JP5630328B2 - Two-component developer - Google Patents

Description

  The present invention relates to a two-component developer used in an electrophotographic image forming method.

  For the toner used in the electrophotographic image forming method, various external additives are used for the purpose of imparting fluidity to the toner, improving chargeability, and improving transfer and cleaning properties. Among these external additives, external additive particles having a large particle size with a sharp particle size distribution are dispersed as primary particles on the toner surface, improving fluidity with respect to the toner, In order to reduce the adhesion force, it is known that it greatly contributes to improvement of transfer efficiency and further improvement of cleaning performance.

  However, the external additive particles having a large particle size are difficult to be fixed on the toner surface, and thus are easily transferred to the carrier surface, thereby reducing the charge imparting ability of the carrier. There is a problem that good charging performance cannot be maintained, toner scattering, transfer failure, and the like occur, so that a high-quality image cannot be formed over a long period of time.

  To solve this problem, so-called trickle development is used in which excess two-component developer is gradually discharged, and the toner amount consumed by development is replenished and the discharged carrier amount is replenished. A method that can be solved by adopting an image forming method of the type is conceivable (for example, see Patent Documents 1 to 3). Thereby, since the carrier in the developing device is gradually replaced with a new one, the migration of the external additive particles to the carrier surface is suppressed to some extent.

  However, such a trickle-developing image forming method does not prevent the external additive particles from detaching from the toner surface, and thus the fundamental problem has not been solved. May not sufficiently suppress the migration of the external additive particles to the carrier surface.

JP 2001-330985 A JP 2004-287269 A JP 2007-079578 A

  The present invention has been made on the basis of the above circumstances, and its object is to suppress the transfer of the external additive of the toner to the carrier and to maintain the good charging performance of the toner. Another object is to provide a two-component developer capable of forming a high-quality image over a long period of time.

The two-component developer of the present invention is a two-component developer comprising a toner and a carrier.
The toner is formed by adding inorganic fine particles having an average primary particle diameter of 60 to 150 nm as an external additive,
The carrier is formed by adding inorganic fine particles having an average primary particle size smaller than the inorganic fine particles in the toner as an external additive,
Inorganic fine particles in the carrier, the charging of the inorganic fine particles in the toner all SANYO is charged to the opposite polarity, and an average primary particle diameter is characterized in that it is of 20 to 50 nm.

In the two-component developer of the present invention, the inorganic fine particles in the toner are silica fine particles,
The inorganic fine particles in the carrier are preferably titanium oxide fine particles or aluminum oxide fine particles.

In the two-component developer of the present invention, the inorganic fine particles in the toner are titanium oxide fine particles,
The inorganic fine particles in the carrier are preferably silica fine particles.

  The two-component developer of the present invention is preferably used for replenishment in a developing type image forming method in which excess two-component developer is discharged and new toner and carrier are replenished.

  According to the two-component developer of the present invention, the average primary particles in which the carrier constituting the two-component developer is smaller than the inorganic fine particles as the external additive in the toner (hereinafter also referred to as “inorganic fine particles for toner”). Inorganic fine particles having a diameter (hereinafter also referred to as “carrier fine particles”) are externally added, and the carrier fine inorganic particles are charged with a polarity opposite to the chargeability of the toner fine inorganic particles. As a result, frictional charging occurs between the inorganic fine particles for toner and the inorganic fine particles for carrier due to a stirring action in the developing device, and as a result, the inorganic fine particles for toner have a large charge. Since the inorganic fine particles for toner are electrostatically attached to the toner surface, the inorganic fine particles for toner are prevented from moving to the carrier surface. Preventing a reduction in the rear of the charge-providing performance, resulting in the maintenance of good charging performance of the toner is achieved, it is possible to form a high quality image over a long period of time.

It is explanatory drawing which showed typically an example of the structure of the two-component developer of this invention.

  Hereinafter, the present invention will be described in detail.

[Two-component developer]
The two-component developer of the present invention comprises a toner and a carrier, and the toner is formed by adding inorganic fine particles for toner having an average primary particle diameter of 60 to 150 nm as an external additive, The carrier has an average primary particle size smaller than that of the inorganic fine particles for toner as an external additive, and is added with inorganic fine particles for carrier that are charged with a polarity opposite to the chargeability of the inorganic fine particles for toner. Is.

〔toner〕
In the toner constituting the two-component developer of the present invention, an external additive composed of inorganic fine particles having an average primary particle diameter of 60 to 150 nm is added to toner particles containing at least a binder resin and a colorant. It will be.
Further, the toner particles may contain an internal additive such as a release agent or a charge control agent as necessary.

[Binder resin]
The binder resin constituting the toner particles is not particularly limited, but when the toner is produced by a pulverization method, a dissolution suspension method, or the like, the binder resin constituting the toner particles may be, for example, a styrene resin. , (Meth) acrylic resins, styrene- (meth) acrylic copolymer resins, vinyl resins such as olefin resins, polyester resins, polyamide resins, polycarbonate resins, polyethers, polyvinyl acetate resins, poly Various known resins such as sulfone, epoxy resin, polyurethane resin, and urea resin can be used. These can be used alone or in combination of two or more.

  Further, when the toner is produced by suspension polymerization, miniemulsion polymerization aggregation, emulsion polymerization aggregation, or the like, as a polymerizable monomer for obtaining a binder resin constituting the toner particles, for example, styrene Styrene or styrene derivatives such as o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene ; Methacrylate derivatives such as methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, and phenyl methacrylate. ; Methyl acrylate, acrylic Acrylic acid ester derivatives such as ethyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate; acrylonitrile, methacrylonitrile And vinyl monomers such as acrylic acid or methacrylic acid derivatives such as acrylamide. These vinyl monomers can be used alone or in combination of two or more.

Further, as the polymerizable monomer for obtaining the binder resin constituting the toner particles, it is preferable to use a combination of those having an ionic dissociation group. The polymerizable monomer having an ionic dissociation group has, for example, a substituent such as a carboxyl group, a sulfonic acid group, and a phosphoric acid group as a constituent group, and specifically includes acrylic acid, methacrylic acid, Maleic acid, itaconic acid, cinnamic acid, fumaric acid, maleic acid monoalkyl ester, itaconic acid monoalkyl ester, styrene sulfonic acid, allyl sulfosuccinic acid, 2-acrylamido-2-methylpropane sulfonic acid, acid phosphooxyethyl And methacrylate and 3-chloro-2-acid phosphooxypropyl methacrylate.
Furthermore, as a polymerizable monomer, for example, divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, neopentyl glycol dimethacrylate, A binder resin having a crosslinked structure can also be obtained using polyfunctional vinyls such as neopentyl glycol diacrylate.

[Colorant]
Examples of the colorant contained in the toner particles include carbon black, a magnetic material, a dye, and a pigment.
Examples of carbon black include channel black, furnace black, acetylene black, thermal black, and lamp black.
Examples of magnetic materials include ferromagnetic metals such as iron, nickel, and cobalt, alloys containing these metals, compounds of ferromagnetic metals such as ferrite and magnetite, and ferromagnetic materials that do not contain ferromagnetic metals but are heat treated. (E.g., Heusler alloys such as manganese-copper-aluminum and manganese-copper-tin, chromium dioxide, etc.).

  Examples of the dye include C.I. I. Solvent Red 1, 49, 52, 58, 63, 111, 122, C.I. I. Solvent Yellow 19, 44, 77, 79, 81, 82, 93, 98, 103, 104, 112, 162, C.I. I. Solvent Blue 25, 36, 60, 70, 93, 95 and the like. These can be used alone or in combination of two or more.

  Examples of the pigment include C.I. Pigment Red 5, 48: 1, 53: 1, 57: 1, 122, 139, 144, 149, 166, 177, 178, 222, C.I. I. Pigment Orange 31 and 43, C.I. I. Pigment Yellow 14, 17, 74, 93, 94, 138, 155, 180, 185, C.I. I. Pigment green 7, C.I. And CI Pigment Blue 15: 3 and 60. These can be used alone or in combination of two or more.

  It is preferable that content of a coloring agent is 4-10 mass parts with respect to 100 mass parts of binder resin, More preferably, it is 5-8 mass parts.

〔Release agent〕
When a release agent is contained as an internal additive of toner particles, a known wax can be used as the release agent. For example, a low molecular weight polyethylene wax, a low molecular weight polypropylene wax, a Fischer-Tropsch wax, a microwax Examples thereof include hydrocarbon waxes such as crystallin wax and paraffin wax, carnauba wax, ester waxes such as pentaerythritol behenate, behenyl behenate, and behenyl citrate. These can be used alone or in combination of two or more.

  It is preferable that content of a mold release agent is 0.1-30 mass parts with respect to 100 mass parts of binder resin, More preferably, it is 1-10 mass parts.

[Charge control agent]
In the case where a charge control agent is contained as an internal additive of toner particles, various known compounds can be used as the charge control agent.

  The content of the charge control agent is preferably 0.1 to 3 parts by mass, more preferably 0.5 to 2 parts by mass with respect to 100 parts by mass of the binder resin.

[Inorganic fine particles for toner]
The external additive added to the toner particles is inorganic fine particles having an average primary particle diameter of 60 to 150 nm. Specific examples of the inorganic fine particles for toner include silica fine particles and titanium oxide fine particles.

The inorganic fine particles for toner have an average primary particle size of 60 to 150 nm, more preferably 80 to 120 nm.
When the average primary particle diameter of the inorganic fine particles for toner is within the above range, excellent fluidity, high transfer efficiency, and excellent cleaning properties can be obtained for the toner.
When the average primary particle diameter of the inorganic fine particles for toner is too small, a sufficient spacer effect cannot be exhibited, and there is a possibility that transferability and cleaning properties cannot be obtained. Further, since the toner particles are easily embedded in the toner particles, the charge amount may be easily reduced. On the other hand, when the average primary particle size of the inorganic fine particles for toner is excessive, the physical and electrostatic adhesion to the toner particles is weak, so that the toner particles are easily transferred to the carrier, and transferability and cleaning properties are sufficient. There is a possibility that it cannot be demonstrated.

The average primary particle diameter of the inorganic fine particles for toner is measured as follows.
That is, using a scanning electron microscope (SEM) “JEM-7401F” (manufactured by JEOL Ltd.), an SEM photograph magnified 30,000 times is captured by a scanner, and an image processing analyzer “LUZEX AP” (manufactured by Nireco) Then, the inorganic fine particles for toner of the SEM photographic image are binarized, the horizontal ferret diameter for 100 inorganic fine particles for toner is calculated, and the average value is taken as the average particle size.

  The inorganic fine particles for toner are preferably those whose surfaces have been subjected to hydrophobic treatment.

The addition amount of the inorganic fine particles for toner is preferably 0.5 to 2.0% by mass in the toner, and more preferably 1.0 to 1.5% by mass.
If the amount of inorganic fine particles for toner is too small, the toner may not be able to maintain good charging performance and may not form a high-quality image. When the toner is excessively large, there is a possibility that excellent fluidity cannot be obtained in the toner.

  In the toner according to the present invention, the method for adding the inorganic fine particles for toner as an external additive is not particularly limited as long as the inorganic fine particles for toner adhere to the surface of the toner particles. For example, dried toner particles And a dry method in which inorganic fine particles for toner are added as a powder and mixed. Examples of the mixing device used in this dry method include mechanical mixing devices such as a Henschel mixer and a coffee mill.

In the toner according to the present invention, other known external additives may be added as external additives in addition to the inorganic fine particles for toner. Examples of other external additives include inorganic oxides such as silica, alumina, titanium oxide, and calcium titanate, and fine particles such as fatty acid metal salts such as calcium stearate and zinc stearate. Such other external additives preferably have a number average primary particle size of 10 to 70 nm.
Further, when the inorganic fine particles for toner and other external additives are used in combination, the amount of other external additives added is preferably 0.1 to 5.0% by mass in the toner.
In the toner according to the present invention, the method of adding other external additives is not particularly limited, and examples thereof include a dry method in which other external additives are added to dried toner particles and mixed. It is done. As a mixing device used in this dry method, various known devices such as a Turbuler mixer, a Henschel mixer, a Nauter mixer, and a V-type mixer can be mentioned.

The toner particles constituting the toner preferably have a volume-based median diameter (D ₅₀ ) of 5.0 to 7.0 μm, more preferably 5.5 to 6.5 μm.
The volume-based median diameter (D ₅₀ ) of toner particles is measured using a measuring apparatus in which a computer system for data processing (Beckman Coulter) is connected to “Coulter Multisizer 3” (Beckman Coulter).・ It is calculated.
Specifically, 0.02 g of a sample (toner) was added to 20 mL of a surfactant solution (for example, a surfactant solution obtained by diluting a neutral detergent containing a surfactant component 10 times with pure water) to be acclimatized. Thereafter, ultrasonic dispersion treatment is performed for 1 minute to prepare a dispersion of toner particles, and this dispersion of toner particles is placed in a beaker containing “ISOTON II” (manufactured by Beckman Coulter) in a sample stand. Pipet until the indicated concentration is 5% to 10%. Here, a reproducible measurement value can be obtained by setting the concentration range. In the measurement apparatus, the measurement particle count is 25000, the aperture diameter is 50 μm, the frequency value is calculated by dividing the measurement range of 1 to 30 μm into 256, and the volume integrated fraction is 50 % Is the volume-based median diameter (D ₅₀ ).

The toner particles preferably have a coefficient of variation (CV value) of 15 to 20% in the particle size distribution of the volume-based median diameter (D ₅₀ ).
When the coefficient of variation (CV value) of the toner particles is in the above range, the toner particles are in a uniform size, and a fine dot image or fine line can be reproduced with higher accuracy.

The coefficient of variation (CV value) in the particle size distribution of the volume-based median diameter (D ₅₀ ) is calculated by the following mathematical formula (1). The smaller the CV value, the sharper the particle size distribution, and thus the more uniform toner particles.
Formula (1): CV value (%) = standard deviation in particle size distribution / median diameter (D ₅₀ ) × 100 in particle size distribution

  The average circularity of the toner particles is preferably 0.940 to 0.980, more preferably 0.950 to 0.970.

The average circularity of the toner particles is measured by “FPIA-2100” (manufactured by Sysmex).
Specifically, the sample (toner) was blended with an aqueous solution containing a surfactant, dispersed by performing ultrasonic dispersion for 1 minute, and then subjected to measurement conditions HPF (by FPIA-2100) (manufactured by Sysmex). In high-magnification imaging mode, photographing is performed at an appropriate density of 3,000 to 10,000 HPF detections, and the circularity of each toner particle is calculated according to the following formula (2). Is added and divided by the total number of toner particles.
Formula (2): Average circularity = (peripheral length of a circle having the same projected area as the particle image) / (peripheral length of the particle image)

[Toner Production Method]
The method for producing the toner is not particularly limited, and a known production method can be adopted. Specific examples include a so-called pulverization method that is produced through kneading, pulverization, and classification steps, and a so-called polymerization method that performs particle formation by controlling the shape and particle size while polymerizing a polymerizable monomer. Examples of the production method by such a polymerization method include an emulsion polymerization method, a suspension polymerization method, a polyester elongation method, and an emulsion polymerization aggregation method. Among these, an emulsion polymerization aggregation method in which a binder resin particle prepared by an emulsion polymerization method is aggregated and associated is preferable because toner particles having a uniform shape and particle diameter can be obtained.

[Carrier]
The carrier constituting the two-component developer of the present invention is obtained by adding an external additive made of carrier fine particles having an average primary particle size smaller than that of toner fine particles to carrier particles made of a magnetic material. The inorganic fine particles for carrier are charged with a polarity opposite to the chargeability of the inorganic fine particles for toner.
Further, the carrier particles may contain an internal additive such as a resistance adjuster as necessary.

  The carrier particles are composed of a magnetic material, but the resin-coated carrier particles in which the surface of the core particles made of the magnetic material is coated with a resin, or fine magnetic powder is dispersed in the resin. It can also be composed of resin-dispersed carrier particles. From the viewpoint of suppressing carrier adhesion to the photoreceptor, it is preferably composed of resin-coated carrier particles.

[Magnetic material]
As the magnetic substance constituting the carrier particles, a substance that is strongly magnetized in the direction by a magnetic field, for example, iron, ferrite represented by the formula (a): MO · Fe ₂ O ₃ , and formula (b): MFe ₂ O ₄ Magnets such as iron, nickel and cobalt, and other metals exhibiting ferromagnetism, or alloys or compounds containing these metals, alloys that do not contain ferromagnetic metal but exhibit ferromagnetism by heat treatment (for example, manganese) -Heusler alloys such as copper-aluminum and manganese-copper-tin, chromium dioxide, etc.).
In the above formulas (a) and (b), M is a monovalent or divalent metal such as Mn, Fe, Ni, Co, Cu, Mg, Zn, Cd, Li, and these are independent. Alternatively, two or more kinds can be used in combination.

  In the case where the carrier particles are composed of resin-coated carrier particles, the core particles constituting the carrier particles have a specific gravity smaller than that of a metal such as iron or nickel. Various ferrites are preferable because the impact force can be reduced.

The saturation magnetization of the core particles is preferably ^{20 to} 80 Am ² / kg.
The saturation magnetization of the core particles is measured by a DC magnetization characteristic automatic recording device “3257-35” (manufactured by Yokogawa Electric Corporation).

  In the case where the carrier particles are composed of resin-coated carrier particles, a resin (hereinafter also referred to as “coating resin”) that forms a resin coating on the surface of the core particles constituting the carrier particles is a vinyl monomer. Preferably, the resin is obtained by polymerizing a polymerizable monomer such as styrene, acrylic acid, methacrylic acid, alkyl acrylate, methacrylic acid. Examples include alkyl-based ones.

  Specific examples of the vinyl monomer include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, p-tert-butylstyrene, p- Styrene or styrene derivatives such as n-hexyl styrene, pn-octyl styrene, pn-nonyl styrene, pn-decyl styrene, pn-dodecyl styrene; methyl methacrylate, ethyl methacrylate, n methacrylate -Butyl, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, lauryl methacrylate, phenyl methacrylate, diethylaminoethyl methacrylate, methacrylic acid Methacrylic acid ester derivatives such as methylaminoethyl and cyclohexyl methacrylate; methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-octyl acrylate, acrylic acid Acrylic acid ester derivatives such as 2-ethylhexyl, stearyl acrylate, lauryl acrylate, phenyl acrylate; olefins such as ethylene, propylene, isobutylene; vinyl chloride, vinylidene chloride, vinyl bromide, vinyl fluoride, vinylidene fluoride, etc. Halogenated vinyls; vinyl esters such as vinyl propionate, vinyl acetate and vinyl benzoate; vinyl ethers such as vinyl methyl ether and vinyl ethyl ether; vinyl methyl ketone and vinyl Vinyl ketones such as ethyl ketone and vinyl hexyl ketone; N-vinyl compounds such as N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone; Vinyl compounds such as vinyl naphthalene and vinyl pyridine; Acrylonitrile, methacrylonitrile, acrylamide, etc. And acrylic acid or methacrylic acid derivatives. These vinyl monomers can be used alone or in combination of two or more.

The glass transition point of the coating resin is not particularly limited, but is preferably 95 to 120 ° C. When the glass transition point of the coating resin is within the above range, an excellent film forming property is exhibited, so that a dense coating layer is formed.
The glass transition point of the coating resin is measured by a differential scanning calorimeter “DSC-7” (manufactured by Perkin Elmer).
Specifically, 4.5 mg of the sample (coating resin) is precisely weighed to two digits after the decimal point, sealed in an aluminum pan, and set in a sample holder. The reference uses an empty aluminum pan, performs heat-cool-heat temperature control at a measurement temperature of 0 to 200 ° C., a temperature increase rate of 10 ° C./min, and a temperature decrease rate of 10 ° C./min. Analysis is performed based on the data in Heat. The glass transition point is the value of the intersection of the baseline extension before the first endothermic peak rises and the tangent line that shows the maximum slope between the first endothermic peak rising portion and the peak apex.

The mass average molecular weight of the coating resin is preferably 200,000 to 500,000. When the mass average molecular weight of the coating resin is within the above range, an excellent film forming property is exhibited, so that a dense coating layer is formed.
The mass average molecular weight of the coating resin is measured by gel permeation chromatography (GPC) soluble in tetrahydrofuran (THF).
Specifically, the molecular weight measurement by GPC is performed as follows.
That is, using an apparatus “HLC-8220” (manufactured by Tosoh Corporation) and a column “TSKguardcolumn + TSKgelSuperHZM-M3 series” (manufactured by Tosoh Corporation), while maintaining the column temperature at 40 ° C., tetrahydrofuran (THF) was used as a carrier solvent at a flow rate of 0. The sample was run at 2 mL / min, and the sample was dissolved in tetrahydrofuran to a concentration of 50 mg / mL under a dissolution condition in which treatment was performed for 5 minutes using an ultrasonic disperser at room temperature, and then treated with a membrane filter having a pore size of 0.2 μm. A sample solution is obtained, and 10 μL of this sample solution is injected into the apparatus together with the above carrier solvent, detected using a refractive index detector (RI detector), and the molecular weight distribution of the sample is determined by monodisperse polystyrene standard particles. It calculates using the calibration curve measured using. As a standard polystyrene sample for calibration curve measurement, molecular weights manufactured by Pressure Chemical Co., Ltd. are 6 × 10 ² , 2.1 × 10 ³ , 4 × 10 ³ , 1.75 × 10 ⁴ , 5.1 × 10 ⁴ , 1 .1 × 10 ⁵ , 3.9 × 10 ⁵ , 8.6 × 10 ⁵ , 2 × 10 ⁶ , 4.48 × 10 ⁶ , and at least about 10 standard polystyrene samples were measured, and a calibration curve Create A refractive index detector is used as the detector.

[Inorganic fine particles for carriers]
The external additive added to the carrier particles has an average primary particle diameter smaller than that of the inorganic fine particles for toner, and is an inorganic fine particle that is charged with a polarity opposite to the charging property of the inorganic fine particles for toner. The

The average primary particle diameter of the inorganic fine particles for carrier is not particularly limited as long as it is smaller than the average primary particle diameter of the inorganic fine particles for toner, but is preferably 20 to 50 nm, for example.
Since the average primary particle diameter of the inorganic fine particles for carrier is smaller than the average primary particle diameter of the inorganic fine particles for toner, the inorganic fine particles for toner can be sufficiently charged. It can be attached electrostatically.

The average primary particle diameter of the carrier fine inorganic particles is measured as follows.
That is, using a scanning electron microscope (SEM) “JEM-7401F” (manufactured by JEOL Ltd.), an SEM photograph magnified 30,000 times is captured by a scanner, and an image processing analyzer “LUZEX AP” (manufactured by Nireco) Then, the carrier inorganic fine particles of the SEM photographic image are binarized, the horizontal ferret diameter for 100 inorganic carrier fine particles is calculated, and the average value is taken as the average particle diameter.

The carrier inorganic fine particles are charged with a polarity opposite to the chargeability of the toner inorganic fine particles. Specifically, as shown in FIG. 1, the toner inorganic fine particles 10A in the toner 10 are negative in the development region. In the case of charging, the carrier inorganic fine particles 20A in the carrier 20 are positively charged.
The inorganic fine particles for carrier are charged with the opposite polarity to the chargeability of the inorganic fine particles for toner, so that the friction between the inorganic fine particles for toner and the inorganic fine particles for carrier is caused by the stirring action in the developing device. Charging occurs, and as a result, the inorganic fine particles for toner have a large charge, and the inorganic fine particles for toner are electrostatically attached to the toner surface, so that the inorganic fine particles for toner may migrate to the carrier surface. As a result, a decrease in charge imparting ability of the carrier is prevented, and as a result, good charging performance of the toner can be maintained, and a high-quality image can be formed over a long period of time.

  As a combination of the inorganic fine particles for toner and the inorganic fine particles for carrier, when the inorganic fine particles for toner are silica fine particles, the inorganic fine particles for carrier are preferably titanium oxide fine particles or aluminum oxide fine particles. In the case where is a fine particle of titanium oxide, the inorganic fine particle for carrier is preferably a fine silica particle.

  The inorganic fine particles for carrier are preferably those whose surfaces have been subjected to a hydrophobic treatment.

The addition amount of the carrier inorganic fine particles is preferably 0.01 to 0.05% by mass in the carrier, and more preferably 0.02 to 0.04% by mass.
When the amount of inorganic fine particles for carrier is too small, good fluidity may not be obtained for the carrier, and uniformity may not be obtained when mixing with toner, while the amount of inorganic fine particles for carrier added. Is excessively large, the carrier inorganic fine particles are easily detached from the surface of the carrier, and image defects may occur due to the detached carrier inorganic fine particles.

  In the carrier according to the present invention, the method for adding the inorganic fine particles for carrier as an external additive is not particularly limited as long as the inorganic fine particles for carrier are attached to the surface of the carrier particles. For example, dried carrier particles And a dry method in which inorganic fine particles for carrier are added as a powder and mixed. Examples of the mixing device used in this dry method include mechanical mixing devices such as a Henschel mixer and a turbuler mixer.

The carrier particles constituting the carrier preferably have a volume average particle size of 25 to 40 μm, more preferably 30 to 35 μm.
The volume average particle diameter of the carrier is measured by a laser diffraction particle size distribution measuring apparatus “HELOS” (manufactured by SYMPATEC) equipped with a wet disperser.

(Image forming method)
The two-component developer of the present invention can be suitably used for an image forming method by electrophotography. In particular, it can be suitably used for an image forming method of a so-called trickle development method in which excess two-component developer is gradually discharged and new toner and carrier are replenished. It can be suitably used for replenishment in the method. By using the two-component developer of the present invention as a replenisher in the image forming method of the trickle development method, the carrier in the developing device is gradually replaced with a new one, so that the inorganic fine particles for toner migrate to the carrier surface It can suppress more reliably.

The mixing ratio of the toner and the carrier in the two-component developer of the present invention is preferably such that the toner concentration in the two-component developer is 5 to 10% by mass when used in an image forming method other than the trickle development method. More preferably, it is 6-8 mass%.
In the case of using as an initial developer in the trickle-development-type image forming method, that is, to be charged in advance in the developing device before performing an image forming operation such as newly installing an image forming apparatus, the toner in the two-component developer It is preferable that a density | concentration is 5-10 mass%, for example, More preferably, it is 6-8 mass%. When used as a replenisher in the trickle development type image forming method, the toner and carrier mixing ratio is preferably such that the toner concentration in the two-component developer is 60 to 98% by mass, for example. Is 80-96 mass%.

  According to the two-component developer of the present invention, the carrier constituting the two-component developer is formed by externally adding carrier inorganic fine particles having an average primary particle size smaller than that of the toner inorganic fine particles, The inorganic fine particles for carrier are charged with the opposite polarity to the chargeability of the inorganic fine particles for toner, so that the friction between the inorganic fine particles for toner and the inorganic fine particles for carrier is caused by the stirring action in the developing device. Charging occurs, and as a result, the inorganic fine particles for toner have a large charge, and the inorganic fine particles for toner are electrostatically attached to the toner surface, so that the inorganic fine particles for toner migrate to the carrier surface. As a result, it is possible to prevent the charge imparting ability of the carrier from being deteriorated, and as a result, it is possible to maintain good charging performance of the toner, and to maintain the toner for a long period of time. It is possible to form a high quality image.

  Examples of the present invention will be described below, but the present invention is not limited to these examples.

<Toner Production Example 1>
[Preparation of resin particles [A]]
First-stage polymerization In a 5 L reaction vessel equipped with a stirrer, temperature sensor, cooling pipe, and nitrogen introducing device, 8 parts by mass of polyoxyethylene (2) sodium dodecyl ether sulfate was dissolved in 3000 parts by mass of ion-exchanged water. The surfactant solution was charged, and the internal temperature was raised to 80 ° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream.
To this surfactant solution, an initiator solution in which 10 parts by mass of a polymerization initiator (potassium persulfate: KPS) was dissolved in 200 parts by mass of ion-exchanged water was added to make the liquid temperature 80 ° C. The mixture liquid is dropped over 1 hour, and the system is heated and stirred at 80 ° C. for 2 hours to carry out a polymerization (first stage polymerization) reaction, thereby dispersing the resin particles [A1]. [A1] was obtained.
Styrene 480 parts by weight n-butyl acrylate 250 parts by weight Methacrylic acid 68 parts by weight n-octyl-3-mercaptopropionate 16 parts by weight

Second-stage polymerization 7 parts by mass of polyoxyethylene (2) sodium dodecyl ether sulfate was dissolved in 800 parts by mass of ion-exchanged water in a 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction device. A monomer in which a surfactant solution was charged and heated to 98 ° C., and then 260 parts by mass of the above dispersion [A1] was added in terms of solid content, and the following monomer mixture was dissolved at 90 ° C. The solution was added and mixed and dispersed for 1 hour by a mechanical disperser “CLEARMIX” (manufactured by M Technique Co., Ltd.) having a circulation path to prepare a dispersion containing emulsified particles.
Next, an initiator solution in which 6 parts by mass of potassium persulfate was dissolved in 200 parts by mass of ion-exchanged water was added to this dispersion, and this system was heated and stirred at 82 ° C. for 1 hour to perform polymerization (second stage). (Polymerization) reaction was performed to obtain a dispersion [A2] in which the resin particles [A2] were dispersed.
Styrene 245 parts by mass n-butyl acrylate 120 parts by mass n-octyl-3-mercaptopropionate 1.5 parts by mass polyethylene wax 190 parts by mass

Third-stage polymerization To the above dispersion [A2], an initiator solution prepared by dissolving 11 parts by mass of potassium persulfate in 400 parts by mass of ion-exchanged water was added, and the following monomers were added under a temperature condition of 82 ° C. The mixture was added dropwise over 1 hour. After completion of the dropwise addition, the polymerization (third stage polymerization) reaction was performed by heating and stirring for 2 hours, and then cooled to 28 ° C. to obtain a dispersion [A] in which the resin particles [A] were dispersed. .
Styrene 435 parts by weight n-butyl acrylate 130 parts by weight Methacrylic acid 33 parts by weight n-octyl-3-mercaptopropionate 8 parts by weight

[Preparation of resin particles [B]]
A surfactant solution in which 2.3 parts by mass of sodium dodecyl sulfate was dissolved in 3000 parts by mass of ion-exchanged water was charged into a 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introduction apparatus, The internal temperature was raised to 80 ° C. while stirring at a stirring speed of 230 rpm.
To this surfactant solution, an initiator solution in which 10 parts by mass of potassium persulfate was dissolved in 200 parts by mass of ion-exchanged water was added, the temperature of the solution was set to 80 ° C., and the following monomer mixture was added for 1 hour. The mixture was heated and stirred at 80 ° C. for 2 hours to carry out a polymerization reaction, thereby obtaining a dispersion [B] in which resin particles [B] were dispersed.
Styrene 520 parts by weight n-butyl acrylate 210 parts by weight Methacrylic acid 68 parts by weight n-octyl-3-mercaptopropionate 16 parts by weight

[Preparation of Colorant Fine Particle [1]]
11.5 parts by mass of sodium n-dodecyl sulfate was dissolved in 160 parts by mass of ion-exchanged water, and 25 parts by mass of the colorant “CI Pigment Blue 15: 3” was gradually added while stirring the solution. Thereafter, the colorant fine particles [1] having a volume-based median diameter of 220 nm were dispersed by carrying out a dispersion treatment using a stirring means “CLEARMIX W Motion CLM-0.8” (manufactured by M Technique Co., Ltd.). Dispersion liquid [1] was prepared.

(1) Preparation of toner particle [1] Dispersion liquid [A] in which resin particles [A] are dispersed in a 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introducing device in terms of solid content. 300 parts by mass, 120 parts by mass of the dispersion [1] in which the colorant fine particles [1] are dispersed, 1400 parts by mass of ion-exchanged water, and 3 parts by mass of polyoxyethylene (2) sodium dodecyl ether sulfate A solution having a part dissolved in 120 parts by mass of ion-exchanged water was added and the liquid temperature was adjusted to 30 ° C., and then a 5N sodium hydroxide aqueous solution was added to the solution to adjust the pH to 10.
Next, an aqueous solution in which 35 parts by mass of magnesium chloride was dissolved in 35 parts by mass of ion-exchanged water was added over 10 minutes at 30 ° C. with stirring, the mixture was left for 3 minutes, and then the temperature was raised. The particle growth reaction was continued while maintaining the temperature at 90 ° C. In this state, the particle size of the associated particles is measured using “Coulter Multisizer III” (manufactured by Beckman Coulter), and when the volume-based median diameter becomes 3.1 μm, the resin particles [B] are dispersed. 260 parts by mass of the resulting dispersion [B] was added in terms of solid content, and the particle growth reaction was continued. When the volume-based median diameter reaches 6.5 μm, an aqueous solution in which 150 parts by mass of sodium chloride is dissolved in 600 parts by mass of ion-exchanged water is added to stop the particle size growth. This was continued by heating and stirring at 95 ° C. until the average circularity reached 0.965, and then cooled to a liquid temperature of 30 ° C.
Then, solid-liquid separation is performed using a basket type centrifuge “MARK III model number 60 × 40” (manufactured by Matsumoto Kikai Co., Ltd.) to form a wet cake of particles, and this wet cake is separated from the basket type centrifuge. The filtrate is repeatedly washed with ion-exchanged water at 40 ° C. until the electrical conductivity of the filtrate reaches 5 μS / cm, and then transferred to “flash jet dryer” (manufactured by Seishin Enterprise Co., Ltd.), so that the water content becomes 0.5 mass% Was dried to obtain toner particles [1].
The toner particles [1] had a volume-based median diameter (D ₅₀ ) of 6.4 μm and an average circularity of 0.960.

(2) Addition of external additive To 100 parts by mass of this toner particle [1], as an external additive, 0.5 parts by mass of hydrophobic silica fine particles having an average primary particle diameter of 100 nm, hydrophobic silica fine particles (number average) Using a “Henschel mixer” (manufactured by Mitsui Mining Co., Ltd.), 1.0 part by mass of primary particle diameter 12 nm) and 1.0 part by mass of hydrophobic titanium oxide fine particles (number average primary particle diameter 20 nm), at a temperature of 30 ° C., Toner [1] was manufactured by performing external addition treatment with a stirring blade peripheral speed of 35 m / sec and a treatment time of 20 minutes, and removing coarse particles using a sieve having a mesh opening of 45 μm.
The particle diameter and average circularity of the toner particles did not change with the addition of the external additive.

<Toner Production Examples 2 to 6>
In Toner Production Example 1, Toners [2] to [6] were produced in the same manner except that the external additives shown in Table 1 were used instead of hydrophobic silica fine particles having an average primary particle size of 100 nm. did.

<Carrier Production Example 1>
(1) Core Preparation MnO particles [1]: 35mol%, MgO: 14.5mol% , Fe 2 O 3: 50mol% and SrO: raw materials were weighed so that 0.5 mol%, was mixed with water The slurry was obtained by pulverizing with a wet media mill for 5 hours.
The obtained slurry was dried with a spray dryer to obtain true spherical particles. In order to adjust the porosity, the particles were adjusted in particle size, and then heated at 950 ° C. for 2 hours to perform preliminary firing. Next, in order to obtain an appropriate fluidity while increasing the porosity, after pulverizing with a wet ball mill for 1 hour using a stainless steel bead with a diameter of 0.3 cm, further pulverizing with a stainless steel bead with a diameter of 0.15 cm for 4 hours did. To this slurry, an appropriate amount of a dispersant is added, and the strength of granulated particles is secured, and the porosity and continuous porosity are adjusted, and PVA (polyvinyl alcohol) as a binder is 1.5 mass in terms of solid content. Then, granulation and drying were performed by a spray dryer, and the main firing was performed in an electric furnace at a temperature of 1100 ° C. and an oxygen concentration of 0 vol% for 3.5 hours.
Thereafter, it was crushed, further classified to adjust the particle size, and then the low magnetic product was fractionated by magnetic separation to obtain core particles [1].
The core particles [1] had a volume average particle size of 30 μm. This volume average particle diameter is a volume-based average particle diameter measured by a laser diffraction particle size distribution measuring apparatus “HELOS” (manufactured by SYMPATEC) equipped with a wet disperser.

(2) Preparation of coating resin particles [C] 3000 parts by mass of ion-exchanged water prepared by adding 1.7 parts by mass of sodium dodecyl sulfate to a reaction vessel equipped with a stirrer, a temperature sensor, a cooling tube, and a nitrogen introduction apparatus were prepared. The internal temperature was raised to 80 ° C. while stirring this surfactant solution at a stirring speed of 230 rpm under a nitrogen stream. Thereafter, an initiator solution in which 10 parts by mass of potassium persulfate is dissolved in 400 parts by mass of ion-exchanged water is added to the surfactant solution, the liquid temperature is set to 80 ° C., and the following monomer mixture is added for 2 hours. It was dripped over.
And it superposed | polymerized by heating and stirring process at 80 degreeC over 2 hours, and prepared the dispersion liquid [C] in which the resin particle [C] for coating | cover was disperse | distributed.
Cyclohexyl methacrylate 400 parts by weight Methyl methacrylate 400 parts by weight The obtained dispersion [C] was dried with a spray dryer to obtain dried coating resin particles [C].

(3) Resin coating on core particle [1] Using a horizontal rotary blade mixer described in JP-A-6-332267, 3000 parts by mass of core particle [1] and 105 resin particles for coating [C] And mixing and stirring at 22 ° C. for 15 minutes under the condition that the peripheral speed of the horizontal rotary blade is 8 m / second, then heating to 120 ° C. and stirring for 40 minutes to form resin-coated carrier particles [1] Was made.
The carrier particles [1] had a volume average particle size of 32 μm.

(4) Addition of external additive To 100 parts by mass of the carrier particles [1], 0.01 part by mass of hydrophobic titanium oxide fine particles having an average primary particle diameter of 20 nm as an external additive was added to a “Henschel mixer” (Mitsui Mine). The product was externally added at a temperature of 30 ° C. with a peripheral speed of 30 m / sec and a processing time of 10 minutes, and coarse particles were removed using a sieve having an opening of 70 μm, and the carrier [ 1] was produced.
The particle diameter of the carrier particles did not change with the addition of the external additive.

<Carrier Production Examples 2 to 6>
Carriers [2] to [6] were produced in the same manner as in Carrier Production Example 1 except that those shown in Table 2 were used as external additives.

<Preparation Examples 1-13 of Two-Component Developer>
The toners [1] to [6] and the carriers [1] to [6] were mixed for 5 minutes with a shaker “Model-YGG” (manufactured by Yayoi Co., Ltd.) at a toner concentration of 7% by mass according to the combinations shown in Table 3. Two-component developers [1] to [13] were prepared.

<Examples 1-6, Comparative Examples 1-7>
The two-component developers [1] to [13] were introduced into each of the image forming apparatus “bizhub PRO C6501” (manufactured by Konica Minolta Business Technologies) and evaluated as follows.

[Evaluation 1: Charging stability]
Under normal temperature and humidity (20 ° C, 50% RH) environmental conditions, 100,000 sheets were printed on a high quality paper (65g / m ² ) of A4 size to form a strip-shaped solid image with a printing rate of 5%. The charge amount of toner at the initial stage and after printing 100,000 sheets was measured and evaluated according to the following evaluation criteria. The charge amount was measured by sampling the two-component developer in the developing device and using a blow-off charge amount measuring device “TB-200” (manufactured by Toshiba Chemical Corporation).
-Evaluation criteria-
A: The fluctuation value Δ of the toner charge amount is less than 4 μC / g after the initial printing and after 100,000 printing. B: The fluctuation value Δ of the toner charge amount is 4 C / g or more and 8 μC / g after the initial printing and after 100,000 printing. Less than g C: The fluctuation value Δ of the toner charge amount is 8 μC / g or more after the initial printing and after 100,000 printing

[Evaluation 2: Image quality (granularity)]
Under normal temperature and humidity (20 ° C, 50% RH) environmental conditions, 100,000 sheets were printed on a high quality paper (65g / m ² ) of A4 size to form a strip-shaped solid image with a printing rate of 5%. A gradation pattern having a gradation ratio of 32 steps at the initial stage and after printing 100,000 sheets was output, and the graininess of the gradation pattern was evaluated according to the following evaluation criteria. Graininess is evaluated by applying a Fourier transform process considering MTF (Modulation Transfer Function) correction to the reading value of the gradation pattern CCD, and measuring the GI value (Graininess Index) according to the human specific visual sensitivity. The GI value was determined. The smaller the GI value, the better. In addition, this GI value is a value published in Journal of the Imaging Society of Japan 39 (2), 84/93 (2000).
-Evaluation criteria-
A: The fluctuation value Δ of the GI value is less than 0.02 at the initial printing and after 100,000 printing B: The fluctuation value Δ of the GI value is 0.02 or more and less than 0.04 at the initial printing and after 100,000 printing C: GI value fluctuation value Δ is 0.04 or more after initial printing and after 100,000 printing

10 Toner 10A Inorganic fine particles for toner 20 Carrier 20A Inorganic fine particles for carrier

Claims (4)

In a two-component developer comprising a toner and a carrier,
The toner is formed by adding inorganic fine particles having an average primary particle diameter of 60 to 150 nm as an external additive,
The carrier is formed by adding inorganic fine particles having an average primary particle size smaller than the inorganic fine particles in the toner as an external additive,
Inorganic fine particles in the carrier, the charging of the inorganic fine particles in the toner all SANYO is charged to the opposite polarity, and two-component, wherein the average primary particle diameter of 20~50nm development Agent. Inorganic fine particles in the toner are silica fine particles,
The two-component developer according to claim 1, wherein the inorganic fine particles in the carrier are titanium oxide fine particles or aluminum oxide fine particles. Inorganic fine particles in the toner are titanium oxide fine particles,
The two-component developer according to claim 1, wherein the inorganic fine particles in the carrier are silica fine particles. 4. The method according to claim 1 , wherein the two-component developer is used for replenishment in an image forming method of a development system in which extra two-component developer is discharged and new toner and carrier are replenished. The two-component developer described.