JP2014052529A - Carrier, and two-component developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier for electrostatic latent image development capable of suppressing the occurrence of fogging in a formed image caused by a reduction in ability of charging a toner of a carrier, in performing printing with high printing rate for a long period, by suppressing scraping-off and peeling-off of a coat layer of the carrier and adhesion of an external additive peeled off from the toner to the surface of the carrier; and to provide a two-component developer including toner and the carrier for electrostatic latent image development.SOLUTION: In a carrier for electrostatic latent image development in which a carrier core is coated with a coat layer, the coat layer comprises a plurality of layers of two or more; an innermost layer and an outermost layer of the plurality of layers are formed of a specific material, respectively; and metal oxide particles are present on at least one boundary surface between the plurality of layers.

Description

  The present invention relates to a carrier and a two-component developer.

  In general, in electrophotography, the surface of a photosensitive drum is charged by corona discharge or the like, and then exposed by a laser or the like to form an electrostatic latent image. The formed electrostatic latent image is developed with toner to form a toner image. Further, the formed toner image is transferred to a recording medium to obtain a high quality image. The toner used to form a normal toner image is obtained by mixing a colorant, a charge control agent, a release agent and the like with a binder resin such as a thermoplastic resin, and then kneading, pulverizing, and classifying steps. Toner particles (toner mother particles) having a particle diameter of 5 to 10 μm are used. For the purpose of imparting fluidity to the toner, imparting suitable charging performance to the toner, and improving the cleaning property of the toner from the photosensitive drum, inorganic fine powders such as silica and titanium oxide are used as the toner base. Externally added to the particles.

  As a developing method using such a toner, a one-component developing method using toner alone as a developer (one-component developer) and a two-component using a developer (two-component developer) in which toner and a carrier are mixed. A development method is known. In the two-component developing method using a two-component developer, the carrier charges the toner by frictional charging and also carries the toner, so that the chargeability and transportability of the toner are relatively low at the start of image formation. There is an advantage that it is easy to stabilize.

  In a two-component developer used in the two-component development method, a carrier in which a carrier core is coated with a coating layer formed of a coating agent such as an acrylic resin, a silicon resin, or an epoxy resin has been conventionally used. It was. When printing at a high printing rate for a long time using a two-component developer containing such a carrier, the external additive adhering to or detached from the toner surface and the carrier are rubbed in the developing unit. As a result, there are problems that the coating layer covering the carrier core is scraped and peeled off, and the external additive detached from the toner adheres to the surface of the coating layer. In this case, the ability to charge the toner of the carrier is reduced, and the formed image is likely to be fogged.

  Therefore, for the purpose of improving the durability of the carrier, the carrier core is coated with a multilayer coating layer of two or more layers in which the lower layer is a fluororesin and the surface layer is a silicone resin (see Patent Document 1), There has been proposed a carrier (see Patent Document 2) in which a carrier core is covered with a coat layer containing a fluororesin, and negative polarity titanium oxide is adhered to the surface of the coat layer.

JP-A-4-3333861 JP 2009-31493 A

  However, when a two-component developer containing a carrier described in Patent Document 1 is used for continuous printing at a high printing rate over a long period of time, the coat layer covering the carrier core is unlikely to peel off, but a silicone resin The surface layer of the coating layer consisting of This is because silicone resin is a relatively soft material.

  In addition, the carrier described in Patent Document 2 is less prone to peeling or scraping of the coating layer covering the carrier core when used as a two-component developer. However, when the two-component developer containing the carrier described in Patent Document 2 is used for continuous printing at a high printing rate over a long period of time, titanium oxide is detached from the surface of the coating layer, and the coating There is a problem that the coating layer is scraped off or the external additive detached from the toner adheres to the layer where the titanium oxide is detached.

  In the present invention, when a two-component developer containing a toner and a carrier for developing an electrostatic latent image is used and printing is performed at a high printing rate over a long period of time, the coating layer covering the carrier core is scraped and peeled off. Providing a carrier for developing an electrostatic latent image that can suppress the occurrence of fogging in a formed image due to a decrease in the ability of the carrier to charge toner by suppressing adhesion of the peeled external additive to the coat layer The purpose is to do. Another object of the present invention is to provide a two-component developer containing a toner and the above-described electrostatic latent image developing carrier.

  For the electrostatic latent image developing carrier in which the carrier core is coated with a coat layer, the present inventors comprise a coat layer composed of two or more layers, and the innermost layer and the outermost layer of the plurality of layers, It has been found that the above-mentioned problems can be solved by forming the metal oxide particles at the interfaces between a plurality of layers, each of which is formed of a specific material, and has completed the present invention. Specifically, the present invention provides the following.

The first aspect of the present invention is:
A carrier for developing an electrostatic latent image, wherein the carrier core is coated with a coat layer composed of two or more layers,
The plurality of layers are:
The innermost layer is a layer containing a fluororesin,
The outermost layer is a layer containing one or more kinds of resins selected from the group consisting of melamine resin, benzoguanamine resin, polyamideimide resin, and phenol resin,
The present invention relates to a carrier for developing an electrostatic latent image, wherein metal oxide particles are present at at least one of interfaces between the plurality of layers.

  A second aspect of the present invention relates to a two-component developer including a toner and the electrostatic latent image developing carrier according to the first aspect.

  According to the present invention, when printing at a high printing rate over a long period using a two-component developer containing a toner and a carrier for developing an electrostatic latent image, the coating layer covering the carrier core is scraped and peeled off. An electrostatic latent image developing carrier capable of suppressing the occurrence of fogging in a formed image due to a decrease in the ability of a carrier to charge toner by suppressing adhesion of an external additive peeled from the toner to the coating layer. Can be provided. In addition, according to the present invention, a two-component developer including toner and the above-described electrostatic latent image developing carrier can be provided.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. In addition, although description may be abbreviate | omitted suitably about the location where description overlaps, the summary of invention is not limited.

[First Embodiment]
In the carrier for developing an electrostatic latent image (hereinafter also simply referred to as a carrier) according to the first embodiment of the present invention, the carrier core is covered with a coat layer composed of two or more layers. Hereinafter, the carrier core, the coat layer, and the carrier manufacturing method constituting the carrier will be described in order.

[Carrier Core]
The type of carrier core is not particularly limited as long as it is a carrier core conventionally used for carriers for two-component developers. Specific examples of carrier cores include particles of materials such as iron, oxidized iron, reduced iron, magnetite, copper, silicon steel, ferrite, nickel, and cobalt, and these materials and metals such as manganese, zinc, and aluminum. Alloy particles, iron-nickel alloy, iron-cobalt alloy particles, titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide, zirconium oxide, silicon carbide, magnesium titanate, barium titanate, titanate Ceramic particles such as lithium, lead titanate, lead zirconate and lithium niobate, particles of high dielectric constant materials such as ammonium dihydrogen phosphate, potassium dihydrogen phosphate, Rochelle salt, and the above magnetic particles in resin And a resin carrier in which is dispersed. Among these, ferrite is preferable as the carrier core.

  The average particle size of the carrier core is not particularly limited as long as the object of the present invention is not impaired, but is preferably 15 μm or more and 150 μm or less, and more preferably 20 μm or more and 100 μm or less. The average particle size of the carrier core and the carrier is measured under the condition of a dispersion pressure of 3.0 bar using a laser diffraction particle size distribution device (HELOS (SYMPATEC)) and a dry dispersion device (RODOS (SYMPATEC)). It can be measured.

  The saturation magnetization of the carrier core is not particularly limited as long as it does not impair the object of the present invention, but is preferably 30 emu / g or more and 90 emu / g or less, more preferably 30 emu / g or more and 60 emu / g or less, and 35 emu / g or more and 45 emu / g. Particularly preferred is g or less. By using a carrier using a carrier core having a saturation magnetization in such a range as a two-component developer, an image having a desired image density can be formed even when printing is continuously performed at a low printing rate. The saturation magnetization of the carrier core can be measured using a vibrating sample magnetometer (BHV-35H (manufactured by Riken Denshi Co., Ltd.)).

[Coat layer]
The coat layer covering the carrier core is composed of two or more layers. In the plurality of layers, the innermost layer and the outermost layer each include a predetermined resin. The structure of the coat layer covering the carrier core is a multilayer composed of two or more layers including the innermost layer and the outermost layer, and metal oxide particles described later are formed at the interface between any two adjacent layers constituting the coat layer. If it exists, it will not specifically limit. The coat layer may include one or more intermediate layers between the innermost layer and the outermost layer. Hereinafter, the innermost layer, the outermost layer, the intermediate layer, and the metal oxide particles will be described.

(Innermost layer)
The innermost layer contains a fluororesin. The fluororesin of the innermost layer is not particularly limited as long as it is conventionally used as a material for a carrier coating layer contained in a two-component developer, and can be appropriately selected and used. Specific examples of the fluororesin include polytetrafluoroethylene (PTFE), perfluoroalkoxy fluororesin (PFA), tetrafluoroethylene-hexafluoropropylene copolymer (FEP), polyvinylidene fluoride (PVDF), poly And chlorotrifluoroethylene (PCTFE). Among these fluororesins, polytetrafluoroethylene (PTFE), perfluoroalkoxy fluororesin (PFA), and tetrafluoroethylene-6-6 are easily adhered to the carrier core surface and easy to form a coat layer. One or more resins selected from the group consisting of a fluorinated propylene copolymer (FEP) are more preferable. Among these, PTFE resin is particularly preferable. The content of the fluororesin in the innermost layer is not particularly limited as long as the object of the present invention is not impaired, but is preferably 80% by mass or more, more preferably 90% by mass or more, and 100% by mass with respect to the mass of the innermost layer. % Is particularly preferred.

  Other materials for the fluororesin contained in the innermost layer include melamine resin, benzoguanamine resin, polyamideimide resin, phenol resin, polyamide resin, polyimide resin, aromatic polyether ketone resin, (meth) acrylic, which will be described later. Polymer, styrene polymer, styrene- (meth) acrylic copolymer, olefin polymer (polyethylene, chlorinated polyethylene, polypropylene, etc.), polyvinyl chloride, polyvinyl acetate, polycarbonate, cellulose resin, polyester resin And resins such as unsaturated polyester resins, polyamide resins, polyurethane resins, epoxy resins, silicone resins, phenol resins, xylene resins, diallyl phthalate resins, polyacetal resins, and amino resins. These resins may be used in combination of two or more.

  Examples of commercially available PTFE resins include Lubron L2, Lubron L5, Lubron L5F (above, Daikin Industries, Ltd.), TLP10F-1, MP1100, MP1300 (above, Mitsui / DuPont Fluorochemical Co., Ltd.), TF9201, TF9205, TF9207 (above, manufactured by Sumitomo 3M Co., Ltd.), PTFE powder (manufactured by Finetech Co., Ltd.), TFW2000, TFW3000, TFW3000F (above, manufactured by Seishin Co., Ltd.). Examples of commercially available PFA resins include MP-10, MP-101, MP-102, MP-300, MP-310, MP-501, MP-502, MP-630, MP-620, MP-621 ( As mentioned above, Mitsui-DuPont Fluoro Chemical Co., Ltd.), ALGOFLON MFA 6010, ALGOFLON MFA 6012, ALGOFLON PFA 7010 (above, Solvay Chemicals) can be mentioned. Examples of commercially available FEP resins include 532-8000, 532-8110, and the like (manufactured by Mitsui DuPont Fluorochemical Co., Ltd.). Examples of commercially available PVDF resins include KYNAR 710, KYNAR 711, KYNAR 720, KYNAR 721, KYNAR 740, KYNAR 741, KYNAR 760, KYNAR 761, KYNAR 460, KYNAR 461, KYNAR 461, HD , HYLAR 461, HYLAR 7201, HYLAR 7301, SOLEF1008, SOLEF 1012, and SOLEF 1015 (above, manufactured by Solvay Chemicals).

  The mass with respect to the carrier core of the innermost layer is not particularly limited as long as the object of the present invention is not impaired. 0.5 mass part or more and 10 mass parts or less are preferable with respect to 100 mass parts of carrier cores, and 2 mass parts or more and 7 mass parts or less are more preferable. When the mass of the coat layer is too small, it is difficult to obtain a carrier capable of charging the toner to a desired charge amount. When the mass of the innermost layer is excessive, carrier particles are likely to associate with each other during the innermost layer coating.

(Outermost layer)
The outermost layer includes one or more types of resins selected from the group consisting of melamine resins, benzoguanamine resins, polyamideimide resins, and phenol resins. These resins are hard and have excellent mechanical strength and wear resistance. For this reason, the outermost layer of the coat layer covering the carrier core contains one or more kinds of resins selected from the group consisting of melamine resin, benzoguanamine resin, polyamideimide resin, and phenol resin. Layer scraping and adhesion of external additives to the coating layer can be suppressed.

  These resins may be used alone or in combination of two or more. Hereinafter, the melamine resin, the benzoguanamine resin, the polyamideimide resin, and the phenol resin included in the outermost layer will be described.

Melamine resin The melamine resin is not particularly limited as long as it does not impair the object of the present invention, and is used by appropriately selecting from melamine resins conventionally used as a material for a carrier coat layer contained in a two-component developer. be able to. The melamine resin can be prepared by addition polymerization of melamine or a melamine derivative with formaldehyde or the like. Examples of the melamine derivative include methylol melamine, methylated melamine, methylated methylol melamine, butylated melamine, butylated methylol melamine, hexamethylol melamine and the like. A melamine resin can be used in combination of 2 or more types.

  Examples of commercially available melamine resins include Super Becamine J-820-60, Super Becamine L-109-65, Super Becamine L-117-60, Super Becamine 13-548, Super Becamine G-821. -60, Super Becamine L-105-60 (above, manufactured by DIC Corporation), Uban 120, Uban 20HS, Uban 2021, Uban 2028, Uban 2061, Uban 20SB, Uban 20SE60, Uban 21R, Uban 22R, Uban 122, Uban 28-60, Uban 20HS, Uban 2020 (manufactured by Mitsui Chemicals, Inc.), Cymel 202, Cymel 232, Cymel 235, Cymel 238, Cymel 254, Cymel 266, Cymel 267, Cymel 272, Cyme 285, Cymel 301, Cymel 303, Cymel 325, Cymel 327, Cymel 350, Cymel 370, Cymel 701, Cymel 703, Cymel 736, Cymel 738, Cymel 771, Cymel 1141, Cymel 1156, Cymel 1158 (and above, Japan Cytec Industries Ltd.) Company-made), MW30-M, MW-30, MS-11, MS-001, MX-730, MX-750 (manufactured by Sanwa Chemical Co., Ltd.).

  The melamine resin may contain a small amount of a hydrophilic methylol group in the resin due to its production method. When such a melamine resin is used as the material of the outermost layer of the coat layer, it is at a level with no problem. The external additive is slightly attached to the surface of the carrier. However, for the carrier according to the first embodiment, the outermost layer of the coating layer is a layer containing a melamine resin, and a hydrophilic metal such as magnetite described later at the interface between the outermost layer and the layer adjacent to the outermost layer. By allowing the oxide particles to be present, it is possible to suppress adhesion of the external additive to the coat layer due to the inclusion of the melamine resin in the outermost layer of the coat layer. This is because the hydrophilic methylol group has the same hydrophilicity by having hydrophilic metal oxide particles such as magnetite at the interface between the outermost layer of the coating layer and the layer adjacent to the outer layer. It is presumed to be oriented to the magnetite side.

  In this way, the outermost layer is a layer containing a melamine resin, and magnetite is present as metal oxide particles to be described later at the interface between the outermost layer and a layer below the outermost layer. Thus, it is possible to obtain a carrier that is excellent in properties, suppresses a decrease in the ability of the carrier to charge the toner, and suppresses occurrence of image defects such as fogging in the formed image.

Benzoguanamine resin The benzoguanamine resin is not particularly limited as long as it does not impair the object of the present invention, and is appropriately selected from benzoguanamine resins conventionally used as materials for carrier coat layers contained in two-component developers. be able to. A benzoguanamine resin can be used in combination of 2 or more types.

  Examples of commercially available benzoguanamine resins include Super Becamine TD-126, Super Becamine 15-594 (above, manufactured by DIC Corporation), BL-60, BX-4000 (above, made by Sanwa Chemical Co., Ltd.). Can be mentioned.

Polyamideimide resin The polyamideimide resin is not particularly limited as long as it does not impair the object of the present invention, and is appropriately selected from polyamideimide resins conventionally used as a material for a carrier coat layer contained in a two-component developer. Can be used. Specific examples of the polyamideimide resin include a polyamideimide resin using trimellitic acid. Polyamideimide resins can be used in combination of two or more.

  Examples of commercially available polyamide-imide resins include Bilomax HR-11NN, Bilomax HR-12N2, Bilomax HR-13NX, Bilomax HR-14ET, Bilomax HR-15ET, Bilomax HR-16NN (above, Toyobo Made by Co., Ltd.), HPC-1000EDP, HPC-1000, HPC-5000, HPC-5010S, HPC-5020, HPC-5030, HPC-6000, HPC-6100, HPC-7200, HPC-9000, HPC-9100 (or more , Hitachi Chemical Co., Ltd.), Teflon (registered trademark) paints 958-203, 958-207, 958-303, 958-406, 959-202, 959-203, 959-205 (manufactured by DuPont) Is mentioned.

-Phenolic resin The phenolic resin is not particularly limited as long as it does not impair the object of the present invention, and is appropriately selected from phenolic resins conventionally used as a material for a carrier coat layer contained in a two-component developer. be able to. A phenol resin can be used in combination of 2 or more types.

  Examples of commercially available phenol resins include J-325, IF-3300, 5010, 5900, TD-2547, J-326K (above, manufactured by DIC Corporation), PL-2211, PL-2243, PL-2407, PL-4222, PL-4246, PL-4329, PL-4826, PL-6752 (manufactured by Gunei Chemical Industry Co., Ltd.) may be mentioned.

  Among the hard resins contained in the outermost layer described above, melamine resins and polyamideimide resins are preferable, and melamine resins are more preferable from the viewpoint of excellent mechanical strength and wear resistance. The content of one or more resins selected from the group consisting of melamine resin, benzoguanamine resin, polyamideimide resin, and phenol resin in the outermost layer is not particularly limited as long as the object of the present invention is not impaired, but is 80 mass. % Or more is preferable, 90 mass% or more is more preferable, and 100 mass% is particularly preferable.

  As other materials of one or more resins selected from the group consisting of melamine resin, benzoguanamine resin, polyamideimide resin, and phenol resin contained in the outermost layer, the above-mentioned fluororesin, polyamide resin, polyimide resin, aromatic Group polyetherketone resin, (meth) acrylic polymer, styrene polymer, styrene- (meth) acrylic copolymer, olefin polymer (polyethylene, chlorinated polyethylene, polypropylene, etc.), polyvinyl chloride, Examples include polyvinyl acetate, polycarbonate, cellulose resin, polyester resin, unsaturated polyester resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin, phenol resin, xylene resin, diallyl phthalate resin, polyacetal resin, and amino resin. Et That. These resins may be used in combination of two or more.

  The mass of the outermost layer relative to the carrier core is preferably 0.1 parts by mass or more and 5 parts by mass or less, and more preferably 0.5 parts by mass or more and 4 parts by mass or less with respect to 100 parts by mass of the carrier core. By setting the mass of the outermost layer in such a range, the surface of the inner layer than the outermost layer in the coat layer can be satisfactorily covered, and the abrasion and peeling of the coat layer and the association between carriers are suppressed. Easy to get a career.

  In order to adjust the ability of the carrier to charge the toner, a charge control agent is added to the material of the outermost layer, or the outermost layer is treated with a silane coupling agent having a positively or negatively charged functional group. be able to. The type of the charge control agent is not particularly limited as long as it does not impair the object of the present invention, and can be appropriately selected from charge control agents that have been conventionally blended in a carrier coat layer. Examples of the charge control agent include quaternary ammonium salts, organometallic complexes, and styrene-acrylic resins having a positively or negatively charged functional group. Moreover, the kind of silane coupling agent is not specifically limited in the range which does not inhibit the objective of this invention, It can select suitably from the silane coupling agent conventionally used for the process of the coat layer of a carrier. Examples of the silane coupling agent include amino silane coupling agents and fluorine-based silane coupling agents.

  Further, the material of the outermost layer can contain a conductive substance for the purpose of adjusting the resistance value of the carrier. Examples of the conductive material include conductive materials such as conductive carbon black, conductive titanium oxide, and magnetite.

  It is preferable that the usage-amount of said charge control agent and a silane coupling agent is 0.5-20 mass parts with respect to 100 mass parts of mass of outermost layers. By using the charge control agent and silane coupling agent in such a range, the toner is charged to a desired charge amount while suppressing the abrasion and peeling of the coat layer when the carrier is used as a two-component developer. Easy to get a career that can be made.

(Middle layer)
The coat layer covering the carrier core can include an intermediate layer between the innermost layer and the outermost layer. The intermediate layer may be a plurality of layers of two or more as long as the object of the present invention is not impaired.

  Examples of the resin that can be used as the material of the intermediate layer include the above-mentioned fluororesin, melamine resin, benzoguanamine resin, polyamideimide resin, and phenol resin, as well as polyamide resin, polyimide resin, aromatic polyether ketone resin, (meta ) Acrylic polymer, styrene polymer, styrene- (meth) acrylic copolymer, olefin polymer (polyethylene, chlorinated polyethylene, polypropylene, etc.), polyvinyl chloride, polyvinyl acetate, polycarbonate, cellulose resin, Examples include polyester resins, unsaturated polyester resins, polyamide resins, polyurethane resins, epoxy resins, silicone resins, phenol resins, xylene resins, diallyl phthalate resins, polyacetal resins, and amino resins. These resins may be used in combination of two or more.

  The mass of the intermediate layer with respect to the carrier core is not particularly limited as long as the object of the present invention is not impaired. Typically, the mass of the intermediate layer with respect to the carrier core is preferably 0.05 parts by mass or more and 5 parts by mass or less, and more preferably 0.1 parts by mass or more and 3 parts by mass or less with respect to 100 parts by mass of the carrier core particles. .

(Metal oxide particles)
In the carrier according to the first embodiment, metal oxide particles are present at at least one of the interfaces between the plurality of layers covering the carrier core. The presence of the metal oxide at the interface between the layers in the coat layer can suppress local peeling between the plurality of layers. Thereby, since the two layers containing the metal oxide particles in the middle in the coat layer can be satisfactorily adhered, peeling of the coat layer can be suppressed. Further, the presence of the metal oxide in the coat layer makes it easy to obtain a carrier that can charge the toner to a desired charge amount even when the carrier core is covered with a coat layer composed of a plurality of layers. . In addition, since the metal oxide is harder than the resin constituting the coat layer, the strength of the coat layer covering the carrier core can be improved by allowing the metal oxide to exist inside the coat layer. . When the metal oxide has conductivity, the developing electric field is easily applied to the toner, and the developability can be improved.

  Examples of the metal oxide particles include iron oxides such as hematite, magnetite, and goethite, titanium oxide, silicon oxide, aluminum oxide, magnesium oxide, zinc oxide, and calcium oxide. Among these, iron oxide is preferable, and magnetite is more preferable. Two or more kinds of metal oxide particles can be used in combination.

  The metal oxide particles can be used after being hydrophobized with a hydrophobizing agent such as an aminosilane coupling agent or a titanate coupling agent. By hydrophobizing the metal oxide particles, the metal oxide particles and the two layers adjacent to the metal oxide particles can easily be firmly attached in the coat layer.

  The particle diameter of the metal oxide particles is not limited as long as the object of the present invention is not impaired. Specifically, the particle diameter of the metal oxide particles is preferably 5 μm or less, and more preferably 1 μm or less. When the particle diameter of the metal oxide particles is excessive, the smoothness of the carrier surface tends to be lowered, and the contact between the carrier and the toner tends to be uneven. In this case, it becomes difficult to charge the toner satisfactorily, and fog is likely to occur in the formed image. The average particle diameter of the metal oxide fine particles was calculated from the average value obtained by measuring 200 or more particles with a scanning electron microscope.

  The amount of the metal oxide particles used is not particularly limited as long as the object of the present invention is not impaired, and is preferably 0.05 parts by mass or more and 5 parts by mass or less, and 0.5 parts by mass or more with respect to 100 parts by mass of the carrier core. 3 parts by mass or less is more preferable.

[Method for producing carrier]
As an example of a method for producing a carrier according to the first embodiment of the present invention, a carrier core is coated with an innermost layer containing a fluororesin, and then metal oxide particles are attached to the surface of the innermost layer, and further a melamine resin , A method of forming an outermost layer including one or more kinds of resins selected from the group consisting of a benzoguanamine resin, a polyamideimide resin, and a phenol resin on the innermost layer. The mass of the coat layer when producing the carrier is 0.65 mass relative to 100 mass parts of the carrier core as the total mass of the layer made of a plurality of resins constituting the coat layer and the mass of the metal oxide particles. Part to 17 parts by mass, preferably 3.00 parts to 14 parts by mass.

  The method for coating the carrier core with the coating layer is not particularly limited, and is appropriately selected from methods conventionally used for producing carriers. The method of coating the carrier core with the coat layer may be a wet method in which the solvent is removed after the solution of the material constituting the coat layer is sprayed on the carrier core, and the powder of the material constituting the coat layer is used as the carrier core. Any of the dry methods for attaching to the surface of the substrate may be used. Further, for example, a method in which a part of the coat layer is formed by a wet method and the remaining coat layer is formed by a dry method, and the carrier core is covered with the coat layer by combining the wet method and the dry method. You can also.

(Dry method)
The method for coating the carrier core with the powder of the material of the coating layer is not particularly limited, and a grinding machine having a rotor and a liner, such as a turbo mill, a pin mill, and a kryptron, a high-speed stirring mixer with stirring blades, a ball mill, and an atomizer. A method using a dry coating apparatus such as a lighter can be mentioned.

(Wet method)
The method for coating the carrier core with the solution of the material for the coating layer is not particularly limited. Specific examples of such a method include a dipping method, a spray method, a brushing method, and a method of causing a carrier core to flow using a fluidized bed and spraying a coating layer material toward the flowing carrier core. In such a coating method, the carrier core is coated with a solution of the material of the coat layer, and then the solvent contained in the solution of the material of the coat layer is removed. When the coating layer is formed by a wet method, examples of the solvent used in the coating layer material solution include various alcohols such as methanol and ethanol, organic solvents such as toluene, acetone, methyl ethyl ketone, methyl isobutyl ketone, and tetrahydrofuran. A solvent is mentioned.

  As a carrier according to the first embodiment of the present invention, a coating layer containing a fluororesin as an innermost layer is formed on the surface of the carrier core by a dry method, and then metal oxide particles are formed on the surface of the innermost layer by a dry method. What is obtained by attaching and then forming a coat layer containing one or more kinds of resins selected from the group consisting of melamine resin, benzoguanamine resin, polyamideimide resin, and phenol resin as the outermost layer by a wet method is preferable.

  After the carrier core is coated with the coat layer by the above method, the carrier core coated with the coat layer is heat-treated to obtain a carrier. The heat treatment method may be either an external heating method or an internal heating method. Examples of the apparatus that can be used for the heat treatment include apparatuses such as a fluid electric furnace, a rotary electric furnace, a burner furnace, and a thermostat.

  Although the temperature of heat processing changes with kinds of resin contained in a coat layer, typically 150 to 350 degreeC is preferable. Moreover, the time which heats a carrier core is not specifically limited, Typically, they are 5 minutes or more and 300 minutes or less. By such heat treatment, the curing reaction of the outermost high-hardness resin proceeds and the hardness of the carrier surface increases.

  The average particle diameter of the carrier is not particularly limited as long as the object of the present invention is not impaired, but is preferably 15 μm or more and 150 μm or less, and more preferably 20 μm or more and 100 μm or less.

  The carrier according to the first embodiment of the present invention described above covers the carrier core when printing at a high printing rate over a long period of time using the two-component developer including the toner and the carrier according to the first embodiment. Suppresses the occurrence of fogging in the formed image due to a decrease in the ability of the carrier to charge the toner by suppressing the abrasion and peeling of the coating layer and the adhesion of the external additive peeled from the toner to the coating layer it can. Therefore, the carrier according to the first embodiment of the present invention is suitably used in various image forming apparatuses that employ a two-component development method.

[Second Embodiment]
The two-component developer according to the second embodiment of the present invention includes a toner and the electrostatic latent image developing carrier according to the first embodiment. Hereinafter, the toner and the method for preparing the two-component developer will be described.

〔toner〕
In the toner included in the two-component developer according to the second embodiment of the present invention, components such as a colorant, a charge control agent, and a release agent are blended in the binder resin as necessary. The toner contained in the two-component developer may be one having an external additive attached to the surface thereof. Hereinafter, the binder resin, the colorant, the charge control agent, the release agent, the external additive, and the toner manufacturing method will be described in order.

[Binder resin]
The binder resin contained in the toner is not particularly limited as long as it is a resin conventionally used as a binder resin for toner. Specific examples of the binder resin include styrene resin, acrylic resin, styrene acrylic resin, polyethylene resin, polypropylene resin, vinyl chloride resin, polyester resin, polyamide resin, polyurethane resin, polyvinyl alcohol resin, vinyl ether. And thermoplastic resins such as styrene resins, N-vinyl resins, and styrene-butadiene resins. Among these resins, styrene acrylic resins and polyester resins are preferable from the viewpoints of dispersibility with respect to the colorant in the toner, chargeability of the toner, and fixing properties with respect to the paper. Hereinafter, the styrene acrylic resin and the polyester resin will be described.

  The styrene acrylic resin is a copolymer of a styrene monomer and an acrylic monomer. Specific examples of the styrene monomer include styrene, α-methylstyrene, vinyl toluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, p-ethylstyrene, and the like. Specific examples of the acrylic monomer include methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, meta Examples include (meth) acrylic acid alkyl esters such as methyl acrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate.

  As the polyester resin, those obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component can be used. Examples of the components used when synthesizing the polyester resin include the following divalent or trivalent or higher alcohol components and divalent or trivalent or higher carboxylic acid components.

  Specific examples of the divalent or trivalent or higher alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1 Diols such as 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; bisphenol A Bisphenols such as hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrol, 1,4-sol Tan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2, Examples include trivalent or higher alcohols such as 4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

  Specific examples of the divalent or trivalent or higher carboxylic acid component include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, Sebacic acid, azelaic acid, malonic acid, or n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid Acid, alkyl such as isododecyl succinic acid, isododecenyl succinic acid, or divalent carboxylic acid such as alkenyl succinic acid; 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5 -Benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4 Naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid , Tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, trivalent or higher carboxylic acid such as empole trimer acid, and the like. These divalent or trivalent or higher carboxylic acid components may be used as ester-forming derivatives such as acid halides, acid anhydrides, and lower alkyl esters. Here, “lower alkyl” means an alkyl group having 1 to 6 carbon atoms.

  When the binder resin is a polyester resin, the softening point of the polyester resin is preferably 80 ° C. or higher and 150 ° C. or lower, and more preferably 90 ° C. or higher and 140 ° C. or lower.

  As the binder resin, it is preferable to use a thermoplastic resin because the toner has good fixability to paper. However, the binder resin is not only used alone, but also used as a crosslinking agent or a thermosetting resin. Can be added. By introducing a partially crosslinked structure into the binder resin, it is possible to improve properties such as the storage stability, form retention, and durability of the toner without deteriorating the fixability of the toner to the paper.

  As the thermosetting resin that can be used together with the thermoplastic resin, for example, an epoxy resin or a cyanate resin is preferable. Specific examples of suitable thermosetting resins include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, cycloaliphatic type epoxy resins, and cyanate resins. . These thermosetting resins can be used in combination of two or more.

  The glass transition point (Tg) of the binder resin is preferably 50 ° C. or higher and 65 ° C. or lower, and more preferably 50 ° C. or higher and 60 ° C. or lower. If the glass transition point of the binder resin is too low, the toners may be fused inside the developing unit of the image forming apparatus, or the storage stability may be reduced. May be partly fused. Further, when the glass transition point is too high, the strength of the binder resin is lowered, and the toner is likely to adhere to the latent image carrier (image carrier: photoconductor). If the glass transition point is too high, the toner tends to be difficult to fix well at low temperatures.

  The glass transition point of the binder resin can be obtained from the change point of the specific heat of the binder resin using a differential scanning calorimeter (DSC). More specifically, the glass transition point of the binder resin can be obtained by measuring the endothermic curve of the binder resin using a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. as a measuring device. 10 mg of a measurement sample is put in an aluminum pan, and an empty aluminum pan is used as a reference. The glass transition point of the binder resin can be determined from the endothermic curve of the binder resin obtained by measurement under normal temperature and humidity under the measurement conditions of a measurement temperature range of 25 to 200 ° C. and a temperature increase rate of 10 ° C./min. .

[Colorant]
The toner contained in the two-component developer according to the second embodiment of the present invention may contain a colorant in the binder resin. When the toner contains a colorant, a colorant appropriately selected from known pigments and dyes can be used according to the desired color of the toner particles. Specific examples of colorants that can be added to the toner include black pigments such as carbon black, acetylene black, lamp black, and aniline black; yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel Titanium Yellow, Navels Yellow, Naphthol Yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake, and other yellow pigments; Orange pigments such as Permanent Orange GTR, Pyrazolone Orange, Vulcan Orange, Indanthrene Brilliant Orange GK; Bengala, Cadmium Red, Lead Red, Mercury Cadmium Sulfide, Permanen Red pigments such as Red 4R, Resol Red, Pyrazolone Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B; Manganese Purple, Fast Violet B, Methyl Purple pigments such as violet lake; blue pigments such as bitumen, cobalt blue, alkali blue lake, Victoria blue partially chlorinated, first sky blue, indanthrene blue BC; chrome green, chromium oxide, pigment green B, malachite green lake , Green pigments such as Final Yellow Green G; white pigments such as zinc white, titanium oxide, antimony white, zinc sulfide; barite powder, barium carbonate, clay, silica, white Bon, talc, extender pigments such as alumina white. These colorants may be used in combination of two or more for the purpose of adjusting the toner to a desired hue.

  The amount of the colorant used is not particularly limited as long as the object of the present invention is not impaired. Specifically, the amount of the colorant used is preferably 2 parts by mass or more and 15 parts by mass or less, and more preferably 4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the binder resin.

(Charge control agent)
The toner contained in the two-component developer according to the second embodiment of the present invention may contain a charge control agent. The charge control agent improves the stability of the charge level of the toner and the charge rise characteristics that indicate whether the toner can be charged to a predetermined charge level in a short time. Used for gaining purposes. When developing with positively charged toner, a positively chargeable charge control agent is used. When developing with negatively charged toner, a negatively chargeable charge control agent is used.

  The type of the charge control agent is not particularly limited as long as the object of the present invention is not impaired, and can be appropriately selected from charge control agents conventionally used in toners. Specific examples of the positively chargeable charge control agent include pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1, 2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, Azine compounds such as phthalazine, quinazoline and quinoxaline; Azin Fast Red FC, Azin Fast Red 12BK, Azine Violet BO, Azine Direct dyes composed of azine compounds such as N-Brown 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Deep Black EW, and Azin Deep Black 3RL; Nigrosine such as Nigrosine, Nigrosine Salt, Nigrosine Derivative Compounds; Acid dyes composed of nigrosine compounds such as nigrosine BK, nigrosine NB, nigrosine Z; metal salts such as naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; benzylmethylhexyldecylammonium, decyltrimethylammonium chloride Such quaternary ammonium salts are mentioned. Among these positively chargeable charge control agents, a nigrosine compound is particularly preferable in that a more rapid start-up property can be obtained. These positively chargeable charge control agents can be used in combination of two or more.

  A resin having a quaternary ammonium salt, carboxylate, or carboxyl group as a functional group can also be used as a positively chargeable charge control agent. More specifically, a styrene resin having a quaternary ammonium salt, an acrylic resin having a quaternary ammonium salt, a styrene-acrylic resin having a quaternary ammonium salt, a polyester resin having a quaternary ammonium salt, and a carboxylate A styrene resin having a carboxylate, an acrylic resin having a carboxylate, a styrene-acrylic resin having a carboxylate, a polyester resin having a carboxylate, a styrene resin having a carboxyl group, an acrylic resin having a carboxyl group, Examples thereof include styrene-acrylic resins having a carboxyl group and polyester resins having a carboxyl group. The molecular weight of these resins is not particularly limited as long as the object of the present invention is not impaired, and may be an oligomer or a polymer.

  Among the resins that can be used as positively chargeable charge control agents, styrene-acrylic resins having a quaternary ammonium salt as a functional group are preferred because the charge amount can be easily adjusted to a value within a desired range. More preferred. In preparing a styrene-acrylic resin having a quaternary ammonium salt as a functional group, specific examples of a preferable acrylic comonomer copolymerized with a styrene unit include methyl acrylate, ethyl acrylate, n-propyl acrylate, Such as iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate Examples include (meth) acrylic acid alkyl esters.

  As the quaternary ammonium salt, a unit derived from a dialkylaminoalkyl (meth) acrylate, dialkyl (meth) acrylamide, or dialkylaminoalkyl (meth) acrylamide through a quaternization step is used. Specific examples of the dialkylaminoalkyl (meth) acrylate include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, and dibutylaminoethyl (meth) acrylate. A specific example of dialkyl (meth) acrylamide is dimethylmethacrylamide. Specific examples of the dialkylaminoalkyl (meth) acrylamide include dimethylaminopropyl methacrylamide. Further, a hydroxy group-containing polymerizable monomer such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, or N-methylol (meth) acrylamide can be used in combination during polymerization.

  Specific examples of the negatively chargeable charge control agent include organometallic complexes and chelate compounds. Examples of organometallic complexes and chelate compounds include acetylacetone metal complexes such as aluminum acetylacetonate and iron (II) acetylacetonate, and salicylic acid metal complexes such as chromium 3,5-di-tert-butylsalicylate. Alternatively, a salicylic acid-based metal salt is preferable, and a salicylic acid-based metal complex or a salicylic acid-based metal salt is more preferable. These negatively chargeable charge control agents can be used in combination of two or more.

  The use amount of the positively chargeable or negatively chargeable charge control agent is not particularly limited as long as the object of the present invention is not impaired. The use amount of the positively or negatively chargeable charge control agent is typically 1.5 parts by mass or more and 15 parts by mass or less, preferably 2.0 parts by mass when the total amount of the toner is 100 parts by mass. Part to 8.0 parts by weight is more preferable, and 3.0 part to 7.0 parts by weight is particularly preferable. When the amount of the charge control agent used is too small, it is difficult to stably charge the toner to a predetermined polarity. In this case, it is difficult to form an image having a desired image density, and it is difficult to maintain the image density of the formed image over a long period of time. In such a case, the charge control agent is difficult to uniformly disperse in the toner, so that the formed image is likely to be fogged or the latent image carrier is easily contaminated. When the amount of the charge control agent used is excessive, charging failure of the toner under high temperature and high humidity tends to occur due to deterioration of environmental resistance. In this case, problems such as image defects and contamination of the latent image carrier are likely to occur.

  Since the two-component developer according to the second embodiment of the present invention includes a negatively chargeable fluororesin in the coat layer of the carrier, when the toner contained in the two-component developer is a positively chargeable toner, the toner It can be charged well. For this reason, the toner contained in the two-component developer is preferably a positively chargeable toner containing a positively chargeable charge control agent.

〔Release agent〕
The toner contained in the two-component developer according to the second embodiment of the present invention may contain a release agent for the purpose of improving fixability and offset resistance. The type of release agent added to the toner is not particularly limited as long as the object of the present invention is not impaired. As the release agent, wax is preferable. Examples of the wax include polyethylene wax, polypropylene wax, fluororesin wax, Fischer-Tropsch wax, paraffin wax, ester wax, montan wax, and rice wax. These release agents can be used in combination of two or more. By adding such a release agent to the toner, the occurrence of offset and image smearing (dirt around the image when the image is rubbed) can be more efficiently suppressed.

  The amount of the release agent used is not particularly limited as long as the object of the present invention is not impaired. The amount of the specific release agent used is preferably 1 part by mass or more and 30 parts by mass with respect to 100 parts by mass of the binder resin. When the toner is produced by a pulverization method to be described later, the amount of the release agent used is more preferably 1 to 8 parts by mass and particularly preferably 2 to 5 parts by mass with respect to 100 parts by mass of the binder resin. If the amount of the release agent used is too small, the desired effect may not be obtained with respect to suppression of occurrence of offset and image smearing in the formed image, and if the amount of release agent used is excessive, the toner The storage stability of the toner may be reduced due to the fusion between the toners.

(External additive)
For the purpose of improving the fluidity, storage stability, cleaning properties, etc. of the toner, an external additive may be attached to the surface of the toner. In the specification of the present application, particles treated with an external additive are referred to as “toner mother particles”.

  The type of external additive is not particularly limited as long as it does not impair the object of the present invention, and can be appropriately selected from external additives conventionally used for toners. Specific examples of suitable external additives include silica and metal oxides such as alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate. These external additives can be used in combination of two or more.

  As these external additives, those whose surfaces are treated with a hydrophobizing agent can be used. Examples of the hydrophobizing agent include hydrophobizing agents such as silicone oil, aminosilane, hexamethyldisilazane, titanate coupling agents, and silane coupling agents. Among the external additives hydrophobized as described above, aminosilane, hexamethyldisilazane, a titanate coupling agent having an amino group, or a silane system having an amino group, can suppress wear on the carrier surface. It is preferable to use hydrophobic silica surface-treated with a hydrophobizing agent having an amino group such as a coupling agent.

  The particle diameter of the external additive is not particularly limited as long as it does not impair the object of the present invention, and typically 0.01 μm or more and 1.0 μm or less is preferable.

  The amount of the external additive used for the toner is not particularly limited as long as the object of the present invention is not impaired. Typically, the amount of the external additive used is preferably 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 0.2 parts by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the toner. When the external additive is used in such an amount, a toner excellent in fluidity, storage stability, and cleaning properties can be easily obtained.

[Toner Production Method]
The method for producing the toner contained in the two-component developer according to the second embodiment of the present invention is not particularly limited as long as the toner containing the above-described components can be produced in the binder resin as necessary. Suitable methods include a pulverization method and an agglomeration method. In the pulverization method, a binder resin and optional components such as a colorant, a charge control agent, and a release agent are mixed, and the resulting mixture is melt-kneaded in a melt-kneader such as a single-screw or twin-screw extruder. The melt-kneaded product is pulverized and classified to obtain toner particles (toner mother particles). In the aggregation method, fine particles of components such as a binder resin, a release agent, and a colorant are aggregated in an aqueous medium to obtain aggregated particles, and then the aggregated particles are heated to form aggregated particles. The contained components are united to obtain toner particles (toner mother particles). The average particle diameter of the toner particles obtained by the above method is not particularly limited as long as the object of the present invention is not impaired, but generally it is preferably 5 μm or more and 10 μm or less.

  If necessary, the surface of the toner base particles obtained in this manner may be treated with an external additive. The processing method of the toner base particles with the external additive is not particularly limited, and can be appropriately selected from conventionally known processing methods with the external additive. Specifically, the processing conditions are adjusted so that the particles of the external additive are not embedded in the toner base particles, and the processing with the external additive is performed by a mixer such as a Henschel mixer or a Nauter mixer.

[Method for producing two-component developer]
The method for producing the two-component developer is not particularly limited as long as the toner and the carrier according to the first embodiment of the present invention can be mixed uniformly. As a suitable method, a method of mixing the toner and the carrier by a mixing device such as a ball mill can be mentioned. The content of the toner in the two-component developer is preferably 1% by mass or more and 20% by mass or less, and more preferably 3% by mass or more and 15% by mass or less with respect to the mass of the two-component developer. By setting the toner content in the two-component developer within such a range, an appropriate image density of the formed image is maintained, and contamination inside the image forming apparatus due to suppression of toner scattering from the developing apparatus or transfer paper is transferred. Adhesion of toner can be suppressed.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited at all by the Example.

[Preparation Example 1]
Toners A and B used for preparing the two-component developers of Examples and Comparative Examples were prepared according to the following method.

(Preparation of toner base particles)
100 parts by mass of a polyester resin (binder resin, copolymer of bisphenol A and fumaric acid), 5 parts by mass of carbon black (colorant, MA-100 (manufactured by Mitsubishi Chemical Corporation)), quaternary ammonium salt compound (charge) Control agent, 2 parts by mass of Bontron P-51 (manufactured by Orient Chemical Co., Ltd.) and 5 parts by mass of carnauba wax (mold release agent, carnauba wax No. 1 (manufactured by Kato Yoko Co., Ltd.)) Mixed). Subsequently, the obtained mixture was melt-kneaded by a twin-screw extruder (manufactured by Toshiba Machine Co., Ltd.) to obtain a kneaded product. The obtained kneaded product was cooled, coarsely pulverized with a hammer mill (manufactured by Hosokawa Micron Corporation), and then finely pulverized with a mechanical pulverizer (turbo mill (manufactured by Freund Turbo Corporation)). The obtained finely pulverized product was classified by an airflow classifier (Elbow Jet (manufactured by Nippon Steel Mining Co., Ltd.)) to obtain toner base particles having a volume average particle size (D ₅₀ ) of 6.8 μm.

(Preparation of Toner A)
100 parts by weight of the obtained toner base particles, 1 part by weight of hydrophobic silica (TG-820 (manufactured by Cabot), silica surface-treated with hexamethyldisilazane (HMDZ) and cyclic silazane), titanium oxide ( 1 part by mass of EC-100 (manufactured by Titanium Industry Co., Ltd.) was mixed with a Henschel mixer (FM-10L (manufactured by Nippon Coke Industries Co., Ltd.)) for 5 minutes under the condition of 30 m / sec to obtain toner mother particles. .

(Preparation of Toner B)
Hydrophobic silica (TG-820 (manufactured by Cabot Corp.)) instead of 1.0 part by mass, hydrophobic silica (REA200 (manufactured by Nippon Aerosil Co., Ltd.), silica surface-treated with amine and silicone oil) 1.8 mass A toner B was obtained in the same manner as the toner A, except that the parts were used.

[Examples 1-7 and Comparative Examples 1-2]
(Manufacture of carriers A to I)
Carriers A to F and I were produced as the carriers of Examples 1 to 7 according to the following method. Carriers G and H were produced as the carriers of Comparative Examples 1 and 2.
100 parts by mass of a saturated magnetization carrier core (ferrite carrier, center particle diameter 35 μm) shown in Table 1 and polytetrafluoroethylene resin fine particles (PTFE, TLP10F-1 (Mitsui / DuPont Fluorochemicals Ltd.) in the amount shown in Table 1 And an average particle diameter of 3 μm) were processed with an attritor (manufactured by Nippon Coke Kogyo Co., Ltd.) for 5 hours, and the carrier core was covered with PTFE to form an innermost layer. Next, magnetite fine particles (KBC-100 (manufactured by Kanto Denka Kogyo Co., Ltd.), average particle size 0.5 μm) in the amount shown in Table 1 were put into an attritor, and the magnetite fine particles were adhered to the surface of the innermost layer. . Thereafter, using a methyl ethyl ketone solution having a concentration of 30% by mass of the materials shown in Table 1 as a coating solution, the outermost layer material in the amount shown in Table 1 is attached to the carrier core covered with the innermost layer. Coating was performed using a wet coating apparatus (Spilacoater (Okada Seiko Co., Ltd.)). Next, the carrier core coated with the coating liquid was heat-treated at 300 ° C. for 1 hour with a heat treatment apparatus (constant temperature oven (manufactured by Espec Corp.)) to obtain carriers A to I.
Abbreviations regarding the material of the outermost layer shown in Table 1 mean the following resins.
PAI: Polyamideimide resin (HPC-5000 (manufactured by Hitachi Chemical Co., Ltd.))
ME: Melamine resin (Uban 20SE60 (Mitsui Chemicals))
PH: Phenolic resin (Resitop PL-2211 (manufactured by Gunei Chemical Industry Co., Ltd.))
BG: Benzoguanamine resin (TD-126 (manufactured by DIC Corporation))

[Examples 8 to 16 and Comparative Examples 3 to 6]
(Manufacture of two-component developer)
A carrier of the types described in Tables 2 and 3 and a toner of the types described in Tables 2 and 3 are ball milled (universal) so that the toner content is 10% by mass with respect to the mass of the two-component developer. It was put into a ball mill UB-32 (manufactured by Yamato Scientific Co., Ltd.) and a carrier and toner were mixed to obtain a two-component developer.

≪Evaluation≫
In the continuous printing test at a printing rate of 25% when the two-component developers of Examples 8 to 16 and Comparative Examples 3 to 6 and the toner of the type described in Tables 2 and 3 were used according to the following method, The image density and the image density and fog after continuous printing were evaluated according to the following methods. For the two-component developers of Examples 10, 12, and 13, the initial image density in the continuous printing test at a printing rate of 1%, the image density after continuous printing, and the fogging were further set to a printing rate of 25. The evaluation method was the same as the evaluation method in%. The evaluation results are shown in Tables 2 and 3. In the comparative example, since the initial image density was determined to be unacceptable, the image density after continuous printing and the evaluation of fogging were not performed. For evaluation, a printer (FS-5200DN (manufactured by Kyocera Document Solutions Co., Ltd.)) was used.

<Image density evaluation method>
For the evaluation of the color after filling the developing device of the printer with the two-component developers of Examples 8 to 16 and Comparative Examples 3 to 6 and filling the toner containers of the types shown in Tables 2 and 3. The sample image was output as the initial image. After outputting the initial image, after outputting 20,000 sheets, a sample image for color evaluation was output. For the initial image and the sample image after output of 20,000 sheets, the image density of the solid image of 2 × 2 cm provided at the left side, the center, and the right side in the sample image is measured, and the image density at the three points is measured. Was the image density of the sample image. The image density was evaluated according to the following criteria. ◎, ○ and △ were judged as acceptable. The image density was measured using a densitometer (RD-19I (manufactured by Gretag Macbeth)).
A: Image density is 1.2 or more.
○: Image density is less than 1.2 and 1.0 or more.
Δ: Image density is less than 1.0, 0.9 or more.
X: Image density is less than 0.9.

<Evaluation method of fogging>
With respect to the sample image after output of 20,000 sheets obtained by measuring the image density, the presence or absence of fogging was visually confirmed on the white paper portion below the solid image. The fogging was evaluated according to the following criteria. ◎, ○ and △ were judged as acceptable.
○: No fogging was confirmed.
(Triangle | delta): Although fog was confirmed, there is no problem practically.
X: Fog was confirmed to some extent in practical use.

  According to Examples 8 to 16, the carrier core is covered with a coating layer composed of a plurality of layers, and the plurality of layers are layers in which the innermost layer contains a fluororesin, and the outermost layers are melamine resin and benzoguanamine resin. , A polyamideimide resin, and a layer containing one or more resins selected from the group consisting of phenol resins, and a two-component developer using a carrier in which metal oxide particles are present at the interface between a plurality of layers. For example, when printing at a high printing rate over a long period of time, the carrier toner is charged by suppressing the abrasion and peeling of the coat layer of the carrier and the adhesion of the external additive peeled from the toner to the carrier surface. It can be seen that the occurrence of fogging in the formed image due to the decrease in capability can be suppressed.

  According to Examples 10, 12, and 13, the lower the saturation magnetization of the carrier core used for manufacturing the carrier, the easier it is to form an image with a desired image density when continuously printing at a low printing rate. I understand. In addition, according to Examples 3 and 4, if a two-component developer containing toner externally added with hydrophobic silica that has been surface-treated with amine and silicone oil is used, printing can be performed at a high printing rate over a long period of time. It can be seen that it is easy to form an image having a desired image density even when it is performed.

  Further, according to Example 12, if the carrier core has a saturation magnetization of 30 emu / g or more and 60 emu / g or less, a two-component developer using a carrier, when performing continuous printing at a low printing rate, It can be seen that it is easier to form an image having a desired image density. Furthermore, according to Example 13, if a two-component developer using a carrier having a saturation magnetization of the carrier core of 35 emu / g or more and 45 emu / g or less is used for continuous printing at a low printing rate, It can be seen that it is easy to form an image having a desired image density.

  According to Comparative Examples 3 and 4, a two-component developer including a carrier in which metal oxide particles do not exist at the interface between a plurality of layers constituting the coat layer and the outermost layer is a layer made of polyamideimide resin is used. When forming an image, it can be seen that the image density of the initial image is lower than a desired value.

  According to Comparative Examples 5 and 6, using a two-component developer containing a carrier in which metal oxide particles do not exist at the interface between the plurality of layers constituting the coat layer and the outermost layer is a layer made of melamine resin. In the case of forming an image, it can be seen that fogging is likely to occur on the blank portion of the formed image after continuous printing.

Claims (5)

A carrier for developing an electrostatic latent image, wherein the carrier core is coated with a coat layer composed of two or more layers,
The plurality of layers are:
The innermost layer is a layer containing a fluororesin,
The outermost layer is a layer containing one or more kinds of resins selected from the group consisting of melamine resin, benzoguanamine resin, polyamideimide resin, and phenol resin,
A carrier for developing an electrostatic latent image, wherein metal oxide particles are present at at least one of the interfaces between the plurality of layers.   The electrostatic latent image developing carrier according to claim 1, wherein the outermost layer is a layer containing a melamine resin.   The carrier for developing an electrostatic latent image according to claim 1, wherein the metal oxide particles are magnetite particles.   The carrier for electrostatic latent image development according to any one of claims 1 to 3, wherein the saturation magnetization of the carrier core is 35 emu / g or more and 45 emu / g or less.   A two-component developer comprising a toner and the electrostatic latent image developing carrier according to claim 1.