JP2009069502A - Two-component developer and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two-component developer and an image forming apparatus, wherein uneven conveyance of the developer is not caused by radical reduction in the fluidity of the two-component developer, even after long-term use. <P>SOLUTION: The two-component developer comprises a toner and a carrier and is characterized in that: the toner contains color resin particles having a volume average particle diameter of 4 to 9 μm and containing a hydrocarbon wax having a melting point of 64 to 77°C, and an external additive having a number average particle diameter of 80 to 300 nm; the carrier contains coated core particles having a volume average particle diameter of 25 to 60 μm, the coated core particles comprising a core particle made of a ferrite component and a coating layer made of a thermosetting straight silicone resin applied on the surfaces of the core particle; and an intensity ratio Si/Fe of the X-ray intensity of Si to the X-ray intensity of Fe measured by fluorescent X-ray analysis of the coated core particles ranges from 0.01 to 0.03. The electrophotographic image forming apparatus using the above developer is also provided. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a two-component developer and also relates to an electrophotographic image forming apparatus using the two-component developer.

  An image forming apparatus using an electrophotographic system is generally composed of apparatuses that perform charging, exposure, development, transfer, cleaning, charge removal, and fixing processes. For example, the surface of the rotationally driven photoconductor is uniformly charged by a charging device, and the charged photoconductor surface is irradiated with laser light (ie, exposed) to form an electrostatic latent image. Subsequently, the electrostatic latent image on the photoreceptor is developed as a toner image by a developing device. The toner image formed on the photoreceptor is transferred onto a transfer material by a transfer device. The transferred toner image is heated by the fixing device and fixed on the transfer material. The toner remaining on the surface of the photoconductor is removed by a cleaning device and collected by a predetermined collecting unit. At the same time, residual charge is removed from the cleaned surface of the photoconductor by a static eliminator to prepare for the next image formation.

  As the developer for developing the electrostatic latent image on the photoreceptor, a one-component developer composed of only toner or a two-component developer composed of toner and carrier is generally used. Since the one-component developer does not use a carrier, it has an advantage that the developing device can be simplified without requiring a stirring mechanism for uniformly mixing the toner and the carrier, but the toner charge amount is difficult to stabilize, etc. There are disadvantages. The two-component developer has a drawback that the developing device becomes complicated because it requires a stirring mechanism for uniformly mixing the toner and the carrier, but the stability of the charge amount and the suitability for a high-speed machine are required. Therefore, it is often used in high-quality image forming apparatuses (particularly color image forming apparatuses) and high-speed image forming apparatuses.

  Also, in color image forming apparatuses, fixing methods that do not use a release agent such as silicone oil have become the mainstream, as with monochrome image forming apparatuses, in order to prevent offset in the fixing apparatus and improve maintainability. In order to cope with this, a toner in which a release agent such as wax is added to a toner has been used as a color toner.

  Further, in recent years, in order to meet the user's demand for higher image quality, a toner having a small particle diameter in which the volume average particle diameter of the colored resin particles is 5 to 9 μm is often used. Such a small particle size toner greatly improves dot reproducibility and is effective for high image quality such as higher resolution and reduced graininess. However, since the fluidity is low, a uniform toner charge amount can be obtained. However, its use did not necessarily lead to high image quality.

In order to obtain high image quality without deteriorating the fluidity of the two-component developer, for example, Japanese Patent Application Laid-Open No. 2006-98615 (Patent Document 1) includes a small particle size toner containing a large particle size external additive, A two-component developer in combination with a small particle size carrier is disclosed.
The fluidity of a two-component developer using a small particle size toner can be enhanced by the addition of a large particle size external additive. However, if a release agent is added to the toner in order to improve oilless fixability, a long-term developer can be obtained. Deteriorates extremely with use. For this reason, a phenomenon in which the two-component developer is conveyed in a mokomoko state without being smoothly stirred and conveyed by the agitation roller in the developing tank (hereinafter sometimes referred to as “debemoco phenomenon”) occurs. As a result, problems such as fogging and toner scattering occur.

JP 2006-98615 A

  In view of the above-described problems, an object of the present invention is to provide a two-component developer and an image forming apparatus that do not cause a debemoko phenomenon caused by extremely low fluidity of the two-component developer even after long-term use. It is to provide.

  As a result of investigating the debemoko phenomenon in order to solve the above-mentioned problem, 80 to 300 nm of external additives are detached from the toner surface and accumulated in a semi-buried state gradually in the resin layer covering the carrier surface. Filming of the low-melting wax existing as a nucleus on the toner surface or in a free state is accelerated. Finally, the carrier surface is coated with the low-melting wax, so that the fluidity of the two-component developer is lost. Turned out to be.

Therefore, the present invention comprises a toner and a carrier, and the toner contains colored resin particles having a volume average particle size of 4 to 9 μm and a number average particle size of 80 to 80 containing a hydrocarbon wax having a melting point of 64 to 77 ° C. The carrier has a volume average particle size of 25 to 60 μm, comprising a core particle made of a ferrite component and a coating layer of a thermosetting straight silicone resin provided on the surface of the core particle. The ratio of Si / Fe between the X-ray intensity of Si and the X-ray intensity of Fe measured by fluorescent X-ray analysis of the coated core particles is 0.01 or more and 0.03 or less. A two-component developer is provided.
The present invention also provides an electrophotographic image forming apparatus using the above two-component developer as a developer.

  According to the present invention, a high-quality image with good dot reproducibility can be formed, but a developer agitation failure (debemoko phenomenon) due to a decrease in fluidity of a two-component developer is difficult to occur even after long-term use. Thus, an image free of toner scattering and fogging can be obtained over a long period of time.

In one embodiment of the two-component developer of the present invention, the hydrocarbon wax is a paraffin wax having a penetration of 7 to 10 at 35 ° C.
According to the present embodiment, the wax is difficult to melt due to frictional heat, and filming on the carrier surface is difficult even under a high temperature environment, so that a decrease in developer fluidity (especially under a high temperature environment) is further suppressed.

In another embodiment of the two-component developer of the present invention, the thermosetting straight silicone resin coating layer has a thickness of 0.3 to 3 μm.
According to the present embodiment, the coating layer is difficult to peel off, and film abrasion due to long-term use is less likely to occur, so that it is easier to maintain the coating layer for a long period of time, and as a result (particularly, for a longer period of time). ) Lowering of developer fluidity is further suppressed.

In still another embodiment of the two-component developer of the present invention, the coating layer of the thermosetting straight silicone resin contains a conductive agent.
According to this embodiment, since the electrostatic adhesion force of the toner and / or toner external additive can be suppressed by lowering the electric resistance of the carrier surface, an effect of reducing filming can be obtained. As a result, a decrease in developer fluidity is further suppressed. In addition, according to this embodiment, an edge effect of an image and an effect of suppressing an increase in charging of toner can be obtained.

In yet another embodiment of the two-component developer of the present invention, the carrier has a volume resistivity of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm.
According to this embodiment, the electrostatic adhesion force of the toner and / or toner external additive to the carrier surface can be suppressed, and filming can be reduced. In addition, the edge effect of the image and the increase in toner charge can be suppressed. Furthermore, carrier adhesion to the photoreceptor can be suppressed, and white spots of the image can be prevented.

In still another embodiment of the two-component developer of the present invention, the external additive is silica fine particles whose surface is treated with hexamethyldisilazane.
According to this embodiment, since the surface of the external additive is excellent in hydrophobicity, high fluidity can be obtained even in a high humidity environment, and the adhesive force to the carrier surface in the high humidity environment can be suppressed. As a result, wax filming on the carrier surface is suppressed, and a decrease in developer fluidity is further suppressed.

In still another embodiment of the two-component developer of the present invention, the colored resin particles have a BET specific surface area of 1.5 to 1.9 m ² / g.
According to this embodiment, the external additive is less likely to get stuck in the recesses on the surface of the colored resin particles, and the external additive can be uniformly attached to the surface. As a result, the decrease in developer fluidity is further suppressed. In addition, since the surface of the colored resin particles has moderate irregularities, the blade cleaning property is excellent, and the occurrence of black streaks due to poor cleaning can be suppressed.

<Two-component developer>
Hereinafter, the developer of the present invention will be described in more detail.
The developer of the present invention is a two-component developer composed of a toner and a carrier.
In the two-component developer of the present invention, the toner includes colored resin particles having a volume average particle size of 4 to 9 μm and a hydrocarbon resin having a melting point of 64 to 77 ° C. and an external additive having a number average particle size of 80 to 300 nm. Including.

  The volume average particle diameter of the colored resin particles being 4 to 9 μm plays an important role when the two-component developer of the present invention forms a high-quality image. When the volume average particle diameter of the colored resin particles is 9 μm or less, dot reproducibility is improved and a high-resolution image with higher resolution can be achieved. On the other hand, when the thickness is 4 μm or more, aggregation is difficult and uniform charging is easily performed, and thus problems such as fogging and poor image density are less likely to occur.

A hydrocarbon wax having a melting point of 64 to 77 ° C. can improve toner fixing property, glossiness, and offset resistance (particularly when used in a color image forming apparatus). When the melting point is 64 ° C. or higher, the toner is less likely to aggregate even in a high temperature environment (particularly in a car under the sun), and when it is 77 ° C. or lower, glossiness of the image (particularly a color image) is obtained. It becomes easy to be done.
External additives having a number average particle size of 80 to 300 nm (hereinafter sometimes referred to as “large particle size external additives”) are difficult to be embedded in the colored resin particles due to stress during stirring, and are detached from the toner surface. Thus, it is difficult for the developer to collect at the bottom of the developing tank, so that the fluidity of the developer can be improved.

In the two-component developer of the present invention, the carrier has a volume average particle size of 25 composed of core particles composed of a ferrite component and a thermosetting straight silicone resin coating layer provided on the surface of the core particles. Contains ˜60 μm coated core particles. The intensity ratio Si / Fe between the X-ray intensity of Si and the X-ray intensity of Fe measured by fluorescent X-ray analysis of the coated core particles is 0.01 or more and 0.03 or less.
Thermosetting straight silicone resin has low surface energy, hardly adheres to external additives and wax, has higher hardness than thermoplastic resin, and has the characteristics that external additives are difficult to embed. Can be suppressed.

  The volume average particle diameter of the core particles (coated core particles) provided with a coating layer of a thermosetting straight silicone resin on the surface is 25 to 60 μm. This means that the two-component developer of the present invention forms a high-quality image. It plays an important role. When the volume average particle diameter of the coated core particles is 25 μm or more, the necessary magnetic force is easily generated, and the white spots of the image due to carrier adhesion to the photosensitive member are less likely to occur, and by being 60 μm or less. A sufficient specific surface area can be obtained, and the charge amount of a small particle size toner (for example, a toner having a volume average particle size of 4 to 9 μm) can be easily stabilized.

In the present invention, the intensity ratio Si / Fe between the X-ray intensity of Si and the X-ray intensity of Fe measured by fluorescent X-ray analysis of the core particles coated with the thermosetting straight silicone resin is 0.01 or more and 0.0. It is important that the value is 03 or less.
When the intensity ratio Si / Fe is less than 0.01, the core particle component (for example, a magnetic component such as ferrite) is more exposed, so that the adhesion of the toner component to the carrier is promoted, and the toner charge amount is increased by long-term use. Decreases. On the other hand, when the strength ratio Si / Fe exceeds 0.03, the accumulation of large particle size external additives having a particle size of 80 to 300 nm increases, and a debemoco phenomenon is likely to occur. Although the details of the mechanism that makes it difficult for external additives and wax to adhere to the carrier surface when the strength ratio Si / Fe is within the above range are not clear, the exposed ferrite component adheres to the surface of the thermosetting straight silicone resin. This is presumably due to the effect of removing the toner component by friction (self-cleaning effect) (however, this inference does not restrict the present invention).

  In the present invention, the X-ray intensity can be measured by the following procedure. That is, in an X-ray fluorescence analyzer (trade name: ZSX-Primus II, manufactured by Rigaku Corporation), an X-ray source target: Rh, an applied voltage to the X-ray source: 40 kV, a current value: 50 mA, and an optical system LiF (target: Si) or pentaerythritol (PET, target: Fe) is used for the spectroscopic crystal. The detector uses a scintillation counter and a photo counter, and the spectroscope scan uses the skip scan method, the PHA range is set to 100 to 300, the angle is set to 0.05 degrees per step, and 2 cm square The characteristic X-ray intensity is measured with Kα rays for 10 mg of the carrier spread on the double-sided tape.

Next, the toner and carrier materials used for producing the two-component developer of the present invention will be described.
The two-component developer of the present invention can be produced by mixing toner and carrier with a mixer such as a Nauter mixer. Usually, the toner is mixed at a ratio of 3 to 15 parts by weight of toner with respect to 100 parts by weight of the carrier.

(toner)
The toner can be produced by externally adding a large particle size external additive to the surface of the colored resin particles using an air flow mixer such as a Henschel mixer. The colored resin particles can be produced by a known method such as a kneading and pulverizing method or a polymerization method. As an example, in the kneading and pulverizing method, a binder resin, a colorant, and a hydrocarbon wax, and optionally other additives (for example, a boron compound as a charge control agent), a Henschel mixer, a super mixer, a mechano mill, and a Q-type mixer are used. The resulting raw material mixture is melt-kneaded at a temperature of about 70 to 180 ° C. by a kneader such as a biaxial kneader or uniaxial kneader, and the obtained kneaded material is cooled and solidified to obtain a solidified product. Can be produced by pulverizing with an air-type pulverizer such as a jet mill and adjusting the particle size such as classification as required.

If the volume average particle diameter of the colored resin particles is in the range of 4 to 9 μm, dot reproducibility is excellent, which is preferable.
In the present invention, the volume average particle diameter of the colored resin particles is a value determined by a Coulter counter method. The measurement of the volume average particle diameter by the Coulter counter method can be performed, for example, with a Coulter counter manufactured by Coulter, Inc., using an aperture of 100 μm.

  Specifically, a Coulter Counter TA-II type or Coulter Multisizer II (manufactured by Coulter, Inc.) can be used as a measuring device. As the electrolytic solution, a 1% NaCl aqueous solution is prepared using primary sodium chloride. For example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used. As a measuring method, 0.1 to 5 ml of a surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the aqueous electrolyte solution, and 2 to 20 mg of a measurement sample is further added. The electrolyte in which the sample is suspended is subjected to a dispersion process for about 1 to 3 minutes with an ultrasonic disperser, and the measuring device is used to measure the volume and number of the toner by measuring the volume and number of toner using a 100 μm aperture as the aperture. Is calculated.

As the colored resin particles, colored resin particles having a volume resistivity of 1 × 10 ⁹ to 2 × 10 ¹¹ Ω · cm can be used. Such colored resin particles can be obtained by appropriately adding a conductive agent such as carbon black or titanium oxide into the binder resin. In particular, although limited to black toner, carbon black having an oil absorption of 90 to 170 ml / 100 g as a conductive agent is preferable because of its excellent dispersibility in the binder resin and easy volume resistivity.

The volume resistivity of the colored resin particles is measured according to the following procedure. First, the colored resin particles after being left for 24 hours in an environment of an air temperature of 25 ° C. and a humidity of 50% are sandwiched between two copper plate electrodes, the pressing pressure is 100 kg / cm ² , and the distance between the copper plate electrodes is 8 mm to A green compact of 10 mm was produced. Next, a voltage of 500 V / cm was applied as the electric field strength, the resistance after 15 seconds was measured, and the value was taken as the volume resistivity of the colored resin particles.

The BET specific surface area of the colored resin particles is preferably 1.5 to 1.9 m ² / g. When the BET specific surface area is 1.9 m ² / g or less, the external additive can be more easily attached to the surface without excessively entering the recess. As a result, the roller effect (effect of improving fluidity) and the spacer effect (preventing charge leakage) of the external additive are more fully exhibited, and fog and toner scattering are less likely to occur. When it is 1.5 m ² / g or more, the surface of the colored resin particles is not too smooth, the occurrence of poor cleaning is reduced, and as a result, the occurrence of fog is further reduced.

  As a method for controlling the BET specific surface area, a known method can be used. For example, a colored resin particle is rotated at a high speed in a cylindrical pipe to take a corner, or a toner is instantaneously melted in a hot air stream. There is a method such as a sufusion system. The measured value of the BET specific surface area is a measured value obtained by a three-point measuring method using a BET specific surface area measuring device Gemini 2360 (manufactured by Shimadzu Corporation) according to the instruction manual.

  As the binder resin, various known styrene / acrylic resins, polyester resins and the like can be used, and linear or nonlinear polyester resins are particularly preferable. The polyester resin is excellent in that it can satisfy the mechanical strength (not easily generated with fine powder), the fixability (not easily peeled off from the paper after fixing), and the hot offset resistance at the same time.

The polyester resin can be obtained by polymerizing a monomer composition composed of a polyhydric alcohol having two or more valences and a polybasic acid.
Examples of the divalent alcohol used for polymerization of the polyester resin include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1 Diols such as 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, bisphenol A alkylene such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A Examples thereof include oxide adducts and the like.

  Examples of the trihydric or higher polyhydric alcohol include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose, 1,2,4- Butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3,5-trihydroxymethyl Benzene and others can be mentioned.

  Examples of the divalent polybasic acid include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, Mention may be made of malonic acid, anhydrides of these acids, lower alkyl esters, or alkenyl succinic acids or alkyl succinic acids such as n-dodecenyl succinic acid, n-dodecyl succinic acid.

  Examples of the tribasic or higher polybasic acid include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, and 2,5,7-naphthalenetricarboxylic acid. 1,2,4-naphthalenetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, tetra (methylenecarboxyl) methane, 1,2,7 , 8-octanetetracarboxylic acid, and anhydrides thereof.

As the colorant, known pigments and dyes generally used for toners can be used.
Specifically, for black toner, carbon black, magnetite and the like can be mentioned.

  For yellow toner, CI pigment yellow 1, 1, 3, 74, 97, 98, etc. acetoacetic acid arylamide monoazo yellow pigments, CI pigment yellow 12, 13, 13, etc. 14 and 17 acetoacetate arylamide disazo yellow pigments, CI pigment yellow 93, condensed monoazo yellow pigments such as 155; CI pigment yellow 180, 150 and 185, etc. Other examples include yellow pigments, yellow dyes such as CI Solvent Yellow 19, 77, 79, and CI Disperse Yellow 164.

  For magenta toner, CI Pigment Red 48, 49: 1, 53: 1, 57, 57: 1, 81, 122, 5, 146, 184, 238 Red or red pigments such as CI Pigment Violet 19; red dyes such as CI Solvent Red 49, 52, 58 and 8;

For cyan toners, CI pigment blue 15: 3, 15: 4, copper phthalocyanine and its blue dyes and derivatives thereof; CI pigment green 7, 36 (phthalocyanine green) Examples thereof include green pigments.
The addition amount of the colorant is preferably about 1 to 15 parts by weight, and more preferably 2 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  In the present invention, a hydrocarbon wax having a melting point of 64 to 77 ° C. is used as the hydrocarbon wax contained in the colored resin particles. In particular, a paraffin wax having a penetration of 7 to 10 at 35 ° C. is compared. It is preferable in that it is easily available, and it is difficult to melt due to frictional heat, and filming on the carrier surface is difficult even in a high temperature environment. As such paraffin wax, for example, trade name: HNP-3, 9, 10, 12, 51 manufactured by Nippon Seiwa Co., Ltd. may be mentioned.

Measurement of the melting point and penetration of hydrocarbon wax is in accordance with Japanese Industrial Standard (JIS K-2235 5.3 and 5.4).
The addition amount of the hydrocarbon wax is not particularly limited, but generally 1 to 5 parts by weight is added to 100 parts by weight of the binder resin.

As the external additive contained in the toner, a large particle size external additive having a number average particle size of 80 to 300 nm is used. For the purpose of further improving the initial fluidity, the primary particle size (using a scanning electron microscope) is used. For example, an external additive (hereinafter also referred to as “small particle size external additive”) having a number average value of about 200 particles) of 5 to 18 nm may be added.
In the present invention, the number average particle diameter of the external additive is measured by measuring the particle diameter of 100 external additives from the obtained image by photographing the external additive using a scanning electron microscope (SEM). And the average value of the obtained particle diameters.

  As an external additive, it is obtained by treating inorganic fine particles such as silica fine particles and titanium oxide fine particles, or inorganic fine particles with a surface treatment agent such as a silane coupling agent, a titanium coupling agent, and silicone oil (especially hydrophobizing treatment). Particles can be used. An external additive obtained by treating silica fine particles with hexamethyldisilazane as a silane coupling agent is preferable because it has excellent hydrophobicity and high fluidity even in a high humidity environment. Silica fine particles whose surface is treated with hexamethyldisilazane are also preferable because they have high resistance and the charge amount of the toner is stable even in a high humidity environment.

The amount of the external additive added to the colored resin particles is usually 0.5 to 2 parts by weight for the large particle size external additive and 100% by weight for the small particle size external additive (when added). ) Is mixed at a ratio of 0.2 to 1.2 parts by weight. If the addition amount is too small, it is difficult to obtain the effect of the external additive, and conversely, if the addition amount is too large, the fixability is lowered. For example, it is preferable to add an external additive (large particle size external additive + small particle size external additive) so as to be 20% to 80%.
The external additive can be added to the colored resin particles by a method known in the art, for example, stirring and mixing in an airflow mixer (eg, Henschel mixer).

(Career)
As the carrier, core particles (coated core particles) having a coating layer of a thermosetting straight silicone resin on the surface are used. If the particle diameter of the coated core particle is too small, the carrier moves from the developing roller to the photoconductor during development, resulting in white spots in the resulting image. If it is too large, the dot reproducibility becomes poor and the image becomes rough. . Therefore, the volume average particle diameter of the coated core particles is preferably 25 to 60 μm.
In the present invention, the volume average particle diameter of the coated core particles is a value determined by a laser diffraction scattering method. The volume average particle size can be measured by the laser diffraction scattering method using, for example, a particle size distribution measuring device MT3300 (manufactured by Nikkiso Co., Ltd.).

The lower the saturation magnetization of the carrier, the softer the magnetic brush in contact with the photoconductor, so that an image faithful to the electrostatic latent image can be obtained, but if it is too low, the carrier adheres to the surface of the photoconductor and white spots occur. On the other hand, if it is too high, it becomes difficult to obtain an image faithful to the electrostatic latent image due to the stiffening of the magnetic brush. Therefore, a carrier having a saturation magnetization in the range of 30 to 100 emu / g is preferably used.
In the present invention, saturation magnetization refers to a value measured using VSMP-1 manufactured by Toei Kogyo Co., Ltd. according to the instruction manual.

The volume resistivity of the carrier is preferably 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm. When the volume resistivity of the carrier is within this range, the electrostatic adhesion force of the toner and / or toner external additive to the carrier surface can be suppressed, and the occurrence of filming can be reduced. In addition, the edge effect of the image, the increase in charge of the toner, and the carrier adhesion to the photoreceptor are suppressed, and the whiteout of the image is prevented.
In the present invention, the volume resistivity of the carrier is a value measured by a bridge method. The carrier resistance is as follows: 0.2 g of carrier is filled between two copper plate electrodes with a width of 30 mm and a height of 10 mm that are installed with a gap of 2.0 mm and an environmental condition of an air temperature of 25 ° C. and a humidity of 50%. Measured 30 seconds after application of a voltage of 500 V with a carrier bridge formed by the magnetic lines of two magnets (220 mT) arranged outside each copper plate electrode so that the N pole and the S pole face each other. To do.

  As the core particles, particles made of a ferrite component can be used. Known particles can be used as the ferrite component particles, for example, zinc ferrite, nickel ferrite, copper ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, copper-magnesium ferrite, manganese-zinc Examples thereof include ferrite and manganese-copper-zinc ferrite.

These ferrite particles can be produced by a known method. For example, Fe ₂ O ₃ and ferrite raw materials such as Mg (OH) ₂ are mixed, and this mixed powder is heated in a heating furnace and calcined. The obtained calcined product is cooled, and then pulverized by a vibration mill so that the average particle diameter becomes about 2 μm or less, and a dispersant and water are added to the pulverized powder to prepare a slurry. The slurry is wet pulverized with a wet ball mill, and the resulting suspension is granulated and dried with a spray dryer to obtain particles composed of a ferrite component having an average volume particle size of about 25 to 60 μm.

In the two-component developer of the present invention, a coating layer of a thermosetting straight silicone resin is provided on the surface of the core particles. The coating layer can be formed by thermally curing a thermosetting straight silicone resin coated on the surface of the core particles by heating.
Examples of the thermosetting straight silicone resin include dimethyl silicone resin, methyl phenyl silicone resin, and methyl hydrogen silicone resin.

〔式中、複数のＲは同一又は異なって１価の有機基を示す。〕 As shown below, the thermosetting silicone resin is a known silicone resin in which hydroxyl groups bonded to Si atoms are crosslinked and cured by a heat dehydration reaction or the like.

[Wherein, a plurality of R are the same or different and each represents a monovalent organic group. ]

The monovalent organic group R may be, for example, a methyl group, a phenyl group, an ethyl group, or a propyl group, but a methyl group is preferable. Since the crosslinked silicone resin in which R is a methyl group has a dense crosslinked structure, a good carrier such as water repellency and moisture resistance can be obtained. However, if the cross-linked structure becomes too dense, the resin coating layer tends to become brittle, so selection of the molecular weight of the cross-linked silicone resin is important.
The weight ratio of silicon to carbon (Si / C) in the cross-linked silicone resin is preferably 0.3 to 2.2. If Si / C is less than 0.3, the hardness of the resin coating layer is lowered, and the carrier life and the like may be lowered. When Si / C exceeds 2.2, the charge imparting property of the carrier with respect to the toner is easily affected by the temperature change, and the resin coating layer may be embrittled.
The number average molecular weight of a straight silicone resin is 4000-20000, for example, Preferably it is 8000-15000.

  The thermosetting straight silicone resin can be appropriately selected from straight silicone resins. Known thermosetting straight silicone resins can be used. For example, trade names: TSR115, TSR114, TSR102, TSR103, YR3061, TSR110, TSR116, TSR117, TSR108, TSR109, TSR180, TSR181, TSR187, TSR144, TSR165 ( GE Toshiba Silicone Co., Ltd.), trade names: KR271, KR272, KR275, KR280, KR282, KR267, KR269, KR211, KR212 (above, manufactured by Shin-Etsu Chemical Co., Ltd.), trade names: SR2405, SR2406, SR2410, SR2411 (manufactured by Toray Dow Corning Co., Ltd.).

  The covering layer may contain a conductive agent in order to control the volume resistivity value of the carrier. Examples of the conductive agent include silicon oxide, alumina, carbon black, graphite, zinc oxide, titanium black, iron oxide, titanium oxide, tin oxide, potassium titanate, calcium titanate, aluminum borate, magnesium oxide, barium sulfate, Examples thereof include a conductive agent such as calcium carbonate.

  Among these conductive agents, carbon black is preferable from the viewpoint of production stability, cost, and low electrical resistance. The type of carbon black is not particularly limited, but those having a DBP (dibutyl phthalate) oil absorption in the range of 90 to 170 ml / 100 g are preferred from the viewpoint of excellent production stability. Further, a primary particle size (number average value obtained by measuring, for example, about 200 using a scanning electron microscope) of 50 nm or less is particularly preferable because of excellent dispersibility. A conductive agent can be used individually by 1 type, or can use 2 or more types together. As a usage-amount of a electrically conductive agent, 0.1-20 weight part is used with respect to 100 weight part of resin.

To coat the core particles with the thermosetting straight silicone resin, a known method can be employed. For example, an immersion method in which core particles are immersed in an organic solvent solution of a thermosetting straight silicone resin, a spray method in which an organic solvent solution of the resin is sprayed on the core particles, and the resin in a state where the core particles are suspended by flowing air And a kneader coater method in which core particles and an organic solvent solution of the resin are mixed in a kneader coater to remove the solvent. If necessary, a conductive agent for controlling the resistance value may be added to the organic solvent solution of the resin together with the resin.
The thermosetting straight silicone resin coated on the surface of the core particle is heated and cured at 180 to 280 ° C. in a fixed heating device or an oven, for example.

In the dipping method, for example, a coating liquid obtained by dissolving a thermosetting straight silicone resin in toluene and core particles made of a ferrite component are put into a container of a stirrer at a predetermined ratio and immersed for a predetermined time. The core particles are coated by stirring. The core particles coated with the silicone resin are loaded into a fixed heating device, and the thermosetting silicone resin is cured by heating, whereby a coated carrier is obtained. Si measured by fluorescent X-ray analysis of the coated core particles The strength ratio Si / Fe between the X-ray intensity of Fe and the X-ray intensity of Fe should be set appropriately for the amount of resin in the coating liquid for coating and the immersion time (coating time) of the core particles in the coating liquid for coating. Can be adjusted by. Generally, the strength ratio Si / Fe increases as the amount of resin in the coating liquid increases and the immersion time increases. Specific coating conditions can be easily determined by a simple preliminary test.

The coating layer of the thermosetting straight silicone resin provided on the core particle surface preferably has a thickness of 0.3 to 3 μm. If the thickness of the coating layer is within this range, it is difficult for the coating layer to peel off, and film abrasion due to long-term use hardly occurs. As a result, it becomes easier to maintain the coating layer over a long period of time.
On the other hand, if the coating layer is too thin, the charge on the surface of the photoreceptor moves to the carrier, and brush streaks are generated in the obtained image. On the other hand, if it is too thick, the counter charge remaining on the carrier at the time of development (after the toner is used for development) cannot be quickly lost, resulting in an edged image. Therefore, also from this point, the thickness of the coating layer is preferably within the above range.

  The thickness of the thermosetting straight silicone resin coating layer provided on the surface of the core particle can be measured under observation with a transmission electron microscope in a thin slice of a carrier sliced. In the present invention, the thickness of the coating layer is a value obtained as an average value from about 200 measured values.

<Image forming apparatus>
As long as the two-component developer according to the present invention is used as a developer, the image forming apparatus according to the present invention is not limited to a specific one with respect to other configurations, and an electrophotographic image forming apparatus using a two-component developer. Any known structure can be employed.

For example, an image forming apparatus of the present invention includes a photosensitive member on which an electrostatic latent image is formed, a charging device that charges the surface of the photosensitive member, an exposure device that forms an electrostatic latent image on the surface of the photosensitive member, a book A developing device that contains the two-component developer according to the invention and supplies toner to the electrostatic latent image on the surface of the photoreceptor to form a toner image; a transfer device that transfers the toner image on the surface of the photoreceptor to a recording medium; The image forming apparatus may include a cleaning device that cleans the surface of the photoreceptor and a fixing device that fixes the toner image on the recording medium.
The image forming apparatus of the present invention can be, for example, an electrophotographic copying machine, a printer, or a facsimile.

The image forming apparatus of the present invention will be specifically described with reference to the drawings.
FIG. 1 is an arrangement side view showing a simplified configuration of an embodiment of an image forming apparatus according to the present invention. The illustrated image forming apparatus is a tandem color image forming apparatus including four image forming units 1 to 4. Of these, reference numeral 1 indicates a first image forming unit 1 for forming a black toner image, and reference numeral 2 indicates a second image formation for forming a cyan toner image. A unit 2 and reference numeral 3 indicate a third image forming unit 3 for forming a magenta toner image, and a reference numeral 4 indicates a fourth image forming unit 4 for forming a yellow toner image. It is.

  Above these four image forming units 1 to 4, an intermediate transfer belt (endless belt) 5 is disposed. The intermediate transfer belt 5 is stretched between two support rolls 6 and rotates in the direction indicated by the arrow R. Hereinafter, upstream and downstream are expressed with reference to the secondary transfer position (transfer position of the image to the recording medium) where the secondary transfer roller 8 is disposed with respect to the rotation direction of the intermediate transfer belt 5. As a material for the intermediate transfer belt 5, a material in which an appropriate amount of an electron conductive conductive agent is contained in a resin such as polyimide or polyamide can be used.

The four image forming units 1 to 4 are, from the upstream side, the first image forming unit 1 (black), the second image forming unit 2 (cyan), the third image forming unit 3 (magenta), and the fourth image forming unit 4. They are arranged in the order of (yellow).
Inside the intermediate transfer belt 5, primary transfer rollers 7 for transferring the single color toner images formed by the image forming units 1 to 4 onto the intermediate transfer belt 5 are respectively photosensitive drums of the image forming units 1 to 4. It is provided so as to oppose. The single color toner images formed by the image forming units 1 to 4 are transferred so as to overlap on the intermediate transfer belt 5 to form one color image.

On the downstream side of the fourth image forming unit 4 (yellow) in the rotation direction R of the intermediate transfer belt 5, a secondary transfer roller 8 that transfers the color image formed on the intermediate transfer belt 5 to a sheet (recording medium). It is arranged.
A belt cleaning unit 10 for cleaning the surface of the intermediate transfer belt 5 is provided downstream of the secondary transfer roller 8 in the rotation direction R of the intermediate transfer belt 5 and upstream of the first image forming unit 1. ing. The belt cleaning unit 10 includes a belt cleaning brush 11 disposed in contact with the intermediate transfer belt 5 and a belt cleaning blade 12. The belt cleaning blade 12 is disposed on the downstream side of the belt cleaning brush 11.

Below the image forming units 1 to 4, a tray 14 for storing paper is disposed. The paper in the tray 14 is conveyed by a plurality of paper feed rollers 13 to a secondary transfer position where the secondary transfer roller 8 faces the intermediate transfer belt 5. An arrow P indicates the sheet conveyance direction.
On the downstream side of the secondary transfer roller 8 in the paper transport direction P, a fixing unit 15 for fixing the color image transferred onto the paper on the paper is provided. On the further downstream side of the fixing unit 15, a paper discharge roller 13 a that discharges the paper on which the color image is fixed from the image forming apparatus is provided.

  In the above-described configuration, each single color toner image formed by the image forming units 1 to 4 is sequentially transferred onto the intermediate transfer belt 5, and one color image is formed on the intermediate transfer belt 5. The color image on the intermediate transfer belt 5 is secondarily transferred to the paper conveyed by the paper feed roller 13 at the secondary transfer position, and then fixed on the paper by the fixing unit 15. The sheet on which the color image is fixed is discharged from the image forming apparatus by the discharge roller 13a. On the other hand, after the secondary transfer, the toner remaining on the intermediate transfer belt 5 without being transferred onto the sheet is removed by the belt cleaning unit 10.

  FIG. 2 shows the first image forming unit 1 shown in FIG. The configurations of the second image forming unit 2, the third image forming unit 3, and the fourth image forming unit 4 are substantially the same. Therefore, a detailed description of the configuration of the second image forming unit 2, the third image forming unit 3, and the fourth image forming unit 4 is omitted.

  Around the photosensitive drum 16, a charger 17 for charging the photosensitive drum 16, an exposure unit 18 for writing an electrostatic latent image on the photosensitive drum 16, and a development for visualizing the electrostatic latent image on the photosensitive drum 16 An apparatus 19 is provided with a photosensitive drum cleaner 20 that removes a residue including toner remaining on the photosensitive drum 16 after the primary transfer.

The charger 17 is composed of, for example, a scorotron charger, and performs corona discharge on the photosensitive drum 16 to charge the photosensitive drum 16 to a predetermined potential. It can also be constituted by a corotron charger, or a contact charger using a charging roller or a charging brush.
The exposure device 18 is composed of, for example, a laser exposure device, performs exposure by laser scanning according to an image signal, and changes the surface potential of the photosensitive drum 16 charged by the charger 17, thereby changing the static potential according to the image information. An electrostatic latent image is formed. An LED array device or the like can also be used as the exposure device.

The developing device 19 accommodates the two-component developer according to the present invention in the developing tank 27 and develops the electrostatic latent image on the surface of the photosensitive drum 16 with toner contained in the developer. In the two-component developer, the toner and the carrier are uniformly mixed in the developing tank 27 by a stirring mechanism so that the charge amount of the toner is stabilized.
The photosensitive drum cleaner 20 includes a cleaning blade 21, a cleaner housing 22, and a seal 23.

  The cleaning blade 21 is disposed in pressure contact with the rotation direction Rd of the photosensitive drum 16 in the counter direction, and scrapes off the residue on the surface of the photosensitive drum 16. The cleaner housing 22 stores the scraped residue, and the cleaning blade 21 is attached to the cleaner housing 22. The seal 23 seals the inside of the cleaner housing 22. One end of the seal 23 is fixed to the cleaner housing 22 on the upstream side of the cleaning blade 21 in the rotation direction Rd of the photosensitive drum 16, and the other end is connected to the photosensitive drum 16. Arranged in contact.

FIG. 3 is a diagram for explaining the developing device 19 shown in FIG. 2 in more detail.
The developing device 19 includes a developing tank 27 in which a two-component developer 31 according to the present invention (hereinafter may be simply referred to as a developer) is accommodated, and the developing tank 27 includes an outer periphery of the photosensitive drum 16. An opening 30 is provided at a position facing the surface.

  In the developing tank 27, at a position facing the opening portion 30, the developer is carried on the outer peripheral surface and conveyed to supply the developer to the photosensitive drum 16 and develop the electrostatic latent image. The developing roller 24 is provided. The developing roller 24 is disposed with a predetermined gap from the outer peripheral surface of the photosensitive drum 16.

  The developing roller 24 is a multipolar magnetized member of multipolar magnetization in which magnetic poles N1, N2, and N3 and magnetic poles S1 and S2 made of bar magnets having a rectangular cross-sectional shape are radially spaced apart at a plurality of circumferential positions. 25 and a nonmagnetic sleeve 26 that is rotatably fitted to the multipolar magnetized member 25.

  Both ends of the multipolar magnetized member 25 are supported non-rotatingly on both side walls of the developing tank 27, and the magnetic pole N1 (peak value 110 mT) is located at a position toward the rotation center of the photosensitive drum 16 and the magnetic pole S1 (peak value). = −78 mT) is upstream from the magnetic pole N1, for example, at a position of 59 °, the magnetic pole N2 (peak value = 56 mT) is upstream from the magnetic pole N1, for example, at a position of 117 °, and the magnetic pole N3 (peak value = 42 mT) is The magnetic pole S2 (peak value = −80 mT) is arranged upstream from the magnetic pole N1, for example, at a position of 282 °, for example.

  On the upstream side of the closest position of the sleeve 26 to the outer peripheral surface of the photosensitive drum 16 with respect to the developer transport direction (sleeve rotation direction), the thickness of the developer layer carried on the sleeve 26 is regulated, and the electrostatic charge of the developer is controlled. A regulating member 28 that regulates the transport amount to the latent image is provided. The regulating member 28 is arranged at a predetermined interval with respect to the surface of the sleeve 26.

An agitating member 29 that agitates the developer 31 inside the developing tank 27 and supplies the developer 31 to the developing roller 24 is rotatably provided in the developing tank 27 at a position facing the developing roller 24.
In the image forming apparatus of the present invention, since the two-component developer according to the present invention is used as a developer, a developer agitation failure (debemoko phenomenon) due to a decrease in developer fluidity occurs even after long-term use. It ’s difficult. As a result, fog and toner scattering hardly occur over a long period of time.

Examples of the present invention will be described below, but the present invention is not limited to the examples.
The toners of Examples and Comparative Examples were prepared by the following method.
Binder resin (polyester resin obtained by polycondensation using bisphenol A propylene oxide, terephthalic acid or trimellitic anhydride as a monomer: HB-7140, manufactured by Kao Corporation; glass transition temperature 64 ° C., softening temperature 115 ° C. ) 100 parts by weight Colorant (CI Pigment Blue 15: 3; Colorx Blue D904, manufactured by Sanyo Dye Co., Ltd.) 5 parts by weight Charge control agent (boron compound: LR-147, Nippon Carlit Co., Ltd.) 2 parts by weight ・ Hydrocarbon wax (melting point 75 ° C., penetration 10/35 ° C.) (paraffin wax HNP-9, manufactured by Nippon Seiwa Co., Ltd.) 3 parts by weight

The toner material was mixed with a Henschel mixer for 10 minutes, and then melt-kneaded and dispersed at 140 ° C. with a kneading and dispersing treatment apparatus (Kneex MOS140-800: manufactured by Mitsui Mining Co., Ltd.). The kneaded product is cooled and solidified, and then coarsely pulverized by a cutting mill, then finely pulverized by a jet type pulverizer (IDS-2 type: manufactured by Nippon Pneumatic Industry Co., Ltd.), and then an air classifier (MP-250 type: Japan). The volume average particle size is 6.5 ± 0.1 μm, the BET specific surface area is 1.8 ± 0.1 m ² / g, and the volume resistivity is 4 ×. Colored resin particles of 10 ⁹ Ω · cm were obtained. The volume average particle size was measured with Coulter Multisizer II (manufactured by Beckman Coulter, Inc.).

  Silica fine particles (R-8200, manufactured by Nippon Aerosil Co., Ltd.) 1.2 parts by weight obtained by subjecting 100 parts by weight of the colored resin particles to surface treatment with hexamethyldisilazane having a number average particle diameter of 12 nm, and a large particle diameter As an external additive, 1 part by weight of silica fine particles (X-24, manufactured by Shin-Etsu Astec Co., Ltd.) surface-treated with hexamethyldisilazane having a number average particle diameter of 110 nm is mixed, and the tip speed of the stirring blade is 15 m / sec. The negatively chargeable toner T1 was produced by stirring for 2 minutes with an airflow mixer (Henschel mixer: manufactured by Mitsui Mining Co., Ltd.)

Toners T2 to T15 shown in Table 1 were prepared in the same manner as the toner T1, except that the type of wax and / or the particle size and / or addition amount of the large particle size external additive were different.

<Career>
The carriers of Examples and Comparative Examples were produced by the following method.
Ferrite raw material MgO (content: 3%), MnO (20%) and Fe ₂ O ₃ (77%) were mixed in a ball mill, and then calcined at 900 ° C. in a rotary kiln. Then, it was finely pulverized to a mean particle size of 2 μm or less using a steel ball as a pulverizing medium by a wet pulverizer. The obtained ferrite fine powder was granulated by a spray drying method, and the granulated product was fired at 1300 ° C. After firing, it is crushed using a crusher, the volume average particle size (by laser diffraction scattering method) is about 50 μm, and the volume resistivity is 1 × 10 ⁸ to 1 × 10 ⁹ Ω · cm (according to the bridge method described above for the carrier). ) Core particles composed of a ferrite component were obtained.

  Next, as a coating solution for coating the core particles, 100 parts by weight of thermosetting straight silicone resin (number average molecular weight: 12000; KR271, manufactured by Shin-Etsu Chemical Co., Ltd.) and carbon black (primary particle size 25 nm) 5 parts by weight of oil absorption 150 ml / 100 g) was dissolved and dispersed in 1000 parts by weight of toluene to prepare a coating solution for coating.

The prepared coating solution for coating was coated on the core particles composed of the ferrite component with a spray coating apparatus (SPIRA COTA (registered trademark), manufactured by Okada Seiko Co., Ltd.) in a coating time of 60 minutes. Toluene was completely removed by evaporation, and the thermosetting straight silicone resin was cured by heating to 240 ° C. to obtain coated core particles (volume average particle size 50 μm). The intensity ratio Si / Fe between the X-ray intensity of Si and the X-ray intensity of Fe measured by fluorescent X-ray analysis of the obtained coated core particles was 0.022, and the film thickness of the coating layer was 1 μm. . This was designated as carrier C1. The carrier C1 had a volume resistivity of 2 × 10 ¹¹ Ω · cm and a saturation magnetization of 65 emu / g.

Carriers C2 to C8 shown in Table 2 were produced in the same manner as carrier C1, except that the amount of resin in the coating liquid and / or the coating time was different. As the carrier C9, a styrene-butyl methacrylate copolymer (number average molecular weight: 5.2 × 10 ⁴ , glass transition point: 78 ° C.) is used as the thermoplastic styrene acrylic resin, and the carriers C10 and C11 are thermoplastic. As the styrene acrylic resin, a styrene-methyl methacrylate-butyl methacrylate copolymer (number average molecular weight: 4.8 × 10 ⁴ , glass transition point: 90 ° C.) is used, and the same resin amount as that of the carrier C1 for the carriers C9 and C10. The carrier C11 was prepared with the same resin amount and coating time as the carrier C6.

<Two-component developer>
By mixing the toner (T1 to T15) and the carrier (C1 to C11), the two-component developers of Examples 1 to 15 and Comparative Examples 1 to 10 shown in Table 3 were produced. The mixing of the two components was performed by charging 6 parts by weight of toner and 94 parts by weight of carrier into a Nauter mixer (VL-0, manufactured by Hosokawa Micron Corporation) and stirring and mixing for 40 minutes.

<Image evaluation>
The produced two-component developer was subjected to a continuous print test using the image forming apparatus shown in FIG. 1 (digital full-color composite machine: MX-4500N, a modified machine manufactured by Sharp Corporation). The continuous print test was performed by using only the image forming unit 1 among the four image forming units of the image forming apparatus and filling the toners of the examples and comparative examples. As the development conditions of the image forming apparatus, the peripheral speed of the photosensitive member is 400 mm / second, the peripheral speed of the developing roller is 560 mm / second, the gap between the photosensitive member and the developing roller is 0.42 mm, and the gap between the developing roller and the regulating blade is 0.5 mm. The surface potential of the photoconductor and the developing bias are adjusted so that the toner adhesion amount on paper in a solid image (100% density) is 0.5 mg / cm ² and the toner adhesion amount in the non-image area is minimized. did. A4 size electrophotographic paper (Multi Receiver: manufactured by Sharp Document System Co., Ltd.) was used as a test paper.

A 50K (50,000) print test was performed on a text image with a coverage of 3% of the print image recorded on the paper, and the toner charge amount was measured, and the image density and fog were evaluated.
The toner charge amount was measured using a suction type small charge amount measuring device (210HS-2A: manufactured by Trek Japan Co., Ltd.).
Regarding the image density, a solid image (100% density) with a side of 3 cm was printed and measured using a reflection densitometer (Macbeth: RD918), and the image density was 1.3 or more (paper fibers were toner) The condition (completely covered) was good, and a value of 1.2 or more and less than 1.3 was a little bad, and a value of less than 1.2 (a condition in which the paper fibers were only insufficiently covered with toner) was judged as bad.

As for the fog density, the density of the non-image area (0% density) was calculated by the following procedure.
White meter: using (Z-Σ90 COLOR MEASURING SYSTEM Nippon Denshoku Industries Co., Ltd.), to measure the whiteness W ₂ in the non-image portion of the paper after printing the previous paper whiteness W ₁ and printing The difference in whiteness (W ₁ −W ₂ ) between the _two was determined as the fog level.
The fog density is less than 0.6 (a state in which the fog is hardly visible to the naked eye), and 0.6 to less than 1.0 is a little poor, and 1.0 or more (a state in which the fog is clearly visible to the naked eye) is bad. .
After the print test, the presence or absence of debemoko phenomenon was also judged. That is, the presence or absence of a developer in a poorly stirred state (concrete concrete) was visually confirmed in the developing tank.

<Result>
Table 3 shows the results of the continuous print test.
As shown in Examples 1 to 15, in the continuous print test of the two-component developer of the present invention, no debemoko phenomenon was observed even after the formation of 50K images, and the toner charge amount was stable. An image without fog was obtained.

  On the other hand, as is clear from Comparative Examples 1 to 4, when the Si / Fe intensity ratio Si / Fe intensity ratio between the X-ray intensity of Si and the X-ray intensity of Fe measured by carrier X-ray fluorescence analysis is too low or too high. After the formation of 50K images, the occurrence of a debemoko phenomenon was observed, the toner charge amount was reduced, and a fogged image was obtained.

As is clear from Comparative Examples 5 to 7, when a resin other than the thermosetting straight silicone resin is used as the carrier coating resin, after the formation of 50K sheets of images, a debemoco phenomenon occurs and the charge amount of the toner decreases. As a result, a fogged image was obtained.
As is apparent from Comparative Examples 8 to 10, even when the melting point of the hydrocarbon wax of the toner is too low, after the image formation of 50K sheets, the occurrence of a debemoco phenomenon is observed, the charge amount of the toner is decreased, and the fog is reduced. An image with was obtained.

1 is a diagram showing an embodiment of an image forming apparatus of the present invention. FIG. 2 is an enlarged view showing an embodiment of an image forming unit in the image forming apparatus of the present invention. FIG. 3 is an enlarged view showing one embodiment of a developing device in the image forming apparatus of the present invention.

Explanation of symbols

  1-4 First to fourth image forming units, 5 Intermediate transfer belt, 6 Support roll, 7 Primary transfer roller, 8 Secondary transfer roller, 10 Belt cleaning unit, 11 Belt cleaning brush, 12 Belt cleaning blade, 13 Paper feed Roller, 13a Paper discharge roller, 14 tray, 15 fixing unit, 16 photoconductor drum, 17 charger, 18 exposure device, 19 developing device, 20 photoconductor drum cleaner, 21 cleaning blade, 22 cleaner housing, 23 seal, 24 development Roller, 25 Multi-pole magnetized member, 26 Sleeve, 27 Developer tank, 28 Restricting member, 29 Stirring member, 30 Opening part, 31 Two-component developer, N, S magnetic pole, R Rotation direction of intermediate transfer belt, P Transport direction, Rd Rotation direction of the photosensitive drum 16

Claims (8)

  The toner comprises a toner and a carrier, and the toner includes colored resin particles having a volume average particle size of 4 to 9 μm and a hydrocarbon-based wax having a melting point of 64 to 77 ° C., and an external additive having a number average particle size of 80 to 300 nm. And the carrier includes coated core particles having a volume average particle diameter of 25 to 60 μm composed of core particles made of a ferrite component and a coating layer of a thermosetting straight silicone resin provided on the surface of the core particles. A two-component characterized in that the intensity ratio Si / Fe between the X-ray intensity of Si and the X-ray intensity of Fe measured by fluorescent X-ray analysis of the coated core particle is 0.01 or more and 0.03 or less Developer.   The two-component developer according to claim 1, wherein the hydrocarbon wax is a paraffin wax having a penetration of 7 to 10 at 35 ° C.   The two-component developer according to claim 1, wherein the coating layer has a thickness of 0.3 to 3 μm.   The two-component developer according to claim 1, wherein the coating layer contains a conductive agent. The two-component developer according to claim 1, wherein the carrier has a volume resistivity of 1 × 10 ⁹ to 1 × 10 ¹⁴ Ω · cm.   6. The two-component developer according to claim 1, wherein the external additive is silica fine particles whose surface is treated with hexamethyldisilazane. The two-component developer according to claim 1, wherein the colored resin particles have a BET specific surface area of 1.5 to 1.9 m ² / g.   An electrophotographic image forming apparatus using the two-component developer according to any one of claims 1 to 7 as a developer.

Images