White toner, electrostatic image developer, toner cartridge, process cartridge, image forming apparatus and image forming method

Abstract

To provide a white toner which is less likely to accelerate wear of a cleaning blade of an intermediate transfer body.SOLUTION: An white toner is provided, comprising toner particles containing a binder resin including a hybrid resin comprising an amorphous resin unit chemically bonded to a crystalline polyester resin unit, surface-treated titanium oxide, and a release agent. On a surface of the surface-treated titanium oxide, an atomic proportion of Al is 3 to 20 atomic%, inclusive, and an atomic proportion of Ti is in a rage of 5 to 15 atomic%, inclusive.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a toner for developing electrostatic images, which contains needle-shaped titanium oxide having an average aspect ratio in the range of 3 to 30 as a white pigment. Patent Document 2 discloses a toner for developing electrostatic images, which has toner particles containing a binder resin including a hybrid resin in which an amorphous resin unit other than a polyester resin and a crystalline polyester resin unit are chemically bonded, and a vinyl resin, and a release agent including a hydrocarbon wax. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2018-045225 [Patent Document 2] Japanese Patent Application Publication No. 2019-168618 Summary of the Invention [Problem to be solved by the invention]

[0004] An object of the present disclosure is to provide a white toner that is less likely to accelerate wear of the cleaning blade of an intermediate transfer body than a white toner in which the atomic ratio of Al on the surface of surface-treated titanium oxide is less than 3 atomic % or more than 20 atomic %, or the atomic ratio of Ti is more than 15 atomic %. [Means for solving the problem]

[0005] The means for solving the above problems include the following aspects.

[0006] <1> A white toner comprising toner particles containing a binder resin including a hybrid resin in which an amorphous resin unit and a crystalline polyester resin unit are chemically bonded, surface-treated titanium oxide, and a release agent, wherein the atomic ratio of Al on the surface of the surface-treated titanium oxide is 3 atomic % or more and 20 atomic % or less, and the atomic ratio of Ti is 5 atomic % or more and 15 atomic % or less. <2> the atomic ratio of Al on the surface of the surface-treated titanium oxide is 5 atomic % or more and 15 atomic % or less, and the atomic ratio of Ti is 6 atomic % or more and 12 atomic % or less; <1> The white toner according to claim 1. <3> the atomic ratio Al / Ti of Al to Ti on the surface of the surface-treated titanium oxide is 0.5 or more and 4.0 or less; <1> or <2> The white toner according to claim 1. <4> the atomic ratio Al / Ti of Al to Ti on the surface of the surface-treated titanium oxide is 1.0 or more and 3.5 or less; <1> ~ <3> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <5> the mass ratio of the amorphous resin unit in the hybrid resin is 50 mass% or more and 90 mass% or less; <1> ~ <4> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <6> the mass ratio of the amorphous resin unit in the hybrid resin is 60 mass% or more and 85 mass% or less; <1> ~ <5> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <7> a mass ratio of the hybrid resin to the surface-treated titanium oxide contained in the toner particles (hybrid resin / surface-treated titanium oxide) of 0.08 or more and 3.0 or less; <1> ~ <6> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <8> the ratio of the mass proportion (mass%) of the amorphous resin unit in the hybrid resin to the atomic proportion (atomic%) of Al on the surface of the surface-treated titanium oxide (mass proportion of amorphous resin unit / atomic proportion of Al) is 2.5 or more and 30 or less; <1> ~ <7> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <9> the content of the hybrid resin contained in the toner particles is 5% by mass or more and 60% by mass or less of the total mass of the toner particles; <1> ~ <8> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <10> The surface-treated titanium oxide has an average major axis length of 20 nm or more and 300 nm or less. <1> ~ <9> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <11> The surface-treated titanium oxide has a BET specific surface area of ​​4m 2 / g or more 12m 2 / g or less, <1> ~ <10> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <12> the content of the surface-treated titanium oxide contained in the toner particles is 20% by mass or more and 60% by mass or less of the total mass of the toner particles; <1> ~ <11> 10. The white toner according to claim 9, wherein the toner is a toner having a thickness of 100 nm or less. <13> <1> ~ <12> 10. An electrostatic image developer comprising the white toner according to any one of claims 1 to 9. <14> <1> ~ <12> 10. A toner cartridge that contains the white toner according to any one of claims 1 to 9 and is detachably mounted on an image forming apparatus. <15> <13> and a developing means for developing an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image, the process cartridge being detachably mountable to an image forming apparatus. <16> an image carrier; a charging means for charging the surface of the image carrier; an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier; <13> a developing means for developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer; an intermediate transfer member onto which the toner image formed on the surface of the image carrier is transferred; a primary transfer means for transferring the toner image formed on the surface of the image carrier to the surface of the intermediate transfer body; a secondary transfer means for transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of a recording medium; 、 a fixing means for fixing the toner image transferred onto the surface of the recording medium; an intermediate transfer body cleaning means having a blade that comes into contact with the surface of the intermediate transfer body and that cleans the toner remaining on the surface of the intermediate transfer body by using the blade after the toner image has been transferred onto the surface of the recording medium; An image forming apparatus comprising: <17> a charging step of charging the surface of the image carrier; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier; <13> 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 claim 1; a primary transfer step of transferring the toner image formed on the surface of the image carrier to the surface of an intermediate transfer member; a secondary transfer step of transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of a recording medium; 、 a fixing step of fixing the toner image transferred onto the surface of the recording medium; an intermediate transfer body cleaning step of contacting a blade with the surface of the intermediate transfer body after the toner image has been transferred to the surface of the recording medium to remove residual toner from the surface of the intermediate transfer body; An image forming method comprising the steps of: [Effects of the Invention]

[0007] <1> , <2> , <10> or <11> According to the present invention, a white toner is provided that is less likely to accelerate wear of the cleaning blade of an intermediate transfer body than a white toner in which the atomic ratio of Al on the surface of surface-treated titanium oxide is less than 3 atomic % or more than 20 atomic %, or the atomic ratio of Ti is more than 15 atomic %. <3> or <4> According to the present invention, a white toner is provided that is less likely to accelerate wear of the cleaning blade of the intermediate transfer body than a white toner in which the atomic weight ratio of Al to Ti on the surface of surface-treated titanium oxide is less than 0.5 or more than 4.0. <5> or <6> According to the invention, a white toner is provided which is less likely to accelerate wear of the cleaning blade of the intermediate transfer member than a white toner in which the mass ratio of the amorphous resin unit in the hybrid resin is less than 50 mass %. <7> According to the present invention, a white toner is provided that is less likely to accelerate wear of the cleaning blade of an intermediate transfer body than a white toner having a mass ratio of hybrid resin to surface-treated titanium oxide (hybrid resin / surface-treated titanium oxide) contained in the toner particles outside the above range. <8> According to the present invention, a white toner is provided that is less likely to accelerate wear of the cleaning blade of an intermediate transfer body than a white toner having a ratio of the mass proportion (mass %) of the amorphous resin unit in the hybrid resin to the atomic proportion (atomic %) of Al on the surface of surface-treated titanium oxide (mass proportion of amorphous resin unit / atomic proportion of Al) outside the above range. <9> According to the invention, a white toner is provided which is less likely to accelerate wear of the cleaning blade of the intermediate transfer member than a white toner having a hybrid resin content outside the above range. <12> According to the invention, a white toner having excellent whiteness is provided compared to a white toner in which the content of surface-treated titanium oxide contained in the toner particles is less than 20% by mass of the total toner particles.

[0008] <13> According to the present invention, an electrostatic image developer is provided that is less likely to accelerate wear of the cleaning blade of the intermediate transfer body than an electrostatic image developer that uses a white toner in which the atomic ratio of Al on the surface of surface-treated titanium oxide is less than 3 atomic % or more than 20 atomic %, or the atomic ratio of Ti is more than 15 atomic %. <14> According to the present invention, a toner cartridge is provided that is less likely to accelerate wear of the cleaning blade of the intermediate transfer body than a toner cartridge that uses a white toner in which the atomic ratio of Al on the surface of surface-treated titanium oxide is less than 3 atomic % or more than 20 atomic %, or the atomic ratio of Ti is more than 15 atomic %. <15> According to the present invention, a process cartridge is provided that is less likely to accelerate wear of the cleaning blade of the intermediate transfer body than a process cartridge that uses a white toner in which the atomic ratio of Al on the surface of surface-treated titanium oxide is less than 3 atomic % or more than 20 atomic %, or the atomic ratio of Ti is more than 15 atomic %. <16> According to the present invention, an image forming apparatus is provided that is less likely to accelerate wear of the cleaning blade of the intermediate transfer body than an image forming apparatus that uses a white toner in which the atomic ratio of Al on the surface of surface-treated titanium oxide is less than 3 atomic % or more than 20 atomic %, or the atomic ratio of Ti is more than 15 atomic %. <17> According to the present invention, an image forming method is provided which is less likely to accelerate wear of the cleaning blade of the intermediate transfer body than an image forming method using a white toner in which the atomic ratio of Al on the surface of surface-treated titanium oxide is less than 3 atomic % or more than 20 atomic %, or the atomic ratio of Ti is more than 15 atomic %. [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]

[0023] The following describes embodiments of the present disclosure. These descriptions and examples are intended to illustrate the embodiments and are not intended to limit the scope of the embodiments.

[0011] In the present disclosure, 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 the numerical ranges described in stages in this disclosure, the upper or lower limit value described in one numerical range may be replaced with the upper or lower limit value of another numerical range described in stages. In addition, in the numerical ranges described in this disclosure, the upper or lower limit value of that numerical range may be replaced with a value shown in the examples.

[0012] In the present disclosure, 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.

[0013] When embodiments of the present disclosure are described with reference to the drawings, the configuration of the embodiment is not limited to the configuration shown in the drawings. Furthermore, the sizes of the components in each drawing are conceptual, and the relative size relationships between the components are not limited to these.

[0014] In the present disclosure, each component may contain multiple corresponding substances. When referring to the amount of each component in a composition in the present disclosure, if multiple substances corresponding to each component are present in the composition, the total amount of the multiple substances present in the composition is meant unless otherwise specified. In the present disclosure, the composition may contain multiple types of particles corresponding to each component. When multiple types of particles corresponding to each component are present in the composition, the particle size of each component means the value for a mixture of the multiple types of particles present in the composition, unless otherwise specified.

[0015] In the present disclosure, "(meth)acrylic" is an expression that includes both acrylic and methacrylic, and "(meth)acrylate" is an expression that includes both acrylate and methacrylate.

[0016] In this disclosure, "toner for developing electrostatic images" is also referred to as "toner," "electrostatic image developer" is also referred to as "developer," and "carrier for developing electrostatic images" is also referred to as "carrier." In the present disclosure, a "hybrid resin in which an amorphous resin unit and a crystalline polyester resin unit are chemically bonded" is also referred to as a "hybrid resin."

[0017] <White toner> The white toner according to this embodiment comprises toner particles containing a binder resin including a hybrid resin in which an amorphous resin unit and a crystalline polyester resin unit are chemically bonded, surface-treated titanium oxide, and a release agent, and the atomic ratio of Al on the surface of the surface-treated titanium oxide is 3 atomic % or more and 20 atomic % or less, and the atomic ratio of Ti is 5 atomic % or more and 15 atomic % or less.

[0018] The white toner according to this embodiment is less likely to accelerate wear of the cleaning blade of the intermediate transfer member. The mechanism behind this is presumed to be as follows.

[0019] Titanium oxide, which is widely used as a white pigment in toner, is generally used in a surface-treated form from the viewpoints of dispersibility in binder resins, weather resistance of white images, etc. However, even surface-treated titanium oxide may aggregate during toner particle granulation depending on its own weight or the degree of affinity depending on the type of binder resin, resulting in uneven distribution of titanium oxide within the toner particles. Toner particles with unevenly distributed titanium oxide have a relatively high dielectric loss factor and a relatively low transfer rate from the intermediate transfer body to a recording medium. Therefore, toner particles with unevenly distributed titanium oxide have a relatively high residual rate on the intermediate transfer body. On the other hand, when a cleaning blade comes into contact with the intermediate transfer body, toner particles remaining on the intermediate transfer body are crushed, exposing pigment particles and causing wear on the cleaning blade. Toner particles with unevenly distributed titanium oxide have a relatively high residual rate on the intermediate transfer body, which accelerates wear on the intermediate transfer body cleaning blade. As a result, toner particles slip through the worn cleaning blade, causing color streaks in the image. The above phenomenon is particularly pronounced when 100% density white images are continuously formed over the entire surface of a recording medium (i.e., without leaving any margins at the edges of the recording medium) in a high temperature and high humidity environment (for example, a temperature of 28°C and a relative humidity of 85%), because the residual rate of toner particles with unevenly distributed titanium oxide on the intermediate transfer body increases.

[0020] In response to the above phenomenon, the present inventors discovered that hybrid resins act as dispersants for surface-treated titanium oxide. They also discovered that specifying the atomic composition of the surface of surface-treated titanium oxide can further enhance the dispersibility of surface-treated titanium oxide with hybrid resins. While the mechanism behind this is not entirely clear, it is believed to be due to a balance between electrostatic repulsion and attraction acting between the hybrid resin and the surface-treated titanium oxide.

[0021] First, the hybrid resin contains a crystalline polyester resin unit as a crystalline resin unit from the viewpoint of low-temperature fixability of the toner. Because the hybrid resin contains an amorphous resin unit and a crystalline polyester resin unit within the molecule, it is likely to be present throughout the toner particle, and therefore is expected to function as a dispersant. Furthermore, during toner particle granulation, the amorphous resin unit within the hybrid resin molecule repels the surface-treated titanium oxide, while the crystalline polyester resin unit attracts the surface-treated titanium oxide, which is presumed to act as a stable dispersant for the surface-treated titanium oxide. On the other hand, if the atomic ratio of Al on the surface of surface-treated titanium oxide is 3 atomic % or more and 20 atomic % or less and the atomic ratio of Ti is 5 atomic % or more and 15 atomic % or less, the affinity with the hybrid resin increases. If the atomic ratio of Al on the surface of the surface-treated titanium oxide is less than 3 atomic %, the affinity of the surface-treated titanium oxide for the hybrid resin molecules is low, resulting in uneven distribution of titanium oxide inside the toner particles. From this viewpoint, the atomic ratio of Al is 3 atomic % or more, and preferably 5 atomic % or more. If the atomic ratio of Al on the surface of the surface-treated titanium oxide exceeds 20 atomic %, aggregation of the surface-treated titanium oxide particles tends to occur. From this viewpoint, the atomic ratio of Al is 20 atomic % or less, and preferably 15 atomic % or less. If the atomic percentage of Ti on the surface of the surface-treated titanium oxide exceeds 15 atomic %, the affinity of the surface-treated titanium oxide for the hybrid resin molecules is low, resulting in uneven distribution of titanium oxide inside the toner particles. From this viewpoint, the atomic percentage of Ti is 15 atomic % or less, and preferably 12 atomic % or less. If the atomic percentage of Ti on the surface of the surface-treated titanium oxide is less than 5 atomic %, the whiteness and hiding power of the white image will be insufficient. From this viewpoint, the atomic percentage of Ti is 5 atomic % or more, and preferably 6 atomic % or more.

[0022] From the above viewpoint, it is preferable that the atomic ratio of Al on the surface of the surface-treated titanium oxide is 5 atomic % or more and 15 atomic % or less, and the atomic ratio of Ti is 6 atomic % or more and 12 atomic % or less.

[0023] From the viewpoint of further improving the dispersibility of the surface-treated titanium oxide in the hybrid resin, the atomic weight ratio Al / Ti of Al to Ti on the surface of the surface-treated titanium oxide is preferably 0.5 or more and 4.0 or less, more preferably 1.0 or more and 3.5 or less, and even more preferably 1.5 or more and 3.0 or less.

[0024] The atomic composition of the surface of the surface-treated titanium oxide is determined by the following measurement method. When the white toner contains external additives, the white toner is placed in a 5% by weight aqueous solution of sodium alkylbenzene sulfonate and stirred. Ultrasonic waves are then applied using a bath-type ultrasonic disperser to liberate the external additives from the surface of the toner particles. The toner particles are then settled by centrifugation, and the supernatant liquid containing the liberated and dispersed external additives is removed. The process from ultrasonic treatment to supernatant removal is repeated three times. The toner particles are then suspended in toluene to dissolve the binder resin and release agent, and the suspension is filtered for solid-liquid separation. The solid is thoroughly washed with water and then dried to obtain a powder. This powder is used as a sample and mapped using an energy dispersive X-ray analyzer (e.g., Horiba, Ltd. EMAX model 6923H) attached to a scanning electron microscope (e.g., Hitachi High-Technologies Corporation S-4800) at an accelerating voltage of 20 kV. 1,000 locations on the particle surface are measured to determine the atomic composition of the particle surface.

[0025] From the viewpoint of further improving the dispersibility of the surface-treated titanium oxide by the hybrid resin, the mass ratio of the hybrid resin to the surface-treated titanium oxide contained in the toner particles (hybrid resin / surface-treated titanium oxide) is preferably 0.08 or more and 3.0 or less, more preferably 0.10 or more and 2.8 or less, and even more preferably 0.12 or more and 2.6 or less.

[0026] The toner according to this embodiment will be described in detail below.

[0027] The toner according to this embodiment is configured to contain toner particles and, if necessary, external additives.

[0028] [Toner particles] The toner particles contain a binder resin containing a hybrid resin, surface-treated titanium oxide, and a release agent, and may also contain other additives as required.

[0029] -Binder resin- The content of the binder resin is preferably 40% by mass to 80% by mass, more preferably 50% by mass to 75% by mass, and even more preferably 60% by mass to 70% by mass, based on the total mass of the toner particles.

[0030] The binder resin preferably contains a hybrid resin and a resin other than the hybrid resin. From the viewpoint of dispersibility of the surface-treated titanium oxide, the mass ratio of the hybrid resin to the entire binder resin is preferably 20% by mass or more and 70% by mass or less, more preferably 30% by mass or more and 60% by mass or less, and even more preferably 40% by mass or more and 50% by mass or less.

[0031] -Hybrid resin- From the viewpoint of dispersibility of the surface-treated titanium oxide, the content of the hybrid resin contained in the toner particles is preferably 5% by mass or more and 60% by mass or less, more preferably 10% by mass or more and 55% by mass or less, and even more preferably 20% by mass or more and 50% by mass or less, based on the total mass of the toner particles.

[0032] The hybrid resin is a resin in which an amorphous resin unit and a crystalline polyester resin unit are chemically bonded. The amorphous resin unit refers to a resin portion having a structure derived from an amorphous resin. The crystalline polyester resin unit refers to a resin portion having a structure derived from a crystalline polyester resin.

[0033] An amorphous resin is a resin in which, when measured in differential scanning calorimetry at a heating rate of 10°C / min, the half-width of the endothermic peak exceeds 10°C, the endothermic amount changes stepwise, or no clear endothermic peak is observed. A crystalline resin is a resin that shows a clear endothermic peak when measured in differential scanning calorimetry at a heating rate of 10°C / min (specifically, a resin whose half-value width of the endothermic peak is within 10°C).

[0034] The melting temperature or glass transition temperature of the hybrid resin is preferably 50°C or higher and 80°C or lower from the viewpoint of low-temperature fixability of the toner. The melting temperature of the hybrid resin is determined from a DSC curve obtained by differential scanning calorimetry in accordance with JIS K7121-1987 "Method for measuring transition temperature of plastics" and "Melting peak temperature." The glass transition temperature of the hybrid resin is determined from a DSC curve obtained by differential scanning calorimetry in accordance with JIS K7121-1987 "Method for measuring transition temperature of plastics" and "Extrapolated glass transition onset temperature."

[0035] From the viewpoint of the dispersibility of the surface-treated titanium dioxide, the weight-average molecular weight (Mw) of the hybrid resin is preferably 5,000 to 100,000, more preferably 7,000 to 50,000, and even more preferably 8,000 to 20,000. The weight-average molecular weight of the hybrid resin is measured by gel permeation chromatography (GPC). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC measuring instrument, a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent. The weight-average molecular weight is calculated from the measurement results using a molecular weight calibration curve prepared using monodisperse polystyrene standards.

[0036] From the viewpoint of dispersibility of the surface-treated titanium oxide, the mass proportion of the amorphous resin unit in the hybrid resin is preferably 50 mass% or more and 90 mass% or less, more preferably 60 mass% or more and 85 mass% or less, and even more preferably 70 mass% or more and 80 mass% or less.

[0037] The ratio of the mass proportion (mass %) of the amorphous resin unit in the hybrid resin to the atomic proportion (atomic %) of Al on the surface of the surface-treated titanium oxide (mass proportion of amorphous resin unit / atomic proportion of Al) is preferably 2.5 or more and 30 or less, more preferably 2.8 or more and 28 or less, and even more preferably 3.0 or more and 25 or less, from the viewpoint of dispersibility of the surface-treated titanium oxide.

[0038] Amorphous resin unit The glass transition temperature (Tg) of the amorphous resin forming the amorphous resin unit is preferably 50° C. or higher and 80° C. or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry in accordance with JIS K7121-1987 "Method for measuring transition temperature of plastics" and "Extrapolated glass transition onset temperature."

[0039] The amorphous resin forming the amorphous resin unit may be a commercially available product or a synthetic product. Examples of the amorphous resin forming the amorphous resin unit include amorphous vinyl resins (e.g., polystyrene resins, styrene (meth)acrylic resins, etc.), epoxy resins, polycarbonate resins, polyurethane resins, and amorphous polyester resins.

[0040] As the amorphous resin forming the amorphous resin unit, from the viewpoint of low-temperature fixability of the toner, at least one selected from the group consisting of polystyrene resin, styrene (meth)acrylic resin, and polyurethane resin is preferred, and a combination of polystyrene resin or styrene (meth)acrylic resin with polyurethane resin is more preferred.

[0041] Examples of polystyrene resins include homopolymers and copolymers of styrene or styrene derivatives, such as alkyl-substituted styrenes (α-methylstyrene, 4-methylstyrene, 2-methylstyrene, 3-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, and 4-ethylstyrene), halogen-substituted styrenes (2-chlorostyrene, 3-chlorostyrene, and 4-chlorostyrene), fluorine-substituted styrenes (4-fluorostyrene and 2,5-difluorostyrene), and vinylnaphthalene.

[0042] Examples of styrene (meth)acrylic resins include resins obtained by copolymerizing styrene or a styrene derivative with (meth)acrylic acid or a (meth)acrylic acid ester in a polymerization ratio (mass basis, former:latter) of 85:15 to 70:30. The styrene derivative is, for example, the above-mentioned monomer. The (meth)acrylic acid ester is, for example, a (meth)acrylic acid alkyl ester (for example, n-methyl (meth)acrylate, n-ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-lauryl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate, n-octadecyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, amyl (meth)acrylate, p) Neopentyl acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, etc.), (meth)acrylic acid aryl esters (for example, phenyl (meth)acrylate, biphenyl (meth)acrylate, diphenylethyl (meth)acrylate, t-butylphenyl (meth)acrylate, terphenyl (meth)acrylate, etc.), dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, β-carboxyethyl (meth)acrylate, (meth)acrylamide, etc.

[0043] Examples of polyurethane resins include polyurethane resins obtained by reacting a resin having a hydroxy group (at least one selected from the group consisting of polyvinyl acetal resin, polyvinyl resin, casein, phenolic resin, etc.) with an isocyanate compound (aromatic polyisocyanate, aliphatic polyisocyanate, alicyclic polyisocyanate, etc.). The isocyanate compound may be a blocked isocyanate compound (a compound in which the isocyanate group is protected with a blocking agent).

[0044] Crystalline polyester resin unit The melting temperature of the crystalline polyester resin forming the crystalline polyester resin unit is preferably 50° C. or higher and 100° C. or lower, more preferably 55° C. or higher and 90° C. or lower, and even more preferably 60° C. or higher and 85° C. or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry in accordance with JIS K7121-1987 "Method for measuring transition temperature of plastics" and "Peak melting temperature."

[0045] The crystalline polyester resin forming the crystalline polyester resin unit may be a commercially available product or a synthetic product. Examples of the crystalline polyester resin forming the crystalline polyester resin unit include a polycondensate of a polycarboxylic acid and a polyhydric alcohol.

[0046] Examples of polycarboxylic acids include aliphatic dicarboxylic acids (e.g., oxalic acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, 1,9-dicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, etc.), aromatic dicarboxylic acids (e.g., dibasic acids such as phthalic acid, isophthalic acid, terephthalic acid, and naphthalene-2,6-dicarboxylic acid), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polycarboxylic acid may be a tricarboxylic or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the tricarboxylic acid include aromatic carboxylic acids (e.g., 1,2,3-benzenetricarboxylic acid, 1,2,4-benzenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, etc.), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). As the polycarboxylic acid, a dicarboxylic acid having a sulfonic acid group and a dicarboxylic acid having an ethylenic double bond may be used in combination with these dicarboxylic acids. The polycarboxylic acids may be used alone or in combination of two or more.

[0047] Examples of polyhydric alcohols include aliphatic diols (for example, straight-chain aliphatic diols having 7 to 20 carbon atoms in the main chain). Examples of aliphatic diols include ethylene glycol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,14-eicosanedecanediol. Among these, 1,8-octanediol, 1,9-nonanediol, and 1,10-decanediol are preferred as aliphatic diols. The polyhydric alcohol may be a trihydric or higher alcohol having a crosslinked or branched structure, such as glycerin, trimethylolethane, trimethylolpropane, or pentaerythritol, in combination with the diol. The polyhydric alcohols may be used alone or in combination of two or more.

[0048] From the viewpoint of low temperature fixability of the toner, the crystalline polyester resin forming the crystalline polyester resin unit is preferably a crystalline aliphatic polyester resin obtained from a polybasic carboxylic acid component and a polyhydric alcohol component.

[0049] Examples of the polycarboxylic acid component in the crystalline aliphatic polyester resin include aliphatic dicarboxylic acids such as oxalic acid, malonic acid, maleic acid, fumaric acid, succinic acid, glutaric acid, adipic acid, suberic acid, azelaic acid, sebacic acid, 1,9-nonanedicarboxylic acid, 1,10-decanedicarboxylic acid, 1,12-dodecanedicarboxylic acid, 1,14-tetradecanedicarboxylic acid, and 1,18-octadecanedicarboxylic acid. Among these, polycarboxylic acid components having 8 to 22 carbon atoms are preferred.

[0050] Examples of the polyhydric alcohol component in the crystalline aliphatic polyester resin include 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, 1,12-dodecanediol, 1,13-tridecanediol, 1,14-tetradecanediol, 1,18-octadecanediol, and 1,20-eicosanediol. Among these, polyhydric alcohol components having 4 to 10 carbon atoms are preferred.

[0051] In the crystalline aliphatic polyester resin, the sum of the number of carbon atoms in the polycarboxylic acid component and the number of carbon atoms in the polyhydric alcohol component is preferably 8 to 22, more preferably 10 to 20, and even more preferably 12 to 18. The number of carbon atoms in the polycarboxylic acid component is the total number of carbon atoms including the carbon atoms in the carboxy group. When a crystalline aliphatic polyester resin is formed using multiple polycarboxylic acid components, the number of carbon atoms in the polycarboxylic acid component is determined as a weighted average based on the molar ratio of each polycarboxylic acid component. When a crystalline aliphatic polyester resin is formed using multiple polyhydric alcohol components, the number of carbon atoms in the polyhydric alcohol component is determined as a weighted average based on the molar ratio of each polyhydric alcohol component.

[0052] -Method for synthesizing hybrid resin- Examples of methods for synthesizing hybrid resins include the following methods (1), (2), and (3).

[0053] (1) A method of synthesizing a hybrid resin by forming an amorphous resin unit in the presence of a preformed crystalline polyester resin. A crystalline polyester resin unit is formed by condensation polymerization of a polycarboxylic acid and a polyhydric alcohol. Next, in the presence of the crystalline polyester resin unit, a monomer constituting the amorphous resin unit is polymerized to form the amorphous resin unit. At this time, a monomer capable of reacting with a carboxy group or a hydroxy group in the crystalline polyester resin unit is coexisted, and the amorphous resin unit is bonded to the crystalline polyester resin unit.

[0054] (2) A method of synthesizing a hybrid resin by condensation polymerization of a crystalline polyester resin unit in the presence of a preformed amorphous resin unit. Monomers constituting the amorphous resin unit are polymerized to form the amorphous resin unit. At this time, it is preferable to also polymerize a monomer capable of reacting with a carboxy group or a hydroxy group in the crystalline polyester resin unit. Next, a polycarboxylic acid and a polyhydric alcohol are condensation polymerized in the presence of the amorphous resin unit to form a crystalline polyester resin unit. During the condensation polymerization of the polycarboxylic acid and the polyhydric alcohol, the carboxy group of the polycarboxylic acid or the hydroxy group of the polyhydric alcohol is addition reacted with the amorphous resin unit.

[0055] (3) A method of synthesizing a hybrid resin by combining a preformed amorphous resin unit and a crystalline polyester resin unit. Monomers constituting the amorphous resin unit are polymerized to form the amorphous resin unit. At this time, it is preferable to also polymerize a monomer capable of reacting with a carboxy group or a hydroxy group in the crystalline polyester resin unit. Separately, a crystalline polyester resin unit is formed by condensation polymerization of a polycarboxylic acid and a polyhydric alcohol. Next, the amorphous resin unit and the crystalline polyester resin unit are reacted and bonded. When reacting the amorphous resin unit and the crystalline polyester resin unit, a compound capable of bonding to both units may be present to bond the two units.

[0056] -Other binder resins- Examples of binder resins other than hybrid 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.

[0057] As the binder resin other than the hybrid resin, a vinyl resin is preferable. The vinyl resin may be a homopolymer or a copolymer.

[0058] Examples of vinyl resins include homopolymers of monomers such as monomers having a styrene skeleton (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), monomers having a (meth)acrylic acid ester skeleton (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.), monomers having an ethylenically unsaturated nitrile skeleton (e.g., acrylonitrile, methacrylonitrile, etc.), monomers having a vinyl ether skeleton (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), monomers having a vinyl ketone skeleton (e.g., vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), and monomers having an olefin skeleton (e.g., ethylene, propylene, butadiene, etc.), and copolymers of two or more of these monomers in combination.

[0059] From the viewpoint of low-temperature fixability of the toner, the vinyl resin is preferably a styrene (meth)acrylic resin obtained by copolymerizing a monomer having a styrene skeleton and a monomer having a (meth)acrylic acid ester skeleton.

[0060] Examples of monomers having a styrene skeleton include styrene, alkyl-substituted styrenes (e.g., α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, etc.), halogen-substituted styrenes (e.g., 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, etc.), vinylnaphthalene, etc. One type of monomer having a styrene skeleton may be used alone, or two or more types may be used in combination. As the monomer having a styrene skeleton, styrene is preferred from the viewpoints of ease of reactivity and ease of reaction control.

[0061] Examples of the monomer having a (meth)acrylic acid ester skeleton include (meth)acrylic acid and (meth)acrylic acid esters. Examples of the (meth)acrylic acid ester include (meth)acrylic acid alkyl esters (e.g., n-methyl (meth)acrylate, n-ethyl (meth)acrylate, n-propyl (meth)acrylate, n-butyl (meth)acrylate, n-pentyl (meth)acrylate, n-hexyl acrylate, n-heptyl (meth)acrylate, n-octyl (meth)acrylate, n-decyl (meth)acrylate, n-dodecyl (meth)acrylate, n-lauryl (meth)acrylate, n-tetradecyl (meth)acrylate, n-hexadecyl (meth)acrylate, n-octadecyl (meth)acrylate, isopropyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, isopentyl (meth)acrylate, amyl (meth)acrylate, Examples of (meth)acrylic acid monomers include neopentyl acrylate, isohexyl (meth)acrylate, isoheptyl (meth)acrylate, isooctyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, t-butylcyclohexyl (meth)acrylate, etc.), (meth)acrylic acid aryl esters (for example, phenyl (meth)acrylate, biphenyl (meth)acrylate, diphenylethyl (meth)acrylate, t-butylphenyl (meth)acrylate, terphenyl (meth)acrylate, etc.), dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, methoxyethyl (meth)acrylate, 2-hydroxyethyl (meth)acrylate, β-carboxyethyl (meth)acrylate, and (meth)acrylamide. One (meth)acrylic acid monomer may be used alone, or two or more may be used in combination.

[0062] The copolymerization ratio (mass basis, former:latter) of the monomer having a styrene skeleton to the monomer having a (meth)acrylic acid ester skeleton is preferably 85:15 to 70:30.

[0063] The styrene (meth)acrylic resin preferably has a crosslinked structure in order to suppress blocking. Examples of the styrene (meth)acrylic resin having a crosslinked structure include a crosslinked product obtained by copolymerizing a monomer having a styrene skeleton, a monomer having a (meth)acrylic acid skeleton, and a crosslinkable monomer. The mass ratio of the crosslinkable monomer to all monomers in the styrene (meth)acrylic resin is preferably 0.2 mass% or more and 3 mass% or less.

[0064] Examples of crosslinkable monomers to be introduced into styrene (meth)acrylic resins include bifunctional or higher crosslinking agents. Examples of bifunctional crosslinking agents include divinylbenzene, divinylnaphthalene, di(meth)acrylate compounds (e.g., diethylene glycol di(meth)acrylate, methylene bis(meth)acrylamide, decanediol diacrylate, glycidyl (meth)acrylate, etc.), polyester-type di(meth)acrylate, and 2-([1'-methylpropylideneamino]carboxyamino)ethyl methacrylate. Examples of polyfunctional crosslinking agents include tri(meth)acrylate compounds (e.g., pentaerythritol tri(meth)acrylate, trimethylolethane tri(meth)acrylate, trimethylolpropane tri(meth)acrylate, etc.), tetra(meth)acrylate compounds (e.g., tetramethylolmethane tetra(meth)acrylate, oligoester (meth)acrylate, etc.), 2,2-bis(4-methacryloxy, polyethoxyphenyl)propane, diallyl phthalate, triallyl cyanurate, triallyl associanurate, triallyl isocyanurate, triallyl trimellitate, diaryl chlorendate, etc.

[0065] The weight-average molecular weight (Mw) of the styrene (meth)acrylic resin is preferably 30,000 to 200,000, more preferably 40,000 to 100,000, and even more preferably 50,000 to 80,000. The weight-average molecular weight of the styrene (meth)acrylic resin is measured by gel permeation chromatography (GPC). Molecular weight measurement by GPC is performed using a Tosoh GPC HLC-8120GPC measuring instrument, a Tosoh TSKgel SuperHM-M (15 cm) column, and THF solvent. The weight-average molecular weight is calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.

[0066] -Surface-treated titanium oxide- The surface-treated titanium oxide is a pigment that imparts white color to the toner, and is titanium oxide whose surface has been treated with at least one of an inorganic compound and an organic compound. The titanium oxide and the surface-treated titanium oxide are in particulate form.

[0067] The crystalline structure of titanium oxide (TiO2) constituting the surface-treated titanium oxide may be any of anatase, rutile, brookite, a mixed crystal structure of these, or an amorphous structure.

[0068] Examples of methods for producing titanium oxide include the chlorine method (gas phase method), the sulfuric acid method (liquid phase method), the sol-gel method using titanium alkoxide, and a method of baking metatitanic acid. An example of the chlorine process (gas phase process) is as follows: Rutile ore, the raw material, is reacted with coke and chlorine to form gaseous titanium tetrachloride, which is then cooled to obtain liquid titanium tetrachloride. Next, the gaseous or vaporous titanium tetrachloride is reacted with oxygen gas at high temperature, and the chlorine gas is separated to obtain titanium oxide.

[0069] The surface treatment method and surface treatment agent for titanium oxide may be selected from known methods and treatment agents from the viewpoints of dispersibility in the binder resin, weather resistance of the white image, etc. Surface treatment methods for titanium oxide are roughly divided into wet treatments and dry treatments. The wet treatment is a treatment method in which a surface treatment agent is added to a slurry in which titanium oxide is dispersed in an aqueous solvent or an organic solvent, and the surface of the titanium oxide is coated with the slurry. Dry treatment is a treatment method in which the vapor or gas of a surface treatment agent is applied to flowing titanium oxide to coat the surface of the titanium oxide. Examples of surface treatment agents for titanium oxide include metal oxides containing Al, metal oxides containing Si, metal oxides containing Zr, fatty acids, silicones, and the like.

[0070] From the viewpoint of dispersibility in binder resins, the surface-treated titanium oxide is preferably titanium oxide coated with alumina (Al2O3). Titanium oxide coated with alumina may have other chemical substances (e.g., silica, zirconia, fatty acids, silicone) disposed between the alumina and titanium oxide, with the alumina preferably being on the outermost surface. In the present disclosure, "coated" refers to adhesion to at least a portion of the surface of an object.

[0071] The average major axis length of the surface-treated titanium oxide is preferably 20 nm or more, more preferably 30 nm or more, and even more preferably 40 nm or more, from the viewpoint of suppressing aggregation of the surface-treated titanium oxide. The average major axis length of the surface-treated titanium oxide is preferably 300 nm or less, more preferably 250 nm or less, and even more preferably 220 nm or less, from the viewpoint of suppressing wear of the intermediate transfer member cleaning blade.

[0072] The BET specific surface area of ​​the surface-treated titanium oxide is 4m from the viewpoint of interacting with the hybrid resin and improving dispersibility. 2 / g or more is preferable, and 6m 2 / g or more is more preferable. The BET specific surface area of ​​the surface-treated titanium oxide is 12m from the viewpoint of excellent whiteness. 2 / g or less is preferable, and 10m 2 / g or less is more preferable.

[0073] The average major axis length and BET specific surface area of ​​the surface-treated titanium oxide are determined by the following measurement methods. When the white toner contains an external additive, the white toner is placed in a 5% by weight aqueous solution of sodium alkylbenzene sulfonate and stirred. Ultrasonic waves are then applied using a bath-type ultrasonic disperser to liberate the external additive from the surface of the toner particles. The toner particles are then settled by centrifugation, and the supernatant liquid containing the liberated and dispersed external additive is removed. The process from ultrasonic treatment to supernatant removal is repeated three times. The toner particles are then suspended in toluene to dissolve the binder resin and release agent, followed by filtration for solid-liquid separation. The solid is thoroughly washed with water and then dried to obtain a powder. This powder is used as a sample for measuring the average major axis length and BET specific surface area. The average major axis length is the arithmetic mean value obtained by photographing a sample at 10,000x magnification using a scanning electron microscope (e.g., S-4700 manufactured by Hitachi High-Technologies Corporation), measuring the major axis lengths of 100 particles using an image processing analyzer (e.g., LUZEX manufactured by Nireco Corporation). The BET specific surface area is a value measured by precisely weighing 1 g of a sample and measuring it with a BET specific surface area meter (for example, SA3100 manufactured by Beckman Coulter) by the BET multipoint method using nitrogen gas.

[0074] The toner particles may contain a white pigment other than the surface-treated titanium oxide. Examples of other white pigments include zinc oxide, silicon dioxide, alumina, calcium carbonate, aluminum hydroxide, satin white, talc, calcium sulfate, magnesium oxide, magnesium carbonate, white carbon, kaolin, aluminosilicate, sericite, bentonite, and smectite. These white pigments may be used alone or in combination of two or more. These white pigments may be added to the toner particles for purposes other than coloring (for example, toner charge control).

[0075] The content of the surface-treated titanium oxide contained in the toner particles is preferably 85% by mass or more and 100% by mass or less, more preferably 90% by mass or more and 100% by mass or less, and even more preferably 95% by mass or more and 100% by mass or less, based on the total amount of the white pigment contained in the toner particles.

[0076] From the viewpoint of whiteness and hiding power, the content of the surface-treated titanium oxide contained in the toner particles is preferably 20% by mass or more and 60% by mass or less, more preferably 25% by mass or more and 55% by mass or less, and even more preferably 30% by mass or more and 50% by mass or less, based on the total mass of the toner particles.

[0077] -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.

[0078] The melting temperature of the release agent is preferably from 50° C. to 110° C., more preferably from 60° C. to 100° C. The melting temperature of the release agent is determined from a DSC curve obtained by differential scanning calorimetry in accordance with JIS K7121-1987 "Method for measuring transition temperature of plastics" and "Peak melting temperature".

[0079] 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.

[0080] -Other additives- Examples of other additives include known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

[0081] -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 covers the core. The toner particles of a core-shell structure may be composed of, for example, a core containing a binder resin, a release agent, and surface-treated titanium oxide, and a coating layer containing a binder resin.

[0082] 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.

[0083] The various average particle sizes and particle size distribution indices of the toner particles are measured using a Coulter Multisizer II (manufactured by Beckman Coulter), and the electrolyte is measured using an ISOTON-II (manufactured by Beckman Coulter). For the measurement, 0.5 mg to 50 mg of the sample to be measured is added to 2 ml of a 5 mass % aqueous solution of a surfactant (preferably sodium alkylbenzene sulfonate) as a dispersant, and this is then added to 100 ml to 150 ml of the electrolyte. The electrolyte solution containing the suspended sample is dispersed in an ultrasonic disperser for 1 minute, and the particle size distribution of particles in the range of 2 μm to 60 μm is measured using a Coulter Multisizer II with an aperture diameter of 100 μm. The number of particles sampled is 50,000. Based on the particle size distribution measured, cumulative distributions of volume and number are drawn for each divided particle size range (channel) from the smallest diameter side, and the particle size at 16% of the cumulative total is defined as the volume particle size D16v, the number particle size D16p, the particle size at 50% of the cumulative total as the volume average particle size D50v, the cumulative number average particle size D50p, and the particle size at 84% of the cumulative total as the volume particle size D84v and the number particle size D84p. Using these, the volumetric particle size distribution index (GSDv) is (D84v / D16v) 1 / 2 , the number particle size distribution index (GSDp) is (D84p / D16p) 1 / 2 It is calculated as:

[0084] The average circularity of the toner particles is preferably 0.94 or more and 1.00 or less, and more preferably 0.95 or more and 0.98 or less.

[0085] The average circularity of toner particles is calculated by (circular equivalent perimeter) / (perimeter) [(perimeter of a circle having the same projected area as the particle image) / (perimeter of the particle projected image)]. Specifically, this value is measured by the following method. First, the toner particles to be measured are sucked and collected, forming a flat flow, and a still image of the particles is captured by instantaneously activating a strobe light, and the particle image is analyzed using a flow-type particle image analyzer (FPIA-3000 manufactured by Sysmex Corporation).The number of samples to be sampled when calculating the average circularity is 3,500. When the toner contains external additives, the toner (developer) to be measured is dispersed in water containing a surfactant, and then ultrasonic treatment is performed to obtain toner particles from which the external additives have been removed.

[0086] [External additives] Examples of external additives include inorganic particles, such as SiO2, TiO2, 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.

[0087] The surfaces of inorganic particles as external additives are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the inorganic particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is usually, for example, 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the inorganic particles.

[0088] Examples of external additives include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning agents (for example, metal salts of higher fatty acids such as zinc stearate, and particles of fluorine-based polymers).

[0089] The amount of the external additive 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.

[0090] [White toner manufacturing method] The white toner according to this embodiment is obtained by producing toner particles and then externally adding an external additive to the toner particles.

[0091] The toner particles may be produced by any of a dry production method (for example, a kneading and pulverization method) and a wet production method (for example, an aggregation and coalescence method, a suspension polymerization method, a dissolution and suspension method). There are no particular limitations on these production methods, and any known production method may be used. Among these, it is preferable to obtain toner particles by the aggregation and coalescence method.

[0092] The aggregation and coalescence method will be described below using toner particles containing a hybrid resin and a vinyl resin as a binder resin as an example. preparing a hybrid resin particle dispersion in which hybrid resin particles are dispersed; preparing a vinyl resin particle dispersion liquid in which vinyl resin particles are dispersed; preparing a surface-treated titanium oxide dispersion in which surface-treated titanium oxide is dispersed; preparing a release agent particle dispersion in which release agent particles are dispersed; a step of aggregating the mixed particles in a mixed dispersion obtained by mixing a hybrid resin particle dispersion, a vinyl resin particle dispersion, a surface-treated titanium oxide dispersion, and a release agent particle dispersion to form aggregated particles (aggregated particle forming step); and a step of heating the aggregated particle dispersion in which the aggregated particles are dispersed to fuse and coalesce the aggregated particles to form toner particles (fusion and coalescence step).

[0093] -Dispersion liquid preparation process- The hybrid resin particle dispersion and the vinyl resin particle dispersion can be prepared by the same method, and will be collectively referred to as the resin particle dispersion hereinafter.

[0094] The resin particle dispersion is prepared, for example, by dispersing resin particles in a dispersion medium using a surfactant.

[0095] Examples of the dispersion medium used in the resin particle dispersion include aqueous media. Examples of aqueous media include water such as distilled water and ion-exchanged water, alcohols, etc. These may be used alone or in combination of two or more.

[0096] Examples of surfactants include anionic surfactants such as sulfate ester salts, sulfonate salts, phosphate esters, and soaps; cationic surfactants such as amine salts and quaternary ammonium salts; and nonionic surfactants such as polyethylene glycols, alkylphenol ethylene oxide adducts, and polyhydric alcohols. Among these, anionic surfactants and cationic surfactants are particularly preferred. Nonionic surfactants may be used in combination with anionic surfactants or cationic surfactants. The surfactants may be used alone or in combination of two or more.

[0097] In a resin particle dispersion, resin particles can be dispersed in a dispersion medium by common dispersion methods such as a rotary shear homogenizer, a ball mill with media, a sand mill, or a Dynomill. Depending on the type of resin particles, the resin particles may be dispersed in a dispersion medium by a phase inversion emulsification method. The phase inversion emulsification method involves dissolving the resin to be dispersed in a hydrophobic organic solvent in which the resin is soluble, neutralizing the organic continuous phase (O phase) by adding a base, and then introducing an aqueous medium (W phase) to invert the phase from W / O to O / W, thereby dispersing the resin in particulate form in the aqueous medium.

[0098] The volume average particle size of the resin particles dispersed in the resin particle dispersion is, for example, preferably 0.01 μm to 1 μm, more preferably 0.08 μm to 0.8 μm, and even more preferably 0.1 μm to 0.6 μm. The volume average particle size of the resin particles is measured using a particle size distribution obtained by measurement with a laser diffraction particle size distribution analyzer (e.g., HORIBA LA-700), and the cumulative distribution for the volume of the divided particle size range (channel) is calculated from the smallest particle size side, and the particle size at which the cumulative 50% of all particles is determined as the volume average particle size D50v. The volume average particle sizes of particles in other dispersions are also measured in the same way.

[0099] The content of resin particles contained in the resin particle dispersion is preferably 5% by mass or more and 50% by mass or less, and more preferably 10% by mass or more and 40% by mass or less.

[0100] The surface-treated titanium oxide dispersion and the release agent particle dispersion are also prepared in the same manner as the resin particle dispersion. The volume average particle size, dispersion medium, dispersion method, and particle content of the particles in the resin particle dispersion are the same for the surface-treated titanium oxide dispersed in the surface-treated titanium oxide dispersion and the release agent particles dispersed in the release agent particle dispersion.

[0101] -Agglomerated particle formation process- Next, the resin particle dispersion, the surface-treated titanium oxide dispersion, and the release agent particle dispersion are mixed together, and the resin particles, the surface-treated titanium oxide, and the release agent particles are hetero-aggregated in the mixed dispersion to form aggregated particles containing the resin particles, the surface-treated titanium oxide, and the release agent particles, and having a diameter close to that of the target toner particles.

[0102] Specifically, for example, an aggregating agent is added to the mixed dispersion, and the pH of the mixed dispersion is adjusted to be acidic (for example, pH 2 or higher and 5 or lower), and a dispersion stabilizer is added as necessary.Then, the mixed dispersion is heated to a temperature close to the glass transition temperature of the resin particles (specifically, for example, the glass transition temperature of the resin particles minus 30°C or higher and the glass transition temperature minus 10°C or lower), causing the particles dispersed in the mixed dispersion to aggregate and form aggregated particles. In the aggregate particle formation step, for example, the mixed dispersion may be stirred with a rotary shear homogenizer, an aggregating agent may be added at room temperature (e.g., 25°C), the pH of the mixed dispersion may be adjusted to an acidic value (e.g., pH 2 or more and 5 or less), a dispersion stabilizer may be added as needed, and then the mixture may be heated.

[0103] Examples of the flocculant include a surfactant having a polarity opposite to that of the surfactant contained in the mixed dispersion, an inorganic metal salt, and a divalent or higher metal complex. When a metal complex is used as the flocculant, the amount of surfactant used can be reduced, and the charging characteristics can be improved. If necessary, an additive that forms a complex or a similar bond with the metal ions of the flocculant may be used together with the flocculant, and a chelating agent is preferably used as this additive.

[0104] Examples of inorganic metal salts include metal salts such as calcium chloride, calcium nitrate, barium chloride, magnesium chloride, zinc chloride, aluminum chloride, and aluminum sulfate; and inorganic metal salt polymers such as polyaluminum chloride, polyaluminum hydroxide, and calcium polysulfide. The chelating agent may be a water-soluble chelating agent, such as hydroxycarboxylic acid (e.g., tartaric acid, citric acid, gluconic acid), or aminocarboxylic acid (e.g., iminodiacetic acid (IDA), nitrilotriacetic acid (NTA), or ethylenediaminetetraacetic acid (EDTA). The amount of the chelating agent added is preferably 0.01 parts by mass or more and 5.0 parts by mass or less, and more preferably 0.1 parts by mass or more and less than 3.0 parts by mass, relative to 100 parts by mass of the resin particles.

[0105] -Fusion / unification process- Next, the aggregated particle dispersion liquid in which the aggregated particles are dispersed is heated, for example, to a temperature equal to or higher than the glass transition temperature of the resin particles (for example, a temperature 10°C to 30°C higher than the glass transition temperature of the resin particles) to fuse and coalesce the aggregated particles, thereby forming toner particles.

[0106] Through the above steps, toner particles are obtained. After obtaining the aggregated particle dispersion in which the aggregated particles are dispersed, the toner particles may be produced through the following steps: a step of further mixing the aggregated particle dispersion with a vinyl resin particle dispersion to cause the aggregated particles to adhere to the surfaces of the vinyl resin particles, thereby forming second aggregated particles; and a step of heating the second aggregated particle dispersion in which the second aggregated particles are dispersed, thereby fusing and coalescing the second aggregated particles, thereby forming toner particles having a core-shell structure.

[0107] After the fusion and coalescence process is completed, the toner particles in the dispersion are subjected to a known washing process, solid-liquid separation process, and drying process to obtain dried toner particles. In the washing process, from the viewpoint of chargeability, it is preferable to perform sufficient substitution washing with ion-exchanged water. In the solid-liquid separation process, from the viewpoint of productivity, it is preferable to perform suction filtration, pressure filtration, etc. In the drying process, from the viewpoint of productivity, it is preferable to perform freeze drying, flash drying, fluidized drying, vibration-type fluidized drying, etc.

[0108] The toner according to this embodiment is produced by, for example, adding an external additive to the obtained dry toner particles and mixing them. The mixing can be carried out using, for example, a V blender, a Henschel mixer, a Loedige mixer, or the like. Furthermore, if necessary, coarse particles may be removed from the toner using a vibrating sieve, an air sieve, or the like.

[0109] <Electrostatic image developer> The electrostatic image developer according to this embodiment contains at least the white toner according to this embodiment. The electrostatic image developer according to this embodiment may be a one-component developer containing only the white toner according to this embodiment, or may be a two-component developer in which the white toner is mixed with a carrier.

[0110] The carrier is not particularly limited, and known carriers can be used. Examples of the carrier include a coated carrier in which the surface of a core material made of magnetic powder is coated with a resin; a magnetic powder dispersion carrier in which magnetic powder is dispersed in a matrix resin; and a resin-impregnated carrier in which porous magnetic powder is impregnated with a resin. The magnetic powder dispersion carrier or the resin-impregnated carrier may be a carrier in which the constituent particles of the carrier are used as a core material and the surface of the core material is coated with a resin.

[0111] Examples of magnetic powder include magnetic metals such as iron, nickel, and cobalt; and magnetic oxides such as ferrite and magnetite.

[0112] Examples of coating resins and matrix resins include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene-acrylic acid ester copolymer, straight silicone resins containing organosiloxane bonds or modified products thereof, fluororesin, polyester, polycarbonate, phenolic resin, and epoxy resin. The coating resin and matrix resin may contain additives such as conductive particles. Examples of conductive particles include particles of metals such as gold, silver, and copper, carbon black, titanium oxide, zinc oxide, tin oxide, barium sulfate, aluminum borate, and potassium titanate.

[0113] Examples of methods for coating the surface of a core material with a resin include a method of coating with a coating layer-forming solution prepared by dissolving the coating resin and various additives (used as needed) in an appropriate solvent. The solvent is not particularly limited and may be selected taking into consideration the type of resin used, its applicability, and the like. Specific resin coating methods include an immersion method in which the core material is immersed in the coating layer-forming solution; a spray method in which the coating layer-forming solution is sprayed onto the core material surface; a fluidized bed method in which the coating layer-forming solution is sprayed onto the core material while suspended in flowing air; and a kneader coater method in which the carrier core material and the coating layer-forming solution are mixed in a kneader coater and then the solvent is removed.

[0114] The mixing ratio (mass ratio) of the toner and the carrier in the two-component developer is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100.

[0115] <Image forming device, image forming method> The image forming apparatus according to the present embodiment includes an image carrier, a charging unit for charging the surface of the image carrier, an electrostatic image forming unit for forming an electrostatic image on the charged image carrier, a developing unit containing an electrostatic image developer and developing the electrostatic image formed on the image carrier as a toner image using the electrostatic image developer, an intermediate transfer member onto which the toner image formed on the image carrier is transferred, a primary transfer unit for transferring the toner image formed on the image carrier to the surface of the intermediate transfer member, a secondary transfer unit for transferring the toner image transferred on the surface of the intermediate transfer member to the surface of a recording medium, a fixing unit for fixing the toner image transferred on the surface of the recording medium, and an intermediate transfer member cleaning unit having a blade that contacts the surface of the intermediate transfer member and uses the blade to clean residual toner from the surface of the intermediate transfer member after the toner image has been transferred to the surface of the recording medium. The electrostatic image developer according to the present embodiment is used as the electrostatic image developer.

[0116] 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 primary transfer step of transferring the toner image formed on the surface of the image carrier to the surface of an intermediate transfer carrier, a secondary transfer step of transferring the toner image transferred to the surface of the intermediate transfer carrier to the surface of a recording medium, a fixing step of fixing the toner image transferred to the surface of the recording medium, and an intermediate transfer carrier cleaning step of contacting a blade with the surface of the intermediate transfer carrier after the toner image has been transferred to the surface of the recording medium to clean any toner remaining on the surface of the intermediate transfer carrier.

[0117] The image forming apparatus according to this embodiment may be a known image forming apparatus such as an apparatus equipped with a cleaning means for cleaning the surface of an image carrier after the transfer of a toner image and before charging; or an apparatus equipped with a discharging means for irradiating the surface of an image carrier with discharging light to discharge it after the transfer of a toner image and before charging it.

[0118] 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 that contains the electrostatic image developer according to the present embodiment and is equipped with the developing means is preferably used.

[0119] The image forming apparatus according to this embodiment may be an image forming apparatus that further uses at least one toner selected from yellow toner, magenta toner, cyan toner, and black toner in addition to the white toner according to this embodiment.

[0120] 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.

[0121] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to this embodiment, and is a diagram showing a five-tandem type and intermediate transfer type image forming apparatus. The image forming apparatus shown in Figure 1 includes first through fifth electrophotographic image forming units 10Y, 10M, 10C, 10K, and 10W (image forming means) that output images in the colors yellow (Y), magenta (M), cyan (C), black (K), and white (W) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, 10K, and 10W are arranged side by side horizontally spaced a predetermined distance apart from one another. These units 10Y, 10M, 10C, 10K, and 10W may be process cartridges that are detachably attached to the image forming apparatus.

[0122] An intermediate transfer belt (an example of an intermediate transfer body) 20 is provided below each of the units 10Y, 10M, 10C, 10K, and 10W and extends through each unit. The intermediate transfer belt 20 is provided wrapped around a drive roll 22, a support roll 23, and an opposing roll 24, which are in contact with the inner surface of the intermediate transfer belt 20, and runs in a direction from the first unit 10Y to the fifth unit 10W. An intermediate transfer body cleaning device (an example of an intermediate transfer body cleaning means) 21 is provided on the image bearing surface side of the intermediate transfer belt 20, facing the drive roll 22.

[0123] The intermediate transfer belt 20 is, for example, a laminate of a base layer and a surface layer disposed on the outer peripheral surface of the base layer. The base layer contains, for example, a resin such as polyimide resin, polyamide resin, polyamideimide resin, polyetherester resin, polyarylate resin, or polyester resin, and a conductive agent. The surface layer contains, for example, at least one of the above resins, a fluororesin, and a conductive agent. The thickness of the intermediate transfer belt 20 is, for example, 50 μm or more and 100 μm or less.

[0124] The developing devices (examples of developing means) 4Y, 4M, 4C, 4K, and 4W of each unit 10Y, 10M, 10C, 10K, and 10W are supplied with yellow, magenta, cyan, black, and white toner contained in toner cartridges 8Y, 8M, 8C, 8K, and 8W, respectively.

[0125] Since the first to fifth units 10Y, 10M, 10C, 10K, and 10W have the same configuration, operation, and function, 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.

[0126] The first unit 10Y has a photoconductor 1Y that acts as an image carrier. Around the photoconductor 1Y, there are arranged in this order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoconductor 1Y to a predetermined potential; an exposure device (an example of an electrostatic image forming means) 3Y that exposes the charged surface to a laser beam based on a color-separated image signal to form an electrostatic image; a developing device (an example of a developing means) 4Y that supplies toner to the electrostatic image to develop it; a primary transfer roll (an example of a primary transfer means) 5Y that transfers the developed toner image onto the intermediate transfer belt 20; and a photoconductor cleaning device (an example of an image carrier cleaning means) 6Y that removes toner remaining on the surface of the photoconductor 1Y after the primary transfer.

[0127] 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, 5K, and 5W 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).

[0128] The operation of forming a yellow image in first unit 10Y will be described below. First, prior to operation, the surface of the photosensitive member 1Y is charged to a potential of −600V to −800V by the charging roll 2Y. The photoconductor 1Y has conductivity (for example, 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 is normally highly resistive (the resistance of ordinary resins), but when irradiated with a laser beam, the resistivity of the irradiated portion changes. Therefore, the charged surface of the photosensitive element 1Y is irradiated with a laser beam from the exposure device 3Y 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.

[0129] An electrostatic image is an image formed on the surface of the photosensitive element 1Y by charging it; it is a so-called negative latent image formed when the resistivity of the irradiated portion of the photosensitive layer is reduced by the laser beam from the exposure device 3Y, 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. 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.

[0130] 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.

[0131] 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.

[0132] After the toner image is transferred to the intermediate transfer belt 20, the photoreceptor 1Y continues to rotate and comes into contact with a cleaning blade provided on the photoreceptor cleaning device 6Y. The toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

[0133] The primary transfer bias applied to the primary transfer rolls 5M, 5C, 5K, and 5W of the second unit 10M and subsequent units is also controlled in accordance with that of 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 fifth units 10M, 10C, 10K, and 10W, and the toner images of each color are superimposed and transferred.

[0134] The intermediate transfer belt 20, onto which the five-color toner images have been multiplex-transferred through the first to fifth units, reaches a secondary transfer section composed of the intermediate transfer belt 20, an opposing roll 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 arranged on the image bearing surface side of the intermediate transfer belt 20. Meanwhile, recording paper (an example of a recording medium) P is fed via a supply mechanism into the gap between the secondary transfer roll 26 and the intermediate transfer belt 20 at a predetermined timing, and a secondary transfer bias is applied to the opposing 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 based on resistance detected by resistance detection means (not shown) that detects resistance in the secondary transfer section, and is voltage-controlled.

[0135] After transferring the toner image onto the recording paper P, the intermediate transfer belt 20 continues to run and comes into contact with a cleaning blade provided on the intermediate transfer body cleaning device 21. Toner remaining on the intermediate transfer belt 20 is removed and collected by the intermediate transfer body cleaning device 21.

[0136] The recording paper P onto which the toner image has been transferred is sent to the pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of a fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image.

[0137] 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.

[0138] 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.

[0139] The image formation mode by the image forming apparatus shown in Fig. 1 is not limited to the above. A mode in which only the fifth unit 10W is operated to form a white image on one side of the recording paper P, and then the recording paper P is sent upstream in the direction of travel of the intermediate transfer belt, and the first unit 10Y to the fourth unit 10K are operated to form a color image on the white image on the recording paper P; A mode in which only the fifth unit 10W is operated to form a white image on one side of the recording paper P, and then the recording paper P is sent upstream in the direction of travel of the intermediate transfer belt, and the first unit 10Y to the fifth unit 10W are operated to form a white image and a color image on the white image on the recording paper P; An example of such a configuration is one in which only the fifth unit 10W is operated to form a white image on one side of the recording paper P, then the recording paper P is sent upstream in the direction of travel of the intermediate transfer belt, only the fifth unit 10W is operated again to overlay a white image on the white image on the recording paper P, the recording paper P is returned upstream in the direction of travel of the intermediate transfer belt, and the first unit 10Y to the fourth unit 10K are operated to form a color image on the multilayer white image on the recording paper P.

[0140] <Process cartridges, toner cartridges> The process cartridge according to this embodiment is a process cartridge that is detachably attached to an image forming apparatus and that contains the electrostatic image developer according to this embodiment and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image.

[0141] The process cartridge according to this embodiment is not limited to the above configuration, and 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.

[0142] 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.

[0143] 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 by, for example, a housing 117 having a mounting rail 116 and an opening 118 for exposure, which integrally holds 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 an image carrier cleaning means), and is formed 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).

[0144] Next, the toner cartridge according to this embodiment will be described. The toner cartridge according to the present embodiment is a toner cartridge that contains the white toner according to the present embodiment and is detachably attached to an image forming apparatus. The toner cartridge contains replenishment toner to be supplied to a developing unit provided in the image forming apparatus.

[0145] The image forming apparatus shown in FIG. 1 has a configuration in which toner cartridges 8Y, 8M, 8C, 8K, and 8W are detachably mounted. The developing devices 4Y, 4M, 4C, 4K, and 4W are connected to toner cartridges corresponding to the respective colors via toner supply pipes (not shown). When the toner stored in a toner cartridge runs low, the toner cartridge is replaced. An example of a toner cartridge according to this embodiment is toner cartridge 8W, which contains white toner according to this embodiment. Toner cartridges 8Y, 8M, 8C, and 8K contain yellow, magenta, cyan, and black toner, respectively. [Example]

[0146] Hereinafter, the embodiments of the present invention will be described in detail with reference to examples, but the embodiments of the present invention are not limited to these examples. In the following description, unless otherwise specified, "parts" and "%" are by mass. All syntheses, processing, preparations, etc. were carried out at room temperature (25°C ± 3°C) unless otherwise noted.

[0147] <Preparation of surface-treated titanium oxide> [White pigment (1)] Titanium tetrachloride was oxidized using oxygen gas in the gas phase, and the resulting vapor containing titanium oxide was then introduced into a gas mixture of aluminum vapor metal ions and oxygen in a 60:40 ratio. The mixture was then heated to 1600°C for 30 minutes to coat the titanium oxide surface with alumina, yielding surface-treated titanium oxide. This was designated white pigment (1). The atomic composition of the surface of white pigment (1) was Al = 14.3 atomic %, Ti = 8.2 atomic %, with an atomic weight ratio of Al / Ti = 1.7.

[0148] [White pigments (2) to (8)] Surface-treated titanium oxides were obtained in the same manner as in the preparation of white pigment (1), except that the size of the titanium oxide prepared by the vapor phase method and the retention time after the vaporized effluent containing titanium oxide was introduced into the mixed gas were changed. These were designated white pigments (2) to (8).

[0149] [White pigment (9)] Untreated titanium oxide was obtained in the same manner as in the preparation of white pigment (1), except that aluminum vapor metal ions were not mixed in, and this was designated as white pigment (9).

[0150] <Preparation of White Pigment Dispersions (1) to (9)> 100 parts of white pigment, 5 parts of anionic surfactant (Neogen RK manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and 90 parts of ion-exchanged water were mixed and dispersed for 30 minutes using a homogenizer (Ultra-Turrax T50 manufactured by IKA Corporation). Ion-exchanged water was added to adjust the solid content to 50%. White pigment dispersions (1) to (9) were obtained from white pigments (1) to (9), respectively.

[0151] <Preparation of hybrid resin> [Hybrid Resin (1)] -Formation of crystalline polyester resin units- A reaction vessel equipped with a stirrer, thermometer, nitrogen inlet tube, and pressure reducer was charged with 260 parts of 1,6-hexanediol, 460 parts of 1,10-decanedicarboxylic acid, and 2 parts of tin octoate as a polymerization catalyst. The mixture was heated to 180°C and reacted at the same temperature for 10 hours under a nitrogen stream while distilling off the water produced. The temperature inside the reaction vessel was then gradually raised to 230°C, and the reaction was continued for 5 hours under a nitrogen atmosphere while distilling off the water. The reaction was then continued under a reduced pressure of 0.007 MPa to 0.026 MPa while distilling off the water. The reaction was stopped when the acid value reached 0.1 mgKOH / g, yielding a crystalline polyester resin unit.

[0152] - Formation of amorphous resin units - A mixture of 140 parts of hexamethylene diisocyanate, 40 parts of acrylic acid, 170 parts of styrene, 50 parts of butyl acrylate, and 50 parts of di-t-butyl peroxide (a polymerization initiator) was placed in a dropping funnel. The dropping funnel was then placed in the reaction vessel (containing 160 parts of a crystalline polyester resin unit), and the mixture was added dropwise from the dropping funnel over one hour while stirring the contents of the reaction vessel at 160°C. After the addition, the reaction was continued for one hour while maintaining the temperature of the reaction vessel at 160°C. The temperature of the reaction vessel was then raised to 200°C and maintained at 10 kPa for one hour, after which the remaining monomer was removed. This resulted in a hybrid resin (1) in which amorphous resin units of polyurethane resin and polystyrene resin were chemically bonded to crystalline polyester resin units.

[0153] [Hybrid Resins (2) to (5)] Hybrid resins (2) to (5) were synthesized in the same manner as in the preparation of hybrid resin (1), except that the monomer composition and the amount of crystalline polyester resin unit used were changed as shown in Table 1.

[0154] [Table 1]

[0155] <Preparation of Hybrid Resin Particle Dispersions (1) to (5)> The hybrid resin was dispersed using a Cavitron CD1010 (manufactured by Eurotech Co., Ltd.) disperser modified to a high-temperature, high-pressure type. 20 parts of the hybrid resin and 80 parts of ion-exchanged water were mixed, and ammonia was added to adjust the pH to 8.5. The mixture was then dispersed at a rotor speed of 60 Hz and a pressure of 5 kg / cm. 2 The Cavitron was operated under the condition of heating at 140°C using a heat exchanger. Ion-exchanged water was added to the dispersion to adjust the solid content to 20%, and hybrid resin particle dispersions (1) to (5) were obtained from hybrid resins (1) to (5), respectively. The volume average particle diameter of the resin particles in each hybrid resin particle dispersion was 120 nm.

[0156] <Preparation of vinyl resin particle dispersion> [Polystyrene acrylic resin particle dispersion (1)] Styrene: 77 parts n-Butyl acrylate: 23 parts 1,10-decanediol diacrylate: 0.4 parts Dodecanethiol: 0.7 parts The above materials were mixed and dissolved, and a solution of 1 part anionic surfactant (Dowfax 2A1, manufactured by Dow Chemical Co.) dissolved in 60 parts ion-exchanged water was added and dispersed and emulsified in a flask to prepare an emulsion. Two parts of anionic surfactant (Dowfax 2A1, manufactured by Dow Chemical Co.) were dissolved in 90 parts ion-exchanged water, and 2 parts of the emulsion were added. Next, 10 parts of ion-exchanged water containing 1 part ammonium persulfate was added. The remaining emulsion was then added over a period of 3 hours. After nitrogen replacement of the reaction vessel, the solution was heated to 65°C in an oil bath with stirring and the reaction continued for 5 hours. After the reaction, ion-exchanged water was added to adjust the solids content to 30%, yielding polystyrene acrylic resin particle dispersion (1). The resin particles in polystyrene acrylic resin particle dispersion (1) had a volume average particle diameter of 102 nm and a weight average molecular weight (Mw) of 57,000.

[0157] <Preparation of Release Agent Particle Dispersion (1)> 270 parts of ester wax (melting temperature 72°C, manufactured by Nippon Seiro Co., Ltd.), 15 parts of anionic surfactant (Neogen RK, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), and 20 parts of ion-exchanged water were mixed, and the release agent was dissolved in the mixture using a pressure discharge homogenizer (Gaulin Homogenizer, manufactured by Gaulin Co., Ltd.) at an internal liquid temperature of 120°C. The mixture was then dispersed at a dispersion pressure of 5 MPa for 120 minutes, followed by 40 MPa for 360 minutes, and cooled. Ion-exchanged water was added to adjust the solid content to 20%, yielding a release agent particle dispersion (1). The volume average particle diameter of the particles in the release agent particle dispersion was 220 nm.

[0158] <Preparation of Toner and Developer> [Example 1] -First agglomerated particle formation process- Polystyrene acrylic resin particle dispersion (1) (solid content 30%): 40 parts Hybrid resin particle dispersion (1) (solid content 20%): 100 parts White pigment dispersion (1) (solid content 50%): 80 parts Release agent particle dispersion (1) (solid content 20%): 30 parts Ion-exchanged water: 200 parts Anionic surfactant (Dowfax 2A1 manufactured by The Dow Chemical Company): 2.0 parts The above materials were placed in a reaction vessel equipped with a thermometer, pH meter, and stirrer, and the pH was adjusted to 3.0 with 1.0% nitric acid at 25°C. Next, while dispersing at 5000 rpm using a homogenizer (IKA Ultra Turrax T50), 100 parts of a 2.0% magnesium chloride aqueous solution was added as a flocculant and dispersed for 6 minutes. Next, a stirrer and mantle heater were installed in the reaction vessel, and the stirring speed was adjusted to ensure sufficient stirring of the slurry. The temperature was increased at a rate of 0.2°C / min up to 40°C, and then at a rate of 0.05°C / min from 40°C to 53°C. Particle size was measured every 10 minutes using a Multisizer II (aperture diameter 50 μm, Beckman Coulter). The temperature was maintained when the volume-average particle size reached 4.2 μm, and this was designated as the first aggregate particle dispersion.

[0159] -Second agglomerated particle formation process- To the first aggregated particle dispersion, 40 parts of polystyrene acrylic resin particle dispersion (1) (solid content: 30%) was added over 5 minutes, and the mixture was held for 20 minutes to prepare a second aggregated particle dispersion.

[0160] -Fusion / unification process- After the second aggregate particle dispersion was maintained at 50°C for 30 minutes, 8 parts of a 20% aqueous solution of EDTA (ethylenediaminetetraacetic acid) were added to the reaction vessel. Next, a 1 mol / L aqueous solution of sodium hydroxide was added to adjust the pH of the dispersion to 9.0. Next, the temperature was increased to 90°C at a rate of 1°C / min while adjusting the pH to 9.0 every 5°C, and the dispersion was maintained at 90°C. The particle shape was observed with an optical microscope, and after particle coalescence was confirmed, the reaction vessel was cooled to 30°C with cooling water.

[0161] After cooling, the slurry was passed through a 15 μm nylon mesh to remove coarse particles. The toner slurry that passed through the mesh was filtered under reduced pressure using an aspirator. The solids remaining on the filter paper were crushed by hand and added to ion-exchanged water in an amount 10 times the solids content at 30°C, followed by stirring and mixing for 30 minutes. The mixture was then filtered under reduced pressure using an aspirator. The solids remaining on the filter paper were crushed by hand and added to ion-exchanged water in an amount 10 times the solids content at 30°C, followed by stirring and mixing for 30 minutes. The mixture was then filtered under reduced pressure using an aspirator again, and the electrical conductivity of the filtrate was measured. This process was repeated until the electrical conductivity of the filtrate reached 10 μS / cm or less, and the solids were washed. The washed solids were crushed using a wet-dry granulator (Comil) and vacuum-dried in an oven at 35°C for 36 hours to obtain toner particles. The volume average particle diameter of the toner particles was 5.7 μm.

[0162] -External addition of hydrophobic silica particles- 1.5 parts of hydrophobic silica particles (RY50 manufactured by Nippon Aerosil Co., Ltd.) were added to 100 parts of the toner particles and mixed at 13,000 rpm for 30 seconds using a sample mill, and then sieved using a vibrating sieve with 45 μm openings to obtain an externally added toner.

[0163] -Mixed with Carrier- 10 parts of the toner with external additives and 100 parts of the carrier were placed in a V-blender and stirred for 20 minutes. After that, the mixture was sieved through a sieve with 212 μm openings to obtain a developer. The carrier was prepared as follows.

[0164] -Creating a carrier- Ferrite particles (volume average particle size 35 μm): 100 parts Toluene: 14 parts Styrene / methyl methacrylate copolymer (copolymerization ratio 15 / 85): 3 parts Carbon black (Cabot, Regal 330): 0.2 parts The above materials except for the ferrite particles were dispersed in a sand mill to prepare a dispersion liquid, which was then placed in a vacuum degassing kneader together with the ferrite particles, and dried under reduced pressure while stirring to obtain a resin-coated carrier.

[0165] [Examples 2 to 17, Comparative Examples 1 to 6] The toner particles, toner with external additives, and developer for each example were prepared in the same manner as in Example 1, except that the type and amount of hybrid resin particle dispersion and the type and amount of white pigment dispersion were changed so as to meet the specifications shown in Table 2.

[0166] <Performance evaluation> [Toner slip-through (wear and tear of intermediate transfer body cleaning blade)] A commercially available electrophotographic intermediate transfer image forming apparatus (DocuCentre III C7600, manufactured by Fuji Xerox Co., Ltd.) was prepared, and the developer was filled into the developing device. In an environment of 28°C and 85% relative humidity, 5,000 sheets of plain paper (A4 size P paper manufactured by Fuji Xerox) were printed with a white image of 20% density, followed by one sheet of white image of 50% density. After image formation, adhesive tape was attached to the surface of the intermediate transfer belt, which was then peeled off and the peeled tape was attached to a piece of black paper. The white toner beneath the tape was visually observed and classified as follows. The results are shown in Table 2. A: No white toner was detected. B: A very small amount of white toner is observed, but this is within the practically acceptable range. C: A small amount of white toner is observed, but this is within the practically acceptable range. D: White toner was observed over the entire adhesive tape, making it unsuitable for practical use.

[0167] [Whiteness] A commercially available electrophotographic intermediate transfer image forming apparatus (DocuCentre III C7600, manufactured by Fuji Xerox Co., Ltd.) was prepared, and the developer was filled into the developing device. A white image with 100% image density was formed on black paper. It was visually observed under natural light indoors and classified as follows. The results are shown in Table 2. A: Bright and good white color. B: Sufficiently white. C: Looks slightly dull white. D: The black base is faintly visible. E: The black of the base is clearly visible and is unacceptable.

[0168] [Table 2] [Explanation of symbols]

[0169] 10Y, 10M, 10C, 10K, 10W Image forming units 1Y, 1M, 1C, 1K, 1W Photoconductor (an example of an image carrier) 2Y, 2M, 2C, 2K, 2W Charging roll (an example of charging means) 3Y, 3M, 3C, 3K, 3W exposure device (an example of electrostatic image forming means) 4Y, 4M, 4C, 4K, 4W developing device (an example of developing means) 5Y, 5M, 5C, 5K, 5W Primary transfer roll (an example of a primary transfer means) 6Y, 6M, 6C, 6K, 6W Photoconductor cleaning device 8Y, 8M, 8C, 8K, 8W toner cartridges 20 Intermediate transfer belt (an example of an intermediate transfer body) 21 Intermediate transfer body cleaning device 22 Drive Roll 23 Support Roll 24 opposing roll 26 Secondary transfer roll (an example of a secondary transfer means) 28 Fixing device (an example of fixing means) P Recording paper (an example of a recording medium) 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 Photoconductor cleaning device 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. The toner particles include a binder resin including a hybrid resin in which an amorphous resin unit and a crystalline polyester resin unit are chemically bonded, a surface-treated titanium oxide, and a release agent; The white toner has an atomic ratio of Al in the surface of the surface-treated titanium oxide of 3 atomic % or more and 20 atomic % or less, and an atomic ratio of Ti in the surface of the surface-treated titanium oxide of 5 atomic % or more and 15 atomic % or less.

2. 2. The white toner according to claim 1, wherein the atomic ratio of Al on the surface of said surface-treated titanium oxide is 5 atomic % or more and 15 atomic % or less, and the atomic ratio of Ti on the surface of said surface-treated titanium oxide is 6 atomic % or more and 12 atomic % or less.

3. 3. The white toner according to claim 1, wherein the atomic weight ratio Al / Ti of Al to Ti on the surface of the surface-treated titanium oxide is 0.5 or more and 4.0 or less.

4. 4. The white toner according to claim 1, wherein the atomic ratio Al / Ti of Al to Ti on the surface of the surface-treated titanium oxide is 1.0 or more and 3.5 or less.

5. 5. The white toner according to claim 1, wherein the mass ratio of the amorphous resin unit in the hybrid resin is 50% by mass or more and 90% by mass or less.

6. 6. The white toner according to claim 1, wherein the mass ratio of the amorphous resin unit in the hybrid resin is 60 mass % or more and 85 mass % or less.

7. 7. The white toner according to claim 1, wherein a mass ratio of the hybrid resin to the surface-treated titanium oxide contained in the toner particles (hybrid resin / surface-treated titanium oxide) is 0.08 or more and 3.0 or less.

8. 8. The white toner according to claim 1, wherein a ratio of a mass proportion (mass %) of the amorphous resin unit in the hybrid resin to an atomic proportion (atomic %) of Al on the surface of the surface-treated titanium oxide (mass proportion of amorphous resin unit / atomic proportion of Al) is 2.5 or more and 30 or less.

9. 9. The white toner according to claim 1, wherein the content of the hybrid resin contained in the toner particles is 5% by mass or more and 60% by mass or less of the total toner particles.

10. 10. The white toner according to claim 1, wherein the surface-treated titanium oxide has an average major axis length of 20 nm or more and 300 nm or less.

11. The surface-treated titanium oxide has a BET specific surface area of ​​4 m ２ / g or more 12m ２ The white toner according to any one of claims 1 to 10, wherein the average molecular weight of the white toner is 1 / g or less.

12. 12. The white toner according to claim 1, wherein the content of the surface-treated titanium oxide contained in the toner particles is 20% by mass or more and 60% by mass or less of the total mass of the toner particles.

13. An electrostatic image developer comprising the white toner according to any one of claims 1 to 12.

14. The white toner according to any one of claims 1 to 12 is contained therein, A toner cartridge that is detachably attached to an image forming device.

15. a developing unit containing the electrostatic image developer according to claim 13 and developing an electrostatic image formed on the surface of an image carrier into a toner image by using the electrostatic image developer, A process cartridge is detachably mounted in an image forming apparatus.

16. an image carrier; a charging means for charging the surface of the image carrier; an electrostatic image forming means for forming an electrostatic image on the charged surface of the image carrier; a developing unit containing the electrostatic image developer according to claim 13 and developing the electrostatic image formed on the surface of the image carrier into a toner image by the electrostatic image developer; an intermediate transfer member onto which the toner image formed on the surface of the image carrier is transferred; a primary transfer means for transferring the toner image formed on the surface of the image carrier to the surface of the intermediate transfer body; a secondary transfer means for transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; an intermediate transfer body cleaning means having a blade that comes into contact with the surface of the intermediate transfer body and that cleans the toner remaining on the surface of the intermediate transfer body by using the blade after the toner image has been transferred onto the surface of the recording medium; An image forming apparatus comprising:

17. a charging step of charging the surface of the image carrier; an electrostatic image forming step of forming an electrostatic image on the charged surface of the image carrier; a developing step of developing the electrostatic image formed on the surface of the image carrier into a toner image by using the electrostatic image developer according to claim 13; a primary transfer step of transferring the toner image formed on the surface of the image carrier to the surface of an intermediate transfer member; a secondary transfer step of transferring the toner image transferred onto the surface of the intermediate transfer body onto the surface of a recording medium; a fixing step of fixing the toner image transferred onto the surface of the recording medium; an intermediate transfer body cleaning step of contacting a blade with the surface of the intermediate transfer body after the toner image has been transferred to the surface of the recording medium to remove residual toner from the surface of the intermediate transfer body; An image forming method comprising the steps of:

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