Toner for developing electrostatic latent images

Abstract

To provide a toner that can further improve low temperature fixability.SOLUTION: A toner for electrostatic latent image development has a toner base particle and silica particles externally added to the toner base particle. The toner base particle includes at least a binder resin and a colorant. The silica particles are subjected to hydrophobic treatment with an alkyl-silane coupling agent. The substantial throughput of the alkyl-silane coupling agent calculated from the following formulas is 0.01 mass% or more and less than 30 mass%. The substantial throughput (mass%) of the alkyl-silane coupling agent=ignition loss-loss on drying. The ignition loss (mass%): the mass reduction ratio when the silica particles are held at a temperature of 500°C for two hours. The loss on drying (mass%): the mass reduction ratio when the silica particles are held at a temperature of 105°C for two hours.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a toner for developing electrostatic latent images, and more particularly to a toner for developing electrostatic latent images (hereinafter sometimes simply referred to as "toner") used in image forming devices that utilize electrophotography, such as facsimiles, printers, and copiers. [Background technology]

[0002] For example, in image forming devices using electrophotography, such as facsimiles, printers, and copiers, a toner image transferred onto a transfer material such as paper is generally heated, melted, and fixed to the transfer material. In response to the growing awareness of energy conservation in recent years, there is a demand for toner that can be fixed at even lower temperatures than conventional toners.

[0003] Various methods have been proposed for fixing toner at low temperatures, including adjusting the molecular weight and molecular weight distribution of the binder resin that constitutes the toner (Patent Document 1) and using a combination of an amorphous resin and a crystalline resin as the binder resin (Patent Document 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-82484 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-160886 Summary of the Invention [Problem to be solved by the invention]

[0005] According to the above-mentioned proposed method, although it is possible to achieve a certain degree of low-temperature fixability of the toner, it cannot be said to be sufficient to cope with the increasing speed of image forming apparatuses in recent years, and further improvement in the low-temperature fixability of the toner is desired.

[0006] The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a toner capable of further improving low-temperature fixability. [Means for solving the problem]

[0007] The toner according to the present invention, which achieves the above-mentioned object, is a toner for developing electrostatic latent images, which comprises toner base particles and silica particles externally added to the toner base particles, wherein the toner base particles contain at least a binder resin and a colorant, the silica particles are hydrophobized with an alkylsilane coupling agent, and the actual treated amount of the alkylsilane coupling agent, calculated from the following formula, is 0.01% by mass or more and less than 30% by mass: Actual treatment amount with alkylsilane coupling agent (mass%) = loss on ignition - loss on drying Ignition loss (mass%): Mass loss rate when silica particles are kept at 500°C for 2 hours Drying loss (mass%): Mass loss rate when silica particles are kept at 105°C for 2 hours

[0008] In the toner having the above-described configuration, the silica particles are preferably fumed silica having an average primary particle diameter of 5 nm to 70 nm or colloidal silica having an average primary particle diameter of 50 nm to 200 nm.

[0009] In the toner having the above-described configuration, the alkylsilane coupling agent preferably has a linear alkyl group having 3 or more carbon atoms and no substituent.

[0010] In the toner having the above-described configuration, the amount of the silica particles added externally is preferably in the range of 0.5% by mass to 10% by mass relative to the toner base particles.

[0011] Furthermore, for the toner having the above-described structure, it is preferable that the volume average particle size of the toner base particles is in the range of 4 μm or more and 15 μm or less.

[0012] According to the present invention, there is also provided a developer for developing electrostatic latent images, comprising any one of the toners described above and a carrier. [Effects of the Invention]

[0013] The toner of the present invention can further improve low-temperature fixability, and the developer of the present invention can also be adapted to high-speed image forming apparatuses. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present inventors have conducted extensive research to improve the low-temperature fixability of toner, and as a result have discovered that the low-temperature fixability of toner is affected not only by the binder resin but also by the external additives in the toner base particles. More specifically, they have discovered that hydrophobically treated silica particles as external additives increase the viscosity of the molten toner, thereby reducing the fixability of the toner image to the transfer material. Further research by the present inventors has led to the discovery that the increase in viscosity of the molten toner can be suppressed by adjusting the type and amount of hydrophobizing agent for the silica particles, which has led to the present invention.

[0015] That is, the toner according to the present invention is a toner having toner base particles and silica particles externally added to the toner base particles, and one of its major features is that the silica particles have been hydrophobized with an alkylsilane coupling agent.

[0016] Silica particles have been widely used as an external toner additive to improve the fluidity and charging properties of toner. Furthermore, because silica particles themselves are hydrophilic and susceptible to temperature and humidity, hydrophobically treated silica particles have been used. HMDS (hexamethyldisilazane) and PDMS (polydimethylsiloxane) have been the main hydrophobizing agents.

[0017] However, according to the results of the inventors' investigations, it was found that although toners to which silica particles treated with HMDS or PDMS are externally added have improved toner fluidity and chargeability, the viscosity of the toner increases when the toner is molten, hindering the fixability of the toner to the transfer material.In addition, it was found that the use of an alkylsilane coupling agent as a hydrophobic treatment agent for silica particles can suppress the increase in viscosity of the molten toner, and that it is best to set the amount of treatment with the alkylsilane coupling agent within a specified range.The alkylsilane coupling agent used in the present invention will be described below.

[0018] (Alkylsilane coupling agent) The alkylsilane coupling agent used in the present invention is preferably a trialkoxyalkylsilane coupling agent represented by the following formula: C n H 2n+1 -Si(OC m H 2m+1 )3 (wherein n is an integer of 3 or more, and m is an integer of 1 to 3) If n is less than 3, the hydrophobic effect may be reduced. The maximum value of n is preferably 18. The larger n is, the more the thickening effect of the molten toner is suppressed. The more preferable range for n is an integer from 8 to 12. Furthermore, if m is greater than 3, the reactivity of the hydrophobic treatment may decrease. The more preferable range for m is an integer from 1 to 2. Furthermore, it is preferable that the alkyl group does not have a substituent.

[0019] The effective amount of alkylsilane coupling agent relative to silica particles calculated from the above formula is in the range of 0.01% by mass or more and less than 30% by mass. If the effective amount of alkylsilane coupling agent is less than 0.01% by mass, hydrophobicity cannot be imparted to the silica particles. On the other hand, if the effective amount of alkylsilane coupling agent is 30% by mass or more, the thickening effect of the molten toner increases. The preferable range of the effective amount of alkylsilane coupling agent is in the range of 1% by mass or more and 10% by mass or less.

[0020] The ignition loss of silica particles is the mass loss rate when the silica particles are kept at 500°C for 2 hours, and refers to the mass ratio of organic matter, volatile components, and moisture present in the silica particles. On the other hand, the drying loss is the mass loss rate when the silica particles are kept at 105°C for 2 hours, and refers to the mass ratio of volatile components and moisture present in the silica particles. Therefore, the organic matter present in the silica particles, i.e., the actual amount of alkylsilane coupling agent present, can be calculated by subtracting the drying loss from the ignition loss.

[0021] The method for hydrophobizing silica particles with an alkylsilane coupling agent is not particularly limited, and any conventionally known method can be used.For example, the method of directly mixing silica particles and an alkylsilane coupling agent using a mixer such as a Henschel mixer, the method of spraying an alkylsilane coupling agent onto silica particles, or the method of adding silica particles to a solution in which an alkylsilane coupling agent is dissolved or dispersed in a suitable solvent, and then removing the solvent can be included.

[0022] (silica particles) The silica particles used in the present invention can be any silica particles produced by a conventionally known method, but from the viewpoint of dispersibility of the silica particles, those produced by a dry method or a high-temperature hydrolysis method are preferred. Specifically, fumed silica or colloidal silica is preferably used. When fumed silica is used as the silica particles, the average primary particle diameter is preferably 5 nm or more and 70 nm or less. When colloidal silica is used as the silica particles, the average primary particle diameter is preferably 50 nm or more and 200 nm or less.

[0023] The average primary particle diameter of silica particles is the average value of the diameters or maximum diameters of a plurality of particles (100 particles) randomly sampled from an image of silica particles taken with a scanning electron microscope (SEM).

[0024] The amount of silica particles externally added to the surface of the toner base particles is preferably in the range of 0.5% to 10% by mass relative to the toner base particles. If the amount of silica particles externally added is less than 0.5% by mass, the fluidity and chargeability of the toner may not be improved. On the other hand, if the amount of silica particles externally added is more than 10% by mass, the viscosity of the toner when melted may increase, resulting in a decrease in low-temperature fixability.

[0025] (Toner base particles) The toner base particles used in the present invention contain at least a binder resin and a colorant. There are no particular limitations on the binder resin, and examples thereof include styrene-acrylic resin and polyester resin. Of course, these resins may be used in combination with other resins as needed.

[0026] Examples of the monomer that serves as the base of the styrene-acrylic resin include styrene derivatives such as styrene, α-methylstyrene, p-methylstyrene, pt-butylstyrene, p-chlorostyrene, and hydroxystyrene; methacrylic acid, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, glycidyl (meth)acrylate, methoxyethyl (meth)acrylate, propoxyethyl (meth)acrylate, methoxydiethylene glycol (meth)acrylate, and ethoxyethyl (meth)acrylate. Examples of (meth)acrylic acid esters include diethylene glycol (meth)acrylate, benzyl (meth)acrylate, cyclohexyl (meth)acrylate, tetrahydrofurfuryl (meth)acrylate, (meth)acrylonitrile, (meth)acrylamide, N-methylol (meth)acrylamide, ethylene glycol di(meth)acrylate, 1,3-butylene glycol di(meth)acrylate, 1,4-butanediol di(meth)acrylate, and trimethylolethane tri(meth)acrylate.

[0027] Polyester resins are mainly obtained by condensation polymerization of polycarboxylic acids and polyhydric alcohols. Examples of polycarboxylic acids include aromatic polycarboxylic acids such as phthalic acid, isophthalic acid, terephthalic acid, succinic acid, 1,2,4-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, and pyromellitic acid; aliphatic dicarboxylic acids such as maleic acid, fumaric acid, succinic acid, adipic acid, sebacic acid, malonic acid, azelaic acid, mesaconic acid, citraconic acid, and glutaconic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid and methylmedic acid; and anhydrides and lower alkyl esters of these carboxylic acids. One or more of these may be used.

[0028] The content of the trivalent or higher valent component depends on the degree of crosslinking, and the amount of the component added can be adjusted to achieve the desired degree of crosslinking. In general, the content of the trivalent or higher valent component is preferably 15 mol % or less.

[0029] On the other hand, examples of polyhydric alcohols used in polyester resins include alkylene glycols such as ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,4-butenediol, neopentyl glycol, 1,5-pentane glycol, and 1,6-hexane glycol; alkylene ether glycols such as diethylene glycol, triethylene glycol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; alicyclic polyhydric alcohols such as 1,4-cyclohexanedimethanol and hydrogenated bisphenol A; bisphenols such as bisphenol A, bisphenol F, and bisphenol S, and alkylene oxides of bisphenols, and these can be used alone or in combination of two or more.

[0030] For the purpose of adjusting the molecular weight or controlling the reaction, a monocarboxylic acid or a monoalcohol may be used as needed. Examples of the monocarboxylic acid include benzoic acid, parahydroxybenzoic acid, toluenecarboxylic acid, salicylic acid, acetic acid, propionic acid, and stearic acid. Examples of the monoalcohol include benzyl alcohol, toluene-4-methanol, and cyclohexanemethanol.

[0031] The binder resin used in the present invention preferably has a glass transition temperature in the range of 45° C. to 90° C. If the glass transition temperature is lower than 45° C., there is a risk of solidification in the toner cartridge or developing device. On the other hand, if the glass transition temperature is higher than 90° C., the toner may not be sufficiently fixed to the transfer material such as paper.

[0032] Examples of colorants used in the present invention include black pigments such as carbon blacks, including acetylene black, orchid black, and aniline black; yellow pigments such as yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa yellow G, Hansa yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, and tartrazine lake; orange pigments such as red yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Balkan orange, induthrene brilliant orange RK, benzidine orange G, and induthrene brilliant orange GK; red pigments such as red iron oxide, cadmium red, red lead, mercury cadmium sulfide, permanent red 4R, and lithol red. Examples of suitable pigments include pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, and brilliant carmine 3B; purple pigments include manganese violet, fast violet B, and methyl violet lake; blue pigments include iron blue, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, fast sky blue, and indanthrene blue BC; green pigments include chrome green, chromium oxide, pigment green B, malachite green lake, and Fanal yellow green G; white pigments include zinc oxide, titanium oxide, antimony white, and zinc sulfide; and white pigments include baryte powder, barium carbonate, clay, silica, white carbon, talc, and alumina white. These colorants may be used alone or in combination.

[0033] The total content of the colorants is preferably in the range of 0.1 to 20 parts by mass, particularly 1 to 15 parts by mass, per 100 parts by mass of the binder resin.

[0034] (Preparation of toner base particles) The toner base particles of the present invention can be produced by known methods such as pulverization classification, melt granulation, spray granulation, suspension / emulsion polymerization, etc., but the pulverization classification method is preferably used in terms of production equipment, productivity, etc. The pulverization classification method is described below.

[0035] First, toner components such as binder resin, colorant, and optionally charge control agent, release agent, and magnetic powder are premixed using a Henschel mixer or V-type mixer, and then melt-kneaded using a melt-kneading device such as a twin-screw extruder. After cooling, the melt-kneaded mixture is coarsely pulverized or finely pulverized, and if necessary, classified to obtain toner base particles with a predetermined particle size distribution. The volume average particle size of the toner base particles is preferably in the range of 4 μm to 15 μm. The volume average particle size of the toner base particles is measured using a Coulter Multisizer II manufactured by Coulter.

[0036] Here, as the charge control agent, a conventionally known charge control agent can be used, for example, as a positively chargeable charge control agent, nigrosine dye, fatty acid modified nigrosine dye, carboxyl group-containing fatty acid modified nigrosine dye, quaternary ammonium salt, amine compound, organometallic compound, etc. can be used, and as a negatively chargeable charge control agent, metal complex of oxycarboxylic acid, metal complex of azo compound, metal complex dye, salicylic acid derivative, etc. The amount of charge control agent added is preferably in the range of 0.1 to 10 parts by mass per 100 parts by mass of binder resin.

[0037] As the release agent, various waxes and low-molecular-weight olefin resins can be used. Examples of waxes that can be used include polyhydric alcohol esters of fatty acids, higher alcohol esters of fatty acids, alkylenebisfatty acid amide compounds, and natural waxes. Examples of low-molecular-weight olefin resins that can be used include polypropylene, polyethylene, and propylene-ethylene copolymers having a number-average molecular weight in the range of 1,000 to 10,000, particularly 2,000 to 6,000, with polypropylene being particularly preferred. The amount of release agent added is preferably in the range of 0.1 to 10 parts by mass per 100 parts by mass of binder resin.

[0038] Examples of magnetic powder include iron oxide (Fe3O4), iron sesquioxide (γ-Fe2O3), zinc iron oxide (ZnFe3O4), and yttrium iron oxide (Y3Fe5O 12 ), cadmium iron oxide (CdFe2O4), gadolinium iron oxide (Gd3Fe5O 12 ), copper iron oxide (CuFe2O4), lead iron oxide (PbFe 12 O 19 ), nickel iron oxide (NiFe2O4), neodymium iron oxide (NdFeO3), barium iron oxide (BaFe 12 O 19 ), magnesium iron oxide (MgFe2O4), manganese iron oxide (MnFe2O4), lanthanum iron oxide (LaFeO3), iron powder (Fe), cobalt powder (Co), nickel powder (Ni), etc. The amount of magnetic powder added is preferably in the range of 0.1 to 5 parts by mass, more preferably in the range of 0.5 to 3.0 parts by mass, per 100 parts by mass of binder resin.

[0039] The toner of the present invention is obtained by adhering the silica particles to the surface of the toner base particles thus prepared. The method for mixing and adding the silica particles to the toner base particles can be a conventionally known method, such as a method in which the toner particles and silica fine particles are charged into a mixer such as a Henschel mixer, a V-type mixer, a Turbula mixer, or a hybridizer, and then stirred and mixed.

[0040] In addition, a surface treatment agent may be added to the toner base particles as needed to adjust the chargeability, fluidity, etc. Examples of the surface treatment agent include one or more of inorganic fine powders such as alumina, zinc oxide, magnesium oxide, and calcium carbonate; organic fine powders such as polymethyl methacrylate; and fatty acid metal salts such as zinc stearate. The amount of the surface treatment agent added is preferably in the range of 0.1 to 2.0 parts by mass per 100 parts by mass of the toner base particles.

[0041] (Electrostatic latent image developer) The toner of the present invention can be used as a one-component developer or a two-component developer. When used as a two-component developer, the carrier used is not limited. For example, magnetic particles produced by sintering and atomizing magnetic materials such as magnetic metals such as iron, nickel, and cobalt, and their alloys, or alloys containing rare earth elements, soft ferrites such as hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, and lithium ferrite, iron oxides such as copper-zinc ferrite, and mixtures thereof, and magnetic particles whose surfaces are coated with a resin can be used. Magnetic material-dispersed resins can also be used as the carrier. In this case, the magnetic material can be the magnetic material described above, and the binder resin can be, for example, vinyl resins, polyester resins, epoxy resins, phenolic resins, urea resins, polyurethane resins, polyimide resins, cellulose resins, polyether resins, or mixtures thereof.

[0042] The particle diameter of the carrier is generally 30 μm to 200 μm, and particularly 50 μm to 150 μm, as measured by electron microscopy. The apparent density of the carrier, when mainly made of a magnetic material, varies depending on the composition and surface structure of the magnetic material, but is generally 2.4 g / cm. 3 ~3.0g / cm 3 The range is preferred.

[0043] The toner concentration in the two-component developer consisting of the toner and carrier is 1% by mass to 10% by mass, and preferably 1% by mass to 7% by mass. If the toner concentration is less than 1% by mass, the image density will be too low, while if the toner concentration exceeds 10% by mass, toner scattering may occur within the developing device, causing problems such as contamination inside the device or toner adhering to background areas of transfer paper, etc. [Example]

[0044] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples in any way.

[0045] (Preparation of Toner Base Particles I) 100 parts by weight of polyester resin (manufactured by Mitsubishi Chemical Corporation, product name: ER-508), 6 parts by weight of carbon black (manufactured by Cabot Corporation, product name: BP-L), 1.0 part by weight of zinc salicylate complex, and 2.0 parts by weight of polypropylene wax (manufactured by Sanyo Chemical Industries, Ltd., product name: 660P) were mixed using a Henschel mixer, and then melted and kneaded using a twin-screw extruder. The resulting mixture was rolled using a cooling press roller and coarsely pulverized using a feather mill. The mixture was then pulverized using an air jet type fine pulverizer and classified using an air flow classifier to obtain toner base particles I having a volume average particle size of 7.5 μm. The glass transition temperature (Tg) and softening temperature (T1 / 2) of the toner base particles I were measured by the following method, and found to be 63°C and 128°C, respectively.

[0046] (Preparation of Toner Base Particles II) A crystalline polyester resin having a melting point of 70° C. and Mw=10,000 was prepared by condensation polymerization of 238 parts by mass of adipic acid, 265 parts by mass of 1,6-hexanediol, and 1 part by mass of hydroquinone. Toner base particles II were prepared in the same manner as toner base particles I, except that 93 parts by mass of polyester resin (manufactured by Mitsubishi Chemical Corporation, product name: ER-508) and 7 parts by mass of the crystalline polyester resin prepared above were used as the polyester resin. The glass transition temperature (Tg) and softening temperature (T1 / 2) of toner base particles II were measured in the same manner as toner base particles I, and the Tg was 50°C and the T1 / 2 temperature was 104°C.

[0047] (glass transition temperature (Tg)) Using a differential scanning calorimeter (Shimadzu Corporation, DSC-60), 10 mg±0.5 mg of sample was weighed into an aluminum pan, and the glass transition temperature Tg was measured from the intersection of the baseline of the chart and the tangent to the endothermic curve at a heating rate of 5°C / min.

[0048] (Softening temperature (T1 / 2)) Using a capillary rheometer (Shimadzu Corporation, Flow Tester CFT-500D), the temperature was measured at a heating rate of 6°C / min, with a nozzle of 1.0 mmφ x 1 mm, a load of 10 kgf, and a sample weight of 1.5 g. The temperature was measured when the piston reached the midpoint in the process from the start to the end of the outflow.

[0049] (Preparation of Silica Particles A) Untreated fumed silica powder (BET specific surface area 130 m 2 100 parts by mass of 100% PEG-400 (1 / g) was mixed with 100 parts by mass of n-propanol using a stirrer. 50 parts by mass of n-propanol and a small amount of diethylamine were added to this mixture and stirred for 1 hour. 100 parts by mass of n-propanol and 4.0 parts by mass of isobutyltriethoxysilane were added to this mixture and heated under reflux for 5 hours while stirring in an inert atmosphere, and then allowed to cool to room temperature. The solvent was removed from this mixture using a rotary evaporator under superheated reduced pressure, and then it was dried in a vacuum oven for 18 hours to produce silica particles A.

[0050] (Preparation of Silica Particles B) Silica particles B were prepared in the same manner as silica particles A, except that isobutyltriethoxysilane was replaced with 5.0 parts by mass of octyltriethoxysilane.

[0051] (Preparation of Silica Particles C) Silica particles C were prepared in the same manner as silica particles A, except that isobutyltriethoxysilane was replaced with 7.0 parts by mass of decyltriethoxysilane.

[0052] (Preparation of Silica Particles D) Untreated fumed silica powder with a BET specific surface area of ​​50m 2 Silica particles D were prepared in the same manner as silica particles A, except that the silica particles D was prepared by changing the amount of silica particles D to 2.5 parts by mass of silica particles A and the isobutyltriethoxysilane was changed to 2.5 parts by mass of decyltriethoxysilane.

[0053] (Preparation of Silica Particles E) Untreated fumed silica powder (BET specific surface area 200 m 2100 parts by mass of silica particles (100% by mass / g) were placed in a reaction vessel, and the powder was fluidized by stirring under a nitrogen atmosphere, followed by spraying with 3.0 parts by mass of octyltrimethoxysilane. With continued stirring, the mixture was heated from room temperature to 340°C and held there for 30 minutes. Silica particles E were obtained by cooling the mixture.

[0054] (Preparation of Silica Particles F) Commercially available hydrophilic colloidal silica dispersion (BET specific surface area 30 m 2 To 100 parts by weight of silica gel (silica gel, 40% solids content) was added a small amount of aqueous ammonia and 2.0 parts by weight of octyltriethoxysilane, and the mixture was stirred at room temperature with an overhead stirrer for 24 hours. The mixture was dried in a forced circulation constant temperature dryer at 128°C to obtain silica particles F.

[0055] (Preparation of Silica Particles G) As silica particles G, commercially available hydrophobic silica particles (fumed silica particles surface-treated with HMDS, manufactured by Clariant, trade name: H13™, average primary particle diameter: 16 nm) were prepared.

[0056] (Silica particles H) As silica particles H, commercially available hydrophobic silica particles (fumed silica particles surface-treated with silicone oil, manufactured by Teika Corporation, trade name: MSN-002, average primary particle diameter: 16 nm) were prepared.

[0057] (Silica particles I) As silica particles I, commercially available hydrophobic silica particles (fumed silica particles surface-treated with silicone oil, manufactured by Aerosil Co., Ltd., trade name: RY-50, average primary particle diameter: 40 nm) were prepared.

[0058] (Silica particles J) As silica particles J, commercially available hydrophobic silica particles (fumed silica particles surface-treated with silicone oil, manufactured by Cabot Corporation, trade name: TG-308F, average primary particle diameter: 12 nm) were prepared.

[0059] (loss on drying) The loss on drying of the silica particles A to J produced or prepared as described above was measured by the following method. The measurement results are shown in Table 1. Place 3 g of sample in a container that has been dried, cooled, and weighed accurately in advance, and weigh it accurately. Dry at 105°C for 2 hours using a heat-drying moisture meter MX-50. Allow to cool in a desiccator for 30 minutes, then weigh the mass and calculate using the following formula. Loss on drying (%) = Loss on drying (g) / Sample weight (g) x 100

[0060] (Ignition loss) The ignition losses of the silica particles A to J produced or prepared as described above were measured by the following method. The measurement results are shown in Table 1. Place 0.5 g of sample in a magnetic crucible that has been dried, cooled, and precisely weighed in advance, and then weigh it precisely. Ignite for 2 hours in an electric furnace (small electric furnace black mini-BS1) set to 500°C. Allow to cool in a desiccator for 1 hour, then weigh the mass and calculate it using the following formula. Ignition loss (%) = Ignition loss (g) / Sample weight (g) × 100

[0061] (viscoelasticity measurement) The viscoelasticity of the silica particles A to J produced or prepared as described above was measured by the following method. The measurement results are shown in Table 1. Samples were prepared by mixing 10 parts by mass of each of silica particles A to J with 90 parts by mass of polyester resin (product name: ER-508, manufactured by Mitsubishi Chemical Corporation) using a Super Mixer Piccolo SMP-2 manufactured by Kawata Co., Ltd., and viscoelasticity measurements were performed on 1.0 g of each sample using a viscoelasticity measuring device (ARES-G2 rheometer manufactured by TA Instruments) under the following conditions. From the measured data, the ratio of the storage modulus G' to the loss modulus G'' at 110°C (G'' / G') was read as tan δ(110°C). Dynamic viscoelasticity measurement conditions Parallel plate diameter: 25mm Measurement frequency: 1.0Hz Measurement distortion: 0.2% Measurement temperature: Heat from 70°C to 200°C at a rate of 3.0°C per minute.

[0062] [Table 1]

[0063] Example 1 100 parts by mass of toner base particles I and 2.0 parts by mass of silica particles A were placed in a Super Mixer Piccolo SMP-2 manufactured by Kawata Corporation, mixed at 3000 revolutions per minute for 6 minutes, and then sieved through a sieve with 74 μm openings to prepare the toner of Example 1. The minimum fixing temperature, low-temperature fixing property, and storage stability of the prepared toner were measured and evaluated using the methods described below. The results are also shown in Table 2.

[0064] Examples 2 to 6 and Comparative Examples 1 to 5 Toners of Examples 2 to 6 and Comparative Examples 1 to 5 were prepared in the same manner as in Example 1, except that the type and amount of silica particles were changed to those shown in Table 2. The minimum fixable temperature, low-temperature fixability, and storage stability of the prepared toners were measured and evaluated by the following methods in the same manner as in Example 1. The results are also shown in Table 2.

[0065] Comparative Example 5 A toner of Comparative Example 5 was prepared in the same manner as in Comparative Example 2, except that the toner base particles were changed to toner base particles II. The minimum fixing temperature, low-temperature fixing property, and storage stability of the prepared toner were measured and evaluated by the following methods in the same manner as in Example 1. The results are also shown in Table 2.

[0066] The amount of silica particles added in the examples and comparative examples was determined by geometric calculation from the particle sizes of the toner base particles and silica particles so that the coverage of the surface of the toner base particles with silica particles was approximately 100%.

[0067] (Lower limit fixing temperature) Commercially available 75g / m 2 On PPC paper, 0.40 mg / cm 2The prepared toner was evenly applied so that the toner adhered to the paper was uniformly even. This PPC paper was fixed using an external fixing tester employing a commercially available heat roller-type toner fixing device, with the fixing speed (heat roller peripheral speed) set at 375 mm / sec and the heat roller temperature set in 10°C increments within the range of 150 to 230°C, to obtain a fixed image. The image density of the resulting fixed image was measured using an X-Rite eXact, and then a peel test was conducted using the method described below. After peeling, the image density was measured again. The fixation rate was calculated using the following formula, and the lowest temperature of the heat rollers at which the fixation rate was 90% or higher was determined as the minimum fixation temperature. Fixation rate (%) = fixed image density after peel test / fixed image density before peel test × 100

[0068] (Peel test method) A mending tape is applied to the fixed image, and a 500 g weight is moved back and forth on the tape at 1 cm / sec 5 times, and then the mending tape is peeled off at 1 cm / sec.

[0069] (low temperature fixability) Based on the results of the minimum fixing temperature, the low-temperature fixing property was evaluated according to the following criteria. 〇: Minimum fixing temperature is 170℃ or less △: Minimum fixing temperature is over 170℃ and 180℃ or less ×: Minimum fixing temperature is over 180°C

[0070] (Storability) 20.0 g of toner was placed in a sealed container and left to stand at a temperature of 50°C for 8 hours. After leaving to stand, the sealed container was tapped, and then the entire amount of toner was transferred to a sieve and sieved using a powder tester under the following conditions. After sieving, the mass of toner remaining on the sieve was measured, and the storage stability was evaluated according to the following criteria: Good: Less than 0.2 g △: 0.2g or more and less than 1.0g ×: 1.0g or more Sieving conditions Equipment: Powder Tester PT-X (manufactured by Hosokawa Micron) Sieve opening: 355 μm Vibration width: 1mm Vibration time: 10 seconds Operation method: A sieve is set on the vibration table of the powder tester, toner is placed on the sieve, and the sieve is vibrated at a vibration amplitude of 1 mm for 10 seconds, and the weight of the toner remaining on the sieve is measured.

[0071] [Table 2]

[0072] As is clear from Table 2, the toners of Examples 1 to 6 all had excellent low-temperature fixing performance with a minimum fixing temperature of 170° C., and also had good storage stability.

[0073] In contrast, the toner of Comparative Example 1, in which silica particles hydrophobized with hexamethylsilazane were externally added, and the toners of Comparative Examples 2 to 4, in which silica particles hydrophobized with polydimethylsiloxane were externally added, had lower limit fixing temperatures of 180°C and 190°C, which were higher than the toners of Examples 1 to 6. Furthermore, the toner of Comparative Example 5, in which silica particles hydrophobized with polydimethylsiloxane were externally added to toner base particles II, had a lower limit fixing temperature of 160°C, which indicated good low-temperature fixing performance, but poor storage stability. [Industrial Applicability]

[0074] The toner of the present invention can further improve low-temperature fixability.

Claims

1. A toner for developing an electrostatic latent image, comprising toner base particles and silica particles externally added to the toner base particles, the toner base particles contain at least a binder resin and a colorant, The silica particles are C n H 2n+1 —Si(OC m H 2m+1 ) 3 (wherein n is an integer of 3 or more, and m is an integer of 1 to 3) The hydrophobic treatment is carried out using only an alkylsilane coupling agent represented by the formula:

1. A toner for developing electrostatic latent images, wherein the actual amount of the alkylsilane coupling agent to be treated is 0.01% by mass or more and less than 30% by mass, as calculated by the following formula: Actual treatment amount with alkylsilane coupling agent (mass%) = loss on ignition - loss on drying Ignition loss (mass%): Mass loss rate when silica particles are kept at a temperature of 500°C for 2 hours Drying loss (mass%): Mass loss rate when silica particles are kept at a temperature of 105°C for 2 hours

2. 2. The toner for developing electrostatic latent images according to claim 1, wherein the silica particles are fumed silica having an average primary particle diameter of 5 nm to 70 nm or colloidal silica having an average primary particle diameter of 50 nm to 200 nm.

3. 3. The toner for developing electrostatic latent images according to claim 1, wherein the alkylsilane coupling agent has an unsubstituted linear alkyl group having 3 or more carbon atoms.

4. 4. The toner for developing electrostatic latent images according to claim 1, wherein the amount of the silica particles added externally is in the range of 0.5% by mass to 10% by mass based on the toner base particles.

5. 5. The toner for developing electrostatic latent images according to claim 1, wherein the volume average particle size of the toner base particles is in the range of 4 μm or more and 15 μm or less.

6. 6. A developer for developing electrostatic latent images, comprising the toner according to claim 1 and a carrier.

Images