JP2007316166A - Carrier and two-component developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier and two-component developer having excellent durability and environmental stability. <P>SOLUTION: The carrier comprises a core material coated with a coating resin, wherein the coating resin is applied ≥5 wt.% and ≤20 wt.% with respect to the weight of the core material on the core material so as to improve the durability. Further, the coating resin contains alumina fine powder, which improves environmental stability. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a two-component developer comprising a toner and a carrier and the carrier.

  As an image forming method using a developer, an electrophotographic method using a Carlson process is widely used. An image forming apparatus using an electrophotographic system forms an image by a charging process, an exposure process, a development process, a transfer process, a cleaning process, a fixing process, and the like. In the charging step, the surface of the photoreceptor is uniformly charged in a dark place. In the exposure step, the original image is projected onto the charged photoconductor, so that the charged portion is removed and an electrostatic latent image is formed on the surface of the photoconductor. In the developing step, a visible toner image is formed by attaching a developer toner to the electrostatic latent image formed on the surface of the photoreceptor. In the transfer process, a recording medium such as paper or sheet is brought into contact with the visible image formed on the surface of the photoreceptor, and corona discharge is performed from the side opposite to the surface of the recording medium that is in contact with the visible image. Transfers a visible image to a recording medium by applying a charge of opposite polarity to the recording medium. In the fixing step, the visible image transferred to the recording medium is fixed by means such as heating and pressing. In the cleaning process, the toner remaining on the surface of the photoreceptor without being transferred to the recording medium is collected. By repeating the above steps, an image forming apparatus using an electrophotographic process forms a desired image on a recording medium.

  Conventionally, it is known that a developer used in an image forming apparatus using an electrophotographic system includes a toner manufactured by a pulverization method, a polymerization method, or the like. The pulverization method is to melt and knead a thermoplastic resin, a colorant, a charge control agent and a wax as an anti-offset agent, then cool and solidify to prepare a melt-kneaded product, and pulverize and classify the melt-kneaded product. This is a method for preparing a toner. The polymerization method is a method for preparing toner by suspension polymerization method or emulsion polymerization method.

  Currently, image forming apparatuses such as copying machines and printers have been increased in speed and size, and in order to obtain high-quality images for a long period of time, development of a developer having excellent durability and environmental stability is required. It has been.

  In the case where the developer is a two-component developer comprising a toner and a carrier, in order to develop a developer having excellent durability and environmental stability, in order to stably charge the developer in the image forming apparatus The development of a carrier, such as optimization of the type of core material, the type of coat resin, and the amount of coat resin, is important along with the development of toner.

  A typical conventional technique for carrier development is described in US Pat. The color developer of Patent Document 1 is a developer composed of a toner and a carrier, and the carrier is 0.1 to 5.0% by weight of a predetermined resin (coat resin) with respect to the weight of the carrier core material (core material). It is a color developer that is coated.

  Another conventional technique is described in Patent Document 2. The two-component developer for electrophotography of Patent Document 2 is a developer composed of a toner and a carrier, and the carrier covers the coating material (coat resin) by more than 5.0% by weight with respect to the weight of the carrier core material. The two-component developer for electrophotography.

  Still another conventional technique is described in Patent Document 3. The carrier of Patent Document 3 is a carrier constituting a two-component developer, in which a core resin is coated with a coat resin, and the coat resin is 5 wt% or more and 20 wt% or less with respect to the weight of the core material. Yes, it is a carrier containing titanium oxide fine powder in the coating resin.

JP-A-4-177369 Japanese Patent Laid-Open No. 2003-255591 JP 2005-345999 A

  The developer needs to have appropriate fluidity and chargeability so that the developer toner can smoothly adhere to the electrostatic latent image formed on the surface of the photoreceptor. The flowability and chargeability of the developer vary depending on the carrier composition.

  According to the color developer disclosed in Patent Document 1, the carrier core material is coated with a carrier that is coated with a predetermined resin in an amount of 0.1 to 5.0% by weight with respect to the weight of the carrier core material. By using it, contamination such as toner forming a thin film on the surface of the carrier can be prevented, and the developer is excellent in durability and environmental stability. However, in recent years, image forming apparatuses have been speeded up and miniaturized, and when an image is formed using such an image forming apparatus, the stress applied to the developer is larger than the previous image forming apparatus. If the toner is used as it is for a long time, the resin peels off from the carrier core and the carrier core is exposed on the surface. In other words, in the case of forming an image using a high-speed and downsized image forming apparatus, the developer is insufficient in durability that cannot maintain the initial carrier characteristics, and the obtained image has an image density. It will be what caused the decline.

  Further, according to the two-component developer for electrophotography disclosed in Patent Document 2, the image forming speed-up and miniaturization is achieved by coating the carrier core material with a coating material exceeding 5.0% by weight. Even if it is used for a long time in the apparatus, the carrier core material is difficult to be exposed on the surface, and it is a developer having superior durability that can maintain the carrier characteristics for a long time. However, since a large amount of coating material is coated on the carrier core material, depending on the type of the coating material, it may not be possible to ensure carrier characteristics such as environmental characteristics. However, since the toner concentration in the developer is not stable and may cause toner scattering and white background fogging, the problem is solved by externally adding magnetite to the toner.

  According to the carrier disclosed in Patent Document 3, by coating the coating resin so that the coating resin is 5% by weight or more and 20% by weight or less with respect to the weight of the core material, the carrier is excellent in durability. By containing titanium oxide fine powder, the carrier has excellent environmental stability. The inventors of the present application have also found that a carrier having excellent environmental stability can be obtained by containing barium titanate fine powder in the coating resin.

  Carriers containing titanium oxide fine powder or barium titanate fine powder in these coating resins are excellent in durability and environmental stability, and can provide high-quality images for a long period of time. However, since these carriers have not been sufficiently studied for the adhesion of the carrier to the photosensitive member when the toner having a reduced particle size is applied to a high-speed machine, the photosensitive member when used within the scope of Patent Document 3 is used. There is a risk of significant carrier adhesion to the surface. Moreover, since the titanium oxide fine powder and the barium titanate fine powder are expensive, materials that are cheaper than these materials and can obtain the same effect are desired.

  Accordingly, it is an object of the present invention to provide a carrier and a two-component developer that are inexpensive, excellent in durability and environmental stability, and excellent in overall real machine characteristics in which carrier adhesion does not easily occur.

The present invention is a carrier constituting a two-component developer,
The core material is coated with a coating resin,
The coating resin is 5% by weight or more and 20% by weight or less based on the weight of the core material,
A carrier characterized in that the coating resin contains fine alumina powder.

  Further, the present invention is characterized in that the coating resin contains 5% by weight or more and 20% by weight or less of alumina fine powder.

The present invention also provides a two-component developer comprising a toner and a carrier,
A two-component developer, wherein the carrier is the carrier described above.

  According to the present invention, the carrier has a core material coated with a coating resin. The coating resin is 5% by weight or more and 20% by weight or less based on the weight of the core material, and the coating resin contains fine alumina powder.

  By coating the coating resin so as to be 5% by weight or more with respect to the weight of the core material, it becomes a carrier having excellent durability, and further, by containing alumina fine powder in the coating resin, environmental stability is improved. It is an excellent carrier that hardly causes carrier adhesion. Alumina fine powder is less expensive than titanium oxide fine powder and barium titanate fine powder.

  From the above, it is possible to obtain a carrier that is inexpensive, excellent in durability and environmental stability, and excellent in overall real machine characteristics in which carrier adhesion does not easily occur.

  According to the present invention, when the fine alumina powder is contained in the coating resin in an amount of 5 wt% or more and 20 wt% or less, the carrier has better environmental stability and is less likely to cause carrier adhesion.

  Further, according to the present invention, the two-component developer comprising a toner and a carrier is used, and the carrier is a two-component developer using the carrier. Since the carrier is inexpensive, excellent in durability and environmental stability, and hardly adheres to the carrier, it is inexpensive, excellent in durability and environmental stability, and has comprehensive real machine characteristics that are difficult to cause carrier adhesion. An excellent two-component developer can be obtained.

  The present invention is a carrier in which a core material is coated with a coating resin containing fine alumina powder and a two-component developer containing the carrier.

[Career]
The carrier according to the present invention is constituted by coating a core resin with a coating resin. The carrier has factors such as powder characteristics, electrical characteristics, and magnetic characteristics, and requires performance that matches the development system. In recent years, a carrier in which a core material is coated with a coating resin has been widely used in order to improve frictional charging, environmental stability, and durability.

(Coat resin)
The carrier includes a coating resin containing alumina fine powder. As the coating resin, a known resin can be used, and examples thereof include a polyester resin, a fluorine resin, an acrylic resin, and a silicone resin. Further, the core material is coated by a method such as spraying or dipping.

(Alumina fine powder)
The coating resin contains an alumina fine powder. By containing alumina fine powder in the coating resin, the carrier has excellent environmental stability. The fine alumina powder is preferably a hydrophobized surface of the fine powder. Examples of the hydrophobizing treatment include treatment with a silane coupling agent such as dimethyldichlorosilane and amylosilane, treatment with silicone oil, treatment with a fluorine-containing component, and the like. The alumina fine powder is preferably contained in an amount of 5% by weight to 20% by weight, more preferably 5% by weight to 10% by weight, based on the coating resin. If it is less than 5% by weight, the effect on environmental stability is reduced, and if it is more than 20% by weight, the carrier rises, which is a phenomenon that the carrier adheres to the photoreceptor and flows out, so-called carrier adhesion. This causes the developer amount to gradually decrease from the beginning to the end of life. Therefore, there is a high possibility that the toner concentration in the developer cannot be controlled well. Further, when the carrier rises significantly, the developer may appear on the recording material, which is not preferable. The preferable average particle diameter of the alumina fine powder is 5 nm or more and 200 nm or less.

(Core material)
The carrier is configured to include a core material. A well-known thing can be used for a core material, and iron powder, a ferrite, etc. can be mentioned. The shape can be from irregular to spherical. Furthermore, an average particle diameter of 10 μm or more and 1000 μm or less can be used, and more preferably 30 μm or more and 100 μm or less. If the thickness is smaller than 10 μm, carrier adhesion, which is a phenomenon in which the carrier adheres to and flows out of the photosensitive member, is caused, and the toner amount in the developer cannot be controlled well by gradually decreasing the developer amount. The possibility increases. Further, when the carrier rise becomes remarkable, the developer appears on the recording material. On the other hand, if it is larger than 1000 μm, when the toner of the developer is moved from the developing roller to the photoreceptor, the two-component developer heads (magnetic brush) are rough and it becomes difficult to supply a stable image quality. This may cause a phenomenon that the component developer spills from the developing tank.

  Moreover, a well-known thing can be used for iron powder, and reduced iron powder, atomized iron powder, iron nitride powder, etc. can be mentioned. Since the reduced iron powder and the iron nitride powder are indefinite, they may be spheroidized. A well-known thing can be used for a ferrite carrier, and ferrite powders, such as copper, nickel, zinc, cobalt, manganese, and calcium, can be mentioned. Since the ferrite carrier is spherical, has good fluidity and is chemically stable, it is preferably used for high image quality and long life.

[toner]
The toner constituting the two-component developer according to the present invention is constituted by adding an external additive to toner base particles including a binder resin, a colorant, a release agent, a charge control agent, and the like.

(Binder resin)
The toner base particles include a binder resin. As the binder resin, known resins can be used. For example, polystyrene, styrene-acrylic copolymer, styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, styrene-acrylic-maleic anhydride copolymer. Examples thereof include polymers, polyvinyl chloride, polyolefin resins, epoxy resins, silicone resins, polyamide resins, polyurethane resins, urethane-modified polyester resins, and acrylic resins. Said resin may be used independently and may be used with a several mixture. The copolymer may be a block copolymer or a graft copolymer. The molecular weight distribution may be one peak or two peaks.

  Moreover, as a thermal property, it is preferable that a glass transition point (Tg) is 40 degreeC or more and 70 degrees C or less. When the temperature is lower than 40 ° C., when the temperature in the image forming apparatus rises, the toner melts and aggregation between the toners occurs. On the other hand, when the temperature is higher than 70 ° C., the fixing property is inferior and the practicality is poor.

(Coloring agent)
The toner base particles include a colorant. As the colorant, known ones can be used, and examples thereof include carbon black, iron black, alloy azo dyes, oil-soluble dyes and pigments. The colorant is preferably 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the binder resin. If the amount is less than 1 part by weight, a sufficient image density cannot be secured. If the amount is more than 10 parts by weight, the colorant cannot be uniformly dispersed in the resin, so that a high-quality image cannot be obtained.

(Release agent)
The toner base particles include a wax as a release agent. As the wax, known ones can be used, and examples thereof include at least one wax selected from polyethylene, polypropylene, ethylene-propylene copolymer, polyolefin and the like. The wax is preferably 1 part by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the binder resin. If the amount is less than 1 part by weight, offset tends to occur. When the amount is more than 10 parts by weight, filming tends to occur.

(Charge control agent)
The toner base particles include a charge control agent. There are two types of charge control agents: positive charge control charge control agents and negative charge control charge control agents, and examples include azo dyes, carboxylate metal complexes, quaternary ammonium compounds, and nigrosine dyes. . The charge control agent is preferably 0.1 parts by weight or more and 5 parts by weight or less with respect to 100 parts by weight of the resin. When the amount is less than 0.1 part by weight, sufficient charging property cannot be imparted. When the amount is more than 5 parts by weight, the charge control agent cannot be mixed uniformly in the resin.

(External additive)
The toner is constituted by adding an external additive to toner base particles. As the external additive, known ones can be used, and examples thereof include fine powders of metal oxide fine particles such as silica, titanium, alumina, magnetite and ferrite, and metal nitride fine particles such as silicon nitride and boron nitride. it can. Furthermore, the surface of the fine powder is preferably hydrophobized. Examples of the hydrophobizing treatment include treatment with a silane coupling agent such as dimethyldichlorosilane and amylosilane, treatment with silicone oil, treatment with a fluorine-containing component, and the like. Among the above external additives, one kind may be used, or two or more kinds may be used. Moreover, as an external additive, a silica is more preferable. Even if only fine particles other than silica are externally added, charging may not be sufficient in the contact between the toner and the carrier. Further, since silica acts as a fluidizing agent for the toner, the amount of toner supply can be stabilized. It can be made.

(Production method)
A resin, a colorant, a release agent, a charge control material, and the like are sufficiently mixed by a mixer such as a Henschel mixer or a supermixer, and the obtained mixture is melt-kneaded by a twin-screw kneader. The kneaded product is pulverized by a jet pulverizer and then classified to obtain toner base particles having a volume average particle diameter of about 5 μm to 15 μm. Further, the toner is manufactured by adding inorganic fine particles to the toner base particles and adhering and uniformly dispersing them with a mixer such as a Henschel mixer or a super mixer.

[Two-component developer]
The two-component developer according to the present invention can be produced by mixing the toner and the carrier as described above with a mixer so as to have a prescribed toner concentration. As a mixer, a well-known thing can be used and a Nauta mixer (The Hosokawa Micron Corporation make: VL-0) can be mentioned.

The present invention will be specifically described below with reference to examples and comparative examples, but is not limited to the examples.

[Example A]
In Example A, the influence of the carrier coat amount of the carrier constituting the two-component developer (weight% of the coat resin with respect to the weight of the core material) was examined.

(Example of toner production)
For 100 parts by weight of the polyester resin, 1.0 part by weight of polyethylene (manufactured by Clariant Japan: PE130) and 1.5 parts by weight of polypropylene (manufactured by Mitsui Chemicals: NP-505) as a wax, carbon black (Cabot Corporation) as a colorant Product: 330R) 5 parts by weight, charge control agent (Hodogaya Chemical Co., Ltd .: S-34) 1 part by weight, magnetite (manufactured by Kanto Denka Co., Ltd .: KBC-100) 1.5 parts by weight were added, and super mixer (Kawada Co., Ltd.) was added. Made by V-20), and the resulting mixture was melt-kneaded by a biaxial kneader (Ikegai Iron Works: PCM-30). The kneaded product was pulverized with a jet type pulverizer (manufactured by Nippon Pneumatic Industrial Co., Ltd .: IDS-2) and classified to obtain toner base particles having a volume average particle size of 7.5 μm. Toner was obtained by externally adding 0.3 part by weight of silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: R972) to the toner base particles.

(Example of carrier production)
Silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd .: KR-255) was used as the coating resin, carbon black (manufactured by Lion Corporation: Ketjen Black EC) was added to 5.0 wt%, and these were dispersed in toluene. . A carrier obtained was obtained by applying a dispersion obtained by using a fluidized bed coating apparatus to a ferrite core material having a particle diameter of 90 μm, and heating at 250 ° C. for 2 hours to cure the applied coating resin. .

Example 1
The toner obtained by the above manufacturing method and the ferrite carrier coated with the coating resin so that the carrier coating amount is 8.0% by weight as shown in Table 1 so that the toner concentration becomes 5% by weight. A two-component developer was produced by stirring for 20 minutes with a Nauta mixer (manufactured by Hosokawa Micron Corporation: VL-0).

(Example 2)
A two-component developer was produced in the same manner as in Example 1 except that the carrier coat amount of the carrier was 5.0% by weight.

(Comparative Example 1)
A two-component developer was produced in the same manner as in Example 1 except that the carrier coat amount of the carrier was 4.1% by weight.

(Comparative Example 2)
A two-component developer was produced in the same manner as in Example 1 except that the carrier coat amount of the carrier was 2.2% by weight.

[Evaluation methods]
Using the two-component developer obtained by the above production method, an original with a printing rate of 5% was printed by a monochrome copying machine (manufactured by Sharp Corporation: AR-450).

  For Examples 1 and 2 and Comparative Examples 1 and 2, image density change evaluation was performed as follows. The physical properties of the two-component developer produced by the above method are evaluated by the following evaluation methods, and the results are shown in Table 1. Note that symbols such as “◯” and “x” described in the description of the evaluation items are symbols indicating the evaluation results used in Table 1. “◯” indicates superiority, and “X” indicates that practical use is difficult.

(Image density)
The image density of an image printed using the developer in the initial state (initial image density) and the image density of an image printed after printing 100,000 sheets of 5% originals intermittently (image density after printing 100,000 sheets) ) Was measured with a Macbeth reflection densitometer (manufactured by Macbeth: RD-914). The image density after printing 100,000 sheets was evaluated based on the following criteria.
○: Image density is 1.30 or more and less than 1.32.
X: The image density is less than 1.30.

  As can be seen from Table 1, the developer (Examples 1 and 2) in which the coating resin used a carrier of 5% by weight or more based on the weight of the core material had an image density even after printing 100,000 sheets. It was a developer with excellent durability that could be maintained. However, the developer (Comparative Examples 1 and 2) using a carrier whose coating material is less than 5% by weight with respect to the weight of the core material has greatly reduced the image density after printing 100,000 sheets.

[Example B]
In Example B, the influence of the addition amount of the alumina fine powder in the coating resin coated on the carrier was examined.

(Example 3)
In Examples 1 and 2 and Comparative Examples 1 and 2 described above, except for changing the pulverization conditions such as the pressure of air when the kneaded material is pulverized by a jet pulverizer (manufactured by Nippon Pneumatic Industry Co., Ltd .: IDS-2). The toner was manufactured in the same manner as the toner used. Toner base particles having a volume average particle diameter of 8.5 μm were obtained, and a toner was obtained by externally adding 0.3 part by weight of silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: R972).

  Silicone resin (manufactured by Shin-Etsu Chemical Co., Ltd .: KR-255) is used as the coating resin, alumina fine powder (manufactured by Nippon Aerosil Co., Ltd .: Alumium Oxide C) (average particle size: about 20 nm) and carbon black (manufactured by Lion Corporation: Ketjen Black EC) was added to 5.0% by weight and they were dispersed in toluene. A dispersion obtained by using a fluidized bed coating apparatus was applied to a ferrite core material having a particle diameter of 90 μm so that the carrier coat amount was 6.0% by weight, and heated at 250 ° C. for 2 hours. A carrier was obtained by curing the applied coating resin.

The obtained toner and carrier were mixed with a Nauter mixer (toner mixer) so that the toner concentration was 5% by weight.
A two-component developer was produced by stirring for 20 minutes with Hosokawa Micron Corporation (VL-0).

Example 4
A two-component developer was produced in the same manner as in Example 3, except that the alumina fine powder in the coating resin was added so as to be 10% by weight so as to be 1% by weight.

(Example 5)
A two-component developer was produced in the same manner as in Example 3, except that the alumina fine powder in the coating resin was added so as to be 4% by weight so as to be 10% by weight.

(Example 6)
A two-component developer was produced in the same manner as in Example 3 except that the alumina fine powder in the coating resin was added so that the amount was 10% by weight.

(Example 7)
A two-component developer was produced in the same manner as in Example 3, except that the alumina fine powder in the coating resin was added so as to be 10% by weight so as to be 20% by weight.

(Example 8)
A two-component developer was produced in the same manner as in Example 3 except that the alumina fine powder in the coating resin was added so as to be 10% by weight and 25% by weight.

(Comparative Example 3)
A two-component developer was produced in the same manner as in Example 3 except that alumina fine powder was not added to the coating resin.

[Evaluation methods]
For Examples 3 to 8 and Comparative Example 3 in Table 2, the following environmental stability evaluation, image density evaluation and carrier adhesion evaluation were performed. The physical properties of the two-component developer produced by the above method are evaluated by the following evaluation methods, and the results are shown in Table 2. Note that symbols such as “◎”, “◯”, “Δ”, and “x” described in the description of the evaluation items are symbols indicating evaluation results used in Table 2. “◎” indicates very good, “○” indicates excellent, “△” indicates that it is practical, and “×” indicates that practical use is difficult. Indicates. However, in the comprehensive evaluation, “◯” indicates that practical use is possible, and “×” indicates that practical use is difficult.

(Environmental stability)
The toner replenishment time after standing for 17 hours under high temperature and high humidity (temperature 35 ° C., relative humidity 85%) is measured, and the white background fog of the printed image after standing for 17 hours is measured by a Hunter whiteness meter (manufactured by Nippon Denshoku Industries Co., Ltd.). ) And the measurement results were evaluated based on the following criteria.
A: The value of white background fog is less than 0.5.
◯: The value of white background fog is 0.5 or more and less than 1.0.
X: The value of white background fog is 1.0 or more.

  The toner replenishment time is the time from the time when the two-component developer starts to be stirred until the time when the toner of the two-component developer is attached to the photoreceptor, the so-called toner supply time. This is because the fluidity and chargeability are changed by leaving the developer for a long time under high temperature and high humidity.

(Image density)
The initial image density was measured by the same method as the above image density change evaluation, and the measured image density was evaluated based on the following criteria.
A: Image density is 1.35 or more.
○: Image density is 1.30 or more and less than 1.35.
X: The image density is less than 1.30.

(Carrier adhesion)
In a standard environment (temperature 25 ° C., relative humidity 50%), a predetermined bias was applied, and the number of carriers adhered on the photoconductor (number in the range of 24 mm in the circumferential width of the photoconductor) was measured.
A: The number of carriers adhering to the photoreceptor is less than 20.
○: The number of carriers adhering to the photoreceptor is 20 or more and less than 40.
Δ: The number of carriers adhering to the photoreceptor is 40 or more.

  As can be seen from Table 2, when alumina fine powder is contained in the coating resin (Examples 3 to 8), the environmental stability and image density are excellent, and the overall actual machine characteristics with little carrier adhesion are excellent. It was a component developer. Furthermore, when the content of the fine alumina powder is 5% by weight or more and 20% by weight or less, which is a preferred range (Examples 3, 6 and 7), the environmental stability and the image density are more excellent, and the carrier adhesion is better. It was a more excellent two-component developer with less overall real machine characteristics.

  Further, when the alumina fine powder was not contained in the coating resin (Comparative Example 3), the carrier coating amount was 5% by weight or more, so that it was a two-component developer having an excellent image density. However, since the alumina fine powder is not contained in the coating resin, it was a two-component developer having inferior actual machine characteristics such as environmental stability.

Claims (3)

A carrier constituting a two-component developer,
The core material is coated with a coating resin,
The coating resin is 5% by weight or more and 20% by weight or less based on the weight of the core material,
A carrier characterized in that the coating resin contains fine alumina powder.   The carrier according to claim 1, wherein the coating resin contains 5 to 20% by weight of alumina fine powder. A two-component developer comprising a toner and a carrier,
A two-component developer, wherein the carrier is the carrier according to claim 1 or 2.