JP5371584B2 - Magnetic carrier, two-component developer and replenishment developer - Google Patents

Description

  The present invention relates to a magnetic carrier contained in a developer used in electrophotography and electrostatic recording, a two-component developer having the magnetic carrier and toner, and a replenishment developer.

  In the process of developing an electrostatic image in electrophotography, an image is formed by attaching charged toner particles on the electrostatic image using electrostatic interaction of the electrostatic image. As a developer for developing an electrostatic charge image, a one-component developer using a magnetic toner obtained by dispersing a magnetic material in a resin, and a two-component developer using a non-magnetic toner mixed with a magnetic carrier. There is. In particular, the latter is preferably used in a full-color image forming apparatus such as a full-color copying machine or a full-color printer that requires high image quality.

  As a magnetic carrier used in a two-component developer, a coated carrier in which a resin is coated on the surface of a ferrite particle or a magnetic material-dispersed resin core is used for the purpose of stabilizing the charge amount and improving the durability of the carrier. Yes.

  There have been many proposals regarding coated carriers. For example, a carrier coated with a fluororesin using a specific monomer as a durable carrier that prevents charge injection has been proposed (Patent Document 1). In this case, the uniform coatability is improved by using a specific fluororesin, but the fluororesin has a strong negative chargeability and the rise of the charge amount may be slower than that of the negative toner. On the other hand, when continuously printing images with a low printing ratio under low humidity, the charge amount may increase.

  In addition, a carrier (Patent Document 2) in which a copolymer of a specific monomer and a methyl methacrylate monomer is coated and a contact angle with respect to water is 95 ° or more has been proposed.

  By using such a coating resin, charging stability can be achieved, release properties can be improved, and durability stability is also excellent. However, depending on the type of the core material, the adhesion between the core and the coating resin is unstable and may be easily peeled off.

  In addition, in order to maintain durability that can withstand high speeds of recent full-color copying machines or full-color printers, there is a tendency to add a large amount of an external additive that imparts toner fluidity. In this case, the concern is a decrease in charging ability due to the external additive contaminating the carrier surface. In order to solve these problems, a further high-performance magnetic carrier, a two-component developer and a replenishing agent are used. There is a long-awaited developer.

Japanese Patent Laid-Open No. 10-307430 JP 2007-279588 A

  An object of the present invention is to provide a magnetic carrier, a two-component developer, and a replenishment developer that solve the above problems.

  Another object of the present invention is to provide a magnetic carrier, a two-component developer, and a replenishment developer that are excellent in development durability and environmental stability and can form a high-quality image over a long period of time.

  Another object of the present invention is to provide a magnetic carrier, a two-component developer, and a replenishing developer that are excellent in charging stability even in a high-load type copying machine and can obtain a stable image over a long period of time in a high-temperature and high-humidity environment. It is to provide an agent.

The present invention is a magnetic carrier having a resin coating layer on the surface of the carrier core,
The resin forming the resin coating layer is
i) At least a resin obtained by copolymerizing a monomer represented by the following formula (A1) and a macromonomer represented by the following formula (A2) and having a weight average molecular weight of 3000 or more and 20000 or less. And the proportion of units derived from the macromonomer is 0.5 mass% or more and 30.0 mass% or less,
ii) The inertial radius Rw in the size exclusion chromatography-online-multi-angle light scattering (SEC-MALLS) measurement in THF-soluble matter in THF is 5 nm to 30 nm, and the number average molecular weight Mn is 2.3 × 10 ^4. 1.0 × 10 ⁵ or less ,
The present invention relates to a magnetic carrier.

  The present invention also relates to a two-component developer having at least the magnetic carrier and toner.

  Furthermore, the present invention is a replenishment developer for use in an image forming method in which development is performed while replenishing a replenishment developer, and the replenishment developer includes at least the magnetic carrier and toner, and the magnetic carrier The present invention relates to a replenishment developer characterized in that the toner is contained in a blending ratio of 2 parts or more and 50 parts or less with respect to 1 part by mass.

  By using the magnetic carrier of the present invention, it is excellent in development durability and environmental stability, and high image quality can be maintained over a long period of time by preventing carrier contamination by external additives. In particular, high chargeability can be maintained even during long-term use in a high-temperature and high-humidity environment, and excellent image quality without fog deterioration and image density reduction can be stably obtained.

1 is a schematic configuration diagram of a full-color image forming apparatus. It is a schematic block diagram of the developing device in FIG. It is a schematic block diagram of the apparatus which measures the specific resistance value of a magnetic carrier and a carrier core. It is a conceptual diagram of the ghost which generate | occur | produces on an image.

  Hereinafter, the present invention will be described in detail.

<Magnetic carrier>
The resin coating layer that covers the surface of the carrier core will be described.

The coating resin used to coat the surface of the carrier core in the present invention is a radius of inertia Rw in size exclusion chromatography-online-multi-angle light scattering (SEC-MALLS) measurement in THF (THF) soluble content. Is 5 nm or more and 30 nm or less, and the number average molecular weight Mn is 2.3 × 10 ⁴ or more and 1.0 × 10 ⁵ or less.

  The inertia radius Rw indicates the spread of the polymer chain. Although details are not clear, when the present inventors examined, it became clear that this inertia radius Rw and the number average molecular weight Mn are greatly concerned in the coating performance to a carrier. That is, as in the present invention, those having an appropriate molecular spread and molecular weight have high adhesion to the carrier core and coating stability, and can form a uniform and crater-free coating layer. In addition, since the number average molecular weight Mn is at a specific value, the rising of the charge is quick, the replenished toner is quickly raised, and a sharp charge amount distribution can be maintained. As a result, a good image without fogging deterioration can be obtained even in the high printing rate image durability under a high temperature and high humidity environment.

  When the inertial radius Rw is smaller than 5 nm, the molecular spread of the coating resin is small, and the frequency of molecular chains entangled with each other is low, so that the adhesion to the carrier core is low. Further, in high load development, the resin coating layer is peeled off. Therefore, the tribo drop and the leak occur in the durability test.

  When the inertial radius Rw exceeds 30 nm, the spread and entanglement of the molecular chain becomes too large, and the uniform coatability on the carrier core is lowered. That is, the carriers tend to agglomerate during coating, and a large number of crater-like leak points (hereinafter referred to as craters) are formed at the interface when the carriers are separated. When such a carrier is used, it becomes easy to receive charge injection, and so-called injection carry adhesion occurs in which the carrier that has been negatively injected by the injection from the beginning of the durability is developed. Of course, such a carrier also has a low charge imparting ability, which causes a significant decrease in tribo particularly in a durability test in a high temperature and high humidity environment.

On the other hand, when the number average molecular weight Mn is smaller than 2.3 × 10 ⁴ , the rising of charging of the toner is delayed. In particular, when a large amount of toner is replenished for high printing durability, the low tribo component increases and the charge amount distribution becomes broad, which causes deterioration of fogging, photoconductor contamination due to toner scattering, and image defects. Resulting in.

On the other hand, when the number average molecular weight Mn exceeds 1.0 × 10 ⁵ , the molecular weight is too large and the viscosity of the varnish is increased, so that the uniformity of the coat is lowered and the smoothness of the carrier surface is impaired. In addition, the number of craters increases and injection carry-over occurs.

In addition, the resin forming the resin coating layer of the present invention preferably has an inertia radius Rw (nm) and a weight average molecular weight Mw in the SEC-MALLS measurement in THF-soluble THF satisfying the following formula. .
2.0 × 10 ⁻⁴ ≦ Rw / Mw ≦ 1.0 × 10 ⁻³

The relationship between the radius of inertia Rw and the weight average molecular weight Mw is closely related to the degree of branching and crosslink density of the molecule. When Rw / Mw is in the range of 2.0 × 10 ⁻⁴ or more and 1.0 × 10 ⁻³ or less, moderate rigidity and dispersibility of other additives such as carbon black can be maintained at a high level. Therefore, even when used in a high-load development system in a high-temperature and high-humidity environment, the coating agent is not peeled off and high developability (charge rising speed) can be maintained, so that ghosting can be suppressed. . In addition, the dispersibility of the carbon black is improved, and the occurrence of leakage is suppressed.

When Rw / Mw is 2.0 × 10 ⁻⁴ or more, it is considered that the distance between cross-linking points is a certain value or more. Therefore, additives such as carbon black can be retained in the molecule, and the dispersibility can be maintained at a high level. On the other hand, when Rw / Mw is 1.0 × 10 ⁻³ or less, since it has a cross-linked structure of a certain level or more, it has an appropriate rigidity and high adhesion to the core.

  The resin forming the resin coating layer of the present invention preferably contains a resin obtained by copolymerizing at least two kinds of monomers containing a macromonomer. By using a macromonomer as a copolymerization component, it becomes easy to achieve the range of the inertial radius Rw and the range of the ratio Rw / Mw of the inertial radius Rw and the weight average molecular weight Mw of the present invention. For this reason, the adhesiveness and coat uniformity of the resin coating layer to the carrier core can be enhanced, and the toughness and wear resistance of the coat resin layer are increased. Furthermore, even if fine particles such as carbon black are added to the coating material, it is difficult to detach from the coating material.

  The macromonomer is at least one or two selected from methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, styrene, acrylonitrile, and methacrylonitrile. It is preferable to use a macromonomer obtained by polymerizing the above monomers. Specifically, it is a macromonomer represented by the following formula (A2).

（式中、Ａはアクリル酸メチル、メタクリル酸メチル、アクリル酸ブチル、メタクリル酸ブチル、アクリル酸２−エチルヘキシル、メタクリル酸２−エチルヘキシル、スチレン、アクリロニトリル、メタクリロニトリルから選ばれる１種又は２種以上のモノマーを重合することにより得られた重合体を示し、Ｒ³はＨまたはＣＨ₃を示す。）

(In the formula, A is one or more selected from methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, styrene, acrylonitrile, and methacrylonitrile. A polymer obtained by polymerizing the monomer of R3, R ³ represents H or CH _3. )

  A macromonomer having the structure as described above is preferable because of good copolymerization reactivity with other monomers. Among them, the macromonomer obtained by polymerizing methyl methacrylate has a high charge imparting ability to the toner and can suppress a decrease in toner charge amount even in a long-term use under a high temperature and high humidity environment. preferable.

  The weight average molecular weight of the macromonomer alone is preferably 3000 or more and 20000 or less. In order to further improve the adhesion and durability and further reduce the residual monomer, the weight average molecular weight is more preferably 4000 or more and 15000 or less.

  The proportion of the macromonomer unit in the copolymer is preferably 0.5% by mass or more and 30.0% by mass or less. By containing the macromonomer unit at a ratio of 0.5% by mass or more and 30.0% by mass or less, the range of the inertia radius Rw and the ratio of the inertia radius Rw to the weight average molecular weight Mw of the present invention can be achieved. This is preferable because it can be easily performed and uniform coverage is enhanced.

  The resin forming the resin coating layer of the present invention is preferably a resin obtained by copolymerizing at least the macromonomer and a monomer represented by the following formula (A1).

（式中、Ｒ¹は炭素数４以上２２以下の炭化水素基を示し、Ｒ²はＨまたはＣＨ₃を示す。）

(In the formula, R ¹ represents a hydrocarbon group having 4 to 22 carbon atoms, and R ² represents H or CH _3. )

By using the monomer having the structure represented by the formula (A1) as a copolymerization component, the crystallinity of the obtained resin is increased, and the releasability from the toner can be improved. Since toner can be quickly charged and high developability can be obtained, ghosting can be suppressed even in long-term use in a high temperature and high humidity environment, which is preferable. Further, in the monomer having the structure represented by the formula (A1), when R ¹ has 4 or more and 22 or less carbon atoms, it can be uniformly coated at a very high level because of its high affinity with the carrier core. For this reason, image defects due to leakage do not occur even in long-term durability under a high temperature and high humidity environment, which is preferable.

Further, the hydrocarbon group having 4 or more carbon atoms of R ¹ may be a chain hydrocarbon group or a cyclic hydrocarbon group. Examples of the monomer having the structure represented by the above formula (A1) in which R ¹ has a hydrocarbon group having 4 or more carbon atoms include the following. Butyl acrylate, butyl acrylate, t-butyl acrylate, 2-ethylhexyl acrylate, lauryl acrylate, dodecyl acrylate, tridecyl acrylate, tetradecyl acrylate, pentadecyl acrylate, hexadecyl acrylate, heptadecyl acrylate, acrylic acid Stearyl, cyclobutyl acrylate, cyclopentyl acrylate, cyclohexyl acrylate, cycloheptyl acrylate, dicyclopentenyl acrylate, dicyclopentanyl acrylate, isobornyl acrylate, butyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, 2-ethylhexyl methacrylate, lauryl methacrylate, dodecyl methacrylate, tridecyl methacrylate, tetradecyl methacrylate, methacrylic acid Tadecyl, hexadecyl methacrylate, heptadecyl methacrylate and octadecyl methacrylate, cyclobutyl methacrylate, cyclopentyl methacrylate, cyclohexyl methacrylate, cycloheptyl methacrylate, isobornyl methacrylate, dicyclopentenyl methacrylate and dicyclopentanyl methacrylate One or two or more of these monomers may be selected.

  In addition, the monomer which has a structure shown by Formula (A1) exists as the following units in a copolymer.

（式中、Ｒ¹は炭素数４以上２２以下の炭化水素基を示し、Ｒ²はＨまたはＣＨ₃を示す。）

(In the formula, R ¹ represents a hydrocarbon group having 4 to 22 carbon atoms, and R ² represents H or CH _3. )

  The resin forming the resin coating layer of the present invention is preferably a resin obtained by copolymerizing at least a macromonomer, a monomer represented by the formula (A1), and a methyl methacrylate monomer, Furthermore, it is preferable that the proportion of the methyl methacrylate monomer unit in the copolymer is 1% by mass or more and 50% by mass or less.

  By containing a methyl methacrylate monomer unit in a proportion of 1% by mass or more in the copolymer, the toner can be imparted with high chargeability, and a decrease in toner charge amount can be suppressed even in a high temperature and high humidity environment. Further, since the copolymerization reactivity with the macromonomer and the monomer represented by the formula (A1) is high, a coating resin in which the macromonomer is uniformly incorporated in the molecular chain can be obtained. Such a resin is preferable because the dispersibility of the additive such as carbon black becomes very good and environmental fluctuation of the toner charge amount can be suppressed.

  Further, since the proportion of the methyl methacrylate monomer unit in the copolymer is 50% by mass or less, the macromonomer unit and the monomer unit represented by the formula (A1) are present in a considerable amount in the copolymer. It will be. For this reason, it is easy to obtain the Rw of the present invention or a preferable value of Rw / Mw, and it is preferable because the release property of the coating resin can be improved.

  The coating resin used in the present invention can be obtained by a conventionally known polymerization method. Specific examples include emulsion polymerization, suspension polymerization, dispersion polymerization, and solution polymerization.

  In order to obtain the inertia radius Rw, the number average molecular weight Mn, and the weight average molecular weight Mw of the coating resin of the present invention, the molecular weight distribution and structure of the coating resin, the type and ratio of the acrylic monomer and macromonomer used, or the initiator used This can be achieved by adjusting the type, amount added, and polymerization temperature. In particular, in order to obtain the range of the number average molecular weight Mn of the present invention, a step of removing the low molecular weight component by reprecipitation of the obtained copolymer resin varnish in a polar solvent such as methanol or water, It is preferable to add a polymerization initiator or to add a step of raising the polymerization temperature together with the addition.

  The resin coating layer of the present invention preferably contains carbon black in the coating resin. Since carbon black has high conductivity, the specific resistance of the electrophotographic carrier can be appropriately controlled. As a result, the counter charge after the toner is developed can be released and the developability can be improved, and the toner charge amount attenuation after being left can be suppressed. Furthermore, the addition of carbon black is preferable because a filler effect is exhibited and rigidity and elasticity can be imparted to the resin coating layer.

The specific surface area of the carbon black used in the present invention is preferably 30 m ² / g or more and 200 m ² / g or less, more preferably 40 m ² / g or more and 150 m ² / g or less. Further, the primary particle diameter is preferably 10 nm or more and 55 nm or less, and more preferably 15 nm or more and 50 nm or less.

When the specific surface area is less than 30 m ² / g, carbon black is easily detached from the coating resin. If it exceeds 200 m ² / g, the coating resin becomes brittle and the coating is liable to peel off.

  If the primary particle size is smaller than 10 nm, uniform dispersion is difficult, and resistance control of the magnetic carrier cannot be performed, and good developability is difficult to obtain. Further, when the average primary particle diameter of carbon black is larger than 55 nm, the carbon black is easily liberated.

  The dispersion diameter of the carbon black contained in the coating resin of the present invention is preferably 0.10 μm or more and 1.00 μm or less on a volume basis. In the measurement method, first, a magnetic carrier is dissolved in toluene, and a resin coating layer is eluted from the magnetic carrier. Then, the particle size distribution of the carbon black particles is measured with the laser diffraction particle size distribution measuring device.

  When the dispersion diameter of the carbon black is less than 0.10 μm, the resistance adjustment effect is small and the resistance of the magnetic carrier is likely to increase, and the developability tends to be lowered. Further, in order to adjust the resistance, it is necessary to add a large amount, and when left untreated, the charge is remarkably leaked, and fog and toner scattering are likely to occur. On the other hand, when the dispersion diameter is larger than 1.00 μm, the carbon black particles are likely to be liberated and cause image defects. Moreover, it is difficult to obtain a sufficient filler effect. A more preferable range of the dispersion diameter is 0.20 μm or more and 0.80 μm or less.

  The content of carbon black added to the coating resin 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. If the amount is less than 0.1 parts by mass, it is difficult to obtain the effect of adding carbon black. If the amount exceeds 20 parts by mass, there is a concern that the color may deteriorate due to the carbon black being detached.

  In addition, the coating resin may contain fine particles for the purpose of enhancing the ability to impart charge to the toner and enhancing the developability. The fine particles contained in the coating resin layer may be any fine particles of an organic material and an inorganic material, but when coated, crosslinked resin fine particles having a strength capable of maintaining the shape of the fine particles or Inorganic fine particles are preferred. Examples of the crosslinked resin forming the crosslinked resin fine particles include a crosslinked polymethyl methacrylate resin, a crosslinked polystyrene resin, a melamine resin, a guanamine resin, a urea resin, a phenol resin, and a nylon resin. Examples of the inorganic fine particles include silica, alumina, titania and the like. The content of the fine particles in the coating layer is preferably 0.1 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the coating resin.

  The method for coating the copolymer on the surface of the carrier core is not particularly limited, and can be performed by a known method. For example, there is a so-called dipping method in which the solvent is volatilized while stirring the magnetic carrier core and the coating resin solution, and the coating resin is coated on the surface of the magnetic carrier core. Specifically, a universal mixing stirrer (manufactured by Fuji Powder Corporation), a nauter mixer (manufactured by Hosokawa Micron Corporation), and the like can be mentioned. There is also a method in which a coating resin solution is sprayed from a spray nozzle while forming a fluidized bed to coat the coating resin on the surface of the magnetic carrier core. Specific examples include a Spira coater (Okada Seiko Co., Ltd.) and Spiraflow (Freund Sangyo Co., Ltd.). There is also a method in which the coating resin is coated in a dry state on the magnetic carrier core in the form of particles. Specifically, a processing method using apparatuses such as a hybridizer (manufactured by Nara Machinery Co., Ltd.), mechano-fusion (manufactured by Hosokawa Micron Co., Ltd.), high flex glal (manufactured by Fukae Powtech), and theta composer (manufactured by Tokusu Kosakusha Co., Ltd.) Can be mentioned.

  Next, the carrier core will be described.

  For the carrier core, known magnetic particles such as magnetite particles, ferrite particles, and magnetic material-dispersed resin particles can be used. Among them, the magnetic substance-dispersed resin particles, the ferrite particles having a hollow shape or a porous shape, or those containing resin in the voids of ferrite particles having such a shape can lower the true density of the carrier. It is suitable for. As the resin to be contained in the voids of the ferrite particles, a copolymer resin used as a coating resin can be used, but not limited to this, a known resin can be used, and among these, a thermosetting resin can be used. preferable. By reducing the true density of the carrier, the stress on the toner can be reduced and the occurrence of toner spent can be suppressed. In addition, dot reproducibility can be improved, and a high-definition image can be obtained.

The ferrite particles having a hollow shape or a porous shape have a solid apparent density of ρ1 (g / cm ³ ) and a true density of ρ2 (g / cm ³ ), and ρ1 is 0.80 or more and 2.40 or less, It is preferable that ρ1 / ρ2 is 0.20 or more and 0.42 or less. It is considered that such a particle having a significantly smaller solid apparent density with respect to the true density has many voids inside the particle. In the particles having such a structure, the flow of electric charges is moderately limited by the presence of voids, and the developability is excellent.

  In order to obtain ferrite particles having a hollow shape or a porous shape, pores are formed by adjusting the temperature during firing to control the crystal growth rate or adding a foaming agent or organic fine particle pore forming agent. The method of letting it be mentioned. Moreover, the carrier atmosphere excellent in developability can be obtained by controlling the resistance of the carrier core by controlling the atmosphere during firing to a low oxygen concentration.

  The ferrite particles having a hollow shape or a porous shape can be used as a carrier core by filling a void inside the particle with a resin component different from the coating resin. The resin component to be filled is preferably one having high wettability with respect to the ferrite component, and either a thermoplastic resin or a thermosetting resin may be used. Preferably, by using a thermosetting resin and coating the coated resin of the present invention on the particles in a cured state, the coating resin can be coated without being exposed on the surface. In particular, when a resin component having high wettability is used, the voids can be easily filled.

  As the thermoplastic resin, a copolymer used as a coating resin is preferable, 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, polyethylene terephthalate, polybutylene terephthalate, polyarylate aromatic polyester resin, polyamide resin, polyacetal resin, Polycarbonate resin, polyether sulfone resin, polysulfone resin, polyphenylene sulfide resin, polyether ketone resin.

  As a thermosetting resin, the following are mentioned, for example. 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, gliptal resin, furan resin, silicone resin, polyimide, polyamideimide resin, polyetherimide resin, polyurethane resin.

  Of the above resins, silicone resins are particularly preferred. As the silicone resin, conventionally known silicone resins can be used. Specifically, a straight silicone resin composed only of an organosiloxane bond and a silicone resin obtained by modifying the straight silicone resin with alkyd, polyester, epoxy, urethane, or the like can be given.

  Examples of the method of filling the voids of ferrite particles having a hollow shape or porous shape with the resin component include a method in which the resin component is diluted with a solvent and added to the porous magnetic core particles in the diluted solution. The solvent used here should just be what can melt | dissolve each resin component. When the resin is soluble in an organic solvent, an organic solvent such as toluene, xylene, cellosolve butyl acetate, methyl ethyl ketone, methyl isobutyl ketone, or methanol may be used. In the case of a water-soluble resin component or an emulsion type resin component, water may be used. As a method of adding a resin component diluted with a solvent inside the porous magnetic core particles, the resin component is impregnated by a coating method such as a dipping method, a spray method, a brush coating method, a fluidized bed, and a kneading method, Then, the method of volatilizing a solvent is mentioned. When the thermosetting resin is filled, it is preferable that after the solvent is volatilized, the temperature is increased to a temperature at which the resin to be used is cured to cause a curing reaction, and then the coating treatment is performed.

  On the other hand, the following method is mentioned as a concrete manufacturing method of a magnetic body dispersion type resin particle. For example, submicron magnetic materials such as iron powder, magnetite particles, and ferrite particles are kneaded so as to be dispersed in a thermoplastic resin, pulverized to a desired carrier particle size, and if necessary, a thermal or mechanical spherical shape It can be obtained by applying a chemical treatment. It is also possible to manufacture by dispersing the magnetic substance in a monomer and polymerizing the monomer to form a resin. Examples of the resin in this case include resins such as vinyl resin, polyester resin, epoxy resin, phenol resin, urea resin, polyurethane resin, polyimide resin, cellulose resin, silicone resin, acrylic resin, and polyether resin. Resin may be 1 type, or 2 or more types of mixed resin may be sufficient as it. In particular, a phenol resin is preferable in terms of increasing the strength of the carrier core. The true density and specific resistance can be adjusted by adjusting the amount of the magnetic material. Specifically, in the case of magnetic particles, it is preferable to add 70% by mass to 95% by mass with respect to the carrier.

  The magnetic carrier core has a volume-based 50% particle size (D50) of 18 μm or more and 98 μm or less, so that the coating resin can be uniformly coated, and the density of the developer magnetic brush for preventing carrier adhesion and obtaining a high-quality image can be obtained. It is preferable for making it moderate. Note that the preferred volume-based 50% particle size (D50) for the magnetic carrier is 20 μm or more and 100 μm or less.

The specific resistance of the magnetic carrier core is preferably 1.0 × 10 ³ Ω · cm or more and 1.0 × 10 ⁹ Ω · cm or less at an electric field strength of 500 V / cm. It is more preferable that it is 1.0 × 10 ⁵ Ω · cm to 5.0 × 10 ⁸ Ω · cm in that the developability can be improved. When the specific resistance value is in the above range, good developability can be obtained even at low electric field strength.

  In addition, about the specific resistance value of a carrier core, it can adjust by adjusting the specific resistance of magnetic bodies, such as a ferrite to contain, and changing the quantity of the magnetic body to contain.

  Next, the magnetic carrier will be described.

The magnetic carrier preferably has a magnetization strength of 40 Am ² / kg or more and 70 Am ² / kg or less under a magnetic field of 1000 / 4π (kA / m). More preferably, it is 45 Am < ² > / kg or more and 65 Am < ² > / kg or less, More preferably, it is 45 Am < ² > / kg or more and 62 Am < ² > / kg or less. When the strength of magnetization of the magnetic carrier is within the above range, the magnetic binding force to the developing sleeve is appropriate, so that the occurrence of carrier adhesion can be suppressed more favorably. Further, since stress applied to the toner in the magnetic brush can be reduced, toner deterioration and adhesion to other members can be satisfactorily suppressed. Moreover, the strength of magnetization of the magnetic carrier can be appropriately adjusted by the amount of resin contained.

It is preferable that the residual magnetization of the carrier is less 20.0Am ² / kg, and more preferably less 5.0Am ² / kg. Further, the coercive force is preferably 20.0 kA / m or less, and preferably 18.0 kA / m or less. When the residual magnetization and coercive force of the carrier are within the above ranges, 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 ³ or more and 4.2 g / cm ³ or less, and more preferably 3.2 g / cm ³ or more and 4.0 g / cm ³ or less. A two-component developer containing a carrier having a true density in this range has a low load on the toner and suppresses toner spent on the carrier. In order to achieve both good developability at low electric field strength and prevention of carrier adhesion, a true density in this range is preferable for the carrier.

  The magnetic carrier preferably has a volume-based 50% particle diameter (D50) of 20 μm or more and 100 μm or less from the viewpoints of imparting triboelectric charge to the toner, suppressing carrier adhesion to the image area, and improving the image quality. More preferably, it is 25 μm or more and 70 μm.

The specific resistance of the magnetic carrier is preferably 1.0 × 10 ⁵ Ω · cm or more and 1.0 × 10 ¹² Ω · cm or less at an electric field strength of 500 V / cm. It is more preferably 1.0 × 10 ⁸ Ω · cm to 1.0 × 10 ¹¹ Ω · cm in terms of enhancing developability and suppressing the occurrence of leakage. When the specific resistance value is in the above range, good developability can be obtained even at low electric field strength.

  The specific resistance value of the magnetic carrier can be adjusted by changing the amount of inorganic fine particles such as carbon black or cross-linked resin fine particles to be added.

<Toner>
Next, the toner contained in the two-component developer together with the magnetic carrier will be described.

  The toner preferably has a weight average particle diameter (D4) of 3.0 μm or more and 8.0 μm or less in order to achieve both high image quality and durability. When the weight average particle diameter (D4) is in the above range, the toner has good fluidity, it is easy to obtain a sufficient charge amount, and good resolution is easily obtained.

  The toner preferably has an average circularity of 0.940 or more and 1.000 or less. When the average circularity of the toner is within the above range, the releasability between the carrier and the toner is good. In addition, good cleaning properties are easily obtained. The average circularity is based on a circularity distribution obtained by analyzing the circularity of particles measured by a flow type particle image measuring apparatus by dividing the circularity range of 0.20 to 1.00 into 800 divided channels. is there. As the flow type particle image measuring apparatus, an apparatus having one field of view of 512 pixels × 512 pixels and a resolution of 0.37 μm × 0.37 μm per pixel was used.

  By using a toner having a weight average particle size in the above range and an average circularity in the above range and a carrier coated with the coating resin of the present invention, the fluidity as a developer can be controlled appropriately. As a result, the transportability of the two-component developer on the developer carrying member is improved, the toner is separated from the carrier, and excellent developability can be obtained. When used with a toner having a large particle size and a high degree of circularity, the releasability between the toner and the carrier becomes too high, so that the developer slips on the developer carrier and easily causes poor conveyance. There is a case. In addition, when a toner having a small particle size and a low circularity is used, the adhesion between the toner and the carrier is too high, so that the developability may be lowered even with the coating resin of the present invention.

  As the toner, toner having toner particles containing a binder resin and a colorant is used.

  Examples of the binder resin contained in the toner particles include the following. Polyester, polystyrene; polymer of styrene derivatives such as poly-p-chlorostyrene and polyvinyltoluene; styrene-p-chlorostyrene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-acrylic Acid ester copolymer, styrene-methacrylic acid ester copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, Styrene copolymers such as styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer; polyvinyl chloride, phenol resin, modified phenol resin, maleic resin, acrylic resin, methacrylic resin, polyvinyl acetate, silicone resin; Polyester resins having as structural units monomers selected from aliphatic polyhydric alcohols, aliphatic dicarboxylic acids, aromatic dicarboxylic acids, aromatic dialcohols and diphenols; polyurethane resins, polyamide resins, polyvinyl butyral, terpenes Resin, coumarone indene resin, petroleum resin.

  The toner may be produced by a pulverization method or may be obtained by a method of producing toner particles in an aqueous medium such as a suspension polymerization method or an emulsion aggregation method.

  In order to obtain a toner having a high average circularity, it is preferable to use a method of producing toner particles in an aqueous medium such as a suspension polymerization method or an emulsion aggregation method.

  Examples of the polymerizable monomer that can be used in carrying out the suspension polymerization method include the following. Styrene monomers, acrylic monomers, methacrylic monomers, monomers of ethylenically unsaturated monoolefins, monomers of vinyl esters, monomers of vinyl ethers, monomers of vinyl ketones, monomers of N-vinyl compounds, other vinyl monomers.

  Examples of the styrenic monomer include the following. Styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-phenylstyrene, p-chlorostyrene, 3,4-dichlorostyrene, p-ethylstyrene, 2,4-dimethyl Styrene, pn-butyl styrene, p-tert-butyl styrene, pn-hexyl styrene, pn-octyl styrene, pn-nonyl styrene, pn-decyl styrene, pn-dodecyl styrene .

  Examples of the acrylic monomer include the following. Methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, dimethylaminoethyl acrylate, acrylic acid Acrylic esters such as phenyl, acrylic acid and acrylic amides.

  Moreover, as a methacrylic monomer, the following are mentioned, for example. Ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, methacryl Methacrylic acid esters such as diethylaminoethyl acid and methacrylic acid and methacrylic acid amides.

  Examples of the monomer of the ethylenically unsaturated monoolefins include ethylene, propylene, butylene, and isobutylene.

  Examples of the vinyl ester monomers include vinyl acetate, vinyl propionate, and vinyl benzoate.

  Examples of vinyl ether monomers include vinyl methyl ether, vinyl ethyl ether, and vinyl isobutyl ether.

  Examples of vinyl ketone monomers include vinyl methyl ketone, vinyl hexyl ketone, and methyl isopropenyl ketone.

  Examples of the monomer of the N-vinyl compound include N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, and N-vinyl pyrrolidone.

  Examples of the other vinyl monomers include acrylic acid derivatives or methacrylic acid derivatives such as vinyl naphthalenes, acrylonitrile, methacrylonitrile, and acrylamide.

  These vinyl monomers can be used alone or in combination of two or more.

  As a polymerization initiator used when manufacturing a vinyl-type resin, the following are mentioned, for example. 2,2′-azobis- (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis Azo or diazo polymerization initiators such as -4-methoxy-2,4-dimethylvaleronitrile, azobisisobutyronitrile, benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, t-butyl hydroperoxide, Di-t-butyl peroxide, dicyl peroxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide, 2,2-bis (4,4-t-butylperoxycyclohexyl) propane, tris- (t-butylperoxy) triazine Peroxidation Initiator having a system initiator or a peroxide in the side chain, potassium persulfate, such as persulfate ammonium persulfate, hydrogen peroxide.

  Examples of radically polymerizable trifunctional or higher polymerization initiators include, for example, tris (t-butylperoxy) triazine, vinyltris (t-butylperoxy) silane, 2,2-bis (4,4- Di-t-butylperoxycyclohexyl) propane, 2,2-bis (4,4-di-t-amylperoxycyclohexyl) propane, 2,2-bis (4,4-di-t-octylperoxycyclohexyl) And radical polymerizable polyfunctional polymerization initiators such as propane and 2,2-bis (4,4-di-t-butylperoxycyclohexyl) butane.

  The toner of the present invention may contain a release agent. For example, the following can be used. Low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, aliphatic hydrocarbon wax such as Fischer-Tropsch wax, oxide of aliphatic hydrocarbon wax such as oxidized polyethylene wax, Or a block copolymer thereof, carnauba wax, montanic acid ester wax, waxes mainly composed of fatty acid esters such as behenyl behenate, and fatty acid esters such as deoxidized carnauba wax partially or fully deoxidized. .

  Suitable release agents include hydrocarbon waxes and paraffin waxes. The toner has one or more endothermic peaks in a temperature range of 30 ° C. to 200 ° C. in the endothermic curve of the toner obtained by differential scanning calorimetry, and the peak temperature of the maximum endothermic peak in the endothermic peak is 50. It is preferable that the temperature is not lower than 110 ° C and not higher than 110 ° C. When such a release agent is used, it is possible to obtain a toner having low adhesion between the toner and the carrier, excellent developability, and excellent low-temperature fixability and durability.

  The content of the release agent is preferably 1 part by mass or more and 15 parts by mass or less, and more preferably 3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the binder resin. When the content of the release agent is within the above range, good releasability can be obtained and contamination to the magnetic carrier can be suppressed.

  The toner may contain a charge control agent. Examples of the charge control agent include organometallic complexes, metal salts, and chelate compounds. Examples of the organometallic complex include a monoazo metal complex, an acetylacetone metal complex, a hydroxycarboxylic acid metal complex, a polycarboxylic acid metal complex, and a polyol metal complex. Other examples include carboxylic acid derivatives such as metal salts of carboxylic acids, carboxylic acid anhydrides, and esters, and condensates of aromatic compounds. Also, phenol derivatives such as bisphenols and calixarenes can be used as the charge control agent. Aromatic carboxylic acid metal compounds are particularly preferred from the standpoint that the toner charge rise is good, since the toner charge rise is good.

  The content of the charge control agent is preferably 0.1 parts by mass or more and 10.0 parts by mass or less, and 0.2 parts by mass or more and 5.0 parts by mass or less with respect to 100 parts by mass of the binder resin. Is more preferable. When the charge control agent is used within the above range, stable triboelectric charging can be performed in an environment from high temperature and high humidity to low temperature and low humidity.

  The absolute value of the triboelectric charge amount of the toner in the two-component developer is preferably 25 mC / kg or more and 65 mC / kg or less. The triboelectric charge amount specified here is a value obtained when a developer prepared so that the toner concentration is 3% by mass or more and 20% by mass or less is placed in a plastic bottle and mixed for 2 minutes by a tumbler mixer or various shakers. The amount of charge. If it is said range, it will be easy to obtain a high quality image and it will be easy to obtain an image without fog.

  Examples of the colorant contained in the toner include the following.

  Examples of the black colorant include carbon black; a magnetic material; a black colorant using a yellow colorant, a magenta colorant, and a cyan colorant.

  As the colorant, a pigment may be used alone, but it is more preferable from the viewpoint of the image quality of a full-color image to improve the sharpness by using a dye and a pigment together.

  Examples of the color pigment 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, 49, 50, 51, 52, 53, 54, 55, 57, 58, 60, 63, 64, 68, 81, 83, 87, 88, 89, 90, 112, 114, 122, 123, 163, 202, 206, 207.209, 238; I. Pigment violet 19; C.I. I. Bat red 1, 2, 10, 13, 15, 23, 29, 35.

  Examples of the magenta toner dye include the following. C. I. Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 81, 82, 83, 84, 100, 109, 121; I. Disper thread 9; I. Solvent violet 8, 13, 14, 21, 27; C.I. I. Oil-soluble dyes such as Disper Violet 1, C.I. I. B. Basic Red 1, 2, 9, 12, 13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 34, 35, 36, 37, 38, 39, 40; I. Basic dyes such as Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27, 28.

  Examples of the color pigment for cyan toner include the following. C. I. Pigment blue 2, 3, 15: 3, 15: 4, 16, 17; I. Bat Blue 6; C.I. I. Acid Blue 45, a copper phthalocyanine pigment in which 1 to 5 phthalimidomethyl groups are substituted on the phthalocyanine skeleton.

  Examples of the color pigment for yellow 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; I. Bat yellow 1, 3, 20

  Examples of the coloring dye for yellow include C.I. I. Solvent yellow 162 may be mentioned.

  The amount of the colorant used is preferably 0.1 to 30 parts by mass, more preferably 0.5 to 20 parts by mass, and most preferably 3 to 15 parts by mass with respect to 100 parts by mass of the binder resin. It is.

  It is preferable that silica particles having a maximum peak particle size of 80 nm or more and 200 nm or less based on the number distribution are externally added to the toner as spacer particles for improving the releasability between the toner and the carrier. In order to more favorably suppress detachment from the toner while functioning as spacer particles, the thickness is more preferably from 100 nm to 150 nm.

  Further, in order to improve the fluidity of the toner, it is preferable to contain inorganic fine particles having a maximum peak particle size of 20 nm or more and 50 nm or less based on the number distribution, and it is also preferable to use both in combination.

  Furthermore, other external additives may be added to the toner particles for the purpose of improving fluidity and transferability. The external additive externally added to the toner particle surface preferably contains 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 additive is preferably 0.3 parts by mass or more and 5.0 parts by mass or less, and 0.8 parts by mass or more and 4.0 parts by mass or less with respect to 100 parts by mass of the toner particles. More preferably. Among them, the content of silica particles having a maximum peak particle size of 80 nm or more and 200 nm or less based on the number distribution is from 0.1 parts by mass to 2.5 parts by mass, more preferably from 0.5 parts by mass to 2.0 parts by mass. Or less. Within this range, the effect as spacer particles becomes more prominent.

  In addition, the surfaces of silica particles and inorganic fine particles used as external additives are preferably subjected to a hydrophobic treatment. The hydrophobizing treatment is preferably performed by a coupling agent such as various titanium coupling agents and silane coupling agents; fatty acids and metal salts thereof; silicone oils; or a combination thereof.

  As a titanium coupling agent, the following are mentioned, for example. Tetrabutyl titanate, tetraoctyl titanate, isopropyl triisostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, bis (dioctyl pyrophosphate) oxyacetate titanate.

  Moreover, as a silane coupling agent, the following are mentioned, for example. 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, phenyl Trimethoxysilane, o-methylphenyltrimethoxysilane, p-methylphenyltrimethoxysilane.

  Examples of the fatty acid include the following. 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, arachidonic acid. Examples of the metal of these fatty acid metal salts include zinc, iron, magnesium, aluminum, calcium, sodium, and lithium.

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

  The hydrophobization treatment is performed by adding a hydrophobizing agent of 1% by mass to 30% by mass (more preferably 3% by mass to 7% by mass) with respect to the particles to be treated. It is preferable to carry out by coating.

  The degree of hydrophobicity of the hydrophobized external additive is not particularly limited. For example, the hydrophobization degree after the treatment is preferably 40 or more and 98 or less. The degree of hydrophobicity indicates the wettability of a sample to methanol and is an index of hydrophobicity.

  In the two-component developer of the present invention, the mixing ratio of the toner and the magnetic carrier is preferably in the range of 2 to 35 parts by mass with respect to 100 parts by mass of the magnetic carrier. More preferably, it is 4 to 25 mass parts, Most preferably, it is 5 to 20 mass parts. If it is less than 2 parts by mass, the image density tends to decrease, and if it exceeds 35 parts by mass, fog and in-flight scattering tend to occur.

  The replenishment developer of the present invention is characterized by containing at least the toner and the magnetic carrier. The replenishment developer can be used in a two-component developer method in which the replenishment developer is developed while being replenished to the developer, and at least the excess magnetic carrier inside the developer is discharged from the developer.

  From the viewpoint of enhancing the durability of the developer, the replenishment developer contains the toner in an amount of 2 parts by mass or more and 50 parts by mass or less with respect to 1 part by mass of the magnetic carrier.

  In the above replenishment developer, when the toner content is less than 2 parts by mass with respect to 1 part by mass of the magnetic carrier, a large amount of replenishment developer is replenished particularly when an image having a high printing density is printed at high speed. Is required. As a result, the developer for replenishment and the developer in the developing device are used for development before being sufficiently mixed, and the toner tends to be non-uniformly charged. As a result, the image quality may deteriorate. In addition, the amount of developer discharged is increased.

  If the toner is contained in an amount of more than 50 parts by mass with respect to 1 part by mass of the magnetic carrier, the deteriorated magnetic carrier may be used for a long time without being discharged, and the deterioration of the magnetic carrier may progress and the image may be lowered.

  The toner and the magnetic carrier used for the two-component developer and the replenishment developer that are initially filled in the developing unit may be the same or different.

  Next, an example of an image forming apparatus provided with a developing device using the replenishing developer of the present invention will be described. However, the developing device used in the developing method of the present invention is not limited to this.

  FIG. 1 is a schematic diagram in which the image forming method of the present invention is applied to a full-color image forming apparatus. The excess carrier increased by the carrier contained in the replenishment developer overflows the capacity UP, is taken into the developer collection auger, and is transported to the replenishment developer container or another collection container.

  The full-color image forming apparatus main body is provided with a first image forming unit Pa, a second image forming unit Pb, a third image forming unit Pc, and a fourth image forming unit Pd. It is formed on a transfer material through development and transfer processes.

  The configuration of each image forming unit provided in the image forming apparatus will be described by taking the first image forming unit Pa as an example.

  The first image forming unit Pa includes a photoreceptor 61a having a diameter of 30 mm as an electrostatic latent image carrier, and the photoreceptor 61a is rotationally moved in the direction of arrow a. The primary charger 62a as a charging means is disposed so that a charging magnetic brush formed on the surface of a sleeve having a diameter of 16 mm contacts the surface of the photoreceptor 61a. The laser beam 67a is irradiated by an exposure device (not shown) in order to form an electrostatic latent image on the photoreceptor 61a whose surface is uniformly charged by the primary charger 62a. A developing device 63a as developing means for developing the electrostatic latent image carried on the photoreceptor 61a to form a color toner image holds color toner. The transfer blade 64a as a transfer means transfers the color toner image formed on the surface of the photoreceptor 61a onto the surface of the transfer material (recording material) conveyed by the belt-like transfer material carrier 68. The transfer blade 64 a is in contact with the back surface of the transfer material carrier 68 and can apply a transfer bias.

  The first image forming unit Pa first uniformly charges the photosensitive member 61a by the primary charger 62a, then forms an electrostatic latent image on the photosensitive member by the exposure device 67a, and colorizes the electrostatic latent image by the developing device 63a. Development is performed using toner, and the developed toner image is applied to the back side of a belt-shaped transfer material carrier 68 that carries and conveys the transfer material at the first transfer portion (contact position between the photosensitive member and the transfer material). Transfer is performed on the surface of the transfer material by applying a transfer bias from the transfer blade 64a in contact therewith.

  When the toner is consumed by the development and the T / C ratio decreases, the decrease is detected by the toner concentration detection sensor 85 that measures the change in the magnetic permeability of the developer using the inductance of the coil, and the amount of consumed toner is calculated. Accordingly, the replenishment developer is replenished from the replenishment developer container 65a. The toner concentration detection sensor 85 has a coil (not shown) inside.

  This image forming apparatus has the same configuration as that of the first image forming unit Pa, and the second image forming unit Pb, the third image forming unit Pc, and the fourth image forming unit having different color toner colors held in the developing device. The image forming unit Pd is provided with four image forming units. For example, yellow toner is used for the first image forming unit Pa, magenta toner is used for the second image forming unit Pb, cyan toner is used for the third image forming unit Pc, and black toner is used for the fourth image forming unit Pd. The transfer of each color toner onto the transfer material is sequentially performed at the transfer portion of each image forming unit. In this step, the color toners are superimposed on each other by moving the transfer material once on the same transfer material while aligning the registration. When the transfer is completed, the transfer material is separated from the transfer material carrier 68 by the separation charger 69. Then, it is sent to the fixing device 70 by a conveying means such as a conveying belt, and a final full-color image is obtained by only one fixing.

  The fixing device 70 includes a pair of a fixing roller 71 having a diameter of 40 mm and a pressure roller 72 having a diameter of 30 mm. The fixing roller 71 includes heating means 75 and 76 therein.

  The unfixed color toner image transferred onto the transfer material passes through the pressure contact portion between the fixing roller 71 and the pressure roller 72 of the fixing device 70 and is fixed onto the transfer material by the action of heat and pressure. The

  In FIG. 1, a transfer material carrier 68 is an endless belt-like member, and this belt-like member is moved in the direction of arrow e by 80 drive rollers. In addition, a transfer belt cleaning device 79 and a belt driven roller 81 have a belt static eliminator 82, and the pair of registration rollers 83 are for conveying the transfer material in the transfer material holder to the transfer material carrier 68. .

  As the transfer means, in place of the transfer blade that contacts the back side of the transfer material carrier, contact transfer means that can contact the back side of the transfer material carrier and directly apply the transfer bias, such as a roller-like transfer roller, can be used. It is possible to use.

  Further, a non-contact transfer unit that performs transfer by applying a transfer bias from a corona charger arranged in a non-contact manner on the back side of a transfer material carrier that is generally used instead of the contact transfer unit described above. It is also possible to use. However, it is more preferable to use the contact transfer means in that the amount of ozone generated when the transfer bias is applied can be controlled.

  FIG. 2 illustrates a method for collecting surplus carriers.

  When the copying operation as described above is repeated, the toner in the developer stored in the developing tank 17 in the developing device of FIG. 2 is gradually consumed, and the ratio of the toner to the carrier, that is, the toner concentration is decreased. To go. This change in toner density is feedback-controlled by a toner density sensor (not shown) so that the toner density always falls within an appropriate range necessary for development. By the above control, the toner is supplied from the supply port of the toner supply unit 9 to the developing tank 17 in the developing device.

  On the other hand, the carrier in the developer in the developing tank 17 is not consumed by the development and is agitated together with the toner in the developing tank 17, and the magnetic force of the magnet roll and the electrostatic latent image carrier. The surface is gradually contaminated and deteriorated due to the influence of contact and the like. As the carrier deteriorates in this way, a predetermined charge amount cannot be imparted to the toner, resulting in a decrease in image quality. Therefore, it is necessary to replace the deteriorated carrier which is not consumed in the developing device with a new carrier. In FIG. 2, as a means for replenishing a new carrier into the developing device, a developer mixed with a replenishment carrier is placed in a toner cartridge for replenishing toner consumed by development. Then, the developing devices 63a, 63b, 63c, and 63d are supplied from the supply port of the toner supply unit 9.

  The excess carrier is discharged from the developer-side developer discharge port as described below.

  1 at positions where the developing units 63a, 63b, 63c, and 63d face the photoconductors 61a, 61b, 61c, and 61d and perform a developing operation, from a developer-side developer discharge port 34 provided in the developing unit. The overflowed developer moves through the communication pipe 36 and is discharged from the developer recovery port 35.

  In the developing method of the present invention, specifically, an AC voltage is applied to the developer carrying member to form an alternating electric field in the developing region, and the developing is performed while the magnetic brush is in contact with the photosensitive member. It is preferable. The distance between the developer carrying member (developing sleeve) 6 and the photosensitive drum (distance between S and D) is preferably 100 to 1000 μm in terms of preventing carrier adhesion and improving dot reproducibility. If it is narrower than 100 μm, the supply of the developer tends to be insufficient, and the image density becomes low, and if it exceeds 1000 μm, the magnetic lines of force from the magnetic pole S 1 spread and the density of the magnetic brush decreases, resulting in poor dot reproducibility and magnetic coat carrier. As a result, the force for restraining is weakened, and carrier adhesion is likely to occur.

  The voltage between the peaks of the alternating electric field is preferably 300 to 3000 V, and the frequency is 500 to 10000 Hz, preferably 1000 to 7000 Hz, which can be appropriately selected depending on the process. In this case, the waveform of the AC bias for forming the alternating electric field includes a triangular wave, a rectangular wave, a sine wave, or a waveform with a changed duty ratio. In order to cope with the change in the formation speed of the toner image sometimes, it is preferable to perform development by applying a developing bias voltage (intermittent alternating voltage) having a discontinuous AC bias voltage to the developer carrier. . When the applied voltage is lower than 300 V, it is difficult to obtain a sufficient image density, and the fog toner in the non-image portion may not be recovered well. If the voltage exceeds 3000 V, the latent image may be disturbed via the magnetic brush, leading to a reduction in image quality.

  By using a two-component developer with well-charged toner, the anti-fogging voltage (Vback) can be lowered and the primary charge of the photoreceptor can be lowered, thus extending the life of the photoreceptor. it can. Vback is 200 V or less, more preferably 150 V or less, although it depends on the development system. The contrast potential is preferably 100 to 400 V so that a sufficient image density is obtained.

  On the other hand, when the frequency is lower than 500 Hz, although related to the process speed, when the toner in contact with the electrostatic latent image carrier is returned to the developing sleeve, sufficient vibration is not applied and fogging is likely to occur. If it exceeds 10,000 Hz, the toner cannot follow the electric field, and the image quality is likely to deteriorate.

  The structure of the photoreceptor may be the same as that of the photoreceptor used in the image forming apparatus. For example, a conductive layer, an undercoat layer, a charge generation layer, and a charge transport layer are sequentially formed on a conductive substrate such as aluminum or SUS. And a photoreceptor having a structure in which a charge injection layer is provided if necessary. The conductive layer, undercoat layer, charge generation layer, and charge transport layer may be those usually used for a photoreceptor. For example, a charge injection layer or a protective layer may be used as the outermost surface layer of the photoreceptor.

  A method for measuring various physical properties of the magnetic carrier and toner will be described below.

<Inertia radius Rw of coating resin, number average molecular weight Mn, weight average molecular weight Mw>
0.04 g of the coating resin of the present invention is dispersed in 20 ml of THF, dissolved, and allowed to stand for 24 hours, followed by filtration with a 0.2 μm filter, and the filtration is used as a sample.

[Analysis conditions]
Separation column: Shodex KF-807 + KF-805 + KF-803 + KF-G
Column temperature: 40 ° C
Mobile phase solvent: THF
Mobile phase flow rate: 1.0 ml / min.
Sample concentration: about 0.2%
Injection volume: 400 μl
Detector 1: Multi-angle light scattering detector Wyatt DAWN EOS
Detector 2: Differential refractive index detector Shodex RI-71

[Measurement theory]
LS = (dn / dc) ² × C × Mw × KLS
LS: Detector measurement voltage value (V)
dn / dc: Increment of refractive index per 1 g of sample (ml / g)
In this invention, it was set to 0.185 ml / g from the literature value of polystyrene.
C: Concentration (g / ml)
KLS: Coefficient of measurement voltage and scattering intensity (reduction Rayleigh ratio) (equipment constant)

In SEC-MALLS, the molecular size is separated by the molecular sieve of the SEC column, and the absolute molecular weight (Mn and Mw) and concentration (C) change and are eluted every moment, so it is necessary to separately measure the concentration detector in combination with MALLS. is there. The signal intensity is converted into a concentration C, and molecular weights (Mn and Mw) are obtained. In the present invention, a differential refractive index detector (RI) is used as a concentration detector, and the signal intensity (RI) of the RI detector is converted into a concentration (C).
RI = (dn / dc) × C × KRI
KRI: Coefficient of measurement voltage and refractive index (RI constant: calibrated with polystyrene standard)

  Molecular size [radius of inertia (Rw)] was calculated by Debye Plot.

<Number of craters on the surface of the magnetic carrier>
The number of craters on the surface of the magnetic carrier can be measured by SEM observation.

  SEM imaging of the magnetic carrier is performed with 4 fields of view at an acceleration voltage of 2.0 kV and a magnification of 500 times. The number of observed magnetic carriers and the number of crater-like irregularities (craters) existing on the surface of the magnetic carrier are counted to calculate the number of craters present in 100 magnetic carriers.

<Method of separating coating resin from magnetic carrier>
Place 10 g of carrier in a beaker containing 50 ml of toluene. Then, a dispersion treatment was performed for 2 minutes using a desktop type ultrasonic cleaner disperser “VS-150” (manufactured by Vervo Creer) having an oscillation frequency of 50 kHz and an electric output of 150 W. Thereafter, only the supernatant liquid is separated while fixing the carrier core with a magnet so that the carrier core does not flow. This operation is repeated 5 times or more, and the collected supernatant is distilled off under reduced pressure with an evaporator, and then dried for 3 hours in a dryer that is flowing with nitrogen at 50 ° C. to obtain a resin solid. Thereafter, the obtained resin solid is dissolved in 8 ml of acetone, centrifuged at 5000 rpm for 10 minutes, only the supernatant liquid is taken out, and additives such as carbon black are removed. The obtained supernatant liquid was distilled off under reduced pressure with an evaporator, put into a drier having a nitrogen flow at 50 ° C., and dried for 24 hours to obtain a coating resin.

<Method of separating carrier core from magnetic carrier>
Place 10 g of carrier in a beaker containing 50 ml of toluene. Then, a dispersion treatment was performed for 2 minutes using a desktop type ultrasonic cleaner disperser “VS-150” (manufactured by Vervo Creer) having an oscillation frequency of 50 kHz and an electric output of 150 W. Thereafter, the supernatant was removed while fixing the carrier core with a magnet so that the carrier core did not flow. This operation was repeated 5 times or more, and then, it was put into a drier having a nitrogen flow at 50 ° C. and dried for 24 hours to obtain a carrier core.

<Carbon black dispersion diameter in the coating resin>
Using a tabletop ultrasonic cleaner disperser (for example, “VS-150” (manufactured by Velvo Crea, etc.) having an oscillation frequency of 50 kHz and an electric output of 150 W with respect to 0.5 g of a magnetic carrier and adding 50 ml of toluene. Dispersion treatment is performed for 2 minutes to elute carbon black particles.Only the supernatant liquid is separated while fixing the carrier core with a magnet.This supernatant liquid is a micro-track particle size distribution measuring device MT3000 (Nikkiso) equipped with a very small sample circulator. Measurements were made at

<Specific resistance of carrier and carrier core>
The specific resistance of the magnetic carrier used in the present invention is measured using a measuring apparatus schematically shown in FIG. A resistance measurement cell E is filled with a magnetic carrier 47, a lower electrode 41 and an upper electrode 42 are arranged so as to be in contact with the filled magnetic carrier, a voltage is applied between these electrodes, and a current flowing at that time is measured. Thus, the specific resistance of the magnetic carrier is obtained.

A sample amount of 10.0 g was measured, the sample was filled in a resistance measurement cell, and the thickness d of the sample was accurately measured. The voltage application conditions were applied in the order of application conditions I, II, and III, and the current at the applied voltage in application condition III was measured. Thereafter, the specific resistance (Ω · cm) at each electric field strength (V / cm) was obtained by the following formula. The specific resistance at the electric field intensity of 100 V / cm under the application condition III (that is, when the applied voltage / d = 100 (V / cm)) was defined as the specific resistance of the porous magnetic core particles.
Application condition I: (Change from 0V to 500V: Increase in steps of 100V every 30 seconds)
II: (Hold for 30 seconds at 500V)
III: (Change from 500V to 0V: Decrease in steps of 100V every 30 seconds)

The measurement conditions for the specific resistance of the magnetic carrier were a contact area S = 2.4 cm ² between the magnetic carrier and the electrode, and a load of 240 g on the upper electrode. A sample amount of 1.0 g was measured, the sample was filled in a resistance measurement cell, and the thickness d of the sample was accurately measured. The voltage application conditions were applied in the order of application conditions I, II, and III, and the current at the applied voltage of application condition III was measured. Thereafter, the specific resistance (Ω · cm) at each electric field strength (V / cm) was obtained by the following formula. The specific resistance at the electric field intensity of 3000 V / cm under the application condition III (that is, when the applied voltage / d = 3000 (V / cm)) was defined as the specific resistance of the magnetic carrier.
Application condition I: (Change from 0V to 1000V: Increase in steps of 200V every 30 seconds)
II: (Hold for 30 seconds at 1000V)
III: (Change from 1000V to 0V: Decrease in steps of 200V every 30 seconds)
Formula): specific resistance (Ω · cm) = (applied voltage (V) / measured current (A)) × S (cm ² ) / d (cm)

  In the above formula, the value of “applied voltage (V) / d (cm)” is 100 (V / cm) in the measurement of the porous magnetic core particles, and 3000 (V / cm) in the measurement of the carrier. is there.

<Measurement method of magnetization intensity of magnetic carrier>
The strength of magnetization of the magnetic carrier can be obtained by a vibrating magnetic field measuring device (Vibrating sample magnetometer) or a direct current magnetization characteristic recording device (BH tracer). In the examples described later, the measurement was performed by the following procedure using an oscillating magnetic field type magnetic property measuring apparatus BHV-30 (manufactured by Riken Electronics Co., Ltd.).

A cylindrical plastic container packed with a carrier sufficiently densely was used as a sample, and the magnetization moment in an external magnetic field of 1000 / 4π (kA / m) was measured. In addition, the actual mass of the carrier filled in the container was measured. From these, the magnetization intensity (Am ² / kg), remanent magnetization (Am ² / kg), and coercive force (kA / m) of the carrier were determined.

<Measurement method of volume distribution standard 50% particle size (D50) of magnetic carrier and ratio (volume%) of 100 μm or more>
The particle size distribution was measured with Microtrac MT3300EX (Nikkiso Co., Ltd.). For the measurement, a Turbotrac sample feeder for dry measurement was attached.

<Method for measuring true density of magnetic carrier and carrier core>
The true density was measured using a dry automatic densimeter autopycnometer (manufactured by Yuasa Ionics).

<Method of measuring the apparent density of the carrier core>
i) In the case of ferrite particles having a hollow shape or a porous shape When ferrite particles having a hollow shape or a porous shape can be prepared as a sample, it is used as a measurement sample. The particles are taken out and used.

10.0 g of a magnetic carrier is prepared and placed in a crucible. Using a muffle furnace (FP-310, manufactured by Yamato Kagaku) equipped with an N ₂ gas inlet and an exhaust unit, heating was performed at 900 ° C. for 16 hours while introducing N ₂ gas. Thereafter, the magnetic carrier was left until the temperature became 50 ° C. or lower.

  The heated magnetic carrier was placed in a 50 ml plastic bottle, 0.2 g of sodium dodecylbenzenesulfonate and 20 g of water were added, and soot attached to the magnetic carrier was washed. At this time, in order to prevent the magnetic carrier from flowing, it was fixed with a magnet. In addition, the sample was rinsed with water 5 times or more so that the alkylbenzene sulfonate does not remain in the sample. Then, it was dried at 60 ° C. for 24 hours. As described above, ferrite particles were taken out from the magnetic carrier.

  Using the ferrite particles taken out as described above, the apparent apparent density was measured with a powder tester PT-R (manufactured by Hosokawa Micron).

In the measurement, a metallic cup was tapped 180 times up and down at an amplitude of 18 mm using a sieve having an opening of 500 μm while vibrating with an amplitude of 1 mm and supplying ferrite particles to exactly 10 ml. Then, the apparent apparent density (g / cm ³ ) was calculated from the mass of the carrier core particles after tapping.

ii) Cases other than ferrite particles having a hollow shape or a porous shape When a carrier core can be prepared as a sample, it is used as a measurement sample, and when there is only a resin-coated magnetic carrier, a coated resin is coated by the following method. Remove and use the carrier core.

  Prepare 10 g of magnetic carrier, put 50 ml of toluene in a beaker, and disperse for 2 minutes using a desktop type ultrasonic cleaner disperser “VS-150” (manufactured by Velvo Crea) with an oscillation frequency of 50 kHz and an electrical output of 150 W. Processed. Next, the supernatant liquid containing the dissolved coating resin was removed while fixing with a magnet so that the carrier core would not flow. These operations were repeated 5 times or more, and it was confirmed that the supernatant became transparent. Then, it put into the dryer which is flowing nitrogen at 50 degreeC, and it was made to dry for 24 hours, and the carrier core was obtained.

Using the carrier core taken out as described above, the hard apparent density (g / cm ³ ) was measured in the same manner as in i).

<Measurement method of apparent density of looseness of carrier core>
After the carrier core is separated in the same manner as the measurement of the apparent apparent density, the measurement is performed according to JIS-Z2504.

<Method for Measuring Toner Weight Average Particle Size (D4)>
The weight average particle diameter (D4) of the toner is determined based on the precise particle size distribution measuring apparatus “Coulter Counter Multisizer 3” (registered trademark, manufactured by Beckman Coulter, Inc.) having a 100 μm aperture tube. Using the attached dedicated software “Beckman Coulter Multisizer 3 Version 3.51” (manufactured by Beckman Coulter, Inc.) for setting and analyzing the measurement data, the measurement data is measured with 25,000 effective channels. Analysis was performed and calculated.

  As the electrolytic aqueous solution used for the measurement, special grade sodium chloride is dissolved in ion-exchanged water so as to have a concentration of about 1% by mass, for example, “ISOTON II” (manufactured by Beckman Coulter, Inc.) can be used.

  Prior to measurement and analysis, the dedicated software was set as follows.

  In the “Standard Measurement Method (SOM) Change Screen” of the dedicated software, set the total count in the control mode to 50000 particles, set the number of measurements once, and set the Kd value to “standard particles 10.0 μm” (Beckman Coulter, Inc.) Set the value obtained using The threshold and noise level are automatically set by pressing the threshold / noise level measurement button. Also, the current is set to 1600 μA, the gain is set to 2, the electrolyte is set to ISOTON II, and the aperture tube flash after measurement is checked.

  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 bin, and the particle size range is set to 2 μm or more and 60 μm or less.

The specific measurement method is as follows.
(1) About 200 ml of the electrolytic solution is placed in a glass 250 ml round bottom beaker exclusively for Multisizer 3, set on a sample stand, and the stirrer rod is stirred counterclockwise at 24 rpm. Then, dirt and bubbles in the aperture tube are removed by the “aperture flush” function of the analysis software.
(2) About 30 ml of the electrolytic aqueous solution is put in a glass 100 ml flat bottom beaker, and "Contaminone N" (nonionic surfactant, anionic surfactant, organic builder pH 7 precision measurement is used as a dispersant therein. About 0.3 ml of a diluted solution obtained by diluting a 10% by weight aqueous solution of a neutral detergent for washing a vessel (made by Wako Pure Chemical Industries, Ltd.) 3 times with ion exchange water is added.
(3) In an aquarium of an ultrasonic disperser “Ultrasonic Dissipation System Tetora150” (manufactured by Nikkei Bios) with two built-in oscillators with an oscillation frequency of 50 kHz with a phase shifted by 180 degrees and an electrical output of 120 W Is charged with a predetermined amount of ion-exchanged water, and about 2 ml of the above-mentioned Contaminone N is added to this water tank.
(4) The beaker of (2) is set in the beaker fixing hole of the ultrasonic disperser, and the ultrasonic disperser is operated. And the height position of a beaker is adjusted so that the resonance state of the liquid level of the electrolyte solution in a beaker may become the maximum.
(5) In a state where the electrolytic aqueous solution in the beaker of (4) is irradiated with ultrasonic waves, about 10 mg of toner is added to the electrolytic aqueous solution little by little and dispersed. Then, the ultrasonic dispersion process is continued for another 60 seconds. In the ultrasonic dispersion, the temperature of the water tank is appropriately adjusted so as to be 10 ° C. or higher and 40 ° C. or lower.
(6) To the round bottom beaker of (1) installed in the sample stand, the electrolyte solution of (5) in which the toner is dispersed is dropped using a pipette, and the measurement concentration is adjusted to about 5%. . Measurement is performed until the number of measured particles reaches 50,000.
(7) The measurement data is analyzed with the dedicated software attached to the apparatus, and the weight average particle diameter (D4) is calculated. The “average diameter” on the analysis / volume statistics (arithmetic average) screen when the graph / volume% is set with the dedicated software is the weight average particle diameter (D4).

<Measuring method of average circularity of toner>
The average circularity of the toner can be measured with a flow type particle image analyzer “FPIA-3000 type” (manufactured by Sysmex Corporation) under measurement / analysis conditions during calibration.

  The measurement principle of the flow-type particle image analyzer “FPIA-3000 type” (manufactured by Sysmex Corporation) is to take a flowing particle as a still image and perform image analysis. The sample added to the sample chamber is fed into the flat sheath flow cell by a sample suction syringe. The sample fed into the flat sheath flow is sandwiched between sheath liquids to form a flat flow. The sample passing through the flat sheath flow cell is irradiated with strobe light at 1/60 second intervals, and the flowing particles can be photographed as a still image. Further, since the flow is flat, the image is taken in a focused state. The particle image is captured by a CCD camera, and the captured image is subjected to image processing at an image processing resolution of 512 × 512 (0.37 × 0.37 μm per pixel), and the contour of each particle image is extracted, Projected area, perimeter, etc. are measured.

Next, the projected area S and the perimeter L of each particle image are obtained. Using the area S and the perimeter L, the equivalent circle diameter and the circularity are obtained. The circular equivalent diameter is the diameter of a circle having the same area as the projected area of the particle image, and the circularity is a value obtained by dividing the circumference of the circle obtained from the circular diameter by the circumference of the projected particle image. Defined and calculated by the following formula.
C = 2 × (π × S) ^1/2 / L

  When the particle image is circular, the circularity is 1.000. The greater the degree of irregularities on the outer periphery of the particle image, the smaller the circularity.

  After calculating the circularity of each particle, the range of the circularity of 0.2 to 1.0 is divided into 800, and the average circularity is calculated using the number of measured particles.

  As a specific measuring method, 0.1 ml of a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant to 20 ml of ion-exchanged water, and then 0.5 g of a measurement sample is added. Then, dispersion was performed for 2 minutes using a desktop type ultrasonic cleaner disperser “VS-150” (manufactured by Vervo Creer) having an oscillation frequency of 50 kHz and an electric output of 150 W to obtain a dispersion for measurement. In that case, it cools suitably so that the temperature of a dispersion liquid may become 10 to 40 degreeC.

  The flow type particle image analyzer equipped with a standard objective lens (10 ×) is used for measurement, and a particle sheath “PSE-900A” (manufactured by Sysmex Corporation) is used as the sheath liquid. The dispersion liquid prepared according to the above procedure is introduced into the flow type particle image analyzer, and 30000 particles are measured in the HPF measurement mode and in the total count mode. The binarization threshold at the time of particle analysis is set to 85%, the analysis particle diameter is limited to the circle equivalent diameter of 2.00 μm to 200.00 μm, and the average circularity of the toner is obtained.

  In measurement, automatic focus adjustment is performed using standard latex particles (Duke Scientific 5200A diluted with ion-exchanged water) before the start of measurement. Thereafter, it is preferable to perform focus adjustment every two hours from the start of measurement.

  In the examples of the present application, a flow-type particle image analyzer that has been issued a calibration certificate issued by Sysmex Corporation, which has been calibrated by Sysmex Corporation, was used. At that time, measurement is performed under the measurement and analysis conditions when the calibration certificate is received, except that the analysis particle diameter is limited to the circle equivalent diameter of 2.00 μm to 200.00 μm.

  EXAMPLES Hereinafter, although this invention is demonstrated more concretely with reference to an Example, this invention is not limited only to these Examples.

<Example of production of copolymer 1 for coating resin>
It is obtained by polymerizing a monomer shown in Table 1 and a monomer having an ethylenically unsaturated group (methacryloyl group) at one end as shown in Formula (1), wherein X is shown in Table 1. The resulting macromonomer was added to a four-necked flask having a reflux condenser, a thermometer, a nitrogen suction tube, and a friction stirrer. Further, 90 parts by mass of toluene, 110 parts by mass of methyl ethyl ketone, and 2.0 parts by mass of azobisisovaleronitrile were added. The resulting mixture was held at 70 ° C. for 10 hours under a nitrogen stream to conduct a polymerization reaction. After completion of the polymerization reaction, the reaction solution is dropped into 5-fold amount of methanol to precipitate, the supernatant is decanted, the solid is taken out, washed with methanol repeatedly, filtered and dried to obtain a graft copolymer solid. Got. 35 parts by mass of the obtained graft copolymer solid was dissolved in 36 parts by mass of toluene and 29 parts by mass of methyl ethyl ketone to obtain a graft copolymer solution (solid content 35% by mass). This is designated as coating resin 1. The physical properties of the resulting coating resin 1 are shown in Table 1.

<Production Examples of Copolymers 2 to 9 and 11 to 15 for Coating Resins>
In the same manner as in the production of coating resin 1, coating resins 2 to 9 and 11 to 15 were obtained by using the monomers shown in Table 1 and the monomers in which X in formula (1) is shown in Table 1. Table 1 shows the physical properties of the obtained coating resins 2 to 9 and 11 to 15.

<Examples of Production of Copolymers 10 and 16 for Coating Resins>
In the same manner as in the production of the coating resin 1, a monomer shown in Table 1 and a monomer in which X in the formula (1) is shown in Table 1 were subjected to a polymerization reaction at 70 ° C. in a nitrogen stream. After holding for 3 hours, 1.0 part by mass of azobisisovaleronitrile was further added, and the reaction temperature was raised to 80 ° C. and held for 5 hours to complete the reaction. After the completion of the polymerization reaction, the reaction solution is dropped into 5-fold amount of methanol to precipitate, the supernatant is decanted, the solid is taken out, washed with methanol repeatedly, filtered and dried to obtain a graft copolymer solid. Got. 35 parts by mass of the obtained graft copolymer solid was dissolved in 36 parts by mass of toluene and 29 parts by mass of methyl ethyl ketone to obtain a graft copolymer solution (solid content 35% by mass). These are designated as coating resins 10 and 16. The physical properties of the obtained coating resin 10 are shown in Table 1.

<Production Example of Copolymers 17 and 18 for Coating Resins>
Similarly to the production of the coating resin 1, the monomer shown in Table 1 and the monomer in which X in the formula (1) is shown in Table 1 are held at 70 ° C. for 10 hours under a nitrogen stream to conduct a polymerization reaction. It was. After completion of the polymerization reaction, a graft copolymer solution (solid content: 33%) was obtained without performing precipitation and washing with methanol. These are designated as coating resins 17 and 18.

  Table 1 shows the physical properties of the obtained coating resins 17 and 18.

<Manufacture of carrier core>
Magnetite fine particles (spherical, number average particle size 250 nm, magnetization strength 65 Am ² / kg, remanent magnetization 4.2 Am ² / kg, coercive force 4.4 kA / m, specific resistance 3.3 × 10 ⁵ Ω at 500 V / cm Cm) and a silane coupling agent (3- (2-aminoethylaminopropyl) trimethoxysilane) (amount of 3.0% by mass with respect to the mass of magnetite fine particles) were introduced into the container. Then, the magnetite fine particles were surface-treated by mixing and stirring at a high temperature at a temperature of 100 ° C. or higher in the container.

-Phenol 10 mass parts-Formaldehyde solution (formaldehyde 37 mass% aqueous solution) 16 mass parts-Surface-treated said magnetite fine particle 84 mass parts The said material was introduce | transduced into the reaction kettle, and it was made into the temperature of 40 degreeC, and was mixed well. Thereafter, the mixture was heated to 85 ° C. at an average temperature increase rate of 3 ° C./min with stirring, and 4 parts by mass of 28% by mass aqueous ammonia and 25 parts by mass of water were added to the reaction kettle. It was held at a temperature of 85 ° C. and cured by polymerization reaction for 3 hours. The peripheral speed of the stirring blade at this time was 1.8 m / sec.

After the polymerization reaction, the mixture was cooled to a temperature of 30 ° C. and water was added. The precipitate obtained by removing the supernatant was washed with water and further air-dried. The obtained air-dried product was dried under reduced pressure (5 hPa or less) at a temperature of 60 ° C., 50% particle size (D50) based on volume distribution in which a magnetic material was dispersed in the resin, 35 μm, loose apparent density 1 A carrier core (a) of 90 g / cm ³ was obtained. The specific resistance of the carrier core (a) was 2.2 × 10 ⁸ Ω · cm, the apparent apparent density was 2.11 g / cm ³ , and the true density was 3.60 g / cm ³ . Further, the magnetization strength was 55 Am ² / kg, the remanent magnetization was 3.5 Am ² / kg, and the coercive force was 4.3 kA / m.

<Production example of magnetic carriers 1 to 18>
The coating resin 1 was dissolved in toluene so as to have a solid content of 10% by mass. Among them, carbon black (primary particle diameter of 27 nm, specific surface area of 80 m ² / g), 15.0 parts by mass with respect to 100 parts by mass of the coating resin solid content, crosslinked melamine particles (maximum peak particle diameter based on number distribution) Was added to 2.0 parts by mass with respect to 100 parts by mass of the coating resin solid content, and sufficiently stirred and dispersed.

  Next, using a universal mixing stirrer (made by Fuji Powder Co., Ltd.) as a coating device, the coating solution is divided into three times so that the coating amount (as solid content) is 1.5 parts by mass with respect to 100 parts by mass of the carrier core. And put it in. At that time, the pressure in the mixer was reduced, nitrogen was introduced, and the atmosphere was replaced with nitrogen. The mixture was heated to a temperature of 65 ° C., stirred while maintaining a reduced pressure (700 MPa) in a nitrogen atmosphere, and the solvent was removed until the carrier further increased. Further, with stirring, the mixture was heated to 100 ° C. while introducing nitrogen and held for 1 hour. After cooling, a magnetic carrier 1 was obtained. Table 2 shows the physical properties of the magnetic carrier 1 obtained.

  Further, similarly to the magnetic carrier 1, magnetic carriers 2 to 18 were obtained by using the coating resin shown in Table 2 (fixed at a resin solid content of 1.5 parts by mass with respect to 100 parts by mass of the carrier core). Table 2 shows the physical properties of the magnetic carriers 2 to 18.

(Toner Production Example 1)
As materials for obtaining a vinyl-based copolymer unit, 10 parts by mass of styrene, 5 parts by mass of 2-ethylhexyl acrylate, 2 parts by mass of fumaric acid, 5 parts by mass of a dimer of α-methylstyrene, 5 parts by mass of dicumyl peroxide The part was placed in a dropping funnel. Moreover, as a material for obtaining a polyester polymer unit, 25 parts by mass of polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, polyoxyethylene (2.2) -2,2 -15 parts by mass of bis (4-hydroxyphenyl) propane, 9 parts by mass of terephthalic acid, 5 parts by mass of trimellitic anhydride, 24 parts by mass of fumaric acid and 0.2 parts by mass of tin 2-ethylhexanoate were added to 4 liters of glass. Placed in a four-necked flask. A thermometer, a stirring rod, a condenser, and a nitrogen introducing tube were attached to this four-necked flask and installed in a mantle heater. Next, after the inside of the four-necked flask was replaced with nitrogen gas, the temperature was gradually raised while stirring, and while stirring at a temperature of 130 ° C., the vinyl monomer and the polymerization initiator were added from the previous dropping funnel. The solution was added dropwise over about 4 hours. Next, the temperature was raised to 200 ° C. and reacted for 4 hours to obtain a hybrid resin having a weight average molecular weight of 78,000 and a number average molecular weight of 3800.

-100 parts by mass of the above hybrid resin-5.0 parts by mass of purified normal paraffin (maximum endothermic peak temperature 80 ° C)-0.5 parts by mass of 3,5-di-t-butylsalicylic acid aluminum compound-C.I. I. Pigment Blue 15: 3 5.0 parts by mass The above-mentioned ingredients were mixed with a Henschel mixer (FM-75 type, manufactured by Mitsui Miike Chemical Co., Ltd.), and then a twin-screw kneader (PCM) set at a temperature of 130 ° C. -30 type, manufactured by Ikekai Tekko Co., Ltd.). The obtained kneaded material was cooled and coarsely pulverized to 1 mm or less with a hammer mill to obtain a coarsely pulverized material. The obtained coarsely pulverized toner was finely pulverized using a collision-type airflow pulverizer using a high-pressure gas. Further, the finely pulverized product obtained was classified, and further subjected to spheroidization treatment 5 times using a hybridizer (manufactured by Nara Machinery Co., Ltd.), weight average particle diameter (D4) 5.8 μm, average circularity 0. 957 cyan toner particles were obtained.

  Similarly, C.I. I. Pigment Blue 15: 3 instead of C.I. I. Pigment Yellow 74 is 7.0 parts by mass, C.I. I. Yellow, magenta, and black toner particles were prepared using 6.0 parts by weight of Pigment Red 122 and 5.0 parts by weight of carbon black used in the manufacture of Magnetic Carrier 1, respectively.

  To 100 parts by mass of each of the obtained toner particles, 1.0 part by mass of silica particles having a maximum peak particle size of 110 nm based on the number distribution and treated with hexamethyldisilazane and having a degree of hydrophobicity of 94 are obtained. 0.9 parts by mass of titanium oxide particles having a peak particle size of 50 nm and a hydrophobization degree of 70, and 0.5 parts by mass of silicone oil-treated silica particles having a maximum peak particle diameter of 20 nm on a number distribution basis and a hydrophobization degree of 98 Added. Then, the toner was mixed with a Henschel mixer (manufactured by Mitsui Miike Chemical Industries) to obtain each color toner having a weight average particle diameter of 5.9 μm and an average circularity of 0.956.

[Example 1]
To 92 parts by mass of carrier 1, 8 parts by mass of each color toner was added and mixed for 2 minutes by a tumbler mixer to prepare a two-component developer.

  On the other hand, 90 parts by mass of toner 1 is added to 10 parts by mass of carrier 1 and mixed for 5 minutes in a V-type mixer in an environment of normal temperature and normal humidity of 23 ° C. and 50% RH to obtain a replenishment developer. The replenishment developer container in the container was filled.

  The results of the following evaluations using the two-component developer and the replenishment developer are shown in the table.

As an image forming device, Canon color copy machine imagePRESS C7000VP was remodeled so that it could be output under the following conditions, and the developer was put in each color developer, and before and after the durability test of 50,000 images with an image area ratio of 30% under the following conditions: Various evaluations were performed.
conditions:
Printing environment Temperature 30 ° C / Humidity 80RH% (hereinafter “H / H”)
Temperature 23 ° C / Humidity 5RH% (hereinafter “N / L”)
Paper (1) Color laser copier paper (81.4 g / m ² )
Paper (2) Color laser copier glossy cardboard NS-701 (150 g / m ² )
(Both are Canon Marketing Japan Inc.)
Image formation speed A4 size, full color was modified to output at 40 sheets / minute.
Development conditions Modified so that development contrast can be changed freely.
Developer idle rotation The sleeve peripheral speed of the main unit developer was changed freely, and it was modified to allow idle rotation.

(1) ΔQ / M on sleeve
The evaluation was made by subtracting the toner charge amount (μC / g) on the sleeve after durability from the toner charge amount (μC / g) on the initial sleeve.
A: 10 or less B: 10 or more, 15 or less C: 15 or more, 20 or less D: 20 or more, 25 or less E: 25 or more

  Note that levels A to C are acceptable as a product.

(2) Evaluation of image crush (after endurance)
After the endurance, the development contrast required for the amount of toner developed on the photoreceptor to be 0.55 mg / cm ² was adjusted, and an A4 full-color image was output to the color laser copier glossy thick paper NS-701. At this time, the number of crushing images on the image that seemed to be white was counted, and the number of crushing images of one A4 sheet image output in a single color was averaged.
A: Within 2 pieces.
B: More than 2 and 4 or less.
C: More than 4 and 6 or less.
D: More than 6 and 8 or less.
E: More than 8 and 11 or less.
F: More than 11 and 15 or less.
G: More than 15 pieces.

  The levels that are not problematic as products are A to D.

(3) Fog (after endurance)
After the endurance, an A4 full solid white image was output with color laser copier paper. For the fog, the whiteness of the white background portion was measured with a reflectometer (manufactured by Tokyo Denshoku), and the fog density (%) was calculated and evaluated from the difference between the whiteness and the whiteness of the transfer paper. The evaluation criteria are as follows.
A: Very good (less than 0.5%)
B: Good (0.5% or more and less than 1.0%)
C: Slightly good (1.0% or more, less than 1.5%)
D: Normal (1.5% or more, less than 2.5%)
E: Slightly bad (2.5% or more, less than 3.0%)
F: Bad (3.0% or more and less than 4.0%)
G: Very bad (over 4.0%)
The levels that are not problematic as products are A to D.

(4) Dot reproducibility (after endurance)
After endurance, a halftone image (30H image) was output with color laser copier paper. This image was visually observed, and the dot reproducibility of the image was evaluated based on the following criteria. The 30H image is a halftone image when 256 gradations are displayed in hexadecimal, 00H is solid white, and FFH is solid black.
A: The image is smooth without feeling any roughness.
B: I don't feel so much.
C: Although there is a slight feeling of roughness, it is at a level where there is no practical problem.
D: There is a feeling of roughness.
E: There is a very rough feeling.
Note that levels A to C are acceptable as a product.

(5) Ghost (after endurance)
After the endurance, the image shown in FIG. 4 was output and visually evaluated according to the following criteria.
A: No ghost is generated.
B: Although a slight ghost is generated, a good image is obtained.
C: Although the ghost is generated, there is no problem in practical use.
D: Image with poor ghost and unpreferable for practical use.

  In Example 1, each evaluation showed very good image characteristics. The results are shown in Table 3.

[Examples 2 to 10, Reference Example 1 ]
Similarly to Example 1, the two-component developer and the replenishment developer were prepared using the magnetic carriers 2 to 11. When evaluation was carried out in the same manner as in Example 1, all image characteristics having no problems were obtained. The results are shown in Table 3.

[Comparative Examples 1 to 7]
In the same manner as in Example 1, the two-component developer and the replenishment developer were prepared using the magnetic carriers 12 to 18. When the evaluation was performed in the same manner as in Example 1, the amount of charge was remarkably reduced, particularly in the HH environment, and the level of image crushing and ghosting was also poor. Moreover, the deterioration of fog was remarkable in the NL environment. The results are shown in Table 3.

  41 Lower electrode, 42 Upper electrode, 43 Insulator, 44 Ammeter, 45 Voltmeter, 46 Constant voltage device, 47 Magnetic carrier, 48 Guide ring, E Resistance measurement cell, L Sample thickness

Claims (5)

It is a magnetic carrier having a resin coating layer on the surface of the carrier core,
The resin forming the resin coating layer is
i) At least a resin obtained by copolymerizing a monomer represented by the following formula (A1) and a macromonomer represented by the following formula (A2) and having a weight average molecular weight of 3,000 to 20,000. The proportion of units derived from the macromonomer is 0.5% by mass or more and 30.0% by mass or less,
ii) The inertial radius Rw in the size exclusion chromatography-online-multi-angle light scattering (SEC-MALLS) measurement in THF-soluble matter in THF is 5 nm to 30 nm, and the number average molecular weight Mn is 2.3 × 10 ^4. 1.0 × 10 ⁵ or less ,
A magnetic carrier characterized by that.

(In the formula, R ¹ represents a hydrocarbon group having 4 to 22 carbon atoms, and R ² represents H or CH _3. )

(In the formula, A is one selected from the group consisting of methyl acrylate, methyl methacrylate, butyl acrylate, butyl methacrylate, 2-ethylhexyl acrylate, 2-ethylhexyl methacrylate, styrene, acrylonitrile, and methacrylonitrile. Or a polymer obtained by polymerizing two or more monomers, and R ³ represents H or CH _3. ) The resin forming the resin coating layer is characterized in that an inertia radius Rw (nm) and a weight average molecular weight Mw in SEC-MALLS measurement in THF-soluble THF satisfy the following formula: The magnetic carrier according to 1.
2.0 × 10 ⁻⁴ ≦ Rw / Mw ≦ 1.0 × 10 ⁻³ The resin forming the resin coating layer is a resin obtained by copolymerizing a macromonomer represented by the formula (A2), a monomer represented by the formula (A1), and a methyl methacrylate monomer. The magnetic carrier according to claim 1 or 2 , wherein the proportion of the methyl methacrylate monomer unit in the resin obtained by copolymerization is at least 1 mass% and not more than 50 mass%. . A two-component developer having at least a magnetic carrier having a resin coating layer on the surface of a carrier core and a toner, wherein the magnetic carrier is the magnetic carrier according to any one of claims 1 to 3. Two-component developer. A replenishment developer for use in an image forming method in which development is performed while replenishing a replenishment developer. The replenishment developer includes at least a magnetic carrier and a toner, and the toner is contained in 1 part by mass of the magnetic carrier. The developer for replenishment according to claim 1, wherein the magnetic carrier is a magnetic carrier according to any one of claims 1 to 3 .

Images