JP2009069499A - Carrier and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier capable of preventing decrease in an image density immediately after using a two-component developer and preventing decrease in a charging ability of a toner even in long-term use. <P>SOLUTION: The carrier comprises a core particle and a resin layer coating the surface of the core particle, wherein the resin layer includes, from the core particle side, two resin layers of an inner layer and an outer layer, and the outer resin layer contains a charge improving agent in a lower content than in the inner resin layer. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a carrier and an image forming apparatus using the carrier. More specifically, the present invention relates to a carrier including core particles and a resin layer covering the core particles, and an image forming apparatus using the carrier. The carrier of the present invention can be suitably used for an image forming apparatus having an electrophotographic printing function such as a copying machine, a printer, and a facsimile machine.

  In general, an image forming apparatus using an electrophotographic system forms an image through each process of charging, exposure, development, transfer, peeling, cleaning, static elimination, and fixing. In the step of forming an image, for example, the surface of the photoconductor rotated by a charging device is uniformly charged, and the surface of the photoconductor charged by the exposure device is irradiated with laser light to form an electrostatic latent image. Subsequently, the electrostatic latent image on the photoconductor is developed by the developing device, and a toner image is formed on the surface of the photoconductor. The toner image on the photosensitive member is transferred onto the transfer material by the transfer device, and then heated by the fixing device, whereby the toner image is fixed on the transfer material. Further, the transfer residual toner remaining on the surface of the photoreceptor is removed by a cleaning device and collected in a predetermined collection unit. In addition, the remaining charge is removed from the surface of the photoreceptor after the cleaning by a static eliminator in order 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, a stirring mechanism or the like for uniformly mixing the toner and the carrier is not required. Therefore, there is an advantage that the developing device is simplified. However, there are drawbacks such as the toner charge amount being difficult to stabilize.

  Since the two-component developer requires a stirring mechanism for uniformly mixing the toner and the carrier, there is a disadvantage that the developing device becomes complicated. However, it has excellent charging stability and compatibility with high-speed machines. Therefore, it is often used in high-speed image forming apparatuses and color image forming apparatuses.

  As the carrier used in the two-component developer, magnetic particles made of ferrite or the like having a particle diameter of 20 to 100 μm are used. This magnetic particle is a resin comprising an acrylic resin or a silicone resin containing a magnetic material as a core particle and a conductive material such as carbon black on its surface in order to prevent humidity dependency and toner component fusion. Carriers with layers are known.

Furthermore, a carrier in which the core particles are coated with an aminosilane coupling agent or the like and then coated with a silicone resin containing a melamine resin or the like is described in, for example, Japanese Patent Application Laid-Open No. 2007-101812 (Patent Document 1). It is said that the carrier of this publication does not change its charge imparting ability in a high temperature and high humidity environment or a low temperature and low humidity environment.
JP 2007-101812 A

  The carrier in which the core particles are coated with a resin layer containing a charge improving agent such as a melamine resin in the above publication is said to have a high charge imparting ability to toner. However, immediately after the two-component developer is replaced with a new agent, there is a problem that the charge amount is remarkably increased, and as a result, the image density is lowered.

The inventors of the present invention, in view of the above problems, as a result of intensive studies, prevented a decrease in image density immediately after using a new two-component developer, and the ability to impart charge to toner even in long-term use. The present inventors have found a carrier capable of preventing the decrease and have reached the present invention.
Thus, according to the present invention, a core particle and a resin layer covering the surface of the core particle are provided, and the resin layer has two resin layers on the inner side and the outer side from the core particle side. There is provided a carrier characterized in that the resin layer contains a charge improving agent at a lower content than the inner resin layer.

  Furthermore, according to the present invention, a photoconductor on which an electrostatic latent image is formed, a charging device that charges the surface of the photoconductor, and an exposure device that forms an electrostatic latent image on the surface of the photoconductor A developing device that contains a two-component developer containing toner and the carrier and supplies the toner to an electrostatic latent image on the surface of the photoconductor to form a toner image; and a toner image on the surface of the photoconductor A transfer device that transfers the toner image to a recording medium, a cleaning device that cleans the surface of the photoreceptor, and a fixing device that fixes the toner image to the recording medium, and forms an image using an electrophotographic system An image forming apparatus is provided.

  In the carrier of the present invention, the charge imparting ability of the outer resin layer is suppressed, and the charge imparting ability of the inner resin layer is enhanced. By having such a configuration, a remarkable increase in the toner charge amount in the initial stage can be suppressed by the outer resin layer. In addition, during the life in which the outer resin layer wears out and the carrier surface is contaminated, the inner resin layer can enhance the charge imparting ability. As described above, according to the carrier of the present invention, the charge amount of the toner can be stabilized from the initial stage to the life, and a stable image quality can be obtained over a long period of time.

  Further, the charge improving agent contained in the inner resin layer and the charge improving agent contained in the outer resin layer contain the same components, thereby preventing a decrease in image density immediately after using a new two-component developer, and Even in long-term use, it is possible to prevent a decrease in charge imparting ability to the toner. In particular, it is possible to prevent a sudden change in charge amount when the outer resin layer is worn.

  Furthermore, since the outer resin layer further contains a conductive material, it prevents a decrease in image density immediately after using a new two-component developer, and also prevents a decrease in charge imparting ability to toner even in long-term use. be able to. In particular, the resistance of the outer resin layer can be lowered. As a result, it is possible to prevent a significant increase in the initial toner charge amount.

  Furthermore, the core particles are coated on the surface with an inner resin layer at a coverage of 50 to 95% to prevent a decrease in image density immediately after using a new two-component developer, and for a long time. Even in use, it is possible to prevent a decrease in charge imparting ability to the toner. In particular, even when the outer resin layer is completely scraped off due to wear, part of the core particles is exposed to the surface from between the outer resin layers. As a result, the increase in the toner charge amount can be suppressed without increasing the resistance of the carrier.

  In addition, the inner resin layer and outer resin layer contain straight silicone resin to prevent the image density from decreasing immediately after using a new two-component developer, and to impart charge to the toner even during long-term use. Capability can be prevented from decreasing. In particular, since filming of the binder resin of the toner hardly occurs, a stable charging property can be obtained over a long period of time.

Furthermore, since the core particles contain a ferrite component, it is possible to prevent a decrease in image density immediately after using a new two-component developer, and to prevent a decrease in charge imparting ability to toner even in long-term use. . In particular, since a carrier having a high saturation magnetization and a low density is obtained, carrier adhesion to the photoconductor hardly occurs, and an image with high dot reproduction due to soft spike formation is obtained.
In addition, since the image forming apparatus of the present invention can stabilize the charge amount of toner from the initial stage to the end of its life, stable image quality can be obtained over a long period of time.

<Description of carrier operation>
The carrier of the present invention will be described.
The carrier of the present invention includes a core particle and a resin layer that covers the surface of the core particle. The resin layer has two resin layers on the inner side and the outer side from the core particle side, and the outer resin layer The charge improver is contained at a lower content than the inner resin layer. According to the carrier of the present invention, the decrease in the charge imparting ability of the carrier caused by the abrasion of the resin layer can be suppressed, and the charge amount of the toner can be stabilized over a long period of time.

The operation of the carrier of the present invention will be described with reference to FIGS.
FIG. 1 is a schematic view showing a coating state in an initial stage of a carrier of an example of the present invention. In FIG. 1, the surface of the core particle 40 having unevenness on the surface is coated with an inner resin layer 41 containing a charge improving agent, and the outer side does not contain a charge improving agent or has a lower content than the inner resin layer 41. The outer resin layer 42 is covered.

FIG. 2 is a schematic view showing a state in which the outer resin layer 42 is scraped due to abrasion and the surface convex portions 40a of the core particles are exposed on the carrier surface by stirring the carrier of FIG. 1 in the developing tank.
The carrier surface immediately after the start (initial stage) is uniformly coated with the outer resin layer, and the carrier surface is not contaminated by components such as the binder resin of the toner. Therefore, the charge imparting ability of the carrier to the toner is high. In such an initial stage, when the charge imparting ability of the carrier is increased, the charge amount of the toner may be significantly increased. However, in the present invention, the initial toner charge amount is controlled by lowering the content of the charge improver. .

  On the other hand, at the stage where the charge imparting ability is lowered due to the progress of the abrasion of the resin layer and the core particles are exposed or the core particle surface is contaminated (filming) (during the life), the carrier surface has an initial charge imparting ability. Compared to In the present invention, the inner resin layer with enhanced charge imparting ability is exposed on the carrier surface. Therefore, it is possible to suppress a decrease in the toner charge amount and stabilize the toner charge amount from the initial stage to the end of the life.

<Composition of carrier>
Next, the configuration of the carrier of the present invention will be described.
The carrier is not particularly limited, but preferably has a volume average particle size of 20 to 100 μm. If the volume average particle diameter is too small, white spots may occur in the resulting image due to the carrier moving from the developing roller to the photosensitive drum during development. On the other hand, if the size is too large, the dot reproducibility may deteriorate and the image may become rough. The volume average particle diameter is more preferably 30 to 60 μm. The definition of the volume average particle diameter is described below.

  The lower the saturation magnetization of the carrier, the softer the magnetic brush in contact with the photosensitive drum, so that an image faithful to the electrostatic latent image can be obtained. However, if the saturation magnetization is too low, carriers adhere to the surface of the photosensitive drum and white spots are likely to occur. On the other hand, if the saturation magnetization 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, the saturation magnetization of the carrier is preferably in the range of 30 to 100 emu / g, and more preferably in the range of 50 to 80 emu / g. The definition of saturation magnetization is described below.

<Core particles>
The carrier comprises core particles. Known magnetic particles can be used as the core particles, but particles containing ferrite components (ferrite particles) are preferred. Ferrite-based particles have high saturation magnetization and can provide carriers with low density. For this reason, carrier adhesion to the photoconductor hardly occurs, and an image with high dot reproducibility can be obtained due to soft spike formation. Known ferrite particles can be used, such as zinc ferrite, nickel ferrite, copper ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, copper-magnesium ferrite, manganese-zinc ferrite, Examples of the particles include manganese-copper-zinc ferrite.

The core particles preferably have a volume resistivity of 1 × 10 ⁶ to 1 × 10 ¹¹ Ω · cm when measured by a bridge method. Ferrite particles having a volume resistivity in this range are generally used because they are inexpensive. When the volume resistivity is low, fog may occur due to poor electrical insulation. On the other hand, when the volume resistivity is high, the counter charge remaining on the carrier surface tends to cause an edge effect at the periphery of the solid image and a decrease in image density. The volume resistivity is more preferably in the range of 1 × 10 ^{8 to} 5 × 10 ¹⁰ Ω · cm. The definition of volume resistivity is described below.

Ferrite particles can be produced by a known method. For example, ferrite raw materials such as Fe ₂ O ₃ and Mg (OH) ₂ are mixed, and this mixed powder is heated in a heating furnace and calcined. After cooling the obtained calcined product, it is pulverized by a vibration mill so as to become particles of about 1 μm, and a dispersant and water are added to the pulverized powder to prepare a slurry. This slurry is wet pulverized with a wet ball mill, and the resulting suspension is granulated and dried with a spray dryer to obtain ferrite-based particles.

<Resin layer>
The resin layer is not particularly limited, and any layer made of a known resin can be used. For example, a layer made of an acrylic resin or a silicone resin can be used.
Examples of the acrylic resin include an acrylic monomer, or a resin obtained by polymerizing an acrylic monomer and a vinyl monomer.

  Known acrylic monomers can be used, for example, acrylic acid having a substituent, methacrylic acid having a substituent, acrylic ester having a substituent, and a substituent. And methacrylic acid ester and the like. Specific examples of the acrylic resin monomer include, for example, methyl acrylate, ethyl acrylate, isopropyl acrylate, n-butyl acrylate, isobutyl acrylate, n-amyl acrylate, isoamyl acrylate, n-hexyl acrylate, acrylic Acrylic acid ester monomers such as 2-ethylhexyl acid, n-octyl acrylate, decyl acrylate, dodecyl acrylate, methyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-amyl methacrylate, Methacrylate monomers such as n-hexyl methacrylate, 2-ethylhexyl methacrylate, n-octyl methacrylate, decyl methacrylate, dodecyl methacrylate, hydroxyethyl acrylate, hydroxy methacrylate Hydroxyl groups such as propyl (hydroxyl) -containing (meth) acrylic ester-based monomer. An acrylic monomer can be used individually by 1 type, or can use 2 or more types together. Known vinyl monomers can be used, and examples thereof include styrene, α-methylstyrene, vinyl bromide, vinyl chloride, vinyl acetate, acrylonitrile and methacrylonitrile. A vinyl monomer can be used individually by 1 type, or can use 2 or more types together. The polymerization is carried out by solution polymerization, suspension polymerization, emulsion polymerization or the like using a general radical initiator.

The silicone resin is not particularly limited, and a silicone resin commonly used in this field can be used, and a straight silicone resin is preferable.
In particular, a carrier having a layer of straight silicone resin (alkyl-substituted silicone resin) is less likely to cause toner component (binder resin) to adhere to the surface (filming), and can maintain the toner charge imparting ability over a long period of time. preferable. The straight silicone resin is, for example, the following general formula:

(Wherein R ₁ and R ₂ represent an alkyl group, and n represents an integer).
As the straight silicone resin, for example, silicone varnish (manufactured by Toshiba: TSR115, TSR114, TSR102, TSR103, YR3061, TSR110, TSR116, TSR117, TSR108, TSR109, TSR180, TSR181, TSR187, TSR144, TSR165, manufactured by Shin-Etsu Chemical Co., Ltd .: KR271, KR272, KR275, KR280, KR282, KR267, KR269, KR211, KR212), alkyd-modified silicone varnish (manufactured by Toshiba Corporation: TSR184, TSR185) and the like.

  Moreover, as a silicone resin, a crosslinkable silicone resin is preferable. As shown below, the crosslinkable silicone resin is a known silicone resin that is cured by crosslinking between hydroxyl groups bonded to Si atoms or a hydroxyl group and a group -OX by a heat dehydration reaction, a room temperature curing reaction, or the like.

[Wherein, a plurality of R are the same or different and each represents a monovalent organic group. The group -OX is an acetoxy group, an aminoxy group, an alkoxy group, an oxime group, and the like. ]
As the crosslinkable silicone resin, either a heat curable silicone resin or a room temperature curable silicone resin can be used. In order to crosslink the thermosetting silicone resin, it is necessary to heat the resin to about 200 to 250 ° C. Heating is not necessary to cure the room temperature curable silicone resin, but it is preferable to heat at 150 to 280 ° C. in order to shorten the curing time. Among the cross-linked silicone resins, those in which the monovalent organic group represented by R is a methyl group are preferable. Since the cross-linked silicone resin in which R is a methyl group has a dense cross-linked structure, a carrier having a good water repellency and moisture resistance can be obtained by forming a resin coating layer of the carrier core material using the cross-linked silicone resin. It is done. However, if the cross-linked structure becomes too dense, the resin coating layer tends to become brittle. Therefore, the molecular weight of the cross-linked silicone resin may be appropriately selected.

  It is preferable that the same resin is contained in the inner resin layer and the outer resin layer. By including the same resin, the interface between the inner resin layer and the outer resin layer is difficult to peel off, and good adhesion between the two resin layers can be obtained.

  The resin layer contains a charge improving agent. The charge improver is not particularly limited as long as it improves the chargeability of the toner. For example, a nitrogen-containing resin such as a melamine resin (for example, methylated melamine or butylated melamine) can be used for a negatively charged toner, and a fluorinated resin (for example, a fluorinated alkyl methacrylate) can be used for a positively charged toner. it can.

  The content of the charge improving agent is expressed in parts by weight with respect to 100 parts by weight of the resin constituting the resin layer. As a content rate of a charge improvement agent, 5-30 weight part is preferable with respect to 100 weight part of resin which comprises a resin layer. If it is less than 5 parts by weight, it may be difficult to obtain the effect of improving charging. On the other hand, when the amount exceeds 30 parts by weight, the resin layer to be coated tends to peel off. Moreover, it is preferable that the content rate of the electrical charge improvement agent contained in an inner side resin layer is 5-30 weight part, and it is more preferable that it is 7-15 weight part. When the content is within this range, the toner charge amount can be stabilized over a long period of time. On the other hand, the content of the charge improving agent contained in the outer resin layer is preferably 0 to 5 parts by weight, and more preferably 0 to 1 part by weight. When the content is in this range, it is possible to suppress initial image density reduction and to suppress fogging during life.

Further, the content of the charge improving agent contained in the outer resin layer is preferably 3 parts by weight or less, preferably less than 5 to 10 parts by weight, compared with the content of the charge improving agent contained in the inner resin layer. It is preferable.
Moreover, it is desirable that the components of the charge improving agent contained in the inner resin layer and the charge improving agent contained in the outer resin layer are the same. By using the same component, it is possible to prevent a sudden change in charge amount when the outer resin layer is worn.

A conductive material can be added to the resin layer in order to control the volume resistivity value of the carrier. In particular, by adding a conductive material to the outer resin layer, an effect of preventing a significant increase in the initial toner charge amount can be obtained.
Examples of the conductive material 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 conductive materials such as calcium carbonate. A conductive material can be used individually by 1 type, or can use 2 or more types together.

  The inner resin layer and the outer resin layer preferably contain the same conductive material. Thereby, a change in chargeability at the interface between the inner resin layer and the outer resin layer can be suppressed. As a result, a sudden change in charge amount when the inner resin layer is exposed can be prevented.

Among these conductive materials, 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 a carbon black having a DBP (dibutyl phthalate) oil absorption in the range of 90 to 170 ml / 100 g is preferable in terms of excellent production stability. In addition, the primary particle size of 50 nm or less is particularly preferable because of excellent dispersibility.

  In the case of the outer resin layer, the amount of the conductive material used is preferably 0.1 to 20 parts by weight with respect to 100 parts by weight of the resin constituting the resin layer. If the amount is less than 0.1 part by weight, the initial image density may be lowered. On the other hand, if the amount is more than 20 parts by weight, initial fog may occur. A more preferable usage amount is 5 to 10 parts by weight. On the other hand, in the case of the inner resin layer, the amount is preferably 0 to 10 parts by weight with respect to 100 parts by weight of the resin constituting the resin layer. If it is more than 10 parts by weight, fog may occur. A more preferable usage amount is 0 to 3 parts by weight. The amount of the conductive material used in the outer resin layer is preferably 2 to 10 times greater than that of the inner resin layer.

  The coverage of the core particles of the inner resin layer is preferably 50 to 95%. If it is less than 50%, when the outer resin layer is scraped off due to abrasion, the exposed amount of the core particles is large, and the carrier resistance may be lowered. Therefore, carrier adhesion and roughness are likely to occur. On the other hand, if it exceeds 95%, the exposed amount of the core particles is small and the carrier resistance may be increased. Therefore, the toner charge amount is likely to increase more than necessary. A more preferable coverage is 70 to 90%.

  On the other hand, the coverage of core particles (including the inner resin layer) of the outer resin layer is preferably 95% or more. If it is less than 95%, the toner charge amount may vary. A more preferable coverage is 100%. The definition of coverage is described below.

  Moreover, it is preferable that the film thickness of an inner side resin layer is 0.1-2 micrometers, and it is more preferable that it is 0.5-1 micrometer. When it is thinner than 0.1 μm, sufficient durability may not be obtained. If it is thicker than 1 μm, the toner charge amount may increase. On the other hand, the maximum film thickness of the outer resin layer is preferably 0.1 to 2 μm, and more preferably 0.5 to 1 μm. If it is thinner than 0.1 μm, the initial charge amount may increase. If it is thicker than 2 μm, the toner charge amount may decrease after use of 5K to 10K sheets and fogging may occur. The above film thickness is calculated from the volume average particle size of the core particles used and the amount of resin added, assuming that the core particles are perfect spheres having a uniform particle size and that the resin is uniformly coated. To do.

The carrier of the present invention provided with the resin layer may cause carrier adhesion to the photoreceptor when the volume resistivity is low, and the toner charge amount is likely to increase when the volume resistivity is high. Therefore, the volume resistivity is preferably in the range of 1 × 10 ^{9 to} 5 × 10 ¹² Ω · cm, and more preferably in the range of 5 × 10 ⁹ to 1 × 10 ¹² Ω · cm. The definition of volume resistivity is described below.

  A known method can be adopted as a method for forming the resin layer. For example, there is an immersion method in which the raw material for the resin layer is dissolved in a solvent (for example, an organic solvent such as toluene or acetone), and the core particles are immersed in the obtained solution. Further, there is a spray method in which the raw material solution for the resin layer is sprayed onto the core particles. Furthermore, there is a fluidized bed method in which the raw material solution of the resin layer is sprayed in a state where the core particles are suspended by the fluidized air. Furthermore, there is a kneader coater method in which the core particles and the raw material solution of the resin layer are mixed in a kneader coater and the solvent is removed. When the resin layer includes a conductive material, the conductive material can be added to the raw material solution of the resin layer together with the resin.

  The coverage can be adjusted by controlling the particle size of the core particles to be used and the amount of resin, as well as the temperature at the time of evaporating the solvent in which the resin is dissolved, and when the particle size of the core particles and the amount of resin are the same, The higher the coating temperature, the higher the coverage. The coating temperature is generally 70 to 250 ° C.

  The carrier of the present invention is mixed with toner and used as a two-component developer. The mixing method with toner can be generally prepared by mixing 3 to 15 parts by weight of toner with respect to 100 parts by weight of carrier and stirring with a mixer such as a Nauta mixer.

<Two-component developer>
The two-component developer includes a toner and a carrier. The carrier of the present invention is used as the carrier. The mixing ratio of carrier and toner is generally 3 to 15 parts by weight of toner with respect to 100 parts by weight of carrier. Examples of the method for mixing the carrier and the toner include a method of stirring with a mixer such as a Nauta mixer.

The toner is not particularly limited, and any known toner can be used. For example, the toner described below can be used.
The toner includes colored resin particles (toner particles) and, if necessary, external additives attached to the surface of the colored resin particles. The external additive is preferably contained in the toner from the viewpoint of preventing the toner from agglomerating and preventing the transfer efficiency when transferring from the photosensitive drum to the recording medium.

  The toner can be produced, for example, by mixing the external additive with the colored resin particles using an air flow mixer such as a Henschel mixer (that is, external addition treatment). The volume average particle diameter of the colored resin particles is preferably in the range of 4 to 7 μm. Within this range, a high-quality image with excellent dot reproducibility and less fog and toner scattering can be obtained. The definition of the volume average particle diameter is described below.

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 exceeds 1.9 m ² / g, unevenness is increased on the surface of the colored resin particles, and the external additive may enter the concave portion, and the external additive may not be uniformly adhered to the surface. In this case, the roller effect (effect of improving fluidity) and the spacer effect (preventing charge leakage) of the external additive cannot be obtained sufficiently, and fog and toner scattering are likely to occur. Moreover, if it is less than 1.5 m < ² > / g, the colored resin particle surface may become too smooth, and fogging may generate | occur | produce when cleaning defect generate | occur | produces.

  A known method can be used as a method for controlling the BET specific surface area. For example, there are a method of rotating colored resin particles in a cylindrical pipe at high speed to take a corner, and a method of a sfusion system that instantaneously melts toner in a hot air stream. The definition of the BET specific surface area is described below.

  The colored resin particles can be produced by a known method such as a kneading and pulverizing method or a polymerization method. Specifically, when the kneading and pulverization method is adopted, the binder resin, the colorant, the charge control agent, the release agent, and other additives are mixed with a mixer such as a Henschel mixer, a super mixer, a mechano mill, or a Q type mixer. Mix. The obtained raw material mixture is melt-kneaded at a temperature of about 100 to 180 ° C. by a kneader such as a twin-screw kneader or a single-screw kneader. The obtained kneaded product is cooled and solidified, and the solidified product is pulverized by an air pulverizer such as a jet mill. Colored resin particles can be produced by adjusting the particle size such as classification of the obtained pulverized product as necessary.

  As the binder resin that can be used for the toner, various known styrene resins, acrylic resins, polyester resins, and the like can be used. A linear or non-linear polyester resin is particularly preferable. The polyester resin is excellent in achieving both mechanical strength (difficult to generate fine powder), fixability (hard to peel off from paper after fixing), and hot offset resistance.

  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 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, Examples include malonic acid, anhydrides and lower alkyl esters of these acids, or alkenyl succinic acids or alkyl succinic acids such as n-dodecenyl succinic acid and n-dodecyl succinic acid.

  If necessary, a trihydric or higher polyhydric alcohol or a polybasic acid may be added to the monomer composition. 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 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 that can be used in the toner, known pigments and dyes generally used in toners can be used.
Specific examples of the black toner include carbon black and magnetite.

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

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

For cyan toner, C.I. I. Pigment Blue 15: 3, 15: 4, and the like, and blue dyes and pigments of copper phthalocyanine and derivatives thereof; I. Examples thereof include green pigments such as CI Pigment Green 7 and 36 (phthalocyanine green).
As content of a coloring agent, it is preferable that it is about 1-15 weight part with respect to 100 weight part of binder resin, More preferably, it is the range of 2-10 weight part.

As the charge control agent that can be used for the toner, known charge control agents can be used.
Specifically, as a charge control agent imparting negative chargeability, chromium azo complex dye, iron azo complex dye, cobalt azo complex dye, salicylic acid or its derivative chromium / zinc / aluminum / boron complex or salt compound, naphtholic acid or Chromium / zinc / aluminum / boron complex or salt compound of its derivative, chrome / zinc / aluminum / boron complex or salt compound of benzylic acid or its derivative, long chain alkyl / carboxylate, long chain alkyl / sulfonate, etc. Can be mentioned.

  Examples of the charge control agent that imparts positive chargeability include nigrosine dyes and derivatives thereof, triphenylmethane derivatives, quaternary ammonium salts, quaternary phosphonium salts, quaternary pyridinium salts, guanidine salts, amidine salts, and the like. be able to.

  The content of these charge control agents is preferably in the range of 0.1 to 20 parts by weight, more preferably in the range of 0.5 to 10 parts by weight with respect to 100 parts by weight of the binder resin. .

  Release agents that can be used for the toner include synthetic waxes such as polypropylene and polyethylene, paraffin wax and derivatives thereof, petroleum waxes such as microcrystalline wax and derivatives thereof, and modified waxes thereof, carnauba wax, rice wax, and candelilla wax. And plant waxes. By including these release agents in the toner, the releasability of the toner with respect to the fixing roller or the fixing belt can be improved, and high temperature / low temperature offset during fixing can be prevented. The amount of the release agent added is not particularly limited, but is generally 1 to 5 parts by weight with respect to 100 parts by weight of the binder resin.

  As the external additive, inorganic particles made of silica, titanium oxide, alumina or the like can be used. Moreover, you may provide hydrophobicity by surface-treating an inorganic particle with a silane coupling agent, a titanium coupling agent, and silicone oil. Inorganic particles to which hydrophobicity is imparted are preferable because the decrease in electrical resistance and charge amount is reduced under high humidity. In particular, silica particles using hexamethyldisilazane (hereinafter sometimes referred to as HMDS) as a silane coupling agent and having a trimethylsilyl group introduced on the surface are excellent in hydrophobicity and insulating properties. The toner to which the silica particles are externally added can provide excellent chargeability even in a high humidity environment.

  Specific external additives include Aerosil 50 (number average particle size: about 30 nm), Aerosil 90 (number average particle size: about 30 nm), Aerosil 130 (number average particle size: about 16 nm) manufactured by Nippon Aerosil Co., Ltd. Aerosil 200 (number average particle size: about 12 nm), Aerosil 300 (number average particle size: about 7 nm), Aerosil 380 (number average particle size: about 7 nm), Aluminum Oxide C (number average particle size: manufactured by West Germany Degussa) About 13 nm), titanium oxide P-25 (number average particle size: about 21 nm), MOX170 (number average particle size: about 15 nm), Ishihara Sangyo TTO-51 (number average particle size: about 20 nm), TTO-55 (Number average particle diameter: about 40 nm). The definition of the number average particle diameter is described below.

  The amount of the external additive added is preferably 0.2 to 3% by weight. If it is less than 0.2% by weight, the toner may not be sufficiently or fluidly provided. On the other hand, if it exceeds 3% by weight, the toner fixability may be lowered.

<Image forming apparatus>
Next, the image forming apparatus of the present invention will be described.
FIG. 3 is an explanatory view showing an embodiment of the image forming apparatus according to the present invention. The image forming apparatus of the present invention is not limited to the configuration shown in FIG. As shown in FIG. 3, the image forming apparatus is a tandem color image forming apparatus including four image forming units 1 to 4.

  Among these, reference numeral 1 indicates a first image forming unit for forming a black toner image, and reference numeral 2 indicates a second image forming unit for forming a cyan toner image. Reference numeral 3 indicates a third image forming unit for forming a magenta toner image, and reference numeral 4 indicates a fourth image forming unit for forming a yellow toner image.

  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 over two support rolls 6 and rotates in the direction indicated by the arrow R. Hereinafter, upstream and downstream are expressed with respect to the rotation direction of the intermediate transfer belt 5 on the basis of the secondary transfer position where the secondary transfer roller indicated by reference numeral 8 is arranged. As a material for the intermediate transfer belt 5, a material in which an appropriate amount of an electronic conductive material 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 in the rotation direction R of the intermediate transfer belt 5, the first image forming unit 1 (black), the second image forming unit 2 (cyan), and the third image forming unit 3 ( Magenta) and the fourth image forming unit 4 (yellow).

Inside the intermediate transfer belt 5, a primary transfer roller 7 that transfers the single-color toner image formed by the image forming units 1 to 4 onto the intermediate transfer belt 5 faces the image forming units 1 to 4. Are provided respectively. The single-color toner images formed by the image forming units 1 to 4 are transferred so as to be superimposed on the intermediate transfer belt 5 to form one color image.
A secondary transfer roller 8 for transferring a color image formed on the intermediate transfer belt 5 to a sheet (recording medium) downstream of the fourth image forming unit 4 (yellow) in the rotation direction R of the intermediate transfer belt 5. Is arranged.

  Further, 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. 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 downstream of the belt cleaning brush 11 in the rotation direction R of the intermediate transfer belt 5.

  Further, below the four image forming units 1 to 4, a tray 14 for storing paper is disposed. The paper in the toner 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.

  A fixing unit 15 for fixing the color image transferred onto the paper on the paper is provided downstream of the secondary transfer roller 8 in the paper conveyance direction P. Further, a discharge roller 13 a that discharges the sheet on which the color image is fixed from the image forming apparatus is provided further downstream of the fixing unit 15 in the sheet conveyance direction P.

  In such a configuration, the single color toner images formed by the image forming units 1 to 4 are sequentially transferred onto the intermediate transfer belt 5 to form a color image 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 to the paper is removed by the belt cleaning unit 10.

  FIG. 4 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 that charges the photosensitive drum 16, an exposure unit 18 that writes an electrostatic latent image on the photosensitive drum 16, and a development that visualizes 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. In addition, it can also be comprised from a contact-type charger using a corotron charger, 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 a developer containing the toner of the present invention in the developing tank, and develops the electrostatic latent image on the surface of the photosensitive drum 16 with the toner contained in the developer. The developer is a two-component developer composed of toner and carrier.

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 and the other end is connected to the photosensitive drum 16 on the upstream side in the rotational direction Rd of the photosensitive drum 16 with respect to the cleaning blade 21. Arranged in contact.

  FIG. 5 is an explanatory diagram showing a configuration around the developing device 19 in FIG. The developing device 19 includes a developing tank 27 in which the two-component developer DV is accommodated, and the developing tank 27 is provided with an opening 30 at a position facing the outer peripheral surface of the photosensitive drum 16.

  The two-component developer is supplied to the photosensitive drum 16 by carrying the two-component developer on the outer peripheral surface at a position facing the open portion 30 inside the developing tank 27, and an electrostatic latent image is formed. A developing roller 24 for developing is provided. The developing roller 24 is disposed with a gap from the outer peripheral surface of the photosensitive drum 16.

  The developing roller 24 is a multi-pole magnetized multi-pole magnet in which magnetic poles N1, N2, and N3 and magnetic poles S1 and S2 made of a bar magnet 31 having a rectangular cross-sectional shape are radially spaced apart at a plurality of circumferential positions. A member 25 and a nonmagnetic sleeve 26 that is rotatably fitted to the multipolar magnetized member 25 are provided.

  Both ends of the multipolar magnetized member 25 are supported non-rotatably 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 disposed upstream from the magnetic pole N1, for example, at a position of 282 °, for example.

  In the vicinity of the opening 30 in the developing tank 27 and on the upstream side in the developer transport direction of the developing roller 24, the thickness of the developer layer carried on the outer peripheral surface of the developing roller 24 is regulated to suppress the developer static. A regulating member 28 that regulates the transport amount to the electrostatic latent image is provided. The regulating member 28 is arranged at a predetermined interval with respect to the outer peripheral surface of the developing roller 24.

A stirring member 29 that stirs the developer in the developing tank 27 and supplies the developer 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, since the toner charge amount is stable, a stable image quality can be obtained over a long period of time.

(Various definitions)
The definitions of the volume average particle diameter, saturation magnetization, volume resistivity, number average molecular weight, coverage, BET specific surface area, and number average particle diameter in the present specification are described below.
"Volume average particle diameter of carrier"
In this specification, the volume average particle diameter of the carrier is measured under the condition of a dispersion pressure of 3.0 bar using a dry dispersion apparatus RODOS (manufactured by SYMPATEC) in a laser diffraction particle size distribution measuring apparatus HELOS (manufactured by SYMPATEC). Means the value.

"Volume average particle diameter of colored resin particles"
In the present specification, the volume average particle diameter of the colored resin particles means a value measured with a Coulter Multisizer II (manufactured by Beckman Coulter, Inc.) using a 100 μm aperture. As the electrolytic solution, a 1% NaCl aqueous solution is prepared using first grade 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 a measuring device is used to measure the volume and number of toner by measuring the volume and number of toner using a 100 μm aperture. calculate. The volume average particle diameter is obtained from the volume distribution.

"Saturation magnetization"
In this specification, saturation magnetization refers to a value measured by VSMP-1 manufactured by Toei Kogyo Co., Ltd.

"Volume resistivity"
In this specification, the measurement of the volume resistivity of a core particle and a carrier means the value performed in the following procedure. First, 0.2 g of core particles or a carrier is filled between two copper plate electrodes 30 mm wide and 10 mm high installed with a gap of 6.5 mm under environmental conditions of an air temperature of 20 ° C. and a humidity of 65%. . Next, a bridge made of core particles or carriers is formed by the magnetic lines of force of two magnets (100 mT) arranged outside each copper plate electrode so that the N pole and the S pole face each other. In this state, a voltage of 500 V is applied, and a value 15 seconds after the application is measured. This measured value is the volume resistivity.

"Coverage"
In the present specification, the coverage means a value calculated by the following method. In other words, a scanning electron microscope (SEM) is used to observe with an electron beam having an acceleration voltage of 2.0 eV without depositing a conductive agent such as gold on the carrier surface. In the carrier, the coating layer is observed white by charge-up. The ratio of the area of the region observed in white to the total area of the carrier is calculated. This calculation is performed for 100 carriers, and the average value obtained is the coverage.

"BET specific surface area"
In this specification, the BET specific surface area means a measurement value obtained by a three-point measurement method using a BET specific surface area measuring device Gemini 2360 (manufactured by Shimadzu Corporation).

"Number average particle size"
In this specification, 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.

<Career>
The carriers of Examples and Comparative Examples were produced by the following method.
After mixing the ferrite raw material (manufactured by Kanto Denka Kogyo Co., Ltd.) with a ball mill, calcining at 900 ° C. with a rotary kiln, the obtained calcined powder is average particle size by a wet pulverizer (using steel balls as the pulverizing medium) Finely pulverized to 2 μm or less. The obtained ferrite powder was granulated by a spray drying method, and the granulated product was fired at 1300 ° C. After firing, core particles made of a ferrite component having a volume average particle diameter of about 45 μm and a volume low efficiency of 1 × 10 ⁹ Ω · cm were obtained by crushing using a crusher.

  Next, the resin layer coating solution for forming the inner resin layer covering the core particles is composed of 100 parts by weight of a silicone resin (number average molecular weight of about 15000: manufactured by Toshiba Silicone) and a melamine resin (manufactured by Dainippon Ink, Inc. -820-60) 10 parts by weight was prepared by dissolving and dispersing in 1000 parts by weight of toluene.

  The prepared coating solution for the resin layer was coated on the core particles made of the ferrite component by a spray coating apparatus (Spiraccoater SP40 manufactured by Okada Seiko Co., Ltd.). Thereafter, toluene was completely removed by evaporation to prepare a primary coated carrier having an inner resin layer coverage of 85%.

  Next, the resin layer coating solution for forming the outer resin layer covering the core particles is composed of 100 parts by weight of a silicone resin (number average molecular weight of about 10,000: manufactured by Toshiba Silicone) and a melamine resin (manufactured by Dainippon Ink, Inc. -820-60) 3 parts by weight were prepared by dissolving and dispersing in 1000 parts by weight of toluene.

The prepared coating solution for the resin layer was coated on the primary coated carrier with a spray coating apparatus (Spiraccoater SP40 manufactured by Okada Seiko Co., Ltd.). Thereafter, toluene (two-layer coated carrier) C1 was produced by completely evaporating and removing toluene. Carrier C1 had a volume average particle size of 46 μm, an outer resin layer coverage of 100%, a volume resistivity of 8 × 10 ¹¹ Ω · cm, and a saturation magnetization of 65 emu / g. Carriers C2 to C14 were produced in the same manner as the carrier C1, except that the inner and outer resin layers were formed with the content of the melamine resin (charge improver) shown in Table 1. Table 1 also shows the coverage, volume average particle diameter, volume resistivity, and saturation magnetization of the inner and outer resin layers of the carriers C1 to C14.

The coverage was adjusted by adjusting the amount of resin used.
The toners of Examples and Comparative Examples were prepared by the following method.

The toner material is described below.
Binder resin (polyester resin obtained by polycondensation using bisphenol A propylene oxide, terephthalic acid or trimellitic anhydride as a monomer: glass transition temperature 60 ° C., softening temperature 115 ° C .: manufactured by Fujikura Kasei Kogyo Co., Ltd.)
100 parts by weight Colorant (CI Pigment Blue 15: 3) 5 parts by weight Charge control agent (boron compound: LR-147 manufactured by Nippon Carlit)
2 parts by weight Release agent (microcrystalline wax: HNP-9 manufactured by Nippon Seiki Co., Ltd.)
3 parts by weight The above toner material was mixed for 10 minutes with a Henschel mixer, and then melt-kneaded and dispersed with a kneading and dispersing apparatus (Mitsui Mining Co., Ltd .: Needix MOS140-800). The kneaded product was coarsely pulverized with a cutting mill and then finely pulverized with a jet pulverizer (manufactured by Nippon Pneumatic Kogyo Co., Ltd .: IDS-2 type). By classifying the finely pulverized product using an air classifier (manufactured by Nippon Pneumatic Industry Co., Ltd .: MP-250 type), the volume average particle size is 6.5 ± 0.1 μm and the BET specific surface area is 1.8 ±. Colored resin particles of 0.1 m ² / g were obtained.

  1 part by weight of silica particles (Degussa) whose surface was treated with hexamethyldisilazane having a number average particle diameter of 7 nm was added to 100 parts by weight of the obtained colored resin particles, and the tip speed of the stirring blade was 15 m / second. A negatively chargeable toner T1 was produced by stirring for 2 minutes with an airflow mixer (manufactured by Mitsui Mining Co., Ltd .: Henschel mixer).

<Two-component developer>
The two-component developers of Examples and Comparative Examples were prepared by mixing the carriers C1 to C14 with the toner T1. The two-component developer was prepared by charging 6 parts by weight of toner and 94 parts by weight of a carrier into a Nauter mixer (trade name: VL-0, manufactured by Hosokawa Micron Corporation) and stirring and mixing for 20 minutes.

<Image evaluation>
A continuous print test was performed using the produced two-component developer and the test image forming apparatus shown in FIG. The continuous print test was performed using only the image forming unit 1 among the four image forming units. 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 photosensitive member and the development bias are set 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 the smallest. Was adjusted respectively. A4 size electrophotographic paper (multi receiver: manufactured by Sharp Document System) was used as a test paper.
50K (50000) print tests were performed on each text image that provides 6% coverage of the print image recorded on the paper.

Image evaluation was performed by measuring the toner charge amount, image density, and fog density. The measurement method for each of these values is described below.
The toner charge amount is measured using a suction type small charge amount measuring device (manufactured by Trek Japan Co., Ltd .: 210HS-2A).

The image density is evaluated as follows. That is, a solid image (100% density) with a side of 3 cm is printed. The image density of the printed part is measured using a reflection densitometer (Macbeth: RD918). The image density is 1.3 or more (paper fiber is completely covered with toner), and 1.2 or more and less than 1.3 is slightly poor, and less than 1.2 (paper fiber is incomplete with toner) The state covered with is considered defective.
As for the fog density, the density of the non-image area (0% density) is calculated by the following procedure.

Using a whiteness meter (Nippon Denshoku Industries Co., Ltd .: Z-Σ90 COLOR MEASURING SYSTEM), the whiteness of the paper before printing is measured in advance. Next, the whiteness in the non-image area of the paper after printing is measured using a whiteness meter, and the difference from the whiteness before printing is obtained. This difference is the fog density.
The fog density is less than 0.6 (a state in which fog is hardly visible to the naked eye), 0.6 to less than 1.0 is slightly poor, and 1.0 or more (a state in which fog is clearly visible to the naked eye) is poor. .

<Result>
Table 2 shows the results of the continuous print test. As shown in Examples 1 to 11, in the C1 to C11 carrier continuous print test, the toner charge amount is stable at the initial stage, immediately after the start (2K sheets), and at the life (50K sheets), and the image density. Was high and an image without fogging was obtained.
On the other hand, as shown in Comparative Examples 1 and 3, a continuous print test using a carrier in which the inner resin layer does not contain a charge improving agent or a carrier (C12, C14) with a low coverage of the inner resin layer. In the life (50K sheets) image, the toner charge amount decreased and fogging was observed.

  Further, as shown in Comparative Examples 2 and 3, in a continuous print test using a carrier (C13, C14) in which the charge improver contained in the outer resin layer is the same or more in the inner resin layer, immediately after the start ( (2K sheets) The toner charge amount increased in the image, and the image density decreased.

It is the schematic of the carrier of this invention. It is the schematic which shows the state in which the surface convex part of the core particle of the carrier of this invention was exposed to the surface. 1 is a schematic diagram of an image forming apparatus. FIG. 2 is a schematic enlarged view of a developing unit of the image forming apparatus. 2 is a schematic enlarged view of a process unit of the image forming apparatus. FIG.

Explanation of symbols

N1, N2, N3, S1, S2 Magnetic pole, P Conveyance direction, R, Rd Rotation direction 1-4 Image forming unit, 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 Toner, 15 Fixing unit, 17 Charger 18 Exposure unit, 19 Developing device, 20 Photosensitive drum cleaner 21 Cleaning blade, 22 Cleaner housing, 23 seal 24 developing roller 25 multipolar magnetized member 26 sleeve 27 developing tank 28 regulating member 29 stirring member 30 opening part 31 bar magnet DV two-component developer

Claims (7)

  A core layer, and a resin layer covering the surface of the core particle, the resin layer having two resin layers on the inner side and the outer side from the core particle side, and the outer resin layer is formed on the inner side. A carrier comprising a charge improving agent at a lower content than the resin layer.   The carrier according to claim 1, wherein the charge improving agent contained in the inner resin layer and the charge improving agent contained in the outer resin layer contain the same component.   The carrier according to claim 1, wherein the outer resin layer further contains a conductive material.   The carrier according to any one of claims 1 to 3, wherein a surface of the core particle is covered with the inner resin layer at a coverage of 50 to 95%.   The carrier according to any one of claims 1 to 4, wherein the inner resin layer and the outer resin layer contain a straight silicone resin.   The carrier according to claim 1, wherein the core particle includes a ferrite component.   7. A photosensitive member on which an electrostatic latent image is formed, a charging device for charging the surface of the photosensitive member, an exposure device for forming an electrostatic latent image on the surface of the photosensitive member, and toner. A developing device that contains the two-component developer including the carrier according to any one of the above and supplies the toner to an electrostatic latent image on the surface of the photoconductor to form a toner image; and A transfer device that transfers the toner image on the surface to a recording medium; a cleaning device that cleans the surface of the photoreceptor; and a fixing device that fixes the toner image to the recording medium. An image forming apparatus for forming an image.

Images