Two component developer

Abstract

To provide a two component developer having stable transfer characteristics and positive chargeability and having excellent drum cleaning property.SOLUTION: The two component developer includes: a positively chargeable toner including: a toner mother particle including a toner core and a shell layer formed from a resin containing an acrylic resin; and an external additive adhering to a surface of the toner mother particle; and a carrier having a surface coated with a resin coating layer containing a silicone resin. The external additive includes silicone-modified acryl resin particles having a volume-average particle size of at least 40nm and no greater than 140nm. When the toner is subjected to an ultrasonic treatment in which ultrasonic vibration at a power of 100W and a frequency of 28kHz is applied for 1 minute in an aqueous dispersion liquid containing the toner and a nonionic surface active agent, the amount of the silicone-modified acryl resin particles detached and liberated from the toner base particles is 0.35 mass% or less with respect to the adhesion amount of the silicone-modified acryl resin particles before the ultrasonic treatment.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a two-component developer containing a positively charging toner for developing electrostatic latent images. [Background technology]

[0002] In general, in electrophotography, the surface of an electrostatic latent image carrier is charged by corona discharge or the like, and then exposed to light 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. The formed toner image is then transferred to a recording medium to obtain a high-quality image. Toners used in such electrophotography are typically prepared by mixing a binder resin such as a thermoplastic resin with a colorant, a charge control agent, a release agent, a magnetic material, and the like, and then kneading, pulverizing, and classifying the mixture to form toner particles (toner base particles).

[0003] Large-diameter inorganic or organic fine particles such as silica or titanium oxide are externally added to the toner base particles for the purposes of imparting fluidity to the toner, imparting suitable charging properties to the toner, improving the cleaning properties of the toner from the photosensitive drum, and suppressing the embedding of external additives in the toner when subjected to various stresses.

[0004] Patent Document 1 proposes the external addition of irregularly shaped (hemispherical) organic silicone resin particles to prevent the detachment of external additives. Patent Document 2 proposes a toner in which large-particle external additives are less likely to detach from the surface of toner particles, preventing them from being embedded in the resin layer on the carrier surface without reducing the spacer effect (improvement of transfer efficiency), and reducing the risk of fogging and toner scattering even after long-term use. Patent Document 3 proposes a toner to which acrylic or methacrylic resin fine particles having an electrostatic property opposite to that of the toner raw powder are externally added. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-36980 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-36980 [Patent Document 3] Japanese Patent Application Laid-Open No. 2011-90168 Summary of the Invention [Problem to be solved by the invention]

[0006] The silicone resin used in the toner of Patent Document 1 has a strong negative charging property, which reduces the charge amount in positively charging toner. The silicone molecules of the silicone resin have surfaces covered with methyl groups that have low interaction, which means that the cohesive force between the entire molecule is weak, and as a result, the surface tension is low, so even if the silicone resin is deformed, it is difficult to fix it to the toner surface.

[0007] The large particle size silica used in the toner in Patent Document 2 is only hydrophobized with hexamethyldisilazane, which causes a problem of significantly reducing the charge amount in positively charged toners. Even in the case of large particle size silica coated with a positively charged treatment, the coating of the positively charged treatment agent peels off due to stress in the actual machine, exposing the surface of the silica base material, which has a high negative charge, and this leads to poor charging of the toner.

[0008] The resin particles used in the toner of Patent Document 3 have higher adhesion of the external additive alone than inorganic particles, which poses a problem that the developability and transferability are inferior to toners with large-diameter silica added when compared at the same particle size.

[0009] In view of the above problems, an object of the present invention is to provide a two-component developer having stable transfer characteristics and positive charging properties, and also having excellent drum cleaning properties. [Means for solving the problem]

[0010] To achieve the above object, the first aspect of the present invention is a two-component developer containing a toner and a carrier capable of positively charging the toner through friction. The toner contains toner base particles and an external additive attached to the surface of the toner base particles. The toner base particles have toner core particles containing at least a binder resin and a colorant, and a shell layer covering the toner core particles. The shell layer is formed of a resin containing an acrylic resin. The external additive contains silicone-modified acrylic resin particles having a volume average particle diameter of 40 nm to 140 nm. When ultrasonic treatment is performed in an aqueous dispersion containing the toner and a nonionic surfactant by applying ultrasonic vibrations at an output of 100 W and a frequency of 28 kHz for 1 minute, the amount of silicone-modified acrylic resin particles that remain attached to the toner base particles without detaching is 0.35 mass% or less of the amount of silicone-modified acrylic resin particles attached before the ultrasonic treatment. The carrier has a carrier core and a resin coating layer that coats the surface of the carrier core, and the resin coating layer contains a silicone resin. [Effects of the Invention]

[0011] According to the first aspect of the present invention, a two-component developer having stable transfer characteristics and positive charging properties, as well as excellent drum cleaning properties, is obtained. [Brief explanation of the drawings]

[0012] [Figure 1] FIG. 1 is a diagram showing an example of a cross-sectional structure of a toner 101 used in a two-component developer of the present invention. DETAILED DESCRIPTION OF THE INVENTION

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

[0014] Hereinafter, the compound name may be followed by "based" to refer to the compound and its derivatives in a comprehensive manner. When the compound name is followed by "based" to refer to the name of a polymer, it means that the repeating unit of the polymer is derived from the compound or its derivative. Also, acrylic and methacrylic may be collectively referred to as "(meth)acrylic." Also, acryloyl (CH 2 =CH-CO-) and methacryloyl (CH 2 =C(CH 3 )-CO-) are sometimes collectively referred to as "(meth)acryloyl".

[0015] The two-component developer according to this embodiment is prepared by mixing, for example, a positively charged toner and a carrier using a mixing device (for example, a ball mill), and can be suitably used for developing electrostatic latent images. The toner is a powder containing a plurality of toner particles (particles each having the configuration described below). In order to form high-quality images using the two-component developer, it is preferable to use a ferrite carrier as the carrier.

[0016] 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, the 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 to 15 parts by mass per 100 parts by mass of carrier. Note that positively charged toner becomes positively charged due to friction with the carrier.

[0017] The toner particles contained in the toner according to this embodiment have a core (hereinafter referred to as a toner core particle) and a shell layer (capsule layer) formed on the surface of the toner core particle. The shell layer is substantially composed of a resin. For example, by covering a toner core that melts at low temperatures with a shell layer that has excellent heat resistance, it is possible to achieve both heat-resistant storage stability and low-temperature fixability of the toner. Additives may be dispersed in the resin that constitutes the shell layer. The shell layer may cover the entire surface of the toner core particle, or may cover only a portion of the surface of the toner core particle. An external additive may be attached to the surface of the shell layer (or to the surface region of the toner core particle that is not covered by the shell layer). Hereinafter, toner particles consisting of a toner core particle and a shell layer before the external additive is attached will be referred to as a toner mother particle. The material for forming the toner core will be referred to as a toner core material. The material for forming the shell layer will be referred to as a shell material.

[0018] The toner according to this embodiment can be used to form an image in, for example, an electrophotographic apparatus (image forming apparatus). An example of an image forming method using an electrophotographic apparatus will be described below.

[0019] First, an electrostatic latent image is formed on a photoreceptor (e.g., the surface of a photoreceptor drum) based on image data. The formed electrostatic latent image is then developed using a developer containing toner. In the development process, toner (e.g., toner charged by friction with a carrier or blade) on a development sleeve (e.g., the surface of a development roller in a developing unit) located near the photoreceptor is attached to 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, the toner image is primarily 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. The toner is then 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.

[0020] [1. Basic composition of toner] Fig. 1 is a diagram showing an example of the cross-sectional structure of toner 101 used in the two-component developer of the present invention. As shown in Fig. 1, in the toner for developing electrostatic latent images (hereinafter also simply referred to as toner) 101 of the present invention, the surface of a toner core particle 102 is coated with a shell layer 103. The toner core particle 102 contains at least a binder resin, a release agent, and a colorant. The toner core particle 102 and the shell layer 103 constitute a toner mother particle 104.

[0021] The thickness of the shell layer 103 is not particularly limited as long as it does not impair the object of the present invention, and is preferably 0.03 μm or more and 1 μm or less, more preferably 0.04 μm or more and 0.7 μm or less, particularly preferably 0.05 μm or more and 0.5 μm or less, and most preferably 0.05 μm or more and 0.3 μm or less.

[0022] If the shell layer 103 is too thick, the shell layer 103 is less likely to be damaged by the pressure applied to the toner 101 when the toner 101 is fixed to a recording medium. In this case, the binder resin and release agent contained in the toner core particles 102 do not soften or melt quickly, making it difficult to fix the toner to a recording medium at low temperatures. On the other hand, if the shell layer 103 is too thin, the strength of the shell layer 103 is reduced. If the strength of the shell layer 103 is low, the shell layer 103 may be damaged by impact during transportation, etc., and when the toner is stored at high temperatures, the toner 101 is more likely to aggregate due to the release agent seeping out onto the surface of the toner 101 from the damaged parts of the shell layer 103.

[0023] The thickness of the shell layer 103 can be measured by observing a cross section of the toner 101 using a transmission electron microscope (TEM) and analyzing the TEM image using commercially available image analysis software, such as WinROOF (manufactured by Mitani Shoji Co., Ltd.).

[0024] In the toner 101 of the present invention, it is not necessary for the entire surface of the toner core particle 102 to be covered with the shell layer 103. In order to achieve both heat-resistant storage stability and low-temperature fixability of the toner 101, it is preferable that the shell layer 103 covers 50% to 99% of the surface area of ​​the toner core particle 102. However, the entire surface of the toner core particle 102 may be covered with the shell layer 103.

[0025] The state of the shell layer 103 covering the surface of the toner 101 can be confirmed using a scanning electron microscope (SEM). The state of the shell layer 103 formed and the inside of the shell layer 103 of the toner 101 can be confirmed by observing a cross section of the toner 101 using a transmission electron microscope (TEM).

[0026] Resin particles 105 are attached to the surface (surface of the shell layer 103) of the toner base particles 104. The resin particles 105 are made of a silicone-modified acrylic resin.

[0027] In the toner 101 of the present invention, by adhering the resin particles 105 to the toner base particles 104, the cleaning properties (e.g., resistance to adhesion to a photosensitive drum) and developing properties (e.g., transfer efficiency) of the toner 101 tend to be improved. This is thought to be because the resin particles 105 function as spacers, making it difficult for the toner 101 to adhere to the photosensitive drum, intermediate transfer belt, etc.

[0028] The volume average particle diameter of the resin particles 105 is 40 nm or more and 140 nm or less. If the volume average particle diameter of the resin particles 105 is less than 40 nm, the resin particles 105 are easily fixed to the surface of the toner 101, but the spacer effect is small, and the effect of preventing the resin particles 105 from being buried is reduced. If the volume average particle diameter of the resin particles 105 exceeds 140 nm, it becomes difficult to fix the resin particles 105 to the surface of the toner mother particles 104, leading to contamination of the carrier by the free resin particles 105 and contamination of components inside the image forming apparatus.

[0029] Furthermore, by coating the surface of the toner core particle 102 with a shell layer 103 containing an acrylic resin as a main component (forming a core-shell structure), the resin particles 105 and the shell layer 103 become the same material, increasing their affinity and making them more likely to be fixed to the surface of the toner base particle 104 by the shear mixing energy generated during the external additive treatment. As a result, the amount of free external additive present in the nip portion of the cleaning blade that cleans the photosensitive drum is reduced, making it less likely for the external additive to slip through, thereby improving drum cleaning performance.

[0030] Furthermore, when the resin particles 105 are subjected to ultrasonic treatment in an aqueous dispersion liquid by applying ultrasonic vibrations at a power of 100 W and a frequency of 28 kHz for 1 minute, the amount of resin particles 105 that have detached and become free from the toner base particles 104 (free resin particle amount) is preferably 0.35% by mass or less relative to the weight of the toner base particles 104. If the free resin particle amount is 0.35% by mass or more, the amount of free resin particles recovered by the cleaning blade increases. Because the resin particles 105 have a smaller particle diameter and are spherical compared to the toner 101, more of the resin particles 105 slip through the cleaning blade, reducing cleaning performance.

[0031] [2. Toner Materials] Next, essential and optional components constituting the toner of the present invention will be described. The toner core particles contain at least a binder resin, a release agent, and a colorant. If necessary, they may also contain a charge control agent, magnetic powder, etc. Furthermore, the toner of the present invention has resin particles externally added to its surface as an external additive.

[0032] The binder resin forming the toner core particles, the release agent, the colorant, the charge control agent, the magnetic powder, the shell material forming the shell layer, and the external additives, as well as the method for producing the toner of the present invention will be described below in this order.

[0033] (binder 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-based resins, acrylic-based resins, styrene-acrylic-based resins, polyethylene-based resins, polypropylene-based resins, vinyl chloride-based resins, polyester resins, polyamide resins, polyurethane resins, polyvinyl alcohol-based resins, vinyl ether-based resins, N-vinyl-based resins, and styrene-butadiene resins. Among these resins, polyester resins are preferred in terms of the dispersibility of colorants in the binder resin, the chargeability of the toner, and the fixability to paper. The polyester resin will be described below.

[0034] The polyester resin can be obtained by condensation polymerization or co-condensation polymerization of a divalent or trivalent or higher alcohol component and a divalent or trivalent or higher carboxylic acid component. The components used in synthesizing the polyester resin include the following alcohol components and carboxylic acid components.

[0035] Specific examples of the dihydric or trihydric or higher alcohol component 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 bisphenols such as hydroxypropylated bisphenol A and polyoxypropylated bisphenol A; and trihydric 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 the divalent or trivalent or higher carboxylic acid component include divalent carboxylic acids such as maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, or 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-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic 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 trimer acid. These divalent 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" refers to 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. or higher and 130° C. or lower, more preferably 80° C. or higher and 120° C. or lower. In order to improve the strength of the toner core and the fixability of the toner, the number average molecular weight (Mn) of the polyester resin is preferably 1,000 or higher and 2,000 or lower. The molecular weight distribution of the polyester resin (the ratio Mw / Mn of the mass average molecular weight (Mw) to the number average molecular weight (Mn)) is preferably 9 or higher and 21 or lower.

[0038] As the binder resin, it is preferable to use a thermoplastic resin because it has good fixability to paper. However, in addition to using a thermoplastic resin alone, a crosslinking agent or a thermosetting resin can be added to the thermoplastic resin. By adding a crosslinking agent or a thermosetting resin to introduce a partial crosslinked structure into the binder resin, it is possible to improve the heat-resistant storage stability and durability of the toner without reducing the fixability of the toner. When a thermosetting resin is used, the amount of crosslinked portions (gel amount) of the binder resin extracted using a Soxhlet extractor is preferably 10% by mass or less, more preferably 0.1% by mass or more and 10% by mass or less, based on the mass of the binder resin.

[0039] Thermosetting resins that can be used together with thermoplastic resins are preferably epoxy resins or cyanate resins. Specific examples of suitable thermosetting resins include bisphenol A epoxy resins, hydrogenated bisphenol A epoxy resins, novolac epoxy resins, polyalkylene ether epoxy resins, cycloaliphatic epoxy resins, and cyanate resins. These thermosetting resins can be used in combination of two or more.

[0040] The glass transition point (Tg) of the binder resin is preferably 40° C. or higher and 70° C. or lower. If the glass transition point is too high, the low-temperature fixability of the toner tends to decrease. If the glass transition point is too low, the heat-resistant storage stability of the toner tends to decrease.

[0041] The glass transition point of the binder resin can be determined from the change point 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 differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. as the measuring device. 10 mg of a measurement 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 of the binder resin obtained by measuring at room temperature and normal humidity in a measurement temperature range of 25°C to 200°C at a heating rate of 10°C / min.

[0042] The weight average molecular weight (Mw) of the binder resin is not particularly limited as long as it does not impair the object of the present invention. Typically, the weight average molecular weight (Mw) of the binder resin is preferably 20,000 or more and 300,000 or less, and more preferably 30,000 or more and 2,000,000 or less. The weight 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 resins.

[0043] (mold release agent) The toner core particles contain a release agent for the purpose of improving fixability and offset resistance. The type of release agent that can be contained in the toner core particles is not particularly limited as long as it does not impair the object of the present invention. Wax is preferred as the release agent, and examples of wax 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. Adding such a release agent to the toner core particles 102 can more efficiently suppress the occurrence of offset and image smearing (staining around the image when the image is rubbed).

[0044] When a 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. When a 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 linear hydrocarbon compound with few isostructural molecules and few side chains, produced by utilizing the Fischer-Tropsch reaction, which is a catalytic hydrogenation reaction of carbon monoxide.

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

[0047] The amount of release agent used is not particularly limited as long as it does not impair the object of the present invention. Specifically, the amount of release agent used is preferably 1% by mass or more and 10% by mass or less, based on the total mass of the toner core particles 102. If the amount of release agent used is too small, the desired effect of suppressing offset and image smearing in the formed image may not be achieved. If the amount of release agent used is too large, the toner particles may fuse together, resulting in a decrease in the heat-resistant storage stability of the toner.

[0048] (coloring agent) The toner core particles contain a colorant. The colorant that can be contained in the toner core particles can be a known pigment or dye, depending on the color of the toner. Specific examples of suitable colorants that can be added to the toner include black pigments such as carbon black, acetylene black, lamp black, and aniline black; yellow pigments such as yellow lead, 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 yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, vulcan 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 suitable colorants include red pigments such as Ron 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 Purple, Fast Violet B, and Methyl Violet Lake; blue pigments such as Prussian Blue, Cobalt Blue, Alkali Blue Lake, Victoria Blue (partially chlorinated), Fast Sky Blue, Indanthrene 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 oxide, antimony white, and zinc sulfide; and extender pigments such as baryte powder, barium carbonate, clay, silica, white carbon, talc, and alumina white. These colorants can also be used in combination of two or more types to adjust the toner to a desired hue.

[0049] The amount of the colorant used is not particularly limited as long as it does not impair the object of the present invention. Specifically, the amount of the 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, based on the total mass of the toner core particles.

[0050] The colorant may also be used as a masterbatch in which the colorant is dispersed in advance in a resin material such as a thermoplastic resin. When the colorant is used as a masterbatch, the resin contained in the masterbatch is preferably the same type of resin as the binder resin.

[0051] (charge control agent) The toner core particles may contain a charge control agent for the purpose of improving the charge level of the toner and the charge rise property, which is an index of whether the toner can be charged to a predetermined charge level in a short time, and obtaining a toner with excellent durability and stability. Since the toner of the present invention is positively chargeable, a positively chargeable charge control agent is used.

[0052] The type of charge control agent that can be contained in the toner core particles is not particularly limited as long as it does not impair the object of the present invention, and can be appropriately selected from charge control agents that have been used in toners. Specific examples of positively chargeable charge control agents include azine compounds such as pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 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 phthalazine; Examples of suitable positively charged charge control agents include direct dyes made from azine compounds such as Fast Red 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 made from 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 more rapid charge buildup. These positively charged charge control agents can be used in combination of two or more.

[0053] Resins having a quaternary ammonium salt, a carboxylate, or a carboxyl group as a functional group can also be used as positively charged charge control agents. More specifically, examples include styrene-based resins having a quaternary ammonium salt, acrylic-based resins having a quaternary ammonium salt, styrene-acrylic resins having a quaternary ammonium salt, polyester resins having a quaternary ammonium salt, styrene-based resins having a carboxylate, acrylic resins having a carboxylate, styrene-acrylic resins having a carboxylate, polyester resins having a carboxylate, styrene-based resins having a carboxyl group, acrylic resins having a carboxyl group, styrene-acrylic resins having a carboxyl group, and polyester resins having a carboxyl group. The molecular weight of these resins is not particularly limited as long as it does not impair the object 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 a quaternary ammonium salt as a functional group are more preferred because the charge amount can be easily adjusted to a value within a desired range. Specific examples of preferred acrylic comonomers to be copolymerized with styrene units in styrene-acrylic resins having a quaternary ammonium salt as a functional group include (meth)acrylic acid alkyl esters such as methyl acrylate, ethyl acrylate, n-propyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and isobutyl methacrylate.

[0055] The quaternary ammonium salt may be a unit derived from a dialkylaminoalkyl (meth)acrylate, a dialkyl (meth)acrylamide, or a dialkylaminoalkyl (meth)acrylamide via a quaternization process. 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 dimethylaminopropyl methacrylamide. Hydroxy-containing polymerizable monomers such as hydroxyethyl (meth)acrylate, hydroxypropyl (meth)acrylate, 2-hydroxybutyl (meth)acrylate, and N-methylol (meth)acrylamide may also be used in combination during polymerization.

[0056] The amount of charge control agent used is not particularly limited as long as it does not impair the objectives of the present invention. The amount of charge control agent used is typically preferably 0.1% by mass or more and 10% by mass or less, based on the total mass of the toner core particles. If the amount of charge control agent used is too small, 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. Furthermore, it is difficult for the charge control agent to be uniformly dispersed, which may result in fogging of the formed image or contamination of the latent image bearing portion by toner components. If the amount of charge control agent used is too large, deterioration of environmental resistance may result in poor charging under high temperature and high humidity conditions, which may lead to image defects in the formed image, or contamination of the latent image bearing portion by toner components.

[0057] (magnetic powder) The 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, chromium dioxide, etc.), or materials that have been subjected to ferromagnetic treatment (more specifically, carbon materials that have been given ferromagnetism by heat treatment, etc.). In order to prevent metal ions (e.g., iron ions) from eluting 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 powders may be used in combination.

[0058] (shell material) The shell layer constituting the toner of the present invention is formed from a vinyl resin. In addition, the vinyl resin used to form the shell layer is a resin containing a charge control resin. When the shell layer is made of a resin containing a charge control resin, the toner can be charged to a desired charge amount when forming images over a long period of time under various environments such as a high-temperature, high-humidity environment or a low-temperature, low-humidity environment, and therefore, an image of a desired density can be formed.

[0059] The vinyl resin is preferably a styrene-acrylic acid resin containing a styrene monomer and one or more acrylic acid monomers. Styrene-acrylic acid resins have strong hydrophobic properties and tend to be easily positively charged. Furthermore, it is believed that forming the shell layer from a styrene-acrylic acid resin increases the affinity with resin particles formed from a silicone-modified acrylic resin that are attached to the toner base particles as an external additive, thereby suppressing detachment of the resin particles from the shell layer.

[0060] The amount of vinyl resin used is not particularly limited as long as it does not impair the object of the present invention. The amount of vinyl resin used is typically preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 3 parts by mass or more and 15 parts by mass or less, per 100 parts by mass of toner core particles. If the amount of vinyl resin used is too small, the entire surface of the toner core particles may not be covered with a shell layer. If the entire surface of the toner core particles cannot be covered with a shell layer, the toner is likely to aggregate during storage at high temperatures, and its heat-resistant storage stability is likely to deteriorate. On the other hand, if the amount of vinyl resin used is excessive, the shell layer is likely to become thick. In this case, it is difficult to obtain a toner with excellent fixability.

[0061] The weight average molecular weight (Mw) of the vinyl resin used to form the shell layer is not particularly limited as long as it does not impair the object of the present invention. Typically, the weight average molecular weight is preferably 20,000 or more and 1,500,000 or less, and more preferably 200,000 or more and 400,000 or less. The weight average molecular weight (Mw) of the vinyl resin can be measured by gel permeation chromatography according to a conventional method.

[0062] The method for polymerizing the above-mentioned monomers is not limited as long as it does not impair the object of the present invention, and any method such as solution polymerization, bulk polymerization, emulsion polymerization, suspension polymerization, etc. can be selected.

[0063] When an aqueous medium is used to perform addition polymerization of a monomer having an unsaturated bond, such as emulsion polymerization or suspension polymerization, a surfactant can be used. The surfactant is not limited as long as it does not impair the objectives of the present invention and can be appropriately selected from the group consisting of anionic surfactants, cationic surfactants, and nonionic surfactants. Examples of anionic surfactants include sulfate ester salt surfactants, sulfonate salt surfactants, phosphate ester salt surfactants, and soap. Examples of cationic surfactants include amine salt surfactants and quaternary ammonium salt surfactants. Examples of nonionic surfactants include polyethylene glycol surfactants, alkylphenol ethylene oxide adduct surfactants, and polyhydric alcohol surfactants, which are derivatives of polyhydric alcohols such as glycerin, sorbitol, and sorbitan. Among these surfactants, it is preferable to use at least one of anionic surfactants and nonionic surfactants. These surfactants may be used alone or in combination of two or more.

[0064] (external additives) The toner of the present invention is prepared by treating toner base particles, which have a shell layer formed on the surface of a toner core particle, with an external additive. The external additive used in the toner of the present invention contains at least resin particles. The resin particles are formed of a silicone-modified acrylic resin having a silicone moiety and an acrylic moiety.

[0065] Silicone-modified acrylic resin has a structure in which silicone side chains are attached to the acrylic backbone, giving it the release and lubricity characteristic of silicone. Silicone-modified acrylic resin is a copolymer of a polydiorganosiloxane macromer with acrylic functional groups and a radically polymerizable organic monomer.

[0066] Furthermore, other monomers can be copolymerized with the above-mentioned monomers. Examples of the other monomers to be copolymerized include styrene-based monomers such as styrene, methylstyrene, methoxystyrene, ethylstyrene, propylstyrene, butylstyrene, phenylstyrene, and chlorostyrene; and acrylic acid ester or methacrylic acid ester-based monomers such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, pentyl acrylate, dodecyl acrylate, stearyl acrylate, ethylhexyl acrylate, lauryl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, pentyl methacrylate, dodecyl methacrylate, stearyl methacrylate, ethylhexyl methacrylate, and lauryl methacrylate.

[0067] Other external additives may also be used together with the resin particles. The type of external additive used together with the resin particles is not particularly limited as long as it does not impair the object of the present invention, and can be appropriately selected from external additives conventionally used for toners. Specific examples of suitable external additives include silica and metal oxides such as alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate. Two or more of these external additives may be used in combination.

[0068] (Toner manufacturing method) Next, a method for producing the toner used in the two-component developer of the present invention will be described. The method for producing the toner is not particularly limited as long as the toner core particles and the shell layer are formed so as to have the predetermined structures. Furthermore, the toner core particles coated with the shell layer are used as toner base particles, and an external additive treatment is performed to attach an external additive to the surface of the toner base particles. As a suitable method for producing the toner for developing electrostatic latent images described above, the method for producing the toner core particles, the method for forming the shell layer, and the external additive treatment method will be described below in order.

[0069] (Method of manufacturing toner core particles) The method for producing toner core particles is not particularly limited as long as it can satisfactorily disperse optional components such as a colorant, a release agent, a charge control agent, and a magnetic powder in a binder resin. A specific example of a suitable method for producing toner core particles includes a method in which a binder resin and components such as a colorant, a release agent, a charge control agent, and a magnetic powder are mixed in a mixer or the like, and then the binder resin and components to be blended in the binder resin are melt-kneaded in a kneader such as a single-screw or twin-screw extruder, and the cooled kneaded product is pulverized and classified. The average particle size of the toner core particles is not particularly limited as long as it does not impair the object of the present invention, but is generally preferably 5 μm or more and 10 μm or less.

[0070] (Method of forming shell layer) The shell layer is formed by adhering fine particles of a vinyl resin to the surface of the toner core particle, thereby covering the surface of the toner core particle.

[0071] A more specific method will be described below. First, hydrochloric acid is added to ion-exchanged water in a mixer to prepare a weakly acidic aqueous medium (for example, a pH selected from 3 to 5). Next, a dispersion (suspension) of vinyl resin fine particles as a shell material and toner core particles are added to the aqueous medium with the adjusted pH.

[0072] Next, while stirring the mixture containing the shell material and toner core particles, the temperature of the mixture is raised to a predetermined holding temperature (e.g., a temperature selected from the range of 50°C to 90°C) at a predetermined rate (e.g., a rate selected from the range of 0.1°C / min to 3°C / min). Furthermore, while stirring the mixture, the temperature of the mixture is maintained at the holding temperature for a predetermined time (e.g., a time selected from the range of 30 minutes to 4 hours). While the temperature of the mixture is maintained at a high temperature, a reaction (solidification of the shell layer) is thought to occur between the toner core particles and the shell material. The shell material bonds with the toner core particles, forming a shell layer. The shell layer is formed on the surface of the toner core particles in the mixture, resulting in a dispersion of toner base particles.

[0073] As described above, by adhering hydrophobic vinyl resin particles to the surfaces of toner core particles in a mixed solution and then heating the mixed solution, the vinyl resin particles can be dissolved and formed into a film. However, film formation of the vinyl resin particles may also proceed when heated in the drying process or when subjected to a physical impact force in the external addition process.

[0074] After the shell layer is formed as described above, the dispersion of toner base particles is neutralized using, for example, sodium hydroxide. The dispersion of toner base particles is then cooled to, for example, room temperature (approximately 25°C). The dispersion of toner base particles is then filtered using, for example, a Buchner funnel. This separates the toner base particles from the liquid (solid-liquid separation), yielding wet cake-like toner base particles. The resulting wet cake-like toner base particles are then washed. The washed toner base particles are then dried. If necessary, the toner base particles and an external additive may be mixed using a mixer (for example, an FM mixer manufactured by Nippon Coke & Engineering Co., Ltd.) to adhere the external additive to the surface of the toner base particles. When a spray dryer is used in the drying process, the drying process and the external additive process can be performed simultaneously by spraying a dispersion of the external additive (for example, silica particles) onto the toner base particles. In this manner, a toner containing a large number of toner particles is produced.

[0075] The content and order of the above-described toner manufacturing method can be arbitrarily changed depending on the required toner configuration or properties, etc. Furthermore, the toner may be sieved after the external addition step. Unnecessary steps may be omitted. For example, if a commercially available product can be used as a material as is, the step of preparing the material can be omitted by using the commercially available product. Furthermore, if the reaction for forming the shell layer proceeds smoothly without adjusting the pH of the mixed solution, the pH adjustment step may be omitted. When no external additive is attached to the surface of the toner base particles (when the external addition step is omitted), the toner base particles correspond to the toner particles. For efficient toner manufacturing, it is preferable to simultaneously form a large number of toner particles. It is considered that the toner particles manufactured simultaneously have substantially the same configuration.

[0076] (External addition treatment method) The method for treating the toner base particles with the external additive is not particularly limited, and the toner base particles can be treated according to a conventionally known method. Specifically, the treatment conditions are adjusted so that the particles of the external additive are not embedded in the toner base particles, and the toner base particles are treated with the external additive using a mixer such as a Henschel mixer or a Nauta mixer.

[0077] The toner of the present invention described above has excellent fixing properties and heat-resistant storage properties, and when images are formed over a long period of time under various environments such as high-temperature and high-humidity environments and low-temperature and low-humidity environments, the toner can be charged to a desired charge amount, thereby enabling the formation of images of a desired density. Therefore, the toner for developing electrostatic latent images of the present invention can be suitably used in various image forming devices.

[0078] [3. Magnetic Carrier Materials] Next, essential and optional components constituting the magnetic carrier used in the two-component developer of the present invention will be described. The magnetic carrier of the present invention includes at least a carrier core and a resin coating layer (coating layer) that coats the carrier core. If necessary, the resin coating layer may also contain a conductive agent. Below, the carrier core that forms the magnetic carrier particles, the resin material that forms the resin coating layer, and the conductive agent, as well as the method for producing the magnetic carrier of the present invention will be described in order.

[0079] (Career Core) The carrier core is not particularly limited, and known two-component carriers for electrophotography can be used, such as ferrite, magnetite, and metals such as iron, nickel, and cobalt; alloys or mixtures of the above-listed metals with metals such as copper, zinc, antimony, aluminum, lead, tin, bismuth, beryllium, manganese, magnesium, selenium, tungsten, zirconium, and vanadium; mixtures of the above-listed ferrites with metal oxides such as iron oxide, titanium oxide, and magnesium oxide; nitrides such as chromium nitride and vanadium nitride; and carbides such as silicon carbide and tungsten carbide; and ferromagnetic ferrites, with ferrite and magnetite being particularly preferred.

[0080] The volume average particle diameter of the carrier core is preferably 20 to 70 μm. This allows for good developability. The volume average particle diameter can be measured using a laser diffraction scattering particle diameter measuring device. Examples of laser diffraction scattering particle diameter measuring devices include the LA-700 (manufactured by Horiba, Ltd.).

[0081] (resin material) The resin material constituting the resin coating layer may be any resin containing a silicone resin. Silicone resins are particularly preferred because they have excellent toner filming properties, durability, and low water vapor permeability. Examples of silicone resins include "KR-255" manufactured by Shin-Etsu Chemical Co., Ltd. Furthermore, the carrier cores can also be coated using a coating agent containing a silicone-based organic treatment agent, such as a silane coupling agent, that controls chargeability. In this case, a resin coating layer containing a silicone resin can also be formed on the surface of the carrier cores.

[0082] (Conductive agent) The resin coating layer preferably further contains a conductive agent, which makes it possible to adjust the electrical resistance of the carrier particles and the ability to impart charge to the toner.

[0083] Examples of the conductive agent include carbon black (particularly conductive carbon black), metal oxide particles (e.g., titanium oxide particles, strontium titanate particles, and tin oxide particles), and organic conductive agents. Preferred conductive agents are carbon black, titanium oxide particles, and strontium titanate particles.

[0084] When the resin coating layer contains carbon black, the content of carbon black is preferably 1.0 to 10.0 parts by mass, more preferably 2.0 to 6.0 parts by mass, per 100 parts by mass of the coating resin.

[0085] (additives) The resin coating layer may contain at least one of a charge control agent, an adhesion improver, and a crosslinking agent as an additive. As the additive, a silane coupling agent (or a component derived from a silane coupling agent) is preferred, and an aminosilane coupling agent (or a component derived from an aminosilane coupling agent) is more preferred. The aminosilane coupling agent (or a component derived from an aminosilane coupling agent) functions as a charge control agent, an adhesion improver, and a crosslinking agent.

[0086] When the resin coating layer contains an additive, the content of the additive is preferably 4.0 parts by mass or more and 20.0 parts by mass or less, and more preferably 8.0 parts by mass or more and 15.0 parts by mass or less, per 100 parts by mass of the resin.

[0087] (Magnetic Carrier Manufacturing Method) An example of a method for producing a carrier of the present invention will be described. The method for producing a carrier includes a coating step of coating a resin coating layer-forming solution onto carrier cores and a heating step of heating the carrier cores after the coating step. The resin coating layer-forming solution contains a silicone resin, a solvent, and other components (e.g., a conductive agent and additives) that are added as needed.

[0088] Examples of solvents for the resin coating layer-forming solution include lactam compounds (e.g., 2-pyrrolidone and N-methyl-2-pyrrolidone), ketone compounds (e.g., methyl ethyl ketone and methyl isobutyl ketone), cyclic ether compounds (e.g., tetrahydrofuran and tetrahydropyran), alcohol compounds (e.g., normal butanol and isobutanol), ester solvents (e.g., ethyl acetate and isobutyl acetate), and aromatic hydrocarbon compounds (e.g., toluene and xylene). N-methyl-2-pyrrolidone is preferred as the solvent for the coating layer-forming solution.

[0089] The solid content concentration of the resin coating layer forming solution is preferably 3% by mass or more and 20% by mass or less.

[0090] (Coating process) Methods for applying the resin coating layer forming solution to the carrier cores include, for example, immersing the carrier cores in the resin coating layer forming solution and spraying the resin coating layer forming solution onto the carrier cores in a fluidized bed. When immersing the carrier cores in the resin coating layer forming solution, a small amount of the resin coating layer forming solution is applied to the convex portions on the surface of the carrier core, while a large amount of the resin coating layer forming solution is applied to the concave portions on the surface of the carrier core, which tends to result in uneven application of the resin coating layer forming solution. In contrast, when spraying the resin coating layer forming solution onto the carrier cores in a fluidized bed, the resin coating layer forming solution tends to be applied uniformly to both the convex portions and the concave portions on the surface of the carrier core. From the above, spraying the resin coating layer forming solution onto the carrier cores in a fluidized bed is preferred as a method for applying the resin coating layer forming solution to the carrier cores.

[0091] (Heating process) In this process, the carrier cores after the coating process are heated to remove the solvent contained in the resin coating layer-forming solution. Furthermore, if the resin coating layer-forming solution contains uncured polyimide silicone resin, the uncured polyimide silicone resin is thermally cured. As a result, a resin coating layer is formed from the resin coating layer-forming solution. Heating conditions can be, for example, a heating temperature of 200°C to 300°C and a heating time of 30 minutes to 90 minutes.

[0092] The effects of the present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. [Example]

[0093] [Manufacturing Example 1] (Production of toner base particles A) A mixture was obtained by mixing 82% by weight of a polyester resin (HP-313, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.) as a binder resin, 6.0% by weight of a colorant (carbon black MA-100, manufactured by Mitsubishi Chemical Corporation), 2.0% by weight of a charge control agent (N-01, manufactured by Orient Chemical Co., Ltd.), 4.0% by weight of a charge control agent (FCA-201-PS, manufactured by Fujikura Chemical Co., Ltd.), and 6.0% by weight of a release agent (WEP-4, manufactured by NOF Corporation) in a Henschel mixer (FM-10, manufactured by Mitsui Mining Co., Ltd.). The mixture was then melt-kneaded in a twin-screw extruder (TEM-26SS, manufactured by Toshiba Machine Co., Ltd.) to obtain a kneaded product. The kneaded product was coarsely pulverized to approximately 2 mm using a Rotoplex pulverizer (manufactured by Toa Machinery Co., Ltd.), and the coarsely pulverized product was then finely pulverized using a mechanical pulverizer (Turbo Mill, manufactured by Turbo Kogyo Co., Ltd.) to obtain a finely pulverized product. The finely pulverized material was classified using an air classifier (EJ-L-3 (LABO) model, manufactured by Nittetsu Mining Co., Ltd.) to obtain toner core particles (toner base particles A) having a volume average particle diameter (D50) of 7.0 μm. The volume average particle diameter was measured using a Coulter Counter Multisizer 3 (manufactured by Beckman Coulter, Inc.).

[0094] [Manufacturing Example 2] (Production of toner base particles B) (2-1. Shell Material Production) A 1 L three-neck flask equipped with a stirrer, thermometer, condenser, and nitrogen inlet tube was placed in a 35°C water bath and used as a reaction vessel. 900 mL of ion-exchanged water and 80 mL of anionic surfactant (Latemul WX, manufactured by Kao Corporation, components: polyoxyethylene alkyl ether sodium sulfate, solids concentration: 26% by mass) were placed in the flask. The temperature inside the flask was then raised to 80°C using a water bath and maintained at that temperature (80°C). Subsequently, the first and second liquids were each added dropwise to the contents of the flask at 80°C over 6 hours. The first liquid was a mixture of 13 g of styrene, 7 g of n-butyl acrylate (BA), 0.5 g of 2-(methacryloyloxy)ethyltrimethylammonium chloride (METAC), and 0.5 g of 2-hydroxyethyl acrylate (HPA). The second liquid was a solution of 0.5 g of potassium persulfate dissolved in 30 mL of ion-exchanged water. Thereafter, the temperature inside the flask was maintained at 80° C. for another 2 hours to polymerize the contents of the flask, resulting in a dispersion of resin fine particles with a volume average particle size of 32 nm.

[0095] (2-2. Shell layer formation) A 1 L three-neck flask equipped with a thermometer and a stirring blade was placed in a water bath, and 400 mL of ion-exchanged water was added to the flask. The temperature inside the flask was then maintained at 35°C using the water bath. Dilute hydrochloric acid was then added to the flask to adjust the pH of the contents to 4. 250 g of the shell material obtained above was then added to the flask. 300 g of the toner base particles A obtained in Production Example 1 was then added to the flask. The contents of the flask were then stirred at a rotation speed of 100 rpm, and the temperature inside the flask was raised to 65°C at a rate of 1°C / min. The contents of the flask were then stirred for 2 hours at a temperature of 65°C and a rotation speed of 100 rpm. Sodium hydroxide was then added to the flask to adjust the pH of the contents to 7. The contents of the flask were then cooled to room temperature (approximately 25°C) to obtain a dispersion of pre-treatment particles (toner base particles before the mechanical treatment described below).

[0096] (2-3. Washing and drying. Mechanical treatment) The dispersion of the untreated particles obtained in Production Example 2-2 was filtered (solid-liquid separation) using a Buchner funnel to obtain wet cake-like untreated particles. The obtained wet cake-like untreated particles were then redispersed in ion-exchanged water. Furthermore, the dispersion and filtration were repeated four times to wash the untreated particles.

[0097] The obtained untreated particles were dispersed in an aqueous ethanol solution with a concentration of 50% by mass. This resulted in a slurry of untreated particles. Subsequently, using a continuous surface modification device (Coatmizer, manufactured by Freund Corporation), hot air was blown at a temperature of 40°C with a blower volume of 2 m 3 The untreated particles in the slurry were dried under the conditions of 1000 rpm / min.

[0098] Next, the untreated particles were subjected to mechanical treatment (more specifically, treatment to apply shear force) for 10 minutes using a fluidized bed mixer (FM-20C / I, manufactured by Nippon Coke & Engineering Co., Ltd.) at a rotation speed of 3500 rpm and a jacket temperature of 20° C. By subjecting the untreated particles to mechanical treatment, a powder of toner base particles B having a volume average particle diameter of 7.2 μm was obtained.

[0099] [Manufacturing Example 3] (Production of resin particles) (3-1. Production of silicone-modified acrylic resin particles) After thoroughly purging the atmosphere in a flask equipped with a stirrer, thermometer, condenser, nitrogen inlet, and dropping funnel with nitrogen gas, 100 g of pure water, 4 g of sodium dodecylbenzenesulfonate, and 1 g of polyethylene glycol nonylphenyl ether were added. 1 g of ammonium persulfate and 0.4 g of sodium bisulfite were added, and the temperature was raised to 60 °C. Next, 35 g of butyl acrylate, 40 g of methyl methacrylate, 20 g of butyl methacrylate, 10 g of vinylsilanetriol potassium salt, and 5 g of 3-methacryloxypropylmethyldimethoxysilane were added dropwise to the flask over 3 hours. The polymerization reaction solution was adjusted to pH 7 with aqueous ammonia solution, and polymerization was carried out. The pH of this solution was then adjusted to 5, and the solution was spray-dried at 100 °C for 3 hours using a spray dryer (Okawahara Chemical Engineering Co., Ltd.: FOC-25) to produce silicone-modified acrylic resin particles (spacer particles C, particle diameter 90 nm).

[0100] Furthermore, particle size was adjusted by changing the nozzle hole diameter and spray speed during spray drying to produce silicone-modified acrylic resin particles with different average particle sizes (spacer particles A, B, D, and E). The average particle size was determined by randomly selecting 50 particles from the SEM image and calculating the average diameter.

[0101] (3-2. Silane coupling agent treatment of silicone-modified acrylic resin particles) 300 g of the silicone-modified acrylic resin particles obtained in Production Example 3-1 and 15 g of a silane coupling agent (isobutyltriethoxysilane, manufactured by Tokyo Chemical Industry Co., Ltd.) were diluted with 50 g of an ethanol aqueous solution (water / alcohol = 1 / 9 mass ratio), charged into a mixer (Nanopersion Piccolo, manufactured by Kawata Co., Ltd.), mixed at 80 ° C for 1 hour, and then dried at 100 ° C for 12 hours. Thereafter, using a grinder (Jet Mill I-2, manufactured by Nippon Pneumatic Mfg. Co., Ltd.) and a ceramic flat plate as a collision plate, the mixture was ground at a grinding pressure of 0.6 MPa to obtain silane coupling agent-treated silicone-modified acrylic resin particles (spacer particles F, particle diameter 91 nm).

[0102] (3-3. Titanate Coupling Agent Treatment of Silicone-Modified Acrylic Resin Particles) 300 g of the silicone-modified acrylic resin particles obtained in Production Example 3-1 and 10 g of a titanate coupling agent (Plenact TTS, manufactured by Ajinomoto Co., Inc.) were placed in a mixer (Nanopersion Piccolo, manufactured by Kawata Co., Ltd.), mixed at 80° C. for 1 hour, and then dried at 100° C. for 12 hours. The mixture was then pulverized using a pulverizer (Jet Mill I-2, manufactured by Nippon Pneumatic Mfg. Co., Ltd.) at a pulverization pressure of 0.7 MPa using a ceramic flat plate as a collision plate to obtain titanate coupling agent-treated silicone-modified acrylic resin particles (spacer particles G, particle diameter 92 nm).

[0103] (3-4. Production of acrylic resin particles) A 2-L separable flask equipped with a stirrer, thermometer, condenser, nitrogen inlet, and dropping funnel was charged with 820 g of ion-exchanged water and heated to 80°C under constant stirring under a nitrogen gas stream. After 30 minutes, 0.7 g of ammonium persulfate was added as a polymerization initiator. Next, 55 g of ion-exchanged water, 36 g of tetramethylolpropane triacrylate with a solubility in water (25°C) of 1% by mass or less, and 20 g of a 15% by mass aqueous solution of sodium dodecylbenzenesulfonate were emulsified using a homogenizer. 108 g of an emulsion dispersion was then added all at once to the flask. The temperature of the polymerization reaction system was maintained at 70°C, and the polymerization reaction was carried out for approximately 3 hours.

[0104] Next, 126 g of ion-exchanged water, 69 g of trimethylolpropane triacrylate (solubility in water (25°C) of 1% by mass or less), 30 g of ethylene glycol dimethacrylate, and 15 g of an 8% by mass aqueous solution of sodium dodecylbenzenesulfonate were emulsified using a homogenizer. 240 g of the resulting emulsion was added dropwise from the dropping funnel at a rate of 1 g / min. The addition was terminated after approximately 3 hours, and the polymerization reaction was continued for another 1.5 hours to produce a crosslinked resin microparticle emulsion. The resulting crosslinked resin microparticle emulsion was then freeze-dried using a freeze dryer to obtain acrylic resin particles (spacer particles H, particle diameter 89 nm) composed of crosslinked resin particles.

[0105] (3-5. Production of PMMA resin particles) A reaction vessel was charged with 100 parts by mass of methyl methacrylate and 300 parts by mass of distilled water, and 4 × 10 -3 mol / L, and copper sulfate was used as a promoter at 2.5 × 10 -5 The mixture was added to give a concentration of 0.01 mol / L, and the mixture was allowed to react for 2 hours at 70°C under a nitrogen stream. After cooling, the mixture was ultrafiltered and dried to obtain polymethyl methacrylate (PMMA) resin particles (spacer particles I, particle diameter 90 nm) consisting of crosslinked resin particles.

[0106] (3-6. Production of styrene-acrylic resin particles) A 2L separable flask equipped with a stirrer, thermometer, nitrogen inlet tube, reflux condenser, and dropping funnel was charged with 100 parts by weight of ion-exchanged water, and 1 part by weight of lauric acid diethanolamide was added and heated to 80°C. Next, 0.1 parts by weight of 2,2'-azobis(2-methylpropionamidine) dihydrochloride was added, followed by dropwise addition of 35 parts by weight of styrene, 40 parts by weight of butyl methacrylate, and 20 parts by weight of dimethylaminoacrylate. The mixture was emulsion-polymerized at 80°C for 2 hours to obtain an emulsion. The resulting emulsion was then purified using an ultrafiltration apparatus and dried by spray drying to obtain styrene-acrylic resin particles (spacer particles J, particle diameter 88 nm) composed of crosslinked resin particles.

[0107] (3-7. Production of Silicone Resin Particles) A reaction vessel was charged with 500 g of ion-exchanged water, and 0.4 g of 48% aqueous sodium hydroxide solution was added to prepare an aqueous solution. 50 g of methyltrimethoxysilane and 47 g of tetraethoxysilane were added to this aqueous solution, and the hydrolysis reaction was carried out for 1 hour while maintaining the temperature at 15°C. 1.8 g of a 10% aqueous sodium dodecylbenzenesulfonate solution was then added, and the hydrolysis reaction was carried out for 4 hours at the same temperature, yielding a transparent reaction product containing a silanol compound. The resulting reaction product was then subjected to a condensation reaction for 4 hours while maintaining the temperature at 30-80°C. The aqueous suspension after the reaction was filtered through a membrane filter, and the effluent was centrifuged to separate white particles. The separated white particles were washed with water and dried with hot air at 150°C for 5 hours to obtain silicone resin particles (spacer particles K, particle diameter 91 nm).

[0108] (3-8. Production of silicone oil-treated acrylic microparticles) A stirrer was placed in a 300 mL Erlenmeyer flask, and 4.0 g of 300 cs polydimethylsiloxane (KF-96, Shin-Etsu Chemical Co., Ltd.) and 100 g of toluene were added. The mixture was stirred at room temperature for 30 minutes using a magnetic stirrer to obtain a silicone oil toluene solution. 20 g of the acrylic microparticles (Spacer Particles H) obtained in Production Example 3-4 were gradually added to this solution over 1 hour, creating a dispersion in which the acrylic microparticles were completely wetted with the silicone oil toluene solution. An ultrasonic irradiation probe was then inserted into the dispersion in the flask, and the mixture was ultrasonically dispersed for 1 hour using a UH-2C ultrasonic disperser (Ultrasonic Industrial Co., Ltd.) while cooling with water from the outside of the flask. Visual inspection of the flask wall confirmed that a highly uniform dispersion without aggregates had been produced.

[0109] The resulting dispersion was transferred to a 500 ml eggplant-shaped flask and treated with a rotary evaporator (Tokyo Rikakikai Co., Ltd.) at a flask bath temperature of 40°C under a reduced pressure of 10 mmHg for 5 hours to distill off the toluene. The resulting solid was transferred to a stainless steel tray and dried in a vacuum dryer (Yamato Scientific Co., Ltd.) at a set temperature of 50°C under a reduced pressure of 1 mmHg or less until a constant weight was reached, yielding silicone oil-treated acrylic resin particles (spacer particles N, particle diameter 90 nm).

[0110] (3-9. Treatment of silicone resin particles with a silane coupling agent) 340 g of the silicone resin particles obtained in Production Example 3-7 and 15 g of a silane coupling agent (isobutyltriethoxysilane, manufactured by Tokyo Chemical Industry Co., Ltd.) were diluted with 50 g of an aqueous ethanol solution (water / alcohol = 1 / 9 mass ratio), placed in a mixer (Nanopersion Piccolo, manufactured by Kawata Co., Ltd.), mixed at 80 ° C for 1 hour, and then dried at 100 ° C for 12 hours. Subsequently, using a grinder (Jet Mill I-2, manufactured by Nippon Pneumatic Mfg. Co., Ltd.) and a ceramic flat plate as a collision plate, the mixture was ground at a grinding pressure of 0.5 MPa to obtain silane coupling agent-treated silicone resin particles (spacer particles L, particle diameter 92 nm).

[0111] (3-10. Titanate Coupling Agent Treatment of Silicone Resin Particles) 340 g of the silicone resin particles obtained in Production Example 3-7 and 10 g of a titanate coupling agent (Plenact TTS, manufactured by Ajinomoto Co., Inc.) were placed in a mixer (Nanopersion Piccolo, manufactured by Kawata Co., Ltd.), mixed at 80° C. for 1 hour, and then dried at 100° C. for 12 hours. Subsequently, using a pulverizer (Jet Mill I-2, manufactured by Nippon Pneumatic Mfg. Co., Ltd.) and a ceramic flat plate as a collision plate, the mixture was pulverized at a pulverization pressure of 0.8 MPa to obtain titanate coupling agent-treated silicone resin particles (spacer particles M, particle diameter 92 nm).

[0112] (3-11. Silane coupling agent treatment of silica particles) A 3-liter glass reactor equipped with a stirrer, dropping funnel, and thermometer was charged with 600 g of methanol, 5 g of water, and 55 g of 28% aqueous ammonia, and the mixture was adjusted to a temperature of 45°C. While stirring the temperature-adjusted mixture, a mixture of 1205.0 g of tetramethoxysilane and 100.6 g of tetrabutoxysilane, and 400 g of 5% aqueous ammonia heated to 40-45°C were simultaneously added dropwise, each over a period of 4 hours. After each addition was completed, stirring of the mixture was continued for an additional 2 hours to allow hydrolysis to occur, yielding a suspension of hydrophilic colloidal silica particles.

[0113] Next, a 3 L glass reactor was fitted with an ester adapter and a condenser, and the resulting suspension of hydrophilic colloidal silica particles was heated to 60-70°C, and the methanol was distilled off (removed by distillation). Water was then added, and the suspension was heated to 70-90°C, and the methanol was completely distilled off (removed by distillation), yielding an aqueous suspension of hydrophilic colloidal silica particles. The resulting aqueous suspension of hydrophilic colloidal silica particles was then purified using an ultrafiltration apparatus and dried by spray drying, yielding colloidal silica particles with a particle diameter of 90 nm.

[0114] 600 g of the resulting colloidal silica particles and 15 g of a silane coupling agent (isobutyltriethoxysilane, manufactured by Tokyo Chemical Industry Co., Ltd.) were diluted with 50 g of an aqueous ethanol solution (water / alcohol = 1 / 9 mass ratio), charged into a mixer (Nanopersion Piccolo, manufactured by Kawata Corporation), mixed for 1 hour at 80 °C, and then dried for 12 hours at 100 °C. The mixture was then pulverized using a pulverizer (Jet Mill I-2, manufactured by Nippon Pneumatic Mfg. Co., Ltd.) at a pulverization pressure of 1.0 MPa using a ceramic flat plate as a collision plate to obtain silane coupling agent-treated silica particles (spacer particles O, particle diameter 92 nm).

[0115] Table 1 shows the types, surface treatment agents, and average particle diameters of the spacer particles A to O obtained in Production Example 3.

[0116] [Table 1]

[0117] [Manufacturing Example 4] (Manufacture of silicone coated carriers) A coating liquid was obtained by mixing 360 g of a silicone resin solution (KR-255, manufactured by Shin-Etsu Chemical Co., Ltd., solid content concentration: 50 mass %, solid content amount: 180 g), 9.0 g of strontium titanate (SW-100, manufactured by Titan Kogyo Co., Ltd.), 5.0 g of carbon black (Ketjen Black EC-300J, manufactured by Lion Specialty Chemicals Co., Ltd.), and 1500 g of toluene using a homomixer.

[0118] Using a fluidized bed coating device (SFC-5, manufactured by Freund Corporation), 5000 g of carrier cores (F-50, manufactured by Powder Tech Co., Ltd., particle diameter 50 μm) were fluidized and the coating liquid was sprayed onto the carrier cores. In this way, carrier particles A (particle diameter 54 μm) coated with the coating liquid were obtained. The coating conditions were an inlet air temperature of 75°C and an inlet air volume of 0.3 m. 3 The rotor rotation speed was 400 rpm. The carrier cores coated with the coating solution were baked in an electric furnace at 200°C for 1 hour to obtain silicone-coated carriers (carrier particles A) in which a silicone coating layer was formed on the surfaces of the carrier cores.

[0119] [Manufacturing Example 5] (Manufacture of fluorine coated carriers) 10 kg of carrier cores (F-50, Powder Tech, particle size 50 μm) were coated with 2 kg of Epicoat 1004 (Japan Epoxy Range) and 0.5 kg of polyvinylidene fluoride-hexafluoropropylene resin (KYNAR2801) using a fluidized bed coating device (SFC-5, Freund Corporation). Then, 100 g of diethylenetriamine and 150 g of phthalic anhydride were added to 20 L of acetone, and hot air at 80°C was blown in. The resulting mixture was placed in a dryer and heated at 180°C for 1 hour to obtain fluorine-coated carriers (carrier particles B, particle size 56 μm) with a fluorine-coated layer formed on the surface of the carrier cores.

[0120] [Manufacturing Example 6] (External addition treatment of toner base particles) 100 parts by weight of toner base particles A or toner base particles B obtained in Production Examples 1 and 2 were mixed with 1.5 parts by weight of positively charged silica particles (CAB-O-SIL TG-308F, manufactured by Cabot Corporation) and 1.0 part by weight of titanium oxide (MT-500B, manufactured by Teika Corporation) in a Henschel mixer (FM-10, manufactured by Mitsui Mining Co., Ltd.) at a rotation speed of 3500 rpm for 5 minutes. Then, a predetermined amount of spacer particles A to O obtained in Production Example 3 was added and mixed at a rotation speed of 3500 rpm for 5 minutes to externally add the spacer particles. The coverage of the spacer particles relative to the surface of the toner base particles was adjusted to 25%. In this manner, toners with different amounts of spacer particles liberated from the toner base particles were prepared.

[0121] [Measurement of the amount of spacer particles adhering to toner] The amount of spacer particles attached to the obtained toner particles was measured by GC-MASS or fluorescent X-ray. Five grams of the toner particles were then weighed and dispersed in 500 mL of a 10% by mass aqueous solution of polyoxyethylene octylphenyl ether (manufactured by Wako Pure Chemical Industries, Ltd.) (25°C), which was an aqueous dispersion. The dispersion was then subjected to ultrasonic treatment using an ultrasonic generator (Ultrasonic Generator model US-300TCVP, manufactured by Nippon Seiki Co., Ltd.) at an output of 100 W and a frequency of 28 kHz for one minute.

[0122] After the treatment, the floating external additives (spacer particles) were removed from the toner surface and collected, and the toner particles were filtered. The collected floating spacer particles and the filtered toner were measured by GC-MASS or X-ray fluorescence, and the remaining rate of spacer particles adhering to the toner particle surface was calculated from the difference in the amount of spacer particles before and after the ultrasonic treatment using the following formula (1). A calibration curve was created using a sample with a known spacer particle content, and the toner before treatment and the filtered toner were measured by GC-MASS or X-ray fluorescence to determine the amount of spacer particles adhering to the toner base particles before treatment (Fbefore) and the amount of spacer particles adhering without detaching from the toner base particles (Fafter). Spacer particle adhesion rate = 100 × Fafter / Fbefore (1)

[0123] (X-ray fluorescence measurement) 2 g of toner is compression molded in a pressure molding machine under pressure conditions of 6 tons for 1 minute. The compression molded sample is then subjected to total elemental analysis using a fluorescent X-ray measurement device (ZSX Primus IV, manufactured by Rigaku Corporation) under measurement conditions of a tube voltage of 40 kV and a tube current of 70 mA to measure the net Si intensity.

[0124] [Manufacturing Example 7] (Manufacturing of two-component developers) Carrier particles A and carrier particles B obtained in Production Examples 4 and 5 and the toner obtained in Production Example 6 were mixed for 30 minutes using a ball mill so that the toner was 8% by mass relative to the carrier, to prepare two-component developers of Inventions 1 to 5 and Comparative Examples 1 to 13. The type of toner base particles constituting the toner in the two-component developer, the type of spacer particles, the amount added, the coverage rate, the detachment rate, and the type of carrier are shown in Table 2. [Table 2]

[0125] [Evaluation of charging stability, transfer characteristics, and drum cleaning performance] The two-component developers of the present inventions 1 to 5 and comparative examples 1 to 13 were installed in the developing device of an evaluation machine (a modified version of TASKalfa4054ci manufactured by Kyocera Document Solutions Inc.), and durability printing of 50,000 sheets was performed at a print rate of 5% in a room temperature environment (temperature 23.5°C, humidity 50%), and the charging stability, transfer characteristics, and drum cleaning properties were evaluated according to the following methods.

[0126] (Charging stability) The developer on the developing roller was collected at the start of printing and after printing 50,000 sheets (after durability testing), 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 small suction-type charge measurement device (manufactured by Trek). The toner charge at the start of printing was also measured in a high-humidity environment (temperature 32.5°C, humidity 80%) using the same method. The evaluation criteria for charge stability are as follows: ◎: Charge amount is 25μC / g or more and less than 35μC / g (practical level) ○: Charge amount is 15 μC / g or more and less than 25 μC / g (practical level) ×: Charge amount is less than 15 μC / g or more than 35 μC / g (outside the practical range)

[0127] (transcription characteristics) As with the charge amount measurement, transfer efficiency was measured at the start of printing and after printing 50,000 sheets (after durability testing). Transfer efficiency was calculated using the following formula (1), where A is the weight of toner attached to the transfer belt when outputting a solid image (evaluation image) 0.5 cm long and 20 cm wide, and B is the amount of toner attached to the media. The toner weight A on the transfer belt and the toner weight B on the media were measured by stopping the evaluation machine immediately after development and immediately before fixing, respectively, and collecting the toner using a small suction-type charge amount measuring device (manufactured by Trek) and measuring its weight on a precision balance. Transfer efficiency (%) = B / A × 100 (1) The evaluation criteria for transfer properties are as follows: ◎: Transfer efficiency is 96% or more (practical level) ○: Transfer efficiency is 92% to 95% (practical level) △: Transfer efficiency is 88% to 91% (outside the practical range) ×: Transfer efficiency is 87% or less (outside the practical range)

[0128] (Drum cleaning ability) After 50,000 sheets of durable printing were performed, a halftone image was printed. The resulting halftone image was visually inspected for vertical streak-like image defects. After printing the halftone image, the surface of the charger was also visually inspected for the presence or absence of toner components adhering thereto. The evaluation criteria for cleaning performance are as follows: ◯: No vertical streak-like image defects were observed in the halftone image, and no toner components were observed adhering to the surface of the charger (practical level). △: No vertical streak-like image defects were observed in the halftone image, and only a small amount of toner components was observed adhering to the surface of the charger (practical level). ×: Vertical stripe-like image defects were observed in the halftone image, and a large amount of toner components was observed adhering to the surface of the charger (outside the practical range).

[0129] The evaluation results of the charge stability, transfer characteristics, and cleaning properties of the two-component developers of the present inventions 1 to 5 and comparative examples 1 to 13 are shown in Table 3. The values ​​in Table 3 indicate the measured values ​​of the charge amount and transfer efficiency.

[0130] [Table 3]

[0131] As is clear from Table 3, the developers of inventions 1 to 5, in which the amount of spacer particles detached from the toner particles was within 0.35%, exhibited good drum cleaning properties. Furthermore, because low-adhesion silicone-modified acrylic resin particles were used as the spacer particles, transfer properties were also good. Furthermore, the spacer particles were fixed to the toner particles, providing a spacer effect. Furthermore, the use of a low-adhesion silicone-coated carrier reduced the amount of external additive contamination of the carrier, resulting in good charging stability.

[0132] In particular, the developers of inventions 4 and 5, which use spacer particles F in which the surface of silicone-modified acrylic resin particles has been treated with a silane coupling agent, or spacer particles G in which the surface of silicone-modified acrylic resin particles has been treated with a titanate coupling agent, have even better charging stability in high-temperature, high-humidity environments than the developers of inventions 1 to 3.

[0133] In contrast, the developer of Comparative Example 1 used spacer particles A with a small particle diameter of 30 nm, which did not provide a sufficient spacer effect, resulting in poor transfer efficiency after durability testing.On the other hand, the developer of Comparative Example 2 used spacer particles E with a large particle diameter of 150 nm, which made it difficult to fix the spacer particles to the toner surface, resulting in poor drum cleaning performance.

[0134] Furthermore, in the developer of Comparative Example 3, which used toner base particles A without a shell layer, the surface of the toner base particles was made of polyester resin, making it difficult to fix the spacer particles, and the drum cleaning performance deteriorated. In the developer of Comparative Example 4, which used toner base particles A and fluorine-coated carrier particles B, it was difficult to fix the spacer particles for the same reasons as in Comparative Example 3. Furthermore, the fluorine-coated carrier was more susceptible to contamination by external additives than the silicone-coated carrier, resulting in a lower charge amount after durability testing. In the developer of Comparative Example 5, which used toner base particles B and carrier particles B with an acrylic resin shell layer formed thereon, it was easier to fix the spacer particles than in Comparative Example 4, but the presence of free spacer particles led to increased contamination of the fluorine-coated carrier, resulting in a lower charge amount after durability testing.

[0135] In addition, in the developers of Comparative Examples 6 to 8, which used acrylic fine particles, PMMA fine particles, or styrene-acrylic fine particles as spacer particles, the high adhesiveness of the spacer particles resulted in poor transfer characteristics.In the developers of Comparative Examples 9 to 11, which used silicone fine particles as spacer particles, the silicone fine particles reduced the positive chargeability of the toner, resulting in poor charge stability.In addition, the low adhesiveness of the spacer particles made it difficult to fix them to the toner particles, resulting in poor drum cleaning properties.

[0136] In the developer of Comparative Example 12, which used silicone oil-treated acrylic resin particles as spacer particles, the silicone oil has higher adhesiveness than the silicone resin, resulting in poor transfer characteristics.In the developer of Comparative Example 13, which used silica particles treated with a silane coupling agent as spacer particles, the silica has a strong negative chargeability, resulting in a poor positive chargeability of the toner.In addition, the spacer particles have low adhesiveness and low affinity with the toner base particles, resulting in poor drum cleaning performance.

[0137] From the above results, it was confirmed that by combining a toner having a spacer particle detachment rate of 35% or less, which uses toner base particles in which an acrylic resin shell layer is formed on the surface of the toner core particles and to which silicone-modified acrylic resin particles with a volume average particle diameter of 40 nm to 140 nm are externally added as spacer particles to the surface of the toner base particles, with a silicone-coated carrier, a two-component developer with excellent charging stability at the start of printing and after durability, transfer characteristics, and drum cleaning properties can be obtained. [Industrial Applicability]

[0138] The present invention can be applied to a two-component developer used in an electrophotographic system. By using the present invention, it is possible to provide a two-component developer having stable transfer characteristics, positive charging properties, and excellent drum cleaning properties. [Explanation of symbols]

[0139] 101 Toner 102 Toner core particles 103 Shell Layer 104 Toner base particles 105 Resin particles (external additives)

Claims

1. toner core particles containing at least a binder resin and a colorant; a shell layer covering the toner core particles; toner base particles having the formula an external additive attached to the surface of the toner base particles; a toner comprising: a carrier capable of positively charging the toner by friction; A two-component developer comprising: the shell layer is formed of a resin containing an acrylic resin, the external additive contains silicone-modified acrylic resin particles having a volume average particle diameter of 40 nm or more and 140 nm or less, when an ultrasonic treatment is performed in an aqueous dispersion containing the toner and a nonionic surfactant by applying ultrasonic vibrations at an output of 100 W and a frequency of 28 kHz for 1 minute, the amount of the silicone-modified acrylic resin particles that remain attached to the toner base particles without being detached is 0.35% by mass or less relative to the amount of the silicone-modified acrylic resin particles attached before the ultrasonic treatment is performed, The two-component developer is characterized in that the carrier has a carrier core and a resin coating layer that coats the surface of the carrier core, and the resin coating layer contains a silicone resin.

2. 2. The two-component developer according to claim 1, wherein the surfaces of the silicone-modified acrylic resin particles are treated with a silane coupling agent or a titanate coupling agent.

3. the toner core particles contain a polyester resin as the binder resin, 3. The two-component developer according to claim 1, wherein the shell layer is formed of a styrene-acrylic acid resin containing a styrene monomer and one or more acrylic acid monomers.

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