Toner for developing electrostatic image and method for manufacturing same

Abstract

Provided are a toner for developing an electrostatic image, which is less prone to cause defective printing even after stored in a developing machine for a long time and is less prone to emit an odor during printing, and having excellent charging stability, and a method for manufacturing the same. The toner for developing an electrostatic image is characterized by containing colored resin particles including a binder resin, a coloring agent, and a mold release agent, wherein the binder resin includes a structural unit derived from a specific styrene-based monovinyl monomer, the content of a structural unit has at least one type of polar group selected from the group consisting of a carboxy group and a hydroxyl group is 0.10 mass% or less in 100 mass% of the binder resin, the colored resin particles has a core-shell structure with a core layer and a shell layer, and the amount of a volatile organic compound when the toner is heated at 100°C for 30 minutes is 150 ppm or less.

Description

Toner for developing electrostatic images and method for producing the same

[0001] The present disclosure relates to a toner for developing electrostatic images used to develop electrostatic latent images in electrophotography, electrostatic recording, electrostatic printing, and the like, and a method for producing the same.

[0002] In image forming devices such as electrophotographic devices, electrostatic recording devices, and electrostatic printing devices, an electrostatic latent image formed on a photoreceptor is developed with toner, the toner image is transferred to a transfer material such as paper, and then fixed by heating or the like to form a fixed image. Styrene-acrylic resins have conventionally been widely used as binder resins used in toners for developing electrostatic images (simply referred to as "toner" in this disclosure). For example, Patent Document 1 discloses a toner containing, as a binder resin, a styrene-acrylic resin in which the benzene ring of the styrene unit has a hydroxy group or an alkoxy group. Patent Document 2 discloses a toner containing, as a binder resin, a styrene-butyl acrylate copolymer.

[0003] JP 2021-107846 A International Publication No. 2022 / 004607

[0004] However, the toner disclosed in Patent Document 1 is manufactured using an emulsion polymerization aggregation method, and therefore a large amount of surfactant remains. When the residual surfactant in the toner decomposes due to heating during fixing, an odor is generated, and therefore the toner disclosed in Patent Document 1 can sometimes cause odor problems during printing. Furthermore, because the emulsion polymerization aggregation method uses a monomer having a carboxy group, such as methacrylic acid, the toner particle surface is highly hydrophilic due to the influence of both the carboxy group contained in the monomer and the residual surfactant, which causes the toner charge amount to be easily affected by temperature or humidity. The toner disclosed in Patent Document 2 is manufactured using a suspension polymerization method, and therefore, by using an inorganic dispersion stabilizer and not using a surfactant, it can be made into a surfactant-free toner. Therefore, problems caused by residual surfactant, such as those occurring with the toner disclosed in Patent Document 1, can be prevented. Meanwhile, in image forming devices using toner, developers with a large toner loading capacity and high print yields are required to reduce the frequency of developer disposal, and toner remains in such developers for long periods of time. However, the toner present between the developing roller and the layer regulating blade in the developing machine is under pressure, and if this state continues for a long period of time, the toner particles may deform and adhere to the developing roller, resulting in the problem of longitudinal streaks appearing in printed matter. The toner disclosed in Patent Document 2 cannot sufficiently suppress this problem.

[0005] An object of the present disclosure is to provide a toner for developing electrostatic images that is less likely to cause printing defects even after long-term storage in a developing machine, is less likely to emit odors during printing, and has excellent charging stability, and a method for producing the same.

[0006]

[0006] The present inventors have conducted extensive research to achieve the above-mentioned object, and have found that, in a suspension polymerization method using an inorganic dispersion stabilizer, by limiting the use of a polymerizable monomer containing a carboxyl group or a hydroxyl group to a specific amount or less and using a styrene-based monovinyl monomer having a specific substituent and another polymerizable monomer that is phase-separable from the styrene-based monovinyl monomer as raw materials for the binder resin, it is possible to make the colored resin particles that serve as the base particles of the toner particles have a core-shell structure, and as a result, the toner is less likely to suffer from printing defects even after long-term storage in a developing machine. The present inventors have further found that a toner obtained by a suspension polymerization method using an inorganic dispersion stabilizer emits fewer volatile organic compounds (VOCs) and is less likely to emit odors during printing, and that by not using a surfactant and limiting the use of a polymerizable monomer containing a carboxyl group or a hydroxyl group to a specific amount or less, a toner with excellent charge stability can be obtained, and have arrived at the present disclosure.

[0007] That is, the present disclosure provides the following toner for developing electrostatic images: [1] A toner for developing electrostatic images containing colored resin particles that include a binder resin, a colorant, and a release agent, wherein the binder resin contains a structural unit represented by general formula (1) described below, the content of structural units having at least one polar group selected from the group consisting of a carboxy group and a hydroxy group is 0.10% by mass or less relative to 100% by mass of the binder resin, the colored resin particles have a core-shell structure having a core layer and a shell layer, and the amount of volatile organic compounds when the toner is heated at 100°C for 30 minutes is 150 ppm or less.

[0008] [2] The electrostatic image developing toner according to [1], wherein the core layer and the shell layer are formed by phase separation of the binder resin. [3] The electrostatic image developing toner according to [1] or [2], wherein, in a cross section of the colored resin particle observed with a transmission electron microscope, an average ratio (t / r) of the thickness t of the shell layer to the distance r from the geometric center of the cross section to the outline is 0.05 or more and 0.50 or less. [4] The electrostatic image developing toner according to any one of [1] to [3], wherein, in a cross section of the colored resin particle observed with a transmission electron microscope, domains of the release agent are present, the average total area ratio of the domains is 10 to 30%, the average number of the domains present per particle is 10 to 40, and the average number ratio of the domains present within an area that is 80% or less of the distance r from the geometric center of the cross section to the outline is 80% or more. [5] The toner for developing electrostatic images according to any one of [1] to [4], wherein the toner has an average circularity of 0.960 or more and 0.995 or less. [6] The toner for developing electrostatic images according to any one of [1] to [5], wherein the colored resin particles further contain a polar resin having an acid value of 0.5 to 20 mgKOH / g. [7] The toner for developing electrostatic images according to [6], wherein the polar resin is an acrylic resin. [8] The toner for developing electrostatic images according to any one of [1] to [7], wherein the colored resin particles further contain a styrene-based thermoplastic elastomer.

[0009] The present disclosure also provides the following method for producing a toner for developing electrostatic images: [9] A method for producing the toner for developing electrostatic images according to any one of [1] to [8], comprising the steps of producing colored resin particles, the steps including: preparing a polymerizable monomer composition containing a polymerizable monomer, a colorant, and a release agent; preparing a suspension in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer; and polymerizing the polymerizable monomer contained in the droplets of the polymerizable monomer composition, wherein the polymerizable monomer comprises a styrene-based monovinyl monomer represented by general formula (1A) described below, and the dispersion stabilizer is an inorganic compound.

[0010] According to the present disclosure, it is possible to provide a toner for developing electrostatic images that is less likely to cause printing defects even after long-term storage in a developing machine, is less likely to produce odors during printing, and has excellent charging stability, and a method for producing the same.

[0011] 1 is a schematic diagram of an example of a cross section of a colored resin particle contained in the toner of the present disclosure, and FIG. 2 is a TEM image of a cross section of the colored resin particle prepared in Example 1.

[0012] The positively charged toner for developing electrostatic images of the present disclosure is a toner for developing electrostatic images containing colored resin particles that include a binder resin, a colorant, and a release agent, wherein the binder resin contains a structural unit represented by general formula (1) described below, the content of structural units having at least one polar group selected from the group consisting of a carboxy group and a hydroxy group is 0.10 mass% or less relative to 100 mass% of the binder resin, the colored resin particles have a core-shell structure having a core layer and a shell layer, and the amount of volatile organic compounds when the toner is heated at 100°C for 30 minutes is 150 ppm or less. Hereinafter, the toner for developing electrostatic images of the present disclosure may be simply referred to as "the toner of the present disclosure" or "toner".

[0013] In the toner of the present disclosure, the colored resin particles serving as the base particles have a core-shell structure, which makes the toner particles less susceptible to deformation due to pressure in high-temperature environments. Therefore, toner particles trapped between the developing roller and the layer-regulating blade in a developing machine are less likely to deform, resulting in less adhesion of the toner to the developing roller. Therefore, even when the toner of the present disclosure is stored in a developing machine for a long period of time, printing defects are less likely to occur. In the present disclosure, the core-shell structure of the colored resin particles is typically formed by phase separation of the binder resin. The reason why the colored resin particles have a core-shell structure and are less susceptible to deformation due to pressure in high-temperature environments is presumably because the binder resin with a relatively low glass transition temperature (Tg) forms the core layer and the material with a relatively high glass transition temperature (Tg) forms the shell layer, thereby increasing the strength of the surface side of the colored resin particles. Furthermore, the toner of the present disclosure is a toner produced by a suspension polymerization method described below, and does not contain a surfactant because an inorganic compound is used as a dispersion stabilizer, but no surfactant is used. Residual surfactants in the toner decompose into volatile organic compounds (VOCs) when heated during fixation, resulting in odors during printing. In contrast, the toner of the present disclosure does not contain a surfactant, and the amount of volatile organic compounds is 150 ppm or less when heated at 100°C for 30 minutes, making it less likely to produce odors during printing. Furthermore, the toner of the present disclosure does not contain a surfactant, and the content of structural units having at least one polar group selected from the group consisting of carboxy groups and hydroxy groups is 0.10% by mass or less per 100% by mass of the binder resin, thereby providing sufficiently low hydrophilicity on the toner particle surface. As a result, the charge amount of the toner is less susceptible to temperature or humidity, and the toner of the present disclosure is less susceptible to changes in charge amount even when the environment (temperature or humidity) changes, resulting in excellent charge stability. In this disclosure, "charge stability" refers to the stability of the charge amount of the toner against changes in temperature or humidity.Furthermore, if the content of structural units having a hydroquinone structure, which is a type of structural unit having a hydroxy group, exceeds 0.10% by mass, the hydroquinone structure acts as a polymerization inhibitor when the shell is formed, and a large amount of unreacted polymerizable monomer that can become a volatile organic compound (VOC) tends to remain in the shell, which may cause an odor during printing. Furthermore, a toner with a large amount of unreacted polymerizable monomer remaining may be prone to deformation of toner particles due to insufficient progress of the polymerization reaction, and therefore may be prone to printing defects when the toner is stored in a developing machine for a long period of time.

[0014] The colored resin particles contained in the toner of the present disclosure, the method for producing the same, and the toner of the present disclosure will be described below in order. In this disclosure, the term "to" in a numerical range means that the numerical values ​​before and after it are included as the lower and upper limits. Furthermore, unless otherwise specified, numerical values ​​described to explain this disclosure are values ​​obtained by rounding off the digit one place below the lowest digit included in the numerical value.

[0015] 1. Colored Resin Particles The colored resin particles contained in the toner of the present disclosure contain at least a binder resin, a colorant, and a release agent, and may further contain other additives such as a charge control agent, a polar resin, and a styrene-based thermoplastic elastomer, and may be provided with a resin coating.

[0016] (Binder Resin) The binder resin contains at least a structural unit represented by the following general formula (1). The core-shell structure containing this structural unit suppresses printing defects after the toner is stored in a developing machine for a long period of time. The structure and proportion of each structural unit constituting the resin are as follows: １ It can be calculated from the integrated value obtained by H-NMR measurement, or can be determined from the composition of the polymerizable monomers used in the synthesis of the resin.

[0017] (In general formula (1), R １ and R ２ are each independently a methyl group or an acetyl group.

[0018] R in the general formula (1) １ and R ２ are each independently a methyl group or an acetyl group, and are not particularly limited, but are preferably a methyl group in view of improving the effect of suppressing printing defects after the toner is stored in a developing machine for a long period of time. The binder resin may contain one type of structural unit represented by the general formula (1) alone or two or more types in combination.

[0019] The content of the structural unit represented by the general formula (1) in 100% by mass of the binder resin is not particularly limited, but is preferably 10 to 80% by mass, more preferably 15 to 75% by mass, from the viewpoints that a core-shell structure is easily formed and the effect of suppressing printing defects after the toner is stored in a developing machine for a long period of time is improved.

[0020] The core-shell structure of the colored resin particles is preferably formed by polymerizing polymerizable monomers used as raw materials for the binder resin in a phase-separated state. Phase separation of the polymerizable monomers occurs due to differences in solubility parameters (SP values) of the polymerizable monomers, and it is thought that structural units derived from polymerizable monomers with a relatively low SP value form the core layer, and structural units derived from polymerizable monomers with a relatively high SP value form the shell layer. For example, when the content of the structural unit represented by the general formula (1) in 100% by mass of the binder resin is 15% by mass or more, particularly 18% by mass or more, it is possible to use a styrene-based monovinyl monomer having an SP value of 8.90 to 11.50, preferably 8.90 to 9.20, in combination with another polymerizable monomer having an SP value of 8.00 to 8.89 and having an SP value difference of 0.20 or more from the styrene-based monovinyl monomer, thereby causing the styrene-based monovinyl monomer to be unevenly distributed toward the surface and the other polymerizable monomer to be unevenly distributed toward the center, thereby achieving phase separation between the two. It is believed that this phase separation of the polymerizable monomers is promoted by the presence of a specific amount or more of the styrene-based monovinyl monomer represented by the general formula (1A) described below, which is used as a raw material for the structural unit represented by the general formula (1). The styrene-based monovinyl monomer represented by the general formula (1A) described below has a relatively high SP value among styrene-based monovinyl monomers, and therefore tends to be unevenly distributed toward the surface of the shell. Although the reason is unclear, it is considered that the presence of a specific amount or more of the styrene-based monovinyl monomer represented by general formula (1A) can cause phase separation between the styrene-based monovinyl monomer having an SP value of 8.90 to 11.50 and another polymerizable monomer having an SP value of 8.00 to 8.89 and having an SP value difference of 0.20 or more from that of the styrene-based monovinyl monomer.The styrene-based monovinyl monomer represented by the general formula (1A) described below has an SP value of 9.00 to 11.50, preferably 9.00 to 9.20 or 9.10 to 11.50, and unsubstituted styrene has an SP value of 8.93. Therefore, by using the styrene-based monovinyl monomer represented by the general formula (1A) described below and unsubstituted styrene in combination with another polymerizable monomer having an SP value of 8.00 to 8.73, it is possible to form a shell layer containing a structural unit represented by the general formula (1) and a styrene unit, and a core layer containing a structural unit derived from the other polymerizable monomer. In addition, when there are multiple types of styrene-based monovinyl monomers or other polymerizable monomers, the difference between the SP value of the styrene-based monovinyl monomer and the SP value of the other polymerizable monomer is the difference between the minimum SP value of the styrene-based monovinyl monomer and the maximum SP value of the other polymerizable monomer. The difference between the SP value of the styrene-based monovinyl monomer and the SP value of the other polymerizable monomer is preferably 0.22 or more, more preferably 0.24 or more. By using the above-mentioned phase-separable polymerizable monomer as a raw material for the binder resin, it is possible to form a core-shell structure having a shell layer containing a structural unit derived from the styrene-based monovinyl monomer, including the structural unit represented by the general formula (1), and a core layer containing a structural unit derived from the other polymerizable monomer.

[0021] On the other hand, when the content of the structural unit represented by the general formula (1) in 100% by mass of the binder resin is less than 15% by mass, particularly when it is 10 to 13% by mass, the amount of the styrene-based monovinyl monomer represented by the general formula (1A) described below, which is used as a raw material for the structural unit represented by the general formula (1), is small, and therefore phase separation of the polymerizable monomer as described above is unlikely to occur. In such cases, by using a styrene-based monovinyl monomer represented by the general formula (1A) described below in combination with a polymerizable monomer having a smaller SP value than the styrene-based monovinyl monomer represented by the general formula (1A), the styrene-based monovinyl monomer represented by the general formula (1A) is unevenly distributed toward the surface, and the polymerizable monomer having a smaller SP value than the styrene-based monovinyl monomer represented by the general formula (1A) is unevenly distributed toward the center, thereby enabling phase separation between the two. Therefore, in such cases, a shell layer containing the structural unit represented by the general formula (1) and a core layer containing a structural unit derived from a polymerizable monomer having a smaller SP value than the styrene-based monovinyl monomer represented by the general formula (1A) can be formed.

[0022] In the present disclosure, the SP value refers to the solubility parameter δ calculated by the following formula (I) using the ΔF and Δv values ​​of various atomic groups given by Okitsu Toshinao in Table 1 below, which is described in "Adhesion," Polymer Publishing Society, Vol. 40, No. 8 (1996), pp. 342-350. δ=ΣΔF / ΣΔv Formula (I) [In the formula, ΔF represents ΔF in Table 1 below, and Δv represents the molar volume Δv in Table 1 below.] For example, the SP value of dimethoxystyrene, which is one of the styrene-based monovinyl monomers represented by general formula (1A) described later, is determined as follows. Dimethoxystyrene contains, as an atomic group, -C ６ H ３ (Arom), two -O-(Arom, Lin), -CH ３ Two -CH = one, CH ２=. The ΔF and Δv values ​​for this atomic group are calculated from Table 1. ΣΔF = 550 + 70 x 2 + 205 x 2 + 116 + 195 = 1411 ΣΔv = 39.0 + 3.8 x 2 + 31.8 x 2 + 13.7 + 31.0 = 154.9 Therefore, the δ of dimethoxystyrene can be calculated from the above formula (I) as follows: δ = ΣΔF / ΣΔv = 1411 / 154.9 = 9.11

[0023]

[0024] As the binder resin, a styrene-acrylic resin is preferred because the colored resin particles are likely to have a core-shell structure and are excellent in suppressing printing defects after long-term storage of the toner in a developing machine. Here, the styrene-acrylic resin contains a structural unit derived from a styrene-based monomer and a structural unit derived from a (meth)acrylic monomer, and may further contain a structural unit derived from another monomer different from the styrene-based monomer or the (meth)acrylic monomer, as long as the object of the present disclosure is not impaired. The (meth)acrylic monomer is a monomer containing at least one selected from the group consisting of an acryloyl group and a methacryloyl group.

[0025] The styrene-acrylic resin preferably used in the present disclosure contains at least a structural unit represented by the general formula (1) as a structural unit derived from a styrene-based monomer. The styrene-acrylic resin may further contain a structural unit derived from another styrene-based monomer different from the structural unit represented by the general formula (1). The styrene-based monomer used in the styrene-acrylic resin may be monofunctional or polyfunctional, but preferably contains at least a structural unit derived from a styrene-based monovinyl monomer. Because the styrene-based monovinyl monomer has a relatively large SP value, it is preferably used as a material for forming a shell layer. Furthermore, in order to improve the effect of suppressing printing defects after long-term storage of the toner in a developing machine, the content of the structural unit represented by the general formula (1) is preferably 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, based on 100% by mass of structural units derived from styrene-based monovinyl monomers. The upper limit is not particularly limited, and the structural unit derived from the styrene-based monovinyl monomer may consist solely of the structural unit represented by the general formula (1).

[0026] Examples of the other styrene-based monomers include styrene-based monovinyl monomers and crosslinkable styrene-based monomers. For example, styrene, vinyltoluene, α-methylstyrene, ethylstyrene, and other styrene-based monovinyl monomers having an SP value of 8.90 to 9.20 are preferably used as materials for the shell layer, with styrene being particularly preferred. These styrene-based monovinyl monomers can be used alone or in combination of two or more.

[0027] When the binder resin contains a structural unit derived from another styrene-based monovinyl monomer other than the structural unit represented by general formula (1), the content of the structural unit derived from the other styrene-based monovinyl monomer in 100% by mass of the binder resin is preferably 15 to 70% by mass, more preferably 20 to 60% by mass, from the viewpoint of improving the low-temperature fixability and hot offset resistance of the toner in a well-balanced manner and widening the fixable temperature range of the toner. The wider the fixable temperature range of the toner, the more likely the toner is to be fixed even with large temperature hunting of the fixing roller. In recent years, temperature hunting during fixing has become larger with the increase in machine speed. The wider the fixable temperature range of the toner, the easier it is to accommodate higher machine speeds. Furthermore, from the viewpoint of improving the effect of suppressing printing defects after long-term storage of the toner in a developing machine, the content of the structural unit derived from styrene in 100% by mass of the structural units derived from the other styrene-based monomer is preferably 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 97% by mass or more.

[0028] In the structural units derived from a (meth)acrylic monomer contained in the styrene-acrylic resin, the (meth)acrylic monomer may be monofunctional or polyfunctional, and examples thereof include a (meth)acrylic monovinyl monomer or a crosslinkable (meth)acrylic monomer. The structural units derived from a (meth)acrylic monomer preferably include at least a structural unit derived from a (meth)acrylic monovinyl monomer. Because the (meth)acrylic monovinyl monomer has a relatively small SP value, it is suitable for use as a material for forming the core layer. By using a (meth)acrylic monovinyl monomer together with the above-mentioned styrene-acrylic monovinyl monomer as raw materials for the styrene-acrylic resin, a core-shell structure is easily formed, thereby improving the effect of suppressing printing defects after long-term storage of the toner in a developing machine. As the (meth)acrylic monovinyl monomer, a (meth)acrylic monovinyl monomer having an SP value of 8.00 to 8.89 is preferably used, and a (meth)acrylic monovinyl monomer having an SP value of 8.00 to 8.73 is more preferably used, because a core-shell structure is easily formed and the effect of suppressing printing defects after long-term storage of the toner in a developing machine is improved. Examples of the (meth)acrylic monovinyl monomer having an SP value of 8.00 to 8.89 include alkyl acrylates having an alkyl group of 2 to 6 carbon atoms, such as ethyl acrylate, propyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; and alkyl methacrylates having an alkyl group of 2 to 6 carbon atoms, such as ethyl methacrylate, propyl methacrylate, butyl methacrylate, and 2-ethylhexyl methacrylate. These (meth)acrylic monovinyl monomers can be used alone or in combination of two or more.

[0029] In the styrene-acrylic resin, the content of the structural unit derived from the (meth)acrylic monovinyl monomer is preferably 5 to 60% by mass, more preferably 10 to 50% by mass, and even more preferably 20 to 40% by mass, based on 100% by mass of the binder resin, from the viewpoint of improving the effect of suppressing printing defects after storing the toner in a developing machine for a long period of time.

[0030] The styrene-acrylic resin used as the binder resin may contain structural units derived from a styrene-based monomer, including at least the structural unit represented by the general formula (1), and may further contain structural units derived from the other preferred styrene-based monovinyl monomers described above. A styrene-acrylic resin in which the structural units derived from a (meth)acrylic monomer include structural units derived from the preferred (meth)acrylic monovinyl monomers described above is particularly preferred. The core-shell structure formed by phase separation of such a styrene-acrylic resin has a shell layer with a relatively high Tg containing structural units derived from a styrene-based monovinyl monomer, and a core layer with a relatively low Tg containing structural units derived from a (meth)acrylic monovinyl monomer, thereby achieving an excellent effect of suppressing printing defects after long-term storage of the toner in a developing machine. The "structural units derived from a styrene-based monovinyl monomer" include the structural units represented by the general formula (1) and structural units derived from unsubstituted styrene. The core-shell structure formed by phase separation of a styrene-acrylic resin may be a core-shell structure having a shell layer having a relatively high Tg containing the structural unit represented by the general formula (1) and a core layer having a relatively low Tg containing the structural unit derived from the other styrene-based monovinyl monomer and the structural unit derived from the (meth)acrylic monovinyl monomer.

[0031] In the styrene acrylic resin, from the viewpoint of improving the effect of suppressing printing defects after long-term storage of the toner in a developing machine, the mass ratio of the structural units derived from the styrene monovinyl monomer to the structural units derived from the (meth)acrylic monovinyl monomer is preferably 50:50 to 90:10, and more preferably 60:40 to 80:20. Furthermore, from the viewpoint of improving the effect of suppressing printing defects after long-term storage of the toner in a developing machine, the styrene acrylic resin preferably has a total content of the structural units derived from the styrene monovinyl monomer and the structural units derived from the (meth)acrylic monovinyl monomer of 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more, based on 100% by mass of the styrene acrylic resin.

[0032] The styrene-acrylic resin may further contain a structural unit derived from a crosslinkable polymerizable monomer. Here, the crosslinkable polymerizable monomer refers to a monomer having two or more polymerizable functional groups. It is preferable that the binder resin contains a structural unit derived from a crosslinkable polymerizable monomer, since this facilitates improving the heat-resistant storage stability and hot offset resistance of the toner. Examples of crosslinkable polymerizable monomers include crosslinkable styrene monomers such as divinylbenzene, N,N-divinylaniline, and derivatives thereof; other aromatic divinyl compounds such as divinylnaphthalene and derivatives thereof; other divinyl compounds such as divinyl ether; compounds having three or more vinyl groups; crosslinkable (meth)acrylic monomers having two or more (meth)acryloyl groups such as ethylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate, 1,6-hexanediol di(meth)acrylate, 1,9-nonanediol di(meth)acrylate, 1,10-decanediol di(meth)acrylate, neopentyl glycol di(meth)acrylate, polyethylene glycol di(meth)acrylate, polypropylene glycol di(meth)acrylate, bisphenol A di(meth)acrylate, and ethoxylated versions of these; and the like. These crosslinkable polymerizable monomers can be used alone or in combination of two or more. In the present disclosure, (meth)acrylate refers to both acrylate and methacrylate.

[0033] When the binder resin contains a structural unit derived from a crosslinkable polymerizable monomer, the content of the structural unit is not particularly limited, but from the viewpoint of achieving a good balance between the low temperature fixability and hot offset resistance of the toner, the content is preferably 0.05 parts by mass or more and 5 parts by mass or less, more preferably 0.06 parts by mass or more and 1.5 parts by mass or less, and even more preferably 0.08 parts by mass or more and 0.8 parts by mass or less, relative to 100 parts by mass of the total amount of structural units derived from monovinyl monomers. Note that a monovinyl monomer is a monomer having only one polymerizable functional group.

[0034] The styrene-acrylic resin may further contain structural units derived from other monovinyl monomers different from styrene-based monomers or (meth)acrylic monomers, as long as the objectives of the present disclosure are not impaired. Examples of the other monovinyl monomers include nitrile compounds such as acrylonitrile and methacrylonitrile; olefins such as ethylene, propylene, and butylene; and amide compounds such as acrylamide and methacrylamide. These other monovinyl monomers may be used alone or in combination of two or more. The content of the structural units derived from the other monovinyl monomers is not particularly limited as long as the objectives of the present disclosure are not impaired, but is preferably 5% by mass or less, more preferably 1% by mass or less, and even more preferably 0.1% by mass or less, based on 100% by mass of the styrene-acrylic resin.

[0035] In the toner of the present disclosure, in addition to the above-mentioned styrene acrylic resin, resins such as polyester resins, polystyrene resins, and epoxy resins, which have conventionally been widely used in toners, can be used in combination as the binder resin, within a range that does not impair the object of the present disclosure. In the toner of the present disclosure, a core-shell structure is easily formed, and the content of the styrene acrylic resin relative to 100% by mass of the binder resin is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass, from the viewpoint of improving the effect of suppressing printing defects after the toner is stored in a developing machine for a long period of time.

[0036] The toner of the present disclosure contains a binder resin containing at least one polar group selected from the group consisting of a carboxy group and a hydroxy group, with a content of 0.10% by mass or less. This reduces the hydrophilicity of the toner particle surface, thereby improving the charge stability of the toner. Furthermore, by limiting the content of structural units having a hydroquinone structure to 0.10% by mass or less, odors during printing and printing defects when the toner is stored in a developing machine for an extended period of time can be suppressed. The structural unit containing at least one polar group selected from the group consisting of a carboxy group and a hydroxy group may be, for example, a structural unit formed by incorporating a polymerizable monomer having the polar group into a polymer through a polymerization reaction, or a structural unit formed by incorporating a protected polymerizable monomer having the polar group into a polymer through a polymerization reaction and then deprotecting the polymerizable monomer to have the polar group; the structural unit is not particularly limited. Examples of polymerizable monomers having a carboxy group include acrylic acid and methacrylic acid, and examples of polymerizable monomers having a hydroxy group include 2-hydroxyethyl (meth)acrylate. The binder resin contained in the toner of the present disclosure may contain a structural unit in which a methoxy group or an acetoxy group in the structural unit represented by the general formula (1) is hydrolyzed to a hydroxy group, in an amount of 0.10% by mass or less. The methoxy group or the acetoxy group in the structural unit represented by the general formula (1) can be hydrolyzed, for example, by adding a thiol under basic conditions and heating.

[0037] The binder resin contained in the toner of the present disclosure usually has an acid value of less than 0.5 mgKOH / g, and may be 0 mgKOH / g. The binder resin and the polar resin described below can be distinguished by their acid values.

[0038] The content of the binder resin is not particularly limited, but from the viewpoint of achieving a good balance between the low-temperature fixability and heat-resistant storage stability of the toner, it is preferably 60 parts by mass or more and 90 parts by mass or less, more preferably 65 parts by mass or more and 85 parts by mass or less, and even more preferably 70 parts by mass or more and 80 parts by mass or less, relative to 100 parts by mass of the colored resin particles.

[0039] (Resin Coating) The colored resin particles may have a resin coating that coats the surface of the colored resin particles. The resin coating coats the surface of the shell layer of a core-shell structure formed by phase separation of the binder resin. The resin coating is included in the shell layer of the core-shell structure. The material for the resin coating is not particularly limited, but from the viewpoint of improving the low-temperature fixability and hot offset resistance of the toner in a well-balanced manner and widening the fixable temperature range of the toner, a polymer having a Tg of more than 80°C is preferably used. Specifically, at least one homopolymer or copolymer selected from the group consisting of styrene, acrylonitrile, and methyl (meth)acrylate is preferably used.

[0040] In the present disclosure, the glass transition temperature (Tg) can be determined, for example, in accordance with ASTM D3418-82. Specifically, a sample is heated at a heating rate of 10°C / min using a differential scanning calorimeter (Seiko Instruments Inc.: SSC5200) or the like, and the temperature at which the maximum heat peak appears in the DSC curve obtained during this process is taken as the glass transition temperature.

[0041] When the colored resin particles have the resin coating, the mass of the resin coating is not particularly limited, but is preferably 1 to 10 parts by mass, more preferably 2 to 7 parts by mass, relative to 100 parts by mass of the binder resin, from the viewpoint of improving the low-temperature fixability and hot offset resistance of the toner in a well-balanced manner and widening the fixable temperature range of the toner.

[0042] (Colorant) The colorant contained in the colored resin particles can be appropriately selected from colorants conventionally used in toners and is not particularly limited, and black, cyan, yellow, or magenta colorants can be used. Examples of black colorants that can be used include carbon black, titanium black, and magnetic powders such as iron zinc oxide and iron nickel oxide. Examples of cyan colorants that can be used include cyan pigments such as copper phthalocyanine pigments and their derivatives, anthraquinone pigments, and cyan dyes. Specific examples include C.I. Pigment Blue 2, 3, 6, 15, 15:1, 15:2, 15:3, 15:4, 16, 17:1, and 60; C.I. Solvent Blue 70, and the like. Examples of yellow colorants that can be used include azo pigments such as monoazo pigments and disazo pigments, yellow pigments such as condensed polycyclic pigments, and yellow dyes. Specific examples include C.I. Pigment Yellow 3, 12, 13, 14, 15, 17, 62, 65, 73, 74, 83, 93, 97, 120, 138, 155, 180, 181, 185, 186, 213, 214; C.I. Solvent Yellow 98, 162, etc. Examples of magenta colorants that can be used include azo pigments such as monoazo pigments and disazo pigments, magenta pigments such as condensed polycyclic pigments, and magenta dyes.Specifically, for example, C.I. Pigment Red 31, 48, 57:1, 58, 60, 63, 64, 68, 81, 83, 87, 88, 89, 90, 112, 114, 122, 123, 144, 146, 149, 150, 163, 170, 184, 185, 187, 202, 206, 207, 209, 237, 238, 251, 254, 255, 269; C.I. Pigment Violet 19; C.I. Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 81, 82, 83, 84, 100, 109, 121; C.I. Disperse Red 9; C.I. Examples of suitable colorants include Solvent Violet 8, 13, 14, 21, and 27; C.I. Disper Violet 1; C.I. Basic Red 1, 2, 9, 12, 13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 34, 35, 36, 37, 38, 39, and 40; and C.I. Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27, and 28. The colorants may be used alone or in combination of two or more. To improve image quality, a pigment and a dye may be used in combination as the colorant.

[0043] In the case of black toner, it is preferable to contain carbon black as a colorant from the viewpoint of forming high-quality images, and in the case of cyan toner, it is preferable to contain copper phthalocyanine pigment and its derivatives as a colorant from the viewpoint of forming high-quality images.

[0044] In the yellow toner, it is preferable to contain as a colorant at least one selected from the group consisting of disazo pigments such as C.I. Pigment Yellow 93, 155, 180, 214, 219, and yellow dyes such as C.I. Solvent Yellow 98, 162, from the viewpoint of easily improving heat-resistant storage stability and being able to form high-quality images, and it is more preferable to contain at least one selected from the group consisting of C.I. Pigment Yellow 155, 214, and C.I. Solvent Yellow 98, and it is even more preferable to contain at least one selected from the group consisting of C.I. Pigment Yellow 214 and C.I. Solvent Yellow 98. Furthermore, in the yellow toner, it is preferable to contain as a colorant a combination of a disazo pigment and a yellow dye, from the viewpoint of easily improving heat-resistant storage stability and being able to form high-quality images, and it is more preferable to contain at least one selected from the group consisting of C.I. Pigment Yellow 155 and C.I. It is more preferable to contain a combination of at least one selected from the group consisting of C.I. Pigment Yellow 214 and C.I. Solvent Yellow 98, and it is even more preferable to contain a combination of C.I. Pigment Yellow 214 and C.I. Solvent Yellow 98. In addition, in the yellow toner, the mass ratio of the yellow pigment to the yellow dye contained in the yellow colorant (yellow pigment:yellow dye) is preferably within a range of 50:50 to 95:5, and more preferably within a range of 60:40 to 90:10.

[0045] In magenta toners, it is preferable to contain C.I. Pigment Red 122 as a colorant, since it is possible to form high-quality images. Furthermore, it is more preferable to use C.I. Pigment Red 122 and C.I. Pigment Violet 19 in combination, and a mixed crystal of C.I. Pigment Violet 19 and C.I. Pigment Red 122 is particularly preferable. A mixed crystal of C.I. Pigment Violet 19 and C.I. Pigment Red 122 can be produced, for example, by the method described in U.S. Pat. No. 3,160,510, in which the mixed crystal components are simultaneously recrystallized from sulfuric acid or other suitable solvent, and if necessary, salt-ground and then treated with a solvent, or by the method described in German Patent Application Publication No. 1,217,333, in which a substituted diaminoterephthalic acid mixture is cyclized and then treated with a solvent. When a magenta toner contains C.I. Pigment Violet 19 and C.I. Pigment Violet 19 as colorants, it is more preferable to use C.I. Pigment Violet 19 and C.I. Pigment Violet 122 in combination. When C.I. Pigment Violet 19 and C.I. Pigment Red 122 are contained, the mass ratio of C.I. Pigment Violet 19 to C.I. Pigment Red 122 is preferably 80:20 to 20:80, more preferably 70:30 to 30:70, and even more preferably 60:40 to 40:60.

[0046] The content of the colorant is adjusted appropriately depending on the type of colorant so as to obtain a desired color development, and is not particularly limited, but is preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 5 parts by mass or more and 15 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0047] (Release Agent) The release agent may be any one that is generally used as a toner release agent without any particular limitation, but from the viewpoint of appropriately improving the hot offset resistance while maintaining an excellent balance between the low-temperature fixability and heat-resistant storage stability of the toner, a fatty acid ester compound is preferred. Note that the "fatty acid ester compound" refers to a product obtained by an esterification reaction between at least one selected from the group consisting of monohydric alcohols and polyhydric alcohols and at least one selected from the group consisting of saturated fatty acids and unsaturated fatty acids.

[0048] Specific examples of monohydric alcohols include monohydric saturated aliphatic alcohols such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 1-hexanol, octanol, 2-ethyl-1-hexanol, nonyl alcohol, lauryl alcohol, cetyl alcohol, stearyl alcohol, 1-eicosanol, and behenyl alcohol; monohydric unsaturated aliphatic alcohols such as allyl alcohol, methallyl alcohol, crotyl alcohol, palmitoleic alcohol, and oleyl alcohol; monohydric alicyclic alcohols such as cyclohexanol; and monohydric aromatic alcohols such as phenol, phenylmethanol (benzyl alcohol), methylphenol (cresol), p-ethylphenol, dimethylphenol (xylenol), nonylphenol, dodecylphenol, phenylphenol, and naphthol.

[0049] Specific examples of polyhydric alcohols include dihydric saturated aliphatic alcohols such as ethylene glycol and propylene glycol; dihydric aromatic alcohols such as catechol and hydroquinone; and trihydric or higher saturated aliphatic alcohols such as glycerin, pentaerythritol, dipentaerythritol, and polyglycerin.

[0050] Among these monohydric alcohols and polyhydric alcohols, monohydric to tetrahydric saturated aliphatic alcohols are preferred, stearyl alcohol, 1-eicosanol, behenyl alcohol and pentaerythritol are more preferred, stearyl alcohol and behenyl alcohol are even more preferred, and behenyl alcohol is particularly preferred.

[0051] As the fatty acid used as the raw material for the fatty acid ester compound, preferably at least one selected from the group consisting of saturated fatty acids and unsaturated fatty acids having 12 to 22 carbon atoms, more preferably at least one selected from the group consisting of saturated fatty acids and unsaturated fatty acids having 14 to 18 carbon atoms, and even more preferably a saturated fatty acid having 14 to 18 carbon atoms is used.

[0052] Specific examples of saturated fatty acids having the above carbon numbers include, but are not limited to, lauric acid (12 carbon atoms), myristic acid (14 carbon atoms), pentadecylic acid (15 carbon atoms), palmitic acid (16 carbon atoms), margaric acid (17 carbon atoms), stearic acid (18 carbon atoms), eicosanoic acid (20 carbon atoms), and behenic acid (22 carbon atoms). Among these saturated fatty acids, stearic acid (18 carbon atoms), eicosanoic acid (20 carbon atoms), and behenic acid (22 carbon atoms) are preferred, with stearic acid (18 carbon atoms) being more preferred.

[0053] Specific examples of unsaturated fatty acids include, but are not limited to, the following compounds: palmitoleic acid (CH ３ (CH ２ ) ５ CH=CH(CH ２ ) ７ COOH) Oleic acid (CH ３ (CH ２ ) ７ CH=CH(CH ２ ) ７ COOH) Vaccenic acid (CH ３ (CH ２ ) ５ CH=CH(CH ２ ) ９ COOH) Linoleic acid (CH ３ (CH ２ ) ３ (CH ２ CH=CH) ２ (CH ２ ) ７ COOH) (9,12,15)-linolenic acid (CH ３ (CH ２ CH=CH) ３ (CH ２ ) ７ COOH) (6,9,12)-linolenic acid (CH ３ (CH ２ ) ３ (CH ２ CH=CH) ３ (CH ２ ) ４ COOH) Eleostearic acid (CH ３ (CH ２ ) ３(CH=CH) ３ (CH ２ ) ７ COOH) arachidonic acid (CH ３ (CH ２ ) ３ (CH ２ CH=CH) ４ (CH ２ ) ３ COOH)

[0054] The at least one selected from the group consisting of saturated fatty acids and unsaturated fatty acids may be used alone or in combination of two or more. Among the saturated fatty acids and unsaturated fatty acids, saturated fatty acids are preferred, palmitic acid, stearic acid, eicosanoic acid, and behenic acid are more preferred, stearic acid, eicosanoic acid, and behenic acid are even more preferred, stearic acid and behenic acid are particularly preferred, and stearic acid is most preferred.

[0055] Specific examples of preferred fatty acid ester compounds include at least one selected from the group consisting of behenyl palmitate, behenyl stearate, behenyl eicosanoate, behenyl behenate, eicosyl palmitate, eicosyl stearate, eicosyl eicosanoate, eicosyl behenate, stearyl stearate, stearyl eicosanoate, stearyl behenate, hexadecyl eicosanoate, hexadecyl behenate, pentaerythritol tetrabehenate, pentaerythritol tetrapalminate, and pentaerythritol tetrastearate.

[0056] The fatty acid ester compounds described above can be produced according to conventional methods. Examples of methods for producing such fatty acid ester compounds include a method of performing an esterification reaction using at least one selected from the group consisting of monohydric alcohols and polyhydric alcohols and at least one selected from the group consisting of saturated fatty acids and unsaturated fatty acids. Commercially available fatty acid ester compounds can also be used. Examples of commercially available fatty acid ester compounds include "WEP2," "WEP3," "WEP4," "WEP5," "WE6," and "WE11" (all trade names) manufactured by NOF Corporation.

[0057] In the present invention, a release agent other than a fatty acid ester compound may be used as the release agent instead of or together with the fatty acid ester compound. Examples of release agents other than fatty acid ester compounds include low-molecular-weight polyolefin waxes and modified waxes thereof; natural plant waxes such as jojoba; petroleum waxes such as paraffin; mineral waxes such as ozokerite; and synthetic waxes such as Fischer-Tropsch wax. These may be used alone or in combination of two or more.

[0058] The number average molecular weight (Mn) of the release agent is not particularly limited, but from the viewpoint of appropriately improving hot offset resistance while maintaining an excellent balance between the low-temperature fixability and heat-resistant storage stability of the toner, it is preferably 500 to 1500, more preferably 550 to 1200, and even more preferably 550 to 1100. The number average molecular weight (Mn) of the release agent can be measured, for example, in terms of polystyrene by gel permeation chromatography (GPC) using tetrahydrofuran.

[0059] The content of the release agent is preferably 1 to 30 parts by mass, more preferably 5 to 28 parts by mass, even more preferably 10 to 26 parts by mass, still more preferably 15 to 25 parts by mass, and particularly preferably 15 to 23 parts by mass, relative to 100 parts by mass of the binder resin. By setting the content of the release agent within the above range, the low-temperature fixability and hot offset resistance of the toner can be improved in a well-balanced manner, and the fixable temperature range of the toner can be widened.

[0060] (Charge Control Agent) The colored resin particles preferably contain a charge control agent. The charge control agent is not particularly limited as long as it is one that is generally used as a charge control agent for toner, but a positively or negatively charged charge control resin is preferred because it has high compatibility with polymerizable monomers, can impart excellent charge stability to the toner, and can improve the dispersibility of the colorant. From the viewpoint of obtaining a positively charged toner, a positively charged charge control resin is preferably used.

[0061] As a positively or negatively chargeable charge control resin, a functional group-containing copolymer can be used because it has high compatibility with polymerizable monomers, can impart excellent charge stability to toners, and can improve the dispersibility of colorants. As a positively chargeable charge control resin, for example, a functional group-containing copolymer containing a structural unit containing a functional group such as an amino group, a quaternary ammonium group, or a quaternary ammonium salt-containing group can be used. Examples of such functional group-containing copolymers include polyamine resins, quaternary ammonium group-containing copolymers, and quaternary ammonium base-containing copolymers. As a negatively chargeable charge control resin, for example, a functional group-containing copolymer containing a structural unit containing a functional group such as a sulfonic acid group, a sulfonate salt-containing group, a carboxy group, or a carboxylate salt-containing group can be used. Examples of such functional group-containing copolymers include sulfonic acid group-containing copolymers, sulfonate salt group-containing copolymers, carboxy group-containing copolymers, and carboxylate salt group-containing copolymers.

[0062] The functional group-containing copolymer used as a positively or negatively chargeable charge control resin preferably has a proportion of functional group-containing structural units of 10% by mass or less, more preferably 5% by mass or less, and even more preferably 3% by mass or less, in terms of high compatibility with polymerizable monomers, imparting excellent charge stability to the toner, and improving the dispersibility of the colorant. On the other hand, in terms of improving the charge stability and heat-resistant storage stability of the toner, the proportion of functional group-containing structural units in the functional group-containing copolymer is preferably 0.5% by mass or more, more preferably 1% by mass or more, and even more preferably 1.5% by mass or more. When the charge control resin contains sufficient functional groups, the charge control resin is more likely to localize near the surface of the colored resin particles, thereby improving the charge stability and heat-resistant storage stability of the toner. The charge control resin is usually contained in the shell layer of a core-shell structure.

[0063] The functional group-containing copolymer used as a positively or negatively chargeable charge control resin is preferably a styrene-acrylic resin, because it has high compatibility with the polymerizable monomer, the charge amount of the toner can be easily adjusted by the amount added, and excellent charge stability can be imparted to the toner. The styrene-acrylic resin used as a charge control resin is preferably a copolymer of two or more monomers including a styrene-based monomer and a (meth)acrylic monomer. In particular, the total content of structural units derived from the styrene-based monomer and structural units derived from the (meth)acrylic monomer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more. The styrene-acrylic resin used as a charge control resin can be distinguished from the styrene-acrylic resin used as a binder resin in that the proportion of the functional group-containing structural units is equal to or greater than the lower limit. The proportion of the functional group-containing structural units in the styrene-acrylic resin used as a binder resin is typically less than 0.10% by mass, and may be 0.01% by mass or less, or even 0% by mass.

[0064] Furthermore, the functional group-containing copolymer used as the positively or negatively chargeable charge control resin preferably has a glass transition temperature (Tg) of 50 to 110° C., more preferably 60 to 100° C. When the glass transition temperature (Tg) of the functional group-containing copolymer is within the above range, a decrease in the Tg of the shell layer is suppressed, and therefore, the effect of suppressing printing defects after storing the toner in a developing machine for a long period of time is improved.

[0065] The charge control resin preferably has a weight average molecular weight Mw in the range of 5,000 to 30,000, more preferably in the range of 10,000 to 25,000. When the weight average molecular weight Mw of the charge control resin is within this range, the toner tends to have a good balance between low-temperature fixability, heat-resistant storage stability, and hot offset resistance. In the present disclosure, the weight average molecular weight Mw of the resin is determined by GPC in terms of polystyrene using a sample dissolved in tetrahydrofuran (THF).

[0066] Furthermore, as the charge control agent, a charge control resin may be used in combination with a charge control agent other than the charge control resin. Examples of other positively chargeable charge control agents include nigrosine dyes, quaternary ammonium salts, triaminotriphenylmethane compounds, and imidazole compounds. Examples of other negatively chargeable charge control agents include azo dyes containing metals such as Cr, Co, Al, and Fe, salicylic acid metal compounds, and alkylsalicylic acid metal compounds. The charge control agents may be used alone or in combination of two or more.

[0067] The content of the charge control agent is not particularly limited, but is preferably 0.01 to 10 parts by mass, more preferably 0.03 to 8 parts by mass, even more preferably 0.1 to 6 parts by mass, and particularly preferably 0.3 to 4 parts by mass, relative to 100 parts by mass of the binder resin, from the viewpoint of being able to impart excellent charge stability to the toner and of suppressing the occurrence of printing defects after the toner has been stored in a developing machine for a long period of time.

[0068] (Polar Resin) The colored resin particles preferably contain a polar resin, since this improves the low-temperature fixability and hot offset resistance of the toner in a well-balanced manner and can widen the fixable temperature range of the toner. In the present disclosure, the polar resin is selected from polymers containing a repeating unit containing a heteroatom. Specific examples of the polar resin include acrylic resins, polyester resins, and vinyl resins containing heteroatoms.

[0069] Furthermore, from the viewpoint of widening the fixable temperature range of the toner, a resin having an acid value of 0.5 to 20 mgKOH / g is preferably used as the polar resin. The acid value of the polar resin is preferably 1.0 to 10.0 mgKOH / g, more preferably 1.5 to 5.0 mgKOH / g, and even more preferably 2.0 to 3.0 mgKOH / g. It is presumed that the polar resin having an acid value easily localizes near the surface of the colored resin particles, thereby widening the fixable temperature range of the toner. The polar resin is usually contained in the shell layer of the core-shell structure.

[0070] The polar resin may be, for example, a homopolymer or copolymer of a heteroatom-containing monomer, or a copolymer of a heteroatom-containing monomer and a non-heteroatom-containing monomer. When the polar resin is a copolymer of a heteroatom-containing monomer and a non-heteroatom-containing monomer, the proportion of the heteroatom-containing monomer units in 100% by mass of all repeating units constituting the copolymer is preferably 50% by mass or more, more preferably 70% by mass or more, and even more preferably 90% by mass or more, in order to widen the fixable temperature range of the toner.

[0071] Examples of heteroatom-containing monomers used in the polar resin include alkyl (meth)acrylates such as methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, sec-pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, neohexyl (meth)acrylate, sec-hexyl (meth)acrylate, tert-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and lauryl (meth)acrylate; and 2-hydroxyethyl (meth)acrylate, ... Examples of suitable monomers include (meth)acrylic acid esters such as propyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, methoxypolyethylene glycol (meth)acrylate, dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, glycidyl (meth)acrylate, and 4-hydroxybutyl acrylate glycidyl ether, as well as (meth)acrylic acid; heteroatom-containing styrene monomers such as halogenated styrene and styrene sulfonic acid; carboxylic acid vinyl ester monomers such as vinyl acetate; halogenated vinyl monomers such as vinyl chloride; halogenated vinylidene monomers such as vinylidene chloride; vinylpyridine; carboxyl group-containing monomers such as ethylenically unsaturated carboxylic acid monomers such as crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butenetricarboxylic acid; and epoxy group-containing monomers such as allyl glycidyl ether. These heteroatom-containing monomers can be used alone or in combination of two or more.

[0072] Examples of the heteroatom-free monomer used in the polar resin include styrene-based monomers that do not contain heteroatoms, such as styrene, vinyltoluene, α-methylstyrene, and p-methylstyrene; monoolefin monomers, such as ethylene, propylene, and butylene; and diene-based monomers, such as butadiene and isoprene. These heteroatom-free monomers can be used alone or in combination of two or more.

[0073] In order to widen the fixable temperature range of the toner, it is preferable that the heteroatom-containing monomer contains a polar group-containing monomer containing at least one polar group selected from the group consisting of a carboxy group, a hydroxy group, a sulfonic acid group, an amino group, a polyoxyethylene group, and an epoxy group. The polar group is preferably at least one selected from the group consisting of a carboxy group and a hydroxy group.

[0074] Examples of polar group-containing monomers include carboxy group-containing monomers such as acrylic acid, methacrylic acid, crotonic acid, cinnamic acid, itaconic acid, fumaric acid, maleic acid, and butenetricarboxylic acid; hydroxy group-containing monomers such as 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, and 4-hydroxybutyl (meth)acrylate; sulfonic acid group-containing monomers such as styrenesulfonic acid; amino group-containing monomers such as dimethylaminoethyl (meth)acrylate and diethylaminoethyl (meth)acrylate; polyoxyethylene group-containing monomers such as methoxypolyethylene glycol (meth)acrylate; and epoxy group-containing monomers such as glycidyl (meth)acrylate, allyl glycidyl ether, and 4-hydroxybutyl acrylate glycidyl ether. These polar group-containing monomers can be used alone or in combination of two or more.

[0075] When the polar resin contains a polar group-containing monomer unit, it is preferable that the polar group is located at the end of the main chain or side chain, or is bonded in a pendant manner to the main chain or side chain, because this makes it easier for the polar resin to be arranged on the surface of the droplets of the polymerizable monomer composition, improves the low-temperature fixability and hot offset resistance of the toner in a well-balanced manner, and widens the fixable temperature range of the toner.

[0076] The polar resin is preferably an acrylic resin because of its excellent effect of widening the fixable temperature range of the toner. The acrylic resin used as the polar resin is a homopolymer or copolymer of a (meth)acrylic monomer, and may be further copolymerized with a monomer not having a (meth)acryloyl group. In the acrylic resin used as the polar resin, the copolymerization ratio of the (meth)acrylic monomer is preferably 70% by mass or more, more preferably 90% by mass or more, and even more preferably 99% by mass or more, from the viewpoint of widening the fixable temperature range of the toner.

[0077] From the viewpoint of widening the fixable temperature range of the toner, the acrylic resin used as the polar resin preferably contains a monomer unit derived from a (meth)acrylic acid alkyl ester, more preferably contains a monomer unit derived from a (meth)acrylic acid alkyl ester having an alkyl group with 3 or less carbon atoms, further preferably contains a monomer unit derived from at least one selected from the group consisting of methyl (meth)acrylate and ethyl (meth)acrylate, and still more preferably contains a monomer unit derived from methyl (meth)acrylate.

[0078] The acrylic resin used as the polar resin is preferably a copolymer of at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters with at least one selected from the group consisting of acrylic acid and methacrylic acid, from the viewpoint of widening the fixable temperature range of the toner, and more preferably a copolymer of an acrylic acid ester, a methacrylic acid ester, and acrylic acid.

[0079] In the acrylic resin, examples of the (meth)acrylic acid ester include the same as the (meth)acrylic acid ester used in the heteroatom-containing monomer. In the acrylic resin, the (meth)acrylic acid ester may or may not contain the polar group, but those not containing the polar group are preferred, and among these, (meth)acrylic acid alkyl esters are preferred. The acrylic acid ester used in the acrylic resin is preferably at least one selected from the group consisting of ethyl acrylate, n-propyl acrylate, isopropyl acrylate, and n-butyl acrylate, and more preferably at least one selected from the group consisting of ethyl acrylate and n-butyl methacrylate. The methacrylic acid ester used in the acrylic resin is preferably at least one selected from the group consisting of methyl methacrylate, n-propyl methacrylate, isopropyl methacrylate, and n-butyl methacrylate, and more preferably methyl methacrylate.

[0080] In the acrylic resin, the ratio of acrylic acid and methacrylic acid relative to the total amount (100% by mass) of the acrylic acid ester, methacrylic acid ester, acrylic acid, and methacrylic acid used in the synthesis of the acrylic resin is preferably 0.05 to 1% by mass, more preferably 0.1 to 0.6% by mass, and even more preferably 0.3 to 0.5% by mass, in terms of high compatibility with the polymerizable monomer, ease of control of the particle size of the colored resin particles, and widening the fixable temperature range of the toner.

[0081] The acrylic resin is preferably a copolymer of monomers containing 50.0% by mass or more of methyl methacrylate relative to 100% by mass of the total mass of the monomers used in the synthesis of the acrylic resin, from the viewpoints of high compatibility with the polymerizable monomer, ease of control of the particle size of the colored resin particles, and widening the fixable temperature range of the toner. The acrylic resin is more preferably a copolymer of a monomer containing 50.0 to 99.9% by mass of methyl methacrylate and 0.1 to 5.0% by mass of (meth)acrylic acid, even more preferably a copolymer of a monomer containing 50.0 to 99.0% by mass of methyl methacrylate and 0.1 to 5.0% by mass of (meth)acrylic acid, even more preferably a copolymer of a monomer containing 50.0 to 98.0% by mass of methyl methacrylate, 1.0 to 5.0% by mass of an alkyl (meth)acrylate other than methyl methacrylate, and 0.1 to 5.0% by mass of (meth)acrylic acid, and particularly preferably a copolymer of a monomer containing 50.0 to 98.0% by mass of methyl methacrylate, 1.0 to 5.0% by mass of an alkyl (meth)acrylate other than methyl methacrylate, and 0.2 to 3.0% by mass of (meth)acrylic acid. Note that the (meth)acrylic acid content refers to the total content of acrylic acid and methacrylic acid.

[0082] As the alkyl (meth)acrylate other than methyl methacrylate, at least one selected from the group consisting of ethyl acrylate and butyl acrylate is preferred, since the glass transition temperature can be controlled.

[0083] The acrylic resin may contain a small amount of monomer units derived from other monomers different from both (meth)acrylic acid esters and (meth)acrylic acid. From the viewpoint of easily controlling the particle size of the colored resin particles and widening the fixable temperature range of the toner, the content of the other monomers is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less, based on 100% by mass of the total amount of monomers used in the synthesis of the acrylic resin. It is most preferable that the acrylic resin does not contain the other monomers. Examples of the other monomers include the heteroatom-free monomers and the heteroatom-containing monomers other than the (meth)acrylic monomers.

[0084] The weight-average molecular weight Mw of the polar resin is usually 6,000 to 50,000, preferably 8,000 to 45,000, more preferably 9,000 to 45,000, and even more preferably 10,000 to 40,000. When the weight-average molecular weight (Mw) of the polar resin is within this range, the fixable temperature range of the toner tends to be wide. Furthermore, when the weight-average molecular weight (Mw) of the polar resin is equal to or greater than the lower limit, a toner with excellent heat-resistant storage stability and durability can be obtained, and when the weight-average molecular weight (Mw) is equal to or less than the upper limit, a toner with excellent low-temperature fixability can be obtained.

[0085] The glass transition temperature (Tg) of the polar resin is preferably 60 to 95° C., more preferably 65 to 90° C., even more preferably 65 to 85° C., and still more preferably 70 to 80° C. When the glass transition temperature of the polar resin is equal to or higher than the lower limit, the heat-resistant storage stability of the resulting toner can be improved, and when the glass transition temperature is equal to or lower than the upper limit, the low-temperature fixability of the resulting toner can be improved.

[0086] The polar resin may be commercially available, or may be produced by polymerizing a monomer containing the heteroatom-containing monomer by a known method such as solution polymerization, aqueous solution polymerization, ionic polymerization, high-temperature high-pressure polymerization, or suspension polymerization. When the polar resin is a copolymer, the copolymer may be a random copolymer, a block copolymer, or a graft copolymer, but is preferably a random copolymer. The polar resin is preferably pulverized to improve solubility.

[0087] The content of the polar resin is preferably 0.2 to 5 parts by mass, more preferably 0.5 to 3 parts by mass, and even more preferably 0.7 to 2 parts by mass, relative to 100 parts by mass of the binder resin. When the content of the polar resin is within the above range, the low-temperature fixability and hot offset resistance of the toner can be improved in a well-balanced manner, and the fixable temperature range of the toner can be widened.

[0088] (Styrene-based thermoplastic elastomer) The colored resin particles may further contain a styrene-based thermoplastic elastomer. By containing a styrene-based thermoplastic elastomer, the fixability of the toner can be improved while maintaining the toner's heat resistance temperature, and the low-temperature fixability and hot offset resistance of the toner can be improved in a well-balanced manner, thereby widening the fixable temperature range of the toner. Here, the elastomer refers to a polymer having rubber-like elasticity, which generally exhibits rubber-like elasticity at room temperature (25°C) and has the property of being plasticized and moldable at high temperatures. Examples of styrene-based thermoplastic elastomers include random, block, graft, and other copolymers of a styrene-based monomer and at least one other monomer selected from the group consisting of monoolefins and diolefins that can be copolymerized with the styrene-based monomer, and hydrogenated products of these copolymers.

[0089] Representative examples of the styrene-based thermoplastic elastomer used in the present disclosure include styrene-butadiene-styrene block copolymers, styrene-butadiene block copolymers, styrene-isoprene-styrene block copolymers, styrene-isoprene block copolymers, styrene-butadiene-isoprene-styrene block copolymers, and hydrogenated products thereof; styrene-ethylene-butylene-styrene block copolymers, styrene-ethylene-propylene-styrene block copolymers, and styrene-ethylene-ethylene-propylene-styrene block copolymers. Among these styrene-based thermoplastic elastomers, styrene-isoprene-styrene block copolymers can be preferably used from the viewpoint of optimizing the balance between the heat-resistant storage stability and low-temperature fixability of the toner and from the viewpoint of widening the fixable temperature range of the toner.

[0090] The content of styrene monomer units in the styrene-based thermoplastic elastomer is preferably 15 to 70% by mass, more preferably 15 to 60% by mass, and even more preferably 20 to 40% by mass. When the styrene content is equal to or greater than the lower limit, the fixed toner is less likely to peel from the fixing surface, thereby suppressing a decrease in fixability. On the other hand, when the styrene content is equal to or less than the upper limit, the compatibility with the binder resin does not become too high, thereby suppressing a decrease in the heat-resistant storage stability of the toner.

[0091] The weight average molecular weight Mw of the styrene-based thermoplastic elastomer is not particularly limited, but is preferably 50,000 to 350,000, and more preferably 80,000 to 250,000, from the viewpoint of achieving an excellent effect of improving the fixability of the toner while maintaining the heat resistance temperature of the toner, and from the viewpoint of widening the fixable temperature range of the toner.

[0092] The styrene-based thermoplastic elastomer may be a commercially available product, such as the Quintac (registered trademark) series manufactured by Zeon Corporation and the Septon (registered trademark) series manufactured by Kuraray Co., Ltd.

[0093] The content of the styrene-based thermoplastic elastomer is not particularly limited, but from the viewpoint of widening the fixable temperature range of the toner, it is preferably 0.5 to 10 parts by mass, more preferably 1 to 8 parts by mass, even more preferably 2 to 6 parts by mass, and still more preferably 2 to 4 parts by mass, relative to 100 parts by mass of the binder resin. The styrene-based thermoplastic elastomers can be used alone or in combination of two or more.

[0094] (Structure of Colored Resin Particles) The colored resin particles contained in the toner of the present disclosure have a core-shell structure having a core layer and a shell layer. The core layer and shell layer are preferably formed by phase separation of the binder resin described above. When the preferred styrene-acrylic resin described above is used as the binder resin, the core-shell structure is formed by polymerizing the styrene-acrylic resin raw materials, a styrene-based monovinyl monomer and a (meth)acrylic monovinyl monomer, in a phase-separated state. Furthermore, the colored resin particles contained in the toner of the present disclosure preferably have multiple domains of the release agent scattered therein. The core-shell structure of the colored resin particles and the domains of the release agent can be confirmed from the cross-section of the colored resin particles observed with a transmission electron microscope (TEM). A cross-section observation sample for observing the cross-section of colored resin particles can be prepared, for example, by mixing colored resin particles with a curable material such as epoxy resin, curing the mixture to obtain a cured product, cutting the resulting cured product into thin sections using a microtome or the like, and staining the thin sections with vapor of a 0.5% aqueous ruthenium tetroxide solution for approximately 5 minutes. Observing the cross-section observation sample prepared in this manner using a transmission electron microscope allows the cross-section of the colored resin particles to be observed, and the core-shell structure and release agent domains that appear in the cross-section of the colored resin particles can be confirmed. In the cross-section of the colored resin particles, the release agent domains are typically observed as white elliptical or rectangular domains with a major axis of approximately 0.2 to 1.0 μm. It is desirable to adjust the measurement conditions for measuring the cross-section observation sample so that the release agent domains are easily observed. For example, it is desirable to adjust the magnification and concentration of the colored resin particles during TEM observation so that the cross-sections of 3 to 10 colored resin particles can be observed within a 28 μm x 35 μm area. In addition, when measuring the sample for cross-section observation, the colored resin particles are measured when the equivalent circle diameter of the cross section of the colored resin particles is within ±3 μm of the volume average particle diameter (Dv) of the colored resin particles. In other words, colored resin particles whose equivalent circle diameter of the cross section exceeds ±3 μm of the volume average particle diameter (Dv) are excluded from the measurement.The cross section of the colored resin particle observed with a transmission electron microscope is measured using image analysis software (for example, "DNP Particle Image Analysis Software" manufactured by Dai Nippon Printing Co., Ltd.).

[0095] FIG. 1 is a schematic diagram of an example of a cross section of a colored resin particle contained in the toner of the present disclosure. The colored resin particle 10 shown in FIG. 1 has a core layer 1 and a shell layer 2 formed by phase separation of a binder resin. A plurality of domains 3 of a release agent are present in the cross section of the colored resin particle 10. Note that in FIG. 1, the cross section of the colored resin particle 10 is schematically represented as a circle, so that the geometric center 10C of the cross section of the colored resin particle 10 is the center of the circle, the outline 10L of the colored resin particle 10 is the circumference, and the distance r from the geometric center 10C to the outline 10L is the radius of the circle. However, the cross section of the colored resin particle is not limited thereto, and may be, for example, an ellipse or an irregular shape.

[0096] In the core-shell structure, the average ratio (t / r) of the thickness t of the shell layer to the distance r from the geometric center 10C to the outline 10L of the cross section of the colored resin particle observed with a transmission electron microscope is preferably 0.05 or more, more preferably 0.10 or more, and even more preferably 0.20 or more, and preferably 0.50 or less, more preferably 0.40 or less, and even more preferably 0.30 or less. When the average ratio (t / r) is within the above range, the effect of suppressing printing defects after long-term storage of the toner in a developing machine is improved. The average ratio (t / r) is the average of t / r values ​​measured from 100 or more colored resin particles. The value of t / r for each colored resin particle is determined by first defining the center of gravity of the cross section of the colored resin particle as the geometric center 10C, and then defining the length of the longest line segment that passes through the geometric center 10C and connects two points on the outline 10L of the cross section of the colored resin particle as the major axis and the length of the shortest line segment as the minor axis. Next, the two endpoints 10LA and 10LB of the line segment from which the major axis was determined are identified, and t / r is calculated using the shell layer thickness t measured on the line connecting the geometric center 10C to endpoint 10LA and the distance r from the geometric center 10C to endpoint 10LA. t / r is similarly calculated using the other endpoint 10LB, and two t / r values ​​are obtained from the line segment from which the major axis was determined. Two t / r values ​​are similarly obtained from the line segment from which the minor axis was determined. In this way, a total of four t / r values ​​are obtained from the cross section of one colored resin particle, and their average value is used as the t / r value for that colored resin particle. The greater the amount of polymerizable monomer with a relatively high SP value used as a binder resin raw material, the greater the shell layer thickness ratio tends to be. Therefore, to ensure that the average ratio (t / r) falls within the above-mentioned preferred range, it is effective to adjust the type and amount of polymerizable monomer used as a binder resin raw material.

[0097] It is preferable that a domain of the release agent is present in the cross section of the colored resin particle. From the viewpoint of improving the low-temperature fixability and hot offset resistance of the toner in a balanced manner and widening the fixable temperature range of the toner, the average total area ratio of the domain of the release agent is preferably 10 to 30%, and may be 15 to 20%. From the viewpoint of widening the fixable temperature range of the toner, the average total area ratio of the domain of the release agent is more preferably 18 to 30%. The average total area ratio of the domain of the release agent is determined by measuring 100 or more colored resin particles and calculating the ratio of the sum of the areas of the domains of the release agent present in the cross section of the colored resin particles to the sum of the cross-sectional areas of the colored resin particles measured. In order to ensure that the average total area ratio of the domain of the release agent falls within the above-mentioned preferred range, for example, it is effective to adjust the amount of the release agent added.

[0098] In the cross section of the colored resin particle, the average number of domains of the release agent present per particle is preferably 10 to 40, and may be 20 to 30, from the viewpoint of improving the low-temperature fixability and hot offset resistance of the toner in a well-balanced manner and widening the fixable temperature range of the toner. From the viewpoint of widening the fixable temperature range of the toner, the average number of domains of the release agent present per particle is more preferably 17 to 40. The average number of domains of the release agent present per particle is determined by measuring 100 or more colored resin particles and dividing the total number of domains of the release agent present in the cross section of the measured colored resin particles by the number of colored resin particles measured. In order to ensure that the average number of domains of the release agent present per particle falls within the above-mentioned preferred range, it is effective to, for example, adjust the type of release agent or the type or amount of styrene-based thermoplastic elastomer added.

[0099] In the cross section of the colored resin particle, the average proportion of the domains of the release agent present within an area of ​​80% or less of the distance r from the geometric center 10C of the cross section to the contour 10L is preferably 80% or more, from the viewpoint of improving the effect of suppressing printing defects after long-term storage of the toner in a developing machine. The upper limit of this average proportion is not particularly limited, and may be 100%, or from the viewpoint of ease of production, it may be 95% or less, or even 90% or less. The average proportion of the domains of the release agent present within an area of ​​80% or less of the distance r from the geometric center 10C of the cross section of the colored resin particle to the contour 10L is determined by measuring 100 or more colored resin particles and dividing the total number of domains of the release agent present within the area of ​​the cross section of the colored resin particle measured by the total number of domains of the release agent present in the cross section of the colored resin particle measured. With regard to a domain of the release agent present in the vicinity of 80% of the distance r from the geometric center 10C of the cross section of the colored resin particle to the outline 10L, the domain is determined to be present within the above-mentioned region if, on a line passing through the geometric center 10C of the cross section of the colored resin particle, the geometric center 3C of the domain, and the outline 10L, the distance from the geometric center 10C of the cross section of the colored resin particle to the geometric center 3C of the domain is 80% or less of the distance from the geometric center 10C of the cross section of the colored resin particle to the outline 10L. In order to ensure that the average proportion of the domains of the release agent present within the above-mentioned region falls within the above-mentioned preferred range, it is effective, for example, to adjust the mass ratio of the styrene-based monovinyl monomer to the (meth)acrylic monovinyl monomer.

[0100] (Physical Properties of Colored Resin Particles) The volume average particle diameter Dv of the colored resin particles is preferably 4.0 to 10.0 μm, more preferably 4.5 to 9.5 μm, and even more preferably 5.0 to 9.0 μm. When the volume average particle diameter Dv of the colored resin particles is equal to or greater than the lower limit, the fluidity of the toner can be improved, and deterioration of transferability and reduction in image density can be suppressed. When Dv is equal to or less than the upper limit, reduction in image resolution can be suppressed.

[0101] Furthermore, from the viewpoint of image reproducibility, the particle size distribution (Dv / Dn), which is the ratio of the volume average particle size (Dv) to the number average particle size (Dn) of the colored resin particles, is preferably 1.00 to 1.30, and more preferably 1.00 to 1.20. When the particle size distribution (Dv / Dn) of the colored resin particles is within the above range, the resulting toner has excellent fluidity and a well-balanced excellent transferability, image density, and image resolution. The volume average particle size Dv and number average particle size Dn of the colored resin particles can be measured, for example, using a particle size distribution measuring device using a Coulter counter (manufactured by Beckman Coulter, product name: Multisizer).

[0102] 2. Method for Producing Colored Resin Particles Generally, methods for producing colored resin particles are broadly divided into dry methods such as pulverization and wet methods such as emulsion polymerization aggregation, suspension polymerization, and dissolution suspension. Wet methods are preferred because they are more likely to produce toners with excellent printing properties such as image reproducibility. Among the wet methods, polymerization methods such as emulsion polymerization aggregation and suspension polymerization are more likely to produce toners with a relatively small particle size distribution on the order of microns. In the present disclosure, it is preferable to produce colored resin particles by suspension polymerization in order to give the colored resin particles a core-shell structure and to suppress the generation of volatile organic compounds (VOCs) from the resulting toner.

[0103] An example of a method for producing colored resin particles used in the present disclosure includes a step of preparing a polymerizable monomer composition, a step of preparing a suspension, and a step of polymerizing the polymerizable monomer contained in the suspension, and may further include other steps. Furthermore, as far as technically possible, two or more of the above steps and other additional steps may be performed simultaneously as a single step, or the order may be reversed. For example, the preparation and suspension of the polymerizable monomer composition may be performed simultaneously in a single step, such as by simultaneously adding materials for preparing the polymerizable monomer composition and suspending the material.

[0104] A preferred example of the method for producing colored resin particles used in the present disclosure is a production method using suspension polymerization, which includes the following steps: (1) Preparation step of polymerizable monomer composition: A step of preparing a polymerizable monomer composition containing a polymerizable monomer, a colorant, and a release agent; (2) Suspension step: A step of preparing a suspension in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer; and (3) Polymerization step: A step of polymerizing the polymerizable monomer contained in the droplets of the polymerizable monomer composition. These three steps and other steps will be described in order below.

[0105] (1) Preparation of Polymerizable Monomer Composition First, a polymerizable monomer, a colorant, a release agent, and, if necessary, other additives such as a charge control agent, a polar resin, a styrene-based thermoplastic elastomer, and a molecular weight modifier are mixed to prepare a polymerizable monomer composition.

[0106] In the present disclosure, a low-molecular-weight compound having a polymerizable functional group is typically used as the polymerizable monomer. The polymerizable monomer contained in the polymerizable monomer composition is polymerized to form a binder resin. Therefore, the polymerizable monomer is a monovinyl monomer or a crosslinkable polymerizable monomer, which are raw materials for the binder resin described above.

[0107] In the method for producing colored resin particles used in the present disclosure, it is preferable that the polymerizable monomer contains a styrene-based monovinyl monomer represented by the following general formula (1A): The styrene-based monovinyl monomer represented by the following general formula (1A) undergoes a polymerization step to become a structural unit represented by the general formula (1) contained in the binder resin.

[0108] (In general formula (1A), R １ and R ２ are each independently a methyl group or an acetyl group.

[0109] The polymerizable monomer preferably further contains a styrene-based monovinyl monomer and a (meth)acrylic monovinyl monomer which are preferably used in the binder resin described above, and also preferably contains a crosslinkable polymerizable monomer. The content of each polymerizable monomer contained in 100% by mass of the polymerizable monomer corresponds to the content of each structural unit contained in 100% by mass of the binder resin.

[0110] The content of the polymerizable monomer is not particularly limited, but from the viewpoint of achieving a good balance between the low-temperature fixability and heat-resistant storage stability of the toner, it is preferably 60 parts by mass or more and 90 parts by mass or less, more preferably 65 parts by mass or more and 85 parts by mass or less, and even more preferably 70 parts by mass or more and 80 parts by mass or less, relative to 100 parts by mass of the total solid content contained in the polymerizable monomer composition. In the present disclosure, the solid content refers to all components other than the solvent, and liquid monomers and the like are also included in the solid content.

[0111] The colorant and release agent contained in the polymerizable monomer composition, as well as the charge control agent, polar resin, and styrene-based thermoplastic elastomer contained as needed, are as described above as the components contained in the colored resin particles.

[0112] The polymerizable monomer composition may further contain other additives as needed, as long as the object of the present disclosure is not impaired. For example, a molecular weight modifier can be preferably used as the other additive. The molecular weight modifier is not particularly limited as long as it is one that is generally used as a molecular weight modifier for toners. Examples include mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, and 2,2,4,6,6-pentamethylheptane-4-thiol; and thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, N,N'-dimethyl-N,N'-diphenylthiuram disulfide, and N,N'-dioctadecyl-N,N'-diisopropylthiuram disulfide. The molecular weight modifiers can be used alone or in combination of two or more. When the polymerizable monomer composition contains a molecular weight modifier, the content of the molecular weight modifier is appropriately adjusted so that the binder resin has a desired molecular weight, and is not particularly limited, but is usually 0.01 parts by mass or more and 10 parts by mass or less, and may be 0.1 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the monovinyl monomer.

[0113] The polymerizable monomer composition may further contain a polymerization initiator, which may be added to the suspension obtained in the suspension step described later. From the viewpoint of facilitating control of the molecular weight of the polymer, it is preferable to add the polymerization initiator to the suspension obtained in the suspension step described later.

[0114] For mixing when preparing the polymerizable monomer composition, a disperser such as an in-line type emulsifying disperser or a media type emulsifying disperser is used. The polymerizable monomer composition is preferably prepared, for example, by a method in which the polymerizable monomer, colorant, polar resin, molecular weight modifier, etc. are mixed using a media type disperser and wet-pulverized, and then a charge control agent, a release agent, a styrene-based thermoplastic elastomer, etc. are added and further mixed. This method makes it easy to obtain a toner having excellent low-temperature fixability, heat-resistant storage stability, and offset resistance.

[0115] (2) Suspension Step Next, a suspension step is performed to prepare a suspension in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer. In this suspension step, the polymerizable monomer composition is dispersed in an aqueous medium containing a dispersion stabilizer, a polymerization initiator is added, and then droplets of the polymerizable monomer composition are formed. The polymerization initiator may be added after the polymerizable monomer composition is dispersed in the aqueous medium and before droplet formation, or it may be added to the polymerizable monomer composition before it is dispersed in the aqueous medium. The method for forming droplets of the polymerizable monomer composition is not particularly limited, and may be performed using an apparatus capable of strong stirring, such as an (in-line type) emulsifying disperser (manufactured by Pacific Machinery Works, trade name: Milder) or a high-speed emulsifying disperser (manufactured by Primix Corporation, trade name: T.K. Homomixer MARK II Type).

[0116] Examples of the polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate; azo compounds such as 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide), 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobisisobutyronitrile; and organic peroxides such as di-t-butyl peroxide, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxy-2-ethylbutanoate, t-hexylperoxy-2-ethylbutanoate, diisopropyl peroxydicarbonate, di-t-butylperoxyisophthalate, and t-butylperoxyisobutyrate. Among these, organic peroxides are preferred because they can reduce the amount of residual polymerizable monomers and improve the printing durability of the toner. Among the organic peroxides, peroxyesters are preferred because they have good initiator efficiency and can reduce the amount of residual polymerizable monomers, and non-aromatic peroxyesters, i.e., peroxyesters without an aromatic ring, are more preferred. These polymerization initiators can be used alone or in combination of two or more.

[0117] The amount of the polymerization initiator used in the polymerization reaction of the polymerizable monomer composition is preferably 0.1 to 20 parts by mass, more preferably 0.3 to 15 parts by mass, and particularly preferably 1 to 10 parts by mass, relative to 100 parts by mass of the monovinyl monomer.

[0118] In the present disclosure, an aqueous medium refers to a medium containing water as a main component. It is preferable that the aqueous medium contains a dispersion stabilizer. In the present disclosure, an inorganic compound is used as the dispersion stabilizer. This allows colored resin particles to be produced without using a surfactant. Examples of inorganic compounds used as dispersion stabilizers include sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal hydroxides such as aluminum hydroxide, magnesium hydroxide, and ferric hydroxide; and silicon dioxide. These dispersion stabilizers can be used alone or in combination of two or more.

[0119] As the aqueous medium containing the dispersion stabilizer, a colloid of a poorly water-soluble metal hydroxide is particularly preferred. By using an inorganic compound, particularly a colloid of a poorly water-soluble metal hydroxide, as the dispersion stabilizer, the particle size distribution of the colored resin particles can be narrowed and the amount of the dispersion stabilizer remaining after washing can be reduced, so that the resulting toner can clearly reproduce images and further suppress deterioration of charging stability.

[0120] (3) Polymerization Step: After droplets of the polymerizable monomer composition are formed in the suspension step, a polymerization step is carried out to polymerize the polymerizable monomer contained in the droplets of the polymerizable monomer composition. Specifically, polymerization of the polymerizable monomer is initiated by heating the aqueous dispersion medium in which the droplets of the polymerizable monomer composition are dispersed in the presence of a polymerization initiator. The polymerizable monomer is in a phase-separated state in the droplets of the polymerizable monomer composition. By subjecting the droplets of the polymerizable monomer composition to a polymerization reaction in this state, colored resin particles with a core-shell structure having a core layer and a shell layer formed by phase separation of the binder resin are formed. The heating conditions are not particularly limited, but the heating temperature is preferably 50°C or higher, and more preferably 60 to 95°C. The heating time is preferably 1 to 20 hours, and more preferably 2 to 15 hours.

[0121] After the polymerization reaction of the polymerizable monomer, or after the polymerization reaction of the polymerizable monomer for coating in the resin coating formation step described below, an inert gas is preferably blown into the aqueous dispersion of colored resin particles at 50 to 95°C for 1 to 20 hours. This operation reduces the amount of volatile organic compounds, and the amount of volatile organic compounds when the toner is heated at 100°C for 30 minutes can be easily reduced to 150 ppm or less. The inert gas is not particularly limited, but nitrogen is preferably used. The flow rate of the inert gas is also not particularly limited, but can be, for example, 1 to 10 L / min.

[0122] (4) Resin Coating Step After the polymerization step, a resin coating step may be performed to form a resin coating on the surface of the shell layer. By coating the surface of the shell layer with a resin having a Tg exceeding 80°C, the toner's low-temperature fixability and hot offset resistance can be balanced and the toner's fixable temperature range can be expanded. There are no particular limitations on the method for forming the resin coating on the surface of the shell layer, and the toner can be produced by a conventionally known method. In situ polymerization is preferred from the viewpoint of production efficiency. The method for forming a resin coating using the in situ polymerization method is described below. Note that, when colored resin particles have a resin coating on the surface of the shell layer, the particles before the resin coating is formed are referred to as "colored resin particle precursors" to distinguish them from the colored resin particles after the resin coating is formed. By adding a polymerizable monomer for forming a resin coating (referred to as a "polymerizable monomer for coating") to an aqueous medium in which the colored resin particle precursor obtained by the polymerization step is dispersed, and polymerizing the resulting colored resin particles, the colored resin particles can be produced having a core-shell structure and a resin coating on the surface of the shell layer.

[0123] As the polymerizable monomer for the coating, a polymerizable monomer that can be used as a raw material for a polymer having a Tg of more than 80°C can be used. The polymerizable monomer for the coating can be used alone or in combination of two or more. The amount of the polymerizable monomer for the coating added is not particularly limited, but from the viewpoint of widening the fixable temperature range of the toner, it is preferably 1 to 10 parts by mass, more preferably 2 to 7 parts by mass, per 100 parts by mass of the polymerizable monomer for forming the binder resin.

[0124] A polymerization initiator may be added during polymerization of the coating polymerizable monomer. Examples of polymerization initiators used for polymerization of the coating polymerizable monomer include water-soluble polymerization initiators such as persulfates, such as potassium persulfate and ammonium persulfate; and azo compounds, such as 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide) and 2,2'-azobis(2-methyl-N-(1,1-bis(hydroxymethyl)2-hydroxyethyl)propionamide). These may be used alone or in combination of two or more. The amount of polymerization initiator is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of the coating polymerizable monomer. Alternatively, if the polymerization initiator added in the suspension step remains after the polymerization step, the polymerization of the coating polymerizable monomer can be carried out without adding a polymerization initiator.

[0125] The polymerization temperature for forming the resin coating is preferably 50° C. or higher, and more preferably 60 to 95° C. The reaction time for the polymerization for forming the resin coating is preferably 1 to 20 hours, and more preferably 2 to 15 hours.

[0126] (5) Washing, Filtration, Dehydration, and Drying Steps After the polymerization is completed, the aqueous dispersion of colored resin particles obtained by polymerization is preferably subjected to filtration, washing to remove the dispersion stabilizer, dehydration, and drying in a conventional manner, which are repeated several times as necessary.

[0127] As for the washing method, when an inorganic compound is used as the dispersion stabilizer, it is preferable to add an acid or alkali to the aqueous dispersion of the colored resin particles to dissolve and remove the dispersion stabilizer in water. When a poorly water-soluble metal hydroxide colloid is used as the dispersion stabilizer, it is preferable to add an acid to adjust the pH of the aqueous dispersion of the colored resin particles to 6.5 or less. The acid to be added may be an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, or an organic acid such as formic acid or acetic acid, but sulfuric acid is particularly preferred because of its high removal efficiency and small burden on the production equipment.

[0128] The dehydration and filtration methods can be any known method, and are not particularly limited. Examples include centrifugal filtration, vacuum filtration, pressure filtration, etc. The drying method is also not particularly limited, and various methods can be used.

[0129] 3. Toner The toner of the present disclosure is an aggregate of "toner particles." Each toner particle may consist solely of colored resin particles, or may contain colored resin particles and an external additive attached to the surface of the colored resin particles. The toner of the present disclosure may be a black toner, or a cyan, yellow, or magenta color toner. The toner of the present disclosure may be used as a one-component developer consisting solely of toner particles, or as a two-component developer in which carrier particles such as ferrite or iron powder are mixed with the toner particles.

[0130] (External Additive) From the viewpoint of adjusting the chargeability, fluidity, heat-resistant storage stability, etc. of the toner, it is preferable to mix and stir the colored resin particles with an external additive to perform an external addition treatment, thereby adhering the external additive to the surface of the colored resin particles, thereby producing the toner of the present disclosure. Examples of external additives include inorganic fine particles such as silica, titanium oxide, aluminum oxide, zinc oxide, tin oxide, calcium carbonate, calcium phosphate, cerium oxide, barium titanate, and strontium titanate; and organic fine particles such as polymethyl methacrylate resin, silicone resin, and melamine resin. Among these, inorganic fine particles are preferred, and among inorganic fine particles, at least one fine particle selected from the group consisting of silica fine particles and titanium oxide fine particles is preferred, with silica fine particles being particularly suitable. Note that these external additives can be used alone, but it is preferable to use two or more of them in combination.

[0131] The external additive preferably contains inorganic fine particles A having a number-average primary particle size of 5 nm to 14 nm and inorganic fine particles B having a number-average primary particle size of 15 nm to 90 nm. When the inorganic fine particles A and B are contained as the external additive, the mass ratio of the inorganic fine particles A to B (inorganic fine particles A:inorganic fine particles B) is not particularly limited and may be, for example, 20:80 to 80:20. The number-average primary particle size of the external additive is measured, for example, by weighing out about 0.1 g of a measurement sample, placing it in a beaker, adding 0.1 mL of an alkylbenzenesulfonic acid aqueous solution (manufactured by Fujifilm Corporation, product name: Drywell) as a dispersant, further adding 10 to 30 mL of a diluent (manufactured by Beckman Coulter, product name: Isoton II) to the beaker, and dispersing the mixture for 3 minutes using a 20 W (Watt) ultrasonic disperser. Thereafter, the number-average primary particle size is measured using a particle size distribution analyzer (manufactured by Beckman Coulter, product name: Multisizer) under the conditions of an aperture diameter of 100 μm, a medium: Isoton II, and a measurement particle count of 100,000.

[0132] The agitator used for the external addition treatment is not particularly limited as long as it is an agitator that can adhere an external additive to the surface of the colored resin particles. For example, the external addition treatment can be performed using an agitator that is capable of mixing and stirring, such as an FM Mixer (trade name, manufactured by Nippon Coke and Engineering Co., Ltd.), a Super Mixer (trade name, manufactured by Kawada Manufacturing Co., Ltd.), a Q Mixer (trade name, manufactured by Nippon Coke and Engineering Co., Ltd.), a Mechanofusion System (trade name, manufactured by Hosokawa Micron Corporation), and a Mechano Mill (trade name, manufactured by Okada Seiko Co., Ltd.).

[0133] In the toner of the present disclosure, the external additive is typically used in an amount of 0.05 to 6 parts by mass, preferably 0.2 to 5 parts by mass, and more preferably 0.5 to 4 parts by mass, relative to 100 parts by mass of the colored resin particles. When the content of the external additive is equal to or greater than the lower limit, the occurrence of transfer residue can be suppressed, and when the content of the external additive is equal to or less than the upper limit, the occurrence of fogging can be suppressed.

[0134] (Physical Properties of Toner) From the viewpoint of image reproducibility, the average circularity of the toner of the present disclosure is preferably 0.960 or more, more preferably 0.970 or more, and even more preferably 0.980 or more. On the other hand, from the viewpoint of ease of production, it is preferably 0.995 or less, more preferably 0.990 or less. When the average circularity of the toner particles is equal to or greater than the above lower limit, the reproducibility of thin lines in print can be improved. The average circularity of the toner particles is 1 or less, and when the measurement sample is a perfect sphere, the average circularity is 1. In the present disclosure, circularity is the value obtained by dividing the perimeter of a circle having the same projected area as the particle image by the perimeter of the projected image of the particle. The average circularity is an index indicating the degree of unevenness on the surface of the measurement sample and can be used as a simple method for quantitatively expressing the shape of particles. The more complex the surface shape of the measurement sample, the smaller the average circularity value. The circularity of the toner particles can be determined, for example, by using an aqueous solution in which toner particles are dispersed as a sample liquid, taking a projected image of the toner particles in the sample liquid using a flow particle image analyzer (for example, manufactured by CIMEX Corporation, product name: FPIA-3000, etc.), measuring the perimeter of a circle equal to the projected area of ​​the particle and the perimeter of the projected image of the particle from the projected image, and then using the following calculation formula 1. The average circularity is the average value of the circularities of 4,000 to 8,000 toner particles. Calculation formula 1: (Circularity) = (Perimeter of a circle equal to the projected area of ​​the particle) / (Perimeter of the projected image of the particle)

[0135] The toner of the present disclosure has a volatile organic compound content of 150 ppm or less when heated at 100°C for 30 minutes. This suppresses odor generation during printing. To further suppress odor generation during printing, the volatile organic compound content is preferably 140 ppm or less, more preferably 130 ppm or less. For example, the colored resin particles contained in the toner can be produced by a suspension polymerization method that does not use a surfactant, and the amount of volatile organic compounds can be reduced to the above upper limit or less by introducing an inert gas into the aqueous dispersion of the colored resin particles obtained after polymerization at a high temperature. Furthermore, when the amount of volatile organic compounds is less than the above upper limit, the amount of surfactant contained in the toner is sufficiently small, so that the hydrophilicity of the toner particle surfaces is not excessively high, thereby suppressing a decrease in the charging stability of the toner.

[0136] The present disclosure will be further described in detail below with reference to examples and comparative examples, but the present disclosure is not limited to these examples. Note that parts and percentages are by mass unless otherwise specified. Furthermore, the weight-average molecular weight Mw and number-average molecular weight Mn of the resin were determined in polystyrene equivalent terms by GPC. The sample for measurement was prepared by dissolving the polymer in tetrahydrofuran (THF) to a concentration of 2 mg / mL, sonicating for 10 minutes, and then passing the solution through a 0.45 μm membrane filter. The measurement conditions were: temperature: 40°C, solvent: tetrahydrofuran, flow rate: 1.0 mL / min, concentration: 0.2 wt%, sample injection volume: 100 μL, and a GPC TSKgel Multipore HXL-M (30 cm x 2 columns) manufactured by Tosoh Corporation was used.

[0137] [Production Example 1: Production of Polar Resin 1] 200 parts of toluene were added to a reaction vessel, and the atmosphere in the reaction vessel was thoroughly replaced with nitrogen while stirring the toluene. The toluene was then heated to 90 ° C. Subsequently, a mixed solution of 96.2 parts of methyl methacrylate (MMA), 3.5 parts of ethyl acrylate (EA), 0.4 parts of acrylic acid (AA), and 2.8 parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O) was added dropwise to the reaction vessel over 2 hours. The mixture was then maintained under toluene reflux for 10 hours to complete the polymerization, and the solvent was then distilled off under reduced pressure. In this way, polar resin 1 (Tg 78 ° C, acid value 2.4 mg KOH / g, weight average molecular weight Mw 12500), an acrylic resin (MMA / EA / AA copolymer), was obtained.

[0138] Example 1 1. Production of Colored Resin Particles (1) Preparation of Polymerizable Monomer Composition 20 parts of 3,4-dimethoxystyrene, 50 parts of styrene, and 30 parts of n-butyl acrylate were used as the binder resin monovinyl monomer raw materials, 0.5 parts of divinylbenzene as a crosslinkable polymerizable monomer, 9 parts of carbon black (manufactured by Mitsubishi Chemical Corporation, product name: #25B) as a black colorant, 1.0 part of t-dodecyl mercaptan as a molecular weight modifier, and 1.0 part of the polar resin 1 obtained in Production Example 1 were mixed and wet-pulverized using a media-type emulsifying disperser. Subsequently, 1.5 parts of a styrene-acrylic resin containing a quaternary ammonium salt (copolymerization ratio of a monomer containing a quaternary ammonium salt group: 2.00% by mass, Tg: 70°C) as a positively charged charge control resin, and behenyl stearate (molecular formula: C) as a mold release agent were added. １７ H ３５ -COO-C ２２ H ４５ 20 parts of a copolymer of 2,4-dimethylaminopropanediol (a copolymer of 2,4-dimethylaminopropanediol, melting point: 70°C, acid value: 0.1 mgKOH / g, hydroxyl value: 0.3 mgKOH / g, esterification rate: 98%) and 3.0 parts of a styrene-based thermoplastic elastomer (styrene-isoprene-styrene type block copolymer, styrene monomer unit content: 24 mass%, weight average molecular weight Mw: 106,000, manufactured by Zeon Corporation) were further added and mixed to obtain a polymerizable monomer composition.

[0139] (2) Suspension Step On the other hand, in a stirring tank at room temperature, an aqueous solution prepared by dissolving 4.1 parts of sodium hydroxide in 50 parts of ion-exchanged water was gradually added under stirring to an aqueous solution prepared by dissolving 7.4 parts of magnesium chloride in 250 parts of ion-exchanged water, to prepare a magnesium hydroxide colloidal dispersion (3.0 parts of magnesium hydroxide).

[0140] The polymerizable monomer composition was added to the magnesium hydroxide colloidal dispersion obtained above at room temperature and stirred until droplets were stabilized. Five parts of t-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, product name: Perbutyl O) was added as a polymerization initiator thereto, and then the mixture was stirred with high shear at a rotation speed of 15,000 rpm using an in-line emulsifying disperser (manufactured by Pacific Machinery Works, Ltd., product name: Milder) to form droplets of the polymerizable monomer composition, thereby obtaining a suspension in which droplets of the polymerizable monomer composition were dispersed.

[0141] (3) Polymerization step The suspension obtained above was placed in a reactor equipped with a stirring blade, and the temperature was raised to 90°C to initiate the polymerization reaction. The polymerization reaction was continued until the polymerization conversion rate of the polymerizable monomer reached approximately 100%, thereby obtaining a colored resin particle precursor.

[0142] (4) Resin Coating Formation Step: When the polymerization conversion rate of the polymerizable monomer reached nearly 100% in the polymerization step, 3.0 parts of methyl methacrylate was added to the reactor as a polymerizable coating monomer. The temperature was then maintained at 90°C for another 3 hours to continue polymerization, thereby forming a resin coating on the surface of the colored resin particle precursor. Next, nitrogen was blown into the reactor at a rate of 3 L / min while maintaining the temperature at 90°C for 10 hours to remove volatile organic compounds, and the reaction was stopped by water cooling to obtain an aqueous dispersion of colored resin particles.

[0143] (4) Washing, Filtration, Dehydration, and Drying Steps While stirring the aqueous dispersion of colored resin particles obtained above at room temperature, sulfuric acid was added dropwise to the aqueous dispersion, and acid washing was performed until the pH reached 6.5 or less. Next, filtration and separation were performed, and 500 parts of ion-exchanged water was added to the obtained solid to re-slurry it, and the water washing treatment (washing, filtration, and dehydration) was repeated several times. Next, filtration and separation were performed, and the obtained solid was placed in a container of a dryer and dried at 45°C for 48 hours to obtain dried colored resin particles.

[0144] 2. Toner Production To 100 parts of dried colored resin particles, 0.7 parts of silica fine particles A having a number-average primary particle size of 10 nm and 1 part of silica fine particles B having a number-average primary particle size of 55 nm that had been hydrophobized with amino-modified silicone oil were added, and the mixture was mixed using a high-speed mixer (manufactured by Nippon Coke and Engineering Co., Ltd., product name: FM Mixer) to carry out external addition treatment, thereby producing the toner of Example 1.

[0145] [Examples 2 to 7 and Comparative Example 1] Toners of Examples 2 to 7 and the toner of Comparative Example 1 were obtained in the same manner as in Example 1, except that the amounts of 3,4-dimethoxystyrene, styrene, behenyl stearate, or styrene-based thermoplastic elastomer added were changed according to Table 2.

[0146] Example 8 A toner of Example 8 was obtained in the same manner as in Example 1, except that 5 parts of 3,4-diacetoxystyrene and 15 parts of 3-methoxy-4-acetoxystyrene were used instead of 20 parts of 3,4-dimethoxystyrene.

[0147] Comparative Example 2 Comparative Example 2 was carried out by the following procedure similar to that of Example 15 of Patent Document 1. (1) Preparation of Binder Resin Particle Dispersion C2 A surfactant solution prepared by dissolving 8 parts of sodium dodecyl sulfate in 3 L of ion-exchanged water was placed in a 5 L stainless steel kettle (SUS kettle) equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introducing device, and the liquid temperature was raised to 80° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream. To this surfactant solution, an initiator solution prepared by dissolving 10 parts of potassium persulfate in 200 parts of ion-exchanged water was added, and the temperature was raised to 80°C. Then, the following monomer mixture was added dropwise over 100 minutes, and the system was heated and stirred at 80°C for 2 hours to carry out polymerization, thereby preparing binder resin particle dispersion C2: <Monomer mixture> 3,4-dimethoxystyrene 534 parts n-butyl acrylate 186 parts methyl methacrylate 40 parts methacrylic acid 44 parts n-octyl-3-mercaptopropionate 5.5 parts

[0148] (2) Preparation of Colorant Dispersion C2 Carbon black 10 parts 20% aqueous solution of sodium dodecylbenzenesulfonate (anionic surfactant) 1.5 parts Ion-exchanged water 90 parts The above components were mixed and dispersed in an SC mill to obtain Colorant Dispersion C2.

[0149] (3) Preparation of release agent dispersion C2 Behenyl stearate 100 parts Sodium dodecyl sulfate 5 parts Ion-exchanged water 240 parts The above components were dispersed in a round stainless steel flask for 10 minutes using a homogenizer, and then the dispersion was carried out using a pressure discharge homogenizer, thereby obtaining a release agent dispersion C2.

[0150] (4) Preparation of Colored Resin Particle Dispersion C2 Binder Resin Particle Dispersion C2 237 parts Colorant Dispersion C2 42 parts Release Agent Dispersion C2 162 parts Polyaluminum Chloride 1.8 parts Ion-exchanged water 600 parts The above components were mixed and dispersed in a round stainless steel flask using a homogenizer. The flask was then heated to 55°C in a heating oil bath with stirring and maintained at 55°C for 30 minutes. The temperature of the heating oil bath was then increased to 56°C and maintained at 56°C for 2 hours. After that, 1 mol / L sodium hydroxide was added to the system to adjust the pH to 5.0, and the stainless steel flask was sealed using a magnetic seal and heated to 98°C with continued stirring. Stirring was continued for 6 hours to prepare Colored Resin Particle Dispersion C2.

[0151] (5) Washing and drying step The colored resin particle dispersion C2 was subjected to solid-liquid separation using a basket centrifuge to form a wet cake of colored resin particles C2. The wet cake was washed with ion-exchanged water at 45°C using the basket centrifuge until the electrical conductivity of the filtrate reached 5 μS / cm, and then dried until the water content reached 0.5% by mass, thereby obtaining colored resin particles C2.

[0152] (6) External Addition Treatment To 100 parts by mass of colored resin particles C2, 1 part by mass of hydrophobic silica (number average primary particle diameter: 12 nm) and 0.3 parts by mass of hydrophobic titania (number average primary particle diameter: 20 nm) were added, and the mixture was mixed using a high-speed stirrer to perform external additive treatment, thereby obtaining toner C2 of Comparative Example 2.

[0153] Comparative Example 3 A toner of Comparative Example 3 was obtained in the same manner as in Example 1, except that the amount of 3,4-dimethoxystyrene added was changed according to Table 2 and 3,4-dihydroxystyrene was added to the polymerizable monomer composition according to Table 2.

[0154] The SP values ​​of the polymerizable monomers used in each example or comparative example are as follows: 3,4-dimethoxystyrene: 9.11 3,4-diacetoxystyrene: 11.3 3-methoxy-4-acetoxystyrene: 10.3 3,4-dihydroxystyrene: 12.4 Styrene: 8.93 n-butyl acrylate: 8.69 Divinylbenzene: 8.43

[0155] [Measurement and Evaluation] (1) Volume Average Particle Size (Dv) of Colored Resin Particles Approximately 0.1 g of the colored resin particles used in the production of the toner was weighed and placed in a beaker, and 0.1 mL of a surfactant aqueous solution (manufactured by Fujifilm Corporation, product name: Drywell) was added as a dispersant. 10 to 30 mL of Isoton II was further added to the beaker, and the mixture was dispersed for 3 minutes using a 20 W (Watt) ultrasonic disperser. Then, the volume average particle size (Dv) of the colored resin particles was measured using a particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name: Multisizer) under the following conditions: aperture diameter: 100 μm, medium: Isoton II, and number of particles measured: 100,000.

[0156] (2) Cross-sectional Observation of Colored Resin Particles by TEM The colored resin particles used in toner production were mixed with a two-component condensation epoxy adhesive (product name: Quick 5, manufactured by Konishi) and cured to obtain a cured product. The resulting cured product was cut into thin sections using a microtome, and the thin sections were stained with vapor of a 0.5% aqueous solution of ruthenium tetroxide for approximately 5 minutes to prepare a cross-sectional observation sample. The cross-sectional observation sample was then observed using a transmission electron microscope (TEM) at a magnification of 5,000 to 6,000x, adjusting the concentration of the colored resin particles so that the cross sections of 3 to 10 colored resin particles could be observed within a 28 μm x 35 μm area. TEM images of the cross sections of the colored resin particles were obtained by observing the sample at a magnification of 5,000 to 6,000x. As an example, a TEM image of the cross section of the colored resin particles prepared in Example 1 is shown in Figure 2. In the TEM image shown in Figure 2, the domains of the release agent are distinguished as white domains. The TEM image of the cross section of the colored resin particle was analyzed using image analysis software (trade name: DNP particle image analysis software, manufactured by Dai Nippon Printing Co., Ltd.) under the condition of an image resolution of 0.037 μm / pixel, to determine the thickness ratio of the shell layer, the average total area ratio of the domains of the release agent, the average number of domains of the release agent present, and the average number ratio of domains present near the center. Note that, in the measurement, colored resin particles whose cross-sectional equivalent circle diameter is within ±3 μm relative to the volume average particle diameter (Dv) of the colored resin particle were used as the measurement object, and the measurement of the domains of the release agent was performed at a resolution of 0.02 μm. ２ The domains with cross-sectional areas of 1000 or more were targeted.

[0157] (2-1) Shell Layer Thickness Ratio For the cross sections of 100 or more colored resin particles, the ratio (t / r) of the shell layer thickness t to the distance r from the geometric center 10C of the cross section to the outline 10L was determined, and the average of the ratios (t / r) determined for each colored resin particle was calculated to be the shell layer thickness ratio. Note that the colored resin particles of the toner obtained in Comparative Example 1 and the toner obtained in Comparative Example 2 did not have a core-shell structure, and so a shell layer could not be confirmed.

[0158] (2-2) Average Total Area Ratio of Domains of Release Agent One hundred or more colored resin particles were measured, and the sum of the cross-sectional areas of the colored resin particles measured and the sum of the areas of the domain portions of the release agent present in the cross-sections of the colored resin particles measured were determined. The ratio of the sum of the areas of the domain portions of the release agent to the sum of the cross-sectional areas of the colored resin particles was calculated, and this was taken as the average total area ratio (%) of the domains of the release agent.

[0159] (2-3) Average Number of Domains of Release Agent 100 or more colored resin particles were measured, and the total number of domains of the release agent present in the cross section of the colored resin particles measured was divided by the number of colored resin particles measured to determine the average number of domains of the release agent present per particle.

[0160] (2-4) Average Number Proportion Present Near the Center 100 or more colored resin particles were used as the measurement object, and the total number of domains of the release agent present within an area that is 80% or less of the distance r from the geometric center 10C of the cross section of the colored resin particle to the outline 10L and the total number of domains of the release agent present on the cross section of the colored resin particle were calculated. The total number of domains of the release agent present in the area was divided by the total number of domains of the release agent present on the cross section of the colored resin particle to calculate the average number proportion (%) present near the center.

[0161] (3) Average Circularity 10 mL of ion-exchanged water was placed in a container, 0.02 g of a surfactant (alkylbenzene sulfonic acid) was added as a dispersant, and 0.02 g of toner was then added. The mixture was dispersed in an ultrasonic disperser at 60 W (Watt) for 3 minutes. The toner particle concentration at the time of measurement was adjusted to 3,000 to 10,000 particles / μL, and the circularity of 4,000 to 8,000 toner particles with a circle-equivalent diameter of 0.4 μm or more was measured using a flow particle image analyzer (manufactured by CIMEX Corporation, product name: FPIA-3000). The average circularity was calculated from the measured values. The circularity is calculated using the following formula 1, and the average circularity was calculated as the average value. Formula 1: (Circularity) = (Perimeter of a circle equal to the projected area of ​​the particle) / (Perimeter of the projected image of the particle).

[0162] The solid black printing performed in the evaluations (4) to (6) below was performed by printing a 5 cm square solid black print (print density 100%) on printing paper. The printing performed in the evaluations below was performed at a resolution of 600 dpi and a printing speed of 30 sheets / minute, and Vitality (trade name) manufactured by Xerox was used as the printing paper.

[0163] (4) Fixable Temperature Range The difference between the temperature at which hot offset occurs and the minimum fixing temperature of the toner is defined as the fixable temperature range of the toner.

[0164] (4-1) Minimum Fixing Temperature A fixing test was conducted using a commercially available non-magnetic single-component development printer modified to allow the temperature of the fixing roll to be changed. In the fixing test, the temperature of the fixing roll of the modified printer was changed in 5°C increments, a solid black print was performed, and the toner fixation rate at each temperature was measured to determine the temperature-fixation rate relationship. The fixation rate was calculated by tape-peeling the solid black print area from the ratio of image density before and after tape-peeling. That is, the image density before tape-peeling was designated ID(before) and the image density after tape-peeling was designated ID(after), and the fixation rate was calculated using the following formula: Fixation Rate (%) = (ID(after) / ID(before)) x 100. The tape-peeling operation involved a series of steps: applying adhesive tape (manufactured by Sumitomo 3M Limited, trade name: Scotch Mending Tape 810-3-18) to the measurement portion of the test paper, pressing it down with a constant pressure to adhere it, and then peeling the adhesive tape at a constant speed in the direction parallel to the paper. The image density was measured using a reflection type image densitometer (manufactured by Macbeth, product name: RD914). In this fixing test, the lowest fixing roll temperature at which the fixing rate exceeded 80% was defined as the minimum fixing temperature of the toner.

[0165] (4-2) Hot Offset Occurrence Temperature A hot offset test was conducted using a commercially available printer with a non-magnetic single-component development system, modified so that the temperature of the fixing roll could be changed. In the hot offset test, the temperature of the fixing roll was changed from 150°C to 220°C in 5°C increments, a solid black print was made, and the occurrence of the hot offset phenomenon, such as the occurrence of toner fusion to the fixing roll, was visually confirmed. In this hot offset test, the lowest set temperature at which toner fusion to the fixing roll occurred was defined as the toner hot offset occurrence temperature.

[0166] (4-3) Evaluation of Fixable Temperature Range The difference between the temperature at which hot offset occurs and the minimum fixing temperature of the toner was calculated as the fixable temperature range of the toner, and evaluated according to the following evaluation criteria. The larger the fixable temperature range of the toner, the more fixable the toner is, even if the temperature hunting of the fixing roller is large. (Evaluation criteria) A: 40°C or higher B: More than 25°C and less than 40°C C: 25°C or lower

[0167] (5) Printing performance after storage in developing machine The toner was filled into the developing machine of a commercially available printer using a non-magnetic single-component development method, and three black solid prints were made in an environment of 23°C and 50% RH. The developing machine was then removed from the printer and left in a thermo-hygrostat at 50°C and 80% RH for 30 days. The developing machine was then removed from the thermo-hygrostat and reinstalled in the printer, and black solid prints were made in an environment of 23°C and 50% RH. The presence or absence of horizontal streaks in the black solid print was visually confirmed and evaluated according to the following evaluation criteria. The less horizontal streaks were observed in the black solid print, the more suppressed the occurrence of printing defects after storing the toner in the developing machine for a long period of time. (Evaluation criteria) A: No horizontal streaks were observed B: Faint horizontal streaks were observed C: Clear horizontal streaks were observed

[0168] (6) Odor Sensory Test The toner was filled into the developing machine of a commercially available printer using a non-magnetic single-component development method, and a solid black print was performed in an environment of 23°C and 50% RH. The odor intensity emitted from the printer fan during printing was judged according to the following criteria. The odor intensity was judged by eight panelists, and the rank given by the largest number of panelists was taken as the evaluation result of the odor sensory test for that toner. (Judgment Criteria) A: Barely detectable odor B: Easily detectable odor C: Strong odor

[0169] (7) Charge Stability After filling the developer of a commercially available non-magnetic single-component development printer with toner, printing paper was set and the printer was left overnight in an environment (LL environment) at a temperature of 10°C and a humidity of 20% RH. Then, under the LL environment, one solid white print (print density 0%) was performed. The printer was stopped midway through the solid white print, and the toner carried on the development roller was sucked using a suction-type charge measurement device (manufactured by Trek Japan, product name: 210HS-2A) to measure the charge amount of the toner. From the measured charge amount of the toner, the charge amount per unit mass of the toner was calculated, and this was used as the initial charge amount (μC / g) under the LL environment. Meanwhile, after filling the developer of a commercially available non-magnetic single-component development printer with toner, printing paper was set and the printer was left overnight in an environment (HH environment) at a temperature of 35°C and a humidity of 80% RH, the charge amount was measured under the HH environment in the same manner as described above. From the measured charge amount of the toner, the charge amount per unit mass of the toner was calculated and taken as the initial charge amount (μC / g) in the HH environment. Evaluation was made according to the following evaluation criteria based on the difference between the initial charge amount in the LL environment and the initial charge amount in the HH environment. The smaller the difference, the better the toner's stability of charge amount against changes in the environment (temperature and humidity). (Evaluation criteria) A: 20 μC / g or less B: More than 20 μC / g but less than 40 μC / g C: 40 μC / g or more

[0170] (8) Amount of VOCs Emitted: 0.1 g of toner was placed in a purge container, and while helium gas was flowing at 50 mL / min as a carrier gas, the purge container was heated from room temperature at a rate of 40°C / min. The temperature was raised to 100°C and maintained at 100°C for 30 minutes. The volatile components generated were collected in a trap tube at -130°C. Next, the trap tube containing the collected volatile components was heated from -130°C to 280°C at a rate of 50°C / min. The peaks in the range of C7 to C16 were integrated using a gas chromatograph under the following conditions to determine the total amount (ppm), which was used as the amount of volatile organic compounds (VOCs) generated. (Gas Chromatography Conditions) Column temperature: 50°C (held for 2 minutes) to 270°C (heating rate: 10°C / min) Sample inlet temperature: 280°C Detection temperature: 280°C Carrier gas: Helium gas, Flow rate: 1 mL / min

[0171]

[0172] [Discussion] The toner of Comparative Example 1 contained a binder resin that did not contain the structural unit represented by the general formula (1) and the colored resin particles did not have a core-shell structure, so that the toner was prone to print defects after long-term storage in a developing machine. The toner of Comparative Example 2 contained a binder resin that contained the structural unit represented by the general formula (1), but the colored resin particles did not have a core-shell structure, so that the toner was prone to print defects after long-term storage in a developing machine. In addition, the toner of Comparative Example 2 was produced by an emulsion polymerization aggregation method using a surfactant and further contained 5.5% by mass of a structural unit having a carboxy group per 100% by mass of the binder resin, which resulted in high hydrophilicity of the toner particle surface and poor charge stability. In addition, the toner of Comparative Example 2 was produced by an emulsion polymerization aggregation method using a surfactant, so that a large amount of volatile organic compounds was generated, resulting in an odor during printing. Furthermore, the toner of Comparative Example 2 did not contain a resin coating, polar resin, or styrene-based thermoplastic elastomer that coated the surface of the shell layer of the colored resin particles, and therefore had a narrow fixable temperature range. The toner of Comparative Example 3 contained 1.0% by mass of a structural unit having a hydroxy group per 100% by mass of binder resin, which resulted in high hydrophilicity of the toner particle surface and poor charge stability. Furthermore, the toner of Comparative Example 3 was prone to printing defects after long-term storage in a developing machine. Although the toner of Comparative Example 3 had a core-shell structure for the colored resin particles, the hydroquinone structure of the 3,4-dihydroxystyrene acted as a polymerization inhibitor, preventing the polymerization reaction from proceeding sufficiently, presumably resulting in deformation of the toner particles. Furthermore, the toner of Comparative Example 3 emitted a large amount of volatile organic compounds and emitted an odor during printing. This is presumably due to the hydroquinone structure of the 3,4-dihydroxystyrene acting as a polymerization inhibitor, leaving a large amount of unreacted polymerizable monomer.

[0173] In contrast, the toners of Examples 1 to 8 are toners according to the present disclosure, in which the binder resin contains a structural unit represented by the general formula (1), the content of structural units having at least one polar group selected from the group consisting of a carboxy group and a hydroxy group is 0.10% by mass or less relative to 100% by mass of the binder resin, the colored resin particles have a core-shell structure having a core layer and a shell layer, and the amount of volatile organic compounds when the toner is heated at 100°C for 30 minutes is 150 ppm or less, and they are toners that are less likely to cause printing defects even after long-term storage in a developing machine, are less likely to emit odors during printing, and have excellent charge stability. Furthermore, the toners of Examples 1 to 8 have a wide fixable temperature range and are capable of dealing with increased temperature hunting during fixing, i.e., are toners that can deal with increased machine speeds.

[0174] 1 Core layer 2 Shell layer 3 Domain of release agent 3C Geometric center of domain of release agent 10 Colored resin particle 10L Outline of cross section of colored resin particle 10C Geometric center of cross section of colored resin particle r Distance from geometric center 10C to outline 10L

Claims

1. A toner for developing electrostatic images, comprising colored resin particles including a binder resin, a colorant and a release agent, wherein the binder resin comprises a structural unit represented by the following general formula (1), the content of structural units having at least one polar group selected from the group consisting of a carboxy group and a hydroxy group is 0.10 mass% or less in 100 mass% of the binder resin, the colored resin particles have a core-shell structure having a core layer and a shell layer, and the amount of volatile organic compounds when the toner is heated at 100°C for 30 minutes is 150 ppm or less. (In general formula (1), R １ and R ２ are each independently a methyl group or an acetyl group.

2. The toner for developing electrostatic images according to claim 1, wherein the core layer and the shell layer are formed by phase separation of the binder resin.

3. The toner for developing electrostatic images according to claim 1 or 2, wherein, in a cross section of the colored resin particle observed by a transmission electron microscope, the average ratio (t / r) of the thickness t of the shell layer to the distance r from the geometric center to the outline of the cross section is 0.05 or more and 0.50 or less.

4. The toner for developing electrostatic images according to claim 1 or 2, wherein in a cross section of the colored resin particle observed by a transmission electron microscope, domains of the release agent are present, the average total area ratio of the domains is 10 to 30%, the average number of the domains present per particle is 10 to 40, and the average number ratio of the domains present within an area that is 80% or less of the distance r from the geometric center of the cross section to the contour is 80% or more.

5. The toner for developing an electrostatic image according to claim 1 or 2, wherein the toner has an average circularity of 0.960 or more and 0.995 or less.

6. The toner for developing electrostatic images according to claim 1 or 2, wherein the colored resin particles further contain a polar resin having an acid value of 0.5 to 20 mgKOH / g.

7. The toner for developing electrostatic images according to claim 6, wherein said polar resin is an acrylic resin.

8. The toner for developing electrostatic images according to claim 1 or 2, wherein the colored resin particles further contain a styrene-based thermoplastic elastomer.

9. A method for producing a toner for developing electrostatic images according to claim 1 or 2, comprising the steps of: preparing a polymerizable monomer composition containing a polymerizable monomer, a colorant and a release agent; preparing a suspension in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer; and polymerizing the polymerizable monomer contained in the droplets of the polymerizable monomer composition, wherein the polymerizable monomer comprises a styrene-based monovinyl monomer represented by the following general formula (1A): and the dispersion stabilizer is an inorganic compound. (In general formula (1A), R １ and R ２ are each independently a methyl group or an acetyl group.

Images