JP2016151615A - Two-component developer and method for producing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a two-component developer capable of suppressing carrier development (carrier adhesion to photosensitive drum) while keeping excellent developing properties.SOLUTION: A two-component developer contains a toner and a carrier. The carrier contains a plurality of carrier cores containing a binder resin, and a plurality of carrier particles having resin layers formed on the surfaces of the carrier cores. The toner contains a plurality of toner particles. A plurality of magnetic particles are dispersed in the binder resin of the carrier core. Among the carrier particles contained in the carrier, the carrier particles having a particle diameter of less than 20 μm have a magnetic force of 70 emu/g or more, and the carrier particles having a particle diameter of 20 μm or more have a magnetic force of 40 emu/g or more and 60 emu/g or less. The carrier contains the carrier particles having a particle diameter of less than 20 μm at a ratio of 7 mass% or more and 15 mass% or less.SELECTED DRAWING: None

Description

  The present invention relates to a two-component developer that can be used for developing an electrostatic latent image and a method for producing the same.

  There is known an image forming apparatus that forms a toner image on a photosensitive drum by developing an electrostatic latent image formed on a photosensitive layer of the photosensitive drum using a two-component developer. The formed toner image is transferred to a recording medium (for example, printing paper), whereby an image is formed on the recording medium.

  A two-component developer can be prepared by mixing a carrier containing a plurality of carrier particles and a toner containing a plurality of toner particles. By using a two-component developer, it becomes easy to form a high-quality image in a high-speed process.

However, when an image is formed using a two-component developer, a phenomenon in which a carrier adheres to the photosensitive drum (hereinafter referred to as carrier development) may occur. For example, in the two-component developer described in Patent Document 1, the carrier particles have a high specific resistance (specifically, 5.0 × 10 ¹³ Ω · cm or more and 1.0 × 10 ¹⁶ Ω when 5000 V / cm ^{2 is} applied). Carrier development is suppressed by setting it to cm or less.

JP 2004-212519 A

  However, if the specific resistance of the carrier particles is increased as in the two-component developer described in Patent Document 1, the developability of the two-component developer tends to be lowered.

  SUMMARY An advantage of some aspects of the invention is that it provides a two-component developer capable of suppressing carrier development (carrier adhesion to a photosensitive drum) while maintaining excellent developability. Another object of the present invention is to provide a two-component developer that is excellent in both stress resistance and durability even when a low-melting toner (low-temperature fixing toner) is used.

  The two-component developer according to the present invention includes a toner and a carrier. The carrier includes a plurality of carrier particles having a carrier core containing a binder resin and a resin layer formed on the surface of the carrier core. The toner includes a plurality of toner particles. A plurality of magnetic particles are dispersed in the binder resin. Among the carrier particles contained in the carrier, carrier particles having a particle diameter of less than 20 μm have a magnetic force of 70 emu / g or more, and carrier particles having a particle diameter of 20 μm or more have a magnetic force of 40 emu / g or more and 60 emu / g or less. The carrier contains carrier particles having a particle diameter of less than 20 μm at a ratio of 7% by mass or more and 15% by mass or less.

  The method for producing a two-component developer according to the present invention includes carrier preparation, magnetic force adjustment, and carrier mixing. In the carrier preparation, a plurality of types of carriers having different particle diameters are prepared. In the adjustment of the magnetic force, the magnetic force is adjusted for each of the plurality of types of carriers. In the mixing of the carriers, after adjusting the magnetic force, by mixing the plurality of types of carriers, among the carriers including the plurality of types of carriers, the magnetic force of carrier particles having a particle diameter of less than 20 μm is set to 70 emu / g or more, The magnetic force of carrier particles having a particle diameter of 20 μm or more is set to 40 emu / g or more and 60 emu / g or less.

  According to the present invention, it is possible to provide a two-component developer capable of suppressing carrier development (carrier adhesion to the photosensitive drum) while maintaining excellent developability. In addition, according to the present invention, it is possible to provide a two-component developer excellent in both stress resistance and durability even when a low-temperature melting toner (low-temperature fixing toner) is used instead of or in addition to this effect. The effect that it becomes possible may be produced.

  Hereinafter, embodiments of the present invention will be described. The two-component developer according to this embodiment includes a toner and a carrier. The toner and the carrier are each a powder composed of a large number of particles. The toner includes a plurality of toner particles having the configuration described below. The carrier includes a plurality of carrier particles having the configuration described below. The toner contained in the two-component developer according to this embodiment can be used as, for example, a positively chargeable toner.

  The toner includes a plurality of toner particles. The toner particles may have an external additive. When the toner particles have an external additive, the toner particles have toner base particles and an external additive. The external additive adheres to the surface of the toner base particles. The toner base particles include a binder resin. If necessary, an internal additive (for example, at least one of a release agent, a colorant, a charge control agent, and a magnetic powder) may be dispersed in the binder resin of the toner base particles. If not necessary, the external additive may be omitted. When omitting the external additive, the toner base particles correspond to the toner particles. The toner according to this embodiment may be a capsule toner. By forming a shell layer on the surface of the toner base particles, a capsule toner can be produced. The shell layer may be substantially made of only a thermosetting resin (for example, melamine resin), or may be substantially made of only a thermoplastic resin (for example, acrylic resin or styrene-acrylic resin). And you may contain both a thermoplastic resin and a thermosetting resin.

  The carrier includes a plurality of carrier particles. The carrier particles have a carrier core containing a binder resin and a resin layer formed on the surface of the carrier core. A plurality of magnetic particles are dispersed in the binder resin of the carrier core. By forming the resin layer on the surface of the carrier core, it becomes easy to improve the fluidity of the two-component developer.

The two-component developer according to the exemplary embodiment includes toner and a carrier having the following configurations (1) and (2).
(1) Among the carrier particles contained in the carrier, carrier particles having a particle diameter of less than 20 μm have a magnetic force of 70 emu / g or more, and carrier particles having a particle diameter of 20 μm or more have a magnetic force of 40 emu / g or more and 60 emu / g or less. .
(2) The carrier contains carrier particles having a particle diameter of less than 20 μm in a proportion of 7% by mass or more and 15% by mass or less.

  The magnetic force of the carrier particles having a predetermined particle diameter in the configuration (1) is measured by the following method or an alternative method thereof.

<Method of measuring magnetic force>
The carrier is sieved using a test sieve having an opening of 20 μm to separate carrier particles having a particle diameter of less than 20 μm and carrier particles having a particle diameter of 20 μm or more in the carrier. When measuring the magnetic force of carrier particles having a particle diameter of less than 20 μm, carrier particles that have passed through the sieve by sieving (carrier particles having a particle diameter of less than 20 μm) are used as the measurement object. When measuring the magnetic force of carrier particles having a particle diameter of 20 μm or more, the carrier particles remaining on the sieve after sieving (carrier particles having a particle diameter of 20 μm or more respectively) are measured.

  Subsequently, the magnetic force (emu / g) to be measured is measured using a vibrating sample magnetometer (for example, “VSM-3S-15” manufactured by Toei Kogyo Co., Ltd.). Specifically, a measurement object placed in a uniform magnetic field is simply vibrated at a constant frequency and constant amplitude, and the magnetic force (saturation magnetization) of the measurement object is based on an induced electromotive force induced in a coil arranged in the vicinity of the measurement object. ).

  The magnetic force of the carrier particles can be adjusted, for example, by changing the type or amount of the magnetic particles contained in the binder resin of the carrier core. As a method for producing a carrier having the configuration (1), a plurality of types of carriers (for example, a first carrier and a second carrier) having different particle diameters (for example, volume average particle diameter (MV)) are prepared. Then, after adjusting the magnetic force for each of the first carrier and the second carrier, a method of mixing the first carrier and the second carrier adjusted to different magnetic forces is preferable.

  Configuration (1) is useful for suppressing carrier development (carrier adhesion to the photosensitive drum) while maintaining the excellent developability of the two-component developer. Specifically, if the magnetic force per carrier particle is lowered, a denser magnetic brush can be formed between the developing roller and the photosensitive drum, and a high-quality image tends to be formed. There is. However, if the magnetic force per carrier particle is lowered, carrier development tends to occur easily. The inventor notices that carrier particles having a small particle size (specifically, carrier particles having a particle size of less than 20 μm) are particularly susceptible to carrier development, and the magnetic force of carrier particles having a particle size of less than 20 μm is set to 70 emu / g or more. It has been found that carrier development can be suppressed. The inventors have also found that high-quality images can be formed while suppressing carrier development by setting the magnetic force of carrier particles having a particle diameter of 20 μm or more to 40 emu / g or more and 60 emu / g or less. By not excessively increasing the magnetic force of carrier particles having a particle diameter of 20 μm or more, it becomes possible to form a denser magnetic brush between the developing roller and the photosensitive drum, so that a high-quality image can be formed. It is thought that it becomes.

  The configuration (2) is useful for improving the stress resistance and durability of the two-component developer. Specifically, the inventor makes the toner stable while maintaining the high fluidity of the two-component developer by setting the ratio (content) of carrier particles having a particle diameter of less than 20 μm in the carrier to 7 mass% or more and 15 mass% or less. The present inventors have found that it is possible to give the charged amount. It is considered that the fluidity of the two-component developer can be improved by setting the content of carrier particles having a particle diameter of less than 20 μm in the carrier to 15% by mass or less. When the fluidity of the two-component developer is increased, the stress resistance of the two-component developer tends to be improved. By setting the content of carrier particles having a particle diameter of less than 20 μm in the carrier to be 7% by mass or more, it is considered that the specific surface area of the carrier particles is increased and a stable charge amount can be given to the toner. It is considered that a high-quality image can be formed by giving a stable charge amount to the toner.

  In order to facilitate the production of the carrier having configurations (1) and (2), it is preferable that the magnetic force of carrier particles having a particle diameter of less than 20 μm be 80 emu / g or less.

  Hereinafter, the toner base particles (binder resin and internal additive) and the external additive will be described in order. Depending on the use of the toner, unnecessary components (for example, a colorant, a release agent, a charge control agent, or a magnetic powder) may be omitted. Acrylic and methacrylic are sometimes collectively referred to as “(meth) acrylic”.

[Toner mother particles]
(Binder resin)
In the toner mother particles, the binder resin often occupies most of all components (for example, 85% by mass or more). For this reason, it is considered that the properties of the binder resin greatly affect the properties of the entire toner base particles.

  In order to improve the storage stability or durability of the toner while maintaining excellent low-temperature fixability of the toner, the glass transition point (Tg) of the binder resin contained in the toner base particles is 45 ° C. or higher and 65 ° C. or lower. It is preferable that it is 50 degreeC or more and 60 degrees C or less.

  The glass transition point (Tg) can be measured using, for example, a differential scanning calorimeter. More specifically, the specific heat in the endothermic curve obtained by measuring the endothermic curve of the sample (for example, binder resin) using a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.). The Tg of the binder resin can be obtained from the change point.

  In order to improve the storage stability or durability of the toner while maintaining excellent low-temperature fixability of the toner, the softening point (Tm) of the binder resin contained in the toner base particles is 80 ° C. or higher and 150 ° C. or lower. It is preferable that the temperature is 90 ° C. or higher and 140 ° C. or lower. By combining a plurality of resins having different Tm, the Tm of the binder resin can be adjusted.

The softening point (Tm) can be measured using, for example, a Koka flow tester. More specifically, a sample (for example, a binder resin) is set in a Koka type flow tester (for example, “CFT-500D” manufactured by Shimadzu Corporation), and the sample is melted and discharged under predetermined conditions. Then, an S-shaped curve (horizontal axis: temperature, vertical axis: stroke) of the sample is measured. The Tm of the sample can be read from the obtained S-shaped curve. In the obtained S-curve, when the maximum stroke value (mm) is S ₁ and the low-temperature baseline stroke value (mm) is S ₂ , the stroke value in the S-curve is “(S ₁ The temperature (° C.) at which “+ S ₂ ) / 2” corresponds to the Tm of the sample.

  In order to improve the fixing property of the toner, it is preferable to use a thermoplastic resin as the binder resin contained in the toner base particles. When the binder resin contained in the toner base particles is a thermoplastic resin, examples of the thermoplastic resin include a styrene resin, an acrylic resin (more specifically, an acrylate polymer or a methacrylate polymer). Etc.), olefin resins (more specifically, polyethylene resins or polypropylene resins), vinyl resins (more specifically, vinyl chloride resins, polyvinyl alcohol, vinyl ether resins, or N-vinyl resins), polyesters, etc. Homopolymers such as resins, polyamide resins, or urethane resins, or copolymers containing the same monomers as these homopolymers (more specifically, styrene-acrylic resins or styrene-butadiene resins) Is preferred. In order to improve the dispersibility of the colorant in the toner core, the charging property of the toner, and the fixing property of the toner to the recording medium, a styrene-acrylic resin or a polyester resin is particularly preferable.

  Hereinafter, a styrene-acrylic resin that can be used as a binder resin for toner base particles will be described. The styrene-acrylic resin is a copolymer of a styrene monomer and an acrylic monomer.

  Examples of the styrene monomer for preparing the styrene-acrylic resin include styrene, α-methylstyrene, p-hydroxystyrene, m-hydroxystyrene, vinyltoluene, α-chlorostyrene, o-chlorostyrene, m- Chlorostyrene, p-chlorostyrene, or p-ethylstyrene is preferred.

  As the acrylic monomer for preparing the styrene-acrylic resin, for example, (meth) acrylic acid, (meth) acrylic acid alkyl ester, or (meth) acrylic acid hydroxyalkyl ester is preferable. Examples of the (meth) acrylic acid alkyl ester include, for example, methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, and (meth) acrylic acid n. -Butyl, iso-butyl (meth) acrylate, or 2-ethylhexyl (meth) acrylate is preferred. Examples of the (meth) acrylic acid hydroxyalkyl ester include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or (meth) acrylic acid 4 -Hydroxybutyl is preferred.

  By using a monomer having a hydroxyl group (more specifically, p-hydroxystyrene, m-hydroxystyrene, (meth) acrylic acid hydroxyalkyl ester, or the like) when preparing a styrene-acrylic resin, styrene -A hydroxyl group can be introduced into an acrylic resin. Moreover, the hydroxyl value of the styrene-acrylic resin obtained can be adjusted by adjusting the usage-amount of the monomer which has a hydroxyl group.

  When preparing a styrene-acrylic resin, a carboxyl group can be introduced into the styrene-acrylic resin by using (meth) acrylic acid (monomer). Moreover, the acid value of the styrene-acrylic resin obtained can be adjusted by adjusting the usage-amount of (meth) acrylic acid.

  When the binder resin is a styrene-acrylic resin, the number average molecular weight (Mn) of the styrene-acrylic resin is 2000 or more and 3000 or less in order to improve the strength of the toner base particles and the fixing property of the toner. Is preferred. The molecular weight distribution of the styrene-acrylic resin (the ratio Mw / Mn of the mass average molecular weight (Mw) to the number average molecular weight (Mn)) is preferably 10 or more and 20 or less. Gel permeation chromatography can be used to measure Mn and Mw of the styrene-acrylic resin.

  Hereinafter, a polyester resin that can be used as a binder resin for toner base particles will be described. The polyester resin is obtained by polycondensation or copolycondensation of a divalent or trivalent or higher alcohol and a divalent or trivalent or higher carboxylic acid.

  For the preparation of the polyester resin, for example, a dihydric alcohol such as diols or bisphenols can be used.

  For the preparation of the polyester resin, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, Diols such as 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol can be suitably used.

  For the preparation of the polyester resin, for example, bisphenols such as bisphenol A, hydrogenated bisphenol A, polyoxyethylene bisphenol A ether, or polyoxypropylene bisphenol A ether can be suitably used.

  For the preparation of the polyester resin, for example, sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1 , 2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, or 1,3,5-trihydroxymethyl Trihydric or higher alcohols such as benzene can be preferably used.

  Preparation of the polyester resin includes, for example, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, succinic acid. Acid, alkyl succinic acid (more specifically, n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, or isododecyl succinic acid), or alkenyl succinic acid (more specifically, , N-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, or isododecenyl succinic acid) can be suitably used.

  For the preparation of the polyester resin, for example, 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4- Naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid A trivalent or higher carboxylic acid such as tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, or empole trimer acid can be preferably used.

  The divalent or trivalent or higher carboxylic acid may be transformed into an ester-forming derivative (more specifically, an acid halide, an acid anhydride, or a lower alkyl ester). Here, “lower alkyl” means an alkyl group having 1 to 6 carbon atoms.

  When preparing the polyester resin, the acid value and hydroxyl value of the polyester resin can be adjusted by changing the amount of alcohol used and the amount of carboxylic acid used. When the molecular weight of the polyester resin is increased, the acid value and hydroxyl value of the polyester resin tend to decrease.

  When the binder resin is a polyester resin, the number average molecular weight (Mn) of the polyester resin is preferably 1000 or more and 2000 or less in order to improve the strength of the toner base particles and the fixing property of the toner. The molecular weight distribution of the polyester resin (the ratio Mw / Mn of the mass average molecular weight (Mw) to the number average molecular weight (Mn)) is preferably 9 or more and 21 or less. Gel permeation chromatography can be used to measure Mn and Mw of the polyester resin.

(Coloring agent)
The toner base particles may contain a colorant. As the colorant, a known pigment or dye can be used according to the color of the toner. The amount of the colorant to be used is preferably 1 part by mass or more and 20 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.

  The toner base particles may contain a black colorant. An example of a black colorant is carbon black. The black colorant may be a colorant that is toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

  The toner base particles may contain a color colorant such as a yellow colorant, a magenta colorant, or a cyan colorant.

  As the yellow colorant, for example, one or more compounds selected from the group consisting of condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds can be used. Examples of the yellow colorant include C.I. I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155 168, 174, 175, 176, 180, 181, 191, or 194), naphthol yellow S, Hansa yellow G, or C.I. I. Vat yellow can be preferably used.

  The magenta colorant is, for example, selected from the group consisting of condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. One or more compounds can be used. Examples of the magenta colorant include C.I. I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81: 1, 122, 144, 146, 150, 166, 169, 177 184, 185, 202, 206, 220, 221 or 254) can be preferably used.

  As the cyan colorant, for example, one or more compounds selected from the group consisting of a copper phthalocyanine compound, a copper phthalocyanine derivative, an anthraquinone compound, and a basic dye lake compound can be used. Examples of cyan colorants include C.I. I. Pigment blue (1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62, or 66), phthalocyanine blue, C.I. I. Bat Blue, or C.I. I. Acid blue can be preferably used.

(Release agent)
The toner base particles may contain a release agent. The release agent is used, for example, for the purpose of improving the fixing property or offset resistance of the toner. In order to improve the fixing property or offset resistance of the toner, the amount of the release agent used is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin. More preferably, it is 20 parts by mass or less.

  Examples of the releasing agent include aliphatic hydrocarbon waxes such as low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, or Fischer-Tropsch wax; Oxides of aliphatic hydrocarbon waxes such as block copolymers; plant waxes such as candelilla wax, carnauba wax, wood wax, jojoba wax, or rice wax; such as beeswax, lanolin, or whale wax Animal waxes; mineral waxes such as ozokerite, ceresin, or petrolatum; waxes based on fatty acid esters such as montanic ester waxes or castor waxes; deacidified carnauba waxes , It can be suitably used waxes in which some or all of the fatty acid ester is de-oxidized. One type of release agent may be used alone, or multiple types of release agents may be used in combination.

  In order to improve the compatibility between the binder resin and the release agent, a compatibilizer may be added to the toner base particles.

(Charge control agent)
The toner base particles may contain a charge control agent. The charge control agent is used, for example, for the purpose of improving the charging stability or charging rising property of the toner. The charge rising characteristic of the toner is an index as to whether or not the toner can be charged to a predetermined charge level in a short time.

  Examples of positively chargeable charge control agents include pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2,4-triazine, 1,3. , 5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3 , 4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline Or an azine compound such as quinoxaline; azine fast red FC, azine fast red 12BK, azine violet BO, azine Direct dyes composed of azine compounds such as Raun 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Deep Black EW, or Azin Deep Black 3RL; Nigrosine such as Nigrosine, Nigrosine Salt, or Nigrosine Derivative Compounds; acid dyes consisting of nigrosine compounds such as nigrosine BK, nigrosine NB, or nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; benzyldecylhexylmethylammonium chloride or decyltrimethylammonium chloride Quaternary ammonium salts are preferred. Further, a resin having a quaternary ammonium salt, a carboxylate, or a carboxyl group can also be used as a positively chargeable charge control agent. A nigrosine compound is particularly preferred in order to obtain a rapid start-up property. One type of charge control agent may be used alone, or a plurality of types of charge control agents may be used in combination.

(Magnetic powder)
The toner base particles may contain magnetic powder. Examples of the material of the magnetic powder include iron (more specifically, ferrite or magnetite), ferromagnetic metal (more specifically, cobalt or nickel), an alloy containing iron and / or ferromagnetic metal, ferromagnetic A ferromagnetic alloy or chromium dioxide that has been subjected to a chemical treatment (more specifically, a heat treatment or the like) can be suitably used. One kind of magnetic powder may be used alone, or a plurality of kinds of magnetic powder may be used in combination.

[External additive]
An external additive may be attached to the surface of the toner base particles. The external additive is used, for example, to improve the fluidity of the two-component developer, the handling property of the toner, or the charging property of the toner. In order to improve the fluidity or handleability of the two-component developer, the amount of the external additive used is preferably 0.5 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the toner base particles. More preferably, the content is 1.0 part by mass or more and 5 parts by mass or less.

  In order to improve the fluidity of the two-component developer, it is preferable to use resin particles (for example, resin beads) as an external additive for toner particles. The resin particles function as a spacer and are considered to improve the fluidity of the two-component developer. In addition, since the resin particles have high adhesion to the toner base particles, it is considered that the resin particles are hardly released from the toner particles. In addition, the resin particles hardly contaminate the carrier. For this reason, it is considered that a stable charge amount can be imparted to the toner particles by using the resin particles.

  When the toner particles include resin particles as an external additive, in order to improve the stress resistance and durability of the two-component developer, the volume average particle diameter (MV) of the resin particles may be 40 nm or more and 150 nm or less. preferable. By setting the volume average particle diameter (MV) of the resin particles to 40 nm or more, it is considered that the embedding of the resin particles in the toner base particles can be suppressed and the stress resistance of the two-component developer can be improved. Further, it is considered that the fluidity of the two-component developer can be improved by setting the volume average particle diameter (MV) of the resin particles to 150 nm or less. The volume average particle diameter (MV) can be measured using a laser diffraction / scattering particle size distribution measuring apparatus (for example, “LA-750” manufactured by Horiba, Ltd.).

  When the toner particles include resin particles as an external additive, an acrylic resin (more specifically, polymethyl methacrylate or the like) or a styrene-acrylic resin can be suitably used as the resin particle material.

  In order to improve the fluidity of the two-component developer and the chargeability of the toner, it is preferable to use inorganic particles as external additives. When the external additive is inorganic particles, the inorganic particles include silica particles or metal oxides (more specifically, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, barium titanate, etc.) These particles can be preferably used.

  As the external additive, one type of particle may be used alone, or a plurality of types of particles may be used in combination. In order to improve the fluidity of the two-component developer and the chargeability of the toner, it is preferable to use both resin particles and inorganic particles as external additives. When both resin particles and inorganic particles are used as the external additive, the particle diameter of each particle may be the same or different.

[Carrier particles]
The carrier particles have a carrier core and a resin layer formed on the surface of the carrier core.

  In order to reduce the stress in the developing unit, the circularity (number average value) of carrier particles contained in the carrier is preferably 0.95 or more and 0.99 or less. The circularity of the carrier particles can be measured using, for example, a flow type particle image analyzer (“FPIA (registered trademark) -3000” manufactured by Sysmex Corporation).

In order to reduce the stress in the developing unit, the true specific gravity of the carrier is preferably 3.0 g / cm ³ or more and 4.0 g / cm ³ or less. The true specific gravity can be measured using, for example, a dry automatic densimeter (“Accumic II 1340 series” manufactured by Micromeritics, Inc .: accessory: multi-volume kit).

In order to improve the developability of the two-component developer, the specific resistance of the carrier (when 5000 V / cm ^{2 is} applied) is preferably less than 1.0 × 10 ¹³ Ω · cm.

  In order to improve the stress resistance and durability of the two-component developer, the fluidity of the two-component developer measured by the following method or its alternative method is preferably 40 seconds / 25 cc or less.

<Measurement method of fluidity>
A sample (two-component developer) is placed in a 25 cc cylindrical container so as to overflow, and the slide glass is reciprocated on the surface of the container to remove the overflowed sample from the container. Then, in a state where the sample is demagnetized, the fluidity of the sample is measured according to “JIS Z 2502”.

(Career core)
The carrier core includes a binder resin. As the binder resin contained in the carrier core, for example, a phenol resin, a melamine resin, a urea resin, or an epoxy resin is preferable, and a phenol resin or a melamine resin is particularly preferable.

  The phenol resin can be synthesized by polymerizing phenol and aldehydes. The urea resin can be synthesized by polymerizing urea and aldehydes. The melamine resin can be synthesized by polymerizing melamine and aldehydes. Bisphenols and epichlorohydrin can be used as starting materials for the epoxy resin.

  A plurality of magnetic particles are dispersed in the binder resin of the carrier core. Examples of magnetic particle materials include magnetite, hematite, γ iron oxide, Mn—Zn ferrite, Ni—Zn ferrite, Mn—Mg ferrite, Ca—Mg ferrite, Li ferrite, or Cu—Zn ferrite. An iron-based oxide such as ferrite is preferred, and magnetite is particularly preferred. As a material for each magnetic particle, one type of magnetic material may be used alone, or two or more types of magnetic materials may be used in combination. In the carrier, one type of magnetic particles may be used alone, or two or more types of magnetic particles may be used in combination.

(Resin layer)
The resin layer is formed on the surface of the carrier core so as to cover the carrier core. The resin constituting the resin layer is preferably an insulating resin. As resin which comprises a resin layer, a thermoplastic resin may be used and a thermosetting resin may be used. Moreover, you may provide crosslinking | crosslinked property to a thermoplastic resin by mixing a thermoplastic resin and a hardening | curing agent. As the resin constituting the resin layer, one type of resin may be used alone, or two or more types of resins may be used in combination.

  When the resin constituting the resin layer is a thermoplastic resin, examples of the thermoplastic resin include polystyrene, polymethyl methacrylate, acrylic resin, styrene-acrylic acid copolymer, styrene-butadiene copolymer, and ethylene-vinyl acetate. Copolymer, polyvinyl chloride, polyvinyl acetate, polyvinylidene fluoride resin, fluorocarbon resin, perfluorocarbon resin, solvent-soluble perfluorocarbon resin, polyvinyl alcohol, polyvinyl acetal, polyvinyl pyrrolidone, petroleum resin, cellulose or derivatives thereof (more specific Cellulose acetate, cellulose nitrate, methylcellulose, hydroxymethylcellulose, or hydroxypropylcellulose), novolac resin, low molecular weight polyethylene, saturated alkyl polyester resin Polyethylene terephthalate, polybutylene terephthalate, aromatic polyester resin (more specifically, polyarylate, etc.), polyamide resin, polyacetal resin, polycarbonate resin, polyethersulfone resin, polysulfone resin, polyphenylene sulfide resin, or polyetherketone resin It can be used suitably.

  When the resin constituting the resin layer is a thermosetting resin, examples of the thermosetting resin include phenol resin, modified phenol resin, maleic resin, alkyd resin, epoxy resin, acrylic resin, maleic anhydride and terephthalic acid. Unsaturated polyester obtained by polycondensation with polyhydric alcohol, urea resin, melamine resin, urea-melamine resin, xylene resin, toluene resin, guanamine resin, melamine resin, acetoguanamine resin, gliptal resin, furan resin, silicone resin, Polyimide, polyamideimide resin, polyetherimide resin, or urethane resin is preferable, and silicone resin is particularly preferable.

[Method for producing two-component developer]
Next, a method for producing toner contained in the two-component developer according to this embodiment will be described.

  The toner base particles can be prepared, for example, by a pulverization method or an aggregation method. These methods facilitate easy dispersion of the internal additive in the binder resin of the toner base particles.

  In an example of the pulverization method, first, a binder resin, a colorant, a charge control agent, and a release agent are mixed. Subsequently, the obtained mixture is melt-kneaded using a melt-kneading apparatus (for example, a single-screw or twin-screw extruder). Subsequently, the obtained melt-kneaded product is pulverized and classified. Thereby, toner mother particles are obtained. When the pulverization method is used, the toner base particles can often be produced more easily than when the aggregation method is used.

  In an example of the aggregating method, first, these fine particles are aggregated in an aqueous medium containing fine particles of the binder resin, the release agent, and the colorant until a desired particle diameter is obtained. Thereby, aggregated particles containing the binder resin, the release agent, and the colorant are formed. Subsequently, the obtained aggregated particles are heated to unite the components contained in the aggregated particles. Thereby, toner mother particles having a desired particle diameter are obtained.

  By mixing the toner base particles and the external additive using a mixing device (for example, “FM mixer” manufactured by Nippon Coke Kogyo Co., Ltd.), the external additive can be attached to the surface of the toner base particles. Toner particles can be obtained by attaching an external additive to the surface of the toner base particles.

  A carrier having the above-described configuration (1) (and thus a two-component developer containing such a carrier) is preferably produced by the following procedure. First, a plurality of types of carriers having different particle diameters are prepared. Subsequently, the magnetic force is adjusted for each of the plurality of types of carriers. Subsequently, by mixing a plurality of types of carriers whose magnetic force is adjusted, among the carriers including these plurality of types of carriers, the magnetic force of carrier particles having a particle size of less than 20 μm is set to 70 emu / g or more, and the particle size of 20 μm or more is set. The magnetic force of the carrier particles is set to 40 emu / g or more and 60 emu / g or less. According to such a method, it becomes possible to easily and accurately manufacture a two-component developer including a carrier having the above-described configuration (1). As the plurality of types of carriers, two types of carriers may be used, or three or more types of carriers may be used. The magnetic force of each of the plurality of types of carrier particles can be adjusted, for example, by changing the type or amount of the magnetic particles contained in the binder resin of the carrier core.

  The two-component developer according to the exemplary embodiment can be manufactured by mixing the toner and the carrier using a mixing device (for example, “Rocking Mixer (registered trademark)” manufactured by Aichi Electric Co., Ltd.). The amount of toner contained in the two-component developer is preferably 1 part by mass or more and 20 parts by mass or less, and more preferably 3 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the carrier.

  Examples of the present invention will be described. Table 1 shows developers A to P (two-component developers for developing electrostatic latent images) according to Examples or Comparative Examples. Tables 2 and 3 show carriers A to L used in developers A to P, respectively.

Hereinafter, the manufacturing method, evaluation method, and evaluation result of developers A to P will be described in order. Note that the evaluation results (values indicating shape, physical properties, etc.) relating to powders containing a plurality of particles (for example, toner base particles, external additives, toners, or carriers) are a considerable number of particles unless otherwise specified. Is the number average of the values measured for. In the evaluation in which an error occurs, a considerable number of measurement values with sufficiently small errors are obtained, and the arithmetic average of the obtained measurement values is used as the evaluation value. Further, the particle diameter of the powder is the equivalent-circle diameter of the primary particles (the diameter of a circle having the same area as the projected area of the particles) unless otherwise specified. Moreover, the measured value of the volume median diameter (D ₅₀ ) is a value measured using “Coulter Counter Multisizer 3” manufactured by Beckman Coulter Co., Ltd. unless otherwise specified. Moreover, the measured value of the volume average particle diameter (MV: Mean Volume diameter) is measured using a laser diffraction / scattering type particle size distribution measuring device (“LA-750” manufactured by Horiba, Ltd.) unless otherwise specified. It is the value. Moreover, the measured value of circularity is the number average of the values measured for 3000 particles using a flow type particle image analyzer (“FPIA-3000” manufactured by Sysmex Corporation) unless otherwise specified. .

[Toner Preparation]
Using a mixer (“FM mixer” manufactured by Nippon Coke Industries, Ltd.), 100 parts by mass of the binder resin, 4 parts by mass of the colorant, 1 part by mass of the charge control agent, and 5 parts by mass of the release agent are mixed. did. As the binder resin, a polyester resin having an acid value of 5.6 mg KOH / g and a melting point of 100 ° C. was used. Examples of the colorant include C.I. I. Pigment Blue 15: 3 (copper phthalocyanine blue pigment) was used. As the charge control agent, “P51” manufactured by Clariant was used. As the release agent, a wax (“Carnauba Wax No. 1” manufactured by Hiroyuki Kato Co., Ltd.) was used.

Subsequently, the obtained mixture was kneaded using a twin-screw extruder (“PCM-30” manufactured by Ikegai Co., Ltd.). Subsequently, the obtained kneaded material was pulverized by using a mechanical pulverizer (“Turbo Mill” manufactured by Freund Turbo). Subsequently, the obtained pulverized product was classified using a classifier (“Elbow Jet EJ-LABO type” manufactured by Nippon Steel Mining Co., Ltd.). As a result, toner mother particles having a volume median diameter (D ₅₀ ) of 6.8 μm were obtained.

  Subsequently, 100 parts by mass of toner base particles and 1 part by mass of hydrophobic silica fine particles (“RA-200H” manufactured by Nippon Aerosil Co., Ltd.) using a mixer (“FM mixer” manufactured by Nippon Coke Industries, Ltd.) By mixing 1 part by mass of resin beads having a volume average particle size (MV) (particle size determined for each of developers A to P) shown in Table 1, an external additive is added to the surface of the toner base particles. (Silica particles and resin beads) were adhered. As resin beads, particles of polymethyl methacrylate resin (PMMA) were used.

  Thereafter, the obtained toner was sieved using a sieve of 200 mesh (aperture 75 μm). As a result, a toner having a large number of toner particles was obtained.

[Career preparation]
A first carrier (powder) having a volume average particle size (MV) of 20 μm and a second carrier (powder) having a volume average particle size (MV) of 40 μm are mixed at a ratio (mass ratio) shown in Table 2. Carriers A to I were prepared.

  The first carriers A and B shown below were used as the first carrier, and the following second carriers A to D were used as the second carrier. Each of the first carrier and the second carrier contained a plurality of carrier particles having a carrier core and a resin layer. When producing the carrier core, a plurality of magnetic particles were dispersed in the binder resin. A phenol resin was used as the binder resin for the carrier core. As the magnetic particles, magnetite particles having a volume average particle diameter (MV) of 0.25 μm were used. Further, the surface of the carrier core was covered with a thermosetting silicone resin film (resin layer). The first carriers A and B had magnetic forces of 75 emu / g and 65 emu / g, respectively. The second carriers A, B, C, and D had magnetic forces of 40 emu / g, 56 emu / g, 35 emu / g, and 60 emu / g, respectively. The magnetic force of each carrier was adjusted by changing the amount (content ratio) of the magnetic particles in the binder resin.

  Carrier A was prepared by mixing first carrier A and second carrier A at a mass ratio of 20:80 (first carrier A: second carrier A).

  Carrier B was prepared by mixing first carrier A and second carrier B at a mass ratio of 20:80 (first carrier A: second carrier B).

  Carrier C was prepared by mixing first carrier A and second carrier A at a mass ratio of 14:86 (first carrier A: second carrier A).

  Carrier D was prepared by mixing first carrier A and second carrier A at a mass ratio of 28:72 (first carrier A: second carrier A).

  Carrier E was prepared by mixing first carrier B and second carrier A at a mass ratio of 20:80 (first carrier B: second carrier A).

  The carrier F was prepared by mixing the first carrier A and the second carrier C in a mass ratio of 20:80 (first carrier A: second carrier C).

  The carrier G was prepared by mixing the first carrier A and the second carrier D at a mass ratio of 20:80 (first carrier A: second carrier D).

  The carrier H was prepared by mixing the first carrier A and the second carrier A at a mass ratio of 35:65 (first carrier A: second carrier A).

  Carrier I was prepared by mixing first carrier A and second carrier A at a mass ratio of 10:90 (first carrier A: second carrier A).

  Carriers J and K each contained a plurality of carrier particles having a carrier core and a resin layer. When the carrier cores of the carriers J and K were produced, a plurality of magnetic particles were dispersed in the binder resin. A phenol resin was used as the binder resin for the carrier core. As the magnetic particles, magnetite particles having a volume average particle diameter (MV) of 0.25 μm were used. Further, the surface of the carrier core was covered with a thermosetting silicone resin film (resin layer). Carriers J and K had magnetic forces of 70 emu / g and 60 emu / g, respectively. The magnetic force of each carrier was adjusted by changing the amount (content ratio) of the magnetic particles in the binder resin.

  As the carrier L, a Mn—Mg—Sr ferrite carrier (“EF-35” manufactured by Powder Tech Co., Ltd.) was used.

  Each of the carriers A to L has a volume average particle size (MV), a content of carrier particles having a particle size of less than 20 μm, a magnetic force of carrier particles having a particle size of less than 20 μm, a magnetic force of carrier particles having a particle size of 20 μm or more, a true specific gravity, The circularity was as shown in Table 3. The true specific gravity was measured using a dry automatic densimeter (“Accumic II 1340 series” manufactured by Micromeritics, Inc .: multi-volume kit). Moreover, each measuring method of the magnetic force of the carrier particle with a particle diameter of less than 20 μm and the magnetic force of the carrier particle with a particle diameter of 20 μm or more was as follows.

<Method of measuring magnetic force>
The carrier was sieved using a test sieve having an opening of 20 μm to separate carrier particles having a particle diameter of less than 20 μm and carrier particles having a particle diameter of 20 μm or more in the carrier. When measuring the magnetic force of carrier particles having a particle diameter of less than 20 μm, carrier particles that passed through the sieve by sieving (carrier particles having a particle diameter of less than 20 μm) were measured. When measuring the magnetic force of carrier particles having a particle size of 20 μm or more, carrier particles remaining on the screen after sieving (carrier particles each having a particle size of 20 μm or more) were measured.

  Subsequently, the magnetic force (emu / g) of the measurement object was measured using a vibrating sample magnetometer (“VSM-3S-15” manufactured by Toei Kogyo Co., Ltd.). Specifically, based on the induced electromotive force induced in a coil arranged in the vicinity of the measurement object by causing the measurement object placed in a uniform magnetic field to vibrate at a constant frequency and constant amplitude under the condition of an external magnetic field of 10 kOe. The magnetic force (saturation magnetization) of the measurement object was measured.

[Production of two-component developer]
100 parts by mass of carriers shown in Table 1 (carriers determined for each of developers A to P) and 10 parts by mass of toner (toners specified for each of developers A to P) shown in Table 1 The mixture was stirred for 30 minutes using a powder mixer (“Rocking Mixer” manufactured by Aichi Electric Co., Ltd.). As a result, developers A to P (two-component developers) were obtained.

  The flow rates of the developers A to P were as shown in Table 1. The fluidity was measured according to “JIS Z 2502” as described above.

[Evaluation method]
The evaluation method of each sample (developers A to P) is as follows. An image was formed using a sample (developer), and image density (ID), fog density (FD), charge amount, image roughness, carrier adhesion, and aggregation degree were evaluated. As an evaluation machine, a color multifunction machine (“TASKalfa 5550ci” manufactured by Kyocera Document Solutions Inc.) was used. The sample (developer) was put into the developing device of the evaluation machine, and the toner (replenishment toner) corresponding to the sample (developer) was put into the toner container of the evaluation machine.

  Using the evaluation machine, a first press life test was performed in which 1000 sheets were continuously printed at a printing rate of 50% in a normal temperature and humidity environment (temperature 23 ° C., humidity 50% RH). Further, after performing the first printing durability test, using the above-mentioned evaluation machine, the second continuous printing is performed for 5000 sheets at a printing rate of 0.1% in a normal temperature and normal humidity environment (temperature 23 ° C., humidity 50% RH). A printing durability test was conducted.

  Before the first printing test (hereinafter referred to as the initial), after the first printing test and before the second printing test (hereinafter described as the first printing test), and after the second printing test At each timing, a sample image including a solid portion and a blank portion was formed on a recording medium (evaluation paper) using the evaluation machine. Thereafter, the charge amount of the toner in the sample (developer) was measured. Specifically, the toner in the sample (developer) 0.10 g (± 0.01 g) is sucked using a suction part of a Q / m meter (“MODEL 210HS” manufactured by Trek), and the amount of the sucked toner Based on the display (charge amount) on the Q / m meter, the charge amount (μC / g) of the toner was calculated. Further, the image density (ID) of the solid portion of the image formed on the recording medium was measured using a reflection densitometer (“RD914” manufactured by Sakata Inx Engineering Co., Ltd.). Further, the image density (ID) of the blank portion of the image formed on the recording medium was measured using a reflection densitometer (“RD914” manufactured by Sakata Inx Engineering Co., Ltd.), and the fog density (FD) was calculated. The fog density (FD) corresponds to a value obtained by subtracting the image density (ID) of the base paper from the image density (ID) of the blank portion of the recording medium after printing.

The measured image density (ID) was evaluated according to the following criteria.
A (very good): The image density was 1.4 or more.
○ (good): The image density was 1.3 or more and less than 1.4.
Δ (Normal): The image density was 1.2 or more and less than 1.3.
X (Poor): The image density was less than 1.2.

The measured fog density (FD) was evaluated according to the following criteria.
A (very good): The fog density (FD) was less than 0.004.
○ (Good): The fog density (FD) was 0.004 or more and less than 0.006.
Δ (Normal): The fog density (FD) was 0.006 or more and less than 0.010.
X (Poor): The fog density (FD) was 0.010 or more.

  When evaluating image roughness, a sample image including a solid portion and a blank portion was initially formed on a recording medium (evaluation paper) using the evaluation machine. Thereafter, the image roughness of the solid portion of the image formed on the recording medium is determined by a method defined in “ISO 13660” using a handy image evaluation system (“MODEL PIAS-II” manufactured by QEA (Quality Engineering Associates)). It was measured by. Note that the image blur indicates a graininess caused by density unevenness in a solid image.

The measured image mottle was evaluated according to the following criteria.
A (very good): Image blur was 0.80 or less.
○ (Good): Image roughness was more than 0.80 and 0.90 or less.
X (Poor): Image roughness was more than 0.90.

  When evaluating carrier adhesion, in the initial stage, the evaluator was instructed to print a sample image including a solid portion and a blank portion, and the printing operation of the evaluator was stopped during printing. Thereafter, the photosensitive drum was taken out from the evaluation machine, and the number of carrier particles attached to the photosensitive drum was determined. Specifically, carrier particles attached to the photosensitive drum were collected using a tape, and the number of carrier particles attached per unit area (2 cm × 2 cm) of the surface of the photosensitive drum was determined. The carrier adhesion was evaluated based on the number of carrier particles (hereinafter referred to as “adhered carrier particles”) adhering to the photosensitive drum.

The evaluation criteria for carrier adhesion are as follows.
A (very good): The number of adhered carrier particles was less than 5.
○ (good): The number of the adhered carrier particles was 5 or more and less than 10.
X (Poor): The number of adhering carrier particles was 10 or more.

In the case of evaluating the degree of aggregation, after the first printing durability test, the developing device was taken out of the evaluation machine, and 5 g of a sample (developer) was collected from the developing device. Then, 5 g of the collected sample was sieved using a 200-mesh (aperture 75 μm) sieve. Then, from the mass of the sample before sieving (= 5 g) and the mass of the sample after sieving (the mass of the sample remaining on the sieve after sieving), the degree of aggregation (mass%) based on the following formula: Asked.
Aggregation degree = 100 × mass of sample after sieving / mass of sample before sieving

The measured degree of aggregation was evaluated according to the following criteria.
○ (Good): The degree of aggregation was 1.0% by mass or less.
X (not good): The degree of aggregation was more than 1.0% by mass.

[Evaluation results]
Tables 4 and 5 show the evaluation results for each of the developers A to P.

  Each carrier of developers A, B, C, D, M, N, O, and P (two-component developers according to Examples 1 to 8) has the above-described configurations (1) and (2). It was. Specifically, in the two-component developers according to Examples 1 to 8, among the carrier particles contained in the carrier, the carrier particles having a particle diameter of less than 20 μm have a magnetic force of 70 emu / g or more, and the carrier having a particle diameter of 20 μm or more. The particles had a magnetic force of 40 emu / g or more and 60 emu / g or less. The carriers of the two-component developers according to Examples 1 to 8 each contained carrier particles having a particle diameter of less than 20 μm at a ratio of 7% by mass or more and 15% by mass or less. As shown in Tables 4 and 5, each of the two-component developers according to Examples 1 to 8 can give a stable charge amount to the toner, and has excellent developability both in the initial stage and after the printing durability test. Was maintained. In the two-component developers according to Examples 1 to 8, carrier development (carrier adhesion to the photosensitive drum) could be suppressed both in the initial stage and after the printing durability test. In addition, each of the two-component developers according to Examples 1 to 8 uses a low-melting toner (specifically, a toner having a binder resin having a melting point of 100 ° C.), but is resistant to stress and durability. Both were excellent.

  The two-component developer according to the present invention can be used for forming an image in, for example, a copying machine, a printer, or a multifunction machine.

Claims (6)

A carrier containing a plurality of carrier particles having a carrier core containing a binder resin and a resin layer formed on the surface of the carrier core;
A toner comprising a plurality of toner particles;
Including
In the binder resin, a plurality of magnetic particles are dispersed,
Among the carrier particles contained in the carrier, carrier particles having a particle size of less than 20 μm have a magnetic force of 70 emu / g or more, carrier particles having a particle size of 20 μm or more have a magnetic force of 40 emu / g or more and 60 emu / g or less,
The carrier is a two-component developer containing carrier particles having a particle diameter of less than 20 μm in a proportion of 7% by mass to 15% by mass. 2. The two-component developer according to claim 1, wherein a true specific gravity of the carrier is 3.0 g / cm ³ or more and 4.0 g / cm ³ or less.   The two-component developer according to claim 1 or 2, wherein the carrier particles have a circularity of 0.95 or more and 0.99 or less.   The two-component developer according to any one of claims 1 to 3, which has a fluidity of 40 seconds / 25 cc or less.   The two-component developer according to claim 1, wherein the toner particles have resin particles having a volume average particle diameter of 40 nm or more and 150 nm or less as an external additive. Preparing multiple types of carriers with different particle sizes;
Adjusting the magnetic force for each of the plurality of types of carriers;
After adjusting the magnetic force, by mixing the plural types of carriers, among the carriers containing the plural types of carriers, the magnetic force of carrier particles having a particle diameter of less than 20 μm is set to 70 emu / g or more, and the carrier having a particle diameter of 20 μm or more. Making the magnetic force of the particles 40 emu / g or more and 60 emu / g or less,
A method for producing a two-component developer.