JP2007147979A - Negative charge type monocomponent toner, method for manufacturing same, and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a negative charge type monocomponent toner which is free of fogging, toner scattering, and toner leakage even after long-time continuous printing, is also free of lowering of transfer efficiency, brings about no increase in the amount of toner to be cleaned, allows miniaturization of a waste toner container, and thereby allows miniaturization of an image forming apparatus, and to provide a method for manufacturing the negative charge type monocomponent toner and a color image forming apparatus. <P>SOLUTION: The negative charge type monocomponent toner is obtained by externally adding (1) negative charge type hydrophobic silica fine particles having a BET specific surface area of 80-300 m<SP>2</SP>/g, (2) negative charge type hydrophobic spherical silica fine particles having a BET specific surface area of 5-40 m<SP>2</SP>/g and a number average primary particle diameter of 80-150 nm, (3) hydrophobic titanium oxide fine particles having a number average primary particle diameter of 10-30 nm, (4) α-alumina fine particles having a BET specific surface area of 4-15 m<SP>2</SP>/g, and (5) metallic soap particles having a number average primary particle diameter of ≤1.5 μm to spherical toner base particles consisting essentially of a binder resin and a colorant. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a negatively chargeable one-component toner in electrophotography, a method for producing the same, and a color image forming apparatus.

  In electrophotography, an electrostatic latent image formed on a latent image carrier provided with a photoconductive substance is developed using a toner containing a colorant, and then the toner image is transferred to an intermediate transfer medium, and further, paper The recording material is re-transferred to a recording material, and fixed by heat, pressure or the like to form a copy or printed matter.

  In such an image forming method, when a negative chargeable one-component toner is used for long-time printing or printing exceeding tens of thousands, usually a large amount of cleaning toner is generated and the waste toner processing container is enlarged. There arises a problem that it is unavoidable, and this is a problem from the viewpoint of downsizing the image forming apparatus. In addition, from the viewpoint of reducing running costs, it is necessary to extend the life of the photosensitive unit and the developing unit, but as a result of drum filming due to negatively chargeable one-component toner, toner scattering, and toner leakage, It is difficult to achieve the desired lifetime of the photosensitive unit and the developing unit, which is a problem from the viewpoint of reducing running costs.

  Conventionally, silica fine particles having an average particle diameter of 1 to 50 μm as toner mother particles, fine particles such as titanium oxide and alumina having an average particle diameter of 6 to 100 μm, and titanic acid having an average particle diameter of 100 to 5000 μm. It is known that three kinds of external additives having different average particle diameters of strontium particles are externally added to form toner particles (Patent Document 1), and external additives having large and small particle diameters are mixed. It is known to impart fluidity and charging characteristics to the toner while preventing the toner from being buried. The toner base particles include spherical inorganic oxide fine particles selected from alumina, silica, zinc oxide, titanium oxide, and iron oxide having a particle size of 10 to 300 nm, a primary particle size of 10 to 50 nm, and a secondary particle size. It is known that good image quality can be maintained over a long period of time by coating silica fine particles having a particle size of 50 to 500 nm (Patent Document 2). In addition, spherical or substantially spherical toner base particles are coated with abrasive fine particles such as strontium titanate having a polarity opposite to the charging characteristics of the toner and a volume average particle size of 0.3 to 2 μm, and a specific gravity of 1.3 to 1. 0.9, monodispersed silica particles having an average particle size of 80 to 300 nm, and organic compounds having a particle size smaller than that of the monodispersed silica particles are externally treated to prevent scattering of external additives and deterioration in image quality while preventing poor cleaning. It is known to prevent (Patent Document 3).

  As described above, toners in which various external additives are combined are known. For the purpose of reducing the running cost of any toner, for example, 50,000 sheets of a toner-supplemented tandem color printer as shown in FIG. When printing is performed, the external additive is detached from the surface of the toner base particles, and the amount of cleaning toner increases as the amount of transfer residual toner and fog toner on the photosensitive member increases, and the waste toner container is frequently replaced. Alternatively, it is necessary to prepare a large waste toner container, which is a problem from the viewpoint of downsizing the image forming apparatus.

In addition, it is known that positively charged silica fine particles, negatively chargeable silica fine particles, and inorganic fine particles having a low electrical resistance value are used as external additives for negatively chargeable toner base particles made of a polyester resin (patent) Reference 4), when used in a non-replenishment type developing device with a built-in toner container, there is no problem when the number of printed sheets is about 10,000, but for example, toner external replenishment type development as shown in FIG. When continuous printing is performed with the device, the toner that has caused the external additives to be removed or the toner that is charged to the opposite polarity accumulates in the developing device, resulting in an increase in fog on the photoreceptor and residual transfer toner and an increase in the amount of cleaning toner. It has been found that this is a problem from the viewpoint of downsizing the image forming apparatus.
JP 63-289559 A JP 11-327195 A JP 2002-318467 A JP 2000-267337 A

  The present invention is a negatively chargeable one-component toner that is free from fogging, toner scattering and toner leakage even after continuous printing for a long time, does not cause a decrease in transfer efficiency, and does not increase the amount of cleaning toner. An object of the present invention is to provide a negatively chargeable one-component toner that can reduce the size of a toner container and that can reduce the size of an image forming apparatus, a manufacturing method thereof, and a color image forming apparatus thereof.

The negatively chargeable one-component toner of the present invention comprises at least a binder resin and a colorant, and the number-based average particle diameter is 4.5 to 9 μm, and the integrated value of the average particle diameter of 3 μm or less is 1% or less. (1) negatively chargeable hydrophobic silica fine particles having a BET specific surface area of 80 to 300 m ² / g, and a toner base particle having a particle size distribution of
(2) negatively chargeable hydrophobic spherical silica fine particles having a BET specific surface area of 5 to 40 m ² / g and a number average primary particle size of 80 to 150 nm,
(3) hydrophobic titanium oxide fine particles having a number average primary particle size of 10 to 30 nm,
(4) α-type alumina fine particles having a BET specific surface area of 4 to 15 m ² / g,
(5) A metal soap particle having a number average primary particle size of 1.5 μm or less is externally added.

Further, it is characterized in that it is further subjected to external addition treatment with positively chargeable hydrophobic silica fine particles having a BET specific surface area of 30 to 50 m ² / g.

  The toner base particles are obtained by a dissolution suspension method.

The method for producing a negatively chargeable one-component toner of the present invention comprises at least a binder resin and a colorant. The number-based average particle diameter is 4.5 to 9 μm, and the integrated value of the average particle diameter of 3 μm or less is A negatively chargeable one-component toner in which a plurality of types of external additives are subjected to a multistage external addition process on toner base particles having a particle size distribution of 1% or less and an average circularity of 0.95 to 0.99. A manufacturing method comprising:
As a first stage of a multistage system adding process, the toner mother particles, negatively chargeable hydrophobic silica fine particles having a BET specific surface area of 80~300m ² / g, and a BET specific surface area of at 5 to 40 m ² / g, and, After externally treating negatively chargeable hydrophobic spherical silica fine particles having a number average primary particle size of 80 to 150 nm in a ratio of 1.0 to 2.5% by mass with respect to the toner base particles,
As a subsequent treatment, hydrophobic titanium oxide fine particles having a number average primary particle size of 10 to 30 nm, α-type alumina fine particles having a BET specific surface area of 4 to 15 m ² / g, and a number average primary particle size of 1. Metal soap particles of 5 μm or less are additionally mixed in a total amount of 0.5 to 1.5% by mass, or a positive BET specific surface area of 30 to 50 m ² / g with respect to the toner base particles. The chargeable hydrophobic silica fine particles are additionally mixed at a ratio of 0.1 to 0.6% by mass.

  The work function of the toner base particles is 5.3 to 5.7 V, the work function of the hydrophobic silica fine particles is 5.0 to 5.3 V, and the work function of the α-type alumina fine particles added in the latter stage is 4. 9 to 5.2 eV, hydrophobic titanium oxide fine particles have a work function of 5.5 to 5.7 eV, positively charged silica fine particles have a work function of 5.2 to 5.4 eV, and metal soap particles have a work function of 5.3. ˜5.8 V, and the post-processing is characterized in that multi-stage processing is performed by combining external additives having a work function difference of at least 0.2 eV or more.

The color image forming apparatus of the present invention forms an electrostatic latent image on a latent image carrier, and sequentially develops the electrostatic latent image by a one-component method using a plurality of developing devices to form a color toner image. In the color image forming apparatus in which the toner image formed on the latent image carrier is transferred to an intermediate transfer medium to form a color toner image, which is transferred onto a recording material and fixed. And a toner transport amount on the developing member in each of the plurality of developing devices is 0.5 to 0.8 mg / cm ^2, and the toner includes at least a binder resin and a colorant The number-based average particle size is 4.5 to 9 μm, the integrated value of the average particle size of 3 μm or less is 1% or less, and the average circularity is 0.95 to To the toner mother particles of 0.99,
(1) negatively chargeable hydrophobic silica fine particles having a BET specific surface area of 80 to 300 m ² / g,
(2) negatively chargeable hydrophobic spherical silica fine particles having a BET specific surface area of 5 to 40 m ² / g and a number average primary particle size of 80 to 150 nm,
(3) hydrophobic titanium oxide fine particles having a number average primary particle size of 10 to 30 nm,
(4) α-type alumina fine particles having a BET specific surface area of 4 to 15 m ² / g,
(5) A negatively chargeable one-component toner obtained by externally adding metal soap particles having a number average primary particle size of 1.5 μm or less.

The toner is a negatively chargeable one-component toner further externally treated with positively chargeable hydrophobic silica fine particles having a BET specific surface area of 30 to 50 m ² / g, and the development method is a non-contact development method. To do.

  The color image forming apparatus employs a tandem developing system.

  In the present invention, the combination of the toner base particles and the external additive prevents fogging, toner scattering and leakage even when used for continuous printing for a long time, suppresses a decrease in transfer efficiency, and reduces the amount of cleaning toner. It has been found that the toner can be drastically reduced, and it has been found that a negatively chargeable one-component toner suitable for application to a color image forming apparatus having an external replenishment type developing device can be obtained.

In the negatively chargeable one-component toner according to the present invention, first, (1) negatively chargeable hydrophobic silica fine particles having a BET specific surface area of 80 to 300 m ² / g and (2) a BET specific surface area of 5 are contained in the toner base particles. Negatively-charged hydrophobic spherical silica fine particles having a number average primary particle diameter of 80 to 150 nm at ˜40 m ² / g are simultaneously externally added. As a result, the surface of the toner base particles is negatively and uniformly charged, and the work functions of both silica fine particles (1) and (2) are made at least 0.2 eV smaller than the work function of the toner base particles, whereby the silica fine particles are It can be prevented from separating from the particle surface, and by blending the spherical silica fine particles having the large particle diameter (2) as spacer particles, a toner that can withstand long-term printing can be obtained.

Further, as post-treatment, (3) hydrophobic titanium oxide fine particles having a number average primary particle diameter of 10 to 30 nm, (4) α-type alumina fine particles having a BET specific surface area of 4 to 15 m ² / g, and (5) number average. Metal soap particles having a primary particle size of 1.5 μm or less are externally added.

  Hydrophobic titanium oxide fine particles having a number average primary particle size of 10 to 30 nm are added for charge adjustment. Further, the titanium oxide fine particles are made into a rutile-anatase type, and the crystal shape is made into a spindle shape. Can be buried in particles.

In addition, since the toner is not consumed in the non-image area on the developing member, when printing is performed for a long period of time, fine particles having a small particle size attached as an external additive are buried in the surface of the toner base particle. (4) Buried by adding α-type alumina fine particles having a BET specific surface area of 4 to 15 m ² / g (the number average particle diameter (Dp 50) is about 100 nm to 600 nm) as an external additive. To prevent. The α-type alumina fine particles have an irregular shape, and the more continuous printing is performed, the more the external additive buried in the use of the regulating member is excavated, and the stable fluidity and charging characteristics can be imparted.

  Further, when the α-type alumina fine particles are, for example, conductive α-type alumina fine particles subjected to zirconium doping treatment, a negative charge is applied through the conductive α-type alumina fine particles due to a negatively chargeable DC voltage applied to the conductive developing member. The surface of the toner base particles injected can be easily negatively charged, and the number of toners charged to the opposite polarity can be reduced to prevent fogging and lowering of transfer efficiency.

If the B type specific surface area of the α-type alumina fine particles has a small particle size exceeding 15 m ² / g, the α-type alumina fine particles tend to be buried in the surface of the toner base particles, and the α-type alumina fine particles have a large particle size smaller than 4 m ² / g. If it is, there is a problem that the OPC which is a photoconductor is excessively polished and the life of the OPC is shortened. Therefore, the metal soap particles of (5) and (5) are externally added. The metal soap particle (5) functions as an adhesive that prevents the release of the external additive to the toner base particle surface and also functions as a lubricant that prevents the polishing effect on the OPC surface by the α-type alumina fine particles. The lifetime of OPC can be extended.

Further, in the case of non-contact development, if continuous printing is performed for a long period of time, the negative charge amount of the toner becomes too high, resulting in a decrease in the development toner amount and a decrease in print image density. However, when combined with low-resistance titanium oxide fine particles and conductive α-type alumina fine particles and positively charged hydrophobic silica fine particles having a BET specific surface area of 30 to 50 m ² / g, overcharge is suppressed, and the image density is lowered. Disappear.

  The negatively chargeable one-component toner of the present invention is applied to a color image forming apparatus having an external replenishing type developing means, and even when continuous printing of 50,000 sheets is performed, a decrease in fog and transfer efficiency is suppressed, and low running An image forming apparatus that can be downsized at low cost can be obtained.

  The negatively chargeable one-component toner in the present invention is formed by adding an external additive to toner base particles. The toner base particles can be produced by any of a pulverization method, a polymerization method, and a dissolution suspension method.

  As a method by the pulverization method, at least a pigment is contained in a binder resin, a release agent, a charge control agent and the like are added, mixed uniformly with a Henschel mixer, etc., melt-kneaded with a twin screw extruder, cooled, Through a pulverization-fine pulverization step, classification is performed to form toner base particles.

  Binder resins include polystyrene, poly-α-methylstyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-acetic acid. Vinyl copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-acrylic acid ester-methacrylic acid ester copolymer, styrene-α-chloroacrylic Homopolymer or copolymer containing styrene or styrene-substituted styrene resin such as acid methyl copolymer, styrene-acrylonitrile-acrylic acid ester copolymer, styrene-vinyl methyl ether copolymer, polyester resin, epoxy Resin, urethane modified epoxy Xylene resin, silicone modified epoxy resin, vinyl chloride resin, rosin modified maleic acid resin, phenyl resin, polyethylene, polypropylene, ionomer resin, polyurethane resin, silicone resin, ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, polyvinyl butyral Resins, terpene resins, phenol resins, aliphatic or alicyclic hydrocarbon resins, etc. can be used alone or in combination.

  A colorant, a release agent, a charge control agent, and the like are added to the binder resin. Colorants for full color include carbon black, lamp black, magnetite, titanium black, chrome yellow, ultramarine, aniline blue, phthalocyanine blue, phthalocyanine green, Hansa Yellow G, rhodamine 6G, calco oil blue, quinacridone, benzidine yellow, rose bengal Malachite Green Lake, Quinoline Yellow, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 184, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 180, C.I. I. Solvent Yellow 162, C.I. I. Pigment blue 5: 1, C.I. I. Dye and pigment such as CI Pigment Blue 15: 3 can be used alone or in combination.

  Examples of the mold release agent include paraffin wax, microwax, microcrystalline wax, cadilla wax, carnauba wax, rice wax, montan wax, polyethylene wax, polypropylene wax, oxidized polyethylene wax, oxidized polypropylene wax and the like. Among these, it is preferable to use polyethylene wax, polypropylene wax, carnauba wax, ester wax and the like.

  As the charge control agent, oil black, oil black BY, Bontron S-22 (manufactured by Orient Chemical Industry Co., Ltd.), Bontron S-34 (manufactured by Orient Chemical Industry Co., Ltd.), salicylic acid metal complex E-81 (Orient Chemical) Industrial Co., Ltd.), thioindigo pigments, sulfonylamine derivatives of copper phthalocyanine, Spiron Black TRH (manufactured by Hodogaya Chemical Co., Ltd.), calixarene compounds, organic boron compounds, fluorine-containing quaternary ammonium salt compounds, Examples include monoazo metal complexes, aromatic hydroxyl carboxylic acid metal complexes, aromatic dicarboxylic acid metal complexes, polysaccharides, and the like. Of these, colorless or white toners are preferred for color toners.

  The component ratio in the toner base particles is 0.5 to 15 parts by weight, preferably 1 to 10 parts by weight, and 1 to 10 parts by weight of the release agent with respect to 100 parts by weight of the binder resin. The charge control agent is 0.1 to 7 parts by mass, preferably 0.5 to 5 parts by mass.

  The pulverized toner is preferably spheroidized in order to improve transfer efficiency. In the pulverization process, a relatively round spherical device capable of being pulverized, for example, a turbo mill known as a mechanical pulverizer (manufactured by Turbo Kogyo Co., Ltd.). ) Can be used to increase the degree of circularity to 0.93, and the degree of circularity can be increased to 1.00 by using a hot air spheronizing device (manufactured by Nippon Pneumatic Industry) for the pulverized toner. .

  As the toner base particles in the present invention, the average circularity is adjusted to 0.95 to 0.99, including toner base particles obtained by a polymerization method described later and toner base particles obtained by a dissolution suspension method. If the circularity is less than 0.95, a desired transfer efficiency cannot be obtained, and if it is more than 0.99, there is a problem in cleaning properties.

  Next, the polymerization toner is obtained by a suspension polymerization method, an emulsion polymerization method, a dispersion polymerization method, or the like, and can be made suitable for a full color toner. In the suspension polymerization method, a polymerizable monomer, a color pigment, a release agent, and a complex added with a dye, a polymerization initiator, a crosslinking agent, a charge control agent, and other additives as necessary are dissolved or dissolved. The dispersed monomer composition is added to an aqueous phase containing a suspension stabilizer (water-soluble polymer, poorly water-soluble inorganic substance) with stirring, granulated, and polymerized to obtain a desired particle size. The colored polymer toner particles are formed. In the materials used for the production of the polymerization toner, the same materials as those of the pulverized toner described above can be used for the colorant, release agent, and charge control agent. In the emulsion polymerization method, polymerization is performed by dispersing a monomer and a mold release agent, and if necessary, a polymerization initiator and an emulsifier (surfactant) in water, and then aggregating with a colorant, a charge control agent, and the like. Colored toner particles having a desired particle size are formed by adding an agent (electrolyte) or the like.

  Examples of the polymerizable monomer component include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-methoxystyrene, p-ethylstyrene, vinyltoluene, 2,4-dimethyl. Styrene, pn-butylstyrene, p-phenylstyrene, p-chlorostyrene, divinylbenzene, methyl acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate, isobutyl acrylate, n-octyl acrylate, Dodecyl acrylate, hydroxyethyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate , N-octyl methacrylate, dodecyl methacrylate, hydroxyethyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, acrylic acid, methacrylic acid, maleic acid, fumaric acid, cinnamic acid, ethylene glycol, Propylene glycol, maleic anhydride, phthalic anhydride, ethylene, propylene, butylene, isobutylene, vinyl chloride, vinylidene chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propyleneate, acrylonitrile, methacrylonitrile, vinyl methyl ether, vinyl Examples include ethyl ether, vinyl ketone, vinyl hexyl ketone, and vinyl naphthalene. Examples of the fluorine-containing monomer include 2,2,2-trifluoroethyl acrylate, 2,2,3,3-tetrafluoropropyl acrylate, vinylidene fluoride, ethylene trifluoride, tetrafluoroethylene, trifluoropropylene, and the like. Can be used as a binder resin in negatively charged toner because fluorine atoms are effective for negative charge control.

  Examples of the emulsifier (surfactant) include sodium dodecylbenzene sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, sodium oleate, sodium laurate, potassium stearate, calcium oleate, dodecyl ammonium chloride, dodecyl ammonium bromide. , Dodecyl trimethyl ammonium bromide, dodecyl pyridinium chloride, hexadecyl trimethyl ammonium bromide, dodecyl polyoxyethylene ether, hexadecyl polyoxyethylene ether, lauryl polyoxyethylene ether, sorbitan monooleate polyoxyethylene ether, and the like.

  Examples of the polymerization initiator include potassium persulfate, sodium persulfate, ammonium persulfate, hydrogen peroxide, 4,4′-azobiscyanovaleric acid, t-butyl hydroperoxide, benzoyl peroxide, 2,2′-azobis- There are isobutyronitrile and the like.

  Examples of the flocculant (electrolyte) include sodium chloride, potassium chloride, lithium chloride, magnesium chloride, calcium chloride, sodium sulfate, potassium sulfate, lithium sulfate, magnesium sulfate, calcium sulfate, zinc sulfate, aluminum sulfate, and iron sulfate. Can be mentioned.

  As a method for adjusting the circularity of the polymerization toner, the emulsion polymerization method can freely change the circularity by controlling the temperature and time during the aggregation process of the secondary particles, and its range is from 0.94 to 1. In the suspension polymerization method, since a true spherical toner is possible, the circularity can be in the range of 0.98 to 1.00. In order to set the average circularity to 0.95 to 0.99, it can be adjusted as appropriate by heat-deforming at or above the Tg temperature of the toner.

  Next, the dissolution suspension method toner will be described. Dissolving suspension method toner mother particles can be produced while controlling emulsification and association. For example, a mixture containing at least a colorant and a polyester resin is emulsified in an aqueous medium to form fine particles of the mixture, and then The fine particles of the colorant-containing resin are aggregated by agglomerating the fine particles, and then the colorant-containing resin fine particles granulated from the aqueous medium are separated, washed and dried, and then the toner mother is obtained. Particles can be produced.

  More specifically, a colorant and a polyester resin, and if necessary, a release agent and a charge control agent are dissolved in an organic solvent and dispersed in an aqueous medium. A mixture containing a polyester resin, a colorant, etc. and an organic solvent can be easily prepared by adding a polyester resin in an organic solvent to dissolve the resin, etc., and adding a pre-dispersed colorant. Can be made. In order to emulsify the prepared dispersion mixture solution in an aqueous medium, the dispersion mixture solution may be mixed with an aqueous medium and emulsified in the presence of a basic neutralizing agent. Emulsification is preferably performed by forming a suspension / emulsion solution by gradually adding an aqueous medium to a mixture solution composed of a polyester resin, a colorant, and the like and an organic solvent.

  The polyester resin to be used is preferably a polyester resin having an acidic group such as a carboxyl group, a sulfone group or a phosphoric acid group. Among them, the carboxyl group-containing polyester resin has a negative dispersion polarity and a negative charge polarity when converted into toner base particles. Therefore, it can be said that the resin is more preferable.

  Examples of the basic neutralizer include inorganic bases such as sodium hydroxide, potassium hydroxide, ammonia, diethylamine, and triethylamine, and organic bases. The use ratio of the organic solvent and the aqueous medium is within the range of 35 to 65% by mass, and it is necessary to determine the use ratio while finely adjusting the resin fine particle size when emulsified. Exchange water is preferred. The organic solvent to be used is hydrocarbons, halogenated hydrocarbons, ethers, ketones, esters, specifically hexane, heptane, toluene, xylene, cyclohexane, methylcyclohexane, methyl chloride, dichloromethane, Ethyl chloride, propyl chloride, dioxane, tetrahydrofuran, acetone, methyl ethyl ketone, ethyl acetate, propyl acetate and the like can be used alone or in combination. Moreover, as a mixer used when emulsifying the above-mentioned dispersion mixture solution, an emulsifying disperser such as a homomixer, a slasher, a homogenizer, a colloid mill, a media mill, and a cavitron can be used.

  The number average particle size of the toner base particles thus obtained and toner particles described later is preferably 9 μm or less, more preferably 8 μm to 4.5 μm. For toner particles having a number average particle size larger than 9 μm, even when a latent image is formed at a high resolution of 1200 dpi or higher, the reproducibility of the resolution is lower than that of a small particle size toner, and is 4.5 μm or less. As a result, the concealability by the toner decreases, and the amount of the external additive used to increase the fluidity increases, and as a result, the fixing performance tends to decrease.

  In the particle size distribution based on the number of toner base particles, the integrated value of particles having an average particle size of 3 μm or less is 1% or less, preferably 0.8% or less. When the average value of the average particle size of 3 μm or less exceeds 1%, charging by the toner layer regulating member becomes insufficient, which causes undesirable generation of reversely charged toner and filming on the latent image carrier. .

  The number average particle diameter, particle size distribution, and average circularity of the above-described toner base particles and toner particles described later in the present invention are values measured by a flow type particle image analyzer (FPIA2100 manufactured by Sysmex).

The toner base particle shape is preferably toner particles having a shape close to a true sphere. Specifically, the toner base particles are represented by the following formula:
R = L ₀ / L ₁
{However, in the formula, L ₁ (μm) is the perimeter of the projected image of the toner particles to be measured, and L ₀ (μm) is a perfect circle having the same area as the projected image of the toner particles to be measured (complete The perimeter of a geometric circle). }
The average circularity (R) represented by the formula is 0.95 to 0.99, preferably 0.972 to 0.983. Maintaining this shape is important in consideration of improvement in transfer efficiency and cleaning properties. When the average circularity (R) is less than 0.95, the transfer efficiency tends to decrease as continuous printing is performed even if the transfer efficiency is initially maintained at about 96%. On the other hand, if the value exceeds 0.99, the remaining toner on the latent image carrier (photoconductor) and intermediate transfer medium (transfer belt, transfer drum) can be cleaned sufficiently using a blade or brush. In particular, it is extremely difficult to perform cleaning at low temperature and low humidity. In order to reduce the circularity of a toner having a high degree of circularity, for example, the toner can be adjusted by placing the toner in a sealed container and pressurizing it near the glass transition temperature of the toner resin. Originally, a toner having a low circularity can be adjusted to a desired value while controlling the surface shape by subjecting the toner to a hot air treatment after pulverization and classification. When a toner is produced by emulsion polymerization, dispersion polymerization, or suspension polymerization, a desired value can be obtained by employing a step of adjusting the shape factor in the middle of the step, for example, means such as association or aggregation.

  Next, the work function (Φ) is known as the energy required to extract electrons from the substance. The smaller the work function, the easier it is to emit electrons, and the larger the work function, the less difficult it is to emit electrons. The work function is measured by the following measurement method, is quantified as energy (eV) for extracting electrons from the material, and can evaluate the chargeability by contact between various materials. Therefore, for example, when silica fine particles having a work function smaller than that of the toner base particles are externally added to the toner base particles, the toner base particles can be more negatively charged, and the silica fine particles have excellent adhesion. It is considered to be.

  Further, even if the external additives are combined and added in the subsequent stage processing, the external additives having a work function difference (at least 0.2 eV) are combined with each other to perform multi-stage processing, that is, the second stage, When additional mixing is performed as the third stage, it is possible to obtain excellent adhesion to each other.

  The work function is measured using a surface analyzer (AC-2, low energy electronic counting method manufactured by Riken Keiki Co., Ltd.). In the present invention, in the apparatus, a developing roller using a deuterium lamp and metal plating is set to an irradiation light amount of 10 nW, and in other measurements, an irradiation light amount of 500 nW is set, and monochromatic light is selected by a spectroscope. The sample is irradiated with a spot size of 4 mm square, an energy scanning range of 3.4 to 6.2 eV, and a measurement time of 10 sec / 1 point. The photoelectrons emitted from the sample surface are detected and can be calculated using work function meter software. The work function is measured with a repeatability (standard deviation) of 0.02 eV. . In addition, as a measurement environment for ensuring data reproducibility, a 24-hour left-over product is used as a measurement sample under the conditions of operating temperature and humidity of 25 ° C. and 55% RH.

  As shown in FIGS. 1 (a) and 1 (b), the toner dedicated measurement cell has a shape having a toner containing recess having a diameter of 10mm and a depth of 1mm at the center of a stainless steel disk having a diameter of 13mm and a height of 5mm. The sample toner is put into the concave portion of the cell without being tamped using a weighing sledge, and then subjected to measurement in a state where the surface is leveled and flattened using a knife edge. After the measurement cell filled with toner is fixed on the specified position of the sample stage, the irradiation light quantity is set to 500 nW, the spot size is set to 4 mm square, and the measurement is performed under the conditions of the energy scanning range of 4.2 to 6.2 eV.

  In addition, in the case where an image forming apparatus member having a cylindrical shape such as a photoconductor or a developing roller, which will be described later, is used as a sample, the cylindrical image forming apparatus member is cut to a width of 1 to 1.5 cm, and then a ridge line 2A to obtain a measurement specimen having the shape shown in FIG. 2A, and then the measurement light is irradiated onto the specified position of the sample stage as shown in FIG. 2B. The irradiation surface is fixed so as to be smooth with respect to the direction. Thereby, the emitted photoelectrons are efficiently detected by the detector (photoelectron tube). When the intermediate transfer belt, the regulating blade, and the photosensitive member are in the form of a sheet, the measurement light is irradiated with a 4 mm square spot as described above, so that the sample piece is cut out to a size of at least 1 cm square. Similar to 2 (b), it is fixed on the sample stage and measured in the same manner.

  In this surface analysis, when the excitation energy of monochromatic light is scanned from low to high, photon emission starts from a certain energy value (eV), and this energy value is called a work function (eV). FIG. 3 shows an example of a chart obtained for the toner. FIG. 3 shows the excitation energy (eV) as the horizontal axis and the normalized photon yield (photon yield per unit photon as the nth power) as the vertical axis, and a constant slope (Y / eV) is obtained. . In the case of FIG. 3, the work function is indicated by the excitation energy value (eV) at the inflection point (A).

Next, production examples of toner mother particles by the dissolution suspension method and respective physical properties are shown.
(Production Example 1 of toner mother particles)
・ Polycondensed polyester resin {manufactured by Sanyo Chemical Industries, Hymer ES-801, mass ratio of non-crosslinked component to crosslinked component (45/55)} 110 parts by mass Carnauba wax 55 parts by mass Cyan pigment (phthalocyanine α type) 55 parts by mass was melt-kneaded with a pressure kneader. After cooling the melt-kneaded product, it is roughly crushed to a size of 1 to 2 mm square, and using a colloid mill manufactured by Nippon Seiki Seisakusho, 210 parts by mass of the melt-kneaded product, 80 parts by mass of the polycondensation polyester resin, 245 parts by mass of methyl ethyl ketone was mixed and stirred.

  Next, after adding 26 parts by mass of 1N ammonia water and sufficiently stirring, 160 parts by mass of ion-exchanged water was added, and the mixture was further stirred at 30 ° C. for 1 hour. And 150 mass parts ion-exchange water was dripped, and the fine particle dispersion was prepared by phase inversion emulsification. Next, after adding 400 parts by mass of ion-exchanged water, the mixture was heated to a temperature equal to or higher than the boiling point of methyl ethyl ketone to remove the solvent, and finally the solid content was adjusted to about 34%.

  Then, 235 parts by mass of the obtained fine particle dispersion was diluted with ion-exchanged water, the solid content was adjusted to about 20%, 60 parts by mass of 20% saline was added, and the temperature was raised to 68 ° C. The mixture was stirred for 60 minutes, and then 0.6 part by weight of nonionic emulsifier NL-250 (Daiichi Kogyo Seiyaku Co., Ltd.) was added and stirred at 70 ° C. for 4 hours to complete granulation.

  The obtained slurry is separated with a centrifuge, washed, and then the water content in the toner base particles is 0.5% or less by mass ratio using a vibrating fluidized bed apparatus manufactured by Chuo Kakoh Co., Ltd. Then, cyan toner base particles were obtained.

  The average particle diameter and average circularity on the basis of the number of the cyan toner base particles obtained measured by “Flow type particle image analyzer FPIA-2100” manufactured by Sysmex Corporation are shown in Table 1 below. Table 1 below similarly shows the results of measuring the work function using the photoelectron spectrometer AC-2 "with a measurement light amount of 500 nW. The integrated value of the average particle diameter of 3 μm or less was 0.34%.

(Toner base particle production example 2)
Magenta toner base particles were produced in the same manner as in Production Example 1 of toner base particles, except that the colorant was changed to Carmine 6B.
The average particle diameter, average circularity, and work function based on the number of magenta toner base particles obtained are similarly shown in Table 1 below. The integrated value of the average particle diameter of 3 μm or less was 0.76%.

(Toner mother particle production example 3)
In Production Example 1 of toner base particles, the colorant was changed to P.I. Y. Yellow toner mother particles were produced in the same manner except that the amount of the toner was changed to 155.
The average particle diameter, average circularity, and work function based on the number of yellow toner base particles obtained are similarly shown in Table 1 below. The integrated value of the average particle diameter of 3 μm or less was 0.31%.

(Toner base particle production example 4)
Black toner base particles were produced in the same manner as in Production Example 1 of toner base particles, except that the colorant was replaced with surface-treated carbon black 1 (carbon M1000 manufactured by Mitsubishi Chemical Corporation). The average particle diameter, average circularity, and work function based on the number of black toner base particles obtained are similarly shown in Table 1 below. The integrated value of the average particle diameter of 3 μm or less was 0.31%.

(Toner mother particle production example 5)
In the toner mother particle production example 1, instead of the polycondensation polyester resin, a polycondensation polyester resin of an aromatic dicarboxylic acid and an alkylene etherified bisphenol A, and a partially crosslinked product of the polycondensation polyester resin with a polyvalent metal compound Cyan toner base particles were prepared in the same manner except that a 50:50 (mass ratio) mixture (manufactured by Sanyo Chemical Industries Co., Ltd.) was used and the colorant was changed to phthalocyanine β type which is a cyan pigment.
The average particle diameter, average circularity, and work function based on the number of cyan toner base particles obtained are similarly shown in Table 1 below. The integrated value of the average particle diameter of 3 μm or less was 0.33%.

(Production Example 6 of toner mother particles)
Magenta toner mother particles were produced in the same manner as in toner mother particle production example 5 except that the colorant was replaced with dimethylquinacridone.
The average particle diameter, average circularity, and work function based on the number of magenta toner base particles obtained are similarly shown in Table 1 below. The integrated value of the average particle diameter of 3 μm or less was 0.42%.

(Toner mother particle production example 7)
In Production Example 5 of toner base particles, the colorant is P.I. Y. Yellow toner mother particles were produced in the same manner except that the particle size was changed to 93.
The average particle diameter, average circularity, and work function based on the number of yellow toner base particles obtained are similarly shown in Table 1 below. The integrated value of the average particle diameter of 3 μm or less was 0.32%.

(Production Example 8 of Toner Base Particles)
Black toner base particles were produced in the same manner as in Production Example 5 of toner base particles, except that the colorant was replaced with surface-treated carbon black 2 (carbon M1000 manufactured by Mitsubishi Chemical Corporation). The average particle diameter (μm), average circularity, and work function (eV) based on the number of black toner base particles obtained are also shown in Table 1 below. The integrated value of the average particle diameter of 3 μm or less was 0.31%.

  The work function of the toner base particles by the dissolution suspension method is preferably 5.3 to 5.7 eV.

  Table 2 shows the work function value of each colorant.

  In the spherical chemical toner by the dissolution suspension method, it can be seen that the work function of the toner base particles is influenced by the work function of the colorant used. This indicates that the colorant is distributed or exposed near the surface of the toner base particles.

  Next, the external additive will be described.

The BET specific surface area that defines the external additive particles is obtained by performing measurement of the BET specific surface area by nitrogen adsorption using “2200 type” manufactured by Micromeritic, and the BET specific surface area is 200 m ^2. If exceeding / g, decrease the amount of sample.

  The number average primary particle size defining the external additive is determined by dropping a droplet in which the external additive is dispersed in isopropyl alcohol onto a measurement sample stage, drying, and scanning fine particles on the sample stage by a factor of 100,000. This is obtained by actually measuring the particle size of 500 arbitrary particles of a scanning electron microscope image using “S-4800” manufactured by Hitachi Technology Co., Ltd.

(1) The negatively charged hydrophobic silica fine particles having a BET specific surface area of 80 to 300 m ² / g are so-called “small particle” silica fine particles, preferably 100 to 250 m ² / g, and the number average primary particles The diameter is 7 to 16 nm, preferably 10 to 12 nm. Examples are those obtained by vapor phase oxidation (dry method) of silicon halogen compounds. The silica fine particles (1) are added in an amount of 0.5 to 2.0 parts by mass, preferably 0.7 to 1.5 parts by mass with respect to 100 parts by mass of the toner base particles.

As the BET specific surface area of the negatively chargeable silica fine particle is large or the number average primary particle diameter is small, the fluidity of the obtained toner increases. However, the BET specific surface area is larger than 300 m ² / g, or the number average primary is obtained. If the particle diameter is smaller than 7 nm, the silica fine particles may be buried in the toner base particles. Further, if the BET specific surface area is smaller than 100 m ² / g or the number average primary particle diameter exceeds 16 nm, the fluidity may be deteriorated.

Next, (2) negatively chargeable hydrophobic spherical silica fine particles having a BET specific surface area of 5 to 40 m ² / g and a number average primary particle size of 80 to 150 nm are so-called “large particle size” silica fine particles. The BET specific surface area is preferably 8 to 35 m ² / g, and the number average primary particle diameter is preferably 85 to 130 nm.

  The spherical silica fine particles are monodispersed, that is, the standard deviation with respect to the average particle size including aggregates is D50 * 0.22 or less, and as a shape, Wadell's sphericity is 0.6 or more, preferably 0.8 or more. It is. Such monodispersed spherical silica fine particles are obtained by a sol-gel method which is a wet method, and have a specific gravity of 1.3 to 2.1. In the case of the large particle size silica (2), 0.2 to 2.0 parts by mass, preferably 0.3 to 1.5 parts by mass is added to 100 parts by mass of the toner base particles.

When the average particle size is smaller than 80 nm and the BET specific surface area is larger than 40 m ² / g, the embedding of the fine particles of silica particles on the surface of the toner base particles is prevented and the fluidity and charging stability are maintained. And the spacer effect cannot be obtained, and if it is larger than 150 nm and smaller than 5 m ² / g, it is difficult to adhere to the toner base particles and to be easily detached from the surface of the toner base particles.

  The addition ratio (mass ratio) of the large particle size silica (2) to the small particle size silica (1) is 1: 3 to 3: 1, preferably 1: 2.8 to 2.8: 1. It is preferable to provide fluidity to the toner and to obtain long-term charging stability. The large particle size silica and the small particle size silica may be added and mixed simultaneously with the toner base particles in the production of the negatively chargeable one-component toner. The large particle size silica and the small particle size silica are 1.0 to 2.5 parts by mass, preferably 1.5 to 2.3 parts in total with respect to 100 parts by mass of the toner base particles in consideration of the mixing ratio of both. Part by mass is added.

  The negatively chargeable silica fine particles (1) and (2) are preferably hydrophobized. By making the surface of the negatively chargeable silica fine particles hydrophobic, the fluidity and chargeability of the toner are further improved. Hydrophobization of silica fine particles can be achieved by using silane compounds such as aminosilane, hexamethyldisilazane and dimethyldichlorosilane; or dimethyl silicone, methylphenyl silicone, fluorine-modified silicone oil, alkyl-modified silicone oil, amino-modified silicone oil, epoxy-modified silicone oil, etc. This silicone oil is used, for example, by a method commonly used by those skilled in the art, such as a wet method or a dry method.

As the hydrophobic negatively-charged silica fine particles (1), “R805” (BET specific surface area 150 m ² / g, number average primary particle diameter 12 nm, work function 5.22 eV) manufactured by Nippon Aerosil Co., Ltd. RX200 "(BET specific surface area 200 m ² / g, number average primary particle diameter 12 nm, work function 5.21 eV) and the like.

Hydrophobic negatively chargeable silica fine particles (2) include “Seahoster KE-P10S” (BET specific surface area 10 m ² / g, number average primary particle diameter 110 nm, work function 5.26 eV) manufactured by Nippon Shokubai Co., Ltd. Is exemplified.

  The work function of the hydrophobic silica particles (1) and (2) is in the range of 5.0 to 5.3 eV, but is preferably at least 0.05 ev smaller than the toner base particles. Thereby, the hydrophobic silica particles can be fixed to the toner base particles by the charge transfer due to the work function difference.

Next, (3) hydrophobic titanium oxide fine particles having a number average primary particle diameter of 10 to 30 nm are preferably 15 to 25 nm, and have a BET specific surface area of 100 to 200 m ² / g, preferably 120 to 180 m. ² / g.

  Titanium oxide has a relatively low electrical resistivity, and can take various crystal forms such as rutile, anatase, and rutile-anatase. In particular, rutile-anatase type titanium oxide has a spindle shape, and charge adjustment is possible. The titanium oxide particles are preferably used because they are easily embedded, and even if the number of printed sheets increases, the titanium oxide particles are not easily embedded in the toner base particles. The titanium oxide fine particles are added in an amount of 0.2 to 2.0 parts by weight, preferably 0.3 to 1.5 parts by weight, based on 100 parts by weight of the toner base particles.

The surface of the titanium oxide fine particles is hydrophobic, so that the change in chargeability with respect to the change in the external environment of the toner is reduced (that is, the stable chargeability is maintained) and the fluidity of the toner is improved. Therefore, it is preferable. Hydrophobization of the titanium oxide fine particles is carried out by the same method as that of the negatively chargeable silica fine particles. Examples of hydrophobic rutile-anatase type titanium oxide fine particles include “STT-30S” (BET specific surface area 135 m ² / g, work function 5.64 eV) manufactured by Titanium Industry Co., Ltd.

  The work function of the hydrophobic titanium oxide particles is in the range of 5.5 to 5.7 eV. The hydrophobic silica particles may be first externally added to the toner base particles and then added as a subsequent process.

  When the work function is substantially the same as that of the toner base particles, it is difficult to adhere directly to the toner base particles. However, since the work function can be attached to the toner base particles through the surface of the hydrophobic silica particles having a small work function, it is excessive. Charge transfer from the charged hydrophobic silica particles can be facilitated, and overcharging in the hydrophobic silica particles can be more effectively prevented, which is preferable.

Next, (4) α-type alumina fine particles having a BET specific surface area of 4 to 15 m ² / g will be described.

  The alumina fine particles are industrially obtained by the so-called Bayer method, in which aluminum hydroxide obtained by treating bauxite raw material with sodium hydroxide is calcined in the atmosphere to form α-type alumina. However, since a large amount of sodium remains and inhibits electrical insulation, JP-A-8-290914, for example, describes α-type alumina fine particles having a high purity and a narrow particle size distribution with a sodium content of 100 ppm or less. In addition, various alumina fine particles have been developed as described in JP-A No. 2003-26419, which describes a method for producing α-type alumina fine particles by acid treatment.

(Production example 1 of α-type alumina fine particles)
This method is described in JP-A-8-290914, and transition alumina obtained by calcining aluminum hydroxide produced by the Bayer method is pulverized so that the average particle size is 0.1 to 0.3 nm. Next, α-type alumina fine particles are obtained by firing at 1150 to 1300 degrees in an atmosphere gas containing 1% by volume or more of hydrogen chloride gas and 0.1% by volume or more of water vapor. The α-type alumina 1 and 3, the conductive α-type alumina, and the α-type alumina 5 and 6 in Table 3 described later are produced by this method.

(Production example 2 of α-type alumina fine particles)
This method is described in JP-A-2003-26419. After adding 10% by mass of DL-lactic acid to an aqueous solution containing 23% by mass of basic aluminum chloride in terms of aluminum oxide, 2 kg / cm ² , 120 ° C., 20 Hydrothermal treatment for a period of time, heating and drying at 60 ° C. to gel so that the average particle size becomes 0.1 to 0.3 nm, and the resulting composite gel is heated at about 600 ° C. in the atmosphere. As a result, α-type alumina fine particles are obtained. Α-type alumina 2 and 4 in Table 3 described later are produced by this method.

  Table 3 shows the BET specific surface area, work function, and commercial name of each α-type alumina fine particle, strontium titanate fine particle, and titanium oxide fine particle used as external additives in Examples described later.

^1): Zirconium-Doped Product The α-type alumina fine particles of (4) which are external additives in the present invention have a BET specific surface area of 4 to 15 m ² / g, preferably 5 to 14 m ² / g, and are number average particles The diameter (Dp 50) is about 100 nm to 600 nm. Each of the α-type alumina fine particles has an irregular shape, and the feature is indicated by the BET specific surface area.

In the present invention, when various α-type alumina fine particles are studied, if the BET specific surface area exceeds 15 m ² / g, the toner is buried in the surface of the toner base particles and has no effect of digging up. In addition, the inventors have found that the number of + toners is large and the amount of cleaning toner increases. In addition, alumina fine particles are generally known as external additives having a polishing function like strontium titanate and titanium oxide. As will be described later, strontium titanate and titanium oxide having the same BET specific surface area are used. It was found that the number of + toners can be suppressed as compared with the above, the increase in the amount of cleaning toner can be suppressed, and that the use of conductive α-type alumina fine particles can provide a more excellent negatively chargeable one-component toner.

When α-type alumina fine particles are externally added to the toner base particles, the more continuous printing is performed, the more effective it is to excavate the buried external additive in the use of the regulating member, and stable fluidity and charging characteristics can be imparted. However, if the BET specific surface area is less than 4 m ² / g, the particle size is large, the adhesion to the toner base particles is reduced, and the OPC as the photoreceptor is excessively polished, resulting in a long life of the OPC. It is not preferable because it shortens life.

  Further, as the α-type alumina fine particles, for example, conductive α-type alumina fine particles subjected to zirconium doping treatment may be used. When the conductive α-type alumina fine particles are used, a negative charge is injected into the toner base particles by a negatively charged direct current voltage applied to the conductive developing member. As a result, the toner base particle surface is easily negatively charged, The number of toners charged to the opposite polarity is reduced, and fog and transfer efficiency can be prevented from being lowered.

  The amount of α-type alumina fine particles added to the toner base particles is 0.05 to 1.3 parts by weight, preferably 0.1 to 1.0 parts by weight, based on 100 parts by weight of the toner base particles. When the amount is less than 0.05 parts by mass, the function as a spacer is not achieved, and when the amount is more than 1.3 parts by mass, the amount of released alumina particles having a large particle size increases, which is not preferable.

  The α-type alumina particles have a work function of 4.9 to 5.2 eV, which is negative by reducing the work function (5.3 to 5.7 eV) of the toner base particles by at least 0.05 eV. The charged toner base particles can be more negatively charged, and the adhesion to the externally added alumina fine particles can be enhanced.

Next, the metal soap particles will be described.
The metal soap particles can reduce the liberation rate of other externally added particles such as α-type alumina fine particles and prevent fogging, and the photosensitive member can be used as a lubricant due to the abrasive action of alumina particles and the like. (OPC) can be protected and the life can be extended. The metal soap particles are metal salts selected from zinc, magnesium, calcium, and aluminum of higher fatty acids, and examples include magnesium stearate, calcium stearate, zinc stearate, monoaluminum stearate, and trialuminum stearate.

  The average particle diameter of the metal soap particles is 0.1 to 1.5 μm, preferably 0.5 to 1.3 μm. The work function of the metal soap particles is in the range of 5.3 to 5.8 eV.

  The addition amount of the metal soap particles is 0.05 to 0.5 parts by mass, preferably 0.1 to 0.3 parts by mass with respect to 100 parts by mass of the toner base particles. When the amount is less than 0.05 parts by mass, the function as a lubricant and the function as a binder are insufficient, and when the amount is more than 0.5 parts by mass, the fog tends to increase. The addition amount of the metal soap particles is preferably 2 to 10 parts by mass with respect to 100 parts by mass of the external additive. When the amount is less than 2 parts by mass, there is no effect as a lubricant or a binder. On the other hand, when the amount exceeds 10 parts by mass, fluidity is lowered and fog is increased.

  (3) Hydrophobic titanium oxide fine particles, (4) α-type alumina fine particles, (5) metal soap particles are (1) negatively chargeable hydrophobic silica fine particles and (2) negatively chargeable hydrophobic particles. After the silica fine particles are added, they may be added as a post-treatment, and they may be additionally mixed in a total amount of (3) to (5) at a ratio of 0.5 to 1.5 mass% with respect to the toner base particles.

  Further, in the case of non-contact development, if continuous printing is performed for a long period of time, the negative charge amount of the toner becomes too high, resulting in a decrease in the development toner amount and a decrease in print image density. However, in the subsequent processing, the positively-charged silica fine particles are mixed and processed, so that overcharge is suppressed and the image density is not lowered.

The positively chargeable silica fine particles have a BET specific surface area of 30 to 50 m ² / g and a number average primary particle diameter of 20 to 40 nm. The positively charged silica fine particles are preferably subjected to a hydrophobic treatment. By making the surface of the positively chargeable silica fine particles hydrophobic, the change in the chargeability with respect to the change in the external environment of the toner is reduced (that is, the stable chargeability is maintained) and the fluidity of the toner is improved. Therefore, it is preferable. Hydrophobization of the positively chargeable silica fine particles is performed using an aminosilane coupling agent, amino-modified silicone oil, or the like. Examples of the hydrophobic positively chargeable silica fine particles include commercially available NA50H manufactured by Nippon Aerosil Co., Ltd. and TG820F manufactured by Cabot Co., Ltd. The work function of the positively chargeable hydrophobic silica fine particles is 5.2 to 5.4 eV.

  The positively chargeable silica fine particles are added in an amount of 0.1 to 1.0 parts by weight, preferably 0.2 to 0.8 parts by weight, based on 100 parts by weight of the toner base particles.

  In addition, the negatively chargeable one-component toner of the present invention can be externally added within the range not impairing the object of the present invention, in addition to the external additive particles described above. For example, as inorganic fine particles, metal oxide fine particles such as strontium oxide, tin oxide, zirconia oxide, magnesium oxide, and indium oxide, nitride fine particles such as silicon nitride, carbide fine particles such as silicon carbide, calcium sulfate, barium sulfate, Examples thereof include fine particles of metal salts such as calcium carbonate, inorganic fine particles such as composites thereof, and fine resin particles.

  In the post-treatment, a plurality of external additive particles may be additionally mixed at the same time. Preferably, however, the work functions of the plurality of external additive particles are added so that the difference in work function is at least 0.2 eV. They may be mixed and have excellent adhesion between the external additive particles. Therefore, a plurality of external additive particles added in the subsequent stage may be divided, and the subsequent process may be mixed as a multistage process such as a second stage or a third stage. The metal soap particles and the positively charged silica fine particles are preferably added at the last stage for the purpose of addition.

  As a method for adding external additives to the toner base particles, it is preferable to use a Henschel mixer (Mitsui Miike Co., Ltd.), a mechano-fusion system (Hosokawa Micron Co., Ltd.), a mechano mill (Okada Seiko Co., Ltd.), etc. When used, the processing operation conditions at each stage are 5,000 rpm to 15,000 rpm, 1 minute to 3 minutes.

  The negatively chargeable one-component toner of the present invention is a number measured by gel permeation chromatograph (GPC) measurement based on polystyrene in THF-soluble matter at the stage of toner mother particles or externally added toner particles. The average molecular weight (Mn) is 1,500 to 20,000, preferably 2,000 to 15,000, more preferably 3,000 to 12,000. When the number average molecular weight (Mn) is smaller than 1,500, although it is excellent in low-temperature fixability, it is inferior in colorant retention, filming resistance, offset resistance, fixed image strength, and storage stability. If it exceeds 20,000, the low-temperature fixability will be poor. The weight average molecular weight (Mw) is 3,000 to 300,000, preferably 5,000 to 50,000, and Mw / Mn is 1.5 to 20, preferably 1.8 to 8.

The flow softening temperature (Tf1 / 2) is in the range of 100 ° C to 140 ° C. When the flow softening temperature is lower than 100 ° C., the high temperature offset property is inferior. When the flow softening temperature is higher than 140 ° C., the fixing strength at a low temperature is inferior. The glass transition temperature (Tg) is in the range of 55 ° C to 70 ° C. When the glass transition temperature (Tg) is lower than 55 ° C., the storage stability is inferior. When the glass transition temperature (Tg) is higher than 70 ° C., Tf1 / 2 increases accordingly, resulting in inferior low-temperature fixability. Further, the toner of the present invention has a melt viscosity of 2 × 10 ^{3 to} 1.5 × 10 ⁴ Pa · s at a 50% outflow point, and can be suitable as an oilless fixing toner.

  The work function of the negatively chargeable one-component toner of the present invention is 5.25 to 5.85 eV, preferably 5.3 to 5.7 eV. When the work function of the toner is less than 5.25 eV, there is a problem that the usable range of the latent image carrier and the intermediate transfer medium is narrowed. When the work function exceeds 5.85 eV, the content of the colorant in the toner is reduced. This means that the colorability is lowered, and there is a problem that the colorability is lowered.

Next, the color image forming apparatus of the present invention will be described.
FIG. 4 is a diagram for explaining the relationship among the latent image carrier, the developing unit, and the intermediate transfer medium in the color image forming apparatus of the present invention. The latent image carrier 1 is provided with a charging unit 2, an exposure unit 3, a developing unit 4 and an intermediate transfer medium 5. Although not shown in the figure, the latent image carrier may be provided with a roll brush (fur brush) as a cleaning means, and the latent image carrier is not provided with a cleaning means but is provided on an intermediate transfer medium. The carrier may be cleaner-less. In the figure, 7 is a backup roller, 8 is a toner supply roller, 9 is a toner regulating blade (toner layer thickness regulating member), 10 is a developing roller, T is a negatively chargeable one-component toner, and L is a developing gap. .

  The latent image carrier 1 is a photosensitive drum rotating at a surface speed of 60 to 300 mm / s with a diameter of 24 to 86 mm. The surface of the latent image carrier 1 is negatively charged uniformly by the corona charger 2 and then corresponds to information to be recorded. An electrostatic latent image is formed by performing exposure 3.

  The latent image carrier may be either an organic single layer type or an organic laminated type, and the organic laminated type photoconductor is formed by sequentially laminating a charge generation layer and a charge transport layer on a conductive support via an undercoat layer. Is.

As the conductive support, a known conductive support can be used. For example, a conductive support having a volume resistance of 10 ¹⁰ Ω · cm or less, for example, 20 mm to 90 mmφ in which an aluminum alloy is processed by cutting or the like. Tubular supports, 20mm ~ 90mmφ tubular, belt-like, plate-like, sheet-like supports formed by depositing aluminum on polyethylene terephthalate film or imparting conductivity by conductive paint or molding conductive polyimide resin Examples include bodies. As another example, a metal belt in which nickel electroformed pipes, stainless steel pipes and the like are made seamless can also be suitably used.

  As the undercoat layer provided on the conductive support, a known undercoat layer can be used. For example, the undercoat layer is provided for the purpose of improving adhesion, preventing moire, improving the coatability of the upper charge generation layer, and reducing the residual potential during exposure. The resin used for the undercoat layer is preferably a resin having high resistance to dissolution with respect to the solvent used for the photosensitive layer in view of coating the photosensitive layer thereon. Soluble resins used include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as vinyl acetate, copolymerized nylon, and methoxymethylated nylon, polyurethane, melamine resin, and epoxy resin. These can be used alone or in combination of two or more. Moreover, you may make these resins contain metal oxides, such as titanium dioxide and a zinc oxide.

  As the charge generation pigment in the charge generation layer, known materials can be used. For example, phthalocyanine pigments such as metal phthalocyanine and metal-free phthalocyanine, azulenium salt pigments, squaric acid methine pigments, azo pigments having a carbazole skeleton, azo pigments having a triphenylamine skeleton, azo pigments having a diphenylamine skeleton, dibenzothiophene skeleton Azo pigments having a fluorene skeleton, azo pigments having an oxadiazole skeleton, azo pigments having a bis-stilbene skeleton, azo pigments having a distyryl oxadiazole skeleton, azo pigments having a distyrylcarbazole skeleton, perylene Pigments, anthraquinone or polycyclic quinone pigments, quinoneimine pigments, diphenylmethane and triphenylmethane pigments, benzoquinone and naphthoquinone pigments, cyanine and azomethine pigments Indigoid pigments, and bisbenzimidazole pigments. These charge generation pigments can be used alone or in combination of two or more.

  Examples of the binder resin in the charge generation layer include polyvinyl butyral resin, partially acetalized polyvinyl butyral resin, polyarylate resin, vinyl chloride-vinyl acetate copolymer, and the like. The composition ratio of the binder resin and the charge generating material is used in the range of 10 to 1000 parts by mass with respect to 100 parts of the binder resin.

  A known material can be used as the charge transport material constituting the charge transport layer, and there are an electron transport material and a hole transport material. Examples of the electron transporting material include electron accepting materials such as chloranil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, paradiphenoquinone derivatives, benzoquinone derivatives, and naphthoquinone derivatives. . These electron transport materials can be used alone or in combination of two or more.

  Examples of hole transport materials include oxazole compounds, oxadiazole compounds, imidazole compounds, triphenylamine compounds, pyrazoline compounds, hydrazone compounds, stilbene compounds, phenazine compounds, benzofuran compounds, butadiene compounds, benzidine compounds, and derivatives of these compounds. Can be mentioned. These electron donating substances can be used alone or in combination of two or more. The charge transport layer may contain an antioxidant, an anti-aging agent, an ultraviolet absorber and the like for preventing the deterioration of these substances.

  As the binder resin in the charge transport layer, polyester, polycarbonate, polysulfone, polyarylate, polyvinyl butyral, polymethyl methacrylate, polyvinyl chloride resin, vinyl chloride-vinyl acetate copolymer, silicone resin, etc. can be used. Polycarbonate is preferable in view of compatibility with a transport material, film strength, solubility, and stability as a coating material. The composition ratio of the binder resin and the charge transport material is used in a range of 25 to 300 parts by mass ratio with respect to 100 parts of the binder resin.

  In order to form the charge generation layer and the charge transport layer, a coating solution may be used, and the solvent varies depending on the type of the binder resin. For example, alcohols such as methanol, ethanol, isopropyl alcohol, acetone, methyl ethyl ketone, cyclohexanone, etc. Ketones, amides such as N, N-dimethylformamide, N, N-dimethylacetamide, ethers such as tetrahydrofuran, dioxane and ethylene glycol monomethyl ether, esters such as methyl acetate and ethyl acetate, chloroform, methylene chloride, Aliphatic halogenated hydrocarbons such as dichloroethylene, carbon tetrachloride, and trichloroethylene, or aromatics such as benzene, toluene, xylene, and monochlorobenzene can be used.

  The charge generating pigment may be dispersed and mixed using a mechanical method such as a sand mill, ball mill, attritor, or planetary mill.

  Coating methods for the undercoat layer, charge generation layer and charge transport layer include dip coating method, ring coating method, spray coating method, wire bar coating method, spin coating, blade coating method, roller coating method, air knife coating method, etc. Use the method. In addition, the drying after coating is preferably performed by drying at room temperature and then heating and drying at a temperature of 30 to 200 ° C. for 30 to 120 minutes. The film thickness after drying is 0.05 to 10 μm, preferably 0.1 to 3 μm, in the charge generation layer. In the charge transport layer, the thickness is in the range of 5 to 50 μm, preferably 10 to 40 μm.

  In addition, the single-layer organic photoreceptor layer has a binder and a binder, such as a charge generating agent, a charge transport agent, and a sensitizer, on the conductive support described in the above-mentioned organic laminated photoreceptor. It is prepared by coating and forming a single-layer organic photosensitive layer made of a solvent or the like. The organic negatively charged single layer type photoreceptor is preferably prepared according to, for example, Japanese Patent Application Laid-Open No. 2000-19746.

  Examples of the charge generator in the single-layer organic photosensitive layer include phthalocyanine pigments, azo pigments, quinone pigments, perylene pigments, quinothiaton pigments, indigo pigments, bisbenzimidazole pigments, and quinacridone pigments. These are phthalocyanine pigments and azo pigments. Examples of the charge transport agent include hydrazone-based, stilbene-based, phenylamine-based, arylamine-based, diphenylbutadiene-based, oxazole-based organic hole-transporting compounds, and sensitizers include various electron-withdrawing organic compounds. Examples thereof include paradiphenoquinone derivatives, naphthoquinone derivatives and chloranil which are also known as electron transport agents. Examples of the binder include thermoplastic resins such as polycarbonate resin, polyarylate resin, and polyester resin.

  The composition ratio of each component is 40 to 75% by mass of the binder, 0.5 to 20% by mass of the charge generating agent, 10 to 50% by mass of the charge transporting agent, and 0.5 to 30% by mass of the sensitizer. They are 45 to 65% by mass, charge generating agent 1 to 20% by mass, charge transporting agent 20 to 40% by mass, and sensitizer 2 to 25% by mass. The solvent is preferably a solvent that is not soluble in the undercoat layer, and examples thereof include toluene, methyl ethyl ketone, and tetrahydrofuran.

  Each component is pulverized / dispersed and mixed with a stirrer such as a homomixer, a ball mill, a sand mill, an attritor, or a paint conditioner to obtain a coating solution. The coating solution is applied onto the undercoat layer by dip coating, ring coating, spray coating or the like so as to have a film thickness of 15 to 40 μm, preferably 20 to 35 μm after drying, to form a single-layer organic photoreceptor layer.

  The developing device reversely develops the electrostatic latent image on the latent image carrying member in a non-contact manner to make a visible image. The developing device is composed of a toner containing portion that contains one-component non-magnetic toner T and does not replenish the toner, and a developing portion that consists of the developing roller 10, and the developing roller is supplied with toner by a supply roller 8 that rotates counterclockwise as shown. 10 is supplied. As shown in the figure, the developing roller rotates counterclockwise, and the toner T conveyed by the supply roller 8 is conveyed to the opposite part of the latent image carrier while being attracted to the surface of the developing roller 1. The electrostatic latent image is visualized.

The developing roller is, for example, a roller in which the surface of a metal pipe having a diameter of 16 to 24 mm is plated or blasted, or a volume resistance value of 10 ⁴ to 10 NBU, SBR, EPDM, urethane rubber, silicon rubber or the like on the central shaft peripheral surface. What formed the conductive elastic body layer of 10 < ⁸ > ohm * cm and hardness 40-70 degrees (Asker A hardness) can be used. A developing bias voltage is applied through the shaft and central axis of the pipe of the developing roller.

As the regulating blade 9, SUS, phosphor bronze, rubber plate, a thin metal plate and a rubber chip bonded to each other are used, and the work function on the toner contact surface may be 4.8 to 5.4 eV. It should be smaller than the function. The regulating blade is pressed against the developing roller by a biasing means such as a spring (not shown) or by using a repulsive force as an elastic body at a linear pressure of 0.08 to 0.6 N / cm. Good when the toner conveyance amount are 0.5~0.8mg / cm ^2, the toner conveyance amount exceeds 0.8 mg / cm ^2, it tends to increase + toner number%, the cleaning toner amount Results in an increase. On the other hand, if the toner conveyance amount is less than 0.5 mg / cm ² , the image density tends to decrease when continuous printing of tens of thousands of sheets is performed, which is not a good idea.

Further, the toner layer thickness on the developing roller is controlled to be 5 to 20 μm, preferably 6 to 15 μm, and the layered form of the toner particles is 1 to 2 layers, so that the frictional charging of the toner particles is sufficiently performed. I can do it. If the thickness of the toner layer on the developing roller is restricted to a thickness exceeding 2 layers (amount of toner transport amount exceeding 0.8 mg / cm ² ), the spherical toner slips out, and the frictional charging action cannot be made sufficient. In addition, the toner having a small particle diameter passes through without being in contact with the toner layer regulating member and becomes a positively charged toner, and tends to be mixed in the toner layer after regulation, causing fogging and a decrease in transfer efficiency. The toner charge amount may be controlled by applying a voltage to the regulating blade 9 and injecting electric charge into the toner contacting the blade.

  The developing roller 10 is opposed to the latent image carrier 1 via the developing gap L. The development gap is preferably 100 to 350 μm. Although not shown, the DC voltage (DC) developing bias is -200 to -500 V, and the superimposed AC voltage (AC) is 1.5 to 3.5 kHz, and the PP voltage is 1000 to 1800 V. It is better to make it a condition. The peripheral speed of the developing roller that rotates counterclockwise is 1.0 to 2.5, preferably 1.2 to 2.2, relative to the latent image carrier that rotates clockwise. It is good to do.

  The toner T vibrates between the surface of the developing roller and the surface of the latent image carrier at the opposing portion of the latent image carrier and the developing roller, and the electrostatic latent image is developed. Since the holder is in contact between the surface of the developing roller and the surface of the latent image carrier while the toner 8 vibrates, even if positively charged toner is present, the negatively charged toner Enable.

  Next, the intermediate transfer medium 5 is sent between the latent image carrier 1 and the backup roller (transfer roller) 7. The transfer roller presses the intermediate transfer medium against the latent image carrier, and a voltage having a polarity opposite to that of the negatively charged toner is applied as a transfer voltage.

  Examples of the intermediate transfer medium include an electronic conductive transfer drum and a transfer belt. First, transfer belt type transfer media can be divided into types using two types of substrates. One is to provide a transfer layer as a surface layer on a resin film or a seamless belt, and the other is to provide a transfer layer as a surface layer on a base layer of an elastic body. The drum type transfer medium can also be divided into types using two kinds of substrates. One is that when an organic photosensitive layer is provided on a drum having a rigid latent image carrier, for example, an aluminum drum, the intermediate transfer medium has an elastic surface layer on a rigid drum substrate such as aluminum. A transfer layer is provided. When the support for the latent image carrier is a belt or a so-called “elastic photoreceptor” in which a photosensitive layer is provided on an elastic support such as rubber, the intermediate transfer medium is made of a rigid material such as aluminum. It is preferable that a transfer layer as a surface layer is provided on a certain drum substrate directly or via a conductive intermediate layer.

As the substrate, a known conductive or insulating substrate can be used. In the case of a transfer belt, a volume resistance of 10 ⁴ to 10 ¹² Ω · cm, preferably 10 ⁶ to 10 ¹¹ Ω · cm is preferable. It can be divided into the following two types depending on the substrate used.

  Films and seamlessly suitable materials and production methods include engineering polyimides such as modified polyimide, thermosetting polyimide, polycarbonate, ethylene tetrafluoroethylene copolymer, polyvinylidene fluoride, nylon alloy, conductive carbon black, conductive titanium oxide A semiconductive film substrate having a thickness of 50 to 500 μm in which a conductive material such as conductive tin oxide or conductive silica is dispersed is formed into a seamless substrate by extrusion molding. Further, there is a seamless belt having a fluorine coating having a thickness of 5 to 50 μm as a surface protective layer for further reducing the surface energy to prevent toner filming. As a coating method, a dip coating method, a ring coating method, a spray coating method, or other methods can be used. Note that a tape such as a PET film having a film thickness of 80 μm and a rib such as urethane rubber are attached to both ends of the transfer belt to prevent cracks, elongation and meandering at the end of the transfer belt.

  In the case of producing a substrate with a film sheet, the belt can be produced by performing ultrasonic welding on the end face to form a belt shape. Specifically, a transfer belt having desired physical properties can be produced by performing ultrasonic welding after providing a conductive layer and a surface layer on a sheet film. Specifically, when a polyethylene terephthalate film having a thickness of 60 to 150 μm is used as an insulating substrate as a substrate, aluminum or the like is vapor-deposited on the surface, and an intermediate made of a conductive material such as carbon black and a resin if necessary. A transfer layer can be obtained by coating a conductive layer and providing a semiconductive surface layer made of urethane resin, fluororesin, conductive material, and fluorine-based fine particles having higher surface resistance. When it is possible to provide a resistance layer that does not require much heat during drying after coating, it is also possible to provide the above-mentioned resistance layer after ultrasonically depositing the aluminum vapor deposited film first, and use it as a transfer belt. is there.

  The material suitable for the elastic substrate such as rubber and the production method include silicon rubber, urethane rubber, NBR (nitrile rubber), EPDM (ethylene propylene rubber), etc., and a thickness of 0.8 to 2.0 mm. After producing the semiconductive rubber belt by extrusion molding, the surface is controlled to a desired surface roughness with an abrasive such as sandpaper or polisher. The elastic layer at this time may be used as it is, but a surface protective layer can be further provided in the same manner as described above.

In the case of a transfer drum, a volume resistance of 10 ⁴ to 10 ¹² Ω · cm, preferably 10 ⁷ to 10 ¹¹ Ω · cm is preferable. The transfer drum is provided with a conductive intermediate layer of an elastic body on a metal cylinder such as aluminum as necessary to form a conductive elastic base. Further, the surface energy is lowered on the transfer drum, and a semiconductive layer is used as a surface protective layer to prevent toner filming. For example, fluorine coating having a thickness of 5 to 50 μm can be produced.

Examples of the conductive elastic substrate include silicon rubber, urethane rubber, NBR (nitrile rubber), EPDM (ethylene propylene rubber), butadiene rubber, styrene-butadiene rubber, isoprene rubber, chloroprene rubber, butyl rubber, epichlorohydrin rubber, and fluorine rubber. A conductive rubber material, such as carbon black, conductive titanium oxide, conductive tin oxide, and conductive silica, blended, kneaded, and dispersed into a rubber material such as carbon black is adhesively molded into an aluminum cylinder with a diameter of 90 to 180 mm. Then, it is preferable that the thickness after polishing is 0.8 to 6 mm and the volume resistance is 10 ⁴ to 10 ¹⁰ Ω · cm. Subsequently, a transfer drum having a desired volume resistance of 10 ⁷ to 10 ¹¹ Ω · cm is provided by providing a semiconductive surface layer made of urethane resin, fluororesin, conductive material, and fluorine-based fine particles with a film thickness of about 15 to 40 μm. be able to. The surface roughness at this time is preferably 1 μmRa or less. As another example, a transfer drum having a desired surface layer and electric resistance is formed by covering a conductive elastic substrate manufactured as described above with a semiconductive tube such as a fluororesin and shrinking by heating. It is also possible to produce it.

  A voltage of +250 to +600 V is applied as the primary transfer voltage to the conductive layer in the transfer drum or the transfer belt, and a voltage of +400 to +2800 V is used as the secondary transfer voltage in the secondary transfer to a transfer material such as paper. Is preferably applied.

The transfer roller 7 has a structure in which an elastic layer, a conductive layer, and a resistive surface layer are laminated in this order on the peripheral surface of a metal shaft having a diameter of 10 to 20 mm. The resistive surface layer can be made of a highly flexible resistive sheet in which conductive fine particles such as conductive carbon are dispersed in a resin such as fluororesin and polyvinyl butyral, and rubber such as polyurethane, and the surface is smooth. The volume resistance value is 10 ⁷ to 10 ¹¹ Ω · cm, preferably 10 ⁸ to 10 ¹⁰ Ω · cm, and the film thickness is 0.02 to 2 mm.

The conductive layer may be selected from a conductive resin in which conductive fine particles such as conductive carbon are dispersed in a polyester resin, a metal sheet, or a conductive adhesive, and has a volume resistance of 10 ⁵ Ω · cm or less. belongs to. The elastic layer is required to be flexibly deformed when the transfer roller is pressed against the latent image carrier, and to return to its original shape as soon as the pressure is released. It is formed using. The foamed structure may be either a continuous foamed (foamed) structure or a closed cell structure, and may have a rubber hardness (Asker C hardness) of 30 to 80, and a film thickness of 1 to 5 mm. Due to the elastic deformation of the transfer roller, the latent image carrier and the intermediate transfer medium can be brought into close contact with each other with a wide nip width. The pressing load applied to the latent image carrier by the transfer roller is 0.245 to 0.588 N / cm, preferably 0.343 to 0.49 N / cm.

  In the color image forming apparatus of the present invention, the residual transfer toner on the latent image carrier can be transferred to the intermediate transfer medium by making the work function of the intermediate transfer medium smaller than the work function of the toner. In addition, the amount of residual toner on the intermediate transfer medium after the transfer from the intermediate transfer medium to a recording member such as paper can be reduced.

The work function (Φ _opc ) on the surface of the latent image carrier (photoconductor) is 5.2 to 5.6 eV, preferably 5.25 to 5.5 eV, and can be used if it is less than 5.2 eV. There is a problem that it is difficult to select a charge transporting agent, and it is difficult to select a usable charge generating agent if it exceeds 5.6 eV.

The work function (Φ _tM ) on the surface of the intermediate transfer medium is 4.9 to 5.5 eV, preferably 4.95 to 5.45 eV. If the work function (Φ _tM ) on the surface of the intermediate transfer medium is larger than 5.5 eV, it is not preferable because the material design as a toner becomes difficult, and if it is smaller than 4.9 eV, the amount of the conductive agent in the intermediate transfer medium is not preferable. There is a problem that the mechanical strength of the intermediate transfer medium is lowered due to excessive increase. In addition, the work function of the regulating blade is preferably made smaller than the work function of the toner, and the generation of the reversely charged toner can be further prevented.

The color image forming apparatus of the present invention can have high transfer efficiency by increasing the average circularity R of the negatively chargeable one-component toner. The relationship between the work function (Φ _t ) of the toner, the work function (Φ _OPC ) of the surface of the latent image carrier in the image forming apparatus, and the work function (Φ _M ) of the intermediate transfer medium is Φ _t > Φ _OPC > Φ _tM By doing so, the transfer efficiency can be further improved, and the amount of toner remaining on the surface of the latent image carrier can be reduced.

The work function (Φ _tM ) on the surface of the intermediate transfer medium can be 4.9 to 5.5 eV, and the work function of the negatively chargeable one-component toner can be 5.25 to 5.85 eV. In this color image forming apparatus, the amount of residual toner on the intermediate transfer medium after transfer to a recording member such as paper is reduced by making the work function of the intermediate transfer medium at least 0.2 eV smaller than the work function of the toner. it can.

  In the image forming apparatus shown in FIG. 4, if the developing process is combined with a developing device and a photoreceptor using four color toners (developers) composed of yellow Y, cyan C, magenta M, and black K, color image formation in the present invention is performed. It becomes a device.

  FIG. 5 is a schematic front view of a toner replenishment type tandem color printer, in which the photoreceptor and the developing unit can be mounted as the same unit, that is, as a process cartridge. In addition, the development may be a contact method, but in a later-described embodiment, a non-contact method is used.

  This image forming apparatus includes an intermediate transfer belt 30 that is stretched by only two rollers, a driving roller 11 and a driven roller 12, and is circulated and driven in the direction indicated by the arrow (counterclockwise). The four single color toner image forming units 20Y, 20C, 20M, and 20K are arranged, and the toner images formed by the plurality of single color toner image forming units 20 are individually transferred to the intermediate transfer belt 30. 15 and 16 are configured to perform primary transfer sequentially. Each primary transfer portion is indicated by T1Y, T1C, T1M, and T1K.

  The monochromatic toner image forming means includes a yellow 20Y, a magenta 20M, a cyan 20C, and a black 20K. Each of these monochromatic toner image forming means 20Y, 20C, 20M, and 20K includes a photosensitive member 21 having a photosensitive layer on the outer peripheral surface, a charging roller 22 as a charging unit that uniformly charges the outer peripheral surface of the photosensitive member 21, and An exposure unit 23 that selectively exposes the outer peripheral surface uniformly charged by the charging roller 22 to form an electrostatic latent image, and a developer (toner) on the electrostatic latent image formed by the exposure unit 23 ) To form a visible image (toner image), and a photosensitive member after the toner image developed by the developing roller 24 is transferred to the intermediate transfer belt 30 as a primary transfer target. And a cleaning blade 25 as a cleaning means for removing the toner remaining on the surface of 21.

  These single color toner image forming units 20Y, 20C, 20M and 20K are arranged on the slack side of the intermediate transfer belt 30. The toner image, which is sequentially primary transferred to the intermediate transfer belt 30 and sequentially superposed on the intermediate transfer belt 30 to become a full color, is secondarily transferred to the recording material S of the recording material such as paper in the secondary transfer portion T2, and fixed. By passing through the roller pair 61, the recording material S is fixed on the recording material S, and is discharged by a paper discharge roller pair 62 to a predetermined place, that is, onto a paper discharge tray (not shown). 51 is a sheet feeding cassette in which recording materials S of recording materials are stacked and held, 52 is a pickup roller for feeding the recording materials S from the sheet feeding cassette 51 one by one, and G is a sheet S to the secondary transfer portion T2. It is a pair of gate rollers that defines the sheet feeding timing.

  Reference numeral 63 denotes a secondary transfer roller as a secondary transfer unit that forms a secondary transfer portion T2 with the intermediate transfer belt 30. Reference numeral 64 denotes toner remaining on the surface of the intermediate transfer belt 30 after the secondary transfer. It is a cleaning blade as a cleaning means to remove. The cleaning blade 64 after the secondary transfer is in contact with the intermediate transfer belt 30 at a portion where the intermediate transfer belt 30 is wound around the driving roller 11 instead of the driven roller 12.

  Hereinafter, the present invention will be described in more detail with reference to examples.

  An example of manufacturing each member in the color image forming apparatus will be described.

Preparation of organophotoreceptor A conductive support of an aluminum tube having a diameter of 30 mm, 6 parts by mass of alcohol-soluble nylon {"CM8000" manufactured by Toray Industries, Inc.} as an undercoat layer, and 4 parts by mass of titanium oxide fine particles treated with aminosilane A coating solution prepared by dissolving and dispersing in 100 parts by mass of methanol was applied by a ring coating method and dried at a temperature of 100 ° C. for 40 minutes to form an undercoat layer having a thickness of 1.5 to 2 μm.

  On this undercoat layer, 1 part by mass of an oxytitanyl phthalocyanine pigment as a charge generation pigment, 1 part by mass of butyral resin {BX-1, manufactured by Sekisui Chemical Co., Ltd.) and 100 parts by mass of dichloroethane are mixed with glass beads having a diameter of 1 mm. The pigment dispersion obtained by dispersing for 8 hours with the used sand mill was applied by a ring coating method and dried at 80 ° C. for 20 minutes to form a charge generation layer having a thickness of 0.3 μm.

  On this charge generation layer, 40 parts by mass of a charge transport material of a styryl compound of the following structural formula (1) and 60 parts by mass of a polycarbonate resin (Panlite TS, manufactured by Teijin Chemicals Ltd.) are dissolved in 400 parts by mass of toluene. The charge transport layer was formed by applying and drying by a dip coating method so that the dry film thickness was 22 μm, and an organic photoreceptor consisting of two layers was produced.

  Structural formula (1)

  A part of the obtained organic photoreceptor was cut out, and a work piece was measured as a sample piece using a surface analyzer (AC-2 type, manufactured by Riken Keiki Co., Ltd.) at an irradiation light amount of 500 nW, 5.47 eV. showed that.

Example of developing roller The surface of an aluminum pipe having a diameter of 18 mm was subjected to nickel plating (thickness 10 μm). The surface roughness (Rz) was 7 μm. The work function on the surface of the developing roller was measured under the same conditions as 4.58 eV.

Production Example of Regulating Blade A conductive urethane rubber chip having a thickness of 1.5 mm was attached to a SUS plate having a thickness of 80 μm with a conductive adhesive. The work function of the urethane rubber surface under the same conditions was 5 eV.

Example of production of intermediate transfer belt 85 parts by mass of polybutylene terephthalate, 15 parts by mass of polycarbonate and 15 parts by mass of acetylene black were premixed by a mixer in a nitrogen atmosphere, and the resulting mixture was continuously produced by a twin-screw extruder in a nitrogen gas atmosphere. Kneaded and pelletized. The pellets were extruded into a tubular film having an outer diameter of 170 mm and a thickness of 160 μm at 260 ° C. by a single screw extruder having an annular die. Next, an inner diameter of the extruded molten tube was regulated by a cooling inside mandrel supported on the same axis as the annular die, and the tube was cooled and solidified to produce a seamless tube. Cut to a specified size, a seamless belt having an outer diameter of 172 mm, a width of 342 mm, and a thickness of 150 μm was obtained. The volume resistance of this transfer belt was 3.2 × 10 ⁸ Ω · cm. When the work function was measured under the same conditions, it was 5.19 eV and a normalized photoelectron yield of 10.88.

Example 1
For toner base particles obtained in Production Example 1 of toner base particles,
(1) Hydrophobic silica having a number average primary particle size of about 12 nm (BET specific surface area 150 m ² / g, work function 5.22 eV, “R805” manufactured by Nippon Aerosil Co., Ltd.). ) Hydrophobic spherical silica having a number average primary particle size of 110 nm (BET specific surface area 23 m ² / g, work function 5.26 eV, “Chihoster KE-P10S” manufactured by Nippon Shokubai Co., Ltd.)
..0.3 mass%
Were added and mixed at 8,000 rpm for 1 minute using a Henschel mixer.

After the mixing process, the toner base particles
(3) Hydrophobic titanium oxide having a number average primary particle size of 20 nm (BET specific surface area 135 m ² / g, work function 5.64 eV, “STT-30S” manufactured by Titanium Industry Co., Ltd.)
-0.5 mass% and (4) Each external additive in Table 3-0.3 mass% and (5) Zinc stearate particles having a number average primary particle size of 1 m (work function 5.36 eV, Japanese fats and oils) "Nissan Electol MZ-2" manufactured by Co., Ltd.) 0.1 mass% and (6) Hydrophobic positively charged silica having a number average primary particle size of 30 nm (treated with hexamethylsilazane and aminosilane, BET Specific surface area 40 m ² / g, work function 5.37 eV, “NA50H” manufactured by Nippon Aerosil Co., Ltd.)
Were added at 8,000 rpm for 1.5 minutes to prepare 9-point negatively chargeable one-component toner for evaluation.

The developing unit containing the negatively chargeable one-component toner thus prepared was set in the cyan developing portion in the non-magnetic one-component non-contact developing color image forming apparatus (external toner replenishing tandem color image forming apparatus) shown in FIG. . The regulated toner transport amount was adjusted to 0.65 mg / cm ² and used, and a continuous printing test of 30,000 sheets was performed. The results are shown in Table 4 below. The toner is supplied while being replenished, and printing is performed in a state where there is no excess or deficiency, and the toner transport amount is converted as an adhesion amount per unit area by a tape transfer method using a mending tape manufactured by Sumitomo 3M. Is.

Table 4 shows the toner charging characteristics on the developing roller after printing 30,000 originals corresponding to a 5% original using a charge amount distribution measuring device “E-SPART Analyzer Type 3” manufactured by Hosokawa Micron Corporation. Measured average charge amount of toner (-μc / g), + toner number%, 5% toner usage amount per A4 original (mg / cm ² ), residual toner on transfer and fog toner on OPC were cleaned. The toner amount (g) is indicated.

  The image forming conditions were a process speed of 210 mm / sec, a surface potential on the OPC of −600 V, the developing bias was variable by patch control, the primary transfer constant voltage control was +320 V, and the secondary transfer voltage was constant current control. The transfer paper used was Ricoh's My Recycle Paper.

  Of the external additives in Table 4, α-type alumina 5, strontium titanate, and titanium oxide are comparative examples.

^1): Zirconium doped product As can be seen from the table, when the BET specific surface area of α-type alumina 5 is as large as 17.3 m ² / g, the number of occurrences of reverse polarity + toner is large. It can be seen that α-type alumina 1 to 4 and α-type alumina 6 generate less + toner amount than strontium titanate or titanium oxide having a BET specific surface area of a certain degree. + When the amount of toner generated is large, the amount of 5% A4 original toner used is large. In the case of α-type alumina 1 to 4 and α-type alumina 6 of the present invention, the amount is 20 to 23 mg / cm ^2. It can be seen that 24-27 mg / cm ² gives a result that the toner consumption is also increased. In addition, it can be seen that the conductive α-type alumina uses less + toner number%, 5% A4 original toner, and the amount of cleaning toner can be reduced.

  As the amount of cleaning toner increases, the waste toner container also increases. In this continuous printing test, the number of waste toner containers was 30,000. However, in an image forming apparatus that is set to exceed this number, the cleaning unit, the waste toner transport unit, It is necessary to increase the capacity of the apparatus including the waste toner container, which leads to an increase in the size of the image forming apparatus, which is disadvantageous for downsizing the image forming apparatus.

(Example 2)
Negative toner for printing evaluation was performed in the same manner except that α-type alumina 1, α-type alumina 4, strontium titanate and titanium oxide shown in Table 3 were used for the toner base particles obtained in Production Example 4 of toner base particles. A chargeable one-component toner was prepared, and 30,000 continuous printing tests were performed in the same manner as in Example 1. The results are shown in Table 5.

Furthermore, using the α-type alumina 3 in Table 3, the toner conveyance amount 0.53 mg / cm ^2, except for using 0.81 mg / cm ² to prepare a negatively chargeable one-component toner for printing evaluation in the same manner The continuous printing test of 30,000 sheets was conducted in the same manner as in Example 1, and the results are shown in Table 5.

  The examples using strontium titanate and titanium oxide in Table 5 are comparative examples.

As can be seen from the table, the toner of the present invention using α-type alumina has a reverse polarity, + the number of generated toners is small, but an example using strontium titanate and titanium oxide having the same specific surface area is + The number% of toner generated was as high as 9 to 11%. This suggests that the toner consumption tends to increase, but even if the toner consumption per 5% A4 original sheet is actually compared, the α-type alumina 4 is about 2.22 mg / cm ² . The result was increased to 26 mg / cm ² .

Further, when the regulated toner transport amount exceeds 0.81 mg / cm ² and 0.8 mg / cm ² , the + toner number% tends to increase, and the cleaning toner amount similarly increases. From this, it can be seen that the toner transport amount is preferably 0.8 mg / cm ² or less. Further, when the transport amount is 0.53 mg / cm ² , the development bias potential that gives the patch image density of 1.4 after 30,000 printing is high from the initial −130 V to −290 V, and the patch It was necessary to increase the control voltage range. In patch control, increasing the developing bias indicates that the chargeability of the toner is increased, and the image density tends to decrease regardless of non-contact development or contact development, which is not preferable development. It can be seen that it is not a good idea to set the toner conveyance amount to 0.5 mg / cm ² or less.

(Example 3)
For the toner base particles obtained in Examples 1 to 4 of the toner base particles,
(1) Hydrophobic silica having a number average primary particle size of about 12 nm (BET specific surface area 150 m ² / g, work function 5.22 eV, Nippon Aerosil Co., Ltd. “R805”)
.. 1.5% by mass and (2) hydrophobic spherical silica having a number average primary particle size of 110 nm (BET specific surface area 23 m ² / g, work function 5.26 eV, “Seahoster KE-P10S” manufactured by Nippon Shokubai Co., Ltd.) )
..0.5% by mass
Were added and mixed at 8,000 rpm for 1 minute using a Henschel mixer.

After the mixing process, the toner base particles
(3) Hydrophobic titanium oxide having a number average primary particle size of 20 nm (BET specific surface area 135 m ² / g, work function 5.64 eV, “STT-30S” manufactured by Titanium Industry Co., Ltd.)
0.2 mass% and (4) α-type alumina 3 in Table 3 (BET specific surface area 7.0 m ² / g) 0.4 mass% and (5) In combination with toner base particles in Table 7
..0.1% by mass and (6) hydrophobic positively charged silica having a number average primary particle size of 30 nm (treated with hexamethylsilazane and aminosilane, BET specific surface area 40 m ² / g, work function 5.37 eV, Nippon Aerosil Co., Ltd. “NA50H”) ・ ・ 0.2% by mass
Were added at 8,000 rpm for 1.5 minutes to prepare a four-point negatively chargeable one-component toner for evaluation.

The developed developing unit containing each color toner was set in each developing section in the color image forming apparatus (non-magnetic one-component non-contact developing tandem color image forming apparatus) shown in FIG. The regulated toner transport amount is adjusted to 0.65 mg / cm ² , and the order of development / transfer is cyan developer unit, magenta developer unit, yellow developer unit, and black developer unit as viewed from the paper supply side. The image forming conditions were the same as in Example 1 except that the primary transfer voltage was + 400V.

  Next, an N-2A “cafeteria” image of standard image data compliant with JIS X 9201-1995 is output after printing 50,000 sheets of the original and 5% original, and the first sheet is the 50,001 sheet. The color reproducibility was evaluated. For color reproducibility, the quality of the first image was set to a maximum of 10 points, and the 50th and 001th images were subjectively evaluated. The results are shown in Table 8 together with the amount of cleaning toner.

Also, in Table 8, in place of α-type alumina 3 in Table 3, α-type alumina 5 (BET specific surface area 17.3 m ² / g) in Table 3 was used, and negative charging for comparison was similarly performed. The result obtained by preparing a single-component toner and evaluating the same is shown as a color toner using an external additive for comparison.

As can be seen from the table, when the BET specific surface area of α-type alumina is 17.3 m ² / g, the cleaning toner amount is 1.6 times or more that of the present invention. In addition, looking at the output image of “cafeteria”, the image quality of the latter tends to give a dull image due to a decrease in the overall saturation in the comparison between the first image and the 50,001 image. Thus, in the present invention, the degree of reduction is small, and color image quality that can withstand use is provided.

Example 4
Using the toner base particles obtained in 5-8 of the toner base particle production examples,
(1) Hydrophobic silica having a number average primary particle size of about 12 nm (BET specific surface area 150 m ² / g, work function 5.22 eV, Nippon Aerosil Co., Ltd. “R805”)
.. 1.5% by mass and (2) hydrophobic spherical silica having a number average primary particle size of 110 nm (BET specific surface area 23 m ² / g, work function 5.26 eV, “Seahoster KE-P10S” manufactured by Nippon Shokubai Co., Ltd.) )
..0.6% by mass
Were added and mixed at 8,000 rpm for 1 minute using a Henschel mixer.

After the mixing process, the toner base particles
(3) Hydrophobic titanium oxide having a number average primary particle size of 20 nm (BET specific surface area 135 m ² / g, work function 5.64 eV, “STT-30S” manufactured by Titanium Industry Co., Ltd.)
・ ・ 0.25 mass% and (4) α-type alumina 4 in Table 3 (BET specific surface area 9.1 m ² / g) ・ ・ 0.3 mass% and (5) Number average primary particle diameter of 30 nm hydrophobicity Positively charged silica (treated with hexamethylsilazane and aminosilane, BET specific surface area 40 m ² / g, work function 5.37 eV, “NA50H” manufactured by Nippon Aerosil Co., Ltd.)
Were added at 8,000 rpm for 1.5 minutes to prepare a four-point negatively chargeable one-component toner for evaluation.

The developed developing unit containing each color toner was set in each developing section in the color image forming apparatus (non-magnetic one-component non-contact developing tandem color image forming apparatus) shown in FIG. The regulated toner transport amount is adjusted to 0.65 mg / cm ² , and the order of development / transfer is cyan developer unit, magenta developer unit, yellow developer unit, and black developer unit as viewed from the paper supply side. The image forming conditions were the same as in Example 1 except that the primary transfer voltage was + 400V.

  Next, an N-2A “cafeteria” image of standard image data compliant with JIS X 9201-1995 is output after printing 50,000 sheets of the original and 5% original, and the first sheet is the 50,001 sheet. The color reproducibility was evaluated. For color reproducibility, the quality of the first image was set to a maximum of 10 points, and the 50th and 001th images were subjectively evaluated. The results are shown in Table 9 together with the amount of cleaning toner.

Further, in Table 9, in place of the α-type alumina 4 in Table 3, the negative chargeability for comparison was similarly obtained except that strontium titanate (BET specific surface area 8.9 m ² / g) in Table 3 was used. A one-component toner was prepared and evaluated in the same manner as a color toner using an external additive for comparison.

As can be seen from the table, the cleaning toner amount is twice that of the present invention when strontium titanate (BET specific surface area 8.9 m ² / g) is used. In addition, looking at the output image of “cafeteria”, the image quality of the latter tends to give a dull image due to a decrease in the overall saturation in the comparison between the first image and the 50,001 image. Thus, in the present invention, the degree of reduction is small, and color image quality that can withstand use is provided.

FIG. 1 is a diagram showing a measurement cell used for measuring the work function of toner, wherein (a) is a front view and (b) is a side view. 2A and 2B are diagrams for explaining a method for measuring a work function of a cylindrical image forming apparatus member. FIG. 2A is a perspective view showing a shape of a measurement sample piece, and FIG. 2B is a view showing a measurement state. . FIG. 3 is an example of a chart in which the work function of the toner is measured using a surface analyzer. FIG. 4 is an explanatory diagram of the non-contact development method. FIG. 5 is an explanatory diagram of an external supply type tandem color image forming apparatus according to the present invention.

Explanation of symbols

  1 is a latent image carrier, 2 is a charging unit, 3 is an exposing unit, 4 is a developing unit, 5 is an intermediate transfer medium, 7 is a backup roller, 8 is a toner supply roller, 9 is a toner regulating blade (toner layer thickness regulating member) ) 10 is a developing roller, T is a negatively chargeable one-component toner, and L is a developing gap.

Claims (8)

It has at least a binder resin and a colorant, has a particle size distribution in which the average particle diameter based on the number is 4.5 to 9 μm, the integrated value of the average particle diameter of 3 μm or less is 1% or less, and the average (1) negatively chargeable hydrophobic silica fine particles having a BET specific surface area of 80 to 300 m ² / g;
(2) negatively chargeable hydrophobic spherical silica fine particles having a BET specific surface area of 5 to 40 m ² / g and a number average primary particle size of 80 to 150 nm,
(3) hydrophobic titanium oxide fine particles having a number average primary particle size of 10 to 30 nm,
(4) α-type alumina fine particles having a BET specific surface area of 4 to 15 m ² / g,
(5) A negatively chargeable one-component toner obtained by externally adding metal soap particles having a number average primary particle size of 1.5 μm or less. ^2. The negatively chargeable one-component toner according to claim 1, further externally treated with positively chargeable hydrophobic silica fine particles having a BET specific surface area of 30 to 50 m < ² > / g. The negatively chargeable one-component toner according to claim 1, wherein the toner base particles are obtained by a dissolution suspension method. It has at least a binder resin and a colorant, has a particle size distribution in which the average particle diameter based on the number is 4.5 to 9 μm, the integrated value of the average particle diameter of 3 μm or less is 1% or less, and the average A method for producing a negatively chargeable one-component toner in which a plurality of types of external additives are subjected to multistage external addition treatment on toner base particles having a circularity of 0.95 to 0.99,
As a first stage of a multistage system adding process, the toner mother particles, negatively chargeable hydrophobic silica fine particles having a BET specific surface area of 80~300m ² / g, and a BET specific surface area of at 5 to 40 m ² / g, and, After externally treating negatively chargeable hydrophobic spherical silica fine particles having a number average primary particle size of 80 to 150 nm in a ratio of 1.0 to 2.5% by mass with respect to the toner base particles,
As a subsequent treatment, hydrophobic titanium oxide fine particles having a number average primary particle size of 10 to 30 nm, α-type alumina fine particles having a BET specific surface area of 4 to 15 m ² / g, and a number average primary particle size of 1. Metal soap particles of 5 μm or less are additionally mixed in a total amount of 0.5 to 1.5% by mass, or a positive BET specific surface area of 30 to 50 m ² / g with respect to the toner base particles. A method for producing a negatively chargeable one-component toner, wherein the chargeable hydrophobic silica fine particles are additionally mixed at a ratio of 0.1 to 0.6% by mass. The work function of the toner base particles is 5.3 to 5.7 eV, the work function of the hydrophobic silica fine particles is 5.0 to 5.3 eV, and the work function of the α-type alumina fine particles added in the latter stage is 4. 9 to 5.2 eV, the work function of hydrophobic titanium oxide fine particles is 5.5 to 5.7 eV, the work function of positively charged silica fine particles is 5.2 to 5.4 V, and the work function of metal soap particles is 5.3. 5. The negatively chargeable one-component toner according to claim 4, wherein the post-stage treatment is multi-stage processed by combining external additives having a work function difference of at least 0.2 eV or more. Manufacturing method. An electrostatic latent image is formed on the latent image carrier, the electrostatic latent image is sequentially developed by a one-component method using a plurality of developing units to form a color toner image, and then the latent image is carried In a color image forming apparatus in which a toner image formed on a body is transferred to an intermediate transfer medium to form a color toner image, which is transferred onto a recording material and fixed, the plurality of developers are externally replenished developing devices. The toner transport amount on the developing member in each of the plurality of developing devices is 0.5 to 0.8 mg / cm ^2, and the toner is composed of at least a binder resin and a colorant. Toner base particles having a particle size distribution in which the diameter is 4.5 to 9 μm, the integrated value of the average particle diameters of 3 μm or less is 1% or less, and the average circularity is 0.95 to 0.99. ,
(1) negatively chargeable hydrophobic silica fine particles having a BET specific surface area of 80 to 300 m ² / g,
(2) negatively chargeable hydrophobic spherical silica fine particles having a BET specific surface area of 5 to 40 m ² / g and a number average primary particle size of 80 to 150 nm,
(3) hydrophobic titanium oxide fine particles having a number average primary particle size of 10 to 30 nm,
(4) α-type alumina fine particles having a BET specific surface area of 4 to 15 m ² / g,
(5) A color image forming apparatus, which is a negatively chargeable one-component toner obtained by externally adding metal soap particles having a number average primary particle size of 1.5 μm or less. The toner is a negatively chargeable one-component toner further externally treated with positively chargeable hydrophobic silica fine particles having a BET specific surface area of 30 to 50 m ² / g, and the development method is a non-contact development method. The color image forming apparatus according to claim 6. 7. The color image forming apparatus according to claim 6, wherein the color image forming apparatus employs a tandem developing system.

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