ADDITIVES FOR TONER PARTICLE CONTAINING POLYMER PARTICLES HAVING INTERPENETRATING POLYMER NETWORK

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

[0001] This application claims priority to Japanese Patent Application No. 2022-169279, filed on October 21, 2022, the entirety of which is incorporated by reference herein.

BACKGROUND

[0002] A method, or an electrophotographic method, of visualizing image information through an electrostatic charge image is used in various fields. In the electrophotographic method, after a surface of a photoreceptor is uniformly charged, an electrostatic charge image is formed on the surface of the photoreceptor, and an electrostatic latent image is developed with a developer containing toner particles to visualize the image as a toner image. The toner image is transferred and fixed onto a surface of a recording medium, thereby forming an image.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003] The disclosure may be understood by the following detailed description and combinations of the accompanying drawings.

[0004] FIG. l is a table showing physical properties of obtained additives according to some examples.

[0005] FIG. 2 is a table showing evaluation results of toner particles according to some examples.

DETAILED DESCRIPTION

[0006] Hereinafter, example additives for a toner particle are described. The example additives for a toner particle may contain polymer particles having an interpenetrating polymer network formed of at least one polymer selected from the group comprising a polystyrene and a poly(meth)acrylate.

[0007] The interpenetrating polymer network (IPN) has a network structure formed of two or more polymers entangled with each other. In some examples, the IPN may be formed of polymers containing a polystyrene and a poly(meth)acrylate, and may be formed of a base particle containing a polystyrene, and a poly(meth)acrylate infiltrated into the base particle.

[0008] The polystyrene may be crosslinked by a crosslinking monomer. Examples of the crosslinking monomer include monomers having a plurality of vinyl groups, such as divinylbenzene, and monomers having a plurality of (meth)acryloyl groups, such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, and triethylene glycol di(meth)acrylate. The content of the crosslinking monomer may be 0.1 parts by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the polystyrene.

[0009] The poly(meth)acrylate may contain, as a monomer unit, at least one selected from the group comprising a methyl (meth)acrylate, a (meth)acrylate having a hydroxy group, and a (meth)acrylate having an ether group.

[0010] The (meth)acrylate having a hydroxy group may be a hydroxyalkyl (meth)acrylate. The number of carbon atoms of the hydroxyalkyl group in the hydroxyalkyl (meth)acrylate may be, for example, one or more and four or less. Examples of the (meth)acrylate having a hydroxy group include hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, and hydroxybutyl (meth)acrylate.

[0011] The (meth)acrylate having an ether group may be, for example, a (meth)acrylate represented by the following formula (1): wherein R ¹ represents a hydrogen atom or a methyl group, R ² represents an alkylene group, m represents an integer of one or more, and R ³ represents an alkyl group.

[0012] The alkylene group represented by R ² may be linear or branched. The number of carbon atoms of the alkylene group represented by R ² may be one or more and four or less. The alkylene group represented by R ² may be an ethylene group. The integer m may be two or more, four or less, or three or less, and may be one or two.

[0013] The alkyl group represented by R ³ may be linear or branched. The number of carbon atoms of the alkyl group represented by R ³ may be one or more and four or less. The alkyl group represented by R ³ may be methyl group.

[0014] The content of the polystyrene may be 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, or 65% by mass or more, and 99% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less, based on the total amount of the polymer particles, from the viewpoint of obtaining a suitable range of relative permittivity and solubility parameter (also referred to as "solubility parameter" or "SP value") and excellent charging rate and charge amount.

[0015] The content of the poly(meth)acrylate may be 1% by mass or more, 5% by mass or more, 10% by mass or more, or 15% by mass or more, and may be 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on the total amount of the polymer particles, from the viewpoint of obtaining a relative dielectric constant and a solubility parameter in suitable ranges.

[0016] The IPN may be formed of the polystyrene and a polymer other than the poly(meth)acrylate. Examples of the polymer other than the poly(meth)acrylate include acrylonitrile; maleic acid derivatives such as maleic acid ester and maleic anhydride; fumaric acid derivatives such as a fumaric acid ester; itaconic acid derivatives such as an itaconic acid ester and itaconic anhydride; and crotonic acid derivatives such as a crotonic acid ester.

[0017] The IPN may be formed of the poly(meth)acrylate and a polymer other than the polystyrene. Examples of the polymer other than the polystyrene include acrylonitrile; maleic acid derivatives such as maleic acid ester and maleic anhydride; fumaric acid derivatives such as a fumaric acid ester; itaconic acid derivatives such as an itaconic acid ester and itaconic anhydride; and crotonic acid derivatives such as a crotonic acid ester.

[0018] The average particle diameter of the polymer particles may be 100 nm or less, 70 nm or less, 50 nm or less, 40 nm or less, 30 nm or less, or 20 nm or less and may be 5 nm or more, 10 nm or more, or 20 nm or more. The average particle diameter of the polymer particles is defined as a volume-based median size (Dv50, for example, Microtrac HRA (manufactured by MicrotracBEL Corp.) is used).

[0019] Next, example methods for producing the above-described additives for a toner particle is described. An example method for producing an additive for a toner particle may include: impregnating precursor particles containing a polymer with a monomer; and polymerizing the monomer to obtain polymer particles having an interpenetrating polymer network formed of at least one polymer selected from the group comprising a polystyrene and a poly(meth)acrylate.

[0020] In some examples, the precursor particles may include a polystyrene, and the monomer may include a (meth)acrylate. In this case, the IPN in the resulting polymer particles is formed of a polymer including a polystyrene and a poly(meth)acrylate.

[0021] The precursor particles may be obtained by, for example, polymerizing styrene and a crosslinking monomer. The details of the crosslinking monomer are as described above. The amount of the crosslinking monomer blended may be 0.1 parts by mass or more and 2 parts by mass or less with respect to 100 parts by mass of styrene.

[0022] The (meth)acrylate may include at least one selected from the group comprising a methyl (meth)acrylate, a (meth)acrylate having a hydroxy group, and a (meth)acrylate having an ether group. The details of the (meth)acrylate having a hydroxy group and the (meth)acrylate having an ether group are as described above.

[0023] The content of the polystyrene (styrene) may be 40% by mass or more, 45% by mass or more, 50% by mass or more, 55% by mass or more, 60% by mass or more, or 65% by mass or more, and may be 99% by mass or less, 95% by mass or less, 90% by mass or less, or 85% by mass or less, based on the total amount of the precursor particles and monomers, from the viewpoint of obtaining a dielectric constant and solubility parameter in a suitable range and excellent charging speed and charge amount.

[0024] The content of the (meth)acrylate may be 5% by mass or more, 10% by mass or more, or 15% by mass or more, and may be 50% by mass or less, 40% by mass or less, or 30% by mass or less, based on the total amount of the precursor particles and the monomer, from the viewpoint of obtaining a dielectric constant and a solubility parameter in a suitable range.

[0025] The method of polymerizing the monomer impregnated into the precursor particles may be, for example, a radical polymerization, a cationic polymerization, or an anionic polymerization. An active species such as a radical, a cation, or an anion may be generated by heat, visible light or ultraviolet light, an electron beam, or the like. By polymerizing the monomer, the IPN is formed of the polymer produced from the monomer and the polymer contained in the precursor particles. In the case where the active species are generated by visible light and/or ultraviolet light, irradiation with visible light and/or ultraviolet light is performed in consideration of attenuation of intensity due to an absorption wavelength of a material.

[0026] Next, an example of a toner particle is described. An example toner particle may include a core particle and an additive externally added to the core particle. The additive may be or include the above-described additive for a toner particle.

[0027] The core particle may include, for example, a binder resin. The binder resin may include one or more resins selected from a group of a polyester resin, an amorphous polyester resin and a crystalline polyester resin. The amorphous polyester resin may be a polyester resin exhibiting no clear endothermic peak in differential scanning calorimetry (DSC). The amorphous polyester resin may be defined as, for example, a polyester resin exhibiting a stepwise endothermic change when measured at a temperature rise rate of 10 °C/min in differential scanning calorimetry, or a polyester resin exhibiting an endothermic peak with a half width of more than 15°C.

[0028] The crystalline polyester resin may be a polyester resin exhibiting a clear endothermic peak in differential scanning calorimetry (DSC). When the binder resin includes the crystalline polyester resin, the image glossiness and the low-temperature fixability of the toner may be achieved.

[0029] The content of the binder resin in the toner particle may be 40% by mass or more, 45% by mass or more, or 50% by mass or more, and 90% by mass or less, 85% by mass or less, or 75% by mass or less, based on the total amount of the toner particle.

[0030] The core particle may further include a colorant. The colorant may include, for example, at least one colorant selected from a black colorant, a cyan colorant, a magenta colorant, and a yellow colorant. The colorant may be used alone or in combination of two or more thereof in consideration of hue, saturation, lightness, weather resistance, dispersibility in the toner, and the like.

[0031] The content of the colorant, based on the total amount of the toner particle, may be 0.5% by mass or more, 1% by mass or more, or 2% by mass or more, from the viewpoint of sufficiently exhibiting a coloring effect, and may be 15% by mass or less, 12% by mass or less, or 10% by mass or less, from the viewpoint of obtaining a sufficient triboelectric charge amount without significantly affecting an increase in a production cost of the toner particle.

[0032] The core particles may further include a release agent. Since the release agent may increase low-temperature fixability, final image durability, and abrasion resistance characteristics of the toner particle, the type and content of the release agent may be determined in consideration of characteristics of the toner.

[0033] The content of the release agent, based on the total amount of the toner particle, may be 1% by mass or more, 2% by mass or more, or 3% by mass or more, from the viewpoint of good low-temperature fixability and sufficient securement of a fixing temperature range, and may be 20% by mass or less, 15% by mass or less, or 10% by mass or less, from the viewpoint of excellent storage stability and economic efficiency.

[0034] The content of the core particle may be 80% by mass or more, 85% by mass or more, or 90% by mass or more, and may be 99% by mass or less, 98% by mass or less, or 97% by mass or less, based on the total amount of the toner particle.

[0035] The average particle diameter of the core particles may be 3 pm or more, 4 pm or more, or 5 pm or more, and may be 12 pm or less, 11 pm or less, 10 pm or less, or 9 pm or less.

[0036] The content (addition amount) of the additive (additive for a toner particle) may be 0.5 parts by mass or more, 0.8 parts by mass or more, or 1 part by mass or more, and may be 5 parts by mass or less, 3 parts by mass or less, or 1.5 parts by mass or less, with respect to 100 parts by mass of the core particle.

[0037] The toner particle may include inorganic particles externally added to the core particle in addition to the above-described additives for a toner particle. Examples of the inorganic particles include silica particles, alumina particles, zirconia particles, and titania particles.

[0038] The toner particle may include a charge control agent. The charge control agent may be internally added to the core particle or may be externally added to the core particle. The charge control agent may be a negative-type charge control agent or a positive-type charge control agent.

[0039] The average particle diameter of the toner particles may be 3 pm or more, 4 pm or more, or 5 pm or more, and may be 12 pm or less, 11 pm or less, 10 pm or less, or 9 pm or less.

[0040] Since the toner particle described above includes the polymer particles having the IPN as an additive, the environmental stability of the toner particle is improved (for example, a charge difference may be small, the charge difference caused by different environments in which the toner particle is placed, e.g., among a low-temperature and low-humidity environment, a normal-temperature and normal-humidity environment and a high-temperature and high-humidity environment) compared to other toner particle (for example, a toner particle to which polymer particles having no IPN are externally added). In addition, in some examples, the above-described toner particle including the polymer particles having the IPN as an additive, may be easily controllable (for example, compared to toner particles to which polymer particles having no IPN are externally added) in terms of controlling charging speed and charging amount under high-temperature and high-humidity environments, normaltemperature and normal-humidity environments, and low-temperature and low-humidity environments, charging stability, fluidity, and storage properties. In addition, in some examples, since the polymer particles having the IPN are externally added to the abovedescribed toner particle, the dielectric constant and solubility parameter can be easily adjusted (can be adjusted by changing the type and content of the polymer constituting the IPN) compared to other toner particles (for example, toner particles to which silica particles are externally added). For example, a toner particle having a low dielectric constant can be obtained as necessary.

[0041] Example methods for producing the toner particle described above are described. An example method for producing the toner particle may include: obtaining polymer particles; and externally adding the polymer particles to a core particle.

[0042] Obtaining polymer particles includes: impregnating precursor particles including a polymer with a monomer; and polymerizing the monomer to obtain polymer particles having an interpenetrating polymer network formed of at least one polymer selected from the group comprising a polystyrene and a poly(meth)acrylate. The details are described above.

[0043] Externally adding the polymer particles to the core particle may be, for example, by mixing the core particles and the polymer particles with a powder mixer.

[0044] The toner particles may be used as a one-component developer. The toner particles may be mixed with a magnetic carrier and used as a two-component developer in order to further increase dot reproducibility and supply a stable image over a long period of time.

[0045] The toner particles may be contained in a toner cartridge, for example. More specifically, the toner particles may be contained within a container in a toner cartridge. That is, another example may be a toner cartridge containing a container accommodating the abovedescribed toner particles.

[0046] Hereinafter, additives for a toner particle and the toner particles are described in more detail with reference to examples, but the additive for a toner particle and the toner particles are not limited to the examples. In examples, "parts" means "parts by mass" unless otherwise specified.

[0047] Preparation of Additive 1 :

[0048] (First Step) Deionized water (1400 g) and 1-hexadecanol (65.44 g) are added to a 500 mL vessel and sonicated until uniform using BRANSON MODEL 102C at the maximum power to break the gel structure of the mixture. Further, to this mixture, styrene (91.42 g), 55% divinylbenzene (0.37 g), sodium dodecyl sulfate (SDS) (154.0 g), and potassium persulfate (KPS) (2.44g) are added, and the mixture is treated five times with pressurized 200 MPa using a microfluidizer LM-20-30 equipped with a Y-shaped chamber sufficiently cooled with ice water to obtain a dispersion. The obtained dispersion is transferred to a reaction vessel equipped with a thermometer, a Dimroth condenser and a stirrer, the internal temperature is raised to 80°C under a nitrogen stream, the same conditions are maintained for 1.5 hours, and then the temperature is lowered to 60°C.

[0049] (Second Step) A mixture of 2 -hydroxy ethyl methacrylate (HEMA) (8.17 g) and 55% divinylbenzene (0.04 g) is added to the vessel cooled to 60°C over 30 minutes using syringe pumps, the internal temperature is raised again to 80°C, and the temperature is maintained for 8 hours to obtain a fine particle dispersion containing styrene-2-hydroxyethyl methacrylate (HEMA).

[0050]

[0051] (Washing)After completion of the reactions, the reactants are cooled to room temperature, the contents are put into a centrifuge tube by about 2.0 mL, ultracentrifugation is performed at 140000 rpm for 10 minutes using a CS150FNX (manufactured by himac) equipped with an angle rotor S MOAT, and the supernatant is removed after separation. Next, an operation of adding deionized water (1.5 mL), performing ultracentrifugation at 140000 rpm for 10 minutes, and removing the supernatant is repeated three times.

[0052]

[0053] (Lyophilization)The washed wet particles are placed in a glass petri dish, several drops of deionized water are added thereto, and the particles are well loosened with a spatula. The petri dish is covered with a filter paper, placed in a freeze dryer DRC-1000 (manufactured by EYELA) connected to an accessory device FDU-2 I I 0, and freeze-dried under vacuum. The lyophilization conditions are (1) preliminary freezing (-40°C, 1 hour, atmospheric), (2) reduced pressure (-40°C, 20 minutes, 1.3 to 13 Pa), (3) first drying (-10°C, 12 hours, 1.3 to 13 Pa), and (4) second drying (20°C, 12 hours, 1.3 to 13 Pa).

[0054] [0055] (Drying and Disintegration)The petri dish taken out of the apparatus is placed in a circulating drier WFO-Eyela (manufactured by 420W), the temperature is raised to 40°C, the petri dish is dried for 10 hours, and the dried dish is loosened by hand to obtain Additive 1 (polymer particles having an IPN).

[0056] Preparation of Additives 2 to 10:

[0057] Additives 2 to 10 (polymer particles having an IPN) are obtained in the same manner as in Additive 1 except that the type and blending amount (g) of the monomer used are changed as shown in FIG. 1.

[0058] Preparation of Additive 11 :

[0059] Additive 11 was obtained by performing the same operation as that of Additive 1 except that the number of times of treatment with the Microfluidizer LM-20-30 is changed to 15 times.

[0060] Preparation of Additive 12:

[0061] Additive 12 is obtained by performing the same operation as that of Additive 1 except that the number of times of treatment with the Microfluidizer LM-20-30 is changed to 2 times. [0062] Measurement of Physical Properties of Additive (Polymer Particles)

[0063] The physical properties of the obtained Additives (polymer particles) are measured as follows. The results are shown in FIG. 1.

[0064] Average Particle Diameter

[0065] Each of the obtained Additives 50 mg is put into deionized water (20 mL) containing 0.1% of Contaminon N, and is irradiated with ultrasonic waves for 30 minutes by an ultrasonic disperser. Thereafter, the dispersion liquid adjusted to a predetermined concentration with deionized water is set in DLS-8000 (manufactured by Otsuka Electronics Co., Ltd.), and the average particle diameter is measured.

[0066] Glass Transition Temperature

[0067] The glass transition temperature of the Additives (polymer particles) is determined from the heat flow obtained by differential scanning calorimetry (DSC). For the measurement, a DSC Q2000 of TA Instruments is used, which is placed in a temperature- controlled and humidity-controlled room at 23°C and 50% RH and is connected to a stabilized power source. The sample (15 mg ± 1 mg) is placed in an aluminum pan, the temperature is raised from 30°C to 150°C at a rate of 10°C per minute, then lowered to 0°C at a rate of 10°C per minute, and then raised again to 150°C at a rate of 1°C per minute. As a result, in the Additives 1 to 12, since two glass transition temperatures as shown in FIG. 1 are measured, it is confirmed that the IPN is formed.

[0068] Preparation of Comparative Additive Cl and Measurement of Physical Properties [0069] The operation of the first step is carried out in the same manner as in Additive 1, except that the amounts of styrene and divinylbenzene are changed to 99.60 g and 0.40 g, respectively, and the stirring time at 80°C is extended to 5 hours. Thereafter, the operations after washing are carried out in the same manner as in Additive 1 without carrying out the operation of the second step to obtain Comparative Additive Cl.

[0070] The average particle diameter and glass transition temperature of the obtained Comparative Additive Cl are measured as described above, and it is found that the average particle diameter is 19 nm, and the glass transition temperature is 100.2°C. Since the glass transition temperature is determined at one point, it is confirmed that IPN is not formed.

[0071] Preparation of Comparative Additive C2 and Measurement of Physical Properties [0072] The operation of the first step is carried out in the same manner as in Additive 1 except that the amounts of styrene and divinylbenzene are changed to 76.55 g and 0.41 g, respectively, 2 -hydroxy ethyl acrylate (23.04 g) is further added, and the stirring time at 80°C is extended to 5 hours. Thereafter, the operations after washing are carried out in the same manner as in Additive 1 without carrying out the operation of the second step to obtain Comparative Additive C2.

[0073] The average particle diameter and glass transition temperature of the obtained Comparative Additive C2 are measured as described above, and it is found that the average particle diameter is 10 nm and the glass transition temperature is 62.8°C. Since the glass transition temperature is determined at one point, it is confirmed that IPN is not formed.

[0074] Preparation of Toner Particles [0075] Synthesis of Binder Resin 1

Terephthalic acid: 30 parts by mole

Fumaric acid: 70 parts by mole

Bisphenol A ethylene oxide adduct: 5 parts by mole

Bisphenol A propylene oxide adduct: 95 parts by mole

[0076] A flask equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a rectifying column is charged with the materials described above, the temperature is raised to 220°C over 1 hour, and 1 part of titanium tetraethoxide is added to 100 parts of the materials described above. The temperature is raised to 230°C over 0.5 hours while distilling off the produced water, and the dehydration condensation reaction is continued at this temperature for 70 minutes, after which the reaction product is cooled. Thus, binder resin 1 (polyester resin) having a weight average molecular weight of 18000, an acid value of 15 mgKOH/g, and a glass transition temperature of 60°C is synthesized. The acid value of the resin is measured by a neutralization titration method in accordance with JIS K0070-1992.

[0077] Synthesis of Binder Resin 2

Terephthalic acid: 30 parts by mole

Fumaric acid: 70 parts by mole

Bisphenol A ethylene oxide adduct: 5 parts by mole

Bisphenol A propylene oxide adduct: 95 parts by mole

[0078] A flask equipped with a stirrer, a nitrogen inlet tube, a temperature sensor, and a rectifying column is charged with the materials described above, the temperature is raised to 220°C over 1 hour, and 0.05 parts of titanium tetraethoxide is added to 100 parts of the materials described above. The dehydration condensation reaction is continued at 220°C for 65 minutes while distilling off the produced water, and then the reaction product is cooled. Thus, binder resin 2 (polyester resin) having a weight average molecular weight of 800 is synthesized.

[0079] Preparation of Resin Particle Dispersion

[0080] A vessel equipped with a temperature adjusting means and a nitrogen replacing means is charged with 40 parts of ethyl acetate and 25 parts of 2-butanol to prepare a mixed solvent. Then, 90 parts of the binder resin 1 and 10 parts of the binder resin 2 are gradually charged and dissolved.

[0081] Next, the inside of the container is replaced with dry nitrogen, the temperature is maintained at 40°C, and 400 parts of ion-exchanged water is added dropwise at a rate of 2 parts/minute while stirring the mixed solution, thereby performing emulsification. After completion of the dropwise addition, the emulsion is returned to room temperature (20°C to 25°C), and bubbling is performed for 48 hours with dry nitrogen while stirring to reduce ethyl acetate and 2-butanol to 1 OOOppm or less, thereby obtaining a resin-particle dispersion in which the resin particles are dispersed. Ion-exchanged water is added to the resin particle dispersion to adjust the solid content to 20% by mass, thereby obtaining a resin particle dispersion.

[0082] Preparation of Release Agent Dispersion

Paraffin wax (HNP-9 manufactured by Nippon Seiro Co., Ltd.): 100 parts

Anionic surfactant (NEOGEN RK manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.): 1 part

Ion-exchanged water: 350 parts

[0083] The above materials are mixed, heated to 100°C, dispersed using a homogenizer (Ultra-Turrax T50 manufactured by IKA), and then subjected to dispersion treatment using a Manton-Gaulin high-pressure homogenizer (manufactured by Gaulin) to obtain a release agent dispersion (solid content: 20% by mass) in which release agent particles having a volume average particle diameter of 200 nm are dispersed.

[0084] Preparation of Cyan Colorant Particle Dispersion

Cyan colorant (Pigment Blue 15:3, manufactured by Clariant): 70 parts

Anionic surfactant (NEOGEN RK manufactured by Dai-ichi Kogyo Seiyaku Co.,

Ltd.): 1 part

Ion-exchanged water: 200 parts

[0085] The above materials are mixed and dispersed for 10 minutes using a homogeniser (Ultra-Turrax T50 manufactured by IKA). Ion-exchanged water is added so that the solid component amount in the dispersion becomes 20% by mass to obtain a cyan colorant dispersion in which cyan colorant particles having a volume average particle diameter of 190 nm are dispersed.

[0086] Production of Core Particle

Resin particle dispersion: 425 parts

Cyan colorant particle dispersion: 25 parts

Release agent dispersion: 50 parts

Anionic surfactant (TaycaPower, manufactured by Tayca Corporation): 2 parts

[0087] The above material is placed in a round stainless flask, 0.1 N of nitric acid is added to adjust the pH to 3.5, and aqueous nitric acid (30 parts) containing 10% by mass of polyaluminum chloride is added. Subsequently, the mixture is dispersed at 30°C using a homogenizer (ULTRA-TURRAX T50 manufactured by IKA), heated to 45°C in an oil bath for heating, and held for 30 minutes. Thereafter, 100 parts of the resin-particle dispersion is slowly added and held for 1 hour, and 0.1 N of sodium hydroxide is added to adjust the pH to 8.5. Thereafter, the mixture is heated to 85°C while stirring is continued, and held for 5 hours. Thereafter, the mixture is cooled to 20°C at a rate of 20 °C/min, filtered, sufficiently washed with ion-exchanged water, and dried to obtain core particles having a volume average particle diameter of 7.5 pm.

[0088] Preparation of Toner Particles

[0089] 1.5 parts of each of the obtained Additives 1 to 12 and Comparative Additives Cl to C2 are mixed with 100 parts of the obtained core particles in a Henschel mixer at a peripheral speed of 30 m/s for 2 minutes to obtain toner particles 1 to 14.

[0090] Each of the obtained toner particles 1 to 14 is evaluated as follows. The results are shown in FIG. 2.

[0091] Charging Speed and Charge Amount

[0092] The toner particles (0.5 g) and carrier particles (9.5 g, 100 pm, Imaging Society of Japan) are placed in a wide-mouthed 100 mL bottle and left for 24 hours under high- temperature and high-humidity conditions (30°C, 80%), normal -temperature and normal- humidity conditions (23°C, 50%), and low-temperature and low-humidity conditions (10°C, 15%) to prepare samples. Thereafter, the toner particles are agitated and shaken in 96 rpm for different periods of time (1 minute and 3 minutes) using a turbula mixer (WAB Co., Switzerland) to apply a load to cause triboelectric charging due to collision with the carrier particles. The charge amount (pC/g) of this toner is measured by a charge amount measuring device (TB-203, manufactured by Kyocera Corporation).

[0093] The ratio of the charge amount after stirring for 1 minute (after stirring for 1 minute / after stirring for 3 minutes) to the charge amount after stirring for 3 minutes is obtained for the sample left in the low-temperature and low-humidity environment, and the charging speed is evaluated according to the following criteria.

A: Very good (the ratio is 90% or more)

B: Good (the ratio is 85% or more and less than 90%)

C: Relatively good (the ratio is 80% or more and less than 85%)

D: Practical (the ratio is 70% or more and less than 80%)

E: Impractical (the ratio is less than 70%)

[0094] After the sample is left to stand in the normal-temperature and normal-humidity environment, the charge amount after stirring for 3 minutes is obtained, and the charge amount is evaluated according to the following criteria.

A: Very good (the charge amount is 47 or more and less than 50)

B: Good (the charge amount is 44 or more and less than 47, or 50 or more and less than 52.

C: Relatively good (the charge amount is 41 or more and less than 44, or 52 or more and less than 54)

D: Practical (the charge amount is 38 or more and less than 41, or 54 or more and less than

56)

E: Impractical (the charge amount is less than 38 or 56 or more)

[0095] Environmental Stability

[0096] The ratio (high-temperature and high-humidity environment / low-temperature and low-humidity environment) of the charge amount after stirring for 3 minutes of the sample the high-temperature high-humidity environment to the charge amount after stirring for 3 minutes of the sample left in the low-temperature low-humidity environment is determined, and the environmental stability is evaluated according to the following criteria.

A: Very good (the ratio is 90% or more)

B: Good (the ratio is 85% or more and less than 90%)

C: Relatively good (the ratio is 80% or more and less than 85%)

D: Practical (the ratio is 70% or more and less than 80%)

E: Impractical (the ratio is less than 70%)

[0097] Fluidity

[0098] Each of the toner particles 5 g is placed in a poly cup of 100 mL, left to stand under normal temperature and normal humidity (23°C / 50% RH) and seasoned for 24 hours, and then the initial aggregation degree is measured by a powder tester (trade name, manufactured by Hosokawa Micron Corporation) equipped with three stage sieves (270 mesh, 325 mesh, and 400 mesh in order from the top). Based on the measured degree of aggregation, flowability is evaluated according to the following criteria.

A: Very good (the degree of aggregation is less than 25)

B: Good (the aggregation degree is 25 or more and less than 30.

C: Relatively good (the degree of aggregation is 30 or more and less than 35)

D: Practical (the degree of aggregation is 35 or more and less than 40)

E: Impractical (the degree of aggregation is 40 or more)

[0099] Storability

[0100] The toner particles (100 g) are left to stand at a temperature of 40°C and a relative humidity of 80% for 180 hours, and then the degree of aggregation is measured in the same manner as described above. Based on the measured degree of aggregation, storage stability is evaluated according to the following criteria.

A: Very good (the degree of aggregation is less than 30)

B: Good (the degree of aggregation is 30 or more and less than 35)

C: Relatively good (the degree of aggregation is 35 or more and less than 40) D: Practical (the degree of aggregation is 40 or more and less than 45)

E: Impractical (the degree of aggregation is 45 or more)

[0101] Although various examples of additives for a toner particle, toner particles, and the like have been specifically described above, it is apparent to those skilled in the art that various modifications and changes may be made within the scope of subject matters disclosed herein. It should be understood that aspects, advantages, and features described herein are not necessarily achieved or included in any one particular example. Indeed, while various examples have been described and shown herein, it should be apparent that other examples may be possible in terms of, for example, arrangement, substitution, combination, and/or configuration. All corrections and modifications included in the scope of the subject matters disclosed herein are claimed.