JP2011158775A - Carrier for electrostatic charge image development, developer for electrostatic charge image development, developer cartridge for electrostatic charge image development, process cartridge and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier for electrostatic charge image development, which allows white voids in an image to be made fewer than those of another carrier having >0.4 of a difference (the absolute value) between the electronegativity of the magnesium contained in a ferrite particle and that of the metal of a metal oxide contained in a covering layer. <P>SOLUTION: The carrier for electrostatic charge image development includes: the ferrite particle containing 3.0-12.0 mass% magnesium; and the covering layer which covers the ferrite particle and contains a resin and a metal oxide particle having ≤10<SP>6</SP>Ω-cm volume resistivity value. The difference (the absolute value) between the electronegativity of the metal of the metal oxide particle and that of the magnesium is ≤0.4. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an electrostatic charge developing carrier, an electrostatic charge developing developer, an electrostatic charge developing 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.

As a carrier used for the two-component developer, for example, a carrier having a resin coating layer in which ferrite particles are coated with a resin is known, and as a carrier material, for example, metallic magnesium, magnesium carbonate other than the resin described above. Magnesium materials such as magnesium compounds represented by the above are used.
As the magnesium material, those contained in a resin coating layer (for example, see Patent Documents 1 and 2) and those contained in ferrite particles (for example, see Patent Documents 3 and 4) have been proposed.

  However, the carrier material is not limited to the magnesium material, and a carrier containing various metal oxides in the resin coating layer (for example, see Patent Documents 5 and 6) has been proposed.

JP-A-6-301245 JP-A-10-142842 JP 2001-154416 A JP 2008-96977 A JP-A-7-219281 JP 2002-287432 A

  In the present invention, the difference between the electronegativity of magnesium contained in the ferrite particles and the metal electronegativity of the metal oxide contained in the coating layer is larger than that of the carrier exceeding 0.4. An object of the present invention is to provide an electrostatic charge developing carrier in which white spots of the toner are suppressed.

The above problem is solved by the following means.
That is, the invention according to claim 1
Ferrite particles containing 3.0% by mass or more and 12.0% by mass or less of magnesium,
Coating the ferrite particles, a coating layer containing a resin and metal oxide particles having a volume resistance of 10 ⁶ Ω · cm or less;
Including
The electrostatic charge developing carrier has a difference (absolute value) between the metal electronegativity of the metal oxide particles and the magnesium electronegativity of 0.4 or less.

The invention according to claim 2
The BET specific surface area of the ferrite particles is electrostatic latent image developing carrier according to claim 1 or less 0.13 m ² / g or more 0.28 m ² / g.

The invention according to claim 3
An electrostatic charge developing developer comprising a toner and the electrostatic charge developing carrier according to claim 1.

The invention according to claim 4
A developer cartridge for electrostatic charge development that is detached from an image forming apparatus and contains the developer for electrostatic charge development according to claim 3.

The invention according to claim 5
A developer that stores the developer for developing electrostatic charge according to claim 3 and that develops the electrostatic latent image formed on the surface of the electrostatic latent image holding member with the developer to form a toner image; The process cartridge is detachable from the image forming apparatus.

The invention according to claim 6
4. An electrostatic latent image holder, charging means for charging the surface of the electrostatic latent image holder, electrostatic latent image forming means for forming an electrostatic latent image on the surface of the electrostatic latent image holder, and Developing means for developing the electrostatic latent image with the developer for electrostatic charge development described in 1 above, forming a toner image, transfer means for transferring the toner image to a recording medium, and fixing the toner image to the recording medium. And an image forming apparatus.

  According to the first aspect of the present invention, the difference (absolute value) between the electronegativity of magnesium contained in the ferrite particles and the metal electronegativity of the metal oxide contained in the coating layer is 0.4. Provided is a carrier for developing an electrostatic charge in which white spots of an image are suppressed as compared with an excess carrier.

According to the invention of claim 2, compared with the case the BET specific surface area of the ferrite particles is 0.13 m ² / g or more 0.28 m ² / g is not less, the convex portion of the ferrite particles is exposed evenly to the carrier surface .

  According to the invention of claim 3, the difference (absolute value) between the electronegativity of magnesium contained in the ferrite particles and the metal electronegativity of the metal oxide contained in the coating layer is 0.4. Provided is an electrostatic charge developing developer in which whiteout of an image is suppressed as compared with an electrostatic charge developing developer containing an excess carrier.

  According to the invention of claim 4, the difference (absolute value) between the electronegativity of magnesium contained in the ferrite particles and the metal electronegativity of the metal oxide contained in the coating layer is 0.4. There is provided an electrostatic charge developing developer cartridge that supplies an electrostatic charge developing developer that suppresses white spots of an image to a developing unit as compared with the case of using an electrostatic charge developing developer containing an excess carrier.

  According to the invention of claim 5, the difference (absolute value) between the magnesium electronegativity contained in the ferrite particles and the metal electronegativity of the metal oxide contained in the coating layer is 0.4. A process cartridge is provided in which whiteout of an image is suppressed as compared with a case where a developer containing an excess carrier is stored.

  According to the invention of claim 6, the difference (absolute value) between the magnesium electronegativity contained in the ferrite particles and the metal electronegativity of the metal oxide contained in the coating layer is 0.4. There is provided an image forming apparatus in which white spots of an image are suppressed as compared with a case of storing a developer containing an excess carrier.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to an exemplary embodiment.

<Carrier for electrostatic charge development>
The electrostatic charge developing carrier includes ferrite particles containing 3.0% by mass or more and 12.0% by mass or less of magnesium, and a metal oxide having a resin and volume resistance of 10 ⁶ Ω · cm or less. A difference (absolute value) between the metal electronegativity of the metal oxide particles and the electronegativity of magnesium is 0.4 or less. Hereinafter, the electrostatic charge developing carrier is also referred to as “carrier”.

In image formation, generally, toner is adsorbed to a charged carrier, and the toner is charged, so that the charged toner develops an electrostatic latent image on the electrostatic latent image holding member to form a toner image. The toner image is transferred to a recording medium and fixed. Under high temperature and high humidity (for example, 30 ° C., 33% RH, the same applies hereinafter), the carrier is difficult to be charged. However, by using ferrite particles containing magnesium with low ionization energy as the core material of the carrier, The carrier can be easily charged even in a wet environment.
On the other hand, depending on the type of metal oxide contained in the coating layer covering the ferrite particles, there is an image defect called so-called white-out where the toner is not attached to the portion where the toner should be attached. was there. This is presumably because when the charge is locally injected from the charged toner into the carrier and the carrier is also charged, the carrier is scattered and attached together with the toner when the toner is developed. The white spots of the image are noticeable when the toner density in the image forming apparatus is low.

The white spots in the image are included in the ferrite particles in order to increase the chargeability of the carrier in a high-temperature and high-humidity environment, and the magnesium content of the ferrite particles is 3.0% by mass or more and 12.0% by mass or less. The difference (absolute value) between the electronegativity of magnesium and the metal electronegativity of the metal oxide particles having a volume resistance of 10 ⁶ Ω · cm or less contained in the coating layer covering the ferrite particles is 0.4. As a result, it has been found that this can occur in the case of exceeding the carrier, and the carrier according to the present embodiment has been completed.

That is, a ferrite particle containing 3.0% by mass or more and 12.0% by mass or less of magnesium as a carrier, and a metal oxide particle that covers the ferrite particle and has a resin and a volume resistance of 10 ⁶ Ω · cm or less. And a carrier having a difference (absolute value) between the metal electronegativity of the metal oxide particles and the electronegativity of magnesium of 0.4 or less. It is considered that local charge injection from the toner to the carrier is suppressed. As a result, it is thought that white spots are prevented from being lost when the carrier is scattered and developed in the portion where the toner is to be developed.

Moreover, it is considered that the local charge injection from the toner to the carrier is suppressed, so that the toner and the carrier that are easily damaged by an impact caused by the local charge injection are prevented from being damaged.
Details of the carrier will be described below.

(Ferrite particles)
The ferrite particles contain 3.0% by mass or more and 12.0% by mass or less of magnesium. Here, the ferrite is generally represented by the following formula (1).
_{(MO) X (Fe 2 O} 3) Y ··· Equation (1)
In the above formula (1), X and Y represent mass molar ratios and satisfy X + Y = 100.

  M in the formula (1) represents a metal containing at least magnesium, and further, a combination of at least one selected from the group consisting of Li, Ca, Mn, Sr, Sn, Cu, Zn, and Ba is used. Also good. Especially, it is preferable to select Li, Ca, and Sr from an environmental viewpoint.

  By setting the content of magnesium in the ferrite particles in the above range, the volume resistance is not easily lowered even in a high temperature and high humidity environment. The content of magnesium in the ferrite particles is preferably 5% by mass or more and 11% by mass or less, and more preferably 6% by mass or more and 10% by mass or less.

The magnesium content in the ferrite particles is measured by fluorescent X-rays. Specifically, as a pretreatment, a specified amount of resin to be embedded and ferrite particles are subjected to pressure molding for 10 tons for 1 minute with a pressure molding machine, and a fluorescent X-ray (SRF-1500) manufactured by Shimadzu Corporation. The measurement conditions are a tube voltage of 49 KV, a tube current of 90 mA, and a measurement time of 30 minutes. The resin to be embedded is preferably a resin composed only of carbon, hydrogen, and oxygen, and cellulose, polyvinyl alcohol, high melting temperature polyethylene, or the like is used.
A magnesium calibration curve is prepared by measurement with fluorescent X-rays under the above conditions, and the magnesium content in the ferrite particles is quantitatively measured with the calibration curve.

Ferrite particles further preferably has a BET specific surface area is less than 0.13 m ² / g or more 0.28 m ² / g.
The BET specific surface area by a 0.13 m ² / g or more 0.28 m ² / g or less, the convex portion of the ferrite particles is exposed evenly to the carrier surface.
This is considered to be due to the following reason.
When the ferrite particle has a BET specific surface area of less than 0.13 m ² / g and a surface with less unevenness, the ferrite particle surface is coated with a resin composition containing a metal oxide and a resin, and the ferrite particle is exposed from the carrier surface. When exposed, the ferrite particles are likely to be exposed on a part of the carrier surface. On the other hand, the surface of the ferrite particle having a BET specific surface area in the above range is more uneven than the surface of the ferrite particle having a BET specific surface area of 0.13 m ² / g. Therefore, when the resin composition containing the metal oxide and the resin is coated and the ferrite particles are exposed on the carrier surface, the convex portions of the ferrite particles are easily exposed on the carrier surface, and the convex portions of the ferrite particles are on the carrier surface. It is thought that it will be exposed evenly.

  It is considered that the local charge injection from the toner to the carrier can be further suppressed because the convex portion of the ferrite particle is exposed to the carrier surface without unevenness, and the charge injection path from the toner to the carrier is also not biased. As a result, it is considered that white spots in the image due to local charge injection from the toner to the carrier are suppressed.

Further, the ferrite particles has a BET specific surface area of not more than 0.13 m ² / g or more 0.28 m ² / g are, BET specific surface area compared with the ferrite particles is less than 0.13 m ² / g, damage to the external force is small, Hard to break. This is presumably because the surface of the ferrite particles is easy to disperse due to the unevenness. Therefore, the BET specific surface area of 0.13 m ² / g or more 0.28 m ² / g by mass or less, the carrier is considered to hardly occur scattered hardly image defects in the image forming apparatus.

BET specific surface area of the ferrite particles is more preferably less 0.14 m ² / g or more 0.25 m ² / g, more preferably not more than 0.16 m ² / g or more 0.18 m ² / g.
The BET specific surface area of the ferrite particles is a value measured by a nitrogen substitution method using a BET specific surface area measuring instrument (manufactured by Shimadzu Corporation: Flow Soap II2300).

Ferrite particles are generally produced by granulating and sintering using a metal oxide or metal salt as a raw material. The ferrite particles adjust the BET specific surface area by, for example, pre-firing, pulverizing, granulating, and main-firing the metal oxide or metal salt as a raw material as follows.
Hereinafter, an example of the manufacturing method of a ferrite particle is shown.

After pulverizing and mixing the raw material magnesium and other metal oxide or metal salt powders of metal that can be contained in a wet ball mill or the like for 8 hours or more and 35 hours or less, granulating and drying with a spray dryer or the like, a rotary kiln, etc. And calcining at 800 ° C. to 1000 ° C. for 8 hours to 10 hours to obtain a calcined product. Temporary baking is performed once to three times as necessary. Here, examples of the metal oxide or metal salt used as a raw material include Mg (OH) ₂ , Fe ₂ O ₃ , MnO ₂ , SrCO _{3, and the} like. For example, the amount of Mg (OH) ₂ is adjusted. This adjusts the content of magnesium in the ferrite particles.

The obtained calcined product is dispersed in water and pulverized by a known pulverization method (for example, a wet ball mill). Specifically, a calcined product, polyvinyl alcohol, a surfactant, and an antifoaming agent are added to water and pulverized with a mortar, ball mill, jet mill, or the like. The pulverization of the temporarily fired product is performed, for example, until the volume average particle size becomes 0.3 μm or more and 2.0 μm or less.
Next, the ground calcined product is granulated with a spray dryer and dried. For the purpose of adjusting the magnetic properties and resistance, the dried pre-fired product is subjected to main firing while controlling the oxygen concentration, and the contained organic matter is removed to obtain the fired product. The firing temperature may be 1000 ° C. or more and 1300 ° C. or less, and the firing time may be 6 hours or more and 10 hours or less.

After the main calcination, it is pulverized and further classified into a desired particle size distribution. At this time, ferrite particles having a desired BET specific surface area are produced by appropriately adjusting the particle size of the pulverized product obtained by pulverizing the temporarily fired product and the temperature of the main firing.
As an average particle diameter of the obtained ferrite particle, 30 micrometers or more and 50 micrometers or less are mentioned, for example. The average particle size of the fired product or ferrite particles is a value measured using a laser diffraction / scattering type particle size distribution analyzer (LS Particle Size Analyzer: LS13 320, manufactured by BECKMAN COULTER). For the particle size range (channel) obtained by dividing the obtained particle size distribution, the number cumulative distribution is subtracted from the small particle size side, and the particle size that becomes 50% cumulative is defined as the number average volume average 50% particle size.

(Coating layer)
The carrier is coated with ferrite particles and includes a coating layer containing a resin and metal oxide particles having a volume resistance of 10 ⁶ Ω · cm or less.

-Resin-
The resin contained in the coating layer is not particularly limited, and various resins may be used. For example, fluorine resin, acrylic resin, epoxy resin, polyester resin, fluorine acrylic resin, acrylic-styrene resin, silicone resin, or modified silicone resin modified with acrylic resin, polyester resin, epoxy resin, alkyd resin, urethane resin, etc. Examples thereof include cross-linked fluorine-modified silicone resins.

Examples of the weight average molecular weight of the resin include 3,000 to 200,000.
The weight average molecular weight was measured using gel permeation chromatography (GPC). GPC uses HLC-8120GPC, SC-8020 (manufactured by Tosoh Corporation), and column uses two TSKgel and SuperHM-H (manufactured by Tosoh Corporation, 6.0 mm ID × 15 cm). THF (tetrahydrofuran) was used. As experimental conditions, the sample concentration was 0.5 mass%, the flow rate was 0.6 ml / min, the sample injection amount was 10 μl, the measurement temperature was 40 ° C., and the experiment was performed using an IR detector. The calibration curve is “polystylen standard sample TSK standard” manufactured by Tosoh Corporation: “A-500”, “F-1”, “F-10”, “F-80”, “F-380”, “A-2500”. ”,“ F-4 ”,“ F-40 ”,“ F-128 ”, and“ F-700 ”.

-Metal oxide particles-
In addition to the resin, the coating layer contains metal oxide particles having a volume resistance of 10 ⁶ Ω · cm or less. The volume resistance value is a value at 20 ° C. Furthermore, the difference (absolute value) between the metal electronegativity of the metal oxide particles and the electronegativity of magnesium contained in the ferrite particles is 0.4.
Therefore, the metal oxide particles contained in the coating layer have a volume resistance value of 10 ⁶ Ω · cm or less, and the electronegativity of the metal constituting the metal oxide particles is ± 0 with respect to the electronegativity of magnesium. .4 is used.
Here, the electronegativity in the present invention means that defined by Pauling's electronegativity (1932).

The metal constituting the metal oxide particles is not particularly limited as long as the difference from the electronegativity of magnesium is 0.4 and the metal oxide has a volume resistance of 10 ⁶ Ω · cm or less. Examples thereof include Mn, Al, Ti, Zn, Ga, Nb, and Ta.
Therefore, the metal _{oxides, MnO 2, Al 2 O 3} , TiO 2, ZnO 2, Ga 2 O 3, Nb 2 O 5 and the like.

The difference between the metal electronegativity of the metal oxide particles and the electronegativity of magnesium is preferably 0.3, and may be 0.
Ti, Zn, Ga, and Nb are preferable as the metal of the metal oxide particles, and TiO ₂ , ZnO ₂ , Ga ₂ O ₃ , and Nb ₂ O ₅ are preferable as the metal oxide.

The metal oxide particles may contain two or more kinds of metals, or may use two or more kinds of metal oxides. In that case, the metal with the highest content in the total metal oxide particles contained in the coating layer has an electronegativity within ± 0.4 with respect to the electronegativity of magnesium, and the metal of the metal The volume resistance value of the oxide particles may be 10 ⁶ Ω · cm or less, and may include a metal having an electronegativity exceeding ± 0.4 with respect to the electronegativity of magnesium.

Examples of the metal oxide particles containing two or more metals include metal oxides doped with other metals. A metal oxide doped with another metal has a new crystal lattice formed by the introduction of another metal into the crystal lattice of the metal oxide, and the metal derived from the metal oxide and the other metal introduced into the metal oxide. It is thought that it is formed. It is considered that the volume resistance value of the metal oxide particles is likely to decrease by doping the metal oxide with another metal. In particular, a combination of a tetravalent metal and a pentavalent metal can be mentioned, and examples thereof include metal oxide particles in which titanium oxide is doped with phosphorus.
The amount of other metals doped into the metal oxide is such that the ratio in the metal oxide particles is not larger than that of the metal oxide metal, and the volume resistance value of the metal oxide can be 10 ⁶ Ω · cm or less. If it is. For example, the phosphorus doping amount of titanium oxide doped with phosphorus is 1% by weight to 20% by weight, and the gallium doping amount of zinc oxide doped with gallium is 1% by weight to 30% by weight.

In addition, as the metal oxide particles using two or more kinds of metal oxides, a metal oxide layer (surface layer) having a low volume resistance value (10 ⁶ Ω · cm or less) on the surface of the metal oxide (core). ). However, if the metal contained in the surface layer is a metal having a difference (absolute value) between magnesium and an electronegativity greater than 0.4, the effect of the present invention is hardly exhibited. Therefore, it is conceivable that the ratio of the metal contained in the surface layer is made smaller than the metal contained in the core. Specifically, if the ratio of “metal in the core” to “metal in the surface layer” (“metal in the core”: “metal in the surface layer”) is 5: 1 or less in molar ratio, Good.

  The production of the metal oxide particles is not limited, and may generally be produced by any method such as crystallization at a high temperature or crystallization with a metal ion solution.

In addition, inorganic particles having a volume resistivity at 20 ° C. of 1 × 10 ⁻⁶ Ωcm or less other than the metal oxide particles may be dispersed in the coating layer. Examples of the inorganic particles include, but are not limited to, metals such as gold, silver, and copper, carbon black, and barium sulfate, aluminum borate, potassium titanate, and carbon black.

Further, the coverage of the ferrite particles by the coating layer is preferably 97% or more.
Here, the coverage is measured by the following method.
As the X-ray electron spectroscopic analyzer, ESCA-9000MX manufactured by NEC Corporation is used, and the carrier is fixed to the sample holder and inserted into the ESCA chamber. The degree of vacuum of the chamber is set to 1 × 10 ⁻⁶ Pa or less, Mg—Kα is used as an excitation source, and the output is set to 200 W. Under the above conditions, the XPS spectra of the magnetic particles and the carrier are measured, and the coverage is calculated from the ratio of the area intensity of the detected Fe peak (2p3 / 2).
Coverage = F2 / F1 × 100
(F1: Fe area strength of magnetic particles, F2: Fe area strength of carriers)

As a method of forming a coating layer on the surface of the ferrite particle, a resin, metal oxide particle, and, if necessary, a solution for forming a coating layer in which various additives are dissolved in an appropriate solvent are used. The method of coating is mentioned.
More specifically, an immersion method in which ferrite particles are immersed in a coating layer forming solution, a spray method in which a coating layer forming solution is sprayed on the surface of the ferrite particles, and a ferrite particle and a coating layer forming solution in a kneader coater. Kneader coater method that mixes and removes solvent

<Developer for electrostatic charge development>
The electrostatic charge developing developer is a so-called two-component developer including toner and the carrier described above.
Hereinafter, the developer for electrostatic charge development is also referred to as “developer”.
The toner is not particularly limited, and examples thereof include a toner containing at least a binder resin, a colorant, and a release agent.

  Since the developer for electrostatic charge development contains the carrier described above, local charge injection from the toner to the carrier is suppressed, so that the carrier is scattered with the toner and developed. The image defect due to is prevented.

  Examples of the toner include a dispersion step of dispersing at least binder resin particles and colorant particles in an aqueous dispersion medium, and an aggregation step of aggregating dispersed binder resin particles and colorant particles with metal ions. Then, a toner manufactured through an additional aggregation process in which only the binder resin particles are added and aggregated, and a heat fusion process in which the aggregated particles are thermally fused are exemplified. In addition, the particles obtained by the kneading and pulverization method, which knead, pulverize, and classify the binder resin and the colorant, and if necessary, the release agent, the charge control agent, etc. And a toner manufactured by a method of changing the shape.

  Examples of the binder resin contained in the toner include known binder resins. For example, polyester, polystyrene, styrene-alkyl acrylate copolymer, styrene-alkyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyethylene, polypropylene Etc. Further examples include polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin wax and the like.

Examples of the colorant and release agent contained in the toner include known colorants and release agents.
For example, magnetic powders such as magnetite and ferrite, carbon black, aniline blue, caryl blue, chrome yellow, ultramarine blue, dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black as colorants Rose Bengal, C.I. I. Pigment red 48: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 57: 1, C.I. I. Pigment yellow 97, C.I. I. Pigment yellow 17, C.I. I. Pigment blue 15: 1, C.I. I. And CI Pigment Blue 15: 3

  Examples of the release agent include low molecular polyethylene, low molecular polypropylene, Fischer tropic wax, montan wax, carnauba wax, rice wax, and candelilla wax.

Furthermore, a known charge control agent such as an azo metal complex compound, a metal complex compound of salicylic acid, or a resin type charge control agent containing a polar group may be added to the toner as necessary.
For toner, silica, titanium oxide, metatitanic acid, aluminum oxide, magnesium oxide, alumina, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, chromium oxide, antimony trioxide, magnesium oxide In addition, a known external additive such as zirconium oxide may be externally added.

  The toner and carrier in the developer are mixed at a ratio of, for example, 1: 100 to 30: 100 (toner: carrier, mass ratio).

<Electrostatic charge developer cartridge, process cartridge, and image forming apparatus>
A developer cartridge for electrostatic charge development (hereinafter also referred to as “cartridge”) is detached from the image forming apparatus and contains the developer described above. With this configuration, the developer is supplied to the developing unit of the image forming apparatus.

  An image forming apparatus includes an electrostatic latent image holding member, a charging unit that charges the surface of the electrostatic latent image holding member, and an electrostatic latent image forming unit that forms an electrostatic latent image on the surface of the electrostatic latent image holding member. Developing means for developing the electrostatic latent image with the developer described above to form a toner image, transfer means for transferring the toner image to a recording medium, and fixing for fixing the toner image on the recording medium Means.

  The process cartridge further includes a developing unit that stores the developer and develops the electrostatic latent image formed on the surface of the electrostatic latent image holding member with the developer to form a toner image. Desorbed.

Since the process cartridge and the image forming apparatus use a developer that suppresses local charge injection from the toner to the carrier as described above, for example, white toner caused by the carrier being scattered with the toner and developed. Image defects due to omission are prevented.
Hereinafter, the image forming apparatus according to the present exemplary embodiment will be described with reference to the drawings.

  FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus according to the present embodiment. The image forming apparatus shown in FIG. 1 is a quadruple tandem color image forming apparatus, and each color of yellow (Y), magenta (M), cyan (C), and black (K) based on color-separated image data. Are provided with first to fourth image forming units 10Y, 10M, 10C, and 10K (image forming means) of an electrophotographic system for outputting the above image. These image forming units (hereinafter simply referred to as “units”) 10Y, 10M, 10C, and 10K are juxtaposed in parallel in the horizontal direction. The units 10Y, 10M, 10C, and 10K may be process cartridges that are detachable from the main body of 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 driving roller 22 and a support roller 24 that are in contact with the inner surface of the intermediate transfer belt 20 that are spaced apart from each other from the left to the right in the drawing. It is designed to travel in the direction toward 10K. The support roller 24 is urged away from the drive roller 22 by a spring or the like (not shown), and tension is applied to the intermediate transfer belt 20 wound around both. Further, 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 driving roller 22.
Further, each of the developing devices (developing means) 4Y, 4M, 4C, and 4K of the units 10Y, 10M, 10C, and 10K includes yellow, magenta, cyan, and the like housed in the developer cartridges 8Y, 8M, 8C, and 8K. Four black developer colors are supplied.

  Since the first to fourth units 10Y, 10M, 10C, and 10K described above 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. Note that the second to fourth units are denoted by reference numerals with magenta (M), cyan (C), and black (K) instead of yellow (Y) in the same parts as the first unit 10Y. Description of 10M, 10C, 10K is omitted.

The first unit 10Y has a photoreceptor 1Y that acts as an electrostatic latent image holding body. Around the photoreceptor 1Y, a charging roller (charging means) 2Y for charging the surface of the photoreceptor 1Y, and the charged surface is exposed by a laser beam 3Y based on the color-separated image signal to form an electrostatic latent image. An exposure device (electrostatic latent image forming means) 3, a developing device (developing means) 4 Y for developing the electrostatic latent image by supplying charged toner to the electrostatic latent image, and the developed toner image on the intermediate transfer belt 20. A primary transfer roller 5Y (primary transfer unit) for transferring the toner onto the surface and a photosensitive member cleaning device (cleaning unit) 6Y for removing the toner remaining on the surface of the photosensitive member 1Y after the primary transfer are sequentially arranged.
The primary transfer roller 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 rollers 5Y, 5M, 5C, and 5K. Each bias power source varies the transfer bias applied to each primary transfer roller 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 the operation, the surface of the photoreceptor 1Y is charged to a potential of about −600V to −800V by the charging roller 2Y.
The photoreceptor 1Y is formed by laminating a photosensitive layer on a conductive substrate (volume resistivity at 20 ° C .: 1 × 10 ⁻⁶ Ωcm or less). This photosensitive layer usually has a high resistance (a resistance equivalent to that of a general resin), 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 latent image of a yellow print pattern is formed on the surface of the photoreceptor 1Y.

  A developer (developer according to this embodiment) containing yellow toner and a carrier is accommodated in the developing device 4Y. 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 charge on the photoreceptor 1Y, and a developer roll (developer holder). 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, and the toner image developed on the photoreceptor 1Y is conveyed to the 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 roller 5Y, and an electrostatic force from the photoreceptor 1Y toward the primary transfer roller 5Y acts on the toner image. Then, the toner image on the photoreceptor 1Y is transferred onto the intermediate transfer belt 20. The transfer bias applied at this time is a (+) polarity opposite to the polarity (−) of the toner, and is controlled to about +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 cleaning device 6Y.
The yellow toner constitutes a developer together with a carrier. For this reason, the change in the charge amount due to stirring or environmental change is suppressed.

Further, the primary transfer bias applied to the primary transfer rollers 5M, 5C, and 5K after the second unit 10M is also controlled according to 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 intermediate transfer belt 20 onto which the four color toner images have been transferred through the first to fourth units is arranged on the image transfer surface side of the intermediate transfer belt 20 and the support roller 24 in contact with the inner surface of the intermediate transfer belt 20. The secondary transfer roller (secondary transfer means) 26 is connected to a secondary transfer portion. On the other hand, a recording sheet (transfer object) P is fed to a gap where the secondary transfer roller 26 and the intermediate transfer belt 20 are pressed against each other via a supply mechanism, and a secondary transfer bias is applied to the support roller 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, and the transfer bias is applied to the intermediate transfer belt 20. The toner image is transferred onto the recording paper P. Note that the secondary transfer bias at this time is determined according to the resistance detected by a resistance detecting means (not shown) for detecting the resistance of the secondary transfer portion, and is voltage-controlled.

Thereafter, the recording paper P is sent to a fixing device (fixing means) 28, where the toner image is heated, and the color-superposed toner image is melted and fixed on the recording paper P. 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.
The image forming apparatus exemplified above is configured to transfer the toner image onto the recording paper P via the intermediate transfer belt 20, but the present invention is not limited to this configuration, and the toner image is directly transferred from the photoconductor. It may be a structure that is transferred to a recording sheet.

EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples. In the following Examples, “part” and “%” mean “part by mass” and “% by mass”, respectively, unless otherwise specified.

(Preparation of ferrite particles)
(Ferrite particles 1)
Fe ₂ O ₃ (2000 parts), MnO ₂ (800 parts), Mg (OH) ₂ (200 parts), and SrCO ₃ (20 parts) were mixed and pulverized with a wet ball mill for 10 hours. Next, after granulating and drying with a spray dryer, pre-baking 1 was performed at 900 ° C. for 7 hours using a rotary kiln. The calcined product 1 thus obtained was pulverized for 2 hours with a wet ball mill to an average particle size of 2 μm, further granulated and dried with a spray dryer, and then temporarily heated at 1000 ° C. for 6 hours using a rotary kiln. Firing 2 was performed. The calcined product 2 thus obtained was pulverized for 5 hours with a wet ball mill to an average particle size of 5 μm, further granulated and dried with a spray dryer, and then heated to 1300 ° C. with an electric furnace for 5 hours. Went. Through the crushing step and the classification step, ferrite particles 1 having an average particle size of 36 μm were prepared.
The obtained ferrite particles 1 had a magnesium content of 3% by mass and a BET specific surface area of 0.17 m ² / g.

(Ferrite particle 2)
Fe ₂ O ₃ (2000 parts), MnO ₂ (320 parts), Mg (OH) ₂ (600 parts), and SrCO ₃ (20 parts) were mixed and pulverized with a wet ball mill for 10 hours. Next, after granulating and drying with a spray dryer, pre-baking 1 was performed at 900 ° C. for 7 hours using a rotary kiln. The calcined product 1 thus obtained was pulverized for 2 hours with a wet ball mill to an average particle size of 2 μm, further granulated and dried with a spray dryer, and then temporarily heated at 980 ° C. for 6 hours using a rotary kiln. Firing 2 was performed. The calcined product 2 thus obtained was pulverized for 6 hours with a wet ball mill to an average particle size of 4.8 μm, further granulated and dried with a spray dryer, and then heated to 1280 ° C. with an electric furnace for 5 hours. Was fired. Ferrite particles 2 having a particle size of 36 μm were prepared through a crushing step and a classification step.
The obtained ferrite particles 2 had a magnesium content of 8% by mass and a BET specific surface area of 0.17 m ² / g.

(Ferrite particle 3)
Fe ₂ O ₃ (2000 parts), MnO ₂ (200 parts), Mg (OH) ₂ (660 parts), and SrCO ₃ (20 parts) were mixed and pulverized with a wet ball mill for 10 hours. Next, after granulating and drying with a spray dryer, pre-baking 1 was performed at 900 ° C. for 7 hours using a rotary kiln. The calcined product 1 thus obtained was pulverized with a wet ball mill for 2 hours to an average particle size of 2 μm, further granulated and dried with a spray dryer, and then temporarily heated at 960 ° C. for 6 hours using a rotary kiln. Firing 2 was performed. The calcined product 2 thus obtained was pulverized with a wet ball mill for 5 hours to have an average particle size of 5.5 μm, further granulated and dried with a spray dryer, and then heated to 1250 ° C. with an electric furnace. Firing was performed for 5 hours. Ferrite particles 3 having a particle size of 37 μm were prepared through a crushing step and a classification step.
The obtained ferrite particles 3 had a magnesium content of 11% by mass and a BET specific surface area of 0.17 m ² / g.

(Ferrite particle 4)
Fe ₂ O ₃ (2000 parts), MnO ₂ (800 parts), Mg (OH) ₂ (200 parts), and SrCO ₃ (20 parts) were mixed and pulverized with a wet ball mill for 10 hours. Next, after granulating and drying with a spray dryer, pre-baking 1 was performed at 900 ° C. for 7 hours using a rotary kiln. The calcined product 1 thus obtained was pulverized for 2 hours with a wet ball mill to an average particle size of 2 μm, further granulated and dried with a spray dryer, and then temporarily heated at 980 ° C. for 6 hours using a rotary kiln. Firing 2 was performed. The calcined product 2 thus obtained was pulverized with a wet ball mill for 5 hours to an average particle size of 4.2 μm, further granulated and dried with a spray dryer, and then heated to 1250 ° C. with an electric furnace. Firing was performed for 5 hours. Ferrite particles 4 having a particle size of 36 μm were prepared through a crushing step and a classification step.
The obtained ferrite particles 4 had a magnesium content of 8% by mass and a BET specific surface area of 0.25 m ² / g.

(Ferrite particle 5)
Fe ₂ O ₃ (2000 parts), MnO ₂ (800 parts), Mg (OH) ₂ (200 parts), and SrCO ₃ (20 parts) were mixed and pulverized with a wet ball mill for 10 hours. Next, after granulating and drying with a spray dryer, pre-baking 1 was performed at 900 ° C. for 7 hours using a rotary kiln. The calcined product 1 thus obtained was pulverized for 2 hours with a wet ball mill to an average particle size of 2 μm, further granulated and dried with a spray dryer, and then temporarily heated at 980 ° C. for 6 hours using a rotary kiln. Firing 2 was performed. The calcined product 2 obtained in this way was pulverized for 4 hours with a wet ball mill to an average particle size of 5.8 μm, then granulated and dried with a spray dryer, and then adjusted to a temperature of 1310 ° C. with an electric furnace. Baked for 5 hours. Ferrite particles 5 having a particle size of 37 μm were prepared through a crushing step and a classification step.
The obtained ferrite particles 5 had a magnesium content of 8% by mass and a BET specific surface area of 0.14 m ² / g.

(Ferrite particle 6)
Fe ₂ O ₃ (2000 parts), MnO ₂ (1000 parts), Mg (OH) ₂ (80 parts), and SrCO ₃ (20 parts) were mixed and pulverized with a wet ball mill for 10 hours. Next, after granulating and drying with a spray dryer, temporary baking was performed at 1000 ° C. for 7 hours using a rotary kiln. The calcined product thus obtained is pulverized with a wet ball mill for 4 hours to have an average particle size of 5.4 μm, further granulated and dried with a spray dryer, and then heated to 1310 ° C. with an electric furnace for 5 hours. Was fired. Ferrite particles 6 having a particle size of 37 μm were prepared through a crushing step and a classification step.
The obtained ferrite particles 6 had a magnesium content of 1% by mass and a BET specific surface area of 0.17 m ² / g.

(Ferrite particle 7)
Fe ₂ O ₃ (2000 parts), MnO ₂ (20 parts), Mg (OH) ₂ (760 parts), and SrCO ₃ (20 parts) were mixed and pulverized with a wet ball mill for 10 hours. Next, after granulating and drying with a spray dryer, preliminary baking 1 was performed at 900 ° C. for 7 hours using a rotary kiln. The calcined product 1 thus obtained was pulverized for 2 hours with a wet ball mill to an average particle size of 2 μm, further granulated and dried with a spray dryer, and then temporarily heated at 950 ° C. for 5 hours using a rotary kiln. Firing 2 was performed. The calcined product 2 thus obtained was pulverized for 6 hours with a wet ball mill to an average particle size of 5.2 μm, further granulated and dried with a spray dryer, and then heated to 1250 ° C. with an electric furnace. Time firing was performed. Through the crushing step and the classification step, ferrite particles 7 having a volume average particle size of 36 μm were prepared.
The obtained ferrite particles 7 had a magnesium content of 13% by mass and a BET specific surface area of 0.18 m ² / g.

(Ferrite particle 8)
Fe ₂ O ₃ (2000 parts), MnO ₂ (320 parts), Mg (OH) ₂ (600 parts), and SrCO ₃ (20 parts) were mixed and pulverized with a wet ball mill for 10 hours. Next, after granulating and drying with a spray dryer, pre-baking 1 was performed at 900 ° C. for 7 hours using a rotary kiln. The calcined product 1 thus obtained was pulverized for 2 hours with a wet ball mill to an average particle size of 2 μm, further granulated and dried with a spray dryer, and then temporarily heated at 980 ° C. for 6 hours using a rotary kiln. Firing 2 was performed. The calcined product 2 thus obtained was pulverized for 5 hours with a wet ball mill to an average particle size of 6 μm, further granulated and dried with a spray dryer, and then heated to 1250 ° C. with an electric furnace for 9 hours. Firing was performed. Ferrite particles 8 having a particle size of 36 μm were prepared through a crushing step and a classification step.
The obtained ferrite particles 8 had a magnesium content of 8% by mass and a BET specific surface area of 0.08 m ² / g.

(Ferrite particle 9)
Fe ₂ O ₃ (2000 parts), MnO ₂ (320 parts), Mg (OH) ₂ (600 parts), and SrCO ₃ (20 parts) were mixed and pulverized with a wet ball mill for 10 hours. Next, after granulating and drying with a spray dryer, pre-baking 1 was performed at 900 ° C. for 7 hours using a rotary kiln. The calcined product 1 thus obtained was pulverized for 2 hours with a wet ball mill to an average particle size of 2 μm, further granulated and dried with a spray dryer, and then temporarily heated at 980 ° C. for 6 hours using a rotary kiln. Firing 2 was performed. The calcined product 2 thus obtained was pulverized for 8 hours with a wet ball mill to an average particle size of 4 μm, further granulated and dried with a spray dryer, and then heated to 1240 ° C. with an electric furnace for 5 hours. Firing was performed. Ferrite particles 9 having a particle size of 36 μm were prepared through a crushing step and a classification step.
The obtained ferrite particles 9 had a magnesium content of 8% by mass and a BET specific surface area of 0.30 m ² / g.

[Preparation of coating solution (coating layer forming solution)]
(Metal oxide particles 1)
Phosphorus trichloride was dissolved in 2N hydrochloric acid. Next, a hydrochloric acid solution of phosphorus trichloride was added to the titanium tetrachloride aqueous solution, stirred, and sodium hydroxide was further added to cause precipitation. Next, the precipitate was washed with 0.5N hydrochloric acid and purified by filtration. The obtained precipitate was dried and then baked in an electric furnace at 1000 ° C. and an oxygen concentration of 5% for 1 hour. After firing, pulverization and pulverization were performed using a pulverizer to obtain metal oxide particles 1 of titanium oxide doped with phosphorus (dope amount 5 wt%).
The obtained metal oxide particles 1 had a volume resistivity of 10 ⁴ Ωcm and a BET specific surface area of 50 m ² / g.

(Coating solution 1)
-Styrene-methyl methacrylate copolymer [80: 20 molar ratio, weight average molecular weight 40,000] 38 parts-15 parts of the metal oxide particles 1-340 parts of toluene-85 parts of isopropyl alcohol

  The above components and glass beads (particle size: 1 mm, same amount as toluene) were put into a sand mill manufactured by Kansai Paint Co., Ltd., stirred for 30 minutes at a rotational speed of 1,200 rpm, and a coating solution having a solid content of 12% 1 was prepared.

(Coating solution 2)
Styrene-methyl methacrylate copolymer [80:20 molar ratio, weight average molecular weight 40,000] 35 parts ・ Pazette GK (manufactured by Hakusui Tech; metal oxide particles) 20 parts ・ Toluene 360 parts ・ Isopropyl alcohol 90 parts

  The above components and glass beads (particle size: 1 mm, same amount as toluene) were put into a sand mill manufactured by Kansai Paint Co., Ltd., stirred for 30 minutes at a rotational speed of 1,200 rpm, and a coating solution 2 having a solid content of 12% Was prepared.

(Coating solution 3)
-Styrene-methyl methacrylate copolymer [80: 20 molar ratio, weight average molecular weight 40,000] 35 parts-Tin (IV) oxide [metal oxide particles] 20 parts-Toluene 360 parts-Isopropyl alcohol 90 parts

  The above components and glass beads (particle size: 1 mm, the same amount as toluene) were put into a sand mill manufactured by Kansai Paint Co., Ltd., stirred for 30 minutes at a rotational speed of 1,200 rpm, and a coating solution 3 having a solid content of 12% Was prepared.

(Coating solution 4)
Styrene - methyl methacrylate copolymer [80:20 molar ratio, weight average molecular weight 40,000] 35 parts _Nb 2 _{O 5} [Junsei Chemical Co., Ltd .; metal oxide particles] 20 parts Toluene 360 parts Isopropyl alcohol 90 Part

In advance, the surface of Nb ₂ O ₅ was coated with cyclohexyldimethoxysilane so that the coverage was 40%. Thereafter, the above components (styrene-methyl methacrylate copolymer, coated Nb ₂ O ₅ , toluene, and isopropyl alcohol) and glass beads (particle size: 1 mm, the same amount as toluene) were combined with Kansai Paint Co., Ltd. ) It was put into a sand mill manufactured by the company and stirred at a rotational speed of 1,200 rpm for 30 minutes to prepare a coating liquid 4 having a solid content of 12%.

(Coating solution 5)
-Styrene-methyl methacrylate copolymer [80: 20 molar ratio, weight average molecular weight 40,000] 35 parts-STT65CS (made by Titanium Industry Co., Ltd .; metal oxide particles) 20 parts-Toluene 360 parts-Isopropyl alcohol 90 parts

  The above components and glass beads (particle size: 1 mm, same amount as toluene) were put into a sand mill manufactured by Kansai Paint Co., Ltd., stirred at a rotational speed of 1,200 rpm for 30 minutes, and a coating solution 5 having a solid content of 12% Was prepared.

[Production of carrier]
(Carrier 1)
In a vacuum degassing type 5 L kneader, 2000 parts of ferrite particles 1 and 470 parts of coating liquid 1 are added, and while stirring, the pressure is reduced to −200 mmHg at 60 ° C. and mixed for 20 minutes. Stirring was carried out for 30 minutes at a temperature of ° C / -720 mHg and dried to obtain ferrite particles provided with a coating layer. Further, sieving was performed with a 75 μmesh sieving mesh to obtain carrier 1.

(Carrier 2)
Carrier 2 was prepared in the same manner except that ferrite particle 1 was replaced with ferrite particle 2 in preparation of carrier 1.

(Carrier 3)
Carrier 3 was prepared in the same manner except that coating liquid 1 was replaced with coating liquid 2 in the preparation of carrier 2.

(Carrier 4)
Carrier 4 was prepared in the same manner except that ferrite particle 1 was replaced with ferrite particle 3 in preparation of carrier 1.

(Carrier 5)
Carrier 5 was prepared in the same manner except that ferrite particle 1 was replaced with ferrite particle 4 in preparation of carrier 1.

(Carrier 6)
Carrier 6 was prepared in the same manner except that ferrite particle 1 was replaced with ferrite particle 5 in preparation of carrier 1.

(Carrier 7)
Carrier 7 was prepared in the same manner except that ferrite particle 1 was replaced with ferrite particle 6 in preparation of carrier 1.

(Carrier 8)
Carrier 8 was prepared in the same manner except that ferrite particle 1 was replaced with ferrite particle 7 in preparation of carrier 1.

(Carrier 9)
A carrier 9 was produced in the same manner as in the production of the carrier 1 except that the ferrite particles 1 were replaced with the ferrite particles 8.

(Carrier 10)
A carrier 10 was produced in the same manner except that the ferrite particles 1 were replaced with the ferrite particles 9 in the production of the carrier 1.

(Carrier 11)
Carrier 11 was prepared in the same manner except that coating liquid 1 was replaced with coating liquid 3 in the preparation of carrier 1.

(Carrier 12)
A carrier 12 was prepared in the same manner as in the preparation of the carrier 2, except that the coating liquid 1 was replaced with the coating liquid 4.

(Carrier 13)
A carrier 13 was prepared in the same manner except that the coating liquid 1 was replaced with the coating liquid 5 in the production of the carrier 2.

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

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

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

  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 obtained emulsion was cooled in the heat-resistant solution to 40 ° C. or lower to obtain a release agent dispersion 1. With respect to the obtained release agent dispersion 1, the volume average particle diameter was measured by a particle size measuring instrument LA-700 manufactured by Horiba Ltd., and it was 240 nm.

(Resin dispersion 1)
-Oil layer components-
Styrene [Wako Pure Chemical Industries, Ltd.] 30 parts n-butyl acrylate [Wako Pure Chemical Industries, Ltd.] 10 parts β-Carboxyethyl acrylate [Rhodia Nikka Co., Ltd.] 1.3 parts Dodecane Thiol [Wako Pure Chemical Industries, Ltd.] 0.4 parts

-Aqueous layer component 1-
・ Ion-exchanged water 17 parts ・ Anionic surfactant [Dowfax, manufactured by Dow Chemical Co., Ltd.] 0.4 parts

-Aqueous layer component 2-
・ Ion-exchanged water 40 parts ・ Anionic surfactant [Dowfax, manufactured by Dow Chemical Co., Ltd.] 0.05 part ・ Ammonium peroxodisulfate [Wako Pure Chemical Industries, Ltd.] 0.4 part

  The oil layer component and the water layer component 1 were placed in a flask and mixed with stirring to prepare a monomer emulsified dispersion in advance. Separately, the aqueous layer component 2 was put into a reaction vessel, the inside of the reaction vessel was replaced with nitrogen, and the reaction system was heated to 75 ° C. with an oil bath while stirring. Into the reaction vessel, the monomer emulsion dispersion prepared in advance was gradually added dropwise 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 to obtain resin particles.

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

(Toner 1)
-Resin particle dispersion 1 150 parts-Colorant particle dispersion 1 30 parts-Release agent particle dispersion 1 40 parts-Polyaluminum chloride 0.4 part

The above components were mixed and dispersed in a stainless steel flask using an IKE Ultra Turrax, and then the stainless steel flask was heated to 48 ° C. with stirring in an oil bath for heating. After holding at 48 ° C. for 80 minutes, 70 parts of the resin particle dispersion 1 was gently added again.
Thereafter, the pH in the system in the stainless steel flask was adjusted to 6.0 using a sodium hydroxide aqueous solution having a concentration of 0.5 mol / L. Thereafter, the stainless steel flask was sealed, the seal of the stirring shaft was magnetically sealed, and the mixture was heated to 97 ° C. and maintained for 3 hours while stirring was continued. After completion of the reaction, the temperature was lowered at a rate of 1 ° C./min, and solid-liquid separation was performed by Nutsche suction filtration.

  The filtrate (solid) was further redispersed in 3 L of ion exchanged water at 40 ° C., stirred for 15 minutes at 300 rpm, and washed. After washing, solid-liquid separation was performed again by filtration. Such a filtered product (solid) was redispersed with ion-exchanged water at 40 ° C., stirred, washed, and filtered again five times. Solid-liquid separation was performed using 5A filter paper. Next, vacuum drying was continued for 12 hours to obtain toner mother particles.

To the obtained toner base particles, silica (SiO ₂ ) particles having an average primary particle size of 40 nm and subjected to surface hydrophobization treatment with hexamethyldisilazane are added so that the coverage of the colored particles on the surface is 40%. Toner 1 was prepared by mixing with a Henschel mixer.

<Example 1>
Docu Center Color400 A developer, in which carrier 1 and toner 1 are mixed at a weight ratio of 100: 6 in a modified machine, is loaded into a developer for cyan developer and a developer for black developer, and is 30 ° C. and 88% RH. In this environment, a single solid image of 25 cm × 18 cm was printed using A3 paper. The image printed at this time was referred to as “image 1”. Next, after printing 1,000 sheets of “A” (10 characters × 10 lines) of 12 points tomorrow, another solid image of 25 cm × 18 cm was printed. The image printed at this time was referred to as “image 2”.

(Image unevenness evaluation)
The obtained image 1 and image 2 were visually observed, and the appearance of the image 2 in comparison with the image 1 was evaluated according to the following criteria.
◎ ・ ・ ・ ・ No density unevenness can be confirmed ○ ・ ・ ・ ・ Slight density unevenness is observed △ ・ ・ ・ ・ Slight density unevenness × ・ ・ ・ ・ There is density unevenness XX ・ ・ ・ Clear image Is thin

(Outline evaluation)
The obtained image 2 was visually observed, and the number of locations where the image 2 had white spots (the state where the toner should not be attached to the image where the toner should be attached) was counted and evaluated according to the following criteria.
◎ ··················································································································・ ・ ・ More than 50 white spots were confirmed per A3 and within 100 white spots XX ・ ・ ・ Over 100 white spots were confirmed per A3

<Example 2>
In Example 1, evaluation was performed in the same manner as in Example 1 except that carrier 2 was used instead of carrier 1. The results are shown in Table 1.

<Example 3>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 3 was used instead of the carrier 1. The results are shown in Table 1.

<Example 4>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 4 was used instead of the carrier 1. The results are shown in Table 1.

<Example 5>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 5 was used instead of the carrier 1. The results are shown in Table 1.

<Example 6>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 6 was used instead of the carrier 1. The results are shown in Table 1.

<Example 7>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 9 was used instead of the carrier 1. The results are shown in Table 1.

<Example 8>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 10 was used instead of the carrier 1. The results are shown in Table 1.

<Example 9>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 12 was used instead of the carrier 1. The results are shown in Table 1.

<Comparative Example 1>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 7 was used instead of the carrier 1. The results are shown in Table 1.

<Comparative example 2>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 8 was used instead of the carrier 1. The results are shown in Table 1.

<Comparative Example 3>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 11 was used instead of the carrier 1. The results are shown in Table 1.

<Comparative example 4>
In Example 1, evaluation was performed in the same manner as in Example 1 except that the carrier 13 was used instead of the carrier 1. The results are shown in Table 1.

In Table 1, “TiO ₂ / P” in the type column of metal oxide particles represents titanium oxide particles doped with phosphorus, and “ZnO ₂ / Ga” represents zinc oxide particles doped with gallium.
The “target metal” in the type column of the metal oxide particles is a metal having the largest ratio among the metals constituting the metal oxide particles, and is a target for calculating a difference in electronegativity with magnesium. It represents a metal, and “electronegativity” represents the electronegativity of the target metal.

  From Table 1 above, it can be seen that the example had no image unevenness and white spots were suppressed as compared with the comparative example.

1Y, 1M, 1C, 1K photoconductor (image carrier)
2Y, 2M, 2C, 2K Charging roller 3Y, 3M, 3C, 3K Laser beam 3 Exposure device 4Y, 4M, 4C, 4K Developing device (developing means)
5Y, 5M, 5C, 5K Primary transfer rollers 6Y, 6M, 6C, 6K Photoconductor cleaning device (cleaning means)
8Y, 8M, 8C, 8K Developer cartridge 10Y, 10M, 10C, 10K Unit 20 Intermediate transfer belt 22 Drive roller 24 Support roller 26 Secondary transfer roller (transfer means)
28 Fixing device (fixing means)
30 Intermediate transfer member cleaning device

Claims (6)

Ferrite particles containing 3.0% by mass or more and 12.0% by mass or less of magnesium,
Coating the ferrite particles, a coating layer containing a resin and metal oxide particles having a volume resistance of 10 ⁶ Ω · cm or less;
Including
A carrier for electrostatic charge development, wherein a difference (absolute value) between an electronegativity of a metal of the metal oxide particles and an electronegativity of magnesium is 0.4 or less. The electrostatic latent image developing carrier according to claim 1 BET specific surface area of the ferrite particles is less than 0.13 m ² / g or more 0.28 m ² / g.   An electrostatic charge developing developer comprising a toner and the electrostatic charge developing carrier according to claim 1.   An electrostatic charge developing developer cartridge which is detached from the image forming apparatus and contains the electrostatic charge developing developer according to claim 3.   A developer that stores the developer for developing electrostatic charge according to claim 3 and that develops the electrostatic latent image formed on the surface of the electrostatic latent image holding member with the developer to form a toner image; A process cartridge that is detachable from the image forming apparatus.   4. An electrostatic latent image holder, charging means for charging the surface of the electrostatic latent image holder, electrostatic latent image forming means for forming an electrostatic latent image on the surface of the electrostatic latent image holder, and Developing means for developing the electrostatic latent image with the developer for electrostatic charge development described in 1 above, forming a toner image, transfer means for transferring the toner image to a recording medium, and fixing the toner image to the recording medium. An image forming apparatus.