Magnetic carrier, two-component developer, and replenishing developer

Abstract

The present invention relates to a magnetic carrier, a two-component developer, and a replenishing developer. The magnetic carrier is a magnetic carrier comprising a magnetic core and a coating resin configured to coat the surface of the magnetic core, wherein the coating resin comprises a graft resin A and a graft resin B, wherein the coating resin (i) comprises 1.0% by mass or more and 50.0% by mass or less of the graft resin A, and (ii) comprises 50.0% by mass or more and 99.0% by mass or less of the graft resin B, wherein the graft resin A has a unit Y1 represented by the following formula (1) and a unit Y2 represented by the following formula (2), wherein the graft resin B (i) is a comb polymer having at least one site selected from, for example, a styrene-based polymer site and a (meth)acrylate-based polymer site as a branch, and (ii) contains a polysiloxane structure site at a content of 0.1% by mass or less, #imgabs0#

Description

Technical Field

[0001] The present invention relates to a magnetic carrier, a two-component developer, and a replenishing developer used in an image forming method for visualizing an electrostatic image by adopting an electrophotographic method. Background Art

[0002] Until now, the following methods have been used as image forming methods for electrophotographic systems. Various units are used to form an electrostatic latent image on an electrostatic image-bearing member, and then toner is attached to the electrostatic latent image to develop the image. For development, the following two-component development system has been widely used. Carrier particles, known as magnetic carriers, impart an appropriate positive or negative charge to the toner through triboelectric charging when mixed with the toner, and this charge serves as a driving force for development.

[0003] The two-component development system offers advantages such as good controllability of developer properties for the following reasons. This system can impart functions such as stirring, transporting, and charging the developer to the magnetic carrier, resulting in a clear division of functions between the carrier and the toner. The magnetic carrier comprises a core having magnetic properties for transporting the toner within the developer unit. Furthermore, the magnetic carrier typically has a core coated with a resin capable of imparting a charge to the toner.

[0004] In recent years, with the advancement of electrophotographic technology, there has been a growing demand for longer lifespans of electrophotographic devices. Developers are required to reduce fogging and toner scattering, maintain image density, and maintain stable development properties even during long-term use.

[0005] In order to achieve the above-mentioned objectives, it is necessary to provide a magnetic carrier that can maintain its charge-imparting ability even after long-term use.

[0006] Generally, when toner components adhere to a magnetic carrier, the number of charged sites on the magnetic carrier decreases, thereby reducing its charge-imparting ability. It is known that this can lead to problems such as changes in image density. Japanese Patent Application Laid-Open No. 2002-91093 describes an example in which a material with low surface free energy, such as a silicone resin, is used as a coating resin as a method for improving resistance to the adhesion of the above-mentioned toner components (hereinafter referred to as "contamination resistance"). Generally, materials with low surface free energy can inhibit the adhesion of toner components, etc.

[0007] However, materials with low surface free energy are easily damaged by external forces, etc., due to weak interactions between their molecules. Therefore, when silicone resins are used as coating resins for magnetic carriers, the coating resins can be worn away by mechanical loads such as those generated during agitation or transport of the carrier in a developer. As a result, the surface resistance of the magnetic carrier decreases, reducing the charge-imparting ability of the magnetic carrier.

[0008] In view of the above, in order to improve the wear resistance of the magnetic carrier, in Japanese Patent Application Laid-Open No. 2015-138230, an example is described in which a siloxane-modified resin having trifunctional silicon bonded to its terminal is used.

[0009] However, the above structure cannot improve the contamination resistance of the magnetic carrier because the structure cannot sufficiently reduce the surface free energy of the surface of the magnetic carrier.

[0010] In addition, Japanese Patent Application Laid-Open No. 2013-3428 describes an example in which, when a resin having a siloxane structure in a side chain is used, the surface free energy between molecules thereof decreases, and thus abrasion resistance becomes insufficient as in the case of using the above-mentioned silicone resin.

[0011] Therefore, in order to maintain stable charge-imparting ability of the magnetic carrier during long-term use, it may be necessary to strike a balance between contamination resistance, which suppresses adhesion of toner components, and wear resistance, which suppresses wear of the carrier coat layer.

[0012] In view of the above, an object of the present invention is to provide a magnetic carrier that can achieve reduced fogging, reduced toner scattering, stable image density, and developability even when used for a long period of time. Summary of the Invention

[0013] The inventors of the present invention conducted extensive research and found that when a graft resin A and a graft resin B having the following structures are used in combination, both the contamination resistance and the wear resistance of the magnetic carrier are achieved, and the carrier can maintain stable charge-imparting ability even during long-term use.

[0014] Graft resin A has the same structure as the organic silicone resin grafted onto its main chain. Graft resin B has a structure having high compatibility with the main chain of graft resin A as a branch. As described above, when only a resin having a siloxane structure grafted thereon, such as graft resin A, is used, the wear resistance of the magnetic carrier is insufficient.

[0015] However, when the coating resin of the magnetic carrier contains graft resin A and graft resin B, the molecular structure of graft resin A is oriented to stabilize energy. Specifically, the siloxane structure of graft resin A is oriented toward the surface of the magnetic carrier. As a result, the surface free energy of the magnetic carrier is reduced, thereby improving its anti-fouling properties.

[0016] Further, the main chain of the graft resin A and the branches of the graft resin B have affinity with each other, and thus abrasion resistance is improved.

[0017] Therefore, when graft resin A and graft resin B having the following structures are used in combination, both the contamination resistance and abrasion resistance of the magnetic carrier are achieved, and the carrier can maintain stable charge-imparting ability even during long-term use. As a result, a magnetic carrier can be provided that achieves reduced fogging, reduced toner scattering, stable image density, and developability even during long-term use.

[0018] That is, according to the present invention, there is provided a magnetic carrier comprising: a magnetic core; and a coating resin configured to coat the surface of the magnetic core, wherein the coating resin comprises a graft resin A and a graft resin B, wherein the coating resin (i) comprises 1.0% by mass or more and 50.0% by mass or less of the graft resin A, and (ii) comprises 50.0% by mass or more and 99.0% by mass or less of the graft resin B,

[0019] wherein the graft resin A has a unit Y1 represented by the following formula (1) and a unit Y2 represented by the following formula (2), wherein when the mass of the graft resin A is represented by X, the mass of the unit Y1 in the graft resin A is represented by "a", and the mass of the unit Y2 in the graft resin A is represented by "b", the "a", the "b", and the X satisfy 0.90≤(a+b) / X≤1.00 and 1.00≤a / b≤30.0, and wherein the graft resin B (i) is a comb polymer having at least one site as a branch, the site being selected from the group consisting of a styrene-based polymer site; a (meth)acrylate-based polymer site; and a styrene-acrylate-based polymer site, and (ii) does not contain a polysiloxane structure site or contains a polysiloxane structure site in an amount of 0.1% by mass or less:

[0020]

[0021] In formula (1) or formula (2), R1 represents H or CH3, R2 represents a hydrocarbon group having 1 or more and 6 or less carbon atoms which may have a substituent, and the substituent is a hydroxyl group or a carboxyl group, R3 represents H or CH3, R4 represents H or CH3, R5 represents a single bond or a hydrocarbon group having 1 to 6 carbon atoms, R6 represents a hydrocarbon group having 1 to 10 carbon atoms, R7 represents H, CH3, or Si(CH3)3, and "l" and "m" each represent an integer greater than 1, and "n" represents an integer greater than 2 and less than 150.

[0022] Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1is a schematic diagram of a surface treatment apparatus for toner used in the two-component developer according to the present invention.

[0024] Figure 2 A schematic diagram of an image forming apparatus in which the magnetic carrier according to the present invention is used.

[0025] Figure 3 A schematic diagram of an image forming apparatus in which the magnetic carrier according to the present invention is used. DETAILED DESCRIPTION

[0026] In the present invention, unless otherwise specified, the description “○○ or more and ×× or less” or “○○ to ××” indicating a numerical range means a numerical range including the lower limit and the upper limit as endpoints.

[0027] The magnetic carrier according to the present invention includes: a magnetic core; and a coating resin configured to coat the surface of the magnetic core, wherein the coating resin contains a graft resin A and a graft resin B, wherein the coating resin (i) contains 1.0% by mass or more and 50.0% by mass or less of the graft resin A, and (ii) contains 50.0% by mass or more and 99.0% by mass or less of the graft resin B, wherein the graft resin A has a unit Y1 represented by the following formula (1) and a unit Y2 represented by the following formula (2), wherein when the mass of the graft resin A is represented by X, the mass of the unit Y1 in the graft resin A is represented by "a". wherein the graft resin B (i) is a comb polymer having at least one site as a branch selected from the group consisting of a styrene-based polymer site; a (meth)acrylate-based polymer site; and a styrene-acrylate-based polymer site, and (ii) does not contain a polysiloxane structure site or contains a polysiloxane structure site in an amount of 0.1% by mass or less:

[0028]

[0029] In formula (1) or formula (2), R1 represents H or CH3, R2 represents a hydrocarbon group having 1 or more and 6 or less carbon atoms which may have a substituent, and the substituent is a hydroxyl group or a carboxyl group, R3 represents H or CH3, R4 represents H or CH3, R5 represents a single bond, a hydrocarbon group having 1 or more and 6 or less carbon atoms, or an aromatic group, R6 represents a hydrocarbon group having 1 or more and 10 or less carbon atoms, R7 represents H, CH3, or Si(CH3)3, and "l" and "m" each represent an integer greater than 1, and "n" represents an integer greater than 2 and less than 150.

[0030] As described above, when only a resin having low surface free energy such as a silicone resin is used as a coating resin for a magnetic carrier, the wear resistance of the magnetic carrier deteriorates.

[0031] Graft resin A has the same structure as the organic silicone resin grafted onto its main chain. Graft resin B has a structure having high compatibility with the main chain of graft resin A as a branch. As described above, when only a resin having a siloxane structure grafted thereon, such as graft resin A, is used, the wear resistance of the magnetic carrier is insufficient.

[0032] However, when the coating resin of the magnetic carrier contains graft resin A and graft resin B, the molecules of graft resin A and graft resin B formed in the coating resin are oriented to stabilize energy. Specifically, the siloxane structure of graft resin A is oriented toward the surface of the magnetic carrier. As a result, the surface free energy of the magnetic carrier is reduced, thereby improving its anti-fouling properties.

[0033] Further, the main chain of the graft resin A and the branches of the graft resin B have affinity with each other, and thus abrasion resistance is improved.

[0034] Therefore, when the graft resin A and the graft resin B having the following structures are used in combination, both the contamination resistance and the abrasion resistance of the magnetic carrier are achieved, and the carrier can maintain stable charge-imparting ability even when used for a long period of time.

[0035] The graft resin A includes a unit Y1 represented by formula (1) and a unit Y2 represented by formula (2). The unit Y2 has a siloxane structure, and the surface free energy is reduced by the siloxane structure. Therefore, the contamination resistance of the magnetic carrier is improved.

[0036] In formula (1), R1 represents H or CH3, and R2 represents a hydrocarbon group having 1 or more and 6 or less carbon atoms which may have a substituent, and the substituent is a hydroxyl group or a carboxyl group. As a specific method for introducing this unit, the unit can be introduced by, for example, copolymerizing any one of the following monomers during the polymerization of resin A: acrylic acid, methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, hexyl acrylate, cyclobutyl acrylate, cyclohexyl acrylate, cyclopentyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, hexyl methacrylate, cyclobutyl methacrylate, cyclohexyl methacrylate, and cyclopentyl methacrylate.

[0037] In formula (2), R3 represents H or CH3, R4 represents H or CH3, R5 represents a single bond or a hydrocarbon group having 1 or more and 6 or less carbon atoms, R6 represents a hydrocarbon group having 1 or more and 10 or less carbon atoms, and R7 represents H, CH3, or Si(CH3)3. R5 preferably represents an alkylene group having 1 to 6 carbon atoms. "l" and "m" each represent an integer greater than 1, and "n" represents an integer greater than 2 and less than 150. The grafted resin A may include a plurality of units Y2. As a specific method of introducing the unit, the unit can be introduced by, for example, copolymerizing an acrylate or methacrylate having an esterified silicone structure when the resin A is polymerized.

[0038] In the graft resin A, when the mass of the graft resin A, the mass of the unit Y1, and the mass of the unit Y2 are represented by X, "a", and "b", respectively, X, "a", and "b" satisfy 0.90≤(a+b) / X≤1.00 and 1.00≤a / b≤30.0.

[0039] This relational expression shows that the content of unit Y1 and unit Y2 in all units of graft resin A is 90% by mass or more, and the mass of unit Y1 ranges from the same mass as unit Y2 to a value obtained by multiplying the mass of unit Y2 by 30.

[0040] When the ratio "(a+b) / X" is less than 0.90, the compatibility of the graft resin A and the graft resin B may be reduced, thereby deteriorating the wear resistance, and the surface free energy may be reduced, thereby deteriorating the stain resistance.

[0041] Furthermore, when the ratio "a / b" is less than 1.00, the proportion of the Y2 unit is high. Consequently, due to the low surface free energy of the unit, the intermolecular forces between the grafted resins are low, resulting in insufficient strength of the coating resin and deteriorating abrasion resistance. When the ratio "a / b" is greater than 30.0, the proportion of the Y2 unit is low, and the surface free energy is reduced, thereby deteriorating stain resistance.

[0042] The proportion of graft resin A in the coating resin needs to be set to 1.0% by mass or more and 50.0% by mass or less. If this proportion is less than 1.0% by mass, the surface free energy increases, and thus the stain resistance deteriorates. If this proportion exceeds 50.0% by mass, the reduction in intermolecular forces due to the low surface free energy becomes more dominant than the wear resistance achieved through the interaction between graft resin A and graft resin B, and thus the wear resistance becomes insufficient. This proportion is more preferably within the range of 1.0% by mass or more and 30.0% by mass or less, and even more preferably 3.0% by mass or more and 20.0% by mass or less.

[0043] The proportion of graft resin B in the coating resin should be set to 50.0% by mass or more and 99.0% by mass or less. If this proportion is less than 50.0% by mass, the resin strength becomes insufficient due to low intermolecular forces caused by low surface free energy, and thus wear resistance deteriorates. If this proportion exceeds 99.0% by mass, the amount of low surface free energy components is small, and thus stain resistance deteriorates. This proportion is more preferably within the range of 70.0% by mass or more and 99.0% by mass or less, and even more preferably 80% by mass or more and 97.0% by mass or less.

[0044] In the graft resin A, "n" represents the number of siloxane structural units of the unit Y2 and represents the length of the siloxane structure of the unit Y2. "n" represents an integer greater than 2 and less than 150. When "n" represents less than 1, the surface free energy of the magnetic carrier surface increases, and thus the contamination resistance deteriorates. When "n" represents greater than 150, the interaction between the graft resin A and the graft resin B becomes smaller, and thus the wear resistance deteriorates. "n" more preferably represents greater than 5 and less than 60 because the wear resistance and contamination resistance are improved. The graft resin A may include a plurality of units Y2.

[0045] When the atomic percentage of Si of the magnetic carrier of the present invention is represented by Si0 when measured by X-ray photoelectron spectroscopy (XPS), the case where the following formula is satisfied is preferred.

[0046] 1.0≤Si0≤15.0

[0047] When SiO is 1.0 atomic % or more, the surface free energy of the magnetic carrier is low, and thus the contamination resistance is further improved. When SiO is 15.0 atomic % or less, the intermolecular force between the resins on the surface of the magnetic carrier becomes higher, and thus the wear resistance is further improved.

[0048] When the total number of units Y1 and units Y2 is represented by "s", the graft resin A preferably satisfies the following formula.

[0049] 50≤s≤250

[0050] When "s" is 50 or more, the resin has a molecular weight sufficient to maintain its strength, and the interaction becomes higher between the graft resin A and the graft resin B. Therefore, the wear resistance and the stain resistance are further improved.

[0051] The graft resin A may have a functional group such as a nitrogen-containing group, a carboxyl group, or a hydroxyl group. The presence of the functional group can suppress excessive charge-up of the developer in a low humidity environment. In addition, the resin preferably has a hydroxyl value because it exhibits a hydrogen bonding effect and thus further improves abrasion resistance.

[0052] The acid value of the graft resin A is preferably 0 mgKOH / g or more and 90.0 mgKOH / g or less, more preferably 30.0 mgKOH / g or more and 80.0 mgKOH / g or less, and even more preferably 40.0 mgKOH / g or more and 70.0 mgKOH / g or less. When the acid value of the graft resin A is 90.0 mgKOH / g or less, self-agglomeration of the resin hardly occurs due to the influence of the acid value, and thus the smoothness of the surface of the resin coating layer (coating film surface) of the magnetic carrier is hardly reduced. The acid value of the graft resin A can be controlled by using a monomer having a polar group such as a carboxyl group or a hydroxyl group when synthesizing the graft resin A; and adjusting the amount of the monomer added.

[0053] The graft resin B preferably includes 75.0% by mass or more of the unit Y3 represented by the following formula (3).

[0054]

[0055] In formula (3), R8 represents CH3, and R9 represents cyclohexyl, cycloheptyl, cyclooctyl, cyclopentyl, cyclobutyl, or cyclopropyl.

[0056] The graft resin B preferably has an alicyclic hydrocarbon group because the surface of the magnetic carrier (the coating film surface of the coating resin) becomes smoother to suppress the adhesion of components derived from the toner (such as toner particles or external additives), thereby further improving the anti-staining property. As the unit Y3, only one structure may be bonded or two or more structures may be bonded.

[0057] The graft resin B preferably includes 1.0% by mass or more and 25.0% by mass or less of the unit Y4 represented by the following formula (4).

[0058]

[0059] In formula (4), R 10 represents H or CH3, and R 11 represents the polymer part.

[0060] When the graft resin B includes a polymer moiety as R 11 When the resin coating layer and the core of the magnetic carrier are combined, the adhesion between the resin coating layer and the core of the magnetic carrier is improved. Therefore, the wear resistance and the charging ability of the magnetic carrier to the toner are improved. As the unit Y4, only one structure can be combined or two or more structures can be combined.

[0061] When the graft resin B includes a polymer moiety as R 11 When , the resin preferably includes a unit Y5 represented by formula (5).

[0062]

[0063] In formula (5), R 12 represents H or CH3, and R 13 It represents a hydrocarbon group having 1 or more and 6 or less carbon atoms.

[0064] R 11 The polymer portion in the graft resin is preferably a polymer of at least one monomer selected from the group consisting of methyl acrylate; methyl methacrylate; butyl acrylate; butyl methacrylate; 2-ethylhexyl acrylate; 2-ethylhexyl methacrylate; styrene; acrylonitrile; and methacrylonitrile. In the case of a polymer, the polymer has an affinity for the backbone of the graft resin A, thereby improving abrasion resistance. Furthermore, the siloxane structure of the graft resin A is effectively oriented toward the surface of the magnetic carrier. As a result, the surface free energy of the magnetic carrier is reduced, thereby improving contamination resistance.

[0065] The weight average molecular weight (Mw) of the polymer portion is preferably 2,000 or more and 10,000 or less, more preferably 3,000 or more and 8,000 or less.

[0066] When synthesizing the graft resin B, by using a macromonomer having a polymer portion as described above, the unit represented by formula (4) can be introduced into the graft resin B. The macromonomer is preferably used in an amount within a range of 5.0 parts by mass or more and 40.0 parts by mass or less relative to 100 parts by mass of all monomers used in the synthesis of the graft resin B for coating.

[0067] Incorporating a macromonomer into the grafted resin B enhances the entanglement of resin molecules, thereby improving the adhesion of the coating resin to the magnetic core. As a result, even when a load is applied to the coating resin by, for example, a stirring member of a developing unit, the coating layer does not peel off. Consequently, the magnetic carrier maintains a stable charge-imparting capability over a long period of time, enabling satisfactory image output.

[0068] From the viewpoint of stabilization of the coating layer, the weight average molecular weight (Mw) of the graft resin B is preferably 20,000 or more and 120,000 or less, and more preferably 30,000 or more and 100,000 or less.

[0069] The acid value of the graft resin B is preferably 0 mgKOH / g or more and 3.0 mgKOH / g or less, more preferably 0 mgKOH / g or more and 2.8 mgKOH / g or less, and even more preferably 0 mgKOH / g or more and 2.5 mgKOH / g or less. When the acid value of the graft resin B is 3.0 mgKOH / g or less, self-agglomeration of the resin hardly occurs due to the influence of the acid value, and therefore the smoothness of the surface of the resin coating (coating film surface) hardly decreases. The acid value of the graft resin B can be controlled by: using a monomer having a polar group such as a carboxyl group or a sulfonic group (sulfonic acid group) when synthesizing the graft resin B for coating; and adjusting the amount of monomer added. However, it is preferred not to use a monomer having a polar group, because the acid value of the graft resin A is preferably low. Even when the resin is synthesized by using only ester bond-forming monomers, a slight acid value will appear in the resin to be synthesized. This is probably because a part of the ester bond decomposes during resin synthesis (polymerization) to produce a carboxyl group.

[0070] When the SP value of the skeleton of the graft resin A is represented by SPa, the SP value of the siloxane structure is represented by SPb, and the SP value of the surface of the magnetic core is represented by SPc, the following relationship is preferably satisfied:

[0071] When 22.0 <SPc≤24.0(J / cm 3 ) 1 / 2 hour,

[0072] SPa-SPc|≤3.0(J / cm 3 ) 1 / 2 and

[0073] 5.0<|SPb-SPc|(J / cm 3 ) 1 / 2 ,or

[0074] When 18.0 <SPc≤21.0(J / cm 3 ) 1 / 2 hour,

[0075] |SPa-SPc|≤2.5(J / cm 3 ) 1 / 2 and

[0076] 4.0<|SPb-SPc|(J / cm 3 ) 1 / 2 .

[0077] Satisfying the above relationship means that the affinity between the skeleton of the grafted resin A and the surface of the magnetic core is higher than the affinity between the siloxane structure and the surface of the magnetic core. In this case, the skeleton of the grafted resin A and the surface of the magnetic core effectively have an affinity for each other, thereby allowing the grafted resin A to be in close contact with the magnetic core. As a result, wear resistance is improved.

[0078] Furthermore, regarding affinity for the magnetic core, the siloxane structure has little affinity for the core compared to the backbone of the grafted resin A, and therefore the molecular structure of the grafted resin A is oriented to stabilize energy. Specifically, the siloxane structure of the grafted resin A is oriented toward the surface of the magnetic carrier. As a result, the surface free energy of the magnetic carrier is reduced, thereby improving anti-fouling properties.

[0079] Therefore, both contamination resistance and abrasion resistance of the magnetic carrier are achieved, and the carrier can maintain stable charge-imparting ability even when used for a long period of time.

[0080] The resin coating of the present invention preferably contains conductive fine particles in its coating resin. The conductive fine particles can appropriately control the specific resistance of the magnetic carrier. As a result, the counter charge after toner development can be allowed to escape to suppress blank spots. The content of the conductive fine particles added to the coating resin is preferably 0.1 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the coating resin. When the content is less than 0.1 parts by mass, the effect of adding conductive fine particles can hardly be obtained, and when the content is greater than 20 parts by mass, the reduction in resin tint (tinge) caused by the separation of the conductive fine particles has attracted attention. Examples of conductive fine particles include carbon black, titanium oxide, and silver.

[0081] In addition, in order to improve the charging ability of the magnetic carrier to the toner or improve its stripping properties, fine particles can be incorporated into the coating resin. Although the fine particles incorporated into the resin coating can be fine particles formed by either organic materials or inorganic materials, cross-linked resin fine particles or inorganic fine particles each having a strength that can maintain its shape when the magnetic core is coated with the resin are preferred. Examples of cross-linked resins for forming cross-linked resin fine particles include cross-linked polymethyl methacrylate resins, cross-linked polystyrene resins, melamine resins, guanamine resins, urea-formaldehyde resins, phenolic resins, and nylon resins. In addition, examples of inorganic fine particles include silicon dioxide, aluminum oxide, and titanium dioxide.

[0082] The content of the fine particles in the resin coating layer is preferably 0.1 parts by mass or more and 20 parts by mass or less relative to 100 parts by mass of the coating resin.

[0083] <Method for Manufacturing Magnetic Core>

[0084] Known magnetic particles such as magnetite particles, ferrite particles, or magnetic-dispersed resin particles can be used as the magnetic core of the present invention. Among them, magnetic particles obtained by filling the pores of porous magnetic particles with a resin or magnetic-dispersed resin particles (i.e., magnetic particles comprising a magnetic oxide and a resin composition) are preferred from the viewpoint that the particles can reduce the specific gravity of the magnetic carrier and thus extend its life.

[0085] When the specific gravity of the magnetic carrier is reduced, the load on the toner in the developer state in the developing unit is reduced, thereby preventing the toner components from adhering to the surface of the magnetic carrier. This also reduces the load between magnetic carrier particles, further suppressing peeling, chipping, and abrasion of the resin coating. Furthermore, the dot reproducibility of the toner can be improved, thereby enabling the production of high-definition images.

[0086] Although the copolymer resin used as the coating resin can be used as a resin to be incorporated into the pores of the porous magnetic particles, the resin is not limited thereto, and known resins can be used. The copolymer used as the coating resin is preferably a thermoplastic resin incorporated into the pores, but in addition, examples of thermoplastic resins include polystyrene, polymethyl methacrylate, styrene-acrylate copolymer, styrene-methacrylate copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinyl acetate, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, solvent-soluble perfluorocarbon resin, polyvinyl pyrrolidone, petroleum resin, novolac resin, saturated alkyl polyester resin, aromatic polyester resins such as polyethylene terephthalate, polybutylene terephthalate or polyarylate, polyamide resin, polyacetal resin, polycarbonate resin, polyether sulfone resin, polysulfone resin, polyphenylene sulfide resin and polyether ketone resin.

[0087] As the thermosetting resin, the following resins are given, for example: phenolic resin, modified phenolic resin, maleic acid resin, alkyd resin, epoxy resin, acrylic resin, unsaturated polyester obtained by polycondensation of maleic anhydride, terephthalic acid and polyol, urea resin, melamine resin, urea-melamine resin, xylene resin, toluene resin, guanamine resin, melamine-guanamine resin, acetoguanamine resin, glyphthalate resin, furan resin, silicone resin, polyimide, polyamideimide resin, polyetherimide resin, and polyurethane resin.

[0088] An example of a method for filling the voids of ferrite particles having a porous shape with a resin component is a method comprising diluting the resin component with a solvent and adding the porous magnetic core particles to the diluted liquid. The solvent used here only needs to be able to dissolve each resin component. In the case of an organic solvent-soluble resin, it is only necessary to use an organic solvent such as toluene, xylene, cellosolve butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, or methanol. In addition, in the case of a water-soluble resin component or an emulsion-type resin component, it is only necessary to use water. An example of a method for adding a resin component diluted with a solvent to the interior of the porous magnetic core particles is a method comprising: impregnating the particles with the resin component by any one of a coating method such as an immersion method, a spraying method, a brushing method, a fluidized bed, and a mixing method; and then volatilizing the solvent. When a thermosetting resin is filled into the voids, the solvent volatilizes, and then the temperature of the resin to be used is raised to a temperature at which the resin to be used is cured to carry out a curing reaction.

[0089] Meanwhile, a specific method for producing magnetic-dispersed resin particles is, for example, the following method. The particles can be obtained by, for example, mixing a submicron magnetic substance such as iron powder, magnetite particles, or ferrite particles to disperse in a thermoplastic resin, pulverizing the mixture to a desired magnetic carrier particle size, and subjecting the pulverized substance to a thermal or mechanical spheroidization treatment as needed. Alternatively, the particles can be produced by dispersing the magnetic substance in a monomer and polymerizing the monomer to form a resin.

[0090] Examples of resins in this case include resins such as vinyl resins, polyester resins, epoxy resins, phenolic resins, urea-formaldehyde resins, polyurethane resins, polyimide resins, cellulose resins, silicone resins, acrylic resins, and polyether resins. The resin can be used alone or as a mixed resin. In particular, phenolic resins are preferred because they improve the strength of the magnetic core. The true density and specific resistance of the core can be adjusted by adjusting the amount of the magnetic body. Specifically, in the case of magnetic particles, the particles are preferably added at a rate of 70% by mass or more and 95% by mass or less relative to the magnetic carrier.

[0091] The volume-based 50% particle size (D50) of the magnetic core is preferably 20 μm or more and 80 μm or less because the core can be uniformly coated with the coating resin and thus the density of the developer magnetic brush for preventing carrier attachment and obtaining high-quality images becomes moderate.

[0092] The specific resistance of the magnetic core is preferably 1.0×10 5 (Ω·cm) or more and 1.0×10 14 (Ω·cm) or less, because satisfactory developability is obtained.

[0093] <Method for producing magnetic carrier>

[0094] The treatment method for coating the surface of the magnetic core with a coating resin is not particularly limited and can be treated by a known method. For example, a so-called impregnation method is available, which includes volatilizing the solvent of the coating resin solution while stirring the magnetic core and the coating resin solution to coat the surface of the magnetic core with the coating resin. The specific example of the equipment used in this method includes a general mixing mixer (manufactured by Fuji Paudal Co., Ltd.) and a Nauta mixer (manufactured by Hosokawa Micron Corporation). In addition, a method is available, which includes spraying the coating resin solution from a nozzle while forming a fluidized bed to coat the surface of the magnetic core with the coating resin. The specific example of the equipment used in this method includes SPIRA COTA (manufactured by Okada Seiko Co., Ltd.) and SPIR-A-FLOW (manufactured by Freund Corporation). In addition, a method including coating the magnetic carrier core with a coating resin in a granular state in a dry manner is available. A specific example of the method may be a treatment method involving use of an apparatus such as HYBRIDIZER (manufactured by Nara Machinery Co., Ltd.), MECHANOFUSION (manufactured by Hosokawa Micron Corporation), HIGHFLEX GRAL (manufactured by Fukae Powtec KK), or THETA COMPOSER (manufactured by Tokuju Corporation).

[0095] <Magnetic Carrier>

[0096] Next, the magnetic carrier is described.

[0097] The magnetic carrier preferably has a magnetization intensity of 40 (Am 2 / kg) and above 70(Am 2 When the magnetization intensity of the magnetic carrier falls within this range, the magnetic binding force on the developing sleeve is moderate, and thus the occurrence of carrier adhesion can be more satisfactorily suppressed. In addition, the stress applied to the toner in the magnetic brush can be reduced, and thus the deterioration of the toner and its adhesion to any other member can be satisfactorily suppressed.

[0098] In addition, the magnetization intensity of the magnetic carrier can be appropriately adjusted by the amount of the resin incorporated therein.

[0099] The residual magnetization of the magnetic carrier is preferably 20.0 (Am 2 / kg) or less, more preferably 10.0 (Am 2 When the residual magnetization of the magnetic carrier falls within this range, particularly satisfactory fluidity as a developer is obtained, and thus satisfactory dot reproducibility is obtained.

[0100] The true density of the magnetic carrier is preferably 2.5 (g / cm 3 ) and above 5.5(g / cm 3 ) or less, more preferably 3.0 (g / cm 3 ) and above 5.0(g / cm 3 ) or less. A two-component developer including a magnetic carrier having a true density within this range imposes a small load on its toner and thus suppresses adhesion of toner constituent components to the magnetic carrier. In addition, in order to simultaneously achieve satisfactory developability and prevent carrier adhesion under low electric field strength, a true density within this range is preferred for the magnetic carrier.

[0101] From the viewpoints of enhancing the carrier's ability to charge the toner, suppressing carrier adhesion to image areas, and improving image quality, the magnetic carrier preferably has a volume-based 50% particle size (D50) of 21 μm or more and 81 μm or less. More preferably, the particle size is 25 μm or more and 60 μm or less.

[0102] Next, the constitution of the toner preferably used to achieve the object of the present invention is described in detail below.

[0103] <Binder Resin>

[0104] In the toner particles of the present invention, for example, the following polymers may each be used as the binder resin: homopolymers of styrene and its substituents, such as polystyrene, polyparachlorostyrene, and polyvinyltoluene; styrene-based copolymers, such as styrene-parachlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylate copolymer, and styrene-methacrylate copolymer; hybrid resins each obtained by mixing a styrene-based copolymer resin, a polyester resin, or a polyester resin and a vinyl resin, or reacting a portion of both resins; and polyvinyl chloride, phenolic resin, natural modified phenolic resin, natural resin-modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin, polyester resin, polyurethane, polyamide resin, furan resin, epoxy resin, xylene resin, polyethylene resin, and polypropylene resin. Among these, polyester resin is preferably used as the main component from the viewpoint of low-temperature fixability.

[0105] Polyols (divalent or trivalent alcohols) and polycarboxylic acids (divalent or trivalent carboxylic acids) or their anhydrides or lower alkyl esters are used as monomers for the polyester unit of the polyester resin. Partial crosslinking within the molecules of the amorphous resin is effective for producing a branched polymer that exhibits "strain curing properties." For partial crosslinking, a polyfunctional compound with a valency of three or more is preferably used. Therefore, the resin preferably contains a trivalent or higher carboxylic acid or its anhydride or lower alkyl ester and / or a trivalent or higher alcohol as raw material monomers for its polyester unit.

[0106] The following polyol monomers can each be used as the polyol monomer used in the polyester unit of the polyester resin.

[0107] Examples of the diol component include ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, diethylene glycol, triethylene glycol, 1,5-pentanediol, 2,6-hexanediol, neopentyl glycol, 2-ethyl-1,3-hexanediol, hydrogenated bisphenol A, bisphenol represented by formula (A), and derivatives thereof:

[0108]

[0109] wherein R represents an ethylene group or a propylene group, "x" and "y" each represent an integer of 0 or greater, and the average value of x+y is 0 or greater and 10 or less, and a diol represented by formula (B):

[0110]

[0111] wherein R′ represents —CH2CH2-, —CH2-CH(CH3)-, or —CH2-C(CH3)2-, x′ and y′ each represent an integer greater than 0, and the average value of x+y is 0 to 10.

[0112] Examples of trivalent or higher alcohol components include sorbitol, 1,2,3,6-hexanetetraol, 1,4-anhydrosorbitol, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylglycerol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trimethylolbenzene. Among them, glycerol, trimethylolpropane, and pentaerythritol are preferably used. These diols and trivalent or higher alcohols can be used alone or in combination.

[0113] The following polycarboxylic acid monomers can each be used as the polycarboxylic acid monomer used in the polyester unit of the polyester resin.

[0114] Examples of the dicarboxylic acid component include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, n-dodecenylsuccinic acid, isododecenylsuccinic acid, n-octenylsuccinic acid, isooctenylsuccinic acid, isooctylsuccinic acid, anhydrides thereof, and lower alkyl esters thereof. Of these, maleic acid, fumaric acid, terephthalic acid, and n-dodecenylsuccinic acid are preferably used.

[0115] The example of tribasic or more carboxylic acid, its anhydride or its lower alkyl ester includes 1,2,4-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-methylenecarboxyl propane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, Empol trimer acid, its anhydride and its lower alkyl ester. Among them, in particular, it is preferred to use 1,2,4-benzenetricarboxylic acid, that is, trimellitic acid or its derivatives, because the acid or its derivatives are cheap and its reaction is easy to control. The above-mentioned dicarboxylic acid etc. and tribasic or more carboxylic acid can be used alone or in combination.

[0116] The method for producing the polyester unit of the present invention is not particularly limited, and a known method can be used. For example, the above-mentioned alcohol monomer and carboxylic acid monomer are simultaneously charged into a reaction vessel and polymerized by an esterification reaction or an ester exchange reaction and a condensation reaction to produce a polyester resin. In addition, the polymerization temperature is not particularly limited, but preferably falls within the range of 180° C. to 290° C. When the polyester unit is polymerized, a polymerization catalyst such as a titanium-based catalyst, a tin-based catalyst, zinc acetate, antimony trioxide, or germanium dioxide can be used. In particular, the binder resin of the present invention is more preferably a polyester unit polymerized using a tin-based catalyst.

[0117] In addition, from the viewpoint of fogging resistance, it is preferred that the acid value of the polyester resin is 5 mgKOH / g or more and 20 mgKOH / g or less, and the hydroxyl value thereof is 20 mgKOH / g or more and 70 mgKOH / g or less, because the amount of moisture absorption of the resin under a high-temperature and high-humidity environment is suppressed, and thus its non-electrostatic adhesion can be suppressed to a low level.

[0118] In addition, a mixture of a low molecular weight resin and a high molecular weight resin may be used as the binder resin. From the viewpoint of low temperature fixability and hot offset resistance, the content ratio between the high molecular weight resin and the low molecular weight resin is preferably 40 / 60 or more and 85 / 15 or less by mass.

[0119] <Release Agent>

[0120] Examples of the wax used in the toner of the present invention include hydrocarbon waxes such as low molecular weight polyethylene, low molecular weight polypropylene, alkylene copolymers, microcrystalline waxes, paraffin waxes, or Fischer-Tropsch waxes; oxides of hydrocarbon waxes such as oxidized polyethylene wax or its block copolymers; waxes containing fatty acid esters as a main component such as carnauba wax; and waxes obtained by deacidifying a part or all of fatty acid esters such as deacidified carnauba wax. Further examples thereof include saturated straight-chain fatty acids such as palmitic acid, stearic acid, or montanic acid; unsaturated fatty acids such as brassenoic acid, eleostearic acid, or stearidonic acid; saturated alcohols such as stearyl alcohol, aralkyl alcohol, behenyl alcohol, carnauba alcohol, ceryl alcohol, or melissyl alcohol. alcohol); polyols such as sorbitol; esters formed by fatty acids such as palmitic acid, stearic acid, behenic acid or montanic acid and alcohols such as stearyl alcohol, arylalkyl alcohol, behenyl alcohol, carnauba alcohol, wax alcohol or myristyl alcohol; fatty acid amides such as linoleamide, oleamide or lauramide; saturated fatty acid diamides such as methylene bisstearamide, ethylene biscaprylamide, ethylene bislauramide or hexamethylene bisstearamide; unsaturated fatty acid amides such as ethylene bisoleamide, hexamethylene bisoleamide, N,N′-dioleyl Adipamide or N,N′-dioleyl sebacamide; aromatic bisamides such as m-xylylbisstearamide or N,N′-distearoylisophthalamide; aliphatic metal salts (commonly referred to as metal soaps) such as calcium stearate, calcium laurate, zinc stearate, or magnesium stearate; waxes obtained by grafting aliphatic hydrocarbon waxes with vinyl monomers such as styrene or acrylic acid; partial esters formed from fatty acids and polyols such as monoglyceride of behenic acid; and methyl ester compounds having a hydroxyl group obtained by hydrogenating vegetable oils and fats.

[0121] Among these waxes, hydrocarbon waxes such as paraffin wax and Fischer-Tropsch wax, or fatty acid ester waxes such as carnauba wax are preferred from the viewpoint of improving the low-temperature fixability and fixation separation properties of the toner. In the present invention, hydrocarbon waxes are more preferred because they further improve the hot offset resistance of the toner.

[0122] In the present invention, the wax is preferably used in an amount of 3 parts by mass or more and 8 parts by mass or less relative to 100 parts by mass of the binder resin.

[0123] Furthermore, in an endothermic curve at a temperature increase measured by a differential scanning calorimeter (DSC), the peak temperature of the highest endothermic peak of the wax is preferably 45° C. or higher and 140° C. or lower. The peak temperature of the highest endothermic peak of the wax preferably falls within this range because both storage stability and hot offset resistance of the toner can be achieved.

[0124] <Colorant>

[0125] The toner particles in the present invention may contain a colorant. Examples of the colorant include the following colorants.

[0126] The black colorant is, for example, carbon black or a colorant toned to black with a yellow colorant, a magenta colorant, and a cyan colorant. Pigments can be used alone as colorants, but from the viewpoint of image quality of full-color images, it is more preferable to use a dye and a pigment in combination to improve color clarity.

[0127] As pigments for magenta toner, for example, CI Pigment Red 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 21, 22, 23, 30, 31, 32, 37, 38, 39, 40, 41, 48:2, 48:3, 48:4, 49, 50, 51, 52, 53, 54, 55, 56 CI Pigment Violet 19; and CI Vat Red 1, 2, 10, 13, 15, 23, 29, or 35.

[0128] As the dye for magenta toner, for example, oil-soluble dyes such as CI Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 81, 82, 83, 84, 100, 109, or 121; CI Disperse Red 9; CI Solvent Violet 8, 13, 14, 21, or 27; and CI Disperse Violet 1; and basic dyes such as CI Basic Red 1, 2, 9, 12, 13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 34, 35, 36, 37, 38, 39, or 40; and CI Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27, or 28 are given.

[0129] As the pigment for cyan toner, there are given, for example: CI Pigment Blue 2, 3, 15:2, 15:3, 15:4, 16, or 17; CI Vat Blue 6; CI Acid Blue 45; and a copper phthalocyanine pigment in which the phthalocyanine skeleton is substituted with 1 to 5 phthalimidomethyl groups.

[0130] The dye for cyan toner is CI Solvent Blue 70, for example.

[0131] As the pigment for yellow toner, for example, CI Pigment Yellow 1, 2, 3, 4, 5, 6, 7, 10, 11, 12, 13, 14, 15, 16, 17, 23, 62, 65, 73, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155, 168, 174, 175, 176, 180, 181, or 185; and CI Vat Yellow 1, 3, or 20 are given.

[0132] The dye for yellow toner is CI Solvent Yellow 162, for example.

[0133] These colorants may be used alone or as a mixture thereof, and each may be used in the state of a solid solution.The colorant is selected based on hue angle, chroma, brightness, light resistance, OHP transparency, and dispersibility in toner.

[0134] The content of the colorant is preferably 0.1 parts by mass or more and 30.0 parts by mass or less relative to 100 parts by mass of the total amount of the resin component.

[0135] <Inorganic fine particles>

[0136] The toner preferably contains inorganic fine particles for the main purpose of improving its fluidity and chargeability, and a morphology in which the fine particles are attached to the surfaces of the toner particles is preferred.

[0137] As inorganic fine particles used as spacer particles to improve the releasability between the toner and the magnetic carrier, silica particles having a maximum peak particle diameter based on number distribution of 80 nm or more and 200 nm or less are preferred. The maximum peak particle diameter based on number distribution is more preferably 100 nm or more and 150 nm or less so that the inorganic fine particles can more satisfactorily suppress separation from the toner while allowing the inorganic fine particles to function as spacer particles.

[0138] In addition, in order to improve the fluidity of the toner, the toner preferably contains inorganic fine particles having a highest peak particle size based on number distribution of 20 nm or more and 50 nm or less, and a form in which the fine particles are used in combination with silica particles is also preferred.

[0139] Further, in order to improve the fluidity and transferability of the toner, any other external additives may be added to the toner particles. The external additives externally added to the toner particle surface preferably contain inorganic fine particles each formed of, for example, titanium oxide, aluminum oxide or silicon dioxide, and a plurality of external additives may be used in combination.

[0140] The total content of external additives is preferably from 0.3 parts by mass to 5.0 parts by mass, more preferably from 0.8 parts by mass to 4.0 parts by mass, per 100 parts by mass of the toner particles. The content of silica particles having a maximum peak particle size of 80 nm to 200 nm based on the number distribution in the external additives is preferably from 0.1 parts by mass to 2.5 parts by mass, more preferably from 0.5 parts by mass to 2.0 parts by mass, per 100 parts by mass of the toner particles. When the content falls within this range, the effect of the particles serving as spacer particles becomes more pronounced.

[0141] In addition, the surface of the silica particles or inorganic fine particles used as the external additive is preferably subjected to a hydrophobic treatment. The hydrophobic treatment is preferably performed using: a coupling agent such as various titanium coupling agents and silane coupling agents; a fatty acid and a metal salt thereof; silicone oil; or a combination thereof.

[0142] Examples of the titanium coupling agent include tetrabutyl titanate, tetraoctyl titanate, isopropyl triisostearyl titanate, isopropyl tridecylbenzenesulfonyl titanate, and bis(dioctyl pyrophosphate)oxyacetate titanate.

[0143] In addition, examples of the silane coupling agent include γ-(2-aminoethyl)aminopropyltrimethoxysilane, γ-(2-aminoethyl)aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-β-(N-vinylbenzylaminoethyl)-γ-aminopropyltrimethoxysilane hydrochloride, hexamethyldisilazane, methyltrimethoxysilane, butyltrimethoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyltrimethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, and p-methylphenyltrimethoxysilane.

[0144] Examples of fatty acids include long-chain fatty acids such as undecanoic acid, dodecanoic acid, tridecanoic acid, lauric acid, myristic acid, palmitic acid, pentadecanoic acid, stearic acid, heptadecanoic acid, arachidic acid, montanic acid, oleic acid, linoleic acid, and arachidonic acid. Metals of these fatty acid metal salts include, for example, zinc, iron, magnesium, aluminum, calcium, sodium, and lithium.

[0145] Examples of the silicone oil include dimethyl silicone oil, methylphenyl silicone oil, and amino-modified silicone oil.

[0146] The hydrophobization treatment is preferably performed by adding 1% by mass or more and 30% by mass or less (more preferably 3% by mass or more and 7% by mass or less) of a hydrophobizing agent to the particles to be treated to coat the particles.

[0147] The hydrophobicity of the hydrophobized external additive is not particularly limited, but the hydrophobicity after treatment is preferably, for example, 40 or more and 98 or less. The hydrophobicity indicates the wettability of a sample with respect to methanol and is an indicator of its hydrophobicity.

[0148] When the magnetic carrier of the present invention is mixed with a toner and used as a two-component developer, the carrier mixing ratio is set to 2% by mass or more and 15% by mass or less, preferably 4% by mass or more and 13% by mass or less, based on the toner concentration in the developer, because generally satisfactory results are obtained. When the toner concentration is less than 2% by mass, the image density tends to decrease, and when the toner concentration exceeds 15% by mass, fogging or toner scattering tends to occur in the image forming apparatus.

[0149] The magnetic carrier of the present invention is used as a replenishing developer. The replenishing developer, which is replenished to a developing unit in response to a decrease in the toner concentration of a two-component developer in the developing unit, contains 2 parts by mass or more and 50 parts by mass or less of toner per 1 part by mass of the replenishing magnetic carrier.

[0150] Next, an image forming apparatus including a developing device using the magnetic carrier, two-component developer, and replenishing developer of the present invention is described by way of example. However, the developing device used in the developing method of the present invention is not limited thereto.

[0151] <Image Forming Method>

[0152] exist Figure 2 In the figure, an electrostatic latent image bearing member 1 rotates in the direction indicated by the arrow. The electrostatic latent image bearing member 1 is charged by a charger 2, serving as a charging unit, and an electrostatic latent image is formed on the surface of the charged electrostatic latent image bearing member 1 by exposure to light from an exposure unit 3, serving as an electrostatic latent image forming unit. The developing unit 4 includes a developing container 5 for storing a two-component developer, and a developer carrying member 6 is rotatably arranged therein. Furthermore, the developer carrying member 6 includes magnets 7, which serve as magnetic field generating means. At least one of the magnets 7 is positioned facing the latent image bearing member. The two-component developer is retained on the developer carrying member 6 by the magnetic field of the magnets 7, and the amount of the two-component developer is adjusted by an adjusting member 8 before being transported to a developing section facing the electrostatic latent image bearing member 1. In the developing section, a magnetic brush is formed by the magnetic field generated by the magnets 7. A developing bias voltage, obtained by superimposing an AC electric field on a DC electric field, is then applied to visualize the electrostatic latent image as a toner image. The toner image formed on the electrostatic latent image bearing member 1 is electrostatically transferred to a recording medium (transfer material) 12 by a transfer charger 11. Here, the following steps may be performed: Figure 2As shown, the toner image is transferred once from the electrostatic latent image bearing member 1 to the intermediate transfer body 9 , and then electrostatically transferred to the recording medium 12 .

[0153] The recording medium 12 is then conveyed to a fixing unit 13, where it is heated and pressurized. The developer's toner is thereby fixed to the recording medium 12. The recording medium 12 is then discharged outside the apparatus as an output image. After the transfer step, the toner remaining on the electrostatic latent image bearing member 1 is removed by a cleaner 15. The electrostatic latent image bearing member 1, cleaned by the cleaner 15, is then electrically initialized by applying light from a pre-exposure unit 16, and the aforementioned image forming operation is repeated.

[0154] Figure 3 A schematic diagram which is an example of a schematic diagram of a case in which the image forming method of the present invention is applied to a full-color image forming apparatus.

[0155] The arrangement of the image forming units represented by, for example, K, Y, C, and M in the figure and the arrows indicating their rotation directions are not limited thereto. Incidentally, K, Y, C, and M represent black, yellow, cyan, and magenta, respectively. Figure 2In the figure, electrostatic latent image bearing members 1K, 1Y, 1C, and 1M each rotate in the direction indicated by the arrow. Each electrostatic latent image bearing member is charged by chargers 2K, 2Y, 2C, and 2M, serving as charging units. Electrostatic latent images are formed on the surfaces of each charged electrostatic latent image bearing member by exposure to light from exposure units 3K, 3Y, 3C, and 3M, serving as electrostatic latent image forming units. The electrostatic latent images are then visualized as toner images using two-component developers carried on developer bearing members 6K, 6Y, 6C, and 6M, included in developing units 4K, 4Y, 4C, and 4M, serving as developing units. Residual toner from the developer on each electrostatic latent image bearing member is removed by cleaners 15K, 15Y, 15C, and 15M, respectively. The toner images are then transferred to the intermediate transfer body 9 by intermediate transfer chargers 10K, 10Y, 10C, and 10M, serving as transfer units. The toner image is then transferred to a recording medium 12 by a transfer charger 11, which serves as a transfer unit. The toner image on the recording medium 12 is fixed under heat and pressure by a fixing unit 13, which serves as a fixing unit, and the medium is output as an image. Then, an intermediate transfer member cleaner 14, which serves as a cleaning member for the intermediate transfer member 9, recovers residual toner and the like after transfer. In the development method of the present invention, development is preferably performed in a state where an AC voltage is applied to each developer-carrying member to form an AC electric field in the development area while a magnetic brush is brought into contact with the photosensitive member. To prevent carrier adhesion and improve dot reproducibility, the distance (SD distance) between the developer-carrying member (developing sleeve) 6 and the photosensitive drum is preferably 100 μm or more and 1,000 μm or less. If the distance is less than 100 μm, insufficient developer supply tends to occur, resulting in reduced image density. If the distance is greater than 1,000 μm, the magnetic lines of force from the magnetic pole S1 diffuse, reducing the density of the magnetic brush. Therefore, dot reproducibility deteriorates, or the restraining force on the magnetic coated carrier weakens, making it easier for carrier adhesion to occur.

[0156] The peak-to-peak voltage (Vpp) of the AC electric field is 300V or more and 3,000V or less, preferably 500V or more and 1,800V or less. In addition, the frequency of the electric field is 500Hz or more and 10,000Hz or less, preferably 1,000Hz or more and 7,000Hz or less, and an electric field having such a peak-to-peak voltage and frequency can be appropriately selected and used according to the process. In this case, the waveform of the AC bias used to form the AC electric field is, for example, a triangular wave, a rectangular wave, a sine wave, or a waveform with a changed duty cycle. In order to adapt to changes in the toner image formation speed, it is sometimes preferred to perform development by applying a developing bias having a discontinuous AC bias (intermittent AC superimposed voltage) to each developer carrying member. When the applied voltage is less than 300V, it is difficult to obtain sufficient image density, and in some cases, the fogged toner in the non-image portion cannot be satisfactorily recovered. In addition, when the applied voltage is greater than 3,000V, the latent image will be disturbed by the magnetic brush, resulting in a reduction in image quality.

[0157] When using a two-component developer containing a satisfactorily charged toner, the fog removal voltage (Vback) can be reduced, thereby reducing the primary charging of the photosensitive member. Consequently, the life of the photosensitive member can be extended. While the preferred value varies depending on the development system, Vback is preferably 200 V or less, more preferably 150 V or less. A contrast potential of 100 V or more and 400 V or less is preferably used to achieve sufficient image density.

[0158] In addition, although the processing speed thereof is affected when the frequency is lower than 500 Hz, the configuration of each electrostatic latent image bearing member can be the same as that of a photosensitive member generally used in an image forming apparatus. For example, a photosensitive member having a configuration in which a conductive layer, an undercoat layer, a charge generating layer, and a charge transporting layer are sequentially provided on a conductive substrate made of, for example, aluminum or SUS, and a charge injection layer is provided as needed is given.

[0159] The conductive layer, undercoat layer, charge generating layer and charge transporting layer may be those generally used in photosensitive members. For example, a charge injection layer or a protective layer may be used as the outermost surface layer of the photosensitive member.

[0160] <Measurement of Pore Diameter and Pore Volume of Porous Magnetic Core>

[0161] The pore size distribution of the porous magnetic core is measured by mercury intrusion porosimetry.

[0162] The measurement principle is described as follows.

[0163] During the measurement, the pressure applied to the mercury is varied, and the amount of mercury that penetrates the pores at that pressure is measured. Taking into account the balance of forces, the conditions under which mercury can penetrate the pores can be expressed by the following equation: PD = -4σcosθ, where P represents pressure, D represents the pore diameter, and θ and σ represent the contact angle and surface tension of mercury, respectively. When the contact angle and surface tension are constant, the pressure P and the diameter D of the pores that mercury can penetrate at that pressure are inversely proportional to each other. Given this, the pore distribution is determined by automatically replacing the abscissa P of the PV curve—obtained by measuring the amount of liquid V that penetrates at pressure P while varying the pressure—with the pore diameter based on this equation.

[0164] The measurement can be performed with a measuring instrument such as the fully automatic multifunctional mercury porosimeter PoreMaster series / PoreMaster-GT series manufactured by Yuasa Ionics or the automatic porosimeter Autopore IV9500 series manufactured by Shimadzu Corporation.

[0165] Specifically, the measurement was performed with Autopore IV9520 manufactured by Shimadzu Corporation under the following conditions by the following procedure.

[0166] Measurement conditions

[0167] Measurement environment: 20℃

[0168] Measurement Room

[0169] Sample volume: 5cm 3

[0170] Pressed volume: 1.1cm 3

[0171] Application: for powder

[0172] Measuring range: 2.0 psia (13.8 kPa) and above and 59,989.6 psia (413.7 MPa) and below

[0173] Measurement steps: 80 steps (when the aperture is expressed on a logarithmic scale, the steps are provided at equal intervals)

[0174] Push parameters

[0175] Exhaust pressure: 50μmHg

[0176] Exhaust time: 5.0 minutes

[0177] Mercury injection pressure: 2.0psia (13.8kPa)

[0178] Equilibration time: 5 seconds

[0179] High voltage parameters

[0180] Equilibration time: 5 seconds

[0181] Mercury parameters

[0182] Advancing contact angle: 130.0 degrees

[0183] Receding contact angle: 130.0 degrees

[0184] Surface tension: 485.0 mN / m (485.0 dynes / cm)

[0185] Mercury density: 13.5335 g / mL

[0186] Measurement process

[0187] (1) Weigh approximately 1.0 g of the porous magnetic core and place it in the sample chamber. Enter the weight.

[0188] (2) The mercury injection amount is measured in the low-pressure portion within a range of 2.0 psia (13.8 kPa) to 45.8 psia (315.6 kPa).

[0189] (3) The mercury injection amount is measured in the high-pressure portion within a range of 45.9 psia (316.3 kPa) to 59,989.6 psia (413.6 MPa).

[0190] (4) The pore size distribution is calculated from the mercury injection pressure and the mercury injection amount.

[0191] Steps (2), (3) and (4) are automatically performed using the software included with the device.

[0192] The pore diameter at which the differential pore volume becomes maximum in the pore diameter range of 0.1 μm or more to 3.0 μm or less is read from the pore diameter distribution measured as described above, and the read pore diameter is used as the pore diameter at which the differential pore volume becomes locally maximum.

[0193] The pore volume was calculated by integrating the differential pore volume in the pore diameter range of 0.1 μm or more to 3.0 μm or less using software included with the device.

[0194] <Method for measuring weight average particle size (D4) and number average particle size (D1)>

[0195] The weight-average particle diameter (D4) and number-average particle diameter (D1) of the toner were measured based on the pore resistance method using a precision particle size distribution measuring apparatus "Coulter Counter Multisizer 3" (trademark, manufactured by Beckman Coulter, Inc.) and its included dedicated software "Beckman Coulter Multisizer 3 Version 3.51" (manufactured by Beckman Coulter, Inc.) for setting measurement conditions and analyzing measurement data. Measurements were performed in 25,000 effective measurement channels, and the measurement data were analyzed to calculate the diameter.

[0196] A product obtained by dissolving guaranteed sodium chloride in ion-exchanged water so as to have a concentration of about 1% by mass, such as "ISOTON II" (manufactured by Beckman Coulter, Inc.) can be used as the aqueous electrolyte solution used in the measurement.

[0197] Prior to measurement and analysis, the dedicated software was set up as follows.

[0198] In the "Change Standard Measurement Method (SOM)" interface of the dedicated software, set the total count of the control mode to 50,000 particles, the number of measurements to 1, and the value obtained by using "standard particles each with a particle size of 10.0 μm" (manufactured by Beckman Coulter, Inc.) as the Kd value. The threshold and noise level are automatically set by pressing the threshold / noise level measurement button. In addition, set the current to 1,600 μA, the gain to 2, and the electrolyte solution to "ISOTON II", and place a check mark in the check box to indicate whether to flush the orifice tube after measurement.

[0199] In the "Pulse-Particle Size Conversion Settings" interface of the dedicated software, the bin interval was set to logarithmic particle size, the number of particle size bins was set to 256, and the particle size range was set to 2 μm to 60 μm.

[0200] The specific measurement method is as follows.

[0201] (1) Place approximately 200 mL of the electrolyte solution in a 250 mL glass round-bottom beaker designed for the Multisizer 3. Place the beaker in the sample stand and stir the solution counterclockwise at 24 rpm using a stirring rod. Then, use the "well flush" function in the analysis software to remove dirt and bubbles from the well tube.

[0202] (2) About 30 mL of an aqueous electrolyte solution was placed in a 100 mL flat-bottom glass beaker made of glass. About 0.3 mL of a dilute solution obtained by diluting "Contaminon N" (a 10% by mass aqueous solution of a neutral detergent for washing precision measuring devices, composed of a nonionic surfactant, an anionic surfactant, and an organic builder, and having a pH of 7, manufactured by Wako Pure Chemical Industries, Ltd.) by three times by mass with ion-exchanged water was added to the solution as a dispersant.

[0203] (3) A predetermined amount of ion-exchanged water was placed in a water tank equipped with an ultrasonic disperser "Ultrasonic Dispersion System Tetra 150" (manufactured by Nikkaki Bios Co., Ltd.) having an electrical output of 120 W and incorporating two oscillators each having an oscillation frequency of 50 kHz with a phase difference of 180°. About 2 ml of Contaminon N was added to the water tank.

[0204] (4) Place the beaker in section (2) in the beaker fixing hole of the ultrasonic disperser and operate the ultrasonic disperser. Then, adjust the height of the beaker so that the liquid level of the electrolyte aqueous solution in the beaker can resonate with the ultrasonic wave from the disperser to the greatest extent.

[0205] (5) While ultrasonic waves are being irradiated on the electrolyte aqueous solution, approximately 10 mg of the toner is gradually added to the electrolyte aqueous solution in the beaker of section (4) and dispersed therein. The ultrasonic dispersion treatment is then continued for a further 60 seconds. During the ultrasonic dispersion, the water temperature in the water tank is appropriately controlled to be 10° C. or higher and 40° C. or lower.

[0206] (6) The aqueous electrolyte solution in section (5) in which the toner has been dispersed is added dropwise to the round-bottomed beaker in section (1) placed in the sample holder using a pipette, and the concentration of the toner to be measured is adjusted to approximately 5%. The measurement is then continued until the particle diameters of 50,000 particles are measured.

[0207] (7) The measurement data was analyzed using the dedicated software included with the device, and the weight-average particle diameter (D4) and the number-average particle diameter (D1) were calculated. When the dedicated software was set to display the graph in volume %, the "Average Diameter" on the "Analysis / Volume Statistics (Arithmetic Mean)" screen of the dedicated software was the weight-average particle diameter (D4), and when the dedicated software was set to display the graph in number %, the "Average Diameter" on the "Analysis / Number Statistics (Arithmetic Mean)" screen was the number-average particle diameter (D1).

[0208] <Calculation method of fine powder amount>

[0209] The amount of fine powder in the toner on a number basis (number %) is calculated as follows.

[0210] For example, in the case of the percentage of particles in a toner each having a particle size of 4.0 μm or less, the particle size is measured using Multisizer 3, and then (1) its dedicated software is set to display the graph in units of number % so that the measurement results can be displayed in units of number %. (2) A check mark is placed in the "<" in the particle size setting section on the "Format / Particle Size / Particle Size Statistics" interface of the software, and "4" is entered in the particle size input section below that section. Then, (3) its "Analysis / Number Statistics (Arithmetic Mean)" interface is displayed. The value in the "<4 μm" display section on the interface at this time is the percentage of particles in the toner each having a particle size of 4.0 μm or less.

[0211] <Calculation method of coarse powder amount>

[0212] The volume-based amount of coarse powder in the toner (volume %) is calculated as described below.

[0213] For example, in the case of the volume percentage of particles each having a particle size of 10.0 μm or larger in a toner, the particle size is measured using Multisizer 3, and then (1) the dedicated software is set to display the graph in volume % so that the measurement results can be displayed in a graph in volume %. (2) A check mark is placed in the ">" box in the particle size setting section on the "Format / Particle Size / Particle Size Statistics" screen, and "10" is entered in the particle size input section below the section. Then, (3) the "Analysis / Volume Statistics (Arithmetic Mean)" screen of the software is displayed. At this time, the value in the ">10 μm" display section on the screen is the volume percentage of particles each having a particle size of 10.0 μm or larger in the toner.

[0214] <Method for measuring molecular weight and molecular weight distribution of resins, etc.>

[0215] The molecular weight and molecular weight distribution of a resin or the like are measured by gel permeation chromatography (GPC) as described below.

[0216] First, the sample was dissolved in tetrahydrofuran (THF) at room temperature for 24 hours. The resulting solution was then filtered through a solvent-resistant membrane filter "MYSYORIDISK" (manufactured by Tosoh Corporation) having a pore size of 0.2 μm to provide a sample solution. The concentration of the THF-soluble component in the sample solution was adjusted to approximately 0.8% by mass. Measurement was performed using the sample solution under the following conditions.

[0217] Apparatus: HLC 8120GPC (detector: RI) (manufactured by Tosoh Corporation)

[0218] Column: 7-column combination of Shodex KF-801, 802, 803, 804, 805, 806, and 807 (manufactured by Showa Denko KK)

[0219] Eluent: tetrahydrofuran (THF)

[0220] Flow rate: 1.0 mL / min

[0221] Oven temperature: 40.0℃

[0222] Sample injection volume: 0.10mL

[0223] In the calculation of the molecular weight of the sample, a molecular weight calibration curve prepared from standard polystyrene resins (trade name: "TSK standard polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F-10, F-4, F-2, F-1, A-5000, A-2500, A-1000, and A-500", manufactured by Tosoh Corporation) is used.

[0224] <Measurement Method of Si Atom Concentration by XPS>

[0225] The magnetic carrier is attached to the indium foil. The carrier particles are evenly attached to the indium foil so that the indium foil is not exposed.

[0226] The measurement conditions are as follows.

[0227] Device: PHI 5000 VERSAPROBE II (ULVAC-PHI, Inc.)

[0228] Applied radiation: Al Kα radiation

[0229] Output: 25W, 15kV

[0230] Pass energy: 58.7eV

[0231] Step size: 0.125eV

[0232] XPS peaks: C1s, O1s, Si2p, Ti2p and Sr3d

[0233] <Resin Structure (NMR)>

[0234] By nuclear magnetic resonance spectroscopy ( 1Analyze the structure of the resin (e.g., 1,2-polybutadiene resin or amorphous resin) in the toner by 1H-NMR.

[0235] Measuring device: JNM-EX400 (manufactured by JEOL Ltd.)

[0236] Measuring frequency: 400 MHz

[0237] Pulse condition: 5.0 μs

[0238] Frequency range: 10,500 Hz

[0239] Number of scans: 1,024 times

[0240] Measuring solvent: DMSO-d6

[0241] Dissolve the sample in DMSO-d6 as much as possible and conduct the measurement under the above conditions. Determine the structure of the sample, etc. from the chemical shift values and proton ratios of the spectra to be obtained. ""

[0242] <Calculation method of SP value>

[0243] The SP value is called the "solubility parameter" and is obtained by converting the ease of solubility of compounds in terms of their chemical structures into numerical values. The case where compounds have closer SP values means that the compounds are more miscible and compatible with each other. Although various methods can be used as the calculation method of this SP value, the commonly used Fedors method is used in the present invention. This method is described in detail, for example, in Polymer Engineering and Science, Vol. 14, pp. 147-154, and the SP value can be calculated by the following equation.

[0244] Equation: SP value = √(Ev / v) = √(∑Δei / ∑Δvi)

[0245] In the equation, Ev represents the evaporation energy (cal / mol) of the compound, "v" represents its molar volume (cm 3 3 / mol), Δei represents the evaporation energy of each atom or atomic group, and Δvi represents the molar volume of each atom or atomic group.

[0246] <Manufacturing method of toner>

[0247] While there are no particular limitations on the method for producing toner particles, a pulverization method is preferred from the perspective of dispersing the release agent and the polymer obtained by grafting a styrene acrylic polymer onto a polyolefin. This is for the following reasons. When toner particles are produced in an aqueous medium, the highly hydrophobic release agent and the polymer obtained by grafting a styrene acrylic polymer onto a polyolefin tend to be localized within the toner particles. Consequently, forming the desired core-shell structure is difficult.

[0248] Now, a method for producing toner based on a pulverization method is described.

[0249] In the raw material mixing step, predetermined amounts of materials for forming toner particles, for example, a binder resin, a release agent, a colorant, a crystalline polyester, and other components such as a charge control agent as needed, are weighed, and the materials are blended and mixed. As a mixing device, for example, a double cone mixer, a V-type mixer, a drum mixer, a super mixer, a Henschel mixer, a Nauta mixer, and a MECHANO HYBRID (manufactured by Nippon Coke & Engineering Co., Ltd.) are given.

[0250] Next, the mixed material is melted and mixed so that wax etc. can be dispersed in the binder resin.In the melting and mixing step, an intermittent mixer or a continuous mixer such as a pressure mixer or a Banbury mixer can be used, and a single screw or twin screw extruder is mainly used because it has the advantage of being able to be continuously manufactured. Examples thereof include KTK-type twin screw extruder (manufactured by Kobe Steel, Ltd.), TEM-type twin screw extruder (manufactured by Toshiba Machine Co., Ltd.), PCM mixer (manufactured by Ikegai Corp.), twin screw extruder (manufactured by KCK), co-mixer (manufactured by BUSS) and Kneadex (manufactured by Nippon Coke & Engineering Co., Ltd.). Further, the resin composition obtained by melting and mixing is rolled with a double-roll mill, and can be cooled with water etc. in a cooling step.

[0251] Next, the quenched product of the resin composition is pulverized to a desired particle size in a pulverization step. In the pulverization step, the quenched product is coarsely pulverized using a pulverizer such as a crusher, a hammer mill, or a feather mill, and then finely pulverized using, for example, a Kryptron system (manufactured by Kawasaki Heavy Industries, Ltd.), a super rotor (manufactured by Nisshin Engineering Inc.), a turbo grinder (manufactured by Turbo Kogyo Co., Ltd.), or a fine pulverizer based on an air jet system.

[0252] Thereafter, the finely pulverized product is classified, as necessary, using a classifier or sifter such as Elbow-Jet (manufactured by Nittetsu Mining Co., Ltd.) of an inertial classification system, or Turboplex (manufactured by Hosokawa Micron Corporation), TSP separator (manufactured by Hosokawa Micron Corporation), or Faculty (manufactured by Hosokawa Micron Corporation) of a centrifugal classification system.

[0253] Afterwards, the surface treatment of the toner particles is performed by heating to increase the circularity of the toner. The surface treatment can be performed by using, for example Figure 1 The surface treatment device shown is performed with hot air.

[0254] A fixed amount of mixture supplied from a raw material quantitative supply unit 1 is introduced into an inlet pipe 3 arranged perpendicular to the raw material supply unit via compressed gas regulated by a compressed gas regulating unit 2. The mixture that has passed through the inlet pipe is evenly dispersed by a conical protrusion-shaped member 4 arranged in the center of the raw material supply unit, introduced into eight radially extending supply pipes 5, and then introduced into a processing chamber 6 where heat treatment is performed.

[0255] At this time, the mixture flow supplied to the treatment chamber is regulated by a regulating unit 9 for regulating the mixture flow, which is arranged in the treatment chamber. Therefore, the mixture supplied to the treatment chamber is heat-treated while swirling in the treatment chamber and then cooled.

[0256] Hot air for heat treating the supplied mixture is supplied from the hot air supply unit 7, and while being spirally swirled by vortex members 13 and 12 for swirling the hot air, the hot air is introduced into the processing chamber. Regarding the configuration of such a member, the vortex member 13 for swirling the hot air has a plurality of blades, and the swirl of the hot air can be controlled according to the number and angle of the blades. The temperature of the hot air supplied into the processing chamber in the outlet portion 11 of the hot air supply unit 7 is preferably 100°C to 300°C. When the temperature in the outlet portion 11 of the hot air supply unit falls within this range, the toner particles can be uniformly subjected to spheroidization treatment while preventing the toner particles from being melted, adhered, and agglomerated due to excessive heating of the mixture.

[0257] Furthermore, the heat-treated toner particles that have been heat-treated are cooled by the cold air supplied from the cold air supply unit 8. The temperature of the cold air supplied from the cold air supply units (8-1, 8-2, and 8-3) is preferably -20°C to 30°C. When the temperature of the cold air falls within this range, the heat-treated toner particles can be effectively cooled, and thus, the melt adhesion and agglomeration of the heat-treated toner particles can be prevented without inhibiting the uniform spheroidization process of the mixture. The absolute moisture content of the cold air is preferably 0.5 g / m 3 Above and 15.0g / m 3 the following.

[0258] Next, the cooled heat-treated toner particles are recovered by a recovery unit 10 located at the lower end of the process chamber. The recovery unit has a configuration in which a blower (not shown) is provided at the top end thereof, and the particles are sucked and conveyed by the blower.

[0259] In addition, the powder particle supply port 14 is arranged so that the vortex direction of the supplied mixture and the vortex direction of the hot air can be the same direction, and the recovery unit 10 of the surface treatment device is arranged in the outer periphery of the treatment chamber so as to maintain the vortex direction of the powder particles that have caused the vortex. Further, the cold air supplied from the cold air supply unit 8 is configured to be supplied from the outer periphery of the device to the inner peripheral surface of the treatment chamber from the horizontal direction and the tangential direction. The vortex direction of the mixture supplied from the powder particle supply port, the vortex direction of the cold air supplied from the cold air supply unit, and the vortex direction of the hot air supplied from the hot air supply unit are all in the same direction. Therefore, no turbulence occurs in the treatment chamber, and the vortex in the device is thus enhanced. Therefore, a strong centrifugal force is applied to the heat-treated colorant particles to further improve the dispersibility of the heat-treated colorant particles. Therefore, colorant particles with a small amount of agglomerated particles and uniform shape can be obtained.

[0260] From the viewpoint of fogging resistance, the average circularity of the toner particles is preferably 0.960 or more and 0.980 or less because the non-electrostatic adhesion force thereof can be suppressed to a low level.

[0261] Afterwards, the heat-treated toner particles are classified into two sides: a fine powder side and a coarse powder side. The toner particles are classified into two sides using, for example, an Elbow-Jet inertial classification system (manufactured by Nittetsu Mining Co., Ltd.). A toner is obtained by externally adding a desired amount of silica fine particles A to each surface of the heat-treated toner particles that have been classified into two sides. Examples of methods for external addition include a method in which the toner particles and fine particles are stirred and mixed using a mixing device such as a double cone mixer, a V-type mixer, a drum mixer, a super mixer, a Henschel mixer, a Nauta mixer, a MECHANO HYBRID (manufactured by Nippon Coke & Engineering Co., Ltd.), or a NOBILTA (manufactured by Hosokawa Micron Corporation) as an external addition machine. At this time, the toner particles may be externally added with an external additive (such as a plasticizer) other than the silica fine particles, as needed.

[0262] Example

[0263] Now, the present invention will be described in more detail with reference to Examples. However, the present invention is not limited to these Examples. Unless otherwise specified, the term "parts" used in the Examples means "parts by mass".

[0264] <Production Example of Magnetic Core 1>

[0265] Magnetic fine particles (spherical, number average particle size: 250 nm, saturation magnetization: 50 (Am 2 / kg), residual magnetization: 4.2(Am 2 / kg), coercive force: 4.4 (kA / m), resistivity at 1,000 (V / cm): 3.3×10 6 (Ω·cm)) and a silane coupling agent (3-(2-aminoethylaminopropyl)trimethoxysilane) (in an amount of 3.0% by mass relative to the mass of the magnetite fine particles) were poured into a container. Then, the materials were mixed and stirred at high speed in the container at a temperature of 100° C. or higher to treat the surface of the magnetite fine particles.

[0266] 10.0 parts by mass of phenol

[0267] Formaldehyde solution (37% formaldehyde aqueous solution) 16.0 parts by mass

[0268] 84.0 parts by mass of the surface-treated magnetite fine particles

[0269] The above materials were introduced into a reaction tank and mixed thoroughly at a temperature of 40°C.

[0270] The mixture was then heated to 85°C while stirring at an average temperature increase rate of 3°C / min. Four parts by mass of 28% by mass ammonia water and 25 parts by mass of water were then added to the reaction tank. The mixture was maintained at 85°C and subjected to polymerization for three hours for curing. The peripheral speed of the stirring blade was set at 1.8 m / sec.

[0271] After the polymerization reaction, the resultant was cooled to 30°C and water was added thereto. The supernatant was removed, and the resulting precipitate was washed with water and air-dried. The resulting air-dried product was dried at 60°C under reduced pressure (5 hPa or less) to provide magnetic body dispersed resin core particles. These particles were used as magnetic core 1. The composition of the resulting magnetic core 1 is summarized in Table 1.

[0272] <Production Example of Porous Magnetic Particles>

[0273] Step 1 (weighing / mixing step)

[0274]

[0275] The ferrite raw material was weighed as described above.

[0276] Afterwards, use zirconia balls The raw materials were pulverized and mixed in a dry ball mill for 2 hours.

[0277] Step 2 (pre-calcination step)

[0278] After pulverization and mixing, the mixture was calcined in air at 950° C. for 2 hours using a burner-type calciner to produce pre-calcined ferrite. The composition of the ferrite is as follows.

[0279] (MnO) a (MgO) b (SrO) c (Fe2O3) d

[0280] In the formula, a=0.40, b=0.07, c=0.01, d=0.52.

[0281] Step 3 (crushing step)

[0282] The pre-calcined ferrite was crushed to about 0.5 mm using a crusher, and then 30 parts by mass of water was added to 100 parts by mass of the pre-calcined ferrite, followed by mixing with zirconia balls. The mixture was pulverized in a wet ball mill for 2 hours. After the balls had been separated, the mixture was pulverized in a wet ball mill using zirconia balls. The pulverized material was pulverized in a wet bead mill of 500 nm for 3 hours to provide a ferrite slurry.

[0283] Step 4 (granulation step)

[0284] 2.0 parts by mass of polyvinyl alcohol as a binder was added to the ferrite slurry relative to 100 parts by mass of the precalcined ferrite, and the mixture was granulated into spherical particles of 40 μm using a spray dryer (manufacturer: Ohkawara Kakohki Co., Ltd.).

[0285] Step 5 (Calcination Step)

[0286] In order to control the calcination atmosphere, the spherical particles were calcined in an electric furnace at 1,150° C. for 4 hours under a nitrogen atmosphere (oxygen concentration: 1.0 volume %).

[0287] Step 6 (sorting step)

[0288] After the aggregated particles had been pulverized, coarse particles were removed by sieving with a sieve having an aperture of 250 μm. Thus, porous magnetic particles were obtained.

[0289] <Manufacturing Example of Magnetic Core 2>

[0290] Step 7 (resin filling step)

[0291] 71.7 parts by mass of the porous magnetic particles

[0292] 15.0 parts by mass of benzoguanamine-n-butanol-formaldehyde co-condensate

[0293] Acrylic resin (manufactured by Mitsui Chemicals, Inc., ALMATEX 748-5M, solid content: 55%) 13.3 parts by mass

[0294] The above materials are loaded into a stirring container of a mixing agitator (universal mixer NDMV type manufactured by Dalton Co., Ltd.) and stirred for 2 hours under a nitrogen atmosphere while maintaining the temperature in the container at 60°C and reducing the pressure therein to 2.3 kPa. Afterwards, the temperature is raised to 100°C and the solvent is removed under reduced pressure, and the material is subsequently filled into porous magnetic particles. After cooling, the resin-filled particles are moved to a mixer with a spiral blade in a rotatable mixing container (drum mixer UD-AT type manufactured by Sugiyama Heavy Industrial Co., Ltd.) and their temperature is raised to 220°C at a heating rate of 2 (°C / min) under a nitrogen atmosphere and normal pressure. The particles are heated and stirred at this temperature for 60 minutes to solidify the resin. After heat treatment, low magnetic products are separated by magnetic separation, and the residue is classified with a sieve having an aperture of 150 μm to provide a magnetic core 2. The composition of the obtained magnetic core 2 is shown in Table 1.

[0295] <Manufacturing Example of Magnetic Core 3>

[0296] Step 7 (resin filling step)

[0297] 100.0 parts by mass of the above-mentioned porous magnetic particles are loaded into a stirring container of a mixing agitator (universal mixer NDMV type manufactured by Dalton Co., Ltd.). Then, while maintaining the temperature in the container at 60°C, the pressure in the container is reduced to 2.3 kPa. During the decompression, nitrogen is introduced into the container, and a silicone resin solution (SR 2410 manufactured by Dow Corning Toray Co., Ltd.) is added dropwise under reduced pressure so that its amount in terms of resin component is 7.5 parts by mass relative to the porous magnetic particles. After the dropwise addition is completed, the mixture is continuously stirred for 2 hours without any other treatment. Afterwards, the temperature is raised to 70°C, and the solvent is removed under reduced pressure. Thus, the silicone resin composition obtained from the silicone resin solution is filled into the particles of the porous magnetic particles. After cooling, the obtained filled core particles are moved to a mixer with a spiral blade in a rotatable mixing container (a drum mixer UD-AT type manufactured by Sugiyama Heavy Industrial Co., Ltd.), and their temperature is raised to 220°C at a heating rate of 2 (°C / min) under a nitrogen atmosphere and normal pressure. The resin is cured by heating and stirring the particles at this temperature for 60 minutes. After heat treatment, low magnetic products are separated by magnetic separation, and the remainder is classified with a sieve having an aperture of 150 μm. Thus, magnetic core 3 is obtained. The composition of the obtained magnetic core 3 is shown in Table 1.

[0298] <Manufacturing Example of Magnetic Core 4>

[0299] Step 1 (weighing / mixing step)

[0300]

[0301] The ferrite raw material was weighed as described above.

[0302] Afterwards, use zirconia balls The raw materials were pulverized and mixed in a dry ball mill for 2 hours.

[0303] Step 2 (pre-calcination step)

[0304] After pulverization and mixing, the mixture was calcined in air at 1,000° C. for 2 hours using a burner-type calciner to produce pre-calcined ferrite. The composition of the ferrite is as follows.

[0305] (MnO) a (MgO) b (SrO) c (Fe2O3) d

[0306] In the formula, a=0.40, b=0.07, c=0.01, d=0.52.

[0307] Step 3 (crushing step)

[0308] The pre-calcined ferrite was crushed to about 0.5 mm using a crusher, and then 30 parts by mass of water was added to 100 parts by mass of the pre-calcined ferrite, followed by mixing with stainless steel balls. The mixture was pulverized in a wet ball mill for 2 hours. After the balls had been separated, the mixture was pulverized in a wet ball mill using stainless steel balls. The pulverized material was pulverized in a wet bead mill of 500 nm for 3 hours to provide a ferrite slurry.

[0309] Step 4 (granulation step)

[0310] 2.0 parts by mass of polyvinyl alcohol as a binder was added to the ferrite slurry relative to 100 parts by mass of the precalcined ferrite, and the mixture was granulated into spherical particles of 45 μm using a spray dryer (manufacturer: Ohkawara Kakohki Co., Ltd.).

[0311] Step 5 (Calcination Step)

[0312] In order to control the calcination atmosphere, the spherical particles were calcined in an electric furnace at 1,200° C. for 6 hours under a nitrogen atmosphere (oxygen concentration: 0.6% by volume).

[0313] Step 6 (sorting step)

[0314] After the aggregated particles were crushed, coarse particles were removed by sieving with a sieve having an aperture of 250 μm. Thus, ferrite core particles were obtained. The particles were used as magnetic core 4. The composition of the obtained magnetic core 4 is shown in Table 1.

[0315] Table 1

[0316]

[0317] <Method for producing graft resin A1>

[0318] 95.2% by mass of a silicone-containing acrylic monomer corresponding to the following unit Y1 and 4.8% by mass of a monomer corresponding to the following unit Y2 were added to a four-necked flask equipped with a reflux condenser, a thermometer, a nitrogen pipette, and a grinding-type stirring device. The structures of the units Y1 and Y2 are shown in Table 2.

[0319] Further, 100 parts by mass of toluene, 100 parts by mass of methyl ethyl ketone, and 2.0 parts by mass of azobisisovaleronitrile were added to the flask. The resulting mixture was kept in a nitrogen stream at 70°C for 10 hours to carry out a polymerization reaction. After the reaction was completed, the resulting product was repeatedly washed to provide a solution of resin A1 (solid content: 35% by mass). The s(l+m) value of the solution calculated by gel permeation chromatography (GPC) was 70.

[0320] <Production Example of Graft Resins A2 to A25>

[0321] Graft resins A2 to A25 were each obtained in the same manner as the production method of graft resin A1 except that the structures of unit Y1 and unit Y2 and the values ​​of "a", "b", "n" and s(l+m) were changed as shown in Table 2.

[0322] Table 2

[0323]

[0324]

[0325]

[0326] <Method for producing graft resin B1 and graft resins B2 to B18>

[0327] The macromonomer (corresponding to unit Y4) used in the graft resin B1 can be synthesized, for example, by the following method.

[0328] The following raw materials were added to a four-necked flask equipped with a reflux condenser, a thermometer, a nitrogen pipette, and a mill-type stirring device.

[0329] Methacryloyl chloride 1.7% by mass

[0330] Polymethyl methacrylate having a hydroxyl group at one end thereof (Mw; about 5,000) 98.3 mass%

[0331] Further, 100 parts by mass of THF and 1.0 parts by mass of 4-tert-butylcatechol were added to 100 parts by mass of the above monomer mixture, and the mixture was heated under reflux for 5 hours under a nitrogen stream. After the reaction was completed, the resultant was washed with sodium bicarbonate to provide a solution of the macromonomer.

[0332] The following monomers and macromonomers were added to a four-necked flask including a reflux condenser, a thermometer, a nitrogen pipette, and a mill-type stirring device.

[0333] Cyclohexyl methacrylate (corresponding to unit Y3) 75.5% by mass

[0334] Methyl methacrylate (corresponding to unit Y5) 0.5 mass%

[0335] Methacrylic acid macromonomer including methyl methacrylate polymer as a polymer (corresponding to unit Y4) 24.0% by mass

[0336] Further, 100 parts by mass of toluene, 100 parts by mass of methyl ethyl ketone and 2.0 parts by mass of azobisisovaleronitrile were added to 106 parts by mass of the above-mentioned monomer mixture. The resulting mixture was kept in a nitrogen stream at 70° C. for 10 hours to carry out a polymerization reaction. After the reaction was completed, the resultant was repeatedly washed to provide a solution of resin B1 (solid content: 35% by mass). The weight average molecular weight of the solution measured by gel permeation chromatography (GPC) was 57,000. The composition of the resin is shown in Table 3.

[0337] Graft resins B2 to B18 were each produced in the same manner as graft resin B1 except that the monomers were changed, thereby obtaining the compositions shown in Table 3.

[0338] Table 3

[0339]

[0340]

[0341] <Production Examples of Magnetic Carriers 1 and 2 to 27>

[0342] Magnetic core 100.0 parts by mass

[0343] Graft resin A1 (toluene solution with a solid content of 50% by mass) 0.2 parts by mass

[0344] Graft resin B1 (50% by mass toluene solution) 3.8 parts by mass

[0345] The above materials were charged into a planetary screw mixer (Nauta Mixer VN Model manufactured by Hosokawa Micron Corporation) and stirred at 60°C under a reduced pressure of 1.5 kPa.

[0346] The charging method was as follows: the graft resin A1 and the graft resin B1 were each charged in an amount corresponding to one third of the total amount thereof, and solvent removal and coating operations were performed for 20 minutes; and the above steps were repeated three times.

[0347] After that, the magnetic carrier coated with the coating resin composition was moved to a mixer with spiral blades in a rotatable mixing container (a drum mixer UD-AT model manufactured by Sugiyama Heavy Industrial Co., Ltd.). While rotating the mixing container 10 times per minute for stirring, the magnetic carrier was heat-treated at a temperature of 120°C in a nitrogen atmosphere for 2 hours. A low-magneticity product was separated from the resulting magnetic carrier 1 by magnetic separation, and the remainder was passed through a sieve with an aperture of 150 μm and then classified with an air classifier. Thus, a magnetic carrier 1 having a volume-based 50% particle size (D50) of 39.1 μm was obtained.

[0348] Table 4 shows the structure of the obtained magnetic carrier 1.

[0349] Magnetic carriers 2 to 27 were each produced in the same manner as in Magnetic Carrier 1, except that the composition was changed to the composition shown in Table 4.

[0350] Table 4

[0351]

[0352]

[0353] <Manufacturing Example of Toner 1>

[0354]

[0355] The above materials were mixed at a rotation speed of 1,500 rpm for 5 minutes using a Henschel mixer (FM-75 type manufactured by Mitsui Mining Co., Ltd.), and thereafter, the mixture was kneaded using a twin-screw mixer (PCM-30 type manufactured by Ikegai Corp.) with a temperature set at 130° C. The kneaded material thus obtained was cooled and coarsely pulverized to less than 1 mm with a hammer mill to provide a coarsely pulverized material. The coarsely pulverized material thus obtained was finely pulverized using a mechanical pulverizer (T-250 manufactured by Turbo Kogyo Co., Ltd.). Further, the finely pulverized material was classified using Faculty (F-300 manufactured by Hosokawa Micron Corporation) to provide toner base particles 1. The operating conditions were as follows: the rotation speed of the classification rotor was set to 11,000 rpm, and the rotation speed of the dispersion rotor was set to 7200 rpm.

[0356] Toner base particles 1 100.0 parts by mass

[0357] Silica fine particles (BET specific surface area: 24 m 2 / g) 2.0 parts by mass

[0358] The raw materials represented by the above formulation were mixed at 1,900 rpm for 3 minutes using a Henschel mixer (FM-10C model manufactured by Mitsui Mining Co., Ltd.). Figure 1 The surface treatment apparatus shown heat-treats the mixture to provide heat-treated toner particles 1. The operating conditions are as follows: feed rate 5 kg / hr, hot air temperature C 160°C, hot air flow rate 6 m 3 / minute, the cold air temperature E is -5℃, and the cold air flow rate is 4m 3 / minute, the blower air flow rate is 20m 3 / min, and the injection air flow rate is 1m 3 / minute.

[0359] The resulting particles were classified using a rotary classifier (trade name: TTSP100, manufactured by Hosokawa Micron Corporation) to remove fine powder and coarse powder. Thus, cyan toner particles 1 were obtained, having a weight-average particle size of 6.0 μm, an abundance ratio of particles each having a particle size of 4.0 μm or less of 27.8% by number, and an abundance ratio of particles each having a particle size of 10.0 μm or greater of 2.2% by volume.

[0360] · Cyan toner particles 1 100.0 parts by mass

[0361] ·Silica fine particles surface treated with 10 wt% polydimethylsiloxane (BET specific surface area: 100 m 2 / g) 0.6 parts by mass

[0362] The above materials were mixed with a Henschel mixer (FM-75 model manufactured by Mitsui Miike Chemical Engineering Machinery, Co., Ltd.) at a rotation number of 1,900 rpm for 3 minutes to provide Toner 1.

[0363] <Example 1>

[0364] 9 parts by mass of Toner 1 was added to 91 parts by mass of Magnetic Carrier 1, and the mixture was shaken with a shaker (YS-8D model: manufactured by Yayoi) to prepare 300 g of a two-component developer. Shaking with the shaker was performed at 150 rpm for 2 minutes.

[0365] Meanwhile, 90 parts by mass of Toner 1 was added to 10 parts by mass of Magnetic Carrier 1, and the materials were mixed for 5 minutes with a V-type mixer under a normal temperature and humidity environment of 23°C / 50%RH to provide a replenishing developer.

[0366] The following evaluations were performed by using a two-component system developer and a replenishing developer: As an image forming apparatus, a modified version of a color copying machine "imageRUNNER ADVANCE C5560" manufactured by Canon Inc. was used.

[0367] Two-component developers were loaded into the developing units of the machine for each color, and replenishing developer containers containing replenishing developers for each color were placed in the units. Images were formed using the machine, and various evaluations were performed before and after the durability test.

[0368] As a durability test, a chart for outputting an FFH image with an image ratio of 40% was used under a printing environment having a temperature of 30°C and a humidity of 80% RH. The symbol "FFH" refers to one of the values ​​obtained by expressing 256 grayscale levels in hexadecimal notation. 00h corresponds to the 1st grayscale level (white portion) of the 256 grayscale levels, and FFH corresponds to the 256th grayscale level (solid portion) of the 256 grayscale levels.

[0369] The number of images to be output is changed according to each evaluation item.

[0370] condition:

[0371] Paper: Use laser beam printing paper CS-814 (81.4g / m 2) (sold by Canon Marketing Japan Inc.).

[0372] Image Formation Speed: The machine has been modified to output full-color images on A4-size paper at 80 sheets per minute.

[0373] Development Conditions: The machine was modified to allow the contrast to be adjusted to any value without activating its automatic calibration function. The AC electric field frequency was modified to be 2.0 kHz, and its peak-to-peak voltage (Vpp) could be varied from 0.7 kV to 1.8 kV in 0.1 kV increments. The machine was modified to output each color image separately.

[0374] The machine was modified to enable development with only the cyan developer unit having a separate color.

[0375] Each evaluation item is as follows.

[0376] (1) Image density

[0377] Image output evaluation was conducted in a high-temperature, high-humidity environment (30°C, 80% RH) at the initial and post-durability stages (A4 landscape format, 40% print rate, 50,000 sheets), and a solid image (FFH) was output. Density measurement was performed using a densitometer X-Rite 404A (manufactured by X-Rite Inc.), and the average of six measured values ​​was used as the image density. The difference between the image density at the initial stage of the durability test and the image density after the durability test was determined using the following criteria. When the evaluation result was any one of A to C, the effects of the present invention were considered to have been achieved.

[0378] A: The density difference is less than 0.10.

[0379] B: The density difference is 0.10 or more and less than 0.15.

[0380] C: The density difference is 0.15 or more and less than 0.20.

[0381] D: The density difference is 0.20 or more and less than 0.25.

[0382] E: The density difference is 0.25 or more.

[0383] (2) Fogging

[0384] After image output evaluation (A4 landscape format, 40% print rate, 50,000 sheets) was conducted in a high-temperature, high-humidity environment (30°C, 80% RH) at the initial and post-durability stages, a solid white image was output across the entire surface of the A4 paper. Regarding fogging, the whiteness of the white portion was measured using a reflectometer (manufactured by Tokyo Denshoku Co., Ltd.), and the fog density (%) was calculated from the difference between the whiteness before and after transfer. Evaluation was performed using the following criteria. When the evaluation result was any of A to C, the effects of the present invention were considered to have been achieved.

[0385] A: less than 1.0%

[0386] B: 1.0% or more and less than 1.5%

[0387] C: 1.5% or more and less than 2.0%

[0388] D: 2.0% or more and less than 2.5%

[0389] E: 2.5% or more

[0390] (3) Halftone developability

[0391] After image output evaluation (A4 landscape format, 40% print rate, 50,000 sheets) was conducted at the initial and final stages of durability in a high-temperature, high-humidity environment (30°C, 80% RH), a halftone image (30H) was printed on a single A4 sheet. The area of ​​1,000 dots was measured using a VHX-500 digital microscope (lens: wide-range zoom lens VH-Z100, manufactured by Keyence Corporation). The number mean (S) and standard deviation (σ) of the dot areas were calculated, and the dot reproducibility index was calculated using the following equation. The roughness of the halftone image was then evaluated based on the dot reproducibility index (I).

[0392] Point reproducibility index (I) = σ / S × 100

[0393] Regarding the evaluation criteria for roughness, evaluation was performed by the following criteria: When the evaluation result was any one of A to C, it was judged that the effect of the present invention was obtained.

[0394] A: I is less than 4.0.

[0395] B: I is 4.0 or more and less than 5.0.

[0396] C: I is 5.0 or more and less than 6.0.

[0397] D:I is 7.0 or more and less than 8.0.

[0398] E:I is 8.0 or more.

[0399] (4) Toner scattering

[0400] After image output evaluation (A4 landscape format, 40% print rate, 50,000 sheets) was performed in a high-temperature, high-humidity environment (30°C, 80% RH) at the initial and post-durability stages, the developer unit was removed from the main body. The toner scattering inside and outside the developer unit and main body was visually observed and evaluated using the following criteria. When the evaluation result was any one of A to D, the effect of the present invention was determined to be achieved.

[0401] A: Toner scattering does not occur.

[0402] B: Extremely slight toner scattering occurs.

[0403] C: Slight toner scattering occurs.

[0404] D: Slight toner scattering occurs.

[0405] E: Remarkable toner scattering occurred.

[0406] The evaluation results of Example 1 are shown in Table 5.

[0407] <Examples 2 to 22 and Comparative Examples 1 to 5>

[0408] The evaluation was performed in the same manner as in Example 1 except that Magnetic Carriers 2 to 27 were used in the same manner as in Example 1. The evaluation results are shown in Table 5.

[0409] Table 5

[0410]

[0411]

[0412] According to the present invention, it is possible to provide a magnetic carrier which achieves reduced fogging, reduced toner scattering, stable image density, and developability even when used for a long period of time.

[0413] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

Claims

1. A magnetic carrier, characterized in that include: magnetic core; and a coating resin configured to coat the surface of the magnetic core, wherein the coating resin comprises graft resin A and graft resin B, wherein the coating resin (i) contains 1.0 mass % or more and 50.0 mass % or less of the graft resin A, and (ii) containing 50.0% by mass or more and 99.0% by mass or less of the graft resin B, wherein the graft resin A has a unit Y1 represented by the following formula (1) and a unit Y2 represented by the following formula (2), wherein when the mass of the graft resin A is represented by X, the mass of the unit Y1 in the graft resin A is represented by "a", and the mass of the unit Y2 in the graft resin A is represented by "b", the "a", the "b" and the X satisfy 0.90≤(a+b) / X≤1.00 and 1.00≤a / b≤30.0, and wherein the grafted resin B (i) is a comb polymer having at least one site as a branch, the site being selected from the group consisting of a styrene-based polymer site; a (meth)acrylate-based polymer site; and a styrene-acrylate-based polymer site, and (ii) does not contain a polysiloxane structure portion or contains a polysiloxane structure portion at a content of 0.1% by mass or less: (1) (2) In formula (1) or formula (2), R1 represents H or CH3, R2 represents a hydrocarbon group having 1 or more and 6 or less carbon atoms which may have a substituent, and the substituent is a hydroxyl group or a carboxyl group, R3 represents H or CH3, R4 represents H or CH3, R5 represents a single bond or a hydrocarbon group having 1 or more and 6 or less carbon atoms, R6 represents a hydrocarbon group having 1 or more and 10 or less carbon atoms, R7 represents H, CH3, or Si(CH3)3, and "1" and "m" each represent an integer of 1 or greater, and "n" represents an integer of 2 or greater and 150 or less.

2. The magnetic carrier according to claim 1, wherein when the atomic percentage of Si of the magnetic carrier is represented by SiO when measured by X-ray photoelectron spectroscopy XPS, the following formula is satisfied: 1.0≤Si0≤15.

0. 3 . The magnetic carrier according to claim 1 , wherein “n” in the formula (2) represents 5 or more and 60 or less.

4. The magnetic carrier according to claim 1 or 2, wherein when the total number of units Y1 and Y2 is represented by "s", the graft resin A satisfies the following formula: 50≤s≤250。 5 . The magnetic carrier according to claim 1 , wherein in the coating resin, the content of the graft resin A is 1.0% by mass or more and 30.0% by mass or less, and the content of the graft resin B is 70.0% by mass or more and 99.0% by mass or less.

6. The magnetic carrier according to claim 1 or 2, wherein the graft resin B includes 75.0% by mass or more of a unit Y3 represented by the following formula (3): (3) In formula (3), R8 represents CH3, and R9 represents cyclohexyl, cycloheptyl, cyclooctyl, cyclopentyl, cyclobutyl, or cyclopropyl.

7. The magnetic carrier according to claim 1 or 2, wherein the graft resin B includes 1.0% by mass or more and 25.0% by mass or less of a unit Y4 represented by the following formula (4): (4) In formula (4), R 10 represents H or CH3, and R 11 represents the polymer part.

8. The magnetic carrier according to claim 7, wherein the graft resin B further comprises a unit Y5 represented by formula (5): (5) In formula (5), R 12 represents H or CH3, and R 13 It represents a hydrocarbon group having 1 or more and 6 or less carbon atoms.

9. A two-component developer comprising a magnetic carrier and a toner, It is characterized by: The magnetic carrier is the carrier according to any one of claims 1 to 8.

10. A replenishing developer, characterized in that: which is replenished into the developing unit according to a decrease in the toner concentration of the two-component developer in the developing unit, the replenishing developer including a magnetic carrier; and toner, The magnetic carrier is a carrier according to any one of claims 1 to 8.

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