Electrostatic charge image developer, process cartridge, image forming method, and image forming apparatus

Abstract

To provide an electrostatic charge image developer that is excellent in fogging prevention properties.SOLUTION: An electrostatic charge image developer has a toner having a toner particle and an external additive on the surface of the toner particle, and a carrier having a magnetic particle and a resin coating layer on the surface of the magnetic particle. The external additive includes a titanium compound. The resin coating layer includes silica particles. The ratio of the Net intensity TiNet of titanium atoms detected from X-ray fluorescence analysis of the toner to the Net intensity SiNet of silicon atoms detected from X-ray fluorescence analysis of the carrier (TiNet / SiNet) is 0.08 or more and 0.7 or less.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] As an external additive for toner for developing electrostatic images, strontium titanate particles described in Patent Document 1 are known. Furthermore, as a carrier for developing electrostatic images, a resin-coated carrier having a resin coating layer on the surface of magnetic particles is known. For example, Patent Document 2 discloses a known resin-coated carrier. Also,

[0003] Patent Document 1 discloses strontium titanate-based fine particles characterized in that the particles contain a perovskite-type titanate compound represented by the general formula SrTiO3 as a main component, contain a third component M selected from La, Mg, Ca, Sn, and Si, have a molar ratio of (Sr+M) to Ti: (Sr+M) / Ti in the range of 0.70 to 0.90, have a spherical shape with an average circularity of 0.80 to 1.00, have an average primary particle diameter of 0.02 μm to 0.06 μm, and have a value obtained by dividing the quartile of the primary particle diameter by the average primary particle diameter of less than 0.20.

[0004] Patent Document 2 discloses a carrier for developing electrostatic images, which comprises magnetic particles and a coating resin layer that coats the magnetic particles and contains silica particles, and in which the ratio of Si on the surface of the coating resin layer, as determined by X-ray photoelectron spectroscopy (XPS), is 6 atom % or more and 12 atom % or less. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-20919 [Patent Document 2] Japanese Patent Publication No. 2022-147733 Summary of the Invention [Problem to be solved by the invention]

[0006] An object of the present invention is to provide an electrostatic image developer that has excellent fogging suppression properties compared to when the ratio TiNet / SiNet of the net intensity of titanium atoms detected by X-ray fluorescence analysis of the toner, TiNet, to the net intensity of silicon atoms, SiNet, detected by X-ray fluorescence analysis of the carrier, is less than 0.08 or exceeds 0.7. [Means for solving the problem]

[0007] Means for solving the above problems include the following aspects. <1> An electrostatic image developer comprising: a toner having toner particles and an external additive on the surfaces of the toner particles; and a carrier having magnetic particles and a resin coating layer on the surfaces of the magnetic particles, wherein the external additive contains a titanium compound and the resin coating layer contains silica particles, and wherein the ratio TiNet / SiNet of the net intensity of titanium atoms detected by fluorescent X-ray analysis of the toner to the net intensity SiNet of silicon atoms detected by fluorescent X-ray analysis of the carrier is 0.08 or more and 0.7 or less. <2> The net strength SiNet of the silicon atoms is 2 kcps or more and 6 kcps or less. <1> Electrostatic image developer according to claim 1. <3> The titanium compound is a metal titanate compound. <1> or <2> Electrostatic image developer according to claim 1. <4> The titanium compound is strontium titanate. <3> Electrostatic image developer according to claim 1. <5> The ratio Pst / Pss of the average primary particle diameter Pst of the titanium compound to the average primary particle diameter Pss of the silica particles is 2 or more and 8 or less. <1> ~ <4> 10. The electrostatic image developer according to claim 9, wherein the electrostatic image developer is a developer containing a fluorine atom or a methyl acrylate. <6> The resin coating layer contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group. <5> Electrostatic image developer according to claim 1. <7> The titanium compound is a silica-doped titanium compound. <1> ~ <6> 10. The electrostatic image developer according to claim 9, wherein the electrostatic image developer is a developer containing a fluorine atom or a methyl acrylate. <8> The titanium compound is a titanium compound whose surface has been hydrophobized. <1> ~ <7> 10. The electrostatic image developer according to claim 9, wherein the electrostatic image developer is a developer containing a fluorine atom or a methyl acrylate. <9> <1> ~ <8> 1. A process cartridge detachably mounted to an image forming apparatus, the process cartridge containing the electrostatic image developer according to any one of claims 1 to 9 and comprising a developing unit that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image. <10> The method includes at least a charging step of charging an image carrier, an exposure step of forming an electrostatic latent image on the surface of the image carrier, a developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic image developer to form a toner image, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a transfer receiving material, and a fixing step of fixing the toner image, wherein the electrostatic image developer is <1> ~ <8> 10. An image forming method using the electrostatic image developer according to any one of the above items. <11> an image carrier; a charging unit for charging the image carrier; an exposure unit for exposing the charged image carrier to light to form an electrostatic latent image on the image carrier; a developing unit for developing the electrostatic latent image with an electrostatic image developer to form a toner image; a transfer unit for transferring the toner image from the image carrier to a transfer receiving member; and a fixing unit for fixing the toner image, wherein the electrostatic image developer is <1> ~ <8> 10. An image forming apparatus, comprising the electrostatic image developer according to any one of the above items. [Effects of the Invention]

[0008] <1> According to the invention, an electrostatic image developer is provided which has excellent fogging suppression properties compared to when the ratio TiNet / SiNet of the net intensity of titanium atoms TiNet detected by X-ray fluorescence analysis of the toner to the net intensity of silicon atoms SiNet detected by X-ray fluorescence analysis of the carrier is less than 0.08 or exceeds 0.7. <2> According to the invention, an electrostatic image developer is provided which is superior in fogging suppression compared to when the net strength SiNet of silicon atoms is less than 2 kcps or more than 6 kcps. <3> or <4> According to the invention, an electrostatic image developer is provided which is superior in fogging suppression properties compared to when the titanium compound is titanium oxide. <5> According to the present invention, an electrostatic image developer is provided which has better fogging suppression properties than when the ratio Pst / Pss of the average primary particle diameter Pst of the titanium compound to the average primary particle diameter Pss of the silica particles is less than 2 or more than 8. <6> According to the invention related to (1), an electrostatic image developer is provided which has better fogging suppression properties than when the resin coating layer contains only an acrylic resin which has a structural unit having an aliphatic cyclic structure and does not have a structural unit having an amino group. <7> According to the invention, an electrostatic image developer is provided which is superior in fogging suppression properties compared to when the titanium compound is a lanthanum-doped titanium compound. <8> According to the invention, an electrostatic image developer is provided which is superior in fogging suppression properties compared to a titanium compound whose surface has not been subjected to a hydrophobic treatment. <9> ~ <11> According to the invention, a process cartridge, an image forming method, or an image forming apparatus is provided that has excellent fogging suppression properties compared to when the ratio TiNet / SiNet of the net intensity of titanium atoms detected by fluorescent X-ray analysis of the toner in the electrostatic image developer to the net intensity SiNet of silicon atoms detected by fluorescent X-ray analysis of the carrier is less than 0.08 or exceeds 0.7. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an embodiment of the present invention. [Figure 2] 1 is a schematic diagram illustrating an example of a process cartridge that is detachably mounted to an image forming apparatus according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described in detail. In this specification, when referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified. In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values ​​before and after "to" as the minimum and maximum values, respectively. In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes, as long as the intended purpose of the process is achieved. In this specification, "electrostatic image developing carrier" is also referred to as "carrier," "electrostatic image developing toner" is also referred to as "toner," and "electrostatic image developer" is also referred to as "developer."

[0011] (Electrostatic image developer) The electrostatic image developer according to this embodiment comprises a toner having toner particles and an external additive on the surface of the toner particles, and a carrier having magnetic particles and a resin coating layer on the surface of the magnetic particles, wherein the external additive contains a titanium compound and the resin coating layer contains silica particles, and the ratio TiNet / SiNet of the net intensity of titanium atoms detected by fluorescent X-ray analysis of the toner to the net intensity SiNet of silicon atoms detected by fluorescent X-ray analysis of the carrier is 0.08 or more and 0.7 or less.

[0012] In a conventional electrostatic image developer consisting of a carrier containing silica particles in a resin coating layer and a toner, when the electrostatic image developer has been subjected to long-term stress and is left standing under a low-temperature, low-humidity environment and then left standing under a high-temperature, high-humidity environment, it is thought that the silica particles in the carrier resin coating layer absorb moisture, which can slow the rise of charge at the beginning of image output and cause fogging. The electrostatic charge image developer according to this embodiment is such that the external additive of the toner contains a titanium compound, the resin coating layer of the carrier contains silica particles, and the ratio TiNet / SiNet of the Net intensity TiNet of titanium atoms detected by fluorescence X-ray analysis of the toner and the Net intensity SiNet of silicon atoms detected by fluorescence X-ray analysis of the carrier is 0.08 or more and 0.7 or less. It is considered that the Ti compound in the toner acts to absorb the surface adsorbed water of the silica particles in the resin coating layer of the carrier, reducing the excessive amount of water adsorbed to the silica particles in the resin coating layer of the carrier and suppressing the occurrence of fogging.

[0013] Hereinafter, the configuration of the electrostatic charge image developer according to this embodiment will be described in detail.

[0014] <Value of TiNet / SiNet> The electrostatic charge image developer according to this embodiment is such that the external additive contains a titanium compound, the resin coating layer contains silica particles, and the ratio TiNet / SiNet of the Net intensity TiNet of titanium atoms detected by fluorescence X-ray analysis of the toner and the Net intensity SiNet of silicon atoms detected by fluorescence X-ray analysis of the carrier is 0.08 or more and 0.7 or less. From the viewpoint of fogging suppression, it is preferably 0.15 or more and 0.65 or less, more preferably 0.25 or more and 0.55 or less, and particularly preferably 0.30 or more and 0.45 or less.

[0015] The method for measuring the Net intensity of titanium atoms in the toner in this embodiment is as follows. First, 0.13 g of the toner as the measurement sample is compression molded into a disk shape with a diameter of 1 cm using a compression molding machine manufactured by Maehara Testing Machine Co., Ltd. at a load of 10 tf, a load speed of 3, and a load time of 60 seconds. Regarding the obtained disk-shaped compression molded body, using a fluorescence X-ray analyzer (XRF1500 manufactured by Shimadzu Corporation), elemental analysis is performed with a measurement area of 10 mmφ according to the element to be analyzed. Here, the element to be analyzed is titanium (Ti), the elemental qualitative analysis is performed using SQX software manufactured by Rigaku Corporation, and the detected peak intensity of the element is adopted as the detection amount (kcps). In the case of titanium (Ti) element, measurements were carried out from 5 deg to 90 deg under the conditions of voltage 60 kV, current 50 mA, filter: F - Al, slit: S2, spectroscopic crystal LiF, detector: SC, and PHA: 100 - 300, and detection peaks were confirmed. The detected elements are indicated by SQX software, and quantitative measurements are carried out individually again for the Ka value of the detected titanium (Ti). The wavelength of the detected peak value and both ends ±4 deg of the peak value as the background are selected, and the peak wavelength is measured for 40 seconds and the wavelengths at both ends of the background are each measured for 10 seconds under the same above conditions, and the detection amount (unit: kilo counts per second, kpcs) of each element is obtained.

[0016] The method for measuring the Net intensity of silicon atoms in the carrier in this embodiment is as follows. Put 0.3 g of the carrier, which is the measurement sample, in the center of a polyethylene terephthalate (PET) sample plate (inner diameter 12 mm) of a container for trace powder, and cover the measurement surface with a polypropylene (PP) film for preventing scattering. At this time, pay attention to ensure that there are no wrinkles in the PP film. Set this trace powder container in a cell for a measurement area of 10 mmφ with the lower plate removed, and perform elemental analysis with an X-ray analyzer (manufactured by Rigaku Corporation, PrimusII). Here, the element to be analyzed is silicon (Si), and the detection peak intensity is quantified as the detection amount (kcps) using the analysis SQX software manufactured by Rigaku Corporation. As the detection conditions for silicon (Si) element, the excitation conditions are tube voltage 60 kV, tube current 50 mA, filter: F - Be, the optical system conditions are slit: S4, spectroscopic crystal RX4, detector PC, and the PHA conditions are lower limit 120 and upper limit 300. The measurement time is 40 seconds for the wavelength of the peak value and 10 seconds for each of the wavelengths at both ends ±4 deg of the peak value as the background.

[0017] <Value of <SiNet>> In this embodiment, the value of the Net intensity SiNet of silicon atoms in the carrier is preferably 1 kcps or more and 7 kcps or less, more preferably 2 kcps or more and 6 kcps or less, and particularly preferably 3 kcps or more and 5 kcps or less. Within the above range, contamination of the external additive due to long-term running is suppressed, moisture absorption is also suppressed, and the fog suppression property is excellent.

[0018] <Value of TiNet> In this embodiment, from the perspective of fog suppression property, the value of the Net intensity TiNet of titanium atoms in the toner is preferably 0.30 kcps or more and 3.0 kcps or less, more preferably 0.60 kcps or more and 2.5 kcps or less, still more preferably 0.75 kcps or more and 2.3 kcps or less, and particularly preferably 1.0 kcps or more and 2.0 kcps or less.

[0019] <Value of the ratio Pst / Pss of the average primary particle diameter Pst of the titanium compound to the average primary particle diameter Pss of the silica particles> In the electrostatic charge image developer according to this embodiment, the value of the ratio Pst / Pss of the average primary particle diameter Pst of the titanium compound to the average primary particle diameter Pss of the silica particles is preferably 1 or more and 10 or less, more preferably 2 or more and 8 or less, and particularly preferably 3 or more and 7 or less. Within the above range, the adsorption action in the resin coating layer by the titanium compound is excellent, and the decrease in the charging level of the toner due to the titanium compound adsorbed with moisture is suppressed, and the fog suppression property is excellent.

[0020] In this embodiment, the primary particle diameter of inorganic particles such as titanium compounds and silica particles is the diameter of a circle (so-called equivalent circle diameter) having the same area as the primary particle image, and the average primary particle diameter of inorganic particles is the particle diameter at which the cumulative value reaches 50% from the smaller diameter side in the number-based distribution of the primary particle diameters. Also, the average primary particle diameter of the inorganic particles is obtained by image analysis of at least 300 inorganic particles.

[0021] <Toner for electrostatic charge image development> The electrostatic image developer according to this exemplary embodiment includes toner particles and a toner having an external additive on the surface of the toner particles, and the external additive contains a titanium compound. Examples of the toner include colored toners containing toner particles containing a binder resin and a colorant, and infrared absorbing toners using an infrared absorbing agent instead of a colorant. The toner may also contain a release agent, various internal additives, etc.

[0022] <Titanium compounds> The external additive includes a titanium compound. The titanium compound is not particularly limited as long as it is a particle containing titanium element, and examples thereof include titanium oxide (titania), calcium titanate particles, strontium titanate particles, and barium titanate particles. Among these, from the viewpoint of the fogging suppression properties obtained, calcium titanate particles, strontium titanate particles, or barium titanate particles are preferred, calcium titanate particles or strontium titanate particles are more preferred, and strontium titanate particles are particularly preferred.

[0023] The average primary particle size of the titanium compound is preferably from 10 to 100 nm, more preferably from 20 to 80 nm, and particularly preferably from 30 to 70 nm, from the viewpoint of the line density of the resulting image and suppression of white voids.

[0024] The average primary particle size of the titanium compound can be controlled, for example, by adjusting various conditions when producing the titanium compound by a wet process.

[0025] In this embodiment, the shape of the titanium compound is not particularly limited, but from the viewpoint of fogging suppression, it is preferable that the shape is rounded rather than cubic or rectangular.

[0026] In this embodiment, the titanium compound, particularly the metal titanate compound, is preferably doped with a metal element (hereinafter also referred to as a dopant) other than elements forming the main structure, such as titanium and metal elements in the metal salt structure. By including a dopant in the metal titanate compound, the crystallinity of the perovskite structure decreases, resulting in a rounded shape.

[0027] The dopant of the titanium compound is preferably a metal element having an ionic radius that can be incorporated into the crystal structure of the titanium compound when ionized. From this viewpoint, the dopant of the titanium compound is preferably a metal element having an ionic radius of 40 pm or more and 200 pm or less, more preferably a metal element having an ionic radius of 60 pm or more and 150 pm or less when ionized.

[0028] Specific examples of dopants for titanium compounds include lanthanoids, silica (silicon), 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. Lanthanoids are preferably lanthanum or cerium. Among these, silica (silicon) or lanthanum are preferred, with silica being more preferred, from the viewpoint of fogging suppression. When the titanium compound is silica-doped, the moisture adsorption effect of the titanium compound is more effectively utilized, resulting in superior fogging suppression.

[0029] As a dopant for the titanium compound, a metal element having an electronegativity of 2.0 or less is preferred in order to prevent the titanium compound from being excessively negatively charged. In this embodiment, the electronegativity is the Allred-Rochow electronegativity. Metal elements with an electronegativity of 2.0 or less include lanthanum (electronegativity 1.08), magnesium (1.23), aluminum (1.47), silica (1.74), calcium (1.04), vanadium (1.45), chromium (1.56), manganese (1.60), iron (1.64), cobalt (1.70), nickel (1.75), copper (1.75), zinc (1.66), gallium (1.82), yttrium (1.11), zirconium (1.22), niobium (1.23), silver (1.42), indium (1.49), tin (1.72), barium (0.97), tantalum (1.33), rhenium (1.46), and cerium (1.06).

[0030] From the viewpoint of achieving a rounded shape while maintaining a perovskite-type crystal structure, the amount of dopant in the metal titanate compound is preferably in the range of 0.1 mol % to 20 mol % of the metal element in the metal salt structure, more preferably in the range of 0.1 mol % to 15 mol %, and even more preferably in the range of 0.1 mol % to 10 mol %.

[0031] In this embodiment, the titanium compound is preferably a titanium compound whose surface has been subjected to a hydrophobic treatment, from the viewpoint of improving the function of the titanium compound. When the titanium compound is subjected to a hydrophobic treatment, the resistance of the titanium compound does not decrease even when moisture is adsorbed, so that low charge is suppressed and fogging is more excellently suppressed. In this embodiment, the titanium compound is more preferably a titanium compound whose surface has been hydrophobized with a silicon-containing organic compound.

[0032] The titanium compound preferably has a surface containing 1% by mass or more and 50% by mass or less (more preferably 5% by mass or more and 40% by mass or less, even more preferably 5% by mass or more and 30% by mass or less, and particularly preferably 10% by mass or more and 25% by mass or less) of a silicon-containing organic compound relative to the mass of the titanium compound. In other words, the amount of hydrophobic treatment with 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, even more preferably 5% by mass or more and 30% by mass or less, and particularly preferably 10% by mass or more and 25% by mass or less, relative to the mass of the inorganic particles. When the amount of hydrophobic treatment is within the above range, fogging is suppressed well.When the amount of hydrophobic treatment is 30 mass % or less, the generation of aggregates due to the hydrophobic treated surface is suppressed.

[0033] The titanium compound may be the titanium compound itself, or may be particles of a titanium compound (sometimes referred to as mother particles) whose surface has been subjected to a hydrophobic treatment. The method for producing the titanium compound (mother particles) is not particularly limited, but a wet method is preferred from the viewpoint of controlling the particle size and shape.

[0034] The wet process for producing a titanium compound is, for example, a production method in which a mixed solution of a titanium oxide source and a strontium source is reacted while adding an alkaline aqueous solution, followed by an acid treatment. In this production method, the particle size of the titanium compound is controlled by the mixing ratio of the titanium oxide source and the strontium source, the concentration of the titanium oxide source at the start of the reaction, the temperature and addition rate of the alkaline aqueous solution, etc.

[0035] The surface treatment of the titanium compound is carried out, for example, by preparing a treatment liquid by mixing a silicon-containing organic compound, which is a hydrophobic treatment agent, with a solvent, and then mixing the titanium compound with the treatment liquid under stirring, and continuing to stir. After the surface treatment, a drying treatment is carried out to remove the solvent from the treatment liquid.

[0036] Examples of silicon-containing organic compounds used for the surface treatment of the titanium compound include alkoxysilane compounds, silazane compounds, silicone oils, etc. Among these, from the viewpoint of fogging suppression, alkoxysilane compounds are preferred, alkyltrialkoxysilanes are more preferred, and i-butyltrimethoxysilane is particularly preferred.

[0037] Examples of alkoxysilane compounds used for the surface treatment of titanium compounds include tetramethoxysilane, tetraethoxysilane; methyltrimethoxysilane, ethyltrimethoxysilane, propyltrimethoxysilane, n-butyltrimethoxysilane, i-butyltrimethoxysilane, hexyltrimethoxysilane, n-octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, vinyltriethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, butyltriethoxysilane, and hexyltrimethoxysilane. Examples include xyltriethoxysilane, decyltriethoxysilane, dodecyltriethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane, phenyltriethoxysilane, benzyltriethoxysilane; dimethyldimethoxysilane, dimethyldiethoxysilane, methylvinyldimethoxysilane, methylvinyldiethoxysilane, diphenyldimethoxysilane, diphenyldiethoxysilane; trimethylmethoxysilane, trimethylethoxysilane.

[0038] Examples of the silazane compound used for the surface treatment of the titanium compound include dimethyldisilazane, trimethyldisilazane, tetramethyldisilazane, pentamethyldisilazane, and hexamethyldisilazane.

[0039] Examples of silicone oils used in the surface treatment of titanium compounds include silicone oils such as dimethylpolysiloxane, diphenylpolysiloxane, and phenylmethylpolysiloxane; and reactive silicone oils such as amino-modified polysiloxane, epoxy-modified polysiloxane, carboxyl-modified polysiloxane, carbinol-modified polysiloxane, fluorine-modified polysiloxane, methacryl-modified polysiloxane, mercapto-modified polysiloxane, and phenol-modified polysiloxane.

[0040] As the solvent used in preparing the treatment liquid, when the silicon-containing organic compound is an alkoxysilane compound or a silazane compound, an alcohol (e.g., methanol, ethanol, propanol, butanol) is preferred, and when the silicon-containing organic compound is a silicone oil, a hydrocarbon (e.g., benzene, toluene, normal hexane, normal heptane) is preferred.

[0041] In the treatment liquid, the concentration of the silicon-containing organic compound is preferably 1% by mass to 50% by mass, more preferably 5% by mass to 40% by mass, and even more preferably 10% by mass to 30% by mass.

[0042] 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 even more preferably 5 parts by mass or more and 30 parts by mass or less, per 100 parts by mass of the titanium compound.

[0043] The amount of the titanium compound added externally is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, based on the toner particles.

[0044] -Binder resin- Examples of binder resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and olefins (e.g., ethylene, propylene, butadiene, etc.), and vinyl resins made of copolymers of two or more of these monomers. Examples of the binder resin include non-vinyl resins such as epoxy resins, polyester resins, polyurethane resins, polyamide resins, cellulose resins, polyether resins, and modified rosin, mixtures of these with the vinyl resins, and graft polymers obtained by polymerizing vinyl monomers in the presence of these. These binder resins may be used alone or in combination of two or more.

[0045] The binder resin is preferably a polyester resin, and examples of the polyester resin include known polyester resins.

[0046] The glass transition temperature (Tg) of the polyester resin is preferably 50°C or higher and 80°C or lower, and more preferably 50°C or higher and 65°C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), and more specifically, is determined from the "extrapolated glass transition onset temperature" described in the method for determining glass transition temperature in JIS K7121-1987 "Method for measuring transition temperature of plastics."

[0047] The weight average molecular weight (Mw) of the polyester resin is preferably 5,000 or more and 1,000,000 or less, and 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, and more preferably 2 or more and 60 or less. The weight average molecular weight and number average molecular weight are measured by gel permeation chromatography (GPC). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC measuring device, a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent. The weight average molecular weight and number average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.

[0048] The content of the binder resin is preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass, based on the total mass of the toner particles.

[0049] -Coloring agent- Examples of colorants include carbon black, chrome yellow, Hansa Yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Balkan orange, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, Examples of suitable dyes include pigments such as ultramarine blue, chalco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate; and dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, and thiazole-based dyes. The colorant may be used alone or in combination of two or more kinds.

[0050] The colorant may be surface-treated as needed, or may be used in combination with a dispersant. Furthermore, a plurality of colorants may be used in combination.

[0051] The content of the colorant is preferably from 1% by mass to 30% by mass, and more preferably from 3% by mass to 15% by mass, based on the total mass of the toner particles.

[0052] -Mold release agent- Examples of release agents include hydrocarbon waxes, natural waxes such as carnauba wax, rice wax, and candelilla wax, synthetic or mineral / petroleum waxes such as montan wax, and ester waxes such as fatty acid esters and montanic acid esters, but are not limited thereto.

[0053] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) by using the "melting peak temperature" described in the method for determining the melting temperature in JIS K7121-1987 "Method for measuring transition temperatures of plastics."

[0054] The content of the release agent is preferably from 1% by mass to 20% by mass, and more preferably from 5% by mass to 15% by mass, based on the total mass of the toner particles.

[0055] -Other additives- Examples of other additives include known additives such as magnetic materials, charge control agents, inorganic powders, resin particles, etc. These additives are contained in the toner particles as internal additives.

[0056] -Characteristics of toner particles, etc.- The toner particles may be toner particles of a single layer structure, or may be toner particles of a so-called core-shell structure composed of a core (core particle) and a coating layer (shell layer) that coats the core. The toner particles of the core-shell structure may be composed of, for example, a core composed of a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer composed of a binder resin.

[0057] The volume average particle size (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less. The volume average particle size (D50v) of toner particles is measured using a Coulter Multisizer II (manufactured by Beckman Coulter) and an ISOTON-II (manufactured by Beckman Coulter). For measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5% by weight aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant. This is then added to 100 ml to 150 ml of electrolyte. The electrolyte containing the suspended sample is dispersed in an ultrasonic disperser for 1 minute, and the particle size distribution of particles ranging from 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. 50,000 particles are sampled.

[0058] -External additives other than titanium compounds- The external additive may contain an external additive other than the titanium compound. Examples of external additives other than titanium compounds include inorganic particles. Examples of the inorganic particles include SiO2, Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, and K2O·(TiO2). n , Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, MgSO4, etc.

[0059] The surfaces of inorganic particles other than the titanium compound as an external additive are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, but examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is, for example, 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles.

[0060] Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning lubricants (for example, metal salts of higher fatty acids such as zinc stearate, and particles of fluorine-based polymers).

[0061] The amount of external additives other than the titanium compound added is preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less, based on the toner particles.

[0062] -Toner manufacturing method- The toner is obtained by producing toner particles and then externally adding an external additive to the toner particles. The toner particles may be produced by either a dry production method (e.g., a kneading and pulverization method) or a wet production method (e.g., an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). There are no particular restrictions on these production methods, and any known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0063] <Career> The electrostatic image developer according to this embodiment includes a carrier having magnetic particles and a resin coating layer on the surface of the magnetic particles, and the resin coating layer contains silica particles.

[0064] -Magnetic particles- The magnetic particles are not particularly limited, and known magnetic particles used as a core material of a carrier can be used. Specific examples of the magnetic particles include particles of magnetic metals such as iron, nickel, and cobalt; particles of magnetic oxides such as ferrite and magnetite; resin-impregnated magnetic particles in which porous magnetic powder is impregnated with resin; and magnetic powder-dispersed resin particles in which magnetic powder is dispersed in resin.

[0065] In this embodiment, ferrite particles are suitable as the magnetic particles. In this embodiment, the ferrite particles preferably contain at least one selected from calcium oxide and strontium oxide. Calcium oxide and strontium oxide are easily incorporated into the surface of ferrite particles, and the presence of calcium or strontium on the surface of ferrite particles is thought to suppress charge leakage from the ferrite particles, thereby resulting in a relatively high charge on the carrier surface. This carrier prevents the toner from becoming low-charged in the developer, thereby further suppressing fogging and improving thin line reproducibility (e.g., suppressing thickening, crushing, or blurring of thin lines). This effect is particularly noticeable when forming a low-density image of the same color after repeatedly forming a high-density, monochromatic image at a higher speed.

[0066] In this embodiment, the ferrite particles contain at least one selected from calcium oxide and strontium oxide, and the total content of calcium and strontium is preferably 0.1% by mass or more and 2.0% by mass or less relative to the total mass of the ferrite particles. When the total content of calcium and strontium is 0.1% by mass or more relative to the total mass of the ferrite particles, charge leakage from the ferrite particles is efficiently suppressed. When the total content of calcium and strontium is 2.0% by mass or less relative to the total mass of the ferrite particles, the crystal structure of the ferrite particles is well-ordered, and the resistivity and magnetic susceptibility fall within appropriate ranges. As a result, fogging is further suppressed, and thin line reproducibility is improved (e.g., thickening, crushing, or blurring of thin lines is suppressed). From the above viewpoints, the total content of calcium element and strontium element is preferably 0.1 mass % or more and 2.0 mass % or less, more preferably 0.2 mass % or more and 1.5 mass % or less, and even more preferably 0.5 mass % or more and 1.2 mass % or less, based on the entire ferrite particles.

[0067] In this embodiment, the ferrite particles contain calcium oxide, and the calcium content is preferably 0.2 mass% or more and 2.0 mass% or less relative to the total mass of the ferrite particles. When the calcium content is 0.2 mass% or more relative to the total mass of the ferrite particles, charge leakage from the ferrite particles is efficiently suppressed. When the calcium content is 2.0 mass% or less relative to the total mass of the ferrite particles, the crystal structure of the ferrite particles is well-ordered, and the resistance value and magnetic susceptibility fall within appropriate ranges. As a result, fogging is further suppressed, and thin line reproducibility is improved (for example, thickening, crushing, or blurring of thin lines is suppressed). From the above viewpoints, the calcium element content is preferably 0.2 to 2.0 mass %, more preferably 0.5 to 1.5 mass %, and even more preferably 0.5 to 1.0 mass %, based on the total mass of the ferrite particles.

[0068] In this embodiment, the ferrite particles contain strontium oxide, and the strontium content is preferably 0.1% by mass or more and 1.0% by mass or less relative to the total mass of the ferrite particles. When the strontium content is 0.1% by mass or more relative to the total mass of the ferrite particles, charge leakage from the ferrite particles is efficiently suppressed. When the strontium content is 1.0% by mass or less relative to the total mass of the ferrite particles, the crystal structure of the ferrite particles is well-ordered, and the resistance and magnetic susceptibility are within appropriate ranges. As a result, fogging is further suppressed, and thin line reproducibility is improved (for example, thickening, crushing, or blurring of thin lines is suppressed). From the above viewpoints, the content of strontium element is preferably 0.1 mass % to 1.0 mass %, more preferably 0.4 mass % to 1.0 mass %, and even more preferably 0.5 mass % to 0.8 mass %, based on the total mass of the ferrite particles.

[0069] The contents of calcium and strontium contained in the ferrite particles are measured by X-ray fluorescence analysis. The X-ray fluorescence analysis of the ferrite particles is performed by the following method. Qualitative and quantitative analysis is performed using an X-ray fluorescence analyzer (Shimadzu Corporation, XRF1500) under the following conditions: X-ray output: 40 V / 70 mA, measurement area: 10 mm diameter, measurement time: 15 minutes. The elements to be analyzed are selected based on the elements detected in the qualitative analysis. The main elements selected are iron (Fe), manganese (Mn), magnesium (Mg), calcium (Ca), strontium (Sr), oxygen (O), and carbon (C). The mass percentage (%) of each element is calculated by referring to separately prepared calibration curve data.

[0070] The volume average particle size of the magnetic particles is, for example, 10 μm or more and 500 μm or less, preferably 20 μm or more and 180 μm or less, and more preferably 25 μm or more and 60 μm or less.

[0071] The magnetic force of the magnetic particles is, for example, 50 emu / g or more, preferably 60 emu / g or more, in terms of saturation magnetization in a magnetic field of 3000 oersteds. The saturation magnetization is measured using a vibrating sample magnetometer VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.). The measurement sample is placed in a cell with an inner diameter of 7 mm and a height of 5 mm and set in the instrument. The measurement is performed by applying a magnetic field and sweeping up to a maximum of 3000 oersteds. The applied magnetic field is then reduced, and a hysteresis curve is created on recording paper. The saturation magnetization, remanent magnetization, and coercive force are determined from the curve data.

[0072] The volume resistivity of the magnetic particles is, for example, 10 5 Ω cm or more 10 9 Ω·cm or less, 10 7 Ω cm or more 10 9 Ω·cm or less is preferable. The volume resistivity (Ω·cm) of magnetic particles is measured as follows: 2 The object to be measured is placed flat on the surface of the circular jig on which the electrode plate is arranged, with a thickness of 1 mm to 3 mm, to form a layer. 2The layer is sandwiched between two electrode plates. To eliminate any gaps between the objects being measured, a 4 kg load is placed on the electrode plates placed on the layer, and then the layer thickness (cm) is measured. The electrodes above and below the layer are connected to an electrometer and a high-voltage power supply generator. A high voltage is applied to both electrodes so that the electric field becomes 103.8 V / cm, and the current value (A) that flows at this time is read. The measurement environment is a temperature of 20°C and a humidity of 50% RH. The formula for calculating the volume electrical resistivity (Ω·cm) of the object being measured is as shown below. R=E×20 / (I-I0) / L In the above formula, R represents the volume electrical resistance (Ω·cm) of the object to be measured, E represents the applied voltage (V), I represents the current value (A), I0 represents the current value (A) at an applied voltage of 0 V, and L represents the layer thickness (cm). The coefficient 20 is the area of ​​the electrode plate (cm 2 )

[0073] -Resin coating layer- The carrier in this embodiment has a resin coating layer on the surface of the magnetic particles. The resin coating layer also contains silica particles. From the viewpoint of fogging suppression, the average primary particle size of the silica particles is preferably from 1 nm to 100 nm, more preferably from 5 nm to 60 nm, even more preferably from 6 nm to 50 nm, and particularly preferably from 7 nm to 20 nm. The average primary particle size of the silica particles can be controlled, for example, by adjusting various conditions in producing the silica particles.

[0074] From the viewpoint of fogging suppression, the content of silica particles contained in the carrier is preferably 0.01% by mass or more and 2.0% by mass or less, more preferably 0.01% by mass or more and 1.5% by mass or less, even more preferably 0.02% by mass or more and 1.0% by mass or less, and even more preferably 0.04% by mass or more and 0.8% by mass or less, relative to the total mass of the carrier.

[0075] The resin coating layer may contain particles other than silica particles, such as carbon black, metals such as gold, silver, and copper, metal compounds such as barium sulfate, aluminum borate, potassium titanate, titanium oxide, zinc oxide, tin oxide, antimony-doped tin oxide, tin-doped indium oxide, and aluminum-doped zinc oxide, metal-coated resin particles, and resin particles. As the resin particles, melamine resin particles are preferred. Among these, from the viewpoint of fogging suppression, the resin coating layer preferably contains silica particles and melamine resin particles, and more preferably contains silica particles, carbon black and melamine resin particles.

[0076] The content of particles other than silica particles contained in the carrier is preferably 0.01% by mass or more and 5.0% by mass or less, more preferably 0.01% by mass or more and 4.0% by mass or less, even more preferably 0.02% by mass or more and 2.0% by mass or less, and even more preferably 0.04% by mass or more and 1.0% by mass or less, relative to the total mass of the carrier.

[0077] Resins that can be used to form the resin coating layer include styrene-acrylic acid copolymers; polyolefin resins such as polyethylene and polypropylene; polyvinyl or polyvinylidene resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; vinyl chloride-vinyl acetate copolymers; straight silicone resins or modified silicone resins consisting of organosiloxane bonds; fluororesins such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene; polyesters; polyurethanes; polycarbonates; amino resins such as urea-formaldehyde resins; and epoxy resins.

[0078] From the viewpoint of fogging suppression, the resin coating layer preferably contains an acrylic resin having an aliphatic cyclic structure and an amino group, and more preferably contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group. The alicyclic structure is preferably a cycloalkyl group, more preferably a cyclohexyl group. The acrylic resin having the alicyclic structure is a resin with low moisture absorption, and exhibits little change in moisture absorption due to changes in temperature and humidity, so that the moisture absorption of the silica particles contained in the carrier is suppressed, and the change in moisture absorption of the silica particles due to changes in temperature and humidity is also suppressed, thereby suppressing fogging. Specific examples of the acrylic resin having a cyclohexyl group include a homopolymer of an acrylic monomer having a cyclohexyl group, and a copolymer of an acrylic monomer having a cyclohexyl group and another monomer. Examples of acrylic monomers having a cyclohexyl group include cyclohexyl acrylate and cyclohexyl methacrylate. Furthermore, preferred examples of structural units having an aliphatic cyclic structure include structural units derived from cyclohexyl (meth)acrylate. From the viewpoint of fogging suppression, the acrylic resin having a structural unit with an aliphatic cyclic structure preferably contains 80% by mass or more of the structural unit with an aliphatic cyclic structure. As the acrylic monomer having an amino group, dialkylaminoalkyl(meth)acrylate is preferred, and dimethylaminoethyl(meth)acrylate is more preferred. From the viewpoint of fogging suppression, the acrylic resin having a structural unit having an amino group preferably contains the structural unit having an amino group in an amount of 0.05% by mass or more and 10% by mass or less, and more preferably 0.1% by mass or more and 5.0% by mass or less. Acrylic resins having amino groups have good charging properties even under high humidity conditions, so they have excellent charging start-up properties and suppress fogging. When the carrier contains a structure having an aliphatic cyclic structure and an acrylic resin having an amino group, the presence of the aliphatic cyclic structure with large steric hindrance around the amino group makes the amino group less susceptible to moisture absorption, and the moisture absorption of the particles contained in the carrier is suppressed even under high humidity conditions or when temperature and humidity changes occur, thereby suppressing fogging.

[0079] Methods for forming a resin coating layer on the surface of magnetic particles include, for example, a wet method and a dry method. The wet method is a method that uses a solvent to dissolve or disperse the resin that constitutes the resin coating layer. On the other hand, the dry method is a method that does not use the solvent.

[0080] Examples of wet manufacturing methods include an immersion method in which magnetic particles are immersed in a resin liquid for forming a resin coating layer to coat them; a spray method in which a resin liquid for forming a resin coating layer is sprayed onto the surface of magnetic particles; a fluidized bed method in which magnetic particles are fluidized in a fluidized bed and a resin liquid for forming a resin coating layer is sprayed onto them; and a kneader coater method in which magnetic particles and a resin liquid for forming a resin coating layer are mixed in a kneader coater and the solvent is removed. The resin liquid for forming the resin coating layer used in the wet manufacturing method is prepared by dissolving or dispersing the resin and other components in a solvent. The solvent is not particularly limited as long as it can dissolve or disperse the resin, and examples of the solvent that can be used include aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, and ethers such as tetrahydrofuran and dioxane.

[0081] An example of a dry manufacturing method is a method in which a mixture of magnetic particles and a resin for forming a resin coating layer is heated in a dry state to form a resin coating layer. Specifically, for example, the magnetic particles and the resin for forming the resin coating layer are mixed in a gas phase and heated to melt, thereby forming a resin coating layer.

[0082] The thickness of the resin coating layer is preferably 0.1 μm or more and 10 μm or less, and more preferably 0.3 μm or more and 5 μm or less.

[0083] The exposed ratio of the magnetic particles on the surface of the carrier is preferably 2% to 20%, more preferably 2% to 10%, and even more preferably 3% to 8%.

[0084] The exposed ratio of the magnetic particles on the surface of the carrier is determined by X-ray photoelectron spectroscopy (XPS) using the following method. The target carrier and magnetic particles with the resin coating layer removed from the target carrier are prepared. Methods for removing the resin coating layer from the resin-coated magnetic particles include, for example, dissolving the resin component in an organic solvent to remove the resin coating layer, or heating to about 800°C to eliminate the resin component and remove the resin coating layer. The carrier and the magnetic particles with the resin coating layer removed are each used as measurement samples, and the Fe (atomic %) is quantified using XPS. The exposed percentage (%) of the magnetic particles is calculated as (Fe in the resin-coated magnetic particles) ÷ (Fe in the magnetic particles) × 100.

[0085] The exposed ratio of the magnetic particles on the surface of the carrier can be controlled by the amount of resin used to form the resin coating layer, and the greater the amount of resin relative to the amount of magnetic particles, the smaller the exposed ratio.

[0086] <Career characteristics> The volume average particle size of the carrier is preferably 15 μm or more and 510 μm or less, more preferably 20 μm or more and 180 μm or less, and even more preferably 25 μm or more and 60 μm or less.

[0087] The magnetic force of the carrier is, for example, 40 emu / g or more, preferably 50 emu / g or more, in terms of saturation magnetization in a magnetic field of 1000 oersted. The saturation magnetization is measured in the same manner as for measuring the saturation magnetization of magnetic particles, except that the magnetic field is swept up to 1000 oersted.

[0088] The volume resistivity of the carrier (at 25°C) is, for example, 1 x 10 7 Ω cm or more 1×10 15 Ω·cm or less, 1×10 8 Ω cm or more 1×10 14 Ω·cm or less is preferable, and 1×108 Ω cm or more 1×10 13 It is more preferable that the volume resistivity of the carrier is Ω·cm or less. The volume resistivity of the carrier is measured in the same manner as that of the magnetic particles.

[0089] The developer according to this embodiment is prepared by mixing the toner and the carrier according to this embodiment in an appropriate ratio. The mixing ratio (mass ratio) of the toner to the carrier is preferably toner:carrier=1:100 to 20:100, and more preferably 3:100 to 15:100.

[0090] <Image forming device, image forming method> An image forming apparatus and an image forming method according to this embodiment will be described. The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, a developing unit that contains an electrostatic image developer and develops the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, a transfer unit that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing unit that fixes the toner image transferred to the surface of the recording medium. The electrostatic image developer according to the present embodiment is used as the electrostatic image developer.

[0091] The image forming apparatus according to this embodiment carries out an image forming method (the image forming method according to this embodiment) that includes a charging step of charging the surface of an image carrier, an electrostatic image forming step of forming an electrostatic image on the surface of the charged image carrier, a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer according to this embodiment, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium.

[0092] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a cleaning means that cleans the surface of the image carrier after the transfer of the toner image but before charging; and an apparatus equipped with a discharging means that irradiates the surface of the image carrier with discharging light to discharge it after the transfer of the toner image but before charging. When the image forming apparatus according to the present embodiment is an apparatus of the intermediate transfer type, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means for primarily transferring the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means for secondarily transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0093] In the image forming apparatus according to the present embodiment, for example, the portion including the developing means may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge equipped with developing means that accommodates the electrostatic image developer according to the present embodiment is suitably used.

[0094] An example of an image forming apparatus according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0095] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to this embodiment. The image forming apparatus shown in Figure 1 includes first through fourth electrophotographic image forming units 10Y, 10M, 10C, and 10K (image forming means) that output images in the colors yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side horizontally spaced apart by predetermined distances. These units 10Y, 10M, 10C, and 10K may be process cartridges that are detachably attached to the image forming apparatus.

[0096] An intermediate transfer belt (an example of an intermediate transfer body) 20 is provided above each of the units 10Y, 10M, 10C, and 10K and extends through each unit. The intermediate transfer belt 20 is provided wrapped around a drive roll 22 and a support roll 24, and runs in a direction from the first unit 10Y to the fourth unit 10K. A force is applied to the support roll 24 by a spring or the like (not shown) in a direction away from the drive roll 22, and tension is applied to the intermediate transfer belt 20 wrapped around them. An intermediate transfer body cleaning device 30 is provided on the image carrier side of the intermediate transfer belt 20, facing the drive roll 22. The developing devices (examples of developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K are supplied with yellow, magenta, cyan, and black toner contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0097] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration and operation, we will explain here the first unit 10Y, which forms a yellow image and is arranged upstream in the direction of travel of the intermediate transfer belt.

[0098] The first unit 10Y has a photoreceptor 1Y that acts as an image carrier. Around the photoreceptor 1Y, there are arranged in this order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential; an exposure device (an example of an electrostatic image forming means) 3 that exposes the charged surface to a laser beam 3Y based on a color-separated image signal to form an electrostatic image; a developing device (an example of a developing means) 4Y that supplies charged toner to the electrostatic image to develop it; a primary transfer roll 5Y (an example of a primary transfer means) that transfers the developed toner image onto an intermediate transfer belt 20; and a photoreceptor cleaning device (an example of a cleaning means) 6Y that removes toner remaining on the surface of the photoreceptor 1Y after the primary transfer. The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is provided at a position facing the photoreceptor 1Y. A bias power supply (not shown) that applies a primary transfer bias is connected to the primary transfer rolls 5Y, 5M, 5C, and 5K of each unit. Each bias power supply changes the value of the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

[0099] The operation of forming a yellow image in the first unit 10Y will be described below. First, prior to operation, the surface of the photosensitive member 1Y is charged to a potential of −600V to −800V by the charging roll 2Y. The photoconductor 1Y has conductivity (for example, a volume resistivity of 1×10 at 20°C). -6 The photosensitive layer is formed by laminating a photosensitive layer on a substrate with a resistivity of Ωcm or less. This photosensitive layer normally has a high resistance (the resistance of ordinary resins), but when irradiated with a laser beam, the resistivity of the irradiated portion changes. Therefore, the exposed surface of the photosensitive element 1Y is irradiated with a laser beam 3Y from the exposure device 3 in accordance with image data for yellow sent from a control unit (not shown). This forms an electrostatic charge image of a yellow image pattern on the surface of the photosensitive element 1Y.

[0100] An electrostatic image is an image formed on the surface of the photosensitive element 1Y by charging it; the laser beam 3Y reduces the resistivity of the irradiated portion of the photosensitive layer, causing the charged charges on the surface of the photosensitive element 1Y to flow, while the charges remain in the portions not irradiated by the laser beam 3Y, forming a so-called negative latent image. The electrostatic image formed on the photoreceptor 1Y rotates to a predetermined development position as the photoreceptor 1Y moves, and at this development position, the electrostatic image on the photoreceptor 1Y is developed into a toner image by the developing device 4Y and made visible.

[0101] The developing device 4Y contains an electrostatic image developer containing, for example, at least yellow toner and a carrier. The yellow toner is frictionally charged by being stirred inside the developing device 4Y, and is held on a developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the charge on the photoreceptor 1Y. As the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed with the yellow toner. The photoreceptor 1Y on which the yellow toner image has been formed continues to travel at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transported to a predetermined primary transfer position.

[0102] When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer position, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y to the primary transfer roll 5Y acts on the toner image, causing the toner image on the photoreceptor 1Y to be transferred onto the intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the (-) polarity of the toner, and is controlled to, for example, +10 μA by a control unit (not shown) in the first unit 10Y. On the other hand, the toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

[0103] The primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K of the second unit 10M and subsequent units is also controlled in accordance with the first unit. In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is conveyed sequentially through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are superimposed and transferred.

[0104] The intermediate transfer belt 20, onto which the four-color toner images have been multiplex-transferred through the first to fourth units, reaches a secondary transfer section composed of the intermediate transfer belt 20, a support roll 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 arranged on the image bearing surface side of the intermediate transfer belt 20. Meanwhile, recording paper (an example of a recording medium) P is fed via a feed mechanism into the gap between the secondary transfer roll 26 and the intermediate transfer belt 20 at a predetermined timing, and a secondary transfer bias is applied to the support roll 24. The transfer bias applied at this time has a negative polarity, the same as the negative polarity of the toner. Electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined according to resistance detected by resistance detection means (not shown) that detects resistance in the secondary transfer section, and is voltage-controlled.

[0105] Thereafter, the recording paper P is sent to the pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image.

[0106] Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copiers, printers, etc. In addition to the recording paper P, examples of the recording medium include overhead projector sheets and the like. To further improve the smoothness of the image surface after fixing, it is preferable that the surface of the recording paper P is also smooth. For example, coated paper in which the surface of plain paper is coated with resin or the like, or art paper for printing, etc., is preferably used.

[0107] The recording paper P on which the color image has been fixed is conveyed toward the discharge section, and the series of color image forming operations is completed.

[0108] <Process cartridge> The process cartridge according to this embodiment will be described. The process cartridge according to this embodiment is a process cartridge that is detachably attached to an image forming apparatus and that contains the electrostatic image developer according to this embodiment and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image.

[0109] The process cartridge according to this embodiment is not limited to the above configuration, but may also be configured to include a developing means and, if necessary, at least one other means selected from an image carrier, a charging means, an electrostatic image forming means, and a transfer means.

[0110] An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this. In the following description, the main parts shown in the drawings will be described, and the description of the rest will be omitted.

[0111] FIG. 2 is a schematic diagram showing the configuration of the process cartridge according to the present embodiment. The process cartridge 200 shown in FIG. 2 is configured to integrally combine and hold a photosensitive member 107 (an example of an image carrier), a charging roll 108 (an example of a charging means) provided around the photosensitive member 107, a developing device 111 (an example of a developing means), and a photosensitive member cleaning device 113 (an example of a cleaning means), which are held by a housing 117 provided with, for example, mounting rails 116 and an opening 118 for exposure, and is made into a cartridge. In FIG. 2, 109 denotes an exposure device (an example of an electrostatic image forming means), 112 denotes a transfer device (an example of a transfer means), 115 denotes a fixing device (an example of a fixing means), and 300 denotes recording paper (an example of a recording medium). [Example]

[0112] The present embodiment will be described in detail below with reference to examples, but the present embodiment is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are by mass.

[0113] <Measurement of the net strength of titanium atoms in toner> First, 0.13 g of the toner as a measurement sample was compression molded into a disk shape with a diameter of 1 cm using a compression molding machine manufactured by Mayekawa Testing Machinery Manufacturing Co., Ltd., under a load of 10 tf, a load speed of 3, and a load time of 60 seconds. The obtained disk-shaped compression molded body was subjected to elemental analysis using an X-ray fluorescence analyzer (Shimadzu Corporation, XRF1500) with a measurement area of ​​10 mmφ, depending on the element to be analyzed. Here, the element to be analyzed was titanium (Ti), and the element was characterized using SQX software from Rigaku Corporation, with the detected peak intensity of the element being used as the detection amount (kcps). For titanium (Ti), measurements were performed from 5° to 90° under the following conditions: voltage 60 kV, current 50 mA, filter: F-Al, slit: S2, analyzing crystal: LiF, detector: SC, PHA: 100-300. The detected peak was confirmed. The detected elements were displayed by the SQX software, and quantitative measurements were performed again for the detected titanium (Ti) Ka values. The wavelength of the detected peak value and the wavelengths ±4° on either side of the peak value were selected as background. Under the same conditions, the peak wavelength was measured for 40 seconds, and the wavelengths on either side of the background were measured for 10 seconds each. The detected amount (kcps) of each element was calculated.

[0114] <Measurement of the net strength of silicon atoms in carriers> 0.3 g of the carrier sample was placed in the center of the polyethylene terephthalate (PET) sample plate (inner diameter 12 mm) of a trace powder container, and a shatterproof polypropylene (PP) film was attached to the measurement surface. Care was taken to prevent wrinkles on the PP film. This trace powder container was placed in a 10 mm diameter measurement cell with the bottom plate removed, and elemental analysis was performed using an X-ray analyzer (Rigaku Corporation, Primus II). The element analyzed here was silicon (Si), and the detected peak intensity was quantified as the detection amount (kcps) using Rigaku Corporation's SQX analysis software. The detection conditions for silicon (Si) element were as follows: excitation conditions: tube voltage 60 kV, tube current 50 mA, filter: F-Be; optical system conditions: slit: S4, analyzing crystal RX4, detector PC; PHA conditions: lower limit 120, upper limit 300. The measurement time was 40 seconds at the peak wavelength and 10 seconds at wavelengths ±4 degrees on either side of the peak value as background.

[0115] <Preparation of strontium titanate particles (1)> The desulfurized and peptized titanium source, metatitanic acid, was collected at 1.86 moles in terms of TiO2 and placed in a reaction vessel. Next, 2.12 moles of strontium chloride aqueous solution were added to the reaction vessel to achieve a Ti molar ratio of 1.14. Sodium silicate was then added to the reaction vessel in an amount equivalent to 1.0 mole per mole of Sr. The initial TiO2 concentration in the mixture of the three materials was adjusted to 0.92 mole / L. The mixture was then stirred and heated to 90°C. While maintaining the temperature at 90°C and stirring, 530 mL of 10 N (=10 mol / L) sodium hydroxide aqueous solution was added over 1.0 hour. Stirring was then continued for another hour while maintaining the temperature at 95°C. The reaction mixture was then cooled to 50°C, and hydrochloric acid was added until the pH reached 5.1, followed by stirring for 1 hour. The precipitate was then washed by repeated decantation and redispersion in water. Hydrochloric acid was added to the slurry containing the washed precipitate to adjust the pH to 2.5, and the solids were filtered off and dried. An ethanol solution of i-butyltrimethoxysilane was added to the dried solids in an amount of 15 parts i-butyltrimethoxysilane per 100 parts solids, and the mixture was stirred for 4 hours. The solids were filtered off and dried in air at 125°C for 9 hours to obtain strontium titanate particles (1).

[0116] <Preparation of calcium titanate particles (2)> Calcium titanate (2) was prepared in the same manner as in the preparation of strontium titanate particles (1), except that the aqueous strontium chloride solution was changed to an aqueous calcium chloride solution.

[0117] <Preparation of strontium titanate particles (3)> Strontium titanate (3) was prepared in the same manner as in the preparation of strontium titanate particles (1), except that the sodium hydroxide aqueous solution was added over 30 minutes.

[0118] <Preparation of strontium titanate particles (4)> Strontium titanate (4) was prepared in the same manner as in the preparation of strontium titanate particles (1), except that the sodium hydroxide aqueous solution was added over 90 minutes.

[0119] <Preparation of strontium titanate particles (5)> Strontium titanate (5) was prepared in the same manner as in the preparation of strontium titanate particles (1), except that the sodium hydroxide aqueous solution was added over 70 minutes.

[0120] <Preparation of strontium titanate particles (6)> Strontium titanate (4) was prepared in the same manner as in the preparation of strontium titanate particles (1), except that sodium silicate was changed to lanthanum chloride.

[0121] <Preparation of strontium titanate particles (7)> Strontium titanate (7) was prepared in the same manner as in the preparation of strontium titanate particles (1), except that sodium silicate was not added.

[0122] <Preparation of strontium titanate particles (8)> Strontium titanate (8) was prepared in the same manner as in the preparation of strontium titanate particles (1), except that the ethanol solution of i-butyltrimethoxysilane was not added to the dried solid content.

[0123] <Preparation of strontium titanate particles (9)> Strontium titanate (9) was prepared in the same manner as in the preparation of strontium titanate particles (1), except that n-decyltrimethoxysilane was used as the dried solid component.

[0124] <Preparation of strontium titanate particles (10)> Strontium titanate (10) was prepared in the same manner as in the preparation of strontium titanate particles (1), except that silicone oil was used instead of the dried solids, and the amount of silicone oil added was changed to 3 parts.

[0125] Titania particles (11): T805, manufactured by Nippon Aerosil Co., Ltd. Alumina particles (12): AluC805, manufactured by Nippon Aerosil Co., Ltd. Silicone oil: Dimethyl silicone oil, KF-96, manufactured by Shin-Etsu Chemical Co., Ltd.

[0126] <Toner Production> [Preparation of Resin Particle Dispersion (1)] Ethylene glycol (Fujifilm Wako Pure Chemical Industries, Ltd.): 37 parts Neopentyl glycol (Fujifilm Wako Pure Chemical Industries, Ltd.): 65 parts 1,9-nonanediol (Fujifilm Wako Pure Chemical Industries, Ltd.): 32 parts Terephthalic acid (Fujifilm Wako Pure Chemical Industries, Ltd.): 96 parts The above materials were charged into a flask, and the temperature was raised to 200°C over 1 hour. After confirming uniform stirring within the reaction system, 1.2 parts of dibutyltin oxide was added. The temperature was raised to 240°C over 6 hours while distilling off the resulting water. Stirring was continued at 240°C for 4 hours, yielding a polyester resin (acid value 9.4 mgKOH / g, weight-average molecular weight 13,000, glass transition temperature 62°C). This polyester resin was transferred in its molten state to an emulsifier / disperser (Cavitron CD1010, Eurotech) at a rate of 100 g / min. Separately, a 0.37% concentration dilute ammonia water, prepared by diluting reagent ammonia water with ion-exchanged water, was placed in a tank and heated to 120°C in a heat exchanger. The emulsifier / disperser was operated at a rotor speed of 60 Hz and a pressure of 5 kg / cm. 2 The operation was carried out under the conditions of (a) to (c) to obtain a resin particle dispersion (1) having a volume average particle size of 160 nm and a solid content of 30%.

[0127] [Preparation of Resin Particle Dispersion (2)] Decanedioic acid (Tokyo Chemical Industry Co., Ltd.): 81 parts Hexanediol (Fujifilm Wako Pure Chemical Industries, Ltd.): 47 parts The above materials were charged into a flask, and the temperature was raised to 160°C over 1 hour. After confirming that the reaction system was uniformly stirred, 0.03 parts of dibutyltin oxide was added. The temperature was raised to 200°C over 6 hours while distilling off the produced water, and stirring was continued at 200°C for 4 hours. The reaction liquid was then cooled, solid-liquid separation was performed, and the solid was dried at 40°C under reduced pressure to obtain polyester resin (C1) (melting point 64°C, weight average molecular weight 15,000).

[0128] Polyester resin (C1): 50 parts Anionic surfactant (Neogen SC, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 2 parts Ion-exchanged water: 200 parts The above materials were heated to 120°C and thoroughly dispersed using a homogenizer (Ultra Turrax T50, IKA), and then dispersed using a pressure discharge homogenizer. When the volume average particle size reached 180 nm, the particles were collected to obtain a resin particle dispersion (2) with a solid content of 20%.

[0129] [Preparation of Colorant Particle Dispersion (1)] Cyan pigment (Pigment Blue 15:3, manufactured by Dainichi Seika Color & Chemicals Mfg. Co., Ltd.): 10 parts Anionic surfactant (Neogen SC, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 2 parts Ion-exchanged water: 80 parts The above materials were mixed and dispersed for 1 hour using a high-pressure impact disperser (Ultimizer HJP30006, Sugino Machine Co., Ltd.) to obtain a colorant particle dispersion (1) with a volume average particle size of 180 nm and a solid content of 20%.

[0130] [Preparation of Release Agent Particle Dispersion (1)] Paraffin wax (HNP-9, manufactured by Nippon Seiro Co., Ltd.): 50 parts Anionic surfactant (Neogen SC, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.): 2 parts Ion-exchanged water: 200 parts The above materials were heated to 120°C and thoroughly dispersed using a homogenizer (Ultra Turrax T50, manufactured by IKA), and then dispersed using a pressure discharge homogenizer. When the volume average particle size reached 200 nm, the particles were collected to obtain a release agent particle dispersion (1) with a solid content of 20%.

[0131] [Preparation of Toner 1] ·Resin particle dispersion (1): 150 parts ·Resin particle dispersion (2): 50 parts Colorant particle dispersion (1): 25 parts Release agent particle dispersion (1): 35 parts Polyaluminum chloride: 0.4 parts Ion-exchanged water: 100 parts The above materials were placed in a round stainless steel flask and thoroughly mixed and dispersed using a homogenizer (Ultra-Turrax T50, IKA). The flask was then heated to 48°C in an oil bath while stirring. The reaction system was maintained at 48°C for 60 minutes, after which 70 parts of resin particle dispersion (1) was slowly added. The pH was then adjusted to 8.0 using a 0.5 mol / L aqueous sodium hydroxide solution. The flask was then sealed, the stirring shaft was magnetically sealed, and the mixture was heated to 90°C with continued stirring and maintained for 30 minutes. The mixture was then cooled at a rate of 5°C / min, solid-liquid separated, and thoroughly washed with ion-exchanged water. The solid-liquid separated product was redispersed in ion-exchanged water at 30°C and washed with stirring at 300 rpm (revolutions per minute) for 15 minutes. This washing operation was repeated six more times, and when the pH of the filtrate reached 7.54 and the electrical conductivity reached 6.5 μS / cm, solid-liquid separation was performed, followed by vacuum drying for 24 hours to obtain toner particles with a volume average particle size of 5.7 μm.

[0132] 100 parts of the above toner particles and 0.8 parts of an external additive shown in Table 1 were mixed in a Henschel mixer to obtain Toner 1.

[0133] <Preparation of Toner 2> Toner 2 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 0.5 g parts.

[0134] <Preparation of Toner 3> Toner 3 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 1.3 g parts.

[0135] <Preparation of Toner 4> Toner 4 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 0.2 g parts.

[0136] <Preparation of Toner 5> Toner 5 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 1.5 g parts.

[0137] <Preparation of Toner 6> Toner 6 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 0.1 g part.

[0138] <Preparation of Toner 7> Toner 7 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 0.1 g part.

[0139] <Preparation of Toner 8> Toner 8 was prepared in the same manner as toner 1, except that the external additive (alumina particles 12) shown in Table 1 was used instead.

[0140] <Preparation of Toner 9> Toner 9 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 0.4 g parts.

[0141] <Preparation of Toner 10> Toner 10 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 1.2 g parts.

[0142] <Preparation of Toner 11> Toner 11 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 0.4 g parts.

[0143] <Preparation of Toner 12> Toner 12 was prepared in the same manner as Toner 1, except that the amount of the external additive shown in Table 1 was changed to 1.3 g parts.

[0144] <Preparation of Toner 13> Toner 13 was prepared in the same manner as Toner 1, except that the external additive type shown in Table 1 was changed to calcium titanate (2).

[0145] <Preparation of Toner 14> Toner 14 was prepared in the same manner as Toner 1, except that the external additive type shown in Table 1 was changed to strontium titanate particles (3) shown in Table 1.

[0146] <Preparation of Toner 15> Toner 15 was prepared in the same manner as Toner 1, except that the external additive type shown in Table 1 was changed to strontium titanate particles (4) shown in Table 1.

[0147] <Preparation of Toner 16> Toner 16 was prepared in the same manner as Toner 1, except that the type of external additive shown in Table 1 was changed to strontium titanate particles (5) shown in Table 1.

[0148] <Preparation of Toner 17> Toner 17 was prepared in the same manner as Toner 1, except that the external additive type shown in Table 1 was changed to strontium titanate particles (6) shown in Table 1.

[0149] <Preparation of Toner 18> Toner 18 was prepared in the same manner as Toner 1, except that the external additive type shown in Table 1 was changed to strontium titanate particles (7) shown in Table 1.

[0150] <Preparation of Toner 19> Toner 19 was prepared in the same manner as Toner 1, except that the external additive type shown in Table 1 was changed to strontium titanate particles (8) shown in Table 1.

[0151] <Preparation of Toner 20> Toner 20 was prepared in the same manner as Toner 1, except that the external additive type shown in Table 1 was changed to strontium titanate particles (9) shown in Table 1.

[0152] <Preparation of Toner 21> Toner 21 was prepared in the same manner as Toner 1, except that the external additive type shown in Table 1 was changed to strontium titanate particles (10) shown in Table 1.

[0153] <Preparation of Toner 22> Toner 22 was prepared in the same manner as Toner 1, except that the external additive type shown in Table 1 was changed to titania particles shown in Table 1.

[0154] <Preparation of Toner 23> 0.8 parts of an external additive shown in Table 1 and 0.8 parts of 50 nm silica particles (X-24-9404) were mixed in a Henschel mixer to obtain toner (23).

[0155] <Preparation of Toner 24> 0.8 parts of an external additive shown in Table 1 and 1.0 part of 80 nm silica particles (X-24-9600A-80) were mixed in a Henschel mixer to obtain toner (24).

[0156] <Preparation of Toner 25> 0.8 parts of an external additive shown in Table 1 and 1.2 parts of 110 nm silica particles (X-24-9163A) were mixed in a Henschel mixer to obtain toner (25).

[0157] <Preparation of ferrite particles (1)> 1,597 parts of Fe2O3, 712 parts of Mn(OH)2, 116 parts of Mg(OH)2, 20 parts of SrCO3, and 30 parts of CaCO3 were mixed, and then a dispersant, water, and 1 mm diameter zirconia beads were added and crushed and mixed using a sand mill. The zirconia beads were filtered off, and the filtrate was dried and then pre-fired using a rotary kiln at a rotation speed of 20 rpm and a temperature of 970°C for 2 hours. The resulting pre-fired product was added with a dispersant and water, and then 8 parts of polyvinyl alcohol was added, followed by crushing and mixing using a wet ball mill for 5 hours. The volume average particle size of the resulting crushed product was 1.2 μm. Next, the product was granulated using a spray dryer to a particle size of 40 μm. The resulting granulated product was then fired in an electric furnace at 1,400°C for 4 hours in an oxygen-nitrogen mixed atmosphere with an oxygen concentration of 1% by volume. The resulting fired product was crushed and classified to obtain ferrite particles (1). The volume average particle size of the ferrite particles (1) was 35 μm.

[0158] <Preparation of Carrier 1> Ferrite particles (1): 1,000 parts Carbon black (Cabot VXC72): 2 parts Melamine resin particles (Eposter S (Nippon Shokubai Co., Ltd.)): 3 parts Silica particles (HM20S, manufactured by Tokuyama Corporation, average primary particle size 10 nm): 6.5 parts Cyclohexyl methacrylate / dimethylaminoethyl methacrylate copolymer (copolymerization ratio 98 mol:2 mol): 20 parts Toluene: 150 parts Of the above materials, silica particles, cyclohexyl methacrylate / methyl methacrylate copolymer, toluene, and glass beads (1 mm diameter, equal amount to toluene) were placed in a sand mill (manufactured by Kansai Paint Co., Ltd.) and stirred at a rotation speed of 1,200 rpm (revolutions per minute) for 30 minutes to obtain a resin coating layer forming solution (1). Ferrite particles (1) were placed in a vacuum degassing kneader, and then the resin coating layer forming solution (1) was added. The mixture was heated and depressurized while stirring to distill off the toluene, and the ferrite particles (1) were coated with resin. Next, fine and coarse powders were removed using an elbow jet to obtain carrier 1.

[0159] <Creating Carrier 2> Carrier 2 was prepared in the same manner as Carrier 1, except that the amount of silica particles used was changed to 3.3 parts.

[0160] <Creating Carrier 3> Carrier 3 was prepared in the same manner as Carrier 1, except that the amount of silica particles used was changed to 9.8 parts.

[0161] <Creating Carrier 4> Carrier 4 was prepared in the same manner as Carrier 1, except that the amount of silica particles used was changed to 2.9 parts.

[0162] <Creating Carrier 5> Carrier 5 was prepared in the same manner as Carrier 1, except that the amount of silica particles used was changed to 10.1 parts.

[0163] <Creating Carrier 6> Carrier 6 was prepared in the same manner as Carrier 1, except that the silica particles were changed to HM30S LeoSeal (manufactured by Tokuyama Corporation, average primary particle size 7 nm).

[0164] <Creating Carrier 7> Carrier 7 was prepared in the same manner as Carrier 1, except that the silica particles were changed to NY50L (manufactured by Nippon Aerosil Co., Ltd., average primary particle size 50 nm).

[0165] <Preparation of Carrier Particles 8> Carrier 8 was prepared in the same manner as Carrier 1, except that the carbon black and melamine resin particles were not added.

[0166] <Preparation of Carrier Particles 9> Carrier 9 was prepared in the same manner as Carrier 1, except that the silica particles were changed to AluC805 (manufactured by Nippon Aerosil Co., Ltd.).

[0167] <Preparation of Carrier Particles 10> Carrier 10 was prepared in the same manner as Carrier 1, except that in the preparation of Carrier 1, the cyclohexyl methacrylate / dimethylaminoethyl methacrylate copolymer was changed to cyclohexyl methacrylate.

[0168] <Preparation of Carrier Particles 11> Carrier 11 was prepared in the same manner as Carrier 1, except that in the preparation of Carrier 1, the cyclohexyl methacrylate / dimethylaminoethyl methacrylate copolymer was changed to methyl methacrylate.

[0169] (Examples 1 to 26 and Comparative Examples 1 to 4) <Preparation of Electrostatic Image Developer> 100 parts of the carrier shown in Table 1 and 8 parts of the toner shown in Table 1 were charged into a V blender and stirred for 20 minutes, after which the mixture was sieved through a sieve with 212 μm openings to obtain developers 1 to 30 (electrostatic image developers), respectively.

[0170] <Evaluation of fogging suppression> For each developer, fogging was evaluated using a DocuCentreColor400CP (manufactured by Fujifilm Business Innovation Co., Ltd.). The toner was applied to the photoconductor at a toner loading of 5 g / m2 in a high-temperature, high-humidity environment (28°C / 85% RH). 2 The development potential was adjusted to 100%, and 300,000 images with an image area ratio of 10% were continuously printed on A4-sized plain paper under high temperature and high humidity (temperature 28°C / relative humidity 85%). After leaving the sheet to stand for 48 hours under low temperature and low humidity (temperature 10°C / relative humidity 15%), and then for 24 hours under high temperature and high humidity (temperature 28°C / relative humidity 85%), 100 images with an image area ratio of 10% were continuously printed. The density of the fog (background area) on the 100 sheets was measured using an X-Rite 938 (manufactured by X-Rite). The evaluation criteria are as follows: G5: Fog density is less than 0.01 G4.5: Fog density is 0.01 or more and less than 0.015 G4.0: Fog density is 0.015 or more and less than 0.020 G3.5: Fog density is 0.020 or more and less than 0.025 G3: Fog density is 0.025 or more and less than 0.05 G2.5: Fog density is 0.05 or more and less than 0.075 G2: Fog density is 0.075 or more and less than 0.1 G1.5: Fog density is 0.1 or more and less than 0.125 G1: Fog density is 0.125 or more (unacceptable for use).

[0171] The evaluation results are summarized in Table 1.

[0172] [Table 1]

[0173] As shown in Table 1, the electrostatic image developers of Examples 1 to 26 were superior in fogging suppression compared to the electrostatic image developers of Comparative Examples 1 to 4.

[0174] (((1))) An electrostatic image developer comprising: a toner having toner particles and an external additive on the surfaces of the toner particles; and a carrier having magnetic particles and a resin coating layer on the surfaces of the magnetic particles, wherein the external additive contains a titanium compound and the resin coating layer contains silica particles; and wherein the ratio TiNet / SiNet of the net intensity of titanium atoms detected by fluorescent X-ray analysis of the toner to the net intensity SiNet of silicon atoms detected by fluorescent X-ray analysis of the carrier is 0.08 or more and 0.7 or less. (((2))) The electrostatic image developer according to (((1))), wherein the net strength of silicon atoms, SiNet, is 2 kcps or more and 6 kcps or less. (((3))) The electrostatic image developer according to (((1))) or (((2))), wherein the titanium compound is a metal titanate compound. (((4))) The electrostatic image developer according to (((3))), wherein the titanium compound is strontium titanate. (((5))) The electrostatic image developer according to any one of (((1))) to (((4))), wherein the ratio Pst / Pss of the average primary particle diameter Pst of the titanium compound to the average primary particle diameter Pss of the silica particles is 2 or more and 8 or less. (((6))) The electrostatic image developer according to (((5))), wherein the resin coating layer contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group. (((7))) The electrostatic image developer according to any one of (((1))) to (((6))), wherein the titanium compound is a silica-doped titanium compound. (((8))) The electrostatic image developer according to any one of (((1))) to (((7))), wherein the titanium compound is a titanium compound whose surface has been subjected to a hydrophobic treatment. (((9))) A process cartridge that is detachably attached to an image forming apparatus, which contains the electrostatic image developer described in any one of (((1))) to (((8))) and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image. (((10))) An image forming method comprising at least a charging step of charging an image carrier, an exposure step of forming an electrostatic latent image on the surface of the image carrier, a developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic image developer to form a toner image, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a transfer recipient, and a fixing step of fixing the toner image, wherein the electrostatic image developer is the electrostatic image developer described in any one of (((1))) to (((8))). (((11))) An image forming apparatus comprising an image carrier, charging means for charging the image carrier, exposure means for exposing the charged image carrier to light to form an electrostatic latent image on the image carrier, developing means for developing the electrostatic latent image with an electrostatic image developer to form a toner image, transfer means for transferring the toner image from the image carrier to a transfer receiving body, and fixing means for fixing the toner image, wherein the electrostatic image developer is the electrostatic image developer described in any one of (((1))) to (((8))).

[0175] According to the invention related to (((1))), an electrostatic image developer is provided which has excellent fogging suppression properties compared to when the ratio TiNet / SiNet of the net intensity of titanium atoms detected by X-ray fluorescence analysis of the toner, TiNet, to the net intensity of silicon atoms, SiNet, detected by X-ray fluorescence analysis of the carrier, is less than 0.08 or exceeds 0.7. According to the invention related to (((2))), an electrostatic image developer is provided which has better fogging suppression properties than when the net strength SiNet of the silicon atoms is less than 2 kcps or more than 6 kcps. According to the invention related to (((3))) or (((4))), an electrostatic image developer is provided which is superior in fogging suppression properties compared to when the titanium compound is titanium oxide. According to the invention related to (((5))), an electrostatic image developer is provided which has better fogging suppression properties than when the ratio Pst / Pss of the average primary particle diameter Pst of the titanium compound to the average primary particle diameter Pss of the silica particles is less than 2 or more than 8. According to the invention related to (((6))), an electrostatic image developer is provided which has better fogging suppression properties than when the resin coating layer contains only an acrylic resin which has a structural unit having an aliphatic cyclic structure and does not have a structural unit having an amino group. According to the invention (((7))), an electrostatic image developer is provided which is superior in fogging suppression properties compared to when the titanium compound is a lanthanum-doped titanium compound. According to the invention related to (((8))), an electrostatic image developer is provided which has better fogging suppression properties than when the titanium compound is a titanium compound whose surface has not been subjected to a hydrophobic treatment. According to the inventions (((9))) to (((11))), a process cartridge, an image forming method, or an image forming apparatus is provided that has excellent fogging suppression properties compared to when the ratio TiNet / SiNet of the net intensity of titanium atoms detected by X-ray fluorescence analysis of the toner in an electrostatic image developer to the net intensity SiNet of silicon atoms detected by X-ray fluorescence analysis of the carrier is less than 0.08 or exceeds 0.7. [Explanation of symbols]

[0176] 1Y, 1M, 1C, 1K Photoconductor (an example of an image carrier) 2Y, 2M, 2C, 2K Charging roll (an example of charging means) 3. Exposure device (an example of an electrostatic image forming means) 3Y, 3M, 3C, 3K laser beam 4Y, 4M, 4C, 4K developing device (an example of developing means) 5Y, 5M, 5C, 5K Primary transfer roll (an example of a primary transfer means) 6Y, 6M, 6C, 6K: Photoconductor cleaning device (an example of a cleaning means) 8Y, 8M, 8C, 8K toner cartridges 10Y, 10M, 10C, 10K image forming units 20 Intermediate transfer belt (an example of an intermediate transfer body) 22 Drive Roll 24 Support Roll 26 Secondary transfer roll (an example of a secondary transfer means) 28 Fixing device (an example of fixing means) 30 Intermediate transfer body cleaning device P Recording paper (an example of a recording medium)

[0177] 107 Photoconductor (an example of an image carrier) 108 Charging roll (an example of charging means) 109 Exposure device (an example of electrostatic image forming means) 111 Developing device (an example of developing means) 112 Transfer device (an example of transfer means) 113 Photosensitive drum cleaning device (an example of cleaning means) 115 Fixing device (an example of fixing means) 116 Mounting Rail 117 Cabinet 118 Exposure opening 200 Process Cartridge 300 Recording paper (an example of a recording medium)

Claims

1. a toner having toner particles and an external additive on the surface of the toner particles; and a carrier having magnetic particles and a resin coating layer on the surface of the magnetic particles, the external additive contains a titanium compound, the resin coating layer contains silica particles, a ratio of a net intensity of titanium atoms (TiNet) detected by X-ray fluorescence analysis of the toner to a net intensity of silicon atoms (SiNet) detected by X-ray fluorescence analysis of the carrier, TiNet / SiNet, of 0.08 or more and 0.7 or less; Electrostatic image developer.

2. 2. The electrostatic image developer according to claim 1, wherein the silicon atom has a net strength SiNet value of 2 kcps or more and 6 kcps or less.

3. 3. The electrostatic image developer according to claim 1, wherein the titanium compound is a metal titanate compound.

4. 4. The electrostatic image developer according to claim 3, wherein said titanium compound is strontium titanate.

5. 3. The electrostatic image developer according to claim 1, wherein a ratio Pst / Pss of an average primary particle diameter Pst of said titanium compound to an average primary particle diameter Pss of said silica particles is 2 or more and 8 or less.

6. 6. The electrostatic image developer according to claim 5, wherein the resin coating layer contains an acrylic resin having a structural unit having an aliphatic cyclic structure and a structural unit having an amino group.

7. 3. The electrostatic image developer according to claim 1, wherein the titanium compound is a silica-doped titanium compound.

8. 3. The electrostatic image developer according to claim 1, wherein the titanium compound has a surface that has been subjected to a hydrophobic treatment.

9. a developing unit containing the electrostatic image developer according to claim 1 or 2 and developing an electrostatic image formed on a surface of an image carrier into a toner image by using the electrostatic image developer, A process cartridge is detachably mounted in an image forming apparatus.

10. a charging step of charging at least an image carrier; an exposure step of forming an electrostatic latent image on the surface of the image carrier; a developing step of developing the electrostatic latent image formed on the surface of the image carrier with an electrostatic image developer to form a toner image; a transfer step of transferring the toner image formed on the surface of the image carrier onto a surface of a transfer receiving material; a fixing step of fixing the toner image, The electrostatic image developer is the electrostatic image developer according to claim 1 or 2. Image forming method.

11. an image carrier; a charging means for charging the image carrier; an exposure unit that exposes the charged image carrier to light to form an electrostatic latent image on the image carrier; a developing means for developing the electrostatic latent image with an electrostatic image developer to form a toner image; a transfer means for transferring the toner image from the image carrier to a transfer receiving member; a fixing means for fixing the toner image, The electrostatic image developer is the electrostatic image developer according to claim 1 or 2. Image forming device.

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