Toner and method for manufacturing the same

Abstract

The present invention provides a toner and a method for manufacturing the same, in which the external additive is uniformly distributed on the surface of the toner particles, thereby fully obtaining the external additive effect and providing excellent fixing strength. [Solution] The toner having toner particles containing a binder resin and a release agent has the following configuration: A first external additive containing associated silica particles, in which two or more primary silica particles are associated, and silica particles, which are primary silica particles, is fixed to the surface of the toner particles. The number-average particle diameter of the associated silica particles is 100 nm to 300 nm, and the number-average particle diameter of the silica particles is 30 nm or less. The coverage rate of the toner particle surface by the associated silica particles is 5% to 40%, and the coverage rate of the toner particle surface by the silica particles is 10% to 70%.

Description

Technical Field

[0001] The present disclosure relates to toner and a method for manufacturing the same.

Background Art

[0002] Toner (toner for developing an electrostatic charge image) used in image forming apparatuses such as copiers, multifunction peripherals, printers, and facsimile apparatuses that utilize an electrophotographic method generally has a configuration in which an external additive is adhered to the surface of toner particles (toner core).

[0003] Toner particles are roughly classified into pulverized toner particles obtained by a pulverization method and polymerized toner particles obtained by a polymerization method from the viewpoint of their manufacturing methods. Pulverized toner particles are manufactured by finely pulverizing a kneaded product of toner raw materials, but the surface of the finely pulverized product has a rough shape. Therefore, for the purpose of enhancing transferability to a recording medium such as paper, a heat spheroidization treatment may be performed to make the shape spherical by applying hot air to the finely pulverized product.

[0004] As an external additive for toner, aggregated silica particles, which are secondary particles formed by combining two or more primary particles of silica (see, for example, Patent Document 1), are known. As a method for manufacturing toner containing such aggregated silica particles, for example, Patent Document 2 discloses a method for manufacturing toner having a first step of strongly adhering aggregated silica particles, which are secondary particles formed by combining three or more primary particles, to toner particles in an external addition step of adhering an external additive to toner particles, and a second step of adhering silica particles, which are primary particles, to toner particles after the first step. In this Patent Document 2, it is said that in the first step, the aggregated silica particles can be firmly adhered to the toner particles by stirring and mixing the toner particles and the aggregated silica particles using a mixing treatment apparatus having a specific structure.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] By the way, when performing a hot spheroidization treatment on pulverized toner particles, it is necessary to add large-diameter silica particles to the toner particles before the hot spheroidization treatment to prevent the toner particles from fusing together.

[0007] Furthermore, in low-temperature fixed toners, which have improved low-temperature fixing properties by including crystalline polyester resin in the toner particles, it is known that the fluidity of the toner deteriorates because the dispersibility of the release agent within the toner particles worsens. Therefore, when adding an external additive to a toner with low fluidity, it is necessary to use silica particles with a small particle size as the external additive in order to improve fluidity.

[0008] Figure 1 is a schematic diagram showing the appearance of large-diameter particles being added to the surface of toner particles before the hot spheroidization treatment, along with small-diameter silica particles. Note that the diagram is intended to explain the distribution of large-diameter particles, and therefore the small-diameter silica particles are not shown. Figure 1(B) shows the case where large-diameter silica particles 92, which are approximately spherical, are added to the surface 91 of the toner particles.

[0009] As shown in Figure 1(B), when large-diameter silica particles 92 are added to the surface 91 of toner particles simultaneously with small-diameter silica particles before the hot spheroidization treatment, the approximately spherical large-diameter silica particles 92 roll around on the surface 91 of the toner particles and accumulate in the depressions on the surface 91. When the hot spheroidization treatment is performed in this state, the large-diameter silica particles 92 remain unevenly distributed on the surface 91 of the toner particles and become embedded in the surface.

[0010] Thus, when the hot spheroidizing treatment is performed, the external additives added before the hot spheroidizing treatment become embedded in the surface of the toner particles. Therefore, in order to ensure the performance of the toner, it is necessary to add external additives separately after the hot spheroidizing treatment. In this disclosure, the external additive added before the hot spheroidizing treatment will also be referred to as the pre-heat treatment external additive, and the external additive added after the hot spheroidizing treatment will also be referred to as the post-heat treatment external additive.

[0011] In Figure 1(B), while it is possible to include large-diameter silica particles 92 in the convex portions of the toner particle surface 91 by using more large-diameter silica particles 92, this results in a problem of reduced low-temperature fixation.

[0012] Figure 2 is a schematic diagram showing the application of an external additive to the surface of toner particles after hot spheroidization treatment. Figure 2(B) shows the case where the external additive 93 is applied after heat treatment, with large-diameter silica particles 92 unevenly distributed and embedded on the surface 91' of the toner particles after hot spheroidization treatment. As shown in Figure 2(B), the external additive 93 after heat treatment does not adhere to the areas where the large-diameter silica particles 92, which are the external additive before heat treatment, are embedded. Therefore, the external additive 93 after heat treatment is not uniformly distributed on the surface 91' of the toner particles.

[0013] Thus, when a post-heat treatment additive is applied to toner particles while the pre-heat treatment additive is unevenly distributed and embedded on the surface, the post-heat treatment additive will not adhere to the areas where the pre-heat treatment additive is embedded. This results in an uneven application of the post-heat treatment additive to the surface of the toner particles. In such a state of application, the effect of the post-heat treatment additive (the effect that should be achieved by applying the post-heat treatment additive) may not be fully obtained. Furthermore, if areas where the additive is densely concentrated are present on the contact surfaces between toner particles, adhesion between toner particles and adhesion between toner and paper may be inhibited.

[0014] The toner and method for manufacturing the same described herein were discovered in view of the above circumstances, and the main objective is to provide a toner and method for manufacturing the same in which the external additive is uniformly present on the surface of the toner particles, thereby obtaining sufficient external additive effect and excellent fixing strength. [Means for solving the problem]

[0015] The toner of this disclosure, made to solve the above problems, is a toner having toner particles containing a binder resin and a release agent, A first external additive containing associated silica particles, which are secondary particles formed by the coalescence of two or more primary silica particles, and silica particles, which are primary silica particles, is fixed to the surface of the toner particles. The number-average particle diameter of the associated silica particles is between 100 nm and 300 nm. The number-average particle diameter of the aforementioned silica particles is 30 nm or less. The coverage rate of the toner particle surface by the associated silica particles is 5% or more and 40% or less. The coating rate of the toner particle surface by the silica particles is characterized by being 10% or more and 70% or less.

[0016] In the case of the above-mentioned toner, it is preferable that the coefficient of variation of the number of associated silica particles, as determined by the measurement method described below, is 0.40 or less. [Method for measuring the coefficient of variation of the number of associated silica particles] In a backscattered electron image of toner particles captured using a scanning electron microscope, the midpoint of the toner particle's maximum diameter is used as the reference point, and a circle is drawn centered on this reference point. Next, straight lines are drawn from this reference point toward the periphery of the toner particle at 45° intervals, dividing the circle into eight regions. The number of associated silica particles present in each of these eight divided regions is counted, and the coefficient of variation of the number of particles between the eight divided regions is calculated. This coefficient of variation calculation is performed for 10 toner particles, and the average value is defined as the "coefficient of variation of the number of associated silica particles."

[0017] Also, in the above toner, the degree of aggregation of the aggregated silica particles is preferably 2.0 or more and 3.5 or less.

[0018] Also, in the above toner, the toner particles contain a crystalline polyester resin, and the glass transition temperature of the toner particles is preferably 60°C or less.

[0019] Also, in the above toner, the roundness of the toner particles is preferably 0.96 or more.

[0020] Also, in the above toner, the number average particle diameter of the silica particles is preferably 6 nm or more and 15 nm or less.

[0021] The above method for producing the toner, which is made to solve the above problems, includes a melt-kneading step of melt-kneading a mixture of toner raw materials containing a binder resin and a release agent to obtain a melt-kneaded product, a fine-pulverization step of finely pulverizing the melt-kneaded product to obtain a finely pulverized product, a classification step of classifying the finely pulverized product to obtain a classified product, a first external addition step of mixing the classified product and the first external additive and attaching the first external additive to the surface of the classified product to obtain toner particles before heat treatment, a heat spheroidization treatment step of spheroidizing the toner particles before heat treatment with hot air to obtain toner particles after heat treatment, and is characterized by including the above steps.

[0022] Also, in the above method for producing the toner, it is preferable to further include a second external addition step of mixing the toner particles after heat treatment and the second external additive and attaching the second external additive to the surface of the toner particles after heat treatment.

Advantages of the Invention

[0023] According to the toner and its production method of the present disclosure, since the external additive is uniformly present on the surface of the toner particles, excellent effects such as sufficient external addition effect of the external additive and excellent fixing strength can be obtained. [Brief explanation of the drawing]

[0024] [Figure 1] This is a schematic diagram showing how large-diameter particles are added to the surface of toner particles simultaneously with small-diameter silica particles before the hot spheroidization process. [Figure 2] This is a schematic diagram showing the application of an external additive to the surface of toner particles after the hot spheroidization process. [Figure 3] This diagram shows the procedure for the bending test. [Figure 4] This schematic diagram illustrates how toner peeling occurs during a bending test when an image is formed using toner with an external additive unevenly attached to the surface of the toner particles. [Modes for carrying out the invention]

[0025] The toner and its manufacturing method described herein will be explained below. In this disclosure, "internal addition" means adding the additive so that it is contained inside the material to be added, and "external addition" means adding the additive so that it adheres to the outer surface (surface) of the material to be added.

[0026] 1. Toner configuration The toner relating to this disclosure is a toner having toner particles containing a binder resin and a release agent, and has a configuration that satisfies the following requirements (A) to (E). The first external additive in requirement (A) corresponds to the pre-heat treatment external additive. (A) A first external additive (a pre-heat treatment external additive in this embodiment) is fixed to the surface of the toner particles, which consists of associated silica particles, which are secondary particles formed by the coalescence of two or more primary silica particles, and silica particles, which are primary silica particles. (B) The number-average particle diameter of the associated silica particles is between 100 nm and 300 nm. (C) The number-average particle diameter of the silica particles is 30 nm or less. (D) The coverage rate of the toner particle surface by the associated silica particles is 5% or more and 40% or less. (E) The coverage rate of the toner particle surface by the silica particles is 10% or more and 70% or less.

[0027] Furthermore, it is preferable that the toner according to this disclosure has a configuration that includes a second external additive that adheres more weakly to the surface of the toner particles than the first external additive. This second external additive corresponds to the post-heat treatment external additive. In this embodiment, a toner with such a configuration will be described.

[0028] In other words, in the toner according to this embodiment, the toner particles have undergone a hot sphere formation treatment, the first external additive is added before the hot sphere formation treatment, and the second external additive is added after the hot sphere formation treatment. Therefore, first, the manufacturing method of the toner according to this embodiment will be described.

[0029] 2. Toner manufacturing method The toner manufacturing method according to this embodiment is: A melt-kneading step involves melt-kneading a mixture of toner raw materials containing a binder resin and a release agent to obtain a melt-kneaded product, A fine grinding step to obtain finely ground material by finely grinding the molten mixture, A classification step of classifying the aforementioned finely ground material to obtain a classified material, A first external additive step involves mixing the classified material with the first external additive and adhering the first external additive to the surface of the classified material to obtain toner particles before heat treatment. A heat spheroidization process is performed in which the toner particles before heat treatment are shaped into spheres by hot air to obtain toner particles after heat treatment. The method includes a second external additive step of mixing the heat-treated toner particles with the second external additive to adhere the second external additive to the surface of the heat-treated toner particles.

[0030] In the melt-kneading process, toner raw materials containing known additives such as binder resin, colorant, and optionally added electrostatic control agent are mixed and melt-kneaded, and then cooled and solidified to obtain a melt-kneaded product. Before proceeding to the next fine grinding process, the melt-kneaded product may be coarsely ground to obtain a coarsely ground product.

[0031] Dry mixing is preferred, and known devices commonly used in the art can be used as the mixer. Examples include Henschel-type mixing devices such as Henschel mixer (trade name, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke Industries Co., Ltd.)), Super Mixer (trade name, manufactured by Kawata Corporation), MechanoMill (trade name, manufactured by Okada Seikou Co., Ltd.), OngMill (trade name, manufactured by Hosokawa Micron Corporation), Hybridization System (trade name, manufactured by Nara Machine Works Co., Ltd.), and Cosmo System (trade name, manufactured by Kawasaki Heavy Industries, Ltd.).

[0032] Furthermore, known devices commonly used in the relevant technical field can be used as the kneader, such as twin-screw extruders, three-roll kneaders, and lab blast mills. Specifically, examples include single-screw or twin-screw extruders such as TEM-100B (trade name, manufactured by Toshiba Machine Co., Ltd.), PCM-65 / 87, and PCM-30 (all trade names, manufactured by Ikegai Co., Ltd.), and open-roll type kneaders such as Nidex (trade name, manufactured by Mitsui Mining Co., Ltd.). Among these, open-roll type kneaders are preferred because they have a strong shear during kneading and can highly disperse colorants such as pigments.

[0033] <Fine grinding process> In the fine grinding process, the molten mixture obtained in the melt-kneading process is finely ground. As the grinder, a known device commonly used in the art can be used, for example, a jet grinder that grinds using a supersonic jet stream, or an impact grinder that grinds by introducing solidified material into the space formed between a high-speed rotating rotor and stator.

[0034] <Classification process> In the classification process, the finely ground material obtained in the fine grinding process described above is classified. For classification, known equipment commonly used in the art, in particular, a classifier capable of removing over-ground toner particles by centrifugal force and wind power, such as a rotary wind classifier, can be suitably used.

[0035] <First external addition process> In the first external additive step, the classified material obtained in the classification step is mixed with the first external additive to obtain pre-heat treatment toner particles in which the first external additive is attached to the surface of the classified material. That is, the first external additive is a pre-heat treatment external additive that is added before the hot spheroidization step. As the mixer in the first external additive step, a known device commonly used in the art can be used, for example, the mixer exemplified in the melt-kneading step described above.

[0036] Figure 1 is a schematic diagram showing the state in which large particle size particles are added to the surface of toner particles before the hot sphere formation treatment, simultaneously with small particle size silica particles. Note that the diagram is intended to explain the distribution of large particle size particles, so the small particle size silica particles are not shown. Figure 1(A) shows the case in which aggregated silica particles 12, which are large particle size particles, are added to the surface 11 of toner particles before the hot sphere formation treatment, and this corresponds to the state of the toner particle surface after the first external addition step in this embodiment. As shown in Figure 1(A), since the aggregated silica particles 12 are non-spherical irregular particles, they do not easily roll on the surface 11 of toner particles and do not easily flow into the depressions on the surface 11 of toner particles. Therefore, even if a small amount of aggregated silica particles 12 are used, it is possible to make the aggregated silica particles 12 adhere to the convex parts on the surface 11 of toner particles.

[0037] <Hot spheroidization process> In the hot sphere formation process, the pre-heat treatment toner particles obtained in the first external addition process are sphere-shaped using hot air to obtain post-heat treatment toner particles. As the hot air device, a known device commonly used in the art can be used, for example, a hot air type sphere formation device such as the surface modifier (product name: Meteor Rainbow) manufactured by Nippon Pneumatic Mfg. Co., Ltd.

[0038] In a hot air sphere shaping device, air is supplied from a secondary air injection nozzle to prevent the toner particles from agglomerating before heat treatment, causing them to collide with a collision member. These toner particles are then sphere-shaped with hot air to become post-heat-treated toner particles, and then cooled with cooling air to prevent thermal fusion between the post-heat-treated toner particles.

[0039] The amount of air supplied from the secondary air injection nozzle is preferably 200 L to 250 L per minute. If the amount of air supplied from the secondary air injection nozzle is too high, the toner particles before heat treatment may be severely damaged by the impact member, and if the amount is too low, the toner particles before heat treatment are likely to aggregate. The amount of hot air supplied is preferably 700 L to 1500 L per minute. If the amount of hot air supplied is too high, the toner particles before heat treatment may melt more than necessary, and if it is too low, the toner particles before heat treatment may not be sufficiently spheroidized.

[0040] The temperature of the hot air is preferably between 50°C and 250°C. If the temperature of the hot air is too high, the toner particles before heat treatment will melt more than necessary, and if it is too low, the spheroidization process of the toner particles before heat treatment will take too long. The supply pressure of the cooling air is preferably between 0.1 MPa and 0.3 MPa. If the supply pressure of the cooling air is too high, the toner particles after heat treatment may not be sufficiently cooled, and if it is too low, the cooling process of the toner particles after heat treatment will take too long.

[0041] The first external additive, which is added before the hot sphere formation process, adheres firmly to the toner particle surface because a portion of it becomes embedded in the softened surface of the toner particles during the hot sphere formation process. In other words, the first external additive can be said to be fixed to the surface of the toner particles. Thus, "fixed" as used in this disclosure refers to a state of firmer adhesion than that achieved by stirring and mixing in the second external additive process, and can be specifically determined based on the "Method for measuring the adhesion strength of the external additive (Method for determining whether or not it is fixed to the surface of the toner particles)" described in the examples below.

[0042] <Second external addition process> In the second external additive step, the heat-treated toner particles obtained in the hot spheroidization step are mixed with the second external additive, causing the second external additive to adhere to the surface of the heat-treated toner particles. In this way, toner with the second external additive adhered to the surface of the heat-treated toner particles is obtained. That is, the second external additive is a heat-treated external additive that is added after the hot spheroidization step. As the mixer in the second external additive step, a known device commonly used in the art can be used, for example, the mixer exemplified in the melt-kneading step described above.

[0043] Figure 2 is a schematic diagram showing the application of an external additive to the surface of toner particles after hot sphere formation treatment. Figure 2(A) shows the case where the second external additive 13 is applied while associated silica particles 12 are embedded in the surface 11' of the toner particles after hot sphere formation treatment. As shown in Figure 2(A), the associated silica particles 12 are uniformly distributed on the surface 11' of the toner particles, so the second external additive 13, which adheres while avoiding the areas where the associated silica particles 12 are embedded, is also uniformly distributed on the surface 11' of the toner particles. Therefore, the toner obtained after the second external additive process exhibits the full effect of the second external additive 13.

[0044] 3. Toner Next, the toner according to this embodiment will be described for each component.

[0045] The toner particles according to this embodiment include a binder resin and an internal additive such as a mold release agent, the internal additive being dispersed in the binder resin. Furthermore, optional components may be included as needed, as long as they do not impair the effects of this disclosure. The volume-average particle diameter of the primary particles of the toner particles can be appropriately selected depending on the purpose, for example, 5 μm to 8 μm.

[0046] As described above, the toner particles according to this embodiment are toner particles obtained after pulverized toner particles have been subjected to a hot sphere-shaping treatment. The circularity of the toner particles according to this embodiment is preferably 0.96 or higher, more preferably 0.965 or higher, and even more preferably 0.97 or higher. If the circularity of the toner particles is below the above lower limit, recesses (grooves) remain on the surface of the toner particles, so the second external additive (i.e., the external additive after heat treatment) does not adhere uniformly to the surface of the toner particles, and the effects according to this disclosure may not be fully obtained. Furthermore, considering the cleanability, the circularity of the toner particles according to this embodiment is preferably 0.98 or lower.

[0047] The following describes the individual components that make up toner particles.

[0048] <Resin> Examples of binder resins in the toner particles according to this embodiment include polyester resins, polystyrene resins such as styrene-acrylic resins, (meth)acrylic acid ester resins, polyolefin resins, polyurethane resins, and epoxy resins. One of these may be used alone, or two or more may be used in combination.

[0049] Polyester resins used as binder resins are typically obtained by polycondensation reactions via esterification or transesterification reactions using known methods, involving one or more components selected from divalent alcohol components and polyvalent alcohol components of trivalent or higher, and one or more components selected from divalent carboxylic acids and polyvalent carboxylic acids of trivalent or higher.

[0050] The conditions for the condensation polymerization reaction can be appropriately set depending on the reactivity of the monomer components, and the reaction should be terminated when the polymer achieves desirable physical properties. For example, the reaction temperature is approximately 170°C to 250°C, and the reaction pressure is approximately 5 mmHg to atmospheric pressure.

[0051] Examples of divalent alcohol components include alkylene oxide adducts of bisphenol A such as polyoxypropylene(2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(3.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene(2.0)-polyoxyethylene(2.0)-2,2-bis(4-hydroxyphenyl)propane, and polyoxypropylene(6)-2,2-bis(4-hydroxyphenyl)propane; ethylene Examples include diols such as lycopropyl glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; bisphenol A; propylene adducts of bisphenol A; ethylene adducts of bisphenol A; and hydrogenated bisphenol A.

[0052] Examples of polyhydric alcohol components with a valency of 3 or higher include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

[0053] In the toner according to this embodiment, one of the above-mentioned divalent alcohol component and trivalent or higher polyvalent alcohol component may be used alone, or two or more may be used in combination.

[0054] Examples of divalent carboxylic acids include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, n-dodecenylsuccinic acid, n-dodecylsuccinic acid, n-octylsuccinic acid, isooctenylsuccinic acid, isooctylsuccinic acid, and their acid anhydrides, lower alkyl esters, etc.

[0055] Examples of polycarboxylic acids with three or more valent values ​​include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalentricarboxylic acid, 1,2,4-naphthalentricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, empoletrimeric acid, and their acid anhydrides and lower alkyl esters.

[0056] In the toner according to this embodiment, one of the above-mentioned divalent carboxylic acids and trivalent or higher polyvalent carboxylic acids may be used alone, or two or more may be used in combination.

[0057] The toner particles according to this embodiment preferably contain a crystalline polyester resin and an amorphous polyester resin. In this case, the crystalline polyester resin is dispersed in the amorphous polyester resin. Furthermore, the toner particles according to this embodiment preferably contain a crystalline polyester resin and have a glass transition temperature of 60°C or lower. With such a configuration, a toner with low-temperature fixing properties can be obtained. In addition, considering the storage properties of the toner, the glass transition temperature of the toner particles is preferably 50°C or higher.

[0058] In this disclosure, crystalline resins and amorphous resins are distinguished by their crystallinity index. Resins with a crystallinity index in the range of 0.6 to 1.5 are defined as crystalline resins, and resins with a crystallinity index of less than 0.6 or greater than 1.5 are defined as amorphous resins. Resins with a crystallinity index greater than 1.5 are amorphous, and resins with a crystallinity index less than 0.6 have low crystallinity and a large amorphous portion.

[0059] The crystallinity index is a physical property that indicates the degree of crystallization of a resin, and is defined by the ratio of the softening point to the highest endothermic peak temperature (softening point / highest endothermic peak temperature). Here, the highest endothermic peak temperature refers to the temperature of the highest-temperature peak among the observed endothermic peaks. In crystalline polyester resins, the highest peak temperature is defined as the melting point, and in amorphous polyester resins, the highest-temperature peak is defined as the glass transition temperature.

[0060] The degree of crystallization can be controlled by adjusting the type and ratio of raw material monomers, as well as the manufacturing conditions (e.g., reaction temperature, reaction time, cooling rate).

[0061] -Amorphous polyester resin- Amorphous polyester resins are polyester resins with a crystallinity index of less than 0.6 or greater than 1.5, but polyester resins with a crystallinity index greater than 1.5 are preferred. Amorphous polyester resins can be obtained, for example, by polycondensation of a polybasic acid and a polyhydric alcohol.

[0062] As polybasic acids, known monomers for polyester synthesis can be used, such as aromatic carboxylic acids including terephthalic acid, isophthalic acid, phthalic anhydride, trimellitic acid, pyromellitic acid, and naphthalenedicarboxylic acid; aliphatic carboxylic acids including maleic anhydride, fumaric acid, succinic acid, alkenyl succinic anhydride, and adipic acid; and methyl esters of these polybasic acids. These polybasic acids may be used individually or in combination of two or more.

[0063] As polyhydric alcohols, known monomers for polyester synthesis can be used, such as aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, and glycerin; alicyclic polyhydric alcohols such as cyclohexanediol, cyclohexanedimethanol, and hydrogenated bisphenol A; and aromatic diols such as ethylene oxide adducts of bisphenol A and propylene oxide adducts of bisphenol A. These polyhydric alcohols may be used individually or in combination of two or more.

[0064] The polycondensation reaction between a polybasic acid and a polyhydric alcohol can be carried out according to conventional methods. For example, it is carried out by contacting the polybasic acid and the polyhydric alcohol in the presence or absence of an organic solvent and in the presence of a polycondensation catalyst (such as tin octoate), and the reaction is terminated when the acid value and softening point of the resulting polyester reach the desired values. This yields an amorphous polyester resin. If a methyl ester of a polybasic acid is used as part of the polybasic acid, a demethanol polycondensation reaction is carried out. In this polycondensation reaction, by appropriately changing the mixing ratio and reaction rate of the polybasic acid and polyhydric alcohol, for example, the carboxyl group content at the ends of the polyester can be adjusted, and consequently, the properties of the resulting amorphous polyester resin can be modified. Furthermore, if trimellitic anhydride is used as the polybasic acid, carboxyl groups can be easily introduced into the main chain of the polyester.

[0065] Furthermore, the polycondensation reaction between polybasic acids and polyhydric alcohols is usually carried out under temperature conditions of 150°C to 300°C, preferably 170°C to 280°C. In addition, the above polycondensation reaction can be carried out under atmospheric pressure, reduced pressure, or pressurized pressure, but it is desirable to appropriately adjust the pressure in the system while monitoring the progress of the polycondensation reaction using physical properties (e.g., acid value, melting point, etc.) and the stirring torque or power value of the reactor.

[0066] The acid value of the amorphous polyester resin is preferably 10 KOH mg / g or more and 30 KOH mg / g or less, and more preferably 15 KOH mg / g or more and 25 KOH mg / g or less.

[0067] The weight-average molecular weight (Mw) of the amorphous polyester resin is preferably between 5,000 and 50,000, and the number-average molecular weight (Mn) is preferably between 1,000 and 10,000. In this disclosure, the weight-average molecular weight and number-average molecular weight are values ​​measured by gel permeation chromatography (GPC), with tetrahydrofuran (THF) used as the mobile phase and polystyrene used as the standard substance.

[0068] The glass transition temperature (Tg) of amorphous polyester resins is preferably between 55°C and 70°C.

[0069] -Crystalline polyester resin- Crystalline polyester resins are polyester resins having a crystallinity index of 0.6 to 1.5, but polyester resins having a crystallinity index of 0.8 to 1.2 are preferred. Furthermore, crystalline polyester resins can be obtained, for example, by polycondensation of a polybasic acid and a polyhydric alcohol. For example, they can be manufactured by known methods such as those described in Japanese Patent Application Publication No. 2006-113473.

[0070] Examples of polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, neopentyl glycol, and 1,4-butenediol. However, it is preferable to use polyhydric alcohols that promote the crystallinity of the resin, such as aliphatic diols having 2 to 8 carbon atoms. These polyhydric alcohols may be used individually or in combination of two or more.

[0071] From the viewpoint of improving the crystallinity of the resin, the content of aliphatic diols having 2 to 8 carbon atoms in the polyhydric alcohol is preferably 80 mol% or more. Furthermore, when two or more aliphatic diols having 2 to 8 carbon atoms are used, it is desirable that the content of one type of aliphatic diol having 2 to 8 carbon atoms be 70 mol% or more in the polyhydric alcohol.

[0072] Examples of polybasic acids include aliphatic dicarboxylic acids having 2 to 30 carbon atoms, preferably 2 to 8, such as fumaric acid, adipic acid, oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, sebacic acid, azelaic acid, n-dodecylsuccinic acid, and n-dodecenylsuccinic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; and polycarboxylic acids with a valency of 3 or more, such as trimellitic acid and pyromellitic acid. To obtain a high degree of crystallinity (crystallinity index), aliphatic dicarboxylic acids are preferred, and aliphatic dicarboxylic acids having 2 to 8 carbon atoms are even more preferred. These polybasic acids may be used individually or in combination of two or more.

[0073] The acid value of the crystalline polyester resin is preferably 5 mg KOH / g or more and 20 mg KOH / g or less. Furthermore, the hydroxyl value of the crystalline polyester resin is preferably 5 mg KOH / g or more and 20 mg KOH / g or less.

[0074] The molecular weight of the crystalline polyester resin is preferably such that the weight-average molecular weight (Mw) is between 5,000 and 100,000, and the number-average molecular weight (Mn) is between 3,000 and 20,000. In this disclosure, the weight-average molecular weight and the number-average molecular weight are values ​​measured by gel permeation chromatography (GPC), with chloroform used as the mobile phase and polystyrene used as the standard substance.

[0075] <Release agent> The toner particles according to this embodiment contain a release agent. As the release agent, waxes commonly used in the field of electrophotography can be used. Examples include petroleum-based waxes such as paraffin wax and its derivatives, microcrystalline wax and its derivatives; hydrocarbon-based synthetic waxes such as Fischer-Tropsch wax and its derivatives, polyolefin wax and its derivatives, polypropylene wax and its derivatives, polyolefin polymer waxes (such as low molecular weight polyethylene wax) and its derivatives; plant-based waxes such as carnauba wax and its derivatives, rice wax and its derivatives, candelilla wax and its derivatives, and wood wax; animal-based waxes such as beeswax and whale wax; oil-based synthetic waxes such as fatty acid amides, phenolic fatty acid esters and their derivatives; silicone polymers, higher fatty acids, etc. One of these may be used alone, or two or more may be used in combination. Derivatives include oxides, block copolymers of vinyl monomers and waxes, graft-modified vinyl monomers and waxes, etc.

[0076] In this embodiment, the content of the release agent in the toner particles is preferably 0.5% by mass or more and 10% by mass or less.

[0077] <Coloring agent> The toner particles according to this embodiment may contain a colorant. As the colorant, various types and colors of organic and inorganic pigments and dyes commonly used in the field of electrophotography can be used, for example, black, white, yellow, orange, red, purple, blue, and green colorants can be used.

[0078] Examples of black colorants include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, non-magnetic ferrite, magnetic ferrite, and magnetite.

[0079] Examples of white colorants include zinc oxide, titanium dioxide, antimony white, and zinc sulfide.

[0080] Examples of yellow colorants include lead yellow, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, tartrazine lake, CI pigment yellow 12, CI pigment yellow 13, CI pigment yellow 14, CI pigment yellow 15, CI pigment yellow 17, CI pigment yellow 93, CI pigment yellow 94, and CI pigment yellow 138.

[0081] Examples of orange colorants include red lead, molybdenum orange, permanent orange GTR, pyrazolone orange, balkan orange, induthrene brilliant orange RK, benzidine orange G, induthrene brilliant orange GK, CI pigment orange 31, and CI pigment orange 43.

[0082] Examples of red colorants include red iron oxide, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, lysol red, pyrazolone red, watching red, calcium salt, lake red C, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B, CI pigment red 2, CI pigment red 3, CI pigment red 5, CI pigment red 6, CI pigment Examples include CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, and CI Pigment Red 222.

[0083] Examples of purple colorants include manganese purple, fast violet B, and methyl violet lake.

[0084] Examples of blue colorants include Prussian blue, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, First Sky Blue, Induthlene Blue BC, CI Pigment Blue 15, CI Pigment Blue 15:2, CI Pigment Blue 15:3, CI Pigment Blue 16, and CI Pigment Blue 60.

[0085] Examples of green colorants include chromium green, chromium oxide, pigment green B, micalite green lake, final yellow green G, and CI pigment green 7.

[0086] In the toner according to this embodiment, one of the above-mentioned colorants may be used alone or in combination of two or more, and the combination may be of different colors or the same color. The colorant content in the toner particles is preferably 0.1% by mass or more and 20% by mass or less, and more preferably 3% by mass or more and 15% by mass or less.

[0087] <Other oral additives> In the toner according to this embodiment, other internal additives may be included as needed. Examples of other internal additives include charge control agents. Charge control agents are added to impart desirable charge properties to the toner. The charge control agent is not particularly limited, and charge control agents used in the field of electrophotography for controlling positive and negative charges can be used.

[0088] Examples of charge control agents for controlling positive charge include quaternary ammonium salts, pyrimidine compounds, triphenylmethane derivatives, guanidine salts, and amidine salts.

[0089] Examples of charge control agents for controlling negative charge include metal-containing azo compounds, azo complex dyes, metal complexes and metal salts of salicylic acid and its derivatives (metals such as chromium, zinc, and zirconium), organobentonite compounds, and boron compounds.

[0090] <First internal additive (external additive before heat treatment)> In this embodiment, the toner particles have the first external additive fixed to their surface. As explained in the "heat spheroidization process" above, the first external additive, which is added before the heat spheroidization process, partially becomes embedded in the softened surface of the toner particles during the heat spheroidization process, and thus adheres firmly to the surface of the toner particles. In other words, the first external additive can be said to be fixed to the surface of the toner particles. Whether or not it is fixed to the surface of the toner particles can be determined based on the "method for determining whether or not the first external additive (external additive before heat treatment) is fixed to the surface of the toner particles" described in the examples below.

[0091] The first external additive contains associated silica particles, which are secondary particles formed by the fusion of two or more primary silica particles, and silica particles, which are primary silica particles.

[0092] (Associated silica particles) In this disclosure, "associated silica particles" refers not to particles formed by the aggregation of primary silica particles into a spherical shape, or to particles in the usual form where primary silica particles have aggregated into a lump, but rather to particles formed by the aggregation of two or more primary silica particles into a chain-like, fibrous, or other irregular shape. Here, "two or more primary particles associating into a lump" means a state in which the primary particles are fixed together so that secondary particles are not broken down by agitation during the external additive process or in the developing apparatus. In other words, in this disclosure, "associated silica particles" does not include particles formed by the aggregation of primary silica particles into a spherical shape, nor to particles in the usual form where primary silica particles have aggregated into a lump.

[0093] Examples of such configurations include arrangements of two primary silica particles, arrangements of three or more particles in a chain, arrangements of three particles at three points, arrangements of four particles in a planar or tetrapod shape, arrangements of five or more particles, and arrangements in which these associated silica groups are bonded together.

[0094] Here, "primary silica particles" refers to the smallest particles that make up the powder. Associated silica particles have a larger contact (adhesion) area with the surface of toner particles than ordinary silica particles, making them less likely to detach from the toner particle surface. In addition, because associated silica particles have an irregular shape, aggregates are less likely to form, and film formation can be suppressed while ensuring a sufficient spacer effect.

[0095] The primary particles constituting the associated silica particles may be spherical, oval, cube-shaped, or rod-shaped, but spherical is preferred for external additive applications. Furthermore, the particle sizes of the primary particles may differ from each other.

[0096] Associated silica particles can be manufactured by the method described in Japanese Patent Publication No. 2012-25596, or commercially available products can be used.

[0097] In this embodiment, the number-average particle diameter of the associated silica particles is 100 nm or more and 300 nm or less, preferably 120 nm or more and 200 nm or less, and more preferably 130 nm or more and 170 nm or less. If the number-average particle diameter of the associated silica particles is less than 100 nm, the spacer effect may not be fully realized. If the number-average particle diameter of the associated silica particles exceeds 300 nm, the associated silica particles become too irregular in shape, making it impossible to secure a contact area with the toner particle surface, and the associated silica particles tend to be unevenly distributed in the depressions on the toner particle surface.

[0098] In this embodiment, the associated silica particles preferably have a number-average particle diameter (average primary particle diameter) of 5 nm to 150 nm, more preferably 20 nm to 100 nm, and even more preferably 40 nm to 70 nm. By having the number-average particle diameter of the primary particles within the above range, it is possible to achieve both the degree of association described later and the number-average particle diameter (average secondary particle diameter) of the associated silica particles described above.

[0099] In the toner according to this embodiment, the coverage rate of the toner particle surface by associated silica particles is 5% to 40%, preferably 10% to 35%, and more preferably 20% to 30%. If the coverage rate of the toner particle surface by associated silica particles is below the lower limit, fusion of toner particles during the hot spheroidization process cannot be prevented, and it may be necessary to increase the particle size of the associated silica particles. If the coverage rate of the toner particle surface by associated silica particles exceeds the upper limit, the amount of associated silica particles added may be too large, resulting in poor low-temperature fixability.

[0100] In the toner according to this embodiment, the coefficient of variation of the number of associated silica particles is preferably 0.40 or less, more preferably 0.30 or less, and even more preferably 0.25 or less. When the coefficient of variation of the number of associated silica particles is within the above range, the associated silica particles are uniformly distributed on the surface of the toner particles, so the second external additive, which is an external additive after heat treatment, adheres uniformly to the surface of the toner particles, allowing its external additive effect to be fully exhibited and excellent fixing strength to be achieved. When the coefficient of variation of the number of associated silica particles is outside the above range, the associated silica particles are not uniformly distributed on the surface of the toner particles, and the effects of this disclosure may not be fully exhibited. The coefficient of variation of the number of associated silica particles can be measured by the method described in "Item 3: Coefficient of variation of the number of associated silica particles" in the examples shown later.

[0101] In the toner according to this embodiment, the degree of association of the associated silica particles is preferably 2.0 or more and 3.5 or less, and more preferably 2.5 or more and 3.0 or less. If the degree of association of the associated silica particles exceeds the above upper limit, the associated silica particles become too irregular in shape, making it impossible to secure a contact area with the toner particle surface, and the associated silica particles tend to be unevenly distributed in the depressions on the toner particle surface. If the degree of association of the associated silica particles is below the above lower limit, the associated silica particles become closer to a spherical shape and tend to roll on the toner particle surface as described above, so the associated silica particles tend to be unevenly distributed in the depressions on the toner particle surface.

[0102] (Silica particles as the first external additive) The silica particles used as the first external additive are primary silica particles. Here, the meaning of "primary silica particles" is the same as explained in the section on "associated silica particles" above.

[0103] In this embodiment, the number-average particle diameter of the silica particles used as the first external additive is 30 nm or less, preferably 6 nm to 15 nm, and more preferably 7 nm to 10 nm. If the number-average particle diameter of the silica particles used as the first external additive exceeds the above upper limit, the effect of imparting fluidity to the toner particles in the first external additive step (external additive step before the hot spheroidization treatment) will be weakened, and the degree of dispersion of associated silica particles on the surface of the toner particles may deteriorate.

[0104] Furthermore, it is preferable that the silica particles used as the first external additive have a smaller number-average particle size than the silica particles used as the second external additive, which will be described later. The silica particles used as the first external additive only need to provide fluidity during mixing in the toner manufacturing stage and do not need to contribute to the fluidity of the finished toner, so it is not a problem if they are embedded in the toner particles. However, if the silica particles used as the second external additive have a small particle size, they will be embedded in the toner particles due to collisions between toners or between toners and carriers, and sufficient fluidity will not be obtained during the image formation job.

[0105] In the toner according to this embodiment, the coverage rate of the toner particle surface by silica particles as the first external additive is 10% to 70%, preferably 20% to 65%, and more preferably 30% to 60%. If the coverage rate of the toner particle surface by silica particles is less than the above lower limit, the effect of imparting fluidity to the toner particles in the first external additive step will be weakened, and the degree of dispersion of associated silica particles on the toner particle surface may deteriorate. If the coverage rate of the toner particle surface by silica particles exceeds the above upper limit, the charging characteristics of the toner may deteriorate.

[0106] Examples of silica particles include silica particles commonly used in the art, such as fumed silica particles obtained by burning silicon tetrachloride, dry silica particles such as arc silica produced by micronizing silica in the gas phase using high energy such as plasma; wet silica particles such as precipitated silica produced under alkaline conditions using an aqueous sodium silicate solution as a raw material, and gel silica produced under acidic conditions; colloidal silica particles obtained by polymerizing acidic silicic acid in an alkaline state; and sol-gel silica particles obtained by hydrolysis of organosilane compounds. These silica particles may be surface-treated with a surface treatment agent to improve their electrical properties.

[0107] Examples of surface treatment agents include surface treatments commonly used in the relevant art, such as hexamethyldisilazane (HMDS), dimethyl-dichlorosilane (DDS), octylsilane (OTAS), and polydimethylsiloxane (PDMS).

[0108] Furthermore, commercially available hydrophobized silica particles may be used as the silica particles, or unhydrophobized silica particles may be treated before use.

[0109] <Second internal additive (external additive after heat treatment)> In the toner according to this embodiment, it is preferable to include a second external additive that adheres more weakly to the surface of the toner particles than the first external additive. Specifically, it is preferable that the adhesion strength of the second external additive to the surface of the toner particles is 60% or more and 80% or less. This adhesion strength can be measured by the "Method for measuring the adhesion strength of the second external additive (post-heat treatment external additive)" described later in the examples. As described above, this second external additive adheres to the surface of the toner particles by stirring and mixing the toner particles and the second external additive in the second external additive step performed after the hot spheroidization step. In other words, the second external additive is a post-heat treatment external additive that is added to the toner particles after the hot spheroidization step.

[0110] In the case where the toner according to this embodiment contains a second external additive, if X is the total coverage rate of the toner particle surface by the first and second external additives, and Y is the coverage rate of the toner particle surface by the first external additive, then Y / X is preferably 0.2 or more and 0.7 or less, and more preferably 0.5 or more and 0.65 or less. If Y / X is below the above lower limit, the effect of imparting fluidity to the toner particles in the first external additive step (external additive step before the hot spheroidization treatment) will be weakened, and the degree of dispersion of associated silica particles on the toner particle surface may deteriorate. If Y / X exceeds the above upper limit, the amount of the second external additive added will be small, and the external additive effect of the second external additive (the effect that should be exerted by the external addition of the second external additive) may not be sufficiently obtained.

[0111] As the second external additive, an external additive used in the relevant art can be appropriately selected according to the effect to be imparted to the toner. Examples include inorganic particles such as silica, titanium oxide, and aluminum oxide (alumina) with an average particle diameter of 7 nm to 200 nm. These inorganic particles may be used individually or in combination of two or more. These inorganic particles are preferably surface-treated with a surface treatment agent such as a silane coupling agent, a titanium coupling agent, or a silicone oil to impart hydrophobicity, as this reduces the decrease in electrical resistance and charge in high-humidity environments.

[0112] Specifically, by using silica particles with a number-average particle diameter of 6 nm to 30 nm as a second external additive, the heat resistance and storage properties of the toner can be improved. The number-average particle diameter of such small silica particles is preferably 6 nm to 15 nm, and more preferably 7 nm to 10 nm.

[0113] Examples of silica particles include silica particles commonly used in the relevant field, such as fumed silica particles obtained by burning silicon tetrachloride, dry silica particles such as arc silica which is atomized in the gas phase using high energy such as plasma; wet silica particles such as precipitated silica synthesized under alkaline conditions using an aqueous sodium silicate solution as a raw material, and gel silica synthesized under acidic conditions; colloidal silica particles obtained by polymerizing acidic silicic acid in an alkaline state; and sol-gel silica particles obtained by hydrolysis of organosilane compounds.

[0114] Furthermore, commercially available hydrophobized silica particles may be used as the silica particles, or unhydrophobized silica particles may be treated before use.

[0115] The content of the second external additive is preferably 0.2 parts by mass or more and 5 parts by mass or less per 100 parts by mass of toner particles after heat treatment. If the content of the external additive is below the lower limit, the effect of improving the fluidity of the toner may not be sufficiently obtained. If the content of the external additive exceeds the upper limit, the fixation of the toner may decrease. [Examples]

[0116] The toner and its manufacturing method will be described in detail below based on examples and comparative examples.

[0117] 1.Measurement / calculation method

[0118] <Method for measuring the volume-average particle size of toner particles> 50 ml of electrolyte (Beckman Coulter, Inc., product name: ISOTON-II) is mixed with 20 mg of toner particles and 1 ml of alkyl ether sulfate sodium. The mixture is then dispersed for 3 minutes at a frequency of 20 kHz using an ultrasonic disperser (AS ONE Corporation, tabletop dual-frequency ultrasonic cleaner, model: VS-D100) to obtain a sample for measurement. The obtained sample is then measured using a particle size distribution analyzer (Beckman Coulter, Inc., model: Multisizer3) under conditions of aperture diameter: 100 μm and number of particles measured: 50,000 counts. The volume-average particle size is determined from the volume particle size distribution of the toner particles.

[0119] <Method for measuring the number-average particle size of external additives> The average particle size of the external additive is determined by imaging the toner using a scanning electron microscope (SEM, Hitachi High-Technologies Corporation, model: S-4800), and randomly measuring the diameter (longest diameter) of 100 external additive particles on the toner surface from the obtained images. The average of these 100 particle sizes is calculated and defined as the number-average particle size of the external additive.

[0120] <Method for measuring the coverage rate of toner particle surfaces> The average particle size and specific gravity of the toner particles, and the average particle size and specific gravity of each external additive, were used to perform model calculations on the projected area, and the coverage ratio of each external additive was determined. Then, the toner was photographed with a scanning electron microscope (SEM, Hitachi High-Technologies Corporation, model: S-4800) to confirm the coverage ratio.

[0121] <Method for calculating the degree of association of associated silica particles> The degree of association of associated silica particles can be calculated by d2 / d1, where d1 is the average primary particle diameter of the primary particles constituting the associated silica particles, and d2 is the average secondary particle diameter of the associated silica particles themselves. A higher degree of association indicates that the shape of the associated silica particles is more irregular.

[0122] <Method for determining whether the first external additive (pre-heat treatment external additive) is adhering to the surface of toner particles> The adhesion strength of the first external additive is measured using the following procedure (1) to (7). If the adhesion strength is 90% or higher, it is determined that the external additive is fixed. (1) Add 2.0 g of toner to 40 mL of a 0.2% by mass Triton (polyoxyethylene octylphenyl ether) aqueous solution and stir for 1 minute. (2) The above aqueous solution is irradiated with ultrasound using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., model: US-300T). (Output: 40 μA, 6 minutes) (3) The aqueous solution after ultrasonic irradiation is left to stand for 3 hours to separate the toner from the liberated external additive. (4) After removing the supernatant liquid, add approximately 50 mL of pure water to the precipitate and stir for 5 minutes. (5) Perform suction filtration using a membrane filter with a pore size of 1 μm (manufactured by Advantec). (6) Vacuum dry any toner remaining on the filter overnight. (7) Using an X-ray fluorescence analyzer (manufactured by Rigaku Corporation, model: ZSX Primus II), the X-ray intensity of specific elements in 1 g of toner additive before and after the series of processes described in (1) to (6) above is analyzed, and the adhesion strength of the first additive is calculated using the following formula. The specific element is "Si" in the case of associated silica particles or silica particles. Adhesion strength of the first external additive (%) = {(X-ray intensity after treatment) / (X-ray intensity before treatment)} × 100

[0123] <Method for measuring the adhesion strength of the second external additive (external additive after heat treatment)> The adhesion strength of the second external additive is measured according to the following procedure (1) to (7). (1) Add 2.0 g of toner to 40 mL of a 0.2% by mass Triton (polyoxyethylene octylphenyl ether) aqueous solution and stir for 1 minute. (2) The above aqueous solution is irradiated with ultrasound using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., model: US-300T). (Output: 40 μA, 4 minutes) (3) The aqueous solution after ultrasonic irradiation is left to stand for 3 hours to separate the toner from the liberated external additive. (4) After removing the supernatant liquid, add approximately 50 mL of pure water to the precipitate and stir for 5 minutes. (5) Perform suction filtration using a membrane filter with a pore size of 1 μm (manufactured by Advantec). (6) Vacuum dry any toner remaining on the filter overnight. (7) Using an X-ray fluorescence analyzer (manufactured by Rigaku Corporation, model: ZSX Primus II), the X-ray intensity of a specific element in 1 g of toner additive before and after the series of processes described in (1) to (6) above is analyzed, and the adhesion strength of the second additive is calculated using the following formula. The specific element is "Si" in the case of silica particles. Adhesion strength of the second external additive (%) = {(X-ray intensity after treatment) / (X-ray intensity before treatment)} × 100

[0124] <Method for measuring the glass transition temperature of toner particles> Using a differential scanning calorimeter (Seiko Electronics Industries Ltd. (now Hitachi High-Tech Science Corporation), model number: DSC220), 1 g of toner particles is heated at a heating rate of 10°C / min and the DSC curve is measured in accordance with Japanese Industrial Standard (JIS) K7121-1987. In the obtained DSC curve, the temperature at the intersection of a straight line extending from the high-temperature baseline of the endothermic peak corresponding to the glass transition to the low-temperature side, and a tangent line drawn at the point where the slope of the curve from the rising part to the apex of the peak is maximum, is defined as the glass transition temperature (Tg).

[0125] <Method for measuring the circularity of toner particles> Measurements are performed using a wet flow-type particle size and shape analyzer (flow-type particle image analyzer, Malvern, model: FPIA-3000) or an apparatus with the same measurement principle. This measurement principle involves capturing still images of particles in a dispersion medium with a CCD camera and performing calculations such as circularity calculation from the obtained images. Specifically, the sample introduced from the chamber is sent to a flat sheath flow cell, where it is sandwiched between the sheath liquid to form a flattened flow. Still images are captured by a CCD camera while strobe light is irradiated onto the sample passing through this cell. The contour of each particle is extracted by image processing of the captured images, and the projected area S and perimeter L of the particle image are measured, from which the equivalent circle diameter and circularity are calculated.

[0126] The equivalent circle diameter is defined as the diameter of a circle having the same area as the projected area of ​​the particle image, and the circularity is defined as the value obtained by dividing the circumference of the circle obtained from the equivalent circle diameter by the circumference of the particle projection image, and is calculated by the following formula. Circularity = 2 × (π × S) 1 / 2 / L

[0127] For example, a particle sheath (Malvern, product name: PSE-900A) is used as the sheath liquid, a 5% by mass aqueous dispersion of a commercially available household detergent is used as the dispersant, and the sample is dispersed using the autosampler of the above-mentioned analyzer. The resulting dispersion is then introduced into the analyzer, and 10,000 toner particles are measured in total count mode. Then, the binarization threshold for particle analysis is set to 85%, and the average circularity of the toner particles is determined across the entire particle size range.

[0128] 2. Preparation and manufacturing of raw materials <Preparation of amorphous polyester resin A> In a reaction vessel, 440 g (2.7 mol) of terephthalic acid, 235 g (1.4 mol) of isophthalic acid, 7 g (0.05 mol) of adipic acid, 554 g (8.9 mol) of ethylene glycol, and 0.5 g of tetrabutoxytitanate as a polymerization catalyst were added. The mixture was reacted at 210°C under a nitrogen stream for 5 hours, while distilling off the water and ethylene glycol produced. Then, the mixture was reacted under reduced pressure of 5 mmHg to 20 mmHg for 1 hour. Next, 103 g (0.54 mol) of trimellitic anhydride was added, and the mixture was reacted under atmospheric pressure for 1 hour. After that, the mixture was reacted under reduced pressure of 20 mmHg to 40 mmHg, and the resin was removed at the predetermined softening point. The recovered ethylene glycol amounted to 219 g (3.5 mol). The obtained resin was cooled to room temperature and then pulverized to form particles. This was designated as amorphous polyester resin A. Amorphous polyester resin A had a glass transition temperature (Tg) of 56°C, a softening temperature (Tm) of 135°C, a peak-top molecular weight (Mp) of 5000, an SP value of 11.0, an acid value of 37 mgKOH / g, and a hydroxyl value of 50 mgKOH / g.

[0129] <Preparation of crystalline polyester resin C> In a reaction vessel, 132 g (1.12 mol) of 1,6-hexanediol, 230 g (1.0 mol) of 1,10-decanedicarboxylic acid, and 3 g of tetrabutoxytitanate as a polymerization catalyst were added, and the reaction was carried out at 210°C under atmospheric pressure for 5 hours while distilling off the water produced. The reaction was then continued under reduced pressure of 5 mmHg to 20 mmHg, and the resin was removed when the acid value fell to 2 mg KOH / g or less. After the obtained resin was cooled to room temperature, it was pulverized into particles. This was designated as crystalline polyester resin C. Crystalline polyester resin C had a melting point Tmp of 80°C, a softening temperature Tm of 88°C, a Tm / Tmp ratio of 1.1, a peak-top molecular weight Mp of 30000, an SP value of 9.5, an acid value of 1 mg KOH / g, and a hydroxyl value of 10 mg KOH / g.

[0130] <Preparation of aggregated silica particles> Associated silica particles were produced by the method described in Japanese Patent Publication No. 2012-25596. Specifically, as described in the said publication, multiple associated silica particles with different sizes (average secondary particle diameters) were produced by optimizing the amount of water used in production, the ratio of water to hydrophilic organic solvent, and the amount of basic substance, as shown in Table 1 below.

[0131] 3. Toner production [Example 1] The following toner raw materials were used to produce the toner particles. • Binding resin Amorphous polyester resin A 67% by mass Crystalline polyester resin C 20% by mass • Colorants CIPigment Blue 15:3 (manufactured by DIC Corporation) 7% by mass • Release agent Monoester wax (manufactured by NOF Corporation, product name: WEP-3) 5% by mass • Antistatic agent Salicylic acid compound (Orient Chemical Industry Co., Ltd., product name: Bontron E-84) 1% by mass

[0132] -Melting and mixing process- The above toner raw materials were pre-mixed for 5 minutes using an air-flow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke Industries Co., Ltd.), model: FM20C), and then melt-kneaded using an open-roll type continuous kneader (manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke Industries Co., Ltd.), model: MOS320-1800) to obtain a molten kneaded product.

[0133] The open roll settings were as follows: heating roll supply temperature 130°C, discharge temperature 100°C; cooling roll supply temperature 40°C, discharge temperature 25°C. A diameter of 320 mm and an effective length of 1550 mm were used for both the heating and cooling rolls, with a roll gap of 0.3 mm on both the supply and discharge sides. The heating roll rotation speed was set to 75 rpm, the cooling roll rotation speed to 65 rpm, and the toner material supply rate to 5.0 kg / h.

[0134] -Coarse grinding process- The resulting molten mixture was cooled using a cooling belt, and then coarsely ground using a speed mill with a φ2 mm screen to obtain a coarsely ground product.

[0135] -Fine grinding process- The obtained coarse pulverized material was finely pulverized using a jet-type pulverizer (manufactured by Nippon Pneumatic Mfg. Co., Ltd., model: IDS-2) to obtain fine pulverized material.

[0136] -Classification process- Next, the obtained pulverized material was classified using an elbow jet classifier (manufactured by Nippon Steel Mining Co., Ltd., model: EJ-LABO) to obtain the classified material.

[0137] -First external addition process- Next, 0.35 parts by mass of silica particles (average particle size: 7 nm, manufactured by Nippon Aerosil Co., Ltd., product name: R976S) and 3.73 parts by mass of associated silica particles (degree of association: 2.8, average particle size: 150 nm) were added to 100 parts by mass of the obtained toner particles as pre-heat treatment external additives (first external additives), and the mixture was stirred for 4 minutes in an air-flow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke Industries Co., Ltd.), model: FM20C) with the tip speed of the stirring blades set to 40 m / sec.

[0138] -Hot spheroidization process- Next, the obtained pre-heat-treated toner was subjected to a spheroidizing process using a hot-air spheroidizing device (manufactured by Nippon Pneumatic Mfg. Co., Ltd., product name: Meteor Rainbow) to obtain post-heat-treated toner particles. The conditions for hot spheroidizing were as follows: the input rate of pre-heat-treated toner particles to the hot-air spheroidizing device was 3.0 kg per hour, the hot air supply rate was 1180 L per minute, the hot air temperature was 250°C, the cooling air supply pressure was 0.15 MPa, and the air supply rate from the secondary air injection nozzle was 230 L per minute. The distance between the cooling air intake and the impact member was set to 2.0 cm. The obtained post-heat-treated toner particles had an average primary particle diameter of 6.7 μm, a circularity of 0.970, and a glass transition temperature (Tg) of 50°C.

[0139] -Second external addition process- Toner was obtained by adding 1.0 part by mass of silica particles (average particle size: 7 nm, manufactured by Nippon Aerosil Co., Ltd., product name: R976S) as a post-heat treatment external additive (second external additive) to 100 parts by mass of the obtained heat-treated toner particles and stirring with an air-flow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke Industries Co., Ltd.), model: FM20C) with the tip speed of the stirring blades set to 40 m / sec.

[0140] -Preparation of a two-component developer- The obtained toner and a ferrite core carrier with a volume-average particle size of 40 μm were mixed in an adjusted manner so that the toner concentration relative to the total amount of the two-component developer was 7%, thereby obtaining a two-component developer with a toner concentration of 7%.

[0141] [Examples 2-11, 23] Toner was obtained in the same manner as in Example 1, except that the type and amount of each external additive were changed, as shown in Table 1 below.

[0142] [Examples 12-17] Toner was obtained in the same manner as in Example 1, except that toner particles were prepared using amorphous polyester resin A at a concentration of 87% by mass, without incorporating crystalline polyester resin C as a toner raw material, and the types and amounts of each external additive were changed as shown in Table 1 below.

[0143] [Examples 18-22] Toner was obtained in the same manner as in Example 1, except that toner particles were produced by modifying the hot sphere formation process as follows, and the types and amounts of each external additive were changed as shown in Table 1 below. In Example 22, toner particles were produced by not incorporating crystalline polyester resin C as a toner raw material, and instead changing the amount of amorphous polyester resin A to 87% by mass.

[0144] -Hot spheroidization process- Next, the obtained pre-heat-treated toner was subjected to a spheroidizing process using a hot-air spheroidizing device (manufactured by Nippon Pneumatic Mfg. Co., Ltd., product name: Meteor Rainbow) to obtain toner particles. The conditions for hot spheroidizing were as follows: the input rate of pre-heat-treated toner particles to the hot-air spheroidizing device was 3.0 kg per hour, the hot air supply rate was 1180 L per minute, the hot air temperature was 200°C, the cooling air supply pressure was 0.15 MPa, and the air supply rate from the secondary air injection nozzle was 230 L per minute. The distance between the cooling air intake and the impact member was 2.0 cm. The obtained toner particles had an average primary particle diameter of 6.7 μm, a circularity of 0.950, and a glass transition temperature (Tg) of 50°C.

[0145] [Comparative Example 1] Toner was obtained in the same manner as in Example 1, except that, in the pre-heat treatment additive (first additive) added in the first external additive step, approximately spherical large-diameter silica particles (average primary particle diameter 150 nm) were used instead of associated silica particles.

[0146] [Comparative Example 2] Toner was obtained in the same manner as in Example 1, except that silica particles were not added as an external additive (second external additive) after heat treatment (i.e., the second external additive step was not performed).

[0147] [Comparative Example 3] Toner was obtained in the same manner as in Example 1, except that the silica particles used as the pre-heat treatment additive (first additive) added in the first external additive step were changed to silica particles with an average particle size of 40 nm (manufactured by Nippon Aerosil Co., Ltd., product name: RY50).

[0148] [Comparative Example 4] Toner was obtained in the same manner as in Example 1, except that silica particles were not added to the pre-heat treatment additive (first additive) added in the first external additive step.

[0149] [Comparative Example 5] Toner was obtained in the same manner as in Example 1, except that associated silica particles were not added to the pre-heat treatment external additive (first external additive) added in the first external additive step, and a hot spheroidization treatment similar to that in Examples 18 to 22 was performed. The reason for performing this hot spheroidization treatment was that, because the pre-heat treatment external additive (first external additive) consisted only of small-particle-diameter silica particles, it was not possible to perform the hot spheroidization treatment under conditions that increased the circularity of the toner particles (conditions that resulted in a circularity of 0.97).

[0150] [Comparative Example 6] Toner was obtained in the same manner as in Example 1, except that the associated silica particles used as the post-heat treatment external additive (second external additive) were changed to those with a larger particle size, as shown in Table 2 below.

[0151] Tables 1 and 2 below show the types and amounts of raw materials used in each example and comparative example. In the tables, silica particles with an average particle diameter of 7 nm are "R976S" (product name, manufactured by Nippon Aerosil Co., Ltd.), silica particles with an average particle diameter of 12 nm are "R974" (product name, manufactured by Nippon Aerosil Co., Ltd.), silica particles with an average particle diameter of 30 nm are "MSP-011" (product name, manufactured by Teika Co., Ltd.), and silica particles with an average particle diameter of 40 nm are "RY50" (product name, manufactured by Nippon Aerosil Co., Ltd.). Furthermore, the coverage ratio Y / X is calculated by setting X as the total coverage of the toner particle surface by the first and second external additives, and Y as the coverage of the toner particle surface by the first external additive.

[0152] [Table 1]

[0153] [Table 2]

[0154] 4. Evaluation <Item 1: Bending test (evaluation of anchoring strength)> Figure 3 shows the procedure for the bending test. Figure 4 is a schematic diagram showing that toner peeling occurs in the bending test when an image is formed using toner in which an external additive has been unevenly attached to the surface of the toner particles after heat treatment.

[0155] Figures 3(A) and (B) both show a procedure in which a recording paper P on which a fixed image T has been formed is folded so that the printed side is facing inward, and then the folded recording paper P is unfolded and the folded portion is checked. As shown in Figure 3(A), the absence of a toner peeling area C indicates greater bending strength (i.e., fixing strength), while as shown in Figure 3(A), a larger toner peeling area C indicates less bending strength.

[0156] As shown in Figure 4(A), when toner 10, on which an external additive is uniformly attached to the surface of toner particles after heat treatment, is fixed to recording paper P, and a bending test is performed on the fixed image 10', toner peeling areas C are unlikely to occur. In contrast, as shown in Figure 4(B), when toner 90, on which an external additive is unevenly attached to the surface of toner particles, is fixed to recording paper P, and a bending test is performed on the fixed image 90', areas 93A where the external additive is concentrated inhibit the adhesion between toner particles and the adhesion between toner particles and recording paper P, so toner peeling areas C are likely to occur.

[0157] Specifically, this bending test was conducted as follows: First, using a commercially available copier modified for evaluation (Sharp Corporation, model: MX-5100FN), a sample image including a solid color image (20mm x 50mm rectangle) was formed as a fixed image on recording paper (Sharp Corporation, PPC paper, product number: SF-4AM3).

[0158] Next, the recording paper with the solid image formed on it was folded so that the printed side was facing inward, and then a load was applied by rolling an 850g roller over it once back and forth to maintain constant pressure. After that, the folded recording paper was unfolded, and the folded portion was blown away with an airbrush. The width of the white line (i.e., toner peeled-off portion C) that was created in the folded portion was measured.

[0159] Based on the measured line width, the "bending strength" was evaluated according to the following criteria. ◎ (Excellent): Line width is 60 μm or less. ○ (Good): Line width is between 60 μm and 80 μm. △ (Acceptable): Line width is greater than 80 μm and 110 μm or less. × (Not acceptable): The line width exceeds 110 μm.

[0160] <Item 2: Evaluation of heat resistance and storage properties> 10g of toner was placed in a 100mL glass bottle and left in a constant temperature bath at 50°C for 24 hours. The toner after this period was placed on three sieves with mesh sizes of 250μm, 150μm, and 75μm, respectively, and sieved for 1 minute using an ultrasonic sieving machine. The degree of coagulation was then calculated using the following formula. In the formula below, G is the degree of coagulation, w is the amount of toner sampled, w1 is the amount of toner remaining on the upper sieve, w2 is the amount of toner remaining on the middle sieve, and w3 is the amount of toner remaining on the lower sieve. G = (w1 + 0.6 × w2 + 0.2 × w3) × 100 / w

[0161] Based on the calculated degree of coagulation, the "heat resistance and storage capacity" of the toner was evaluated according to the following criteria. ◎ (Good): The degree of cohesion is 10 or less. ○ (Acceptable): The degree of cohesion is greater than 10 and less than or equal to 20. × (Not acceptable): The degree of cohesion is greater than 20.

[0162] <Item 3: Evaluation of the coefficient of variation in the number of associated silica particles> A smaller coefficient of variation in the number of associated silica particles indicates that the associated silica particles are uniformly distributed on the toner particle surface. This means that the post-heat treatment additive adheres uniformly to the toner particle surface, resulting in a toner that fully utilizes the effects of the post-heat treatment additive.

[0163] The coefficient of variation of the number of associated silica particles was measured using the following procedure. First, a backscattered electron image of the toner particles was taken using a scanning electron microscope at a magnification of 20,000x. In this backscattered electron image, the midpoint of the largest diameter of the toner particles was used as the reference point, and a circle with a radius of 2.0 μm centered on this reference point was drawn.

[0164] Next, straight lines were drawn at 45° intervals from the reference point toward the periphery of the toner particle, dividing the circle into eight regions. The number of associated silica particles in each of these eight regions was counted, and the coefficient of variation of the number of particles between the eight regions was calculated. This coefficient of variation calculation was performed for 10 toner particles, and the average value was defined as the "coefficient of variation of the number of associated silica particles."

[0165] The calculated "coefficient of variation of the number of associated silica particles" was evaluated according to the following criteria. ◎ (Excellent): The coefficient of variation in the number of items is 0.3 or less. ○ (Good): The coefficient of variation in the number of items is greater than 0.3 and less than or equal to 0.4. △ (Acceptable): The coefficient of variation in the number of items is greater than 0.4 and less than or equal to 0.5. × (Not acceptable): The coefficient of variation in the number of items is greater than 0.5.

[0166] [Table 3]

[0167] Table 3 shows the evaluation results for each example and comparative example. According to Table 3, the toners of Examples 1 to 23, which have toner particles containing a binder resin and a release agent and satisfy the following requirements (A) to (E), exhibited excellent fixing strength because the external additive was uniformly distributed on the surface of the toner particles. Furthermore, they also exhibited excellent heat resistance, which is the external additive effect of the second external additive, thus fully obtaining the external additive effect of the external additive. (A) A first external additive (a pre-heat treatment external additive in this embodiment) is fixed to the surface of the toner particles, which consists of associated silica particles, which are secondary particles formed by the coalescence of two or more primary silica particles, and silica particles, which are primary silica particles. (B) The number-average particle diameter of the associated silica particles is between 100 nm and 300 nm. (C) The number-average particle diameter of the silica particles is 30 nm or less. (D) The coverage rate of the toner particle surface by the associated silica particles is 5% or more and 40% or less. (E) The coverage rate of the toner particle surface by the silica particles is 10% or more and 70% or less.

[0168] In contrast, Comparative Examples 1 to 6, which did not meet these requirements, were inferior to the examples in at least one of the evaluations among the bending test, heat resistance and storage performance, and coefficient of variation of particle size. In Comparative Example 5, because the first external additive consisted only of small-particle-diameter silica particles, it was not possible to perform the hot spheroidization treatment under the condition of increasing the circularity of the toner particles (a condition of circularity of 0.97). Therefore, the coefficient of variation of particle size was evaluated as "×" without even needing to measure it.

[0169] In the examples other than Examples 3 and 10, the evaluation of the coefficient of variation in the number of particles was "○" or "◎", indicating that the coefficient of variation in the number of associated silica particles was 0.40 or less. Example 3 is an example in which the silica particles as the first external additive have a large average particle diameter, and Example 10 is an example in which the coverage rate of the toner particle surface by the silica particles as the first external additive is small. From this, it is preferable that the average particle diameter of the silica particles as the first external additive is 20 nm or less, and that the coverage rate of the toner particle surface by the silica particles as the first external additive is 15% or more.

[0170] Example 1, in which the degree of association of the associated silica particles is between 2.0 and 3.5, is superior to Examples 6 and 7, in the bending test and evaluation of the coefficient of variation of the number of particles, compared to Examples 6 and 7, in which the degree of association of the associated silica particles is outside the above range. This is thought to be because if the degree of association of the associated silica particles is too high, the associated silica particles become too irregular in shape, making it impossible to secure a contact area with the toner particle surface, and the associated silica particles tend to be unevenly distributed in the depressions on the toner particle surface. Conversely, if the degree of association of the associated silica particles is too low, the associated silica particles become closer to spherical, which is thought to worsen the dispersion of the associated silica particles on the toner particle surface.

[0171] Examples 1-11 and 18-21 are examples in which the toner particles contain a crystalline polyester resin. In contrast, Examples 12-17 and 22 are examples in which the toner particles do not contain a crystalline polyester resin. For example, comparing Example 1 and Example 12, it can be seen that Example 1, in which the toner particles contain a crystalline polyester resin, performs better in the bending test evaluation than Example 12, in which the crystalline polyester resin does not. This is thought to be because, when the toner particles do not contain a crystalline polyester resin, the fluidity of the toner particles improves and the dispersion of the external additive also improves, but the low-temperature fixability deteriorates.

[0172] Examples 1 to 17 are examples where the circularity of the toner particles is 0.96 or higher. In contrast, Examples 18 to 22 are examples where the circularity of the toner particles is less than 0.96. For example, comparing Example 1 and Example 18, it can be seen that Example 1, where the circularity of the toner particles is 0.96 or higher, performs better in the bending test evaluation than Example 18, where the circularity of the toner particles is less than 0.96. This is thought to be because when the circularity of the toner particles after the hot spheroidization treatment is low, recesses (grooves) remain on the surface of the toner particles compared to when the circularity is high, and therefore the dispersion of the second external additive (i.e., the external additive after heat treatment) on the surface of the toner particles does not improve.

[0173] Examples 1 and 2, in which the number-average particle size of the silica particles used as the first external additive is between 6 nm and 15 nm, show superior performance in the bending test and evaluation of the coefficient of variation of the number of particles compared to Example 3, in which the number-average particle size exceeds the above upper limit. This is thought to be because increasing the particle size of the silica particles used as the first external additive reduces the effect of imparting fluidity to the toner particles, worsening the dispersion of the external additive on the surface of the toner particles.

[0174] If X is the total coverage rate of the toner particle surface by the first and second external additives, and Y is the coverage rate of the toner particle surface by the first external additive, then Example 1, where Y / X is between 0.2 and 0.7, is superior in various evaluations compared to Example 10, where Y / X is below the lower limit, and is particularly superior in the bending test and the evaluation of the coefficient of variation of the number of particles. This is thought to be because when the amount of the first external additive added is small, the effect of imparting fluidity to the toner particles decreases, and the degree of dispersion of the external additive on the surface of the toner particles deteriorates.

[0175] Furthermore, it can be seen that Example 1, where Y / X is between 0.2 and 0.7, is superior to Example 11, where Y / X exceeds the above upper limit, in terms of evaluation of heat resistance and storage properties. This is thought to be because if the amount of silica particles added as the second external additive is small, it is not possible to sufficiently impart a heat resistance and storage improvement effect to the toner.

[0176] The embodiments disclosed herein are illustrative in all respects and are not intended to be restrictive. Therefore, the technical scope of this disclosure is not construed solely by the embodiments described above, but is defined by the claims. This includes all modifications within the meaning and scope of the claims. [Explanation of Symbols]

[0177] 10 Toners 10′ Toner after fixing 11 Toner particle surface before the hot spheroidization process 11′ Toner particle surface after the hot spheroidization process 12 Associated silica particles 13. Second external additive (external additive after heat treatment)

Claims

1. A toner having toner particles containing a binder resin and a release agent, A first external additive containing associated silica particles, which are secondary particles formed by the coalescence of two or more primary silica particles, and silica particles, which are primary silica particles, is fixed to the surface of the toner particles. The number-average particle diameter of the associated silica particles is between 100 nm and 300 nm. The number-average particle diameter of the silica particles is 30 nm or less. The coverage rate of the toner particle surface by the associated silica particles is 5% or more and 40% or less. A toner characterized in that the coverage rate of the toner particle surface by the silica particles is 10% or more and 70% or less.

2. The toner according to claim 1, A toner characterized in that the coefficient of variation of the number of associated silica particles, as determined by the measurement method described below, is 0.40 or less. [Method for measuring the coefficient of variation of the number of associated silica particles] In a backscattered electron image of toner particles captured using a scanning electron microscope, the midpoint of the toner particle's maximum diameter is used as the reference point, and a circle is drawn centered on this reference point. Next, straight lines are drawn at 45° intervals from the reference point toward the periphery of the toner particle, dividing the circle into eight regions. The number of associated silica particles present in each of these eight divided regions is counted, and the coefficient of variation of the number of particles between the eight divided regions is calculated. This coefficient of variation calculation is performed for 10 toner particles, and the average value is defined as the "coefficient of variation of the number of associated silica particles."

3. The toner according to claim 1, The toner is characterized in that the degree of association of the associated silica particles is 2.0 or more and 3.5 or less.

4. The toner according to claim 1, The toner particles contain a crystalline polyester resin, The toner is characterized in that the glass transition temperature of the toner particles is 60°C or lower.

5. The toner according to claim 1, The toner is characterized in that the circularity of the toner particles is 0.96 or higher.

6. The toner according to claim 1, The toner is characterized in that the number-average particle diameter of the silica particles is 6 nm or more and 15 nm or less.

7. A toner according to any one of claims 1 to 6, The toner particle surface contains a second external additive that adheres more weakly than the first external additive, Let X be the total coverage rate of the toner particle surface by the first and second external additives. If Y is the coverage rate of the toner particle surface by the first external additive, A toner characterized by satisfying the relationship shown in equation (1) below. 0.7 ≥ Y / X ≥ 0.2 ... (1)

8. A method for manufacturing toner according to any one of claims 1 to 6, A melt-kneading step involves melt-kneading a mixture of toner raw materials containing a binder resin and a release agent to obtain a melt-kneaded product, A fine grinding step to obtain finely ground material by finely grinding the molten mixture, A classification step of classifying the aforementioned finely ground material to obtain a classified material, A first external additive step involves mixing the classified material with the first external additive and adhering the first external additive to the surface of the classified material to obtain toner particles before heat treatment. A heat spheroidization process is performed in which the toner particles before heat treatment are shaped into spheres by hot air to obtain toner particles after heat treatment. A method for manufacturing toner, characterized by including [the specified ingredient / feature].

9. A method for manufacturing toner according to claim 7, A melt-kneading step involves melt-kneading a mixture of toner raw materials containing a binder resin and a release agent to obtain a melt-kneaded product, A fine grinding step to obtain finely ground material by finely grinding the molten mixture, A classification step of classifying the aforementioned finely ground material to obtain a classified material, A first external additive step involves mixing the classified material with the first external additive and adhering the first external additive to the surface of the classified material to obtain toner particles before heat treatment. A heat spheroidization process is performed in which the toner particles before heat treatment are shaped into spheres by hot air to obtain toner particles after heat treatment. A second external additive step involves mixing the heat-treated toner particles with the second external additive to adhere the second external additive to the surface of the heat-treated toner particles, A method for manufacturing toner, characterized by including [the specified ingredient / feature].

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