Toner and method for manufacturing toner

Abstract

To provide a toner that can form a high-quality image even in a high temperature and high humidity environment, and a method for manufacturing toner.SOLUTION: A toner includes a toner particle. The toner particle contains a binder resin and a positively-charged charge control agent. A resin included in the binder resin in the largest amount based on mass is a styrene-acrylic resin having an acid value of 7.0 mgKOH / g or more. The charge attenuation constant of the toner particle is -0.0200 or more in an environment of a temperature of 32.5°C and a relative humidity of 80%. A method for manufacturing toner includes a treatment step of treating untreated toner particles with alcohol to obtain toner particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a toner and a method for producing the toner. [Background technology]

[0002] In image formation by electrophotography, for example, a toner containing toner particles is used. In the toner described in Patent Document 1, the toner particles include toner base particles. The toner base particles contain a binder resin, a magnetic powder, and a charge control agent. The binder resin contains a block polymer, and this block polymer has a polyester portion and a vinyl polymer portion. The charge control agent contains a styrene acrylic resin having a quaternary ammonium group. The content of the charge control agent in the toner base particles is 1.5% by mass or more and 12.0% by mass or less. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-56379 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the toner described in Patent Document 1 has room for improvement in terms of forming high-quality images in a high-temperature, high-humidity environment.

[0005] The present invention has been made in view of the above problems, and an object of the present invention is to provide a toner and a method for producing the toner that can form high-quality images even in a high-temperature, high-humidity environment. [Means for solving the problem]

[0006] The toner according to the present invention includes toner particles. The toner particles contain a binder resin and a positively charged charge control agent. The resin contained in the binder resin in the largest amount by mass is a styrene-acrylic resin having an acid value of 7.0 mgKOH / g or more. The charge decay constant of the toner particles is -0.0200 or more under an environment of a temperature of 32.5°C and a relative humidity of 80%.

[0007] The toner manufacturing method according to the present invention is a method for manufacturing the toner described above. The toner manufacturing method according to the present invention includes a treatment step of treating untreated toner particles with alcohol to obtain the toner particles. [Effects of the Invention]

[0008] The toner of the present invention and the toner produced by the production method of the present invention can form high-quality images even in a high-temperature, high-humidity environment. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 2 is a diagram illustrating an example of a toner particle contained in a toner according to an embodiment of the present invention. [Figure 2] 2A to 2C are diagrams illustrating an example of processing steps included in a toner manufacturing method according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] Hereinafter, an embodiment of the present invention will be described. First, the terms used in this specification will be described. A toner is an aggregate of toner particles (for example, powder). An external additive is an aggregate of external additive particles (for example, powder). Unless otherwise specified, the evaluation results (values ​​indicating shape, physical properties, etc.) of a powder (more specifically, a powder of toner particles, a powder of external additive particles, etc.) are the number average of values ​​measured for each of a considerable number of particles selected from the powder. The volume median diameter (the cumulative 50% value D in the volume-based particle size distribution) 50Unless otherwise specified, the glass transition temperature (Tg) is a value measured using a laser diffraction / scattering particle size analyzer (LA-950, manufactured by Horiba, Ltd.) in accordance with JIS (Japanese Industrial Standards) K7121-2012 using a differential scanning calorimeter (DSC-6220, manufactured by Seiko Instruments Inc.). In the endothermic curve measured with the differential scanning calorimeter (vertical axis: heat flow (DSC signal), horizontal axis: temperature), the temperature of the inflection point due to the glass transition (specifically, the temperature at the intersection of the extrapolated line of the baseline and the extrapolated line of the falling line) corresponds to Tg (glass transition temperature). Unless otherwise specified, the acid value is a value measured in accordance with JIS (Japanese Industrial Standards) K0070-1992. Unless otherwise specified, the relative humidity is a value measured in accordance with JIS (Japanese Industrial Standards) Z8806:2001. Unless otherwise specified, the charge amount (unit: μC / g) is a value measured using a small suction-type charge amount measuring device (Trek Model 210HS) under an environment of 25°C temperature and 50% RH relative humidity. The strength of hydrophobicity can be expressed, for example, by the contact angle of a water droplet. The larger the contact angle of the water droplet, the stronger the hydrophobicity. Acrylic and methacrylic may be collectively referred to as "(meth)acrylic." Acrylonitrile and methacrylonitrile may be collectively referred to as "(meth)acrylonitrile." Unless otherwise specified, the "main component" of a material refers to the component that is most abundant in the material by mass. Each component described in this specification may be used alone or in combination of two or more. The terms used in this specification have been explained above.

[0011] [toner] The toner of the present embodiment is described below. The toner of the present embodiment includes toner particles. The toner particles contain a binder resin and a positively charged charge control agent. The resin contained most abundantly in the binder resin by mass is a styrene acrylic resin having an acid value of 7.0 mgKOH / g or more. The charge decay constant of the toner particles is -0.0200 or more in an environment of a temperature of 32.5°C and a relative humidity of 80%.

[0012] Hereinafter, the "resin that is most abundant in the binder resin by mass" may be referred to as the "most abundant resin." The "environment of a temperature of 32.5°C and a relative humidity of 80%" may be referred to as the "specified HH environment."

[0013] The toner of the present embodiment, having the above-described configuration, can form high-quality images (particularly high-quality images without missing fine lines and toner scattering) even in a high-temperature, high-humidity environment. The reason for this is presumed to be as follows.

[0014] In order to sufficiently charge toner particles in a high-temperature, high-humidity environment, it is effective to increase the acid value of the binder resin and allow a large amount of positively chargeable charge control agent to be present in the toner particles. Therefore, in this embodiment, the resin contained in the binder resin at the maximum amount is a styrene-acrylic resin with an acid value of 7.0 mgKOH / g or more. Styrene-acrylic resins with an acid value of 7.0 mgKOH / g or more have many carboxyl groups, which electrostatically attract a large amount of positively chargeable charge control agent during toner production. As a result, a large amount of positively chargeable charge control agent can be contained in the toner particles, allowing the toner to be sufficiently charged even in a high-temperature, high-humidity environment.

[0015] However, increasing the acid value of the binder resin tends to cause the charge of the toner particles to decay quickly in a high-temperature, high-humidity environment. Therefore, in this embodiment, the charge decay constant of the toner particles is set to −0.0200 or more in a predetermined HH environment. If the charge decay constant of the toner particles in a high-temperature, high-humidity environment (e.g., a predetermined HH environment) is −0.0200 or more, the charge of the toner particles is less likely to decay, and the charge amount of the toner is less likely to decrease over time. As a result, high-quality images can be formed without missing fine lines or toner scattering, even in a high-temperature, high-humidity environment.

[0016] The above has explained the reason why the toner of this embodiment can form high-quality images (particularly high-quality images without missing fine lines and toner scattering) even in a high-temperature, high-humidity environment.

[0017] <Toner particles> The toner particles contain a binder resin and a positively chargeable charge control agent. The toner particles may further contain an internal additive (for example, at least one of a colorant, a release agent, and other components other than those mentioned above) as needed. From the viewpoint of forming a good image, the volume median diameter (D 50 ) is preferably 4 μm or more and 9 μm or less.

[0018] As already mentioned, the charge decay constant of the toner particles is −0.0200 or more under a specified HH environment. In order to form high-quality images without missing fine lines or toner scattering under a high-temperature, high-humidity environment, the charge decay constant of the toner particles is preferably −0.0190 or more, more preferably −0.0180 or more. In order to form images by sufficiently charging the toner under a high-temperature, high-humidity environment, the charge decay constant of the toner particles is preferably −0.0100 or less. The charge decay constant of the toner particles can be adjusted, for example, by treating untreated toner particles with alcohol in the treatment step described below, and reducing the acid value near the surface of the treated toner particles. Note that when the toner particles contain an external additive described below, the “charge decay constant of the toner particles” refers to the charge decay constant of the toner base particles (toner base particles before the external additive).

[0019] In order to form an image by sufficiently charging the toner in a high-temperature, high-humidity environment, the charge amount of the toner particles is preferably +10.0 μC / g or more, more preferably +10.0 μC / g or more and +30.0 μC / g or less, and even more preferably +15.0 μC / g or more and +20.0 μC / g or less, under a specified HH environment. Note that when the toner particles contain an external additive described later, the "charge amount of the toner particles" refers to the charge amount of the toner base particles (toner base particles before the external additives are added).

[0020] In order to sufficiently charge toner in a high-temperature, high-humidity environment, it is effective to increase the acid value of the binder resin and to have a large amount of positively chargeable charge control agent present in the toner particles. The amount of positively chargeable charge control agent contained in the surface region of the toner particles particularly affects the charging of toner particles. For example, the more the amount of positively chargeable charge control agent contained in the surface region of the toner particles is greater than the amount of positively chargeable charge control agent contained in the internal region of the toner particles, the easier the toner particles become to charge.

[0021] On the other hand, if the acid value of the binder resin is increased, the charge of the toner particles tends to decay quickly in a high-temperature, high-humidity environment. The acid value of the surface region of the toner particles particularly affects the charge decay of the toner particles. For example, if the acid value of the surface region of the toner particles is lower than the acid value of the internal region of the toner particles, the charge of the toner particles will not decay easily.

[0022] Hereinafter, a case where the toner particles contained in the toner of the present embodiment are capsule toner particles will be described as an example.

[0023] The structure of a toner particle contained in the toner of this embodiment will be described below with reference to FIG. 1. FIG. 1 shows toner particle 1, which is an example of a toner particle contained in the toner of this embodiment. Toner particle 1 has a toner core 2 and a shell layer 3 that coats the toner core 2. Toner particle 1 is a capsule toner particle that includes the shell layer 3. When toner particle 1 is a capsule toner particle, toner core 2 contains a binder resin, and shell layer 3 contains a positively charged charge control agent. The surface of toner core 2 includes a coated region 21 coated with shell layer 3 and an exposed region 22 that is not coated with shell layer 3. The exposed region 22 is, for example, scattered on the surface of toner core 2. Toner core 2 has an internal region 23. The internal region 23 is a spherical region centered at the center X of toner core 2, and the radius of the internal region 23 is, for example, one-fifth the radius of toner core 2.

[0024] The structure of the toner particles contained in the toner of this embodiment has been described above with reference to FIG. 1. However, the toner particles contained in the toner of this embodiment are not limited to the toner particles 1 described above and may be modified in the following ways. For example, while the toner particles 1 shown in FIG. 1 are toner particles that do not contain external additives, this is not a limitation. The toner particles may contain external additives. When the toner particles contain external additives, the toner particles 1 shown in FIG. 1 correspond to toner base particles, and the external additives are attached to the surfaces of the toner base particles. For example, while the toner particles 1 shown in FIG. 1 have a shell layer 3, this is not a limitation. The toner particles may be non-capsule toner particles that do not have a shell layer. For example, while the shell layer 3 of the toner particles 1 shown in FIG. 1 covers a portion of the toner core 2 (including the coated region 21 and the exposed region 22), this is not a limitation. The shell layer of the toner particles may cover the entire toner core.

[0025] Next, for ease of understanding, an outline of the treatment steps performed when producing the toner according to this embodiment will be described with reference to FIG. 2. FIG. 2 is a diagram illustrating the treatment steps included in the toner production method according to this embodiment. Untreated toner particles 10 before the treatment step include a toner core 2 and a shell layer 3 covering the toner core 2. The surface of the toner core 2 of the untreated toner particles 10 includes a coated region 21 covered with the shell layer 3 and an exposed region 22 not covered with the shell layer 3. The toner core 2 has a carboxy group (—COOH group) possessed by a styrene acrylic resin binder resin having an acid value of 7.0 mgKOH / g or more. In the treatment step, the untreated toner particles 10 are treated with an alcohol (R—OH, where R represents an alkyl group). This brings the alcohol into contact with the exposed region 22 of the toner core 2. Then, in the exposed region 22 of the toner core 2, the carboxyl group of the styrene acrylic resin contained in the toner core 2 undergoes an esterification reaction with the alcohol to form an alkoxycarbonyl group (-COOR group, where R represents an alkyl group). As a result, the toner core 2 has an alkoxycarbonyl group in the exposed region 22. In this way, the treated toner particle 1 is obtained. The outline of the treatment process has been described above with reference to FIG. 2. The details of the treatment process will be described later.

[0026] The toner core contains a styrene-acrylic resin with an acid value of 7.0 mgKOH / g or more as the resin contained in the binder resin in the largest amount. This allows a large amount of the positively chargeable charge control agent, which is the shell material, to be attracted to the toner core containing the binder resin with a high acid value in the shell layer formation process described below. As a result, a large amount of the positively chargeable charge control agent can be present in the surface region of the toner particles, allowing the toner to be sufficiently charged even in a high-temperature, high-humidity environment.

[0027] As already mentioned, the toner core contains a binder resin, and the shell layer contains a positively charged charge control agent. The above-described material arrangement results in a greater amount of positively charged charge control agent contained in the surface region of the toner particle than in the internal region of the toner particle. As a result, the toner particles are more easily charged, and the toner can be sufficiently charged even in a high-temperature, high-humidity environment. In order to increase the amount of positively charged charge control agent contained in the surface region of the toner particle compared to the amount of positively charged charge control agent contained in the internal region of the toner particle, it is preferable that the toner core does not contain a positively charged charge control agent.

[0028] In the treatment process, alcohol comes into contact with the exposed surface regions of the toner cores. As a result, carboxy groups in the exposed regions are converted to alkoxycarboxy groups, so that the acid value of the exposed surface regions of the toner cores contained in the toner particles after the treatment process is lower than the acid value of the exposed surface regions of the toner cores contained in the untreated toner particles before the treatment process. On the other hand, in the treatment process, alcohol does not come into contact with the internal regions of the toner cores. Because the carboxy groups in the internal regions of the toner cores are not converted to alkoxycarboxy groups, the acid value of the internal regions of the toner cores contained in the toner particles after the treatment process is equal to the acid value of the internal regions of the toner cores contained in the untreated toner particles before the treatment process. Therefore, by performing the treatment process, the acid value of the exposed surface regions of the toner cores can be made lower than the acid value of the internal regions of the toner cores. This makes the acid value of the surface regions of the toner particles lower than the acid value of the internal regions of the toner particles. As a result, the charge of the toner particles is less likely to decay, enabling the formation of high-quality images without missing fine lines or toner scattering, even in high-temperature, high-humidity environments.

[0029] <Toner core> The toner core contains a binder resin. The toner core may further contain an internal additive (for example, at least one of a colorant, a release agent, and other components other than those described above) as necessary. The toner core may contain a positively chargeable charge control agent, but as described above, it is preferable that the toner core does not contain a positively chargeable charge control agent. Note that when the toner core contains a positively chargeable charge control agent, the same positively chargeable charge control agent as that contained in the shell layer can be used.

[0030] (binder resin) The content of the binder resin is preferably 60% by mass or more and 95% by mass or less, and more preferably 75% by mass or more and 90% by mass or less, based on the mass of the toner core.

[0031] As already mentioned, the resin contained in the binder resin in the greatest amount is a styrene-acrylic resin having an acid value of 7.0 mgKOH / g or more. In order to attract a large amount of the positively charged charge control agent, which is the shell material, to the toner core in the shell layer forming step, the content of the styrene-acrylic resin having an acid value of 7.0 mgKOH / g or more is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 95% by mass, even more preferably 65% ​​by mass to 90% by mass, and particularly preferably 70% by mass to 80% by mass, based on the mass of the binder resin.

[0032] In order to attract a large amount of the positively charged charge control agent, which is the shell material, to the toner core in the shell layer formation process, the content of the styrene acrylic resin having an acid value of 7.0 mgKOH / g or more is preferably 50% by mass or more and 95% by mass or less, more preferably 55% by mass or more and 80% by mass or less, and even more preferably 60% by mass or more and 70% by mass or less, relative to the mass of the toner core.

[0033] As already mentioned, the acid value of the styrene-acrylic resin is 7.0 mgKOH / g or more. In order to sufficiently charge the toner in a high-temperature, high-humidity environment, the acid value of the styrene-acrylic resin is preferably 7.0 mgKOH / g or more and 20.0 mgKOH / g or less, more preferably 8.0 mgKOH / g or more and 18.0 mgKOH / g or less, and even more preferably 10.0 mgKOH / g or more and 15.0 mgKOH / g or less.

[0034] The glass transition point of the styrene-acrylic resin is preferably 40°C or higher and 65°C or lower, and more preferably 45°C or higher and 60°C or lower.

[0035] The styrene-acrylic resin is a polymer of at least one styrene-based monomer and at least one acrylic acid-based monomer.

[0036] The styrene-based monomer is styrene or a derivative thereof. Examples of the styrene-based monomer include styrene, alkylstyrenes (more specifically, α-methylstyrene, p-ethylstyrene, 4-tert-butylstyrene, etc.), and halogenated styrenes (more specifically, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, etc.).

[0037] The acrylic acid monomer is (meth)acrylic acid or a derivative thereof. Examples of the acrylic acid monomer include (meth)acrylic acid, (meth)acrylamide, (meth)acrylonitrile, (meth)acrylic acid alkyl esters, and (meth)acrylic acid hydroxyalkyl esters. Examples of (meth)acrylic acid alkyl esters include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate (specifically, n-propyl (meth)acrylate, iso-propyl (meth)acrylate, etc.), butyl (meth)acrylate (specifically, n-butyl (meth)acrylate, iso-butyl (meth)acrylate, etc.), and 2-ethylhexyl (meth)acrylate. Examples of (meth)acrylic acid hydroxyalkyl esters include 2-hydroxyethyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate.

[0038] The binder resin may contain only a styrene-acrylic resin having an acid value of 7.0 mgKOH / g or more. However, the binder resin may further contain other resins (hereinafter sometimes referred to as other binder resins) in addition to the styrene-acrylic resin having an acid value of 7.0 mgKOH / g or more.

[0039] From the viewpoint of providing a toner with excellent low-temperature fixability, the other binder resin is preferably a thermoplastic resin. Examples of thermoplastic resins include styrene resin, acrylic resin, olefin resin (e.g., polyethylene resin and polypropylene resin), vinyl resin (e.g., vinyl chloride resin, polyvinyl alcohol, vinyl ether resin, and N-vinyl resin), polyester resin, polyamide resin, and urethane resin. Copolymers of these resins, i.e., copolymers in which any repeating unit is introduced into the above-mentioned resins (e.g., styrene-acrylic resin and styrene-butadiene resin having an acid value of less than 7.0 mgKOH / g), can also be used as the other binder resin. As the other binder resin, styrene-acrylic resin or polyester resin having an acid value of less than 7.0 mgKOH / g is preferred.

[0040] The acid value of the other binder resin is preferably less than 7.0 mgKOH / g, more preferably 0.1 mgKOH / g or more and 5.0 mgKOH / g or less. The glass transition temperature of the other binder resin is preferably 40°C or more and 65°C or less, more preferably 45°C or more and 60°C or less.

[0041] The content of the other binder resins is preferably more than 0% by mass and not more than 50% by mass, more preferably 5% by mass or more and 40% by mass or less, even more preferably 10% by mass or more and 35% by mass or less, and particularly preferably 20% by mass or more and 30% by mass or less, relative to the mass of the binder resin.

[0042] The content of the other binder resins is preferably 5% by mass or more and 49% by mass or less, more preferably 10% by mass or more and 40% by mass or less, and even more preferably 20% by mass or more and 30% by mass or less, relative to the mass of the toner core.

[0043] (coloring agent) As the colorant, a known pigment or dye can be used in accordance with the color of the toner. From the viewpoint of forming a high-quality image using the toner, the content of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

[0044] Examples of the colorant include a black colorant and color colorants, such as a yellow colorant, a magenta colorant, and a cyan colorant.

[0045] An example of a black colorant is carbon black. The black colorant may also be a colorant toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

[0046] The yellow colorant may be, for example, one or more compounds selected from the group consisting of condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds. Examples of the yellow colorant include CI Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155, 168, 174, 175, 176, 180, 181, 191, and 194), Naphthol Yellow S, Hansa Yellow G, and CI Vat Yellow.

[0047] Examples of magenta colorants that can be used include one or more compounds selected from the group consisting of condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. Examples of magenta colorants include CI Pigment Red (2, 3, 5, 6, 7, 19, 23, 48:2, 48:3, 48:4, 57:1, 81:1, 122, 144, 146, 150, 166, 169, 177, 184, 185, 202, 206, 220, 221, and 254).

[0048] The cyan colorant may be, for example, one or more compounds selected from the group consisting of copper phthalocyanine compounds, anthraquinone compounds, and basic dye lake compounds, including, for example, CI Pigment Blue (1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, and 66), phthalocyanine blue, CI Vat Blue, and CI Acid Blue.

[0049] (mold release agent) The release agent is used, for example, for the purpose of imparting offset resistance to the toner. From the viewpoint of imparting sufficient offset resistance to the toner, the content of the release agent is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

[0050] Examples of release agents include aliphatic hydrocarbon waxes, oxides of aliphatic hydrocarbon waxes, plant waxes, animal waxes, mineral waxes, ester waxes primarily composed of fatty acid esters, and waxes in which the fatty acid esters are partially or completely deoxidized. Examples of aliphatic hydrocarbon waxes include low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymers, polyolefin waxes, microcrystalline waxes, paraffin wax, and Fischer-Tropsch wax. Examples of oxides of aliphatic hydrocarbon waxes include oxidized polyethylene wax and block copolymers of oxidized polyethylene wax. Examples of plant waxes include candelilla wax, carnauba wax, Japan wax, jojoba wax, and rice wax. Examples of animal waxes include beeswax, lanolin, and spermaceti. Examples of mineral waxes include ozokerite, ceresin, and petrolatum. Examples of ester waxes primarily composed of fatty acid esters include Montan acid ester wax and castor wax. Examples of waxes in which the fatty acid esters have been partially or completely deoxidized include deoxidized carnauba wax. As the release agent, ester wax is preferred.

[0051] (Other ingredients) Other components that the toner core may contain include, for example, a charge control agent, a magnetic powder, a compatibilizer, and known additives. However, as described above, it is preferable that the toner core does not contain a charge control agent (e.g., a positively charged charge control agent). The toner core may also not contain a magnetic powder.

[0052] <Shell layer> The shell layer contains, for example, a positively charged charge control agent and a resin. Hereinafter, the "resin contained in the shell layer" may be referred to as the "shell resin." If a shell resin having positive charging properties is used, the shell resin can also function as a positively charged charge control agent. The shell layer may further contain other components in addition to those described above, as necessary. In order to obtain a toner suitable for image formation, the thickness of the shell layer is preferably 1 nm or more and 400 nm or less, and more preferably 5 nm or more and 50 nm or less.

[0053] (Positively charged charge control agent) The content of the positively chargeable charge control agent relative to the mass of the shell layer is preferably 1% by mass to 30% by mass, more preferably 5% by mass to 20% by mass, and particularly preferably 8% by mass to 17% by mass. When the content of the positively chargeable charge control agent relative to the mass of the shell layer is within this range, a large amount of the positively chargeable charge control agent can be present in the surface region of the toner particles, and the toner can be sufficiently charged even in a high-temperature, high-humidity environment.

[0054] The ratio WP / WC of the mass WP of the positively chargeable charge control agent to the mass WC of the toner core is preferably 0.0010 or more and 0.0040 or less, and more preferably 0.0015 or more and 0.0035 or less. When the ratio WP / WC is a value within this range, a large amount of the positively chargeable charge control agent can be present in the surface region of the toner particles, and the toner can be sufficiently charged even in a high-temperature, high-humidity environment.

[0055] In order to allow the positively chargeable charge control agent to remain in the toner particles without dissolving in alcohol during the treatment steps in the toner production, the positively chargeable charge control agent is preferably poorly soluble or insoluble in alcohol.

[0056] Examples of positively chargeable charge control agents include thermoplastic resins having a quaternary ammonium base, thermosetting nitrogen-containing resins, azine compounds, direct dyes, acid dyes, metal salts of naphthenic acid, metal salts of higher organic carboxylic acids, alkoxylated amines, alkylamides, and quaternary ammonium salt compounds. The positively chargeable charge control agent is preferably a thermoplastic resin having a quaternary ammonium base because it is easily attracted to a toner core containing a styrene-acrylic resin having an acid value of 7.0 mgKOH / g or more in the shell layer formation process and the positively chargeable charge control agent can also serve as a shell resin.

[0057] Examples of thermoplastic resins having a quaternary ammonium salt group include vinyl resins having a quaternary ammonium salt group. More specifically, examples include polymers of at least one vinyl compound having a quaternary ammonium salt group and polymers of at least one vinyl compound having a quaternary ammonium salt group and at least one other vinyl compound. The other vinyl compounds do not have a quaternary ammonium salt group. The vinyl compound contains a vinyl group (CH═CH—) or a group in which a hydrogen atom in the vinyl group is substituted (e.g., (CH═C(CH)—)) in the molecule. A polymer (vinyl resin) is formed from the vinyl compound by addition polymerization caused by cleavage of the carbon-carbon double bond (C═C) contained in the vinyl group.

[0058] Examples of vinyl compounds having a quaternary ammonium base include vinylbenzyltrialkylammonium salts, 2-(acryloyloxy)ethyltrialkylammonium salts, and 2-(methacryloyloxy)ethyltrialkylammonium salts.

[0059] Examples of vinylbenzyltrialkylammonium salts include vinylbenzyltrimethylammonium salts (more specifically, vinylbenzyltrimethylammonium chloride, etc.), vinylbenzyltriethylammonium salts (more specifically, vinylbenzyltriethylammonium chloride, etc.), vinylbenzyldimethylethylammonium salts (more specifically, vinylbenzyldimethylethylammonium chloride, etc.), vinylbenzyldimethylisopropylammonium salts (more specifically, vinylbenzyldimethylisopropylammonium chloride, etc.), vinylbenzyl n-butyldimethylammonium salts (more specifically, vinylbenzyl n-butyldimethylammonium chloride, etc.), and vinylbenzyldimethylpentylammonium salts (more specifically, vinylbenzyldimethylpentylammonium chloride, etc.).

[0060] Examples of 2-(acryloyloxy)ethyltrialkylammonium salts include 2-(acryloyloxy)ethyltrimethylammonium salts (more specifically, 2-(acryloyloxy)ethyltrimethylammonium chloride, etc.), 2-(acryloyloxy)ethyldimethylethylammonium salts (more specifically, 2-(acryloyloxy)ethyldimethylethylammonium chloride, etc.), 2-(acryloyloxy)ethyltriethylammonium salts (more specifically, 2-(acryloyloxy)ethyltriethylammonium chloride, etc.), and 2-(acryloyloxy)ethyldimethyl n-pentylammonium salts (more specifically, 2-(acryloyloxy)ethyldimethyl n-pentylammonium chloride, etc.).

[0061] Examples of 2-(methacryloyloxy)ethyltrialkylammonium salts include 2-(methacryloyloxy)ethyltrimethylammonium salts (more specifically, 2-(methacryloyloxy)ethyltrimethylammonium chloride, etc.), 2-(methacryloyloxy)ethyldimethylethylammonium salts (more specifically, 2-(methacryloyloxy)ethyldimethylethylammonium chloride, etc.), and 2-(methacryloyloxy)ethyldimethyl n-pentylammonium salts (more specifically, 2-(methacryloyloxy)ethyldimethyl n-pentylammonium chloride, etc.).

[0062] As the vinyl compound having a quaternary ammonium salt group, 2-(methacryloyloxy)ethyltrialkylammonium salt is preferred, 2-(methacryloyloxy)ethyltrimethylammonium salt is more preferred, and 2-(methacryloyloxy)ethyltrimethylammonium chloride is even more preferred.

[0063] Examples of the other vinyl compounds include the same styrene-based monomers and acrylic acid-based monomers that can be used to synthesize the styrene-acrylic resin contained in the binder resin. As the other vinyl compounds, (meth)acrylic acid alkyl esters are preferred, methyl (meth)acrylate and butyl (meth)acrylate are more preferred, and methyl methacrylate and butyl acrylate are particularly preferred.

[0064] As the thermoplastic resin having a quaternary ammonium salt group, a vinyl resin having a quaternary ammonium salt group is preferred, a polymer of a vinyl compound having a quaternary ammonium salt group and another vinyl compound is more preferred, a polymer of a 2-(methacryloyloxy)ethyltrialkylammonium salt and two or more kinds of (meth)acrylic acid alkyl esters is even more preferred, a polymer of a 2-(methacryloyloxy)ethyltrimethylammonium salt, methyl (meth)acrylate, and butyl (meth)acrylate is even more preferred, and a polymer of 2-(methacryloyloxy)ethyltrimethylammonium chloride, methyl methacrylate, and butyl acrylate is particularly preferred.

[0065] (shell resin) In order to sufficiently charge the toner in a high-humidity environment, the shell resin is preferably hydrophobic. Examples of the shell resin include thermosetting resins, thermoplastic resins, and mixtures of thermosetting resins and thermoplastic resins. In order to improve the low-temperature fixability of the toner, the shell resin is preferably a thermoplastic resin. Examples of the thermoplastic resin include polyester resins, styrene resins, and styrene-acrylic resins. The shell resin is preferably a styrene-acrylic resin because it can satisfactorily coat the toner core containing the styrene-acrylic resin.

[0066] The styrene-acrylic resin is a polymer of at least one styrene-based monomer and at least one acrylic acid-based monomer. Examples of the styrene-based monomer and acrylic acid-based monomer that can be used in the polymerization of the shell resin include the same styrene-based monomer and acrylic acid-based monomer that can be used in the polymerization of the binder resin.

[0067] The styrene-acrylic resin that can be used as the shell resin is preferably a polymer of styrene and an alkyl (meth)acrylate, more preferably a polymer of styrene and butyl (meth)acrylate, and even more preferably a polymer of styrene and butyl acrylate.

[0068] When a styrene-acrylic resin is used as the shell resin, the content of the styrene-acrylic resin is preferably 70% by mass or more and 99% by mass or less, more preferably 80% by mass or more and 95% by mass or less, and particularly preferably 83% by mass or more and 92% by mass or less, relative to the mass of the shell layer.

[0069] The ratio WP / WS of the mass WP of the positively chargeable charge control agent to the mass WS of the styrene acrylic resin is preferably 0.05 or more and 0.50 or less, and more preferably 0.10 or more and 0.20 or less.

[0070] The ratio WS / WC of the mass of the styrene acrylic resin WS to the mass of the toner core WC is preferably 0.01 or more and 0.05 or less.

[0071] The glass transition point of the styrene-acrylic resin that can be used as the shell resin is preferably 60°C or higher and 100°C or lower, and more preferably 65°C or higher and 75°C or lower.

[0072] (Other ingredients) Other components that the shell layer may contain include, for example, a pH adjuster, an emulsifier, and known additives other than those mentioned above.

[0073] <External additives> When the toner particles contain an external additive, examples of the external additive include inorganic particles, more specifically, silica particles and particles of metal oxides (specifically, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, barium titanate, etc.). The surface of the external additive may be subjected to one or both of a positive charging treatment and a hydrophobic treatment. The content of the external additive is preferably 0.5 parts by mass or more and 10.0 parts by mass or less relative to 100.0 parts by mass of the toner base particles. The number average primary particle diameter of the external additive is preferably 5 nm or more and 80 nm or less.

[0074] <Toner manufacturing method> A method for producing the toner of this embodiment will be described below. The toner of this embodiment can be produced, for example, by an untreated toner particle forming step and a treating step. When the toner is a capsule toner, the untreated toner particle forming step includes, for example, a toner core forming step and a shell layer forming step. When the toner is a non-capsule toner, the shell layer forming step is omitted, and the toner core forming step corresponds to the untreated toner particle forming step. Each step will be described below.

[0075] <Untreated Toner Particle Formation Process> In the untreated toner particle forming step, untreated toner particles containing a binder resin, a positively chargeable charge control agent, and optional components are obtained.

[0076] (Toner core formation process) In the toner core forming step, the toner core is formed by, for example, an aggregation method or a pulverization method.

[0077] The aggregation method includes, for example, an aggregation step and a coalescence step. In the aggregation step, fine particles containing components constituting the toner core are aggregated in an aqueous medium to form aggregated particles. In the coalescence step, components contained in the aggregated particles are coalesced in the aqueous medium to form toner cores.

[0078] Next, the pulverization method will be described. The pulverization method allows toner cores to be formed relatively easily and also reduces manufacturing costs. When the pulverization method is used to form toner cores, the toner core formation process includes, for example, a mixing process, a kneading process, and a pulverization process. Furthermore, the toner core formation process may further include at least one of a fine pulverization process and a classification process after the pulverization process.

[0079] In the mixing step, a binder resin and an internal additive, which is added as needed, are mixed to obtain a mixture. In the kneading step, the obtained mixture is kneaded while being melted to obtain a kneaded product. In the pulverizing step, the obtained kneaded product is cooled, for example, to room temperature (25°C), and then pulverized to obtain a pulverized product. If it is necessary to reduce the diameter of the pulverized product obtained in the pulverizing step, a fine pulverizing step may be carried out to further pulverize the pulverized product. Furthermore, if the particle size of the pulverized product is to be uniform, a classification step may be carried out to classify the pulverized product. By the above steps, a pulverized product, i.e., a toner core, is obtained.

[0080] (Shell layer forming process) In the shell layer forming step, a shell layer is formed on the surface of the toner core. Examples of methods for forming the shell layer include an in-situ polymerization method, a liquid hardening coating method, and a coacervation method. Specific examples of suitable methods include the following.

[0081] First, a material for forming a shell layer (hereinafter sometimes referred to as a shell material) and the toner cores obtained in the toner core formation step are placed in an aqueous medium. Examples of the shell material include a positively chargeable charge control agent and optional components (e.g., a shell resin and at least one other component). The aqueous medium containing the shell material and toner cores is heated to promote polymerization of the shell material, forming a shell layer on the surface of the toner core. In this way, untreated toner particles are obtained, which include a toner core and a shell layer covering the surface of the toner core.

[0082] When the shell material is resin particles (for example, hydrophobic resin particles and positively charged resin particles that also serve as a positively charged charge control agent), an aqueous medium containing the resin particles and toner cores is heated to cause the resin particles to adhere to the surface of the toner cores while promoting film formation of the resin particles, thereby forming a shell layer on the surface of the toner cores.

[0083] As already mentioned, the toner core contains a styrene-acrylic resin having an acid value of 7.0 mgKOH / g or more as the resin contained in the binder resin in the largest amount. The carboxyl group of the styrene-acrylic resin converts to an anionic group (e.g., -COO - The positive charge control agent, which is the shell material, is attracted in large quantities to the toner core containing a binder resin with a high acid value. Furthermore, since a shell layer containing the positive charge control agent is formed, the positive charge control agent can be concentrated near the surface of the untreated toner particles. As a result, a toner that can be sufficiently charged even in a high-temperature, high-humidity environment can be produced.

[0084] The temperature at which the aqueous medium containing the shell material and the toner cores is heated (shelling temperature) is preferably higher than the glass transition point of the shell material. The shelling temperature is preferably 50°C or higher and 90°C or lower, and more preferably 60°C or higher and 80°C or lower. The time at which the aqueous medium containing the shell material and the toner cores is heated (shelling time) is preferably 0.1 hours or higher and 3.0 hours or lower, and more preferably 0.3 hours or higher and 1.0 hour or lower.

[0085] <Processing process> In the treatment step, the untreated toner particles obtained in the untreated toner particle formation step are treated with alcohol to obtain toner particles. For example, a treatment method may include adding alcohol to the untreated toner particles and stirring the mixture while heating. In the shell layer formation step, if the untreated toner particles are obtained in the form of a dispersion of the untreated toner particles in an aqueous medium, alcohol may be added to the dispersion of the untreated toner particles in the aqueous medium.

[0086] In order to suitably reduce the acid value of the exposed surface region of the toner core, examples of alcohols that can be used in the treatment step include alcohols having 1 to 3 carbon atoms, more specifically, methanol, ethanol, and propanol (e.g., 1-propanol and 2-propanol).

[0087] In order to suitably reduce the acid value of the exposed surface regions of the toner cores, the amount of alcohol added in the treatment step is preferably 0.05 mL to 0.10 mL, and more preferably 0.06 mL to 0.07 mL, per gram of untreated toner particles. For the same reason, the heating temperature in the treatment step is preferably 40° C. to 60° C., and more preferably 45° C. to 50° C. For the same reason, the stirring time in the treatment step is preferably 0.1 hours to 5.0 hours, and more preferably 1.0 hours to 3.0 hours.

[0088] To sufficiently charge the toner under high-temperature, high-humidity conditions, the acid value of the binder resin contained in the toner core is increased (specifically, the acid value of the styrene-acrylic resin is set to 7.0 mgKOH / g or more), and a shell layer containing a large amount of a positively chargeable charge control agent is formed in the shell layer formation process. As a result, the toner can be sufficiently charged under high-temperature, high-humidity conditions. However, increasing the acid value of the binder resin tends to cause the charge of the toner particles to decay quickly under high-temperature, high-humidity conditions. Therefore, in the treatment process, an alcohol is used to reduce the acid value of the surface region of the untreated toner particles (more specifically, the acid value of the exposed surface region of the toner core contained in the untreated toner particles). As a result, the charge of the toner particles is less likely to decay under high-temperature, high-humidity conditions. By performing the above-described shell layer formation process and treatment process, it is possible to achieve both sufficient toner charge under high-temperature, high-humidity conditions and suppress excessive charge decay.

[0089] As described above with reference to FIG. 2, the toner core has alkoxycarbonyl groups in the exposed regions thereof formed by the esterification reaction between the carboxy groups of the styrene-acrylic resin and alcohol. The esterification reaction converts the carboxy groups in the exposed regions of the toner core surface into alkoxycarbonyl groups, so that the acid value B of the toner particle surface after the treatment step is lower than the acid value A of the untreated toner particle surface before the treatment step. In order to adjust the charge decay constant of the toner particles to a value within a desired range, it is preferable that the acid value A of the untreated toner particle surface and the acid value B of the toner particle surface obtained in the treatment step satisfy the following formula (1): B / A≦0.7 (1)

[0090] In addition, when the toner particles contain external additives, "the acid value A of the surface of the untreated toner particles" and "the acid value B of the surface of the toner particles obtained in the treatment step" mean the acid value of the untreated toner base particles (the untreated toner base particles before external additives) and the acid value of the treated toner base particles (the treated toner base particles before external additives), respectively. The treatment step may further include at least one of a cooling step, a washing step, and a drying step, as necessary.

[0091] <External addition process> The toner particles obtained in the treatment step (corresponding to toner base particles when an external addition step is performed) may be subjected to an external addition step, if necessary. In the external addition step, toner particles are obtained by adhering an external additive to the surface of the toner base particles. Examples of a method for adhering an external additive to the surface of the toner base particles include a method in which the toner base particles and the external additive are stirred with a mixer or the like. [Example]

[0092] Examples of the present invention will be described below, but the present invention is not limited to the scope of the examples. First, the methods for measuring the various physical properties will be described.

[0093] [Number average primary particle size] The number average primary particle diameter of the resin particles in the suspension was measured using a transmission electron microscope.

[0094] [Glass transition temperature] The glass transition points (Tg) of the resin and resin particles were measured using a differential scanning calorimeter (Seiko Instruments Inc., DSC-6220) in accordance with JIS (Japanese Industrial Standards) K7121-2012.

[0095] [Binder resin] The resins used as binder resins are shown in Table 1 below. The binder resins (ST-1) to (ST-4) shown in Table 1 are all manufactured by Fujikura Kasei Co., Ltd. The binder resins (PE-A) to (PE-B) shown in Table 1 are all manufactured by Kao Corporation.

[0096] [Table 1]

[0097] [Suspension for forming shell layer] Suspensions SA and SB used for forming the shell layer were prepared by the following method.

[0098] <Hydrophobic resin particle suspension SA> A three-neck flask equipped with a thermometer and a stirring blade was charged with 875 mL of ion-exchanged water and 75 mL of an anionic surfactant ("Latemul (registered trademark) WX" manufactured by Kao Corporation, component: polyoxyethylene alkyl ether sodium sulfate, solids concentration: 26% by mass). The contents of the flask were heated to 80°C using a water bath. Two types of liquid (a first liquid and a second liquid) were each added dropwise to the flask over a period of 5 hours. The first liquid was a mixture of 18 mL of styrene and 2 mL of butyl acrylate. The second liquid was a solution of 0.5 g of potassium persulfate dissolved in 30 mL of ion-exchanged water. The contents of the flask were then stirred for 2 hours while maintaining the temperature inside the flask at 80°C, thereby polymerizing the contents. Suspension SA was thus obtained. Suspension SA contained hydrophobic resin particles composed of a polymer of styrene and butyl acrylate. The number-average primary particle diameter of the hydrophobic resin particles in Suspension SA was 32 nm, and the glass transition temperature was 71°C.

[0099] <Positively charged resin particle suspension SB> A three-neck flask equipped with a thermometer, condenser, nitrogen inlet, and stirring blade was charged with 90 g of isobutanol, 100 g of methyl methacrylate, 35 g of butyl acrylate, 30 g of 2-(methacryloyloxy)ethyltrimethylammonium chloride (Alfa Aesar), and 6 g of 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] (VA-086, Wako Pure Chemical Industries, Ltd.). The contents of the flask were reacted for 3 hours at 80°C under a nitrogen atmosphere. 3 g of VA-086 was then added to the flask, and the reaction was continued for another 3 hours at 80°C under a nitrogen atmosphere to obtain a polymer solution. This polymer solution was dried under reduced pressure at 150°C and crushed to obtain a positively charged resin. Using a mixer (PRIMIX Corporation, "HIBISMIX® 2P-1"), 200 g of a positively charged resin and 184 mL of ethyl acetate (Wako Pure Chemical Industries, Ltd., special grade) were stirred at 20 rpm for 1 hour. As a result, a highly viscous, homogeneous solution was obtained. To this solution, a third liquid was added. The third liquid was an aqueous solution prepared by dissolving 18 mL of 1N hydrochloric acid, 20 g of anionic surfactant (Kao Corporation, "EMAL® 0," component: sodium lauryl sulfate), and 16 g of ethyl acetate in 562 g of ion-exchanged water. Suspension SB was thus obtained. Suspension SB contained positively charged resin particles composed of a positively charged resin. The number-average primary particle diameter of the positively charged resin particles in Suspension SB was 35 nm.

[0100] [toner] The toners used in the examples and comparative examples were prepared by the following method, and the details of the toners are shown in Table 2 below.

[0101] [Table 2]

[0102] In Table 2, "parts" refers to parts by mass. As the "release agent" shown in Table 2, ester wax ("Nissan Electol (registered trademark) WEP-3" manufactured by NOF Corporation) was used. As the "colorant" shown in Table 2, carbon black ("REGAL (registered trademark) 330" manufactured by Cabot Corporation) was used. In Table 2, "SB" indicates the above-mentioned suspension SB of positively charged resin particles, and "-" indicates that suspension SB was not added. The positively charged resin particles in suspension SB correspond to the charge control agent.

[0103] <Toner (T-A1)> (Toner core formation process) 63 parts by weight of binder resin (ST-1), 24 parts by weight of binder resin (PE-A), 5 parts by weight of release agent, and 8 parts by weight of colorant were mixed using an FM mixer at a rotation speed of 2400 rpm. The resulting mixture was melted and kneaded using a twin-screw extruder under conditions of a material input rate of 5 kg / hour, an axis rotation speed of 160 rpm, and a set temperature range of 80°C to 130°C. The resulting kneaded mixture was cooled. The cooled kneaded mixture was coarsely pulverized using a Rotoplex (registered trademark) mill. The resulting coarsely pulverized product was finely pulverized using a jet mill (Nippon Pneumatic Mfg. Co., Ltd., "Ultrasonic Jet Mill Type I"). The resulting finely pulverized product was classified using an elbow jet (Nitetsu Mining Co., Ltd., "EJ-LABO") to obtain toner cores.

[0104] (Shell layer forming process) 100 mL of ion-exchanged water was placed in a three-neck flask equipped with a thermometer and a stirring blade. The temperature of the flask contents was maintained at 30°C using a water bath. Dilute hydrochloric acid was added to the flask to adjust the pH of the flask contents to 4. 250.0 mL of Suspension SA and 2.5 mL of Suspension SB were added as shell materials to the flask. 300 g of toner cores were added to the flask, and the contents were stirred at 200 rpm for 1 hour. Next, 300 mL of ion-exchanged water was added to the flask. While stirring the contents of the flask at 100 rpm, the internal temperature of the flask was increased to 70°C at a heating rate of 1°C / min. After the temperature increase, the contents of the flask were stirred at 100 rpm at 70°C for 30 minutes. The contents of the flask were then cooled to 50°C to obtain a dispersion containing untreated toner base particles. The untreated toner base particles had toner cores and a shell layer covering the toner cores. The shell layer was composed of a hydrophobic resin derived from the hydrophobic resin particles in Suspension SA and a positively charged resin derived from the positively charged resin particles in Suspension SB.

[0105] (Processing process) 20 mL of 1-propanol was added to the dispersion liquid containing the untreated toner base particles, and the mixture was stirred for 2 hours at 50° C. In this way, a dispersion liquid containing treated toner base particles was obtained.

[0106] (cooling process) Sodium hydroxide was added to the dispersion liquid containing the treated toner base particles in the flask, and the pH of the contents of the flask was adjusted to 7, and the contents were cooled to room temperature (25° C.).

[0107] (Cleaning process) Using a Buchner funnel, a wet cake of toner base particles was filtered from the dispersion containing the toner base particles. The wet cake of toner base particles was dispersed in ion-exchanged water to wash the toner base particles (washing operation). This washing operation was repeated five times.

[0108] (drying process) The wet cake of the washed toner base particles was dispersed in an aqueous ethanol solution with a concentration of 50% by mass to obtain a slurry. Using a continuous surface modification device ("Coatmizer (registered trademark)" manufactured by Freund Corporation), hot air was blown at a temperature of 45°C and a blower volume of 2 m 3 The toner base particles in the slurry were dried under conditions of 0.15 / min. In this way, dried toner base particles were obtained. When the surfaces of the dried toner base particles were observed using a scanning electron microscope, the granularity of the suspension particles remained, but no separation of the suspension particles was observed.

[0109] (External addition process) 100.0 parts by mass of dried toner base particles, 2.0 parts by mass of silica ("RA-200H" manufactured by Nippon Aerosil Co., Ltd.), and 1.5 parts by mass of titanium oxide ("EC-100" manufactured by Titanium Kogyo Co., Ltd.) were mixed for 5 minutes using an FM mixer (manufactured by Nippon Coke Co., Ltd., capacity 10 L). This allowed the external additives (silica and titanium oxide) to adhere to the surfaces of the toner base particles. The toner base particles with the external additives adhered thereto were passed through a 200 mesh (75 μm opening) sieve. In this way, a toner (T-A1) containing toner particles was obtained.

[0110] <Toner (T-A2) to (T-A6) and (T-B1) to (T-B5)> Toners (T-A2) to (T-A6) and (T-B1) to (T-B5) were produced in the same manner as toner (T-A1), except that the type and amount of binder resin and amount of colorant used in the toner core formation step, the amount of suspension SB of positively charged resin particles used in the shell layer formation step, and whether or not a treatment step was performed were all as shown in Table 2. When the treatment step was not performed, the cooling step was performed using a dispersion containing untreated toner base particles obtained in the shell layer formation step instead of a dispersion containing treated toner base particles.

[0111] [measurement] The ratio B / A, charge amount, and charge decay constant of each toner were measured by the following methods. The measurement results are shown in Table 3 below.

[0112] <Ratio B / A> The following acid value measurements were performed on the measurement objects (untreated toner base particles before the external addition process and treated toner base particles before the external addition process). For the measurement of acid value A, untreated toner base particles (untreated toner base particles before the external addition process) were used as the measurement object, which were not subjected to the treatment process after the shell layer formation process but were obtained through the cooling process, washing process, and drying process. For the measurement of acid value B, toner base particles (treated toner base particles before the external addition process) were used as the measurement object, which were subjected to the treatment process after the shell layer formation process and were obtained through the cooling process, washing process, and drying process. From the measured acid values ​​A and B, the ratio B / A was calculated according to the formula "ratio B / A = acid value B / acid value A." Note that a lower ratio B / A indicates that the esterification reaction between the carboxyl groups of the styrene-acrylic resin contained in the binder resin and the alcohol used in the treatment process has progressed, resulting in the formation of alkoxycarbonyl groups and the reduction of carboxyl groups in the exposed regions of the toner core.

[0113] (Acid value measurement) First, potassium hydroxide ethanol solution a to be used for titration was prepared. Specifically, 7 g of potassium hydroxide specified in JIS (Japanese Industrial Standards) K 8574 was dissolved in 5 mL of water to obtain an aqueous solution of potassium hydroxide. Ethanol (purity: volume fraction 95%) specified in JIS (Japanese Industrial Standards) K 8102 was added to this aqueous solution of potassium hydroxide to make up a total volume of 1 L. In this way, potassium hydroxide ethanol solution a with a concentration of 0.1 mol / L was prepared.

[0114] Next, 0.5 g of an anionic surfactant ("EMAL (registered trademark) 0" manufactured by Kao Corporation, component: sodium lauryl sulfate) was dissolved in 100 g of ion-exchanged water to obtain a surfactant aqueous solution b. 0.2 g of the object to be measured was dispersed in this surfactant aqueous solution b using an ultrasonic water bath to obtain a dispersion liquid c to be measured. While measuring the pH of the dispersion liquid c using a pH meter (WQ-300 manufactured by Horiba, Ltd.), the potassium hydroxide ethanol solution a was continuously added dropwise to the dispersion liquid c. The acid value of the object to be measured (unit: mgKOH / g) was then calculated from the titration amount when the pH of the dispersion liquid c reached 7.00.

[0115] <Amount of charge> 10.0 g of uncoated ferrite carrier ("EF-35" manufactured by Powder Tech Co., Ltd.) and 0.8 g of toner base particles (toner base particles before the external addition process) obtained in the drying process were sealed in a 20 mL plastic container. The container was left to stand for 12 hours in a predetermined HH environment. Next, the contents of the container were stirred for 30 minutes in the predetermined HH environment using a Rocking Mixer (registered trademark) at a stirring speed of 30 rpm. After stirring, a sample was taken from the container, and the charge amount (unit: μC / g) of the toner base particles contained in the sample was measured using a Q / m meter ("MODEL 210HS" manufactured by Trek Corporation).

[0116] <Charge decay constant> The charge decay constant of the toner base particles was measured using an electrostatic diffusivity measurement device (NS-D100 manufactured by Nano Seeds Co., Ltd.) according to JIS (Japanese Industrial Standards) C61340-2-1-2006. Specifically, toner base particles obtained in the drying process (toner base particles before the external addition process) were placed in a measurement cell. The measurement cell was a metal cell with an inner diameter of 10 mm and a recessed portion with a depth of 1 mm. The toner base particles were pressed into the cell from above using a glass slide, filling the recessed portion with the toner base particles. The toner base particles that overflowed from the cell were removed by moving the glass slide back and forth over the surface of the cell. The amount of toner base particles filled in the measurement cell was 0.05 g. The measurement cell filled with the toner base particles was left standing in a specified HH environment for 12 hours. Next, the grounded measurement cell was placed in the electrostatic diffusivity measurement device, and ions were supplied to the toner base particles by corona discharge, charging them. The probe gap was 1 mm, and the discharge time was 0.5 seconds. The surface potential of the toner particles was continuously measured at a sampling frequency of 1 Hz starting 0.7 seconds after the end of the corona discharge. The charge decay constant (charge decay rate) α was calculated from the measured surface potential of the toner particles using the formula "V = V0exp(α√t)". In the formula, V is the surface potential of the toner particles (unit: V), V0 is the initial surface potential of the toner particles (unit: V), and t is the decay time (unit: seconds).

[0117] [evaluation] Images formed using each toner were evaluated for fine lines and toner scattering using the following methods. The evaluation results are shown in Table 3 below.

[0118] <thin line> A two-component developer containing the toner to be evaluated and A4-sized paper were placed in an evaluation machine (TASKalfa9003i manufactured by Kyocera Document Solutions Inc.) and left to stand for 12 hours in a specified HH environment. Next, an evaluation image was formed on the paper using the evaluation machine in the specified HH environment. The evaluation image was an image of five thin lines. Each thin line was arranged parallel to the vertical direction (length direction) of the paper, the font size of each thin line was 0.25 points, and the length of each thin line was the same as the vertical length of the paper. The left and right margins of the paper were 30 mm, and the line spacing between each thin line was approximately 20 mm. The thin lines were evaluated according to the following criteria.

[0119] (thin line standard) A (Good): No defects of 0.5 mm or more were found in the fine wire. B (Poor): A defect of 0.5 mm or more was found in the fine wire.

[0120] <Toner scattering> The evaluation image formed in the above-mentioned fine line evaluation was visually observed to check for stains near the fine lines due to toner scattering. If stains were present, the image density of the stained area was measured at five locations, and the average value was taken as the stain image density IX. In addition, the image density of the blank area of ​​the evaluation image was measured at five locations, and the average value was taken as the blank image density IY. The image density difference was calculated using the formula "image density difference = stain image density IX - blank image density IY". Toner scattering was judged according to the following criteria.

[0121] (Toner scattering standard) A (good): No staining due to toner scattering, or staining due to toner scattering is present, but the image density difference is less than 0.01. B (poor): Stains due to toner scattering are observed, and the image density difference is 0.01 or more.

[0122] [Table 3]

[0123] In Table 3, "Image formation impossible" indicates that the toner was not sufficiently charged and the evaluation image could not be printed on the paper. "-" indicates that the evaluation of the thin line was poor, so the evaluation of the toner scattering was not performed.

[0124] The resin contained most abundantly in toners (T-B1) to (T-B2) (more specifically, each of binder resins (ST-4) and (PE-A)) was not a styrene acrylic resin with an acid value of 7.0 mgKOH / g or more. It was not possible to print evaluation images on paper using toners (T-B1) to (T-B2).

[0125] The charge decay constant of the toner particles contained in the toners (T-B3) to (T-B4) was not -0.0200 or more in the specified HH environment. The evaluation of the toners (T-B3) to (T-B4) for thin lines was poor.

[0126] The toner particles contained in the toner (T-B5) did not contain a positively chargeable charge control agent (more specifically, a positively chargeable resin derived from the positively chargeable resin particles in the suspension SB). It was not possible to print an evaluation image on paper using the toner (T-B5).

[0127] On the other hand, the toner particles contained in toners (T-A1) to (T-A6) contained a binder resin and a positively charged charge control agent (more specifically, a positively charged resin derived from the positively charged resin particles in suspension SB). The resin contained most predominantly in the binder resin (more specifically, any of binder resins (ST-1) to (ST-3)) was a styrene acrylic resin with an acid value of 7.0 mg KOH / g or more. The charge decay constant of the toner particles was -0.0200 or more in a specified HH environment. The evaluation of thin lines and toner scattering for toners (T-A1) to (T-A6) were both good.

[0128] From the above, it is concluded that the toners of the present invention, including toners (T-A1) to (T-A6), and the toners produced by the production method of the present invention can form high-quality images without missing fine lines or toner scattering, even in high-temperature, high-humidity environments. [Industrial Applicability]

[0129] The toner of the present invention and the toner produced by the production method of the present invention can be used to form images in, for example, a copier, a printer, or a multifunction machine. [Explanation of symbols]

[0130] 1: Toner particles 2: Toner core 3: Shell layer 10: Untreated toner particles 21: Covered area 22:Exposed area 23: Internal area

Claims

1. A toner comprising toner particles, the toner particles contain a binder resin and a positively chargeable charge control agent, The resin contained in the binder resin in the largest amount by mass is a styrene-acrylic resin having an acid value of 7.0 mgKOH / g or more, The toner has a charge decay constant of −0.0200 or more in an environment of a temperature of 32.5° C. and a relative humidity of 80%.

2. 2. The toner according to claim 1, wherein the toner particles have a charge amount of +10.0 μC / g or more in an environment of a temperature of 32.5° C. and a relative humidity of 80%.

3. 3. The toner according to claim 1, wherein the positively chargeable charge control agent is a thermoplastic resin having a quaternary ammonium salt group.

4. the toner particles have a toner core and a shell layer that covers the toner core, the toner core contains the binder resin, The toner according to claim 1 or 2, wherein the shell layer contains the positively chargeable charge control agent.

5. The toner of claim 4 , wherein the toner core does not contain the positively charging charge control agent.

6. a surface of the toner core including a covered region covered with the shell layer and an exposed region not covered with the shell layer, The toner according to claim 4 , wherein the exposed region of the surface of the toner core has a lower acid value than the inner region of the toner core.

7. a surface of the toner core including a covered region covered with the shell layer and an exposed region not covered with the shell layer, The toner according to claim 4 , wherein the toner core has an alkoxycarbonyl group in the exposed region.

8. A method for producing the toner according to claim 1 or 2, comprising the steps of: A method for producing a toner, comprising a treating step of treating untreated toner particles with an alcohol to obtain said toner particles.

9. The method for producing a toner according to claim 8 , wherein an acid value A of the surface of the untreated toner particles and an acid value B of the surface of the toner particles obtained in the treatment step satisfy the following formula (1): B / A≦0.7...(1)

10. the toner particles have a toner core and a shell layer that covers the toner core, the toner core contains the binder resin, the shell layer contains the positively chargeable charge control agent, a surface of the toner core including a covered region covered with the shell layer and an exposed region not covered with the shell layer, The method for producing a toner according to claim 8 , wherein the toner core has, in the exposed region, an alkoxycarbonyl group formed by an esterification reaction between a carboxy group of the styrene-acrylic resin and the alcohol.

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