JP2011034012A - Resin-coated carrier, method for producing the same, two-component developer which contains the resin-coated carrier, developing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin-coated carrier which prevents its resin-coated layer formed on a surface of a carrier core material from being inconsistent in thickness to stably electrify a toner. <P>SOLUTION: The resin-coated carrier 50 has the carrier core material 51 and the resin-coated layer 52 formed on the surface of the carrier core material 51. The carrier core material 51 is composed of a porous material in which surface pores 51a are formed, and its apparent density is 1.6 g/cm<SP>3</SP>or larger and 2.0 g/cm<SP>3</SP>or smaller. The resin-coated layer 52 is a layer; which is formed by a spray coating method and includes 1 pt.wt. or more and 5 pts.wt. or less of resin per 100 pts.wt. of the carrier core material 51; and contains crosslinked type resin microparticles 53. Then, the resin-coated carrier 50 is composed so that a volume average particle diameter of the crosslinked type resin microparticles 53 contained in the resin-coated layer 52 and an area average diameter of the surface pores 51a may satisfy a prescribed relational expression. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a resin-coated carrier used in an electrophotographic system for developing and visualizing an electrostatic latent image formed on an image carrier, a method for producing the same, and a two-component developer including the resin-coated carrier, The present invention relates to a developing device and an image forming apparatus using the two-component developer.

With the recent remarkable development of OA (Office Automation) equipment, image forming apparatuses such as copying machines, printers, and facsimile machines that perform image forming processing using an electrophotographic system have become widespread.

  In an image forming apparatus using such an electrophotographic system, for example, a charging process, an exposure process, a development process, a transfer process, a fixing process, and a cleaning process are performed in order to form an image. In the charging step, the surface of the photoconductor as an image carrier is uniformly charged in a dark place. In the exposure step, the signal light of the original image is projected onto the charged photoconductor to remove the charge at the exposed portion and form an electrostatic image (electrostatic latent image) on the surface of the photoconductor. In the development step, an electrostatic image developing toner (hereinafter simply referred to as “toner” unless otherwise specified) is supplied to the electrostatic image on the surface of the photoreceptor to form a toner image (visible image). In the transfer step, the toner image on the surface of the photoreceptor is transferred to the recording medium by applying a charge having a polarity opposite to that of the toner to the recording medium. In the fixing step, the toner image on the recording medium is fixed by means such as heating and pressing. In the cleaning process, the toner remaining on the surface of the photoreceptor without being transferred to the recording medium is collected. An image forming apparatus using an electrophotographic system forms a desired image on a recording medium through the above steps.

  In an image forming apparatus using an electrophotographic system, a one-component developer containing only toner or a two-component developer containing toner and carrier is used as a developer for developing a toner image. The two-component developer is given a function of stirring, transporting and charging the toner by the carrier. Therefore, since the two-component developer does not require the toner to have a carrier function, the functions are separated and the controllability is improved and a high-quality image is easily obtained as compared with the one-component developer containing the toner alone. It has the characteristics.

  The carrier has two basic functions: a function of stably charging the toner to a desired charge amount, and a function of transporting the toner to the photoreceptor. The carrier is stirred in the developing tank, conveyed onto the magnet roller, forms a magnetic spike, passes through the regulating blade, returns to the developing tank again, and is repeatedly used. The carrier is required to develop a stable basic function, particularly to stably charge the toner, as it is continuously used. However, since the carrier generally has a high density and a large stirring torque, a large amount of driving power is required for stirring in the developing tank.

  Here, in recent years, the carrier for reducing the power consumption of the image forming apparatus has been improved, and in order to reduce the agitation torque of the developing tank and reduce the power consumption, many studies have been made to reduce the density of the carrier. ing. Furthermore, low density carriers tend to be studied from the viewpoint of extending the life of carriers. In order to reduce the carrier density, it is important to reduce the density of the carrier core itself.

  In order to solve such a problem, Patent Documents 1 and 2 disclose a carrier in which a void is formed in a carrier core material provided with a void to reduce the density and the surface of the carrier core material is coated with a silicone resin. It is disclosed.

JP 2006-337579 A JP 2007-57943 A

  The amount of resin used for coating the carrier core material is usually about 2 parts by weight with respect to the carrier core material, but the carrier disclosed in Patent Documents 1 and 2 requires at least 10 parts by weight and is a manufacturing viewpoint. Therefore, it is not realistic. Specifically, the amount of resin used increases the cost for carrier production. Also, since the amount of resin used is large, it is difficult to control the thickness of the resin coating covering the surface of the carrier core material filled with the resin, and when adding a resin that can sufficiently impregnate the voids of the carrier core material Carrier particles easily adhere to each other, and a uniform resin film cannot be formed. Thus, the resin-coated carrier with a non-uniform thickness of the resin coating layer formed on the surface of the carrier core material has a non-uniform wear ratio of the resin coating layer due to stirring in the developing tank, and stabilizes the toner. Cannot be charged.

  Therefore, an object of the present invention is to prevent the resin coating layer formed on the surface of the carrier core material made of a porous material from being uneven in thickness, thereby reducing the power consumption and increasing the number of printed sheets. Another object of the present invention is to provide a resin-coated carrier capable of stably charging a toner and a method for producing the same. Another object of the present invention is to provide a two-component developer including the resin-coated carrier, and a developing device and an image forming apparatus using the two-component developer.

The present invention is a resin-coated carrier having a carrier core material and a resin coating layer formed on the surface of the carrier core material,
The carrier core material is composed of a porous material in which pores are formed on the surface, and the apparent density is 1.6 g / cm ³ or more and 2.0 g / cm ³ or less,
The resin coating layer is a layer formed of a resin in an amount of 1 part by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the carrier core material formed by a spray coating method, and contains crosslinked resin fine particles.
A resin-coated carrier satisfying the following formula (1) when the volume average particle diameter of the crosslinked resin fine particles is Da (μm) and the area average diameter of the pores is Db (μm). .
(Db + 0.3 μm)>Da> Db (1)

Further, the invention is characterized in that the resin coating layer contains conductive particles.
The present invention is also characterized in that the volume average particle size is 25 μm or more and 50 μm or less.

  Further, the present invention is characterized in that the crosslinked resin fine particles are silicone resin fine particles.

  In the present invention, the ratio of the total projected area of the crosslinked resin fine particles to the total surface area of the carrier core material ((total projected area of the crosslinked resin fine particles / total surface area of the carrier core material) × 100) is 10% or more. % Or less.

The present invention is also a method for producing the resin-coated carrier,
Crosslinked resin fine particles are adhered to the surface of a carrier core material that is composed of a porous material having pores formed on the surface and has an apparent density of 1.6 g / cm ³ or more and 2.0 g / cm ³ or less. A cross-linking resin fine particle addition step;
Coated resin containing 1 part by weight or more and 5 parts by weight or less of resin with respect to 100 parts by weight of the carrier core material with respect to the carrier core material having the cross-linked resin fine particles attached to the surface, obtained in the step of adding the crosslinkable resin fine particles A coating step of forming a resin coating layer by spraying the liquid by a spray coating method,
The carrier core material and the crosslinkable resin fine particles used in the crosslinkable resin fine particle addition step have a volume average particle diameter of the crosslinkable resin fine particles as Da (μm) and an area average diameter of the pores as Db (μm). In this case, the resin-coated carrier is produced by satisfying the following formula (1).
(Db + 0.3 μm)>Da> Db (1)

  The present invention is also a two-component developer comprising the resin-coated carrier and a toner containing a binder resin and a colorant.

  In addition, the present invention is a developing device that performs development using the two-component developer.

  The present invention also provides an image forming apparatus comprising the developing device.

According to the present invention, the resin-coated carrier has a carrier core material and a resin coating layer formed on the surface of the carrier core material. The carrier core material is made of a porous material having pores formed on the surface, and has an apparent density of 1.6 g / cm ³ or more and 2.0 g / cm ³ or less. The resin coating layer contains cross-linked resin fine particles. In the resin-coated carrier, the volume average particle diameter of the crosslinked resin fine particles and the area average diameter of the pores formed on the surface of the carrier core material satisfy the above formula (1). It is blocked by fine particles. Therefore, it can prevent that resin which comprises a resin coating layer transfers to the space | gap inside the carrier core material of a porous material, and is impregnated. Accordingly, a resin coating layer having a uniform thickness is formed on the surface of the carrier core material in which the pores formed on the surface are blocked with the cross-linked resin fine particles. A resin-coated carrier that can be stably charged can be obtained.

  The resin coating layer is a layer made of a resin having an amount of 1 part by weight or more and 5 parts by weight or less based on 100 parts by weight of the carrier core material formed by spray coating. By forming the resin coating layer by spray coating, a thick resin coating layer can be formed with a relatively small resin amount of 1 to 5 parts by weight with respect to 100 parts by weight of the carrier core material. it can. Thus, when the amount of resin used for forming the resin coating layer is small, it becomes easy to control the thickness of the resin coating layer during the manufacture of the resin-coated carrier, and further, the adhesion between the carrier core materials is suppressed and uniform. A resin coating layer can be formed. In addition, the cost for manufacturing the carrier can be reduced. And since the resin coating layer is thick, a long-life resin-coated carrier can be obtained. Thus, a resin-coated carrier having a uniform resin coating layer and a large film thickness can have good toner chargeability over a long period of time.

  According to the invention, the resin coating layer contains conductive particles. As a result, the resin-coated carrier has an improved charge imparting property to the toner.

  According to the invention, the resin-coated carrier has a volume average particle size of 25 μm or more and 50 μm or less. A resin-coated carrier having a volume average particle diameter of 25 μm or more has less carrier adhesion, which is a phenomenon in which the carrier itself adheres to an image carrier on which an electrostatic latent image is formed, and can prevent image quality from deteriorating. it can. In addition, a resin-coated carrier having a volume average particle diameter of 50 μm or less has a high toner holding ability, and can suppress deterioration of graininess of an image formed by the toner. Therefore, a resin-coated carrier having a volume average particle diameter of 25 μm or more and 50 μm or less can form a high-definition high-quality image.

  Further, according to the present invention, by using silicone resin fine particles as the crosslinkable resin fine particles, the toner coating can be imparted to the toner for a long period of time without giving a large change in charging performance to the resin coating layer formed on the surface of the carrier core material. Ability can be stabilized.

  According to the invention, the ratio of the total projected area of the crosslinked resin fine particles to the total surface area of the carrier core material ((total projected area of the crosslinked resin fine particles / total surface area of the carrier core material) × 100) is 10% or more. By setting the ratio to less than or equal to%, the pores of the carrier core material can be blocked and aggregation of the crosslinked resin fine particles can be suppressed, so that the resin coating layer can be uniformly formed on the surface of the carrier core material.

  According to the invention, the method for producing a resin-coated carrier includes a crosslinking resin fine particle addition step and a coating step. In the cross-linking resin fine particle addition step, the cross-linking resin fine particles are adhered to the surface of the carrier core material. In the coating step, a resin coating layer is formed on the carrier core material having the cross-linked resin fine particles attached to the surface. Here, in the cross-linking resin fine particle addition step, since the cross-linking resin fine particles and the carrier core material satisfying the above formula (1) are used, the pores formed on the surface are blocked by the cross-linking resin fine particles. The obtained carrier core material can be obtained. The resin coating layer is formed on the surface of the carrier core material by forming the resin coating layer on the carrier core material in which the pores formed on the surface are blocked with the crosslinked resin fine particles. A resin-coated carrier can be obtained. Thereby, it is possible to obtain a resin-coated carrier with low power consumption and capable of stably charging the toner even when the number of printed sheets is increased.

  In the coating step, a coating resin solution containing 1 to 5 parts by weight of resin with respect to 100 parts by weight of the carrier core material is sprayed by a spray coating method. By forming the resin coating layer by spray coating, a thick resin coating layer can be formed with a relatively small resin amount of 1 to 5 parts by weight with respect to 100 parts by weight of the carrier core material. it can. Thus, when the amount of resin used for forming the resin coating layer is small, it becomes easy to control the thickness of the resin coating layer during the manufacture of the resin-coated carrier, and further, the adhesion between the carrier core materials is suppressed and uniform. A resin coating layer can be formed. In addition, the cost for manufacturing the carrier can be reduced. And since the resin coating layer is thick, a long-life resin-coated carrier can be obtained. Thus, a resin-coated carrier having a uniform resin coating layer and a large film thickness has good toner chargeability over a long period of time.

  According to the invention, the two-component developer includes the resin-coated carrier according to the invention and a toner containing a binder resin and a colorant. Since the resin-coated carrier according to the present invention can give a stable charge amount to the toner, it can be a two-component developer having a stable charge amount even when the number of printed sheets is increased. When such a two-component developer is used, an image can be reproduced with high definition, color reproducibility is good, image density is high, and a high-quality image free from image defects such as fog is stably obtained over a long period of time. Can be formed.

  Further, according to the present invention, since the developing device performs development using the two-component developer according to the present invention, it is possible to perform development with toner having a stable charge amount even when the number of printed sheets increases, and high definition. Thus, a toner image without fog can be stably formed over a long period of time.

  According to the invention, the image forming apparatus includes the developing device according to the invention. Since the developing device according to the present invention can stably form a high-definition, fog-free toner image over a long period of time, the image forming device can reproduce an image with high definition and color reproducibility. It is possible to stably form a high-quality image having a good image density and a high image density free from image defects such as fogging over a long period of time.

It is a figure which shows the structure of the resin coating carrier 50 which is one Embodiment of this invention. 1 is a cross-sectional view showing a configuration of a fluidized bed type coating apparatus 100. 1 is a diagram illustrating a configuration of a developing device 20 according to an embodiment of the present invention.

1. Resin-coated carrier FIG. 1 is a diagram showing a configuration of a resin-coated carrier 50 according to an embodiment of the present invention. The resin-coated carrier 50 is used for an electrophotographic developer that develops an electrostatic latent image formed on a photoconductor, which is an image carrier, and visualizes the toner. Two basic functions, i.e., a function of stably charging toner and a function of transporting toner to the photoreceptor. The resin-coated carrier 50 includes a carrier core material 51 and a resin coating layer 52 formed on the surface of the carrier core material 51.

(1) Carrier core material The carrier core material 51 constituting the resin-coated carrier 50 of the present embodiment is composed of a porous material in which voids 51b are formed and pores 51a are formed on the surface. The apparent density is 1.6 to 2.0 g / cm ³ . In the resin-coated carrier 50 of the present embodiment, pores 51a (hereinafter referred to as “surface pores 51a”) formed on the surface of the carrier core material 51 are cross-linked resins contained in the resin coating layer 52 described later. The opening is closed by the fine particles 53.

The resin-coated carrier 50 including the carrier core material 51 having an apparent density of 2.0 g / cm ³ or less can reduce the driving torque of a magnet roller or the like inside the developing tank during the agitation, thereby saving power. become. Further, the toner and the resin-coated carrier 50 are constantly stirred inside the developing tank during development, but if the apparent density is sufficiently small, the stirring stress applied to the resin-coated carrier 50 and the wear of the resin-coated layer 52 are reduced. Therefore, even if the number of printed sheets increases, the resin-coated carrier 50 that can give a stable charge amount to the toner can be obtained. In addition, since the carrier core material 51 having an apparent density of 1.6 g / cm ³ or more does not have an excessively large area average diameter of the surface pores 51a, the crosslinked resin fine particles contained in the resin coating layer 52 are used. Thus, the resin-coated carrier 50 in which the surface pores 51 a are sufficiently blocked by the 53 can be obtained.

  In the resin-coated carrier 50 of the present embodiment, the surface pores 51 a of the carrier core material 51 are formed so that the total area is a ratio of 5% to 30% with respect to the total surface area of the carrier core material 51. Yes. Further, the surface pores 51a are formed so that the area average diameter is 0.3 μm or more and 1.0 μm or less. When the area ratio of the surface pores 51a is less than 5%, the carrier core material 51 having a sufficiently small apparent density cannot be obtained. Further, when the area ratio of the surface pores 51a exceeds 30% or the area average diameter exceeds 1 μm, the resin in which the surface pores 51a are sufficiently blocked by the silicone resin fine particles 53 contained in the resin coating layer 52. The coated carrier 50 cannot be used. Here, the area average diameter of the surface pores 51a is the area percentage of the accumulated area with respect to all the surface pores in the accumulated area distribution obtained by integrating the surface pores 51a formed on the surface of the carrier core material 51 from the smaller diameter side. The equivalent circle diameter is 50%.

  As the carrier core material 51, those commonly used in this field can be used. For example, magnetic metals such as iron, copper, nickel and cobalt, and magnetic oxides such as ferrite and magnetite can be used.

Ferrite, which is a magnetic oxide, is a group of iron oxides generally having a composition of MO · Fe ₂ O ₃ . Examples of M include divalent metal ions such as Fe ²⁺ , Mn ²⁺ , Mg ²⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , and Zn ²⁺ . Ferrite is obtained by mixing powders of these metal oxides containing divalent metal ions and iron oxide, and after compression molding and firing, the metal oxide may be only one kind, and 2 It may be more than types. When the metal oxide has a mixed composition, the controllable range of magnetic characteristics in the carrier core material 51 is widened.

As a raw material of M, Fe ₂ O ₃ is suitable if it is a metal oxide containing Fe ²⁺ . MnCO ₃ is suitable as long as it is a metal oxide containing Mn ²⁺ , but Mn ₃ O ₄ or the like may be used. As the metal oxide containing Mg ²⁺ , MgCO ₃ and Mg (OH) ₂ are preferable.

  The ferrite includes soft ferrite exhibiting soft magnetism and hard ferrite exhibiting hard magnetism. In this embodiment, the magnetic oxide is preferably soft ferrite. Since hard ferrite is a magnet, the residual magnetization is large. If the magnetic oxide is hard ferrite, the resin-coated carrier particles adhere to each other and the fluidity as a developer decreases, or the resin-coated carrier 50 is magnetized. Although it may be difficult to separate from the roller, the magnetic oxide is soft ferrite, so the residual magnetization can be reduced to 10 emu / g or less, the flowability as a developer is good, and the resin coating is easy to separate from the magnet roller etc. Carrier 50 can be used.

(2) Resin Coating Layer The resin coating layer 52 is formed by a resin coating composition comprising a resin in an amount of 1 part by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the carrier core material 51. It is a layer formed by spray coating so as to cover, and contains cross-linked resin fine particles 53. Examples of the crosslinked resin fine particles 53 include silicone resin fine particles, melamine resin fine particles, benzoguanamine resin fine particles, and amorphous silica fine particles, and silicone resin fine particles are preferable. By using silicone resin fine particles as the crosslinkable resin fine particles 53, the charge imparting ability to the toner can be provided over a long period of use without giving a large change in charging performance to the resin coating layer 52 formed on the surface of the carrier core material 51. A stable resin-coated carrier 50 can be obtained. The resin coating composition constituting the resin coating layer 52 includes a cross-linked silicone resin and additives such as conductive particles, amino group-containing silane coupling agents, resins other than silicone resins, and bifunctional silicone oils as necessary. It is a mixture in which one or more selected ones are mixed.

The crosslinked resin fine particles 53 contained in the resin coating layer 52 satisfy the following formula (1) when the volume average particle diameter Da is Db as the area average diameter of the surface pores 51a of the carrier core material 51, It is comprised so that the surface pore 51a of the carrier core material 51 may be plugged up.
(Db + 0.3 μm)>Da> Db (1)

  At this time, in the resin-coated carrier 50, the total area of the open surface pores 51a (surface pores not blocked by the crosslinked resin fine particles) after the addition of the crosslinked resin fine particles 53 with respect to the total surface area of the carrier core material 51 is obtained. The crosslinkable resin fine particles 53 are carrier cores so that the ratio P1 ((total area of the open surface pores 51a after addition of the crosslinkable resin fine particles 53 / total surface area of the carrier core material) × 100) is 0 to 5%. The surface pores 51a of the material 51 are blocked.

  When the ratio P1 (hereinafter referred to as “opening surface pore ratio P1”) exceeds 5%, the resin-coated carrier 50 in which the surface pores 51a are sufficiently blocked by the crosslinked resin fine particles 53 cannot be obtained. .

  The opening surface pore ratio P1 is calculated as follows. First, the carrier core material 51 before and after the addition of the crosslinkable resin fine particles 53 is photographed at a magnification of 1000 times with an electron microscope (trade name: VE-9500, manufactured by Keyence Corporation). Next, a half of the radius of the carrier core material 51 from the center of the carrier core material 51 is trimmed from the photograph, and image analysis software (trade name: A image-kun, manufactured by Asahi Kasei Engineering Co., Ltd.) By extracting and analyzing the contour of the surface pore 51 a of the carrier core material 51, the total surface pore area and the area average diameter of the carrier core material 51 are calculated. Such an analysis is performed for each of the 50 particles with respect to the carrier core material 51 before and after the addition of the crosslinkable resin fine particles 53, and the average value is defined as the total surface pore area and the area average diameter of the carrier core material 51. Then, the area of the trimmed region is defined as the total surface area of the carrier core material 51, and the aperture surface pore ratio P1 is calculated.

  Further, in the resin-coated carrier 50, the ratio P2 of (the total projected area of the cross-linked resin fine particles) of the total projected area of the cross-linked resin fine particles 53 to the total surface area of the carrier core material 51 (the total projected area of the cross-linked resin fine particles). The cross-linked resin fine particles 53 are preferably added to the resin coating layer 52 so that the total surface area of the carrier core material) × 100) is 10% or more and 30% or less. When the ratio P2 (hereinafter referred to as “resin fine particle addition ratio P2”) is less than 10%, the resin-coated carrier 50 in which the surface pores 51a are sufficiently blocked by the crosslinked resin fine particles 53 cannot be obtained. . Moreover, when the resin fine particle addition ratio P2 exceeds 30%, aggregation between the cross-linked resin fine particles 53 increases, and the uniformity of the resin coating layer 52 is deteriorated.

  The resin fine particle addition ratio P2 is calculated as follows. First, the surface area (or projected area) per particle is calculated from the radius of the crosslinked resin fine particles 53 (1/2 of the volume average particle diameter). Further, the number of added particles of the crosslinkable resin fine particles 53 with respect to the carrier core material 51 is calculated from the radius of the crosslinkable resin fine particles 53, the apparent density of the carrier core material 51 and the added weight of the crosslinkable resin fine particles 53. Then, using the surface area per particle of the crosslinked resin fine particles 53 calculated as described above and the number of added particles of the crosslinked resin fine particles 53, the total projected area of the crosslinked resin fine particles is calculated. Using this calculation result, the resin fine particle addition ratio P2 is calculated.

  As described above, since the crosslinked resin fine particles 53 contained in the resin coating layer 52 satisfy the formula (1) and close the surface pores 51 a of the carrier core material 51, the resin coating layer 52. It is possible to prevent the resin in the resin coating composition constituting the resin from being transferred to and impregnated into the void 51b inside the carrier core material 51 of the porous material. Therefore, the thickness of the resin coating layer 52 formed on the surface of the carrier core material 51 is prevented from becoming non-uniform, and the wear rate of the resin coating layer 52 due to stirring in the developing tank becomes uniform, thereby stabilizing the toner. Thus, the resin-coated carrier 50 can be charged.

  The cross-linked resin fine particles 53 have a volume average particle diameter Da set to 0.3 μm or more and 1.0 μm or less. When the volume average particle diameter Da of the crosslinked resin fine particles 53 is less than 0.3 μm, the resin-coated carrier 50 in which the surface pores 51 a are sufficiently blocked by the crosslinked resin fine particles 53 cannot be obtained. Moreover, when the volume average particle diameter Da of the crosslinkable resin fine particles 53 exceeds 1.0 μm, aggregation between the crosslinkable resin fine particles 53 increases, and the uniformity of the resin coating layer 52 is deteriorated.

  The resin coating layer 52 may contain conductive particles as a conductive material. As a result, the resin-coated carrier 50 has an improved charge imparting property to the toner. As the conductive particles, for example, conductive carbon black, oxides such as conductive titanium oxide and tin oxide are used. Carbon black is suitable for developing conductivity with a small addition amount, but there is a concern that the color toner may be desorbed from the resin coating layer 52 of the resin-coated carrier 50. In such a case, conductive titanium oxide doped with antimony is suitable.

(3) Resin-coated carrier The resin-coated carrier 50 formed by forming the resin coating layer 52 on the surface of the carrier core material 51 preferably has a volume average particle diameter of 25 μm or more and 50 μm or less. The resin-coated carrier 50 having a volume average particle diameter of 25 μm or more has less carrier adhesion, which is a phenomenon that the carrier itself adheres to an image carrier on which an electrostatic latent image is formed, and prevents image quality from deteriorating. Can do. In addition, the resin-coated carrier 50 having a volume average particle diameter of 50 μm or less has a high toner holding ability, and can suppress the deterioration of the graininess of an image formed by the toner. Therefore, the resin-coated carrier 50 having a volume average particle diameter of 25 to 50 μm can form a high-definition high-quality image.

  Further, in the resin-coated carrier 50 of the present embodiment, the void 51b formed inside the carrier core material 51 is not filled with resin. Therefore, it is possible to reduce the amount of resin used at the time of manufacturing than the resin-coated carrier 50 in which the voids 51b are filled with resin, and to suppress adhesion between carrier particles due to the large amount of resin used at the time of manufacturing. be able to. Further, the manufacturing cost can be reduced.

(4) Manufacturing method of resin-coated carrier The manufacturing method of the resin-coated carrier 50 of the present embodiment includes a weighing process, a mixing process, a pulverizing process, a granulating process, a calcining process, a baking process, and a crushing process. A process, a classification process, a silicone resin fine particle addition process, and a coating process.

[Weighing process, mixing process]
In this step, raw materials of the carrier core material 51 such as magnetic oxide are weighed and mixed to obtain a metal raw material mixture. When two or more kinds of magnetic oxides are used, the blending ratio of the two or more kinds of magnetic oxides is weighed so as to match the intended composition of the magnetic oxide.

Next, resin particles are added to the metal raw material mixture. Examples of the resin particles added here include carbon-based resin particles such as polyethylene and acrylic, and resin particles containing silicone such as silicone resin (hereinafter referred to as “silicone-based resin particles”). The carbon-based resin particles and the silicone-based resin particles are the same in that they burn in a calcining step described later and a hollow structure is generated in the calcined powder by the gas generated during the combustion. However, after the combustion, the carbon-based resin particles only generate a hollow structure in the calcined powder, but the silicone-based resin particles become SiO ₂ after combustion and remain in the generated hollow structure.

  The volume average particle diameter of the resin particles is preferably 2 to 8 μm. Moreover, it is preferable that the addition amount of a resin particle is 0.1-20 wt% with respect to the whole quantity of the raw material of the carrier core material 51. FIG. Here, by adjusting the addition amount of the resin particles, the area average diameter of the surface pores 51a formed in the obtained carrier core material 51 and the area ratio with respect to the total surface area of the carrier core material 51 can be controlled. .

[Crushing process]
In this step, the metal raw material mixture and the resin particles are introduced into a pulverizer such as a vibration mill and pulverized to a volume average particle size of 0.5 to 2.0 μm, preferably 1 μm. Next, water, 0.5 to 2 wt% binder, and 0.5 to 2 wt% dispersant are added to the pulverized product to obtain a slurry having a solid content concentration of 50 to 90 wt%. Etc. Wet pulverize. Here, polyvinyl alcohol or the like is preferable as the binder, and ammonium polycarboxylate or the like is preferable as the dispersant.

[Granulation process]
In this step, the wet-pulverized slurry is introduced into a spray dryer, sprayed into hot air at 100 to 300 ° C. and dried to obtain a granulated powder having a volume average particle size of 10 to 200 μm. In consideration of the volume average particle diameter of the resin-coated carrier 50 produced by the present production method, the obtained granulated powder is adjusted in particle size by removing coarse particles and fine powder that deviate from it using a vibration sieve. Specifically, since the volume average particle diameter of the resin-coated carrier 50 is preferably 25 to 50 μm, it is preferable to adjust the volume average particle diameter of the granulated powder to 15 to 100 μm.

[Calcination process]
In this step, the granulated powder is put into a furnace heated to 800 ° C. to 1000 ° C. and calcined in the atmosphere to obtain a calcined product. At this time, a hollow structure is formed in the granulated powder by the gas generated by burning the resin particles. When silicone resin particles are used as the resin particles, SiO ₂ that is a nonmagnetic oxide is generated in the hollow structure.

[Baking process]
In this step, the calcined product in which the hollow structure is formed is put into a furnace heated to 1100 to 1250 ° C. and fired, and converted into a ferrite to obtain a fired product. When the firing temperature is high, iron oxidation proceeds and the magnetic force decreases, so that the residual magnetization of the carrier core material 51 can be adjusted, for example, by the firing temperature. The atmosphere at the time of firing is appropriately selected according to the type of metal raw material such as magnetic oxide among the carrier core raw materials. For example, when the metal raw material is Fe and Mn (molar ratio 100: 0 to 50:50), the nitrogen atmosphere is used. When the metal raw material is Fe, Mn and Mg, a nitrogen atmosphere or an oxygen partial pressure adjusting atmosphere is preferable. When the metal raw material is Fe, Mn and Mg and the molar ratio of Mg exceeds 30%, the air atmosphere may be used. .

[Disintegration process, classification process]
In this step, the fired product obtained in the firing step is coarsely pulverized by hammer mill pulverization or the like, and then primary classified by an airflow classifier. Further, after aligning the particle size with a vibration sieve or an ultrasonic sieve, the carrier core material 51 having voids 51b inside and having surface pores 51a formed on the surface by removing non-magnetic components by applying a magnetic separator. Get.

[Crosslinking type resin fine particle addition process]
In this step, using a fluidized bed type coating apparatus, the carrier core material 51 obtained in the classification step is sprayed with a crosslinked resin fine particle dispersion in which the crosslinked resin fine particles 53 are dispersed in an organic solvent, Cross-linked resin fine particles 53 are attached to the surface of the carrier core material 51. The organic solvent is not particularly limited as long as it does not dissolve the cross-linked resin fine particles 53, and examples thereof include toluene. In the crosslinked resin fine particle dispersion, the content of the crosslinked resin fine particles 53 with respect to 100 parts by weight of the organic solvent is preferably 10 parts by weight or more and 100 parts by weight or less. If the content of the crosslinkable resin fine particles 53 is 10 parts by weight or less, it is necessary to spray a large amount of the crosslinkable resin fine particle dispersion in order to attach sufficient crosslinkable resin fine particles 53 to the surface of the carrier core material 51. A large amount of organic solvent is used, which is not preferable. When the content of the crosslinkable resin fine particles 53 is 100 parts by weight or more, the crosslinkable resin fine particles 53 cannot be uniformly dispersed in the organic solvent in the crosslinkable resin fine particle dispersion.

  As the fluidized bed type coating apparatus, for example, a fluidized bed type coating apparatus disclosed in JP 2008-229603 A can be used. FIG. 2 is a cross-sectional view showing the configuration of the fluidized bed type coating apparatus 100. In this step, a fluidized bed type coating apparatus is used, and then the coating step described later is performed as it is with the same fluidized bed type coating apparatus. The fluidized bed type coating apparatus 100 is a Wurster type fluidized bed coating apparatus.

  The fluidized bed type coating apparatus 100 includes a fluidized bed container 101, a filter system 2 installed in an upper space of the fluidized bed container 101, a draft tube 4 disposed inside the fluidized bed container 101, and a fluidized bed container 101. A spray nozzle 5 disposed at the bottom of the fluidized bed, and a gas dispersion plate 3 disposed at the bottom of the fluidized bed container 101.

  The draft tube 4 is supported by a height control mechanism (not shown) so as to be movable and adjustable in the height direction (vertical direction), and its lower end opening faces the gas dispersion plate 3 with a predetermined gap therebetween.

  The gas dispersion plate 3 includes a central region 3a provided at a position facing the lower end opening of the draft tube 4 and a peripheral region 3b around the central region 3a, and the aperture ratio is set constant over both the regions 3a and 3b. .

  A fluidized gas, for example, fluidized air (hot air) is introduced into the fluidized bed container 101 through the gas dispersion plate 3. Fluidized air is supplied to the central region 3a of the gas dispersion plate 3 via a first supply passage (not shown), and flows to the peripheral region 3b of the gas dispersion plate 3 via a second supply passage (not shown). Converted air is supplied. In the present embodiment, fluidized air supplied from an air supply source (not shown) is heated to a predetermined temperature by a heater, and is branched into a first air supply path and a second air supply path on the downstream side of the anemometer. The amount of air supplied from the first air supply path and the amount of air supplied from the second air supply path can be individually adjusted by an air volume adjusting damper (not shown). The temperature of fluidized air is preferably 20 ° C. or higher and 80 ° C. or lower. By setting such a temperature, the organic solvent in the cross-linked resin fine particle dispersion is volatilized at an appropriate speed, so that the cross-linked resin fine particles 53 can be uniformly added to the surface of the carrier core material 51.

  The spray nozzle 5 atomizes the cross-linked resin fine particle dispersion with atomizing air and sprays it upward toward the carrier core material 51 in the draft tube 4. The spray amount of the crosslinked resin fine particle dispersion is preferably 1.0 g / min or more and 10 g / min or less. When the spray amount of the cross-linked resin fine particle dispersion is less than 1.0 g / min, an amount of the cross-linked resin fine particle dispersion necessary for sufficiently attaching the cross-linked resin fine particles 53 to the surface of the carrier core material 51 is added. It takes too much time to spray, which is not preferable. If the spray amount of the crosslinked resin fine particle dispersion exceeds 10 g / min, it is difficult to uniformly adhere the crosslinked resin fine particles 53 to the surface of the carrier core material 51.

  The fluidized air (constant pressure and constant air volume) ejected from the central region 3a of the gas dispersion plate 3 into the fluidized bed container 101 through the first air supply path flows into the draft tube 4 from the lower end opening thereof. Ascending air flow is generated in the draft tube 4. Further, an upward spray flow from the spray nozzle 5 is added to this rising air flow, and a high-speed air flow is generated in the direction of the arrows 100 a and 100 b in the draft tube 4. The carrier core material 51 in the draft tube 4 rises in the draft tube 4 by riding on this high-speed air flow. Then, when passing through the upper end opening of the draft tube 4, the flow area of the air is rapidly expanded, so that the flow velocity of the air flow is reduced, and the carrier core material 51 is separated from the inner wall of the fluidized bed container 101 and the draft tube 4 by gravity. The space between the outside is lowered.

On the other hand, the fluidized air ejected from the peripheral region 3b of the gas dispersion plate 3 into the fluidized bed container 101 is fluidized so that the amount of air is ejected from the central region 3a due to the influence of the adjustment of the supply air amount by the air amount adjusting damper. Smaller than air. The carrier core material 51 that descends the space outside the draft tube 4 and reaches the bottom of the fluidized bed container 101 is dispersed by fluidized air ejected from the peripheral region 3b of the gas dispersion plate 3 with a relatively low air volume. Then, the air is sucked into the draft tube 4 where the high-speed air flow is generated by the ejector effect (suction effect), and rises again in the draft tube 4. The amount of fluidized air ejected from the central region 3a and the peripheral region 3b of the gas dispersion plate 3 is preferably 0.1 m ³ / min to 5.0 m ³ / min. By setting it as such a range, an appropriate ascending airflow can be generated in the draft tube 4.

  As described above, in the carrier core material 51 in the fluidized bed container 101, the inside of the draft tube 4 is raised, and the space between the inner wall of the fluidized bed container 101 and the outside of the draft tube 4 is lowered. A fluidized bed that circulates and forms is formed. Then, the cross-linked resin fine particle dispersion is sprayed upward from the spray nozzle 5 toward the carrier core material 51 that rises on the rising air flow in the draft tube 4. The carrier core material 51 in the draft tube 4 is wetted by the mist of the crosslinkable resin fine particle dispersion sprayed from the spray nozzle 5, and at the same time, the crosslinkable resin fine particles 53 contained in the crosslinkable resin fine particle dispersion are It adheres to the surface of the particles and solidifies by drying. As a result, the carrier core material 51 in which the surface pores 51 a are closed with the crosslinked resin fine particles 53 is obtained. The amount of the carrier core material 51 put into the fluidized bed container 101 is preferably 0.5 kg or more and 5.0 kg or less. By setting it in such a range, the crosslinked resin fine particles 53 can be uniformly attached to the surface of the carrier core material 51.

  The fluidized air rising in the fluidized bed container 101 passes through the filter system 2 and is exhausted to the outside of the apparatus by an exhaust means (exhaust fan or the like) 2a.

  The crosslinkable resin fine particles 53 contained in the crosslinkable resin fine particle dispersion are selected from those whose volume average particle diameter Da satisfies the above formula (1).

  The surface formed on the carrier core material 51 by measuring in advance the volume average particle diameter Da of the cross-linked resin fine particles 53 added to the organic solvent and adjusting the amount of resin particles added in the mixing step. You may make it satisfy | fill said Formula (1) by controlling the area average diameter Db of the pore 51a.

  The opening surface pore ratio P1 can be controlled by adjusting the addition amount of the crosslinkable resin fine particles 53 added to the crosslinkable resin fine particle dispersion.

[Coating process]
In this step, the surface of the carrier core material 51 obtained in the cross-linking resin fine particle addition step, the surface pores 51a of which are closed with the cross-linking resin fine particles 53, is applied to the resin coating composition described above. Is coated by a spray coating method using a coating resin solution dissolved in an organic solvent such as toluene to form a resin coating layer 52 on the surface of the carrier core material 51. In this way, a resin-coated carrier 50 is obtained.

  The amount of the resin as the resin coating composition is adjusted to be 1 part by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the carrier core material. By forming the resin coating layer 52 by spray coating, a thick resin coating layer 52 is formed with a relatively small resin amount of 1 to 5 parts by weight with respect to 100 parts by weight of the carrier core material. Can do. Since the amount of resin used for forming the resin coating layer 52 is small, the thickness of the resin coating layer 52 can be easily controlled during the production of the resin-coated carrier, and the adhesion between the carrier core materials 51 can be suppressed and uniform. The resin coating layer 52 can be formed. Further, since the amount of resin used for forming the resin coating layer 52 is small, the cost for manufacturing the carrier can be reduced. And since the resin coating layer 52 is thick, a long-life resin-coated carrier can be obtained. Thus, the resin-coated carrier having a uniform resin coating layer 52 and a large film thickness has good toner chargeability over a long period of time.

  For the formation of the resin coating layer 52 by the spray coating method, for example, the fluidized bed type coating apparatus 100 shown in FIG. 2 described above can be used. By using the fluidized bed type coating apparatus 100, the film thickness can be stably increased. The resin coating layer 52 can be formed. In addition, the film thickness of the resin coating layer 52 is preferably 0.1 μm or more and 5.0 μm or less. By setting it as such a range, the resistance reduction of the resin coating carrier 50 by surface exposure can be prevented, and aggregation of the resin coating carriers 50 can be prevented. The thickness of the resin-coated layer 52 of the resin-coated carrier 50 can be obtained by crushing the resin-coated carrier 50 with a mortar and then observing a cross section of the crushed resin-coated carrier 50 with a scanning electron microscope.

  In the coating resin solution, the content of the resin coating composition with respect to 100 parts by weight of the organic solvent is preferably 1.0 part by weight or more and 50 parts by weight or less. By setting it as such a range, aggregation of the carrier core materials 51 can be prevented, and the resin coating layer 52 can be uniformly formed on the surface of the carrier core material 51.

  In the cross-linking resin fine particle addition step, the carrier core material 51 is caused to flow in the fluidized bed container 101 and the cross-linking resin fine particle dispersion is sprayed from the spray nozzle 5, but in this step, the surface pores 51a are cross-linked resin fine particles. The carrier core material 51 closed with 53 is caused to flow in the fluidized bed container 101, and the coating resin liquid is sprayed from the spray nozzle 5.

  In this step, the temperature of the fluidized air is preferably 20 ° C. or higher and 80 ° C. or lower. By setting it as such a range, it can prevent that resin contained in a coating resin liquid hardens | cures before adhering to the carrier core material 51 surface, and the uniform resin coating layer 52 can be formed.

Further, the amount of fluidized air ejected from the central region 3a and the peripheral region 3b of the gas dispersion plate 3 is preferably 0.5 m ³ / min to 5.0 m ³ / min. By setting it as such a range, an appropriate ascending airflow can be generated in the draft tube 4.

  Furthermore, the spray amount of the coating resin liquid is preferably 1.0 g / min or more and 10 g / min or less. By setting it as such a range, it can prevent that resin contained in a coating resin liquid hardens | cures before adhering to the carrier core material 51 surface, and the uniform resin coating layer 52 can be formed.

  In the resin-coated carrier 50 thus obtained, no resin enters the gap 51b of the carrier core material 51. The size of the gap 51b is about 0.7 μm, and in order for the resin to enter the carrier core material 51 having this size of the gap 51b, the resin needs to permeate by capillary action. In the embodiment, since the surface pores 51 a of the carrier core material 51 are blocked by the silicone resin fine particles 53, the resin does not enter the voids 51 b formed inside the carrier core material 51.

2. Two-component developer The two-component developer includes the above-described resin-coated carrier 50 and a toner containing a binder resin and a colorant. Since the resin-coated carrier 50 can give a stable charge amount to the toner, a two-component developer having a stable charge amount even when the number of printed sheets is increased. When such a two-component developer is used, an image can be reproduced with high definition, color reproducibility is good, image density is high, and a high-quality image free from image defects such as fog is stably obtained over a long period of time. Can be formed.

(1) Toner The toner includes toner base particles, and the toner base particles include a binder resin and a colorant as essential components, and additionally include a charge control agent, a release agent, and the like. The toner contains two or more external additives having different particle diameters.

(Binder resin)
The binder resin is not particularly limited, and a known binder resin for black toner or color toner can be used. Examples include polyester resins, styrene resins such as polystyrene and styrene-acrylic acid ester copolymer resins, acrylic resins such as polymethyl methacrylate, polyolefin resins such as polyethylene, polyurethane, and epoxy resins. Moreover, you may use resin obtained by mixing a raw material monomer mixture with a mold release agent and performing a polymerization reaction. Binder resin may be used individually by 1 type, and may use 2 or more types together.

  When a polyester resin is used as the binder resin, examples of the aromatic alcohol component for obtaining the polyester resin include bisphenol A, polyoxyethylene- (2.2) -2,2-bis (4-hydroxyphenyl) propane. , Polyoxyethylene- (2.0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene- (2.0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene -(2.2) -Polyoxyethylene- (2.0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene- (6) -2,2-bis (4-hydroxyphenyl) propane , Polyoxypropylene- (2.2) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene (2.4) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene - (3.3) -2,2-bis (4-hydroxyphenyl) propane and derivatives thereof.

  The polybasic acid component of the polyester resin includes succinic acid, adipic acid, sebacic acid, azelaic acid, dodecenyl succinic acid, n-dodecyl succinic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid. , Dibasic acids such as cyclohexanedicarboxylic acid, orthophthalic acid, isophthalic acid and terephthalic acid, acids having three or more bases such as trimellitic acid, trimetic acid and pyromellitic acid, and anhydrides thereof, and lower alkyl esters. From the viewpoint of heat-resistant aggregation, terephthalic acid or its lower alkyl ester is preferred.

  Here, the acid value of the polyester resin constituting the toner is preferably 5 to 30 mgKOH / g. When the acid value is less than 5 mgKOH / g, the charging characteristics of the resin are lowered, and the charge control agent is hardly dispersed in the polyester resin. This adversely affects the charge amount stability of repeated development due to rising of the charge amount or continuous use. Therefore, the above range is preferable.

(Coloring agent)
As the colorant, various colorants can be used according to a desired color, and examples thereof include a yellow toner colorant, a magenta toner colorant, a cyan toner colorant, and a black toner colorant. .

  Examples of the colorant for yellow toner include C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 5, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 15, C.I. I. Azo pigments such as CI Pigment Yellow 17; inorganic pigments such as yellow iron oxide and ocher; I. Nitro dyes such as Acid Yellow 1, C.I. I. Solvent Yellow 2, C.I. I. Solvent Yellow 6, C.I. I. Solvent Yellow 14, C.I. I. Solvent Yellow 15, C.I. I. Solvent Yellow 19, C.I. I. Examples thereof include oil-soluble dyes such as Solvent Yellow 21.

  Examples of the colorant for magenta toner include C.I. I. Pigment red 49, C.I. I. Pigment red 57, C.I. I. Pigment red 81, C.I. I. Pigment red 122, C.I. I. Solvent Red 19, C.I. I. Solvent Red 49, C.I. I. Solvent Red 52, C.I. I. Basic Red 10, C.I. I. Disperse Red 15 etc. are mentioned.

  Examples of the colorant for cyan toner include C.I. I. Pigment blue 15, C.I. I. Pigment blue 16, C.I. I. Solvent Blue 55, C.I. I. Solvent Blue 70, C.I. I. Direct Blue 25, C.I. I. Direct Blue 86 and the like can be mentioned.

  Examples of the colorant for black toner include carbon black such as channel black, roller black, disk black, gas furnace black, oil furnace black, thermal black, and acetylene black. From these various types of carbon black, an appropriate carbon black may be appropriately selected according to the design characteristics of the toner to be obtained.

  As the colorant, in addition to these pigments, a red pigment, a green pigment, or the like may be used. A coloring agent may be used individually by 1 type, and may use 2 or more types together. Two or more of the same color can be used, and one or more of the different colors can also be used.

  The colorant may be used in the form of a masterbatch. The master batch of the colorant can be produced in the same manner as a general master batch. For example, it can be produced by kneading a melt of a synthetic resin and a colorant to uniformly disperse the colorant in the synthetic resin, and then granulating the resulting melt-kneaded product. As the synthetic resin, the same kind as that of the toner binder resin or one having good compatibility with the toner binder resin is used. At this time, the use ratio of the synthetic resin and the colorant is not particularly limited, but is preferably 30 to 100 parts by weight with respect to 100 parts by weight of the synthetic resin. The master batch is granulated to a particle size of about 2 to 3 mm.

  The amount of the colorant used is not particularly limited, but is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the binder resin. This is not the amount of the master batch but the amount of the colorant itself contained in the master batch. By using the colorant in this range, an image having a high image density and a very good image quality can be formed without impairing various physical properties of the toner.

(Charge control agent)
The charge control agent is added for the purpose of controlling the triboelectric chargeability of the toner. As the charge control agent, a charge control agent for positive charge control or negative charge control commonly used in this field can be used. Examples of charge control agents for controlling positive charge include nigrosine dyes, basic dyes, quaternary ammonium salts, quaternary phosphonium salts, aminopyrines, pyrimidine compounds, polynuclear polyamino compounds, aminosilanes, nigrosine dyes and derivatives thereof, and triphenylmethane. Derivatives, guanidine salts, amidine salts and the like can be mentioned.

  Examples of charge control agents for controlling negative charges include oil-soluble dyes such as oil black and spiron black, metal-containing azo compounds, azo complex dyes, naphthenic acid metal salts, metal complexes and metal salts of salicylic acid and its derivatives ( Examples of the metal include chromium, zinc, zirconium, etc.), boron compounds, fatty acid soaps, long-chain alkyl carboxylates, and resin acid soaps. Among these, a boron compound is particularly preferable as it does not contain a heavy metal.

  The charge control agent for controlling the positive charge and the charge control agent for controlling the negative charge may be properly used according to the respective uses. A charge control agent may be used individually by 1 type, and may use 2 or more types together as needed. The amount of the charge control agent used is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.5 to 3 parts by weight with respect to 100 parts by weight of the binder resin.

(Release agent)
As the release agent, those commonly used in this field can be used, for example, petroleum wax such as paraffin wax and derivatives thereof, microcrystalline wax and derivatives thereof, Fischer-Tropsch wax and derivatives thereof, polyolefin wax and derivatives thereof, Low molecular weight polypropylene wax and derivatives thereof, hydrocarbon-based synthetic waxes such as polyolefin polymer waxes (low molecular weight polyethylene wax and the like) and derivatives thereof, carnauba wax and derivatives thereof, rice wax and derivatives thereof, candelilla wax and derivatives thereof , Plant waxes such as wood wax, animal waxes such as beeswax and spermaceti, synthetic oil waxes such as fatty acid amides and phenol fatty acid esters, long chain carboxylic acids and their derivatives , Long chain alcohols and derivatives thereof, silicone polymers, such as higher fatty acids. Derivatives include oxides, block copolymers of vinyl monomers and waxes, graft modified products of vinyl monomers and waxes, and the like. The amount of the release agent used is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

(External additive)
As the external additive for the toner, those commonly used in this field can be used, and examples thereof include silicon oxide, titanium oxide, silicon carbide, aluminum oxide, and barium titanate. In the present embodiment, two or more kinds of external additives having different particle diameters are used in combination, and the volume average particle diameter of at least one primary particle diameter is 0.1 to 0.2 μm. When an external additive having at least one primary particle size of 0.1 to 0.2 μm is used, particularly in a color toner, transferability is improved and the external additive adheres to the carrier surface. The toner can be charged for a long time and stably without causing a decrease in charge. The amount of the external additive used is not particularly limited, but is preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the toner.

  The raw materials of these toners are mixed by a mixer such as a Henschel mixer, a super mixer, a mechano mill, and a Q-type mixer, excluding external additives, and the resulting raw material mixture is a twin-screw kneader, a single-screw kneader, and a continuous type 2 After being melt-kneaded at a temperature of about 70 to 180 ° C. by a kneader such as a roll-type kneader, the mixture is cooled and solidified. The melted and kneaded product of the toner raw material after cooling and solidification is roughly pulverized by a cutter mill, a feather mill or the like. The resulting coarsely pulverized product is finely pulverized. For fine pulverization, a jet mill, a fluidized bed type jet pulverizer, or the like is used. These pulverizers pulverize the toner particles by causing the toner particles to collide with each other by colliding the air flow containing the toner particles from a plurality of directions. As a result, non-magnetic toner base particles having a specific particle size distribution can be produced. The particle diameter of the toner base particles is not particularly limited, but the volume average particle diameter is preferably in the range of 3 to 10 μm. Furthermore, particle size adjustment such as classification may be performed as necessary. The external additive is added to the toner base particles thus produced by a known method. The toner manufacturing method is not limited to the above.

(2) Two-component developer The two-component developer can be used in a developing device to be described later, and is produced by mixing the toner and the resin-coated carrier 50. The mixing ratio of the toner and the resin-coated carrier 50 is not particularly limited, but considering the use in a high-speed image forming apparatus (40 sheets / minute or more for A4-size images), the volume average particle diameter of the resin-coated carrier 50 is / The ratio of the total projected area of the toner (the sum of the projected areas of all the toner particles) to the total surface area of the resin-coated carrier 50 (the total surface area of all the resin-coated carrier particles) when the volume average particle diameter of the toner is 5 or more ((Total projected area of toner / total surface area of resin-coated carrier 50) × 100) may be 30 to 70%. As a result, the chargeability of the toner can be stably maintained in a sufficiently good state, and it can be used as a suitable two-component developer that can form a high-quality image stably and for a long time even in a high-speed image forming apparatus.

  For example, when the volume average particle diameter of the toner is 6.5 μm, the volume average particle diameter of the resin-coated carrier 50 is 50 μm, and the ratio of the total projected area of the toner to the total surface area of the resin-coated carrier 50 is 30 to 70%, two components The developer contains about 2.2 to 5.3 parts by weight of toner with respect to 100 parts by weight of the resin-coated carrier. When high-speed development is performed with such a two-component developer, the toner consumption amount and the toner supply amount supplied to the developing tank of the developing device according to the toner consumption are maximized, and the balance between supply and demand is not lost. . When the amount of the resin-coated carrier 50 in the two-component developer is larger than about 2.2 to 5.3 parts by weight, not only the charge amount tends to be lower and desired development characteristics cannot be obtained, but also the toner. The amount of toner consumption is greater than the supply amount, and sufficient charge cannot be imparted to the toner, leading to degradation of image quality. On the other hand, when the amount of the resin-coated carrier 50 is small, the charge amount tends to be high, and it becomes difficult for the toner to be separated from the resin-coated carrier 50 by an electric field, resulting in deterioration of image quality.

  In the present embodiment, the total projected area of the toner is calculated as follows. The specific gravity of the toner is assumed to be 1.0, and calculation is performed based on the volume average particle diameter obtained with a Coulter counter (trade name: Coulter Counter Multisizer II, manufactured by Beckman Coulter, Inc.). That is, the number of toners with respect to the toner weight to be mixed is calculated, and the number of toners × the toner area (calculated assuming a circle) is set as the total toner projected area. Similarly, the surface area of the resin-coated carrier 50 is calculated from the weight of the resin-coated carrier mixed based on the particle diameter obtained from Microtrac (trade name: Microtrac MT3000, manufactured by Nikkiso Co., Ltd.). The specific gravity of the resin-coated carrier 50 at this time is 3.7. The mixing ratio is calculated by (total projected total area of toner / total surface area of resin-coated carrier 50) × 100 obtained above.

3. Development Device FIG. 3 is a diagram illustrating a configuration of the development device 20 according to an embodiment of the present invention. The developing device 20 performs development using the two-component developer 1 described above. As shown in FIG. 3, the developing device 20 includes a developing unit 10 that stores the two-component developer 1 and a developer carrier (developer conveyance) that conveys the two-component developer 1 to an image carrier (photoconductor) 15. Support) 13.

  When the two-component developer 1 composed of the resin-coated carrier 50 and the toner, which has been put in advance in the developing unit 10, is stirred by the stirring screw 12, the two-component developer 1 is charged. The two-component developer 1 is transported to a developer carrier 13 having a magnetic field generating unit (not shown) disposed therein, and is held on the surface of the developer carrier 13. The two-component developer 1 held on the surface of the developer carrier 13 is adjusted to have a constant layer thickness by the developer regulating member 14 and is formed in a proximity region between the developer carrier 13 and the image carrier 15. It is conveyed to. By applying an AC bias to the two-component developer 1 conveyed to the development area, the electrostatic charge image on the image carrier 15 is visualized by a reversal development method, and a visible image is formed on the image carrier 15. It is formed.

  Toner consumption due to visible image formation is detected by the toner concentration sensor 16 as a change in toner concentration, which is a toner weight ratio with respect to the two-component developer weight. The consumed amount is replenished from the toner hopper 17 until the toner concentration sensor 16 detects that the predetermined specified toner concentration has been reached, so that the toner concentration in the two-component developer 1 in the developing unit 10 is substantially the same. Kept constant. In this embodiment, the gap between the developer carrier 13 and the developer regulating member 14 and the gap between the developer carrier 13 and the image carrier 15 in the development region are set to 0.4 mm, for example. This is merely an example, and is not limited to this value. As described above, the developing device 20 according to the present embodiment performs development using the two-component developer according to the present embodiment. Therefore, even when the number of printed sheets increases, the developing device 20 can perform development with toner having a stable charge amount. A high-definition and fog-free toner image can be stably formed over a long period of time.

4. Image Forming Apparatus The image forming apparatus according to the present embodiment includes the developing device 20 described above. Other configurations can be the same as those of a known electrophotographic image forming apparatus. For example, an image carrier, a charging unit, an exposure unit, a transfer unit, a fixing unit, and an image carrier. A cleaning unit; and an intermediate transfer member cleaning unit. The image carrier has a photosensitive layer capable of forming an electrostatic charge image on the surface. The charging unit charges the surface of the image carrier to a predetermined potential. The exposure means irradiates the image carrier with the surface charged with signal light corresponding to the image information to form an electrostatic charge image (electrostatic latent image) on the surface of the image carrier. The transfer unit transfers the toner image on the surface of the image carrier developed by the toner supplied from the developing device 20 to the intermediate transfer member, and then transfers the toner image to the recording medium. The fixing unit fixes the toner image on the surface of the recording medium to the recording medium. The image carrier cleaning means removes toner and paper dust remaining on the surface of the image carrier after the transfer of the toner image to the recording medium. The intermediate transfer member cleaning unit removes excess toner and the like attached to the intermediate transfer member.

  The image forming apparatus of this embodiment includes the developing device 20 described above. Since the developing device 20 can stably form a high-definition, non-fogging toner image over a long period of time, the image forming device of this embodiment also reproduces an image with high definition and color reproduction. It is possible to stably form a high-quality image having good properties and high image density and free from image defects such as fogging over a long period of time.

(Example)
Examples and comparative examples according to the present invention will be described below. The present invention is not limited to this example unless it exceeds the gist. In the following, “part” means “part by weight”. Unless otherwise specified, “%” indicates “% by weight”.

  The apparent density of the carrier core material, the area average diameter of the surface pores of the carrier core material, the volume average particle diameter of the resin-coated carrier, and the volume average particle diameter of the toner used in the examples and comparative examples are as follows. The measurement was performed as described above.

[Apparent density of carrier core]
The apparent density of the carrier core material was measured according to JIS Z2504 2000.

[Area average diameter of surface pores of carrier core material]
The carrier core material before and after the addition of the crosslinkable resin fine particles was photographed with an electron microscope (trade name: VE-9500, manufactured by Keyence Corporation) at a magnification of 1000 times. Next, an area of ½ of the radius of the carrier core material from the center of the carrier core material is trimmed from the photograph, and the carrier core is imaged from that area by image analysis software (trade name: A Image-kun, manufactured by Asahi Kasei Engineering Co., Ltd.). By extracting and analyzing the outline of the surface pores of the material, the total surface pore area and the area average diameter of the carrier core material were calculated. Such an analysis was performed for each of the 50 particles with respect to the carrier core material before and after the addition of the crosslinkable resin fine particles, and the average value was defined as the total surface pore area and the area average diameter of the carrier core material.

[Volume average particle diameter of resin-coated carrier]
Emulgen 109P (manufactured by Kao Corporation, polyoxyethylene lauryl ether HLB 13.6) 5% About 10 to 15 mg of a measurement sample was added to 10 mL and dispersed with an ultrasonic disperser for 1 minute. About 1 mL of this was added to a predetermined location of Microtrac MT3000 (Nikkiso Co., Ltd.) and then stirred for 1 minute to confirm that the scattered light intensity was stable and measured.

[Volume average particle diameter of toner]
In a 100 mL beaker, 20 mL of a 1% aqueous solution (electrolytic solution) of sodium chloride (first grade) was added, 0.5 mL of alkylbenzene sulfonate (dispersant) and 3 mg of a toner sample were sequentially added thereto, and ultrasonically dispersed for 5 minutes. . To this, a 1% aqueous solution of sodium chloride (first grade) was added so that the total amount would be 100 mL, and again ultrasonically dispersed for 5 minutes was used as a measurement sample. For this measurement sample, a Coulter Counter TA-III (trade name, manufactured by Coulter, Inc.) was used, and measurement was performed under the conditions of an aperture diameter of 100 μm and a measurement target particle diameter of 2 to 40 μm on a number basis. Calculated.

  A method for producing resin-coated carriers and toners of Examples and Comparative Examples will be described.

<Production of resin-coated carrier>
Example 1
[Weighing process, mixing process]
As a raw material for the carrier core material, finely pulverized Fe ₂ O ₃ and MgCO ₃ were prepared, weighed so that the molar ratio was Fe ₂ O ₃ : MgCO ₃ = 80: 20, and mixed to obtain a metal raw material mixture. Obtained. Polyethylene resin particles (trade name: LE-1080, manufactured by Sumitomo Seika Co., Ltd.) having a volume average particle diameter of 5 μm corresponding to 5 wt% with respect to all raw materials of the carrier core material, and polycarboxylic acid corresponding to 1.5 wt% An aqueous solution was prepared by adding an ammonium-based dispersant, SN wet 980 corresponding to 0.05 wt% (wetting agent, manufactured by San Nopco Co., Ltd.), and polyvinyl alcohol (binder) corresponding to 0.02 wt% to water. .

[Crushing process]
The metal raw material mixture was added to the aqueous solution and stirred to obtain a slurry having a concentration of 75 wt%. This slurry was wet pulverized by a wet ball mill and stirred for a while until the volume average particle diameter became 1 μm.

[Granulation process]
The slurry was sprayed with a spray dryer to obtain a dried granulated product having a volume average particle size of 10 to 200 μm. Coarse grains were separated from the granulated product using a sieve net having a mesh size of 61 μm.

[Calcination process]
The dried granulated product was calcined by heating at 900 ° C. in the atmosphere, and the resin particle component was decomposed to obtain a calcined product.

[Baking process]
The calcined product was calcined for 5 hours in a nitrogen atmosphere at 1160 ° C. to be converted into a ferritic product.

[Disintegration process, classification process]
The fired product was crushed with a hammer mill, fine powder was removed using an air classifier, and the particle size was adjusted with a vibrating screen having a mesh size of 54 μm to obtain a carrier core material C1. The obtained carrier core material C1 had an apparent density of 1.80 g / cm ³ and an area average diameter of surface pores of 0.60 μm.

[Crosslinking type resin fine particle addition process]
Silicone resin fine particles S1 (trade name: Tospearl, manufactured by Momentive Performance Materials Japan LLC) having a volume average particle diameter of 0.70 μm were used as the crosslinked resin fine particles. The weight of the silicone resin fine particles S1 is adjusted so that the ratio of the total projected area of the silicone resin fine particles S1 to the total surface area of the carrier core material C1 is 20%, and the silicone resin fine particles S1 are ultrasonically dispersed in 5 parts by weight of toluene. Thus, a crosslinked resin fine particle dispersion was obtained.

The carrier core material is sprayed using a fluidized bed coater (Worster fluidized bed coater, trade name: GM-140, manufactured by Dalton Co., Ltd.) shown in FIG. C1 Silicone resin fine particles S1 were attached to the surface of 100 parts by weight, and a carrier core material C1 in which the surface pores were closed with the silicone resin fine particles S1 was obtained. In the fluidized bed type coating apparatus, the spray amount of the crosslinked resin fine particle dispersion from the spray nozzle was 5 g / min. Furthermore, the temperature of the fluidized air was 60 ° C., and the amount of fluidized air ejected from the central region and the peripheral region of the gas dispersion plate was 0.5 m ³ / min.
At this time, the aperture surface pore ratio P1 was adjusted to 3%.

[Coating process]
1.5 parts of crosslinked silicone resin A (trade name: KR240, manufactured by Shin-Etsu Chemical Co., Ltd.) and 1.5 parts of crosslinked silicone resin B (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) in 15 parts of toluene Dissolved there, conductive particles (trade name: VULCAN XC-72, manufactured by Cabot Corporation) 0.20 parts, and coupling agent (trade name: AY43-059, manufactured by Toray Dow Corning Corporation) 0.20 A coating resin solution was prepared by internally adding or dispersing a part.

  In this step, 18.4 parts of the coating resin liquid is sprayed from a spray nozzle onto a carrier core material C1 whose surface pores are closed with silicone resin fine particles S1, which are in a fluid state in the fluidized bed type coating apparatus. Thus, the surface of the carrier core material C1 whose surface pores were closed with the silicone resin fine particles S1 was coated.

  Then, after passing through a curing process with a curing temperature of 200 ° C. and a curing time of 1 hour, the resin-coated carrier of Example 1 was obtained by passing through a sieve having an opening of 150 μm. The obtained resin-coated carrier of Example 1 had a volume average particle diameter of 45 μm.

The spray amount of the coating resin liquid from the spray nozzle was 5 g / min. Furthermore, the temperature of the fluidized air was 60 ° C., and the amount of fluidized air ejected from the central region and the peripheral region of the gas dispersion plate was 0.5 m ³ / min.

(Example 2)
In the coating step, the addition amount of the crosslinkable silicone resin A was changed from 1.5 parts to 0.5 parts, and the addition amount of the crosslinkable silicone resin B was changed from 1.5 parts to 0.5 parts. In the same manner as in Example 1, a resin-coated carrier of Example 2 was obtained. The resin-coated carrier of Example 2 had a volume average particle size of 45 μm.

(Example 3)
In the coating step, the addition amount of the crosslinkable silicone resin A was changed from 1.5 parts to 2.5 parts, and the addition amount of the crosslinkable silicone resin B was changed from 1.5 parts to 2.5 parts. The resin-coated carrier of Example 3 was obtained in the same manner as Example 1. The resin-coated carrier of Example 3 had a volume average particle size of 45 μm.

(Comparative Example 1)
In the coating process, except that the addition amount of the crosslinkable silicone resin A was changed from 1.5 parts to 0.3 parts, and the addition amount of the crosslinkable silicone resin B was changed from 1.5 parts to 0.3 parts. In the same manner as in Example 1, a resin-coated carrier of Comparative Example 1 was obtained. The resin-coated carrier of Comparative Example 1 had a volume average particle size of 45 μm.

(Comparative Example 2)
In the coating step, except that the addition amount of the crosslinkable silicone resin A was changed from 1.5 parts to 3.0 parts and the addition amount of the crosslinkable silicone resin B was changed from 1.5 parts to 3.0 parts. In the same manner as in Example 1, a resin-coated carrier of Comparative Example 2 was obtained. The resin-coated carrier of Comparative Example 2 had a volume average particle size of 45 μm.

(Comparative Example 3)
A resin-coated carrier of Comparative Example 3 was obtained in the same manner as in Example 1 except that the resin coating layer was produced by the dipping method. Specifically, first, a carrier core material C1 was obtained by the same method as in Example 1. The carrier core material was immersed in the cross-linked resin fine particle dispersion and heated with stirring to attach the silicone resin fine particles S1 to the surface of 100 parts by weight of the carrier core material C1. The cross-linked resin fine particle dispersion is the same as the cross-linked resin fine particle dispersion of Example 1. Next, the coated resin liquid was coated on the carrier core material C1 whose surface pores were closed with the silicone resin fine particles S1, and then the organic solvent was removed by volatilization to obtain the resin-coated carrier of Comparative Example 3. The coating resin solution is the same as the coating resin solution of Example 1, except that the addition amount of the crosslinkable silicone resin A is changed from 1.5 parts to 0.5 parts and the addition amount of the crosslinkable silicone resin B is changed from 1.5 parts. It is changed to 0.5 part.

<Production of toner>
87.5 parts of a polyester resin (trade name: FC1494, manufactured by Mitsubishi Rayon Co., Ltd.) as a binder resin, C.I. I. Pigment Red 57: 1 5 parts, release agent (trade name: HNP11, manufactured by Nippon Seiki Co., Ltd.) 6 parts, charge control agent (trade name: LR-147, manufactured by Nippon Carlit Co., Ltd.) 1.5 parts, After premixing with a Henschel mixer, the mixture was melt-kneaded with a twin-screw extrusion kneader to obtain a kneaded product.

  The kneaded product was coarsely pulverized with a cutting mill, then finely pulverized with a jet mill, and classified with an air classifier to produce toner base particles having a volume average particle size of 6.5 μm. Next, 97.8% by weight of the classified toner base particles, 1.2% by weight of silica having a primary particle diameter of 0.1 μm hydrophobized with i-butyltrimethoxysilane, and primary hydrophobized with HMDS A negatively chargeable magenta toner (non-magnetic magenta toner) was prepared by adding 1.0% by weight of silica fine particles having a particle size of 12 nm, mixing with a Henschel mixer, and performing external addition treatment.

<Preparation of two-component developer>
After putting the resin-coated carriers of the examples and comparative examples and the toner into a resin-made cylindrical container at a weight ratio such that the ratio of the total projected area of the toner to the total surface area of the resin-coated carrier is 70%, A two-component developer was prepared by mixing and stirring on a shaft-driven polybottle rotating base under the conditions of a rotation speed of 200 rpm for 1 hour.

<Evaluation>
The following evaluation was performed using the two-component developer.

[Charging rise characteristics]
A 5 ml glass bottle containing the two-component developer was stirred for 1 minute in a rotary incubator at 32 rpm, and then the two-component developer was collected and a suction-type charge amount measuring device (trade name: 210H-2A Q / M Meter) , Manufactured by TREK Co.). Further, after stirring for 3 minutes, the charge amount was measured in the same manner.

The evaluation criteria for the charge rising characteristics are as follows.
○: Good. The difference between the charge amount after 1 minute and the charge amount after 3 minutes is 5 μC / g or less in absolute value.
Δ: Yes. The difference between the charge amount after 1 minute and the charge amount after 3 minutes is more than 5 μC / g and 7 μC / g or less in absolute value.
X: Defect. The difference between the charge amount after 1 minute and the charge amount after 3 minutes is larger than 7 μC / g in absolute value.

[Life characteristics]
The two-component developer is set in a copying machine (trade name: MX-3600FN, color printing speed 36 ppm, monochrome printing speed 36 ppm, manufactured by Sharp Corporation), and an image having a printing rate of 5% is obtained at 50000 (50K) at room temperature and humidity. ) After the photograph was taken, the image density in the image area, the whiteness in the non-image area, and the charge amount of the two-component developer were measured. The image density was measured with an X-Rite 938 spectrocolorimeter. For whiteness, tristimulus values X, Y, and Z were determined using an SZ90 type spectroscopic color difference meter manufactured by Nippon Denshoku Industries Co., Ltd. The charge amount of the two-component developer at the initial stage and after actual copying of 50K sheets was measured using a suction type charge amount measuring device.

The image density evaluation criteria are as follows.
○: Good. The image density is 1.4 or higher.
Δ: Yes. The image density is 1.3 or more and less than 1.4.
X: Defect. The image density is less than 1.3.

The evaluation criteria for whiteness are as follows.
○: Good. The value of Z is 0.5 or less.
Δ: Yes. The value of Z is more than 0.5 and 0.7 or less.
X: Defect. The value of Z exceeds 0.7.

The evaluation criteria for the charging stability of the two-component developer are as follows.
○: Good. The difference between the initial charge amount and the charge amount after 50K is 3 μC / g or less in absolute value.
Δ: Yes. The difference between the initial charge amount and the charge amount after 50K is more than 3 μC / g and 5 μC / g or less in absolute value.
X: Defect. The difference between the initial charge amount and the charge amount after 50K is larger than 5 μC / g in absolute value.

[Torque measurement]
The torque was measured by stirring the two-component developer in the developing tank of the copying machine.

The evaluation criteria for torque measurement are as follows.
○: Good. The torque value is 11.5 g · cm or less.
Δ: Yes. The torque value exceeds 11.5 g · cm and is 12.5 g · cm or less.
X: Defect. The torque value exceeds 12.5 g · cm.

[Carrier adhesion]
The two-component developer was set in the copying machine, and the number of carriers adhered in a fixed area (297 mm × 24 mm) in the non-image area on the image carrier was determined. When determining the number of adhered carriers, the DC bias voltage applied to the developer carrier was 200 V, the AC bias voltage was 400 V, the frequency was 9 kHz, and the surface of the image carrier was not charged.

The evaluation criteria for carrier adhesion are as follows.
○: Good. The number of carriers attached is 14 or less.
Δ: Yes. The number of carrier attachments is 15 or more and 20 or less.
X: Defect. The number of carriers attached is 21 or more.

[Granularity]
The two-component developer is set in the copying machine, an image test chart is printed, and the granularity score value when the color difference from white is 30, 50, and 70 is used as an automatic printer image quality evaluation system (trade name: APQS). , Manufactured by Oji Scientific Instruments). The lower the graininess score value, the less the roughness of the image and the higher the image quality.

The evaluation criteria for graininess are as follows.
○: Good. The maximum score value for each color difference is smaller than 11500.
Δ: Yes. The maximum score value of each color difference is 11500 or more and 12000 or less.
X: Defect. The maximum score value for each color difference is greater than 12000.

[Comprehensive evaluation]
The evaluation criteria for comprehensive evaluation using the above evaluation results are as follows.
A: All the evaluation results of the above evaluations are “◯”.
○: The evaluation result of the above evaluation includes “Δ” but does not include “×”.
X: "x" is included in the evaluation result of the above evaluation.
The evaluation results are shown in Table 1.

From Table 1, the apparent density of the carrier core material is 1.6 g / cm ³ or more and 2.0 g / cm ³ or less, and the volume average particle diameter of the silicone resin fine particles contained in the resin coating layer and the surface of the carrier core material There is a relationship satisfying the above formula (1) between the area average diameters of the pores, the crosslinked resin fine particles are configured to block the surface pores of the carrier core material, and the resin coating layer is formed by a spray coating method. Thus, it can be seen that the resin-coated carriers of Examples 1 to 3 having a resin amount of 1 to 5 parts by weight with respect to 100 parts by weight of the carrier core material are satisfactory evaluation results.

In the resin-coated carrier of Comparative Example 1, since the amount of resin forming the resin coating layer was too small, a uniform resin coating layer could not be formed, and carrier adhesion occurred. In the resin-coated carrier of Comparative Example 2, since the amount of the resin forming the resin coating layer is too large, adhesion between the carrier core materials occurs and a uniform resin coating layer cannot be formed, and the charging stability is lowered. Since the resin-coated carrier of Comparative Example 3 was prepared by an immersion method, a uniform resin-coated layer could not be formed when the amount of resin forming the resin-coated layer was 1 part by weight with respect to 100 parts by weight of the carrier core material. Stability decreased and carrier adhesion occurred.

DESCRIPTION OF SYMBOLS 1 Two-component developer 20 Developing apparatus 50 Resin coated carrier 51 Carrier core material 51a Surface pore 51b Void 52 Resin coating layer 53 Crosslinkable resin fine particles

Claims (9)

A resin-coated carrier having a carrier core material and a resin coating layer formed on the surface of the carrier core material,
The carrier core material is composed of a porous material in which pores are formed on the surface, and the apparent density is 1.6 g / cm ³ or more and 2.0 g / cm ³ or less,
The resin coating layer is a layer formed of a resin in an amount of 1 part by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the carrier core material formed by a spray coating method, and contains crosslinked resin fine particles.
A resin-coated carrier that satisfies the following formula (1), where Da (μm) is the volume average particle diameter of the crosslinked resin fine particles and Db (μm) is the area average diameter of the pores.
(Db + 0.3 μm)>Da> Db (1)   The resin-coated carrier according to claim 1, wherein the resin-coated layer contains conductive particles.   The resin-coated carrier according to claim 1 or 2, wherein a volume average particle diameter is 25 µm or more and 50 µm or less.   The resin-coated carrier according to any one of claims 1 to 3, wherein the crosslinked resin fine particles are silicone resin fine particles.   The ratio of the total projected area of the crosslinked resin fine particles to the total surface area of the carrier core material ((total projected area of the crosslinked resin fine particles / total surface area of the carrier core material) × 100) is 10% or more and 30% or less. The resin-coated carrier according to any one of claims 1 to 4. A method for producing a resin-coated carrier according to any one of claims 1 to 5,
Crosslinked resin fine particles are adhered to the surface of a carrier core material that is composed of a porous material having pores formed on the surface and has an apparent density of 1.6 g / cm ³ or more and 2.0 g / cm ³ or less. A cross-linking resin fine particle addition step;
Coated resin containing 1 part by weight or more and 5 parts by weight or less of resin with respect to 100 parts by weight of the carrier core material with respect to the carrier core material having the cross-linked resin fine particles attached to the surface, obtained in the step of adding the crosslinkable resin fine particles A coating step of forming a resin coating layer by spraying the liquid by a spray coating method,
The carrier core material and the crosslinkable resin fine particles used in the crosslinkable resin fine particle addition step have a volume average particle diameter of the crosslinkable resin fine particles as Da (μm) and an area average diameter of the pores as Db (μm). A method for producing a resin-coated carrier, wherein the following formula (1) is satisfied.
(Db + 0.3 μm)>Da> Db (1)   A two-component developer comprising the resin-coated carrier according to claim 1 and a toner containing a binder resin and a colorant.   A developing device that performs development using the two-component developer according to claim 7.   An image forming apparatus comprising the developing device according to claim 8.

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