Magnetic carrier, two-component developer, and replenishment developer

Abstract

To provide a magnetic carrier that, even for a long-term use, achieves reduction of fogging, reduction of scattering of toner, stable image density, and improvement of dot reproducibility in a high temperature and high humidity environment.SOLUTION: A magnetic carrier has a magnetic core and a coating resin coating the surface of the magnetic core. The coating resin contains a graft resin A. The graft resin A has a unit Y1 represented by a specific structural formula (1) and a unit Y2 represented by a specific structural formula (2). When the SP value of a stem of the graft resin A is SPa, the SP value of a siloxane unit is SPb, and the SP value of the surface of the magnetic core is SPc, the magnetic carrier satisfies the formulas (3)-(5). (3) 22.0<Spc≤24.0 (J / cm3); (4) |Spa-SPc|≤3.0 (J / cm3); (5) 5.0<|SPb-SPc| (J / cm3).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a magnetic carrier, a two-component developer, and a replenishment developer used in an image forming method for visualizing an electrostatic image using electrophotography. [Background technology]

[0002] Conventionally, electrophotographic image formation methods generally involve forming an electrostatic latent image on an electrostatic latent image carrier using various means, and then developing the electrostatic latent image by attaching toner to the electrostatic latent image. For this development, a two-component development method is widely used in which carrier particles called magnetic carriers are mixed with the toner, and the toner is frictionally charged to impart an appropriate amount of positive or negative charge to the toner, with the charge acting as a driving force for development.

[0003] In two-component development, the magnetic carrier can be given functions such as stirring, transporting, and charging the developer, so the division of functions between the magnetic carrier and the toner is clear. This has the advantage of good controllability of developer performance. Here, the magnetic carrier has a core with magnetic properties to transport the toner within the developing device. In addition, magnetic carriers often have a core coated with a resin that can impart charge to the toner.

[0004] In recent years, technological advances in the field of electrophotography have led to a demand for greater longevity of the main body, and developers are required to reduce fogging, reduce toner scattering, and stabilize image density and developability even under long-term use. In order to solve the above problems, it is necessary to provide a magnetic carrier that can maintain its charge-imparting ability even after long-term use.

[0005] Generally, when toner components adhere to a magnetic carrier, the number of charging sites on the magnetic carrier decreases, resulting in a decrease in the charge-imparting ability of the magnetic carrier. This is known to cause problems such as changes in image density. As a means of improving resistance to the adhesion of the above-mentioned toner components (hereinafter referred to as contamination resistance), there is an example in which a material with low surface free energy, such as a silicone resin, is used as a coating resin (Patent Document 1). In general, materials with low surface free energy can suppress the adhesion of toner components and the like.

[0006] However, materials with low surface free energy have weak molecular interactions and are easily destroyed by external forces. Therefore, when silicone resin is used as the coating resin for magnetic carriers, the coating resin can be worn away by mechanical loads that occur during stirring and transport in the developing device. As a result, the surface resistance of the magnetic carrier decreases, and the charging ability of the magnetic carrier decreases.

[0007] Therefore, in order to improve abrasion resistance, there is an example in which a silicone-modified resin in which trifunctional silicon is bonded to the terminal is used (Patent Document 2). However, with the above structure, the surface free energy of the magnetic carrier surface cannot be sufficiently reduced, and therefore there is a possibility that the contamination resistance will not be improved. Furthermore, when a resin having a siloxane structure in the side chain is used, the surface free energy between molecules becomes small, and abrasion resistance becomes insufficient, as in the case of using the above-mentioned silicone resin (Patent Document 3). [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-91093 [Patent Document 2] Japanese Patent Application Laid-Open No. 2015-138230 [Patent Document 3] Japanese Patent Application Laid-Open No. 2013-3428 Summary of the Invention [Problem to be solved by the invention]

[0009] Therefore, in order for the magnetic carrier to maintain stable charge-imparting ability over long-term use, it is believed that it is necessary to achieve both contamination resistance, which prevents adhesion of toner components, and wear resistance, which prevents wear of the coating resin. In view of the above, an object of the present invention is to provide a magnetic carrier that achieves reduced fogging, reduced toner scattering, stable image density, and developability even after long-term use. [Means for solving the problem]

[0010] After extensive research, the present inventors have found that the use of graft resin A, shown in the structure below, in combination with a magnetic core with a controlled SP value can suppress adhesion of toner components and wear of the coating resin. As a result, it has been found that the coating resin can achieve both contamination resistance and wear resistance, and can maintain stable charge-imparting ability even during long-term use.

[0011] Graft resin A has a structure in which a structure similar to that of the silicone resin is grafted to the main chain. The surface of the magnetic core has a structure that is highly compatible with the main chain of graft resin A. As mentioned above, when only a resin with a grafted siloxane structure such as graft resin A was used, the contamination resistance was insufficient.

[0012] However, when the coating resin of the magnetic carrier contains graft resin A and the magnetic core surface has a structure that is highly compatible with the main chain of the graft resin A, the molecular structure is oriented to be energetically stabilized. Specifically, the siloxane structure of graft resin A is oriented on the carrier surface layer, and the main chain of graft resin A is oriented on the magnetic core side. As a result, the surface free energy of the carrier is reduced, and contamination resistance is improved.

[0013] Furthermore, even if a siloxane moiety with weak intermolecular interactions is present, the main chain of graft resin A and the magnetic core surface have affinity for each other, improving adhesion. As a result, peeling of the coating resin is suppressed, and wear resistance is improved.

[0014] Therefore, by using graft resin A shown in the structure below in combination with a magnetic core with a controlled SP value, it is possible to achieve both contamination resistance that suppresses adhesion of toner components and wear resistance that suppresses wear of the coating, and to maintain stable charge-imparting ability even during long-term use. As a result, it is possible to provide a magnetic carrier that achieves reduced fog, reduced toner scattering, stable image density, and developability even during long-term use.

[0015] That is, the carrier of the present invention is A magnetic carrier having a magnetic core and a coating resin that coats the surface of the magnetic core, The coating resin contains a graft resin A, The graft resin A has a unit Y1 represented by formula (1) and a unit Y2 represented by formula (2), When the mass of the graft resin A is X, the mass of the unit Y1 represented by formula (1) contained in the graft resin A is a, and the mass of the unit Y2 represented by formula (2) contained in the graft resin A is b, the a, b, and X are 0.90≦(a+b) / X≦1.00 1.00≦a / b≦30.0 Fulfilling A magnetic carrier characterized by satisfying formulas (3) to (5) when the SP value of the trunk of the graft resin A is SPa, the SP value of the siloxane unit in formula (2) is SPb, and the SP value of the surface of the magnetic core is SPc. Equation (3)22.0 <Spc≦24.0 (J / cm 3 ) Equation (4)|Spa-SPc|≦3.0 (J / cm 3 ) Equation (5) 5.0<|SPb-SPc| (J / cm 3 ) [The SP value is calculated using the following formula. Formula: SP value = √(Ev / v) = √(ΣΔei / ΣΔvi) In the formula, Ev: evaporation energy (cal / mol), v: molar volume (cm3 / mol), Δei: evaporation energy of each atom or atomic group, Δvi: molar volume of each atom or atomic group] [ka] [ka] [In formula (1) or formula (2), R1 represents H or CH3; R2 represents a hydrocarbon group having 1 to 6 carbon atoms which may have a substituent, and the substituent is a hydroxy group or a carboxy 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; l and m are integers of 1 or more, and n is an integer of 2 or more and 150 or less.] [Effects of the Invention]

[0016] According to the present invention, a carrier is provided which, even when used for a long period of time, reduces fogging, reduces toner scattering, provides stable image density, and improves dot reproducibility in a high-temperature, high-humidity environment. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a schematic view of a surface treatment device for a toner used in a two-component developer according to the present invention. [Figure 2] 1 is a schematic view of an image forming apparatus in which a carrier according to the present invention is used. [Figure 3] 1 is a schematic view of an image forming apparatus in which a carrier according to the present invention is used. [Figure 4] FIG. 2 is a schematic diagram of a measuring device used to measure the resistivity of a magnetic carrier and a porous magnetic core. DETAILED DESCRIPTION OF THE INVENTION

[0018] In the present invention, unless otherwise specified, the expressions "xx or more and xx or less" and "xx to xx" representing a numerical range mean a numerical range including the lower and upper limits, which are the endpoints. The present invention provides a magnetic carrier having a magnetic core and a coating resin that coats the surface of the magnetic core, The coating resin contains a graft resin A, The graft resin A has a unit Y1 represented by formula (1) and a unit Y2 represented by formula (2), When the mass of the graft resin A is X, the mass of the unit Y1 represented by formula (1) contained in the graft resin A is a, and the mass of the unit Y2 represented by formula (2) contained in the graft resin A is b, the a, b, and X are 0.90≦(a+b) / X≦1.00 1.00≦a / b≦30.0 Fulfilling [ka] [ka] A magnetic carrier characterized in that, when the SP value of the trunk of the graft resin A is SPa, the SP value of the siloxane unit is SPb, and the SP value of the surface of the magnetic core is SPc, the formulas (3) to (5) are satisfied. Equation (3)22.0 <Spc≦24.0 (J / cm 3 ) Equation (4)|Spa-SPc|≦3.0 ( J / cm 3 ) Equation (5) 5.0<|SPb-SPc| ( J / cm 3 ) [The SP value is calculated using the following formula. Formula: SP value = √(Ev / v) = √(ΣΔei / ΣΔvi) In the formula, Ev: evaporation energy (cal / mol), v: molar volume (cm 3 / mol), Δei: evaporation energy of each atom or atomic group, Δvi: molar volume of each atom or atomic group)] [In formula (1) or formula (2), R1 represents H or CH3; R2 represents a hydrocarbon group having 1 to 6 carbon atoms which may have a substituent, and the substituent is a hydroxy group or a carboxy 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; l and m are integers of 1 or more, and n is an integer of 2 or more and 150 or less.]

[0019] Graft resin A has a structure in which a structure similar to that of the silicone resin is grafted to the main chain. The surface of the magnetic core has a structure that is highly compatible with the main chain of graft resin A. As mentioned above, when only a resin with a grafted siloxane structure such as graft resin A was used, the contamination resistance was insufficient.

[0020] However, when the coating resin of the magnetic carrier contains graft resin A and the magnetic core surface has a structure that is highly compatible with the main chain of the graft resin A, the molecular structure is oriented to be energetically stabilized. Specifically, the siloxane structure of graft resin A is oriented on the carrier surface layer, and the main chain of graft resin A is oriented on the magnetic core side. As a result, the surface free energy of the carrier is reduced, and contamination resistance is improved.

[0021] Furthermore, even if siloxane moieties with weak intermolecular interactions are present, the main chain of graft resin A and the magnetic core surface have affinity and improve adhesion, which results in suppression of coating peeling and improved wear resistance.

[0022] Therefore, by using a graft resin A having the structure shown below in combination with a magnetic core having a controlled SP value on the magnetic core surface, the magnetic carrier of the present invention achieves both contamination resistance, which suppresses adhesion of toner components, and wear resistance, which suppresses wear of the coating. As a result, the magnetic carrier of the present invention can maintain stable charge-imparting ability even after long-term use. The present invention can provide a magnetic carrier that can achieve reduced fog, reduced toner scattering, stable image density, and developability even after long-term use.

[0023] The graft resin A has a unit Y1 represented by formula (1) and a unit Y2 represented by formula (2). The unit Y2 has a siloxane structure, and the siloxane structure reduces the surface free energy, thereby improving the contamination resistance of the magnetic carrier. In formula (1), R1 represents H or CH3, and R2 represents a hydrocarbon group of 1 to 6 carbon atoms which may have a substituent. Preferably, it is an alkyl group of 1 to 6 carbon atoms which may have a substituent. The substituent in R2 is a hydroxy group or a carboxy group. Specific methods for introducing R1 and R2 include, for example, copolymerizing the following monomers when polymerizing 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, cyclopentyl methacrylate, 2-hydroxyethyl acrylate, 2-carboxyethyl acrylate, 2-hydroxyethyl methacrylate, and 2-carboxyethyl methacrylate. In formula (2), 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, and R7 represents H, CH3, or Si(CH3)3. R5 is preferably an alkylene having 1 to 6 carbon atoms. 1 and m represent integers of 1 or more, and n represents an integer of 2 or more and 150 or less. Graft resin A may contain multiple units Y2. A specific method for introducing units Y2 is, for example, to copolymerize an acrylate or methacrylate ester in which a silicone structure has been esterified when polymerizing resin A.

[0024] 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 X, a, and b, respectively, X, a, and b satisfy the following conditions: 0.90≦(a+b) / X≦1.00 1.00≦a / b≦30.0 Meet the following.

[0025] The above relational expression indicates that the graft resin A contains the units Y1 and Y2 in an amount of 90 mass % or more of all units, and that the unit Y2 accounts for the same mass % as the unit Y1, so that the mass of Y1 is calculated by multiplying Y2 by 30.

[0026] If (a+b) / X is less than 0.90, the affinity with the magnetic core may decrease, resulting in poor adhesion, or the surface free energy may decrease, resulting in poor stain resistance. Furthermore, if the ratio a / b is less than 1.00, the proportion of the Y2 unit is large, which can lead to insufficient resin strength due to low intermolecular forces resulting from low surface free energy, potentially resulting in poor abrasion resistance.If the ratio a / b is greater than 30.0, the proportion of the Y2 unit is small, which can lead to low surface free energy and poor stain resistance.

[0027] When the SP value of the trunk of graft resin A is SPa, the SP value of the siloxane structure is SPb, and the SP value of the surface of the magnetic core is SPc, the relationship between formulas (3) to (5) is satisfied. Equation (3)22.0 <SPc≦24.0 (J / cm 3 ) 1 / 2 in the case of, Equation (4)|SPa-SPc|≦3.0 (J / cm 3 ) 1 / 2 Equation (5) 5.0<|SPb-SPc| (J / cm 3 ) 1 / 2

[0028] Satisfying the relationship between formulas (3) to (5) means that the affinity between the trunk of graft resin A and the magnetic core surface is higher than the affinity between the siloxane structure and the magnetic core surface. In this case, the trunk of graft resin A effectively has affinity with the magnetic core surface, and graft resin A adheres closely to the magnetic core, improving the wear resistance of the magnetic carrier.

[0029] Furthermore, since the siloxane structure has a relatively lower affinity with the magnetic core than the trunk of graft resin A, the molecular structure is oriented to be energetically stabilized. Specifically, the siloxane structure of graft resin A is oriented on the surface layer of the magnetic carrier. As a result, the surface free energy of the magnetic carrier is reduced, improving contamination resistance. Therefore, the magnetic carrier can have both contamination resistance and wear resistance, and can maintain stable charge-imparting ability even during long-term use.

[0030] Here, in the graft resin A, n represents the length of the siloxane structure of the unit Y2. When n is 2 or more and 150 or less, the abrasion resistance and contamination resistance of the magnetic carrier are ensured. When n is less than 2, the siloxane structure is less likely to be effectively oriented on the carrier surface layer, resulting in poor contamination resistance. When n is more than 150, the surface free energy decreases, resulting in weaker intermolecular interactions of the coating resin, resulting in poor abrasion resistance.

[0031] Furthermore, when n, which indicates the length of the siloxane structure, is 5 or more and 60 or less, the abrasion resistance and contamination resistance of the magnetic carrier are improved, which is preferable.

[0032] The magnetic carrier of the present invention preferably satisfies formula (6) when the Si atomic % determined by X-ray photoelectron spectroscopy (XPS) analysis of the surface layer of the magnetic carrier is taken as Si0. Equation (6) 1.0≦Si0≦15.0 When the Si content is 1.0 atomic % or more, the surface free energy of the carrier surface layer is low, further improving contamination resistance.When the Si content is 15.0 atomic % or less, the intermolecular force between resin molecules in the carrier surface layer is strong, further improving wear resistance.

[0033] The graft resin A preferably satisfies formula (10) when the total number of units Y1 and units Y2 is s. Formula (10) 50≦s≦250 When s is 50 or more, the molecular weight is sufficient to maintain the resin strength, and when it is 250 or less, good adhesion to the magnetic core can be ensured.

[0034] The graft resin A may have a functional group such as a nitrogen-containing group, a carboxyl group, or a hydroxyl group. By having such a functional group, charge-up of the developer in a low-humidity environment can be suppressed. In addition, by having a hydroxyl value, the effect of hydrogen bonding is also exerted, which is preferable because it further improves abrasion resistance.

[0035] 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 mgKOH / g or more and 80.0 mgKOH / g or less, and even more preferably 40 mgKOH / g or more and 70.0 mgKOH / g or less. If the acid value of the graft resin A is 40.0 mgKOH / g or less, self-aggregation of the resin due to the influence of the acid value is unlikely to occur, and the smoothness of the surface of the resin coating layer (coating surface) is unlikely to decrease. The acid value of the graft resin A can be controlled by using a monomer having a polar group such as a carboxy group or a hydroxy group during the synthesis of the graft resin A and adjusting the amount of the monomer added.

[0036] When the magnetic core is made of either a magnetic substance dispersed resin core material or a resin-filled ferrite core material, it is preferable because the SP value of the magnetic core surface can be controlled by changing the binder resin. The binder resin of the magnetic resin core material and the filler resin of the resin-filled ferrite core material are preferably any of phenol resin, epoxy resin, and acrylic resin, which have little affinity with the siloxane structure of the graft resin A.

[0037] The coating resin preferably contains a graft resin A and a graft resin B. The graft resin B is (i) a comb polymer having, as a branch, any moiety selected from the group consisting of a styrene-based polymer moiety, a (meth)acrylic acid ester-based polymer moiety, and a styrene-acrylic acid ester-based polymer moiety; (ii) It is preferable that the resin does not have a polysiloxane structural portion or that the content of the polysiloxane structural portion is 0.1 mass % or less.

[0038] The proportion of the graft resin A contained in the coating resin is preferably 1.0% by mass or more and 50.0% by mass or less, and more preferably in the range of 1.0% by mass or more and 20.0% by mass or less. If the content is less than 1.0 mass%, the surface free energy increases, resulting in poor stain resistance. If the content is more than 50.0 mass%, the abrasion resistance obtained through the interaction with graft resin B is overshadowed by the reduced intermolecular force due to the low surface free energy, resulting in insufficient abrasion resistance.

[0039] The proportion of the graft resin B contained in the coating resin is 50.0% by mass or more and 99.0% by mass or less, and a more preferable range is 80.0% by mass or more and 99.0% by mass or less. If the proportion of graft resin B is less than 50.0% by mass, the resin strength will be insufficient due to a decrease in intermolecular forces caused by low surface free energy, resulting in poor abrasion resistance.If the proportion of graft resin B is more than 99.0% by mass, the low surface free energy component will be insufficient, resulting in poor stain resistance.

[0040] The graft resin B preferably contains 75.0% by mass or more of the unit Y3 represented by the formula (7). [ka] [In formula (7), R8 represents CH3, and R9 represents a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclopentyl group, a cyclobutyl group, or a cyclopropyl group.] The inclusion of an alicyclic hydrocarbon group is preferred because it makes the surface layer of the magnetic carrier (the coating surface of the coating resin) smooth, suppresses adhesion of toner particles, external additives, and other toner-derived components, and further improves contamination resistance. The unit Y3 may contain only one type of structure, or two or more types.

[0041] The graft resin B preferably contains 1.0% by mass or more and 25.0% by mass or less of the unit Y4 represented by the formula (8). [ka] [In formula (8), R 10 is H or CH3, R 11 indicates the polymer moiety.] R 11 When the polymer portion is contained as the unit Y4, the adhesion between the resin coating layer and the magnetic core is improved. This improves the abrasion resistance and the ability of the magnetic carrier to impart charge to the toner. The unit Y4 may contain only one type of structure, or two or more types.

[0042] The graft resin B preferably further has a unit Y5 represented by formula (9). [ka] [In formula (9), R 12 is H or CH3, R 13 represents a hydrocarbon group having 1 to 6 carbon atoms.

[0043] R 11The polymer moiety as the carrier 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. The presence of such a polymer improves abrasion resistance by providing affinity with the main chain of graft resin A. Furthermore, the siloxane structure of graft resin A is effectively oriented on the carrier surface. As a result, the surface free energy of the carrier is reduced, improving contamination resistance. The weight average molecular weight (Mw) of the polymer portion is preferably 2,000 or more and 10,000 or less, and more preferably 3,000 or more and 8,000 or less.

[0044] When synthesizing graft resin B, a macromonomer having the above polymer moiety can be used to introduce the polymer moiety into graft resin B. The macromonomer is preferably used in an amount of 5.0 parts by mass or more and 40.0 parts by mass or less, based on 100 parts by mass of all monomers used in synthesizing graft resin B for coating. The addition of macromonomers strengthens molecular entanglement and improves the adhesion of the coating resin to the magnetic core, preventing the coating from peeling off even when subjected to loads such as from the agitating members of the developing device, maintaining stable charge imparting ability over the long term, and enabling the output of high-quality images. 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, from the viewpoint of coating stability. The acid value of 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 graft resin B is 3.0 mgKOH / g or less, self-aggregation of the resin due to the acid value is less likely to occur, and the smoothness of the surface of the resin coating layer (coating surface) is less likely to decrease. The acid value of graft resin B can be controlled by using a monomer having a polar group such as a carboxy group or a sulfo group (sulfonic acid group) during the synthesis of graft resin A for coating and adjusting the amount of monomer added. However, since a low acid value of graft resin A is preferred, it is preferable not to use a monomer having a polar group. Even when a resin is synthesized using only monomers that form ester bonds, a slight acid value may occur in the synthesized resin. This is thought to be due to the decomposition of some ester bonds during resin synthesis (polymerization), resulting in the generation of carboxy groups.

[0045] The resin coating layer of the present invention preferably contains conductive fine particles in the coating resin. The conductive fine particles can appropriately control the resistivity of the electrophotographic carrier. As a result, countercharge after toner development can be released, suppressing white spots. The content of the conductive fine particles added to the coating resin is preferably 0.1 to 20 parts by mass per 100 parts by mass of the coating resin. If the content is less than 0.1 part by mass, the effect of adding the conductive fine particles is difficult to obtain, and if the content exceeds 20 parts by mass, there is a risk of color deterioration due to detachment of the conductive fine particles. Examples of conductive fine particles include carbon black, titanium oxide, and silver.

[0046] Furthermore, fine particles may be contained in the coating resin for the purpose of enhancing the ability to impart charge to the toner and improving releasability. The fine particles contained in the resin coating layer may be fine particles of either organic or inorganic materials, but crosslinked resin fine particles or inorganic fine particles that have the strength to maintain the shape of the fine particles when coated are preferred. Examples of crosslinked resins that form crosslinked resin fine particles include crosslinked polymethyl methacrylate resins, crosslinked polystyrene resins, melamine resins, guanamine resins, urea resins, phenolic resins, and nylon resins. Examples of inorganic fine particles include silica, alumina, titania, etc. The content of the fine particles in the resin coating layer is 0.1 mass parts per 100 mass parts of the coating resin. It is preferable that the content is 20 parts by mass or more and 20 parts by mass or less.

[0047] <Method of manufacturing magnetic core and magnetic carrier> Magnetic particles obtained by filling the pores of porous magnetic particles with resin or magnetic material-dispersed resin particles, i.e., magnetic particles containing a magnetic oxide and a resin composition, are preferred because the SP value of the magnetic core surface can be controlled by changing the resin used. Furthermore, the specific gravity of the magnetic carrier can be reduced, which is preferable from the viewpoint of extending the life of the carrier. Reducing the specific gravity of the magnetic carrier reduces the load on the toner in the developer state in the developing device, prevents the adhesion of toner components to the surface layer of the magnetic carrier, reduces the load on the carrier itself, and further suppresses peeling, chipping, and abrasion of the resin coating layer. It also improves dot reproducibility, making it possible to obtain high-resolution images.

[0048] The resin to be contained in the pores of the porous magnetic particles can be a copolymer resin used as a coating resin, but is not limited to this and any known resin can be used. As the thermoplastic resin, the copolymer used as the coating resin is preferred, but other examples include the following: polystyrene, polymethyl methacrylate, styrene-acrylic acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinyl acetate, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, solvent-soluble perfluorocarbon resin, polyvinylpyrrolidone, petroleum resin, novolac resin, saturated alkyl polyester resin, aromatic polyester resin such as polyethylene terephthalate, polybutylene terephthalate, polyarylate, polyamide resin, polyacetal resin, polycarbonate resin, polyethersulfone resin, polysulfone resin, polyphenylene sulfide resin, and polyetherketone resin.

[0049] Examples of thermosetting resins include phenolic resins, modified phenolic resins, maleic resins, alkyd resins, epoxy resins, acrylic resins, unsaturated polyesters obtained by polycondensation of maleic anhydride, terephthalic acid, and polyhydric alcohols, urea resins, melamine resins, urea-melamine resins, xylene resins, toluene resins, guanamine resins, melamine-guanamine resins, acetoguanamine resins, glyptal resins, furan resins, silicone resins, polyimides, polyamide-imide resins, polyetherimide resins, and polyurethane resins.

[0050] One method for filling the voids of porous ferrite particles with a resin component is to dilute the resin component in a solvent and then add the diluted solution to the porous magnetic core particles. The solvent used here can be any solvent capable of dissolving each resin component. For organic solvent-soluble resins, organic solvents such as toluene, xylene, cellosolve butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, and methanol can be used. For water-soluble or emulsion-type resins, water can be used. Methods for adding solvent-diluted resin components to the interior of the porous magnetic core particles include impregnating the resin component using a coating method such as dipping, spraying, brushing, fluidized bed coating, or kneading, followed by volatilizing the solvent. When filling with a thermosetting resin, the solvent is volatilized, followed by raising the temperature to the curing temperature of the resin used to initiate a curing reaction.

[0051] On the other hand, specific methods for producing magnetic material-dispersed resin particles include the following. For example, submicron magnetic materials such as iron powder, magnetite particles, and ferrite particles are kneaded in a thermoplastic resin so as to disperse them, and then pulverized to the desired carrier particle size, followed by thermal or mechanical spheronization as necessary. Alternatively, magnetic material-dispersed resin particles can be produced by dispersing the magnetic material in a monomer and polymerizing the monomer to form a resin.

[0052] In this case, examples of the resin include vinyl resin, polyester resin, epoxy resin, phenol resin, urea resin, polyurethane resin, polyimide resin, cellulose resin, silicone resin, acrylic resin, and polyether resin. The resin may be a single type or a mixture of two or more types. Phenolic resin is particularly preferred because it increases the strength of the magnetic core. The true density and resistivity can be adjusted by adjusting the amount of magnetic material. Specifically, in the case of magnetic particles, it is preferable to add 70% by mass or more and 95% by mass or less of the magnetic core.

[0053] The magnetic core preferably has a volume-based 50% diameter (D50) of 20 μm or more and 80 μm or less in order to be able to uniformly coat the coating resin, prevent carrier adhesion, and ensure an appropriate density of the developer magnetic brush to obtain high-quality images.

[0054] The resistivity of the magnetic core is 1.0 x 10 at an electric field strength of 1000 (V / cm). 5 (Ω cm) or more 1.0×10 14 (Ω·cm) or less is preferable because good developability can be obtained.

[0055] Next, a method for producing the magnetic carrier will be described. The method for coating the magnetic core surface with the coating resin is not particularly limited and can be performed by any known method. For example, there is the so-called immersion method, in which the magnetic core and coating resin solution are stirred while the solvent is volatilized, and the coating resin is coated on the magnetic core surface. Specific examples include a universal mixer (manufactured by Fuji Paudal Co., Ltd.) and a Nauta Mixer (manufactured by Hosokawa Micron Corporation). Another method involves spraying the coating resin solution from a spray nozzle while forming a fluidized bed to coat the magnetic core surface with the coating resin. Specific examples include a Spiracoater (manufactured by Okada Seiko Co., Ltd.) and a Spiraflow (manufactured by Freund Corporation). Another method involves dry coating the magnetic core with the coating resin in particle form. Specific examples include treatment methods using devices such as a Hybridizer (manufactured by Nara Machinery Works Co., Ltd.), a Mechanofusion (manufactured by Hosokawa Micron Corporation), a Hyflex Gral (manufactured by Fukae Powtec), and a Theta Composer (manufactured by Tokuju Kogyosho Co., Ltd.).

[0056] <Magnetic carrier> Next, the magnetic carrier will be described. The magnetic carrier has a magnetization strength of 40 (Am) under a magnetic field of 5000 / 4π (kA / m). 2 / kg) or more 90(Am 2 / kg) or less. When the magnetization strength of the magnetic carrier is within the above range, the magnetic binding force to the developing sleeve is appropriate, so that carrier adhesion can be more effectively suppressed. In addition, the stress applied to the toner in the magnetic brush can be reduced, so that toner deterioration and adhesion to other components can be effectively suppressed. The strength of magnetization of the magnetic carrier can be adjusted appropriately by the amount of resin contained therein.

[0057] The residual magnetization of the magnetic carrier is 20.0 (Am 2 / kg) or less, and 10.0 (Am 2 When the residual magnetization of the magnetic carrier is within the above range, particularly good fluidity can be obtained as a developer, and good dot reproducibility can be obtained.

[0058] The magnetic carrier has a true density of 2.5 (g / cm 3 ) or more 5.5 (g / cm 3 ) or less, and 3.0 (g / cm 3 ) or more 5.0 (g / cm 3 ) or less is more preferable. A two-component developer containing a magnetic carrier having a true density in this range exerts a small load on the toner, and adhesion of the toner components to the magnetic carrier is suppressed. Furthermore, a true density in this range is preferable for the magnetic carrier in order to achieve both good developability at low electric field strength and prevention of carrier adhesion.

[0059] The magnetic carrier preferably has a volume-based 50% diameter (D50) of 21 μm or more and 81 μm or less from the viewpoints of the ability to charge the toner, suppressing carrier adhesion to the image area, and achieving high image quality, and more preferably 25 μm or more and 60 μm or less.

[0060] Next, the toner constitution that is preferable for achieving the object of the present invention will be described in detail below. <Binder resin> The toner particles of the present invention may use the following polymers as the binder resin: homopolymers of styrene and its substituted derivatives, such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene; styrene-based copolymers, such as styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylic acid ester copolymer, and styrene-methacrylic acid ester copolymer; styrene-based copolymer resins, polyester resins, mixtures of polyester resins and vinyl resins, or hybrid resins in which both are partially reacted; polyvinyl chloride, phenolic resins, naturally modified phenolic resins, naturally resin-modified maleic acid resins, acrylic resins, methacrylic resins, polyvinyl acetate, silicone resins, polyester resins, polyurethanes, polyamide resins, furan resins, epoxy resins, xylene resins, polyethylene resins, and polypropylene resins. Among these, those containing polyester resins as the main component are preferred from the viewpoint of low-temperature fixability.

[0061] Monomers used in the polyester unit of the polyester resin include polyhydric alcohols (divalent or trivalent or higher alcohols), polycarboxylic acids (divalent or trivalent or higher carboxylic acids), their acid anhydrides, or their lower alkyl esters. To create a branched polymer that exhibits "strain hardening," partial crosslinking within the molecule of the amorphous resin is effective, and for this purpose, it is preferable to use a polyfunctional compound with a valence of three or more. Therefore, it is preferable to include a trivalent or higher carboxylic acid, its acid anhydride, or its lower alkyl ester, and / or a trivalent or higher alcohol as the raw material monomer for the polyester unit.

[0062] As the polyhydric alcohol monomer used in the polyester unit of the polyester resin, the following polyhydric alcohol monomers can be used. Dihydric alcohol components include ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,6-hexanediol, neopentyl glycol, 2-ethyl-1,3-hexanediol, hydrogenated bisphenol A, and bisphenols represented by formula (A) and their derivatives; [ka] (In the formula, R is an ethylene or propylene group, x and y are each an integer of 0 or more, and the average value of x+y is 0 or more and 10 or less.) Diols represented by formula (B); [ka] (In the formula, R' represents -CH2CH2-, -CH2-CH(CH3)-, or -CH2-C(CH3)2-, x' and y' are integers of 0 or more, and the average value of x+y is 0 to 10.)

[0063] Examples of trihydric or higher alcohol components include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene. Among these, glycerol, trimethylolpropane, and pentaerythritol are preferred. These dihydric and trihydric or higher alcohols can be used alone or in combination.

[0064] As the polycarboxylic acid monomer used in the polyester unit of the polyester resin, the following polycarboxylic acid monomers can be used. Examples of dicarboxylic acid components 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-dodecylsuccinic acid, isododecylsuccinic acid, n-octenylsuccinic acid, n-octylsuccinic acid, isooctenylsuccinic acid, isooctylsuccinic acid, anhydrides of these acids, and lower alkyl esters thereof. Of these, maleic acid, fumaric acid, terephthalic acid, and n-dodecenylsuccinic acid are preferably used. Examples of trivalent or higher carboxylic acids, their acid anhydrides, or their lower alkyl esters include 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-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, empol trimer acid, and their acid anhydrides or lower alkyl esters. Among these, 1,2,4-benzenetricarboxylic acid, i.e., trimellitic acid or its derivatives, is particularly preferred due to its low cost and easy reaction control. These divalent carboxylic acids and trivalent or higher carboxylic acids can be used alone or in combination.

[0065] The method for producing the polyester unit of the present invention is not particularly limited, and known methods can be used. For example, the aforementioned alcohol monomer and carboxylic acid monomer are simultaneously charged and polymerized via an esterification reaction or transesterification reaction and a condensation reaction to produce a polyester resin. The polymerization temperature is not particularly limited, but is preferably in the range of 180°C to 290°C. Polymerization of the polyester unit can be performed using a polymerization catalyst such as a titanium-based catalyst, a tin-based catalyst, zinc acetate, antimony trioxide, or germanium dioxide. In particular, the binder resin of the present invention preferably contains a polyester unit polymerized using a tin-based catalyst. In addition, it is preferable from the viewpoint of fogging that the acid value of the polyester resin is 5 mgKOH / g or more and 20 mgKOH / g or less, and the hydroxyl value is 20 mgKOH / g or more and 70 mgKOH / g or less, since this reduces the amount of moisture adsorption in a high-temperature, high-humidity environment and keeps the non-electrostatic adhesion force low.

[0066] The binder resin may be a mixture of a low molecular weight resin and a high molecular weight resin. The ratio of the high molecular weight resin to the low molecular weight resin is preferably 40 / 60 or more and 85 / 15 or less by mass from the viewpoint of low temperature fixability and hot offset resistance.

[0067] <Release agent> Examples of waxes that can be used in the toner of the present invention include: hydrocarbon waxes such as low-molecular-weight polyethylene, low-molecular-weight polypropylene, alkylene copolymers, microcrystalline wax, paraffin wax, and Fischer-Tropsch wax; oxides of hydrocarbon waxes such as oxidized polyethylene wax or block copolymers thereof; waxes containing fatty acid esters as the main component such as carnauba wax; and partially or completely deoxidized fatty acid esters such as deoxidized carnauba wax. Further examples include the following. Saturated straight-chain fatty acids such as palmitic acid, stearic acid, and montanic acid; unsaturated fatty acids such as brassidic acid, eleostearic acid, and valinaric acid; saturated alcohols such as stearyl alcohol, aralkyl alcohols, behenyl alcohol, carnaubyl alcohol, ceryl alcohol, and melissyl alcohol; polyhydric alcohols such as sorbitol; esters of fatty acids such as palmitic acid, stearic acid, behenic acid, and montanic acid with alcohols such as stearyl alcohol, aralkyl alcohols, behenyl alcohol, carnaubyl alcohol, ceryl alcohol, and melissyl alcohol; fatty acid amides such as linoleic acid amide, oleic acid amide, and lauric acid amide; methylene bisstearic acid amide, ethylene biscapric acid amide, ethylene bislauric acid amide, hexamethylene Saturated fatty acid bisamides such as bisstearamide; unsaturated fatty acid amides such as ethylene bisoleamide, hexamethylene bisoleamide, N,N'-dioleyl adipamide, and N,N'-dioleyl sebacamide; aromatic bisamides such as m-xylene bisstearamide and N,N'-distearyl isophthalamide; fatty metal salts (commonly known as metal soaps) such as calcium stearate, calcium laurate, zinc stearate, and magnesium stearate; waxes obtained by grafting aliphatic hydrocarbon waxes with vinyl monomers such as styrene and acrylic acid; partial esters of fatty acids and polyhydric alcohols such as behenic acid monoglyceride; and methyl ester compounds having hydroxyl groups obtained by hydrogenating vegetable oils and fats.

[0068] 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 low-temperature fixability and fixation separation property, and in the present invention, hydrocarbon waxes are more preferred from the viewpoint of further improving hot offset resistance.

[0069] 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 per 100 parts by mass of the binder resin. Furthermore, in an endothermic curve during temperature rise measured with a differential scanning calorimetry (DSC) device, the peak temperature of the maximum endothermic peak of the wax is preferably 45° C. or higher and 140° C. or lower. If the peak temperature of the maximum endothermic peak of the wax is within the above range, it is preferable because it is possible to achieve both storage stability and hot offset resistance of the toner.

[0070] <Coloring agent> The toner particles of the present invention may contain a colorant. Examples of the colorant include the following.

[0071] Examples of black colorants include carbon black, and those toned to black using a yellow colorant, a magenta colorant, and a cyan colorant. As the colorant, a pigment may be used alone, but it is more preferable to use a dye and a pigment in combination to improve the clarity from the viewpoint of the image quality of a full-color image.

[0072] Examples of pigments for magenta toner include 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, 57:1, 58, 60, 63, 64, 68, 81:1, 83, 87, 88, 89, 90, 112, 114, 122, 123, 146, 147, 150, 163, 184, 202, 206, 207, 209, 238, 269, 282; CI Pigment Violet 19; CI Bat Red 1, 2, 10, 13, 15, 23, 29, 35.

[0073] Dyes for magenta toner include solvent dyes such as CI Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 81, 82, 83, 84, 100, 109, and 121; CI Disperse Red 9; CI Solvent Violet 8, 13, 14, 21, and 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, and 40; and CI Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27, and 28.

[0074] Examples of pigments for cyan toner include CI Pigment Blue 2, 3, 15:2, 15:3, 15:4, 16, and 17; CI Vat Blue 6; and CI Acid Blue 45, and copper phthalocyanine pigments having 1 to 5 phthalimidomethyl groups substituted on the phthalocyanine skeleton. An example of a dye for cyan toner is CI Solvent Blue 70.

[0075] Yellow toner pigments include the following: 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, 185; CI Vat Yellow 1, 3, 20. An example of a dye for yellow toner is CI Solvent Yellow 162. These colorants may be used alone or in combination, or in the form of a solid solution. The colorant is selected in consideration of hue angle, chroma, brightness, lightfastness, transparency on an overhead projector, and dispersibility in toner.

[0076] The content of the colorant is preferably 0.1 parts by mass or more and 30.0 parts by mass or less relative to the total amount of the resin components.

[0077] <Inorganic fine particles> The toner preferably contains inorganic fine particles, mainly for the purpose of improving fluidity and chargeability, and the inorganic fine particles are preferably attached to the surface of the toner particles. As inorganic fine particles serving as spacer particles for improving the releasability between the toner and the carrier, silica particles having a maximum peak particle size based on the number distribution of 80 to 200 nm are preferred, and in order to function as spacer particles while better suppressing separation from the toner, silica particles having a maximum peak particle size based on the number distribution of 100 to 150 nm are more preferred. In order to improve the fluidity of the toner, the toner preferably contains inorganic fine particles having a maximum peak particle size of 20 nm or more and 50 nm or less based on the number distribution, and it is also a preferred embodiment to use them in combination with the silica particles.

[0078] Furthermore, other external additives may be added to the toner particles in order to improve fluidity and transferability. The external additives added to the surface of the toner particles preferably contain inorganic fine particles such as titanium oxide, alumina oxide, and silica, and a plurality of types may be used in combination. The total content of the external additives is preferably 0.3 to 5.0 parts by weight, more preferably 0.8 to 4.0 parts by weight, per 100 parts by weight of toner particles. Among these, the content of silica particles having a number distribution-based maximum peak particle size of 80 to 200 nm is 0.1 to 2.5 parts by weight, more preferably 0.5 to 2.0 parts by weight, per 100 parts by weight of toner particles. Within this range, the effect as spacer particles becomes more pronounced.

[0079] The surfaces of silica particles or inorganic fine particles used as external additives are preferably subjected to a hydrophobic treatment, preferably using a coupling agent such as a titanium coupling agent or a silane coupling agent, a fatty acid or a metal salt thereof, a silicone oil, or a combination thereof. Examples of titanium coupling agents include the following: tetrabutyl titanate, tetraoctyl titanate, isopropyl triisostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, and bis(dioctyl pyrophosphate)oxyacetate titanate. Examples of silane coupling agents 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. Examples of fatty acids include long-chain fatty acids such as undecylic acid, lauric acid, tridecylic acid, dodecylic acid, myristic acid, palmitic acid, pentadecylic acid, stearic acid, heptadecylic acid, arachidic acid, montanic acid, oleic acid, linoleic acid, and arachidonic acid. Examples of metals in these fatty acid metal salts include zinc, iron, magnesium, aluminum, calcium, sodium, and lithium. Examples of silicone oils include dimethyl silicone oil, methylphenyl silicone oil, and amino-modified silicone oil.

[0080] The hydrophobic treatment is preferably carried out by adding a hydrophobic treatment agent to the particles to be treated in an amount of 1% by mass or more and 30% by mass or less (more preferably 3% by mass or more and 7% by mass or less) relative to the particles to be treated, thereby coating the particles to be treated. The degree of hydrophobicity of the hydrophobized external additive is not particularly limited, but for example, the degree of hydrophobicity after the treatment is preferably 40 or more and 98 or less. The degree of hydrophobicity indicates the wettability of the sample with respect to methanol, and is an index of hydrophobicity.

[0081] When the magnetic carrier of the present invention is mixed with a toner to be used as a two-component developer, good results are usually obtained when the carrier mixing ratio is 2% by mass to 15% by mass, preferably 4% by mass to 13% by mass, in terms of the toner concentration in the developer. If the toner concentration is less than 2% by mass, the image density tends to decrease, and if it exceeds 15% by mass, fogging and in-machine scattering tend to occur.

[0082] The magnetic carrier of the present invention is also used as a replenishment developer. In the replenishment developer to be replenished to a developing device in response to a decrease in the toner concentration of the two-component developer in the developing device, the amount of toner is 2 parts by mass or more and 50 parts by mass or less per part by mass of the replenishment magnetic carrier.

[0083] Next, an image forming apparatus equipped with a developing device using the magnetic carrier, two-component developer, and replenishment developer of the present invention will be described by way of example, but the developing device used in the developing method of the present invention is not limited to this.

[0084] <Image forming method> In Figure 2, electrostatic latent image carrier 1 rotates in the direction of the arrow. Electrostatic latent image carrier 1 is charged by charger 2, which serves as a charging means. The charged surface of electrostatic latent image carrier 1 is exposed to light by exposure device 3, which serves as an electrostatic latent image forming means, forming an electrostatic latent image. Developing device 4 includes a developer container 5 containing a two-component developer. Developer carrier 6 is rotatably arranged, and magnets 7, which serve as magnetic field generating means, are housed within developer carrier 6. At least one of the magnets 7 is positioned facing the latent image carrier. The two-component developer is held on developer carrier 6 by the magnetic field of magnet 7. The amount of two-component developer is regulated by regulating member 8, and the developer is transported to the developing section facing electrostatic latent image carrier 1. In the developing section, the magnetic field generated by magnet 7 forms a magnetic brush. The electrostatic latent image is then visualized as a toner image by applying a developing bias consisting of a DC electric field superimposed on an AC electric field. The toner image formed on the electrostatic latent image carrier 1 is electrostatically transferred to a recording medium (transfer material) 12 by a transfer charger 11. Here, as shown in FIG. 2, the image may be transferred from the electrostatic latent image carrier 1 to an intermediate transfer body 9, and then electrostatically transferred to the recording medium 12. The recording medium 12 is then transported to a fixing device 13, where it is heated and pressed to fix the toner onto the recording medium 12. The recording medium 12 is then discharged outside the apparatus as an output image. After the transfer process, any toner remaining on the electrostatic latent image carrier 1 is removed by a cleaner 15. After that, the electrostatic latent image carrier 1, which has been cleaned by the cleaner 15, is electrically initialized by light irradiation from a pre-exposure device 16, and the above image forming operation is repeated.

[0085] FIG. 3 is a schematic diagram showing an example of the application of the image forming method of the present invention to a full-color image forming apparatus. The arrangement of image forming units (K, Y, C, M) and the arrows indicating their rotation directions are not limited to the above. Incidentally, K represents black, Y represents yellow, C represents cyan, and M represents magenta. In Figure 3, electrostatic latent image carriers 1K, 1Y, 1C, and 1M rotate in the direction of the arrows. Each electrostatic latent image carrier is charged by chargers 2K, 2Y, 2C, and 2M, which serve as charging means. The charged surface of each electrostatic latent image carrier is exposed by exposure devices 3K, 3Y, 3C, and 3M, which serve as electrostatic latent image forming means, to form an electrostatic latent image. The electrostatic latent image is then visualized as a toner image by two-component developers carried on developer carriers 6K, 6Y, 6C, and 6M, which are provided in developing devices 4K, 4Y, 4C, and 4M, which serve as developing means. The image is then transferred to intermediate transfer member 9 by intermediate transfer chargers 10K, 10Y, 10C, and 10M, which serve as transfer means. The image is then transferred to a recording medium 12 by a transfer charger 11, which serves as a transfer means. The recording medium 12 is then heated and pressure-fixed by a fixing device 13, which serves as a fixing means, and output as an image. An intermediate transfer body cleaner 14, which cleans the intermediate transfer body 9, collects residual toner and other toner. Specifically, the development method of the present invention preferably involves applying an AC voltage to the developer carrier to form an AC electric field in the development area while the magnetic brush is in contact with the photosensitive drum. A distance (SD distance) between the developer carrier (developing sleeve) 6 and the photosensitive drum of 100 μm or more and 1000 μm or less is effective for preventing carrier adhesion and improving dot reproducibility. A distance less than 100 μm tends to result in insufficient developer supply and low image density. A distance greater than 1000 μm widens the magnetic field lines from the magnetic pole S1, reducing the density of the magnetic brush, resulting in poor dot reproducibility and a weakened carrier binding force, making carrier adhesion more likely.

[0086] The peak-to-peak voltage (Vpp) of the alternating electric field is 300V to 3000V, preferably 500V to 1800V. The frequency is 500Hz to 10000Hz, preferably 1000Hz to 7000Hz, and can be appropriately selected depending on the process. In this case, the waveform of the AC bias for forming the alternating electric field can be a triangular wave, a square wave, a sine wave, or a waveform with a varied duty ratio. To accommodate changes in the toner image formation speed, it is preferable to apply a development bias voltage (intermittent AC superimposed voltage) having a discontinuous AC bias voltage to the developer carrier for development. If the applied voltage is less than 300V, it is difficult to obtain sufficient image density, and fogging toner in non-image areas may not be effectively recovered. Furthermore, if the voltage exceeds 3000V, the latent image may be disturbed by the magnetic brush, resulting in a deterioration in image quality.

[0087] By using a two-component developer with a well-charged toner, the fog removal voltage (Vback) can be lowered, and the primary charge of the photoreceptor can be reduced, thereby extending the life of the photoreceptor. Vback depends on the development system, but it is best to set it to 200V or less, more preferably 150V or less. The contrast potential is preferably between 100V and 400V to produce sufficient image density.

[0088] Furthermore, although a frequency lower than 500 Hz affects the process speed, the configuration of the electrostatic latent image bearing photoreceptor may be the same as that of a photoreceptor typically used in an image forming apparatus, such as a photoreceptor having a conductive substrate made of aluminum, SUS, or the like, on which a conductive layer, an undercoat layer, a charge generation layer, a charge transport layer, and optionally a charge injection layer are provided in this order. The conductive layer, undercoat layer, charge generating layer, and charge transport layer may be layers that are generally used in photoreceptors. As the outermost surface layer of the photoreceptor, for example, a charge injection layer or a protective layer may be used.

[0089] <Measurement of magnetic carrier resistivity> The resistivity of the magnetic carrier and the porous magnetic core is measured using a measuring device shown in Fig. 4. The resistivity of the magnetic carrier is measured at an electric field strength of 2000 (V / cm). Resistance measurement cell A has a cross-sectional area of ​​2.4 cm 2 The device is composed of a cylindrical container (made of PTFE resin) 17 with holes, a lower electrode (made of stainless steel) 18, a support base (made of PTFE resin) 19, and an upper electrode (made of stainless steel) 20. The cylindrical container 17 is placed on the support base 19, and a sample (magnetic carrier or porous magnetic core) 21 is filled to a thickness of approximately 1 mm. The upper electrode 20 is placed on the filled sample 5, and the thickness of the sample is measured. As shown in Figure 4(a), the gap when there is no sample is d1, and as shown in Figure 4(b), the gap when the sample is filled to a thickness of approximately 1 mm is d2. The sample thickness d can be calculated using the following formula. d = d2 - d1 (mm) At this time, the mass of the sample is appropriately changed so that the thickness d of the sample is 0.95 mm or more and 1.04 mm or less. The resistivity of the sample can be determined by applying a DC voltage between the electrodes and measuring the current that flows at that time. For the measurement, an electrometer 22 (Kesley 6517A, manufactured by Kesley) and a processing computer 23 for control are used. The control system and control software (LabVEIW, National Instruments) manufactured by National Instruments were used as the control processing computer. The measurement conditions were: contact area between the sample and the electrode S = 2.4 cm 2 The measured value d is input so that the thickness of the sample is between 0.95 mm and 1.04 mm. The load on the upper electrode is set to 270 g, and the maximum applied voltage is set to 1000 V. Resistivity (Ω·cm) = (applied voltage (V) / measured current (A)) × S (cm 2 ) / d(cm) Electric field strength (V / cm) = applied voltage (V) / d (cm) The resistivity of the magnetic carrier and the porous magnetic core at the electric field strength is read from the graph as the resistivity at the electric field strength on the graph.

[0090] <Method for measuring the 50% diameter (D50) of a magnetic carrier or porous magnetic core based on volume> The particle size distribution was measured using a laser diffraction / scattering particle size distribution measuring device "Microtrac MT3300EX" (manufactured by Nikkiso Co., Ltd.). The 50% diameter (D50) on a volume basis of the magnetic carrier and porous magnetic core was measured using a sample supply device for dry measurement, the "One-Shot Dry Sample Conditioner Turbotrac" (manufactured by Nikkiso Co., Ltd.). The supply conditions for the Turbotrac were a dust collector used as the vacuum source, with an air volume of approximately 33 l / sec and a pressure of approximately 17 kPa. Control was performed automatically on the software. The particle size was calculated as the 50% diameter (D50), which is the cumulative value on a volume basis. Control and analysis were performed using the accompanying software (version 10.3.3-202D). The measurement conditions were as follows: SetZero time: 10 seconds Measurement time: 10 seconds Number of measurements: 1 Particle refractive index: 1.81% Particle shape: non-spherical Upper limit of measurement: 1408 μm Measurement lower limit: 0.243μm Measurement environment: 23°C, 50% RH

[0091] <Measurement of pore diameter and pore volume of porous magnetic core> The pore size distribution of the porous magnetic core is measured by mercury intrusion porosimetry. The measurement principle is as follows. In this measurement, the pressure applied to the mercury is varied, and the amount of mercury that penetrates into the pores is measured. The conditions under which mercury can penetrate into the pores can be expressed from the balance of forces as PD = -4σCOSθ, where P is the pressure, D is the pore diameter, θ is the contact angle of the mercury, and σ is the surface tension. If the contact angle and surface tension are constants, then the pressure P and the pore diameter D into which mercury can penetrate at that time are inversely proportional. For this reason, the pressure P and the amount of infiltrated liquid V at that time are measured by varying the pressure, and the horizontal axis P of the PV curve, obtained by this measurement, is then directly substituted for the pore diameter in this equation to determine the pore distribution. Measurement can be performed using a measuring device such as a fully automatic multi-function mercury porosimeter PoreMaster series or PoreMaster-GT series manufactured by Yuasa Ionics Co., Ltd., or an automatic porosimeter Autopore IV 9500 series manufactured by Shimadzu Corporation.

[0092] Specifically, the measurement was carried out using an Autopore IV9520 manufactured by Shimadzu Corporation under the following conditions and procedures. Measurement conditions Measurement environment: 20℃ Measurement cell sample volume 5cm 3 , indentation volume 1.1cm 3 , Application for powder Measurement range: 2.0 psia (13.8 kPa) or more and 59989.6 psia (413.7 kPa) or less Measurement steps: 80 steps (When the pore diameter is calculated logarithmically, the steps are spaced at equal intervals.) Pressurization parameters: Exhaust pressure 50μmHg Exhaust time 5.0 min Mercury injection pressure 2.0 psia (13.8 kPa) Equilibrium time 5secs High pressure parameters Equilibration time 5secs Mercury parameters Advancing contact angle 130.0 degrees Receding contact angle 130.0degrees Surface tension 485.0mN / m(485.0dynes / cm) Mercury density 13.5335g / mL

[0093] Measurement procedure (1) Approximately 1.0 g of the porous magnetic core is weighed and placed in the sample cell. Enter the weighing value. (2) In the low-pressure section, measure the range of 2.0 psia (13.8 kPa) to 45.8 psia (315.6 kPa). (3) In the high-pressure section, the range measured was between 45.9 psia (316.3 kPa) and 59,989.6 psia (413.6 MPa). (4) The pore size distribution is calculated from the mercury injection pressure and the amount of mercury injected. (2), (3), and (4) were performed automatically using the software provided with the device. From the pore size distribution measured as described above, the pore size at which the differential pore volume is maximum in the pore size range of 0.1 μm to 3.0 μm is read, and this is taken as the pore size at which the differential pore volume is maximum. In addition, the pore volume obtained by integrating the differential pore volume in the pore diameter range of 0.1 μm to 3.0 μm was calculated using the attached software.

[0094] <Measuring method for weight average particle size (D4) and number average particle size (D1)> The weight-average particle size (D4) and number-average particle size (D1) of the toner were measured using a precision particle size distribution measuring device, "Coulter Counter Multisizer 3" (registered trademark, manufactured by Beckman Coulter, Inc.), equipped with a 100 μm aperture tube and employing the narrow-pore electrical resistance method, and the accompanying dedicated software, "Beckman Coulter Multisizer 3 Version 3.51" (manufactured by Beckman Coulter, Inc.), for setting measurement conditions and analyzing measurement data. Measurements were made with an effective number of 25,000 measurement channels, and the measurement data was analyzed and calculated. The aqueous electrolyte solution used for the measurement is prepared by dissolving special grade sodium chloride in ion-exchanged water to a concentration of approximately 1% by mass, such as "ISOTON II" (manufactured by Beckman Coulter). Before carrying out the measurements and analysis, the dedicated software was set up as follows. In the "Change Standard Measurement Method (SOM)" screen of the dedicated software, set the total count in control mode to 50,000 particles, the number of measurements to 1, and the Kd value obtained using "Standard Particles 10.0 μm" (Beckman Coulter). Press the threshold / noise level measurement button to automatically set the threshold and noise level. Also, set the current to 1600 μA, the gain to 2, the electrolyte to ISOTON II, and check "Flush aperture tube after measurement." In the dedicated software's "Pulse to particle size conversion setting screen," set the bin interval to logarithmic particle size, the particle size bin to 256 particle size bins, and the particle size range from 2 μm to 60 μm.

[0095] The specific measurement method is as follows. (1) Pour approximately 200 ml of the electrolyte solution into a 250 ml round-bottom glass beaker made specifically for the Multisizer 3, set it on the sample stand, and stir the stirrer rod counterclockwise at 24 revolutions per second. Then, use the "aperture flush" function of the analysis software to remove any dirt or air bubbles from inside the aperture tube. (2) Approximately 30 ml of the electrolyte solution is placed in a 100 ml flat-bottom glass beaker. A 10% by weight aqueous solution of "Contaminon N" (a neutral detergent for cleaning precision measuring instruments, pH 7, consisting of a nonionic surfactant, anionic surfactant, and organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) is added as a dispersant. Add approximately 0.3 ml of a diluted solution prepared by diluting 100% ethanol (manufactured by Epson) with ion-exchanged water three times by mass. (3) A predetermined amount of ion-exchanged water is placed in the water tank of an ultrasonic disperser, "Ultrasonic Dispension System Tetora 150" (manufactured by Nikkaki Bios Co., Ltd.), which has two built-in oscillators with an oscillation frequency of 50 kHz and a phase difference of 180 degrees and an electrical output of 120 W. Approximately 2 ml of the Contaminon N is added to this water tank. (4) Set the beaker (2) in the beaker fixing hole of the ultrasonic disperser, operate the ultrasonic disperser, and adjust the height of the beaker so that the resonance state of the liquid surface of the electrolytic solution in the beaker is maximized. (5) While the electrolyte solution in the beaker in (4) is irradiated with ultrasonic waves, approximately 10 mg of toner is added little by little to the electrolyte solution and dispersed. The ultrasonic dispersion process is then continued for another 60 seconds. During the ultrasonic dispersion, the water temperature in the water tank is appropriately adjusted to be between 10°C and 40°C. (6) Using a pipette, add the electrolyte solution (5) containing the dispersed toner to the round-bottom beaker (1) placed in the sample stand, and adjust the measurement concentration to approximately 5%. Then, measure the particle count until it reaches 50,000 particles. (7) The measurement data is analyzed using the dedicated software provided with the device to calculate the weight average particle size (D4) and number average particle size (D1). Note that when the dedicated software is set to Graph / Volume %, the "Average diameter" on the Analysis / Volume Statistics (Arithmetic Mean) screen is the weight average particle size (D4), and when the dedicated software is set to Graph / Number %, the "Average diameter" on the Analysis / Number Statistics (Arithmetic Mean) screen is the number average particle size (D1).

[0096] <Calculation method for the amount of fine powder> The amount of fine powder (number %) in the toner is calculated as follows. For example, to determine the percentage of particles 4.0 μm or smaller in a toner, after performing the measurement using the Multisizer 3 mentioned above, (1) set the dedicated software to Graph / Number% and display the measurement results chart as a percentage of the number. (2) Check the "<" in the particle size setting section on the Format / Particle Size / Particle Size Statistics screen and enter "4" in the particle size input section below. Then, (3) when the Analysis / Number Statistics (Arithmetic Mean) screen is displayed, the value in the "<4 μm" display section is the percentage of particles 4.0 μm or smaller in the toner.

[0097] <Calculation method for coarse powder amount> The amount of coarse particles (vol %) on a volume basis in the toner is calculated as follows. For example, to determine the volume percentage of particles 10.0 μm or larger in a toner, after performing the measurement using the Multisizer 3 mentioned above, (1) set the dedicated software to Graph / Volume% and display the measurement results chart as a volume percentage. (2) Check the ">" in the particle size setting section on the Format / Particle Size / Particle Size Statistics screen and enter "10" in the particle size input section below. Then, (3) when the Analysis / Volume Statistics (Arithmetic Mean) screen is displayed, the value in the ">10 μm" display section is the volume percentage of particles 10.0 μm or larger in the toner.

[0098] <Method for Measuring Molecular Weight and Molecular Weight Distribution of Resin etc.> The molecular weight and molecular weight distribution of resin etc. are measured by gel permeation chromatography (GPC) as follows. First, dissolve the sample in tetrahydrofuran (THF) over 24 hours at room temperature. Then, filter the obtained solution with a solvent-resistant membrane filter "Maeshory Disc" (manufactured by Tosoh Corporation) with a pore diameter of 0.2 μm to obtain a sample solution. Note that the sample solution is adjusted so that the concentration of the components soluble in THF is about 0.8 mass%. Using this sample solution, measurement is carried out under the following conditions. Apparatus: HLC8120 GPC (Detector: RI) (manufactured by Tosoh Corporation) Column: 7 columns of Shodex KF-801, 802, 803, 804, 805, 806, 807 (manufactured by Showa Denko K.K.) Eluent: Tetrahydrofuran (THF) Flow rate: 1.0 mL / min Oven temperature: 40.0 °C Sample injection volume: 0.10 mL When calculating the molecular weight of the sample, a molecular weight calibration curve prepared using a standard polystyrene resin (product 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, A-500", manufactured by Tosoh Corporation) is used.

[0099] <Method for Measuring Si Atom Concentration by XPS> Attach the magnetic carrier on the indium foil. At that time, attach the particles uniformly so that the indium foil part is not exposed.\ The measurement conditions are as follows. Apparatus: PHI5000VERSAPROBE II (ULVAC-PHI, Inc.) Irradiation ray: Al Kα ray Output: 25W 15kV PassEnergy: 58.7 eV Stepsize: 0.125 eV XPS peaks: C1s, O1s, Si2p, Ti2p, Sr3d

[0100] <Structure of resin (NMR)> The structure of the resin (such as 1,2-polybutadiene resin, amorphous polyester, etc.) contained in the toner is analyzed by nuclear magnetic resonance spectroscopy ( 1 H-NMR). Measuring device: JNM-EX400 (manufactured by JEOL Ltd.) Measuring frequency: 400 MHz Pulse condition: 5.0 μs Frequency range: 10500 Hz Number of integrations: 1024 times Measuring solvent: DMSO-d6 Dissolve the sample in DMSO-d6 as much as possible and perform the measurement under the above conditions. Determine the structure of the sample from the chemical shift values and proton ratios of the obtained spectrum.

[0101] <Calculation method of SP value> The SP value is what is called the solubility parameter, which numerically represents how easily substances dissolve in each other in terms of chemical structure. The closer the SP values of compounds are to each other, the easier they are to mix and dissolve in each other. There are various methods for calculating the SP value, but in the present invention, the commonly used Fedors method is used. Specifically, for example, it is described in detail in Polymer engineering and science, Vol. 14, pages 147 to 154, and the SP value can be calculated by the following formula. Formula: SP value = √(Ev / v) = √(ΣΔei / ΣΔvi) (In the formula, Ev: evaporation energy (cal / mol), v: molar volume (cm 3 / mol), Δei: evaporation energy of each atom or atomic group, Δvi: molar volume of each atom or atomic group)

[0102] <Method for manufacturing toner> The method for producing toner particles is not particularly limited, but a pulverization method is preferred from the viewpoint of dispersing the release agent and the polymer in which a styrene-acrylic polymer is graft-polymerized onto a polyolefin. The reason for this is that when toner particles are produced in an aqueous medium, the highly hydrophobic release agent and the polymer in which a styrene-acrylic polymer is graft-polymerized onto a polyolefin tend to be localized inside the toner particles. This makes it difficult to form a core-shell structure using the heat treatment device described above.

[0103] The procedure for producing toner by the pulverization method will be described below. In the raw material mixing process, predetermined amounts of materials constituting the toner particles, such as binder resin, release agent, colorant, crystalline polyester, and optionally other components such as charge control agent, are weighed, blended, and mixed. Examples of mixing devices include 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 and Engineering Co., Ltd.). Next, the mixed materials are melt-kneaded to disperse the wax and other components in the binder resin. In this melt-kneading process, a batch kneader such as a pressure kneader or a Banbury mixer, or a continuous kneader can be used. Single- or twin-screw extruders are commonly used due to their advantage of continuous production. Examples include a KTK twin-screw extruder (manufactured by Kobe Steel, Ltd.), a TEM twin-screw extruder (manufactured by Toshiba Machine Co., Ltd.), a PCM kneader (manufactured by Ikegai Iron Works), a twin-screw extruder (manufactured by KCK Corporation), a Co-Kneader (manufactured by Buss Co., Ltd.), and a Kneadex (manufactured by Nippon Coke and Engineering Co., Ltd.). Furthermore, the resin composition obtained by melt-kneading may be rolled using a twin roll or the like and cooled with water or the like in a cooling process. The cooled resin composition is then pulverized to a desired particle size in a pulverization step, which involves coarse pulverization using a pulverizer such as a crusher, hammer mill, or feather mill, followed by further pulverization using a pulverizer such as a Kryptron System (Kawasaki Heavy Industries), a Super Rotor (Nisshin Engineering), a Turbo Mill (Turbo Kogyo), or an air jet pulverizer. Thereafter, as necessary, the mixture is classified using a classifier or sieve such as an inertial classification type Elbow Jet (manufactured by Nittetsu Mining Co., Ltd.), a centrifugal classification type Turboplex (manufactured by Hosokawa Micron Corporation), a TSP Separator (manufactured by Hosokawa Micron Corporation), or a Faculty (manufactured by Hosokawa Micron Corporation).

[0104] Thereafter, the toner particles are subjected to a surface treatment by heating to increase the circularity of the toner. For example, the surface treatment can be performed by using a surface treatment device shown in FIG. 1 with hot air. The mixture supplied by the material supply means 1 is introduced into an introduction pipe 3, which is installed vertically to the material supply means, by compressed gas adjusted by a compressed gas adjustment means 2. The mixture that passes through the introduction pipe is uniformly dispersed by a conical protruding member 4 installed in the center of the material supply means, and is then introduced into eight supply pipes 5 that radiate outward, and into a treatment chamber 6 where heat treatment is carried out. At this time, the flow of the mixture supplied to the processing chamber is regulated by a regulating means 9 provided in the processing chamber for regulating the flow of the mixture, so that the mixture supplied to the processing chamber is heat-treated while swirling within the processing chamber and then cooled. Hot air for heat-treating the supplied mixture is supplied from hot air supply means 7, and is introduced into the treatment chamber by spirally swirling it using a swirling member 13 for swirling the hot air. The swirling member 13 for swirling the hot air has a plurality of blades, and the swirling of the hot air can be controlled by adjusting the number and angle of the blades. The hot air supplied into the treatment chamber preferably has a temperature of 100°C to 300°C at the outlet of the hot air supply means 7. If the temperature at the outlet of the hot air supply means is within the above range, it is possible to uniformly spheronize the toner particles while preventing fusion and coalescence of the toner particles due to excessive heating of the mixture.

[0105] The heat-treated toner particles are then cooled by cold air supplied from the cold air supply means 8, and the temperature of the cold air supplied from the cold air supply means 8 is preferably -20°C to 30°C. If the temperature of the cold air is within the above range, the heat-treated toner particles can be cooled efficiently, and the fusion and coalescence of the heat-treated toner particles can be prevented without impeding the uniform spheroidization of the mixture. The absolute moisture content of the cold air is 0.5 g / m 3 More than 15.0g / m 3 It is preferable that: Next, the cooled heat-treated toner particles are collected by the collecting means 10 at the bottom end of the processing chamber. A blower (not shown) is provided ahead of the collecting means, and the toner particles are sucked and transported by the blower. The powder particle supply port 14 is positioned so that the swirling direction of the supplied mixture and the swirling direction of the hot air are the same, and the recovery means 10 of the surface treatment device is positioned on the outer periphery of the treatment chamber to maintain the swirling direction of the swirled powder particles. Furthermore, the cold air supplied from the cold air supply means 8 is configured to be supplied horizontally and tangentially from the outer periphery of the device to the circumferential surface of the treatment chamber. The swirling directions of the mixture supplied from the powder supply port, the cold air supplied from the cold air supply means, and the hot air supplied from the hot air supply means are all the same. This prevents turbulence within the treatment chamber, strengthens the swirling flow within the device, applies a strong centrifugal force to the heat-treated toner particles, and further improves the dispersibility of the heat-treated toner particles, resulting in toner particles with fewer coalescence and uniform shapes.

[0106] When the average circularity of the toner particles is 0.960 or more and 0.980 or less, the non-electrostatic adhesion can be kept low, which is preferable from the viewpoint of fogging. The mixture is then divided into two, one fine powder side and one coarse powder side. For example, this can be done using an inertial classification system called Elbow Jet (manufactured by Nittetsu Mining Co., Ltd.). The desired amount of silica fine particles A is then added to the surface of each of the two heat-treated toner particles to obtain the toner. Examples of methods for adding silica fine particles include a double cone mixer, V-type mixer, drum mixer, super mixer, Henschel mixer, Nauta mixer, Mechano Hybrid (manufactured by Nippon Coke & Engineering Co., Ltd.), and Nobilta (manufactured by Hosokawa Micron Corporation) and other mixing devices used as external additives, and the mixture is stirred and mixed. If necessary, external additives other than silica fine particles, such as a fluidizing agent, can also be added. [Example]

[0107] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Parts used in the examples are by weight unless otherwise specified.

[0108] <Magnetic core 1 manufacturing example> Magnetite 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 1000 (V / cm) 3.3 x 10 6 (Ω·cm) and a silane coupling agent (3-(2-aminoethylaminopropyl)trimethoxysilane) (3.0 mass% of the mass of the magnetite microparticles) were introduced into the vessel. Then, the mixture was mixed and stirred at high speed at a temperature of 100°C or higher in the vessel to surface treat the magnetite microparticles. Phenol 10.0 parts by mass Formaldehyde solution (37% formaldehyde aqueous solution) 16.0 parts by mass 84.0 parts by mass of the above surface-treated magnetite particles The above materials were introduced into a reactor and mixed thoroughly at a temperature of 40°C. The mixture was then heated to 85°C at an average heating rate of 3°C / min while stirring, and 4 parts by mass of 28% ammonia water and 25 parts by mass of water were added to the reactor. The temperature was maintained at 85°C, and the mixture was polymerized and cured for 3 hours. The peripheral speed of the stirring blade was 1.8 m / sec. After the polymerization reaction, the mixture was cooled to 30°C and water was added. The supernatant was removed, and the resulting precipitate was washed with water and then air-dried. The air-dried product was dried under reduced pressure (5 hPa or less) at 60°C to obtain magnetic material-dispersed resin core particles. This is designated as Magnetic Core 1. The configuration of the obtained Magnetic Core 1 is summarized in Table 1.

[0109] <Production Example of Porous Magnetic Core Particle 1> Process 1 (weighing and mixing process) Fe2O361.7% by mass MnCO334.2% by mass Mg(OH)23.0% by mass SrCO31.1% by mass The ferrite raw material was weighed so that Thereafter, the mixture was ground and mixed for 2 hours in a dry ball mill using zirconia balls (φ10 mm). Process 2 (pre-firing process) After crushing and mixing, the mixture was fired in air at 950°C for 2 hours in a burner-type firing furnace to produce calcined ferrite. The composition of the ferrite was as follows: (MnO)a(MgO)b(SrO)c(Fe2O3)d In the above formula, a=0.40, b=0.07, c=0.01, d=0.52 Process 3 (crushing process) After crushing to about 0.5 mm using a crusher, 30 parts by mass of water was added to 100 parts by mass of the calcined ferrite and crushed in a wet ball mill using zirconia balls (φ1.0 mm) for 2 hours. After separating the balls, the mixture was crushed in a wet bead mill using zirconia beads (φ1.0 mm) for 3 hours to obtain a ferrite slurry. Process 4 (granulation process) To the ferrite slurry, 2.0 parts by mass of polyvinyl alcohol was added as a binder per 100 parts by mass of the calcined ferrite, and the mixture was granulated into 40 μm spherical particles using a spray dryer (manufacturer: Okawahara Kakoki). Step 5 (baking process) In order to control the firing atmosphere, firing was carried out in an electric furnace under a nitrogen atmosphere (oxygen concentration 1.0% by volume) at 1150°C for 4 hours. Process 6 (sorting process) The aggregated particles were broken down and then sieved through a sieve with 250 μm openings to remove coarse particles, thereby obtaining porous magnetic core particles 1.

[0110] <Magnetic core 2 manufacturing example> Process 7 (resin filling process) Porous magnetic core particles 1 72.0 parts by mass Epoxy resin (Dainippon Ink Co., Ltd., Epiclon 1050) 17.0 parts by mass Hardener (Dainippon Ink Co., Ltd., Epicron Hardener B1019) 1.0 parts by mass The above materials were placed in a mixing vessel of a mixer (Dalton Corporation, Model NDMV universal mixer) and stirred for 2 hours under a nitrogen atmosphere at 60°C while reducing the pressure to 2.3 kPa. The temperature was then raised to 100°C, the solvent was removed under reduced pressure, and the above materials were filled into the particles of magnetic core 1. After cooling, the resulting resin-filled particles were transferred to a mixer (Sugiyama Heavy Industries, Model UD-AT drum mixer) equipped with a spiral blade in a rotatable mixing vessel and heated to 350°C at a rate of 2°C / min under a nitrogen atmosphere and atmospheric pressure. The resin was heated and stirred at this temperature for 60 minutes to harden. After heat treatment, low-magnetic-force particles were separated by magnetic separation and classified using a 150 μm sieve to obtain magnetic core 2. The composition of the resulting magnetic core 2 is shown in Table 1.

[0111] <Magnetic core 3 manufacturing example> Process 1 (weighing and mixing process) Fe2O361.7% by mass MnCO334.2% by mass Mg(OH)23.0% by mass SrCO31.1% by mass The ferrite raw material was weighed so that Thereafter, the mixture was ground and mixed for 2 hours in a dry ball mill using zirconia balls (φ10 mm). Process 2 (pre-firing process) After crushing and mixing, the mixture was fired in air at 1000°C for 2 hours in a burner-type firing furnace to produce calcined ferrite. The composition of the ferrite was as follows: (MnO)a(MgO)b(SrO)c(Fe2O3)d In the above formula, a=0.40, b=0.07, c=0.01, d=0.52 Process 3 (crushing process) After crushing to about 0.5 mm using a crusher, 30 parts by mass of water was added to 100 parts by mass of the calcined ferrite using stainless steel balls (φ1.0 mm) and crushed for 2 hours in a wet ball mill. After separating the balls, the mixture was crushed for 3 hours in a wet bead mill using stainless steel balls (φ1.0 mm) to obtain a ferrite slurry. Process 4 (granulation process) To the ferrite slurry, 2.0 parts by mass of polyvinyl alcohol was added as a binder per 100 parts by mass of the calcined ferrite, and the mixture was granulated into 45 μm spherical particles using a spray dryer (manufacturer: Okawahara Kakoki). Step 5 (baking process) In order to control the firing atmosphere, firing was carried out in an electric furnace under a nitrogen atmosphere (oxygen concentration 0.6% by volume) at 1200°C for 6 hours. Process 6 (sorting process) After the aggregated particles were crushed, the particles were sieved through a sieve with 250 μm openings to remove coarse particles, thereby obtaining ferrite core particles, which are designated as magnetic core 3. The configuration of the obtained magnetic core 3 is shown in Table 1.

[0112] [Table 1]

[0113] <Method for producing graft resin A1 and graft resins A2 to A19> Unit Y shown below 1 equivalent to Mo95.2% by mass of monomer and unit Y 2 and 4.8% by mass of a monomer corresponding to the above were added to a four-neck flask equipped with a reflux condenser, a thermometer, a nitrogen inlet tube, and a rotary stirrer. The structures of units Y1 and Y2 are shown in Table 2. 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. The resulting mixture was maintained at 70°C for 10 hours under a nitrogen stream. After the polymerization reaction was completed, washing was repeated to obtain a resin A1 solution (solid content 35% by mass). The s(l+m) value of this solution calculated by gel permeation chromatography (GPC) was 70.

[0114] Graft resins A2 to A20 were produced in the same manner as graft resin A1, except that the monomers were changed to have the compositions shown in Table 2.

[0115] [Table 2]

[0116] <Method for producing graft resin B1 and graft resins B2 to B20> The macromonomer (corresponding to unit Y4) used in the graft resin B1 can be synthesized, for example, by the following method. The raw materials shown below were added to a four-neck flask equipped with a reflux condenser, thermometer, nitrogen inlet, and ground-floor stirrer. Methacrylic acid chloride 1.7% by mass Polymethyl methacrylate with terminal hydroxyl groups (Mw: approximately 5000) 98.3% by mass Further, 100 parts by mass of THF and 1.0 part by mass of 4-tert-butylcatechol were added, and the mixture was heated under reflux for 5 hours under a nitrogen stream. After the reaction was completed, the mixture was washed with sodium hydrogen carbonate to obtain a macromonomer solution. The monomers shown below and the macromonomer were added to a four-neck flask equipped with a reflux condenser, a thermometer, a nitrogen inlet tube, and a rotary stirrer. Cyclohexyl methacrylate (corresponding to unit Y3) 75.5% by mass Methyl methacrylate (corresponding to unit Y5) 0.5% by mass Methacrylic acid macromonomer (corresponding to unit Y4) 24.0% by mass 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. The resulting mixture was maintained at 70°C for 10 hours under a nitrogen stream. After the polymerization reaction was completed, the mixture was repeatedly washed to obtain a resin B1 solution (solid content 35% by mass). The weight average molecular weight of this solution measured by gel permeation chromatography (GPC) was 57,000. The composition is shown in Table 3.

[0117] Graft resins B2 to B20 were produced in the same manner as graft resin B1, except that the monomers were changed so as to have the compositions shown in Table 3.

[0118] [Table 3]

[0119] <Production Examples of Magnetic Carriers 1 and 2 to 27> Magnetic core 1 100.0 parts by mass Graft resin A1 (toluene solution with a solid content of 50% by mass) 0.2 parts by mass Graft resin B1 (toluene solution with a solid content of 50% by mass) 3.8 parts by mass The above materials were charged into a planetary mixer (Nauta Mixer VN type manufactured by Hosokawa Micron Corporation) and stirred at 60°C under a reduced pressure of 1.5 kPa. The graft resins A1 and B1 were added in amounts of 1 / 3, and the solvent was removed for 20 minutes and the coating operation was repeated three times. The magnetic carrier coated with the coating resin composition was then transferred to a mixer (Sugiyama Heavy Industries Co., Ltd., Model UD-AT drum mixer) equipped with spiral blades and placed in a rotatable mixing container. The mixing container was stirred at 10 revolutions per minute, and heat-treated at 120°C for 2 hours in a nitrogen atmosphere. The resulting magnetic carrier 1 was separated by magnetic separation to separate out low-magnetic-force particles, which were then passed through a sieve with 150 μm openings and then classified using an air classifier. Magnetic carrier 1 with a volume-based 50% diameter (D50) of 39.1 μm was obtained. The composition of the obtained magnetic carrier 1 is shown in Table 4.

[0120] Magnetic Carriers 2 to 27 were produced in the same manner as Magnetic Carrier 1, except that the composition was changed to that shown in Table 4.

[0121] [Table 4]

[0122] <Toner 1 manufacturing example> 100 parts binder resin (Polyester with Tg: 57°C, acid value: 12 mg KOH / g, hydroxyl value: 15 mg KOH / g) CI Pigment Blue 15:3 5.5 parts 0.2 parts of 3,5-di-t-butylsalicylic acid aluminum compound Normal paraffin wax (melting point: 90°C) 6 parts The above materials were mixed using a Henschel mixer (FM-75, manufactured by Mitsui Mining Co., Ltd.) at a rotation speed of 1500 rpm for 5 minutes, and then kneaded in a twin-screw kneader (PCM-30, manufactured by Ikegai Corporation) set at a temperature of 130°C. The resulting kneaded mixture was cooled and coarsely pulverized to 1 mm or less using a hammer mill to obtain a coarsely pulverized product. The coarsely pulverized product was then finely pulverized using a mechanical pulverizer (T-250, manufactured by Turbo Kogyo Co., Ltd.). Further, classification was performed using a Faculty (F-300, manufactured by Hosokawa Micron Corporation) to obtain toner base particles 1. The operating conditions were a classifying rotor rotation speed of 11000 rpm and a dispersing rotor rotation speed of 7200 rpm. Toner base particles 1 100.0 parts Silica particles surface-treated with 4 wt% hexamethyldisilazane (BET specific surface area 24 m 2 / g) 2.0 copies The raw materials shown in the above recipe were mixed using a Henschel mixer (FM-10C, manufactured by Mitsui Mining Co., Ltd.) at a rotation speed of 1900 rpm for a rotation time of 3 minutes, and then heat-treated using the surface treatment device shown in Figure 1 to obtain heat-treated toner particles 1. The operating conditions were feed rate = 5 kg / hr, hot air temperature C = 160°C, and hot air flow rate = 6 m 3 / min, cold air temperature E=-5℃, cold air flow rate=4m 3 / min, Blower air volume = 20m 3 / min, injection air flow rate = 1m 3 / min.

[0123] The obtained particles were classified using a rotary classifier (product name: TTSP100, manufactured by Hosokawa Micron Corporation) to remove fine powder and coarse powder. Cyan toner particles 1 were obtained, having a weight average particle size of 6.0 μm, a proportion of particles with a particle size of 4.0 μm or less being 27.8% by number, and a proportion of particles with a particle size of 10.0 μm or more being 2.2% by volume. Cyan toner particles 1 100.0 parts Silica particles (BET specific surface area 100m) surface-treated with 10% by mass of polydimethylsiloxane 2 / g) 0.6 parts The above materials were mixed in a Henschel mixer (FM-75 model, manufactured by Mitsui Miike Chemical Engineering Co., Ltd.) at a rotation speed of 1900 rpm for a rotation time of 3 minutes to obtain Toner 1.

[0124] Example 1 9 parts by mass of toner 1 was added to 91 parts by mass of magnetic carrier 1, and the mixture was shaken in a shaker (YS-8D model, manufactured by Yayoi Co., Ltd.) to prepare 300 g of a two-component developer. The vibration conditions of the shaker were 150 rpm and 2 minutes. Separately, 90 parts by mass of toner 1 was added to 10 parts by mass of magnetic carrier 1, and mixed for 5 minutes in a V-type mixer in an environment of room temperature and humidity 23° C. / 50% RH to obtain a replenishment developer. The following evaluations were carried out using this two-component developer and the replenishment developer. The image forming apparatus used was a modified Canon imageRUNNER ADVANCE C5560 color copying machine. A two-component developer was placed in each color developing device, and a replenishment developer container containing a replenishment developer for each color was set, and an image was formed, and various evaluations were made before and after the durability test. For durability testing, a FFH output chart with an image ratio of 40% was used in a printing environment of 30°C temperature and 80% RH. FFH is a value that represents 256 gradations in hexadecimal, with 00h being the first gradation (white background) of the 256 gradations and FFH being the 256th gradation (solid area).

[0125] The number of images output was changed depending on each evaluation item. conditions: Paper: Laser beam printer paper CS-814 (81.4 g / m 2 ) (Sold by Canon Marketing Japan Inc.) was used. Image formation speed: Modified to be able to output A4 size, full color at 80 sheets / min. Development conditions: The development contrast was adjusted to any value, and the automatic correction by the main unit was disabled. The peak-to-peak voltage (Vpp) of the alternating electric field was adjusted to a frequency of 2.0 kHz, from 0.7 kV to 1.8 kV in 0.1 kV increments. Each color was modified so that a monochrome image could be output.

[0126] The evaluation items are shown below. The cyan developer was modified so that it could develop in a single color only.

[0127] The evaluation items are shown below. (Evaluation 1) Image density After initial durability and durability image output evaluation (A4 landscape, 40% print ratio, 50,000 sheets) under a high temperature and humidity environment (30°C, 80% RH), a solid image (FFH) was output. Density was measured using a densitometer X-Rite 404A (manufactured by X-Rite), and the average value of six points was taken as the image density. The difference in image density between the initial durability and the durability image output was judged according to the following criteria. When the evaluation was A to C, it was determined that the effects of the present invention were obtained. A: The difference in concentration is less than 0.10 B: The difference in density is 0.10 or more and less than 0.15 C: The difference in density is 0.15 or more and less than 0.20 D: The difference in density is 0.20 or more and less than 0.25 E: The difference in density is 0.25 or more and less than 0.30

[0128] (Rating 2) Overlay After initial durability and durability image output evaluation (A4 landscape, 40% print ratio, 50,000 sheets) were performed in a high temperature and high humidity environment (30°C, 80% RH), an A4 full-page solid white image was output. Fog was measured by measuring the whiteness of the white background with a reflectometer (Tokyo Denshoku Co., Ltd.), and the fog density (%) was calculated from the difference in whiteness before and after transfer and evaluated according to the following criteria. When the evaluation was A to C, it was determined that the effects of the present invention were achieved. A: Less than 1.0% B: 1.0% or more and less than 1.5% C: 1.5% or more and less than 2.0% D: 2.0% or more and less than 2.5% E: 2.5% or more and less than 3.0%

[0129] (Evaluation 3) Halftone developability After initial durability and durability image output evaluations (A4 landscape, 40% print ratio, 50,000 sheets) were conducted under a high-temperature, high-humidity environment (30°C, 80% RH), a halftone image (30H) was printed on one A4 sheet, and the area of ​​1,000 dots was measured using a digital microscope VHX-500 (lens wide-range zoom lens VH-Z100, Keyence Corporation). The number average dot area (S) and standard deviation of dot area (σ) were calculated, and the dot reproducibility index was calculated using the following formula. The roughness of the halftone image was then evaluated using the dot reproducibility index (I). Dot reproducibility index (I) = σ / S × 100 The roughness was evaluated according to the following criteria: When the evaluation was A to C, it was determined that the effects of the present invention were obtained. A:I is less than 4.0 B: I is 4.0 or more and less than 5.0 C:I is 5.0 or more and less than 6.0 D:I is 7.0 or more and less than 8.0 E:I is 8.0 or more and less than 9.0

[0130] (Rating 4) Toner scattering After initial durability and durability image output evaluation (A4 landscape, 40% print ratio, 50,000 sheets) were performed in a high temperature and high humidity environment (30°C, 80% RH), the developing unit was removed from the main body, and the toner scattering status inside and outside the developing unit and the main body was visually inspected and evaluated according to the following criteria: When the evaluation was A to D, it was determined that the effects of the present invention were achieved. A: No toner scattering B: Very slight toner scattering C: Slight toner scattering D: Slight toner scattering E: Significant toner scattering The evaluation results of Example 1 are shown in Table 5.

[0131] <Examples 1 to 21 and Comparative Examples 1 to 5> Evaluation was carried out in the same manner as in Example 1, except that magnetic carriers 2 to 21 were used as in Example 1. The evaluation results are shown in Table 5.

[0132] [Table 5] [Explanation of symbols]

[0133] 1 Electrostatic latent image carrier 2 Charger 3 Exposure device 4 Developer 5 Developer container 6 Developer carrier 7. Magnet 8 Regulatory Members 11 Transfer charger 12 Recording Media 13 Fixing unit

Claims

1. A magnetic carrier having a magnetic core and a coating resin that coats the surface of the magnetic core, The coating resin contains a graft resin A, The graft resin A has a unit Y1 represented by formula (1) and a unit Y2 represented by formula (2), When the mass of the graft resin A is X, the mass of the unit Y1 represented by formula (1) contained in the graft resin A is a, and the mass of the unit Y2 represented by formula (2) contained in the graft resin A is b, a, b, and X satisfy the following formula: 0.90≦(a+b) / X≦1.00 1.00≦a / b≦30.0 Fulfilling The magnetic carrier is characterized in that, when the SP value of the trunk of the graft resin A is SPa, the SP value of the siloxane unit is SPb, and the SP value of the surface of the magnetic core is SPc, the formulas (3) to (5) are satisfied. Formula (3) 22.0<Spc≦24.0 (J / cm ３ ) Formula (4) |Spa-SPc|≦3.0 (J / cm ３ ) Formula (5) 5.0 < |SPb-SPc| (J / cm ３ ) [The SP value is calculated by the following formula. Formula: SP value = √(Ev / v) = √(ΣΔei / ΣΔvi) In the formula, Ev: evaporation energy (cal / mol), v: molar volume (cm ３ / mol), Δei: evaporation energy of each atom or atomic group, Δvi: molar volume of each atom or atomic group)] 【Chemical 1】 【Chemistry 2】 [In formula (1) or formula (2), R １ is H or CH ３ represents R ２ represents a hydrocarbon group having 1 to 6 carbon atoms which may have a substituent, and the substituent is a hydroxy group or a carboxy group, R ３ is H or CH ３ represents R ４ is H or CH ３ represents R ５ represents a single bond or a hydrocarbon group having 1 to 6 carbon atoms, R ６ represents a hydrocarbon group having 1 to 10 carbon atoms, R ７ is H, CH ３ or Si(CH ３ ) ３ represents l and m are integers of 1 or more, and n is an integer of 2 or more and 150 or less.

2. 2. The magnetic carrier according to claim 1, wherein the formula (6) is satisfied when the Si atomic % of the magnetic carrier measured by X-ray photoelectron spectroscopy (XPS) is taken as Si0. Formula (6) 1.0≦Si0≦15.0

3. 3. The magnetic carrier according to claim 1, wherein n in formula (2) is 5 or more and 60 or less.

4. 4. The magnetic carrier according to claim 1, wherein the graft resin A satisfies formula (10) when the total number of units Y1 and Y2 is s. Formula (10) 50≦s≦250

5. 5. The magnetic carrier according to claim 1, wherein the magnetic core is either a magnetic material dispersed resin core material or a resin-filled ferrite core material.

6. 6. The magnetic carrier according to claim 5, wherein the binder resin of the magnetic material dispersed resin core material and the filler resin of the resin-filled ferrite core material contain any one of phenol resin, epoxy resin, and acrylic resin.

7. The coating resin contains a graft resin B, the content of graft resin A relative to the coating resin is 1.0% by mass or more and 50.0% by mass or less, and the content of graft resin B relative to the coating resin is 50.0% by mass or more and 99.0% by mass or less, 7. The magnetic carrier according to claim 1, wherein the graft resin B has a polysiloxane content of 0.1% by mass or less.

8. The magnetic carrier according to any one of claims 1 to 7, wherein the coating resin contains a graft resin A in an amount of 1.0% by mass or more and 20.0% by mass or less, and a resin B in an amount of 80.0% by mass or more and 99.0% by mass or less.

9. 9. The magnetic carrier according to claim 8, wherein the graft resin B contains 75.0% by mass or more of the unit Y3 represented by formula (7). 【Chemistry 3】 [In formula (7), R ８ is CH ３、 R ９ represents a cyclohexyl group, a cycloheptyl group, a cyclooctyl group, a cyclopentyl group, a cyclobutyl group, or a cyclopropyl group.

10. 10. The magnetic carrier according to claim 7, wherein the graft resin B contains 1.0% by mass or more and 25.0% by mass or less of the unit Y4 represented by formula (8). 【Chemistry 4】 [In formula (8), R １０ is H or CH ３ , R １１ indicates the polymer moiety.

11. The R １１ 11. The magnetic carrier according to claim 10, wherein the polymer portion has a unit Y5 represented by formula (9), and the weight average molecular weight (Mw) of the polymer portion is 3,000 or more and 8,000 or less. 【Chemistry 5】 [In formula (9), R １２ is H or CH ３ , R １３ represents any hydrocarbon group having 1 to 6 carbon atoms.

12. In a two-component developer containing a magnetic carrier and a toner, A two-component developer, wherein the magnetic carrier is the magnetic carrier according to any one of claims 1 to 11.

13. A replenishment developer to be replenished to a developing device in response to a decrease in toner concentration of a two-component developer in the developing device, A replenishment developer which is the two-component developer according to claim 12.

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