Electrophotographic carrier and two-component developer

Abstract

This electrophotographic carrier is a resin-coated carrier having magnetic core particles and a coating layer covering the surfaces of the core particles with a resin. The coating layer contains at least an acrylic resin and a silicone monomer or a silicone oligomer in a state of being mixed with the acrylic resin, or a cured object obtained by curing a silicone monomer or oligomer in a state of being mixed with an acrylic resin. The content of components derived from the silicone monomer or the silicone oligomer in the resin forming the coating layer is 2-20 mass%. In this two-component developer, said electrophotographic carrier is used.

Description

Electrophotographic carrier and two-component developer

[0001] The present invention relates to a carrier for electrophotography and a two-component developer using the same. The carrier of the present invention is a carrier for an electrostatic latent image developer.

[0002] Two-component electrophotographic developers used in electrophotography consist of toner and carrier. The carrier is mixed and stirred with the toner in a developer tank, causing frictional charging, imparting the desired charge to the toner, and transporting the charged toner to an electrostatic latent image on a photoreceptor to form a toner image. The carrier then returns from the magnet roll to the developer tank, where it is mixed and stirred again with newly replenished toner for repeated use. Therefore, the carrier must consistently exhibit the desired characteristics for the toner under all environmental conditions throughout its use, and must particularly impart stable charging characteristics. For this reason, carriers with a resin coating layer formed on the surface of magnetic particles are commonly used.

[0003] In the technology of electrophotographic copiers and printers, the relationship between toner spent, which occurs when resin components, wax, and external additives from deteriorated toner adhere to the carrier surface after long-term printing, and carrier resistance and the charge amount of the developer is known. The increase in carrier resistance associated with toner spent leads to carrier adhesion, such as carrier transfer to the edge of the photoreceptor when printing halftone images, because the charge on the carrier surface does not completely leak out immediately after development. On the other hand, toner spent often leads to a decrease in the charge amount of the developer.

[0004] In addition, frictional collisions between carrier particles, between the carrier and the developing sleeve, and contact between the doctor blade and the carrier become more likely, causing the carrier coating to peel off and wear, resulting in excessive exposure of the core material, which in turn causes a decrease in carrier resistance.Similarly, the increase in carrier charge over time is also a problem in stable long-term printing.

[0005] Conventional coating resins include acrylic resins and silicone resins. Acrylic resin-coated carriers have high adhesion to core materials, making them less susceptible to resin peeling, and are excellent in the ability to impart charge to toner, particularly to negatively charged toner, but have the drawback of poor spent resistance and charge retention. On the other hand, silicone resin-coated carriers have low surface energy, a low coefficient of friction, and excellent spent resistance, but are poor in the ability to impart charge.

[0006] Patent Document 1 describes an electrophotographic carrier having at least a surface coating layer made of a resin, the resin containing at least an acrylic resin and a silicone resin, and the acrylic resin ratio in the coating layer made of the acrylic resin and the silicone resin is 10 to 90 wt %. The same document also describes an electrophotographic carrier having a coating layer made of a resin containing an acrylic resin and a silicone resin, and an electrophotographic carrier having a plurality of coating layers made of an acrylic resin layer and a silicone resin layer.

[0007] Patent Document 2 describes a carrier for electrophotography having a core material on which a layer containing a silicone resin as a lower layer and a layer containing an acrylic resin as an upper layer, or a carrier having a core material containing a silicone resin and a layer containing an acrylic resin on the core material, in which the exposure rate of the silicone resin on the carrier surface is 0.5 area % or more and 20 area % or less.

[0008] Patent Document 3 describes an electrophotographic carrier having a core material and a resin coating layer that coats the surface of the core material, wherein the resin coating layer contains an acrylic resin, a silicone resin, and a silicone-modified acrylic resin, and the proportions of the acrylic resin, the silicone resin, and the silicone-modified acrylic resin in the resin coating layer are in a specific ratio.

[0009] Patent Document 4 describes a carrier for developing electrostatic latent images having a resin coating layer in which the surfaces of magnetic particles are coated with a resin, characterized in that the resin coating layer contains silicone resin particles having a number average primary particle diameter of 200 to 5000 nm in a resin layer mainly composed of acrylic resin, in an amount of 5 to 60 mass % relative to the total mass of the resin coating layer.

[0010] US-A1-2003 / 0186154 US-A1-2020 / 0096888 JP 2015-138230 A JP 2010-145471 A

[0011] In recent years, in order to conserve energy, there has been an increasing use of low-temperature fixing toners, which are prone to causing spent, a contamination of the carrier surface, in order to reduce the power consumption of the fixing process, which is the largest power consumption in electrophotography, and there is also a demand for longer life carriers to reduce the amount of waste. Under these conditions, the characteristics required of electrophotographic carriers, such as charge retention, resistance retention, and spent resistance, are increasing year by year.

[0012] However, the applicant has found that in a resin coating layer containing an acrylic resin and a silicone resin as in Patent Document 1, the compatibility between the two resins is poor, the resin peel resistance of the acrylic resin is not obtained, and the spent resistance of the silicone-based resin is not exhibited.

[0013] Furthermore, Patent Documents 2 to 4 also do not fully consider a configuration for achieving spent resistance by utilizing both the resin peel resistance of the acrylic resin and the spent resistance of the silicone resin to achieve both resistance stability and charging stability over a long period of printing.

[0014] The object of the present invention is to solve the problems of the above-mentioned conventional techniques, and to provide a carrier having excellent stability in carrier resistance, stable charge amount, and excellent spent resistance even over a long period of printing, and a developer using the same.

[0015] As a result of extensive research into solving the above problems, the inventors have surprisingly found that the above problems can be solved by forming the resin coating layer of the carrier from a resin made from acrylic resin and silicone oligomer under specific conditions, and have thus completed the present invention.

[0016] The present invention provides a resin-coated carrier having magnetic core particles and a coating layer that coats the surfaces of the core particles with a resin, wherein the coating layer contains at least an acrylic resin and a silicone monomer or silicone oligomer in a mixed state with the acrylic resin, or a cured product obtained by curing the silicone monomer or silicone oligomer in a mixed state with the acrylic resin, and the content of components derived from the silicone monomer or silicone oligomer in the resin that constitutes the coating layer is 2% by mass or more and 20% by mass or less. Also provided is an electrophotographic carrier and a two-component developer using the same.

[0017] The present invention also provides a method for producing an electrophotographic carrier having magnetic core particles and a coating layer that coats the surfaces of the core particles with a resin, the method comprising the step of contacting the core particles with a resin coating composition containing an acrylic resin and a silicone monomer or a silicone oligomer, wherein the content of the silicone monomer or silicone oligomer in the resin contained in the resin coating composition is 2% by mass or more and 20% by mass or less.

[0018] According to the present invention, there is provided an electrophotographic carrier which has excellent stability in carrier resistance and charge amount even over a long period of printing, and which has excellent resistance to spent. The electrophotographic carrier of the present invention and a two-component developer using the same can meet the demand for a long life even in the recent situation where spent is likely to occur.

[0019] FIG. 1 is a schematic diagram showing a resistance measuring device used in the examples and comparative examples.

[0020] The following describes in detail the embodiments of the present invention, but the present invention is not limited to the following embodiments and can be implemented by making appropriate modifications within the scope of the object of the present invention. Note that, where the description overlaps, the description may be omitted as appropriate, but this does not limit the gist of the invention.

[0021] The present invention provides a resin-coated carrier having magnetic core particles and a coating layer that coats the surfaces of the core particles with a resin, wherein the coating layer contains at least an acrylic resin and a silicone monomer or oligomer mixed with the acrylic resin, or a cured product obtained by curing the silicone monomer or oligomer in a mixed state with the acrylic resin. The content of components derived from the silicone monomer or oligomer in the resin that constitutes the coating layer is 2% by mass or more and 20% by mass or less.

[0022] The present inventors have discovered that the carrier of the present invention exhibits excellent carrier resistance stability, stable charge amount, and excellent spent resistance even over long periods of printing under conditions prone to spent. While the reasons for this are unclear, they are thought to be as follows: Acrylic resins have high charge-imparting ability and are resistant to resin peeling, but their ability to suppress contamination by toner components is insufficient. On the other hand, silicone monomers or oligomers have insufficient charge-imparting ability but excellent contamination suppression. Furthermore, silicone monomers or oligomers have better compatibility with acrylic resins than silicone resins, making it easier to form uniform films and coating layers that have high coverage and are resistant to peeling. Combining these two materials, each with the specific condition that the content of components derived from the silicone monomer or oligomer is 2% by mass or more and 20% by mass or less, to form a resin that constitutes a coating layer is thought to provide excellent spent resistance while maintaining or even improving the resistance to resin peeling of the acrylic resin. This makes it possible to obtain an electrophotographic carrier with excellent charge stability, resistance stability, and contamination suppression.

[0023] In contrast, in the case of an electrophotographic carrier provided with a plurality of resin layers, i.e., an acrylic resin layer and a silicone resin layer, as in Patent Documents 1 and 2, since only one of the acrylic resin and the silicone resin is present on the surface, only one of the resin peeling resistance of the acrylic resin and the spent resistance of the silicone resin is exhibited, and the above-mentioned improved effect cannot be obtained. Also, in the method of using silicone resin as particles as in Patent Document 4, the film lacks uniformity, and it is thought that the effect of spent resistance resulting from the use of a silicone-based component cannot be sufficiently obtained, and it is also thought that it is difficult to prevent resin peeling.

[0024] [Core Particles] Magnetic particles are used as the core particles in the present invention. Hereinafter, the core particles will also be referred to as "core material." There are no particular limitations on the magnetic particles, and any of the above ferrite groups containing iron powder, magnetite, Mn ferrite, Mn-Zn ferrite, Mn-Mg ferrite, Mn-Mg-Sr ferrite, Mg ferrite, and other alkali metals, alkaline earth metals, and light metals can be used depending on the purpose, and those that have been subjected to oxidation treatment or the like as necessary can be suitably used. Among these, ferrite-based core materials are preferred as the core particles, and ferrite-based core materials containing Mn or Mg are more preferred.

[0025] The average particle size of the core particles is not particularly limited, but is preferably 20 μm or more, more preferably 30 μm or more, and preferably 90 μm or less, more preferably 80 μm or less. The average particle size of the carrier (a carrier having a resin coating layer on the surface of the core particles) is also preferably 20 μm or more, more preferably 30 μm or more, and preferably 90 μm or less, more preferably 80 μm or less. The average particle sizes of the core particles and carrier can be measured using a dry dispersion device (RODOS (SYMPATEC)) in a laser diffraction particle size analyzer (HELOS (SYMPATEC)). In the present invention, the average particle size of the core particles and carrier refers to the volume average particle size.

[0026] The saturation magnetization of the core particles is not particularly limited, but is preferably 20 Am 2 / kg or more is preferable, and 30 Am 2 / kg or more is more preferable, and 35 Am2 / kg or more is more preferable. 2 / kg or less is preferable, and 100Am 2 / kg or less is more preferable, 2 The saturation magnetization in the present invention can be measured using a vibrating sample magnetometer BHV-35H manufactured by Riken Denshi Co., Ltd., by filling a sample into a measurement capsule (0.0565 cc) and applying a magnetic field of 1.1 (MA / m). The saturation magnetization of the carrier (carrier having a resin coating layer on the surface of the core particles) is also 20 Am 2 / kg or more is preferable, and 30 Am 2 / kg or more is more preferable, and 35 Am 2 / kg or more is more preferable. 2 / kg or less is preferable, and 100Am 2 / kg or less is more preferable, 2 / kg or less is more preferable.

[0027] [Resin Coating Layer] A coating layer that coats the surface of a core particle with a resin is also referred to as a "resin coating layer" or "coating layer." In the present invention, the resin constituting the resin coating layer contains an acrylic resin and a silicone monomer or oligomer, or a cured product of a mixture containing an acrylic resin and a silicone monomer or oligomer. Hereinafter, "(meth)acrylic" refers to "acrylic" and / or "methacrylic" (i.e., "acrylic," "methacrylic," or both "acrylic" and "methacrylic").

[0028] First, the acrylic resin will be described. Examples of the acrylic resin include acrylic polymers and derivatives thereof.

[0029] Acrylic polymers refer to polymers having structural units derived from acrylic monomers. Examples of acrylic monomers include (meth)acrylic acid, (meth)acrylic acid esters, amide group-containing acrylic monomers, and (meth)acrylonitrile. Examples of (meth)acrylic acid esters include (meth)acrylic acid alkyl esters such as methyl methacrylate, ethyl methacrylate, ethyl acrylate, butyl acrylate, and 2-ethylhexyl acrylate; hydroxy group-containing (meth)acrylates such as 2-hydroxyethyl methacrylate; and quaternary ammonium salt-containing (meth)acrylates such as dimethylaminoethyl methacrylate methyl chloride quaternary salt, 2-(dimethylamino)ethyl acrylate benzyl chloride quaternary salt, and trimethylaminoethyl methacrylate chloride quaternary salt. Examples of amide group-containing acrylic monomers include (meth)acrylamide and N-hydroxyethyl(meth)acrylamide. The acrylic polymer may be used alone or in combination of two or more.

[0030] Examples of acrylic polymers include polymers obtained by polymerizing the above-mentioned acrylic monomers. For example, a homopolymer consisting of a structural unit derived from one selected from acrylic monomers; a copolymer consisting of structural units derived from two or more selected from acrylic monomers; a copolymer consisting of a structural unit derived from an acrylic monomer and a structural unit derived from an acrylic monomer and other monomers, the copolymer mainly comprising a portion derived from an acrylic monomer. "Mainly comprising a portion derived from an acrylic monomer" means that the proportion of structural units derived from an acrylic monomer in all structural units is preferably 50% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 92% by mass or more, particularly preferably 95% by mass or more, and even more preferably 98% by mass or more. Furthermore, the proportion of components derived from acrylic monomers in the total acrylic resin in the coating layer is preferably 80% by mass or more, more preferably 90% by mass or more, and particularly preferably 98% by mass or more.

[0031] For example, the acrylic resin may contain a styrene component. Examples of acrylic resins containing a styrene component include copolymers having structural units derived from an acrylic monomer and structural units derived from a styrene monomer, or derivatives thereof. Examples include copolymers of an acrylic monomer and / or an acrylic oligomer with a styrene monomer and / or a styrene oligomer. The copolymers may be random copolymers, block copolymers, alternating copolymers, or graft copolymers.

[0032] Examples of styrene-based monomers include styrene; α-position alkyl-substituted styrenes such as α-methylstyrene; and nuclear-substituted styrenes in which a hydrogen atom on the benzene ring is substituted with an alkyl or alkoxy group having 5 or less carbon atoms, such as ο-methylstyrene, p-methylstyrene, p-methoxystyrene, p-t-butylstyrene, p-n-butylstyrene, p-tert-butylstyrene, and p-chlorostyrene. Suitable examples of styrene-based monomers include nuclear-substituted or α-substituted styrenes in which a hydrogen atom in styrene is substituted with a substituent having 3 or less carbon atoms, more preferably at least one selected from ο-methylstyrene, p-methylstyrene, and α-methylstyrene, and most preferably styrene.

[0033] The acrylic resin may contain a constituent unit derived from a Si-containing monomer among all its constituent units, but in order to ensure excellent charge-imparting ability and resin peel resistance of the acrylic resin, it is preferable that the proportion of the constituent unit derived from a Si-containing monomer is small. Specifically, the proportion of the constituent unit derived from a Si-containing monomer among all the constituent units of the acrylic resin may be 10% by mass or less, 8% by mass or less, 5% by mass or less, or 2% by mass or less.

[0034] Examples of the acrylic polymer derivatives include acrylic polymers that have been modified in various ways, such as by terminal modification or introduction of a substituent group, etc. Examples of modifications include glycidyl ether modification, oxirane introduction, hydroxyl group modification, carboxyl group modification, sulfonic acid modification, and quaternary ammonium salt modification.

[0035] The acrylic resin preferably has a weight-average molecular weight of 5,000 to 1,000,000. A weight-average molecular weight of 5,000 or more is preferred because it prevents excessive depletion of the resin coating layer formed on the surface of the core particles from the coating resin, while a weight-average molecular weight of 1,000,000 or less is preferred because it prevents a decrease in charge amount due to migration of external additives from the toner particles to the surface of the carrier particles. From this perspective, the acrylic resin more preferably has a weight-average molecular weight of 7,000 to 500,000, and particularly preferably 10,000 to 100,000.

[0036] The weight-average molecular weight can be determined by gel permeation chromatography (GPC) as a standard polystyrene equivalent. The weight-average molecular weight can be measured, for example, using a GPC (HLC-8320GPC) manufactured by Tosoh Corporation, using tetrahydrofuran as the elution solvent, polystyrene as the calibration curve polystyrene standard, and two TSKgel GMHXL columns and one TSKgel Multipore HXL-M (manufactured by Tosoh Corporation). The measurement temperature can be 40°C, and the flow rate can be 1 mL / min.

[0037] In order to obtain favorable spent resistance, charging stability, and resistance stability, the acrylic resin preferably has a structural unit derived from an alkyl (meth)acrylate, and in terms of charging ability and resin peeling resistance, a structural unit derived from an alkyl (meth)acrylate of 50% by mass or more is preferred, more preferably 70% by mass or more, particularly preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 92% by mass or more, still more preferably 95% by mass or more, and most preferably 98% by mass or more. The alkyl group in the alkyl (meth)acrylate preferably has 10 or less carbon atoms, more preferably 4 or less, and particularly preferably 2 or less. Furthermore, the alkyl (meth)acrylate is preferably an alkyl methacrylate. For these reasons, the acrylic resin is more preferably a polymer of methyl methacrylate or a polymer of ethyl methacrylate, and most preferably polymethyl methacrylate.

[0038] The acrylic resin preferably has a glass transition temperature of 40° C. or higher, more preferably 80° C. or higher, and even more preferably 100° C. or higher. The acrylic resin preferably has a glass transition temperature of 140° C. or lower, more preferably 120° C. or lower. The glass transition temperature of the acrylic resin is usually measured by a differential scanning calorimeter (DSC), and can be measured by a method in accordance with JIS K7121-1987 or JIS K6240.

[0039] The acid value of the acrylic resin is preferably 60 mgKOH / g or less, more preferably 10 mgKOH / g or less, and even more preferably 5 mgKOH / g or less. The acid value of the acrylic resin is measured in accordance with JIS K 0070-1992. The acrylic resin A-1 used in the examples has a glass transition temperature in the range of 100 to 120°C and an acid value of 5 mgKOH / g or less.

[0040] In order to obtain favorable anti-spent properties, charging stability, and resistance stability, the electrophotographic carrier of the present invention preferably contains the acrylic resin in an amount of 50 parts by mass or more, more preferably 60 parts by mass or more, even more preferably 70 parts by mass or more, and particularly preferably 80 parts by mass or more, per 100 parts by mass of the resin constituting the coating layer. Furthermore, the acrylic resin is preferably contained in an amount of 98 parts by mass or less, more preferably 95 parts by mass or less, even more preferably 93 parts by mass or less, and particularly preferably 90 parts by mass or less, per 100 parts by mass of the resin constituting the coating layer.

[0041] Next, a silicone monomer or oligomer and a cured product thereof will be described. In the electrophotographic carrier of the present invention, the coating layer preferably contains a cured product obtained by curing a silicone monomer or oligomer in a mixed state with other components such as an acrylic resin. In one embodiment of the present invention, a silicone oligomer is preferably used as the silicone monomer or oligomer. Suitable examples of the silicone oligomer include organosilicon polymers having a molecular weight of 300 to 20,000. In this specification, the molecular weight of the silicone oligomer is a weight-average molecular weight. Because of excellent compatibility with acrylic resins, the molecular weight of the silicone oligomer is preferably 15,000 or less, more preferably 10,000 or less, and particularly preferably 7,000 or less. Furthermore, because the electrophotographic carrier has good charging stability, the molecular weight of the silicone oligomer is preferably 500 or more, more preferably 700 or more, and particularly preferably 900 or more. In particular, when the silicone oligomer is a compound represented by the following formula (1) or a condensation polymer thereof, the molecular weight is preferably within the above range. Needless to say, from the viewpoint of excellent compatibility with acrylic resins, the silicone oligomer which is a condensation polymer of a compound represented by the following formula (2) can adopt the above-mentioned upper and lower molecular weight limits without any restrictions, but the upper limit of the molecular weight is more preferably 5000 or less, and particularly preferably 3000 or less. Furthermore, from the viewpoint of improving the charging stability of an electrophotographic carrier, the silicone oligomer which is a condensation polymer of a compound represented by the following formula (2) preferably has a molecular weight of 300 or more, more preferably 350 or more, even more preferably 400 or more, even more preferably 500 or more, even more preferably 700 or more, and particularly preferably 900 or more.

[0042] The weight-average molecular weight of the silicone oligomer can be determined by gel permeation chromatography (GPC) as a standard polystyrene equivalent. The weight-average molecular weight can be obtained, for example, by measuring using a GPC (HLC-8320GPC) manufactured by Tosoh Corporation, using tetrahydrofuran as the elution solvent, polystyrene as the calibration curve polystyrene standard, and two TSKgel GMHXL columns and one TSKgel Multipore HXL-M (manufactured by Tosoh Corporation). The measurement temperature can be 40°C, and the flow rate can be 1 mL / min.

[0043] In order to improve the charging stability of the electrophotographic carrier, the molecular weight of the silicone monomer is preferably 30 or more, more preferably 150 or more, and particularly preferably 200 or more. In order to achieve excellent compatibility with the acrylic resin, the molecular weight of the silicone monomer is preferably 1,500 or less, more preferably 1,000 or less, and particularly preferably 500 or less.

[0044] In one embodiment of the present invention, the silicone oligomer is preferably a condensation polymer of a compound represented by the following general formula (1). The condensation polymer mentioned here includes partial hydrolysis condensation polymer. R 1 -Si(OR 2 )3 (1) (wherein, R 1 represents a hydrogen atom or an optionally substituted hydrocarbon group having 1 to 15 carbon atoms; R 2 each independently represents an optionally substituted hydrocarbon group having 1 to 15 carbon atoms.

[0045] R 1 and R 2 are each an optionally substituted hydrocarbon group having 1 to 15 carbon atoms, R 1 and R 2 may be the same or different.

[0046] R 1 and R 2Examples of the hydrocarbon group represented by the formula (I) include an alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, an aryl group having 6 to 15 carbon atoms, and an arylalkyl group having 7 to 15 carbon atoms.

[0047] R 1 and R 2 Examples of the unsubstituted alkyl group having 1 to 15 carbon atoms in R include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, and a butyl group. 1 and R 2 Examples of the unsubstituted alkenyl group having 2 to 15 carbon atoms in R include a vinyl group and an allyl group. 1 and R 2 Examples of the unsubstituted aryl group having 6 to 15 carbon atoms in R include a phenyl group and a tolyl group. 1 and R 2 Examples of the unsubstituted arylalkyl group having 7 to 15 carbon atoms in the formula (I) include a benzyl group.

[0048] R 1 and R 2 The hydrocarbon group in R may be unsubstituted or substituted with a substituent. 1 and R 2 In the case where the hydrocarbon group in R is substituted, examples of the substituent include a halogen atom, an amino group, a hydroxy group, a mercapto group, an isocyanate group, a glycidoxy group, an epoxycyclohexyl group, an acryl group, a methacryl group, an acryloyloxy group, a methacryloyloxy group, and a ureido group. Examples of the halogen atom include fluorine, chlorine, bromine, and iodine. 1 or R 2 When R has an aromatic ring, the substituent directly bonded to the aromatic ring also includes an alkyl group or an alkenyl group. In this specification, the number of carbon atoms of the substituent is also included in the specified number of carbon atoms. 1 or R 2When the hydrocarbon group in R is substituted with a substituent, the substituent is preferably an alkyl group, an alkenyl group, an acryl group, a methacryl group, an acryloyloxy group, or a methacryloyloxy group. For example, when it has a substituent bonded to a carbon atom constituting an aromatic ring, the substituent is preferably an alkyl group, an alkenyl group, an acryloyloxy group, or a methacryloyloxy group. Furthermore, when it has a substituent bonded to a carbon atom constituting a chain hydrocarbon group, the substituent is preferably an acryl group, a methacryl group, an acryloyloxy group, or a methacryloyloxy group, and more preferably an acryloyloxy group or a methacryloyloxy group. Furthermore, when R 1 The hydrocarbon group in the formula (I) may have an alkyl chain interrupted by -O-, -S-, -NR-, -CO-, or a combination thereof, and R represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

[0049] The compound represented by formula (1) includes R 2is preferably an alkyl group, and examples thereof include methyltrimethoxysilane, methyltriethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane, n-propyltrimethoxysilane, n-propyltriethoxysilane, isopropyltrimethoxysilane, isopropyltriethoxysilane, n-butyltrimethoxysilane, n-butyltriethoxysilane, n-pentyltrimethoxysilane, n-hexyltrimethoxysilane, n-hexyltriethoxysilane, n-heptyltrimethoxysilane, and n-octyltrimethoxysilane. Silane, vinyltrimethoxysilane, vinyltriethoxysilane, allyltrimethoxysilane, cyclohexyltrimethoxysilane, cyclohexyltriethoxysilane, phenyltrimethoxysilane, phenyltriethoxysilane, 3-chloropropyltrimethoxysilane, 3-chloropropyltriethoxysilane, 3,3,3-trifluoropropyltrimethoxysilane, 3,3,3-trifluoropropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-aminopropyltriethoxysilane, 2-hydroxyethyl Trimethoxysilane, 2-hydroxyethyltriethoxysilane, 2-hydroxypropyltrimethoxysilane, 2-hydroxypropyltriethoxysilane, 3-hydroxypropyltrimethoxysilane, 3-hydroxypropyltriethoxysilane, 3-mercaptopropyltrimethoxysilane, 3-mercaptopropyltriethoxysilane, 3-isocyanatopropyltrimethoxysilane, 3-isocyanatopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane Examples of trialkoxysilanes include silane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltriethoxysilane, 3-(meth)acryloxypropyltrimethoxysilane, 3-(meth)acryloxypropyltriethoxysilane, 3-(meth)acryloyloxypropyltri-n-propoxysilane, 3-(meth)acryloyloxypropyltriisopropoxysilane, 3-ureidopropyltrimethoxysilane, and 3-ureidopropyltriethoxysilane.

[0050] As the compound represented by formula (1), R 2 is preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 2 carbon atoms, and particularly preferably a methyl group.

[0051] As the compound represented by formula (1), R 1 is an optionally substituted alkyl group having 1 to 10 carbon atoms or an optionally substituted aryl group having 6 to 12 carbon atoms, and among these, compounds in which R 1 is more preferably an alkyl group having 1 to 8 carbon atoms which may be substituted or a phenyl group which may be substituted, and even more preferably an unsubstituted methyl group, ethyl group, or n-propyl group, or a group having 1 to 8 carbon atoms which is substituted with a substituent such as one of these, or a phenyl group. 1 is an unsubstituted alkyl group having 1 to 3 carbon atoms is even more preferred, a compound in which R is a methyl group or an ethyl group is particularly preferred, and a compound in which R is a methyl group is particularly preferred. 1 is an unsubstituted alkyl group having 1 to 3 carbon atoms (particularly, a methyl group), is preferably 50 mol % or more, more preferably 80 mol % or more, more preferably 90 mol % or more, even more preferably 95 mol % or more, and particularly preferably 99 mol % or more, of all the compounds represented by formula (1).

[0052] When the silicone oligomer used in the resin constituting the coating layer is a condensation polymer of the compound represented by formula (1), the alkoxy content of the silicone oligomer is preferably 5% by mass or more, more preferably 10% by mass or more, and even more preferably 15% by mass or more. Furthermore, the alkoxy content of the silicone oligomer is preferably 60% by mass or less, more preferably 55% by mass or less, and even more preferably 50% by mass or less. The alkoxy content can be quantified, for example, by gas chromatographic analysis of the amount of alcohol, such as methanol or ethanol, in the decomposition solution obtained by decomposing silica with a potassium hydroxide-isopropyl alcohol solution.

[0053] In another embodiment of the present invention, it is preferable to use a compound represented by the following general formula (2) or a condensation polymer thereof as the silicone monomer or oligomer. The condensation polymerization referred to here includes partial hydrolysis condensation polymerization. Si(OR 3 )4 (2) (wherein, R 3 each independently represents an optionally substituted hydrocarbon group having 1 to 15 carbon atoms.

[0054] R 3 Examples of the hydrocarbon group having 1 to 15 carbon atoms represented by the formula (I) include an alkyl group having 1 to 15 carbon atoms, an alkenyl group having 2 to 15 carbon atoms, an aryl group having 6 to 15 carbon atoms, and an arylalkyl group having 7 to 15 carbon atoms.

[0055] R 3 Examples of the unsubstituted alkyl group having 1 to 15 carbon atoms in R include a methyl group, an ethyl group, an n-propyl group, an i-propyl group, and a butyl group. 3 Examples of the unsubstituted alkenyl group having 2 to 15 carbon atoms in R include a vinyl group and an allyl group. 3 Examples of the unsubstituted aryl group having 6 to 15 carbon atoms in R include a phenyl group and a tolyl group. 3 Examples of the unsubstituted arylalkyl group having 7 to 15 carbon atoms in the formula (I) include a benzyl group.

[0056] R 3The hydrocarbon group in R may be unsubstituted or substituted with a substituent. 3 In the case where the hydrocarbon group in R is substituted, examples of the substituent include a halogen atom, an amino group, a hydroxy group, a mercapto group, an isocyanate group, a glycidoxy group, an epoxycyclohexyl group, an acryloyloxy group, a methacryloyloxy group, and a ureido group. Examples of the halogen atom include fluorine, chlorine, bromine, and iodine. 3 When R has an aromatic ring, the substituents directly bonded to the aromatic ring include alkyl groups and alkenyl groups. In this specification, the number of carbon atoms of the substituents is also included in the specified number of carbon atoms. 3 The hydrocarbon group in the formula (I) may have an alkyl chain interrupted by -O-, -S-, -NR-, -CO-, or a combination thereof, and R represents a hydrogen atom or an alkyl group having 1 to 5 carbon atoms.

[0057] Specific examples of the compound represented by formula (2) include tetramethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetraisopropoxysilane, tetra-n-butoxysilane, tetraisobutoxysilane, tetra-sec-butoxysilane, tetra-tert-butoxysilane, monomethoxytriethoxysilane, monomethoxytripropoxysilane, monomethoxytributoxysilane, monoethoxytrimethoxysilane, monoethoxytrippropoxysilane, and monoethoxysilane. Examples of tetraalkoxysilanes include monoalkoxytributoxysilane, monopropoxytrimethoxysilane, monopropoxytriethoxysilane, monopropoxytributoxysilane, monobutoxytrimethoxysilane, monobutoxytriethoxysilane, monobutoxytripropoxysilane, dimethoxydiethoxysilane, dimethoxydipropoxysilane, dimethoxydibutoxysilane, diethoxydipropoxysilane, diethoxydibutoxysilane, and dipropoxydibutoxysilane. These may be used alone or in combination of two or more.

[0058] As the compound represented by formula (2), R 3is preferably an alkyl group or a phenyl group, and particularly preferably R 3 is an alkyl group, and particularly, R 3 is preferably an alkyl group having 1 to 4 carbon atoms, more preferably an alkyl group having 1 to 3 carbon atoms, and even more preferably an alkyl group having 1 or 2 carbon atoms.

[0059] The silicone monomer or oligomer, which is a simple substance or a condensation polymer of the compound represented by formula (2), preferably has an SiO content of 10% by mass or more, more preferably 20% by mass or more, and even more preferably 25% by mass or more, in order to improve the charging stability of the electrophotographic carrier. Furthermore, in order to have excellent compatibility with acrylic resins, the SiO content is preferably 80% by mass or less, more preferably 70% by mass or less, and even more preferably 60% by mass or less. The SiO content can be quantified using a nuclear magnetic resonance analyzer (NMR) or the like. In NMR measurement, on the premise that the functional group structure is known, 1 H-NMR is measured. Deuterated chloroform, for example, can be used as the solvent. For quantification, a calibration curve using a solution of polydimethylsiloxane in deuterated chloroform as the standard may be used.

[0060] Regardless of the type of silicone monomer or oligomer, in the electrophotographic carrier of the present invention, the proportion of components derived from silicone monomers or oligomers in the resin constituting the coating layer is particularly 2% by mass or more. The silicone monomer or oligomer-derived components in the resin constituting the coating layer refer to the silicone monomer or oligomer or its cured product. The content of the silicone monomer or oligomer-derived components is the content of the silicone monomer or oligomer or its cured product in the resin forming the coating layer, and can be achieved, for example, by setting the proportion of silicone monomers or oligomers in the resin constituting the raw material of the coating layer to 2% by mass or more and 20% by mass or less. By setting the proportion of silicone monomers or oligomers derived from the silicone monomer or oligomer in the resin constituting the coating layer to 2% by mass or more, the addition of the silicone monomer or oligomer can achieve the effect of improving charging stability and resistance stability. From this perspective, the proportion of silicone monomers or oligomers derived from the silicone monomer or oligomer in the resin constituting the coating layer is preferably 2% by mass or more, more preferably 5% by mass or more, and particularly preferably 10% by mass or more.

[0061] Furthermore, the proportion of components derived from silicone monomers or oligomers in the resin constituting the coating layer is particularly 20% by mass or less. By making the content of components derived from silicone monomers or oligomers 20% by mass or less, the effect of improving charging stability by using silicone monomers or oligomers can be obtained. From this viewpoint, the proportion of components derived from silicone monomers or oligomers in the resin constituting the coating layer is preferably 20% by mass or less, more preferably 18% by mass or less, and particularly preferably 15% by mass or less.

[0062] The coating layer in the present invention may contain a fluororesin. A fluororesin is a resin that does not fall under the category of acrylic resin or silicone monomer or oligomer, and that contains a structural unit derived from a fluoroalkylene in its structure. It is preferably a resin that contains a structural unit derived from a perfluoroalkylene in its structure, and more preferably a resin that contains a structural unit derived from tetrafluoroethylene in its structure. Suitable examples of fluororesins include homopolymers comprising structural units derived from tetrafluoroethylene, and copolymers comprising structural units derived from tetrafluoroethylene and other fluorine-containing monomers. Suitable other fluorine-containing monomers include fluorine-containing monomers copolymerizable with tetrafluoroethylene. Examples of such fluorine-containing monomers include fluoroalkylenes and fluoroalkyl vinyl ethers, and particularly preferred are perfluoroalkylenes such as perfluoropropylene, and perfluoroalkyl vinyl ethers such as perfluoro(propyl vinyl ether) and perfluoro(ethyl vinyl ether). Therefore, suitable fluororesins include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymers, tetrafluoroethylene-hexafluoropropylene copolymers, and the like.

[0063] Among these, it is preferable that the proportion of constituent units derived from tetrafluoroethylene in the fluororesin is high, and the content of tetrafluoroethylene units is suitably 50 mol % or more, more preferably 90 mol % or more, based on the total amount of monomer units in the fluororesin, and polytetrafluoroethylene is most preferred.

[0064] The fluororesin is preferably present in the coating resin layer as fine particles. When the fluororesin is in the form of fine particles, the average primary particle diameter is preferably 0.01 to 1 μm, more preferably 0.1 to 0.7 μm. The primary particle diameter of the fluororesin is the average value of the Feret diameter of the particles in an image observed under a scanning electron microscope. Specifically, it is determined by taking the average of 50 or more random particles at a magnification of preferably about 10,000 to 200,000 times. The fluororesin particles should have a BET specific surface area of ​​2 to 15 m. 2 / g, and 2 to 11 m 2 The BET specific surface area of ​​the fluororesin particles is measured using nitrogen gas.

[0065] The melting point of the fluororesin is preferably 250 to 410° C., more preferably 300 to 360° C. The melting point here is measured by a differential scanning calorimeter (DSC). The weight average molecular weight of the fluororesin is preferably adjusted so that the melting point of the fluororesin falls within the above range.

[0066] The content of the fluororesin is preferably less than 20 parts by mass, more preferably 17.5 parts by mass or less, per 100 parts by mass of the resin constituting the coating layer, since this makes it easier to uniformly cover the surfaces of the core particles with the resin constituting the coating layer. The content of the fluororesin is preferably 2.5 parts by mass or more, more preferably 5 parts by mass or more, per 100 parts by mass of the resin constituting the coating layer.

[0067] In the present invention, the coating layer may contain a resin other than an acrylic resin, a silicone monomer or oligomer or a cured product thereof, and a fluororesin, and examples of such a resin include styrene resins such as polystyrene.

[0068] In the present invention, when the coating layer contains a silane coupling agent, the content of the silane coupling agent is counted as part of the amount of the resin constituting the coating layer.

[0069] [Other Components] In the present invention, it is preferable that the resin coating layer contains a conductive powder from the viewpoint of charge stability and resistance adjustment for obtaining a good image, and from this viewpoint it is preferable that the resin coating layer contains carbon black.

[0070] The carbon black can be selected from carbon blacks such as ketjen black, furnace black, acetylene black, channel black, etc. Commercially available products include, for example, VULCAN XC72R, REGAL330R, BLACK PEARLS 2000, MONARCH 120 (all manufactured by Cabot), MA100, MA7 (all manufactured by Mitsubishi Chemical), etc.

[0071] Carbon black has a specific surface area of ​​25 to 1500 m2 as measured by the BET method. 2 / g. The average particle size of carbon black is preferably 100 nm or less. The average particle size of carbon black is a Feret's diameter measured from a photograph taken with a transmission electron microscope, and is the average size of, for example, 50 or more particles. The average particle size of carbon black is preferably 1 nm or more.

[0072] In the electrophotographic carrier of the present invention, the content of carbon black in the resin coating layer is preferably 1 to 15 parts by mass per 100 parts by mass of the resin in the resin coating layer.

[0073] Furthermore, in the present invention, the resin coating layer may contain an inorganic filler. This configuration allows the charge amount and resistance to be adjusted by the filler, and also provides advantages such as suppressing changes in carrier characteristics under high-temperature, high-humidity environments and low-temperature, low-humidity environments. Examples of inorganic fillers include hydrotalcite, silica, titania, magnesia, alumina, zinc oxide, and barium sulfate.

[0074] When the inorganic filler is hydrotalcite, its average particle size, D50 (volume cumulative particle size at 50% cumulative volume) on a volume basis, is preferably 0.01 to 1.0 μm, more preferably 0.05 to 0.8 μm. The amount of hydrotalcite used is preferably 0.1 to 100 parts by mass, more preferably 1 to 50 parts by mass, per 100 parts by mass of the resin constituting the coating layer. The volume-based D50 is measured by a laser diffraction / scattering method.

[0075] When the inorganic filler is silica, its specific surface area is 10 to 400 m 2 / g, and 30 to 350m 2 The amount of silica used is preferably 0.1 to 100 parts by mass, more preferably 1 to 50 parts by mass, per 100 parts by mass of the resin constituting the coating layer.

[0076] The total amount of the inorganic filler may be 0.1 to 100 parts by mass, or may be 1 to 50 parts by mass, relative to 100 parts by mass of the resin that constitutes the coating layer.

[0077] In the present invention, the coating layer preferably contains an organometallic catalyst. The organometallic catalyst is preferably an organometallic catalyst that has the effect of accelerating the curing of a silicone monomer or oligomer. As the organometallic catalyst, an organic compound containing a metal selected from Sn, Ti, Al, Fe, and Zr, such as an alkoxide, chelate compound, or metal soap containing the metal, can be used. Preferred examples include compounds in which an alkoxy group or a carboxylic acid group is coordinated to a metal (such as a metal alkoxide or a carboxylate-type metal catalyst). From the viewpoint of curability, organometallic catalysts containing a metal selected from Sn, Ti, and Zr are preferred, and from the viewpoints of safety and environmental impact, organometallic catalysts containing a metal selected from Ti and Zr are more preferred. More preferably, the alkoxy group bonded to the metal selected from Sn, Ti, and Zr has 4 or fewer carbon atoms. Commercially available organometallic catalysts include Neostan U-200, U-100, U-810, and U-820 (Sn catalysts manufactured by Nitto Kasei Co., Ltd.), Orgatix TC-100, TC-400, TC-401, and TC-750 (Ti catalysts manufactured by Matsumoto Fine Chemical Co., Ltd.), and Orgatix ZC-580 and ZC-700 (Zr catalysts manufactured by Matsumoto Fine Chemical Co., Ltd.). When the resin coating layer contains an organometallic catalyst, the content X (parts by weight) of the organometallic catalyst per 100 parts by weight of the resin in the coating layer and the content Y (parts by weight, corresponding to the content of the silicone monomer or oligomer per 100 parts by weight of the resin in the coating composition) preferably satisfy the relationship (Y / 30)≦X≦(Y / 3). When X is Y / 3 or less, the coating properties are good, and when X is Y / 30 or more, a good cured state can be obtained.

[0078] The method for forming a resin coating layer on the surface of the core particles is not particularly limited, and suitable methods include dipping and spray coating using a fluidized bed. A heat treatment step may be added after coating, or heat treatment may be performed in a coating treatment device simultaneously with coating. When heat treatment is performed after coating, a heat circulation oven, a fluidized bed electric furnace, a microwave heating furnace, or the like may be used.

[0079] The amount of resin coating varies depending on the type of resin and the charging and electrical resistance properties required of the carrier, but it is preferable that the amount of resin in the resin coating layer be 0.1 to 10 parts by mass per 100 parts by mass of core particles. If the amount of resin is 0.1 part by mass or more, it becomes easy to uniformly cover the surface of the core particles with the coating resin, and if the amount of resin is 10 parts by mass or less, problems such as increased particle aggregation can be suppressed. This resin amount is the amount of resin converted into solid content. In this specification, solid content means the amount excluding the solvent.

[0080] Next, a method for producing an electrophotographic carrier of the present invention will be described. This method is a method for producing an electrophotographic carrier having magnetic core particles and a coating layer that coats the surfaces of the core particles with a resin, and includes a step of contacting the core particles with a resin coating composition containing an acrylic resin and a silicone monomer or oligomer, wherein the content of the silicone monomer or oligomer in the resin constituting the resin coating composition is 2% by mass or more and 20% by mass or less. This method is suitable as a method for producing the electrophotographic carrier of the present invention.

[0081] The step of contacting the core particles with the resin coating composition can be carried out by the method described above as a means for forming a resin coating layer on the surface of the core particles. The components contained in the resin coating composition can be appropriately selected from those described for the resin coating layer. The components contained in the resin coating composition can be appropriately selected from those described for the coating layer of the electrophotographic carrier. For example, the resin coating composition can be prepared by mixing the above-mentioned acrylic resin, silicone monomer or oligomer, and optionally other components such as fluororesin, carbon black, inorganic filler, and catalyst with a liquid medium. The preferred embodiments and contents of these components can be appropriately selected from those described for the coating layer of the electrophotographic carrier. The resin coating composition preferably contains 3 to 60 mass% of resin in terms of solid content. Furthermore, when the resin coating composition uses a liquid medium, it can be prepared using toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, ethyl acetate, butyl acetate, tetrahydrofuran, diethyl ether, acetone, N-methylpyrrolidone, etc. As shown in the examples, the resin coating composition can be used as a resin solution containing such a solvent. This production method may include a step of contacting core particles with a resin coating composition to form a coating layer that coats the surfaces of the core particles. This step may be a step of contacting core particles with a resin coating composition to coat the surfaces of the core particles with the resin coating composition, and then heating to form a coating layer that coats the surfaces of the core particles. The heating temperature may be 70 to 170°C, and more preferably 100 to 140°C. The heating atmosphere may be air or a nitrogen atmosphere. The heating time is preferably 30 minutes to 3 hours, and more preferably 1 to 2 hours.

[0082] The electrophotographic carrier of the present invention preferably has a resistance value of 1E+5 to 1E+13 Ω, and more preferably 1E+6 to 1E+12 Ω, when 500 V is applied. When the carrier resistance value is within the above range, the carrier resistance is excellent in stability, the charge amount is stable, and excellent anti-spent effects are exhibited, thereby enabling stable printing to be fully exhibited.

[0083] The present invention relates to a two-component developer for electrophotography comprising the electrophotographic carrier of the present invention and a toner. The toner may be any type, such as a toner produced by a pulverization method or a toner produced by a polymerization method. Depending on the image forming device, a developer may be constructed by selecting either a positively charged toner or a negatively charged toner. For the positively charged toner for the electrophotographic carrier of the present invention, a toner produced using a nigrosine dye or a quaternary ammonium salt as a charge control agent is preferred, while for the negatively charged toner for the electrophotographic carrier of the present invention, a toner produced using a monoazo dye is preferred.

[0084] The toner used in the present invention is preferably one in which a colorant, a charge control agent, etc. are dispersed in a binder resin. There are no particular limitations on the binder resin, and examples include polystyrene resin, styrene-acrylic resin, polyester resin, epoxy resin, and polyurethane resin. Conventionally known colorants and charge control agents can be appropriately selected. Waxes and external additives can also be used as needed. Examples of external additives include inorganic fine particles such as silica, titania, alumina, titania, zirconia, and zinc oxide, as well as melamine-based and fluorine-based organic fine particles. The term "two-component" used with respect to a developer is a convenient way of expressing that the developer is primarily composed of two components, a carrier and a toner, and does not exclude the inclusion of other components.

[0085] The present invention provides the following: [1] A resin-coated carrier for electrophotography having magnetic core particles and a coating layer that coats the surfaces of the core particles with a resin, wherein the coating layer contains at least an acrylic resin and a silicone monomer or oligomer mixed with the acrylic resin, or a cured product obtained by curing the silicone monomer or oligomer in a mixed state with the acrylic resin, and the content of components derived from the silicone monomer or oligomer in the resin that constitutes the coating layer is 2% by mass or more and 20% by mass or less. [2] A resin-coated carrier for electrophotography having magnetic core particles and a coating layer that coats the surfaces of the core particles with a resin, wherein the coating layer contains at least an acrylic resin and a silicone oligomer mixed with the acrylic resin, or a cured product obtained by curing the silicone oligomer in a mixed state with the acrylic resin, and the content of components derived from the silicone oligomer in the resin that constitutes the coating layer is 2% by mass or more and 20% by mass or less. [3] The electrophotographic carrier according to [1] or [2], wherein the molecular weight of the silicone oligomer is 300 or more and 20,000 or less. [4] The electrophotographic carrier according to any one of [1] to [3], wherein the silicone oligomer is a condensation polymer of a compound represented by the following general formula (1): 1 -Si(OR 2 ) 3 (1) (wherein, R 1 represents a hydrogen atom or an optionally substituted hydrocarbon group having 1 to 15 carbon atoms; R 2 each independently represents a hydrocarbon group having 1 to 15 carbon atoms which may be substituted. [5] The carrier for electrophotography according to [1], wherein the silicone monomer or oligomer is a simple substance or a condensation polymer of a compound represented by the following general formula (2): Si(OR 3 )4 (2) (wherein, R 3each independently represents a hydrocarbon group having 1 to 15 carbon atoms which may be substituted.) [6] The carrier for electrophotography according to [5], wherein the molecular weight of the silicone monomer or oligomer is 30 or more and 20,000 or less. [7] The carrier for electrophotography according to any one of [1] to [6], wherein the acrylic resin accounts for 80% by mass or more and 98% by mass or less of the resin constituting the coating layer. [8] The carrier for electrophotography according to any one of [1] to [7], wherein the coating layer contains carbon black. [9] A two-component developer comprising the carrier for electrophotography according to any one of [1] to [8].

[10] A method for producing an electrophotographic carrier having magnetic core particles and a coating layer that coats the surfaces of the core particles with a resin, the method comprising the step of contacting the core particles with a resin coating composition containing an acrylic resin and a silicone monomer or oligomer, wherein the content of the silicone monomer or oligomer in the resin contained in the resin coating composition is 2% by mass or more and 20% by mass or less.

[0086] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these. In the following examples and comparative examples, the following components were used to prepare the coating resin solutions. The blend amounts in Tables 1 and 2 are in parts by mass.

[0087] In the following examples, the weight average molecular weight of the silicone oligomer was measured as described above.

[0088] <Acrylic resin> A-1: ​​Polymethyl methacrylate (weight average molecular weight 30,000)

[0089] <Silicone Oligomer> B-1: Silicone oligomer (compound represented by the formula (1) (R 1 is methyl, R 2 B-2: a partial hydrolysis polycondensate of a compound (R 1 ) represented by the formula (1), weight average molecular weight 900, alkoxy content 45% by mass; 1 is methyl, R 2B-3: a partial hydrolysis polycondensate of a compound (R 1 ) represented by the formula (1), weight average molecular weight 1,300, alkoxy content 40% by mass; B-4: a silicone oligomer (a compound (R 2 ) represented by the formula (1) 1 is methyl, R 2 B-4: Silicone oligomer (a compound represented by the formula (1) (R 1 is methyl, R 2 B-5: a partial hydrolysis polycondensate of a compound (R 1 ) represented by the formula (1), weight average molecular weight 6,600, alkoxy content 24% by mass; 1 is methyl / phenyl, R 2 B-6: a partial hydrolysis polycondensate of a compound (R 1 ) represented by the formula (1), weight average molecular weight 2,500, alkoxy content 20% by mass; 1 is a methacrylic group-substituted hydrocarbon group / methyl, R 2 B'-1: a partial hydrolysis polycondensate of a compound (R 3 is ethyl), weight average molecular weight 210, SiO content 29% by mass; B'-2: silicone oligomer (a compound (R 3 B'-3: a partial hydrolysis polycondensate of a compound represented by the formula (2) (R 3 B'-4: a partial hydrolysis polycondensate of a compound represented by the formula (2) (R 3 Partially hydrolyzed polycondensate of methyl), weight average molecular weight 480, SiO2 content 51% by mass

[0090] <Silicone resins> Silicone resin b1: SR2410, manufactured by Toray Dow Corning Silicones, weight average molecular weight 26,000 Silicone resin b2: KR251, manufactured by Shin-Etsu Silicones, weight average molecular weight 220,000 Si coupling agent: KBM13, manufactured by Shin-Etsu Silicones, molecular weight 136

[0091] <Fluororesin> C-1: PTFE (polytetrafluoroethylene, average primary particle diameter 0.3 μm, "Fluon PTFE Lub L170JE" manufactured by AGC Inc., melting point 332° C., BET specific surface area measured using N 2 8.2 m 2 / g.)

[0092] <Others> D-1: Carbon black (average particle size 30 nm, BET specific surface area 254 m 2 / g) D-2: Catalyst (Matsumoto Fine Chemical Co., Ltd., Orgatics TC-750) D-3: Silica particles (BET specific surface area of ​​50 m 2 / g) D-4: Hydrotalcite (volume-based D50 is 0.1 μm)

[0093] Example 1 500 parts by mass of a solvent (toluene) was placed in a container, and 98 parts by mass of acrylic resin A-1 and 2 parts by mass of silicone oligomer B-2 were added and mixed at 70°C to dissolve. 5 parts by mass of carbon black (D-1) and 0.4 parts by mass of catalyst (D-2) were added as additives and mixed to obtain a coating resin solution. The obtained coating resin solution was then coated with a core material (MnMg ferrite, average particle size 40 μm, saturation magnetization 63 Am 2 The resin solid content was adjusted to 1.5 parts by mass per 100 parts by mass of the carrier (100% by mass / kg), and the mixture was spray coated using a fluidized bed coating device. After the solvent was dried, the mixture was heat-treated in a heat circulation oven at 120°C for 2 hours, and then coarse particles were removed using a sieve with 75 μm openings to obtain a carrier with an average particle size of 40 μm (see Table 1).

[0094] Examples 2 to 10, Comparative Examples 1 and 2 Carriers of the present invention were obtained in the same manner as in Example 1, except that the amount of acrylic resin A-1, the composition of silicone oligomer, and the amount of catalyst were changed as shown in Table 1.

[0095] Example 11 500 parts by mass of solvent (toluene) was placed in a container, and 80 parts by mass of acrylic resin A-1 and 5 parts by mass of silicone oligomer B-2 were added, followed by mixing at 70°C to dissolve. 15 parts by mass of fluororesin (C-1) was then added and mixed. 5 parts by mass of carbon black (D-1) and 1 part by mass of catalyst (D-2) were added as additives and mixed to obtain a coating resin solution. A carrier was obtained in the same manner as in Example 1, except that the above solution was used as the coating resin solution.

[0096] Examples 12 and 13 500 parts by mass of solvent (toluene) was placed in a container, and 85 parts by mass of acrylic resin A-1 and 15 parts by mass of silicone oligomer B-2 were added, followed by mixing and dissolution at 70°C. 5 parts by mass of carbon black (D-1) and 3 parts by mass of catalyst (D-2) were added as additives, and either silica (D-3) or hydrotalcite (D-4) was added in the amount shown in Table 1 and mixed to obtain a coating resin solution. A carrier was obtained in the same manner as in Example 1, except that the above solution was used as the coating resin solution.

[0097] Comparative Examples 3 and 4 A carrier was obtained in the same manner as in Example 4, except that the silicone resin shown in Table 1 was used instead of the silicone oligomer.

[0098] Comparative Example 5 A carrier was obtained in the same manner as in Example 4, except that a silane coupling agent was used instead of the silicone oligomer.

[0099] Comparative Example 6 A carrier was obtained in the same manner as in Example 11, except that the amount of acrylic resin was changed and the silicone oligomer and curing catalyst were not used.

[0100] Comparative Example 7 A carrier was obtained in the same manner as in Example 12, except that the amount of acrylic resin was changed and the silicone oligomer and curing catalyst were not used.

[0101] <Preparation of Developer> In an environment of a temperature of 22°C and a relative humidity of 55%, 93 parts by mass of the carrier prepared in the Examples or Comparative Examples and 7 parts by mass of a commercially available negatively charged toner (cyan toner, for LaserJet Enterprise Color MFPM776zs manufactured by HP Corporation) were placed in a V-type blender and stirred and mixed for 30 minutes to obtain a developer.

[0102] <Evaluation> Next, as a deterioration treatment, the developer was used and stirred for 1 hour using a deterioration device modified from a copier, after which the toner was removed using an Epping q / m-meter, and then the same amount of toner was newly added, and a developer was prepared in the same manner and stirred in the deterioration device. This process was repeated four times, and then the developer was evaluated using the following method. If there were two or fewer Bs and the remainder were A, it was considered to be acceptable, and if there were three or more Bs or one or more Cs, it was considered to be unacceptable.

[0103] <Charge Stability> The charge amount of the developer after the first and fourth degradation treatments was compared. The triboelectric charge amount Q was measured using a q / m-meter manufactured by Epping, and the AT value was calculated from the formula <AT=Q / m×T / D (Q is the triboelectric charge amount, m is the mass of the developer, T is the toner concentration, and D is the weight of the developer)>. The absolute value of the rate of change ((AT1-AT4) / AT1×100(%) (AT1 and AT4 are the AT values ​​after the first and fourth degradation treatments, respectively)) was determined and evaluated according to the following criteria: A: The absolute value of the rate of change was less than 10% B: The absolute value of the rate of change was 10% or more but less than 20% C: The absolute value of the rate of change was 20% or more

[0104] <Resistance Stability> The resistance of the carrier was measured before the degradation treatment and after the fourth degradation treatment and after toner removal. Measurements were performed using a measuring device with opposing north and south poles and a magnetic pole spacing of 6 mm (magnetic poles: surface magnetic flux density 1500 G, opposing magnetic pole area 10 mm × 30 mm). A schematic circuit diagram of the measuring device is shown in FIG. 1. As shown in FIG. 1, non-magnetic parallel plate electrodes 2, 2' (electrode area 10 mm × 40 mm, electrode spacing 2 mm) were placed between magnetic poles 3, 3'. 200 mg of electrophotographic carrier 1 (sample) was placed between electrodes 2, 2', and electrophotographic carrier 1 was held between electrodes 2, 2' by magnetic force. The electrical resistance value (Ω) when a DC voltage of 500 V was applied was measured using an insulation resistance measuring device (TR-8601, manufactured by Takeda Riken) and logarithmically converted. From the logarithmic transformation value of the obtained resistance, the absolute value of the change (R0 - R4 (where R0 and R4 are the logarithmic transformation values ​​of the resistance of the carrier before the degradation treatment and after the degradation treatment four times and toner removal, respectively)) was calculated and evaluated according to the following criteria. In FIG. 1, reference numeral 1 is the carrier and reference numeral 4 is the support base. A: The absolute value of the change is less than 0.7 B: The absolute value of the change is 0.7 or more but less than 1 C: The absolute value of the change is 1 or more

[0105] <Spent Resistance> The Si intensity of the carrier before the degradation treatment and after the four times of degradation treatment and toner removal was measured using a fluorescent X-ray analyzer (ZSX Primus IV manufactured by Rigaku Corporation). The Si intensity Si0 (unit: kcps) before the degradation treatment and the Si intensity Si4 (unit: kcps) after the four times of degradation treatment and toner removal were determined, and the change therebetween (Si4 - Si0) was calculated and evaluated according to the following criteria: A: The change was less than 3 kcps B: The change was 3 kcps or more but less than 4.5 kcps C: The change was 4.5 kcps or more

[0106]

[0107] As shown in Table 1, the electrophotographic carriers of each Example, in which the coating layer was formed using an acrylic resin and a silicone oligomer and the silicone oligomer component accounted for 2 to 20% of the resin constituting the coating layer, exhibited stable charging even after degradation treatment, minimal resistance fluctuation, and effective suppression of toner contamination. In contrast, the electrophotographic carriers of Comparative Examples 1 and 7, which did not contain silicone oligomer, were prone to a decrease in charging due to toner spent, and Comparative Example 1 also exhibited unstable resistance. Furthermore, when a silicone resin with a larger molecular weight than the oligomer was used, compatibility with the acrylic resin was poor, resulting in problems such as the acrylic resin's resin peel resistance not being achieved (Comparative Example 3) and the silicone-based resin's spent resistance not being exhibited (Comparative Example 4). Furthermore, as shown in Comparative Example 5, when a silane coupling agent was used instead of the silicone oligomer, charging stability was insufficient. Furthermore, as shown in Comparative Example 6, when a fluororesin was used instead of the silicone oligomer, the contribution to charging stability and resistance stability was insufficient. In Comparative Example 2, in which the amount of silicone oligomer in the resin constituting the coating layer is 25%, the toner has anti-spent properties, but the chargeability is reduced due to the amount of silicone oligomer.

[0108] Example 14 500 parts by mass of a solvent (toluene) was placed in a container, and 98 parts by mass of acrylic resin A-1 and 2 parts by mass of silicone oligomer B'-2 were added and mixed at 70°C to dissolve. 5 parts by mass of carbon black (D-1) and 0.4 parts by mass of catalyst (D-2) were added as additives and mixed to obtain a coating resin solution. The obtained coating resin solution was mixed with a core material (MnMg ferrite, average particle size 40 μm, saturation magnetization 63 Am 2 The resin solid content was adjusted to 1.5 parts by mass per 100 parts by mass of the carrier (100% by mass / kg), and the mixture was spray coated using a fluidized bed coating device. After the solvent was dried, the mixture was heat-treated in a heat circulation oven at 120°C for 2 hours, and then coarse particles were removed using a sieve with 75 μm openings to obtain a carrier with an average particle size of 40 μm (see Table 2).

[0109] Examples 15 to 21 Carriers of the present invention were obtained in the same manner as in Example 14, except that the amount of acrylic resin A-1, the composition of silicone monomer or oligomer, and the amount of catalyst were changed as shown in Table 2.

[0110] Example 22 500 parts by mass of solvent (toluene) was placed in a container, and 80 parts by mass of acrylic resin A-1 and 5 parts by mass of silicone oligomer B'-2 were added and mixed at 70°C to dissolve. 15 parts by mass of fluororesin (C-1) was then added and mixed. 5 parts by mass of carbon black (D-1) and 1 part by mass of catalyst (D-2) were added as additives and mixed to obtain a coating resin solution. A carrier was obtained in the same manner as in Example 14, except that the above solution was used as the coating resin solution.

[0111] Example 23 500 parts by mass of solvent (toluene) was placed in a container, and 85 parts by mass of acrylic resin A-1 and 15 parts by mass of silicone oligomer B'-2 were added, and mixed and dissolved at 70°C. 5 parts by mass of carbon black (D-1) and 3 parts by mass of catalyst (D-2) were added as additives, and 10 parts by mass of silica (D-3) was further added and mixed to obtain a coating resin solution. A carrier was obtained in the same manner as in Example 14, except that the above solution was used as the coating resin solution.

[0112] Using the carriers of Examples 14 to 23, developers were prepared and evaluated in the same manner as described above.

[0113]

[0114] As shown in Table 2, in the electrophotographic carriers of the examples in which the coating layer was formed using an acrylic resin and a silicone monomer or oligomer, which was a simple substance or a condensation polymer of the compound represented by formula (2), and in which the silicone oligomer component accounted for 2 to 20% of the resin constituting the coating layer, charging was stable even after the deterioration treatment, resistance fluctuation was small, and component contamination by toner was effectively suppressed.

[0115] According to the electrophotographic carrier of the present invention, charging stability, resistance stability and toner-spent resistance are all obtained, it is also possible to use a low-temperature fixing toner, and it is possible to achieve a long life for the carrier.

Claims

1. An electrophotographic carrier having magnetic core particles and a coating layer that coats the surfaces of the core particles with resin, wherein the coating layer contains at least an acrylic resin and a silicone monomer or silicone oligomer mixed with the acrylic resin, or a cured product obtained by curing the silicone monomer or silicone oligomer in a mixed state with the acrylic resin, and the content of components derived from the silicone monomer or oligomer in the resin that constitutes the coating layer is 2% by mass or more and 20% by mass or less.

2. An electrophotographic carrier having magnetic core particles and a coating layer that coats the surfaces of the core particles with resin, wherein the coating layer contains at least an acrylic resin and a silicone oligomer mixed with the acrylic resin, or a cured product obtained by curing the silicone oligomer in a mixed state with the acrylic resin, and the content of components derived from the silicone oligomer in the resin that constitutes the coating layer is 2% by mass or more and 20% by mass or less.

3. The electrophotographic carrier according to claim 2, wherein the molecular weight of the silicone oligomer is 300 or more and 20,000 or less.

4. The electrophotographic carrier according to claim 1, wherein the silicone monomer has a molecular weight of 30 or more and 1,500 or less.

5. The carrier for electrophotography according to claim 2 or 3, wherein the silicone oligomer is a condensation polymer of a compound represented by the following general formula (1): 1 -Si(OR 2 )3 (1) (wherein, R 1 represents a hydrogen atom or an optionally substituted hydrocarbon group having 1 to 15 carbon atoms; R 2 each independently represents an optionally substituted hydrocarbon group having 1 to 15 carbon atoms.

6. The carrier for electrophotography according to claim 1 or 2, wherein the silicone monomer or silicone oligomer is a simple substance or a condensation polymer of a compound represented by the following general formula (2): Si(OR 3 )4 (2) (wherein, R 3 each independently represents an optionally substituted hydrocarbon group having 1 to 15 carbon atoms.

7. The electrophotographic carrier according to claim 1 or 2, wherein the acrylic resin accounts for 80% by mass or more and 98% by mass or less of the resin constituting the coating layer.

8. The electrophotographic carrier according to claim 1 or 2, wherein the coating layer contains carbon black.

9. A two-component developer comprising the electrophotographic carrier according to claim 1 or 2.

10. A method for manufacturing an electrophotographic carrier having magnetic core particles and a coating layer that coats the surfaces of the core particles with a resin, the method comprising the step of contacting the core particles with a resin coating composition containing an acrylic resin and a silicone monomer or silicone oligomer, wherein the content of the silicone monomer or silicone oligomer in the resin contained in the resin coating composition is 2% by mass or more and 20% by mass or less.

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