WO2024091231A1

WO2024091231A1 - Alumina-coated silica toner surface additives

Info

Publication number: WO2024091231A1
Application number: PCT/US2022/047824
Authority: WO
Inventors: Dongwon Kim; Seungsik Woo; Kyeonghwan CHOI; Donghong LIM; Sungjun Cho; Jinmo HONG
Original assignee: Hewlett-Packard Development Company, L.P.
Priority date: 2022-10-26
Filing date: 2022-10-26
Publication date: 2024-05-02

Abstract

An example a toner composition includes a toner particle including a binder resin, a releasing agent, and a pigment and an additive disposed on an external surface of the toner particle, the additive including alumina-coated silica particles.

Description

ALUMINA-COATED SILICA TONER SURFACE ADDITIVES BACKGROUND [0001] Toner particles may be used to form an electrostatic latent image. For instance, an electrostatic charge image may be developed by a developer including a toner to be visualized as a toner image. This toner image may be transferred and fixed onto a surface of a recording medium to form a corresponding image. [0002] Surface characteristics of toner particles can impact charging uniformity, charging stability, transferability, and/or a cleaning ability of the toner particles, among other qualities of the toner particles. An external additive may be added to a surface of a toner particle to alter surface characteristics of the toner particle. DETAILED DESCRIPTION [0003] Surface characteristics of toner particles may affect charging uniformity, charging stability, transferability, and/or a cleaning ability of the toner particles. An external additive may be added to a surface of a toner particle to alter surface characteristics of the toner particle. [0004] Some approaches may employ titanium dioxide particles and/or silica particles as surface additives. However, toner particles having titanium dioxide particles and/or silica particles as a surface additive may not exhibit charging uniformity. For example, fumed silica has a strong negative polarity and thus toner particles with fumed silica as a surface additive may exhibit excessive charge-up. [0005] As such, some other approaches may add titanium dioxide particles, in addition to fumed silica particles, to mitigate frictional charging due to the excessive charge-up phenomenon caused by the presence of the fumed silica particles. However, since titanium dioxide has a low electric resistance and a good charge exchangeability, a reverse or weakly charged toner may be produced. Moreover, titanium dioxides may be costly to procure and/or the use of titanium dioxides may be disfavored and/or restricted, for instance, due to environmental concerns (e.g., pollution concerns, carcinogenic concerns), or for other reasons. Additionally, surface additives such as titanium dioxide, strontium oxide and/or polymer beads may have positive charge characteristics which may cause filming on the organic photoconductor (OPC) roller and/or contamination of the charge roller due to a strong adhesion of the surface additives to a surface of the charge roller or OPC roller through which a strong negative voltage flows. [0006] Moreover, silica particles may be porous and/or have hydrophilic surfaces. Thus, if a toner particle with silica particles as a surface additive is used in a high-temperature and high-humidity environment, the toner particle may not be well charged due to excessive absorption of moisture, which may serve as an electrical conductor. On the other hand, a toner particle with silica particles as a surface additive may be excessively charged in a low-temperature and low- humidity environment. That is, charging stability of a toner particle with silica particles as a surface additive may vary and/or be deteriorated depending on environmental conditions (e.g., humidity and/or temperature). [0007] In an effort to address the above mentioned variance and/or deterioration in environmental charge stability (e.g., caused by moisture), silica particles and/or titanium dioxide particles may be treated with a surface treating agent such as hydrophobic silicone oil. However, using various surface treating agents may reduce flowability of the toner particles. [0008] In preparing fumed silica particles, the silica particles may form agglomerates, which may lower dispersibility of the fumed silica particles. Using such an external additive with an inherently poor dispersibility may also lower flowability, anti-caking ability, fusability, and/or cleaning properties of the resulting toner particles. [0009] To prevent the aggregation of the fumed silica particles, sol-gel silica powder may be used. As used herein, sol-gel silica powder refers to silica powder prepared using a sol-gel method. For example, sol-gel silica powder may be prepared by hydrolysis and condensation of alkoxy silane in an organic solvent in the presence of water, and removing the solvent from a silica sol suspension resulting from the condensation. Sol-gel silica powder prepared by a sol-gel method may include spherical silica particles having a uniform particle diameter and spherical shape. Using spherical sol-gel silica powder particles having a sphericity near to 1 as an external additive may deteriorate cleaning properties of the toner particles. For instance, it may be difficult to clean any toner particles remaining in the OPC such that charge roller contamination or filming may occur. [0010] Use of small-diameter toner particles has been increased, for instance, to provide high image quality. However, the smaller the toner particle diameter, the more ineffective the flowability of the toner particles may become, and a greater quantity of inorganic particles may be required as an external additive. The external additive is exposed to friction against a supply roller and a blade or due to stirring within a developing unit during electrophotography. Stress exerted on the toner particle during this process may cause the external additive to be separated from the toner particle surface or to be buried in (e.g., embedded in) the toner particle surface. As a result, the toner particles may have ineffective flowability, may be unable to be smoothly supplied in an electrophotographic imaging system, and may have increased adhesion to a developing roller, resulting in sharp reductions in development characteristics and durability (e.g., charge retention). [0011] Alumina-coated silica toner surface additives are described herein. For instance, alumina-coated silica toner surface particles can provide enhanced surface characteristics of a toner particle when disposed on a surface of toner particle and thus can provide resultant toner compositions that exhibit enhanced performance (e.g., charge retention, thermal stability, etc.) as compared to other approaches such as those that employ silica particles (e.g., sol-gel silica powder) and/or titanium dioxide particles. The toner compositions herein can be used to develop an electrostatic latent image, as described herein. [0012] Notably, the above mentioned enhanced surface characteristics can be realized in the absence of (without the presence of any of) titanium dioxide (e.g., TiO2), strontium oxide, and/or polymer beads. Stated differently, the toner composition herein can be titanium dioxide-free (e.g., including 0 percent titanium dioxide by weight of a total weight of the toner composition), sol-gel silica powder- free, strontium oxide-free, and polymer beads-free, and thus can avoid incurring any cost, performance characteristic reduction, and/or environmental impact associated with use of titanium dioxide, sol-gel silica, strontium oxide, and/or polymer beads. [0013] The toner compositions herein include toner particles (core particles) and an additive disposed on an external surface of the toner particles. The additive can include alumina-coated silica toner surface particles. In some examples, the additive can include alumina-coated silica toner surface particles and fumed silica particles, as described herein. [0014] Each of the toner particles includes a core particle including a binder resin, a pigment, and a releasing agent. Examples of the binder resin may include, but are not limited to, a styrenic resin, an acrylic resin, a vinyl resin or polyolefin resin, a polyether-based polyol resin, a phenolic resin, a silicone resin, a polyester resin, an epoxy resin, a polyimide resin, a polyurethane resin, a polybutadiene resin, or any mixture thereof. [0015] Examples of the styrenic resin may include, but are not limited to, polystyrene, a homopolymer of a styrenic monomer such as poly-p-chlorostyrene or polyvinyltoluene, a styrene-based copolymer such as a styrene-p- chlorostyrene copolymer, a styrenevinyltoluene copolymer, a styrene-vinyl naphthalene copolymer, a styrene-acrylic acid ester copolymer, a styrene- methacrylic acid ester copolymer, a styrene-methyl achloromethacrylate copolymer, a styrene-acrylonitrile copolymer, a styrene-vinyl methyl ether copolymer, a styrene-vinyl ethyl ether copolymer, a styrene-vinyl methyl ketone copolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer, or a styrene-acrylonitrile-indene copolymer, or any mixture thereof. [0016] Examples of the acrylic resin may include, but are not limited to, a polymer of acrylic acid, a polymer of methacrylic acid, a polymer of methyl methacrylate, a polymer of methyl Į-chloromethacrylate, or any mixture thereof. [0017] Examples of the vinyl resin or polyolefin resin may include, but are not limited to, polyvinyl chloride, polyethylene, polypropylene, polyacrylonitrile, polyvinyl acetate, or any mixture thereof. [0018] The polyester resin may be prepared via reaction between an aliphatic, alicyclic, or aromatic polybasic carboxylic acid or alkyl ester thereof and polyhydric alcohol via direct esterification or trans-esterification. Examples of the polybasic carboxylic acid may include phthalic acid, isophthalic acid, terephthalic acid, tetrachlorophthalic acid, chlorophthalic acid, nitrophthalic acid, p- carboxyphenylacetic acid, p-phenylene-2-acetic acid, m-phenylenediglycolic acid, p-phenylenediglycolic acid, ophenylenediglycolic acid, diphenylacetic acid, diphenyl-p,pƍ-dicarboxylic acid, naphthalene-1,4-dicarboxylic acid, naphthalene- 1,5-dicarboxylic acid, naphthalene-2,6-dicarboxylic acid, anthracenedicarboxylic acid, and/or cyclohexane dicarboxylic acid. Also, in addition to the dicarboxylic acid, a polybasic carboxylic acid such as trimellitic acid, pyromellitic acid, naphthalene tricarboxylic acid, naphthalene tetracarboxylic acid, pyrene tricarboxylic acid, and pyrene tetracarboxylic acid may be used. Also, derivatives of a carboxylic acid in which the carboxylic group thereof is reacted to form an anhydride, oxychloride, or ester group may be used. Among them, terephthalic acid or lower esters thereof, diphenyl acetic acid, cyclohexane di-carboxylic acid, or the like may be used. The lower ester refers to an ester of aliphatic alcohol having one to eight carbon atoms. Examples of the polyhydric alcohol may include an aliphatic diol such as ethylene glycol, diethylene glycol, triethylene glycol, propylene glycol, butane diol, hexane diol, neopentyl glycol, or glycerine, an alicyclic diol such as cyclohexane diol, cyclohexane dimethanol, or hydrogen- added bisphenol A, and an aromatic diol such as ethylene oxide adduct of bisphenol A or propylene oxide adduct of bisphenol A. One or more than one of the polyhydric alcohol may be used. Among these polyhydric alcohols, an aromatic diol and an alicyclic diol may be used. For example, an aromatic diol may be used. In addition, a polyhydric alcohol having three or more —OH groups, such as glycerin, trimethylol propane, or pentaerythritol may be used together with the diol to have a cross-linked structure or a branched structure to increase fixability or fusability of the toner. [0019] A number average molecular weight of the binder resin may be in the range of about 700 to about 1,000,000 g/ mole (mol) or about 10,000 to about 500,000 g/mol. The binder resin used in the present disclosure may include a combination of a high molecular weight binder resin and a low molecular weight binder resin in an appropriate ratio. A number average molecular weight of the high molecular weight binder resin may be, for example, from about 100,000 to about 500,000 g/mol, and a number average molecular weight of the low molecular weight binder resin may be, for example, from about 1,000 to about 100,000 g/mol. The two types of binder resins having different molecular weights may have independent functions. For instance, the low molecular weight binder resin has little molecular chain entanglements, and may thereby contribute to fusability and gloss. On the contrary, the high molecular weight binder resin may maintain a certain level of elasticity even at a high temperature due to many molecular chain entanglements, and may thereby contribute to a higher hot offset occurring temperature. [0020] The pigment may be, for example, a black pigment, a yellow pigment, a magenta pigment, a cyan pigment, or any combination thereof. For example, the black pigment may be carbon black, aniline black, or any mixture thereof. [0021] For example, the yellow pigment may be a condensed nitrogen compound, an isoindolinon compound, an anthraquinone compound, an azo metal complex, an allyl imide compound, or any mixture thereof. More particularly, the yellow pigment may be, but is not limited to, “C.I. Pigment Yellow” 12, 13, 14, 17, 62, 74, 83, 93, 94, 95, 109, 110, 111, 128, 129, 147, 168, or 180. [0022] For example, the magenta pigment may be a condensed nitrogen compound, an anthraquinone compound, a quinacridone compound, a base dye lake, a naphthol compound, a benzoimidazole compound, a thioindigo compound, a perylene compound, or any mixture thereof. More particularly, the magenta pigment may be, but is not limited to, “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, or 254. [0023] For example, the cyan pigment may be a copper phthalocyanine compound or a derivative thereof, an anthraquinone compound, a base dye lake, or any mixture thereof. More particularly, the cyan pigment may be, but is not limited to, “C.I. Pigment Blue” 1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, or 66. [0024] The amount of the pigment included in the core particle may be, for example, from about 0.1 parts by weight to about 20 parts by weight, for example, from about 2 parts by weight to about 10 parts by weight, based on 100 parts by weight of the binder resin, without being limited thereto. [0025] Examples of the releasing agent may include, but are not limited to, a polyethylene-based wax, a polypropylene-based wax, a silicone-based wax, a paraffin-based wax, an ester-based wax, a carnauba-based wax, a metallocene- based wax, or any mixture thereof. [0026] The releasing agent may have, for example, a melting point of from about 50 °C to about 150 °C, without being limited thereto. The amount of the releasing agent included in the core particle may be, for example, from about 1 part by weight to about 20 parts by weight, or from about 1 part by weight to about 10 parts by weight, based on 100 parts by weight of the binder resin. The releasing agent may prevent the toner particles from sticking to a heating roller of a fixing device. [0027] The core particles may be prepared by, for example, a pulverization process, an aggregation process, or a spraying process. The pulverization process may be performed by, for example, pulverizing after melting and mixing a binder resin, a pigment, and a releasing agent. The aggregation process may be performed by, for example, mixing a binder resin dispersion, a pigment dispersion, and a releasing agent dispersion; aggregating these particles of the binder resin, the pigment, and the releasing agent; and combining the resulting aggregates. [0028] A volume average particle diameter of the core particles may be, but is not limited to, from about 4 ^m to about 20 ^m or from about 5 ^m to about 10 ^m. [0029] A shape of the core particles is also not particularly limited. As the shape of the core particles is closer to a sphere, charging stability of the toner and dot reproducibility of a print image may be more enhanced. For example, the core particles may have a sphericity in a range of, for example, about 0.90 to about 0.99. The sphericity of the core particles can be measured by a flow particle image analyzer, FLOWCAM 8000 manufactured by YOKOGAWA Corp. using an analysis software (VISUALSPREADSHEET such as version 5.9.1.78). Specifically, in a 100 milliliter (mL) glass beaker, 0.1 mL to 0.5 mL of a surfactant, preferably Benzene, 1,1-oxybis, tetrapropylene derivatives, sulfonated, sodium salts (DOWFAX 2A1 manufactured by THE DOW CHEMICAL CO., LTD.) is loaded, approximately 0.1 gram (g) to 0.5 g of each toner is further added and stirred with a micro spatula, and then 80 mL of ion-exchanged water is added. Next, the obtained dispersion liquid is dispersed by an ultrasonic dispersion for about 3 minutes. The shape and distribution of the toner are measured using FLOWCAM 8000, until the number of analyzed particles in the dispersion reaches 30,000. [0030] External additives can be attached to a surface of the core particles. As described herein, it has been discovered that having alumina-coated silica particles (e.g., alumina-coated silica toner surface particles) attached to surface of a core particle provides a resultant toner composition exhibiting good charging properties (charge retention rate, charge decrease rate, charging rate, and charging speed), exhibiting good image characteristics (e.g., good image background performance), and exhibiting good long-term thermal stability, as described herein. [0031] In some examples, the alumina-coated silica particles can have an average particle diameter in a range from about 10 nanometers (nm) to about 39 nm. All individual values from about 10 nm to about 39 nm are included. For instance, the alumina-coated silica particles can have an average particle diameter in a range from 15 nm to 25 nm or in a range from 10 nm to 39 nm. In some examples, the alumina-coated silica particles can have an average particle diameter of about 5 nm, about 10 nm, about 20 nm, about 25 nm, about 30 nm, about 35 nm, or about 39 nm, among other possible values. As used herein, the average particle diameter refers to or includes the diameter of a spherical particle, or the average diameter of a non-spherical particle (e.g., the average of multiple diameters across the non-spherical particle). The average particle diameter of particles may be measured by a particle diameter distribution measuring device (manufacturer: MICROTRAC, trade name: NANOTRAC FLEX). [0032] The alumina-coated silica particles can be present in an amount to cover 16 percent to 33 percent of a total surface area of an external surface of a toner particle and the fumed silica particles can be present in an amount to cover 27 percent to 65 percent of the total surface area of the external surface of the toner particle. All individual values and sub-ranges from about 16 percent to about 33 percent and from about 27 percent to about 65 percent are included. For instance, in some examples, the alumina-coated silica particles can be present in an amount to cover 21 percent to 31 percent, 16 percent to 24 percent, 16 to 27 percent, or 16 percent to 33 percent of the total surface area of the external surface of the toner particle, among other possibilities. In some examples, the fumed silica particles can be present in an amount to cover 45 percent to 50 percent, 27 percent to 36 percent, 55 percent to 65 percent, or 27 to 65 percent of the total surface area of the external surface of the toner particle, among other possibilities. [0033] In some examples, the alumina-coated silica particles can be present in a range from about 0.4 weight percent to about 0.8 weight percent of a total weight of the toner particle. As used herein, a total weight of the toner particle refers to a total weight of the toner particle prior to an additive being disposed on the surface of the toner particle. All individual values and sub-ranges from about 0.4 weight percent to about 0.8 weight percent are included. For instance, the alumina-coated silica particles can be present in a range from about 0.4 weight percent to about 0.6 weight percent, a range from about 0.5 weight percent to about 0.8 weight percent, or a range from about 0.4 weight percent to 0.8 weight percent of a total weight of the toner particle. In some examples, the alumina-coated silica particles can be present in a range from 0.4 weight percent to 0.6 weight percent, a range from 0.5 weight percent to 0.8 weight percent, or a range from 0.4 weight percent to 0.8 weight percent of a total weight of the toner particle. In some examples, the alumina-coated silica particles can be present at about 0.4 weight percent, about 0.5 weight percent, about 0.6 weight percent, or about 0.8 weight percent of a total weight of the toner particle, among other possibilities. In some examples, the alumina-coated silica particles can be present at 0.4 weight percent, 0.5 weight percent, 0.6 weight percent, or 0.8 weight percent of a total weight of the toner particle, among other possibilities. [0034] In some examples, the alumina-coated silica particles can include alumina and silica. For instance, the alumina can be present in a range from about 8 percent to about 40 percent of a total weight of a alumina-coated silica particle and the silica present in a range from about 43 percent to about 80 percent of the total weight of the alumina-coated silica particle. All individual values and sub- ranges from about 8 percent to 40 percent (for the alumina) and from 43 percent to 80 percent (for the silica) of the total weight of the alumina-coated silica particle are included. For instance, in some examples the alumina can be present in a range from 8 percent to 40 percent of a total weight of a alumina-coated silica particle and the silica present in a range from 43 percent to 80 percent of the total weight of the alumina-coated silica particle. [0035] In some examples, the alumina-coated silica particles can form 100 weight percent of a total weight of an additive added to a surface of toner particles. However, in some examples, the additive can include additional additives added to the surface of the toner particles, as described herein. For example, the additional additives can have an average particle diameter in a range from 10 nm to 150 nm. The additional additives may include but are not limited to titanium dioxide particles, aluminum oxide particles, strontium titanate particles, cerium oxide particles, silicon dioxide particles, tin oxide particles, zinc oxide particles, magnesium oxide particles, or any combination thereof. [0036] For instance, in some examples, the additional particles can be fumed silica particles (uncoated fumed silica particles which are not prepared by a sol-gel method) having an average particle diameter in a range from about 10 nm to about 20 nm. All individual values and sub-ranges from about 10 nm to about 20 nm are included. For example, the fumed silica particles can have an average particle diameter in a range from 12 nm to 18 nm or in a range from 10 nm to 20 nm, among other possibilities. [0037] In some examples, the fumed silica particles can be present in a range from about 0.6 weight percent to about 1.0 weight percent of a total weight of a toner particle. As mentioned, the total weight of the toner particle refers to a weight of the toner particle refers to a total weight of the toner particle prior to an additive being disposed on the surface of the toner particle. All individual values and sub-ranges from about 0.6 weight percent to about 1.0 weight percent are included. For instance, in some examples the fumed silica particles can be present in a range from 0.6 weight percent to 1.0 weight percent of a total weight of a toner particle. In some examples, the fumed silica particles can be present in a range from about 0.65 weight percent to about 0.75 weight percent, about 0.60 weight percent to about 0.80 weight percent, or about 0.80 weight percent to about 1.00 weight percent of a total weight of the toner particle. In some examples, the fumed silica particles can be present in a range from 0.65 weight percent to 0.75 weight percent, 0.60 weight percent to 0.80 weight percent, or 0.80 weight percent to 1.00 weight percent of a total weight of the toner particle. In some examples, the fumed silica particles can be present at about 0.6 weight percent, about 0.65 weight percent, about 0.75 weight percent, about 0.80 weight percent, about 0.90 weight percent, or about 1.00 weight percent of a total weight of the toner particle, among other possibilities. In some examples, the fumed silica particles can be present at 0.6 weight percent, 0.65 weight percent, 0.75 weight percent, 0.80 weight percent, 0.90 weight percent, or 1.00 weight percent of a total weight of the toner particle, among other possibilities. [0038] The alumina-coated silica particles can be present in an amount to cover about 16 percent to about 33 percent of a total surface area of the external surface of the toner particle (based on a total surface area of the toner particle prior to deposition of the additive on the external surface of the toner particle). The fumed silica particles can be present in an amount to cover about 27 percent to about 65 percent of the total surface area of the external surface of the toner particle (based on a total surface area of the toner particle prior to deposition of the additive on the external surface of the toner particle). For instance, the alumina-coated silica particles can be present in an amount to cover about 16 percent to about 33 percent of a total surface area of the external surface of the toner particle and the fumed silica particles can be present in an amount to cover about 27 percent to about 65 percent of the total surface area of the external surface of the toner particle. In some examples, the alumina-coated silica particles can be present in an amount to cover 16 percent to 33 percent of a total surface area of the external surface of the toner particle and the fumed silica particles can be present in an amount to cover 27 percent to 65 percent of the total surface area of the external surface of the toner particle. In some examples, the alumina-coated silica particles can be present in an amount to cover about 21 percent to about 31 percent, about 16 percent to about 24 percent, about 16 percent to about 33 percent, or about 16 to about 27 percent of a total surface area of the toner particle, while the fumed silica particles are present in an amount to cover about 45 percent to about 50 percent, about 27 percent to about 36 percent, about 27 percent to about 65 percent, or about 55 percent to about 65 percent of a total surface of the toner particle (e.g., the silica toner particle), among other possibilities. In some examples, the fumed silica particles can be present in an amount to cover 45 percent to 50 percent, 27 percent to 36 percent, or 55 percent to 65 percent of a total surface of the toner particle (e.g., the silica toner particle), among other possibilities. [0039] The percentage of the surface area of the toner particles covered by an additive (e.g., the alumina-coated silica particles) can be determined in accordance with the formula I: [0040] ^ ൌ ^כ^^ ^^ ^ଷ ଶ_గ^ כ ^ _ௗכ^ଶ^ כ ^ (Formula I) [0041] where: [0042] f is the percentage of the surface area of the additive; [0043] D is toner size (average particle diameter); [0044] p1 is toner density; [0045] d is additive material size (average particle size); [0046] p2 is additive material density; and [0047] C is additive content (weight percent based on a total weight of the toner particles). [0048] In some examples, a sum of a weight percent of the alumina-coated silica particles and the weight percent of the silica particles can be equal to a total weight of an additive that is added to a surface of a toner particle. Stated differently, a sum of the weight percentage of the alumina-coated silica particles and a weight percentage of the silica particles (e.g., fumed silica particles) can be equal to 100 weight percent of the additive disposed on an external surface of the toner particle. However, in some examples, additional additives can be present on the external surface of the toner particle. [0049] In some examples, a sum of a percent of a surface area covered by the alumina-coated silica particles and a percent of a surface area covered by the silica particles can be in a range from about 48 percent to about 88 percent of a total surface area of a toner particle (based on a total surface of the toner particle before deposition of the additive on the toner particle). For instance, a sum of a percent of a surface area covered by the alumina-coated silica particles and a percent of a surface area covered by the silica particles can be in a range from 48 percent to 88 percent of a total surface area of a toner particle. Stated differently, the additive herein (e.g., the alumina-coated silica particles and the fumed silica particles) can, in some examples, cover 48 percent to 88 percent of a total surface area of an exterior surface of the toner particle. [0050] In some examples, enhanced performance characteristics (good charge retention, good charge decrease, good environmental charge stability, good image background performance, good charging speed, and/or good thermal stability, etc.) of the toner compositions with alumina-coated silica particles can be realized in the absence of (having 0.0 weight percent based on a total weight of a toner composition) titanium dioxide, strontium oxide, sol-gel silica, and/or polymer beads. Stated differently, the toner composition herein can be titanium dioxide-free, strontium oxide-free, sol-gel silica powder and polymer beads-free, and thus can avoid incurring a cost, performance characteristic reductions, and/or environmental impacts associated with use of titanium dioxide, strontium oxide, sol-gel silica, and/or polymer beads. [0051] The external additive particles such as the alumina-coated silica particles may be attached to the surfaces of the core particles of the toner by using, for example, a powder mixing apparatus without being limited thereto. Examples of the powder mixing apparatus may be, but are not limited to, a HENSCHEL mixer, a V shape mixer, a ball mill, or a NAUTA mixer. [0052] In some examples, the toner compositions herein can exhibit a charge retention satisfying the condition R2/R1 > than 0.8, where: R1 is an initial charge per an amount of the toner composition; and R2 is a charge per the amount of the toner composition measured after printing 300,000 sheets with the toner composition, as described herein. [0053] In some examples, the toner compositions herein can exhibit a charge decrease satisfying the condition R2/R1 > than 0.9, where: R1 is an initial charge per an amount of the toner composition at ambient conditions, and R2 a charge per amount of toner after the toner is maintained under high-temperature and high-humidity (HH) condition (50° C., relative humidity of 80% for 48 hours), as described herein. [0054] In some examples, the toner compositions herein can exhibit an environmental charging stability satisfying the condition high humidity (HH)/ low humidity (LL) of 0.8 to 1.0, wherein high temperature/humidity (HH) performance of the toner composition is measured after the toner composition is maintained at 50° C and a relative humidity of 80% for 48 hours and the low temperature/humidity (LL) performance of the toner composition is measured after the toner composition is maintained at 10° C and a relative humidity of 10%, as described herein. [0055] In some examples, the toner compositions herein can exhibit an image background performance satisfying the condition where the optical density is less on 0.02, as described herein. [0056] In some examples, the toner compositions herein can exhibit a charging speed performance satisfying the condition where charging density is in a range from 1.0 to 2.0, as described herein. [0057] In some examples, the toner compositions herein can exhibit a thermal stability performance satisfying the condition where the cohesion is less than 25, as described herein. [0058] The toner compositions herein can be employed in an electrophotographic imaging apparatus which has a charging roller and/or an electrophotographic cartridge. Examples of electrophotographic imaging apparatus include a printer, a copier, a scanner, a fax machine, or a multifunction peripheral incorporating two or more of these. [0059] The electrophotographic imaging apparatus may include an electrophotographic cartridge. The electrophotographic cartridge may include an electrophotographic photoconductor drum that is charged by a charging roller according to an example, which is a charging means disposed in contact with the electrophotographic photoconductor drum. The electrophotographic photoconductor drum may be rotationally driven at a predetermined circumferential speed about an axis. The electrophotographic photoconductor drum may be subjected to uniform charging of a positive or a negative predetermined potential on its surface by the charging roller in the rotation process. The voltage applied to the charging roller may be, for example, a DC voltage. However, the voltage applied to the charging roller may be, for example, a combination of an AC voltage and a DC voltage. In the electrophotographic imaging apparatus according to an example, even when a DC voltage is applied to the charging roller, stable charging characteristics may be maintained for a longer period of time, and a high-quality output image may be obtained. [0060] The charging roller may charge the surface of the electrophotographic photoconductor drum to a uniform potential value while rotating in contact with the electrophotographic photoconductor drum. The image portion is exposed by laser light to form an electrostatic latent image on the electrophotographic photoconductor drum. After the electrostatic latent image is made a visible image, for example, a toner image, by a developing unit, the toner image is transferred to an image receiving member such as paper by a transfer unit such as the transfer roller to which a voltage is applied. Toner remaining on a surface of the electrophotographic photoconductor drum after the image transfer is cleaned by a cleaning unit, for example, a cleaning blade. The electrophotographic photoconductor drum may be used again for image formation. The developing unit includes a regulating blade, a developing roller, and a supply roller. [0061] The electrophotographic cartridge according to an example may integrally support the electrophotographic photoconductor drum, the charging roller, and the cleaning blade, may be attached to the electrophotographic imaging apparatus, and may be detached from the electrophotographic imaging apparatus. Another cartridge may integrally support the developing unit including the regulating blade, the developing roller, and the supply roller, may be attached to the electrophotographic imaging apparatus, and may be detached from the electrophotographic imaging apparatus. Toner compositions such as those described herein (e.g., toner) may be located inside the developing unit. [0062] Examples [0063] Hereinafter, various examples will be described. However, the scope of the disclosure is not limited thereto. [0064] Formation of toner compositions of Examples 1 to 3 and Comparative Examples 1 to 6: [0065] The types and properties of the surface additives (SA) and the toner particles used in Examples 1 to 3 and Comparative Examples 1 to 6 are described below. [0066] The toner particles for each of Examples 1 to 3 and Comparative Examples 1 to 6 are available from XEROX. [0067] Different additives were added in the amounts shown in Tables 1A and 1B to an external surface of the toner particles to form the toner compositions of Examples 1 to 3 and Comparative Examples 1 to 6. [0068] The surface additives are described as follows: [0069] Surface additive 1 (SA 1): Alumina-coated silica particles having an average particle diameter of 15, 20, 25, or 40 nanometers, as indicated in Table 1A. SA 1 is available from TITAN KOGYO LTD. [0070] Surface additive 2 (SA 2): Aluminum oxide particles having an average particle diameter of 13 nanometers, as indicated in Table 1A. SA 2 is available from EVONIK INDUSTRIES AG. [0071] Surface additive 3 (SA 3): Fumed silica particles having an average particle diameter of 12 or 18 nanometers, as indicated in Table 1A. SA 3 additive is available from EVONIK INDUSTRIES AG. [0072] Surface additive 4 (SA 4): Sol-gel silica particles having an average particle diameter of 30 nanometers, as indicated in Table 1B. SA 4 additive is available from SHIN-ETSU CHEMICAL CO., LTD. [0073] Surface additive 5 (SA 5): Sol-gel silica particles having an average particle diameter of 110 nanometers, as indicated in Table 1B. SA 5 is available from SHIN-ETSU CHEMICAL CO., LTD. [0074] The type and amounts of surface additive(s), as indicated in Tables 1A and 1B, were added to the surface of the toner particles by mixing the toner particles and the surface additives using Powder mixer (Model No. KM-LS-2K, manufactured by KM TECH) at 6000 rpm for 3 minutes to obtain the toner compositions of the examples and comparative examples. [0075] Example 1 (EX 1): SA 1 (alumina-coated silica particles having an average particle diameter of 15 nm) was added at an amount sufficient to cover 21 percent to 33 percent of the toner particles exterior surface and SA 3 (fumed silica particles having an average particle diameter of 12 nm) was added at an amount sufficient to cover 45 percent to 50 percent of the toner particles exterior surface. [0076] Example 2 (EX 2): SA 2 (alumina-coated silica particles having an average particle diameter of 20 nm) was added at an amount sufficient to cover 16 percent to 24 percent of the toner particles exterior surface and SA 3 (fumed silica particles having an average particle diameter of 12 nm) was added at an amount sufficient to cover 27 percent 36 percent of the toner particles exterior surface. [0077] Example 3 (EX 1): SA 1 (alumina-coated silica particles having an average particle diameter of 25 nm) was added at an amount sufficient to cover 16 percent to 27 percent and SA 3 (fumed silica particles having an average particle diameter of 12 nm) was added at an amount sufficient to cover 55 percent to 65 percent of the toner particles exterior surface. [0078] Comparative Example 1 (CE 1): SA 2 (alumina oxide particles having an average particle diameter of 13 nm) was added at an amount sufficient to cover 6 percent to 10 percent of the toner particles exterior surface and SA 3 is added at an amount sufficient to cover 45 percent 50 percent of the toner particles exterior surface area. [0079] Comparative Example 2 (CE 2): SA 1 (alumina-coated silica particles having an average particle diameter of 40 nm) was added at an amount sufficient to cover 16 percent to 24 percent of the toner particles exterior surface and SA 3 was added at an amount sufficient to cover 55 percent to 65 percent of the toner particles exterior surface area. [0080] Comparative Example 3 (CE 3): SA 1 (alumina-coated silica particles having an average particle diameter of 40 nm) was added at an amount sufficient to cover 16 percent to 24 percent of the toner particles exterior surface and SA 3 is added at an amount sufficient to cover 27 percent to 36 percent of the toner particles exterior surface area, as indicated in Table 1A and Table 1B. [0081] Comparative Example 4 (CE 4): SA 1 (alumina-coated silica particles having an average particle diameter of 20 nm) was added at an amount sufficient to cover 16 percent to 24 percent of the toner particles exterior surface and SA 4 (sol-gel silica particles having an average particle diameter of 30 nm) are added at an amount sufficient to cover 21 percent 33 percent of the toner particles exterior surface. [0082] Comparative Example 5 (CE 5): SA 1 (alumina-coated silica particles having an average particle diameter of 20 nm) was added at an amount sufficient to cover 16 percent to 24 percent of the toner particles exterior surface and SA 5 (sol-gel silica particles having an average particle diameter of 110 nm) was added at an amount sufficient to cover 16 percent to 24 percent of the toner particles exterior surface. [0083] Comparative Example 6 (CE 6): SA 1 (alumina-coated silica particles having an average particle diameter of 20 nm) was added at an amount sufficient to cover 16 percent to 24 percent of the toner particles exterior surface and SA 2 (alumina oxide particles having an average particle diameter of 13 nm) was added at an amount sufficient to cover 6 percent to 10 percent of the toner particles exterior surface. [0084] Table 1A

and Comparative Examples 1-6 are summarized in Table 2. [0087] Table 2: Examples (EX) and Comparative Examples (CE)

[0088] Charge retention rate: [0089] Charge retention rate evaluation was performed by using an EPPING charge per mass (q/m) meter as a measuring device under the conditions of a voltage of 3.0 volts (V) and an air flow rate of 2.0 liters/minute according to the following procedure. [0090] 1.6 g of a toner composition and 18.4 g of a carrier were added to a 50 ml bottle and mixed using a TURBULAR mixer for about 3 minutes to prepare a toner composition sample. An amount of the toner composition was evaluated at initial conditions “R1” (measured at 50° Celsius (C.), relative humidity of 80% prior to printing any sheets with the toner composition) using the EPPING q/m matter and at subsequent conditions “R2” (50° C., relative humidity of 80% after printing 300,000 sheets with the toner composition sample) using the following criteria: [0091] A: R2/R1 > 0.8 (Good charge retention); [0092] B: R2/R1 > 0.6 (Poor charge retention); and [0093] C: R2/R1 > 0.4 (Very poor charge retention). [0094] Charge decrease: [0095] Charge decrease evaluation was performed by using an EPPING charge per mass (q/m) meter as a measuring device under the conditions of a voltage of 3.0 V and an air flow rate of 2.0 liters/minute according to the following procedure. [0096] 1.6 g of a toner composition and 18.4 g of a carrier were added to a 50 ml bottle and mixed using a TURBULAR mixer for about 3 minutes to prepare a toner composition sample. The toner composition was evaluated at initial ambient temperature and humidity conditions “R1” using the EPPING q/m matter and at “R2” (after the toner composition sample was maintained under high- temperature and high-humidity (HH) condition (50° C., relative humidity of 80% for 48 hours) using the following criteria: [0097] A: R2/R1 > 0.9 (Good charge decrease); [0098] B: R2/R1 > 0.8 (Poor charge decrease); and [0099] C: R2/R1 > 0.7 (Very poor charge decrease). [00100] Environmental Charging Stability (charging property): [00101] Evaluation was performed by using an EPPING q/m meter as a measuring device under the conditions of a voltage of 3.0 V and an air flow rate of 2.0 L/min according to the following procedure. [00102] 1.6 g of a toner composition and 18.4 g of a carrier were added to a 50 ml bottle and mixed using a TURBULAR mixer for about 3 minutes to prepare a toner composition sample. The toner composition sample was maintained under a low-temperature and low-humidity (LL) condition (10° C., relative humidity of 10%) and a high-temperature and high-humidity (HH) condition (50° C., relative humidity of 80% for 48 hours), respectively. Then, charging performance thereof was evaluated to measure a charge amount in each environment and charging stability was evaluated according to the following criteria. [00103] A: Charge amount ratio of HH/LL of 0.8 to 1.0 (Good state in which almost no difference between charge amounts in different environmental conditions was found); [00104] B: Charge amount ratio HH/LL of 0.7 to less than 0.8 (Poor state in which a small difference between charge amounts in different environmental conditions was found); and [00105] C: Charge amount ratio of HH/LL of less than 0.7 (Very poor state in which a large difference between charge amounts in different environmental conditions was found). [00106] Image background (OPC background performance): [00107] Since the background image is generated under printing conditions with high temperature/high humidity, the above test was conducted under high temperature/high humidity conditions. After each of the toner compositions of the examples and comparative examples were loaded into a toner cartridge of a two- component development system printer (SCX-6555, available from SAMSUNG) and 7K images with 2% coverage were printed at 32 degrees Celsius and 80% humidity. An average image background was determined by measuring the optical density reading at three non-image locations of the OCP drum. Each optical density reading was measured using an "ELECTROEYE" reflection densitometer. Image background performance was classified according to the following criteria. [00108] ^: less than 0.02 optical density (the toner composition has very good OPC background performance). [00109] ż: optical density of 0.02 or more and less than 0.03 (the toner composition has good OPC background performance). [00110] ^: optical density of 0.03 or more and less than 0.05 (the toner composition has poor OPC background performance). [00111] ×: optical density of 0.05 or more (the toner composition has very poor OPC background performance). [00112] Charging speed: [00113] Charging speed was evaluated by measurement of the charge distribution amount of the toner compositions after the developing device was stopped after being driven for a predetermined time, the developer on the developing roller was sampled, and the charge distribution amount of the sampled developer was measured. The drive time of the developing device was set to 10 seconds, 15 seconds, 20 seconds, 30 seconds and 60 seconds, for respective tests. An E-SPART analyzer manufactured by HOSOKAWA MICRON CORPORATION was used to measure the charge distribution amount in accordance with the following criteria. [00114] - CV= q/d ı (Standard Deviation) /X (average) [00115] - CV peak= CV(10sec) / CV min [00116] The closer the CV peak value is to 1, better the charging speed of the toner composition. [00117] Level 1 : 1.0 to less than 2.0; [00118] Level 2 : 2.0 to less than 3.0; and [00119] Level 3 : 3.0 to 4.0 or greater. [00120] Thermal stability: [00121] The change in the degree of cohesion when the toner particles were left for 16 hours in an environment of a temperature of 50 °C. and a humidity of 80 relative humidity was measured. For the degree of cohesion, POWDER TESTER (manufactured by HOSOKAWA Co., Ltd., sieve 53, 45, 38 micrometers (^m)) was used. Sieves were set in the order of 53 ^m, 45 ^m, and 38 ^m from the top.2 g of toner particles were placed on the top sieve, and the mass of the toner particles remaining on each sieve when the sieve was vibrated was measured. The degree of aggregation was calculated according to the following formula (amplitude 1 mm, vibration time 40 seconds). [00122] Cohesion = (T / 2 + C / 2 × (3/5) + B / 2 × (1/5)) / 100 [00123] In the formula, T: the mass of the toner particles remaining on the upper sieve, C: the mass of the toner particles remaining on the interrupted sieve, and B: the mass of the toner particles remaining on the lower sieve. The ratio of the degree of cohesion after being left for 16 hours (after being left / before being left) with respect to the degree of cohesion before being left for 16 hours in the above environment was defined as the degree of cohesion ratio. [00124] Thermal stability performance was classified according to the following criteria: [00125] A : cohesion less than 25; [00126] B: cohesion less than or equal to 35; and [00127] C :cohesion greater than 35. [00128] When the cohesion ratio is less than 25, it was determined that the heat-resistant storage property was good. [00129] Referring to Tables 1A, 1B, and 2, it was observed that the toner compositions of Examples 1 to 3 each have good charge retention, good charge decrease, good environmental charge stability, good image background performance, good charging speed, and good thermal stability. [00130] A reason for the above performance may be that the alumina- coated silica particles provide a reduction in an amount of friction when printing with the toner particles and/or provide more effective charging characteristics (e.g., as compared to the toner (core) particles alone and/or toner particles using different surface additives). Additionally, unlike other additives which may be prone to caking on and/or embedding in the surface of a toner particles, the alumina-coated silica surface additives herein may provide enhanced charging characteristics over an operational lifetime of an image forming apparatus and/or for various different environmental conditions (e.g., for both high humidity and low humidity environments). Further, the relative size of the alumina-coated silica particles (e.g., the relative size of the alumina-coated silica particles and the fumed silica particles) herein can yield good charge retention, good charge decrease, good environmental charge stability, good image background performance, good charging speed, and/or good thermal stability, as compared to other approaches that may employ different sized surface additives. [00131] Although examples of the disclosure have been illustrated and described hereinabove, the disclosure is not limited thereto, and may be variously modified and altered by those skilled in the art to which the disclosure pertains without departing from the disclosure. These modifications and alterations are to fall within the scope of the disclosure. As used herein the term “about” refers to value(s) that are within 10 percent, within 5 percent or within 1 percent of a given value that the term about modifies. For instance, the term about can refer to a value(s) that are within 10 percent (+/- 10 percent) of a given value.

Claims

WHAT IS CLAIMED IS: 1. A toner composition comprising: a toner particle including a binder resin, a releasing agent, and a pigment; and an additive disposed on an external surface of the toner particle, the additive comprising alumina-coated silica particles. 2. The toner composition of claim 1, wherein the alumina-coated silica particles have an average particle diameter in a range from 10 nanometers (nm) to 39 nm. 3. The toner composition of claim 1, wherein the alumina-coated silica particles have an average particle diameter in a range from 15 nanometers (nm) to 25 nm. 4. The toner composition of claim 1, wherein the alumina-coated silica particles are present in a range from 0.4 weight percent to 0.8 weight percent of a total weight of the toner particle. 5. The toner composition of claim 1, wherein the additive further comprises fumed silica particles. 6. The toner composition of claim 5, wherein a sum of the weight percent of the alumina-coated silica particles and the weight percent of the fumed silica particles is equal to the total weight of the additive. 7. The toner composition of claim 5, wherein the fumed silica particles are present in a range from 0.6 weight percent to 1.0 weight percent of the total weight of the toner particle. 8. The toner composition of claim 5, wherein the fumed silica particles have an average particle diameter in a range from 10 nm to 20 nm. 9. The toner composition of claim 5, wherein the fumed silica particles have an average particle diameter in a range from 12 nm to 18 nm. 10. A toner composition comprising: a silica toner particle including a binder resin, a releasing agent, and a pigment; and an additive disposed on an external surface of the silica toner particle, the additive comprising: alumina-coated silica particles having an average particle diameter in a range from 10 nanometers (nm) to 39 nm; and fumed silica particles having an average particle diameter in a range from 10 nm to 20 nm. 11. The toner composition of claim 10, wherein the alumina-coated silica particles are present in an amount to cover 16 percent to 33 percent of a total surface area of the external surface of the silica toner particle. 12. The toner composition of claim 11, wherein the fumed silica particles are present in an amount to cover 27 percent to 65 percent of the external surface of the silica toner particle. 13. The toner composition of claim 10, wherein the toner composition exhibits a charge retention satisfying the condition R2/R1 > than 0.8, wherein: R1 is an initial charge per an amount of the toner composition; and R2 is a charge per the amount of the toner composition measured after printing 300,000 sheets with the toner composition. 14. The toner composition of claim 10, wherein the alumina-coated silica particles include: alumina present in a range from 8 percent to 40 percent of a total weight of the alumina-coated silica particles; and silica present in a range from 43 percent to 80 percent of the total weight of the alumina-coated silica particles. 15. An image forming apparatus to form an image by supplying the toner composition according to claim 10.