JP5586421B2 - Electrophotographic carrier, method for producing electrophotographic carrier, and developer - Google Patents

Description

  The present invention relates to an electrophotographic carrier, a method for producing the electrophotographic carrier, and a developer including the electrophotographic carrier.

  An image forming apparatus using an electrophotographic system, such as a copying machine, a printer, a facsimile machine, and a composite machine of these, includes an image carrier, a charging device that uniformly charges the surface of the image carrier, and a charged image carrier. An exposure device for forming an electrostatic latent image on the surface of the image carrier by exposing the surface of the body; and supplying toner to the surface of the image carrier on which the electrostatic latent image is formed. A developing device that develops an electrostatic latent image as a toner image, a transfer device that transfers toner constituting the toner image from the image carrier to a recording medium, and heating and pressurizing the transferred toner image, A fixing device for fixing the recording medium is provided. Such an image forming apparatus forms a toner image on the image carrier by each of the above-described apparatuses, transfers the toner image to a recording medium, and then fixes the toner image to the recording medium. Are formed on the recording medium.

  Examples of the developing device provided in such an image forming apparatus include one using a one-component developer containing toner and not containing a carrier, and one using a two-component developer containing toner and a carrier. Such a developing device charges the toner by stirring the developer in advance before supplying the toner to the surface of the photosensitive drum as an image carrier. In the case of a developing device using a two-component developer, when the developer is stirred, the toner is stirred in the presence of the carrier. Therefore, a developing device using a two-component developer is preferably used as compared with a developing device using a one-component developer because it is easier to secure the charge amount of the toner. Further, it is known that a developing device using a two-component developer is more advantageous in terms of life compared to a developing device using a one-component developer.

  Among developing devices using a two-component developer, a so-called hybrid developing type developing device is preferably used because it can form a high-quality image. The developing device of the hybrid developing system is arranged to face a magnetic roller, which is a developer carrying member that carries and conveys a two-component developer, and to face each of the image carrier and the magnetic roller. And a developing roller that is a toner carrying member that carries and conveys only the toner to be conveyed. That is, the two-component developer is carried on the surface of the magnetic roller and conveyed, and the conveyed two-component developer is brought into contact with or close to the developing roller, whereby the toner of the two-component developer is removed from the surface of the developing roller. A developing device that shifts upward, carries the transferred toner on a developing roller, conveys the toner to the vicinity of the image carrier, and causes the conveyed toner to fly toward the surface of the image carrier. As described above, the developing device of the hybrid development system uses the two-component developer, but the two-component developer is configured not to directly contact the image carrier, so that the carrier for the image carrier is used. Adhesion and wrinkling of the image carrier can be suppressed, and a high-quality image can be formed.

  Further, since a developing device using a two-component developer uses toner when performing image formation, new toner is replenished in order to perform image formation over a long period of time. On the other hand, in the case of a general developing device, the same carrier is repeatedly used even if image formation is performed over a long period of time. In the case of a developing device using a general two-component developer, as described above, compared to a developing device using a one-component developer, it is easier to secure the charge amount of toner, and a high-quality image is formed as an image to be formed. However, it is known that when an image is formed over a long period of time, the carrier is repeatedly used for a long period of time, and the performance of the carrier, such as the charge imparting performance of the toner, is reduced. For this reason, it is known that the charge amount of the toner is reduced, the fog of the developer is easily generated, and it is difficult to form a good image. Therefore, as a developing device using a two-component developer, it is considered to use not only a toner but also a developing device that replenishes a replenishing developer containing toner and a carrier, a so-called trickle developing type developing device.

  As described above, the image forming apparatus has been improved by various improvements such as high speed and high image quality. In order to satisfy such a demand for high performance, not only the improvement of the image forming apparatus as described above but also the development of the developer used in the image forming apparatus is required.

  Specific examples of the developer used in such an image forming apparatus include those described in Patent Document 1 and Patent Document 2.

In Patent Document 1, in a developer for a trickle development system composed of a mixture of a toner and a carrier for use in forming a full-color image, the toner contains inorganic fine particles therein, and the volume average particle diameter D _{50V of the} toner. Is in the range of 5.0 to 9.0 μm, an external additive is added to the toner, and the carrier has a true specific gravity in the range of 3.00 to 4.60. Is a developer for a trickle development system in which the ratio of the volume average particle diameter of the carrier to the volume average particle diameter of the toner is in the range of 3.00 to 7.00. .

Patent Document 2 discloses a two-component development in which a developer for replenishment containing at least toner and a magnetic carrier is developed while being replenished to the developer, and at least the excess carrier inside the developer is discharged from the developer. A replenishment developer for use in the method, wherein the replenishment developer contains 2 to 50 parts by mass of toner with respect to 1 part by mass of the magnetic carrier, and the toner contains at least It is obtained by an emulsion aggregation method obtained through an aging step in which polymer fine particles and colorant fine particles are aggregated to cause fusion between fine particles of the fine particle aggregate, and the weight average diameter (D4) is 3. The proportion of particles having an equivalent circle diameter of 0.6 μm to 2.0 μm of 0 μm to 11.0 μm is 30% by number or less, and the magnetic carrier has a 50% particle size (D50) of 15 on a volume distribution basis. To 70μ m, the true specific gravity is 2.5 to 4.2 g / cm ³ , and the strength of magnetization is 40 to 70 Am ² / kg under a magnetic field of 1000 / 4π (kA / m). Is described.

JP 2001-330985 A JP 2007-114578 A

  Further, in order to form a higher quality image in an image forming apparatus using an electrophotographic system, it is conceivable to use a developer containing a toner having a relatively small particle diameter as a developer to be used. When a developer containing such a small particle size toner is used, it can be expected that an image to be formed has high resolution and excellent gradation.

  Patent Document 1 discloses that a trickle developing system developer having toner deterioration resistance, excellent transferability, carrier contamination resistance, and stable charging performance can be provided. Patent Document 2 discloses that in the developing device, the developer in the developing device and the replenishment developer can be mixed efficiently, and high durability and high image quality can be obtained.

  However, the trickle developing system developer as described above tends to lower the image density or easily causes fogging of the developer with toner, and it may be difficult to form a good image. In particular, when the toner particle size is reduced in order to form a higher quality image, it may be difficult to form a good image. This is presumed to be due to the following. First, it is considered that when the particle size of the toner is reduced, the mixing property between the toner and the carrier is lowered. If the toner and the carrier are not sufficiently mixed as described above, it is considered that the toner is not sufficiently charged. In addition, when the toner particle size is reduced, it is considered that the developer tends to stay in a space or the like in the developing device that is not used for stirring the developer. If the developer stays in this way, it is considered that the image density is likely to be lowered, or the developer is likely to be fogged with toner.

  The present invention has been made in view of such circumstances, and even when image formation is performed over a long period of time, a high image density can be maintained and occurrence of fogging can be suppressed. An object of the present invention is to provide an electrophotographic carrier capable of forming a film. Another object of the present invention is to provide a method for producing the electrophotographic carrier and a developer containing the electrophotographic carrier.

  The inventor of the present invention pays attention to the carrier contained in the developer to be used in order to achieve high image quality of the image to be formed, and its BET specific surface area, average particle radius, and density increase the image density, As a result of intensive studies on the relationship capable of suppressing the occurrence of fogging, it has been found that the above object can be achieved by the present invention described below.

  The electrophotographic carrier according to one embodiment of the present invention includes a core material and a resin layer that covers the core material, and satisfies the following formula (1).

1 ≦ (S × r × D) /3≦1.5 (1)
In the formula (1), S represents the BET specific surface area (m ² / g) of the electrophotographic carrier, r represents the average particle radius (m) of the electrophotographic carrier, and D represents The density (g / m ³ ) of the electrophotographic carrier is shown.

  According to such a configuration, even when image formation is performed for a long period of time, high image density can be maintained, occurrence of fogging, and the like can be suppressed, and thus high-quality images can be formed over a long period of time. A carrier can be provided.

  This is presumed to be due to the following.

  First, (S × r × D) / 3 is considered to indicate the ratio of the BET specific surface area of the carrier to the specific surface area when the carrier is assumed to be a true sphere. That is, the closer the ratio [(S × r × D) / 3] is to 1, the smoother the surface of the carrier is, the closer the shape is to a true sphere, and the smaller the specific surface area, which is the surface area per unit mass. It is thought to show. Further, as the ratio [(S × r × D) / 3] is farther from 1, the surface of the carrier is more uneven, the carrier has a elliptical cross section, etc. This is considered to indicate that the specific surface area becomes large.

  Further, if the specific surface area of the carrier is large, that is, if the ratio [(S × r × D) / 3] is large, the contact area between the toner and the carrier is increased, so that it is considered that the charge imparting performance to the toner is enhanced. . On the other hand, if the specific surface area of the carrier is too large, that is, if the ratio [(S × r × D) / 3] is too large, it is considered that the charge imparting performance with respect to the toner is lowered. This is considered to be because the fluidity of the developer tends to be lowered when the toner concentration is increased. In this case, it is considered that the developer having a high toner concentration does not flow and stays in the developing device, and the developer having a low toner concentration is preferentially consumed. Therefore, it is considered that it tends to be difficult to achieve a suitable image density.

  From these facts, by making the ratio [(S × r × D) / 3] within the above range, the carrier has excellent charge imparting performance to the toner and changes in fluidity when used as a developer. It is considered that both can be achieved together. Therefore, by setting the ratio [(S × r × D) / 3] within the above range, high image density can be maintained even when image formation is performed over a long period of time, and occurrence of fogging can be suppressed. Therefore, it is considered that a high-quality image can be formed over a long period of time.

  In addition, in the electrophotographic carrier, the fluidity of the mixture obtained by mixing the electrophotographic carrier and the toner when the toner concentration with respect to the electrophotographic carrier is 5% by mass is FR ( 5%), and the fluidity of the mixture obtained by mixing the electrophotographic carrier and the toner when the concentration of the toner with respect to the electrophotographic carrier is 10% by mass is FR (10%). When it does, it is preferable to satisfy | fill following formula (2).

1 ≦ FR (10%) / FR (5%) ≦ 1.3 (2)
According to such a configuration, even when image formation is performed over a long period of time, higher image density can be maintained, and occurrence of fogging can be further suppressed.

  This is considered to be due to the following. First, it is considered that the change in the fluidity of the developer due to the change in the toner density becomes small. Therefore, it is considered that the phenomenon that the developer having a low toner concentration is consumed preferentially can be further suppressed. From this, it is considered that even when image formation is performed over a long period of time, higher image density can be maintained, and occurrence of fogging can be further suppressed.

  In the electrophotographic carrier, it is preferable that the core material has silica particles attached to the surface.

  According to such a configuration, even when image formation is performed over a long period of time, higher image density can be maintained, and occurrence of fogging can be further suppressed. This is considered to be due to the following. If the core material has silica particles attached to the surface, the ratio [(S × r × D) / 3] of the carrier is likely to be within the above range.

  In the electrophotographic carrier, the core material is preferably Mn—Mg—Sr ferrite particles.

  According to such a configuration, even when image formation is performed over a long period of time, higher image density can be maintained, and occurrence of fogging can be further suppressed. This is because the Mn—Mg—Sr-based ferrite particles have high saturation magnetization and the ratio [(S × r × D) / 3] of the carrier tends to be within the above range. Conceivable.

  In addition, the electrophotographic carrier includes: a developing tank that contains a two-component developer that includes toner and a carrier; and a replenishing unit that replenishes the developing tank with a replenishing developer that includes toner and a carrier. The carrier is preferably used as a carrier contained in each of the two-component developer and the replenishment developer.

  According to such a configuration, by using the electrophotographic carrier as a carrier contained in each of the two-component developer and the replenishment developer, high image density can be maintained and occurrence of fogging and the like can be suppressed. The effect of being able to be achieved can be sufficiently exhibited even when image formation is performed for a longer period of time. That is, a high-quality image can be formed over a longer period.

  This is presumed to be due to the following.

  First, an image forming apparatus including a developing tank that contains a two-component developer including toner and a carrier and a replenishing unit that replenishes the developing tank with a replenishing developer that includes toner and a carrier, that is, a trickle developing system is applied. Since the image forming apparatus replenishes not only the toner but also the carrier, it is considered that the deterioration of the carrier can be suppressed.

  However, even in such an image forming apparatus, when image formation is performed, a portion where toner is consumed in the developing tank, a portion where toner is not consumed and the toner density is maintained, and a replenishment developer are included. It is considered that a replenished portion or the like is generated, and a difference in toner density occurs in the developing tank. Then, as in the case of using a conventional carrier, when the difference in developer fluidity tends to occur depending on the toner concentration, stagnation tends to occur in the developing tank. That is, it is considered that the developer having a high toner concentration stays in the developing tank. In such a state, even if the developer tank is replenished with the replenishment developer, the developer contained in the replenishment developer that has been relatively replenished in the developer tank is contained in the replenishment developer. It seems that there is a tendency that it is difficult to mix uniformly. In such a situation, the deteriorated carrier tends to stay in the developing tank, and the fresh carrier contained in the supplied replenishment developer tends to be discharged.

  On the other hand, it is considered that the developer obtained by using the carrier is unlikely to have a difference in fluidity depending on the toner concentration. Therefore, it is considered that the carrier contained in the supplied replenishment developer is likely to be uniformly mixed with the developer that is in the developing tank and contains a relatively large amount of deteriorated carrier.

  Therefore, by using the carrier as a carrier contained in each of the two-component developer and the replenishment developer, it is possible to suppress the occurrence of developer stagnation in the developing tank, and the advantage of the trickle development method. It is thought that can be fully demonstrated. Therefore, it is considered that a high-quality image can be formed over a longer period.

  In addition, a method for producing an electrophotographic carrier according to another aspect of the present invention includes a heat treatment step of heat-treating a core material, and a coating step of coating a resin layer on a surface of the heat-treated core material, The electrophotographic carrier satisfies the following formula (3).

1 ≦ (S × r × D) /3≦1.5 (3)
In the formula (3), S represents the BET specific surface area (m ² / g) of the electrophotographic carrier, r represents the average particle radius (m) of the electrophotographic carrier, and D represents The density (g / m ³ ) of the electrophotographic carrier is shown.

  According to such a configuration, even when image formation is performed for a long period of time, high image density can be maintained, occurrence of fogging, and the like can be suppressed, and thus high-quality images can be formed over a long period of time. Carrier can be easily manufactured.

  This is considered to be because the core material approaches a true sphere by heat-treating the core material in the heat treatment step. And it is thought that the carrier for electrophotography which satisfy | fills said Formula (3) can be manufactured by coat | covering the resin layer to the core material which approached the true sphere at the said coating process. And, since the obtained electrophotographic carrier satisfies the formula (3), for the reasons described above, even when image formation is performed over a long period of time, high image density can be maintained, occurrence of fog, etc. can be suppressed, Therefore, it is considered that a high-quality image can be formed over a long period of time.

  In the method for producing an electrophotographic carrier, the heat treatment step is preferably a step of blowing hot air onto the core material in the presence of silica particles.

  According to such a configuration, an electrophotographic carrier capable of forming a high-quality image over a long period of time can be more easily manufactured.

  This is considered to be due to the ability to easily form a core material approaching a true sphere. Moreover, it is considered that the reason why the core material approaching the true sphere can be easily formed is as follows. First, in the said heat processing process, it is thought that it disperses | distributes in gas in the state which the surface softened by spraying a hot air on a core material. Then, it is considered that the presence of silica particles causes the core materials whose surfaces are softened to collide with each other without agglomeration, and to bring the shape closer to a true sphere.

  A developer according to another embodiment of the present invention contains the electrophotographic carrier and a toner.

  According to such a configuration, even when image formation is performed for a long period of time, a developer that can maintain a high image density and can suppress the occurrence of fogging and the like, and thus can form a high-quality image for a long period of time. Can be provided.

  The image forming apparatus includes: a developing tank that stores a two-component developer including a toner and a carrier; and a replenishing unit that replenishes the developing tank with a replenishing developer including a toner and a carrier. It is preferably used as a two-component developer and the replenishment developer.

  According to such a configuration, by using the developer as the two-component developer and the replenishment developer, it is possible to maintain the high image density and to suppress the occurrence of fogging for a longer period of time. Even if image formation is performed over a wide range, it can be sufficiently exerted. That is, a high-quality image can be formed over a longer period. This is considered to be due to the fact that the stagnation of the developer in the developing tank can be suppressed and the advantages of the trickle development method can be fully exhibited for the reasons described above. Therefore, it is considered that a high-quality image can be formed over a longer period.

  According to the present invention, even when image formation is performed over a long period of time, a high image density can be maintained, occurrence of fogging and the like can be suppressed, and thus a high-quality image can be formed over a long period of time. Can be provided. Also provided are a method for producing the electrophotographic carrier and a developer containing the electrophotographic carrier.

6 is a graph schematically showing a relationship between factors relating to the shape of the carrier according to the present embodiment and the charge amount of the toner separated from the developer containing the carrier. 1 is a schematic cross-sectional view showing an overall configuration of an image forming apparatus used in the present embodiment. FIG. 2 is an enlarged schematic cross-sectional view showing a developing device provided in the image forming apparatus used in the present embodiment and its periphery. It is a conceptual diagram for explaining development by a developing device provided in the image forming apparatus used in the present embodiment. FIG. 5 is a schematic cross-sectional view showing the agitating / conveying member and its surroundings as seen from a cutting plane line VV in the developing device shown in FIG.

  Hereinafter, although the embodiment concerning the present invention is described, the present invention is not limited to these.

[Electrophotographic carrier]
The electrophotographic carrier according to the present embodiment includes a core material and a resin layer that covers the core material, and satisfies the following formula (4).

1 ≦ (S × r × D) /3≦1.5 (4)
S represents a BET specific surface area (m ² / g) of the electrophotographic carrier, r represents an average particle radius (m) of the electrophotographic carrier, and D represents the electrophotographic carrier. The density (g / m ³ ) is indicated. The average particle radius r of the electrophotographic carrier is half the volume average particle diameter, and the density of the electrophotographic carrier is true specific gravity (true density).

  By using such an electrophotographic carrier, high image density can be maintained even when image formation is performed over a long period of time, and occurrence of fogging can be suppressed. That is, a high-quality image can be formed over a long period of time.

  This is presumed to be due to the following.

  First, (S × r × D) / 3 is considered to indicate the ratio of the BET specific surface area of the carrier to the specific surface area when the carrier is assumed to be a true sphere, as will be described later. That is, the closer the ratio [(S × r × D) / 3] is to 1, the smoother the surface of the carrier is, the closer the shape is to a true sphere, and the smaller the specific surface area, which is the surface area per unit mass. It is thought to show. Further, as the ratio [(S × r × D) / 3] is farther from 1, the surface of the carrier is more uneven, the carrier has a elliptical cross section, etc. This is considered to indicate that the specific surface area becomes large.

  FIG. 1 is a graph schematically showing the relationship between factors relating to the shape of the carrier according to the present embodiment and the charge amount of the toner separated from the developer containing the carrier. Here, the factor relating to the shape of the carrier is the ratio [(S × r × D) / 3]. In FIG. 1, the vertical axis represents the charge amount (Q / M) of the toner separated from the developer in the developing tank after image formation over a long period, and the horizontal axis represents the ratio [(( S × r × D) / 3].

  First, from the tendency of the region having a relatively small ratio [(S × r × D) / 3] shown in FIG. 1, when the specific surface area of the carrier is large, that is, the ratio [(S × r × D) / 3. ] Is large, the charge amount of the toner separated from the developer containing the carrier tends to increase. This is considered to be because the contact area between the toner and the carrier increases, and the charge imparting performance to the toner is enhanced.

  On the other hand, from the tendency of the region having a relatively large ratio [(S × r × D) / 3] shown in FIG. 1, if the specific surface area of the carrier is too large, it is considered that the charge imparting performance with respect to the toner is lowered. This is considered to be because the fluidity of the developer tends to be lowered when the toner concentration is increased. In this case, it is considered that the developer having a high toner concentration does not flow and stays in the developing device, and the developer having a low toner concentration is preferentially consumed. Therefore, it is considered that it tends to be difficult to achieve a suitable image density. That is, if the ratio [(S × r × D) / 3] is too large, it may be difficult to achieve a suitable image density.

  The ratio [(S × r × D) / 3] being 1 means that the specific surface area when the carrier is assumed to be a true sphere and the ratio of the BET specific surface area of the carrier are the same value. Indicates. Therefore, since it is difficult to make the ratio [(S × r × D) / 3], which is 1 or less, 1 is the lower limit.

  From these facts, by making the ratio [(S × r × D) / 3] within the above range, the carrier has excellent charge imparting performance to the toner and changes in fluidity when used as a developer. It is considered that both can be achieved together. Therefore, by setting the ratio [(S × r × D) / 3] within the above range, high image density can be maintained even when image formation is performed over a long period of time, and occurrence of fogging can be suppressed. Therefore, it is considered that a high-quality image can be formed over a long period of time.

  In the case of a general carrier, this ratio [(S × r × D) / 3] is often about 1.75. When image formation is performed over a long period of time, a high image density can be maintained, It is difficult to sufficiently suppress the occurrence of fogging.

  Further, as described above, when the ratio [(S × r × D) / 3] is 1 or more and less than 1.5, an effect of forming a high-quality image over a long period of time can be exhibited. It is preferable at a point and it is more preferable that it is 1.15-1.35.

The BET specific surface area S of the electrophotographic carrier is not particularly limited as long as the above formula (4) is satisfied, but is preferably 0.03 to 0.06 m ² / g.

The average particle radius r of the electrophotographic carrier is not particularly limited as long as the above formula (4) is satisfied, but is preferably 1.5 × 10 ^{−5 to} 5 × 10 ⁻⁵ m (15 to 50 μm). .

The density D of the electrophotographic carrier is not particularly limited as long as the above formula (4) is satisfied, but is preferably 4.2 × 10 ^{6 to} 4.6 × 10 ⁶ g / m ³ .

  Next, the ratio [(S × r × D) / 3] of the BET specific surface area of the carrier to the specific surface area assuming that the carrier is a true sphere will be described.

  First, the BET specific surface area S of the carrier can be measured using, for example, a fully automatic BET specific surface area measuring device.

  Actually, the BET specific surface area is calculated based on the following formula (5) and the following formula (6) by measuring the adsorption amount Vm of the monomolecular layer with respect to the carrier using a fully automatic BET specific surface area measuring device or the like. It is calculated by.

Total = (Vm × N × Acs) × M0 (5)
S = Total / W (6)
Here, Total represents the total surface area (m ² ) of the carrier, Vm represents the monomolecular layer adsorption amount (−), N represents the Avogadro number, and Acs represents the adsorption cross section (m ² ). , M0 represents the molecular weight (−), S represents the BET specific surface area (m ² / g), and W represents the mass (g) of the carrier.

  Then, the ratio [(S × r × D) / 3] is calculated from the measured BET specific surface area as follows.

  First, assuming that the carrier is a true sphere, the volume Vc of one carrier particle, the mass Wc of one carrier particle, the number Nc in the carrier 1g, the specific surface area of the carrier (surface area per 1 g) S0 are as follows: It is shown like Formula (7)-(10).

Vc = 4/3 × πr ³ (7)
Wc = D × Vc = 4D / 3 × πr ³ (8)
Nc = 1 / Wc = 1 / (4D / 3 × πr ³ ) = 3 / 4Dπr ³ (9)
S0 = 4πr ² × Nc = 4πr ² × 3 / 4Dπr ³ = 3 / rD (10)
Note that Vc represents the volume (m ³ ) of one carrier particle assuming that the carrier is a true sphere, r represents the average particle radius (m) of the carrier, and Wc is the true sphere of the carrier. The mass (g) of one carrier particle when assumed to be present, D represents the true density (true specific gravity) of the carrier (g / m ³ ), and Nc represents the true sphere of the carrier The number of the carriers in 1 g of the carrier is shown, and S0 represents the specific surface area of the carrier (surface area per 1 g) (m ² / g) when the carrier is assumed to be a true sphere.

  From the above formula, the ratio R [(S × r × D) / 3] of the BET specific surface area of the carrier with respect to the specific surface area when the carrier is assumed to be a true sphere is shown as the following formula (11). It is.

R = S / S0 = S / (3 / rD) = SrD / 3 (11)
From this, (S × r × D) / 3 is considered to indicate the ratio of the BET specific surface area of the carrier to the specific surface area when the carrier is assumed to be a true sphere, as described above. That is, the closer the ratio [(S × r × D) / 3] is to 1, the smoother the surface of the carrier is, the closer the shape is to a true sphere, and the smaller the specific surface area, which is the surface area per unit mass. It is thought to show. Further, as the ratio [(S × r × D) / 3] is farther from 1, the surface of the carrier is more uneven, the carrier has a elliptical cross section, etc. This is considered to indicate that the specific surface area becomes large.

  The average particle radius r of the carrier is a half value of the volume average particle diameter, and can be measured using a general particle size meter. Specifically, it can be measured using, for example, a laser diffraction / scattering particle size distribution measuring apparatus (LA-700 manufactured by Horiba, Ltd.).

  The true density (true specific gravity) D of the carrier can be measured by, for example, a pycnometer method or the like. Specifically, for example, it can be measured by the following method. First, about 50 g of a carrier that is a measurement object is weighed. The weighed carrier is put into a graduated cylinder containing about 50 ml of pure water and a small amount of surfactant (about 0.5 ml). And the volume of a carrier is measured from the water level change. From the measured volume and mass of the carrier, the true specific gravity of the carrier is calculated.

  The BET specific surface area S of the carrier is a specific surface area measured by the BET method, and can be measured using, for example, a fully automatic BET specific surface area measuring device. Specifically, it can be measured using, for example, a fully automatic BET specific surface area measuring device (Macsorb HM Model-1208 manufactured by Mountec Co., Ltd.).

  The core material of the carrier is not particularly limited as long as it can be used as a core material of an electrophotographic carrier, that is, a so-called carrier core material. Specifically, for example, particles containing a magnetic metal such as iron, cobalt, nickel, and the like can be given. Each of these magnetic metals may be contained alone or in combination of two or more. Moreover, these particles may contain rare earth metals and the like. More specifically, for example, manganese-zinc ferrite (Mn—Zn ferrite) particles, nickel-zinc ferrite (Ni—Zn ferrite) particles, manganese-magnesium ferrite (Mn—Mg ferrite) particles, Ferrite particles such as lithium-based ferrite (Li-based ferrite) particles, copper-zinc-based ferrite (Cu-Zn-based ferrite) particles, and manganese-magnesium-strontium-based ferrite (Mn-Mg-Sr-based ferrite) particles, hematite particles, And magnetite particles. Among these, Mn—Mg—Sr ferrite particles are preferable. When Mn—Mg—Sr ferrite particles are used as the core material, a higher image density can be maintained even when image formation is performed over a long period of time, and the occurrence of fogging can be further suppressed. This is because the Mn—Mg—Sr-based ferrite particles have high saturation magnetization and the ratio [(S × r × D) / 3] of the carrier tends to be within the above range. Conceivable.

  Moreover, it is preferable that the average particle radius of the said core material is 15-50 micrometers, and it is preferable that it is 15-30 micrometers. Even if the core material is too small or too large, when image formation is performed over a long period of time, it may not be possible to maintain high image density or sufficiently suppress the occurrence of fogging. This is considered to be due to the fact that the ratio [(S × r × D) / 3] of carriers may be difficult to be within the above range. Therefore, if the average particle radius of the core material is within the above range, it is considered that higher image density can be maintained even when image formation is performed over a long period of time, and occurrence of fogging can be further suppressed. This is considered because the ratio [(S × r × D) / 3] of the carrier tends to be within the above range. The average particle radius of the core material is approximately the same value as the average particle radius of the carrier, and can be measured by the same method.

  The resin layer is not particularly limited as long as it can be used as an electrophotographic carrier by covering the surface of the carrier core material. Specific examples of the resin layer include a layer containing a fluorine-based resin such as polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, and perfluorooctylethyl acrylate-methyl methacrylate copolymer. . That is, the resin layer formed by apply | coating and drying the surface coating agent containing the said fluororesin on the surface of the said carrier core material is mentioned. When the resin layer is a layer containing such a fluororesin, a higher image density can be maintained even when image formation is performed over a long period of time, and the occurrence of fogging can be further suppressed. This is considered to be due to the effect of suppressing the adhesion of the toner component to the surface of the carrier.

  The electrophotographic carrier preferably has the following relationship in fluidity of the mixture (developer) when mixed with toner. Here, the toner may be a general toner, and examples thereof include a toner described later. Specifically, the fluidity of the mixture obtained by mixing the electrophotographic carrier and the toner when the concentration of the toner with respect to the electrophotographic carrier is 5% by mass is FR (5%). Furthermore, the fluidity of the mixture obtained by mixing the electrophotographic carrier and the toner when the toner concentration with respect to the electrophotographic carrier is 10% by mass is FR (10%). It is preferable that the following formula (12) is satisfied.

1 ≦ FR (10%) / FR (5%) ≦ 1.3 (12)
If FR (10%) is too large with respect to FR (5%), when image formation is performed over a long period of time, high image density may not be maintained, and fogging may not be sufficiently suppressed. There is. This is considered to be due to the fact that the fluidity when the toner concentration is low is too higher than the fluidity when the toner concentration is high, and the developer having a low toner concentration is preferentially consumed.

  Therefore, by using an electrophotographic carrier in which the relationship between FR (5%) and FR (10%) satisfies the above formula (12), a higher image density can be maintained even when image formation is performed over a long period of time. The occurrence of fogging can be further suppressed. This is considered to be due to the following. First, it is considered that the change in the fluidity of the developer due to the change in the toner density becomes small. Therefore, it is considered that the phenomenon that the developer having a low toner concentration is consumed preferentially can be further suppressed. From this, it is considered that even when image formation is performed over a long period of time, higher image density can be maintained, and occurrence of fogging can be further suppressed.

  The flow rate ratio, for example, FR (10%) / FR (5%) is, for example, a constant amount of powder (here, a mixture of toner and carrier) injected into a fixed-shaped funnel, It is the ratio of the required time when it is discharged from. Further, when the fluidity is low, the fluidity is high, and when the fluidity is high, the fluidity is low.

  Specifically, for example, it can be measured as follows.

  First, 50 g each of a mixture having a toner concentration of 10% by mass and a mixture having a toner concentration of 5% by mass is weighed. Then, using a set of equipment such as a funnel defined in JIS-Z2502, the time required for injecting each mixture into the funnel and discharging it from the bottom of the funnel was measured three times, and the average value was calculated. calculate. By correcting the average value with the funnel eigenvalue, the fluidity of the mixture with each toner concentration can be calculated. Then, the fluidity ratio is calculated.

  The electrophotographic carrier can be used by mixing with a toner described later. What is obtained by mixing with this toner may be used as a two-component developer of an image forming apparatus to which a two-component developing system is applied. In an image forming apparatus to which a so-called trickle developing system is applied, a two-component developer is used. And as a replenishing developer. In other words, the electrophotographic carrier is preferably used as a carrier contained in each of the two-component developer and the replenishment developer in an image forming apparatus to which a trickle developing method described later is applied. More specifically, the electrophotographic carrier includes a developing tank that contains a two-component developer including toner and a carrier, and a replenishing unit that replenishes the developing tank with a replenishing developer that includes toner and a carrier. The image forming apparatus is preferably used as a carrier contained in each of the two-component developer and the replenishment developer. Thus, by using the electrophotographic carrier as a carrier contained in each of the two-component developer and the replenishment developer, it is possible to maintain a high image density and to suppress the occurrence of fogging. Even when image formation is carried out over a longer period, it can be sufficiently exerted. That is, a high-quality image can be formed over a longer period.

  This is presumed to be due to the following.

  First, an image forming apparatus including a developing tank that contains a two-component developer including toner and a carrier and a replenishing unit that replenishes the developing tank with a replenishing developer that includes toner and a carrier, that is, a trickle developing system is applied. Since the image forming apparatus replenishes not only the toner but also the carrier, it is considered that the deterioration of the carrier can be suppressed.

  However, even in such an image forming apparatus, when image formation is performed, a portion where toner is consumed in the developing tank, a portion where toner is not consumed and the toner density is maintained, and a replenishment developer are included. It is considered that a replenished portion or the like is generated, and a difference in toner density occurs in the developing tank. Then, as in the case of using a conventional carrier, when the difference in developer fluidity tends to occur depending on the toner concentration, stagnation tends to occur in the developing tank. That is, it is considered that the developer having a high toner concentration stays in the developing tank. In such a state, even if the developer tank is replenished with the replenishment developer, the developer contained in the replenishment developer that has been relatively replenished in the developer tank is contained in the replenishment developer. It seems that there is a tendency that it is difficult to mix uniformly. In such a situation, the deteriorated carrier tends to stay in the developing tank, and the fresh carrier contained in the supplied replenishment developer tends to be discharged.

  On the other hand, it is considered that the developer obtained by using the carrier is unlikely to have a difference in fluidity depending on the toner concentration. Therefore, it is considered that the carrier contained in the supplied replenishment developer is likely to be uniformly mixed with the developer that is in the developing tank and contains a relatively large amount of deteriorated carrier.

  Therefore, by using the carrier as a carrier contained in each of the two-component developer and the replenishment developer, it is possible to suppress the occurrence of developer stagnation in the developing tank, and the advantage of the trickle development method. It is thought that can be fully demonstrated. Therefore, it is considered that a high-quality image can be formed over a longer period.

  The toner content in the two-component developer with respect to 100 parts by mass of the carrier is preferably 3 to 20 parts by mass, and more preferably 5 to 15 parts by mass. That is, the so-called toner concentration (T / C) is preferably 3 to 20% by mass, and more preferably 5 to 15% by mass. If the toner density is too low, the image density tends to be too thin. On the other hand, when the toner concentration is too high, toner scattering occurs in the developing device, and there is a possibility that the toner adheres to undesired spots on the transfer paper or transfer paper.

  Unlike the two-component developer, the replenishment developer has a higher toner content than the carrier. That is, the replenishment developer replenishes toner to the developing tank and replenishes a small amount of carrier. Specifically, the content of the carrier is preferably 1 to 20 parts by mass and more preferably 1 to 10 parts by mass with respect to 100 parts by mass of the toner. If the carrier content is too low, there is a possibility that the effect of sufficiently suppressing the deterioration in the performance of the carrier that can be exhibited over a long period of time cannot be sufficiently exhibited by replenishing the carrier when replenishing the toner. . In other words, there is a possibility that the effect of using the trickle development method cannot be sufficiently exhibited. Therefore, there is a possibility that the lifetime of the image forming apparatus cannot be sufficiently achieved. On the other hand, if the carrier content is too high, the carrier may be segregated before being supplied to the developing tank, that is, in the developer supply container. In addition, if the agitation in the developer supply container is increased in order to prevent this segregation, the carrier may be deteriorated. Therefore, by setting the carrier content of the replenishment developer within the above range, a higher quality image can be formed over a longer period.

  The method for producing the electrophotographic carrier is not particularly limited as long as it includes a core material and a resin layer covering the core material and can satisfy the formula (4). Specifically, a manufacturing method including a heat treatment step for heat-treating the core material and a coating step for covering the surface of the heat-treated core material with a resin layer, wherein the electrophotographic carrier satisfies the above formula (4), etc. Is mentioned. By doing so, the electrophotographic carrier can be easily manufactured.

  This is considered to be because the core material approaches a true sphere by heat-treating the core material in the heat treatment step. And it is thought that the carrier for electrophotography which satisfy | fills said Formula (4) can be manufactured by coat | covering the resin layer with the core material which approached the true sphere at the said coating | coated process. And, since the obtained electrophotographic carrier satisfies the formula (4), for the reasons described above, even when image formation is performed over a long period of time, high image density can be maintained, occurrence of fog, etc. can be suppressed, Therefore, it is considered that a high-quality image can be formed over a long period of time.

  The heat treatment step is not particularly limited as long as it is a step of heat treating the core material. Specifically, the process etc. which spray a hot air on a core material are mentioned, for example. When hot air is blown onto the core material, it is preferable that not only the core material but also silica particles exist. That is, the heat treatment step is preferably a step of blowing hot air onto the core material in the presence of silica particles from the viewpoint of easier production of the electrophotographic carrier. This is considered to be because the core material close to a true sphere can be easily formed by blowing hot air on the core material in the presence of silica particles. Moreover, it is considered that the reason why the core material approaching the true sphere can be easily formed is as follows. First, in the said heat processing process, it is thought that it disperses | distributes in gas in the state which the surface softened by spraying a hot air on a core material. Then, it is considered that the presence of silica particles causes the core materials whose surfaces are softened to collide with each other without agglomeration, and to bring the shape closer to a true sphere. Moreover, it is thought that the core material obtained by the process which sprays a hot air on a core material in presence of a silica particle has the silica particle adhered to the surface. If such a core material has silica particles attached to the surface, the ratio [(S × r × D) / 3] of the carrier is likely to be within the above range.

  Moreover, the said coating | covering process will not be specifically limited if it is a process which can coat | cover a resin layer on the surface of the said heat-processed core material. Specific examples include a method of applying and drying a resin constituting the resin layer, for example, a surface coating agent containing the fluororesin on the surface of the heat-treated core material.

[Developer]
The electrophotographic carrier is used as a developer together with the toner. That is, the developer contains toner and the electrophotographic carrier. When such a developer is used, since the electrophotographic carrier is included, even when image formation is performed over a long period of time, a high image density can be maintained, and occurrence of fogging can be suppressed. A high-quality image can be formed.

  The developer may be used in a general two-component development type image forming apparatus, but may be used as a two-component developer and a replenishment developer used in an image forming apparatus to which a so-called trickle development method is applied. Is preferred. That is, the image forming apparatus includes: a developing tank that contains a two-component developer containing toner and carrier as the developer; and a replenishing unit that replenishes the developing tank with a replenishing developer containing toner and carrier. It is preferably used as a two-component developer and the replenishment developer. By doing so, the effects of maintaining a high image density and suppressing the occurrence of fogging and the like can be sufficiently exhibited even when image formation is performed for a longer period of time. That is, a high-quality image can be formed over a longer period. This is considered to be due to the fact that the stagnation of the developer in the developing tank can be suppressed and the advantages of the trickle development method can be fully exhibited for the reasons described above. Therefore, it is considered that a high-quality image can be formed over a longer period.

  Further, the toner contained in the developer is not particularly limited. Specific examples include the following toners. Examples of the toner include toner including toner base particles containing a binder resin and a colorant, and inorganic fine particles added externally to the toner base particles.

<Toner base particles>
The toner base particles are not particularly limited as long as the toner base particles can be used as toner base particles. Moreover, as the particle diameter, specifically, for example, the volume average particle diameter is preferably 4.5 to 9 μm.

(Binder resin)
The binder resin can be used without particular limitation as long as it is conventionally used as a binder resin for toner base particles. Specifically, for example, polystyrene resins such as styrene-acrylic resins and styrene-butadiene resins; acrylic resins; olefin resins such as polyethylene resins and polypropylene resins; vinyl chloride resins; polyester resins; polyamides Polyurethane resin; polyvinyl alcohol resin; vinyl ether resin; N-vinyl resin and the like. Among these, polyester resins are preferably used because they have a relatively low softening point, excellent low-temperature fixability, and a wide non-offset temperature range. Moreover, as said binder resin, each said binder resin may be used independently, and may be used in combination of 2 or more type.

  Examples of the polyester-based resin include those obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component. Moreover, the following are mentioned as a component used when synthesize | combining a polyester-type resin.

  The alcohol component is not particularly limited as long as it can be used as an alcohol for synthesizing a polyester resin. In addition, the alcohol component needs to contain an alcohol having two or more hydroxyl groups in the molecule (a divalent or higher alcohol). Specific examples of the divalent alcohol among those used as the alcohol component include, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4- Butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol Diols such as bisphenol A, hydrogenated bisphenol A, bisphenols such as polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A, and the like. Further, among the alcohols used as the alcohol component, as the trivalent or higher alcohol, specifically, for example, sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dithiol Pentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, tri Examples include methylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene and the like. Moreover, as said alcohol component, said each component may be used independently and may be used in combination of 2 or more type.

  The carboxylic acid component is not particularly limited as long as it can be used as a carboxylic acid for synthesizing a polyester resin. The carboxylic acid component includes not only carboxylic acids but also acid anhydrides and lower alkyl esters of carboxylic acids. And as said carboxylic acid component, it is necessary to contain the carboxylic acid (divalent or more carboxylic acid) which has 2 or more of hydroxyl groups in the molecule | numerator of carboxylic acid. Specific examples of the divalent carboxylic acid used as the carboxylic acid include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and cyclohexanedicarboxylic acid. Examples include acids, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, alkyl succinic acid, and alkenyl succinic acid. Examples of the alkyl succinic acid include n-butyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid, and the like. Examples of the alkenyl succinic acid include n-butenyl succinic acid and isobutyl succinic acid. , Isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, isododecenyl succinic acid and the like. Further, among the carboxylic acids used as the carboxylic acid, the trivalent or higher carboxylic acid specifically includes, for example, 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid. Acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2 -Methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, empole trimer acid, etc. Can be mentioned. Moreover, as said carboxylic acid component, said each component may be used independently and may be used in combination of 2 or more type.

  The polystyrene resin may be a styrene homopolymer or a copolymer with another copolymerizable monomer copolymerizable with styrene. Examples of the copolymerizable monomer include p-chlorostyrene; vinyl naphthalene; olefinic hydrocarbons (alkene) such as ethylene, propylene, butylene, and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide, and vinyl fluoride; vinyl acetate. Vinyl esters such as vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, 2-chloroethyl acrylate Acrylic esters such as phenyl acrylate and methyl α-chloroacrylate; methacrylic esters such as methyl methacrylate, ethyl methacrylate and butyl methacrylate; acrylics such as acrylonitrile, methacrylonitrile and acrylamide Derivatives; Vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone, and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl pyrrole N-vinyl compounds, such as den, etc. are mentioned. Moreover, as said copolymerization monomer, said each monomer may be used independently and may be used in combination of 2 or more type.

  As the binder resin, it is preferable to use the thermoplastic resin as described above from the viewpoint of fixability, but it is not necessary to use only the thermoplastic resin, and a crosslinking agent or a thermosetting resin is combined with the thermoplastic resin. May be used. By introducing a partially crosslinked structure into the binder resin as described above, it is possible to improve the offset resistance while suppressing a decrease in fixability at the time of fixing the toner onto the paper.

  Specific examples of the thermosetting resin include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, and cyclic aliphatic type epoxy resins. And cyanate resins such as cyanate resins and cyanate resins. These may be used alone or in combination of two or more.

(Coloring agent)
As the colorant, a known pigment or dye can be used so as to obtain a desired color as the toner. Specifically, for example, the following colorants may be mentioned depending on the color.

  Examples of the black pigment include carbon black such as acetylene black, lamp black, and aniline black. Examples of yellow pigments include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, and Benzidine Yellow. GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake, C.I. I. And CI Pigment Yellow 180. Examples of the orange pigment include reddish yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, indanthrene brilliant orange RK, benzidine orange G, indanthrene brilliant orange GK and the like. As red pigments, Bengala, cadmium red, red lead, mercury cadmium sulfide, permanent red 4R, risor red, pyrazolone red, watching red calcium salt, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, Brilliant Carmine 3B, C.I. I. Pigment red 238 and the like. Examples of purple pigments include manganese purple, fast violet B, and methyl violet lake. Examples of blue pigments include bitumen, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, phthalocyanine blue partially chlorinated, first sky blue, induslen blue BC, C.I. I. And CI Pigment Blue 15: 3 (copper phthalocyanine blue pigment). Examples of the green pigment include chrome green, chromium oxide, pigment green B, malachite green lake, and final yellow green G. Examples of white pigments include zinc white, titanium oxide, antimony white, zinc sulfide, barite powder, barium carbonate, clay, silica, white carbon, talc, and alumina white. For example, as a colorant for cyan toner, C.I. I. Pigment Blue 15: 3 (copper phthalocyanine blue pigment) is preferred. Examples of the dye include acid violet.

  Although it does not specifically limit as content of the said coloring agent, In order to achieve a suitable image density, it is preferable that it is 1-10 mass parts with respect to 100 mass parts of said binder resin.

(wax)
The toner base particles generally contain a wax in order to improve fixability and offset property.

  The wax can be used without particular limitation as long as it is conventionally used as a wax for toner base particles. Preferable examples include olefin waxes such as polyethylene wax and polypropylene wax, fluororesin waxes such as polytetrafluoroethylene wax, Fischer-Tropsch wax, paraffin wax, ester wax, montan wax, and rice wax. These waxes may be used alone or in combination of two or more. By adding such wax, offset property and image smearing can be more efficiently prevented.

  Although it does not specifically limit as content of the said wax, It is preferable that it is 1-5 mass parts with respect to 100 mass parts of said binder resins. If the wax content is too small, there is a possibility that offset property, image smearing, and the like cannot be effectively prevented. On the other hand, when the amount of the wax is too large, the toners are fused with each other, and the storage stability may be lowered.

(Charge control agent)
The toner base particles generally contain a charge control agent in order to control chargeability such as frictional chargeability of the toner. The charge control agent is blended in order to remarkably improve the charge level and charge rising characteristics (indicator of whether to charge to a constant charge level in a short time), and to obtain characteristics excellent in durability and stability. . That is, when the toner is positively charged for development, a positively chargeable charge control agent (positively chargeable charge control agent) can be added. When negatively charged for development, the toner is negatively charged. Charge control agent (negatively chargeable charge control agent) can be added.

  The charge control agent is not particularly limited as long as it is conventionally used as a charge control agent for toner base particles.

  Specific examples of the positively chargeable charge control agent include, for example, pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2,4- Triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxa Azine compounds such as triazine, phthalazine, quinazoline, quinoxaline; Azin Fast Red FC, Azin Fast Red 12BK, Azine Violet BO Direct dyes comprising azine compounds such as azine brown 3G, azine light brown GR, azine dark green BH / C, azine deep black EW, and azine black 3RL; nigrosine compounds such as nigrosine, nigrosine salt, nigrosine derivatives; nigrosine BK, nigrosine Examples include acid dyes composed of nigrosine compounds such as NB and nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; quaternary ammonium salts such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride. These may be used alone or in combination of two or more. In particular, the nigrosine compound is optimal for use as a positively chargeable toner from the viewpoint of obtaining a quicker charge rising property.

  Further, as the positively chargeable charge control agent, a quaternary ammonium salt, a carboxylate or a resin or oligomer having a carboxyl group as a functional group can be used. More specifically, a styrene resin having a quaternary ammonium salt, an acrylic resin having a quaternary ammonium salt, a styrene-acrylic resin having a quaternary ammonium salt, a polyester resin having a quaternary ammonium salt, a carboxylic acid Styrene resin with salt, acrylic resin with carboxylate, styrene-acrylic resin with carboxylate, polyester resin with carboxylate, polystyrene resin with carboxyl group, acrylic with carboxyl group Examples thereof include a resin, a styrene-acrylic resin having a carboxyl group, and a polyester resin having a carboxyl group. These may be used alone or in combination of two or more.

  In particular, a styrene-acrylic copolymer resin having a quaternary ammonium salt as a functional group is optimal from the viewpoint that the charge amount can be easily adjusted to a value within a desired range. In this case, preferred acrylic comonomers to be copolymerized with the styrene units include methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, Examples include (meth) acrylic acid alkyl esters such as 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate. As the quaternary ammonium salt, a unit derived from a dialkylaminoalkyl (meth) acrylate through a quaternization step is used. Examples of the derived dialkylaminoalkyl (meth) acrylate include di (amino) ethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, dibutylaminoethyl (meth) acrylate and the like ( Lower alkyl) aminoethyl (meth) acrylate; dimethylmethacrylamide and dimethylaminopropylmethacrylamide are preferably used. Further, hydroxy group-containing polymerizable monomers such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and N-methylol (meth) acrylamide can be used in combination during polymerization.

  As the charge control agent exhibiting negative chargeability, for example, organometallic complexes and chelate compounds are effective. Examples of the chelate compound include aluminum acetylacetonate, iron (II) acetylacetonate, chromium 3,5-di-tert-butylsalicylate, and the like. As the organometallic complex, an acetylacetone metal complex, a salicylic acid metal complex or a salt is preferable, and a salicylic acid metal complex or a salicylic acid metal salt is particularly preferable.

  The content of the charge control agent is preferably 0.5 to 15 parts by mass, more preferably 0.5 to 8 parts by mass with respect to 100 parts by mass of the binder resin. More preferably, it is 5-7 mass parts. If the content of the charge control agent is too small, it may be difficult to stably charge the toner to a predetermined polarity. Therefore, when developing an electrostatic latent image using toner that has become difficult to stably charge the toner to such a predetermined polarity, the image density decreases or the image density decreases. May be difficult to maintain at a constant level. In addition, the charge control agent tends to be poorly dispersed, causing so-called fogging, and the contamination of the photoconductor tends to be severe. On the other hand, when the amount of the charge control agent added is too large, it may cause environmental resistance, in particular, charging failure and image failure under high temperature and high humidity, and may easily cause defects such as photoconductor contamination.

(Production method)
The method for producing the toner base particles is not particularly limited. Specific examples include a pulverization method and a polymerization method. As a method for producing the toner base particles by the pulverization method, for example, it can be produced as follows.

  First, the components constituting the toner base particles such as the binder resin and the colorant are mixed with a mixer or the like. As the mixer, a known one can be used, and examples thereof include a Henschel type mixing device such as a Henschel mixer, a super mixer, and a mechano mill, an ang mill, a hybridization system, and a cosmo system. Among these, a Henschel mixer is preferable.

  Next, the obtained mixture is melt-kneaded with a kneader or the like. A well-known thing can be used as said kneading machine, For example, extruders, such as a twin-screw extruder, a 3 roll mill, a lab blast mill, etc. are mentioned, An extruder is used suitably. Further, the temperature at the time of melt kneading is preferably a temperature that is not lower than the softening point of the binder resin and lower than the thermal decomposition temperature of the binder resin.

  Next, the obtained melt-kneaded product is cooled with a cooler to form a solid, and the solid is pulverized with a pulverizer or the like. A well-known thing can be used as said cooler, For example, a drum flake etc. are mentioned. Also, as the pulverizer, known ones can be used, for example, an airflow pulverizer such as a jet pulverizer (jet mill) that pulverizes using a supersonic jet stream, a mechanical pulverizer such as a turbo mill, Examples thereof include an impact pulverizer, and an airflow pulverizer is preferably used.

  Finally, the obtained pulverized product is classified with a classifier or the like. By classification, excessively pulverized material and coarse powder can be removed, and desired toner base particles can be obtained. As the classifier, known ones can be used, and examples thereof include a wind classifier such as a swirling wind classifier (rotary wind classifier) such as an elbow jet classifier, a centrifugal classifier, and the like. A machine is preferably used.

(External)
The toner may be composed only of toner base particles, but is generally obtained by externally adding inorganic fine particles as external additives to the toner base particles. That is, it is obtained by subjecting the toner base particles to an external addition treatment.

  As the external addition treatment, any conventionally known external addition treatment can be used without limitation. Specifically, for example, an external additive is added to the toner base particles and stirred with a stirrer or the like to attach or fix the external additive to the surface of the toner base particles.

  The inorganic fine particles are not particularly limited as long as they can be used as an external additive for toner. Specific examples include inorganic fine particles such as titanium dioxide particles (titania particles), silicon dioxide particles (silica particles), aluminum oxide particles (alumina particles), zinc oxide particles, and magnetite particles. Among these, titanium dioxide particles, silicon dioxide particles, and aluminum oxide particles are preferable from the viewpoint of excellent fluidity, chargeability, and polishing properties. Moreover, as said external additive, the said external additive may be used independently, and may be used in combination of 2 or more type.

  The amount of the external additive added to the toner base particles is preferably 0.2 to 3 parts by mass with respect to 100 parts by mass of the toner base particles.

  As the stirrer, a conventionally known stirrer can be used without limitation. Specifically, for example, a general stirrer such as a turbine-type stirrer, a Henschel mixer, a supermixer or the like can be used, and a Henschel mixer is preferably used.

  Such a developer is a developer in which the electrophotographic carrier and the toner are mixed at an appropriate ratio, and can be used, for example, in an image forming apparatus described later.

[Image forming apparatus]
The image forming apparatus using the developer is not particularly limited. Specifically, a general two-component developing apparatus may be used, but as described above, an image forming apparatus to which a so-called trickle developing system is applied is preferable. Hereinafter, an image forming apparatus to which the trickle developing method is applied will be described.

  Here, a tandem image forming apparatus will be described as an example of the image forming apparatus. However, any image forming apparatus using an electrophotographic method may be used, and the image forming apparatus is not limited to a tandem image forming apparatus. The type of image forming apparatus will be described by taking a color printer as an example. However, for example, it may be a copying machine, a facsimile machine, a multifunction machine, or the like, and is not limited to a color printer.

  FIG. 2 is a schematic diagram showing the overall configuration of the image forming apparatus 10 according to the embodiment of the present invention. An image forming apparatus 10 according to an embodiment of the present invention performs an image forming process based on image information transmitted from an external device such as a computer. A so-called tandem type image forming apparatus (color printer) 10 is provided. An example will be described.

  As shown in FIG. 2, the image forming apparatus 10 includes a paper feeding unit 12 that feeds paper P and is fed from the paper feeding unit 12. An image forming unit 13 that forms a toner image based on image information on the paper P, and a fixing unit 14 that performs a fixing process for fixing an unfixed toner image formed on the paper P by the image forming unit 13 to the paper P. Is provided. Further, on the upper part of the apparatus main body 11, a paper discharge unit 15 for discharging the paper P subjected to the fixing process by the fixing unit 14 is formed.

  At an appropriate position on the upper surface of the apparatus main body 11, an unillustrated operation panel for inputting an output condition for the paper P is provided. The operation panel is provided with a power key and various keys for inputting output conditions.

  Further, a sheet conveyance path 111 extending in the vertical direction is formed in the apparatus main body 11 at a position on the left side of the image forming unit 13 shown in FIG. A pair of conveying rollers 112 is provided at an appropriate position on the sheet conveying path 111. The paper transport path 111 transports the paper P from the paper feeding unit 12 to the paper discharge unit 15 by the transport roller pair 112, and the paper P being transported passes through the transfer unit and the fixing unit 14 of the image forming unit 13. It is formed to pass.

  The paper feed unit 12 includes a paper feed tray 121, a pickup roller 122, and a paper feed roller pair 123. The paper feed tray 121 is detachably attached to the apparatus main body 11 at a position below the image forming unit 13 in the apparatus main body 11 and stores a sheet bundle in which a plurality of sheets P are stacked. The pickup roller 122 is provided at an upper position on the upstream side of the paper feed tray 121 in the conveyance direction of the paper P, specifically, at an upper left position shown in FIG. The top sheet P is taken out one by one. The paper feed roller pair 123 sends the paper P taken out by the pickup roller 122 to the paper transport path 111. Through these operations, the paper feeding unit 12 feeds the paper P toward the image forming unit 13.

  The paper feeding unit 12 further includes a manual feed tray 124, a pickup roller 125, and a paper feed roller pair 126 that are attached to the right side surface of the apparatus main body 11 shown in FIG. The manual feed tray 124 is for supplying the paper P toward the image forming unit 13 by manual feed operation. The manual feed tray 124 can be stored on the side surface of the apparatus main body 11, and when the paper P is manually fed, as shown in FIG. 2, the manual feed tray 124 is pulled out from the side surface of the apparatus main body 11 to be manually fed. The pickup roller 125 takes out the paper P placed on the manual feed tray 124. The paper P taken out by the pickup roller 125 is sent out to the paper transport path 111 by the paper feed roller pair 126. Through these operations, the paper feeding unit 12 feeds the paper P toward the image forming unit 13.

  The image forming unit 13 forms an image such as a color image on the paper P fed from the paper feeding unit 12 by predetermined image processing. The image forming unit 13 includes a plurality of image forming units 131, an intermediate transfer belt (intermediate transfer member) 132, a primary transfer roller 133, and a secondary transfer roller 134.

  In the present embodiment, the image forming unit 131 is magenta (M), which is sequentially disposed from the upstream side to the downstream side in the rotation direction of the intermediate transfer belt 132 (from the right side to the left side in FIG. 2). Magenta unit 131M using a color developer, cyan unit 131C using a cyan (C) developer, yellow unit 131Y using a yellow (Y) developer, and black (K) developer A black unit 131K using the above is provided. Each unit 131 includes a photosensitive drum 135 as an image carrier, and forms a toner image corresponding to each color on the photosensitive drum 135 based on image information, and performs primary transfer onto the intermediate transfer belt 132.

  In the image forming unit 131, a photosensitive drum 135 as an image carrier is arranged at the center position so as to be rotatable in the direction of an arrow (indicated by an arrow A in FIG. 2). Then, when the position (primary transfer) transferred by the primary transfer roller 133 is set to the most upstream side in the rotation direction of the photosensitive drum 135 around the photosensitive drum 135, the position moves from there to the downstream side. In this order, the cleaning position by the cleaning device 24, the charging position by the charging device 21, the exposure position by the exposure device 22, and the developing position by the developing device 23 are arranged in order.

  The photosensitive drum 135 is for forming a toner image corresponding to each color on the peripheral surface based on image information by charging processing, exposure processing, development processing, charge removal processing, and the like, which will be described later. . The photoconductor drum 135 is not particularly limited as long as it is a photoconductor drum that can be provided in the image forming apparatus, and examples thereof include an organic photoconductor (OPC) drum and an amorphous silicon (a-Si) photoconductor drum. It is done.

  The charging device 21 charges the peripheral surface of the photosensitive drum 135 rotated in the direction of the arrow. The charging device 21 is not particularly limited as long as it is a charging device that can be provided in the image forming apparatus. Specifically, for example, a charging roller equipped with a charging roller, and applying a predetermined charging bias voltage to the charging roller to charge the peripheral surface of the photosensitive drum 135, or a non-contact discharging type charging device is used. Examples include a corotron type and a scorotron type charging device.

  The exposure device 22 irradiates the peripheral surface of the photosensitive drum 135 whose peripheral surface is charged by the charging device 21 with laser light or LED light based on image information, and converts the image information onto the peripheral surface of the photosensitive drum 135. For forming an electrostatic latent image based thereon. The exposure device 22 is not particularly limited as long as it is an exposure device provided in the image forming apparatus. Specifically, an LED head unit, a laser scanning unit (LSU), etc. are mentioned, for example.

  The developing device 23 is for developing the electrostatic latent image formed on the peripheral surface of the photosensitive drum 135 into a toner image. The configuration of the developing device 23 will be described later.

  The cleaning device 24 transfers (primary transfer) the toner image on the peripheral surface of the photosensitive drum 135 to the intermediate transfer belt 132 by the primary transfer roller 133 and then remains on the peripheral surface of the photosensitive drum 135. This is for removing the toner. The peripheral surface of the photosensitive drum 135 from which the toner remaining after the primary transfer is removed by the cleaning device 24 is directed to a charging position by the charging device 21 for a new image forming process. The waste toner removed from the photosensitive drum 135 by the cleaning device 24 passes through a predetermined path and is collected and stored in a toner collection bottle (not shown).

  Further, before the toner is removed by the cleaning device 24, the peripheral surface of the photosensitive drum 135 may be neutralized by a neutralizing device (not shown). By doing so, the toner remaining on the peripheral surface of the photosensitive drum 135 after the primary transfer is suitably removed by the cleaning device 24.

  The intermediate transfer belt 132 is for transferring (primary transfer) a toner image based on image information to the peripheral surface (contact surface) of the plurality of image forming units 131. In other words, in the present embodiment, the intermediate transfer belt 132 is a transfer target that is sandwiched between the photosensitive drum 135 and the primary transfer roller 133 and has a peripheral surface to which a toner image is transferred from the photosensitive drum 135. .

  The intermediate transfer belt 132 is an endless belt-like rotator, and the driving roller 136, the belt support roller 137, and the tension roller 139 so that the circumferential surface side thereof is in contact with the circumferential surface of each photoconductor 135. It is stretched over. Further, the intermediate transfer belt 132 is pressed against each photoconductive drum 135 by each primary transfer roller 133 disposed at a position facing each photoconductive drum 135 via the intermediate transfer belt 132, and the driving roller 136. It is comprised so that it may rotate endlessly by rotational drive. The driving roller 136 is rotationally driven by a driving source such as a stepping motor, and provides a driving force for rotating the intermediate transfer belt 132 endlessly. The belt support roller 137 and the tension roller 139 are rotatably driven rollers that are driven to rotate in accordance with the endless rotation of the intermediate transfer belt 132 by the driving roller 136. These driven rollers 137 and 139 are driven to rotate via the intermediate transfer belt 132 according to the main rotation of the driving roller 136 and support the intermediate transfer belt 132. Further, the tension roller 139 applies tension (tension) to the intermediate transfer belt so that the intermediate transfer belt 132 does not slack. The tension roller 139 is biased by a biasing member such as a spring body, for example, so that the intermediate transfer belt 132 is moved from the back surface (inner periphery side) to the front surface (outer periphery side). The tension is generated by applying a pressing force to the belt 132.

  The primary transfer roller 133 is for primary transfer of the toner image formed on the photosensitive drum 135 to the intermediate transfer belt 132. That is, in this embodiment, the primary transfer roller 133 holds the intermediate transfer belt 132 between the photosensitive drum 135 and the toner image on the circumferential surface of the photosensitive drum 135 to the intermediate transfer belt 132 for primary transfer. It is a transfer part to be made.

  Further, the primary transfer roller 133 is disposed at a position facing each photosensitive drum 135 with the intermediate transfer belt 132 interposed therebetween. The primary transfer roller 133 is provided for each photosensitive drum 135. Further, the primary transfer roller 133 is rotated in accordance with the endless rotation of the intermediate transfer belt 132 while being in contact with the intermediate transfer belt 132. At that time, by applying a primary transfer bias voltage having a polarity opposite to the charging polarity of the toner to each primary transfer roller 133, the toner image formed on each photoconductor drum 135 is changed to each photoconductor drum. Primary transfer is performed on the intermediate transfer belt 132 between the 135 and the corresponding primary transfer rollers 133. As a result, the toner images formed on the respective photoconductive drums 135 are sequentially primary-transferred sequentially in an overcoated state on the intermediate transfer belt 132 that circulates in the direction of an arrow (clockwise in FIG. 2).

  The secondary transfer roller 134 is for transferring (secondary transfer) the toner image on the intermediate transfer belt 132 onto the paper P fed from the paper feeding unit 12. In other words, in the present embodiment, the secondary transfer roller 134 is in contact with the peripheral surface of the intermediate transfer belt 132 to form a nip portion, and the intermediate transfer belt 132 is formed on a sheet P that is a recording medium passing through the nip portion. 2 is a secondary transfer portion for secondary transfer of the toner image on the peripheral surface of the toner.

  The secondary transfer roller 134 is disposed at a position facing the driving roller 136 with the intermediate transfer belt 132 interposed therebetween. Further, the secondary transfer roller 134 is rotated in accordance with the endless rotation of the intermediate transfer belt 132 while being in contact with the intermediate transfer belt 132. At that time, the toner on the peripheral surface of the intermediate transfer belt 132 is secondarily transferred between the secondary transfer roller 134 and the driving roller 136 onto the paper P fed from the paper feeding unit 12. As a result, the toner image based on the image information is transferred onto the paper P in an unfixed state.

  The image forming unit 13 further includes a belt cleaning device 138 at a position downstream of the secondary transfer position in the rotational direction of the intermediate transfer belt 132 and upstream of the primary transfer position in the rotational direction. The belt cleaning device 138 is for cleaning the intermediate transfer belt 132 by removing the toner remaining on the peripheral surface of the intermediate transfer belt 132 after the secondary transfer. The peripheral surface of the intermediate transfer belt 132 cleaned by the belt cleaning device 138 goes to the primary transfer position for a new primary transfer process. The waste toner removed by the belt cleaning device 138 is collected and stored in a toner collection bottle (not shown) through a predetermined path.

  The fixing unit 14 performs a fixing process on the toner image on the paper P that is secondarily transferred by the secondary transfer roller 134. The fixing unit 14 is stretched between a heating roller 141 having an energization heating element as a heating source therein, a fixing roller 142 disposed opposite to the heating roller 141, and the fixing roller 142 and the heating roller 141. The image forming apparatus includes a fixing belt 143 and a pressure roller 144 disposed to face the fixing roller 142 with the fixing belt 143 interposed therebetween.

  The paper P supplied to the fixing unit 14 is heated and pressed by passing through a fixing nip formed between the fixing belt 143 and the pressure roller 144. As a result, the toner image secondarily transferred onto the paper P by the secondary transfer roller 134 is fixed on the paper P. The paper P for which the fixing process has been completed is discharged from a paper discharge unit 15 provided on the top of the apparatus main body 11 by a paper discharge roller pair 152 via a paper conveyance path 111 extending from the upper part of the fixing unit 14. The paper is discharged toward the tray 151.

  The paper discharge unit 15 is formed by recessing the top of the apparatus main body 11, and a paper discharge tray 151 for receiving the discharged paper P is formed at the bottom of the concave portion.

  Next, the developing device 23 will be described with reference to FIGS.

  FIG. 3 is an enlarged schematic cross-sectional view showing the developing device 23 provided in the image forming apparatus 10 according to the embodiment of the present invention and its periphery. FIG. 4 is a conceptual diagram for explaining development by the developing device 23 provided in the image forming apparatus 10 according to the embodiment of the present invention. The photosensitive drum 135, the developing roller 231, the magnetic roller 232, and The positional relationship of the ear cutting blade 235 is different from that in FIG.

  As described above, the developing device 23 is for developing the electrostatic latent image formed on the peripheral surface of the photosensitive drum 135 into a toner image. As shown in FIG. 3, the developing device 23 is provided with a developing roller 231, a magnetic roller 232, and a stirring / conveying member 237 provided in a developing container 236. As shown in FIG. 4, a developing bias voltage applying unit 239 is connected to the developing roller 231, and a toner supply bias voltage applying unit 238 is connected to the magnetic roller 232.

  The developing container 236 is a developing tank that constitutes the outline of the developing device 23 and contains a two-component developer including a carrier and toner. The developing container 236 has an opening 236 a that exposes the developing roller 231 toward the photosensitive drum 135. The developing container 236 is formed with a first transport path 236c and a second transport path 236d that are partitioned by a partition portion 236b. Further, the developing container 236 rotatably holds the developing roller 231, the magnetic roller 232, and the stirring and conveying member 237.

  The developing roller 231 is opposed to each of the photosensitive drum 135 and the magnetic roller 232 and is spaced apart with their opposed peripheral surfaces being close to each other. That is, the developing roller 231 and the photosensitive drum 135 are spaced apart from each other with their peripheral surfaces being close to each other, thereby forming a developing region D for supplying toner to the photosensitive drum 135. Further, the developing roller 231 and the magnetic roller 232 are also arranged apart from each other with their peripheral surfaces close to each other.

  The magnetic roller 232 carries a two-component developer containing toner on the peripheral surface thereof by a magnetic pole member M fixedly disposed therein, and is rotated in that state, whereby the two-component developer is brought to the vicinity of the developing roller 231. Transport. By doing so, the magnetic roller 232 supplies the toner of the two-component developer to the developing roller 231.

  The developing roller 231 carries the toner supplied from the magnetic roller 232 on its peripheral surface and rotates it in that state, thereby conveying the toner to the vicinity of the photosensitive drum 135. By doing so, the electrostatic latent image previously formed on the peripheral surface of the photosensitive drum 135 is visualized (developed) as a toner image.

  The stirring and conveying member 237 includes a first stirring and conveying member (stirring mixer) 234 and a second stirring and conveying member (paddle mixer) 233. The first stirring and conveying member 234 is provided in the first conveying path 236c, and the second stirring and conveying member 233 is provided in the second conveying path 236d.

  The paddle mixer 233 and the agitation mixer 234 have spiral blades and agitate while conveying the two-component developer in opposite directions to charge the toner contained in the two-component developer. Further, the paddle mixer 233 supplies a two-component developer containing charged toner to the magnetic roller 232.

  The ear cutting blade 235 has one end opposed to the peripheral surface of the magnetic roller 232 and regulates the thickness of the two-component developer carried on the magnetic roller 232.

  The magnetic roller 232 includes a roller shaft 232a, a magnetic pole member M, and a nonmagnetic sleeve 232b made of a nonmagnetic material. As described above, the magnetic roller 232 carries the developer supplied by the paddle mixer 233 of the stirring and conveying member 237 and supplies toner to the developing roller 231 from the carried developer. The magnetic pole member M is formed by alternately arranging a plurality of magnets having different outer peripheral magnetic poles formed in a sector fan shape and fixed to the roller shaft 232a by adhesion or the like. The roller shaft 232a is supported by the developing container 236 in a non-rotatable manner within the nonmagnetic sleeve 232b with a predetermined gap between the magnetic pole member M and the nonmagnetic sleeve 232b. The non-magnetic sleeve 232b is rotated in the direction of the arrow (the same direction as the developing roller 231 and the clockwise direction in FIG. 3) by a driving mechanism including a motor and gears (not shown).

  The developing roller 231 includes a fixed shaft 231a, a magnetic pole member 231b, a developing sleeve 231c formed of a nonmagnetic metal material in a cylindrical shape, and the like. The fixed shaft 231a is supported by the developing container 236 so as not to rotate. The magnetic pole member 231b is fixed to the roller shaft 231a by adhesion or the like. The fixed shaft 231a is provided with a predetermined interval between the magnetic pole member 231b and the developing sleeve 231c so that the developing sleeve 231c is rotatable. The developing sleeve 231c is rotated in the direction of the arrow (in the clockwise direction in FIG. 3) by a driving mechanism including a motor and gears (not shown).

  The toner supply bias voltage application unit 238 is for applying a toner supply bias voltage to the magnetic roller 232. By applying the toner supply bias voltage, the toner of the two-component developer conveyed to the vicinity of the developing roller 231 by the magnetic roller 232 is caused to fly to the developing roller 231.

  The development bias voltage application unit 239 is for applying a development bias voltage to the development roller 231. By applying a developing bias voltage, the toner conveyed to the vicinity of the photosensitive drum 135 by the developing roller 231 is caused to fly to the photosensitive drum 135.

  Specifically, development is performed as follows (see FIG. 4).

  The two-component developer 303 containing the toner 301 and the carrier 302 charged by the paddle mixer 233 and the stirring mixer 234 is supplied to the magnetic roller 232. The two-component developer 303 supplied to the magnetic roller 232 is conveyed toward the developing roller 231 by the magnetic roller 232. The two-component developer 303 conveyed by the magnetic roller 232 passes between the earbrush blade 235 and the magnetic roller 232 before being conveyed to the vicinity of the developing roller 231, so that the developer layer The thickness of the is regulated. A potential difference is generated between the developing roller 231 and the magnetic roller 232 by the toner supply bias voltage applied by the toner supply bias voltage application unit 236. Therefore, when the two-component developer 303 whose developer layer thickness is regulated moves to the vicinity of the developing roller 231, only the charged toner 301 moves to the developing roller 231 due to this potential difference. The toner 301 moved to the developing roller 231 becomes a uniform toner layer.

  As the two-component developer 303, for example, a developer containing toner 301 and a carrier 302 is used. Examples of the toner 301 include toner particles including a toner particle containing a binder resin, a colorant, a release agent, and the like, and an external additive externally added to the toner particle. As this toner 301, what is called a non-magnetic toner is preferably used. The carrier 302 is magnetic particles made of ferrite or the like, and is for charging the toner 301.

  A predetermined amount of toner 301 and carrier 302 is filled in advance in the developing container 236 of the developing device 23. The toner 301 is appropriately supplied into the developing container 236 from a supply unit such as a developer supply container (not shown). Further, in the case of the image forming apparatus according to the present embodiment, not only the toner 301 but also the carrier 302 is supplied together with the toner 301 from the supply unit. That is, the replenishment developer including the toner 301 and the carrier 302 is appropriately replenished.

  A potential difference is also generated between the photosensitive drum 135 and the developing roller 231 by the developing bias voltage applying unit 239. Therefore, when the toner on the developing roller 231 moves to the vicinity of the photosensitive drum 135, the toner 301 flies due to this potential difference, and the image portion of the electrostatic latent image formed on the peripheral surface of the photosensitive drum 135. So-called non-magnetic non-contact development is performed. In this way, the developing device 23 can perform development based on the electrostatic latent image.

  The development bias voltage application unit 239 includes an AC power source that applies an AC voltage. That is, the development bias voltage applied by the development bias voltage application unit 239 includes an AC component. The development bias voltage application unit 239 may further include a DC power source that applies a DC voltage. That is, the development bias voltage applied by the development bias voltage application unit 239 may be a superimposed voltage in which an AC component is superimposed on a DC component.

  The toner supply bias voltage application unit 236 includes an AC power source that applies an AC voltage and a DC power source that applies a DC voltage. That is, the toner supply bias voltage applied by the toner supply bias voltage application unit 236 is a superimposed voltage in which an AC component is superimposed on a DC component.

  Next, the stirring and conveying member 237 will be described with reference to FIG. FIG. 5 is a schematic cross-sectional view showing the agitating / conveying member 237 and its periphery as seen from the section line IV-IV in the developing device 23 shown in FIG.

  As described above, the developing container 236 is formed with the first transport path 236c, the second transport path 236d, and the partition portion 236b. The developer container 236 further includes an upstream communication portion 236e, a downstream communication portion 236f, a developer supply port 236g, a developer discharge port 236h, an upstream side wall portion 236i, and a downstream side wall portion 236j. Is formed. In the first transport path 236c, the left side in FIG. 5 is the upstream side, the right side in FIG. 5 is the downstream side, and in the second transport path 236d, the right side in FIG. 5 is the upstream side, and the left side in FIG. . Further, the communication part and the side wall part are referred to as upstream and downstream on the basis of the second transport path 236d.

  The partition part 236b extends in the longitudinal direction of the developing container 236 and partitions the first transport path 236c and the second transport path 236d in parallel. The right end portion in the longitudinal direction of the partition portion 236b forms an upstream communication portion 236e together with the inner wall portion of the upstream side wall portion 236i. On the other hand, the left end portion in the longitudinal direction of the partition portion 236b forms a downstream communication portion 236f together with the inner wall portion of the downstream side wall portion 236j. The developer can circulate in the first conveyance path 236c, the upstream communication portion 236e, the second conveyance path 236d, and the downstream communication portion 236f.

  The developer supply port 236g is an opening provided in the upper part of the developer container 236 for supplying new toner and carrier, that is, a supply developer, into the developer container 236 from a developer supply container (not shown). The developer supply port 236g is disposed on the upstream side (left side in FIG. 5) of the first transport path 236c.

  The developer discharge port 236h is an opening for discharging the developer remaining in the first and second transport paths 236c and 236d due to the supply of the developer. The developer discharge port 236h is provided continuously in the longitudinal direction of the second transport path 236d on the downstream side of the second transport path 236d.

  A first agitating and conveying member 234 is disposed in the first conveying path 236c. A second agitating and conveying member 233 is disposed in the second conveying path 236d.

  The first agitation transport member 234 includes a rotation shaft 234b and a first spiral blade 234a. The first spiral blade 234a is provided integrally with the rotation shaft 234b, and is formed in a spiral shape at a constant pitch in the axial direction of the rotation shaft 234b. The first spiral blade 234a extends to both ends in the longitudinal direction of the first transport path 236c, and is provided to face the upstream and downstream communication portions 236e and 236f. The rotation shaft 234b is rotatably supported by the upstream side wall portion 236i and the downstream side wall portion 236j of the developing container 236.

  The second agitation transport member 233 has a rotation shaft 233b and a second spiral blade 233a. The second spiral blade 233a is provided integrally with the rotation shaft 233b, and is a blade having the same pitch as the first spiral blade 234a in the axial direction of the rotation shaft 233b (opposite phase) with respect to the first spiral blade 234a. It is formed in a spiral shape. Further, the second spiral blade 233 a has a length equal to or longer than the axial length of the magnetic roller 232. Further, the second spiral blade 233a is provided to extend to a position facing the upstream communication portion 236e. The rotation shaft 233b is disposed in parallel with the rotation shaft 234b. The rotating shaft 233b is rotatably supported by the upstream side wall 236i and the downstream side wall 236j of the developing container 236.

  In addition to the second spiral blade 233a, the speed reduction conveyance unit 241, the regulation unit 242, and the discharge blade 243 are integrally disposed on the rotation shaft 233b.

  The decelerating conveyance unit 241 is disposed adjacent to the left side of the second spiral blade 233a and opposed to the downstream side communication unit 236f. Further, the deceleration conveying unit 241 is formed in a spiral shape with a plurality of blades facing in the same direction as the second spiral blade 233a, and has a size equal to or smaller than the outer diameter of the second spiral blade 233a and a pitch of the second spiral blade 233a. It is set smaller than the pitch of the blades 233a. The blade pitch of the decelerating conveyance unit 241 is 1/6 to 1/3 of the pitch of the second spiral blade 233a, and these blades face the opening width in the longitudinal direction of the downstream communication unit 236f. . Note that the blades of the decelerating and conveying unit 241 do not have to face the entire width of the downstream communication unit 236f, but in this case, the blades on the regulation unit 242 side face the opening of the downstream communication unit 236f. It is good.

  With this configuration, when the rotating shaft 233b rotates, the developer is transported relatively quickly in the second transport path 236d by the second spiral blade 233a. On the other hand, since the speed reduction conveyance part 241 has a blade pitch smaller than the pitch of the second spiral blade 233a, it develops more in the second conveyance path 236d where the speed reduction conveyance part 241 is provided than the second spiral blade 233a. The conveying speed of the agent will decrease. Accordingly, the developer to be transported moves in the transport path so as to follow the outer periphery of the blades of the second spiral blade 233a. At this time, if the pitch of the spiral blades is relatively large like the second spiral blade 233a, the developer moves fast while the bulkiness of the developer varies greatly. On the other hand, when the pitch of the spiral blades is relatively small as in the case of the speed reduction conveyance unit 241, the change in the bulk of the developer is small, and the developer moves slowly.

  The restricting unit 242 blocks the developer conveyed downstream in the second conveying path 236d, and conveys the developer that has reached a predetermined amount or more in the deceleration conveying unit 241 to the developer discharge port 236h. Is possible. The restricting portion 242 is formed of a spiral blade provided on the rotation shaft 233b. The restricting portion 242 is formed in a spiral shape with blades facing in the opposite direction to the second spiral blade 233a (in reverse phase). Further, the restricting portion 242 is set to be substantially the same as the outer diameter of the second spiral blade 233a and smaller than the pitch of the second spiral blade 233a. In addition, the restricting portion 242 forms a predetermined amount of gap between the inner wall portion of the developing container 236 such as the downstream side wall portion 236j and the outer peripheral portion of the restricting portion 242. Excess developer is discharged from this gap.

  The rotating shaft 233b extends into the developer discharge port 236h. A discharge blade 243 is provided on the rotation shaft 233b in the developer discharge port 236h. The discharge blade 243 is a spiral blade that faces in the same direction as the second spiral blade 233a. And the discharge blade | wing 243 has a pitch smaller than the 2nd spiral blade | wing 233a, and the outer periphery of a blade | wing is small. Therefore, when the rotating shaft 233b rotates, the discharge blade 243 also rotates. As the discharge blade 243 rotates, the surplus developer that has passed over the regulating portion 242 and has been transported into the developer discharge port 236h is sent to the left side of FIG. It is like that. In addition, the discharge blade 243, the regulating portion 242, the deceleration conveying portion 241, and the second spiral blade 233a are resin-molded integrally with the rotating shaft 233b with a synthetic resin.

  Gears 251 to 254 are disposed on the outer wall of the developing container 236. The gears 251 and 252 are fixed to the rotary shaft 234a. The gear 254 is fixed to the rotating shaft 233b. The gear 253 is rotatably held by the developing container 236 and meshes with the gears 252 and 254.

  Therefore, during development without newly replenishing the developer, when the gear 251 is rotated by a drive source such as a motor, the first spiral blade 234a is rotated together with the rotating shaft 234b. Then, the developer in the first transport path 236c is transported in the arrow P direction by the rotation of the first spiral blade 234a. Thereafter, the transported developer is transported into the second transport path 236d through the upstream communication portion 236e. Further, when the second spiral blade 233a interlocked with the rotation shaft 233b rotates together with the rotation shaft 233b, the developer transported into the second transport path 236d by the second spiral blade 233a is transported in the arrow Q direction, It is conveyed to the decelerating conveyance unit 241. At that time, the developer is transported relatively quickly while the bulkiness of the developer is greatly changed by the rotation of the first spiral blade 234a and the second spiral blade 233a. On the other hand, in the vicinity of the decelerating and conveying unit 241, the change in the bulk of the developer is small due to the rotation of the decelerating and conveying unit 241, and the developer is conveyed relatively slowly. By being transported relatively slowly as described above, the developer is transported to the first transport path 236c through the downstream communication section 236f without getting over the restricting section 242.

  Thus, the developer is agitated while circulating from the first conveyance path 236c to the upstream communication portion 236e, the second conveyance path 236d, and the downstream communication portion 236f, and the agitated developer is fed to the magnetic roller 232. Supplied.

  Next, a case where the developer is supplied from the developer supply port 236g will be described. When the toner is consumed by the development, the replenishment developer including the toner and the carrier is replenished from the developer replenishment port 236g into the first transport path 236c.

  The replenished developer is transported in the direction of arrow P in the first transport path 236c by the first spiral blade 234a, as in the development. Thereafter, the transported developer is transported into the second transport path 236d through the upstream communication portion 236e. Further, the developer is transported in the second transport path 236d in the direction of arrow Q by the second spiral blade 233a and transported to the deceleration transport unit 241. When the restricting portion 242 rotates with the rotation of the rotating shaft 233b, the restricting portion 242 applies a transport force in the direction opposite to the developer transport direction by the second spiral blade 233a to the developer. By this restricting portion 242, the developer is blocked in the vicinity of the decelerating and conveying portion 241 and becomes bulky, and excess developer passes over the restricting portion 242 and is discharged out of the developing container 236 through the developer discharge port 236 h. .

  The image forming apparatus 10 forms an image on a sheet by the image forming operation as described above. In such an image forming apparatus, since the electrophotographic carrier is used as the carrier contained in the two-component developer and the replenishment developer, a high-quality image can be obtained even when image formation is performed over a long period of time. Can be formed.

  Further, the image forming apparatus is an apparatus that once transfers a plurality of color toner images to an intermediate transfer belt and transfers the plurality of color toner images transferred to the intermediate transfer belt onto a sheet. The image forming apparatus is not limited. For example, an image forming apparatus that directly transfers a toner image onto a sheet may be used.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited at all by the Example.

[Example 1]
(Electrophotographic carrier)
First, as a core material, Mn—Mg—Sr ferrite particles (EF-35 manufactured by Powder Tech Co., Ltd., average particle radius (half value of volume average particle size): 17.5 μm, true specific gravity: 4.5 × 10 ⁶ g / m ³ ) 0.1 part by mass of silica particles (RA200 manufactured by Nippon Aerosil Co., Ltd.) was added to 100 parts by mass, and they were mixed by stirring for 10 minutes with a ball mill. Then, the mixture was heat-processed using the hot air processing machine (The surffusion made from Hosokawa Micron Corporation). In that case, it heat-processed on the conditions which spray a hot air of 900 degreeC on a mixture with the process rate of 30 g / sec. To 100 parts by mass of the heat-treated carrier thus obtained, 10 parts by mass of toluene and 2 parts by mass of perfluorooctylethyl acrylate / methyl methacrylate copolymer were added to a degassing kneader, and 140 Stir at 20 ° C. for 20 minutes to mix. Thereafter, toluene was volatilized and removed from the mixture, and then passed through a 150 mesh sieve. This passed product was obtained as an electrophotographic carrier (resin-coated carrier). The true specific gravity D of the obtained electrophotographic carrier was 4.45 × 10 ⁶ g / m ³ . Further, the average particle radius (half value of volume average particle diameter) r of the carrier for electrophotography was 17.7 μm. The BET specific surface area S of the electrophotographic carrier was 0.049 m ² / g.

  The true specific gravity of the core material and the electrophotographic carrier here was measured using a pycnometer method. Specifically, it measured by the following method. First, about 50 g of a core material and a carrier as a measurement object were weighed. The measured measurement object was put into a graduated cylinder containing about 50 ml of pure water and a small amount of surfactant (about 0.5 ml). And the volume of the measuring object was measured from the water level change. The true specific gravity of the carrier was calculated from the volume and mass of the measured object.

  Further, the average particle radius of the core material and the electrophotographic carrier here is a half value of the volume average particle diameter, and a laser diffraction / scattering type particle size distribution measuring apparatus (LA-700 manufactured by Horiba, Ltd.) is used. It was measured.

  The BET specific surface area S of the electrophotographic carrier was measured using a fully automatic BET specific surface area measuring apparatus (Macsorb HM Model-1208 manufactured by Mountec Co., Ltd.).

(Two-component developer)
First, 10 parts by mass of toner (TK-881K toner manufactured by Kyocera Mita Co., Ltd.) was added to 100 parts by mass of the electrophotographic carrier, and they were stirred and mixed for 10 minutes by a ball mill. By doing so, a developer having a toner concentration (T / C) of 10% by mass was obtained. Further, a developer having a toner concentration (T / C) of 10% by mass was used as a two-component developer. On the other hand, a developer having a toner concentration (T / C) of 5% by mass was obtained in the same manner as described above except that 5 parts by mass of toner was added instead of 10 parts by mass of toner.

  The flow rate of the developer (mixture of toner and carrier) with a toner concentration of 10% by mass [FR] with respect to the flow rate [FR (5%)] of developer (mixture of toner and carrier) with a toner concentration of 5% by mass. (10%)] ratio [FR (10%) / FR (5%)] was measured. This FR (10%) / FR (5%) is the ratio of the required time when a fixed amount of powder (here, a mixture of toner and carrier) is injected into a fixed shape funnel and discharged from the bottom. is there. Specifically, for example, the measurement was performed as follows.

  First, 50 g each of a developer having a toner concentration of 10% by mass and a developer having a toner concentration of 5% by mass were weighed. Then, using a set of equipment such as a funnel specified in JIS-Z2502, each developer was poured into the funnel, and the time required for discharging the developer from the lower part of the funnel was measured three times. Was calculated. By correcting the average value with the funnel eigenvalue, FR (5%) and FR (10%) were calculated, and FR (10%) / FR (5%) was calculated.

  The FR (5%), FR (10%), and FR (10%) / FR (5%) measured in this manner were 80, 90, and 1.13, respectively.

  The flow rate FR and the carrier S, r, and D are summarized in Table 1.

(Replenishment developer)
First, 90 parts by mass of toner (TK-881K toner manufactured by Kyocera Mita Co., Ltd.) was added to 10 parts by mass of the electrophotographic carrier, and these were stirred and mixed for 10 minutes by a ball mill. By doing so, a replenishment developer was obtained.

[Example 2]
It is the same as that of Example 1 except having changed the processing speed of the heat processing using a hot air processing machine (The surf fusion made from Hosokawa Micron Corporation) from 30 g / sec to 15 g / sec. Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Example 3]
It is the same as that of Example 1 except having changed the processing speed of the heat processing using a hot air processing machine (The surf fusion made from Hosokawa Micron Corporation) from 30 g / sec to 45 g / sec. Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Example 4]
As a core material, Mn—Mg—Sr ferrite particles (EF-35 manufactured by Powder Tech Co., Ltd., average particle radius (half value of volume average particle diameter): 17.5 μm, true specific gravity: 4.5 × 10 ⁶ g / In place of m ³ ), except that the coarse particle side of EF-35 was removed (particles on the larger particle diameter side were removed) and the average particle radius was 15 μm, the same as Example 1 was used. is there. Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Example 5]
As a core material, Mn—Mg—Sr ferrite particles (EF-35 manufactured by Powder Tech Co., Ltd., average particle radius (half value of volume average particle diameter): 17.5 μm, true specific gravity: 4.5 × 10 ⁶ g / Example 3 is the same as Example 1 except that instead of m ³ ), the fine particle side of EF-35 is removed (particles on the smaller particle diameter side are removed) and the average particle radius is 25 μm. . Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Example 6]
As a core material, Mn—Mg—Sr ferrite particles (EF-35 manufactured by Powder Tech Co., Ltd., average particle radius (half value of volume average particle diameter): 17.5 μm, true specific gravity: 4.5 × 10 ⁶ g / In place of m ³ ), Mn—Mg—Sr ferrite particles (EF-80 manufactured by Powder Tech Co., Ltd.), average particle radius (half value of volume average particle diameter): 40 μm, true specific gravity: 4.4 × 10 ⁶ g / M ³ ) The same as Example 1 except that it was used. Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Comparative Example 1]
It is the same as that of Example 1 except that no silica particles are added to the core material and heat treatment using a hot air treatment machine (Surfusion made by Hosokawa Micron Corporation) is not performed. Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Comparative Example 2]
It is the same as that of Example 1 except having changed the processing speed of the heat processing using a hot air processing machine (The surffusion made from Hosokawa Micron Corporation) from 30 g / sec to 60 g / sec. Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Comparative Example 3]
As a core material, Mn—Mg—Sr ferrite particles (EF-35 manufactured by Powder Tech Co., Ltd., average particle radius (half value of volume average particle diameter): 17.5 μm, true specific gravity: 4.5 × 10 ⁶ g / In place of m ³ ), the coarse particle side of EF-35 is removed (the particle on the larger particle diameter side is removed) and the average particle radius is 15 μm. Further, silica particles are used as the core material. It is the same as that of Example 1 except not performing the heat processing using a hot-air processing machine (Hosokawa Micron Corporation surffusion) without adding. Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Comparative Example 4]
As a core material, Mn—Mg—Sr ferrite particles (EF-35 manufactured by Powder Tech Co., Ltd., average particle radius (half value of volume average particle diameter): 17.5 μm, true specific gravity: 4.5 × 10 ⁶ g / In place of m ³ ), the fine particle side of EF-35 is removed (particles on the smaller particle diameter side are removed) and the average particle radius is 25 μm, and silica particles are added to the core material. Without performing heat treatment using a hot air processing machine (Surfusion manufactured by Hosokawa Micron Corporation), the same as in Example 1. Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Comparative Example 5]
As a core material, Mn—Mg—Sr ferrite particles (EF-35 manufactured by Powder Tech Co., Ltd., average particle radius (half value of volume average particle diameter): 17.5 μm, true specific gravity: 4.5 × 10 ⁶ g / In place of m ³ ), Mn—Mg—Sr ferrite particles (EF-80 manufactured by Powder Tech Co., Ltd.), average particle radius (half value of volume average particle diameter): 40 μm, true specific gravity: 4.4 × 10 ⁶ g / M ³ ), silica particles are not added to the core material, and heat treatment using a hot-air treatment machine (surfofusion manufactured by Hosokawa Micron Corporation) is not performed. is there. Carrier S, r and D, developer fluidity FR and the like were measured by the same method as in Example 1, and the results are shown in Table 1 above.

[Evaluation]
First, an image forming apparatus in which the developing device of the image forming apparatus (LS-C8500DN manufactured by Kyocera Mita Co., Ltd.) is modified to the trickle developing method is used, and the two-component developer is accommodated in the developing tank of the modified image forming apparatus. Furthermore, the developer for replenishment was accommodated in a developer replenishment container. Using the image forming apparatus thus obtained, the development correction (calibration) function cannot be performed, and an image is formed in a normal temperature and humidity environment at a temperature of 20 to 23 ° C. and a relative humidity of 50 to 65% RH. The following evaluation was performed.

  Specifically, first, the image forming apparatus was turned on and stabilized. Thereafter, an image having a printing rate of 5% was output. This image was used as the initial image (first image). Next, 300,000 images with a printing rate of 5% were printed while supplying the developer for replenishment. The following evaluation was performed.

(Charge amount)
After the initial image printing, the developer after printing 100,000 sheets, 200,000 sheets, and 300,000 sheets was taken out, and 1 g of the developer was weighed. The weighed developer was sucked by a suction portion of a suction type small charge amount measuring device (Q / M meter manufactured by Trek Japan Co., Ltd.). By doing so, only the toner was sucked, and the charge amount was measured with a suction type small charge amount measuring device (Q / M meter manufactured by Trek Japan Co., Ltd.). The toner charge amount (μC / g) was calculated from the measured toner amount and charge amount.

(Image density)
For each of the initial image, the 100,000th printed image, the 200,000th printed image, and the 300,000th printed image, the reflection density was measured using a reflection densitometer (manufactured by Tokyo Denshoku Co., Ltd.). Five points were measured. The average value was taken as the image density of the obtained image.

  If the measured image density of the 300,000th printed image is 1.2 or more, it is evaluated as “◯”, and if it is 1.1 or more and less than 1.2, it is evaluated as “Δ”. If it was less than "x", it evaluated as "x".

(Cover)
For each of the initial image, the 100,000th print image, the 200,000th print image, and the 300,000th print image, from the value of the image density of the white paper equivalent measured by the reflection densitometer, The value obtained by subtracting the image density value of the base paper (that is, the white paper before image output) was defined as the fog density.

  If the maximum fog density value measured in the 300,000th printed image is 0.007 or less, it is evaluated as “◯”, and if it exceeds 0.007 and less than 0.010, it is evaluated as “Δ”. And it evaluated as "x" if it was 0.010 or more.

  These results are summarized in Table 2 below.

  As can be seen from Tables 1 and 2, an electrophotographic carrier comprising a core material and a resin layer covering the core material and having (S × r × D) / 3 of 1 to 1.5 is used. (Examples 1 to 6) printed 300,000 sheets compared to the case of using an electrophotographic carrier (S × r × D) / 3 exceeding 1.5 (Comparative Examples 1 to 5). Even after that, it was found that the image density was high and the occurrence of fog was suppressed. It was also found that the toner charge amount did not decrease much even after printing 300,000 sheets. By using an electrophotographic carrier in which (S × r × D) / 3 is 1 or more and 1.5 or less, a high image density can be maintained even when image formation is performed over a long period of time, and fogging occurs. It was found that generation and the like can be suppressed, and thus a high-quality image can be formed over a long period of time. Further, this is presumed to be due to suppression of a decrease in the charge amount of the toner.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Apparatus main body 12 Paper supply part 13 Image forming part 14 Fixing part 15 Paper discharge part 21 Charging apparatus 22 Exposure apparatus 23 Developing apparatus 24 Electric discharge apparatus 131 Image forming unit 231 Developing roller 232 Magnetic roller 233 2nd stirring conveyance member (Paddle mixer)
234 First stirring and conveying member (stirring mixer)
236 Developer tank (Developer container)
237 Stirring conveyance member 301 Toner 302 Carrier 303 Two-component developer

Claims (6)

A core material with silica particles attached to the surface ;
A resin layer covering the core material with silica particles attached to the surface ;
An electrophotographic carrier characterized by satisfying the following formula (1).
1 ≦ (S × r × D) /3≦1.5 (1)
[In Formula (1), S shows the BET specific surface area (m < ² > / g) of the said electrophotographic carrier, r shows the half value (m) of the volume average particle diameter of the said electrophotographic carrier, D Represents the true specific gravity (g / m ³ ) of the electrophotographic carrier. ] The electrophotographic carrier according to claim 1, wherein the core material is Mn—Mg—Sr ferrite particles. The two-component developer and the replenishment of an image forming apparatus comprising: a developing tank that contains a two-component developer containing toner and a carrier; and a replenishing unit that replenishes the developing tank with a replenishing developer containing toner and carrier. The electrophotographic carrier according to claim 1 , wherein the electrophotographic carrier is used as a carrier contained in each developer. A method for producing an electrophotographic carrier comprising:
A heat treatment process for heat treating the core material;
A coating step of coating a resin layer on the surface of the heat-treated core material,
The heat treatment step is a step of blowing hot air on the core material in the presence of silica particles,
The method for producing an electrophotographic carrier, wherein the electrophotographic carrier satisfies the following formula (3).
1 ≦ (S × r × D) /3≦1.5 (3)
[In Formula (3), S shows the BET specific surface area (m < ² > / g) of the said electrophotographic carrier, r shows the half value (m) of the volume average particle diameter of the said electrophotographic carrier, D Represents the true specific gravity (g / m ³ ) of the electrophotographic carrier. ] A developer comprising the electrophotographic carrier according to any one of claims 1 to 3 and a toner. The two-component developer and the replenishment of an image forming apparatus comprising: a developing tank that contains a two-component developer containing toner and a carrier; and a replenishing unit that replenishes the developing tank with a replenishing developer containing toner and carrier. The developer according to claim 5 , wherein the developer is used as a developer.

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