DEVELOPER CONTAINING TONER PARTICLE WITH ALUMINA PARTICLES AND CARRIER PARTICLE WITH LAYERED DOUBLE HYDROXIDE PARTICLE COATING BACKGROUND [0001] Methods for rendering image information visual through electrostatically charged images, such as electrophotography, have been utilized in a variety of fields. In electrophotography, the surface of a photoreceptor is uniformly charged. Subsequently, an electrostatic latent image which is an electrostatically charged image is formed on this photoreceptor surface. The electrostatic latent image is developed with a developer including toner particles, and thereby the electrostatic latent image is rendered visual as a toner image. This toner image is transferred and fixed onto the surface of a recording medium, to form an image on the recording medium. In the electrophotography method, a two-component developer composed of toner particles and carrier particles may be used. DETAILED DESCRIPTION [0002] Hereinafter, examples of a developer will be described. The developer according to some examples, may contain toner particles and carrier particles. [0003] The toner particle includes a toner core particle and alumina particles externally added to the toner core particle. The toner core particle contains, for example, a binder resin. The binder resin includes, for example, one or more amorphous polyester resins and one or more crystalline polyester resins. [0004] The amorphous polyester resin may be a polyester resin exhibiting no distinct endothermic peak in a differential scanning calorimetry (DSC) curve. The amorphous polyester resin may be defined as, for example, a polyester resin exhibiting a stepwise endothermic change when measured at a temperature increase rate of 10 °C/min by differential scanning calorimetry, or a polyester resin exhibiting an endothermic peak with a half width of more than 15°C. [0005] An amorphous polyester resin is, for example, a reaction product of a polyhydric alcohol and a polycarboxylic acid. In other words, the amorphous polyester resin includes, as monomer units, a polyhydric alcohol and a polycarboxylic acid. [0006] The polyhydric alcohol may be, for example, a diol. Examples of the diol include: aliphatic diols such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, and glycerin; alicyclic diols such as cyclohexanediol, cyclohexanedimethanol, and hydrogenated bisphenol A; and aromatic diols such as an ethylene oxide adduct of bisphenol A and a propylene oxide adduct of bisphenol A. These polyhydric alcohols may be used singly or in combination of two or more kinds thereof. The diol may be an aromatic diol in some examples, or an alicyclic diol in other examples. In order to form a crosslinked structure or a branched structure that provides a suitable fixability, the polyhydric alcohol may further include, in addition to a diol, a polyhydric alcohol having a valency of 3 or higher (for example, glycerin, trimethylolpropane, or pentaerythritol). [0007] According to examples, the content of the polyhydric alcohol may be 50% by mole or more, 55% by mole or more, or 60% by mole or more, and may be 80% by mole or less, 75% by mole or less, or 70% by mole or less, based on the total amount of the monomer units in the amorphous polyester resin. [0008] The polycarboxylic acid may include, for example, an aromatic polycarboxylic acid having an aromatic ring, and may include an anhydride of the aromatic polycarboxylic acid. The polycarboxylic acid may include, for example, an aromatic dicarboxylic acid, and may include an anhydride of an aromatic dicarboxylic acid. Examples of such a polycarboxylic acid include phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p-carboxyphenylacetic acid, p- phenylene-2-acetic acid, m-phenylene diglycolic acid, p-phenylene diglycolic acid, o-phenylene diglycolic acid, diphenylacetic acid, diphenyl-p,p'- dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene-1,5- dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, anthracene dicarboxylic acid, and anhydrides of these. These polycarboxylic acids may be used singly or in combination of two or more kinds thereof. [0009] The polycarboxylic acid may further include, for example, an aromatic polycarboxylic acid having 3 or more valences, and may further include an anhydride of an aromatic polycarboxylic acid having 3 or more valences. Examples of the polycarboxylic acid include trimellitic acid, pyromellitic acid, naphthalenetricarboxylic acid, naphthalenetetracarboxylic acid, pyrenetricarboxylic acid, pyrenetetracarboxylic acid, and acid anhydrides of these carboxylic acids. [0010] According to examples, the content of the polycarboxylic acid may be 20% by mass or more, 25% by mass or more, or 30% by mass or more, and may be 50% by mass or less, 45% by mass or less, or 40% by mass or less, based on the total amount of the monomer units in the amorphous polyester resin. [0011] In order to increase the dispersibility of the crystalline polyester resin in the amorphous polyester resin, the weight average molecular weight of the amorphous polyester resin may be 5,000 or more, 10,000 or more, or 12,000 or more, and may be 50,000 or less, 45,000 or less, or 40,000 or less, depending on examples. [0012] The weight average molecular weight of the amorphous polyester resin according to the present disclosure is measured according to gel permeation chromatography (GPC) of a tetrahydrofuran (THF)-soluble fraction. For example, the weight average molecular weight may be determined by the following method. Waters e2695 (manufactured by Nihon Waters K.K.) is used as a measuring apparatus, and two sets of Inertsil CN-3 25 cm (manufactured by GL Sciences, Inc.) are used as columns. A filtrate obtained by introducing 10 mg of the amorphous polyester resin into 10 mL of tetrahydrofuran (THF) (containing a stabilizer, manufactured by Wako Pure Chemical Industries, Ltd.), stirring the mixture for 1 hour, and then filtering the mixture through a 0.2 Pm filter, is used as a sample solution. The sample solution is injected into the measuring apparatus in an amount of 20 PL, and measurement is made under the conditions of 40qC and a flow rate of 1.0 mL/min. [0013] The glass transition temperature (Tg) of the amorphous polyester resin may be 50qC or more and may be 80qC or less or 70qC or less, depending on examples. [0014] According to examples, the content of the first amorphous polyester resin may be 60% by mass or more, 70% by mass or more, or 80% by mass or more, and may be 95% by mass or less, 92% by mass or less, or 90% by mass or less, based on the total mass of the binder resin. According to examples, the content of the amorphous polyester resin may be 50% by mass or more, 55% by mass or more, or 60% by mass or more, and may be 90% by mass or less, 85% by mass or less, or 80% by mass or less, based on the total mass of the toner particle. [0015] The crystalline polyester resin may be a polyester resin exhibiting a clear endothermic peak in a modified differential scanning calorimetry (MDSC) curve. When the binder resin includes a crystalline polyester resin, enhancement of the image glossiness of the toner and enhancement of the low-temperature fixability can be promoted. [0016] A crystalline polyester resin is, for example, a reaction product between a polyhydric alcohol and a polycarboxylic acid. For example, a crystalline polyester resin may include a polyhydric alcohol and a polycarboxylic acid as monomer units. [0017] The polyhydric alcohol may be, for example, a diol or an aliphatic diol. In order to more easily achieve a crystalline polyester resin having an appropriate melting point for the toner particle, the number of carbon atoms of the polyhydric alcohol may be 8 or more or 9 or more, and may be 12 or less or 10 or less, depending on examples. Accordingly, the number of carbon atoms of the polyhydric alcohol may be 9 in some examples, or 10 in other examples. Examples of the polyhydric alcohol include 1,9-nonanediol. [0018] The content of the polyhydric alcohol may be 30% by mass or more, 35% by mass or more, or 40% by mass or more, and may be 60% by mass or less, 55% by mass or less, or 50% by mass or less, based on the total amount of monomer units in the crystalline polyester resin. [0019] The polycarboxylic acid may be, for example, an aliphatic polycarboxylic acid. In some examples, the aliphatic polycarboxylic acid may be an aliphatic dicarboxylic acid in order to increase linearity of the structure of the crystalline polyester resin, so as to increase the affinity with the amorphous polyester resin. In order to more easily achieve a crystalline polyester resin having an appropriate melting point for the toner particle, the number of carbon atoms of the polycarboxylic acid (provided that the number of carbons excludes the carbons constituting a carboxyl group) may be 8 or more or 9 or more, and may be 12 or less or 10 or less, depending on examples. Accordingly, the number of carbon atoms may be 9 in some examples, or 10 in other examples. Examples of the polycarboxylic acid include 1,10-decane dicarboxylic acid and 1,12-dodecane dicarboxylic acid. [0020] According to examples, the content of the polycarboxylic acid may be 40% by mass or more, 45% by mass or more, or 50% by mass or more, and may be 70% by mass or less, 65% by mass or less, or 60% by mass or less, based on the total amount of monomer units in the crystalline polyester resin. [0021] In order to suppress a decrease in the strength of the binder resin and a decrease in the glass transition temperature of the toner particle, and in order to promote low-temperature fixability, the intensity of images fixed on paper, and the preservability of the toner particle, the weight average molecular weight of the crystalline polyester resin may be 5,000 or more, 5,500 or more, or 6,000 or more, and may be 15,000 or less, 10,000 or less, or 8,000 or less, depending on examples. The weight average molecular weight of the crystalline polyester resin is measured by the same method as that for the weight average molecular weight of the amorphous polyester resin. [0022] In order to suppress aggregation of the toner particles, and to promote the preservability of fixed images and the low-temperature fixability, the melting temperature (Tm) of the crystalline polyester resin may be 60qC or more and may be 100qC or less or 75qC or less, depending on examples. [0023] According to examples, the content of the crystalline polyester resin may be 5% by mass or more, 8% by mass or more, or 10% by mass or more, and may be 40% by mass or less, 30% by mass or less, or 20% by mass or less, based on the total mass of the binder resin. According to examples, the content of the crystalline polyester resin may be 3% by mass or more, 5% by mass or more, or 8% by mass or more, and may be 30% by mass or less, 20% by mass or less, or 15% by mass or less, based on the total mass of the toner particle. [0024] The binder resin may further include other resins in addition to the amorphous polyester resin and crystalline polyester resin. Examples of the other resins include a styrene-(meth)acrylic copolymer, an epoxy resin, and a styrene-butadiene copolymer. The styrene-(meth)acrylic copolymer may be a copolymer of a styrene-based monomer and a (meth)acrylic acid ester- based monomer. Examples of the styrene-based monomer include styrene, o- (m-, p-) methylstyrene and m- (p-) ethylstyrene. Examples of the (meth)acrylic acid ester-based monomer include methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, octyl (meth)acrylate, dodecyl (meth)acrylate, stearyl (meth)acrylate, behenyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, dimethylaminoethyl (meth)acrylate, and diethylaminoethyl (meth)acrylate. [0025] According to examples, the total content of the amorphous polyester resin and crystalline polyester resin in the binder resin may be 80% by mass or more, 85% by mass or more, or 90% by mass or more, and may be 98% by mass or less or 95% by mass or less, based on the total mass of the binder resin. [0026] According to examples, the content of the binder resin in the toner particle may be 40% by mass or more, 45% by mass or more, or 50% by mass or more, and may be 90% by mass or less, 85% by mass or less, or 75% by mass or less, based on the total mass of the toner particle. [0027] The core particle may further include a colorant. The colorant can include at least one colorant selected from, for example, a black colorant, a cyan colorant, a magenta colorant, and a yellow colorant. Regarding the colorant, one kind may be used alone, or two or more kinds thereof may be used as a mixture, in consideration of hue, chroma, brightness, weather- resistance, dispersibility in toner, and the like. [0028] The black colorant may be carbon black or aniline black. The yellow colorant may be a condensed nitrogen compound, an isoindolinone compound, an anthraquine compound, an azo metal complex, or an allylimide compound. Some examples of the yellow colorant include C.I. Pigment Yellow 12, 13, 14, 17, 62, 74, 83, 93, 94, 95, 109, 110, 111, 128, 129, 147, 168, and 180. [0029] The magenta colorant may be a condensed nitrogen compound, anthraquine, a quinacridone compound, a basic dye lake compound, a naphthol compound, a benzimidazole compound, a thioindigo compound, or a perylene compound. Some examples of the magenta colorant include C.I. Pigment Red 2, 3, 5, 6, 7, 23, 48:2, 48:3, 48:4, 57:1, 81:1, 122, 144, 146, 166, 169, 177, 184, 185, 202, 206, 220, 221, and 254. [0030] The cyan colorant may be a copper phthalocyanine compound or a derivative thereof, an anthraquine compound, or the like. Some examples of the cyan colorant include C.I. Pigment Blue 1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, and 66. [0031] According to examples, the content of the colorant may be 0.5% by mass or more, 1% by mass or more, or 2% by mass or more, based on the total mass of the toner particle, in order to achieve a sufficient coloration effect, and the content of the colorant may be 15% by mass or less, 12% by mass or less, or 10% by mass or less, based on the total mass of the toner particle, in order to achieve a sufficient amount of frictional electrification without having significant influence on the increase in the production cost of the toner particle. [0032] The core particle may further include a release agent. Since the release agent promotes low-temperature fixability, final image durability, and abrasion resistance of the toner particles, the type and content of the release agent may be determined in consideration of the properties of the toner. [0033] The release agent may include, for example, a wax. The wax may be a natural wax or a synthetic wax. The wax can be selected, for example, from the group consisting of polyethylene wax, polypropylene wax, silicon wax, paraffin wax, ester wax, carnauba wax, beeswax, and metallocene wax. [0034] According to examples, the content of the release agent may be 1% by mass or more, 2% by mass or more, or 3% by mass or more, based on the total mass of the toner particle, in order to achieve a suitable low-temperature fixability and a sufficient fixing temperature range, and may be 20% by mass or less, 15% by mass or less, or 10% by mass or less, based on the total mass of the toner particle, in order to achieve suitable storage stability and economic efficiency. [0035] According to examples, the content of the toner core particle may be 80% by mass or more, 85% by mass or more, or 90% by mass or more, and may be 99% by mass or less, 98% by mass or less, or 97% by mass or less, based on the total mass of the toner particle. [0036] The average particle diameter of the toner core particle may be 3 μm or more, 4 μm or more, or 5 μm or more, and may be 12 μm or less, 11 μm or less, 10 μm or less, or 9 μm or less, depending on examples. The average particle diameter of the core particle is measured by the method described further below with reference to Test Examples. [0037] In some examples, the toner core particle may include a central portion including an amorphous polyester resin and a crystalline polyester resin as the binder resin, and a coating portion coating the central portion and including an amorphous polyester resin as the binder resin. In this case, the average diameter of the central portion may be 2.8 μm or more, 3.5 μm or more, or 4 μm or more, and may be 11 μm or less, 10 μm or less, or 9 μm or less, depending on examples. The average diameter of the central portion is measured by the method described further below with reference to the Test Examples. The thickness of the coating portion may be 0.2 μm or more, 0.4 μm or more, or 0.5 μm or more, and may be 2.0 μm or less, 1.4 μm or less, or 0.8 μm or less, depending on examples. [0038] The alumina particles externally added to the toner core particles have an average particle diameter of 10 to 50 nm. The lower limit of the average particle diameter of the alumina particles may be 15 nm. The upper limit of the average particle diameter of the alumina particles may be 40 nm, 30 nm, or 20 nm. The average particle diameter of the alumina particles is measured by the method described further below with reference to the Test Examples. [0039] The alumina particles have a hydrophobicity of 30 to 70%. The lower limit of the hydrophobicity of the alumina particles may be 40%, 45%, or 50%. The upper limit of the hydrophobicity of the alumina particles may be 65%, 60%, or 55%. The degree of hydrophobicity of the alumina particles is measured by the method described further below with reference to the Test Examples. [0040] The alumina particles having the hydrophobicity as described above are obtained by surface-treating the alumina particles with a surface treatment agent. Namely, the alumina particles in some examples are surface-treated with a surface treatment agent. [0041] The surface treatment agent may be a surface treatment agent that imparts hydrophobicity to the surface of the alumina particles. The surface treatment agent may be, for example, a silane compound. The silane compound may be, for example, an alkyltrialkoxysilane. The number of carbon atoms of the alkyl group in the alkyltrialkoxysilane may be of 1 to 8, for example. In some examples, the number of carbon atoms of the alkoxy group in the alkyltrialkoxysilane may be of 1 to 4. In some examples, the surface treatment agent contains no fluorine atom. In a case where the fluorine atom that enhances the negative chargeability of the toner particles is not contained in the surface treatment agent, an excessive increase in charging is suppressed in a low-temperature and low-humidity environment, and thus the charging stability of the toner particles is promoted. In addition, when the surface treatment agent contains no fluorine atom, the alumina particles are prevented from being detached from the toner particles and prevented from adhering to the surfaces of the carrier particles, so that the chargeability of the carrier particles is better stabilized. [0042] According to examples, the content of the alumina particles may be 0.1 parts by mass or more, 0.5 parts by mass or more, or 0.8 parts by mass or more, and may be 3 parts by mass or less, 2.5 parts by mass or less, or 2 parts by mass or less, based on 100 parts by mass of the toner core particle. [0043] The toner particle may further include silica particles externally added to the toner core particle. The average particle diameter of the silica particles may be 10 nm or more, 15 nm or more, or 20 nm or more, and may be 250 nm or less, 200 nm or less, or 150 nm or less, depending on examples. The average particle diameter of the silica particles is measured by the method described further below with reference to the Test Examples. As the silica particles, two or more types of silica particles having different average particle diameters may be used in combination. [0044] According to examples, the content of the silica particles may be 0.3 parts by mass or more, 1 part by mass or more, or 2 parts by mass or more, and may be 8 parts by mass or less, 6 parts by mass or less, or 5 parts by mass or less, based on 100 parts by mass of the toner core particle. [0045] The toner particle may further contain a charge control agent in some examples. The charge control agent may be internally added so as to be contained in the toner core particle, or may be externally added so as to adhere to the surface of the toner core particle. The charge control agent may be a negative charge control agent or a positive charge control agent. [0046] Examples of the negative charge control agent include a salicylic acid metal compound, a naphthoic acid metal compound, a dicarboxylic acid metal compound, a polymer type compound having sulfonic acid or carboxylic acid in a side chain, a polymer type compound having a sulfonic acid salt or a sulfonic acid esterification product in a side chain, a polymer type compound having a carboxylic acid salt or a carboxylic acid esterification product in a side chain, a boron compound, a urea compound, a silicon compound, and a calixarene. [0047] Examples of the positive charge control agent include a quaternary amount salt, a polymer type compound having a quaternary ammonium salt in a side chain, a guanidine compound, and an imidazole compound. [0048] The average particle diameter of the toner particles may be 3 Pm or more, 4 Pm or more, or 5 Pm or more, and may be 12 Pm or less, 11 Pm or less, 10 Pm or less, or 9 Pm or less, depending on examples. The average particle diameter of the toner particles is measured by the method described further below with reference to the Test Examples. [0049] The carrier particle includes a carrier core particle and a coating layer coating the carrier core particle. Examples of the carrier core particle include, for example, metal particle such as iron, lithium, calcium, magnesium, nickel, copper, zinc, cobalt, manganese, chromium, and rare earths, alloy particles thereof, oxide particle thereof, magnetic particle such as ferrite, and the like. [0050] The coating layer, in some examples, contains a resin and layered double hydroxide particles. Examples of the resin include an acrylic resin and a silicone resin. The acrylic resin may be a resin obtained by homopolymerizing or copolymerizing acrylic monomer(s), and contains an acrylic monomer unit. The acrylic monomer is a monomer having an acrylic group (acryloyl group) or a methacrylic group (methacryloyl group). Some examples of the acrylic monomer include acrylic acid, methacrylic acid and esters thereof, acrylamide, methacrylamide, acrylonitrile and methacrylonitrile. Some examples of the acrylic resin include poly(acrylic acid), poly(methacrylic acid), poly(methyl acrylate), poly(methyl methacrylate), poly(isobutyl acrylate), poly(isobutyl methacrylate), poly(cyclohexylmethyl acrylate), and copolymers of styrene and an acrylic monomer constituting these acrylic resins. [0051] Examples of the silicone resin include a straight silicone resin and a modified silicone resin. Examples of the straight silicone resin include commercially available products such as KR 271, KR 255, and KR 152 manufactured by Shin-Etsu Chemical Co., Ltd., and SR 2400, SR 2406, and SR 2410 manufactured by Dow Corning Toray Co., Ltd. In this case, the silicone resin may be used alone, or may be used together with a component that crosslinks with the silicone resin, a charge amount adjusting component, and the like. Examples of the modified silicone resin include commercially available products such as KR 206 (alkyd-modified), KR 5208 (acrylic- modified), ES 1001N (epoxy-modified), and KR 305 (urethane-modified) manufactured by Shin-Etsu Chemical Co., Ltd., and SR 2115 (epoxy- modified) and SR 2110 (alkyd-modified) manufactured by Dow Corning Toray Silicone Co., Ltd. [0052] The layered double hydroxide particles may refer to an inorganic layered compound in which a divalent metal (e.g., magnesium, iron, zinc, calcium, nickel, cobalt, and copper) and a hydroxide of a divalent metal (e.g., aluminum, iron, and manganese) are combined to form a layered structure. The layered double hydroxide particles have a layered structure in which negatively charged anions are interposed between basic layers of a positively charged metal hydroxide. The layered double hydroxide has, for example, a composition represented by the following formula: [M ²⁺ _1-x M ³⁺ _x (OH) ₂ ][A ^n- _x/n · yH ₂ O] wherein M ²⁺ represents Mg ²⁺ , Fe ²⁺ , Zn ²⁺ , Ca ²⁺ , Mn ²⁺ , Ni ²⁺ , Cu ²⁺ or Co ²⁺ , M ³⁺ represents Fe ³⁺ , Al ³⁺ , Mn ³⁺ , Ga ³⁺ , Cr ³⁺ or La ³⁺ , and A ^n- represents an n-valent anion (n is an integer of 1 to 3). [0053] The layered double hydroxide particles may include, for example, at least one selected from hydrotalcite, motsucoleite, manasseite, stichtite, pyroaurite, takovite, eardolite, greenlast, and meixenelite. For example, the layered double hydroxide particles may include hydrotalcite in some examples. Hydrotalcite has a composition represented by Mg6Al2(OH)16CO3·4H2O. [0054] The layered double hydroxide particles have an average particle diameter of 100 to 600 nm. The lower limit of the average particle diameter of the layered double hydroxide particles may be 120 nm, 200 nm, or 300 nm. The upper limit of the average particle diameter of the layered double hydroxide particles may be 570 nm, 560 nm, or 550 nm. The average particle diameter of the layered double hydroxide particles is measured by the method described further below with reference to the Test^Examples. [0055] The average particle diameter of the carrier particles may be 30 Pm or more, 35 Pm or more, or 40 Pm or more, and may be 45 Pm or less, 44 Pm or less, or 43 Pm or less, depending on examples. [0056] According to examples, the content of the toner particles in the developer may be 2% by mass or more or 4% by mass or more, and may be 15% by mass or less or 13% by mass or less, based on the total amount of the developer. According to examples, the content of the carrier particles in the developer may be 85% by mass or more or 87% by mass or more, and may be 98% by mass or less or 96% by mass or less, based on the total amount of the developer. [0057] The toner particles and the carrier particles described above may be present in the image forming apparatus, constantly (e.g., substantially permanently) in some cases, or temporarily in other cases. Accordingly, it can be considered that the above-described developer is present in the image forming apparatus, in some examples. Namely, an example image forming apparatus includes the above-described developer (the toner particles and carrier particles). The image forming apparatus may include, for example, a photoreceptor, a charging device, an exposure device that forms an electrostatic latent image on the photoreceptor, a developing device that applies the developer to the electrostatic latent image to develop the electrostatic latent image, and a transfer device that transfers a toner image on the photoreceptor onto a transfer material. [0058] In some examples, the developer (the toner particles and carrier particles) may be accommodated in a toner cartridge. In some examples, the developer (the toner particles and carrier particles) may be accommodated within a container in a toner cartridge. For example, a toner cartridge may include a container that accommodates the developer (the toner particles and carrier particles) described above. Test Examples [0059] Hereinafter, the toner particle will be described by way of Test Examples, although the toner particle is not limited to the Test Examples described. [0060] Preparation of amorphous polyester resin The polycarboxylic acid, the polyhydric alcohol, and the esterification catalyst were introduced according to the respective amounts (parts by mass) shown in Table 1 in a 500 ml four flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple. The mixture was heated to 230°C under a nitrogen atmosphere, and reacted until the reaction rate reached 90%, and then reacted at 8.3 kPa until a targeted weight average molecular weight was reached, thereby obtaining amorphous polyester resin 1 and amorphous polyester resin 2. [0061] Preparation of crystalline polyester resin The polycarboxylic acid, the polyhydric alcohol, and the esterification catalyst were introduced according to the respective amounts (parts by mass) shown in Table 1 in a 500 ml four flask equipped with a nitrogen inlet tube, a dehydration tube, a stirrer, and a thermocouple. The mixture was heated to 180°C under a nitrogen atmosphere, and reacted until the reaction rate reached 90%, and then reacted at 8.3 kPa until the a targeted weight average molecular weight was reached, thereby obtaining a crystalline polyester resin. [0062] Measurement of weight average molecular weight The weight average molecular weight (Mw) of the obtained amorphous polyester resins and crystalline polyester resin was determined by gel permeation chromatography (GPC) measurement. Namely, Waters e2695 (manufactured by Nihon Waters K. K.) was used as a measuring apparatus, and Inertsil CN-325 cm two series (manufactured by GL Sciences Inc.) were used as a column. In addition, 30 mg of the polyester resin was added to 20 mL of tetrahydrofuran (THF) (containing a stabilizer, manufactured by Wako Pure Chemical Industries, Ltd.), stirred for 1 hour, and then filtered with a 0.2 μm filter to obtain a filtrate, which was used as a sample solution. The tetrahydrofuran (THF) sample solution (20 μL) was injected into the measurement apparatus, and measurement was performed under the conditions of 40°C and a flow rate of 1.0 mL/min. [0063] Measurement of glass transition temperature of amorphous polyester resin The glass transition temperature (Tg) of the obtained amorphous polyester resins was determined from a differential scanning calorimetry curve obtained by differential scanning calorimetry measurement specified in ASTM D3418- 08. Specifically, using a DSC Q2000 (manufactured by TA Instruments), the temperature was raised from room temperature to 150°C at a rate of 10°C per minute as a first temperature raising step, and after holding at 150°C for 5 minutes, the temperature was lowered to 0°C at a rate of 10°C per minute by liquefied nitrogen. Then, after holding at 0°C for 5 minutes, the temperature was raised again from 0°C to 150°C at a rate of 10°C per minute as a second temperature raising step, and the glass transition temperature was determined from the obtained DSC curve. [0064] Measurement of melting point of crystalline polyester resin The melting point (Tm) of the crystalline polyester resin was determined from a differential scanning calorimetry curve obtained by differential scanning calorimetry (DSC) as defined in ASTM D341-08. Namely, using a DSC Q2000 (manufactured by TA Instruments), the temperature was raised from room temperature to 150°C at a rate of 10°C per minute as a first temperature raising step, and after holding at 150°C for 5 minutes, the temperature was lowered to 0°C at a rate of 10°C per minute by liquefied nitrogen. Then, after holding at 0°C for 5 minutes, the temperature was raised again from 0°C to 150°C at a rate of 10°C per minute as a second temperature raising step, and the heat absorption peak temperature at the time of melting of the crystalline polyester resin was taken as Tm from the obtained DSC curve. [0065] Measurement of acid value The acid value (mgKOH/g) of the obtained amorphous polyester resin and crystalline polyester resin was determined according to the neutralization titration method of the acid value measurement method specified in JIS K0070-1992 "Testing methods for acid value, saponification value, ester value, iodine value, hydroxyl value and unsaponifiable matter of chemical products". [0066] The measurement results of the properties of the respective polyester resins are shown in Table 1.

[Table 1]

[0067] The abbreviations in Table 1 have the following meanings. BP-2P: bisphenol A propylene oxide 2 mol adduct (trade name, manufactured by Sanyo Chemical Industries, Ltd.) EG: ethylene glycol DBTO: dibutyltin oxide [0068] Production of resin latex 1 300g of the amorphous polyester resin 1 obtained above, 250g of methyl ethyl ketone, and 50g of isopropyl alcohol were introduced into a 3 L double jacket reaction vessel, and the content of the reaction vessel was stirred using a semi-moon type impeller at about 30°C to dissolve the resin. While the obtained resin solution was stirred, 20g of a 5% aqueous ammonia solution was slowly added to the reaction vessel, and then 1200g of water was added thereto at a rate of 20 g/min to prepare an emulsion. Thereafter, the mixed solvent of methyl ethyl ketone and isopropyl alcohol was removed from the emulsion by a vacuum distillation method until the concentration of amorphous polyester resin 1 as a solid content reached 20% by mass, thereby obtaining resin latex 1. [0069] Production of resin latex 2 Resin latex 2 was obtained in a similar manner as the resin latex 1 with the exception that the amorphous polyester resin 1 was changed to the amorphous polyester resin 2. [0070] Production of resin latex 3 Resin latex 3 was obtained in a similar manner as the resin latex 1 with the exception that the amorphous polyester resin 1 was changed to the crystalline polyester resin. [0071] Preparation of colorant dispersion 10g of an anionic reactive emulsifier (HS-1, manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) was placed in a milling bath together with 60g of a cyan pigment (C. I. Pigment Blue 15:3, manufactured by Clariant Co., Ltd.). To this, 400g of glass beads having a diameter of 0.8 to 1 mm were added, and milling was performed at room temperature to obtain a colorant dispersion. [0072] Preparation of release agent dispersion 270g of a paraffin wax (HNP-9 (trade name) manufactured by Nippon Seiro Co., Ltd.), 2.7g of an anion surfactant (Dowfax2A1 (trade name) manufactured by Dow Chemical Co., Ltd.), and 400g of ion-exchanged water were introduced into a reaction vessel. Thereafter, the content of the reaction vessel was heated to 110°C, and the mixture was dispersed using a homogenizer (ULTRA-TURRAX T50 (trade name), manufactured by IKA), and then further dispersed using a high-pressure homogenizer (NanoVater NVL-ES 008 (trade name), manufactured by Yoshida Kikai Co., Ltd.) to obtain a release agent dispersion. [0073] Production of toner core particle 450g of the resin latex 1, 150g of the resin latex 2, 100g of the resin latex 3, and 560g of deionized water were introduced into a 3-liter reaction vessel. Thereafter, 70g of the colorant dispersion liquid and 80g of the release agent dispersion liquid were added to the reaction vessel while stirring the inside of the reaction vessel, and then 30g of nitric acid having a concentration of 0.3N and 25g of polysilica iron PSI-100 (manufactured by SUIDO KIKO KAISHA, LTD.) were further added thereto. Thereafter, the temperature of the mixed solution in the flask was raised to 50°C at a rate of 1 °C/min while the inside of the reaction vessel was stirred using a homogenizer (ULTRA-TURRAX T50 (trade name) manufactured by IKA) to form primary aggregated particles (central portion) having a volume average particle diameter of 5.2 μm. [0074] The volume average particle diameter of the primary aggregated particles was measured by the following method by taking out a part of the mixed solution from the reaction vessel and collecting the primary aggregated particles contained in the solution. A Coulter counter (manufactured by Beckman Coulter, Inc.) was used as a measurement device, ISOTON II (manufactured by Beckman Coulter, Inc.) was used as an electrolyte, and measurement was performed under the condition of a measured particle number of 30,000 using an aperture tube having an aperture diameter of 100 μm. Based on the measured size distribution of the particles, the volumes occupied by the particles included in the divided particle size ranges are accumulated from the small diameter side, and the size at which the accumulation is 50% is defined as a volume average particle diameter Dv50. [0075] Thereafter, 300g of the resin latex 1 was added to the reaction vessel while stirring the inside of the reaction vessel, and the primary aggregated particles and the amorphous polyester resin 1 in the added resin latex 1 were aggregated for 30 minutes, and the primary aggregated particles were coated with the amorphous polyester resin 1 to obtain coated aggregated particles. Thereafter, a 0.1N aqueous sodium hydroxide solution was added to the reaction vessel to adjust the pH of the mixed solution in the reaction vessel to 9.5. After 20 minutes, the temperature of the mixed solution in the reaction vessel was raised to 83°C, and the particles in the coated aggregated particles were coalesced for 2 hours to obtain toner core particles having a central portion and a coating portion on the outer surface thereof. Thereafter, the mixed solution in the reaction vessel was cooled to 28°C or less, and then filtered to collect and dry the toner core particles. The average particle diameter of the obtained core particles was measured in the same manner as the volume average particle diameter of the primary aggregated particles, and was found to be 5.7 μm. The obtained toner core particles were used commonly in all the Test Examples and Comparative Test Examples. [0076] Production of alumina particles While alumina particles Alu-C manufactured by Evonik Industries were stirred, 30 parts by mass of methyltrimethoxysilane was added to 100 parts by mass of the alumina particles and mixed so that the alumina particles did not coalesce. Thereafter, the alumina particles were dried and pulverized to obtain alumina particles Al ₂ O ₃ -1 (alumina particles surface-treated with methyltrimethoxysilane) having a hydrophobicity of 70% and an average particle diameter of 15 nm. With respect to the alumina particles Al ₂ O ₃ -2, Al ₂ O ₃ -3, Al ₂ O ₃ -6 and Al ₂ O ₃ -7, each of the alumina particles having different hydrophobicity was obtained in a similar manner as in Al ₂ O ₃ -1 with the exception that the addition amount of methyltrimethoxysilane was changed as shown in Table 2. With respect to the alumina particles Al ₂ O ₃ -4 and Al ₂ O ₃ -5, since the alumina particles were produced by the fumed method, the particle size was controlled by fine adjustment of the flame temperature and the raw material supply amount during synthesis, and then the alumina particles were subjected to a hydrophobic treatment by the same method as in Al ₂ O ₃ -1 to obtain alumina particles having different average particle diameters. [0077] 50g of distilled water was introduced in a beaker, and then 0.2g of the alumina particles to be evaluated was gently added to obtain a mixture. While this mixture was stirred with a magnetic stirrer, methanol was added drop by drop, and the time when all the alumina particles floating on the water surface were submerged in the solution was defined as the end point. The methanol titration amount suitable to the end point was defined as W (g), and the hydrophobicity was determined by the following equation: Hydrophobicity (%) = {W / (50 + W)} × 100 The results are shown in Table 2. [0078] As the silica particles 1 to 3, the following were used. Silica particles 1: R8200 (trade name, manufactured by Nippon Aerosil Co., Ltd., average diameter: 12 nm) Silica particles 2: RY50 (trade name, manufactured by Nippon Aerosil Co., Ltd., average diameter: 40 nm) Silica particles 3: X24-9163A (trade name, manufactured by Shin- Etsu Chemical Co., Ltd., average diameter: 110 nm) [0079] 100g of the toner core particles were introduced into a mixer (KM- LS2K (trade name) manufactured by Daewha TECH), and then 0.97g of the alumina particles of the type shown in Tables 4 and 5, 0.3g of the silica particles 1, 1.7g of the silica particles 2, and 1.7g of the silica particles 3 were added. Thereafter, the mixture was stirred at a stirring speed of 8000 rpm for 4 minutes to obtain toner particles in which the alumina particles and the silica particles 1 to 3 were externally added to the toner core particles. [0080] Measurement of average particle diameter of alumina particles The alumina particles on the surfaces of the toner core particles were photographed at a magnification of 50,000 times using a scanning electron microscope "SU 8000" (manufactured by HITACHI). The diameters of 100 or more particles were measured, and the number average value thereof was calculated as the average particle diameter of the alumina particles. The alumina particles to be measured were determined using an energy dispersive X-ray analyzer or the like attached to the scanning electron microscope. The results are shown in Table 2. [0081] [Table 2] [0082] Preparation of carrier core particle Commercially available MnCO ₃ , Mg(OH) ₂ , SrCO ₃ and Fe ₂ O ₃ were blended so that the Mn content was 21.0 mol% in terms of MnO, the Mg content was 3.3 mol% in terms of MgO, the Sr content was 0.7 mol% in terms of SrO, and the Fe content was 75.0 mol% in terms of Fe ₂ O ₃ . Then, water was added thereto, and the mixture was mixed while being pulverized for 10 hours in a ball mill (manufactured by Seiwa Giken). Then, calcination was performed at 950°C for 4 hours to obtain calcined ferrite. Subsequently, the calcined ferrite was coarsely pulverized, water was added again, and the mixture was pulverized in a ball mill for 24 hours to obtain a ferrite slurry. To 100 parts by mass of the obtained ferrite slurry, 2 parts by mass of polyvinyl alcohol was added, and an appropriate amount of silica particles and ammonium polycarboxylate were added as a dispersant to stabilize the dispersion state. Then, the mixture was granulated and dried with a spray dryer (manufactured by OHKAWARA KAKOHKI Co., Ltd.) to obtain spherical particles having an average particle size of about 43 μm. The obtained spherical particles were fired at 1100 °C for 4 hours in a nitrogen atmosphere, and then the aggregated particles were crushed and sieved to remove coarse particles, thereby obtaining magnetic particles (carrier core particles). [0083] Preparation of layered double hydroxide particles Synthetic hydrotalcite particles (manufactured by Kyowa Chemical Industry Co., Ltd.) were pulverized using a jet mill (manufactured by HOSOKAWA MICRON Co., Ltd.) to prepare hydrotalcite particles HT1 to HT4 having different average particle diameters as shown in Table 3. [0084] Preparation of coating layer resin solution 1 As a resin component constituting a coating layer for coating carrier core particles, 20 parts by mass of a methyl methacrylate (MMA) / styrene (St) copolymer (molar ratio: 98/2) was dissolved in 2,000 parts by mass of toluene, and 2 parts by mass (10 parts by mass based on 100 parts by mass of the resin component) of carbon black (manufactured by CABOT) and 2 parts by mass (10 parts by mass based on 100 parts by mass of the resin component) of the hydrotalcite particles "HT1" were dispersed in the resin solution to obtain a coating layer solution 1. [0085] Production of carrier particles 1 Using SPIRA COTA (manufactured by OKADA SEIKO Co., Ltd.), the resin solution 1 for a coating layer obtained above was applied in a heated atmosphere at 70 °C so that the amount of the resin component was 2 parts by mass based on 100 parts by mass of the carrier core particles. Thereafter, the mixture was heated at 100 °C for 5 hours to remove toluene. Next, coarse particles were removed by a sieve having an opening of 75 μm using a sieve shaker (manufactured by KOEI SANGYO Co., Ltd.) to obtain carrier particles (magnetic carrier) 1 having an average particle diameter of 41 μm. [0086] Production of carrier particles 2 to 5 Carrier particles 2 to 4 were produced by the same production method as the carrier particles 1 except that the hydrotalcite particles were changed to the types shown in Table 4. Carrier particles 5 were produced in a similar manner as the carrier particles 1 with the exception that the hydrotalcite particles were not added. [0087] Average particle diameter of the hydrotalcite particles Average particle diameter of the hydrotalcite particles in the carrier particles, a cross section of the carrier particles was exposed with a focused ion beam processing and observation apparatus "FB 2200" (manufactured by HITACHI), and the cross section was observed with a scanning electron microscope "S-4700" (manufactured by HITACHI) at a magnification of 15,000 times or more. The diameters of 50 or more particles were measured, and the number average value thereof was calculated as the average particle diameter of the hydrotalcite particles. The alumina particles to be measured were determined using an energy dispersive X-ray analyzer or the like attached to the scanning electron microscope. The results are shown in Table 3. [0088] [Table 3] [0089] Evaluation of charge stability 1.4g of the toner particles of the type shown in Tables 4 and 5 and 18.6g of the carrier particles of the type shown in Tables 4 and 5 were placed in a 50 mL plastic bottle with a lid. These particles were allowed to stand in each of a low-temperature and low-humidity environment (temperature: 10 °C, humidity: 10%) and a high-temperature and high-humidity environment (temperature: 30 °C, humidity: 85%) for 24 hours with the lid opened. A sample was taken after 60 minutes while stirring with a Turbula mixier T2F type (manufactured by Willy A. Bachofen AG), and the toner average charge amount Q/M (μC/g) was measured by a suction Faraday cage method. Namely, the sample was directly suctioned by a suction pump and collected by the Faraday cage containing a filter paper. The charge amount of the sample collected on the filter paper was measured by a q/m Meter Model 210- HS manufactured by Treck Corporation connected to the Faraday cage. The toner average charge amount Q/M (μC/g) was calculated from the mass M of the collected toner particles and the charge amount Q thereof. The ratio of the charge amount in the high-temperature and high-humidity environment to the charge amount in the low-temperature and low-humidity environment was calculated and defined as the charge stability of the developer. The closer this ratio is to 1, the better the charging stability of the developer. The results are shown in Tables 4 and 5.

[0090] [Table 4]

[0091] [Table 5]

[0092] As demonstrated above, the above-described example toner particles and example carrier particles may be combined to achieve a suitable charge stability. [0093] It is to be understood that not all aspects, advantages and features described herein may necessarily be achieved by, or included in, any one particular example. Indeed, having described various examples herein, it should be apparent that other examples may be modified in arrangement and detail is omitted.