JP7793364B2 - Magnetic carrier, two-component developer, and replenishment developer - Google Patents

Description

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.

Traditionally, electrophotographic image formation methods 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 it. In this development process, carrier particles known as magnetic carrier impart an appropriate amount of positive or negative charge to the toner through frictional charging when mixed with the toner. A two-component development method is widely used, in which this charge is used as the driving force for development.

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 unit. Furthermore, magnetic carriers often have a core coated with a resin that can impart a charge to the toner.

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.

Generally, when toner components adhere to a magnetic carrier, the number of charging sites on the magnetic carrier decreases, reducing its ability to impart charge. This is known to cause problems such as changes in image density. One example of a method for improving resistance to the adhesion of the aforementioned toner components (hereinafter referred to as contamination resistance) is to use a material with low surface free energy, such as a silicone resin, as a coating resin (Patent Document 1). Generally, materials with low surface free energy can inhibit the adhesion of toner components and the like.

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.
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 as with the above-mentioned silicone resin, the abrasion resistance becomes insufficient (Patent Document 3).

Japanese Patent Application Laid-Open No. 2002-91093 JP 2015-138230 A JP 2013-3428 A

Therefore, in order for the magnetic carrier to maintain stable charge-imparting ability during long-term use, it is believed that it is necessary to achieve both contamination resistance to prevent adhesion of toner components and wear resistance to prevent wear of the coating.
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.

After extensive research, the inventors have discovered that by using a combination of graft resin A and graft resin B, which have the structures shown below, the contamination resistance and abrasion resistance of the magnetic carrier can be achieved at the same time, and stable charge-imparting performance can be maintained even during long-term use.

Graft resin A has a structure in which a structure similar to that of the silicone resin is grafted to the main chain. Graft resin B has a structure as a branch 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 abrasion resistance of the magnetic carrier was insufficient.

However, when the coating resin of the magnetic carrier contains graft resin A and graft resin B, the molecular structure is oriented so as to be energetically stabilized. Specifically, the siloxane structure of graft resin A is oriented on the surface of the magnetic carrier. As a result, the surface free energy of the magnetic carrier decreases, and the contamination resistance improves.
Furthermore, the affinity between the main chain of graft resin A and the branches of graft resin B improves the abrasion resistance.

Therefore, by using graft resin A and graft resin B, which have the structures shown below, in combination, the magnetic carrier can achieve both contamination resistance and abrasion resistance, and maintain stable charge-imparting ability even during long-term use. As a result, it is possible to provide a magnetic carrier that achieves reduced fogging, reduced toner scattering, stable image density, and developability, even during long-term use.

That is, the magnetic 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 and a graft resin B,
The coating resin is
(i) The graft resin A is contained in an amount of 1% by mass or more and 50% by mass or less,
(ii) The graft resin B is contained in an amount of 50% by mass or more and 99% by mass or less, and the graft resin A has a unit Y1 represented by the following formula (1) and a unit Y2 represented by the following formula (2),
When the mass of the graft resin A is X, the mass of the unit Y1 represented by the formula (1) contained in the graft resin A is a, and the mass of the unit Y2 represented by the formula (2) contained in the graft resin A is b, a, b, and X are
0.90≦(a+b)/X≦1.00
1.00≦a/b≦30.0
Fulfilling
The graft resin B is
(i) a comb polymer having, as a branch, at least one 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) does not have a polysiloxane structural moiety, or the content of the polysiloxane structural moiety is 0.1 mass% or less;
A magnetic carrier characterized by:
[In formula (1) or formula (2),
_R1 represents H or _CH3 ;
_R2 represents a hydrocarbon group having from 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.

The present invention provides a magnetic carrier that reduces fogging, reduces toner scattering, and achieves stable image density and developability even with long-term use.

1 is a schematic view of a surface treatment device for a toner used in a two-component developer according to the present invention. 1 is a schematic diagram of an image forming apparatus in which a magnetic carrier according to the present invention is used. 1 is a schematic diagram of an image forming apparatus in which a magnetic carrier according to the present invention is used.

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 endpoints, that is, the lower and upper limits.

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 and a graft resin B,
The coating resin is
(i) The graft resin A is contained in an amount of 1% by mass or more and 50% by mass or less,
(ii) The graft resin B is contained in an amount of 50% by mass or more and 99% by mass or less,
The graft resin A has a unit Y1 represented by the following formula (1) and a unit Y2 represented by the following formula (2),
When the mass of the graft resin A is X, the mass of the unit Y1 represented by the formula (1) contained in the graft resin A is a, and the mass of the unit Y2 represented by the formula (2) contained in the graft resin A is b, a, b, and X are
0.90≦(a+b)/X≦1.00
1.00≦a/b≦30.0
Fulfilling
The graft resin B is
(i) a comb polymer having, as a branch, at least one 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) A magnetic carrier that does not have a polysiloxane structural portion, or the content of the polysiloxane structural portion is 0.1% by mass or less.
[In formula (1) or formula (2),
_R1 represents H or _CH3 ;
_R2 represents a hydrocarbon group having from 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, a hydrocarbon group having 1 to 6 carbon atoms, or an aromatic group;
_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.

As mentioned above, if only a resin with low surface free energy, such as a silicone resin, is used as the coating resin for the magnetic carrier, the abrasion resistance of the magnetic carrier may decrease.

Graft resin A has a structure in which a structure similar to that of the silicone resin is grafted to the main chain. Graft resin B has a structure as a branch 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 abrasion resistance of the magnetic carrier was insufficient.

However, when the coating resin of the magnetic carrier contains graft resin A and graft resin B, the molecules constituting graft resin A and graft resin B in the coating resin are oriented so as to be energetically stabilized. Specifically, the siloxane structure of graft resin A is oriented on the surface of the magnetic carrier. As a result, the surface free energy of the magnetic carrier is reduced, and the contamination resistance is improved.
Furthermore, the affinity between the main chain of graft resin A and the branches of graft resin B improves the abrasion resistance.
Therefore, by using graft resin A and graft resin B having the following structure in combination, the contamination resistance and abrasion resistance of the magnetic carrier can be achieved at the same time, and stable charge-imparting ability can be maintained even during long-term use.

The graft resin A has a unit Y1 represented by the above formula (1) and a unit Y2 represented by the above 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 having from 1 to 6 carbon atoms which may have a substituent, the substituent being a hydroxy group or a carboxy group. Specific examples of the introduction method include 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, and cyclopentyl methacrylate.
In formula (2), _R3 represents H or _CH3 , _R4 represents H or _CH3 , _R5 represents a single bond or a hydrocarbon group having from 1 to 6 carbon atoms, _R6 represents a hydrocarbon group having from 1 to 10 carbon atoms, _{and R7} represents H, _CH3 , or Si( _CH3 ) ₃ . _R5 is preferably an alkylene group having from 1 to 6 carbon atoms. 1 and m represent integers of 1 or more, and n represents an integer of 2 to 150. The graft resin A may contain a plurality of units Y2. A specific method for introducing the units Y2 is, for example, to copolymerize an acrylic acid ester or methacrylic acid ester in which a silicone structure has been esterified when polymerizing the resin A.

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 are
0.90≦(a+b)/X≦1.00
1.00≦a/b≦30.0
Meet the following.

The above relational expression indicates that in the graft resin A, the units Y1 and Y2 account for 90% by mass or more of all units, and that the mass of unit Y1 is the same as that of unit Y2, multiplied by 30.

If (a+b)/X is less than 0.90, compatibility with the graft resin B may decrease, resulting in reduced abrasion resistance, or the surface free energy may decrease, resulting in reduced stain resistance.

Furthermore, when a/b is less than 1.00, the proportion of unit Y2 is large, which can result in insufficient resin strength due to low intermolecular forces resulting from low surface free energy, potentially reducing abrasion resistance. When a/b is greater than 30.0, the proportion of unit Y2 is small, which reduces surface free energy and reduces stain resistance.

The proportion of graft resin A contained in the coating resin must be 1.0% by mass or more and 50.0% by mass or less. If it is less than 1.0% by mass, the surface free energy will be high, resulting in reduced contamination resistance. If it is more than 50.0% by mass, the reduced intermolecular forces due to low surface free energy will dominate over the abrasion resistance obtained through interaction with graft resin B, resulting in insufficient abrasion resistance. A more preferred range is 1.0% by mass or more and 30.0% by mass or less. Even more preferred is 3.0% by mass or more and 20.0% by mass or less.

The proportion of graft resin B contained in the coating resin must be 50.0% by mass or more and 99.0% by mass or less. If it is less than 50.0% by mass, the resin strength will be insufficient due to the low intermolecular forces caused by the low surface free energy, resulting in reduced abrasion resistance. If it is more than 99.0% by mass, the low surface free energy component will be too small, resulting in reduced contamination resistance. A more preferred range is 70.0% by mass or more and 99.0% by mass or less. Even more preferred is 80% by mass or more and 97.0% by mass or less.

In the graft resin A, n is the number of siloxane structural units in the unit Y2 and indicates the length of the siloxane structure of Y2. n is an integer of 2 or more and 150 or less. If n is less than 1, the surface free energy of the magnetic carrier surface increases, which may result in reduced contamination resistance. If n is more than 150, the interaction between the graft resin A and the graft resin B decreases, which results in reduced abrasion resistance. If n is 5 or more and 60 or less, this is more preferred because it improves abrasion resistance and contamination resistance. The graft resin A may have a plurality of Y2 units.
The magnetic carrier of the present invention is preferably used when the following formula is satisfied, where Si atomic % as measured by X-ray photoelectron spectroscopy (XPS) is taken as Si0.
1.0≦Si0≦15.0
When the SiO content is 1.0 atomic % or more, the surface free energy of the magnetic carrier becomes low, further improving contamination resistance.When the SiO content is 15.0 atomic % or less, the intermolecular force between resin molecules on the magnetic carrier surface becomes strong, further improving wear resistance.

The graft resin A preferably satisfies the following formula, where s is the total number of units Y1 and Y2.
50≦s≦250
When s is 50 or more, the molecular weight is sufficient to maintain the resin strength, and the interaction between graft resin A and graft resin B is enhanced, further improving the abrasion resistance and stain resistance.

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. Furthermore, by having a hydroxyl value, the effect of hydrogen bonding is also exerted, which is preferable because it further improves wear resistance.
The acid value of the graft resin A is preferably 0 mgKOH/g or more and 90.0 mgKOH/g or less, more preferably 30.0 mgKOH/g or more and 80.0 mgKOH/g or less, and even more preferably 40.0 mgKOH/g or more and 70.0 mgKOH/g or less. If the acid value of the graft resin A is 90.0 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.

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

Graft resin B preferably contains an alicyclic hydrocarbon group, which makes the magnetic carrier surface (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. Unit Y3 may contain only one type of structure, or two or more types.

The graft resin B preferably contains 1.0% by mass or more and 25.0% by mass or less of units Y4 represented by the following formula (4).
[In formula (4), R ₁₀ represents H or CH ₃ , and R ₁₁ represents a polymer moiety.]

When the graft resin B contains a polymer moiety as _R11 , the adhesion between the resin coating layer and the magnetic carrier core is improved. As a result, the abrasion resistance and the ability of the magnetic carrier to impart charge to the toner are improved. The unit Y4 may contain only one type of structure, or two or more types.

When the graft resin B has a polymer moiety as R ₁₁ , it preferably has a unit Y 5 represented by formula (5).
[In formula (5), R ₁₂ represents H or CH ₃ , and R ₁₃ represents a hydrocarbon group having 1 to 6 carbon atoms.]

The polymer portion in _R11 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 above polymer has affinity with the main chain of graft resin A, improving abrasion resistance. Furthermore, the siloxane structure of graft resin A is effectively oriented on the surface of the magnetic carrier. As a result, the surface free energy of the magnetic 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.

When synthesizing graft resin B, by using a macromonomer having the above-described polymer moiety, it is possible to introduce the unit represented by formula (4) 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, when the total amount of all monomers used in synthesizing graft resin B for coating is taken as 100 parts by mass.
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 the graft resin B is preferably 0 mgKOH/g or more and 3.0 mgKOH/g or less, more preferably 0 mgKOH/g or more and 2.8 mgKOH/g or less, and even more preferably 0 mgKOH/g or more and 2.5 mgKOH/g or less. When the acid value of the graft resin B is 3.0 mgKOH/g or less, self-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 the 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 the graft resin B for coating and adjusting the amount of monomer added. However, since a low acid value of the 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) to generate carboxy groups.

When the SP value of the trunk of the 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, it is preferable that the following relational expression be satisfied.
When 22.0<SPc≦24.0 (J/cm ³ ) ^1/2 ,
|SPa-SPc|≦3.0 (J/ ^cm3 ) ^1/2
5.0<|SPb-SPc| (J/ ^cm3 ) ^1/2
Or,
When 18.0<SPc≦21.0 (J/cm ³ ) ^1/2 ,
|SPa-SPc|≦2.5 (J/ ^cm3 ) ^1/2
4.0<|SPb-SPc| (J/ ^cm3 ) ^1/2

Satisfying the above relational expression 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 adheres to the magnetic core surface, and the graft resin A adheres closely to the magnetic core, improving wear resistance.
Furthermore, since the siloxane structure has a relatively lower affinity with the magnetic core than the trunk of the graft resin A, the molecular structure is oriented to be energetically stabilized. Specifically, the siloxane structure of the graft resin A is oriented on the surface of the magnetic carrier. As a result, the surface free energy of the magnetic carrier is reduced, improving the 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.

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 magnetic carrier. As a result, countercharge can be released after the toner is developed, and white spots can be suppressed. The content of conductive fine particles added to the coating resin is preferably 0.1 to 20 parts by weight per 100 parts by weight of the coating resin. If the amount is less than 0.1 part by weight, it is difficult to obtain the effect of adding the conductive fine particles, and if the amount is more than 20 parts by weight, 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.

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 preferably 0.1 parts by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the coating resin.

<Magnetic core manufacturing method>
The magnetic core of the present invention can be made of known magnetic particles such as magnetite particles, ferrite particles, magnetic material-dispersed resin particles, etc. Among these, magnetic particles obtained by filling the pores of porous magnetic particles with a resin or magnetic material-dispersed resin particles, i.e., magnetic particles containing a magnetic oxide and a resin composition, are preferred from the viewpoint of extending the life of the magnetic carrier, since they can reduce the specific gravity of the magnetic carrier.

Reducing the specific gravity of the magnetic carrier reduces the load on the toner in the developer state inside the developing unit, prevents the adhesion of toner components to the magnetic carrier surface, and reduces the load between magnetic carrier particles, further preventing peeling, chipping, and abrasion of the resin coating layer. It also improves dot reproducibility, making it possible to obtain high-resolution images.

The resin to be contained in the pores of porous magnetic particles can be the copolymer resin used as the coating resin, but is not limited to this and any known resin can be used. The thermoplastic resin is preferably the copolymer used as the coating resin, 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 resins such as polyethylene terephthalate, polybutylene terephthalate, and polyarylate, polyamide resin, polyacetal resin, polycarbonate resin, polyethersulfone resin, polysulfone resin, polyphenylene sulfide resin, and polyetherketone resin.

Examples of thermosetting resins include: phenolic resin, modified phenolic resin, maleic resin, alkyd resin, epoxy resin, acrylic resin, unsaturated polyester obtained by polycondensation of maleic anhydride, terephthalic acid, and polyhydric alcohol, urea resin, melamine resin, urea-melamine resin, xylene resin, toluene resin, guanamine resin, melamine-guanamine resin, acetoguanamine resin, glyptal resin, furan resin, silicone resin, polyimide, polyamide-imide resin, polyetherimide resin, and polyurethane resin.

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 the resin components. For organically 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 the resin component diluted with a solvent 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, and then the temperature is raised to the curing temperature of the resin used to initiate the curing reaction.

Specific methods for producing magnetic-material-dispersed resin particles include the following. For example, submicron magnetic materials such as iron powder, magnetite particles, or ferrite particles are kneaded into a thermoplastic resin to disperse them, then pulverized to the desired magnetic carrier particle size, and optionally subjected to thermal or mechanical spheronization. Magnetic-material-dispersed resin particles can also be produced by dispersing the magnetic material in a monomer and polymerizing the monomer to form a resin.

In this case, examples of resins 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% to 95% by weight of the magnetic carrier.

It is preferable for the magnetic core to have a 50% particle size (D50) based on volume of 20 μm or more and 80 μm or less in order to allow the coating resin to be uniformly coated, prevent carrier adhesion, and ensure an appropriate density of the developer magnetic brush to obtain high-quality images.

The specific resistance of the magnetic core is preferably 1.0×10 ⁵ Ω·cm or more and 1.0×10 ¹⁴ Ω·cm or less at an electric field strength of 1000 V/cm, since good developability can be obtained.

<Method for manufacturing magnetic carrier>
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 volatilizing the solvent, thereby coating the magnetic core surface with the coating resin. 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 carrier core with the coating resin in particle form. Specific examples include treatment methods using devices such as a Hybridizer (manufactured by Nara Machinery Works, Ltd.), a Mechanofusion (manufactured by Hosokawa Micron Corporation), a Hiflex Gral (manufactured by Fukae Powtec), and a Theta Composer (manufactured by Tokuju Kogyosho Co., Ltd.).

<Magnetic Carrier>
Next, the magnetic carrier will be described.
The magnetic carrier preferably has a magnetization strength of 40 ^Am2 /kg or more and 70 ^Am2 /kg or less under a magnetic field of 5000/4πkA/m. 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.

The residual magnetization of the magnetic carrier is preferably 20.0 ^Am2 /kg or less, and more preferably 10.0 ^Am2 /kg or less. When the residual magnetization of the magnetic carrier is within the above range, particularly good fluidity is obtained as a developer, and good dot reproducibility is obtained.

The magnetic carrier preferably has a true density of 2.5 g/cm or ^more and 5.5 g/cm ^{or less} , and more preferably 3.0 g/cm or ^more and 5.0 g/cm or ^less . A two-component developer containing a magnetic carrier having a true density in this range places less load on the toner, and adhesion of 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.

The magnetic carrier preferably has a volume-based 50% particle size (D50) of 21 μm or more and 81 μm or less from the perspective of its ability to impart charge to the toner, suppressing carrier adhesion to the image area, and achieving high image quality. A diameter of 25 μm or more and 60 μm is more preferable.

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 substitution products, 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.

Monomers used in the polyester unit of polyester resins include polyhydric alcohols (divalent, trivalent or higher alcohols), polycarboxylic acids (divalent, 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 amorphous resin molecule 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 trivalent or higher carboxylic acids, their acid anhydrides or lower alkyl esters, and/or trivalent or higher alcohols as raw material monomers for the polyester unit.

As the polyhydric alcohol monomer used in the polyester unit of the polyester resin, the following polyhydric alcohol monomers can be used.
Examples of 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 derivatives thereof;
(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);
(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.)

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. Of these, glycerol, trimethylolpropane, and pentaerythritol are preferred. These dihydric alcohols and trihydric or higher alcohols can be used alone or in combination.

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. Of these, 1,2,4-benzenetricarboxylic acid, i.e., trimellitic acid or its derivatives, is particularly preferred due to its low cost and ease of reaction control. These divalent carboxylic acids and trivalent or higher carboxylic acids can be used alone or in combination.

The method for producing the polyester unit of the present invention is not particularly limited, and known methods can be used. For example, the above-mentioned 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. When polymerizing the polyester unit, for example, a polymerization catalyst such as a titanium-based catalyst, a tin-based catalyst, zinc acetate, antimony trioxide, or germanium dioxide can be used. In particular, the binder resin of the present invention preferably contains a polyester unit polymerized using a tin-based catalyst.
Furthermore, 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 can reduce the amount of moisture adsorption in a high-temperature, high-humidity environment and keep the non-electrostatic adhesion force low.

The binder resin may also be a mixture of low molecular weight resin and high molecular weight resin. From the perspective of low temperature fixability and hot offset resistance, it is preferable that the content ratio of high molecular weight resin to low molecular weight resin is 40/60 or more and 85/15 or less by weight.

<Release Agent>
Examples of waxes that can be used in the toner of the present invention include the following: 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 alcohol, 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 alcohol, 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 bis saturated fatty acid bisamides such as stearic acid amide; unsaturated fatty acid amides such as ethylene bisoleic acid amide, hexamethylene bisoleic acid amide, N,N'-dioleyl adipamide, and N,N'-dioleyl sebacic acid amide; aromatic bisamides such as m-xylene bisstearic acid amide and N,N'-distearyl isophthalamide; aliphatic 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 a hydroxyl group obtained by hydrogenating vegetable oils and fats.

Of 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 properties. In the present invention, hydrocarbon waxes are more preferred from the viewpoint of further improving hot offset resistance.

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.

<Coloring Agent>
The toner particles of the present invention may contain a colorant. Examples of the colorant include the following.

Black colorants include carbon black, and those toned to black using yellow, magenta, and cyan colorants. While pigments may be used alone as colorants, using a combination of dyes and pigments to improve the clarity of full-color images is more preferable in terms of image quality.

Examples of pigments for magenta toner include the following: C.I. 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; C.I. C.I. Pigment Violet 19; C.I. Vat Red 1, 2, 10, 13, 15, 23, 29, 35.
Dyes for magenta toner include the following: solvent dyes such as C.I. Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 81, 82, 83, 84, 100, 109, and 121; C.I. Disperse Red 9; C.I. Solvent Violet 8, 13, 14, 21, and 27; and C.I. Disperse Violet 1; and basic dyes such as C.I. 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 C.I. Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27, and 28.

Examples of pigments for cyan toner include C.I. Pigment Blue 2, 3, 15:2, 15:3, 15:4, 16, and 17; C.I. Vat Blue 6; C.I. 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 C.I. Solvent Blue 70.

Yellow toner pigments include the following: C.I. 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; C.I. Vat Yellow 1, 3, 20.
Examples of yellow toner dyes include C.I. Solvent Yellow 162.

These colorants can be used alone or in combination, or in the form of a solid solution. The colorant is selected in consideration of hue angle, saturation, brightness, light resistance, transparency for overhead projectors (OHPs), and dispersibility in toner.
The content of the colorant is preferably 0.1 parts by mass or more and 30.0 parts by mass or less per 100 parts by mass of the total amount of the resin components.

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

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 parts by mass to 5.0 parts by mass, and more preferably 0.8 parts by mass to 4.0 parts by mass, relative to 100 parts by mass of toner particles. Among them, the content of silica particles having a maximum peak particle size of 80 nm to 200 nm based on the number distribution standard is 0.1 parts by mass to 2.5 parts by mass, and more preferably 0.5 parts by mass to 2.0 parts by mass, relative to 100 parts by mass of toner particles. Within this range, the effect as spacer particles becomes more pronounced.

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.
Furthermore, examples of silane coupling agents include the following: 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.

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.

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

The magnetic carrier of the present invention can also be used as a replenishment developer. In replenishment developers used to replenish a two-component developer in a developing device in response to a decrease in the toner concentration in the developer, the amount of toner is 2 to 50 parts by weight per 1 part by weight of the replenishment magnetic carrier.

Next, we will explain an example of an image forming apparatus equipped with a developing device that uses the magnetic carrier, two-component developer, and replenishment developer of the present invention, but the developing device used in the development method of the present invention is not limited to this.

<Image forming method>
In FIG. 2 , the electrostatic latent image carrier 1 rotates in the direction of the arrow. The electrostatic latent image carrier 1 is charged by a charger 2, which serves as a charging means. The surface of the charged electrostatic latent image carrier 1 is exposed to light by an exposure device 3, which serves as an electrostatic latent image forming means, to form an electrostatic latent image. The developing device 4 includes a developer container 5 containing a two-component developer. The developer carrier 6 is rotatably disposed, and the developer carrier 6 contains magnets 7, which serve as magnetic field generating means. At least one of the magnets 7 is positioned so as to face the latent image carrier. The two-component developer is held on the developer carrier 6 by the magnetic field of the magnets 7. The amount of the two-component developer is regulated by a regulating member 8, and the developer is transported to a developing section facing the electrostatic latent image carrier 1. In the developing section, the magnetic field generated by the magnets 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. The electrostatic latent image carrier 1, which has been cleaned by the cleaner 15, is then electrically initialized by light irradiation from a pre-exposure device 16, and the above image forming operation is repeated.

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 such as K, Y, C, and M and the arrows indicating their rotation directions are not limited to these. Incidentally, K represents black, Y represents yellow, C represents cyan, and M represents magenta. In FIG. 2, 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 provided in developing devices 4K, 4Y, 4C, and 4M, which serve as developing means. Residual toner on each electrostatic latent image carrier is removed by cleaners 15K, 15Y, 15C, and 15M, respectively. The image is then transferred to intermediate transfer body 9 by intermediate transfer chargers 10K, 10Y, 10C, and 10M, which serve as transfer means. Transfer charger 11 then transfers the image to recording medium 12, which is then fixed by heat and pressure using fixing device 13, which serves as fixing means, and output as an image. An intermediate transfer body cleaner 14, which cleans 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 alternating electric field in the development area, while developing with the magnetic brush in contact with the photosensitive drum. A distance (SD distance) between developer carrier (developing sleeve) 6 and the photosensitive drum of 100 μm or more and 1,000 μm or less is effective in preventing carrier adhesion and improving dot reproducibility. A distance less than 100 μm tends to result in insufficient developer supply, resulting in low image density. If it exceeds 1000 μm, the magnetic field lines from the magnetic pole S1 will spread, the density of the magnetic brush will decrease, dot reproducibility will deteriorate, and the force binding the magnetic coated carrier will weaken, making carrier adhesion more likely to occur.

The peak-to-peak voltage (Vpp) of the AC electric field is 300 V or higher and 3,000 V or lower, preferably 500 V or higher and 1,800 V or lower. The frequency is 500 Hz or higher and 10,000 Hz or lower, preferably 1,000 Hz or higher and 7,000 Hz or lower, and can be appropriately selected depending on the process. In this case, the waveform of the AC bias used to form the AC electric field can be a triangular wave, a rectangular 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 lower than 300 V, it is difficult to obtain sufficient image density, and fogging toner in non-image areas may not be effectively collected. Furthermore, if it exceeds 3,000 V, the latent image may be disturbed by the magnetic brush, resulting in a deterioration in image quality.

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

Furthermore, if the frequency is lower than 500 Hz, the process speed will be affected, but the configuration of the electrostatic latent image bearing photoreceptor may be the same as that of a photoreceptor normally 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 layer of the photoreceptor, for example, a charge injection layer or a protective layer may be used.

<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 = -4σ cos θ, where P is the pressure, D is the pore diameter, and θ and σ are the contact angle and surface tension of the mercury, respectively. 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 P-V curve is 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.

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 5 cm ³ , Indentation volume 1.1 cm ³ , Use: Powder Measurement range: 2.0 psia (13.8 kPa) to 59989.6 psia (413.7 MPa) Measurement steps: 80 steps
(When the pore diameter is calculated logarithmically, the steps are spaced at equal intervals.)
Pressurization parameters: Exhaust pressure 50 μmHg
Exhaust time: 5.0 min
Mercury injection pressure: 2.0 psia (13.8 kPa)
Equilibrium time 5secs
High pressure parameters Equilibration time 5 seconds
Mercury parameters Advancing contact angle 130.0 degrees
Receding contact angle 130.0 degrees
Surface tension 485.0mN/m (485.0dynes/cm)
Mercury density 13.5335g/mL

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, the pressure range is measured between 2.0 psia (13.8 kPa) and 45.8 psia (315.6 kPa).
(3) In the high-pressure section, the range measured was 45.9 psia (316.3 kPa) or more and 59,989.6 psia (413.6 MPa) or less.
(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 or more and 3.0 μm or less 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.

<Method for measuring weight average particle diameter (D4) and number average particle diameter (D1)>
The weight average particle diameter (D4) and number average particle diameter (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 using the narrow hole 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. Measurement was performed with an effective number of measurement channels of 25,000, 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 about 1 mass %, for example, "ISOTON II" (manufactured by Beckman Coulter).

Before carrying out the measurements and analysis, the dedicated software was set up as follows.
On 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 to the value obtained using "Standard Particles 10.0 μm" (manufactured by 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 the "Flush aperture tube after measurement" box.
In the "Pulse to particle size conversion setting screen" of the dedicated software, the bin interval is set to logarithmic particle size, the particle size bin is set to 256 particle size bins, and the particle size range is set to 2 μm to 60 μm.

The specific measurement method is as follows.
(1) Approximately 200 ml of the electrolyte solution is placed in a 250 ml round-bottom glass beaker designed specifically for the Multisizer 3, and the beaker is set on the sample stand. The stirrer rod is stirred counterclockwise at 24 revolutions per second. Then, the "aperture flush" function of the analysis software is used to remove any dirt or air bubbles from inside the aperture tube.
(2) Approximately 30 ml of the aqueous electrolyte solution is placed in a 100 ml flat-bottom glass beaker, and approximately 0.3 ml of a dilution of "Contaminon N" (a 10% aqueous solution of a pH 7 neutral detergent for cleaning precision measuring instruments, consisting of a nonionic surfactant, an anionic surfactant, and an organic builder, manufactured by Wako Pure Chemical Industries, Ltd.) diluted three times with ion-exchanged water is added as a dispersant.
(3) A predetermined amount of ion-exchanged water is placed in the water tank of an ultrasonic disperser "Ultrasonic Dispersion 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) The beaker (2) is set in the beaker fixing hole of the ultrasonic disperser, and the ultrasonic disperser is operated. Then, the height of the beaker is adjusted 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 being 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, the aqueous electrolyte solution (5) containing the dispersed toner is dropped into the round-bottom beaker (1) placed in the sample stand, and the measurement concentration is adjusted to about 5%. Then, measurement is continued until the number of particles measured reaches 50,000.
(7) The measurement data is analyzed using the dedicated software provided with the device to calculate the weight average particle diameter (D4) and number average particle diameter (D1). 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 diameter (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 diameter (D1).

<Calculation method for the amount of fine powder>
The amount of fine particles in the toner based on the number (% by number) is calculated as follows.
For example, to determine the percentage by number of particles of 4.0 μm or less in a toner, after performing measurements using the Multisizer 3 described above, (1) set the dedicated software to Graph/Number % and display the measurement results chart as a percentage by 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 by number of particles of 4.0 μm or less in the toner.

<How to calculate the amount of coarse powder>
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 measurements using the Multisizer 3 described above, (1) set the dedicated software to Graph/Volume% and display the measurement results chart as volume%. (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.

<Method for measuring molecular weight and molecular weight distribution of resins, etc.>
The molecular weight and molecular weight distribution of a resin or the like are measured by gel permeation chromatography (GPC) as follows.
First, a sample is dissolved in tetrahydrofuran (THF) at room temperature for 24 hours. The resulting solution is then filtered through a solvent-resistant membrane filter "Maesholidisc" (manufactured by Tosoh Corporation) with a pore size of 0.2 μm to obtain a sample solution. The sample solution is adjusted so that the concentration of components soluble in THF is approximately 0.8% by mass. This sample solution is used for measurements 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, and 807 (manufactured by Showa Denko K.K.)
Eluent: tetrahydrofuran (THF)
Flow rate: 1.0mL/min
Oven temperature: 40.0°C
Sample injection volume: 0.10 mL
In calculating the molecular weight of the sample, a molecular weight calibration curve prepared using standard polystyrene resins (trade names "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.

<Method for Measuring Si Atomic Concentration by XPS>
The magnetic carrier is attached to the indium foil, and the particles are attached evenly so that the indium foil is not exposed.
The measurement conditions are as follows.
Apparatus: PHI5000VERSAPROBE II (ULVAC-PHI, Inc.)
Irradiation radiation: Al Kα ray output: 25W 15kV
Pass Energy: 58.7eV
Step size: 0.125eV
XPS peaks: C1s, O1s, Si2p, Ti2p, Sr3d

<Resin structure (NMR)>
The structure of the resin (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.)
Measurement frequency: 400 MHz
Pulse condition: 5.0 μs
Frequency range: 10,500 Hz
Number of accumulations: 1024 Measurement solvent: DMSO-d6
The sample is dissolved in DMSO-d6 as much as possible and measured under the above conditions. The structure of the sample is determined from the chemical shift value and proton ratio of the spectrum obtained.

<How to calculate SP value>
The SP value is called the solubility parameter and is a numerical representation of how easily two compounds dissolve in each other in terms of their chemical structure. The closer the SP values of two 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, the SP value can be calculated using the following formula, which is described in detail in, for example, Polymer Engineering and Science, Vol. 14, pp. 147-154.
Formula: SP value = √(Ev/v) = √(ΣΔei/ΣΔvi)
(wherein Ev is the evaporation energy (cal/mol), v is the molar volume (cm ³ /mol), Δei is the evaporation energy of each atom or atomic group, and Δvi is the molar volume of each atom or atomic group).

<Toner manufacturing method>
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 the desired core-shell structure.

The procedure for producing toner by the pulverization method will be described below.
In the raw material mixing step, materials constituting the toner particles, such as a binder resin, a release agent, a colorant, a crystalline polyester, and optionally other components such as a charge control agent, are weighed out in predetermined amounts, blended, and mixed. Examples of mixing devices include a double con 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 the like 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, with single- or twin-screw extruders being the mainstream due to their advantage of enabling 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 Kneedex (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 (manufactured by Kawasaki Heavy Industries, Ltd.), a Super Rotor (manufactured by Nisshin Engineering Co., Ltd.), a Turbo Mill (manufactured by Turbo Kogyo), or an air jet pulverizer.
Thereafter, if necessary, the mixture is classified using a classifier or sieve such as an inertial classification type Elbow Jet (manufactured by Nittetsu Mining Co., Ltd.) or a centrifugal classification type Turboplex (manufactured by Hosokawa Micron Corporation), TSP Separator (manufactured by Hosokawa Micron Corporation), or Faculty (manufactured by Hosokawa Micron Corporation).

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 hot air using a surface treatment apparatus shown in FIG.
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 passing through the introduction pipe is uniformly dispersed by a conical protruding member 4 provided 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 swirling members 13 and 12 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 11 of the hot air supply means 7. If the temperature at the outlet 11 of the hot air supply means 7 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.

The heat-treated toner particles are then cooled by cold air supplied from cold air supply means 8, and the temperature of the cold air supplied from the cold air supply means (8-1, 8-2, and 8-3) 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 efficiently cooled, and fusion and coalescence of the heat-treated toner particles can be prevented without impeding the uniform spheronization of the mixture. The absolute moisture content of the cold air is preferably 0.5 g/ ^m3 or more and 15.0 g/ ^m3 or less.
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 so as 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 particles and uniform shapes.

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 a fine powder portion and a coarse powder portion. For example, this can be done using an inertial classification system, such as an Elbow Jet (manufactured by Nittetsu Mining Co., Ltd.). A desired amount of silica fine particles A is externally added to the surface of each of the divided heat-treated toner particles to obtain a toner. Examples of methods for externally adding the silica fine particles include stirring and mixing using a mixing device such as a Double Con mixer, a V-type mixer, a drum mixer, a Super mixer, a Henschel mixer, a Nauta mixer, a Mechano Hybrid (manufactured by Nippon Coke & Engineering Co., Ltd.), or a Nobilta (manufactured by Hosokawa Micron Corporation). In this process, external additives other than silica fine particles, such as a fluidizing agent, may be externally added, if necessary.

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.
Examples 20 to 22 are for reference only.

<Manufacturing example of magnetic core 1>
Magnetite microparticles (spherical, number-average particle size 250 nm, saturation magnetization 50 Am ² /kg, remanence 4.2 Am ² /kg, coercive force 4.4 kA/m, specific resistance at 1000 V/cm 3.3×10 ⁶ (Ω·cm)) and a silane coupling agent (3-(2-aminoethylaminopropyl)trimethoxysilane) (amount of 3.0 mass% relative to the mass of the magnetite microparticles) were introduced into a container. Then, the magnetite microparticles were surface-treated by high-speed mixing and stirring at a temperature of 100°C or higher in the container.
Phenol 10.0 parts by mass Formaldehyde solution (37% by mass aqueous formaldehyde solution) 16.0 parts by mass Surface-treated magnetite fine particles 84.0 parts by mass The above materials were introduced into a reaction vessel and mixed well at a temperature of 40°C.
The mixture was then heated to 85°C at an average temperature increase rate of 3°C/min while stirring, and 4 parts by mass of 28% by mass aqueous ammonia 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 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.

<Example of manufacturing porous magnetic particles>
Process 1 (weighing and mixing process)
Fe ₂ O ₃ 61.7% by mass
MnCO ₃ 34.2% by mass
Mg(OH) ₂ 3.0% by mass
SrCO ₃ 1.1% by mass
The ferrite raw material was weighed so that
Thereafter, the mixture was pulverized and mixed for 2 hours in a dry ball mill using zirconia balls (φ10 mm).
Step 2 (pre-firing step)
After pulverization and mixing, the mixture was fired in air at 950°C for 2 hours using 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
Step 3 (pulverization step)
After crushing the calcined ferrite 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 calcined ferrite 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 step)
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.
Step 6 (sorting step)
After the aggregated particles were broken down, the particles were sieved through a sieve with 250 μm openings to remove coarse particles, thereby obtaining porous magnetic particles.

<Manufacturing example of magnetic core 2>
Process 7 (resin filling process)
71.7 parts by mass of the porous magnetic particles; 15.0 parts by mass of benzoguanamine-n-butyl alcohol-formaldehyde co-condensate; and acrylic resin (manufactured by Mitsui Chemicals, Inc., Almatex 748-5M, solid content 55%).
The above material (13.3 parts by mass) was placed in the stirring vessel of a mixer/stirrer (Dalton Corporation, universal mixer, NDMV type), and stirred for 2 hours under a nitrogen atmosphere, maintaining the temperature at 60°C, and 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 material was filled into the porous magnetic particles. After cooling, the resulting resin-filled particles were transferred to a mixer (Sugiyama Heavy Industries, Ltd., UD-AT type drum mixer) equipped with a spiral blade in a rotatable mixing vessel, and heated to 220°C at a heating 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 products were separated by magnetic separation and classified using a 150 μm sieve to obtain magnetic core 2. The configuration of the resulting magnetic core 2 is shown in Table 1.

<Manufacturing example of magnetic core 3>
Process 7 (resin filling process)
100.0 parts by mass of the porous magnetic particles were placed in the stirring vessel of a mixer/stirrer (Dalton Corporation, universal mixer, NDMV type). While maintaining the temperature at 60°C, nitrogen was introduced while reducing the pressure to 2.3 kPa. A silicone resin solution (SR2410, manufactured by Toray Dow Corning Co., Ltd.) was added dropwise under reduced pressure to a resin content of 7.5 parts by mass relative to the porous magnetic particles. Stirring was continued for 2 hours after the completion of the dropwise addition. The temperature was then raised to 70°C, the solvent was removed under reduced pressure, and the porous magnetic particles were filled with the silicone resin composition obtained from the silicone resin solution. After cooling, the resulting filled core particles were transferred to a mixer (Sugiyama Heavy Industries Co., Ltd., drum mixer, UD-AT type) equipped with a spiral blade in a rotatable mixing vessel. The mixture was heated to 220°C at a heating rate of 2°C/min under a nitrogen atmosphere and atmospheric pressure. The resin was cured by heating and stirring at this temperature for 60 minutes. After the heat treatment, low magnetic force products were separated by magnetic separation and classified using a sieve with openings of 150 μm to obtain the magnetic core 3. The configuration of the obtained magnetic core 3 is shown in Table 1.

<Manufacturing example of magnetic core 4>
Process 1 (weighing and mixing process)
Fe ₂ O ₃ 61.7% by mass
MnCO ₃ 34.2% by mass
Mg(OH) ₂ 3.0% by mass
SrCO ₃ 1.1% by mass
The ferrite raw material was weighed so that
Thereafter, the mixture was pulverized and mixed for 2 hours in a dry ball mill using zirconia balls (φ10 mm).
Step 2 (pre-firing step)
After pulverization and mixing, the mixture was fired in air at 1000°C for 2 hours using 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
Step 3 (pulverization step)
After crushing the calcined ferrite 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 the mixture was crushed in a wet ball mill for 2 hours. After separating the balls, the mixture was crushed in a wet bead mill using stainless steel balls (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 45 μm spherical particles using a spray dryer (manufactured by Okawahara Kakoki).
Step 5 (baking step)
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.
Step 6 (sorting step)
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 4. The configuration of the obtained magnetic core 4 is shown in Table 1.

<Method for producing graft resin A1>
95.2% by mass of a silicone-containing acrylic monomer corresponding to unit Y1 shown below and 4.8% by mass of a monomer corresponding to unit Y2 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 unit Y1 and unit 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, the mixture was repeatedly washed 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.

<Production Examples of Graft Resins A2 to A25>
Resins A2 to A25 were obtained in the same manner as in the production of Resin A1, except that the structures of Units Y1 and Y2 and the values of a, b, n, and s(l+m) were changed as shown in Table 2.

<Method for producing graft resin B1 and graft resins B2 to B18>
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 having terminal hydroxyl groups (Mw: about 5000)...98.3% by mass
Furthermore, 100 parts by mass of THF and 1.0 part by mass of 4-tert-butylcatechol were added to 100 parts by mass of the above monomer mixture, and the mixture was heated under reflux for 5 hours under a nitrogen stream. After the reaction was completed, the mixture was washed with sodium bicarbonate 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 having a polymer of methyl methacrylate as a polymer (corresponding to unit Y4)...24.0 mass%
Furthermore, 100 parts by mass of toluene, 100 parts by mass of methyl ethyl ketone, and 2.0 parts by mass of azobisisovaleronitrile were added to 106 parts by mass of the above monomer mixture. 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.

Graft resins B2 to B18 were produced in the same manner as graft resin B1, except that the monomers were changed to achieve the composition shown in Table 3.

<Production Examples of Magnetic Carriers 1 and 2 to 27>
Magnetic core 100.0 parts by mass Graft resin A1 (toluene solution with 50% solids by mass) 0.2 parts by mass Graft resin B1 (toluene solution with 50% solids by mass) 3.8 parts by mass The above materials were placed in 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 (UD-AT type drum mixer manufactured by Sugiyama Heavy Industries Co., Ltd.) equipped with a spiral blade in a rotatable mixing container. While stirring at 10 revolutions per minute, the mixing container was heat-treated for 2 hours at 120°C in a nitrogen atmosphere. The obtained magnetic carrier 1 was separated into low magnetic particles by magnetic separation, passed through a sieve with 150 μm openings, and then classified with an air classifier. Magnetic carrier 1 with a volume-based 50% particle size (D50) of 39.1 μm was obtained.
The composition of the obtained magnetic carrier 1 is shown in Table 4.

Magnetic Carriers 2 to 27 were manufactured in the same manner as Magnetic Carrier 1, except for the changes in composition shown in Table 4.

<Production Example of Toner 1>
Binder resin: 100 parts by mass (polyester having a Tg of 57°C, an acid value of 12 mgKOH/g, and a hydroxyl value of 15 mgKOH/g)
C.I. Pigment Blue 15:3 5.5 parts by weight, 3,5-di-t-butylsalicylic acid aluminum compound 0.2 parts by weight, normal paraffin wax (melting point: 90°C) 6.0 parts by weight. 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 using a hammer mill to obtain a coarsely pulverized product of 1 mm or less. The resulting 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 11,000 rpm and a dispersing rotor rotation speed of 7,200 rpm.
Toner base particles 1 100.0 parts by mass Silica fine particles (BET specific surface area 24 m ² /g) surface-treated with 4% by mass of hexamethyldisilazane 2.0 parts by mass The raw materials shown in the above formulation were mixed using a Henschel mixer (FM-10C model, 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, hot air flow rate = 6 m ³ /min, cold air temperature E = -5°C, cold air flow rate = 4 m ³ /min, blower air flow rate = 20 m ³ /min, and injection air flow rate = 1 m ³ /min.
The obtained particles were classified using a rotary classifier (product name: TTSP100, manufactured by Hosokawa Micron Corp.) to remove fine powder and coarse powder, thereby obtaining cyan toner particles 1 having a weight average particle size of 6.0 μm, a content of particles having a particle size of 4.0 μm or less being 27.8% by number, and a content of particles having a particle size of 10.0 μm or more being 2.2% by volume.
- Cyan toner particles 1 100.0 parts by mass - Silica microparticles surface-treated with 10% by mass of polydimethylsiloxane (BET specific surface area 100 ^m2 /g) 0.6 parts by mass 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.

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 weight of toner 1 was added to 10 parts by weight 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 image forming apparatus used in the following evaluation using this two-component developer and replenishment developer was a modified Canon imageRUNNER ADVANCE C5560 color copier.
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 the durability test, a chart with FFH output and an image ratio of 40% was used in a printing environment of 30°C temperature and 80% RH. FFH is a value representing 256 gradations in hexadecimal, with 00h representing the first gradation (white background) of the 256 gradations and FFH representing the 256th gradation (solid area).
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.) Image forming speed: Modified so that it could output A4 size, full color, 80 sheets/min.
Development conditions: The development contrast was adjusted to any value and the automatic correction by the main body was disabled. The peak-to-peak voltage (Vpp) of the alternating electric field was adjusted to a frequency of 2.0 kHz and Vpp was changed in 0.1 kV increments from 0.7 kV to 1.8 kV. Each color was modified so that a monochrome image could be output.
The cyan developer was modified so that it could develop in a single color only.

The evaluation items are shown below.
(1) Image Density After initial durability and durability image output evaluation (A4 landscape, 40% print ratio, 50,000 sheets) under a high temperature and high 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 judged that the effects of the present invention were obtained.
A: The density difference is less than 0.10. B: The density difference is 0.10 or more and less than 0.15. C: The density difference is 0.15 or more and less than 0.20. D: The density difference is 0.20 or more and less than 0.25. E: The density difference is 0.25 or more.

(2) Fog After initial durability and durability image output evaluation (A4 landscape, 40% print ratio, 50,000 sheets) under a high temperature and high humidity environment (30°C, 80% RH), an A4 full-page solid white image was output. Fog was evaluated by measuring the whiteness of the white background with a reflectometer (manufactured by Tokyo Denshoku Co., Ltd.), calculating the fog density (%) from the difference in whiteness before and after transfer, and evaluating it 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

(3) Halftone Developability After initial durability and durability image output evaluation (A4 landscape, 40% print ratio, 50,000 sheets) under a high-temperature, high-humidity environment (30°C, 80% RH), one halftone image (30H) was printed on an A4 sheet. Using a digital microscope VHX-500 (lens wide-range zoom lens VH-Z100, manufactured by Keyence Corporation), the area of 1,000 dots was measured. The number average (S) of the dot area and the standard deviation (σ) of the dot area 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

(4) Toner Scattering After initial durability and durability image output evaluation (A4 landscape, 40% print ratio, 50,000 sheets) under a high temperature and high humidity environment (30°C, 80% RH), the developing unit was removed from the main body, and the state of toner scattering 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 obtained.
A: No toner scattering B: Very slight toner scattering C: Slight toner scattering D: Slight toner scattering E: Significant toner scattering Table 5 shows the evaluation results of Example 1.

<Examples 2 to 22 and Comparative Examples 1 to 5>
Evaluation was carried out in the same manner as in Example 1, except that magnetic carriers 2 to 27 were used as in Example 1. The evaluation results are shown in Table 5.

REFERENCE SIGNS LIST 1 electrostatic latent image carrier 2 charger 3 exposure device 4 developing device 5 developing container 6 developer carrier 7 magnet 8 regulating member 11 transfer charger 12 recording medium 13 fixing device

Claims (9)

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 and a graft resin B,
The coating resin is
(i) the graft resin A is contained in an amount of 1.0% by mass or more and 50.0% by mass or less,
(ii) The graft resin B is contained in an amount of 50.0% by mass or more and 99.0% by mass or less,
The graft resin A has a unit Y1 represented by the following formula (1) and a unit Y2 represented by the following formula (2),
The mass of the graft resin A is X,
The mass of the unit Y1 represented by the formula (1) contained in the graft resin A is a,
When the mass of the unit Y2 represented by the 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
The graft resin B is
(i) a comb polymer having, as a branch, at least one 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) does not have a polysiloxane structural moiety, or the content of the polysiloxane structural moiety is 0.1 mass% or less;
A magnetic carrier characterized by:
[In formula (1) or formula (2),
_R1 represents H or _CH3 ;
_R2 is a functional group selected from the group consisting of a 2-hydroxyethyl group, a 2-carboxyethyl group, a butyl group, and a methyl group ;
_R3 represents H or _CH3 ;
_R4 represents H or _CH3 ;
_R5 represents a single bond or trimethylene ;
_R6 represents any functional group selected from the group consisting of a methyl group, a propyl group, an ethyl group, a butyl group, a hexyl group, and a cyclohexyl group ;
_R7 represents H, _CH3 or Si( _CH3 ) ₃ ;
l and m are integers of 1 or more, and n is an integer of 5 or more and 60 or less. 2. The magnetic carrier according to claim 1, wherein the following formula is satisfied when the Si atomic % of the magnetic carrier measured by X-ray photoelectron spectroscopy (XPS) is taken as Si ₀ :
1.0≦Si0 _≦ 15.0 3. The magnetic carrier according to claim 1, wherein the graft resin A satisfies the following formula, where s is the total number of units Y1 and Y2:
50≦s≦250 4. The magnetic carrier according to claim 1 , wherein the coating resin contains 1.0% by mass or more and 30.0% by mass or less of graft resin A and 70.0% by mass or more and 99.0% by mass or less of graft resin B. 5. The magnetic carrier according to claim 1 , wherein the graft resin B contains 75.0% by mass or more of a unit Y3 represented by the following formula (3):
[In formula (3), _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.] 6. The magnetic carrier according to claim 1, wherein the graft resin B contains 1.0% by mass or more and 25.0% by mass or less of a unit Y4 represented by the following formula ( 4 ):
[In formula (4), R ₁₀ represents H or CH ₃ , and R ₁₁ represents any polymer selected from the group consisting of methyl methacrylate polymer, methyl acrylate polymer, ethyl methacrylate polymer, propyl methacrylate polymer, butyl methacrylate polymer, pentyl methacrylate polymer, hexyl methacrylate polymer, 2-hydroxyethyl methacrylate polymer, 2-hydroxyethyl acrylate polymer, and phenyl acrylate polymer .] 7. The magnetic carrier according to claim 6 , wherein the graft resin B further has a unit Y5 represented by formula (5).
[In formula (5), R ₁₂ represents H or CH ₃ , and R ₁₃ represents any functional group selected from the group consisting of a methyl group, an ethyl group, a propyl group, a butyl group, and a pentyl group .] 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 7 . 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,
The replenishment developer is the two-component developer according to claim 8 .