Positively charged toner and two-component developer containing positively charged toner

Abstract

The present invention provides a positively charged toner and a two-component developer containing the positively charged toner, which suppress the generation of UFP due to the thermal decomposition of the mold release agent component, and which have excellent electrostatic stability, transfer characteristics, and drum cleaning properties. [Solution] The positively charged toner consists of toner particles comprising toner matrix particles and an external additive. The toner matrix particles contain at least a binder resin, a colorant, and a release agent. The external additive contains inorganic particles and resin particles. The resin particles contain a cationic surfactant, have a volume-average particle diameter of 40 nm to 110 nm, and have a hardness of 1 μN or more when measured with a probe displacement of 40 nm. When the difference between the SP value of the release agent and the SP value of the resin particles is ΔSP1, and the difference between the SP value of the binder resin and the SP value of the resin particles is ΔSP2, then 0.8 ≤ ΔSP1 ≤ 1.1 (cal / cm 3 ) 1 / 2 , 1.3 ≤ ΔSP2 ≤ 1.6 (cal / cm 3 ) 1 / 2 It satisfies the condition.

Description

Technical Field

[0001] The present invention relates to a positively charged toner for developing an electrostatic latent image and a two-component developer containing the positively charged toner.

Background Art

[0002] Generally, in electrophotography, after the surface of an electrostatic latent image carrier is charged by corona discharge or the like, it is exposed by a laser or the like to form an electrostatic latent image. The formed electrostatic latent image is developed with toner to form a toner image. Further, the formed toner image is transferred to a recording medium to obtain a high-quality image. Usually, for the toner applied to such electrophotography, after mixing a colorant, a charge control agent, a release agent, etc. with a binder resin such as a thermoplastic resin, kneading, pulverizing, and classifying are performed to obtain toner particles (toner mother particles).

[0003] With the recent trend of lowering the melting point of toner, when the toner is heated in the fixing unit, the components of the binder resin and the release agent (wax) are thermally decomposed and volatilized, becoming a source of ultra-fine particles (UFP; Ultra Fine Particle).

[0004] Patent Document 1 discloses an electrostatic charge developing toner in which the melting peak temperature Tmc derived from a crystalline polyester resin, the melting peak temperature Tmw derived from a release agent, and the glass transition point Tg of the toner are in a specific range and satisfy Tg < Tmw ≤ Tmc. In Patent Document 1, excellent low-temperature fixing properties are achieved while ensuring fixing separation properties, suppressing the generation of UFP and the occurrence of gloss unevenness.

[0005] Patent Document 2 discloses that in the cross-section of a resin particle including an embedded portion embedded in the surface of a toner mother particle and a protruding portion protruding to the outside in the radial direction of the toner mother particle, when the maximum length of the embedded portion in the radial direction of the toner mother particle is LA and the maximum length of the protruding portion in the radial direction of the toner mother particle is LB, the relationship of 0.50 ≤ LA / (LA + LB) ≤ 0.80 is satisfied. When the SP value of the binder resin contained in the toner mother particle is SPT and the SP value of the resin constituting the resin particle is SPE, 0.3 (cal / cm3 ) 1 / 2 ≦ |SPT - SPE| ≦ 0.5 (cal / cm 3 ) 1 / 2 A toner satisfying the following relationship is described. In Patent Document 2, by designing toner particles so as to satisfy the above conditions, the charging stability and heat-resistant storage stability of the toner are improved.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In order to satisfy Tg < Tmw ≦ Tmc as in Patent Document 1, it is necessary to make Tmc higher than Tmw. Therefore, there is a problem that the melting temperature of the toner becomes high and low-temperature fixing in the fixing unit becomes difficult.

[0008] In the toner of Patent Document 2, resin particles are likely to be buried in toner mother particles due to mechanical stress or environmental changes, and it becomes difficult to maintain the above relationship as the number of printed sheets increases. As a result, there is a problem that stable charging characteristics cannot be maintained over a long period of time.

[0009] In view of the above problems, an object of the present invention is to provide a positively charged toner that suppresses the generation of UFPs due to thermal decomposition of a release agent and has excellent charging stability, transfer characteristics, and drum cleaning properties, and a two-component developer containing the positively charged toner.

Means for Solving the Problems

[0010] To achieve the above object, a first configuration of the present invention is a positively charged toner composed of toner particles containing toner mother particles and external additives. The toner mother particles contain at least a binder resin, a colorant, and a release agent. The external additives adhere to the surface of the toner mother particles. The external additives contain inorganic particles and resin particles. The resin particles contain a cationic surfactant, have a volume average particle diameter of 40 nm or more and 110 nm or less, and have a hardness of 1 μN or more when measured with a probe displacement of 40 nm. When the difference between the SP value of the release agent and the SP value of the resin particles is ΔSP1, and the difference between the SP value of the binder resin and the SP value of the resin particles is ΔSP2, the following formulas (1) and (2) are satisfied. 0.8 ≦ ΔSP1 ≦ 1.1 (cal / cm 3 ) 1 / 2 ···(1) 1.3 ≦ ΔSP2 ≦ 1.6 (cal / cm 3 ) 1 / 2 ···(2)

Effects of the Invention

[0011] According to the first configuration of the present invention, the generation of UFPs due to the thermal decomposition of the release agent can be suppressed, and a positively charged toner having excellent charge stability, transfer characteristics, and drum cleaning properties can be obtained.

Brief Description of the Drawings

[0012] [Figure 1] A diagram showing an example of the cross-sectional structure of toner 101 used in the two-component developer of the present invention

Embodiments for Carrying Out the Invention

[0013] Embodiments of the present invention will be described in detail below. Unless otherwise specified, the evaluation results (values ​​indicating shape or physical properties, etc.) for the powder (more specifically, toner core particles, toner mother particles, external additives, or toner, etc.) are the number average values ​​of the values ​​measured for each of the average particles selected from the powder. Unless otherwise specified, the number average particle diameter of the powder is the number average value of the equivalent circle diameter (the diameter of a circle having the same area as the projected area of ​​the particle) of the primary particles measured using a microscope. Unless otherwise specified, the measured value of the median volume diameter (D50) of the powder is the value measured using a laser diffraction / scattering particle size distribution analyzer ("LA-750" manufactured by Horiba, Ltd.). Unless otherwise specified, the measured values ​​of the acid value and hydroxyl value are the values ​​measured according to "JIS (Japanese Industrial Standards) K0070-1992". Furthermore, unless otherwise specified, the measured values ​​for number-average molecular weight (Mn) and mass-average molecular weight (Mw) are those obtained using gel permeation chromatography.

[0014] The softening point (Tm), unless otherwise specified, is the value measured using a high-temperature flow tester (Shimadzu Corporation "CFT-500D"). In the S-curve (horizontal axis: temperature, vertical axis: stroke) measured by the high-temperature flow tester, the temperature at which "(baseline stroke value + maximum stroke value / 2)" corresponds to Tm (softening point). The melting point (Mp), unless otherwise specified, is the temperature of the maximum endothermic peak in the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) measured using a differential scanning calorimeter (Seiko Instruments Inc. "DSC-6220"). This endothermic peak is due to the melting of the crystallized portion. It appears as follows. Unless otherwise specified, the glass transition temperature (Tg) is the value measured using a differential scanning calorimeter (Seiko Instruments Inc. "DSC-6220") in accordance with "JIS (Japanese Industrial Standards) K7121-2012". In the endothermic curve measured by the differential scanning calorimeter (vertical axis: heat flow (DSC signal), horizontal axis: temperature), the temperature at the inflection point due to the glass transition (more specifically, the temperature at the intersection of the baseline extrapolation line and the falling line extrapolation line) corresponds to Tg (glass transition temperature).

[0015] The SP value (solubility parameter) is a parameter defined by the formula "SP value = (E / V) 1 / 2 " (E: cohesive energy [cal / mol], V: molar volume [cm 3 / mol]), and if not otherwise specified, it is the value calculated according to Fedors' calculation method (unit: [(cal / cm 3 ) 1 / 2 , temperature: 25 °C). The details of Fedors' calculation method are described in "R.F. Fedors, "Polymer Engineering and Science", 1974, Vol. 14, No. 2, p147-154".

[0016] Hereinafter, when comprehensively referring to a compound and its derivatives by attaching "system" after the compound name, it may be used. When representing a polymer name by attaching "system" after the compound name, it means that the repeating unit of the polymer is derived from the compound or its derivative. Also, acrylic and methacrylic may be comprehensively referred to as "(meth)acrylic". Also, acryloyl (CH 2 =CH-CO-) and methacryloyl (CH 2 =C(CH 3 )-CO-) may be comprehensively referred to as "(meth)acryloyl".

[0017] The toner according to this embodiment can be suitably used for developing an electrostatic latent image as a positively charged toner. The toner of this embodiment is a powder containing a plurality of toner particles (particles having the configurations described later). The toner may be used as a one-component developer. Also, a two-component developer may be prepared by mixing the toner and a carrier using a mixing device (for example, a ball mill). In order to form a high-quality image, it is preferable to use a ferrite carrier as the carrier.

[0018] Furthermore, in order to form high-quality images over a long period of time, it is preferable to use magnetic carrier particles having a carrier core and a resin layer covering the carrier core. To produce magnetic carrier particles, the carrier core may be formed from a magnetic material (e.g., ferrite), or from a resin in which magnetic particles are dispersed. Alternatively, magnetic particles may be dispersed in the resin layer covering the carrier core. In order to form high-quality images, the amount of toner in the two-component developer is preferably 5 parts by mass or more and 15 parts by mass or less per 100 parts by mass of carrier. Note that positively charged toner becomes positively charged due to friction with the carrier.

[0019] The toner particles contained in this embodiment comprise toner mother particles and an external additive attached to the surface of the toner mother particles. That is, toner particles before the external additive is attached are referred to as toner mother particles. Furthermore, if the toner mother particles have a shell layer, the particles before the shell layer is formed are referred to as toner core particles. If the toner mother particles do not have a shell layer, the toner mother particles are also referred to as toner core particles.

[0020] The toner according to this embodiment can be used, for example, to form images in an electrophotographic apparatus (image forming apparatus). An example of an image forming method using an electrophotographic apparatus will be described below.

[0021] First, an electrostatic latent image is formed on the photoreceptor (e.g., the surface of the photoreceptor drum) based on the image data. Next, the formed electrostatic latent image is developed using a developer containing toner. In the development process, toner (e.g., toner charged by friction with a carrier or blade) on a developing sleeve (e.g., the surface of the developing roller in the developing unit) placed near the photoreceptor is deposited onto the electrostatic latent image, forming a toner image on the photoreceptor. Then, in the subsequent transfer process, the toner image on the photoreceptor is directly transferred to a recording medium (e.g., paper). Alternatively, it is first transferred to an intermediate transfer medium (e.g., a transfer belt), and then the toner image on the intermediate transfer medium is secondarily transferred to the recording medium. After that, the toner is heated to fix it to the recording medium. As a result, an image is formed on the recording medium. For example, a full-color image can be formed by superimposing toner images of four colors: black, yellow, magenta, and cyan.

[0022] [1. Basic Toner Configuration] Figure 1 shows an example of the cross-sectional structure of the positively charged toner 101 of the present invention. As shown in Figure 1, the positively charged toner (hereinafter also simply referred to as toner) 101 of the present invention comprises toner matrix particles 102 and an external additive 103 attached to the surface of the toner matrix particles 102. The toner matrix particles 102 include at least a binder resin, a colorant, and a release agent. The external additive 103 includes inorganic particles 104 and resin particles 105.

[0023] The resin particles 105 are used as spacer particles. The volume-average particle diameter of the resin particles 105 is between 40 nm and 140 nm. If the volume-average particle diameter of the resin particles 105 is less than 40 nm, the resin particles 105 are easily immobilized on the surface of the toner 102, but the spacer effect is small, and the effect of suppressing the embedding of the resin particles 105 is small. If the volume-average particle diameter of the resin particles 105 exceeds 140 nm, it becomes difficult to immobilize the resin fine particles 105 on the surface of the toner matrix particles 102, which can lead to carrier contamination by the freed resin particles 105 and contamination of components within the image forming apparatus.

[0024] In the toner 101 of the present invention, in order to suppress the thermal decomposition of the release agent contained in the toner matrix particles 102, when the difference between the SP value of the release agent exposed on the surface of the toner matrix particles 102 and the SP value of the resin particles 105 is ΔSP1, the following equation (1) is satisfied. 0.8 ≤ ΔSP1 ≤ 1.1 (cal / cm 3 ) 1 / 2 ...(1)

[0025] When ΔSP1 satisfies equation (1), the shear mixing energy during the external additive treatment facilitates the immobilization of the resin particles 105 to the release agent exposed on the surface of the toner matrix particles 102. As a result, when the toner reaches the fixing section in the image forming apparatus and is subjected to thermal energy and pressure, the thermal decomposition of the release agent that is not necessary for release is suppressed, and the amount of UFP generated can be reduced.

[0026] When ΔSP1 is less than 0.8, the resin particles 105 become more easily embedded in the release agent exposed on the surface of the toner matrix particles 102, and their effectiveness as spacers decreases, reducing their durability against mechanical stress. On the other hand, when ΔSP1 exceeds 1.1, the shear mixing energy during the external additive process makes it difficult to fix the resin particles 105 to the release agent exposed on the surface of the toner matrix particles 102, and the resin particles 105 tend to detach. As a result, when the toner reaches the fixing section in the image forming apparatus, the thermal decomposition of the release agent progresses, and the amount of UFP generated increases.

[0027] Furthermore, when ΔSP2 is the difference between the SP value of the binder resin contained in the toner matrix particle 102 and the SP value of the resin particle 105, the following equation (2) is satisfied. 1.3 ≤ ΔSP² ≤ 1.6 (cal / cm 3 ) 1 / 2 ...(2)

[0028] When ΔSP2 satisfies equation (2), the resin particles 105 are more easily fixed to the binder resin exposed on the surface of the toner matrix particles 102, improving the durability of the spacer effect against mechanical stress and environmental changes. In addition, the amount of free resin particles 105 present on the edge of the cleaning blade that contacts the surface of the photoreceptor drum is reduced, suppressing the penetration of the external additive 103 and improving drum cleaning performance.

[0029] When ΔSP2 is less than 1.3, the resin particles 105 can be easily immobilized on the binder resin, but the embedding of the resin particles 105 progresses easily, worsening the toner's charge stability and fluidity. On the other hand, when ΔSP2 exceeds 1.6, it becomes difficult to immobilize the resin particles 105 on the binder resin, and a sufficient spacer effect cannot be obtained. Furthermore, when toner is developed on the surface of the photoreceptor drum, the detached resin particles 105 migrate to the photoreceptor drum along with the toner and remain on the surface of the photoreceptor drum even after transfer. As a result, the resin particles 105 that are not removed from the surface of the photoreceptor drum and pass through the cleaning blade contaminate the charging roller, making it easier for variations in the surface potential of the photoreceptor drum to occur.

[0030] Furthermore, the hardness of the resin particles 105 is set to 1 μN or higher (when the probe displacement is 40 nm). This suppresses the filming of the resin particles 105 onto the surface of the photoreceptor drum, thereby suppressing the occurrence of drum cleaning defects. If the hardness of the resin particles 105 is less than 1 μN, the resin particles 105 will film onto the surface of the photoreceptor drum, causing the stick-slip motion of the cleaning blade to become unstable, and drum cleaning defects are more likely to occur.

[0031] [2. Toner Materials] Next, the essential or optional components constituting the toner of the present invention will be described. The toner core particles contain at least a release agent and a colorant in the binder resin. They may also contain a charge control agent, magnetic powder, etc., as needed, and a shell layer may be formed on the surface of the toner core particles. Furthermore, in the toner of the present invention, the surface of the toner core particles (toner mother particles) is treated with an external additive.

[0032] The binder resin, release agent, colorant, charge control agent, and magnetic powder used to form toner core particles, as well as the shell material used when forming a shell layer on the toner core particles, the external additives added to the toner core particles (toner matrix particles), and the method for manufacturing the toner of the present invention will be described in order below.

[0033] (Binding resin) The toner core particles constituting the toner of the present invention contain a binder resin. The binder resin that can be contained in the toner core particles is not particularly limited as long as it is a resin that has been conventionally used as a binder resin for toner. Specific examples of binder resins include thermoplastic resins such as styrene resins, acrylic resins, styrene-acrylic resins, polyethylene resins, polypropylene resins, vinyl chloride resins, polyester resins, polyamide resins, polyurethane resins, polyvinyl alcohol resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. Among these resins, polyester resins are preferred in terms of the dispersibility of the colorant in the binder resin, the electrostatic properties of the toner, and the fixation to paper. Polyester resins will be described below.

[0034] Polyester resins can be obtained by condensation polymerization or copolymerization of a divalent or trivalent or higher alcohol component with a divalent or trivalent or higher carboxylic acid component. The following alcohol and carboxylic acid components are examples of components used in the synthesis of polyester resins.

[0035] Specific examples of divalent or trivalent or higher alcohol components include diols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; bisphenol A, hydrogenated bisphenol A, and polyoxyethylene Examples include bisphenols such as bisphenol A and polyoxypropylene bisphenol A; and trivalent or higher alcohols such as sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

[0036] Specific examples of divalent or trivalent or higher carboxylic acid components include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebatic acid, azelaic acid, malonic acid, or divalent alkyl or alkenyl succinic acids such as n-butylsuccinic acid, n-butenylsuccinic acid, isobutylsuccinic acid, isobutenylsuccinic acid, n-octylsuccinic acid, n-octenylsuccinic acid, n-dodecylsuccinic acid, n-dodecenylsuccinic acid, isododecylsuccinic acid, and isododecenylsuccinic acid. Carboxylic acids include trivalent or higher carboxylic acids such as 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalentricarboxylic acid, 1,2,4-naphthalentricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, and empol trimeric acid. These divalent or trivalent or higher carboxylic acid components may be used as ester-forming derivatives such as acid halides, acid anhydrides, and lower alkyl esters. Here, "lower alkyl" means an alkyl group having 1 to 6 carbon atoms.

[0037] When the binder resin is a polyester resin, the softening point of the polyester resin is preferably 70°C to 130°C, and more preferably 80°C to 120°C. To improve the strength of the toner core and the fixation of the toner, the number-average molecular weight (Mn) of the polyester resin is preferably 1000 to 2000. The molecular weight distribution of the polyester resin (ratio of mass-average molecular weight (Mw) to number-average molecular weight (Mn) Mw / Mn) is preferably 9 to 21.

[0038] As the binder resin, a thermoplastic resin is preferable because it has good adhesion to paper. However, thermoplastic resins can be used alone, or crosslinking agents or thermosetting resins can be added to them. By adding crosslinking agents or thermosetting resins and introducing a partially crosslinked structure into the binder resin, the heat resistance, storage properties, and durability of the toner can be improved without reducing the toner's adhesion. When using a thermosetting resin, the amount of crosslinked portion (gel amount) of the binder resin extracted using a Soxhlet extractor is preferably 10% by mass or less, and more preferably 0.1% by mass or more and 10% by mass or less, relative to the mass of the binder resin.

[0039] Epoxy resins and cyanate resins are preferred thermosetting resins that can be used with thermoplastic resins. Specific examples of suitable thermosetting resins include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, cyclic aliphatic type epoxy resins, and cyanate resins. Two or more of these thermosetting resins can be used in combination.

[0040] The glass transition temperature (Tg) of the binder resin is preferably between 40°C and 70°C. If the glass transition temperature is too high, the low-temperature fixability of the toner tends to decrease. If the glass transition temperature is too low, the heat resistance of the toner tends to decrease.

[0041] The glass transition point of a binder resin can be determined from the point of change in the specific heat of the binder resin using a differential scanning calorimeter (DSC). More specifically, the glass transition point of the binder resin can be determined by measuring the endothermic curve of the binder resin using a Seiko Instruments Inc. DSC-6200 differential scanning calorimeter as the measuring device. A 10 mg sample is placed in an aluminum pan, and an empty aluminum pan is used as a reference. The glass transition point of the binder resin can be determined from the endothermic curve obtained by measuring the binder resin at room temperature and humidity with a temperature range of 25°C to 200°C and a heating rate of 10°C / min.

[0042] The mass-average molecular weight (Mw) of the binder resin is not particularly limited as long as it does not hinder the objectives of the present invention. Typically, the mass-average molecular weight (Mw) of the binder resin is preferably 20,000 to 300,000, and more preferably 30,000 to 2,000,000. The mass-average molecular weight of the binder resin can be determined by gel permeation chromatography (GPC) using a calibration curve prepared in advance using standard polystyrene resin.

[0043] (Release agent) Toner core particles contain a release agent to improve adhesion and offset resistance. The type of release agent that can be included in the toner core particles is not particularly limited as long as it does not hinder the objectives of the present invention. Wax is preferred as the release agent, and examples of waxes include carnauba wax, synthetic ester wax, polyethylene wax, polypropylene wax, fluororesin wax, Fischer-Tropsch wax, paraffin wax, montan wax, and rice wax. Two or more of these release agents can be used in combination. By adding such release agents to toner core particles, the occurrence of offset and image smearing (smudges around the image when the image is rubbed) can be suppressed more efficiently.

[0044] When polyester resin is used as the binder resin, from the viewpoint of compatibility, one or more release agents selected from the group consisting of carnauba wax, synthetic ester wax, and polyethylene wax are preferably used as the release agent. Similarly, when polystyrene resin is used as the binder resin, from the viewpoint of compatibility, Fischer-Tropsch wax and / or paraffin wax are preferably used as the release agent.

[0045] Fischer-Tropsch wax is a straight-chain hydrocarbon compound with few iso-structure molecules or side chains, produced using the Fischer-Tropsch reaction, which is a catalytic hydrogenation reaction of carbon monoxide.

[0046] Among Fischer-Tropsch waxes, those with a mass-average molecular weight of 1,000 or more and whose endothermic peak bottom temperature observed by DSC measurement is in the range of 100°C to 120°C are more preferable. Examples of such Fischer-Tropsch waxes include Sazol wax C1 (endothermic peak bottom temperature: 106.5°C), Sazol wax C105 (endothermic peak bottom temperature: 102.1°C), and Sazol wax SPRAY (endothermic peak bottom temperature: 102.1°C), all available from Sazol.

[0047] The amount of release agent used is not particularly limited as long as it does not hinder the objectives of the present invention. Preferably, the amount of release agent used is 1% by mass or more and 10% by mass or less, relative to the total mass of the toner core particles 102. If the amount of release agent used is too little, the desired effect of suppressing offset and image smearing in the formed image may not be obtained, and if the amount of release agent used is too much, the heat resistance of the toner may decrease due to fusion of toners.

[0048] (Coloring agent) Toner core particles contain a colorant. The colorant that can be included in the toner core particles can be any known pigment or dye, depending on the color of the toner. Specific examples of suitable colorants that can be added to toner include: black pigments such as carbon black, acetylene black, lamp black, and aniline black; yellow pigments such as lead yellow, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, tartrazine lake, monoazo yellow, and diazo yellow; orange pigments such as red lead yellow, molybdenum orange, permanent orange GTR, pyrazolone orange, balkan orange, and induthrene brilliant orange GK; red iron oxide, cadmium red, red lead, mercury cadmium sulfide, permanent red 4R, lithol red, and pyrazolone. Examples of colorants include red pigments such as Lon Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B, and Monoazo Red; purple pigments such as Manganese Violet, Fast Violet B, and Methyl Violet Lake; blue pigments such as Prussian Blue, Cobalt Blue, Alkali Blue Lake, Victoria Blue Partial Chloride, Fast Sky Blue, Induthlene Blue BC, and Phthalocyanine Blue; green pigments such as Chrome Green, Chromium Oxide, Pigment Green B, Malachite Green Lake, and Final Yellow Green G; white pigments such as Zinc Oxide, Titanium Dioxide, Antimony White, and Zinc Sulfide; and extender pigments such as Barite Powder, Barium Carbonate, Clay, Silica, White Carbon, Talc, and Alumina White. Two or more of these colorants can also be used in combination to adjust the toner to a desired hue.

[0049] The amount of colorant used is not particularly limited as long as it does not hinder the objective of the present invention. Specifically, the amount of colorant used is preferably 1% by mass or more and 10% by mass or less, and more preferably 2% by mass or more and 7% by mass or less, relative to the total mass of the toner core particles.

[0050] Furthermore, a colorant can also be used as a masterbatch in which the colorant is pre-dispersed in a resin material such as a thermoplastic resin. When using a colorant as a masterbatch, it is preferable that the resin contained in the masterbatch is the same type of resin as the binder resin.

[0051] (Charge control agent) Toner core particles preferably contain a charge control agent to improve the charge level of the toner and the charge rise characteristics, which are indicators of whether or not it can be charged to a predetermined charge level in a short time, and to obtain a toner with excellent durability and stability. Since the toner of the present invention is positively charged, a positively charged charge control agent is used.

[0052] The types of charge control agents that can be contained in toner core particles are not particularly limited as long as they do not hinder the objectives of the present invention, and can be appropriately selected from charge control agents that have been conventionally used in toners. Specific examples of positively charged charge control agents include azine compounds such as pyridazine, pyrimidine, pyrazine, orthoxazine, metaoxazine, paraoxazine, orthothiaidine, metathiaidine, parathiaidine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline, and quinoxaline; azine compounds Examples include direct dyes consisting of azine compounds such as Stread FC, Azin Fast Red 12BK, Azin Violet BO, Azin Brown 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Deep Black EW, and Azin Deep Black 3RL; nigrosine compounds such as nigrosine, nigrosine salts, and nigrosine derivatives; acid dyes consisting of nigrosine compounds such as nigrosine BK, nigrosine NB, and nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; and quaternary ammonium salts such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride. Among these positively charged charge control agents, nigrosine compounds are particularly preferred because they provide a faster charge rise. Two or more of these positively charged charge control agents can be used in combination.

[0053] Resins having quaternary ammonium salts, carboxylates, or carboxyl groups as functional groups can also be used as positively charged charge control agents. More specifically, examples include styrene resins having quaternary ammonium salts, acrylic resins having quaternary ammonium salts, styrene-acrylic resins having quaternary ammonium salts, polyester resins having quaternary ammonium salts, styrene resins having carboxylates, acrylic resins having carboxylates, styrene-acrylic resins having carboxylates, polyester resins having carboxylates, styrene resins having carboxyl groups, acrylic resins having carboxyl groups, styrene-acrylic resins having carboxyl groups, and polyester resins having carboxyl groups. The molecular weight of these resins is not particularly limited as long as it does not hinder the objectives of the present invention, and they may be oligomers or polymers.

[0054] Among resins that can be used as positively charged charge control agents, styrene-acrylic resins having quaternary ammonium salts as functional groups are more preferred because the amount of charge can be easily adjusted to a value within a desired range. Specific examples of preferred acrylic comonomers copolymerized with styrene units in styrene-acrylic resins having quaternary ammonium salts as functional groups include alkyl (meth)acrylates such as methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate.

[0055] Furthermore, as quaternary ammonium salts, dialkylaminoalkyl(meth)acrylates, dialkyl(meth)acrylamides, or units derived from dialkylaminoalkyl(meth)acrylamides through a quaternization process can be used. Specific examples of dialkylaminoalkyl(meth)acrylates include dimethylaminoethyl(meth)acrylate, diethylaminoethyl(meth)acrylate, dipropylaminoethyl(meth)acrylate, and dibutylaminoethyl(meth)acrylate. Specific examples of dialkyl(meth)acrylamides include dimethylmethacrylamide, and specific examples of dialkylaminoalkyl(meth)acrylamides include dimethylaminopropylmethacrylamide. In addition, hydroxyl group-containing polymerizable monomers such as hydroxyethyl(meth)acrylate, hydroxypropyl(meth)acrylate, 2-hydroxybutyl(meth)acrylate, and N-methylol(meth)acrylamide can be used in combination during polymerization.

[0056] The amount of charge control agent used is not particularly limited as long as it does not hinder the objectives of the present invention. Typically, the amount of charge control agent used is preferably 0.1% by mass or more and 10% by mass or less, relative to the total mass of the toner core particles. If the amount of charge control agent used is insufficient, it is difficult to stably charge the toner to a predetermined polarity, which may result in the image density of the formed image falling below the desired value or making it difficult to maintain the image density over a long period of time. In addition, because the charge control agent is difficult to disperse uniformly, the formed image is more prone to blurring, and contamination of the latent image-carrying area by toner components is more likely to occur. If the amount of charge control agent used is excessive, the environmental resistance deteriorates, making it easier for image defects in the formed image due to poor charging under high temperature and high humidity conditions, and contamination of the latent image-carrying area by toner components to occur.

[0057] (magnetic powder) Toner core particles may contain magnetic powder. Suitable materials for the magnetic powder include, for example, ferromagnetic metals (more specifically, iron, cobalt, nickel, or alloys containing one or more of these metals), ferromagnetic metal oxides (more specifically, ferrite, magnetite, or chromium dioxide), or materials that have undergone ferromagnetic treatment (more specifically, carbon materials to which ferromagnetism has been imparted by heat treatment). To suppress the elution of metal ions (e.g., iron ions) from the magnetic powder, it is preferable to use surface-treated magnetic particles as the magnetic powder. One type of magnetic powder may be used alone, or multiple types of magnetic powder may be used in combination.

[0058] (Shell material) Toner core particles may optionally have their surfaces coated with a shell layer. When a shell layer is formed on toner core particles, the shell layer is formed of resin fine particles. In order to give the shell layer an appropriate surface adsorption force, it is particularly preferable that the shell layer contains a resin film mainly composed of aggregates of resin particles with a glass transition temperature of 50°C to 100°C, the number-average circularity of the heat-resistant particles constituting the resin film is 0.55 to 0.75, the heat-resistant particles contain a resin containing one or more repeating units derived from styrene monomers, repeating units having alcoholic hydroxyl groups, and repeating units derived from nitrogen-containing vinyl compounds, and that the repeating unit having the highest mass proportion among the repeating units contained in the resin contained in the heat-resistant particles is the repeating unit derived from styrene monomers.

[0059] The shell layer constituting the toner of the present invention includes vinyl resin fine particles with a relatively small average particle diameter (first resin fine particles) and vinyl resin fine particles with a relatively large average particle diameter (second resin fine particles). The first resin fine particles form the sea-like regions of the shell layer. The second resin fine particles form the convex portions of the shell layer. The average particle diameter of the first resin fine particles is preferably about 10 nm to 40 nm. The average particle diameter of the second resin fine particles is preferably about 70 nm to 150 nm.

[0060] Regarding the shell layer described above (i.e., a resin film mainly composed of an aggregate of heat-resistant particles), in order to ensure sufficient heat resistance, fixability, and electrostatic properties of the toner, it is preferable that the thickness of the shell layer be between 10 nm and 35 nm. The thickness of the shell layer can be measured by analyzing a TEM (transmission electron microscope) image of the cross-section of the toner particle using commercially available image analysis software (for example, "WinROOF" manufactured by Mitani Corporation). If the thickness of the shell layer is not uniform in a single toner particle, the thickness of the shell layer is measured at four evenly spaced locations (specifically, two perpendicular lines are drawn at approximately the center of the cross-section of the toner particle, and the thickness of the shell layer is measured at four locations where these two lines intersect the shell layer), and the arithmetic mean of the four obtained measurements is taken as the evaluation value (shell layer thickness) of that toner particle. The boundary between the toner core particle and the shell layer can be confirmed, for example, by selectively staining only the shell layer among the toner core particle and the shell layer. If the boundary between the toner core particles and the shell layer is unclear in the TEM image, the boundary can be clarified by combining TEM and electron energy loss spectroscopy (EELS) to map characteristic elements contained in the shell layer within the TEM image.

[0061] Regarding the shell layer described above (i.e., a resin film mainly composed of an aggregate of heat-resistant particles), in order to ensure sufficient heat resistance, fixability, and electrostatic properties of the toner, it is preferable that the shell layer covers 50% to 80% of the surface area of ​​the toner core particles. The area ratio of the surface area of ​​the toner core particles covered by the shell layer can be measured by taking an image of the surface of the toner particles (for example, pre-stained toner particles) with an electron microscope and analyzing the resulting image using commercially available image analysis software.

[0062] (External additive) The toner of the present invention is obtained by treating toner matrix particles with an external additive. The external additive used in the toner of the present invention includes at least inorganic particles and resin particles.

[0063] (Inorganic particles) Inorganic particles can include metal oxides such as silica, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate. Silica or titanium oxide are particularly preferred. These particles may be used individually or in combination of two or more. The average particle size of the inorganic particles is preferably between 10 nm and 100 nm.

[0064] (Resin particles) The material of the resin particles is not particularly limited, as long as the aforementioned ΔSP1 and ΔSP2 can be adjusted to the ranges of equations (1) and (2), respectively. The resin particles may also be surface-treated. Examples of surface treatments in this case include hydrophobic treatment, positive charging treatment, and conductive treatment.

[0065] When the toner matrix particles contain a polyester resin as a binder resin, and the resin constituting the resin particles is a crosslinked resin, it is preferable that the crosslinked resin is a polymer of a styrene monomer, an acrylic acid monomer, and a crosslinking agent having two or more unsaturated bonds (hereinafter also referred to as a specific crosslinked polymer) in order to easily adjust ΔSP2 to satisfy formula (2).

[0066] Examples of styrene-based monomers for synthesizing specific crosslinked polymers include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, pt-butylstyrene, pn-hexylstyrene, pn-octylstyrene, pn-nonylstyrene, pn-decylstyrene, and pn-dodecylstyrene.

[0067] Examples of acrylic acid monomers for synthesizing specific crosslinked polymers include (meth)acrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, t-butyl (meth)acrylate, n-octyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, stearyl (meth)acrylate, lauryl (meth)acrylate, and phenyl (meth)acrylate.

[0068] Examples of crosslinking agents having two or more unsaturated bonds for synthesizing specific crosslinked polymers include N,N'-methylenebisacrylamide, divinylbenzene, ethylene glycol diacrylate, ethylene glycol dimethacrylate, diethylene glycol diacrylate, tetraethylene glycol diacrylate, polyethylene glycol diacrylate, 1,4-butanediol diacrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, pentaerythritol triacrylate, pentaerythritol tetraacrylate, 1,4-butanediol dimethacrylate, and 1,6-hexanediol dimethacrylate.

[0069] To obtain a toner with superior electrostatic stability and heat resistance, ethylene glycol dimethacrylate is preferred as the crosslinking agent having two or more unsaturated bonds.

[0070] To obtain a toner with even better electrostatic stability and heat resistance, it is preferable that the binder resin of the toner matrix particles is a polyester resin, and that the resin constituting the resin particles is a polymer (crosslinked polymer) of styrene, methyl methacrylate, and ethylene glycol dimethacrylate.

[0071] The method for forming the resin particles is not particularly limited. Examples of resin particle formation methods include emulsion polymerization, seed polymerization, and dispersion polymerization. In this embodiment, commercially available resin particles may also be used.

[0072] In addition, other external additives can be used along with the inorganic particles and resin particles described above. The type of external additive used with the resin particles is not particularly limited as long as it does not hinder the objective of the present invention, and can be appropriately selected from external additives conventionally used for toner. Two or more of these external additives can be used in combination.

[0073] [Toner manufacturing method] Next, the method for manufacturing the toner of the present invention will be described. The method for manufacturing the toner includes a method for manufacturing toner core particles and an external additive treatment method for attaching an external additive to the surface of toner matrix particles. The method for manufacturing the toner core particles is not particularly limited as long as the toner core particles are formed to have a predetermined structure. In addition, toner core particles coated with a shell layer may be used as toner matrix particles as necessary. As a preferred method for manufacturing the positively charged toner described above, the method for manufacturing toner core particles, the method for forming the shell layer, and the external additive treatment method will be described in order below.

[0074] (Method for manufacturing toner core particles) The method for producing toner core particles is not particularly limited, as long as any component such as a colorant, release agent, charge control agent, or magnetic powder can be well dispersed in the binder resin. Suitable methods for producing toner core particles include, for example, grinding or agglomeration.

[0075] The pulverization method involves mixing the binder resin with components such as colorants, release agents, charge control agents, and magnetic powder using a mixer, then melt-kneading the binder resin and the components incorporated into the binder resin using a kneader such as a single-screw or twin-screw extruder, and finally pulverizing and classifying the cooled kneaded material. The average particle size of the toner core particles is not particularly limited as long as it does not hinder the objectives of the present invention, but is generally preferably 5 μm to 10 μm.

[0076] The agglutination method involves agglutinating fine particles of a binder resin, release agent, charge control agent, and colorant in an aqueous medium until these fine particles reach a desired particle size. This forms agglutinated particles containing the binder resin, release agent, charge control agent, and colorant. Subsequently, the resulting agglutinated particles are heated to unify the components contained within them. This yields toner core particles with the desired particle size.

[0077] (Method for forming the shell layer) When the surface of toner core particles is coated with a shell layer, resin microparticles are attached to the surface of the toner core particles to form the shell layer.

[0078] Let me explain the method in more detail. First, in a mixing device, hydrochloric acid is added to deionized water to prepare a weakly acidic aqueous medium (for example, a pH selected from 3 to 5). Next, a dispersion (suspension) of resin microparticles (first resin microparticles and second resin microparticles) as shell material and toner core particles are added to the pH-adjusted aqueous medium.

[0079] Next, while stirring the mixture containing the shell material and toner core particles, the temperature of the mixture is raised at a predetermined rate (for example, a rate selected from 0.1°C / min to 3°C / min) to a predetermined holding temperature (for example, a temperature selected from 50°C to 90°C). Furthermore, while stirring the mixture, the temperature of the liquid is maintained at the above holding temperature for a predetermined time (for example, a time selected from 30 minutes to 4 hours). It is believed that a reaction (immobilization of the shell layer) proceeds between the toner core particles and the shell material while the temperature of the mixture is maintained at a high temperature. A shell layer is formed when the shell material binds to the toner core particles. A dispersion of toner matrix particles is obtained when a shell layer is formed on the surface of the toner core particles in the mixture.

[0080] (External processing method) The method for treating toner matrix particles with external additives is not particularly limited, and the toner matrix particles can be treated according to conventionally known methods. Specifically, the treatment conditions are adjusted so that the particles of the external additive do not become embedded in the toner matrix particles, and the toner matrix particles are treated with the external additive using a mixer such as a Henschel mixer or a Nauter mixer.

[0081] The toner of the present invention, as described above, has excellent fixability and heat resistance for storage. When forming images over a long period of time in various environments such as high temperature and high humidity environments or low temperature and low humidity environments, the toner can be charged to a desired amount of charge, thereby enabling the formation of images of a desired density. For this reason, the electrostatic latent image developing toner of the present invention can be suitably used in various image forming apparatuses. The effects of the present invention will be further described in detail below with reference to examples. However, the present invention is not limited in any way by these examples. [Examples]

[0082] [Manufacturing Example 1] (Manufacturing of toner matrix particles) As a binder, 82% by mass of polyester resin (HP-313, manufactured by Nippon Synthetic Chemical Co., Ltd.), 6.0% by mass of carbon black (MA-100, manufactured by Mitsubishi Chemical Corporation) as a coloring agent, 2.0% by mass of charge control agent (N-01, manufactured by Orient Chemical Co., Ltd.), 4.0% by mass of charge control agent (FCA-201-PS, manufactured by Fujikura Chemical Co., Ltd.), and 6.0% by mass of ester wax (WEP-3, manufactured by NOF Corporation) as a release agent were mixed using a Henschel mixer (FM-10 type, manufactured by Mitsui Mining Co., Ltd.) to obtain a mixture. Next, the mixture was melt-kneaded using a twin-screw extruder (TEM-26SS, manufactured by Toshiba Machine Co., Ltd.) to obtain a kneaded product. The kneaded product was coarsely pulverized to about 2 mm using a Rotoplex pulverizer (manufactured by Toa Machinery Co., Ltd.), and then the coarsely pulverized product was finely pulverized using a mechanical pulverizer (Turbo Mill, manufactured by Turbo Industrial Co., Ltd.) to obtain a finely pulverized product. The finely ground material was classified using an air-powered classifier (EJ-L-3 (LABO) type, manufactured by Nippon Steel Mining Co., Ltd.) to obtain toner matrix particles with a volume-average particle size (D50) of 7.0 μm. The volume-average particle size was measured using a Coulter Counter Multisizer 3 (manufactured by Beckman Coulter).

[0083] [Manufacturing Example 2] (Manufacturing of resin particles) 28 parts by mass of styrene, 42 parts by mass of acrylonitrile, 30 parts by mass of ethylene glycol dimethacrylate, 4.5 parts by mass of potassium persulfate (water-soluble polymerization initiator), 100 parts by mass of deionized water, and 2.0 parts by mass of cationic surfactant (cetyltrimethylammonium chloride) were placed in a round-bottom flask and stirred at 100 rpm with an anchor-type stirring blade. Emulsification polymerization was carried out at 70°C for 8 hours using a soap-free polymerization method to obtain a dispersion of resin particles.

[0084] The obtained dispersion was purified using an ultrafiltration system, and then dried by spray drying to produce resin microparticles. The particle size was adjusted by controlling the nozzle pore size and spray speed to produce resin particle A. The average primary particle size of resin particle A, measured using a scanning electron microscope (JSM-7600F, JEOL Ltd.), was 42 nm.

[0085] Furthermore, resin particles B to M were obtained using the same method as resin particle A, except that the type and amount of monomer were changed. Also, resin particle N was obtained using the same method as resin particle A, except that the surfactant was changed from a cationic surfactant to an anionic surfactant (sodium dodecylbenzenesulfonate).

[0086] (Measurement of hardness of resin particles) An "AFM5000II" (manufactured by Hitachi High-Tech Science Co., Ltd.) was used as the measuring device. A "SI-DF40 back A1 coated" (manufactured by Hitachi High-Tech Science Co., Ltd.) cantilever was used. The cantilever had the following specifications: tip radius R: 10 nm, probe height D: 12.5 μm, lever length L: 125 μm, lever width W: 30 μm, lever thickness T: 4 μm, and spring constant: 42 N / m. A force curve was obtained by measuring the AFM surface hardness of the surface layer of the resin microparticles. To stabilize the sample base, a resin microparticle pellet with a diameter of 20 mm was prepared for measurement. The measurement conditions were: chamber temperature: 23.5 °C, chamber humidity: 50% RH, measurement atmosphere: air, measurement area: 6 μm × 6 μm, torsional spring constant: 1 N / m, and resonance frequency: 150 Hz. The stress at a probe displacement of 40 nm was measured at 30 points and averaged.

[0087] Table 1 shows the SP values, hardness, and particle size of resin particles A to N, along with the types and amounts (parts by mass) of monomers and surfactants used in the production of resin particles A to N.

[0088] [Table 1] *1; Ethylene glycol dimethacrylate

[0089] [Manufacturing Example 3] (External treatment of toner matrix particles) To 100 parts by mass of toner matrix particles obtained in Production Example 1, 1.5 parts by mass of positively charged silica fine particles (CAB-O-SIL TG-308F, manufactured by Cabot Corporation) and 1.0 part by mass of titanium dioxide (MT-500B, manufactured by Teika Corporation) were mixed in a Henschel mixer (FM-10 type, manufactured by Mitsui Mining Co., Ltd.) at a rotation speed of 3500 rpm for 5 minutes. Then, resin particles A to N obtained in Production Example 2 were added in predetermined parts by mass and mixed at a rotation speed of 3500 rpm for 5 minutes to externally add the resin particles. The coating rate of the resin particles on the surface of the toner matrix particles was adjusted to 30%. In this way, toners used in Inventions 1 to 5 and Comparative Examples 1 to 9, with different resin particles externally added, were prepared.

[0090] [Manufacturing Example 4] (Carrier manufacturing) After dissolving 2 kg of epoxy resin (Epicoat 1004, manufactured by Japan Epoxy Range Co., Ltd.) in 20 L of acetone, 100 g of diethylenetriamine and 150 g of phthalic anhydride were added and mixed to prepare the coating solution.

[0091] Using a fluidized bed coating apparatus (SFC-5, manufactured by Freund Industrial Co., Ltd.), 10 kg of carrier cores (F-50, manufactured by Powdertech, particle size 50 μm) were fluidized while 80°C hot air was supplied and a coating solution was sprayed onto the carrier cores to obtain carrier cores coated with the coating solution. The carrier cores coated with the coating solution were then fired in an electric furnace at 180°C for 1 hour to obtain carrier particles.

[0092] [Manufacturing Example 5] (Manufacturing of two-component developers) The carrier particles obtained in Production Example 4 and the toner obtained in Production Example 3 were mixed using a ball mill for 30 minutes so that the toner amounted to 8% by mass relative to the carrier, thereby preparing the two-component developers of Invention 1-5 and Comparative Examples 1-9.

[0093] [Evaluation of UFP generation amount and image characteristics] (Method for evaluating UFP generation) The intake port of a high-speed response particle sizer (FMPS 3091, Tokyo Direc Co., Ltd.) was attached to the exhaust port of a differential thermogravimetric (TG / DTA) simultaneous measurement device (STA7200, Hitachi High-Tech Science Co., Ltd.). The exhaust volume of the differential thermogravimetric simultaneous measurement device was set to 0.1 L / min, and the intake volume of the high-speed response particle sizer was set to 10 L / min. Subsequently, using the differential thermogravimetric simultaneous measurement device, 10 mg of the measurement sample (specifically, each of the two-component developers of Invention 1-5 and Comparative Examples 1-9) was heated from room temperature to 220°C at a heating rate of 20°C / min, and the temperature of the measurement sample was maintained at 220°C for 10 minutes. Simultaneously with the start of the measurement program using the differential thermogravimetric simultaneous measurement device, the particle number concentration of the generated fine particles was measured. The evaluation criteria for UFP generation amount are shown below. ○: The total number concentration of UFP is 1.50 × 105 pieces / cm 3 Less than (practical level) ×: The total number concentration of UFP is 1.50 × 10 5 pieces / cm 3 (Outside the practical scope)

[0094] (Method for evaluating image characteristics) The two-component developers of Invention 1-5 and Comparative Examples 1-9 were installed in the developing unit of an evaluation machine (a modified TASKalfa6054ciW manufactured by Kyocera Document Solutions Corporation). Durable printing of 5 million sheets was performed at a print density of 5% under normal temperature conditions (temperature 23.5°C, humidity 50%), and the toner's charge stability, transfer characteristics, drum cleaning properties, and drum filming properties were evaluated according to the following method. (Static stability) At the start of printing and after 5 million prints (after durability testing), the developer on the developing roller was collected, and the toner charge was measured by sucking only the toner through a 38 μm mesh sieve (stainless steel, twill weave, wire diameter: 0.0027 mm) using a suction-type small charge measuring device (manufactured by Trek). The toner charge at the start of printing was also measured using the same method under high humidity conditions (temperature 32.5°C, humidity 80%). The evaluation criteria for charge stability are shown below. ◎: Charge level of 25 μC / g or more and less than 35 μC / g (practical level) ○: Charge level of 15 μC / g or more and less than 25 μC / g (practical level) ×: Charge level less than 15 μC / g, or 35 μC / g or more (outside the practical range)

[0095] (Transfer characteristics) Similar to the measurement of charge amount, the transfer efficiency was measured after printing 5 million sheets (after durability testing). The transfer efficiency is calculated using the following formula (1), where A is the weight of toner attached to the transfer belt and B is the amount of toner attached to the media when outputting a solid image (evaluation image) with dimensions of 0.5 cm vertically and 20 cm horizontally. The toner weight A on the transfer belt and the toner weight B on the media were determined by stopping the evaluation machine immediately after development and immediately before fixing, respectively, and collecting the toner using a suction-type small charge amount measuring device (manufactured by Trek), and then measuring the weight on a precision balance. Transfer efficiency (%) = B / A × 100 ... (1) The evaluation criteria for transcriptional properties are shown below. ◎: Transfer efficiency of 90% or higher (practical level) ○: Transfer efficiency is 85% to 90% (practical level) ×: Transfer efficiency is 85% or less (outside the practical range)

[0096] (Drum cleaning ability) After performing 5 million print runs, a halftone image was printed. The resulting halftone image was visually inspected for the presence of vertical streaks or other image defects. Furthermore, after printing the halftone image, the surface of the charger was visually inspected for any toner residue. The evaluation criteria for cleaning performance are shown below. ○: No vertical streaks were observed in the halftone image, and no toner residue was found on the surface of the charger (practical level). △: No vertical streaks were observed in the halftone image, but a small amount of toner residue was found on the surface of the charger (at a practical level). ×: Vertical streaks were observed in the halftone image, and a significant amount of toner residue was found on the surface of the charger (outside the practical range).

[0097] (Drum filming capability) After performing 5 million print runs, the presence or absence of toner adhesion on the surface of the photoconductor drum was visually inspected. The criteria for drum filming performance are shown below. ○: No toner adhesion was observed upon visual inspection (practical level). ×: Toner residue was observed upon visual inspection (outside the practical range).

[0098] Table 2 shows the evaluation results for UFP generation amount, charge stability, transfer characteristics, drum cleaning properties, and drum filming properties of the two-component developers of Inventions 1-5 and Comparative Examples 1-9. The values ​​for UFP generation amount, toner charge amount, and transfer properties in Table 2 represent the respective measured values.

[0099] [Table 2]

[0100] As is clear from Table 2, the difference ΔSP1 between the SP value of the release agent in the toner matrix particles and the SP value of the resin particles is 0.8 to 1.1 (cal / cm²). 3 ) 1 / 2 In the developers of the present invention 1 to 5, the amount of UFP generated is 0.6 to 1.4 (pieces / cm³). 3 The amount was small. This is thought to be because the resin particles are easily fixed to the release agent exposed on the surface of the toner matrix particles, and when thermal energy and pressure are applied in the fixing section, the thermal decomposition of unnecessary release agent during demolding is suppressed, thereby suppressing the amount of UFP generated.

[0101] Furthermore, the developers of the present invention 1 to 5 have a difference ΔSP2 between the SP value of the binder resin in the toner matrix particles and the SP value of the resin particles of 1.3 to 1.6 (cal / cm²). 3 ) 1 / 2 Therefore, the resin particles are less likely to become embedded in the toner matrix particles due to environmental changes or mechanical stress. As a result, the electrostatic stability was also good. Furthermore, because the hardness of the resin particles in the developers of the present invention 1 to 5 is 1 μN or higher, toner adhesion (filming) to the surface of the photoreceptor drum can be suppressed, and cleaning performance is also good.

[0102] In contrast, the developer in Comparative Example 1 had a ΔSP2 of 1.7 (cal / cm²). 3 ) 1 / 2 Because the SP values ​​of the binder resin and the resin particles are significantly different, the resin particles are not easily fixed to the binder resin exposed on the surface of the toner matrix particles, and the amount of resin particle detachment is large, resulting in poor drum cleaning performance.

[0103] Furthermore, in the developers of Comparative Examples 2 and 3, ΔSP2 was 1.2 (cal / cm²). 3 ) 1 / 2 Because the SP values ​​of the binder resin and resin particles are small, the resin particles tend to become embedded in the toner matrix particles, resulting in a decrease in the stability of the toner's charge.

[0104] Furthermore, in the developers of Comparative Examples 4-6, the hardness of the resin particles was less than 1 μN, which caused toner to adhere to the surface of the photoreceptor drum (filming). This led to instability in the stick-slip motion of the cleaning blade, resulting in poor drum cleaning.

[0105] Furthermore, in the developer of Comparative Example 7, the particle size of the resin particles was large (120 nm), making it difficult to fix them to the surface of the toner matrix particles. This resulted in a large amount of resin particle detachment, leading to poor drum cleaning. On the other hand, in the developer of Comparative Example 8, the particle size of the resin particles was small (30 nm), resulting in a small spacer effect. Mechanical stress made the resin particles more prone to embedding in the toner matrix particles, thus reducing electrostatic stability. In the developer of Comparative Example 9, the use of anionic surfactants in the resin particles reduced the positive charge properties of the toner, resulting in reduced electrostatic stability. Additionally, the transferability decreased as the toner became less responsive to the transfer field.

[0106] Based on these results, it was confirmed that by adjusting ΔSP1, ΔSP2, the hardness of the resin particles, and the particle size to an appropriate range, the amount of UFP generation can be suppressed, and a two-component developer with excellent static stability at the start of printing and after durability, transfer characteristics, drum cleaning properties, and drum filming properties can be obtained. [Industrial applicability]

[0107] The present invention is applicable to positively charged toners and two-component developers containing positively charged toners used in electrophotographic systems. By utilizing the present invention, it is possible to provide positively charged toners and two-component developers containing positively charged toners that suppress the generation of UFPs due to the thermal decomposition of release agents, while also having excellent transfer characteristics and drum cleaning properties. [Explanation of Symbols]

[0108] 101 Toner 102 Toner matrix particles 103 External additives 104 Inorganic particles 105 Resin particles

Claims

1. Toner matrix particles containing at least a binder resin, a colorant, and a release agent, An external additive that adheres to the surface of the toner matrix particles, A positively charged toner comprising toner particles containing, The aforementioned external additive comprises inorganic particles and resin particles. The resin particles contain a cationic surfactant, have a volume-average particle diameter of 40 nm or more and 110 nm or less, and have a hardness of 1 μN or more when measured with a probe displacement of 40 nm. A positively charged toner characterized in that, when ΔSP1 is the difference between the SP value of the mold release agent and the SP value of the resin particles, and ΔSP2 is the difference between the SP value of the binder resin and the SP value of the resin particles, it satisfies the following equations (1) and (2). 0.8≦ΔSP1≦1.1(cal / cm 3 ) 1 / 2 ・・・(1) 1.3≦ΔSP2≦1.6(cal / cm 3 ) 1 / 2 ・・・(2)

2. The positively charged toner according to claim 1, characterized in that the amount of resin particles added is 0.6 parts by mass or more and 1.1 parts by mass or less per 100 parts by mass of toner matrix particles.

3. The positively charged toner according to claim 1, characterized in that the toner matrix particles contain a polyester resin as the binder resin.

4. The positively charged toner according to claim 3, characterized in that the resin particles are formed from a polymer of a styrene monomer, an acrylic acid monomer, and a crosslinking agent.

5. The positively charged toner according to claim 4, characterized in that the crosslinking agent is ethylene glycol dimethacrylate.

6. A positively charged toner according to any one of claims 1 to 5, A carrier capable of positively charging the positively charged toner by friction, A two-component developer containing the following:

Images