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

Abstract

To provide a toner for electrostatic charge image development that can prevent the occurrence of fogging when image formation is repeatedly performed in a low temperature and low humidity environment, at a low image density, and in a low R / L condition.SOLUTION: A toner for electrostatic charge image development has toner particles having an average circularity Cc of 0.80 or more and less than 0.98, and an external additive including monodisperse silica particles and titanic acid compound particles. The ratio Rt / Rs of the average primary particle diameter Rt of the titanic acid compound particles to the average primary particle diameter Rs of the monodisperse silica particles is 0.5 or more and 3.5 or less. When the external coverage of the monodisperse silica particles on the surface of the toner particle is defined as A%, and the external coverage of the titanic acid compound particles on the surface of the toner particle as B%, A / B satisfies the following formula (1). Formula (1) 0<A / B≤2.00.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] Patent Document 1 proposes "an electrophotographic toner comprising toner base particles having an average particle size of 10 μm or less, which contain at least a release agent, a colorant, and a binder resin, strontium titanate microparticles, and hydrophobic inorganic microparticles having an average particle size of 1 / 10 to 1 / 3 of the average particle size of the strontium titanate microparticles, wherein the strontium titanate microparticles and the hydrophobic inorganic microparticles are externally added to the toner base particles." [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-148405 Summary of the Invention [Problem to be solved by the invention]

[0004] In the case of toner particles having an average circularity of less than 0.98, when a large load is applied inside the developing means, the external additive may migrate to the recesses of the toner particles. For example, when images with low image density (e.g., 1% image density) are repeatedly formed under conditions (hereinafter referred to as "low R / L conditions") in a low-temperature, low-humidity environment (e.g., a temperature of 10°C and a humidity of 15%), with warm-up intervals between each image (these conditions are also referred to as "low R / L conditions"), a large load is placed on the toner inside the developing unit. In toner that has been subjected to a large load inside the developing unit, the external additives may migrate to the recesses of the toner particles, causing a significant change in the external additive structure. When new toner is added to the toner, a difference in the charge series occurs between the toner with a significantly changed external additive structure and the newly added toner, and this may cause the toner to adhere to and fix in non-image areas due to mutual charging (hereinafter referred to as "fogging").

[0005] The present invention aims to provide a toner for developing electrostatic images, which comprises toner particles having an average circularity Cc of 0.80 or more but less than 0.98 and an external additive containing monodispersed silica particles and titanic acid compound particles, and which suppresses the occurrence of fogging when images are repeatedly formed in a low-temperature, low-humidity environment, at a low image density, and with a low R / L ratio, compared to a toner in which the ratio Rt / Rs is less than 0.50 or exceeds 3.50, the proportion of monodispersed silica particles contained in aggregates containing titanic acid compound particles among the monodispersed silica particles present on the surface of the toner particles is less than 20% by number, or the A / B value exceeds 2.00. [Means for solving the problem]

[0006] Specific means for solving the above problems include the following aspects.

[0007] <1> toner particles having an average circularity Cc of 0.80 or more and less than 0.98; an external additive containing monodispersed silica particles and titanic acid compound particles; and a ratio Rt / Rs of an average primary particle diameter Rt of the titanate compound particles to an average primary particle diameter Rs of the monodispersed silica particles is 0.50 or more and 3.50 or less; A toner for developing electrostatic images, wherein A / B satisfies the following formula (1): A% is the coverage rate of the monodisperse silica particles on the surface of the toner particles, and B% is the coverage rate of the titanate compound particles on the surface of the toner particles. Formula (1) 0

[0008] <2> toner particles having an average circularity Cc of 0.80 or more and less than 0.98; an external additive containing monodispersed silica particles and titanic acid compound particles; and A toner for developing electrostatic images, wherein the proportion of the number of monodispersed silica particles contained in aggregates containing the titanic acid compound particles among the monodispersed silica particles present on the surfaces of the toner particles is 20% or more by number.

[0009] <3> The monodisperse silica particles have an average primary particle size Rs of 20 nm or more and 70 nm or less, The titanate compound particles have an average primary particle size Rt of 20 nm or more and 70 nm or less. <1> or <2> 2. The toner for developing electrostatic images according to claim 1. <4> The monodisperse silica particles have an external additive coverage A of 5% or more and 50% or less, The titanate compound particles have an external additive coverage B of 5% or more and 50% or less. <1> ~ <3> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images.

[0010] <5> The monodisperse silica particles have an average circularity Ca of more than 0.86 but less than 0.94, The titanate compound particles have an average circularity Cb of more than 0.78 and less than 0.94. <1> ~ <4> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <6> the average circularity Ca of the monodispersed silica particles is greater than the average circularity Cb of the titanate compound particles; <5> 2. The toner for developing electrostatic images according to claim 1. <7> ​The monodisperse silica particles have a specific gravity Da of 1.1 or more and 1.3 or less, The specific gravity Db of the titanate compound particles is greater than the specific gravity Da of the monodisperse silica particles. <1> ~ <6> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <8> The specific gravity Db of the titanate compound particles is 4.0 or more and 6.5 or less. <7> 2. The toner for developing electrostatic images according to claim 1.

[0011] <9> The titanate compound particles are alkaline earth metal titanate particles. <1> ~ <8> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <10> The titanate compound particles contain a dopant. <1> ~ <9> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <11> the dopant is at least one of lanthanum and silica; <10> 2. The toner for developing electrostatic images according to claim 1.

[0012] <12> The toner particles have a volume average particle size of 5 μm or more. <1> ~ <11> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <13> The toner particles have a small diameter volume particle size distribution index of 1.25 or more. <1> ~ <12> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <14> The toner particles contain a crystalline polyester resin. <1> ~ <13> 10. The toner for developing electrostatic images according to claim 9, wherein the toner is a toner for developing electrostatic images. <15> The exposure rate of the crystalline polyester resin on the surface of the toner particles is 2% or more and 10% or less. <14> 2. The toner for developing electrostatic images according to claim 1.

[0013] <16> <1> ~ <15> 10. An electrostatic image developer comprising the toner for developing electrostatic images according to any one of claims 1 to 9. <17> <1> ~ <15> The toner for developing electrostatic images according to any one of the above items is contained in the container. A toner cartridge that is detachably attached to an image forming device. <18> <16> and a developing means for 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. <19> 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; <16> 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; a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; An image forming apparatus comprising: [Effects of the Invention]

[0014] <1> According to the invention, there is provided a toner for developing electrostatic images, which comprises toner particles having an average circularity Cc of 0.80 or more and less than 0.98 and an external additive containing monodisperse silica particles and titanic acid compound particles, and which suppresses the occurrence of fogging when images are repeatedly formed in a low-temperature, low-humidity environment, under conditions of low image density and low R / L, compared to when the ratio Rt / Rs is less than 0.50 or exceeds 3.50, or the value of A / B exceeds 2.00.

[0015] <2> According to the invention, there is provided a toner for developing electrostatic images, which comprises toner particles having an average circularity Cc of 0.80 or more but less than 0.98 and an external additive containing monodispersed silica particles and titanic acid compound particles, and which suppresses the occurrence of fogging when images are repeatedly formed under conditions of a low temperature and low humidity environment, low image density, and low R / L, compared to a case in which the proportion of monodispersed silica particles contained in aggregates containing titanic acid compound particles among the monodispersed silica particles present on the surface of the toner particles is less than 20% by number.

[0016] <3> According to the invention, there is provided a toner for developing electrostatic images which suppresses the occurrence of fogging when images are repeatedly formed in a low temperature and low humidity environment under conditions of low image density and low R / L, compared to when the average primary particle diameter Rs of monodispersed silica particles is less than 20 nm or more than 70 nm and the average primary particle diameter Rt of titanate compound particles is less than 20 nm or more than 70 nm. <4> According to the invention, there is provided a toner for developing electrostatic images which suppresses the occurrence of fogging when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, compared to when the external additive coverage rate A of monodisperse silica particles exceeds 50% or the external additive coverage rate B of titanate compound particles is less than 5%.

[0017] <5> According to the invention, there is provided a toner for developing electrostatic images which suppresses the occurrence of fogging when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, compared to when the average circularity Ca of monodispersed silica particles is 0.86 or less or 0.94 or more, or when the average circularity Cb of titanate compound particles is 0.78 or less or 0.94 or more. <6> According to the present invention, there is provided a toner for developing electrostatic images which suppresses the occurrence of fogging when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, compared to when the average circularity Ca of monodispersed silica particles is smaller than the average circularity Cb of titanate compound particles. <7> According to the invention, there is provided a toner for developing electrostatic images which suppresses the occurrence of fogging when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, compared to when the specific gravity Da of the monodispersed silica particles is less than 1.1 or exceeds 1.3, or when the specific gravity Db of the titanate compound particles is smaller than the specific gravity Da of the monodispersed silica particles. <8> According to the present invention, there is provided a toner for developing electrostatic images that suppresses the occurrence of fogging when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, compared to when the specific gravity Db of the titanate compound particles is less than 4.0 or more than 6.5.

[0018] <9> According to the present invention, there is provided a toner for developing electrostatic images that suppresses the occurrence of fog when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L, compared to when the titanate compound particles are not alkaline earth metal titanate particles. <10> According to the present invention, there is provided a toner for developing electrostatic images that suppresses the occurrence of fog when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L, compared to when the titanate compound particles do not contain a dopant. <11> According to the invention, there is provided a toner for developing electrostatic images that suppresses the occurrence of fog when images are repeatedly formed under conditions of low temperature and low humidity, low image density, and low R / L, compared to when the dopant is not lanthanum or silica.

[0019] <12> According to the invention, there is provided a toner for developing electrostatic images in which, even when the volume average particle size of the toner particles is 5 μm or more, the occurrence of fogging is suppressed when images are repeatedly formed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, compared to when the ratio Rt / Rs is less than 0.50 or exceeds 3.50, the proportion of monodispersed silica particles contained in aggregates containing titanate compound particles among the monodispersed silica particles present on the surface of the toner particles is less than 20% by number, or the value A / B exceeds 2.00. <13> According to the invention relating to (1), there is provided a toner for developing electrostatic images in which, even if the toner particles have a small diameter side volume particle size distribution index of 1.25 or more, the occurrence of fogging is suppressed when images are repeatedly formed in a low temperature, low humidity environment, under conditions of low image density and low R / L, compared to when the ratio Rt / Rs is less than 0.50 or exceeds 3.50, the proportion of monodispersed silica particles contained in aggregates containing titanate compound particles among the monodispersed silica particles present on the surface of the toner particles is less than 20% by number, or the value A / B exceeds 2.00. <14> According to the present invention, there is provided a toner for developing electrostatic images that is less likely to cause fogging when images are repeatedly formed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, compared to when the binder resin of the toner particles is made of an amorphous polyester resin. <15> According to the present invention, there is provided a toner for developing electrostatic images that suppresses the occurrence of fog when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L, compared to when the exposure rate of the crystalline polyester resin on the surface of the toner particles is less than 2%.

[0020] <16> , <17> , <18> , or <19> According to the invention, there is provided an electrostatic image developer, a toner cartridge, a process cartridge, or an image forming apparatus equipped with a toner for developing electrostatic images that suppresses the occurrence of fogging when repeated image formation is performed under conditions of a low temperature, low humidity environment, a low image density, and a low R / L, compared to when a toner having an Rt / Rs ratio of less than 0.50 or more than 3.50, in which the proportion of monodispersed silica particles contained in aggregates containing titanate compound particles among the monodispersed silica particles present on the surface of the toner particles is less than 20% by number, or an A / B value of more than 2.00 is used. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a process cartridge according to the present embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, an embodiment of the present invention will be described. These descriptions and examples are intended to illustrate the embodiment and are not intended to limit the scope of the invention. In the present specification, the upper or lower limit of one numerical range may be replaced with the upper or lower limit of another numerical range. In addition, in the present specification, the upper or lower limit of a numerical range may be replaced with a value shown in the examples.

[0023] Each component may contain multiple types of the corresponding substance. When referring to the amount of each component in a composition, if there are multiple substances corresponding to each component in the composition, the amount refers to the total amount of those multiple substances present in the composition, unless otherwise specified.

[0024] <Toner for developing electrostatic images> (First embodiment) The electrostatic image developing toner according to the first embodiment (hereinafter, the electrostatic image developing toner may be referred to as "toner") comprises toner particles having an average circularity Cc of 0.80 or more but less than 0.98, and an external additive containing monodispersed silica particles and titanic acid compound particles. The ratio Rt / Rs of the average primary particle diameter Rt of the titanic acid compound particles to the average primary particle diameter Rs of the monodispersed silica particles is 0.50 or more but 3.50 or less, and when the coverage of the monodispersed silica particles on the toner particle surfaces is A%, and the coverage of the titanic acid compound particles on the toner particle surfaces is B%, A / B satisfies the following formula (1): Formula (1) 0 ​The coverage ratio of the monodisperse silica particles on the toner particle surface means the ratio (%) of the area covered by the monodisperse silica particles to the total surface area of ​​the toner particle. Similarly, the coverage ratio of the titanate compound particles on the toner particle surface means the ratio (%) of the area covered by the titanate compound particles to the total surface area of ​​the toner particle.

[0025] As mentioned above, when low-density images are repeatedly formed under low-temperature, low-humidity conditions and low R / L conditions, a large load is placed on the toner inside the developing unit, which can cause external additives on the surface of the toner particles to migrate. In particular, for toner particles with an average circularity of less than 0.98, the toner particle surfaces are uneven, so the large load can cause the external additives to migrate to the recesses of the toner particles, significantly changing the external additive structure. When new toner is added to this mixture, a difference in the charge series occurs between the toner with a significantly changed external additive structure and the newly added toner, which can cause fogging due to mutual charging.

[0026] In contrast, in this embodiment, the ratio Rt / Rs is within the above range, and A / B satisfies the above formula (1). Therefore, the occurrence of fog is suppressed when image formation is repeatedly performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L. The reason for this is unclear, but is presumed to be as follows.

[0027] Titanate compound particles tend to be positively charged by frictional charging. On the other hand, monodisperse silica particles tend to be negatively charged by frictional charging. Therefore, when the ratio Rt / Rs is within the above range, the particle size of the titanate compound particles and the particle size of the monodisperse silica particles are similar, and therefore, it is thought that the titanate compound particles and the monodisperse silica particles attract each other and undergo mild aggregation. Furthermore, titanic acid compound particles, which have a larger specific gravity than monodisperse silica particles, are less likely to move on the surface of toner particles and are more likely to be fixed to the convex portions of the toner particle surface, which are subject to the greatest load. Therefore, it is believed that, among the monodisperse silica particles present on the convex portions, the monodisperse silica particles that are loosely agglomerated with the titanic acid compound particles are fixed to the convex portions together with the titanic acid compound particles, and are prevented from moving to the concave portions.

[0028] Furthermore, when A / B satisfies the above formula (1), it is believed that there are fewer monodispersed silica particles present alone on the toner particle surface without loosely agglomerating with the titanate compound particles. Therefore, even if the average circularity of the toner particles is less than 0.98, the bias of the titanate compound particles and monodispersed silica particles present on the unevenness of the toner particle surface is small, and the external additive structure is unlikely to change even under a large load, so it is presumed that the triboelectric series difference is unlikely to occur and the occurrence of fogging is suppressed. For the above reasons, it is presumed that the toner for developing electrostatic images according to the first embodiment suppresses the occurrence of fogging when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L.

[0029] Second Embodiment The toner for developing electrostatic images according to the second embodiment includes toner particles having an average circularity Cc of 0.80 or more but less than 0.98, and an external additive containing monodisperse silica particles and titanic acid compound particles, and the proportion of the monodisperse silica particles contained in aggregates containing the titanic acid compound particles among the monodisperse silica particles present on the surfaces of the toner particles is 20% by number or more. Hereinafter, the ratio (%) of the number of monodispersed silica particles contained in aggregates containing titanic acid compound particles to the number of monodispersed silica particles present on the surface of a toner particle will also be referred to as "aggregated silica ratio".

[0030] As mentioned above, when low-density images are repeatedly formed under low-temperature, low-humidity conditions and low R / L conditions, a large load is placed on the toner inside the developing unit, which can cause external additives on the surface of the toner particles to migrate. In particular, for toner particles with an average circularity of less than 0.98, the toner particle surfaces are uneven, so the large load can cause the external additives to migrate to the recesses of the toner particles, significantly changing the external additive structure. When new toner is added to this mixture, a difference in the charge series occurs between the toner with a significantly changed external additive structure and the newly added toner, which can cause fogging due to mutual charging.

[0031] In contrast, in the present embodiment, the aggregated silica ratio is within the above range. Therefore, the occurrence of fogging is suppressed when image formation is repeatedly performed under conditions of a low temperature and humidity environment, a low image density, and a low R / L. The reason for this is unclear, but is presumed to be as follows. Since titanate compound particles tend to be positively charged by triboelectric charging, and monodisperse silica particles tend to be negatively charged by triboelectric charging, the titanate compound particles and the monodisperse silica particles may attract each other and cause loose aggregation. Furthermore, titanate compound particles, which have a high specific gravity, are less likely to move on the surface of toner particles than monodisperse silica particles, and are more likely to be fixed even on the convex parts of the toner particle surface that are subject to the greatest load. Therefore, it is thought that, among the monodisperse silica particles present on the convex parts, the monodisperse silica particles that are loosely aggregated with the titanate compound particles are fixed on the convex parts together with the titanate compound particles, and are prevented from moving to the concave parts.

[0032] And, when the aggregated silica ratio is within the above range, that is, when the ratio of monodispersed silica particles contained in the aggregate containing titanic acid compound particles is high, it means that there are many monodispersed silica particles loosely aggregated with titanic acid compound particles and few monodispersed silica particles present alone on the toner particle surface without loosely aggregated with titanic acid compound particles. Therefore, when the aggregated silica ratio is within the above range, even if the average circularity of the toner particles is less than 0.98, the bias of the titanic acid compound particles and monodispersed silica particles present on the unevenness of the toner particle surface is small, and it is thought that the external additive structure is unlikely to change even under a large load. As a result, it is presumed that the triboelectric series difference is unlikely to occur and the occurrence of fogging is suppressed. For the above reasons, it is presumed that the toner for developing electrostatic images according to the second embodiment suppresses the occurrence of fogging when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L.

[0033] Hereinafter, a toner that corresponds to both the toner according to the first embodiment and the toner according to the second embodiment will be referred to as “toner according to the present embodiment.” However, an example of the toner of the present invention may be a toner that corresponds to at least one of the toner according to the first embodiment and the toner according to the second embodiment. The toner according to this embodiment will be described in detail below.

[0034] (toner particles) The toner particles are composed of, for example, a binder resin, and, if necessary, a colorant, a release agent, and other additives.

[0035] -Binder resin- Examples of binder resins include homopolymers of monomers such as styrenes (e.g., styrene, parachlorostyrene, α-methylstyrene, etc.), (meth)acrylic acid esters (e.g., methyl acrylate, ethyl acrylate, n-propyl acrylate, n-butyl acrylate, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (e.g., acrylonitrile, methacrylonitrile, etc.), vinyl ethers (e.g., vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (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.

[0036] As the binder resin, a polyester resin is preferable. The polyester resin may be, for example, a known amorphous polyester resin. The polyester resin may be a crystalline polyester resin in combination with the amorphous polyester resin. In this embodiment, the toner particles preferably contain a crystalline polyester resin. By containing the crystalline polyester resin in the toner particles, the occurrence of fog is further suppressed when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L. The reason for this is not clear, but is presumed to be as follows. In the case of aggregates of titanate compound particles and monodisperse silica particles, the titanate compound particles, which tend to be positively charged by friction, and the monodisperse silica particles, which tend to be negatively charged, cancel out the charges, but the charges may not be completely canceled out and remain on the surface of the toner particles. If charges remain in the aggregates, the aggregates may repel each other, making them more likely to move on the surface of the toner particles. On the other hand, when the toner particles contain a crystalline polyester resin, the charge of the aggregates is released due to the de-electrifying properties of the crystalline polyester resin, and the repulsion between the aggregates is suppressed, so that the external additive structure is less likely to change even under a large load, and the occurrence of fogging is suppressed. The crystalline polyester resin is preferably used in an amount of 2% by mass or more and 40% by mass or less (preferably 2% by mass or more and 20% by mass or less) relative to the total binder resin.

[0037] The "crystalline" nature of a resin refers to the presence of a clear endothermic peak rather than a stepwise change in endothermic heat in differential scanning calorimetry (DSC). Specifically, this refers to the half-width of the endothermic peak being within 10°C when measured at a heating rate of 10°C / min. On the other hand, the term "amorphous" for a resin means that the half-width exceeds 10°C, that the endothermic amount exhibits a stepwise change, or that no clear endothermic peak is observed.

[0038] Amorphous polyester resin Examples of the amorphous polyester resin include a condensation polymer of a polycarboxylic acid and a polyhydric alcohol. Note that, as the amorphous polyester resin, a commercially available product or a synthesized product may be used.

[0039] Examples of polycarboxylic acids include aliphatic dicarboxylic acids (such as oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenylsuccinic acid, adipic acid, and sebacic acid), alicyclic dicarboxylic acids (such as cyclohexanedicarboxylic acid), aromatic dicarboxylic acids (such as terephthalic acid, isophthalic acid, phthalic acid, and naphthalenedicarboxylic acid), anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). Among these, aromatic dicarboxylic acids are preferred as polycarboxylic acids. The polycarboxylic acid may be a trivalent or higher carboxylic acid having a crosslinked or branched structure in combination with a dicarboxylic acid. Examples of the trivalent or higher carboxylic acid include trimellitic acid, pyromellitic acid, anhydrides thereof, and lower alkyl esters thereof (e.g., having 1 to 5 carbon atoms). The polycarboxylic acids may be used alone or in combination of two or more.

[0040] Examples of polyhydric alcohols include aliphatic diols (e.g., ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, etc.), alicyclic diols (e.g., cyclohexanediol, cyclohexanedimethanol, hydrogenated bisphenol A, etc.), and aromatic diols (e.g., ethylene oxide adducts of bisphenol A, propylene oxide adducts of bisphenol A, etc.). Among these, preferred polyhydric alcohols are aromatic diols and alicyclic diols, and more preferred are aromatic diols. As the polyhydric alcohol, a trihydric or higher polyhydric alcohol having a crosslinked or branched structure may be used in combination with the diol. Examples of trihydric or higher polyhydric alcohols include glycerin, trimethylolpropane, and pentaerythritol. The polyhydric alcohols may be used alone or in combination of two or more.

[0041] The glass transition temperature (Tg) of the amorphous polyester resin is preferably 50°C or higher and 80°C or lower, and more preferably 50°C or higher and 65°C or lower. The glass transition temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC), more specifically, from the "extrapolated glass transition onset temperature" described in JIS K 7121-1987 "Method for measuring transition temperatures of plastics."

[0042] The weight average molecular weight (Mw) of the amorphous polyester resin is preferably 5,000 or more and 1,000,000 or less, and more preferably 7,000 or more and 500,000 or less. The number average molecular weight (Mn) of the amorphous polyester resin is preferably 2,000 or more and 100,000 or less. The molecular weight distribution Mw / Mn of the amorphous polyester resin is preferably 1.5 or more and 100 or less, and more preferably 2 or more and 60 or less. The weight-average molecular weight and number-average molecular weight are measured by gel permeation chromatography (GPC). Molecular weight measurements by GPC are performed using a Tosoh GPC HLC-8120GPC measuring device and a Tosoh TSKgel SuperHM-M (15 cm) column in THF solvent. The weight-average molecular weight and number-average molecular weight are calculated from the measurement results using a molecular weight calibration curve prepared with monodisperse polystyrene standard samples.

[0043] The amorphous polyester resin can be obtained by a known manufacturing method, for example, by carrying out the reaction at a polymerization temperature of 180°C or higher and 230°C or lower, reducing the pressure in the reaction system as necessary, and removing water and alcohol generated during the condensation. If the raw material monomer is not soluble or compatible at the reaction temperature, a high-boiling solvent may be added as a solubilizer to dissolve it. In this case, the polycondensation reaction is carried out while distilling off the solubilizer. If a monomer with poor compatibility is present, it is advisable to first condense the poorly compatible monomer with the acid or alcohol to be polycondensed, and then polycondense the monomer with the main component.

[0044] Crystalline polyester resin The crystalline polyester resin may be, for example, a polycondensate of a polycarboxylic acid and a polyhydric alcohol. Note that, as the crystalline polyester resin, a commercially available product or a synthesized product may be used. Here, the crystalline polyester resin is preferably a polycondensate using a polymerizable monomer having a linear aliphatic group rather than a polymerizable monomer having an aromatic group, since it easily forms a crystalline structure.

[0045] 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-nonanedicarboxylic 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.

[0046] 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.

[0047] Here, the polyhydric alcohol has an aliphatic diol content of 80 mol % or more, preferably 90 mol % or more.

[0048] The melting temperature of the crystalline polyester resin 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 (DSC) by using the "melting peak temperature" described in the method for determining the melting temperature in JIS K7121-1987 "Method for measuring transition temperatures of plastics."

[0049] The weight average molecular weight (Mw) of the crystalline polyester resin is preferably 6,000 or more and 35,000 or less.

[0050] The crystalline polyester resin can be obtained by a known manufacturing method, for example, in the same manner as the amorphous polyester resin.

[0051] The content of the binder resin is, for example, preferably 40% by mass to 95% by mass, more preferably 50% by mass to 90% by mass, and even more preferably 60% by mass to 85% by mass, based on the total mass of the toner particles.

[0052] -Coloring agent- Examples of colorants include carbon black, chrome yellow, Hansa Yellow, benzidine yellow, threne yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, Balkan orange, watch young red, permanent red, brilliant carmine 3B, brilliant carmine 6B, DuPont oil red, pyrazolone red, lithol red, rhodamine B lake, lake red C, pigment red, rose bengal, aniline blue, ultramarine blue, and the like. Examples of the dye include various pigments such as phosphorus blue, chalco oil blue, methylene blue chloride, phthalocyanine blue, pigment blue, phthalocyanine green, and malachite green oxalate, and various dyes such as acridine-based, xanthene-based, azo-based, benzoquinone-based, azine-based, anthraquinone-based, thioindigo-based, dioxazine-based, thiazine-based, azomethine-based, indigo-based, phthalocyanine-based, aniline black-based, polymethine-based, triphenylmethane-based, diphenylmethane-based, and thiazole-based dyes. The colorant may be used alone or in combination of two or more kinds.

[0053] The colorant may be surface-treated as needed, or may be used in combination with a dispersant. Furthermore, a plurality of colorants may be used in combination.

[0054] The content of the colorant is, for example, preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 15% by mass or less, based on the total mass of the toner particles.

[0055] -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.

[0056] The melting temperature of the release agent is preferably 50°C or higher and 110°C or lower, and more preferably 60°C or higher and 100°C or lower. The melting temperature is determined from a DSC curve obtained by differential scanning calorimetry (DSC) by using the "melting peak temperature" as described in the method for determining the melting temperature in JIS K 7121-1987 "Method for measuring transition temperatures of plastics."

[0057] The content of the release agent is, for example, preferably 1% by mass or more and 20% by mass or less, and more preferably 5% by mass or more and 15% by mass or less, based on the total mass of the toner particles.

[0058] -Other additives- Examples of other additives include well-known additives such as magnetic materials, charge control agents, inorganic powders, etc. These additives are contained in the toner particles as internal additives.

[0059] -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 part (core particle) and a coating layer (shell layer) that coats the core part. Here, the toner particles having a core-shell structure may be composed of, for example, a core containing a binder resin and, if necessary, other additives such as a colorant and a release agent, and a coating layer containing the binder resin.

[0060] The volume average particle size (D50v) of the toner particles may be 5 μm or more, 5 μm or more and 10 μm or less, or 5 μm or more and 8 μm or less.

[0061] The smaller diameter side volume particle size distribution index (hereinafter also referred to as "lower GSDv") of the toner particles may be 1.25 or more, but is preferably 1.25 or more and 1.50 or less. When the smaller diameter side volume particle size distribution index is in the above range, the external additive is likely to be coated on the toner particles in a nearly uniform state, the charge distribution becomes sharp, and the effect of suppressing fogging when repeated image formation is performed under conditions of a low temperature and low humidity environment, low image density, and low R / L is likely to be exhibited. The lower GSDv is a value calculated based on the following formula. Formula: Lower GSDv=(D50v / D16v) 1 / 2 In the above formula, D16v and D50v respectively mean the particle size (D16v) at 16% cumulative volume and the particle size (D50v) at 50% cumulative volume, based on the particle size distribution and the cumulative distribution drawn from the smallest diameter side.

[0062] 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% 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 for 1 minute using an ultrasonic disperser, and the particle size distribution of particles with a particle size 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.

[0063] The average circularity Cc of the toner particles is 0.80 or more and less than 0.98, may be 0.90 or more and 0.98 or less, or may be 0.93 or more and 0.98 or less.

[0064] The average circularity Cc 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 Cc 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.

[0065] When the toner particles contain a crystalline polyester resin, the exposure rate of the crystalline polyester resin on the surface of the toner particles is preferably 2% or more and 10% or less, more preferably 3% or more and 9% or less, and even more preferably 4% or more and 9% or less. When the exposure rate of the crystalline polyester resin is within the above range, the occurrence of fogging is further suppressed when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, compared to when the exposure rate is lower than the above range. The reason for this is presumably that the high exposure rate of the crystalline polyester resin makes it easier to obtain the neutralization effect of the crystalline polyester resin. Furthermore, when the exposure rate of the crystalline polyester resin is within the above range, the charge retention is better than when it is higher than the above range. The reason for this is thought to be that the crystalline polyester resin has low electrical resistance, and if the exposure rate is too high, it may cause a decrease in charge. It is also presumed that when the exposure rate of the crystalline polyester resin is within the above range, the deterioration of fogging due to the decrease in charge is suppressed.

[0066] The exposure rate of the crystalline polyester resin on the surface of the toner particles is measured as follows. Specifically, the surfaces of toner particles are stained with osmium tetroxide or ruthenium tetroxide in a desiccator. The stained toner particles are then observed under a scanning electron microscope (SEM). The areas where the crystalline polyester resin is exposed and the areas where it is not are distinguished by the shade of the staining caused by the osmium tetroxide or ruthenium tetroxide, and this is used to determine the exposure rate of the crystalline polyester resin. Specifically, the percentage of the area where the crystalline polyester resin is exposed relative to the total surface area of ​​the toner particles is defined as the exposure rate of the crystalline polyester resin (%). In addition, when an external additive is added to the surface of the toner particles to be measured, the external additive is removed by ultrasonic treatment for 20 minutes together with a mixed solution of ion-exchanged water and a surfactant, and the measurement is performed after removing the surfactant, drying the toner particles, and recovering the toner particles. The external additive removal treatment may be repeated until the external additive is removed.

[0067] (external additives) The external additive includes monodisperse silica particles and titanate compound particles.

[0068] -Monodispersed silica particles- The monodisperse silica particles may be particles containing silica, i.e., SiO2, as the main component. In this specification, the term "main component" refers to a component that accounts for 50% by mass or more of the total mass of a mixture of multiple components. In this specification, the term "monodisperse" refers to a particle size distribution index shown below of 1.25 or less.

[0069] The average primary particle size Rs of the monodispersed silica particles is preferably 20 nm or more and 70 nm or less. When the average primary particle diameter Rs of the monodispersed silica particles is within the above range, embedding of the monodispersed silica particles in toner particles is suppressed when low-density images are continuously formed, compared with when the average primary particle diameter Rs is smaller than the above range, thereby suppressing the deterioration of transfer efficiency, low charge, deterioration of image quality, etc., which would otherwise be caused by embedding of the monodispersed silica particles in toner particles. Furthermore, when the average primary particle diameter Rs of the monodispersed silica particles is within the above range, liberation from the toner particles is suppressed when high-density images are continuously formed, compared with when the average primary particle diameter Rs is greater than the above range, thereby suppressing low charge due to migration of liberated monodispersed silica particles to the carrier, deterioration of image quality due to changes in the external additive structure, and the like. The average primary particle size Rs of the monodispersed silica particles is more preferably 25 nm or more and 70 nm or less, and further preferably 30 nm or more and 65 nm or less.

[0070] Monodisperse silica particles have a particle size distribution index of 1.25 or less. From the viewpoint of further suppressing aggregation of the monodispersed silica particles and further suppressing the occurrence of fogging when images are repeatedly formed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, the particle size distribution index of the monodispersed silica particles is preferably 1.05 or more and 1.25 or less, more preferably 1.05 or more and 1.2 or less, and even more preferably 1.05 or more and 1.15 or less.

[0071] Here, the average primary particle size and particle size distribution index of the monodisperse silica particles are measured by the following method. The silica particles to be measured are dispersed in resin particles (e.g., polyester resin, weight-average molecular weight Mw = 500,000) with a volume average particle size of 100 μm. The resulting primary particles are observed using a scanning electron microscope (SEM) (S-4100, manufactured by Hitachi, Ltd.) and images are taken (40,000 magnification). 200 silica particles to be measured are randomly selected, and the image information is imported into an image analyzer (Winroof). The area of ​​each particle is measured by image analysis, and the equivalent circle diameter is calculated from this area value. The 50% diameter of the volume-based cumulative frequency of the obtained equivalent circle diameter is taken as the average primary particle size. Then, the 16% diameter (D16) and 84% diameter (D84) in the cumulative frequency of the obtained circle equivalent diameter on a volume basis are calculated. The square root of the calculated 84% diameter (D84) divided by the 16% diameter (D16) is used as the particle size distribution index (= (D84 / D16) 1 / 2 The magnification of the electron microscope is adjusted so that 10 to 50 silica particles to be measured are visible in one field of view, and the circle-equivalent diameter of the primary particle is determined by combining the observations of multiple fields of view.

[0072] The surfaces of the monodisperse silica particles are preferably subjected to a hydrophobic treatment. The hydrophobic treatment is carried out, for example, by immersing the monodisperse silica particles in a hydrophobic treatment agent. The hydrophobic treatment agent is not particularly limited, but examples thereof include known organosilicon compounds having an alkyl group (e.g., a methyl group, an ethyl group, a propyl group, a butyl group, etc.). Specific examples thereof include silane-based coupling agents such as silazane compounds (e.g., silane compounds such as methyltrimethoxysilane, dimethyldimethoxysilane, trimethylchlorosilane, and trimethylmethoxysilane; hexamethyldisilazane; tetramethyldisilazane, etc.). Other examples of the hydrophobic treatment agent include silicone oil, titanate-based coupling agents, and aluminum-based coupling agents. These may be used alone or in combination of two or more. The amount of the hydrophobic treatment agent is, for example, 1 part by mass or more and 200 parts by mass or less per 100 parts by mass of the monodisperse silica particles.

[0073] The content of the monodisperse silica particles is preferably from 0.01 to 10% by mass, more preferably from 0.05 to 5% by mass, and even more preferably from 0.1 to 2.5% by mass, based on the mass of the toner particles.

[0074] -Production of monodispersed silica particles- The monodisperse silica particles are preferably produced by a wet method. In this embodiment, the "wet method" is distinguished from the gas phase method, and is a production method in which sodium silicate is neutralized with a mineral acid or an alkoxysilane is hydrolyzed. Among the wet methods, it is preferable to produce monodisperse silica particles by a sol-gel method.

[0075] Hereinafter, the method for producing monodisperse silica particles used in this embodiment will be described using the sol-gel method as an example. However, the method for producing monodisperse silica particles is not limited to the sol-gel method. The particle size of the monodispersed silica particles can be freely controlled by the weight ratio of alkoxysilane, ammonia, alcohol and water in the hydrolysis and polycondensation steps of the sol-gel method, the reaction temperature, the stirring speed and the supply speed.

[0076] The method for producing monodisperse silica particles by the sol-gel method will be specifically described below. That is, tetramethoxysilane is added dropwise to the mixture in the presence of water and alcohol, using aqueous ammonia as a catalyst, while heating and stirring. Next, the solvent is removed from the silica sol suspension obtained by the reaction, and the mixture is dried to obtain the desired monodisperse silica particles. Thereafter, the obtained monodisperse silica particles are subjected to a hydrophobic treatment, if necessary.

[0077] When monodisperse silica particles are produced by the sol-gel method, the surfaces of the silica particles may be simultaneously subjected to a hydrophobic treatment. In this case, as described above, the silica sol suspension obtained by the reaction is centrifuged to separate it into wet silica gel, alcohol, and ammonia water, and then a solvent is added to the wet silica gel to make it into a silica sol again, and a hydrophobic treatment agent is added to hydrophobize the surfaces of the silica particles. Next, the solvent is removed from this hydrophobic treated silica sol and it is dried to obtain the desired monodisperse silica particles. The monodisperse silica particles thus obtained may be subjected to a hydrophobic treatment again.

[0078] The hydrophobization treatment for the silica particle surfaces may be carried out by a dry method such as a spray-drying method in which a hydrophobization treatment agent or a solution containing a hydrophobization treatment agent is sprayed onto silica particles suspended in a gas phase, a wet method in which silica particles are immersed in a solution containing a hydrophobization treatment agent and then dried, or a mixing method in which a hydrophobization treatment agent and silica particles are mixed in a mixer. After the hydrophobic treatment of the silica particle surfaces, a step of washing the silica particles with a solvent to remove the remaining hydrophobic treatment agent and low-boiling point residues may be added.

[0079] -Titanium oxide compound particles- The titanate compound particles may be particles containing a titanate compound as a main component. Titanate compounds are called metatitanates and are salts formed from, for example, titanium oxide and other metal oxides or other metal carbonates.

[0080] The titanic acid compound particles are preferably alkaline earth metal titanate particles. Here, the alkaline earth metal titanate is a salt represented by the general formula RTiO3 (wherein R is one or more alkaline earth metals).

[0081] By using alkaline earth metal titanate particles as titanate compound particles, the time required to reach saturated charge is shortened, and therefore the occurrence of fogging is further suppressed when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L. Specific examples of titanate compound particles include particles of strontium titanate (SrTiO3), calcium titanate (CaTiO3), magnesium titanate (MgTiO3), barium titanate (BaTiO3), zinc titanate (PbTiO3), and the like. From the viewpoint of further suppressing the occurrence of fogging when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L, it is preferable that the titanate compound particles be at least one selected from the group consisting of strontium titanate particles, calcium titanate particles, and magnesium titanate particles. These titanic acid compound particles may be used alone or in combination of two or more kinds.

[0082] The titanate compound particles preferably have an average primary particle size Rt of 20 nm or more and 70 nm or less. When the average primary particle diameter Rt of the titanate compound particles is within the above range, the titanate compound particles are less likely to be embedded in toner particles when continuously forming low-density images, compared to when the average primary particle diameter Rt is smaller than the above range, thereby suppressing the deterioration of transfer efficiency, low charge, and deterioration of image quality that would otherwise result from the embedding of the titanate compound particles in toner particles. Furthermore, when the average primary particle diameter Rt of the titanate compound particles is within the above range, liberation from the toner particles is suppressed when high-density images are continuously formed, compared with when the average primary particle diameter Rt is greater than the above range, thereby suppressing low charge due to migration of liberated titanate compound particles to the carrier, deterioration of image quality due to changes in the external additive structure, and the like. The average primary particle size Rt of the titanate compound particles is more preferably 25 nm or more and 70 nm or less, and further preferably 30 nm or more and 65 nm or less.

[0083] Here, the calculation of the average primary particle size of the titanate compound particles is the same as the calculation of the average primary particle size of the monodisperse silica particles.

[0084] The titanate compound particles preferably contain a dopant. By incorporating a dopant, the titanate compound particles have a reduced crystallinity and a moderately angular shape. This, for example, makes it easier for the titanate compound particles to have an average circularity Cb in the range of more than 0.78 and less than 0.94. This makes it easier for the titanate compound particles to be fixed to the toner particle surface. This further reduces the liberation of the titanate compound particles from the toner particles. From the above, it is estimated that the occurrence of fogging is further reduced when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L.

[0085] The dopant for the titanate compound particles is preferably a metal element that, when ionized, has an ionic radius that can be incorporated into the crystal structure that constitutes the titanate compound particles. From this perspective, the dopant for the titanate compound particles is preferably a metal element that, when ionized, has an ionic radius of 40 pm or more and 200 pm or less, more preferably a metal element that has an ionic radius of 60 pm or more and 150 pm or less.

[0086] Specific examples of dopants for titanate compound particles include lanthanoids, silica, aluminum, magnesium, calcium, barium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, gallium, niobium, molybdenum, ruthenium, palladium, indium, antimony, tantalum, tungsten, rhenium, iridium, platinum, bismuth, yttrium, zirconium, niobium, silver, and tin. Lanthanoids are preferably lanthanum and cerium. Among these, at least one of lanthanum and silica is preferred, from the viewpoint of having an ionic radius that is easily incorporated into the crystal structure constituting the strontium titanate particles and from the viewpoint of easily forming the titanate compound into a moderately angular shape.

[0087] In order to give the titanate compound a moderately angular shape, the amount of dopant in the titanate compound particles is preferably in the range of 0.1 mol % to 20 mol % relative to the alkaline earth metal atoms contained in the titanate compound particles, more preferably in the range of 0.1 mol % to 15 mol %, and even more preferably in the range of 0.1 mol % to 10 mol %.

[0088] The surfaces of the titanic acid compound particles may be subjected to a hydrophobic treatment. Examples of the hydrophobic treatment agent include known surface treatment agents, such as silane coupling agents and silicone oils. Examples of silane coupling agents include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, benzyldimethylchlorosilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-butyltrimethoxysilane, n-hexadecyltrimethoxysilane, n-octadecyltrimethoxysilane, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, and vinyltriacetoxysilane. Examples of silicone oils include dimethylpolysiloxane, methylhydrogenpolysiloxane, and methylphenylpolysiloxane.

[0089] The mass ratio of the content of titanate compound particles to the content of monodispersed silica particles is preferably 0.1 or more and 20 or less, more preferably 0.2 or more and 18 or less, and even more preferably 0.3 or more and 15 or less.

[0090] The content of the titanic acid compound particles is preferably from 0.01 to 10% by mass, more preferably from 0.05 to 8% by mass, and even more preferably from 0.1 to 5% by mass, based on the mass of the toner particles.

[0091] -Production of titanic acid compound particles- The method for producing the titanic acid compound particles is not particularly limited, but from the viewpoint of controlling the particle size and shape, a wet production method is preferred. The wet method for producing titanate compound particles is, for example, a method of reacting a mixture of metal element sources contained in a titanate compound while adding an alkaline aqueous solution, followed by acid treatment. In this production method, the particle size of the titanate compound particles can be controlled by the mixing ratio of the metal element sources, the concentration of the metal element sources at the beginning of the reaction, the temperature and addition rate of the alkaline aqueous solution, etc.

[0092] Here, examples of the source of the metal element contained in the titanic acid compound include mineral acid peptized products of hydrolyzed titanium compounds, and nitrates and chlorides containing metal elements other than titanium. Specifically, when the titanic acid compound particles are alkaline earth metal titanate particles, examples of the suitable materials include mineral acid peptized products of hydrolyzed titanium compounds and nitrates and chlorides containing alkaline earth metal elements. More specifically, when the titanate compound particles are strontium titanate particles, examples of the source include a mineral acid peptized product of a hydrolyzed titanium compound (hereinafter also referred to as a titanium source), strontium nitrate, strontium chloride, etc. (hereinafter also referred to as a strontium source).

[0093] Hereinafter, a method for producing strontium titanate particles will be described as an example of a method for producing titanate compound particles, but the present invention is not limited to this. The mixing ratio of the titanium oxide source to the strontium source is preferably an SrO / TiO molar ratio of 0.9 to 1.4, more preferably 1.05 to 1.20. The concentration of the titanium oxide source in terms of TiO at the start of the reaction is preferably 0.05 to 1.3 mol / L, more preferably 0.5 to 1.0 mol / L.

[0094] It is preferable to add a dopant source to a mixed solution of a titanium oxide source and a strontium source. Examples of the dopant source include oxides of metals other than titanium and strontium. The metal oxide as the dopant source is added as a solution dissolved in, for example, nitric acid, hydrochloric acid, sulfuric acid, or the like. The amount of the dopant source added is preferably an amount such that the amount of the dopant metal is 0.1 mol or more and 10 mol or less, and more preferably an amount such that the amount is 0.5 mol or more and 10 mol or less, per 100 mol of strontium.

[0095] The dopant source may be added when the alkaline aqueous solution is added to the mixed solution of the titanium oxide source and the strontium source. In this case, the metal oxide of the dopant source may be added as a solution dissolved in nitric acid, hydrochloric acid, or sulfuric acid.

[0096] The alkaline aqueous solution is preferably a sodium hydroxide aqueous solution. The higher the temperature at which the alkaline aqueous solution is added, the more likely it is that strontium titanate particles with good crystallinity will be obtained. In this embodiment, the temperature is preferably in the range of 60°C or higher and 100°C or lower. The slower the addition rate of the alkaline aqueous solution, the larger the particle size of the resulting strontium titanate particles, and the faster the addition rate, the smaller the particle size of the resulting strontium titanate particles. The addition rate of the alkaline aqueous solution is, for example, from 0.001 equivalents / h to 1.2 equivalents / h, and preferably from 0.002 equivalents / h to 1.1 equivalents / h, relative to the amount of the raw material.

[0097] After the addition of the alkaline aqueous solution, an acid treatment is carried out to remove unreacted strontium source, for example, by adjusting the pH of the reaction solution to 2.5 to 7.0, more preferably 4.5 to 6.0, using hydrochloric acid. After the acid treatment, the reaction liquid is subjected to solid-liquid separation, and the solid content is dried to obtain strontium titanate particles. By adjusting the conditions for drying the solid content, the moisture content of the strontium titanate particles can be controlled. To be controlled. When the surfaces of the strontium titanate particles are subjected to a hydrophobic treatment, the moisture content may be controlled by adjusting the conditions of the drying treatment after the hydrophobic treatment. Here, preferred drying conditions for controlling the moisture content are, for example, a drying temperature of 90°C or higher and 300°C or lower (preferably 100°C or higher and 150°C or lower) and a drying time of 1 hour or higher and 15 hours or lower (preferably 5 hours or higher and 10 hours or lower).

[0098] Hydrophobic treatment The hydrophobic treatment of the surfaces of strontium titanate particles is carried out, for example, by preparing a treatment liquid by mixing a hydrophobic treatment agent with a solvent, mixing the strontium titanate particles with the treatment liquid under stirring, and continuing to stir. After the surface treatment, a drying treatment is carried out in order to remove the solvent from the treatment solution.

[0099] Examples of the hydrophobic treatment agent include those already mentioned above. The solvent used to prepare the treatment liquid is preferably an alcohol (for example, methanol, ethanol, propanol, or butanol), or a hydrocarbon (for example, benzene, toluene, normal hexane, or normal heptane).

[0100] In the treatment liquid, the concentration of the hydrophobic treatment agent is preferably from 1% to 50% by mass, more preferably from 5% to 40% by mass, and even more preferably from 10% to 30% by mass.

[0101] As described above, the amount of the hydrophobic treatment agent used in the hydrophobic treatment is preferably 1% by mass or more and 50% by mass or less, more preferably 5% by mass or more and 40% by mass or less, even more preferably 5% by mass or more and 30% by mass or less, and particularly preferably 10% by mass or more and 25% by mass or less, relative to the mass of the strontium titanate particles.

[0102] -Other external additives- The toner used in this embodiment may contain other particles other than the monodisperse silica particles and titanic acid compound particles described above as other external additives. The other particles include inorganic particles other than silica particles and titanic acid compound particles. Examples of inorganic particles include Al2O3, CuO, ZnO, SnO2, CeO2, Fe2O3, MgO, BaO, CaO, K2O, Na2O, ZrO2, CaO·SiO2, K2O·(TiO2)n, Al2O3·2SiO2, CaCO3, MgCO3, BaSO4, and MgSO4.

[0103] The surfaces of inorganic particles as other 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 preferably 1 part by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the inorganic particles.

[0104] Other examples of particles include resin particles (resin particles such as polystyrene, polymethyl methacrylate, and melamine resin), cleaning agents (for example, particles of fluorine-based high molecular weight materials), and the like.

[0105] When other external additives are contained, the content of the other external additives is preferably 1% by mass or more and 99% by mass or less, more preferably 10% by mass or more and 90% by mass or less, and even more preferably 20% by mass or more and 85% by mass or less, relative to the total content of the external additives.

[0106] (Physical properties of external additives) -Ratio of average primary particle size- The ratio Rt / Rs of the average primary particle diameter Rt of the titanate compound particles to the average primary particle diameter Rs of the monodisperse silica particles is from 0.5 to 3.5. From the viewpoint of further suppressing the occurrence of fogging when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, the ratio Rt / Rs is preferably from 0.6 to 2.00, more preferably from 0.7 to 1.50, and even more preferably from 0.80 to 1.20.

[0107] -Average circularity Ca and average circularity Cb- It is preferred that the average circularity Ca of the monodispersed silica particles is more than 0.86 and less than 0.94, and the average circularity Cb of the titanate compound particles is more than 0.78 and less than 0.94.

[0108] By setting the average circularity of the monodispersed silica particles and titanate compound particles within the above range, the occurrence of fogging is further suppressed when images are repeatedly formed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L. The reason for this is presumed to be as follows. By setting the average circularity Ca of the monodispersed silica particles and the average circularity Cb of the titanate compound particles within the above-mentioned ranges, both the monodispersed silica particles and the titanate compound particles tend to have moderately irregular shapes. This makes it difficult for the monodispersed silica particles and the titanate compound particles to roll on the toner particles, further suppressing migration to the carrier and migration to recesses on the toner particle surface even under heavy loads inside the developing device. Based on the above, it is presumed that by setting the average circularity Ca of the monodispersed silica particles and the average circularity Cb of the titanate compound particles within the above-mentioned ranges, the occurrence of fogging is further suppressed when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L.

[0109] From the viewpoint of further suppressing the occurrence of fogging when images are repeatedly formed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, the average circularity C of the monodispersed silica particles is more preferably 0.87 or more and 0.93 or less, and even more preferably 0.88 or more and 0.92 or less. From the viewpoint of further suppressing the occurrence of fogging when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, the average circularity Cb of the titanate compound particles is more preferably 0.79 or more and 0.93 or less, and even more preferably 0.80 or more and 0.92 or less.

[0110] The average circularity Ca of the monodispersed silica particles is preferably greater than the average circularity Cb of the titanate compound particles. By satisfying the above relationship between the average circularity Ca of the monodispersed silica particles and the average circularity Cb of the titanate compound particles, the titanate compound particles tend to have a more angular shape than the monodispersed silica particles. As a result, the titanate compound particles are more easily fixed to the toner particle surface than the monodispersed silica particles. On the other hand, the monodispersed silica particles tend to have a more rounded shape than the titanate compound particles. As a result, the monodispersed silica particles tend to roll on the toner particle surface more easily than the titanate compound particles, and are more likely to undergo loose aggregation with the titanate compound particles fixed to both the protrusions and recesses of the toner particle surface. As a result, the monodispersed silica particles are more likely to be present on both the protrusions and recesses of the toner particle surface, and migration to the recesses is suppressed. Based on the above, it is speculated that by making the average circularity Ca of the monodispersed silica particles greater than the average circularity Cb of the titanate compound particles, the occurrence of fogging is more effectively suppressed during repeated image formation under conditions of low temperature and low humidity, low image density, and low R / L.

[0111] In order to further suppress the occurrence of fogging when repeated image formation is performed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L, the difference (Ca-Cb) between the average circularity Ca of the monodispersed silica particles and the average circularity Cb of the titanate compound particles is preferably 0.01 or more and 0.16 or less, more preferably 0.03 or more and 0.15 or less, and even more preferably 0.05 or more and 0.14 or less.

[0112] Here, the average circularity of the monodispersed silica particles and titanic acid compound particles is measured by the following method. The particles to be measured (monodispersed silica particles or titanic acid compound particles) externally added to the surface of the toner particles are observed using a scanning electron microscope (SEM) (S-4100, manufactured by Hitachi, Ltd.) and images are taken (40,000 magnification). 200 particles to be measured are randomly selected, and the image information is imported into an image analyzer (Winroof). The particle diameter is calculated from the planar image analysis of the obtained primary particles using the following formula: Formula: Circularity = (4π × A) / I 2 [In the formula, I represents the perimeter of the primary particle on the image, and A represents the projected area of ​​the primary particle.] The average circularity of the particles to be measured (monodispersed silica particles or titanic acid compound particles) is obtained as the 50% circularity in the cumulative frequency of the circularities of 200 primary particles obtained by the planar image analysis. When measuring the average circularity of monodispersed silica particles and titanic acid compound particles before they are externally added to toner particles, the particles to be measured (monodispersed silica particles or titanic acid compound particles) may be dispersed in resin particle bodies (e.g., polyester resin, weight average molecular weight Mw=500,000) with a volume average particle size of 100 μm, and the primary particles may be observed.

[0113] -Specific gravity of monodispersed silica particles Da and specific gravity of titanate compound particles Db- It is preferable that the specific gravity Da of the monodispersed silica particles is 1.1 or more and 1.3 or less, and the specific gravity Db of the titanate compound particles is greater than the specific gravity Da of the monodispersed silica particles.

[0114] When the specific gravity Da of the monodispersed silica particles and the specific gravity Db of the titanate compound particles satisfy the above relationship, the occurrence of fogging is further suppressed when images are repeatedly formed under conditions of a low temperature and low humidity environment, a low image density, and a low R / L. The reason for this is presumed to be as follows. When the specific gravity Db of the titanate compound particles is greater than the specific gravity Da of the monodisperse silica particles, the titanate compound particles tend to preferentially adhere to the toner particle surface when the monodisperse silica particles and titanate compound particles are externally added to the toner particles. This facilitates loose aggregation of the monodisperse silica particles with the titanate compound particles fixed to both the convex and concave portions of the toner particle surface, making them more likely to be present on both the convex and concave portions of the toner particle surface and inhibiting migration to the concave portions. Based on the above, it is presumed that by setting the specific gravity of the monodisperse silica particles and titanate compound particles within the above range, the occurrence of fogging can be further suppressed when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L.

[0115] The specific gravity Db of the titanate compound particles is preferably 4.0 or more and 6.5 or less, more preferably 4.1 or more and 5.5 or less, and even more preferably 4.2 or more and 5.0 or less.

[0116] By setting the specific gravity Db of the titanate compound particles within the above range, the adhesion of the titanate compound particles to the toner particle surface is further improved. Therefore, the monodispersed silica particles and titanate compound particles are further prevented from being separated from the toner particles, and the migration of the monodispersed silica particles to the recesses on the toner particle surface is further suppressed. This is presumably further suppressing the occurrence of fogging when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L.

[0117] In order to further suppress the occurrence of fogging when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L, the difference (Db-Da) between the specific gravity Da of the monodispersed silica particles and the specific gravity Db of the titanate compound particles is preferably 2.7 or more and 5.4 or less, more preferably 3.0 or more and 5.0 or less, and even more preferably 3.5 or more and 4.5 or less.

[0118] The specific gravity Da of the monodisperse silica particles and the specific gravity Db of the titanic acid compound particles are measured using a Le Chatelier pycnometer in accordance with JIS K 0061 (2001) as follows. (1) Pour approximately 250 ml of ethyl alcohol into the Le Chatelier pycnometer and adjust so that the meniscus is at the scale. (2) Immerse the pycnometer in a thermostatic water bath, and when the liquid temperature reaches 20.0±0.2°C, accurately read the meniscus position on the pycnometer's scale (with an accuracy of 0.025 ml). (3) Weigh out approximately 100 g of the sample and let its mass be W (g). (4) Place the weighed sample in a density bottle and remove any bubbles. (5) Immerse the pycnometer in a thermostatic water bath, and when the liquid temperature reaches 20.0±0.2°C, accurately read the meniscus position on the pycnometer's scale (with an accuracy of 0.025 ml). (6) Calculate the specific gravity using the following formula. D=W / (L2-L1) ρ=D / 0.9982 In the formula, D is the density of the sample (20°C) (g / cm 3 ), ρ is the specific gravity of the sample (20°C), W is the apparent mass of the sample (g), L1 is the meniscus reading (20°C) (ml) before the sample is placed in the pycnometer, L2 is the meniscus reading (20°C) (ml) after the sample is placed in the pycnometer, and 0.9982 is the density of water at 20°C (g / cm 3 )

[0119] -External coating rate of monodispersed silica particles and external coating rate of titanic acid compound particles- When the coverage of the monodisperse silica particles on the toner particle surface is A%, and the coverage of the titanate compound particles on the toner particle surface is B%, A / B satisfies the following formula (1): From the viewpoint of further suppressing the occurrence of fogging when images are repeatedly formed in a low-temperature, low-humidity environment, at a low image density, and with a low R / L, A / B preferably satisfies the following formula (2), more preferably the following formula (3), and even more preferably the following formula (4). Formula (1) 0 Formula (2) 0.05≦A / B≦1.50 Formula (3) 0.10≦A / B≦1.20 Formula (4) 0.20≦A / B≦1.00

[0120] The external additive coverage A% of the monodisperse silica particles is, for example, in the range of 5% to 50%, preferably 5% to 40%, more preferably 5% to 20%, and even more preferably 5% to 15%. When the external additive coverage A% of the monodisperse silica particles is within the above range, the occurrence of fogging is more suppressed when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L, compared to when the coverage A% is higher than the above range. The reason for this is unclear, but it is presumed that this is because there are fewer silica particles that do not loosely aggregate with the titanate compound particles and are present alone on the surface of the toner particles. Furthermore, by having the external additive coverage A% of the monodisperse silica particles in the above range, the toner has better fluidity than when the coverage is lower than the above range. The external additive coverage A% of the monodisperse silica particles can be controlled by adjusting, for example, the amount of monodisperse silica particles added and the external additive conditions (for example, when a Henschel mixer is used, the stirring speed, mixing time, etc.).

[0121] The external additive coverage rate B% ​​of the titanate compound particles is, for example, in the range of 5% or more and 50% or less, preferably 5% or more and 40% or less, more preferably 8% or more and 30% or less, and even more preferably 10% or more and 20% or less. ​When the external additive coverage B% of the titanate compound particles is within the above range, the occurrence of fogging is more suppressed when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L, compared to when the coverage B% is lower than the above range. The reason for this is unclear, but it is presumed to be because there are fewer silica particles that do not loosely aggregate with the titanate compound particles and are present alone on the surface of the toner particles. Furthermore, when the external additive coverage B% of the titanate compound particles is within the above range, the charge retention is improved compared to when it is higher than the above range. The reason for this is thought to be that titanate compound particles have low electrical resistance, and excessive coverage can lead to a decrease in charge, so by setting the external additive coverage B% within the above range, the deterioration of fogging due to the decrease in charge is suppressed. The external additive coverage rate B % of the titanate compound particles can be controlled by adjusting, for example, the amount of titanate compound particles added and the external addition conditions (for example, stirring speed, mixing time, etc. when a Henschel mixer is used).

[0122] The external coating rate A % of the monodisperse silica particles and the external coating rate B % of the titanic acid compound particles are determined as follows. The toner is observed and images are taken using a scanning electron microscope (SEM) (Hitachi, Ltd.: S-4700) at 50,000x magnification and 100 fields of view. From the SEM images obtained, the total surface area of ​​the toner particles, the area of ​​the region where the monodispersed silica particles are attached, and the area of ​​the region where the titanic acid compound particles are attached are calculated. In the SEM image, the regions where monodisperse silica particles are attached, the regions where titanate compound particles are attached, and the regions where neither monodisperse silica particles nor titanate compound particles are attached are distinguished as follows: Specifically, mapping is performed at an accelerating voltage of 20 kV using an energy dispersive X-ray analyzer EMAX model 16923H (manufactured by HORIBA, Ltd.) attached to an S4100 electron microscope, and the image area of ​​the external additives with the external additive type identified is determined. Next, the coverage of each external additive is calculated according to the following formula. Formula (5): A (%) = (area of ​​monodisperse silica particle adhesion region) / (total surface area of ​​toner particles) × 100 Equation (6): B (%) = (area of ​​titanic acid compound particle adhesion region) / (total surface area of ​​toner particles) × 100

[0123] -The ratio of the number of monodispersed silica particles contained in the aggregates containing titanate compound particles- The ratio of the number of monodisperse silica particles contained in the aggregate containing titanic acid compound particles to the number of monodisperse silica particles present on the surface of the toner particles, that is, the aggregated silica ratio, is 20% by number or more. The aggregated silica percentage is preferably 20% by number to 70% by number, more preferably 30% by number to 65% by number, and even more preferably 40% by number to 60% by number. By having an aggregated silica percentage within this range, the occurrence of fogging is more effectively suppressed when repeated image formation is performed under conditions of low temperature and low humidity, low image density, and low R / L, compared to when the aggregated silica percentage is lower than this range. Furthermore, by having an aggregated silica percentage within this range, the monodispersed silica is not excessively unevenly distributed, the charge distribution is sharper, and the occurrence of fogging is consequently suppressed, compared to when the aggregated silica percentage is higher than this range.

[0124] The aggregated silica percentage is determined as follows. The toner is observed and images are taken using a scanning electron microscope (SEM) (Hitachi, Ltd.: S-4700) at 50,000x magnification and 100 fields of view. From the SEM images obtained, the total number of monodispersed silica particles present on the surface of the toner particles, among the external additives attached to the toner particles, and the number of monodispersed silica particles contained in aggregates containing titanic acid compound particles are confirmed, and the aggregated silica ratio is calculated using the following formula (7). Formula (7): Aggregated silica ratio (%) = (number of monodispersed silica particles contained in aggregates containing titanic acid compound particles) / (total number of monodispersed silica particles present on the surface of a toner particle) × 100 In the SEM image, the regions where monodispersed silica particles are present, the regions where titanate compound particles are present, and the regions where neither monodispersed silica particles nor titanate compound particles are present are distinguished as follows: Specifically, mapping is performed at an accelerating voltage of 20 kV using an energy dispersive X-ray analyzer EMAX model 16923H (manufactured by HORIBA, Ltd.) attached to an electron microscope S4100, and the type of external additive is identified.

[0125] (Toner manufacturing method) Next, a method for producing the toner according to this embodiment will be described. The toner according to this exemplary embodiment is obtained by producing toner particles and then externally adding an external additive to the toner particles.

[0126] 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). The method for producing the toner particles is not particularly limited, and any well-known production method may be used.

[0127] Among these, it is preferable to obtain toner particles by the kneading and pulverizing method in order to obtain toner particles having an average circularity Cc of less than 0.98.

[0128] Specifically, for example, when toner particles are produced by a kneading and pulverization method, the toner particles are produced through a kneading step in which the components of the toner particles, including a binder resin and a release agent used as needed, are melted and kneaded together, a cooling step in which the molten and kneaded mixture is cooled, a pulverization step in which the kneaded mixture after cooling is pulverized, and a classification step in which the pulverized mixture is classified.

[0129] Each step will be described in detail below. In the following description, a method for obtaining toner particles containing a colorant and a release agent will be described, but the colorant and the release agent are used as needed. Of course, additives other than the colorant and the release agent may also be used.

[0130] -Kneading process- The kneading step is a step in which constituent components (toner particle forming materials) including a binder resin, a colorant, and a release agent are melted and kneaded to obtain a kneaded product. Examples of kneaders used in the kneading step include a three-roll type, a single-screw type, a twin-screw type, and a Banbury mixer type. The melting temperature may be determined depending on the types and compounding ratios of the binder resin and release agent to be kneaded. In the kneading step, 0.5 to 5 parts by mass of an aqueous medium (for example, water such as distilled water or ion-exchanged water, or alcohols) may be added to 100 parts by mass of the toner particle forming material.

[0131] -Cooling process- The cooling step is a step of cooling the kneaded material formed in the kneading step. In the cooling step, in order to maintain the dispersed state immediately after the completion of the kneading step, it is preferable to cool the kneaded mixture from the temperature at the end of the kneading step to 40° C. or less at an average cooling rate of 4° C. / sec or more. The average temperature decreasing rate refers to the average rate at which the temperature of the kneaded material is decreased from the temperature at the end of the kneading step to 40°C.

[0132] Examples of the cooling method in the cooling step include a method using a rolling roll through which cold water or brine is circulated and a pinch-type cooling belt. When cooling is performed by the above method, the cooling rate is determined by the speed of the rolling roll, the flow rate of brine, the amount of the kneaded material supplied, the slab thickness of the kneaded material when rolled, etc. The slab thickness is preferably 1 mm or more and 3 mm or less.

[0133] -Crushing process- The kneaded product cooled in the cooling step is pulverized in the pulverization step to form particles. In the pulverization step, for example, a mechanical pulverizer, a jet pulverizer, or the like is used. If necessary, the particles obtained by the pulverization step may be heat-treated with hot air or the like. If necessary, the surfaces of at least one of the particles obtained in the pulverization step and the particles obtained in the classification step described below may be coated with a resin. The coating of the particle surfaces with a resin may be carried out, for example, by mechanically colliding resin particles with the particle surfaces using a dry particle composite device.

[0134] -Classification process- The particles obtained in the pulverization step may be classified in a classification step, if necessary. In the classification step, a conventional centrifugal classifier, inertial classifier, or the like is used to remove fine particles (i.e., particles smaller than the target particle size range) and coarse particles (i.e., particles larger than the target particle size range). Through the above steps, toner particles are obtained.

[0135] The toner according to the present embodiment is produced by, for example, adding an external additive to the obtained toner particles and mixing them. The mixing can be carried out using, for example, a V blender, a Henschel mixer, a Loedige mixer, etc. Furthermore, if necessary, coarse particles may be removed from the toner using a vibrating sieve, an air sieve, etc.

[0136] <Electrostatic image developer> The electrostatic image developer according to this embodiment contains at least the toner according to this embodiment. The electrostatic image developer according to this embodiment may be a one-component developer containing only the toner according to this embodiment, or may be a two-component developer containing the toner mixed with a carrier.

[0137] The carrier is not particularly limited, and examples thereof include known carriers, such as coated carriers in which the surface of a core material made of magnetic powder is coated with a coating resin, magnetic powder dispersion carriers in which magnetic powder is dispersed and blended in a matrix resin, and resin-impregnated carriers in which porous magnetic powder is impregnated with a resin. The magnetic powder dispersion type carrier and the resin impregnated type carrier may be a carrier in which the constituent particles of the carrier are used as a core material and are coated with a coating resin.

[0138] Examples of magnetic powder include magnetic metals such as iron, nickel, and cobalt, and magnetic oxides such as ferrite and magnetite.

[0139] 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, fluororesins, polyesters, polycarbonates, phenolic resins, and epoxy resins. The coating resin and the matrix resin may contain other 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.

[0140] Here, the method of coating the surface of the core material with a coating resin includes a method of coating with a solution for forming a coating layer in which the coating resin and, if necessary, various additives are dissolved in an appropriate solvent. The solvent is not particularly limited and may be selected taking into consideration the coating resin to be used, its applicability, etc. Specific resin coating methods include an immersion method in which the core material is immersed in a solution for forming a coating layer, a spray method in which the solution for forming a coating layer is sprayed onto the surface of the core material, a fluidized bed method in which the solution for forming a coating layer is sprayed onto the core material while it is suspended in flowing air, and a kneader coater method in which the core material of the carrier and the solution for forming a coating layer are mixed in a kneader coater and the solvent is removed.

[0141] In the two-component developer, the mixing ratio (mass ratio) of toner to carrier is preferably toner:carrier=1:100 to 30:100, and more preferably 3:100 to 20:100.

[0142] <Image forming device / image forming method> An image forming apparatus and an image forming method according to this embodiment will be described. The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, a developing unit that contains an electrostatic image developer and develops the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer, a transfer unit that transfers the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing unit that fixes the toner image transferred to the surface of the recording medium. The electrostatic image developer according to the present embodiment is used as the electrostatic image developer.

[0143] The image forming apparatus according to this embodiment carries out an image forming method (the image forming method according to this embodiment) that includes a charging step of charging the surface of an image carrier, an electrostatic image forming step of forming an electrostatic image on the surface of the charged image carrier, a developing step of developing the electrostatic image formed on the surface of the image carrier as a toner image using the electrostatic image developer according to this embodiment, a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of a recording medium, and a fixing step of fixing the toner image transferred to the surface of the recording medium.

[0144] The image forming apparatus according to the present embodiment may be any of known image forming apparatuses, such as a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; an intermediate transfer type apparatus that primarily transfers a toner image formed on the surface of an image carrier to the surface of an intermediate transfer medium, and then secondarily transfers the toner image transferred to the surface of the intermediate transfer medium to the surface of a recording medium; an apparatus equipped with a cleaning means that cleans the surface of the image carrier after the transfer of the toner image but before charging; and an apparatus equipped with a discharging means that irradiates the surface of the image carrier with discharging light to discharge it after the transfer of the toner image but before charging. In the case of an intermediate transfer type device, the transfer means is configured to have, for example, an intermediate transfer body onto whose surface a toner image is transferred, a primary transfer means which primarily transfers the toner image formed on the surface of the image carrier onto the surface of the intermediate transfer body, and a secondary transfer means which secondarily transfers the toner image transferred onto the surface of the intermediate transfer body onto the surface of the recording medium.

[0145] In the image forming apparatus according to the present embodiment, for example, a portion including the developing means may have a cartridge structure (process cartridge) that is detachably attached to the image forming apparatus. As the process cartridge, for example, a process cartridge equipped with developing means that accommodates the electrostatic image developer according to the present embodiment is preferably used.

[0146] 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. Note that only the main parts shown in the drawings will be described, and descriptions of other parts will be omitted.

[0147] FIG. 1 is a schematic diagram showing the configuration of an image forming apparatus according to this embodiment. The image forming apparatus shown in Figure 1 includes first through fourth electrophotographic image forming units 10Y, 10M, 10C, and 10K (image forming means) that output images in the colors yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. These image forming units (hereinafter sometimes simply referred to as "units") 10Y, 10M, 10C, and 10K are arranged side by side horizontally spaced a predetermined distance apart from one another. Note that these units 10Y, 10M, 10C, and 10K may also be process cartridges that are detachable from the image forming apparatus.

[0148] Above each of the units 10Y, 10M, 10C, and 10K in the drawing, an intermediate transfer belt 20 serving as an intermediate transfer body extends through each unit. The intermediate transfer belt 20 is wound around a drive roll 22 and a support roll 24 that are spaced apart from each other and arranged from left to right in the drawing, and is configured to run in a direction from the first unit 10Y to the fourth unit 10K. A force is applied to the support roll 24 in a direction away from the drive roll 22 by a spring or the like (not shown), thereby applying tension to the intermediate transfer belt 20 wound around them. In addition, an intermediate transfer body cleaning device 30 is provided on the image carrier side of the intermediate transfer belt 20, facing the drive roll 22. In addition, the developing devices (developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K are supplied with toner including four colors of toner, yellow, magenta, cyan, and black, contained in toner cartridges 8Y, 8M, 8C, and 8K, respectively.

[0149] Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration, the first unit 10Y, which forms a yellow image and is disposed upstream in the direction of travel of the intermediate transfer belt, will be described here as a representative. Note that parts equivalent to those of the first unit 10Y are given reference numerals with magenta (M), cyan (C), and black (K) instead of yellow (Y), and descriptions of the second to fourth units 10M, 10C, and 10K will be omitted.

[0150] The first unit 10Y has a photoreceptor 1Y that acts as an image carrier. Around the photoreceptor 1Y, there are arranged in this order: a charging roll (an example of a charging means) 2Y that charges the surface of the photoreceptor 1Y to a predetermined potential; an exposure device (an example of an electrostatic image forming means) 3 that exposes the charged surface to a laser beam 3Y based on a color-separated image signal to form an electrostatic image; a developing device (an example of a developing means) 4Y that supplies charged toner to the electrostatic image to develop it; a primary transfer roll 5Y (an example of a primary transfer means) that transfers the developed toner image onto an intermediate transfer belt 20; and a photoreceptor cleaning device (an example of a cleaning means) 6Y that removes toner remaining on the surface of the photoreceptor 1Y after the primary transfer. The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20 and is positioned opposite the photoreceptor 1Y. Furthermore, a bias power supply (not shown) that applies a primary transfer bias is connected to each of the primary transfer rolls 5Y, 5M, 5C, and 5K. Each bias power supply varies the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

[0151] 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, volume resistivity at 20°C: 1×10 -6 The photosensitive layer is formed by laminating a photosensitive layer on a substrate with a resistivity of Ωcm or less. This photosensitive layer normally has a high resistance (the resistance of ordinary resins), but when irradiated with a laser beam 3Y, the resistivity of the irradiated portion changes. Therefore, a laser beam 3Y is output to the charged surface of the photosensitive element 1Y via an exposure device 3 in accordance with image data for yellow sent from a control unit (not shown). The laser beam 3Y is irradiated onto the photosensitive layer on the surface of the photosensitive element 1Y, thereby forming an electrostatic charge image of a yellow image pattern on the surface of the photosensitive element 1Y.

[0152] An electrostatic image is an image formed on the surface of the photosensitive element 1Y by charging it; the laser beam 3Y reduces the resistivity of the irradiated portion of the photosensitive layer, causing the charged charges on the surface of the photosensitive element 1Y to flow, while the charges remain in the portions not irradiated by the laser beam 3Y, forming a so-called negative latent image. The electrostatic image formed on the photoreceptor 1Y is rotated to a predetermined development position as the photoreceptor 1Y travels. At this development position, the electrostatic image on the photoreceptor 1Y is made visible as a toner image (developed image) by the developing device 4Y.

[0153] The developing device 4Y contains an electrostatic image developer containing, for example, at least yellow toner and a carrier. The yellow toner is frictionally charged by stirring inside the developing device 4Y and is held on a developer roll (an example of a developer holder) with a charge of the same polarity (negative polarity) as the charge on the photoreceptor 1Y. As the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner electrostatically adheres to the discharged latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed with the yellow toner. The photoreceptor 1Y with the yellow toner image formed thereon continues to travel at a predetermined speed, and the toner image developed on the photoreceptor 1Y is transported to a predetermined primary transfer position.

[0154] When the yellow toner image on the photoreceptor 1Y is transported to the primary transfer, 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 in the first unit 10Y, for example, it is controlled to +10 μA by a control unit (not shown). On the other hand, the toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

[0155] Furthermore, the primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K of the second unit 10M and subsequent units is also controlled in accordance with the first unit. In this way, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is conveyed sequentially through the second to fourth units 10M, 10C, and 10K, and the toner images of each color are superimposed and transferred.

[0156] The intermediate transfer belt 20, onto which the four-color toner images have been multiplex-transferred through the first to fourth units, reaches a secondary transfer section composed of the intermediate transfer belt 20, a support roll 24 in contact with the inner surface of the intermediate transfer belt, and a secondary transfer roll (an example of a secondary transfer means) 26 arranged on the image bearing surface side of the intermediate transfer belt 20. Meanwhile, recording paper (an example of a recording medium) P is fed via a 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 support roll 24. The transfer bias applied at this time has a negative polarity, the same as the negative polarity of the toner. Electrostatic force from the intermediate transfer belt 20 toward the recording paper P acts on the toner image, transferring the toner image on the intermediate transfer belt 20 onto the recording paper P. The secondary transfer bias at this time is determined according to resistance detected by resistance detection means (not shown) that detects resistance in the secondary transfer section, and is voltage-controlled.

[0157] Thereafter, the recording paper P is sent to the pressure contact portion (nip portion) of a pair of fixing rolls in a fixing device (an example of fixing means) 28, where the toner image is fixed onto the recording paper P, forming a fixed image.

[0158] Examples of the recording paper P onto which the toner image is transferred include plain paper used in electrophotographic copying machines, 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, is preferably used.

[0159] 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.

[0160] <Process cartridges / toner cartridges> The process cartridge according to this embodiment will be described. The process cartridge according to this embodiment is a process cartridge that is detachably attached to an image forming apparatus and that contains the electrostatic image developer according to this embodiment and is equipped with a developing means that develops an electrostatic image formed on the surface of an image carrier using the electrostatic image developer into a toner image.

[0161] The process cartridge according to this embodiment is not limited to the above configuration, but may also be configured to include a developing device 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.

[0162] An example of a process cartridge according to the present embodiment will be described below, but the present invention is not limited to this. Note that only the main parts shown in the drawings will be described, and descriptions of other parts will be omitted.

[0163] FIG. 2 is a schematic diagram showing the configuration of the process cartridge according to the present embodiment. The process cartridge 200 shown in FIG. 2 is configured to integrally combine and hold a photosensitive member 107 (an example of an image carrier), a charging roll 108 (an example of a charging means) provided around the photosensitive member 107, a developing device 111 (an example of a developing means), and a photosensitive member cleaning device 113 (an example of a cleaning means), which are held by a housing 117 provided with, for example, mounting rails 116 and an opening 118 for exposure, and is made into a cartridge. In FIG. 2, 109 denotes an exposure device (an example of an electrostatic image forming means), 112 denotes a transfer device (an example of a transfer means), 115 denotes a fixing device (an example of a fixing means), and 300 denotes recording paper (an example of a recording medium).

[0164] Next, the toner cartridge according to this embodiment will be described. The toner cartridge according to the present embodiment is a toner cartridge that contains the toner according to the present embodiment and is detachably attached to an image forming apparatus. The toner cartridge contains replenishment toner to be supplied to a developing unit provided in the image forming apparatus.

[0165] 1 is an image forming apparatus having a configuration in which toner cartridges 8Y, 8M, 8C, and 8K can be attached and detached, and developing devices 4Y, 4M, 4C, and 4K are connected to the toner cartridges corresponding to each developing device (color) by toner supply pipes (not shown). When the toner stored in a toner cartridge runs low, the toner cartridge is replaced. [Example]

[0166] Examples will be described below, but the present invention is not limited to these examples. In the following description, unless otherwise specified, all "parts" and "%" are by mass.

[0167] <Toner particles (A)> (Production of amorphous polyester resin 1) 76.9 parts by weight (0.167 mol) of polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, 24.1 parts by weight (0.145 mol) of terephthalic acid, and 0.5 parts by weight of titanium tetrabutoxide were placed in a 4-liter, four-necked glass flask. A thermometer, a stirrer, a condenser, and a nitrogen inlet tube were attached, and the flask was placed in a mantle heater. The atmosphere in the flask was then purged with nitrogen gas, and the temperature was gradually increased with stirring. The mixture was allowed to react for 3.5 hours at 200°C while stirring (first reaction step). 2.0 parts by weight (0.010 mol) of trimellitic anhydride was then added, and the mixture was allowed to react for 1 hour at 180°C (second reaction step), yielding amorphous polyester resin 1.

[0168] The acid value of this amorphous polyester resin 1 was 10 mgKOH / g, the hydroxyl value was 65 mgKOH / g, and the molecular weights measured by GPC were a weight average molecular weight (Mw) of 7,800, a number average molecular weight (Mn) of 3,300, and a peak molecular weight (Mp) of 5,500.

[0169] (Production of amorphous polyester resin 2) 71.3 parts by mass (0.155 mol) of polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, 24.1 parts by mass (0.145 mol) of terephthalic acid, and 0.6 parts by mass of titanium tetrabutoxide were placed in a 4-liter, four-necked glass flask. A thermometer, a stirrer, a condenser, and a nitrogen inlet tube were attached, and the flask was placed in a mantle heater. After the atmosphere in the flask was purged with nitrogen gas, the temperature was gradually raised with stirring, and the mixture was allowed to react for 2 hours at 200°C while stirring (first reaction step). Subsequently, 5.8 parts by mass (0.030 mol%) of trimellitic anhydride was added, and the mixture was allowed to react for 9 hours at 180°C (second reaction step), yielding amorphous polyester resin 2.

[0170] The amorphous polyester resin 2 had an acid value of 15 mgKOH / g and a hydroxyl value of 7 mgKOH / g. The molecular weights measured by GPC were a weight average molecular weight (Mw) of 190,000, a number average molecular weight (Mn) of 5,000, and a peak molecular weight (Mp) of 10,000.

[0171] (Production of styrene acrylic resin 3) Low-density polyethylene (Mw 1380, Mn 840, maximum endothermic peak at 100°C by DSC) 18 parts by mass Styrene 66 parts by mass n-Butyl acrylate 13.5 parts by mass 2.5 parts by mass of acrylonitrile The mixture was charged into an autoclave, and after replacing the atmosphere in the system with nitrogen, the temperature was raised and maintained at 180°C with stirring. 50 parts by mass of a 2% by mass solution of t-butyl hydroperoxide in xylene was continuously added dropwise to the system for 4.5 hours. After cooling, the solvent was separated and removed to obtain styrene acrylic resin 3 in which the vinyl resin component had reacted with the low-density polyethylene. The molecular weight of styrene acrylic resin 3 was measured, and it was found to have a weight-average molecular weight (Mw) of 7,000 and a number-average molecular weight (Mn) of 3,000.

[0172] (Production of Crystalline Polyester Resin 4) Decanedioic acid: 81 parts Hexanediol: 47 parts The above materials were charged into a flask, and the temperature was raised to 160°C over 1 hour. After confirming that the reaction system was uniformly stirred, 0.03 parts of dibutyltin oxide was added. The temperature was raised to 200°C over 6 hours while distilling off the produced water, and stirring was continued at 200°C for 4 hours. The reaction liquid was then cooled, solid-liquid separation was performed, and the solid was dried at 40°C under reduced pressure to obtain crystalline polyester resin 4 (melting temperature 64°C, weight average molecular weight 15,000).

[0173] (Production of toner particles (A)) Amorphous polyester resin 1 50.0 parts by mass Amorphous polyester resin 2 50.0 parts by mass Styrene acrylic resin 3 5.0 parts by mass Crystalline polyester resin 4 2.0 parts by mass Fischer-Tropsch wax (DSC maximum endothermic peak 76°C) 6.0 parts by mass CI Pigment Blue 15:3 5.0 parts by weight 0.5 parts by mass of 3,5-di-t-butylsalicylic acid aluminum compound The raw materials shown in the above recipe were mixed in a Henschel mixer (FM-75 model, manufactured by Nippon Coke and Engineering Co., Ltd.) at a rotation speed of 20 s -1The mixture was mixed for 5 minutes at 100°C, and a rotation time of 5 minutes was used to obtain toner composition (A). The mixture was then kneaded in a twin-screw kneader (PCM-30, manufactured by Ikegai Corporation) set at a temperature of 125°C to obtain molten and kneaded material (A). The resulting molten and kneaded material (A) was cooled, coarsely pulverized to 1 mm or less using a hammer mill, and then finely pulverized in a mechanical pulverizer (T-250, manufactured by Turbo Kogyo Co., Ltd.) to obtain pulverized material (A).

[0174] The obtained pulverized material (A) was subjected to a surface modification treatment using a surface modification device, Hybridization System (manufactured by Nara Machinery Works) or Mechanofusion System (manufactured by Hosokawa Micron Corporation), in order to obtain a desired circularity.

[0175] Next, coarse particles were removed using a fixed mesh surface type air sieve to obtain toner particles (A). The fixed mesh surface type air sieve was equipped with a wire mesh having a diameter of 30 cm, a screen opening of 20 μm, and an average wire diameter of 30 μm. The toner powder was blown through the air at a rate of 5 Nm 3 The air was fed at a rate of 150 kg / hr with an airflow of 1.0 kPa / min and collected directly through a bag filter. The volume average particle size (D50v) of the toner particles (A) was 6.74 μm, the small diameter volume particle size distribution index (lower GSDv) was 1.41, the average circularity Cc was 0.952, and the surface exposure rate of the crystalline polyester resin was 8.61%.

[0176] <Toner particles (B)> Toner particles (B) were obtained in the same manner as toner particles (A), except that crystalline polyester resin 4 was not used. The toner particles (B) had a volume average particle size (D50v) of 6.77 μm, a small diameter volume particle size distribution index (lower GSDv) of 1.40, an average circularity Cc of 0.950, and an exposure rate of the crystalline polyester resin on the surface of 0%.

[0177] <Monodispersed silica particles (S1)> (Preparation of Silica Particle Dispersion (1)) 320 parts of methanol and 72 parts of 10% aqueous ammonia were added to a glass reaction vessel equipped with a stirrer, a dropping nozzle, and a thermometer and mixed to obtain an alkaline catalyst solution. This alkaline catalyst solution was adjusted to 34°C (dropping start temperature), and then 45 parts of tetramethoxysilane and 9 parts of 8% aqueous ammonia were simultaneously dropped into the solution while stirring to obtain a hydrophilic silica particle dispersion (solid content 12%). The dropping time was 10 minutes. The resulting silica particle dispersion was then concentrated to a solid content of 40% using a rotary filter R-Fine (manufactured by Kotobuki Industries Co., Ltd.). This concentrated solution was designated silica particle dispersion (1).

[0178] (Preparation of monodisperse silica particles (S1)) Using silica particle dispersion (1), silica particles were surface treated with a siloxane compound in a supercritical carbon dioxide atmosphere as follows: For the surface treatment, an apparatus equipped with a carbon dioxide cylinder, a carbon dioxide pump, an entrainer pump, an autoclave (500 ml capacity) equipped with a stirrer, and a pressure valve was used.

[0179] First, 300 parts of silica particle dispersion (1) was placed in an autoclave (volume 500 ml) equipped with a stirrer, and the stirrer was rotated at 100 rpm. Subsequently, liquefied carbon dioxide was injected into the autoclave, and the temperature was increased with a heater while the pressure was increased with a carbon dioxide pump, bringing the autoclave into a supercritical state of 150°C and 15 MPa. While maintaining the pressure inside the autoclave at 15 MPa with a pressure valve, supercritical carbon dioxide was circulated from the carbon dioxide pump, and methanol and water were removed from the silica particle dispersion (1) (solvent removal step), yielding silica particles (untreated silica particles).

[0180] Next, when the amount of supercritical carbon dioxide circulated (cumulative amount: measured as the amount of carbon dioxide circulated under standard conditions) reached 900 parts, the circulation of the supercritical carbon dioxide was stopped. Thereafter, the temperature was maintained at 150 ° C. using a heater, and the pressure was maintained at 15 MPa using a carbon dioxide pump. While maintaining the supercritical state of carbon dioxide in the autoclave, a treatment solution was prepared by dissolving 20 parts of hexamethyldisilazane (HMDS: manufactured by Yuki Gosei Yakuhin Kogyo Co., Ltd.) as a hydrophobic treatment agent and 0.3 parts of dimethylsilicone oil (DSO: trade name "KF-96 (manufactured by Shin-Etsu Chemical Co., Ltd.)") with a viscosity of 10,000 cSt per 100 parts of the silica particles (untreated silica particles). The treatment solution was then injected into the autoclave using an entrainer pump, and the mixture was allowed to react at 180 ° C. for 20 minutes while stirring. Then, supercritical carbon dioxide was again circulated, and the excess treatment solution was removed. Then, the stirring was stopped, the pressure valve was opened, and the pressure in the autoclave was released to atmospheric pressure, and the temperature was lowered to room temperature (25 ° C.). In this way, the solvent removal step and the surface treatment with HMDS and DSO were carried out in sequence to obtain monodisperse silica particles (S1).

[0181] The obtained monodisperse silica particles (S1) had an average primary particle size Rs of 45 nm, a particle size distribution index of 1.25 or less, an average circularity Ca of 0.90, and a specific gravity Da of 1.2.

[0182] <Monodispersed silica particles (S2)> Monodispersed silica particles (S2) were obtained in the same manner as monodispersed silica particles (S1), except that in the preparation of the silica particle dispersion, 320 parts of methanol was changed to 340 parts of methanol, 72 parts of 10% ammonia water was changed to 76 parts of 10% ammonia water, 9 parts of 8% ammonia water was changed to 15 parts of 8% ammonia water, the dropwise addition time was changed from 10 minutes to 13 minutes, and the dropwise addition start temperature was changed from 34°C to 31°C. The obtained monodisperse silica particles (S2) had an average primary particle size Rs of 70 nm, a particle size distribution index of 1.25 or less, an average circularity Ca of 0.94, and a specific gravity Da of 1.2.

[0183] <Titanium oxide compound particles (T1)> 0.7 moles of desulfurized and peptized metatitanic acid, the titanium source, was collected and placed in a reaction vessel. Next, 0.77 moles of strontium chloride aqueous solution was added to the reaction vessel to achieve a SrO / TiO molar ratio of 1.1. Next, a solution of lanthanum oxide dissolved in nitric acid was added to the reaction vessel in an amount equivalent to 1.0 mole of lanthanum per 100 moles of strontium. The initial TiO concentration in the mixture of the three materials was adjusted to 0.75 moles / L. The mixture was then stirred and heated to 90°C. While maintaining the temperature at 90°C and stirring, 153 mL of 10 N (mol / L) aqueous sodium hydroxide solution was added over 2 hours. Stirring was continued for another 1 hour while maintaining the temperature at 90°C. The reaction mixture was then cooled to 40°C, and hydrochloric acid was added until the pH reached 5.5, followed by stirring for 1 hour. The precipitate was then washed by repeated decantation and redispersion in water. Hydrochloric acid was added to the slurry containing the washed precipitate to adjust the pH to 6.5, and the solids were filtered off and dried. An ethanol solution of i-butyltrimethoxysilane (i-BTMS) was added to the dried solids in an amount of 20 parts i-BTMS per 100 parts solids, and the mixture was stirred for 1 hour. The solids were filtered off and dried in air at 130°C for 7 hours to obtain titanic acid compound particles (T1). The obtained titanic acid compound particles (T1) had an average primary particle size Rt of 45 nm, an average circularity Cb of 0.86, and a specific gravity Db of 4.6.

[0184] <Titanium oxide compound particles (T2)> Titanic acid compound particles (T2) were obtained in the same manner as titanic acid compound particles (T1), except that the time for adding the aqueous sodium hydroxide solution was changed from 2 hours to 7 hours. The obtained titanic acid compound particles (T2) had an average primary particle size Rt of 70 nm, an average circularity Cb of 0.86, and a specific gravity Db of 4.6.

[0185] <Titanium oxide compound particles (T3)> Titanic acid compound particles (T3) were obtained in the same manner as titanic acid compound particles (T1), except that the time for adding the aqueous sodium hydroxide solution was changed from 2 hours to 10 hours. The obtained titanic acid compound particles (T3) had an average primary particle size Rt of 90 nm, an average circularity Cb of 0.90, and a specific gravity Db of 4.6.

[0186] <Example 1: Preparation of Toner 1> To 100 parts of the toner particles (A), 0.12 parts of monodisperse silica particles (S1) and 1.4 parts of titanic acid compound particles (T1) were added as external additives, and the mixture was mixed in a 5 L Henschel mixer at a stirring peripheral speed of 30 m / sec for 15 minutes to obtain Toner 1.

[0187] <Examples 2 to 9: Preparation of Toners 2 to 9> Toners 2 to 9 were obtained in the same manner as in Example 1, except that the types and amounts of monodispersed silica particles and the types and amounts of titanic acid compound particles were as shown in Table 1.

[0188] Example 10: Preparation of Toner 10 Toner 10 was obtained in the same manner as in Example 1, except that 100 parts of toner particles (B) were used instead of 100 parts of toner particles (A).

[0189] <Comparative Examples 1 to 3: Preparation of Toners C1 to C3> Toners C1 to C3 were obtained in the same manner as in Example 1, except that the types and amounts of monodispersed silica particles and the types and amounts of titanic acid compound particles were as shown in Table 1.

[0190] <Measurement and Evaluation> (Toner characteristics) The ratio Rt / Rs of the obtained toner is shown in Table 1. In addition, the external additive coverage rate A% of the monodispersed silica particles, the external additive coverage rate B% ​​of the titanic acid compound particles, the A / B value, and the aggregated silica ratio ("Aggregated ratio" in the table) of the obtained toner were determined using the above-mentioned methods and are shown in Table 1.

[0191] (Preparation of developer) Each of the obtained toners and the following resin-coated carrier were placed in a V blender in a ratio of toner:carrier=9.2:91.8 (mass ratio), and stirred for 20 minutes to obtain a developer.

[0192] -Career- Mn-Mg-Sr ferrite particles (average particle size 40 μm): 100 parts Toluene: 14 parts Polymethyl methacrylate: 2 parts Carbon black (VXC72: manufactured by Cabot): 0.12 parts The above materials except for the ferrite particles were mixed with glass beads (1 mm diameter, same amount as toluene) and stirred for 30 minutes at a rotation speed of 1200 rpm using a sand mill manufactured by Kansai Paint Co., Ltd. to obtain a dispersion liquid. This dispersion liquid and the ferrite particles were placed in a vacuum degassing kneader and dried under reduced pressure while stirring to obtain a resin-coated carrier.

[0193] (Fog evaluation) The obtained developer was placed in the developing device of a modified image forming apparatus "DocuCentre-VI C7771 (manufactured by Fuji Xerox Co., Ltd.)" (a modified apparatus in which the automatic density control sensor for environmental fluctuations was removed). Fog evaluation was carried out using this modified image forming apparatus. Specifically, in a low temperature and humidity environment (10°C, 15% RH), under low R / L conditions, i.e., with the power turned off and a 10-second warm-up period between image formations, 10,000 images with an image density of 1% were repeatedly formed on A4 paper, and the fogging evaluation of the last 30 images was carried out. The fogging evaluation index is as follows, and the results are shown in Table 1. [Fog evaluation index] G1: No overlapping is observed on any of the 30 sheets. G2: There is a slight amount of fogging on one sheet, but it is within the practically acceptable range. G3: Slight fogging is observed on several sheets, but is within the practically acceptable range. G4: Obvious fogging is observed on multiple sheets, making it unsuitable for practical use. G5: There is complete overlap on all 30 sheets.

[0194] [Table 1]

[0195] From the above results, it can be seen that the toner of this example suppresses the occurrence of fog when image formation is repeatedly performed under conditions of low temperature and low humidity, low image density, and low R / L. [Explanation of symbols]

[0196] 1Y, 1M, 1C, 1K Photoconductor (an example of an image carrier) 2Y, 2M, 2C, 2K Charging roll (an example of charging means) 3. Exposure device (an example of an electrostatic image forming means) 3Y, 3M, 3C, 3K laser beam 4Y, 4M, 4C, 4K developing device (an example of developing means) 5Y, 5M, 5C, 5K Primary transfer roll (an example of a primary transfer means) 6Y, 6M, 6C, 6K: Photoconductor cleaning device (an example of a cleaning means) 8Y, 8M, 8C, 8K toner cartridges 10Y, 10M, 10C, 10K image forming units 20 Intermediate transfer belt (an example of an intermediate transfer body) 22 Drive Roll 24 Support Roll 26 Secondary transfer roll (an example of a secondary transfer means) 30 Intermediate transfer body cleaning device 107 Photosensitive body (an example of an image carrier) 108 Charging roll (an example of charging means) 109 Exposure device (an example of electrostatic image forming means) 111 Developing device (an example of developing means) 112 Transfer device (an example of transfer means) 113 Photosensitive drum cleaning device (an example of cleaning means) 115 Fixing device (an example of fixing means) 116 Mounting Rail 117 Cabinet 118 Exposure opening 200 Process Cartridge 300 Recording paper (an example of a recording medium) P Recording paper (an example of a recording medium)

Claims

1. toner particles having an average circularity Cc of 0.80 or more and less than 0.98; an external additive containing monodispersed silica particles and titanic acid compound particles; and a ratio Rt / Rs of an average primary particle diameter Rt of the titanate compound particles to an average primary particle diameter Rs of the monodispersed silica particles is 0.50 or more and 3.50 or less; When the coverage rate of the monodisperse silica particles on the toner particle surface is A %, and the coverage rate of the titanic acid compound particles on the toner particle surface is B %, A / B satisfies the following formula (1): the monodisperse silica particles have an external additive coverage A of 5% or more and 50% or less; the titanate compound particles have an external additive coverage B of 5% or more and 50% or less; the toner particles contain a crystalline polyester resin, The toner for developing electrostatic images, wherein the exposed ratio of the crystalline polyester resin on the surface of the toner particles is 2% or more and 10% or less. Formula (1) 0<A / B≦2.00

2. 2. The toner for developing electrostatic images according to claim 1, wherein the ratio A / B satisfies the following formula (1'): Formula (1') 0<A / B≦1.00

3. the monodisperse silica particles have an average primary particle size Rs of 20 nm or more and 70 nm or less; the titanate compound particles have an average primary particle size Rt of 20 nm or more and 70 nm or less; The toner for developing electrostatic images according to claim 1 or 2.

4. the average circularity Ca of the monodispersed silica particles is more than 0.86 and less than 0.94; 4. The toner for developing electrostatic images according to claim 1, wherein the titanic acid compound particles have an average circularity Cb of more than 0.78 but less than 0.

94.

5. 5. The toner for developing electrostatic images according to claim 4, wherein the average circularity Ca of the monodisperse silica particles is greater than the average circularity Cb of the titanic acid compound particles.

6. the specific gravity Da of the monodisperse silica particles is 1.1 or more and 1.3 or less, 6. The toner for developing electrostatic images according to claim 1, wherein the specific gravity Db of the titanic acid compound particles is greater than the specific gravity Da of the monodisperse silica particles.

7. 7. The toner for developing electrostatic images according to claim 6, wherein the specific gravity Db of the titanic acid compound particles is 4.0 or more and 6.5 or less.

8. 8. The toner for developing electrostatic images according to claim 1, wherein the titanic acid compound particles are alkaline earth metal titanate particles.

9. 9. The toner for developing electrostatic images according to claim 1, wherein the titanic acid compound particles contain a dopant.

10. 10. The toner for developing electrostatic images according to claim 9, wherein said dopant is at least one of lanthanum and silica.

11. The toner for developing electrostatic images according to any one of claims 1 to 10, wherein the toner particles have a volume average particle size of 5 µm or more.

12. The toner for developing electrostatic images according to any one of claims 1 to 11, wherein the toner particles have a small diameter volume particle size distribution index of 1.25 or more.

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

14. A toner for developing electrostatic images 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; a transfer means for transferring the toner image formed on the surface of the image carrier to the surface of a recording medium; a fixing means for fixing the toner image transferred onto the surface of the recording medium; An image forming apparatus comprising:

Images