 type manufactured by Shimadzu Corporation), and the weight loss on heating (the mass lost by heating) is measured. Then, based on the measured weight loss on heating, the water content is calculated using the following formula. Water content (mass%) = (weight loss on heating from 30°C to 250°C) ÷ (mass before heating after humidity conditioning) × 100

[0069] The titanate compound particles are preferably titanate compound particles having a hydrophobized surface from the viewpoint of improving the action of the titanate compound particles, and more preferably titanate compound particles having a surface hydrophobized with a silicon-containing organic compound.

[0070] - Method for producing titanate compound particles - The method for producing titanate compound particles is not particularly limited, but from the viewpoint of controlling the particle size and shape, a wet method is preferably used.

[0071] · Production of titanate compound particles by a wet method The wet method for producing titanate compound particles is, for example, a production method in which an aqueous alkali solution is added to a mixed solution of a titanium oxide source and a metal source such as strontium while reacting, and then an acid treatment is performed. In this production method, the particle size of the titanate compound particles is controlled by the mixing ratio of the titanium oxide source and the metal source, the concentration of the titanium oxide source at the initial stage of the reaction, the temperature and the addition rate when adding the aqueous alkali solution, and the like.

[0072] As the titanium oxide source, a mineral acid peptized product of a hydrolyzate of a titanium compound is preferable. Examples of the metal source include nitrates and chlorides. When the metal is strontium, examples of the strontium source include strontium nitrate and strontium chloride.

[0073] When the mixing ratio of the titanium oxide source and the metal source is expressed with the metal as MO, the molar ratio of MO / TiO 2 is preferably 0.9 or more and 1.4 or less, and more preferably 1.05 or more and 1.20 or less. The concentration of the titanium oxide source at the initial stage of the reaction is preferably 0.05 mol / L or more and 1.3 mol / L or less, and more preferably 0.5 mol / L or more and 1.0 mol / L or less in terms of TiO 2 .

[0074] From the viewpoint of making the shape of the titanate compound particles not cubic or rectangular parallelepiped but rounded, it is preferable to add a dopant source to the mixed solution of the titanium oxide source and the metal source. Examples of the dopant source include metal oxides other than titanium and strontium. The metal oxide as the dopant source is added, for example, as a solution dissolved in nitric acid, hydrochloric acid or sulfuric acid. The addition amount of the dopant source is preferably an amount such that the metal contained in the dopant source is 0.1 mol or more and 10 mol or less, and more preferably 0.1 mol or more and 5 mol or less, per 100 mol of the metal contained in the metal source such as strontium.

[0075] As the alkaline aqueous solution, a sodium hydroxide aqueous solution is preferable. The higher the temperature of the reaction solution when adding the alkaline aqueous solution, the better the crystallinity of the obtained titanate compound particles. From the viewpoint of having a perovskite-type crystal structure and a rounded shape, the temperature range of the reaction solution when adding the alkaline aqueous solution is preferably 60°C or more and 100°C or less. The slower the addition rate of the alkaline aqueous solution, the larger the particle diameter of the obtained titanate compound particles, and the faster the addition rate, the smaller the particle diameter of the obtained titanate compound particles. The addition rate of the alkaline aqueous solution is, for example, 0.001 equivalent / h or more and 1.2 equivalents / h or less with respect to the charged raw materials, and 0.002 equivalent / h or more and 1.1 equivalents / h or less is appropriate.

[0076] After adding an aqueous alkali solution, an acid treatment is performed for the purpose of removing unreacted metal sources. The acid treatment is carried out, for example, using hydrochloric acid to adjust the pH of the reaction solution to 2.5 to 7.0, more preferably 4.5 to 6.0. After the acid treatment, the reaction solution is subjected to solid-liquid separation, and the solid content is dried to obtain titanate compound particles.

[0077] ·Surface treatment The surface treatment of the titanate compound particles is performed, for example, by preparing a treatment liquid obtained by mixing a silicon-containing organic compound, which is a hydrophobizing agent, and a solvent, mixing the titanate compound particles and the treatment liquid under stirring, and further continuing the stirring. After the surface treatment, a drying treatment is carried out for the purpose of removing the solvent of the treatment liquid.

[0078] Examples of the silicon-containing organic compound used for the surface treatment of the titanate compound particles include alkoxysilane compounds, silazane compounds, silicone oils, and the like.

[0079] Examples of the alkoxysilane compounds used for the surface treatment of the titanate compound particles include tetramethoxysilane, tetraethoxysilane; methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, hexyltriethoxysilane, decyltriethoxysilane, dodecyltriethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, phenyltriethoxysilane, benzyltriethoxysilane; dimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane; trimethylmethoxysilane, trimethylethoxysilane;

[0080] Examples of the silazane compound used for the surface treatment of the titanate compound particles include dimethyldisilazane, trimethyldisilazane, tetramethyldisilazane, pentamethyldisilazane, hexamethyldisilazane, and the like.

[0081] Examples of the silicone oil used for the surface treatment of the titanate compound particles include silicone oils such as dimethylpolysiloxane, diphenylpolysiloxane, and phenylmethylpolysiloxane; 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; and the like.

[0082] As the solvent used for the preparation of the treatment liquid, when the silicon-containing organic compound is an alkoxysilane compound or a silazane compound, alcohol (for example, methanol, ethanol, propanol, butanol) is preferable, and when the silicon-containing organic compound is a silicone oil, hydrocarbons (for example, benzene, toluene, normal hexane, normal heptane) are preferable.

[0083] In the treatment liquid, the concentration of the silicon-containing organic compound is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, and still more preferably 10% by mass or more and 30% by mass or less.

[0084] The amount of the silicon-containing organic compound used for the 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 still more preferably 5 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the titanate compound particles.

[0085] The external addition amount of the titanate compound particles is preferably 0.2 part by mass or more and 4 parts by mass or less, more preferably 0.4 part by mass or more and 3 parts by mass or less, and still more preferably 0.6 part by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the toner particles.

[0086] The amount of the externally added titanate compound particles is preferably 10 parts by mass or more and 100 parts by mass or less, more preferably 20 parts by mass or more and 90 parts by mass or less, and still more preferably 30 parts by mass or more and 80 parts by mass or less with respect to 100 parts by mass of the silica particles.

[0087] [Relationship between silica particles and titanate compound particles] (Number primary particle size distribution curve) FIG. 2 is a diagram showing the number primary particle size distribution curve of the particles (hereinafter, may be referred to as mixed particles in some cases) combining the titanate compound particles and the silica particles externally added to the toner of the present embodiment. In FIG. 2, the vertical axis represents the number ratio of the primary particles, and the horizontal axis represents the particle size. Further, in FIG. 2, in addition to the number primary particle size distribution curve of the mixed particles, the number primary particle size distribution curve of the titanate compound particles externally added to the toner and the number primary particle size distribution curve of the silica particles externally added to the toner shown in FIG. 1 are also shown together. Note that each number primary particle size distribution curve shown in FIG. 2 is an example for explanation and is not necessarily accurate.

[0088] As shown in FIG. 2, the particles combining the titanate compound particles and the silica particles have a first peak (indicated by reference numeral P1 in FIG. 2; the same applies hereinafter) existing in the range of 20 nm or more and less than 80 nm and a second peak (P2) existing in the range of 80 nm or more and less than 130 nm in the number primary particle size distribution curve. Here, from the viewpoint of suppressing the concentration of the large-diameter silica particles with respect to the titanate compound particles, it is preferable that the titanate compound particles and the small-diameter silica particles have closer particle size distributions. From the above viewpoint, in the number primary particle size distribution curve of the particles combining the titanate compound particles and the silica particles, it is preferable that the first peak existing in the range of 20 nm or more and less than 80 nm is composed of the peak (PT) in the number primary particle size distribution curve of the titanate compound particles and the small-diameter side peak (PS1) in the number primary particle size distribution curve of the silica particles.

[0089] Note that the first peak being composed of the peak (PT) in the number-based primary particle size distribution curve of the titanate compound particles and the small-diameter side peak (PS1) in the number-based primary particle size distribution curve of the silica particles means that the shoulder peak is not formed on the first peak or the first peak is not split into a plurality of peaks, by the peak (PT) in the number-based primary particle size distribution curve of the titanate compound particles or the small-diameter side peak (PS1) in the number-based primary particle size distribution curve of the silica particles.

[0090] Also, in the number-based primary particle size distribution curve of the combined particles of the titanate compound particles and the silica particles, the second peak existing in the range of 80 nm or more and less than 130 nm is preferably composed of the large-diameter side peak (PS2) in the number-based primary particle size distribution curve of the silica particles.

[0091] (Coating rate) Let the coating rate of the titanate compound particles with respect to the toner particles be A (%) and the coating rate of the small-diameter silica particles with respect to the toner particles be B (%). From the viewpoint of achieving both the improvement of the charging characteristics by the titanate compound particles and the suppression of the concentration of the large-diameter silica particles, the titanate compound particles and the small-diameter silica particles according to the present embodiment preferably satisfy the following formula (1) in terms of the ratio (A / A + B) of the coating rate of the titanate compound particles to the total coating rate. 0.2 ≦ A / A + B ≦ 0.8 ···(1)

[0092] When the ratio of the coating rate of the titanate compound particles to the total coating rate of the titanate compound particles and the small-diameter silica particles is less than 0.2, the effect of improving the charging characteristics by the titanate compound particles tends to be difficult to obtain. When the ratio of the coating rate of the titanate compound particles to the total coating rate of the titanate compound particles and the small-diameter silica particles exceeds 0.8, the effect of suppressing the concentration of the large-diameter silica particles with respect to the titanate compound particles tends to be difficult to obtain.

[0093] The ratio (A / A+B) of the coating rate of the titanate compound particles to the total coating rate of the titanate compound particles and the small-diameter silica particles preferably satisfies the following formula (1)'. 0.2 ≦ A / A+B ≦ 0.5 ···(1)'

[0094] Also, for the titanate compound particles and the silica particles, it is preferable that the total coating rate (A+B) of the titanate compound particles and the small-diameter silica particles with respect to the toner particles satisfies the following formula (2). 10 ≦ A+B ≦ 50 ···(2) When the total coating rate of the titanate compound particles and the small-diameter silica particles with respect to the toner particles is less than 10%, the large-diameter silica particles may easily dissociate from the toner particle surface. Also, when the total coating rate of the titanate compound particles and the small-diameter silica particles with respect to the toner particles exceeds 50%, it may be difficult to obtain good charging characteristics.

[0095] [Other external additives] The toner according to this embodiment may contain other external additives other than the silica particles and the titanate compound particles as long as the effects of this embodiment can be obtained. Examples of other external additives include the following inorganic particles and resin particles.

[0096] Examples of other external additives include inorganic particles. Examples of the inorganic particles include TiO 2 , Al 2 O 3 , CuO, ZnO, SnO 2 , CeO 2 , Fe 2 O 3 , MgO, BaO, CaO, K 2 O, Na 2 O, ZrO 2 , CaO·SiO 2 , K 2 O·(TiO 2 ) n , Al 2 O 3 ·2SiO 2 , CaCO 3 , MgCO 3 , BaSO 4, MgSO 4 etc. can be mentioned.

[0097] The surface of the inorganic particles as an external additive is preferably subjected to a hydrophobization treatment. The hydrophobization treatment is performed, for example, by immersing the inorganic particles in a hydrophobizing agent. The hydrophobizing agent is not particularly limited, and examples include silane-based coupling agents, silicone oils, titanate-based coupling agents, aluminum-based coupling agents, etc. These may be used alone or in combination of two or more. The amount of the hydrophobizing agent is usually 1 part by mass or more and 50 parts by mass or less with respect to 100 parts by mass of the inorganic particles.

[0098] Other external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate, melamine resin), cleaning agents (for example, particles of fluorine-based high molecular weight substances, particles of fatty acid metal salts), etc.

[0099] The addition amount of other external additives 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 with respect to the toner particles.

[0100] [Method for manufacturing toner] Next, the method for manufacturing the toner according to this embodiment will be described. The toner according to this embodiment is obtained by externally adding an external additive to the toner particles after manufacturing the toner particles.

[0101] The toner particles may be manufactured by either a dry method (for example, kneading and pulverizing method, etc.) or a wet method (for example, aggregation and coalescence method, suspension polymerization method, dissolution and suspension method, etc.). There are no particular restrictions on these manufacturing methods, and known manufacturing methods are adopted. Among these, it is preferable to obtain the toner particles by the aggregation and coalescence method.

[0102] Specifically, for example, when manufacturing toner particles by the aggregation-unification method, a step of preparing a resin particle dispersion liquid in which resin particles serving as a binder resin are dispersed (resin particle dispersion liquid preparation step), a step of aggregating resin particles (and other particles as necessary) in the resin particle dispersion liquid (or in the dispersion liquid after mixing other particle dispersion liquids as necessary) to form aggregated particles (aggregated particle formation step), and a step of heating the aggregated particle dispersion liquid in which the aggregated particles are dispersed to fuse and unify the aggregated particles to form toner particles (fusion-unification step) are performed to manufacture the toner particles.

[0103] Details of each step will be described below. In the following description, a method for obtaining toner particles containing a colorant and a release agent will be described. However, the colorant and the release agent are used as necessary. Of course, other additives other than the colorant and the release agent may be used.

[0104] - Resin Particle Dispersion Liquid Preparation Step - Together with the resin particle dispersion liquid in which resin particles serving as a binder resin are dispersed, for example, a colorant particle dispersion liquid in which colorant particles are dispersed and a release agent particle dispersion liquid in which release agent particles are dispersed are prepared.

[0105] The resin particle dispersion liquid is prepared, for example, by dispersing resin particles in a dispersion medium with a surfactant. Examples of the dispersion medium used for the resin particle dispersion liquid include aqueous media. Examples of the aqueous medium include water such as distilled water and ion-exchanged water, and alcohols. These may be used alone or in combination of two or more.

[0106] Examples of surfactants include anionic surfactants such as sulfate ester salts, sulfonates, phosphate esters, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; nonionic surfactants such as polyethylene glycols, alkylphenol ethylene oxide adducts, and polyhydric alcohols. Among these, anionic surfactants and cationic surfactants are particularly mentioned. Nonionic surfactants may be used in combination with anionic surfactants or cationic surfactants. Surfactants may be used alone or in combination of two or more.

[0107] In the resin particle dispersion, examples of methods for dispersing resin particles in a dispersion medium include general dispersion methods such as rotary shear homogenizers and ball mills, sand mills, dyno mills, etc. having media. Depending on the type of resin particles, the resin particles may be dispersed in the dispersion medium by the phase inversion emulsification method. The phase inversion emulsification method is a method in which the resin to be dispersed is dissolved in a hydrophobic organic solvent in which the resin is soluble, a base is added to the organic continuous phase (O phase) for neutralization, and then an aqueous medium (W phase) is added to perform a phase inversion from W / O to O / W, and the resin is dispersed in the aqueous medium in a particulate form.

[0108] The volume average particle size of the resin particles dispersed in the resin particle dispersion is preferably, for example, 0.01 μm or more and 1 μm or less, more preferably 0.08 μm or more and 0.8 μm or less, and still more preferably 0.1 μm or more and 0.6 μm or less. The volume average particle size of the resin particles is measured using the particle size distribution obtained by measurement with a laser diffraction particle size distribution analyzer (for example, LA-700 manufactured by Horiba, Ltd.). For the divided particle size ranges (channels), the cumulative distribution is drawn from the small particle size side with respect to the volume, and the particle size at which the cumulative percentage is 50% with respect to all particles is measured as the volume average particle size D50v. The volume average particle size of the particles in other dispersions is measured in the same manner.

[0109] The content of the 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.

[0110] In the same manner as the resin particle dispersion, for example, a colorant particle dispersion and a release agent particle dispersion are also prepared. That is, regarding the volume average particle diameter, dispersion medium, dispersion method, and content of particles in the resin particle dispersion, the same applies to the colorant particles dispersed in the colorant particle dispersion and the release agent particles dispersed in the release agent particle dispersion.

[0111] -Agglomerated Particle Formation Step- Next, the resin particle dispersion, the colorant particle dispersion, and the release agent particle dispersion are mixed. Then, in the mixed dispersion, the resin particles, the colorant particles, and the release agent particles are hetero-aggregated to form agglomerated particles containing the resin particles, the colorant particles, and the release agent particles, which have a diameter close to the diameter of the target toner particles.

[0112] Specifically, for example, a flocculant is added to the mixed dispersion, the pH of the mixed dispersion is adjusted to acidic (for example, pH 2 or more and 5 or less), and a dispersion stabilizer is added as necessary. Then, the mixture 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 more and the glass transition temperature of the resin particles - 10°C or less) to aggregate the particles dispersed in the mixed dispersion and form agglomerated particles. In the agglomerated particle formation step, for example, the mixed dispersion may be stirred with a rotary shear homogenizer at room temperature (for example, 25°C), a flocculant is added, the pH of the mixed dispersion is adjusted to acidic (for example, pH 2 or more and 5 or less), and a dispersion stabilizer is added as necessary, and then heating is performed.

[0113] Examples of the flocculant include surfactants having a polarity opposite to that of the surfactant contained in the mixed dispersion, inorganic metal salts, and metal complexes having a valence of 2 or more. When a metal complex is used as the flocculant, the amount of surfactant used is reduced, and the charging characteristics are improved. An additive that forms a complex or a similar bond with the metal ions of the flocculant may be used as necessary together with the flocculant. As this additive, a chelating agent is preferably used.

[0114] Examples of the inorganic metal salts include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate; inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, and calcium polysulfide; and the like. As the chelating agent, a water-soluble chelating agent may be used. Examples of the chelating agent include oxycarboxylic 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 addition amount of the chelating agent is preferably 0.01 part by mass or more and 5.0 parts by mass or less, more preferably 0.1 part by mass or more and less than 3.0 parts by mass, based on 100 parts by mass of the resin particles.

[0115] -Fusion and unification step- Next, the aggregated particle dispersion in which the aggregated particles are dispersed is heated to, for example, 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 unify the aggregated particles and form toner particles.

[0116] Through the above steps, toner particles are obtained. After obtaining the aggregated particle dispersion in which the aggregated particles are dispersed, the aggregated particle dispersion and the resin particle dispersion in which the resin particles are dispersed are further mixed and aggregated so that the resin particles further adhere to the surface of the aggregated particles to form second aggregated particles, and the second aggregated particle dispersion in which the second aggregated particles are dispersed is heated to fuse and unify the second aggregated particles to form toner particles having a core-shell structure, whereby toner particles may be manufactured.

[0117] After the fusion and integration process is completed, the toner particles formed in the solution are subjected to known cleaning, solid-liquid separation, and drying processes to obtain toner particles in a dried state. From the perspective of chargeability, it is advisable to perform sufficient replacement cleaning with ion-exchanged water in the cleaning process. From the perspective of productivity, it is advisable to perform suction filtration, pressure filtration, etc. in the solid-liquid separation process. From the perspective of productivity, it is advisable to perform freeze drying, airflow drying, fluidized drying, vibration-type fluidized drying, etc. in the drying process.

[0118] And the toner according to this embodiment is manufactured, for example, by adding and mixing an external additive to the obtained toner particles in a dried state. The mixing may be performed, for example, by a V blender, a Henschel mixer, a Lodige mixer, etc. Further, if necessary, coarse particles of the toner may be removed using a vibrating sieve, an air classifier, etc.

[0119] <Electrostatic charge image developer> The electrostatic charge image developer according to this embodiment includes at least the toner according to this embodiment. The electrostatic charge image developer according to this embodiment may be a one-component developer containing only the toner according to this embodiment, or a two-component developer in which the toner and a carrier are mixed.

[0120] There is no particular limitation on the carrier, and known carriers can be mentioned. Examples of the carrier include a coated carrier in which a resin is coated on the surface of a core material made of magnetic powder; a magnetic powder dispersion type carrier in which magnetic powder is dispersed and blended in a matrix resin; a resin-impregnated type carrier in which porous magnetic powder is impregnated with resin; etc. The magnetic powder dispersion type carrier and the resin-impregnated type carrier may be carriers in which the constituent particles of the carrier are used as the core material and a resin is coated on this surface.

[0121] Examples of the magnetic powder include magnetic metals such as iron, nickel, and cobalt; magnetic oxides such as ferrite and magnetite; etc.

[0122] Examples of the resin for coating and the matrix resin include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene-acrylic ester copolymer, straight silicone resin containing an organosiloxane bond or a modified product thereof, fluororesin, polyester, polycarbonate, phenol resin, epoxy resin, etc. Additives such as conductive particles may be included in the resin for coating and the matrix resin. Examples of the conductive particles include metals such as gold, silver, and copper, and particles such as carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, and potassium titanate.

[0123] To coat the surface of the core material with a resin, methods such as coating with a coating layer forming solution in which the resin for coating and various additives (used as necessary) are dissolved in an appropriate solvent can be mentioned. The solvent is not particularly limited and may be selected in consideration of the type of resin to be used, coating applicability, etc. 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 while the core material is suspended by flowing air; 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; etc.

[0124] The mixing ratio (mass ratio) of the toner and the carrier in the two-component developer is preferably toner:carrier = 1:100 to 20:100, and more preferably 3:100 to 15:100.

[0125] <Image forming apparatus, image forming method> The image forming apparatus / image forming method according to this embodiment will be described. The image forming apparatus according to this embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic charge image forming unit that forms an electrostatic charge image on the charged surface of the image carrier, a developing unit that stores an electrostatic charge image developer and develops the electrostatic charge image formed on the surface of the image carrier as a toner image using the electrostatic charge 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. And, as the electrostatic charge image developer, the electrostatic charge image developer according to this embodiment is applied.

[0126] In the image forming apparatus according to this embodiment, an image forming method (image forming method according to this embodiment) including a charging step of charging the surface of the image carrier, an electrostatic charge image forming step of forming an electrostatic charge image on the charged surface of the image carrier, a developing step of developing the electrostatic charge image formed on the surface of the image carrier as a toner image using the electrostatic charge 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 is performed.

[0127] The image forming apparatus according to this embodiment is a direct transfer type apparatus that directly transfers the toner image formed on the surface of the image carrier to a recording medium; an intermediate transfer type apparatus that first transfers the toner image formed on the surface of the image carrier to the surface of an intermediate transfer member and then secondarily transfers the toner image transferred to the surface of the intermediate transfer member to the surface of a recording medium; an apparatus provided with cleaning means for cleaning the surface of the image carrier after transfer of the toner image and before charging; an apparatus provided with charge removal means for irradiating the surface of the image carrier with charge removal light for charge removal after transfer of the toner image and before charging; and other known image forming apparatuses are applicable. When the image forming apparatus according to this embodiment is an intermediate transfer type apparatus, the transfer unit has a configuration including, for example, an intermediate transfer member on the surface of which a toner image is transferred, a primary transfer unit that primarily transfers the toner image formed on the surface of the image carrier to the surface of the intermediate transfer member, and a secondary transfer unit that secondarily transfers the toner image transferred to the surface of the intermediate transfer member to the surface of a recording medium.

[0128] In the image forming apparatus according to the present embodiment, for example, a portion including developing means may be a cartridge structure (process cartridge) that is detachable from the image forming apparatus. As the process cartridge, for example, a process cartridge including developing means that houses the electrostatic charge image developer according to the present embodiment is preferably used.

[0129] Hereinafter, an example of the image forming apparatus according to the present embodiment will be described, but the present invention is not limited thereto. In the following description, the main parts shown in the drawings will be described, and the description of the others will be omitted.

[0130] FIG. 3 is a schematic configuration diagram showing the image forming apparatus according to the present embodiment. The image forming apparatus shown in FIG. 3 includes first to fourth image forming units 10Y, 10M, 10C, and 10K (image forming means) of an electrophotographic system that output images of respective colors of yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter, may be simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side at a predetermined distance from each other in the horizontal direction. These units 10Y, 10M, 10C, and 10K may be process cartridges that are detachable from the image forming apparatus.

[0131] Above each of the units 10Y, 10M, 10C, and 10K, an intermediate transfer belt (an example of an intermediate transfer member) 20 extends through each unit. The intermediate transfer belt 20 is provided by being wound around a driving roll 22 and a support roll 24 that are in contact with the inner surface of the intermediate transfer belt 20, and is configured to travel in a direction from the first unit 10Y to the fourth unit 10K. A force is applied to the support roll 24 in a direction away from the driving roll 22 by a spring or the like (not shown), and tension is applied to the intermediate transfer belt 20 wound around both of them. An intermediate transfer belt cleaning device 30 is provided on the image holding surface side of the intermediate transfer belt 20 so as to face the driving roll 22.

[0132] To each of the developing devices (an example of developing means) 4Y, 4M, 4C, and 4K of the respective units 10Y, 10M, 10C, and 10K, yellow, magenta, cyan, and black toners stored in toner cartridges 8Y, 8M, 8C, and 8K are supplied.

[0133] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, here, the first unit 10Y that forms a yellow image disposed on the upstream side in the intermediate transfer belt running direction will be described as a representative.

[0134] The first unit 10Y has a photoreceptor 1Y that acts as an image holding member. Around the photoreceptor 1Y, a charging roll (an example of charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential, an exposure device (an example of electrostatic charge image forming means) 3 that exposes the charged surface with a laser beam 3Y based on a color-separated image signal to form an electrostatic charge image, a developing device (an example of developing means) 4Y that supplies charged toner to the electrostatic charge image to develop the electrostatic charge image, a primary transfer roll (an example of primary transfer means) 5Y that transfers the developed toner image onto the intermediate transfer belt 20, and a photoreceptor cleaning device (an example of image holding member cleaning means) 6Y that removes the toner remaining on the surface of the photoreceptor 1Y after primary transfer are arranged in order.

[0135] The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is provided at a position facing the photoreceptor 1Y. Bias power supplies (not shown) for applying a primary transfer bias are connected to the primary transfer rolls 5Y, 5M, 5C, and 5K of each unit, respectively. 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).

[0136] Hereinafter, the operation of forming a yellow image in the first unit 10Y will be described. First, prior to the operation, the surface of the photoreceptor 1Y is charged to a potential of -600 V to -800 V by the charging roll 2Y. The photoreceptor 1Y has conductivity (for example, a volume resistivity of 1×10 at 20°C-6 It is formed by laminating a photosensitive layer on a substrate with a resistance of less than [[Ωcm]]. This photosensitive layer usually has a high resistance (the resistance of a general resin), but when irradiated with a laser beam, it has the property that the specific resistance of the irradiated part changes. Therefore, a laser beam 3Y is irradiated from an exposure device 3 onto the surface of the charged photoreceptor 1Y according to the yellow image data sent from a control unit (not shown). Thereby, an electrostatic charge image of a yellow image pattern is formed on the surface of the photoreceptor 1Y.

[0137] An electrostatic charge image is an image formed on the surface of the photoreceptor 1Y by charging. By the laser beam 3Y, the specific resistance of the irradiated part of the photosensitive layer decreases, the charged charges on the surface of the photoreceptor 1Y flow, while the charges in the part not irradiated by the laser beam 3Y remain, forming a so-called negative latent image. The electrostatic charge image formed on the photoreceptor 1Y rotates to a predetermined development position according to the travel of the photoreceptor 1Y. And at this development position, the electrostatic charge image on the photoreceptor 1Y is developed and visualized as a toner image by a developing device 4Y.

[0138] Inside the developing device 4Y, for example, an electrostatic charge image developer containing at least yellow toner and carrier is accommodated. The yellow toner is triboelectrically charged by being agitated inside the developing device 4Y and has the same polarity (negative polarity) charge as the charged charges on the photoreceptor 1Y and is held on a developer roll (an example of a developer holding body). Then, as the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image part on the surface of the photoreceptor 1Y, and the latent image is developed by the yellow toner. The photoreceptor 1Y on which the yellow toner image is formed continues to travel at a predetermined speed, and the toner image developed on the photoreceptor 1Y is conveyed to a predetermined primary transfer position.

[0139] When the yellow toner image on the photoreceptor 1Y is conveyed to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and the electrostatic force from the photoreceptor 1Y toward the primary transfer roll 5Y acts on the toner image, transferring the toner image on the photoreceptor 1Y onto the intermediate transfer belt 20. The transfer bias applied at this time has the opposite polarity (+) to the polarity (-) of the toner, and in the first unit 10Y, it is controlled, for example, to +10 μA by a control unit (not shown). The toner remaining on the photoreceptor 1Y is removed and recovered by the photoreceptor cleaning device 6Y.

[0140] The primary transfer biases applied to the primary transfer rolls 5M, 5C, and 5K after the second unit 10M are also controlled according to the first unit. In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred in the first unit 10Y is sequentially conveyed through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are overlapped and multi-transferred.

[0141] The intermediate transfer belt 20 onto which the four-color toner images have been multi-transferred through the first to fourth units reaches the secondary transfer unit composed of the intermediate transfer belt 20, the support roll 24 in contact with the inner surface of the intermediate transfer belt, and the secondary transfer roll (an example of secondary transfer means) 26 disposed on the image holding surface side of the intermediate transfer belt 20. On the other hand, the recording paper (an example of a recording medium) P is fed at a predetermined timing to the gap where the secondary transfer roll 26 and the intermediate transfer belt 20 are in contact via a feeding mechanism, and a secondary transfer bias is applied to the support roll 24. The transfer bias applied at this time has the same polarity (-) as the polarity (-) of the toner, and the 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 the resistance detected by a resistance detection means (not shown) that detects the resistance of the secondary transfer unit and is voltage-controlled.

[0142] The recording paper P onto which the toner image has been transferred is fed into the nip portion (pressure contact portion) of a pair of fixing rolls in the fixing device (an example of fixing means) 28, and the toner image is fixed onto the recording paper P to form a fixed image. The recording paper P on which the fixing of the color image has been completed is carried out toward the discharge unit, and a series of color image forming operations are terminated.

[0143] Examples of the recording paper P for transferring the toner image include plain paper used in electrophotographic copiers, printers, etc. Examples of the recording medium include OHP sheets in addition to the recording paper P. In order to further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper obtained by coating the surface of plain paper with a resin or the like, art paper for printing, etc. are preferably used.

[0144] <Process cartridge, toner cartridge> The process cartridge according to the present embodiment accommodates the electrostatic charge image developer according to the present embodiment, and includes developing means for developing the electrostatic charge image formed on the surface of the image carrier as a toner image, and is a process cartridge that is detachable from the image forming apparatus.

[0145] The process cartridge according to the present embodiment may have a configuration including developing means and at least one selected from other means such as an image carrier, charging means, electrostatic charge image forming means, and transfer means, as necessary.

[0146] Hereinafter, an example of the process cartridge according to the present embodiment is shown, but it is not necessarily limited thereto. In the following description, the main parts shown in the drawings will be described, and the others will be omitted from the description.

[0147] FIG. 4 is a schematic configuration diagram showing an example of the process cartridge according to the present embodiment. The process cartridge 200 shown in FIG. 4 is configured by integrally combining and holding, for example, a photoreceptor 107 (an example of an image holding member), a charging roll 108 (an example of charging means) provided around the photoreceptor 107, a developing device 111 (an example of developing means), and a photoreceptor cleaning device 113 (an example of cleaning means) with a housing 117 provided with an attachment rail 116 and an opening 118 for exposure, and is cartridgeized. In FIG. 4, 109 indicates an exposure device (an example of electrostatic charge image forming means), 112 indicates a transfer device (an example of transfer means), 115 indicates a fixing device (an example of fixing means), and 300 indicates a recording paper (an example of a recording medium).

[0148] Next, the toner cartridge according to the present embodiment will be described. The toner cartridge according to the present embodiment is a toner cartridge that houses the toner according to the present embodiment and is detachable from the image forming apparatus. The toner cartridge houses replenishing toner for supplying to developing means provided in the image forming apparatus.

[0149] The image forming apparatus shown in FIG. 3 is an image forming apparatus having a configuration in which toner cartridges 8Y, 8M, 8C, 8K are detachable, and the developing devices 4Y, 4M, 4C, 4K are connected by toner supply pipes (not shown) to the corresponding toner cartridges. When the toner housed in the toner cartridge runs low, the toner cartridge is replaced.

Example

[0150] Hereinafter, embodiments of the invention will be described in detail by way of examples, but the embodiments of the invention are not limited to these examples in any way. In the following description, unless otherwise specified, "parts" and "%" are based on mass.

[0151] <Manufacture of toner particles> -Preparation of resin particle dispersion- ·Terephthalic acid: 30 mol parts ·Fumaric acid: 70 mol parts · Ethylene oxide adduct of bisphenol A: 5 parts by mole · Propylene oxide adduct of bisphenol A: 95 parts by mole The above materials were charged into a flask equipped with a stirring device, a nitrogen inlet tube, a temperature sensor and a rectification column, the temperature was raised to 220 °C over 1 hour, and 1 part of titanium tetraethoxide was added to 100 parts of the above materials. While distilling off the generated water, the temperature was raised to 230 °C over 30 minutes, and after continuing the dehydration condensation reaction at this temperature for 1 hour, the reaction product was cooled. Thus, a polyester resin having a weight average molecular weight of 18,000 and a glass transition temperature of 60 °C was obtained.

[0152] 40 parts of ethyl acetate and 25 parts of 2-butanol were charged into a container equipped with a temperature adjusting means and a nitrogen replacement means to obtain a mixed solvent, and then 100 parts of the polyester resin was gradually charged and dissolved. Here, a 10 mass% aqueous ammonia solution (equivalent to 3 times the molar ratio with respect to the acid value of the resin) was added and stirred for 30 minutes. Next, the inside of the container was replaced with dry nitrogen, the temperature was maintained at 40 °C, and 400 parts of ion-exchanged water was dropped at a rate of 2 parts / min while stirring the mixed solution. After the dropping was completed, the temperature was returned to room temperature (20 °C to 25 °C), and bubbling was performed with dry nitrogen for 48 hours while stirring to obtain a resin particle dispersion liquid in which ethyl acetate and 2-butanol were reduced to 1000 ppm or less. Ion-exchanged water was added to the resin particle dispersion liquid to adjust the solid content to 20 mass%, and a resin particle dispersion liquid was obtained.

[0153] - Preparation of Colorant Particle Dispersion · C.I.Pigment Blue 15:3 (Dainichi Seika Kogyo): 70 parts · 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, trade name Ultra Turrax T50). Ion-exchanged water was added so that the solid content in the dispersion liquid became 20 mass%, and a colorant particle dispersion liquid in which colorant particles having a volume average particle diameter of 170 nm were dispersed was obtained.

[0154] - Preparation of Toner Particles · Resin particle dispersion: 403 parts · Colorant particle dispersion: 12 parts · Release agent particle dispersion: 50 parts · Anionic surfactant (Tayca Power): 2 parts The above materials were put into a round stainless steel flask, 0.1N nitric acid was added and adjusted to pH 3.5, and then 30 parts of an aqueous nitric acid solution with a polyaluminum chloride concentration of 10% by mass was added. Subsequently, after dispersing at a liquid temperature of 30 °C using a homogenizer (IKA, trade name Ultra Turrax T50), it was heated to 45 °C in a heating oil bath and held for 30 minutes. Then, 100 parts of the resin particle dispersion was added and held for 1 hour. After adding a 0.1N aqueous sodium hydroxide solution to adjust the pH to 8.5, it was heated to 84 °C and held for 2.5 hours. Next, it was 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 diameter of the toner particles was 5.7 μm.

[0155] <Manufacture of silica particles> [Silica particles (1)] In a 1.5 L glass reactor equipped with a stirrer, a dropping nozzle, and a thermometer, 320 parts of methanol and 72 parts of 10% aqueous ammonia were added to obtain an alkali catalyst solution. This alkali catalyst solution was maintained at 35°C, and while stirring, 45 parts of tetramethoxysilane (TMOS) and 9 parts of 8.0% aqueous ammonia were simultaneously dropped to obtain a hydrophilic silica particle dispersion (solid content concentration: 12.0% by mass). Here, the dropping time was set to 10 minutes. Thereafter, the obtained silica particle dispersion was concentrated to a solid content concentration of 40% by mass using a rotary R-fine (manufactured by Kotobuki Industries Co., Ltd.). An ester adapter and a condenser were attached to the reaction vessel used for preparing this concentrated silica particle dispersion. The silica particle dispersion was heated to 60°C to 70°C, and when methanol was distilled off, water was added. Then, it was further heated to 70°C to 90°C to distill off methanol, obtaining an aqueous dispersion of silica particles. To 100 parts of the solid content in this aqueous dispersion, 3 parts of methyltrimethoxysilane were added at room temperature (25°C), and the surface of the silica particles was treated by reacting for 2 hours. After adding methyl isobutyl ketone to the aqueous dispersion after this surface treatment, it was heated to 80°C to 110°C to distill off methanol and water. To 100 parts of the silica solid content in the obtained dispersion, 60 parts of hexamethyldisilazane were added at room temperature (25°C), and the mixture was reacted at 120°C for 3 hours. After cooling, it was dried by spray drying to obtain surface-treated silica particles (1).

[0156] [Silica Particles (2) to Silica Particles (10)] Silica particles (2) to silica particles (10) with surface treatment were obtained in the same manner as in Example 1, except that the temperature of the alkali catalyst solution, the dropping amount of tetramethoxysilane, the dropping amount of 8.0% aqueous ammonia, and the dropping time were changed as shown in Table 1 when dropping tetramethoxysilane and 8.0% aqueous ammonia into the alkali catalyst solution.

[0157]

Table 1

[0158] <Production of Strontium Titanate Particles> [Strontium Titanate Particles (1)] 0.7 mol of metatitanic acid, which is a desulfurized and peptized titanium source, was taken as TiO 2 and placed in a reaction vessel. Next, an aqueous strontium chloride solution was added to the reaction vessel in an amount of 0.77 mol so that the SrO / TiO 2 molar ratio became 1.1. Next, a solution prepared by dissolving lanthanum oxide in nitric acid was added to the reaction vessel in an amount such that the amount of lanthanum was 2.5 mol per 100 mol of strontium. The initial TiO 2 concentration in the mixture of the three materials was adjusted to 0.75 mol / L. Next, the mixture was stirred, and the mixture was heated to 90 °C. While maintaining the liquid temperature at 90 °C and stirring, 153 mL of a 10N aqueous sodium hydroxide solution was added dropwise over 3.8 hours, and further stirring was continued for 1 hour while maintaining the liquid temperature at 90 °C. Next, the reaction solution was cooled to 40 °C, hydrochloric acid was added until the pH reached 5.5, and stirring was carried out for 1 hour. Next, the precipitate was washed by repeating decantation and redispersion in water. Hydrochloric acid was added to the slurry containing the washed precipitate to adjust the pH to 6.5, solid-liquid separation was carried out by filtration, and the solid content was dried. An ethanol solution of i-butyltrimethoxysilane was added to the dried solid content in an amount such that the amount of i-butyltrimethoxysilane was 20 parts per 100 parts of the solid content, and stirring was carried out for 1 hour. Solid-liquid separation was carried out by filtration, and the solid content was dried in air at 130 °C for 7 hours to obtain strontium titanate particles (1).

[0159] [Strontium titanate particles (2)] Strontium titanate particles (2) were prepared in the same manner as the preparation of strontium titanate particles (1), except that the time taken for dropping the 10N aqueous sodium hydroxide solution was changed to 0.2 hours.

[0160] [Strontium titanate particles (3)] Strontium titanate particles (3) were prepared in the same manner as the preparation of strontium titanate particles (1), except that the time taken for dropping the 10N aqueous sodium hydroxide solution was changed to 8 hours.

[0161] [Strontium titanate particles (4)] Strontium titanate particles (4) were prepared in the same manner as the preparation of strontium titanate particles (1), except that the time taken for dropping the 10N sodium hydroxide aqueous solution was changed to 0.8 hours.

[0162] [Strontium titanate particles (5)] Strontium titanate particles (5) were prepared in the same manner as the preparation of strontium titanate particles (1), except that the time taken for dropping the 10N sodium hydroxide aqueous solution was changed to 0.1 hours.

[0163] [Strontium titanate particles (6)] Strontium titanate particles (6) were prepared in the same manner as the preparation of strontium titanate particles (1), except that the time taken for dropping the 10N sodium hydroxide aqueous solution was changed to 6 hours.

[0164] [Strontium titanate particles (7)] Strontium titanate particles (7) were prepared in the same manner as the preparation of strontium titanate particles (1), except that the time taken for dropping the 10N sodium hydroxide aqueous solution was changed to 0.25 hours.

[0165] [Preparation of 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 part The above materials except ferrite particles were dispersed in a sand mill to prepare a dispersion. This dispersion was put into a vacuum degassing kneader together with ferrite particles, and the pressure was reduced and dried while stirring to obtain a carrier.

[0166] [Preparation of toner and developer: Examples 1 to 11, Comparative Examples 1 to 5] To 100 parts of toner particles, 1 part of any one of silica particles (1) to (6), 1 part of any one of silica particles (7) to (10), and 1 part of any one of strontium titanate particles (1) to (7) were added according to the combinations shown in Table 2, and they were mixed for 15 minutes at a stirring peripheral speed of 30 m / second using a Henschel mixer. Subsequently, sieving was performed using a vibrating sieve with an opening of 45 μm to obtain externally added toner.

[0167]

Table 2

[0168] 10 parts of externally added toner and 100 parts of carrier were put into a V blender and stirred for 20 minutes. Thereafter, sieving was performed using a sieve with an opening of 212 μm to obtain a developer.

[0169] <Analysis of Toner and Externally Added Agent> [Shape Characteristics of Silica Particles (Number Primary Particle Size Distribution Curve, Average Circularity)] Toner to which an externally added agent containing silica particles and strontium titanate particles was added was imaged at a magnification of 40,000 times using a scanning electron microscope (SEM) (manufactured by Hitachi High-Technologies, S-4800) equipped with an energy dispersive X-ray analyzer (EDX analyzer) (manufactured by Horiba, Ltd., EMAX Evolution X-Max80mm 2 ). Based on the presence of Si, more than 300 primary particles of silica were identified from within one field of view by EDX analysis. The SEM was observed at an acceleration voltage of 15 kV, an emission current of 20 μA, and WD15 mm, and the EDX analysis was performed under the same conditions with a detection time of 60 minutes. The identified silica particles were analyzed using image processing analysis software WinRoof (manufactured by Mitani Shosha Co., Ltd.) to obtain the equivalent circle diameter, area, and perimeter of each primary particle image. Furthermore, circularity = 4π × (area) ÷ (perimeter) 2 was obtained. The number of individual particles was plotted from the smaller side of the equivalent circle diameter to obtain a number-based primary particle size distribution curve. In the obtained number-based primary particle size distribution curve, the maximum peak in the range of particle size less than 80 nm was defined as the small-diameter side peak, the maximum peak in the range of particle size 80 nm or more was defined as the large-diameter side peak, and the minimum minimum value between the small-diameter side peak and the large-diameter side peak was defined as the valley, and the positions of the respective particle sizes were determined. Also, for the silica particles having a particle size less than the valley in the number-based primary particle size distribution curve, a distribution curve was drawn from the side with a smaller circularity, and the circularity at which the cumulative percentage reached 50% from the smaller side was defined as the average circularity of the small-diameter silica particles. In each of the examples, the silica particles had one peak each in the range of particle size less than 80 nm and the range of particle size 80 nm or more in the number-based primary particle size distribution curve.

[0170] [Shape characteristics of strontium titanate particles (number-based primary particle size distribution curve, average circularity)] A toner externally added with an external additive containing silica particles and strontium titanate particles was photographed at a magnification of 40,000 times using a scanning electron microscope equipped with the above EDX device. Based on the presence of Ti, more than 300 primary particles of strontium titanate were identified from within one field of view by EDX analysis. The SEM was observed at an acceleration voltage of 15 kV, an emission current of 20 μA, and WD 15 mm, and the EDX analysis was performed under the same conditions with a detection time of 60 minutes. The identified strontium titanate particles were analyzed using the above image processing and analysis software WinRoof to obtain the equivalent circle diameter, area, and perimeter length of each primary particle image. Furthermore, circularity = 4π × (area) ÷ (perimeter length) 2 was obtained. The number of individual particles was plotted from the smaller side of the equivalent circle diameter to obtain a number-based primary particle size distribution curve. In the obtained number-based primary particle size distribution curve, the position of the particle size of the maximum peak in the range of particle size less than 80 nm was determined. Also, the number of individual particles was plotted from the side with a smaller circularity to obtain a distribution curve, and the circularity at which the cumulative percentage reached 50% from the smaller side was defined as the average circularity of the strontium titanate particles. In each of the examples, the particle size distribution of the strontium titanate particles was monodisperse.

[0171] [Number-based primary particle size distribution curve of particles combining silica particles and strontium titanate particles] By superimposing the number-based primary particle size distribution curve obtained for silica particles and the number-based primary particle size distribution curve obtained for strontium titanate particles, a number-based primary particle size distribution curve of particles combining silica particles and strontium titanate particles was obtained. In the obtained number-based primary particle size distribution curve, the maximum peaks in the range of particle size less than 80 nm and in the range of particle size 80 nm or more were defined as the first peak and the second peak, respectively, and the positions of the respective particle sizes were determined.

[0172] [Coating rate of external additive] Toner externally added with an external additive containing silica particles and strontium titanate particles was imaged at a magnification of 400,000 times under low acceleration SEM conditions using a scanning electron microscope equipped with the above EDX device. When binarization processing was performed between each external additive particle and the toner mother particle, since it was under low acceleration SEM conditions, the external additive could be visually distinguished such that silica particles were white and strontium titanate particles were gray. For the silica particles, further, they were distinguished into small-diameter silica particles having a particle size less than the trough in the above number-based primary particle size distribution curve and large-diameter silica particles having a particle size greater than the trough, and the following coating rates were determined respectively. · Coating rate (A) of strontium titanate particles: Ratio of the area occupied by strontium titanate particles to the total area of the toner · Coating rate (B) of small-diameter silica particles: Ratio of the area occupied by small-diameter silica particles to the total area of the toner · Coating rate (C) of large-diameter silica particles: Ratio of the area occupied by large-diameter silica particles to the total area of the toner (In this example, silica particles and strontium titanate particles could be identified. However, when identification is difficult, it is determined by elemental separation of Si and Ti using EDX.) In the present invention, as described above, the coverage ratio uses the ratio obtained from image analysis. On the other hand, it can be calculated by the following formula (1) from the toner particle size, toner specific gravity, external additive particle size, and external additive specific gravity. As the particle size of the external additive, the particle size at the peak position in the above-described number-based primary particle size distribution curve is used, and the specific gravity is the measurement result by a pycnometer.

[0173]

Equation

[0174] In Equation (1), Dt represents the average primary particle size of the toner, ρt represents the toner specific gravity, Da represents the external additive particle size, and ρa represents the external additive specific gravity. The average primary particle size of the toner mother particles (before adding the external additive) was 5.7 nm. Also, the following measured values of the specific gravity of each substance were used. · Toner specific gravity: 1.1 · Specific gravity of silica particles: 1.2 · Specific gravity of strontium titanate particles: 3.6 The true specific gravity of silica is 2.2, and the true specific gravity of strontium titanate is 5.1. All of the measured values of the specific gravity are small. This is presumably due to the voids in the compound and the internally retained water present when the external additive is manufactured by the wet method. Since the mutual charging of the external additives is proportional to the amount of the external additive present on the surface of the toner particles, in the present invention, the coverage ratio of the external additive uses the coverage ratio obtained by the above-described image analysis.

[0175] <Evaluation of the developer> [Evaluation of fogging] The developer was loaded into the developing device of a digital multi-function printer (manufactured by Fujifilm Business Innovation Co., Ltd., Apeos PortIV C5575 refitted machine). The toner loading amount on the photoreceptor was 5 g / m 2The developing potential was adjusted so as to obtain the following results. Under high temperature and high humidity (temperature: 28°C / relative humidity: 85%), images with an image area ratio of 1% were continuously output 300,000 sheets in total on A4-sized plain paper. For the last 30 sheets of the output images, fogging (fogging of the background portion) was measured for density using an image densitometer X-Rite938 (manufactured by X-Rite, Inc.). Then, the average value of the fogging density of the 30 images was evaluated according to the following evaluation criteria. The visual image is also shown in parentheses in the criteria for reference. The evaluation criteria are such that A to C are within the acceptable range. A: The fogging density is less than 0.1 (fogging is not visible with a magnifying glass). B: The fogging density is 0.1 or more and less than 0.2 (fogging is visible with a magnifying glass but not visible to the naked eye). C: The fogging density is 0.2 or more and less than 0.25 (slight fogging is visible to the naked eye). D: The fogging density is 0.25 or more and less than 0.3 (partial fogging is visible to the naked eye). E: The fogging density is 0.3 or more (obvious fogging is visible to the naked eye).

[0176] As analysis results of the toner and the developer, Table 3 shows the particle sizes of the peaks and valleys in the number-based primary particle size distribution curve of each particle externally added to the toner, and Table 4 shows the coating rate and average circularity of each particle. Also, Table 3 and Table 4 show the evaluation results together with the analysis results.

[0177]

Table 3

[0178]

Table 4

Explanation of Signs

[0179] 1Y, 1M, 1C, 1K Photoreceptor (an example of an image holding member) 2Y, 2M, 2C, 2K Charging Roll (an example of a charging means) 3 Exposure Device (an example of an electrostatic charge 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 primary transfer means) 6Y, 6M, 6C, 6K photoreceptor cleaning device (an example of image carrier cleaning means) 8Y, 8M, 8C, 8K toner cartridge 10Y, 10M, 10C, 10K image forming unit 20 intermediate transfer belt (an example of intermediate transfer body) 22 drive roll 24 support roll 26 secondary transfer roll (an example of secondary transfer means) 28 fixing device (an example of fixing means) 30 intermediate transfer belt cleaning device (an example of intermediate transfer body cleaning means) P recording paper (an example of recording medium)

[0180] 107 photoreceptor (an example of image carrier) 108 charging roll (an example of charging means) 109 exposure device (an example of electrostatic charge image forming means) 111 developing device (an example of developing means) 112 transfer device (an example of transfer means) 113 photoreceptor cleaning device (an example of image carrier cleaning means) 115 fixing device (an example of fixing means) 116 mounting rail 117 housing 118 opening for exposure 200 process cartridge 300 recording paper (an example of recording medium)

Claims

1. Toner particles, titanate compound particles externally added to the toner particles, having a peak in the range of 20 nm or more and less than 80 nm in the number-based primary particle size distribution curve, and having an average circularity of 0.88 or more and 0.94 or less, silica particles externally added to the toner particles, having a small-diameter side peak in the range of 20 nm or more and less than 80 nm, a large-diameter side peak in the range of 80 nm or more and less than 130 nm, and a valley existing between the small-diameter side peak and the large-diameter side peak in the number-based primary particle size distribution curve, wherein the particle size difference between the peak in the number-based primary particle size distribution curve of the titanate compound particles and the small-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 20 nm or less, when the silica particles having a particle size less than the valley are defined as small-diameter silica particles and the silica particles having a particle size of the valley or more are defined as large-diameter silica particles in the number-based primary particle size distribution curve of the silica particles, the average circularity of the small-diameter silica particles is 0.88 or more and 0.94 or less A toner for developing an electrostatic charge image.

2. In the number-based primary particle size distribution curve of the particles obtained by combining the titanate compound particles and the silica particles, having a maximum value in the range of 20 nm or more and less than 80 nm, a first peak composed of the titanate compound particles and the small-diameter silica particles, and a second peak existing in the range of 80 nm or more and 130 nm or less and composed of the large-diameter silica particles The toner for developing an electrostatic charge image according to claim 1, characterized by having the above.

3. The toner for developing an electrostatic charge image according to claim 1, characterized in that the coating rate A (%) of the titanate compound particles with respect to the toner particles and the coating rate B (%) of the small-diameter silica particles with respect to the toner particles satisfy the following formula (1). 0.2 ≦ A / (A + B) ≦ 0.8 … (1)

4. The toner for developing an electrostatic charge image according to claim 3, characterized in that the coating rate A (%) of the titanate compound particles with respect to the toner particles and the coating rate B (%) of the small-diameter silica particles with respect to the toner particles satisfy the following formula (2). 10 ≦ A + B ≦ 50 … (2)

5. The toner for developing an electrostatic charge image according to claim 4, characterized in that the coating rate of the large-diameter silica particles with respect to the toner particles is 20% or more and 40% or less.

6. The toner for electrostatic charge image development according to claim 1, wherein the particle size difference between the small-diameter side peak and the large-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 20 nm or more and 70 nm or less.

7. The toner for electrostatic charge image development according to claim 1, wherein the particle size difference between the peak in the number-based primary particle size distribution curve of the titanate compound particles and the large-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 20 nm or more and 70 nm or less.

8. The toner for electrostatic charge image development according to claim 1, wherein the difference between the average circularity of the titanate compound particles and the average circularity of the small-diameter silica particles is 0.08 or less.

9. The toner for electrostatic charge image development according to claim 1, wherein the half-value width of the small-diameter side peak in the number-based primary particle size distribution curve of the silica particles is 25 nm or less.

10. The toner for electrostatic charge image development according to claim 1, wherein the titanate compound particles are strontium titanate particles.

11. The toner for electrostatic charge image development according to claim 10, wherein the strontium titanate particles are strontium titanate particles doped with lanthanum.

12. An electrostatic charge image developer containing the toner for electrostatic charge image development according to any one of claims 1 to 11.

13. A toner cartridge that houses the toner for electrostatic charge image development according to any one of claims 1 to 11 and is detachable from an image forming apparatus.

14. A process cartridge that houses the electrostatic charge image developer according to claim 12 and includes developing means for developing an electrostatic charge image formed on the surface of an image carrier as a toner image with the electrostatic charge image developer, and is detachable from an image forming apparatus.

15. An image carrier, charging means for charging the surface of the image carrier, electrostatic charge image forming means for forming an electrostatic charge image on the charged surface of the image carrier, developing means for housing the electrostatic charge image developer according to claim 12 and developing an electrostatic charge image formed on the surface of the image carrier as a toner image with the electrostatic charge image developer, transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, fixing means for fixing the toner image transferred to the surface of the recording medium, and an image forming apparatus comprising the same.

16. A charging step of charging the surface of an image carrier, an electrostatic charge image forming step of forming an electrostatic charge image on the charged surface of the image carrier, A developing step of developing an electrostatic charge image formed on the surface of the image carrier as a toner image with the electrostatic charge 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 to the surface of the recording medium; An image forming method comprising the steps.

Images