toner

Abstract

To provide a toner which enables formation of an image which has desired image concentration and little fogging, even after printing of a large number of sheets.SOLUTION: A toner contains toner particles. The toner particles have toner base particles, and an external additive provided on the surface of the toner base particles. The toner base particles contain a binder resin, and magnetic powder. The external additive contains alumina particles. A number average primary particle diameter of the alumina particles is 150 nm or more and 400 nm or less. A time constant of the toner is 1.0 second or more and 10.0 seconds or less. A zeta potential at pH2 of a precipitate separated from a dispersion liquid of the toner is 0.0 mV or more and 20.0 mV or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a toner. [Background technology]

[0002] In image formation by electrophotography, a toner containing toner particles is used. The toner particles include, for example, toner base particles and external additives attached to the surfaces of the toner base particles. For example, the magnetic toner described in Patent Document 1 includes magnetic toner base particles containing a binder resin and a magnetic material, a first external additive, and a second external additive. The absolute value of the difference |ζ(T)-ζ(A1)| between the zeta potential ζ(T) of the magnetic toner particles when the magnetic toner particles are dispersed in water and the zeta potential ζ(A1) of the first external additive when the first external additive is dispersed in water is 50 mV or less. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-45854 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the inventors have found through their investigations that the magnetic toner described in Patent Document 1 has room for improvement in terms of forming images that have a desired image density and little fog when a large number of sheets are printed.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a toner that can form images having a desired image density and little fog, even when a large number of sheets are printed. [Means for solving the problem]

[0006] The toner according to the present invention includes toner particles. The toner particles have toner base particles and an external additive provided on the surface of the toner base particles. The toner base particles contain a binder resin and a magnetic powder. The external additive includes alumina particles. The alumina particles have a number average primary particle diameter of 150 nm or more and 400 nm or less. The toner has a time constant of 1.0 second or more and 10.0 seconds or less. The zeta potential at pH 2 of the sediment separated from the toner dispersion is 0.0 mV or more and 20.0 mV or less. [Effects of the Invention]

[0007] The toner according to the present invention can form images having a desired image density and little fog, even when a large number of sheets are printed. DETAILED DESCRIPTION OF THE INVENTION

[0008] Hereinafter, an embodiment of the present invention will be described. First, the terms used in this specification will be described. A toner is an aggregate (for example, powder) of toner particles. An external additive is an aggregate (for example, powder) of external additive particles. A magnetic powder is an aggregate (powder) of magnetic particles. Unless otherwise specified, evaluation results (values ​​indicating shape, physical properties, etc.) for powders (more specifically, powders of toner particles, powders of external additive particles, etc.) are the number averages of values ​​measured for a considerable number of particles selected from the powder.

[0009] Volume median diameter of powder (D 50 Unless otherwise specified, the measured values ​​of ) are values ​​measured based on the Coulter principle (pore electrical resistance method) using a Coulter Counter Multisizer 3 manufactured by Beckman Coulter, Inc.

[0010] Unless otherwise specified, the number average primary particle diameter of a powder is the number average value of the equivalent circle diameters of primary particles (Heywood diameter: diameter of a circle having the same area as the projected area of ​​a primary particle) measured using a scanning electron microscope. The number average primary particle diameter of a powder is, for example, the number average value of the equivalent circle diameters of 100 primary particles. Unless otherwise specified, the number average primary particle diameter of a powder refers to the number average primary particle diameter of particles in the powder.

[0011] Unless otherwise specified, the term "chargeability" refers to the chargeability in frictional charging. The strength of positive chargeability (or negative chargeability) in frictional charging can be confirmed using a known triboelectric series.

[0012] Unless otherwise specified, the softening point (Tm) is a value measured using a high-speed flow tester (Shimadzu Corporation, CFT-500D). In the S-shaped curve measured using the high-speed flow tester (horizontal axis: temperature, vertical axis: stroke), the temperature at which "(baseline stroke value + maximum stroke value) / 2" is obtained corresponds to Tm (softening point).

[0013] Unless otherwise specified, the glass transition point (Tg) is a value measured in accordance with JIS (Japanese Industrial Standards) K7121-2012 using a differential scanning calorimeter (DSC-6220 manufactured by Seiko Instruments Inc.). In the endothermic curve measured with the differential scanning calorimeter (vertical axis: heat flow (DSC signal), horizontal axis: temperature), the temperature of the inflection point due to glass transition (more specifically, the temperature at the intersection of the extrapolated line of the baseline and the extrapolated line of the falling line) corresponds to Tg (glass transition point).

[0014] Unless otherwise specified, the acid value is a value measured in accordance with "JIS (Japanese Industrial Standards) K0070-1992."

[0015] Unless otherwise specified, the weight average molecular weight (Mw) is a value measured using gel permeation chromatography.

[0016] Unless otherwise specified, the electrical resistivity is a value measured using an electrical resistance meter ("R6561" manufactured by Advantest Corporation) in an environment at a temperature of 25°C and a humidity of 50% RH.

[0017] Unless otherwise specified, the "major component" of a material means the component that is contained in the largest amount in the material on a mass basis.

[0018] The strength of hydrophobicity (or strength of hydrophilicity) can be expressed, for example, by the contact angle of a water droplet (ease of wetting with water). The larger the contact angle of the water droplet, the stronger the hydrophobicity. Hydrophobic treatment refers to a treatment that strengthens hydrophobicity. Hydrophilic treatment refers to a treatment that strengthens hydrophilicity.

[0019] Hereinafter, the compound and its derivatives may be collectively referred to by adding "based" after the compound name. When the compound name is followed by "based" to represent the name of a polymer, it means that the repeating unit of the polymer is derived from the compound or its derivative.

[0020] Acrylic and methacrylic may be collectively referred to as "(meth)acrylic." Acrylate and methacrylate may be collectively referred to as "(meth)acrylate." Acrylonitrile and methacrylonitrile may be collectively referred to as "(meth)acrylonitrile." Unless otherwise specified, alkyl groups are linear or branched and unsubstituted. "Independently" in the description of the formula means that they may represent the same group or different groups. Unless otherwise specified, each component described below may be used alone or in combination of two or more. The terms used in this specification have been explained above.

[0021] <Toner> A toner according to an embodiment of the present invention includes toner particles. The toner particles have toner base particles and an external additive. The external additive is provided on the surface of the toner base particles. The toner base particles contain a binder resin and a magnetic powder. The external additive includes alumina particles. The alumina particles have a number average primary particle diameter of 150 nm or more and 400 nm or less. The toner has a time constant (τ) of 1.0 second or more and 10.0 seconds or less. The sediment separated from the toner dispersion has a zeta potential of 0.0 mV or more and 20.0 mV or less at pH 2.

[0022] Hereinafter, the "zeta potential of the sediment separated from the toner dispersion at pH 2," the "zeta potential of the sediment separated from the toner dispersion at pH 5" (described later), the "zeta potential of the supernatant separated from the toner dispersion at pH 2" (described later), and the "zeta potential of the supernatant separated from the toner dispersion at pH 5" (described later) may be referred to as "zeta potential (D-pH2)," "zeta potential (D-pH5)," "zeta potential (U-pH2)," and "zeta potential (U-pH5)," respectively. Furthermore, the "sediment separated from the toner dispersion" and the "supernatant separated from the toner dispersion" may be simply referred to as the "sediment" and the "supernatant," respectively.

[0023] The toner according to the present embodiment, having the above-described structure, can form images with a desired image density and little fog even when a large number of sheets are printed. The reason for this is presumed to be as follows.

[0024] An image forming apparatus equipped with a developing roller and a toner charging member will be described as an example. A toner layer is formed on the circumferential surface of the developing roller (specifically, the circumferential surface of the developing sleeve). First, the mechanism by which the toner layer formed on the developing sleeve is charged will be described. The toner particles constituting the toner layer on the developing sleeve are charged by friction with the toner charging member (e.g., a blade). Then, charge transfers from one charged toner particle to another adjacent toner particle, resulting in the overall charging of the toner particles contained in the toner layer. The charge transfer speed in the toner layer tends to depend on the toner's time constant (the product of the toner's electrical resistance and dielectric constant). Specifically, a toner layer formed with a toner having a small time constant tends to have a high charge transfer speed and a narrow toner charge distribution. A narrow charge distribution of the toner contained in the toner layer improves the toner's developability, enabling the formation of an image with a desired image density. However, a toner layer formed with a toner having an excessively small time constant tends to lose charge from the toner to the developing sleeve, causing the charge amount to fall below the desired value (charge relaxation), and the toner layer to become excessively thin. If the toner layer is excessively thin, the developability of the toner will decrease.

[0025] Here, the time constant of the toner according to this embodiment is 1.0 seconds or more and 10.0 seconds or less. When the toner time constant is 1.0 seconds or more, charge is less likely to be released from the toner to the developing sleeve, and the toner charge amount is less likely to fall below the desired value (charge relaxation). As a result, images with less fog can be formed. On the other hand, when the toner time constant is 10.0 seconds or less, the charge migration speed in the toner layer is maintained high even when multiple sheets are printed, and the toner charge amount distribution becomes narrow. When the charge amount distribution of the toner contained in the toner layer is narrow, the toner developability is improved, and images with the desired image density can be formed even when multiple sheets are printed.

[0026] Furthermore, when the zeta potential (D-pH2) is 0.0 mV or higher, the toner has high charging properties, and the toner layer formed on the developing sleeve does not become excessively thin even when multiple sheets are printed. As a result, images with the desired image density can be formed even when multiple sheets are printed. On the other hand, when the zeta potential (D-pH2) is 20.0 mV or lower, images with the desired image density and little fog can be formed even when multiple sheets are printed.

[0027] Furthermore, when the number average primary particle diameter of the alumina particles is 150 nm or more and 400 nm or less, detachment of the alumina particles from the toner base particles is suppressed, and an image having a desired image density can be formed even when a large number of sheets are printed. The reason why an image having a desired image density and less fog can be formed even when a large number of sheets are printed has been explained above.

[0028] The toner according to this embodiment can be suitably used for developing electrostatic latent images, for example, as a positively charged magnetic toner (single-component developer). The time constant of the toner according to this embodiment, as well as the zeta potential of the precipitate and supernatant, will be described below. The external additives and toner base particles contained in the toner according to this embodiment will also be described.

[0029] [Time constant] As already mentioned, the toner time constant is 1.0 seconds or more and 10.0 seconds or less. In this specification, the toner time constant is a value measured in an environment of 20°C temperature and 65% RH humidity. In order to form images with desired image density and little fog even when printing multiple sheets, the toner time constant is preferably 1.5 seconds or more and 6.0 seconds or less. The toner time constant is measured by the method described in the Examples or a method based thereon. The toner time constant is adjusted, for example, in the case of alumina particles as an external additive, by the ratio of the total mass of tin and antimony in the conductive metal oxide contained in the conductive layer to the mass of the substrate.

[0030] [Zeta potential] The zeta potential of the sediment is an index of the toner's chargeability. The higher the zeta potential of the sediment, the higher the toner's chargeability tends to be. On the other hand, the zeta potential of the supernatant is affected by external additives liberated from the toner base particles.

[0031] In this specification, the zeta potentials of the sediment and the supernatant are values ​​measured at 20°C. The following describes an outline of the method for measuring the zeta potentials of the sediment and the supernatant. First, 20 mg of toner is dispersed in 2 mL of an aqueous surfactant solution to obtain a toner dispersion. The aqueous surfactant solution is a 10% by mass solution of a nonionic surfactant with an HLB value of 15.3. The toner dispersion is diluted 50 times with ion-exchanged water to obtain a diluted toner dispersion. The diluted toner dispersion is magnetically separated using a neodymium magnet with a residual magnetic flux density of 1.25 T. Then, sediment attracted to the magnet and supernatant not attracted to the magnet are obtained. The zeta potentials of the obtained sediment and supernatant are each measured using a laser Doppler zeta potential meter. The above is an outline of the method for measuring the zeta potentials of the sediment and the supernatant. Specific methods for measuring the zeta potentials of the sediment and the supernatant will be described later in the Examples.

[0032] As already mentioned, the zeta potential (D-pH2) is 0.0 mV or more and 20.0 mV or less. In order to form an image having a desired image density and little fog, the zeta potential (D-pH2) is preferably 5.0 mV or more and 15.0 mV or less. The zeta potential (D-pH2) is adjusted, for example, by the type of surface treatment agent used when surface treating the alumina particles, which are external additives.

[0033] In order to form an image having a desired image density and little fog, the zeta potential (D-pH5) is preferably -60.0 mV or more and less than 0.0 mV. By controlling the zeta potential (D-pH5) in addition to the zeta potential (D-pH2), the chargeability of the toner can be suitably controlled. The zeta potential (D-pH5) is adjusted, for example, by the same method as that for adjusting the zeta potential (D-pH2).

[0034] In order to adjust the zeta potential (D-pH2) and the zeta potential (U-pH2) to be approximately the same, the zeta potential (U-pH2) is, for example, 0.0 mV or more and 20.0 mV or less. In order to adjust the zeta potential (D-pH5) and the zeta potential (U-pH5) to be approximately the same, the zeta potential (U-pH5) is, for example, -60.0 mV or more and less than 0.0 mV. The zeta potential (U-pH2) and the zeta potential (U-pH5) are each adjusted, for example, by the amount of a conductive treatment agent used to conductively treat the alumina particles, which are external additives, and the type of surface treatment agent used to surface treat the alumina particles.

[0035] The half-value width of the zeta potential of the precipitate separated from the toner dispersion is an index showing the variety of external additives. The more types of external additives are contained in the toner base particles, the larger the half-value width of the precipitate tends to be. In order to form an image with a desired image density and little fog, the half-value width of the zeta potential (D-pH2) is preferably 0.0 mV to 30.0 mV, and more preferably 20.0 mV to 30.0 mV. For the same reason, the half-value width of the zeta potential (D-pH5) is preferably 0.0 mV to 30.0 mV, and more preferably 20.0 mV to 30.0 mV. From the viewpoint of adjusting the half-width of the zeta potential (D-pH2) and the half-width of the zeta potential (U-pH2) to be approximately the same, the half-width of the zeta potential (U-pH2) is preferably 0.0 mV to 30.0 mV, more preferably 20.0 mV to 30.0 mV. From the viewpoint of adjusting the half-width of the zeta potential (D-pH5) and the half-width of the zeta potential (U-pH5) to be approximately the same, the half-width of the zeta potential (U-pH5) is preferably 0.0 mV to 30.0 mV, more preferably 20.0 mV to 30.0 mV.

[0036] [External additives] The external additive contains alumina particles. Preferably, the external additive further contains organic particles in addition to the alumina particles. The external additive may further contain silica particles as needed. The external additive may further contain external additive particles other than alumina particles, organic particles, and silica particles (hereinafter, sometimes referred to as other external additive particles).

[0037] <Alumina particles> The zeta potential of alumina particles tends to be close to that of the magnetic powder contained in the toner base particles. Toners containing alumina particles with a zeta potential close to that of the magnetic powder tend to have a narrow charge distribution. A narrow charge distribution of the toner improves the developability of the toner, and images with the desired image density can be formed even when multiple sheets are printed.

[0038] As already mentioned, the number average primary particle diameter of the alumina particles is 150 nm or more and 400 nm or less. In order to form images with a desired image density even when multiple sheets are printed, the number average primary particle diameter of the alumina particles is preferably 250 nm or more and 350 nm or less.

[0039] The amount of alumina particles is preferably 1 part by mass to 100 parts by mass, and more preferably 1 part by mass to 20 parts by mass, per 1000 parts by mass of toner base particles. The amount of alumina particles is preferably 30 parts by mass to 60 parts by mass, and more preferably 40 parts by mass to 50 parts by mass, per 100 parts by mass of external additive. When the external additive further contains silica particles in addition to alumina particles, the amount of alumina particles is preferably 0.5 parts by mass to 1.5 parts by mass per 1.0 part by mass of silica particles.

[0040] The alumina particles preferably include a substrate, a conductive layer, and a surface treatment layer. The conductive layer covers the substrate. The surface treatment layer covers the conductive layer. Of the two layers covering the substrate, the inner layer (on the substrate side) is the conductive layer, and the outer layer is the surface treatment layer. The substrate, the conductive layer, and the surface treatment layer will be described below.

[0041] (Base) The substrate contains alumina. Alumina particles tend to be positively charged, so a toner containing alumina particles is easily positively charged. The alumina content in the substrate is preferably 80% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass.

[0042] (Conductive layer) The conductive layer is a layer formed by a conductive treatment agent. The conductive layer is provided by alumina particles, which are an external additive, and this appropriately reduces the electrical resistance of the toner. This makes it easy to adjust the toner's time constant (the product of the toner's electrical resistance and dielectric constant) to a desired range.

[0043] The conductive layer preferably contains a conductive oxide, and more preferably contains a conductive metal oxide (hereinafter, sometimes referred to as a conductive metal oxide). Examples of conductive metal oxides include metal oxides containing tin oxide (e.g., antimony-doped tin oxide (ATO), indium tin oxide (ITO), and fluorine-doped tin oxide (FTO)), and metal oxides containing zinc oxide (e.g., aluminum-doped zinc oxide (AZO) and gallium-doped zinc oxide (GZO)). The conductive layer preferably contains antimony-doped tin oxide. The content of the conductive metal oxide in the conductive layer is preferably 80% by mass or more, more preferably 95% by mass or more, and even more preferably 100% by mass.

[0044] The conductive metal oxide contained in the conductive layer preferably contains tin and antimony, since this allows the toner time constant to be easily adjusted within the desired range. The total mass of tin and antimony in the conductive metal oxide contained in the conductive layer is preferably 10.0 parts by mass or more and 50.0 parts by mass or less, and more preferably 12.5 parts by mass or more and 26.0 parts by mass or less, relative to 100.0 parts by mass of the substrate, since this allows the toner time constant to be easily adjusted within the desired range.

[0045] In order to easily adjust the time constant of the toner to the desired range, in the conductive metal oxide contained in the conductive layer, the ratio (MSn / MSb) of the mass of tin (MSn) to the mass of antimony (MSb) is preferably 0.10 or more and 0.50 or less, and more preferably 0.20 or more and 0.40 or less.

[0046] (Surface treatment layer) The surface treatment layer is a layer formed by a surface treatment agent. The surface treatment layer imparts good charge stability to the toner while suppressing peeling of the conductive layer. The surface treatment agent is, for example, a hydrophobic treatment agent. Specific examples of the surface treatment agent include titanate coupling agents, aluminate coupling agents, and fatty acid metal salts. Titanate coupling agents or aluminate coupling agents are preferred as the surface treatment agent because they allow for easy adjustment of the zeta potential (D-pH2) to a desired range.

[0047] Examples of titanate coupling agents include isopropyl trialkanoyl titanate, isopropyl tris(dioctyl pyrophosphate) titanate, isopropyl tri(N-aminoethyl-aminoethyl) titanate, tetraoctyl bis(ditridecyl phosphite) titanate, isopropyl trioctanoyl titanate, isopropyl dimethacryl isostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, isopropyl isostearoyl diacryl titanate, and isopropyl tri(dioctyl phosphate) titanate. As the titanate coupling agent, isopropyl trialkanoyl titanate is preferred, and isopropyl triisostearoyl titanate is more preferred. Isopropyl trialkanoyl titanate is represented by formula (1).

[0048] [ka]

[0049] In formula (1), R 1 represents an alkyl group. 1The alkyl group represented by R is preferably an alkyl group having 3 to 30 carbon atoms, more preferably an alkyl group having 15 to 20 carbon atoms, and even more preferably an alkyl group having 17 carbon atoms. 1 When represents an alkyl group having 17 carbon atoms, the compound represented by formula (1) is isopropyl triisostearoyl titanate.

[0050] Examples of aluminate coupling agents include aluminum ethylate, aluminum isopropylate, aluminum alkyl acetoacetate dialkylate, mono-sec-butoxyaluminum diisopropylate, aluminum sec-butylate, aluminum tris(ethyl acetoacetate), aluminum monoacetylacetonate bis(ethyl acetoacetate), aluminum tris(acetylacetonate), cyclic aluminum oxide isopropylate, and cyclic aluminum oxide isostearate. Aluminum alkyl acetoacetate dialkylate is preferred, and aluminum alkyl acetoacetate diisopropylate is more preferred. Aluminum alkyl acetoacetate dialkylate is represented by formula (2):

[0051] [ka]

[0052] In formula (2), R 3 , R 4 , and R 5 R each independently represents an alkyl group. 3 The alkyl group represented by R is preferably an alkyl group having 8 to 30 carbon atoms, more preferably an alkyl group having 15 to 20 carbon atoms, and even more preferably an alkyl group having 18 carbon atoms. 3 , and R 4The alkyl groups represented by R are each independently preferably an alkyl group having 1 to 6 carbon atoms, more preferably an alkyl group having 2 to 4 carbon atoms, even more preferably an alkyl group having 3 carbon atoms, and particularly preferably an isopropyl group. 4 , and R 5 When represents an isopropyl group, the compound represented by formula (2) is an aluminum alkylacetoacetate diisopropylate.

[0053] The surface treatment layer is preferably a titanate coupling agent treatment layer or an aluminate coupling agent treatment layer, since the zeta potential (D-pH2) can be easily adjusted to a desired range. That is, the surface treatment layer preferably contains a component derived from a titanate coupling agent or an aluminate coupling agent.

[0054] The mass of the surface treatment layer is preferably 1 part by mass or more and 100 parts by mass or less, and more preferably 1 part by mass or more and 10 parts by mass or less, relative to 100 parts by mass of the substrate. When the mass of the surface treatment layer is within this range, it is possible to impart appropriate hydrophobicity to the toner particles.

[0055] The alumina particles may further include other layers in addition to the conductive layer and the surface treatment layer. The conductive layer may directly or indirectly coat the substrate. The surface treatment layer may directly or indirectly coat the conductive layer. The conductive layer and the surface treatment layer are each preferably a single layer, but may be multilayered.

[0056] <Organic particles> When the toner according to this embodiment is used as a one-component developer, the toner particles form a toner layer (toner chain) supported by magnetic binding force on the developing roller. By providing organic particles as an external additive, the toner chain becomes fluid when passing through the nip between the developing roller and the regulating member, promoting its replacement and improving the developability of the toner.

[0057] In order to fluidize the toner chains and promote their replacement when passing through the nip between the developing roller and the regulating member, the number average primary particle diameter of the organic particles is preferably 30 nm or more and 80 nm or less, and more preferably 35 nm or more and 75 nm or less.

[0058] The organic particles are preferably resin particles. The resin constituting the resin particles is preferably an acrylic resin or a styrene-acrylic resin, more preferably an acrylic resin. The acrylic resin is a polymer of at least one acrylic acid-based monomer.

[0059] Examples of acrylic acid monomers include (meth)acrylic acid, (meth)acrylamide, (meth)acrylonitrile, (meth)acrylic acid alkyl esters, (meth)acrylic acid hydroxyalkyl esters, and alkylene glycol di(meth)acrylates. Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, and 2-ethylhexyl (meth)acrylate. Examples of (meth)acrylic acid hydroxyalkyl esters include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate. Examples of alkylene glycol di(meth)acrylates include ethylene glycol di(meth)acrylate.

[0060] As the acrylic acid-based monomer, (meth)acrylic acid alkyl ester and alkylene glycol di(meth)acrylate are preferred, methyl (meth)acrylate, n-butyl (meth)acrylate, and ethylene glycol di(meth)acrylate are more preferred, and methyl methacrylate, n-butyl acrylate, and ethylene glycol dimethacrylate are even more preferred.

[0061] The amount of organic particles is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, per 1,000 parts by mass of toner base particles. The amount of organic particles is preferably 1 to 10 parts by mass, more preferably 1 to 5 parts by mass, per 100 parts by mass of external additive. When the external additive further contains silica particles in addition to the organic particles, the amount of organic particles is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass, per 10 parts by mass of silica particles.

[0062] <Silica particles> Examples of silica particles include fumed silica and wet silica (more specifically, silica produced by a precipitation method, sol-gel silica, etc.). The surface of the silica particles may be rendered hydrophobic and / or positively charged by a surface treatment agent. Examples of surface treatment agents include silane coupling agents (more specifically, 3-aminopropyltrimethoxysilane, etc.), silazane compounds (more specifically, linear silazane compounds, cyclic silazane compounds, etc.), polysiloxanes (more specifically, dimethylpolysiloxane, etc.), and silicone oils (more specifically, dimethylsilicone oil, etc.).

[0063] The amount of silica particles is preferably 1 part by mass to 100 parts by mass, and more preferably 1 part by mass to 20 parts by mass, relative to 1000 parts by mass of toner base particles, and is preferably 30 parts by mass to 60 parts by mass, and more preferably 45 parts by mass to 55 parts by mass, relative to 100 parts by mass of external additive.

[0064] <Other external additive particles> Other external additive particles include, for example, titanium oxide particles, magnesium oxide particles, zinc oxide particles, and particles of organic acid compounds such as fatty acid metal salts (specifically, zinc stearate, etc.).

[0065] [Toner base particles] The toner base particles contain a binder resin and a magnetic powder. The toner base particles may further contain a release agent and a charge control agent, if necessary. From the viewpoint of forming a good image, the volume median diameter (D 50 ) is preferably 4 μm or more and 9 μm or less. The toner base particles may be non-encapsulated toner particles that do not have a shell layer. Alternatively, they may be encapsulated toner particles that have a shell layer. In the encapsulated toner particles, the toner base particles have, for example, a toner core containing a binder resin and a magnetic powder, and a shell layer that covers the surface of the toner core. The binder resin, magnetic powder, release agent, and charge control agent will be described below.

[0066] <Binder resin> The toner base particles contain, for example, a binder resin as a main component. From the viewpoint of providing a toner with excellent low-temperature fixability, the toner base particles preferably contain a thermoplastic resin as the binder resin, and more preferably contain the thermoplastic resin in a proportion of 85% by mass or more of the total binder resin. Examples of thermoplastic resins include styrene resins, acrylic ester resins, olefin resins (more specifically, polyethylene resins, polypropylene resins, etc.), vinyl resins (more specifically, vinyl chloride resins, polyvinyl alcohol, vinyl ether resins, N-vinyl resins, etc.), polyester resins, polyamide resins, and urethane resins. Copolymers of these resins, i.e., copolymers in which any repeating unit is introduced into the above resins (more specifically, styrene-acrylic resins, styrene-butadiene resins, etc.), can also be used as the binder resin. The binder resin is preferably a polyester resin or a styrene-acrylic resin.

[0067] The polyester resin preferably has a mass average molecular weight of 3,000 or more and 150,000 or less, more preferably 3,000 or more and 10,000 or less. The polyester resin preferably has an acid value of 5.0 mgKOH / g or more and 15.0 mgKOH / g or less. The polyester resin preferably has a softening point of 90.0°C or more and 130.0°C or less. The polyester resin preferably has a glass transition point of 50.0°C or more and 60.0°C or less. Examples of polyester resins include non-crosslinked polyester resins that are not crosslinked with a crosslinking agent, and crosslinked polyester resins that are crosslinked with a crosslinking agent.

[0068] The mass average molecular weight of the styrene acrylic resin is preferably 3,000 or more and 150,000 or less, and more preferably 100,000 or more and 130,000 or less. The softening point of the styrene acrylic resin is preferably 90.0°C or more and 130.0°C or less. The glass transition point of the styrene acrylic resin is preferably 50.0°C or more and 60.0°C or less.

[0069] The content of the binder resin relative to the mass of the toner base particles is preferably 30% by mass or more and 70% by mass or less, and more preferably 40% by mass or more and 60% by mass or less.

[0070] <Magnetic powder> Examples of materials for the magnetic powder include ferromagnetic metals (more specifically, iron, cobalt, nickel, and alloys containing one or more of these metals), ferromagnetic metal oxides (more specifically, ferrite, magnetite, chromium dioxide, etc.), and materials that have been subjected to ferromagnetic treatment (more specifically, carbon materials that have been given ferromagnetism by heat treatment, etc.).

[0071] To prevent metal ions (e.g., iron ions) from eluting from the magnetic powder, it is preferable to subject the magnetic powder to a surface treatment. By preventing metal ions from eluting from the magnetic powder, adhesion between toner base particles is further prevented.

[0072] The electrical resistivity of the magnetic powder is 1×10 5Ω cm or more 1×10 8 It is preferable that the resistance is Ω·cm or less, and 2×10 5 Ω cm or more 8×10 7 The number average primary particle size of the magnetic powder is preferably 0.1 μm or more and 1.0 μm or less, and more preferably 0.1 μm or more and 0.3 μm or less.

[0073] From the viewpoint of forming high-quality images, the content of the magnetic powder is preferably 20 parts by mass or more and 120 parts by mass or less, and more preferably 30 parts by mass or more and 50 parts by mass or less, per 100 parts by mass of the binder resin.

[0074] <Release agent> The release agent is used, for example, for the purpose of imparting offset resistance to the toner. Examples of the release agent include aliphatic hydrocarbon waxes, oxides of aliphatic hydrocarbon waxes, plant-derived waxes, animal-derived waxes, mineral-derived waxes, ester waxes mainly composed of fatty acid esters, and waxes in which fatty acid esters are partially or completely deoxidized. Plant-derived waxes are preferred. Examples of plant-derived waxes include candelilla wax, carnauba wax, Japan wax, jojoba wax, and rice wax. Carnauba wax is preferred as the plant-derived wax. From the viewpoint of imparting sufficient offset resistance to the toner, the content of the release agent is preferably 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the binder resin.

[0075] <Charge control agent> Charge control agents are used, for example, for the purpose of providing a toner with better charge stability or excellent charge buildup characteristics. The charge buildup characteristics of a toner are an indicator of whether the toner can be charged to a predetermined charge level in a short period of time. The cationic nature of the toner base particles can be enhanced by incorporating a positively chargeable charge control agent (more specifically, pyridine, nigrosine, quaternary ammonium salt, or the like) into the toner base particles. From the viewpoint of imparting sufficient chargeability to the toner, the content of the charge control agent is preferably 1 part by mass or more and 20 parts by mass or less per 100 parts by mass of the binder resin. However, if sufficient chargeability is ensured in the toner, it is not necessary to incorporate a charge control agent into the toner base particles.

[0076] <Other ingredients> The toner base particles may further contain additives as needed. The toner base particles may further contain a black colorant as needed to adjust the color tone.

[0077] [Toner manufacturing method] The toner manufacturing method according to this embodiment includes, for example, a toner base particle manufacturing step and an external addition step. The toner base particle manufacturing step is preferably carried out by a pulverization method or an aggregation method, and more preferably carried out by a pulverization method. In the external addition step, an external additive containing alumina particles is adhered to the surface of the toner base particles. The method for adhering the external additive to the surface of the toner base particles is not particularly limited, but examples thereof include a method in which the toner base particles and the external additive are stirred with a mixer or the like.

[0078] Although the toner according to the present invention has been described above, a toner different from the above toner (hereinafter referred to as a toner of another embodiment) can also be suitably used. The toner of another embodiment has the following configuration. That is, the toner includes toner particles, and the toner particles include toner base particles and an external additive provided on the surface of the toner base particles. The toner base particles contain a binder resin and a magnetic powder. The external additive includes alumina particles. The alumina particles have a number-average primary particle diameter of 150 nm or more and 400 nm or less. The alumina particles include a substrate containing alumina, a conductive layer coating the substrate, and a surface treatment layer coating the conductive layer. The conductive layer contains a metal oxide having conductivity. The metal oxide contains tin and antimony. The total mass of tin and antimony in the metal oxide is 10.0 parts by mass or more and 50.0 parts by mass or less per 100.0 parts by mass of the substrate. The surface treatment layer is a titanate coupling agent treatment layer or an aluminate coupling agent treatment layer. The toner of another embodiment has been described above. According to the toner of another embodiment, even when a large number of sheets are printed, an image having a desired image density and little fog can be formed. In the toner of another embodiment, the time constant and zeta potential (D-pH2) of the toner are not particularly limited. [Example]

[0079] The present invention will be described in more detail below using examples, but the present invention is not limited to the scope of the examples.

[0080] [Preparation of alumina particles] Alumina particles (AA) to (AI) used as external additives were prepared by the following method. The composition of each of the alumina particles (AA) to (AI) is shown in Table 1. To prepare these alumina particles, one of substrates (X1) to (X4) prepared by the following method was used.

[0081] <Preparation of substrate (X1)> Aluminum isopropoxide was hydrolyzed to obtain aluminum hydroxide. The aluminum hydroxide was pulverized using a jet mill and calcined at 1170°C to obtain alumina. 100 parts by mass of alumina and 1 part by mass of propylene glycol as a grinding aid were mixed for 6 hours using a vibration mill filled with 15 mm diameter alumina beads, and the alumina was pulverized. Alumina particles (a) with a number-average primary particle diameter of 0.2 μm were obtained by pulverization. 20 parts by mass of alumina particles (a) and 80 parts by mass of an aluminum chloride aqueous solution (pH = 2) were mixed for 24 hours using a ball mill filled with 700 parts by mass of 2 mm diameter alumina beads to obtain alumina slurry (b). Next, 241.3 g of aluminum chloride hexahydrate (AlCl3·6H2O, Wako Pure Chemical Industries, Ltd.) was mixed with pure water to obtain a 1 L volume of aluminum chloride aqueous solution (c). A vessel was charged with 250 mL of aqueous aluminum chloride solution (c) and 7.1 g of alumina slurry (b). While stirring the contents of the vessel at 25°C, 39.3 g of 25% aqueous ammonia (Wako Pure Chemical Industries, Ltd.) was supplied to the vessel at a supply rate of 4 g / min using a micro rotary pump. When the supply was completed, the contents of the vessel had become slurry (d) in which aluminum hydrolyzate had precipitated. The pH of slurry (d) was 3.8. The slurry (d) was allowed to stand at 25°C to gel, yielding a gelled product. The water in the gelled product was evaporated in a thermostatic bath at 60°C, yielding a dry powder of aluminum hydrolyzate. The aluminum hydrolyzate was crushed in a mortar to obtain a crushed product. The crushed product was placed in an alumina crucible. Using a box-type electric furnace, the crushed material placed in an alumina crucible was heated from room temperature to 920°C at a temperature increase rate of 300°C / hour under atmospheric conditions, and then fired at 920°C for 3 hours. This yielded a substrate (X1) that was untreated alumina particles (alumina particles that had not been subjected to conductive treatment or surface treatment).

[0082] <Preparation of substrate (X2)> Substrate (X2) was prepared in the same manner as substrate (X1), except that the alumina beads having a diameter of 15 mm were replaced with alumina beads having a diameter of 5 mm.

[0083] <Preparation of substrate (X3)> Substrate (X3) was prepared in the same manner as substrate (X1), except that the 3-hour firing was changed to 1 hour firing and the 15 mm diameter alumina beads were changed to 5 mm diameter alumina beads.

[0084] <Preparation of substrate (X4)> Substrate (X4) was prepared in the same manner as substrate (X1), except that the calcination time was changed from 3 hours to 5 hours.

[0085] <Preparation of alumina particles (AA)> (Conductive treatment) Using a PRIMIX Corporation "Homomixer MARK II 2.5," 100.0 g of substrate (X1) was dispersed in 1 L of water to obtain dispersion (e). 11.6 g of stannous chloride pentahydrate (SnCl4·5H2O), a conductive treatment agent, was dissolved in 100 mL of separately prepared 2 N hydrochloric acid to obtain solution (f). Dispersion (e) was then placed in a container and heated to 70°C. Solution (f) and 12 g of 5 N aqueous ammonia solution were added dropwise to the heated dispersion (e) over 40 minutes. During the parallel addition, the liquid in the container was maintained at 70°C, and the amount of addition was adjusted so that the pH of the liquid in the container was maintained between 7 and 8. 37.9 g of antimony trichloride (SbCl3), a conductive treatment agent, and 5.4 g of stannous chloride pentahydrate (SnCl4·5H2O), another conductive treatment agent, were dissolved in 450 mL of separately prepared 2N hydrochloric acid to obtain solution (g). Solution (g) and 12 g of 5N aqueous ammonia were then added dropwise to the solution in the container over 40 minutes. During the parallel addition, the solution in the container was maintained at 70°C, and the amount added was adjusted so that the pH of the solution in the container was maintained between 7 and 8. The solution in the container was then filtered to obtain a residue. Water was added to the residue, which was then filtered again to obtain a wet cake of conductively treated alumina. The wet cake of conductively treated alumina was dried at 110°C for 12 hours to obtain a dried powder. The dried powder was then calcined for 1 hour in a nitrogen gas flow at a rate of 1 L / min in an electric furnace at 500°C. This resulted in a conductive treated substrate (a substrate coated with a conductive layer).The volume resistivity of the conductive treated substrate was 1.3 Ω·cm.

[0086] (Surface treatment) Using a ball mill, 50.0 g of the obtained conductively treated substrate, 2.5 g of a surface treatment agent, a titanate coupling agent (Ajinomoto Co., Inc.'s "Plenact (registered trademark) TTS", isopropyl triisostearoyl titanate), and 40 mL of toluene were mixed for 2 hours to obtain a slurry. The slurry was dried at 110°C for 12 hours to obtain a dried product. The dried product was pulverized using a pulverizer at a pulverization pressure of 0.6 MPa. Alumina particles (AA) were thus obtained. The number-average primary particle diameter of the alumina particles (AA) was 250 nm.

[0087] <Preparation of alumina particles (AB) to (AI)> Alumina particles (AB) to (AI) were prepared by the same method as that for preparing alumina particles (AA), except for the following changes.

[0088] In the preparation of the alumina particles (AB), the substrate (X1) was changed to the substrate (X2).

[0089] In preparing the alumina particles (AC), the surface treatment agent was changed from a titanate coupling agent (Ajinomoto Co., Inc.'s "Plenact (registered trademark) TTS") to an aluminate coupling agent (Ajinomoto Co., Inc.'s "Plenact (registered trademark) AL-M", aluminum alkylacetoacetate diisopropylate).

[0090] In the preparation of alumina particles (AD), the total amount of stannous chloride pentahydrate added was changed from 17.0 g to 8.5 g, and the amount of antimony trichloride added was changed from 37.9 g to 18.0 g.

[0091] In the preparation of alumina particles (AE), the total amount of stannous chloride pentahydrate added was changed from 17.0 g to 3.4 g, and the amount of antimony trichloride added was changed from 37.9 g to 7.6 g.

[0092] In the preparation of alumina particles (AF), the total amount of stannous chloride pentahydrate added was changed from 17.0 g to 42.5 g, and the amount of antimony trichloride added was changed from 37.9 g to 94.8 g.

[0093] In preparing the alumina particles (AG), the surface treatment agent was changed from 2.5 g of titanate coupling agent ("Plenact (registered trademark) TTS" manufactured by Ajinomoto Co., Inc.) to 0.7 g of 3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.3 g of hexamethyldisilazane.

[0094] In the preparation of alumina particles (AH), the substrate (X1) was changed to the substrate (X3).

[0095] In the preparation of alumina particles (AI), the substrate (X1) was changed to the substrate (X4).

[0096] [Preparation of organic particles] Organic particles (OA) and (OB) to be used as external additives were prepared by the following method.

[0097] <Preparation of organic particles (OA)> A flask equipped with a dropping funnel, a stirrer, a nitrogen gas inlet tube, a thermometer, and a reflux condenser was charged with 200 g of ion-exchanged water and 3 g of sodium lauryl sulfate. The contents of the flask were heated to 80°C under a nitrogen gas atmosphere. While maintaining the temperature of the contents of the flask at 80°C, 1 g of ammonium persulfate was added to the flask, and the monomer mixture was then added dropwise over 1 hour. The monomer mixture consisted of 30 g of methyl methacrylate, 30 g of n-butyl acrylate, and 40 g of ethylene glycol dimethacrylate. After the dropwise addition, the contents of the flask were stirred for an additional 1 hour to obtain a reaction solution. The reaction solution was cooled to room temperature. The reaction solution was filtered through a 300-mesh sieve to obtain an emulsion containing organic particles (OA). The emulsion was dried to obtain organic particles (OA).

[0098] <Preparation of organic particles (OB)> Organic particles (OB) were obtained in the same manner as in the preparation of organic particles (OA), except that the amount of sodium lauryl sulfate added was changed from 3 g to 10 g.

[0099] [Preparation of silica particles] Silica particles (SA) to (SC) used as external additives were prepared by the following method.

[0100] <Preparation of Silica Particles (SA)> 30 g of dimethylpolysiloxane (manufactured by Shin-Etsu Chemical Co., Ltd.) and 15 g of 3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.) were dissolved in 200 g of toluene to obtain a solution. The solution was diluted 10 times with toluene to obtain a diluted solution. 200 g of fumed silica (manufactured by Nippon Aerosil Co., Ltd., "AEROSIL® 130") was added dropwise to the fumed silica over 10 minutes while stirring at a stirring speed of 120 rpm. The fumed silica to which the diluted solution had been added dropwise was stirred at a stirring speed of 120 rpm for 30 minutes while irradiating with ultrasound to obtain a mixture. An ultrasonic cleaner (manufactured by NND Corporation, "US-30D") was used for ultrasonic irradiation. The ultrasonic irradiation conditions were an output of 850 W and a frequency of 38 kHz. The mixture was heated in a constant temperature bath at 150°C. Toluene was removed from the mixture using a rotary evaporator to obtain a solid. The solid was dried using a vacuum dryer set at 50°C until no weight loss was observed, yielding a dried product. The dried product was heated in an electric furnace at 200°C for 3 hours under a nitrogen stream to yield a coarse powder. The coarse powder was pulverized using a jet mill and collected using a bag filter to obtain silica particles (SA).

[0101] <Preparation of Silica Particles (SB)> Silica particles (SB) were obtained in the same manner as in the preparation of silica particles (SA), except that 200 g of fumed silica ("AEROSIL (registered trademark) 130" manufactured by Nippon Aerosil Co., Ltd.) was changed to 150 g of wet silica ("E-220A" manufactured by Tosoh Silica Corporation, silica produced by a precipitation method).

[0102] <Preparation of Silica Particles (SC)> Silica particles (SC) were obtained by the same method as for preparing silica particles (SA), except that 200 g of fumed silica ("AEROSIL (registered trademark) 130" manufactured by Nippon Aerosil Co., Ltd.) was changed to 150 g of wet silica ("QSG-30" manufactured by Shin-Etsu Chemical Co., Ltd., silica produced by the sol-gel method).

[0103] [Toner Preparation] Toners (TA-1) to (TA-9) and (TB-1) to (TB-6) were prepared by the following method.

[0104] <Preparation of Toner (TA-1)> (Preparation of Toner Base Particles) Using an FM mixer ("FM-20B" manufactured by Nippon Coke and Engineering Co., Ltd.), 1100 g of polyester resin A (manufactured by Kao Corporation, non-crosslinked polyester resin, Mw: 6500, acid value: 8.2 mgKOH / g, Tm: 96.3°C, Tg: 54.4°C) as a binder resin, 1090 g of polyester resin B (manufactured by Kao Corporation, crosslinked polyester resin, Mw: unmeasurable due to crosslinked polyester resin, acid value: 11.8 mgKOH / g, Tm: 118.5°C, Tg: 59.6°C, gel component concentration: 36% by mass) as a binder resin, and 1090 g of magnetic powder ("MRO-15A" manufactured by Toda Kogyo Co., Ltd., electrical resistivity: 2 × 10 5 1450 g of acrylic resin (resistivity: Ω·cm), 200 g of a charge control agent ("FCA-482PLV" manufactured by Fujikura Kasei Co., Ltd.), and 160 g of carnauba wax ("Carnauba Wax No. 1" manufactured by Kato Yoko Co., Ltd.) as a release agent were mixed at 200 rpm for 5 minutes to obtain a mixture.

[0105] The resulting mixture was melt-kneaded using a twin-screw extruder (Toshiba Machine Co., Ltd., "TEM-26SS") at a cylinder temperature of 120°C, a shaft rotation speed of 100 rpm, and a flow rate of 75 g / min. The resulting kneaded mixture was cooled. The cooled kneaded mixture was coarsely pulverized using a pulverizer (formerly Toa Kikai Seisakusho, "Rotoplex (registered trademark) 16 / 8 type") to obtain a coarsely pulverized product. The coarsely pulverized product was finely pulverized using a pulverizer (Freund Turbo Corporation, "Turbo Mill TA type") to obtain a finely pulverized product. The finely pulverized product was then fed into a jet mill (Hosokawa Micron Corporation, "MJT-1"), where it was further pulverized and classified. Toner base particles were thus obtained.

[0106] (external attachment) 1 kg of the obtained toner base particles, 11 g of silica particles (SA) as external additives, 10 g of alumina particles (AA) as external additives, and 1 g of organic particles (OA) as external additives were mixed using an FM mixer ("FM-10" manufactured by Nippon Coke & Engineering Co., Ltd.) at a rotation speed of 3,500 rpm for 5 minutes. In this way, the external additives were adhered to the toner base particles. The toner base particles with the adhered external additives were sieved using a 100 mesh (opening 150 μm) sieve to obtain toner (TA-1).

[0107] <Preparation of Toners (TA-2) to (TA-8), (TB-1) to (TB-2), and (TB-4) to (TB-6)> Toners (TA-2) to (TA-8), (TB-1) to (TB-2), and (TB-4) to (TB-6) were obtained by the same method as for preparing toner (TA-1), except that the binder resin, magnetic powder, silica particles, alumina particles, and organic particles shown in Table 2 were used.

[0108] <Preparation of Toner (TA-9)> Toner (TA-9) was obtained in the same manner as in the preparation of toner (TA-1), except that 1100 g of polyester resin A and 1090 g of polyester resin B were changed to 2190 g of styrene acrylic resin C ("Tiz-524" manufactured by Fujikura Chemical Co., Ltd., Mw: 117000, Tm: 119.0°C, Tg: 55.9°C).

[0109] <Preparation of Toner (TB-3)> Toner (TB-3) was obtained in the same manner as in the preparation of toner (TA-1), except that no alumina particles were used.

[0110] [measurement] <Measurement of number average primary particle size> A scanning electron microscope (JEOL Ltd., "JSM-6700F") was used to take a cross-sectional image of the toner (magnification: 30,000 times). Based on the cross-sectional image, the circle-equivalent diameters of 100 external additive particles (specifically, either alumina particles (AA) to (AI) or organic particles (OA) to (OB)) were analyzed using image analysis software (Mitani Corporation, "WinROOF"), and the average value was taken as the number-average primary particle diameter. The number-average primary particle diameters of alumina particles (AA) to (AI) and organic particles (OA) to (OB) are shown in Table 2.

[0111] <Zeta potential measurement> Zeta potential measurements were performed in an environment at 20°C. A 10% by weight surfactant aqueous solution was prepared by mixing 10 parts by weight of a nonionic surfactant (Kao Corporation's "Emulgen (registered trademark) 120," component: polyoxyethylene lauryl ether, HLB value: 15.3) with 90 parts by weight of ion-exchanged water. 20 mg of the measurement target (specifically, any of toners (TA-1) to (TA-9) and (TB-1) to (TB-6)) was added to 2 mL of this surfactant aqueous solution and ultrasonically irradiated to obtain a toner dispersion. The ultrasonic irradiation conditions were a frequency of 40 kHz, an output of 500 W, and an irradiation time of 1 minute. The toner dispersion was diluted 50 times with ion-exchanged water to obtain a diluted toner dispersion. Using a neodymium magnet (residual magnetic flux density: 1.25 T), the diluted toner dispersion was magnetically separated into a sediment attracted to the magnet and a supernatant liquid not attracted to the magnet. The separated supernatant was used as the measurement solution (LU).

[0112] The precipitate separated above was added to 2 mL of the surfactant aqueous solution and subjected to ultrasonic irradiation to obtain a dispersion of the precipitate. The ultrasonic irradiation conditions were a frequency of 40 kHz, an output of 500 W, and an irradiation time of 1 minute. The dispersion of the precipitate was diluted 50 times with ion-exchanged water to obtain a diluted dispersion of the precipitate. The obtained diluted dispersion of the precipitate was used as the test solution (LD).

[0113] The pH of the test solution (LU) was adjusted using 0.1N aqueous sodium hydroxide and 0.1N aqueous nitric acid to obtain a test solution (LU) with a pH of 2 and a test solution (LU) with a pH of 5. The pH of the test solution (LD) was also adjusted using 0.1N aqueous sodium hydroxide and 0.1N aqueous nitric acid to obtain a test solution (LD) with a pH of 2 and a test solution (LD) with a pH of 5. The zeta potential of the test solution (more specifically, the pH of the test solution (LU), the pH of the test solution (LU), the pH of the test solution (LD), and the pH of the test solution (LD)) was measured using a laser Doppler zeta potential meter ("ELSZ-1000" manufactured by Otsuka Electronics Co., Ltd.) to obtain the zeta potential distribution. The zeta potential distribution was shown as a graph with the zeta potential (unit: mV) on the horizontal axis and the intensity on the vertical axis. The zeta potential value (peak value) and half-width of the test solution were calculated from the zeta potential distribution.

[0114] The zeta potential value and half-width of the measurement solution (LD) at pH 2 are shown in the "Value" and "Half-width" columns of "pH 2" under "Precipitate" in Table 3, respectively. The zeta potential value and half-width of the measurement solution (LD) at pH 5 are shown in the "Value" and "Half-width" columns of "pH 5" under "Precipitate" in Table 3, respectively. The zeta potential value and half-width of the measurement solution (LU) at pH 2 are shown in the "Value" and "Half-width" columns of "pH 2" under "Supernatant" in Table 3, respectively. The zeta potential value and half-width of the measurement solution (LU) at pH 5 are shown in the "Value" and "Half-width" columns of "pH 5" under "Supernatant" in Table 3, respectively.

[0115] <Time constant measurement> The time constant was measured under an environment of 20°C temperature and 65% RH humidity. 20 mg of the measurement object (specifically, any of the toners (TA-1) to (TA-9) and (TB-1) to (TB-6)) was sandwiched between the electrodes of an "SE-43 type powder electrode" manufactured by Ando Electric Co., Ltd. Then, a load of 40 kgf / cm was applied. 2 The test object was pelletized (100 μm thick) by adding a voltage of 1 V. Next, a frequency response analyzer (Solartron Analytical's "1260 Frequency Response Analyzer") was connected to both ends of the electrodes. The electrical characteristics of the test object were measured using the frequency response analyzer, and a Cole-Cole plot was created. The electrical characteristics were measured under the following conditions: maximum to minimum voltage (Vpp) of 1 V, frequency of 100 kHz to 40 Hz (5 pt / decade), and measurement cycles of 3. The electrical resistance and dielectric constant of the test object were measured by fitting the test object as an RC equivalent parallel circuit. The time constant [seconds] (the product of the electrical resistance and dielectric constant) of the test object was calculated based on the electrical resistance and dielectric constant of the test object. The calculated time constants of the test object are shown in Table 3.

[0116] [evaluation] The image density and fogging resistance of each toner were evaluated by the following methods. The evaluation results are shown in Table 3.

[0117] <Evaluation device and evaluation environment> A monochrome multifunction printer (TASKalfa (registered trademark) 3212i manufactured by Kyocera Document Solutions Inc.) was used as the evaluation machine. Toner was placed in the developing device of the evaluation machine. In addition, replenishment toner (specifically, the same toner as the toner placed in the developing device) was placed in the toner container of the evaluation machine. The evaluation was carried out in an environment with a temperature of 23.0°C and a humidity of 50.0% RH (NN environment).

[0118] <Evaluation of image density> Using an evaluation machine, image I (an image including a solid image area and a text image area with a print rate of 1%) was printed on both sides of 5,000 sheets of paper. The reflection density (initial ID) of the solid image area of ​​the first printed image I (image I printed on the front side of the first sheet) was measured. In addition, the reflection density (post-print ID) of the solid image area of ​​the last printed image I (image I printed on the back side of the 5,000th sheet) was measured. A white light meter (TC-6DX manufactured by Tokyo Denshoku Co., Ltd.) was used to measure the reflection density. The image density was evaluated according to the following criteria.

[0119] (Image density evaluation criteria) Good: ID is 1.20 or higher Bad: ID less than 1.20

[0120] <Evaluation of fogging resistance> After the evaluation of the image density described above, Image II (a character image with a printing rate of 5%) was printed on 1,000 sheets of paper using the evaluation machine. For each printed sheet, the reflection density X of the non-printed area (white area) was measured using a white photometer (Tokyo Denshoku Co., Ltd., "TC-6DX"). The reflection density Y of the unprinted paper was also measured using a white photometer (Tokyo Denshoku Co., Ltd., "TC-6DX"). Then, for each printed sheet, the fog density was calculated using the formula "Fog density = Reflection density X - Reflection density Y," and the maximum value was used as the evaluation value of the fog density (FD). Fog resistance was evaluated based on the following criteria:

[0121] (Evaluation Criteria for Fog Resistance) Good: FD is 0.008 or less Poor: FD is greater than 0.008

[0122] The meanings of the terms in Tables 1 to 3 are as follows: ·SnCl4·5H2O: stannic chloride pentahydrate SbCl3: Antimony trichloride Sn in the converted amount column: The mass of tin (Sn) contained in the metal oxide obtained when stannic chloride pentahydrate is reacted at a yield of 100%. The mass of tin was calculated using the formula "Mass of tin = Amount of stannic chloride pentahydrate added × Atomic weight of tin / Formula weight of stannic chloride pentahydrate = Amount of stannic chloride pentahydrate added × 118.7 / 350.5". Sb in the converted amount column: Mass of antimony (Sb) contained in the metal oxide obtained when antimony trichloride is reacted at a yield of 100%. The mass of antimony was calculated using the formula "Mass of antimony = Amount of antimony trichloride added × Atomic weight of antimony / Formula weight of antimony trichloride = Amount of antimony trichloride added × 121.8 / 228.1". Sn+Sb in the converted amount column: The total mass of tin and antimony in the metal oxide. This is the sum of the Sn value in the converted amount column and the Sb value in the converted amount column. TTS: Titanate coupling agent (Ajinomoto Co., Inc.'s "Plenact (registered trademark) TTS", isopropyl triisostearoyl titanate) AL-M: Aluminate coupling agent (Ajinomoto Co., Inc.'s "Plenact (registered trademark) AL-M", aluminum alkyl acetoacetate diisopropylate) AS: 3-aminopropyltrimethoxysilane HDS: Hexamethyldisilazane PES: Polyester resin A and polyester resin B SA: Styrene acrylic resin C MRO-15A: Magnetic powder (Toda Kogyo Co., Ltd. "MRO-15A", electrical resistivity: 2 x 10 5 Ω·cm) MTS-D3: Magnetic powder ("MTS-D3" manufactured by Toda Kogyo Co., Ltd., electrical resistivity: 8 x 10 7 Ω·cm) Silica: Silica particles Alumina: Alumina particles ·Organic: organic particles Diameter: Number average primary particle diameter ·NG: Bad

[0123] [Table 1]

[0124] [Table 2]

[0125] [Table 3]

[0126] As shown in Table 3, the time constant of toner (TB-1) was more than 10.0 seconds. As shown in Table 3, the evaluation of the image density after printing of toner (TB-1) was poor.

[0127] As shown in Table 3, the time constant of toner (TB-2) was less than 1.0 second. As shown in Table 3, the evaluation of the fogging resistance of toner (TB-2) was poor.

[0128] As shown in Table 2, toner (TB-3) did not contain alumina particles as an external additive. Furthermore, as shown in Table 3, the zeta potential (D-pH2) of toner (TB-3) was less than 0.0 mV. As shown in Table 3, the image density of toner (TB-3) after repeated printing was evaluated as poor.

[0129] As shown in Table 2, the number average primary particle diameter of the alumina particles in the toner (TB-4) was less than 150 nm. As shown in Table 3, the evaluation of the image density after printing of the toner (TB-4) was poor.

[0130] As shown in Table 2, the number average primary particle diameter of the alumina particles in the toner (TB-5) was greater than 400 nm. As shown in Table 3, the image density of the toner (TB-5) after repeated printing was evaluated as poor.

[0131] As shown in Table 3, the zeta potential (D-pH2) of the toner (TB-6) was greater than 20.0 mV. As shown in Table 3, the evaluation of the image density and the evaluation of the fogging resistance of the toner (TB-6) after printing were poor.

[0132] On the other hand, as shown in Tables 2 and 3, toners (TA-1) to (TA-9) had the following configurations: The external additives provided in the toner contained alumina particles. The number average primary particle diameter of the alumina particles was 150 nm or more and 400 nm or less. The time constant of the toner was 1.0 second or more and 10.0 seconds or less. The zeta potential (D-pH2) was 0.0 mV or more and 20.0 mV or less. As shown in Table 3, the evaluation of the image density and the evaluation of the fogging resistance after printing of toners (TA-1) to (TA-9) were both good.

[0133] From the above, it is judged that the toners of the present invention, including toners (TA-1) to (TA-9), can form images with desired image density and little fog, even when printing multiple sheets. [Industrial Applicability]

[0134] The toner according to the present invention can be used to form images in, for example, a copier, a printer, or a multifunction machine.

Claims

1. A toner comprising toner particles, The toner particles include toner base particles and an external additive provided on the surface of the toner base particles, the toner base particles contain a binder resin and a magnetic powder, the external additive contains alumina particles, the alumina particles have a number average primary particle diameter of 150 nm or more and 400 nm or less; the alumina particles include a substrate containing alumina, a conductive layer covering the substrate, and a surface treatment layer covering the conductive layer; the conductive layer contains a metal oxide having electrical conductivity, the metal oxide contains tin and antimony; a total mass of the tin and the antimony in the metal oxide is 10.0 parts by mass or more and 50.0 parts by mass or less relative to 100.0 parts by mass of the base; The surface treatment layer is a titanate coupling agent treatment layer or an aluminate coupling agent treatment layer. The toner is a treatment layer.

2. 2. The toner according to claim 1, wherein the external additive further contains organic particles, and the number average primary particle diameter of the organic particles is 30 nm or more and 80 nm or less.

Images