JP6237381B2 - Electrostatic image developing carrier, electrostatic image developer, developer cartridge, process cartridge, and image forming apparatus - Google Patents

Description

  The present invention relates to an electrostatic charge image developing carrier, an electrostatic charge image developer, a developer cartridge, a process cartridge, and an image forming apparatus.

  In electrophotography, an electrostatic latent image formed on the surface of an electrostatic latent image holding member (photoreceptor) is developed with toner containing a colorant, and the obtained toner image is transferred to the surface of a recording medium. An image can be obtained by fixing with a heat roll or the like. Further, the latent image holding member is cleaned with the transfer residual toner to form an electrostatic latent image again, and the cleaning process is omitted when there is almost no transfer residual toner as in the case of using spherical toner. In some cases. As described above, dry developers used for electrophotography and the like are divided into a one-component developer using a toner in which a binder is mixed with a colorant and the like, and a two-component developer in which the toner is mixed with a carrier. Broadly divided.

Patent Document 1 states that “a toner composed mainly of a binder resin and a colorant, and a saturation magnetization value of ZnO 5 to 40 mol% and Fe ₂ O ₃ 60 to 95 mol%, and an applied magnetic field of 3000 Oersted. Is an electrophotographic developer characterized by comprising a ferrite carrier having a 70 to 100 emu / g. "

Patent Document 2 states that “a metal having magnetism or an oxide of the metal is used as a core, and the surface of the core is coated with a resin, and satisfies the following formulas (1) and (2): A carrier for developing an electrostatic image.
0.5 × 10 ⁻² ≦ Wc / Wo ≦ 1.6 × 10 ⁻² (1)
1.0 × 10 ⁻² ≦ C · Wc / (Wo + Wc) ≦ 4.3 × 10 ⁻² (2)
However, Wc: Weight of carrier core material coating resin (g), Wo: Weight of carrier core material (g), C: Carbon concentration of carrier (mg / g) ”are disclosed.

  Patent Document 3 states that, in a carrier for developing an electrostatic latent image composed of magnetic core material particles and a coating layer formed on the surface of the core material particles, the carrier has a weight average particle diameter Dw of 22 to 32 μm. The ratio of the weight average particle diameter Dw to the number average particle diameter Dp, Dw / Dp is 1.0 <Dw / Dp <1.2, and the content of particles having a particle diameter smaller than 20 μm is 0 to 7 wt. %, The content of particles having a particle size smaller than 36 μm is 90 to 100% by weight, and the core particles have a log (R1) of electrical resistivity R1 (Ω · cm) at an applied electric field of 50 V / mm, When a DC voltage is applied in the form of a chain of core particles using 1500 Gauss magnetic poles with parallel plate electrodes facing each other with a spacing of 2 mm and a parallel plate electrode of 2 mm, an electric field at an applied electric field of 250 V / mm Resistivity is R2 (Ω · cm), When the electric resistivity at an applied electric field of 50 V / mm is R3 (Ω · cm), the value of Log (R2) / Log (R3) is in the range of 0.85 to 1.0. Latent image developing carrier "is disclosed.

Patent Document 4 states that “a carrier for electrophotographic development having a soft ferrite core material, and the cumulative value of the volume particle size distribution accumulated from the small particle size side of the particles of the carrier for electrophotographic development is 16 wt. % Particle diameter is d ₁₆ , the particle diameter of 50% by weight particle is d ₅₀ , and the particle diameter of 84% by weight particle is d ₈₄ , 20 μm ≦ d ₅₀ ≦ 50 μm, (D ₈₄ −d ₁₆ ) / 2 ≦ (0.25 × d ₅₀ ), and the magnetic force when the core material is in a magnetic field of 1 kOe is in the range of 35 emu / g or more and 75 emu / g or less. The carrier for electrophotographic development characterized by the above. "

Japanese Patent Laid-Open No. 5-134462 JP 2000-66456 A JP 2006-293266 A JP 2006-323211 A

  An object of the present invention is to provide a carrier for developing an electrostatic charge image in which a change in image density is suppressed even when the speed of image formation changes.

  In order to achieve the above object, the following invention is provided.

The invention according to claim 1 includes resin-coated particles in which at least a part of the surface of magnetic particles containing manganese ferrite containing Sr and Si is coated with a resin containing cyclohexyl acrylate resin, and a magnetic field in a magnetic field applied with 1 kOe. 5kOe ratio of magnetization B of the applied magnetic field (B / a) is 1.01 to 1.10 in which the electrostatic image developing carrier with respect of a.
The invention according to claim 2 is characterized in that the resistance of the magnetic particles is 10 ⁶ Ωcm or more and 10 ⁹ Ωcm or less under an electric field of 24000 V / cm in an environment of 30 ° C. and 85% relative humidity. Carrier for developing charge image.
Invention, the 1kOe magnetization A at an applied magnetic field, 60 emu / g or more in a claim 1 or an electrostatic image developing carrier according to claim 2 according to claim 3.

  According to a fourth aspect of the present invention, there is provided an electrostatic charge image developer comprising the electrostatic charge image developing toner and the electrostatic charge image developing carrier according to any one of the first to third aspects.

The invention according to claim 5 is a developer cartridge that contains the electrostatic charge image developer according to claim 4 and is detachable from the image forming apparatus.
The invention according to claim 6 contains the electrostatic charge image developer according to claim 4 and develops the electrostatic charge image formed on the surface of the image carrier as a toner image by the electrostatic charge image developer. And a process cartridge that is detachably attached to the image forming apparatus.
According to a seventh aspect of the present invention, there is provided an image carrier, a charging unit for charging the surface of the image carrier, an electrostatic charge image forming unit for forming an electrostatic image on the charged surface of the image carrier, and 4. A developing unit that contains the electrostatic charge image developer according to claim 4 and develops the electrostatic charge image formed on the surface of the image carrier as a toner image with the electrostatic image developer, and the surface of the image carrier. An image forming apparatus comprising: transfer means for transferring the toner image formed on the surface of the recording medium; and fixing means for fixing the toner image transferred to the surface of the recording medium.

According to the invention of claim 1, comprising magnetic particles containing manganese ferrite, the ratio of the magnetization B at 5kOe applied magnetic field for magnetization A in 1kOe applied magnetic field (B / A) is 1.01 or more Provided is an electrostatic charge image developing carrier in which the change in density of an image is suppressed even when the speed of image formation is changed as compared with an electrostatic charge image developing carrier outside the range of 1.10 or less.

According to the invention of claim 2, when the resistance of the magnetic particles under an electric field of 24000 V / cm in an environment of 30 ° C. and a relative humidity of 85% is outside the range of 10 ⁶ Ωcm to 10 ⁹ Ωcm. In comparison, it is possible to provide an electrostatic charge image developing carrier capable of suppressing image loss even when the image formation speed changes under high temperature and high humidity.

According to the invention of claim 3, compared with the case magnetization A in 1kOe applied magnetic field is less than 60 emu / g, developing an electrostatic image density change in the image even after changing the speed of the image formation is inhibited Carriers are provided.

According to the invention of claim 4, comprising magnetic particles containing manganese ferrite, the ratio of the magnetization B at 5kOe applied magnetic field for magnetization A in 1kOe applied magnetic field (B / A) is 1.10 As compared with the case where the carrier for developing an electrostatic charge image is exceeded, an electrostatic charge image developer is provided in which the change in image density is suppressed even when the speed of image formation changes.

According to the invention of claim 5, 6, 7, has a magnetic particle containing manganese ferrite, the ratio of the magnetization B at 5kOe applied magnetic field for magnetization A in 1kOe applied magnetic field (B / A) is, Compared to the case where a developer including an electrostatic charge image developing carrier exceeding 1.10 is applied, a developer cartridge, a process cartridge, and an image forming apparatus, in which a change in image density is suppressed even when the image forming speed changes, are provided. Provided.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment. It is a schematic block diagram which shows an example of the process cartridge which concerns on this embodiment.

  Hereinafter, an embodiment which is an example of the present invention will be described in detail.

<Carrier for developing electrostatic image>
The electrostatic image developing carrier according to the present embodiment has a magnetic particle containing manganese ferrite, the ratio of the magnetization B at 5kOe applied magnetic field for magnetization A in 1kOe applied magnetic field (B / A) is 1 .01 or more and 1.10 or less.

  When an electrostatic charge image developer (hereinafter, also referred to as “developer”) including the electrostatic charge image developing carrier (hereinafter sometimes referred to as “carrier”) according to the present embodiment is used, an image is obtained. Even if the formation speed changes, the change in the density of the image is suppressed. The reason is not clear, but is presumed as follows.

  In general, image formation by electrophotography is performed in the following steps. The developer in the developing device is stirred and the developer is charged. The charged developer is conveyed to a developer holding member of the developing device, and the electrostatic latent image formed on the surface of the opposite electrophotographic photosensitive member is developed with toner. At this time, a magnetic brush made of the developer based on the magnetic force is formed on the developer holder. The magnetic brush is a phenomenon in which the developer spikes around the carrier, which is a magnetic material, along the magnetic force lines of the developer holder.

  A magnetic brush has an influence on the image due to its density and the length of the ears. When the printing speed is fast, the rotation of the developer holder becomes faster. When the developer holding member rotates rapidly, the followability of magnetic brush formation is deteriorated, the density of the magnetic brush is low, and the heading tends to be shortened. In this case, reduction in image density and unevenness are likely to occur. Conversely, when the printing speed is slow, the rotation of the developer holder is slow. If the rotation of the developer holding member is slow, the density of the magnetic brush increases and the earing tends to be long. In this case, unevenness in image density or white spots due to transfer of the carrier to the photoconductor is likely to occur. In general, parameters are adjusted at a certain printing speed, but it is difficult to cover a printing area from high speed to low speed.

In the present embodiment, a stable image can be obtained even when the printing speed is changed by setting the applied magnetic field dependence of the magnetization of the carrier containing manganese ferrite in a specific range.
A magnetic carrier having a small magnetic field dependency with respect to a change in printing speed has a small fluctuation of the magnetic brush. Carriers having a small change in magnetization relative to a change in magnetic field have a fast magnetization rise and small fluctuations in magnetization. For this reason, it is considered that the magnetic brush changes less easily because the magnetization is stabilized early and the fluctuation is small with respect to the change in the rotation speed of the developer holding member due to the change in the printing speed.

Moreover, when the ferrite used for the core of the carrier is manganese ferrite, the balance between magnetization and resistance is good. Manganese tends to increase magnetization as a constituent ion of ferrite, and resistance is difficult to decrease. For this reason, it is considered that scattering of the carrier onto the photosensitive member is suppressed.
A carrier comprising a Mn ferrite, the ratio of magnetization A of magnetization of the carrier is in the magnetization B and 1kOe applied magnetic field at 5kOe applied magnetic field (B / A) is 1.01 or more, it is 1.10 or less, high speed It is considered that the transfer of the carrier to the photoconductor can be suppressed even under printing conditions from low to low.

Further, the toner and the carrier in the developer at high temperature and high humidity are likely to transfer the carrier to the photoreceptor due to charge injection from the toner. In particular, the carrier according to the present embodiment is less dependent on the magnetic field of magnetization and has a high temperature and high humidity (30 ° C., 85% RH) under an electric field of 24,000 V / cm. When the resistance of the magnetic particles is 10 ⁶ Ωcm or more and 10 ⁹ Ωcm or less, it is considered that the transfer of the carrier to the photoreceptor is suppressed even under high temperature and high humidity and printing conditions from high speed to low speed.

  Next, the physical properties of the carrier according to this embodiment will be described.

- magnetization -
Carrier according to the present embodiment, the ratio of the magnetization B at 5kOe applied magnetic field for magnetization A in 1kOe applied magnetic field (B / A) is, is 1.01 to 1.10, preferably, 1. 02 or more and 1.07 or less.
When the above-mentioned magnetization ratio (B / A) of the carrier is less than 1.01, there is a case where the carrier is easily aggregated when the carrier is separated from the developer holding member and returned to the developing device. On the other hand, when the magnetization ratio (B / A) exceeds 1.10, the rise of magnetization is slow, and the magnetic brush is likely to fluctuate and image loss may occur.

Carrier according to the present embodiment is preferably magnetization A in 1kOe applied magnetic field is 40 emu / g or more, more preferably 50 emu / g or more, more preferably 60 emu / g or more. The upper limit of the magnetization A in 1kOe applied magnetic field is not particularly limited, but is generally less 64emu / g.

The carrier according to the present embodiment is preferably the magnetization B at 5kOe applied magnetic field is less than 41emu / g or more 70 emu / g, more preferably not more than 51emu / g or more 66emu / g.

  The magnetic characteristics of the carrier according to the present embodiment are measured by a method of an example described later using a vibration sample type magnetometer VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.).

-Carrier resistance-
In the carrier according to this embodiment, the resistance of the magnetic particles constituting the carrier is preferably 10 ⁶ Ωcm or more and 10 ⁹ Ωcm or less under an electric field of 24000 V / cm at 30 ° C. and 85% RH. More preferably, it is 10 Ωcm or more and 10 ⁸ Ωcm or more. In some cases, magnetic particles are used as they are for the carrier, but in general, resin coating is often performed in consideration of the charging property with the toner. The resistance of the resin-coated carrier is greatly influenced by the resin. Particularly, when the relationship between the electric field and the resistance is observed, the resistance of the low electric field is strongly influenced by the resin. However, in an electric field with a high electric field (24000 V / cm or more), the resistance of the magnetic particles has a stronger influence than the resin. For this reason, it is necessary to control the resistance of the magnetic particles with respect to the resistance of the carrier in the vicinity of 24000 V / cm.
When the resistance of the magnetic particles is 10 ⁶ Ωcm or more, charge injection to the carrier is difficult to occur, and image defects (white spots) due to carrier transfer to the photoreceptor are difficult to occur. On the other hand, when the resistance of the magnetic particles is 10 ⁹ Ωcm or less, the image density is suppressed from being lowered.

  In addition, the resistance of the magnetic particles according to this embodiment is measured by a method of an example described later.

  Next, materials constituting the carrier according to the present embodiment will be described.

(Magnetic particles)
The carrier according to the present embodiment has magnetic particles containing manganese ferrite as a core material. Manganese ferrite contains at least Fe and Mn as metals and has a good balance between magnetization and resistance. Manganese ferrite contained in the magnetic particles according to the present embodiment may contain metals other than Fe and Mn, and examples thereof include Mn—Mg ferrite and Mn—Zn ferrite.
The magnetic particles according to this embodiment, if 5kOe ratio of magnetization B of the applied magnetic field (B / A) is 1.01 to 1.10 or less for the magnetization A in 1kOe applied magnetic field, manganese ferrite As other ferrite, for example, magnetite may be included.

  The method for producing magnetic particles containing manganese ferrite according to the present embodiment is not particularly limited, but can be produced, for example, as follows.

  Hereinafter, an example of a method for producing magnetic particles containing manganese ferrite according to the present embodiment will be described by showing specific materials and conditions, but the magnetic particles according to the present embodiment are limited to the materials and numerical values described below. Is not to be done.

Fe ₂ O ₃ and Mn (OH) ₂ are mixed so that Fe and Mn are in a molar ratio of 2: 1, 0.6% by mass of SrCO ₃ is added, and 1000 ° C. while flowing in a rotary kiln, Heat for 2 hours (preliminary firing) and mix.
Next, a dispersant, water, polyvinyl alcohol as a binder resin, and 1.0% by mass silica of the mixture are added to this mixture, and mixed and pulverized by a wet ball mill. When the pulverized particle size becomes 1 μm or less in terms of volume average particle size, 0.1% by mass of carbon black is further added to the mixture, and pulverization and mixing are further performed for 30 minutes, and then pulverization is stopped.
Next, granulation and drying are performed with a spray dryer so that the particles have a volume average particle diameter of 38 μm.
Next, the dried particles are heated to 1400 ° C. in an electric furnace, and calcination is performed for 4 hours while adjusting the oxygen concentration to 1% in a mixed gas of oxygen and nitrogen.
After firing, heating is performed at 950 ° C. for 2 hours in the atmospheric state.
Thereafter, ferrite particles having a volume average particle size of 35 μm are obtained through a crushing step and a classification step.

According to the method as described above, crystallization is likely to proceed uniformly by causing a slight amount of ferritization in the pre-firing, and further dispersing the carbon therein and performing the firing. Further, the presence of silica dispersed in the interior and slightly uniform presence at the ferrite grain interface can reduce the magnetization sensitivity to the magnetic field.
The resistance value at 30 ° C. and 85% RH can be controlled by the heating conditions after firing. The heating time is, for example, 1 hour or more and 3 hours or less, and the resistance decreases even if it is short or long.

Examples of the volume average particle diameter (D50v) of the magnetic particles used in this embodiment include 30 μm or more and 50 μm or less.
The volume average particle size of the magnetic particles and pulverized particles is a value measured with a laser diffraction particle size distribution analyzer LA-700 (manufactured by Horiba, Ltd.). With respect to the particle size range (channel) obtained by dividing the obtained particle size distribution, the volume average particle size (D50v) is defined as a particle size that becomes 50% cumulative by subtracting the volume cumulative distribution from the small particle size side.

  The carrier according to the present embodiment may be composed only of magnetic particles containing manganese ferrite, or may be a resin-coated carrier in which at least a part of the surface of the magnetic particles is coated with a resin.

  Examples of the resin (coating resin) for coating the magnetic particles include polyethylene, polypropylene, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl ether, polyvinyl ketone, vinyl chloride-vinyl acetate copolymer, styrene. -Acrylic acid copolymer, cyclohexyl acrylate resin, cyclohexyl methacrylate resin, straight silicone resin comprising an organosiloxane bond or a modified product thereof, fluororesin, polyester, polycarbonate, phenol resin, epoxy resin and the like.

For example, the coating resin may contain other additives such as a conductive material.
Examples of the conductive particles include metal oxides such as carbon black, various metal powders, titanium oxide, tin oxide, magnetite, and ferrite. These may be used individually by 1 type and may use 2 or more types together. Among these, carbon black particles are desirable from the viewpoints of production stability, cost, conductivity, and the like. The type of carbon black is not particularly limited, but carbon black having a DBP oil absorption of about 50 ml / 100 g or more and 250 ml / 100 g or less is preferable because of excellent production stability.

In order to coat the surfaces of magnetic particles with a coating resin, for example, a method of coating with a coating resin and a coating layer forming solution in which various additives are dissolved in an appropriate solvent as necessary may be mentioned. The solvent is not particularly limited, and may be selected in consideration of the coating resin to be used, coating suitability, and the like.
Specific resin coating methods include a dipping method in which magnetic particles are immersed in a coating layer forming solution, a spray method in which the coating layer forming solution is sprayed on the surface of the core material, and magnetic particles are suspended in flowing air. Examples thereof include a fluidized bed method in which a coating layer forming solution is sprayed, a kneader coater method in which the magnetic particles of the carrier and the coating layer forming solution are mixed in a kneader coater, and the solvent is removed.

  Here, the coating amount of the coating resin layer on the magnetic particles is, for example, 0.5% by mass or more (preferably 0.7% by mass or more and 6% by mass or less, more preferably 1.0% by mass with respect to the mass of the entire carrier. % To 5.0% by mass).

Here, the coating amount is obtained as follows.
In the case of a solvent-soluble coating resin, a precise amount of carrier is dissolved in a soluble solvent (for example, toluene), the magnetic powder is held by a magnet, and the solution in which the coating resin is dissolved is washed away. By repeating this several times, the magnetic powder from which the clothing resin has been removed remains. The coating amount is calculated by drying, measuring the mass of the magnetic powder, and dividing the difference by the carrier amount.
Specifically, 20.0 g of the carrier is measured, put into a beaker, 100 g of toluene is added, and the mixture is stirred with a stirring blade for 10 minutes. A magnet is applied to the bottom of the beaker, and toluene is allowed to flow so that the core material (magnetic powder) does not flow out. This is repeated 4 times, and the beaker after washing is dried. After drying, the amount of magnetic powder is measured, and the coating amount is calculated by the formula [(carrier amount−magnetic powder amount after washing) / carrier amount].
On the other hand, in the case of a solvent-insoluble coating resin, Rigaku's Thermo plus EVOII differential type differential thermobalance TG8120 is heated in a nitrogen atmosphere in the range of room temperature (25 ° C.) to 1000 ° C., and its mass is reduced. From this, the coating amount is calculated.

<Electrostatic image developer>
An electrostatic charge image developer according to the exemplary embodiment (hereinafter, appropriately referred to as a developer) includes an electrostatic charge image developing toner and the above-described electrostatic charge image development carrier.
The toner contained in the developer according to the exemplary embodiment includes toner particles and, if necessary, an external additive.

(Toner particles)
The toner particles include, for example, a binder resin and, if necessary, a colorant, a release agent, and other additives.

-Binder resin-
Examples of the binder resin include styrenes (eg, styrene, parachlorostyrene, α-methylstyrene, etc.), (meth) acrylic acid esters (eg, methyl acrylate, ethyl acrylate, n-propyl acrylate, acrylic acid). n-butyl, lauryl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, etc.), ethylenically unsaturated nitriles (for example, acrylonitrile, Methacrylonitrile, etc.), vinyl ethers (eg, vinyl methyl ether, vinyl isobutyl ether, etc.), vinyl ketones (vinyl methyl ketone, vinyl ethyl ketone, vinyl isopropenyl ketone, etc.), olefins (eg, ethylene, propylene, etc.) Emissions, a homopolymer of a monomer such as butadiene) and the like, or a vinyl-based resin composed of these monomers with two or more combinations copolymer.
As the binder resin, for example, epoxy resin, polyester resin, polyurethane resin, polyamide resin, cellulose resin, polyether resin, non-vinyl resin such as modified rosin, a mixture of these with the vinyl resin, or these Examples also include a graft polymer obtained by polymerizing a vinyl monomer in the coexistence.
These binder resins may be used alone or in combination of two or more.

  The content of the binder resin is, for example, preferably 40% by weight to 95% by weight, more preferably 50% by weight to 90% by weight, and more preferably 60% by weight to 85% by weight with respect to the entire toner particles. Further preferred.

-Colorant-
Examples of the colorant include carbon black, chrome yellow, hansa yellow, benzidine yellow, selenium yellow, quinoline yellow, pigment yellow, permanent orange GTR, pyrazolone orange, vulcan orange, watch young red, permanent red, brilliantamine 3B, brilliant. Carmine 6B, Dupont Oil Red, Pyrazolone Red, Resol Red, Rhodamine B Lake, Lake Red C, Pigment Red, Rose Bengal, Aniline Blue, Ultramarine Blue, Calco Oil Blue, Methylene Blue Chloride, Phthalocyanine Blue, Pigment Blue, Phthalocyanine Green, Various pigments such as malachite green oxalate, or acridine series, xanthene series, azo series Various dyes such as benzoquinone, azine, anthraquinone, thioindico, dioxazine, thiazine, azomethine, indico, phthalocyanine, aniline black, polymethine, triphenylmethane, diphenylmethane, and thiazole Can be mentioned.
A colorant may be used individually by 1 type and may use 2 or more types together.

  As the colorant, a surface-treated colorant may be used as necessary, or it may be used in combination with a dispersant. A plurality of colorants may be used in combination.

  The content of the colorant is, for example, preferably 1% by mass or more and 30% by mass or less, and more preferably 3% by mass or more and 15% by mass or less with respect to the entire toner particles.

-Release agent-
Examples of mold release agents include hydrocarbon waxes; natural waxes such as carnauba wax, rice wax, and candelilla wax; synthetic or mineral / petroleum waxes such as montan wax; and ester waxes such as fatty acid esters and montanic acid esters. And so on. The release agent is not limited to this.

The melting temperature of the release agent is preferably 50 ° C. or higher and 110 ° C. or lower, and more preferably 60 ° C. or higher and 100 ° C. or lower.
The melting temperature is determined from the DSC curve obtained by differential scanning calorimetry (DSC) according to the “melting peak temperature” described in JIS K-1987 “Method for measuring the transition temperature of plastics”.

  The content of the release agent is, for example, preferably 1% by mass to 20% by mass and more preferably 5% by mass to 15% by mass with respect to the entire toner particles.

-Other additives-
Examples of other additives include known additives such as a magnetic material, a charge control agent, and inorganic powder. These additives are contained in the toner particles as internal additives.

-Toner particle characteristics-
The toner particles may be toner particles having a single layer structure, or toner particles having a so-called core / shell structure composed of a core (core particle) and a coating layer (shell layer) covering the core. May be.
Here, the core / shell structure toner particles include, for example, a core portion including a binder resin and, if necessary, other additives such as a colorant and a release agent, and a binder resin. It is good to be comprised with the comprised coating layer.

  The volume average particle diameter (D50v) of the toner particles is preferably 2 μm or more and 10 μm or less, and more preferably 4 μm or more and 8 μm or less.

The various average particle diameters and various particle size distribution indexes of the toner particles are measured using Coulter Multisizer II (manufactured by Beckman-Coulter), and the electrolyte is measured using ISOTON-II (manufactured by Beckman-Coulter). The
In the measurement, 0.5 mg to 50 mg of a measurement sample is added as a dispersant to 2 ml of a 5% aqueous solution of a surfactant (preferably sodium alkylbenzenesulfonate). This is added to 100 ml or more and 150 ml or less of the electrolytic solution.
The electrolyte in which the sample is suspended is dispersed for 1 minute with an ultrasonic disperser, and the particle size distribution of particles having a particle size in the range of 2 μm to 60 μm is measured using a 100 μm aperture with a Coulter Multisizer II. taking measurement. The number of particles to be sampled is 50,000.
A cumulative distribution is drawn from the smaller diameter side to the particle size range (channel) divided based on the measured particle size distribution, and the cumulative particle size of 16% is the volume particle size D16v. D16p, a particle size that is 50% cumulative is defined as a volume average particle size D50v, a cumulative number average particle size D50p, and a particle size that is 84% cumulative is defined as a volume particle size D84v and a number particle size D84p.
Using these, the volume average particle size distribution index (GSDv) is calculated as (D84v / D16v) ^1/2 and the number average particle size distribution index (GSDp) is calculated as (D84p / D16p) ^1/2 .

  The shape factor SF1 of the toner particles is preferably 110 or more and 150 or less, and more preferably 120 or more and 140 or less.

The shape factor SF1 is obtained by the following formula.
Formula: SF1 = (ML ² / A) × (π / 4) × 100
In the above formula, ML represents the absolute maximum length of the toner, and A represents the projected area of the toner.
Specifically, the shape factor SF1 is quantified mainly by analyzing a microscope image or a scanning electron microscope (SEM) image using an image analyzer, and is calculated as follows. That is, by capturing an optical microscope image of particles dispersed on the surface of a slide glass into a Luzex image analyzer using a video camera, obtaining the maximum length and projected area of 100 particles, calculating by the above formula, and obtaining the average value can get.

(External additive)
Examples of the external additive include inorganic particles. As the inorganic particles, SiO ₂ , TiO ₂ , Al ₂ O ₃ , CuO, ZnO, SnO ₂ , CeO ₂ , Fe ₂ O ₃ , MgO, BaO, CaO, K ₂ O, Na ₂ O, ZrO ₂ , CaO. _{SiO 2, K 2 O · (} TiO 2) n, Al 2 O 3 · 2SiO 2, CaCO 3, MgCO 3, BaSO 4, MgSO 4 , and the like.

The surface of the inorganic particles as an external additive is preferably subjected to a hydrophobic treatment. The hydrophobic treatment is performed, for example, by immersing inorganic particles in a hydrophobic treatment agent. The hydrophobizing agent is not particularly limited, and examples thereof include silane coupling agents, silicone oils, titanate coupling agents, and aluminum coupling agents. These may be used individually by 1 type and may use 2 or more types together.
The amount of the hydrophobizing agent is usually, for example, 1 part by mass or more and 10 parts by mass with respect to 100 parts by mass of the inorganic particles.

  Examples of external additives include resin particles (resin particles such as polystyrene, PMMA, and melamine resin), cleaning activators (for example, metal salts of higher fatty acids typified by zinc stearate, particles of a fluorine-based high molecular weight substance), and the like. Can be mentioned.

  The external addition amount of the external additive is, for example, preferably 0.01% by mass or more and 5% by mass or less, and more preferably 0.01% by mass or more and 2.0% by mass or less with respect to the toner particles.

(Toner production method)
Next, a toner manufacturing method according to this embodiment will be described.
The toner according to the exemplary embodiment can be obtained by externally adding an external additive to the toner particles after the toner particles are manufactured.

The toner particles may be produced by any of a dry production method (for example, a kneading and pulverizing method) and a wet production method (for example, an aggregation coalescence method, a suspension polymerization method, a dissolution suspension method, etc.). The production method of the toner particles is not particularly limited, and a known production method is adopted.
Among these, it is preferable to obtain toner particles by an aggregation and coalescence method.

  The toner according to the exemplary embodiment is manufactured, for example, by adding an external additive to the obtained dry toner particles and mixing them. Mixing may be performed, for example, with a V blender, a Henschel mixer, a Ladyge mixer, or the like. Furthermore, if necessary, coarse toner particles may be removed using a vibration classifier, a wind classifier, or the like.

  In the developer according to the exemplary embodiment, the mixing ratio (mass ratio) of the toner and the carrier is preferably toner: carrier = 1: 100 to 30: 100, and more preferably 3: 100 to 20: 100.

<Image Forming Apparatus / Image Forming Method>
The image forming apparatus / image forming method according to the present embodiment will be described.
The image forming apparatus according to the present embodiment includes an image carrier, a charging unit that charges the surface of the image carrier, an electrostatic image forming unit that forms an electrostatic image on the surface of the charged image carrier, and an electrostatic charge. Development means for containing an image developer and developing the electrostatic image formed on the surface of the image carrier as a toner image with the electrostatic image developer, and the toner image formed on the surface of the image carrier as a recording medium Transfer means for transferring to the surface of the recording medium, and fixing means for fixing the toner image transferred to the surface of the recording medium. The electrostatic charge image developer according to this embodiment is applied as the electrostatic charge image developer.

  In the image forming apparatus according to this embodiment, a charging process for charging the surface of the image carrier, an electrostatic charge image forming process for forming an electrostatic image on the surface of the charged image carrier, and an electrostatic charge according to this embodiment. A developing step of developing an electrostatic charge image formed on the surface of the image carrier as a toner image with an image developer; a transfer step of transferring the toner image formed on the surface of the image carrier to the surface of the recording medium; An image forming method (an image forming method according to the present embodiment) including a fixing step of fixing the toner image transferred onto the surface of the recording medium is performed.

The image forming apparatus according to the present embodiment is a direct transfer type apparatus that directly transfers a toner image formed on the surface of an image carrier to a recording medium; the toner image formed on the surface of the image carrier is transferred to an intermediate transfer member An intermediate transfer type apparatus that primarily transfers the toner image transferred to the surface of the intermediate transfer body and then secondary transfer the toner image to the surface of the recording medium; after the toner image is transferred, the surface of the image carrier before charging is cleaned. An apparatus provided with a cleaning unit; a known image forming apparatus such as an apparatus provided with a charge removing unit that discharges the surface of an image holding member by irradiating a discharge light after charging a toner image and before charging is applied.
In the case of an intermediate transfer type apparatus, the transfer means includes, for example, an intermediate transfer body on which a toner image is transferred to the surface, and a primary transfer that primarily transfers the toner image formed on the surface of the image holding body to the surface of the intermediate transfer body. And a secondary transfer unit that secondarily transfers the toner image transferred onto the surface of the intermediate transfer member onto the surface of the recording medium.

  In the image forming apparatus according to the present embodiment, for example, the part including the developing unit may have a cartridge structure (process cartridge) that is detachable from the image forming apparatus. As the process cartridge, for example, a process cartridge that accommodates the electrostatic charge image developer according to this embodiment and includes a developing unit is preferably used.

  Hereinafter, an example of the image forming apparatus according to the present embodiment will be described, but the present invention is not limited thereto. In addition, the main part shown to a figure is demonstrated and the description is abbreviate | omitted about others.

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to the present embodiment.
The image forming apparatus shown in FIG. 1 is a first to first electrophotographic method that outputs yellow (Y), magenta (M), cyan (C), and black (K) images based on color-separated image data. Fourth image forming units 10Y, 10M, 10C, and 10K (image forming means) are provided. These image forming units (hereinafter sometimes simply referred to as “units”) 10Y, 10M, 10C, and 10K are arranged in parallel at a predetermined distance from each other in the horizontal direction. The units 10Y, 10M, 10C, and 10K may be process cartridges that are detachable from the image forming apparatus.

Above each of the units 10Y, 10M, 10C, and 10K, an intermediate transfer belt 20 as an intermediate transfer member is extended through each unit. The intermediate transfer belt 20 is provided by being wound around a drive roll 22 and a support roll 24 that are in contact with the inner surface of the intermediate transfer belt 20 that are spaced apart from each other in the left to right direction in the drawing. The vehicle travels in the direction toward the unit 10K. The support roll 24 is applied with a force in a direction away from the drive roll 22 by a spring or the like (not shown), and tension is applied to the intermediate transfer belt 20 wound around the support roll 24. An intermediate transfer member cleaning device 30 is provided on the side of the image carrier of the intermediate transfer belt 20 so as to face the drive roll 22.
Further, each of the developing devices (developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K has yellow, magenta, cyan, and black contained in the toner cartridges 8Y, 8M, 8C, and 8K. The toner including the four color toners is supplied.

  Since the first to fourth units 10Y, 10M, 10C, and 10K have the same configuration, here, the first unit that forms a yellow image disposed on the upstream side in the intermediate transfer belt traveling direction. 10Y will be described as a representative. It should be noted that reference numerals with magenta (M), cyan (C), and black (K) are attached to the same parts as those of the first unit 10Y instead of yellow (Y). Description of the units 10M, 10C, and 10K will be omitted.

The first unit 10Y includes a photoreceptor 1Y that functions as an image holding member. Around the photoreceptor 1Y, a charging roll (an example of a charging unit) 2Y for charging the surface of the photoreceptor 1Y to a predetermined potential, and the charged surface is exposed by a laser beam 3Y based on a color-separated image signal. Then, an exposure device (an example of an electrostatic image forming unit) 3 that forms an electrostatic image, and a developing device (an example of a developing unit) 4Y that develops the electrostatic image by supplying toner charged to the electrostatic image, developed A primary transfer roll 5Y (an example of a primary transfer unit) that transfers a toner image onto the intermediate transfer belt 20, and a photoconductor cleaning device (an example of a cleaning unit) 6Y that removes toner remaining on the surface of the photoconductor 1Y after the primary transfer. Are arranged in order.
The primary transfer roll 5Y is disposed inside the intermediate transfer belt 20, and is provided at a position facing the photoreceptor 1Y. Further, a bias power source (not shown) for applying a primary transfer bias is connected to each of the primary transfer rolls 5Y, 5M, 5C, and 5K. Each bias power source varies the transfer bias applied to each primary transfer roll under the control of a control unit (not shown).

Hereinafter, an operation of forming a yellow image in the first unit 10Y will be described.
First, prior to operation, the surface of the photoreceptor 1Y is charged to a potential of −600V to −800V by the charging roll 2Y.
The photoreceptor 1Y is formed by laminating a photosensitive layer on a conductive substrate (for example, volume resistivity at 20 ° C .: 1 × 10 ⁻⁶ Ωcm or less). This photosensitive layer usually has a high resistance (general resin resistance), but has a property that the specific resistance of the portion irradiated with the laser beam changes when irradiated with the laser beam 3Y. Therefore, a laser beam 3Y is output to the surface of the charged photoreceptor 1Y via the exposure device 3 in accordance with yellow image data sent from a control unit (not shown). The laser beam 3Y is applied to the photosensitive layer on the surface of the photoreceptor 1Y, whereby an electrostatic charge image having a yellow image pattern is formed on the surface of the photoreceptor 1Y.

The electrostatic charge image is an image formed on the surface of the photoreceptor 1Y by charging, and the specific resistance of the irradiated portion of the photosensitive layer is lowered by the laser beam 3Y, and the charged charge on the surface of the photoreceptor 1Y flows. On the other hand, this is a so-called negative latent image formed by the charge remaining in the portion not irradiated with the laser beam 3Y.
The electrostatic charge image formed on the photoreceptor 1Y is rotated to a predetermined development position as the photoreceptor 1Y travels. At this development position, the electrostatic charge image on the photoreceptor 1Y is visualized (developed image) as a toner image by the developing device 4Y.

  In the developing device 4Y, for example, an electrostatic charge image developer including at least yellow toner and the carrier according to the present embodiment is accommodated. The yellow toner is triboelectrically charged by being agitated inside the developing device 4Y, and has a charge of the same polarity (negative polarity) as the charged electric charge on the photoreceptor 1Y, and has a developer roll (a developer holding member). Example) is held on. As the surface of the photoreceptor 1Y passes through the developing device 4Y, the yellow toner is electrostatically attached to the latent image portion on the surface of the photoreceptor 1Y, and the latent image is developed with the yellow toner. . The photoreceptor 1Y on which the yellow toner image is formed continues to run at a predetermined speed, and the toner image developed on the photoreceptor 1Y is conveyed to a predetermined primary transfer position.

When the yellow toner image on the photoreceptor 1Y is conveyed to the primary transfer, a primary transfer bias is applied to the primary transfer roll 5Y, and an electrostatic force from the photoreceptor 1Y toward the primary transfer roll 5Y is applied to the toner image, so that the photoreceptor is exposed. The toner image on 1Y is transferred onto the intermediate transfer belt 20. The transfer bias applied at this time has a (+) polarity opposite to the polarity (−) of the toner, and is controlled to +10 μA by the control unit (not shown) in the first unit 10Y, for example.
On the other hand, the toner remaining on the photoreceptor 1Y is removed and collected by the photoreceptor cleaning device 6Y.

Further, the primary transfer bias applied to the primary transfer rolls 5M, 5C, and 5K after the second unit 10M is also controlled in accordance with the first unit.
Thus, the intermediate transfer belt 20 onto which the yellow toner image has been transferred by the first unit 10Y is sequentially conveyed through the second to fourth units 10M, 10C, and 10K, and the toner images of the respective colors are superimposed and transferred in a multiple manner. The

  The intermediate transfer belt 20 on which the four color toner images are transferred in multiple ways through the first to fourth units is disposed on the image transfer surface side of the intermediate transfer belt 20, the support roll 24 in contact with the inner surface of the intermediate transfer belt 20. The secondary transfer roll (an example of a secondary transfer unit) 26 is formed to a secondary transfer portion configured. On the other hand, a recording paper (an example of a recording medium) P is fed at a predetermined timing into a gap where the secondary transfer roll 26 and the intermediate transfer belt 20 are in contact via a supply mechanism, and the secondary transfer bias is supplied to the support roll. 24. The transfer bias applied at this time is a (−) polarity that is the same polarity as the polarity (−) of the toner, and an electrostatic force from the intermediate transfer belt 20 toward the recording paper P is applied to the toner image, so The toner image is transferred onto the recording paper P. The secondary transfer bias at this time is determined according to the resistance detected by a resistance detection means (not shown) for detecting the resistance of the secondary transfer portion, and is voltage-controlled.

  Thereafter, the recording paper P is fed into the pressure contact portions (nip portions) of a pair of fixing rolls in a fixing device (an example of a fixing unit) 28, and the toner image is fixed on the recording paper P to form a fixed image.

Examples of the recording paper P to which the toner image is transferred include plain paper used in electrophotographic copying machines, printers, and the like. In addition to the recording paper P, the recording medium may be an OHP sheet.
In order to further improve the smoothness of the image surface after fixing, the surface of the recording paper P is also preferably smooth. For example, coated paper with the surface of plain paper coated with resin, art paper for printing, etc. are preferably used. Is done.

  The recording paper P on which the color image has been fixed is carried out toward the discharge unit, and a series of color image forming operations is completed.

<Process cartridge / Developer cartridge>
The process cartridge according to this embodiment will be described.
The process cartridge according to the present embodiment accommodates the electrostatic charge image developer according to the present embodiment, and develops the electrostatic charge image formed on the surface of the image carrier as a toner image by the electrostatic charge image developer. And a process cartridge that can be attached to and detached from the image forming apparatus.

  Note that the process cartridge according to the present embodiment is not limited to the above-described configuration, and other means such as a developing device and other units such as an image carrier, a charging unit, an electrostatic charge image forming unit, and a transfer unit, if necessary. And at least one selected from the above.

  Hereinafter, an example of the process cartridge according to the present embodiment will be shown, but the present invention is not limited to this. In addition, the main part shown to a figure is demonstrated and the description is abbreviate | omitted about others.

FIG. 2 is a schematic configuration diagram showing a process cartridge according to the present embodiment.
The process cartridge 200 shown in FIG. 2 is provided around the photoconductor 107 and the photoconductor 107 by, for example, a housing 117 provided with an attachment rail 116 and an opening 118 for exposure. A charging roller 108 (an example of a charging unit), a developing device 111 (an example of a developing unit), and a photoconductor cleaning device 113 (an example of a cleaning unit) are integrally combined and held to form a cartridge. Yes.
In FIG. 2, 109 is an exposure device (an example of an electrostatic charge image forming unit), 112 is a transfer device (an example of a transfer unit), 115 is a fixing device (an example of a fixing unit), and 300 is a recording paper (a recording medium). An example).

Next, the developer cartridge according to this embodiment will be described.
The developer cartridge according to the present embodiment is a developer cartridge that houses the developer according to the present embodiment and is detachable from the image forming apparatus.
For example, in the image forming apparatus shown in FIG. 1, the toner cartridges 8Y, 8M, 8C, and 8K may be developer cartridges according to the present embodiment. When the developer stored in the cartridge becomes low, the cartridge is replaced.

EXAMPLES Hereinafter, although this invention is demonstrated more concretely based on an Example and a comparative example, this invention is not limited to a following example at all.
Unless otherwise specified, “part” means “part by mass”.

[Production of Toner 1]

(Colorant dispersion 1)
Cyan pigment: Copper phthalocyanine B15: 3 (manufactured by Dainichi Seika Kogyo Co., Ltd.) 50 parts by mass Anionic surfactant: Neogen SC (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) 5 parts by mass Ion-exchanged water 200 parts by mass

  The above were mixed, and dispersed for 5 minutes with an Ultra-Turrax made by IKA and further for 10 minutes with an ultrasonic bath to obtain a colorant dispersion 1 having a solid content of 21% by mass. It was 160 nm when the volume average particle diameter was measured with a Horiba Seisakusho particle size measuring instrument LA-700.

(Releasing agent dispersion 1)
Paraffin wax: HNP-9 (Nippon Seiki Co., Ltd.) 19 parts by weight Anionic surfactant: Neogen SC (Daiichi Kogyo Seiyaku Co., Ltd.) 1 part by weight Ion-exchanged water 80 parts by weight

  The above was mixed in a heat-resistant container, heated to 90 ° C., and stirred for 30 minutes. Next, the molten liquid is circulated from the bottom of the container to the gorin homogenizer, and under a pressure condition of 5 MPa, a circulation operation corresponding to 3 passes is performed. Then, the pressure is increased to 35 MPa, and further a circulation operation corresponding to 3 passes is performed. It was. The emulsion thus prepared was cooled in the heat-resistant solution to 40 ° C. or lower to obtain a release agent dispersion 1. It was 240 nm when the volume average particle diameter was measured with a Horiba Seisakusho particle size measuring instrument LA-700.

(Resin particle dispersion 1)
-Oil layer-
Styrene (manufactured by Wako Pure Chemical Industries, Ltd.) 30 parts by mass n-butyl acrylate (manufactured by Wako Pure Chemical Industries, Ltd.) 10 parts by mass β-carboxyethyl acrylate (manufactured by Rhodia Nikka Co., Ltd.) 1.3 masses Part Dodecanethiol (Wako Pure Chemical Industries, Ltd.) 0.4 parts by mass

-Water layer 1-
17 parts by weight of ion-exchanged water Anionic surfactant (Dowfax, manufactured by Dow Chemical Company) 0.4 parts by weight

-Water layer 2-
Ion-exchanged water 40 parts by weight Anionic surfactant (Dowfax, manufactured by Dow Chemical Company) 0.05 parts by weight Ammonium peroxodisulfate (Wako Pure Chemical Industries, Ltd.) 0.4 parts by weight

  The above oil layer component and water layer 1 component were placed in a flask and mixed with stirring to obtain a monomer emulsion dispersion. The components of the aqueous layer 2 were charged into the reaction vessel, the inside of the vessel was sufficiently replaced with nitrogen, and the reaction system was heated to 75 ° C. with an oil bath while stirring. The above monomer emulsified dispersion was gradually dropped into the reaction vessel over 3 hours to carry out emulsion polymerization. After completion of the dropping, the polymerization was further continued at 75 ° C., and the polymerization was terminated after 3 hours.

  The obtained resin particles were 250 nm when the volume average particle diameter D50v of the resin particles was measured with a laser diffraction particle size distribution analyzer LA-700 (manufactured by Horiba, Ltd.). Moreover, it was 53 degreeC when the glass transition point of resin was measured with the temperature increase rate of 10 degree-C / min using the differential scanning calorimeter (DSC-50 Shimadzu Corp. make). Moreover, it was 13,000 when the number average molecular weight (polystyrene conversion) was measured using THF as a solvent using the molecular weight measuring device (made by HLC-8020 Tosoh Corporation). As a result, a resin particle dispersion 1 having a volume average particle size of 250 nm, a solid content of 42% by mass, a glass transition point of 52 ° C., and a number average molecular weight Mn of 13,000 was obtained.

(Preparation of Toner 1)
Resin particle dispersion 1 150 parts by weight Colorant particle dispersion 1 30 parts by weight Release agent dispersion 1 40 parts by weight Polyaluminum chloride 0.4 part by weight

  The above components were thoroughly mixed and dispersed in a stainless steel flask using an IKE Ultra Turrax, and then heated to 48 ° C. while stirring the flask in a heating oil bath. After maintaining at 48 ° C. for 80 minutes, 70 parts by mass of the same resin particle dispersion 1 as above was gradually added thereto.

  Then, after adjusting the pH in the system to 6.0 using an aqueous sodium hydroxide solution having a concentration of 0.5 mol / L, the stainless steel flask is sealed, and the stirring shaft seal is magnetically sealed while stirring is continued. Heat to 97 ° C. and hold for 3 hours. After completion of the reaction, the temperature lowering rate was cooled at 1 ° C./min, filtered and thoroughly washed with ion-exchanged water, and then solid-liquid separation was performed by Nutsche suction filtration. This was further redispersed with 3 L of ion exchanged water at 40 ° C., and stirred and washed at 300 rpm for 15 minutes. This washing operation was further repeated 5 times. When the pH of the filtrate was 6.54 and the electric conductivity was 6.5 μS / cm, No. 2 was obtained by Nutsche suction filtration. Solid-liquid separation was performed using 5A filter paper. Next, vacuum drying was continued for 12 hours to obtain toner particles.

The volume average particle diameter D50v of the toner particles was measured with a Coulter counter and found to be 6.2 μm, and the volume average particle size distribution index GSDv was 1.20. When the shape was observed with a Luzex image analyzer manufactured by Luzex, the shape factor SF1 of the particles was 135, and it was observed that the particles had a potato shape.
The glass transition point of the toner particles was 52 ° C.

Furthermore, the primary particle average particle size which is a reaction product of silica (SiO ₂ ) particles having a primary particle average particle size of 40 nm, which has been subjected to surface hydrophobization treatment with hexamethyldisilazane, and metatitanic acid and isobutyltrimethoxysilane. Toner 1 was prepared by adding 20 nm of metatitanic acid compound particles so that the coverage with respect to the surface of the toner particles was 40% and mixing with a Henschel mixer.

(Preparation of coating solution 1)
Cyclohexyl acrylate resin (weight average molecular weight Mw 50,000) 36 parts by mass Carbon black VXC72 (manufactured by Cabot) 4 parts by mass Toluene 250 parts by mass Isopropyl alcohol 50 parts by mass

  The above components and the same amount of glass beads (particle size: 1 mm) as toluene were put into a sand mill manufactured by Kansai Paint Co., Ltd., and stirred for 30 minutes at a rotational speed of 1200 rpm to prepare a coating liquid 1 having a solid content of 11% by mass.

(Preparation of ferrite particles 1)
-Temporary firing-
1597 parts by mass of Fe ₂ O ₃ , 890 parts by mass of Mn (OH) ₂ and 15 parts by mass of SrCO ₃ were mixed, and heated at 1000 ° C. for 2 hours while being fluidly stirred in a rotary kiln.

Next, this mixture was added with polycarboxylic acid, water, and zirconia beads having a media diameter of 1 mm as a dispersant, and pulverized and mixed with a sand mill.
Further, 6.6 parts by mass of polyvinyl alcohol and 25 parts by mass of silica were added, and pulverization was performed until the pulverized particle size became 1 μm or less. Further, 2.5 parts by mass of carbon black was added, pulverized and mixed for 30 minutes, and then granulated and dried with a spray dryer so that the dry particle size was 38 μm.

-Baking-
Furthermore, firing was performed in an electric furnace in an oxygen-nitrogen mixed atmosphere at a temperature of 1400 ° C. and an oxygen concentration of 1% for 4 hours.

-Oxidation-
Subsequently, heating was performed at 950 ° C. for 2 hours in the atmospheric state, and the obtained particles were subjected to a crushing step and a classification step, and then magnetic particles (ferrite particles 1) were obtained.
The particle diameter of the ferrite particle 1 was 35 μm.

(Preparation of ferrite particles 2 to 10)
Ferrite particles 2 to 10 were produced in the same manner as the production of the ferrite particles 1 except that the conditions were changed as shown in Table 1 in the production of the ferrite particles 1.

<Example 1>
(Preparation of carrier 1)
In a vacuum degassing type 5 L kneader, 2000 g of ferrite particles 1 and 560 g of coating liquid 1 are added, and while stirring, the pressure is reduced to −200 mmHg at 60 ° C. and mixed for 15 minutes. The mixture was stirred and dried at 720 mmHg for 30 minutes to obtain resin-coated particles. Next, sieving was performed with a 75 μm mesh sieving net to obtain Carrier 1.

The measured magnetization of the carrier 1 at VSM, a 64emu / g at the time of 1 kOe 60 emu / g, at the time of 5 kOe, the ratio of magnetization at 5 kOe at a 1 kOe was 1.07.
The resistance of the magnetic particles under an electric field of 30 ° C., 85% RH (relative humidity) and 24000 V / cm was 10 ⁷ Ωcm.

<Examples 2 to 7, Comparative Examples 1 to 3>
(Production of carriers 2 to 10)
Carriers 2 to 10 were produced in the same manner as in the production of carrier 1 except that the magnetic particles used in the production of carrier 1 were changed as shown in Table 2.

[Evaluation]
The Fuji Xerox DCC400 was modified so that the print speed could be set from 80 sheets / minute to 5 sheets / minute. Next, carrier 1 and toner 1 were mixed so as to have a toner concentration of 9% by mass, and charged at the Cyan position. One sheet of 20 cm square solid printing (image density 100%) was performed at a printing speed of 40 sheets per minute in an atmosphere of 23 ° C. and 50%.
Next, 80 blank sheets were printed at a printing speed of 80 sheets per minute.
Thereafter, one 20 cm square solid printing was performed at a printing speed of 5 sheets per minute. This was designated as printed matter 2.
Furthermore, the environment was set at 30 ° C. and 85% RH, and the plate was left still for one day. Five sheets of 20 cm square were printed at a printing speed of five sheets per minute, and the fifth image was collected to obtain a printed matter 3.

The presence or absence of image defects (white spots) in the printed material 2 was evaluated according to the following criteria.
Further, the density change was evaluated by the color difference (ΔE) between the printed material 1 and the printed material 3.

Image defect (white dot): Print 2
A: No image loss visually (no white spots)
B: 1 or more and 4 or less white spots (images with white particles) C: 5 to 9 white spots visually D: 10 or more white spots visually

Density change (ΔE): ΔE difference between printed material 1 and printed material 3 A: ΔE difference is 1 or less B: ΔE difference is more than 1 and less than 2.5 C: ΔE difference is 2.5 or more and less than 3.0 D: ΔE difference is 3.0 or more

<Measurement method>
The physical properties of the magnetic particles and the carrier and the method for measuring the image density are as follows.

(Particle size)
The volume average particle diameter of the magnetic particles and pulverized particles was measured with a laser diffraction particle size distribution measuring apparatus LA-700 (manufactured by Horiba, Ltd.). With respect to the particle size range (channel) obtained by dividing the obtained particle size distribution, the volume average particle size is determined by subtracting the volume cumulative distribution from the small particle size side to obtain a cumulative 50%.

(Resistance of magnetic particles)
Two electrode plates were opposed in parallel with a width of 1 mm, 0.25 g of magnetic particles were put between them, held by a magnet having a cross-sectional area of 2.4 cm ² , an applied voltage of 1000 V was applied, and the current value was measured. The electric field at this time is 24000 V / cm. The resistance value is calculated from the obtained current value.

(Magnetization)
The magnetic characteristics of the carrier are measured using a vibration sample type magnetometer VSMP10-15 (manufactured by Toei Industry Co., Ltd.). The measurement sample is packed in a cell having an inner diameter of 7 mm and a height of 5 mm and set in the apparatus. The measurement is performed by applying an applied magnetic field and sweeping up to 5000 oersted (5 kOe). Next, the applied magnetic field is decreased to create a hysteresis curve on the recording paper. Saturation magnetization, residual magnetization, and coercive force are obtained from the curve data.

(Image density)
For the image density, a reflection densitometer X-rite 938 (manufactured by X-rite) was used, and the color difference (ΔE) was measured. The color difference (ΔE) is obtained by taking the square root of the square sum of the distance difference in the L * a * b * space in the CIE 1976 (L * a * b *) color system. The CIE 1976 (L * a * b *) color system is a color space recommended by the CIE (International Lighting Commission) in 1976, and is defined in “JIS Z 8729” in the Japanese Industrial Standards.

  In Example 1, an image was formed and evaluated in the same manner as in Example 1 except that the developer was changed to a developer containing a carrier and a toner shown in Table 3.

  Table 3 shows the evaluation results of Examples and Comparative Examples.

1Y, 1M, 1C, 1K photoconductor (an example of an image carrier)
2Y, 2M, 2C, 2K charging roll (an example of charging means)
3. Exposure device (an example of electrostatic charge image forming means)
3Y, 3M, 3C, 3K Laser beams 4Y, 4M, 4C, 4K Developing device (an example of developing means)
5Y, 5M, 5C, 5K primary transfer roll (an example of primary transfer means)
6Y, 6M, 6C, 6K Photoconductor cleaning device (an example of cleaning means)
8Y, 8M, 8C, 8K Toner cartridge 10Y, 10M, 10C, 10K Image forming unit 20 Intermediate transfer belt (an example of an intermediate transfer member)
22 Drive roll 24 Support roll 26 Secondary transfer roll (an example of secondary transfer means)
30 Intermediate transfer member cleaning device 107 Photosensitive member (an example of an image holding member)
108 Charging roll (an example of charging means)
109 Exposure apparatus (an example of electrostatic charge image forming means)
111 Developing device (an example of developing means)
112 Transfer device (an example of transfer means)
113 photoconductor cleaning device (an example of cleaning means)
115 Fixing device (an example of fixing means)
116 Attachment rail 118 Opening 117 for exposure 117 Case 200 Process cartridge 300 Recording paper (an example of recording medium)
P Recording paper (an example of a recording medium)

Claims (7)

At least a part of the surface of the magnetic particles containing manganese ferrite containing Sr and Si, has a resin-coated particles coated with a resin containing cyclohexyl acrylate resin, at 5kOe applied magnetic field for magnetization A in 1kOe applied magnetic field the ratio of the magnetization B (B / a) is 1.01 to 1.10 in which the electrostatic image developing carrier. 2. The electrostatic charge image developing carrier according to claim 1, wherein the resistance of the magnetic particles in an environment of 30 ° C. and a relative humidity of 85% under an electric field of 24000 V / cm is 10 ⁶ Ωcm or more and 10 ⁹ Ωcm or less. The 1kOe applied magnetization A in magnetic field, 60 emu / g or more in a claim 1 or an electrostatic image developing carrier according to claim 2.   An electrostatic image developer comprising: an electrostatic image developing toner; and the electrostatic image developing carrier according to claim 1. Containing the electrostatic charge image developer according to claim 4;
A developer cartridge attached to and detached from the image forming apparatus. A developing means for containing the electrostatic charge image developer according to claim 4 and developing the electrostatic charge image formed on the surface of the image carrier as a toner image by the electrostatic charge image developer,
A process cartridge attached to and detached from the image forming apparatus. An image carrier,
Charging means for charging the surface of the image carrier;
An electrostatic charge image forming means for forming an electrostatic charge image on the surface of the charged image carrier;
Development means for containing the electrostatic charge image developer according to claim 4 and developing the electrostatic charge image formed on the surface of the image carrier as a toner image by the electrostatic charge image developer;
Transfer means for transferring a toner image formed on the surface of the image carrier to the surface of a recording medium;
Fixing means for fixing the toner image transferred to the surface of the recording medium;
An image forming apparatus comprising: