JP2008185739A - Magnetic ferrite carrier and electrophotographic developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier which prevents carrier deposition on a photoreceptor, so that the occurrence of image defects can be prevented, and which allows the formation of a high-definition and high-resolution high-quality image, and an electrophotographic developer. <P>SOLUTION: In the magnetic ferrite carrier in which a silicone resin covering layer is formed on a surface of a magnetic ferrite particle, an intensity ratio Si/Fe of X-ray intensity of Si measured by fluorescent X-ray analysis to X-ray intensity of Fe measured by fluorescent X-ray analysis is 3.5×10<SP>-2</SP>to <7.0×10<SP>-2</SP>, a saturation magnetization of the carrier in an external magnetic field of 5 kOe is 50-80 emu/g, a resistance of the carrier at an applied voltage of 500 V measured by the bridge system electric resistance measuring method is 1.0×10<SP>11</SP>-1.0×10<SP>15</SP>Ω cm, and the carrier has a volume average particle diameter of 30-70 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a magnetic ferrite carrier and an electrophotographic developer.

  In an image forming apparatus using electrophotographic technology such as a copying machine, a laser printer, a fax machine, etc., an electrostatic latent image is developed in various development processes on a photosensitive member in which a photosensitive layer is formed on the surface of a core metal. The electrostatic latent image in the developing area on the photosensitive member is developed with the toner contained in the developer stored in the developing device, and the resulting toner image is transferred to the recording material. The image is recorded by heating and pressing to fix the image on the recording material.

  Recently, with the remarkable development of electrophotographic technology accompanying the spread of computers, for example, the durability of various devices constituting the image forming apparatus has been improved, and the life of the image forming apparatus has been extended. Further, the developer used for image formation in the image forming apparatus is also required to have a long life, that is, to stabilize the charging characteristics throughout its use period. The developer charging characteristics are stable over a long period of time, and a constant charge is imparted to the toner contained in the developer, so that there is no variation in the image density of the image recorded on the recording material, and there is even less image defects. An image can be formed stably.

  The developer includes a binder resin and a colorant, and includes two-component development including toner particles for developing an electrostatic latent image and a magnetic carrier that is stirred together with the toner particles in the developing device and frictionally charges the toner particles. Agents are widely used. In the development using a two-component developer, a developer layer called a magnetic brush is formed on the surface of a developing roller containing a magnet, and a carrier and toner are mixed and frictionally charged to each other, and the toner is applied to a photoreceptor. It is mainly performed by a magnetic brush method for electrostatic attachment. As the carrier, a coated carrier comprising a carrier core material that is magnetic particles and a coating agent that coats the carrier core material, a magnetic powder-dispersed carrier comprising magnetic particles dispersed in a binder resin, Is common.

  With regard to high definition and high resolution of images, the reduction of the carrier diameter is one of the problems to be solved. Among such small-diameter carriers, carriers having excellent durability for the purpose of extending the life have been proposed (see, for example, Patent Documents 1 and 2).

The carrier disclosed in Patent Document 1 is a coated carrier in which a silicone resin is used as a coating agent, has a true specific gravity of 2.0 to 4.5, and a magnetization strength at 1000 / 4π (kA / m). σ ₁₀₀₀ is 25 to 60 (Am ² / kg), the ratio of Si intensity to Fe intensity by fluorescence X-ray measurement (Si / Fe) is 0.005 to 0.035, and the volume average particle diameter Is a small particle size carrier of 25-60 μm.

  The carrier disclosed in Patent Document 2 is a coated carrier in which magnetic powder-containing core particles in which metal compound particles are dispersed in a binder resin are further coated with a silicone resin, and the carrier has a Si / Fe ratio of 0. 003 or more and 0.03 or less, the Si / Fe ratio reduction rate of the carrier after washing with toluene is 1.5% or more and 15% or less, and the light transmittance when the carrier is dispersed in an aqueous solution is 95% or more And a small particle size carrier having a volume average particle size of 15 to 60 μm.

  The carriers disclosed in Patent Documents 1 and 2 can realize a small particle size carrier excellent in durability by suitably setting the carrier physical properties such as the volume average particle size of the carrier and the Si / Fe ratio. However, a carrier having a small particle size has a problem that it tends to cause carrier adhesion to be transferred from the developer carrying member to the photosensitive member. When carrier adhesion occurs, an image defect occurs at a portion where the carrier adheres. Patent Documents 1 and 2 describe that the number of carriers attached to the photoreceptor is reduced by using a carrier that satisfies the above physical property values. However, the degree of reduction is sufficient in actual image formation. Further improvement is required in terms of preventing carrier adhesion.

JP 2004-271660 A JP 2002-91093 A

  An object of the present invention is to provide a carrier and an electrophotographic developer capable of forming a high-definition and high-resolution high-quality image, preventing carrier adhesion to the photoreceptor, and preventing occurrence of image defects. Is to provide an agent.

The present invention provides a magnetic ferrite carrier comprising magnetic ferrite particles and a silicone resin coating layer formed on the surface of the magnetic ferrite particles.
The intensity ratio Si / Fe between the X-ray intensity of Si measured by fluorescent X-ray analysis and the X-ray intensity of Fe measured by fluorescent X-ray analysis is 3.5 × 10 ⁻² or more and 7.0 × 10 Less than ^-2 ,
The saturation magnetization in an external magnetic field of 5 kOe is 50 emu / g or more and 80 emu / g or less,
The resistance value at the time of applying a voltage of 500 V measured by a bridge-type electrical resistance measurement method is 1.0 × 10 ¹¹ Ω · cm or more and 1.0 × 10 ¹⁵ Ω · cm or less,
A magnetic ferrite carrier having a volume average particle diameter of 30 μm or more and 70 μm or less.

In the present invention, the strength ratio Si / Fe is 4.0 × 10 ⁻² or more and 6.0 × 10 ⁻² or less.

Further, the present invention is characterized in that the silicone resin coating layer contains conductive fine powder.
In the present invention, the conductive fine powder is carbon black.

  The present invention also provides an electrophotographic developer comprising the magnetic ferrite carrier of the present invention and a toner containing a binder resin and a colorant.

According to the present invention, a magnetic ferrite carrier including magnetic ferrite particles (hereinafter simply referred to as “ferrite particles”) and a silicone resin coating layer (hereinafter sometimes simply referred to as “coating layer”) formed on the surface of the ferrite particles. (Hereinafter simply referred to as “carrier”), the intensity ratio Si / Fe between the X-ray intensity of Si measured by X-ray fluorescence analysis and the X-ray intensity of Fe measured by X-ray fluorescence analysis is 3.5. × 10 ⁻² or more and less than 7.0 × 10 ⁻² . In the carrier having the strength ratio Si / Fe in such a range, the thickness of the coating layer formed on the surface of the ferrite particle is uniform, and the variation in the resistance value is small. Therefore, such a carrier can increase the adhesion between the carriers as compared with the carrier having a variation in the thickness of the coating layer, and can form a magnetic brush in which the adhesion between the carriers is not easily broken. Accordingly, the carrier can be prevented from being detached from the magnetic brush, the occurrence of carrier adhesion in which the carrier detached from the magnetic brush is transferred to the photoconductor can be suppressed, and the occurrence of image loss can be prevented. .

  Further, since the saturation magnetization (hereinafter simply referred to as “saturation magnetization”) of the carrier at an external magnetic field of 5 kOe is not less than 50 emu / g and not more than 80 emu / g, adhesion between the carrier and the developing roller by the magnetic pole provided in the developing roller becomes good. The magnetic brush is formed with moderate flexibility. As a result, the occurrence of carrier adhesion can be more reliably prevented, and deterioration of the carrier and toner can be suppressed. In addition, a high-definition image can be formed.

In addition, the resistance value (hereinafter simply referred to as “resistance value”) when a voltage of 500 V measured by the carrier bridge type electrical resistance measurement method is 1.0 × 10 ¹¹ Ω · cm or more and 1.0 × 10 ¹⁵ Ω · Since it is equal to or less than cm, excessive charging of the carrier is suppressed, and the toner can be stably supplied to the latent image carrier. Thereby, a high-quality image can be obtained. Further, the charge amount of the entire developer can be suitably maintained, and an image having a suitable image density can be formed.

  Further, since the volume average particle diameter of the carrier is 30 μm or more and 70 μm or less, a high-definition and high-resolution high-quality image can be formed.

Further, according to the present invention, since the strength ratio Si / Fe is 4.0 × 10 ⁻² or more and 6.0 × 10 ⁻² or less, the thickness of the coating layer is more uniform and the resistance value hardly varies. Absent. Therefore, the occurrence of carrier adhesion can be more reliably suppressed.

  Moreover, according to this invention, a coating layer contains electroconductive fine powder. By containing the conductive fine powder in the coating layer and adjusting the content of the conductive fine powder, the resistance value of the carrier can be set to the above-mentioned preferred value without significantly changing the coating amount of the coating layer on the ferrite particles. Can be a range value.

  According to the invention, the conductive fine powder is carbon black. Since carbon black has a lower specific gravity than ferrite, the resistance value of the carrier can be adjusted to a value within the above-mentioned preferred range without significantly changing the specific gravity of the carrier.

  According to the invention, the electrophotographic developer includes a carrier having the above effect and a toner containing a binder resin and a colorant. Such an electrophotographic developer is excellent in durability and excellent in charge imparting performance to the toner of the carrier. Further, since carrier adhesion to the photosensitive member can be suppressed, a high-definition and high-resolution high-quality image can be formed without image loss.

The magnetic ferrite carrier of the present invention is a magnetic ferrite carrier including magnetic ferrite particles and a silicone resin coating layer formed on the surface of the magnetic ferrite particles, and the X-ray intensity of Si measured by fluorescent X-ray analysis The intensity ratio Si / Fe with the X-ray intensity of Fe measured by fluorescent X-ray analysis is 3.5 × 10 ⁻² or more and less than 7.0 × 10 ⁻² , and the external magnetic field is 5 kilo-Oersted (kOe). The saturation magnetization is 50 emu / g or more and 80 emu / g or less, and the resistance value when applying a voltage of 500 V measured by the bridge type electric resistance measurement method is 1.0 × 10 ¹¹ Ω · cm or more and 1.0 × 10 ¹⁵ Ω · cm or less, and the volume average particle size is 30 μm or more and 70 μm or less.

  Carriers whose strength ratio Si / Fe is in the above range have a uniform thickness of the coating layer formed on the surface of the ferrite particles and a small variation in resistance value. The adhesion between the carriers can be increased, and a magnetic brush that is difficult to cut can be formed. Accordingly, it is possible to prevent the carrier from being detached from the magnetic brush and to suppress the occurrence of carrier adhesion in which the carrier detached from the magnetic brush is transferred to the photosensitive member, thereby forming a good image without image loss. be able to.

When the strength ratio Si / Fe is less than 3.5 × 10 ⁻² , the coating layer does not cover the entire surface of the ferrite particles, and the ferrite particles are partially exposed. When a magnetic brush is formed using such a carrier, the magnetic brush is easily cut off at the exposed portion of the ferrite particles, and the carrier is easily detached from the magnetic brush. As a result, the carrier detached from the magnetic brush causes carrier adhesion that adheres to the photoreceptor, and an image defect occurs in the formed image. When the strength ratio Si / Fe is 7.0 × 10 ⁻² or more, the thickness of the coating layer increases and the variation in the thickness of the coating layer also increases. Even when a magnetic brush is formed using such a carrier, the magnetic brush is likely to be cut off due to the variation in thickness, and the carrier that is detached from the magnetic brush adheres to the photoconductor.

The strength ratio Si / Fe is more preferably 4.0 × 10 ⁻² or more and 6.0 × 10 ⁻² or less. In the carrier having the strength ratio Si / Fe in such a range, the thickness uniformity of the coating layer is further improved, and there is almost no variation in the resistance value of the carrier surface and the resistance value between individual carriers. Therefore, the occurrence of carrier adhesion can be more reliably prevented.

  The X-ray intensity of Si measured by X-ray fluorescence analysis and the X-ray intensity of Fe measured by X-ray fluorescence analysis are, for example, a fluorescent X-ray analyzer (trade name: ZSX-Primus II, manufactured by Rigaku Corporation). Can be measured by. In such an apparatus, the target of the X-ray source: Rh, the applied voltage to the X-ray source: 40 kV, the current value: 50 mA, and LiF (target: Si) or pentaerythritol (PET, target) for the spectroscopic crystal of the optical system : Fe). In addition, a scintillation counter and a photo counter are used for the detector, and the spectroscope is scanned using the skip scan method, the PHA range is set to 100 to 300, and the angle is set to 0.05 degree per step. The X-ray intensity is measured.

  The saturation magnetization of the carrier at an external magnetic field of 5 kOe is 50 emu / g or more and 80 emu / g or less. When the carrier has such saturation magnetization, adhesion between the carrier and the developing roller by the magnetic pole provided in the developing roller becomes good, and the magnetic brush is formed with appropriate flexibility. As a result, the occurrence of carrier adhesion can be more reliably prevented, and deterioration of the carrier and toner can be suppressed. In addition, a high-definition image can be formed. When the saturation magnetization of the carrier is less than 50 emu / g, the magnetic adhesion force of the carrier to the developing roller is weak, the magnetic brush ears are shortened, and the density is increased, so that the reproducibility of the fine lines is improved. However, since the adhesion force is weak, it is difficult to restrain the carrier on the developing roller, and carrier adhesion occurs in which the carrier moves to the photosensitive member. When the saturation magnetization of the carrier exceeds 80 emu / g, the magnetic adhesion force of the carrier to the developing roller becomes too strong, and the magnetic brush ear becomes longer and stiffened. As a result, the durability of the developer is deteriorated and the carrier is hardly peeled off from the developing roller, so that the carrier is selectively deteriorated. In addition, since the magnetic brush density is reduced by increasing the length of the magnetic brush head, the image quality of the formed image is deteriorated, and further, the ear of the magnetic brush contacts the surface of the photoconductor and causes a sweep on the output image. There is a fear.

  The saturation magnetization of the carrier was obtained by applying 5 kOe to an external magnetic field using, for example, a high-sensitivity vibration sample type magnetometer (trade name: VSM-P7-15, manufactured by Toei Kogyo Co., Ltd.) dedicated to room temperature. It can be determined from the hysteresis curve.

Moreover, the resistance value at the time of applying a voltage of 500 V measured by the bridge-type electrical resistance measurement method of the carrier is 1.0 × 10 ¹¹ Ω · cm or more and 1.0 × 10 ¹⁵ Ω · cm or less. When the carrier has such a resistance value, overcharging of the carrier is suppressed and the toner can be stably supplied to the latent image carrier, so that a high-quality image can be obtained. Further, the charge amount of the entire developer can be suitably maintained, and an image having a suitable image density can be formed. When the resistance value is less than 1.0 × 10 ¹¹ Ω · cm, the charge imparting performance of the carrier to the toner is poor, and only the carrier is excessively charged and carrier adhesion occurs. When the resistance value exceeds 1.0 × 10 ¹⁵ Ω · cm, the charge imparting performance of the carrier with respect to the toner is lowered, resulting in poor image quality.

  The resistance value of the carrier can be measured by a bridge type electric resistance measuring device. The bridge-type electrical resistance measuring apparatus includes two facing electrode cells provided at a predetermined interval and an insulation resistance meter that applies a voltage to the facing electrode cell. For example, a carrier weighed to 0.20 g is filled between two facing electrode cells, a magnet is set from the outside of the facing electrode cell, and the magnet is reciprocated five times back and forth. A voltage of 500 V is applied by an insulation resistance meter, and the value displayed after 1 minute is taken as the resistance value of the carrier.

  The volume average particle diameter of the carrier is 30 μm or more and 70 μm or less. When the carrier has such a volume average particle diameter, a high-definition and high-resolution high-quality image can be formed. When the volume average particle diameter of the carrier is less than 30 μm, the charge amount of the carrier increases, and carrier adhesion occurs in which the carrier moves to the photoreceptor. When the volume average particle diameter of the carrier exceeds 70 μm, there is a possibility that a high-definition and high-resolution high-quality image cannot be formed. Further, since the specific surface area of the carrier is reduced and the charge imparting performance to the toner is lowered, the charge amount of the toner is small and the image density may be lowered.

  The volume average particle diameter of the carrier can be measured by, for example, Coulter Counter TA-III (trade name, manufactured by Coulter). Specifically, 20 mL of a 1% aqueous solution (electrolyte) of sodium chloride (first grade) is placed in a 100 mL beaker, and 0.5 mL of alkylbenzene sulfonate (dispersant) and 3 mg of a sample are sequentially added thereto for 5 minutes. Disperse ultrasonically. To this, a 1% aqueous solution of sodium chloride (first grade) is added so that the total amount becomes 100 mL, and then ultrasonically dispersed again for 5 minutes is used as a measurement sample. This measurement sample is measured using a Coulter counter TA-III under the conditions of an aperture diameter of 100 μm and the number of measured particles: 50000 count, and the volume average particle diameter is obtained from the volume particle size distribution of the sample particles.

  The carrier of the present invention as described above may be a carrier in which each value of the intensity ratio Si / Fe, the saturation magnetization, the resistance value, and the volume average particle diameter is included in the above-described range. The carrier of the present invention includes magnetic ferrite particles and a silicone resin coating layer formed on the surface of the magnetic ferrite particles, and the manufacturing method thereof is not particularly limited.

As magnetic ferrite particles, magnetite, ferrite particles containing iron and metal elements other than iron can be used, and those represented by the following formula (1) can be used.
(MO) _x. (Fe ₂ O ₃ ) _y (1)

However represent mole% of each x and y MO and _Fe 2 _{O 3} in the above formula (1), which is x + y = 100. M in the above formula (1) represents one or more metals selected from Fe, Cu, Zn, Mn, Mg, Ni, Sr, Ca, and Li, and MO represents an oxide thereof. It represents one or a combination of two or more selected. Therefore, as ferrite containing metal elements other than iron, for example, zinc ferrite, nickel ferrite, copper ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, copper-magnesium ferrite, manganese-zinc ferrite And manganese-copper-zinc ferrite.

  These ferrite particles are obtained by mixing raw materials, calcining and pulverizing, and then firing, and by changing the firing temperature, the surface shape of the particles can be changed. Although the dimension of the core material is not particularly limited, it is a dimension such that the volume average particle size after forming a coating layer described later is 30 μm or more and 70 μm or less. The shape of the ferrite particles is not particularly limited, and may be any of spherical, granular, indefinite shape, flake shape, etc., but is preferably spherical. A core material can be used individually by 1 type, or can use 2 or more types together.

In the above-mentioned formula (1), the ferrite particles preferably have y of 40 or more and 100 or less, and more preferably 50 or more and 90 or less. When y is less than 40, that is, when Fe ₂ O ₃ in the ferrite particles is less than 40 mol%, the saturation magnetization of the carrier becomes small, and carrier adhesion may occur. The MO is preferably MnO, MgO or a combination of MnO and MgO.

  The silicone resin coating layer formed on the surface of the ferrite particles contains a silicone resin. The silicone resin can be easily heat-treated to improve the adhesion between the ferrite particles and the coating layer, and can reduce the variation in the charge imparting performance of each carrier to the toner. Also, wear resistance, heat resistance, mechanical strength, etc. are good. Specific examples of the silicone resin include, for example, silicone varnish (trade names: TSR115, TSR114, TSR102, TSR103, YR3061, TSR110, TSR116, TSR117, TSR108, TSR109, TSR180, TSR181, TSR187, TSR144, TSR165, Shin-Etsu Chemical Co., Ltd. KR271, KR272, KR275, KR280, KR282, KR267, KR269, KR211, KR212, etc., manufactured by Toshiba Corporation, alkyd-modified silicone varnishes (trade names: TSR184, TSR185, etc., manufactured by Toshiba Corporation), epoxy-modified silicone varnishes (Trade name: TSR194, YS54, etc., manufactured by Toshiba Corporation), polyester-modified silicone varnish (trade name: TSR187, etc., stock Manufactured by Toshiba), acrylic-modified silicone varnish (trade names: TSR170, TSR171, etc., manufactured by Toshiba Corporation), urethane-modified silicone varnish (trade name: TSR175, manufactured by Toshiba Corporation), reactive silicone resin (trade name: KA1008) , KBE1003, KBC1003, KBM303, KBM403, KBM503, KBM602, KBM603, etc., manufactured by Shin-Etsu Chemical Co., Ltd.). These silicone resins can be used alone or in combination of two or more.

The silicone resin coating layer preferably contains a conductive fine powder for adjusting the resistance value of the obtained carrier. The conductive fine powder is a fine powder having a volume resistivity of 10 ⁻² Ω · cm to 10 ¹⁰ Ω · cm. Examples of such conductive fine powder include powders such as carbon black and magnetite. Among these, carbon black is preferable. The conductive fine powder can be used alone or in combination of two or more. Although there is no restriction | limiting in particular in the usage-amount of electroconductive fine powder, Preferably it is 0.1-20 weight part with respect to 100 weight part of silicone resins in a silicone resin coating layer. The conductive fine powder preferably has a number average particle size of primary particles of 10 nm to 50 nm in consideration of dispersibility in the silicone resin.

  The carrier of the present invention can be produced by coating ferrite particles with a silicone resin and subjecting them to drying treatment and heat treatment as necessary. The silicone resin contains conductive fine powder as necessary.

  In coating the ferrite particles with the silicone resin, a known coating method such as a dipping method, a spray method, a fluidized bed method, or a kneader coater method can be employed. For example, according to the dipping method, the carrier of the present invention can be obtained by dipping ferrite particles in a silicone resin solution or an aqueous dispersion (hereinafter simply referred to as “resin solution”). According to the spray method, the carrier of the present invention can be obtained by spraying a resin solution onto ferrite particles. According to the fluidized bed method, the carrier of the present invention can be obtained by spraying a resin solution onto ferrite particles that are in a floating state with fluidized air. According to the kneader coater method, the carrier of the present invention can be obtained by mixing ferrite particles and a resin solution in a kneader coater and removing liquid components such as a solvent and water. Here, the solvent for preparing the resin solution is not particularly limited as long as it can dissolve or disperse the silicone resin. For example, aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, Examples include ethers such as tetrahydrofuran and dioxane, higher alcohols, water, and mixed solvents of two or more of these. When the conductive fine powder is contained in the silicone resin, the conductive fine powder is added when preparing the resin solution.

  The drying treatment is performed to remove liquid components such as a solvent and water remaining in or around the silicone resin coating layer. The heat treatment is performed, for example, for the purpose of improving the mechanical strength by curing the silicone resin coating layer and improving the adhesion between the resin coating layer and the core material. The heat treatment temperature is about 150 to 260 ° C.

The coating of the silicone resin is performed by adjusting the coating amount so that the above-mentioned strength ratio Si / Fe is 3.5 × 10 ⁻² or more and less than 7.0 × 10 ⁻² . Adjustment of the coating amount of the silicone resin can be performed by adjusting the concentration of the silicone resin in the resin solution, and can also be performed by adjusting the usage amount of the resin solution.

The carrier coated with the silicone resin as described above preferably has a true specific gravity of 2.5 g / cm ³ or more and 4.0 g / cm ³ or less. If the true specific gravity of the carrier is less than 2.5 g / cm ³ , the specific gravity of the carrier becomes too small, and there is a possibility of carrier adhesion in which the carrier moves onto the photoreceptor. Further, the charge imparting performance to the toner may be reduced, and the image density may be reduced. If the true specific gravity of the carrier exceeds 4.0 g / cm ³ , the specific gravity and density of the carrier become too large, and it is necessary to increase the stirring force in the developing container, and the carrier and toner deteriorate due to the increase in stirring force. For example, there is a possibility that carrier spent may be generated in which toner fine particles adhere to the carrier and contaminate the carrier.

  The carrier of the present invention as described above is used as a two-component electrophotographic developer (hereinafter referred to as “two-component developer”) together with the toner. The toner used together with the carrier of the present invention contains a binder resin and a colorant, and may contain a toner additive such as a release agent and a charge control agent. Further, the toner production method is not particularly limited, and examples thereof include dry methods such as a pulverization method, suspension polymerization methods, emulsion aggregation methods, dispersion polymerization methods, dissolution suspension methods, and melt emulsion methods. . A method for producing toner by the pulverization method will be described below.

  As the binder resin, those commonly used in this field can be used. For example, styrene polymer, polyvinyl chloride, phenol resin, naturally modified phenol resin, naturally modified maleic acid resin, acrylic resin, methacrylic resin, polyvinyl acetate. , Silicone resin, polyester, polyurethane, polyamide resin, furan resin, epoxy resin, xylene resin, polyvinyl butyral, terpene resin, coumarone indene resin, petroleum resin and the like. Among these, a styrene polymer and polyester are preferable.

  Styrene polymers include styrene homopolymers and styrene copolymers. Examples of the styrene homopolymer include homopolymers of styrene-substituted products such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene. On the other hand, in the styrene copolymer, a known vinyl monomer can be used as a comonomer used together with styrene, such as acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, acrylic acid. (Meth) acrylic acid esters such as octyl, 2-ethylhexyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, and substituted products thereof, maleic acid, maleic acid Dicarboxylic acids having a double bond such as butyl, methyl maleate and dimethyl maleate and substituted products thereof, vinyl esters such as vinyl chloride, vinyl acetate and vinyl benzoate, ethylene-based olefins such as ethylene, propylene and butylene, Sulfonyl methyl ketone, ketones such as vinyl hexyl ketone, vinyl methyl ether, vinyl ethyl ether, vinyl ethers such as vinyl isobutyl ether, acrylonitrile, methacrylonitrile, acrylamide and the like. A vinyl monomer can be used individually by 1 type, or can use 2 or more types together. Specific examples of the styrene copolymer containing such a vinyl monomer include, for example, a styrene-p-chlorostyrene copolymer, a styrene-vinyltoluene copolymer, a styrene-vinylnaphthalene copolymer, and styrene. -Acrylate ester copolymer, styrene-methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer Examples thereof include a polymer, a styrene-vinyl methyl ketone copolymer, a styrene-butadiene copolymer, a styrene-isoprene copolymer, and a styrene-acrylonitrile-indene copolymer.

  Among these, a styrene polymer crosslinked by a crosslinking agent is preferable. As the crosslinking agent, a compound having two or more polymerizable double bonds is mainly used. For example, aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene, carboxylic acid esters having two double bonds such as ethylene glycol diacrylate, ethylene glycol dimethacrylate, and 1,3-butanediol dimethacrylate, divinylaniline, divinyl And divinyl compounds such as vinyl ether, divinyl sulfide and divinyl sulfone, and compounds having three or more vinyl groups. A crosslinking agent can be used individually by 1 type, or can use 2 or more types together.

Furthermore, among these, the weight average molecular weight (Mw) in gel permeation chromatography (GPC) is 15 × 10 ^{4 to} 25 × 10 ⁴ , and the number average molecular weight (Mn) is 2 × 10 ³ to 4 × 10 ³ . Those are preferred. Further, it is particularly preferable that the softening point is 145 ° C. to 165 ° C. and the loss elastic modulus G ″ at 140 ° C. is 1 × 10 ⁴ dyn / cm ² to 2 × 10 ⁴ dyn / cm ² .

  Moreover, as polyester, the polycondensation product of a polyhydric alcohol and polyhydric carboxylic acid is mentioned. Here, the polyhydric alcohol includes aliphatic polyhydric alcohol, alicyclic polyhydric alcohol, aromatic polyhydric alcohol, and the like. Examples of the aliphatic polyhydric alcohol include ethylene glycol, propylene glycol, 1,3-propanediol, 2,3-butanediol, 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol. , Neopentyl glycol, diethylene glycol, dipropylene glycol, 2,2,4-trimethyl-1,3-pentanediol, polyethylene glycol, polytetramethylene glycol and other aliphatic diols, trimethylolethane, trimethylolpropane, glycerin, Examples include triols such as pentaerythritol, tetraols and the like. Examples of the alicyclic polyhydric alcohol include 1,4-cyclohexanediol, 1,4-cyclohexanedimethanol, spiroglycol, hydrogenated bisphenol A, ethylene oxide adduct and propylene oxide adduct of hydrogenated bisphenol A, tri Examples include cyclodecanediol and tricyclodecane dimethanol. Examples of aromatic polyhydric alcohols include para-xylene glycol, meta-xylene glycol, ortho-xylene glycol, 1,4-phenylene glycol, 1,4-phenylene glycol ethylene oxide adduct, bisphenol A, and bisphenol A ethylene oxide addition. And propylene oxide adducts. A polyhydric alcohol can be used individually by 1 type, or can use 2 or more types together. The polyhydric alcohol may include monoalcohols such as aliphatic alcohols, aromatic alcohols, and alicyclic alcohols.

  Examples of the polyvalent carboxylic acid include terephthalic acid, isophthalic acid, orthophthalic acid, 1,5-naphthalenedicarboxylic acid, 2,6-naphthalenedicarboxylic acid, anthracene dipropionic acid, anthracene dicarboxylic acid, diphenic acid, sulfoterephthalic acid, 5-sulfoisophthalic acid, 4-sulfophthalic acid, 4-sulfonaphthalene-2,7-dicarboxylic acid, 5- (4-sulfophenoxy) isophthalic acid, aromatic dicarboxylic acids such as metal salts and ammonium salts thereof, and succinic acid , Aliphatic dicarboxylic acids such as adipic acid, azelaic acid, sebacic acid and dodecanedicarboxylic acid, aliphatic unsaturated polycarboxylic acids such as fumaric acid, maleic acid, itaconic acid, citraconic acid, and aromatics such as phenylenediacrylic acid Unsaturated polycarboxylic acid, hexahydrophthal Alicyclic dicarboxylic acids such as tetrahydrophthalic acid, trimellitic acid, trimesic acid, such as trihydric or higher polycarboxylic acids such as pyromellitic acid. A polyvalent carboxylic acid can be used individually by 1 type, or can use 2 or more types together. If necessary, a monocarboxylic acid can be used together with a polyvalent carboxylic acid. As the monocarboxylic acid, an aromatic monocarboxylic acid is preferable. Examples of the aromatic monocarboxylic acid include benzoic acid, chlorobenzoic acid, bromobenzoic acid, p-hydroxybenzoic acid, naphthalenecarboxylic acid, tert-butylnaphthalenecarboxylic acid, anthracenecarboxylic acid, 4-methylbenzoic acid, 3- Methylbenzoic acid, tert-butylbenzoic acid, salicylic acid, thiosalicylic acid, phenylacetic acid, their lower alkyl esters, sulfobenzoic acid monoammonium salt, sulfobenzoic acid monosodium salt, cyclohexylaminocarbonylbenzoic acid, n-dodecylaminocarbonylbenzoic acid An acid etc. are mentioned.

The polycondensation of the polyhydric alcohol and the polycarboxylic acid can be carried out according to a known method.
As the colorant, those commonly used in this field can be used, and examples thereof include a yellow toner colorant, a magenta toner colorant, a cyan toner colorant, and a black toner colorant.

  Examples of the colorant for yellow toner include C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 5, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 15, C.I. I. Azo pigments such as CI Pigment Yellow 17; inorganic pigments such as yellow iron oxide and ocher; I. Nitro dyes such as Acid Yellow 1, C.I. I. Solvent Yellow 2, C.I. I. Solvent Yellow 6, C.I. I. Solvent Yellow 14, C.I. I. Solvent Yellow 15, C.I. I. Solvent Yellow 19, C.I. I. Examples thereof include oil-soluble dyes such as Solvent Yellow 21.

  Examples of the colorant for magenta toner include C.I. I. Pigment red 49, C.I. I. Pigment red 57, C.I. I. Pigment red 81, C.I. I. Pigment red 122, C.I. I. Solvent Red 19, C.I. I. Solvent Red 49, C.I. I. Solvent Red 52, C.I. I. Basic Red 10, C.I. I. Disperse Red 15 etc. are mentioned.

  Examples of the colorant for cyan toner include C.I. I. Pigment blue 15, C.I. I. Pigment blue 16, C.I. I. Solvent Blue 55, C.I. I. Solvent Blue 70, C.I. I. Direct Blue 25, C.I. I. Direct Blue 86 and the like can be mentioned.

  Examples of the colorant for black toner include carbon black such as channel black, roller black, disk black, gas furnace black, oil furnace black, thermal black, and acetylene black. From these various types of carbon black, an appropriate carbon black may be appropriately selected according to the design characteristics of the toner to be obtained.

  A coloring agent can be used individually by 1 type, or can use 2 or more types together. Two or more of the same color can be used, and one or more of the different colors can also be used.

  The amount of the colorant used is not particularly limited, but is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the binder resin. By using the colorant in this range, an image having a high image density and a very good image quality can be formed without impairing various physical properties of the toner.

  As the charge control agent, those for positive charge control and negative charge control commonly used in this field can be used. Examples of the charge control agent for controlling positive charge include basic dyes, quaternary ammonium salts, aminopyrines, pyrimidine compounds, polynuclear polyamino compounds, aminosilanes, and nigrosine dyes. Examples of the charge control agent for controlling negative charges include oil-soluble dyes such as oil black and nest pyrone black, metal-containing azo compounds, metal naphthenates, metal salicylates, fatty acid soaps, and resin acid soaps. The charge control agent can be used alone or in combination of two or more as required. The amount of the charge control agent used is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.5 to 3 parts by weight with respect to 100 parts by weight of the binder resin.

  As the release agent, those commonly used in this field can be used, for example, petroleum wax such as paraffin wax and derivatives thereof, microcrystalline wax and derivatives thereof, Fischer-Tropsch wax and derivatives thereof, polyolefin wax and derivatives thereof, low Hydrocarbon synthetic waxes such as molecular weight polypropylin wax and derivatives thereof, low molecular weight polyethylene wax and derivatives thereof, carnauba wax and derivatives thereof, rice wax and derivatives thereof, candelilla wax and derivatives thereof, plant waxes such as wood wax, beeswax , Animal waxes such as spermaceti, fats and oils synthetic waxes such as fatty acid amides and phenol fatty acid esters, long chain carboxylic acids and their derivatives, long chain alcohols and their derivatives, etc. It is below. Derivatives include oxides, block copolymers of vinyl monomers and waxes, graft modified products of vinyl monomers and waxes, and the like. The amount of the wax used is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  The fluidity improver is used as an external additive. For example, the effect is exhibited by adhering to the toner surface. As the fluidity improver, those commonly used in this field can be used, and examples thereof include silicon oxide, titanium oxide, silicon carbide, aluminum oxide, and barium titanate. A fluidity improver can be used individually by 1 type, or can use 2 or more types together. The amount of the fluidity improver used is not particularly limited, but is preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the toner particles.

  The toner particles used in the two-component developer of the present invention can be produced according to a known method. For example, a binder resin, a colorant, a charge control agent, and other additives are mixed by a mixer such as a Henschel mixer, a super mixer, a mechano mill, or a Q-type mixer, and the resulting raw material mixture is mixed with a two-screw kneader, one screw A kneader such as a kneader or a continuous two-roll kneader is melt-kneaded at a temperature of about 70 to 180 ° C., the resulting kneaded product is cooled and solidified, and the solidified product is cooled by an air-type pulverizer such as a jet mill. By pulverizing and adjusting the particle size such as classification as necessary, toner particles having a volume average particle diameter of preferably 3 to 15 μm, more preferably 6.0 to 7.5 μm are obtained.

  Considering that the colorant and other additives are uniformly dispersed in the binder resin and that the toner is efficiently manufactured without impairing the physical properties of the binder resin, a master batch method is adopted in the production of the toner particles. Is preferred. According to the master batch method, a binder resin less than a predetermined amount and a predetermined amount of colorant are mixed by a mixer in the same manner as described above, and the resulting raw material mixture is mixed by a continuous two-roll kneader. Kneading while applying shear force. The obtained kneaded product is cooled and solidified, and further coarsely crushed to obtain a kneaded crushed product. The remaining binder resin and other additives are mixed into this kneaded coarsely crushed product, diluted and kneaded with an extruder, and the resulting kneaded product is cooled and solidified in the same manner as above, pulverized, and the particle size is adjusted as necessary. Thus, toner particles can be obtained.

  The use ratio of the toner and the carrier of the present invention in the two-component developer of the present invention is not particularly limited, and the image forming speed, image density, developing bias voltage, supply bias voltage, and developing device set in the image forming apparatus are set. Although the toner replenishment capability and other various conditions can be appropriately selected from a wide range, the ratio of the surface area of the carrier to the projected area of the toner (hereinafter referred to as “coverage”) is in the range of 30 to 70%. It is preferable to mix the toner and the carrier. When the usage ratio of the toner within the range of the coverage is expressed on the basis of weight, the toner is about 1 to 10 parts by weight, preferably about 1.5 to 5.5 parts by weight with respect to 100 parts by weight of the carrier.

(Example)
Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. In the following, “parts” and “%” mean “parts by weight” and “% by weight” unless otherwise specified. In Examples and Comparative Examples, X-ray intensity of Si and Fe by fluorescent X-ray analysis, saturation magnetization of carriers, carrier resistance value and volume average particle diameter by bridge-type electric resistance measurement method are measured as follows. did.

[X-ray intensity]
In an X-ray fluorescence analyzer (trade name: ZSX / Primus II, manufactured by Rigaku Corporation), the target of the X-ray source is Rh, the applied voltage to the X-ray source is 40 kV, the current value is 50 mA, and the optical system is used as a spectral crystal. LiF (target: Si) or pentaerythritol (PET, target: Fe) was used. In addition, a scintillation counter and a photo counter are used for the detector, and the spectroscope is scanned using the skip scan method, the PHA range is set to 100 to 300, and the angle is set to 0.05 degree per step. X-ray intensity was measured.

[Carrier saturation magnetization]
From a hysteresis curve obtained by applying a high-sensitivity vibration sample type magnetometer (trade name: VSM-P7-15, manufactured by Toei Kogyo Co., Ltd.) to room temperature and applying 5 kilo-Oersted (kOe) to an external magnetic field Asked. Specifically, a VSM-P7 type magnetometer body (manufactured by Toei Industry Co., Ltd.), a TRG-3 type Gauss meter (manufactured by Toei Industry Co., Ltd.), a VSM data analysis system, an electromagnet generating a maximum of 15 kOe, and a constant Using a voltage constant current automatic sweep type power supply, measurement was performed as follows in a normal temperature (25 ° C.) environment. Set the EMU of Main Amp to 5 emu, the time constant to 0.03 seconds, the range A of the gauss meter to 5 kOe, select the standard Ni that is close to the sample geometry, set it in the sample holder, and vibrate It was. A magnetic field of 5 kOe was applied, the sample was adjusted to be the center of the magnetic field, and the value of the main amp panel meter was set to 1000V. Next, the sample cell made of acrylic resin was placed on an electronic balance having a minimum scale of 0.1 mg, the zero point was adjusted, the sample was filled in the cell, and weighed. The sample cell filled with this sample was vibrated under the same conditions as described above, and the saturation magnetization was measured.

[Resistance value]
By a bridge-type electrical resistance measuring device comprising two facing electrode cells (manufactured by Dowa Iron Powder Industry Co., Ltd.) and an insulation resistance meter (trade name: SM-5E, Toa DK Corporation) that applies a voltage to the facing electrode cell Measured in a room temperature (25 ° C.) environment. Specifically, 0.20 g of carrier weighed by an electronic balance having a minimum scale of 1 mg is filled between two facing electrode cells, a magnet is set from the outside of the facing electrode cell, and the magnet is reciprocated five times back and forth. Then, a voltage of 500 V was applied by an insulation resistance meter, and the value displayed after 1 minute was taken as the resistance value.

[Volume average particle size]
In a 100 mL beaker, 20 mL of a 1% aqueous solution (electrolytic solution) of sodium chloride (first grade) was added, and 0.5 mL of alkylbenzene sulfonate (dispersant) and 3 mg of a sample were sequentially added thereto and ultrasonically dispersed for 5 minutes. . To this, a 1% aqueous solution of sodium chloride (first grade) was added so that the total amount would be 100 mL, and again ultrasonically dispersed for 5 minutes was used as a measurement sample. For this measurement sample, measurement was performed using a Coulter Counter TA-III (trade name, manufactured by Coulter, Inc.) under the conditions of an aperture diameter of 100 μm and the number of measured particles: 50000 counts. The diameter was determined.

(Example 1)
100 parts of silicone resin (trade name: KR-255, manufactured by Shin-Etsu Chemical Co., Ltd.) (in terms of solid content) was dispersed in toluene to prepare a dispersion for forming a resin coating layer. 3 parts of the resin coating layer dispersion obtained above by spraying is applied to 100 parts of Mn—Mg ferrite (particle size: 37 to 38 μm, core material) having a saturation magnetization of 60 emu / g by a fluidized bed coating apparatus. The carrier of Example 1 was manufactured by heating at 0 ° C. for 2 hours.

(Example 2)
A carrier of Example 2 was produced in the same manner as Example 1 except that the amount of the resin coating layer forming dispersion was changed to 3.3 parts.

(Example 3)
A carrier of Example 3 was produced in the same manner as in Example 1 except that the amount of the resin coating layer forming dispersion was changed to 4.2 parts.

Example 4
A carrier of Example 4 was produced in the same manner as Example 1 except that the amount of the resin coating layer-forming dispersion used was changed to 5.0 parts.

(Example 5)
A carrier of Example 5 was produced in the same manner as in Example 1 except that the amount of the resin coating layer forming dispersion was changed to 5.7 parts.

(Example 6)
Implemented except that the core material was changed to a Mn-Mg based ferrite (particle size 37-38 μm, core material) with a saturation magnetization of 50 emu / g, and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. The carrier of Example 6 was produced in the same manner as Example 1.

(Example 7)
Implemented except that the core material was changed to Mn-Mg ferrite (particle size 37-38 μm, core material) with saturation magnetization of 80 emu / g, and the amount of dispersion for forming the resin coating layer was changed to 4.2 parts The carrier of Example 7 was produced in the same manner as Example 1.

(Example 8)
Example 1 except that the core material was changed to a Mn—Mg based ferrite (particle size: 37 to 38 μm) having a low resistance value, and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. Similarly, the carrier of Example 8 was produced.

Example 9
Example 1 except that the core material was changed to a Mn-Mg based ferrite (particle size: 37 to 38 μm) having a high resistance value, and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. Similarly, the carrier of Example 9 was produced.

(Example 10)
In the same manner as in Example 1 except that the core material was changed to another Mn—Mg based ferrite (particle size: 28 to 29 μm) and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. The carrier of Example 10 was manufactured.

(Example 11)
In the same manner as in Example 1 except that the core material was changed to another Mn—Mg based ferrite (particle size 66 to 67 μm) and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. The carrier of Example 11 was manufactured.

(Example 12)
5 parts of carbon black (trade name: Ketjen Black EC, manufactured by Lion Corporation) was added to the dispersion for forming the resin coating layer, and the amount of the dispersion for forming the resin coating layer was changed to 3.2 parts. A carrier of Example 12 was produced in the same manner as Example 1 except for the above.

(Comparative Example 1)
A carrier of Comparative Example 1 was produced in the same manner as in Example 1 except that the amount of the resin coating layer forming dispersion was changed to 2 parts.

(Comparative Example 2)
A carrier of Comparative Example 2 was produced in the same manner as in Example 1 except that the amount of the resin coating layer forming dispersion was changed to 6.5 parts.

(Comparative Example 3)
Example 1 except that the core material was changed to Mn—Mg based ferrite (particle size: 37 to 38 μm) having a saturation magnetization of 40 emu / g and the amount of the dispersion for forming the resin coating layer was changed to 4.2 parts. Similarly, the carrier of Comparative Example 3 was produced.

(Comparative Example 4)
Example 1 except that the core material was changed to Mn—Mg ferrite (particle size: 37 to 38 μm) having a saturation magnetization of 90 emu / g and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. Similarly, the carrier of Comparative Example 4 was produced.

(Comparative Example 5)
Example 1 except that the core material was changed to a Mn—Mg based ferrite (particle size: 37 to 38 μm) having a low resistance value, and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. Similarly, the carrier of Comparative Example 5 was produced.

(Comparative Example 6)
Example 1 except that the core material was changed to a Mn-Mg based ferrite (particle size: 37 to 38 μm) having a high resistance value, and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. Similarly, the carrier of Comparative Example 6 was produced.

(Comparative Example 7)
In the same manner as in Example 1 except that the core material was changed to another Mn—Mg based ferrite (particle size: 18 to 19 μm) and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. A carrier of Comparative Example 7 was produced.

(Comparative Example 8)
In the same manner as in Example 1 except that the core material was changed to another Mn—Mg based ferrite (particle size: 75 to 76 μm) and the amount of the resin coating layer forming dispersion was changed to 4.2 parts. A carrier of Comparative Example 8 was produced.

  Using the carriers of Examples and Comparative Examples as described above and the toner produced by the following production method, both were mixed at a ratio such that the coverage of the silicone resin carrier with toner particles was 35%. Two-component developers containing the carriers of Examples and Comparative Examples were produced.

[Toner Preparation Method]
Polyester resin (glass transfer point: 60 ° C.) 100 parts Polyethylene wax (release agent, trade name: PE130, manufactured by Clariant Japan Ltd.) 1.0 part Polypropylene (release agent, trade name: NP-505, Mitsui Chemicals) 1.5 parts Carbon black (colorant, trade name: 330R, manufactured by Cabot) 5 parts Charge control agent (trade name: S-34, manufactured by Hodogaya Chemical Co., Ltd.) 1 part Magnetite (trade name: KBC) -100, manufactured by Kanto Denka Kogyo Co., Ltd.) 1.5 parts

  The above raw materials are mixed by a super mixer (trade name: V-20, manufactured by Kawata Co., Ltd.), and this mixture is melt-kneaded by a biaxial kneader (trade name: PCM-30, manufactured by Ikegai Co., Ltd.). The product was pulverized with a jet type pulverizer (trade name: IDS-2, manufactured by Nippon Pneumatic Industry Co., Ltd.) and classified to produce toner base particles having a volume average particle diameter of 7.5 μm. To 100 parts of the toner base particles, 0.3 part of silica particles (trade name: R972, manufactured by Nippon Aerosil Co., Ltd.) was added and mixed to produce a black toner.

  Using the two-component developers containing carriers obtained in Examples and Comparative Examples, image quality and carrier adhesion were evaluated as follows. Based on this evaluation result, comprehensive evaluation was performed.

[Image quality evaluation]
Two-component developer containing carriers of Examples and Comparative Examples is filled in a monochrome copying machine (trade name: AR-705S, manufactured by Sharp Corporation), and A4 size recording paper defined in Japanese Industrial Standard (JIS) P0138 One original with a printing rate of 5% was printed on top, and an initial image was obtained. Thereafter, 50k sheets were printed and aged to obtain images after printing 50k sheets. For the obtained initial image and the image after printing 50k sheets, the image density and the edge portion of the image were evaluated as image quality evaluation, respectively. The image density evaluation and the edge evaluation of the image are both good (good), one of them is good, the other is bad △ (bad), and both are bad X (very bad). The image density was evaluated as good when the value measured by a Macbeth reflection densitometer (trade name: RD-914, manufactured by Macbeth) was 1.30 or more. In addition, the evaluation of the edge portion of the image was good unless a defect such as an image defect was visually confirmed.

[Evaluation of carrier adhesion]
Two-component developer containing carriers of Examples and Comparative Examples is filled in a monochrome copying machine (trade name: AR-705S, manufactured by Sharp Corporation), and A4 size recording paper defined in Japanese Industrial Standard (JIS) P0138 A white solid image was formed on the top. The number of carriers adhering to the photoreceptor after the formation of the solid image was confirmed by visual observation, and あ る (good) when the number of carriers attached was 15 or less, and the number of carriers attached was 16 or more and 30 or less. Some were evaluated as ◯ (no problem in actual use), and those with 31 or more carriers attached were evaluated as x (defect).

〔Comprehensive evaluation〕
The evaluation criteria for comprehensive evaluation are as follows.
A: Very good. There is no Δ or x in the image quality evaluation, and the evaluation of carrier adhesion is ◎.
○: Good. There is no Δ or x in the image quality evaluation, and the carrier adhesion evaluation is ○.
X: Defect. There are Δ and X in the image quality evaluation and the carrier adhesion evaluation.

  Example and Comparative Example Carrier Strength Ratio Si / Fe, Saturation Magnetization in External Magnetic Field of 5 kOe, Resistance Value at Voltage Application of 500 V Measured by Bridge Type Electrical Resistance Measurement Method, Volume Average Particle Size, and Silicone Resin 100 Table 1 shows the amount of carbon black added to the coating layer and the evaluation results.

  From Table 1, it can be seen that when an image is formed with the two-component developer containing the carrier of the present invention, an image with good image quality can be obtained and carrier adhesion is prevented.

Claims (5)

In a magnetic ferrite carrier including magnetic ferrite particles and a silicone resin coating layer formed on the surface of the magnetic ferrite particles,
The intensity ratio Si / Fe between the X-ray intensity of Si measured by fluorescent X-ray analysis and the X-ray intensity of Fe measured by fluorescent X-ray analysis is 3.5 × 10 ⁻² or more and 7.0 × 10 Less than ^-2 ,
The saturation magnetization in an external magnetic field of 5 kOe is 50 emu / g or more and 80 emu / g or less,
The resistance value at the time of applying a voltage of 500 V measured by a bridge-type electrical resistance measurement method is 1.0 × 10 ¹¹ Ω · cm or more and 1.0 × 10 ¹⁵ Ω · cm or less,
A magnetic ferrite carrier having a volume average particle size of 30 μm or more and 70 μm or less. The magnetic ferrite carrier according to claim 1, wherein the strength ratio Si / Fe is 4.0 × 10 ⁻² or more and 6.0 × 10 ⁻² or less.   The magnetic ferrite carrier according to claim 1 or 2, wherein the silicone resin coating layer contains a conductive fine powder.   4. The magnetic ferrite carrier according to claim 3, wherein the conductive fine powder is carbon black.   An electrophotographic developer comprising the magnetic ferrite carrier according to any one of claims 1 to 4 and a toner containing a binder resin and a colorant.