JP4139337B2 - Two-component developer - Google Patents

Description

  The present invention relates to a two-component developer composed of a toner and a 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.

  If the developer is a two-component developer consisting of 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 coating material, and the amount of coating material, 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 (coating material) 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 (coating material) in excess of 5.0% by weight with respect to the weight of the carrier core material. The two-component developer for electrophotography.

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

  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 depend on the toner and carrier composition.

  According to the color developer disclosed in Patent Document 1, a carrier in which a carrier is coated with a predetermined resin so as to be 0.1 to 5.0% by weight with respect to the weight of the carrier core. 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.

  Furthermore, the inventors of the present invention have determined durability and environmental stability by defining the toner concentration by the coverage of the toner to the carrier even when the carrier coating amount is 5.0% by weight or more with respect to the core material. It was found that an excellent developer can be obtained. Here, the coverage of the toner with respect to the carrier is obtained by calculating the shape of the toner and the carrier as a spherical shape having no irregularities. In the case where the toner and the carrier are spheres with small irregularities, a toner having excellent durability and environmental stability was obtained by setting the toner concentration within the range defined by the coverage. However, if toner or carrier with large irregularities and large specific surface area is used, even if the toner concentration is higher than the specified range, the chance of contact between the toner and the carrier increases, so the durability and environmental stability are excellent. It has been found that there are cases where a developer can be obtained.

  Accordingly, an object of the present invention is to achieve excellent durability and environmental stability regardless of whether the shape of the toner and carrier constituting the two-component developer is a spherical shape with large irregularities or a spherical shape with small irregularities. It is to provide a component developer.

  The present invention is a two-component developer comprising a toner and a carrier,
  The carrier is a core material coated with a coating material,
  The coating material is 5% by weight or more and 20% by weight or less based on the weight of the core material,
  For the toner, the toner concentration in the developer satisfies the following formula (1).The specific gravity of the toner is 1.2, the specific gravity of the carrier is 4.8, and the specific surface area of the toner is 7800 cm. ² / Cm ³ More than 7810cm ² / Cm ³ The specific surface area of the carrier is 895 cm ² / Cm ³ More than 1010cm ² / Cm ³ IsIt is a two-component developer characterized by the above.
      100 / (0.75k + 1) ≦ X ≦ 100 / (0.34k + 1) (1)
                X  = Toner concentration (% by weight)
                k  = Cover factor (k = S_tρ_c / S_cρ_t)
                ρ_c = Specific gravity of carrier
                ρ_t = Specific gravity of toner
                S_c = Specific surface area of the carrier (cm²/ Cm³)
                S_t = Specific surface area of toner (cm²/ Cm³)

According to the present invention, the toner includes inorganic fine particles as an external additive.
In the present invention, the inorganic fine particles are silica.

According to the present invention, a two-component developer comprising a toner and a carrier. The carrier includes a core material and a coating material, and the coating material is coated by 5% by weight to 20% by weight with respect to the weight of the core material. Further, the toner concentration in the developer satisfies the above formula (1). At this time, the specific gravity of the toner is 1.2, the specific gravity of the carrier is 4.8, the specific surface area of the toner is 7800 cm ² / cm ³ or more and 7810 cm ² / cm ³ or less, and the specific surface area of the carrier is 895 cm ^2. / Cm ³ or more and 1010 cm ² / cm ³ or less.

  When the coating amount on the carrier is 5% by weight or more based on the weight of the core material, the durability of the developer is improved, and the toner concentration is determined so as to satisfy the above formula (1), thereby improving environmental stability. An excellent two-component developer can be produced.

  Further, according to the present invention, the toner contains inorganic fine particles as external additives, so that the chargeability can be improved and the toner concentration can be stably changed under high temperature and high humidity. A two-component developer having better stability can be produced.

  Further, according to the present invention, when silica is used as the inorganic fine particles, a two-component developer having a great effect in improving the chargeability and having excellent durability and environmental stability can be produced.

  The two-component developer according to the present invention is a two-component developer composed of a toner and a carrier. The carrier includes a core material and a coating material, and the coating material is coated on the core material by 5 wt% to 20 wt% with respect to the weight of the core material.

[Toner density]
The two-component developer according to the present invention defines the toner concentration based on the coverage. In the case where the toner and carrier are spheres with small irregularities, if the toner concentration is defined by the coverage calculated assuming that the toner and carrier are spheres without irregularities, a toner having excellent durability and environmental stability is obtained. I was able to.

  However, when the shape of the toner or carrier is a large and uneven sphere, a developer having excellent durability and environmental stability can be obtained even if the toner concentration is made higher than the range defined by the coverage. It turns out that there are cases.

  Therefore, in order to obtain a two-component developer having excellent durability and environmental stability regardless of whether the shape of the toner and the carrier is a spherical shape with large unevenness or a spherical shape with small unevenness, The toner concentration was defined as described below based on the coverage determined from the specific gravity and specific surface area of the carrier, that is, the coverage considering the unevenness of the toner and the carrier.

The coverage in consideration of the unevenness of the toner and the carrier can be represented by the ratio of the surface areas of the toner and the carrier as shown in the following formula.
Coverage = toner surface area / carrier surface area

When the surface areas of the toner and the carrier are expressed using the specific gravity and specific surface area of the toner and the carrier, they are expressed by the following equations.
Coverage ratio = (S _t / ρ _t ) / (S _c / ρ _c )
ρ _c = specific gravity of carrier
ρ _t = specific gravity of toner
S _c = specific surface area of the carrier (cm ² / cm ³ )
S _t = specific surface area of toner (cm ² / cm ³ )

In consideration of the toner concentration, the coverage can be transformed as the following formula using the coverage per 100 g of developer.
Coverage ratio = (S _t / ρ _t ) × X / (S _c / ρ _c ) × (100−X)
= _{St [} rho] _cX / _{Sc [} rho] _t (100-X)
X = Toner concentration (% by weight)
Here, it is possible to obtain a two-component developer excellent in durability and environmental stability by defining a preferable range of the value of S _t ρ _c X / S _c ρ _t (100-X) which is the coverage. it can.

However, when a two-component developer having a preferable toner concentration is to be manufactured, if the preferable range is set as described above, the coverage ratio S _t ρ _c X / S _c ρ _t (100-X) Must be calculated.

  Therefore, in order to define the toner density, the coverage of the toner on the carrier is modified as described later.

First, in order to simplify the equation, it is transformed into an equation in the range of the reciprocal of the coverage as shown in the following equation.
A ≦ S _c ρ _t (100−X) / S _t ρ _c X ≦ B

Here, when k = S _t ρ _c / S _c ρ _t , the following equation can be obtained.
A ≦ (100−X) / kX ≦ B
AkX ≦ 100−X ≦ BkX
(Ak + 1) X ≦ 100 ≦ (Bk + 1) X
100 / (Bk + 1) ≦ X ≦ 100 / (Ak + 1)

Further, based on the examples described later, the specific gravity of the toner is 1.2, the specific gravity of the carrier is 4.8, and the specific surface area of the toner is 7800 cm ² / cm ³ or more and 7810 cm ² / cm ³ or less, When the specific surface area of the carrier is 895 cm ² / cm ³ or more and 1010 cm ² / cm ³ or less, A is determined to be 0.34 and B is 0.75, the specific gravity of the toner is 1.2, and the specific gravity of the carrier is In the two-component developer , which is 4.8, the specific surface area of the toner is 7800 cm ² / cm ³ or more and 7810 cm ² / cm ³ or less, and the specific surface area of the carrier is 895 cm ² / cm ³ or more and 1010 cm ² / cm ³ or less. As shown in equation (1), the toner density can be defined.

  When the toner density is smaller than 100 / (0.75 k + 1), the coverage of the toner with respect to the carrier becomes insufficient, and a sufficient image density cannot be obtained. On the other hand, when the ratio is larger than 100 / (0.34k + 1), the coverage of the toner with respect to the carrier becomes too large, the environmental stability is deteriorated, and white background fogging occurs.

  The toner density indicates the ratio of the developer toner to the carrier at the time of manufacture, and the ratio needs to be maintained in the developing device during operation of the apparatus.

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

(resin)
The toner base particles include a resin. As the resin, known resins can be used, such as polystyrene, styrene-acrylic copolymer, styrene-acrylonitrile copolymer, styrene-maleic anhydride copolymer, styrene-acrylic-maleic anhydride copolymer, polychlorinated. Examples thereof include vinyl, polyolefin resin, epoxy resin, silicone resin, polyamide resin, polyurethane resin, urethane-modified polyester resin, and acrylic resin. 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.

  As a thermal property, the glass transition point (Tg) is preferably 40 ° C. or higher and 70 ° C. or lower. When the temperature is lower than 40 ° C., the toner melts when the temperature inside the apparatus rises, and aggregation of 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. A well-known thing can be used for a coloring agent, and carbon black, iron black, an alloy azo dye, an oil-soluble dye, a pigment, etc. can be mentioned. 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 resin component. If the amount is less than 1 part by weight, a sufficient image density cannot be ensured. 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. Known waxes 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 resin component. 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, carboxylic acid 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. One kind of the above external additives 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)
Resins, colorants, release agents, charge control materials and the like were sufficiently mixed by a mixer such as a Henschel mixer or a super mixer, and the resulting mixture was 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.

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

(Core material)
The carrier is configured to include a core material. As the core material, a known carrier can be used as the core material, and examples thereof include an iron powder carrier and a ferrite carrier. The shape can be from irregular to spherical. Furthermore, an average particle diameter of 10 μm or more and 1 mm or less can be used, and more preferably 50 μm or more and 100 μm or less. If it is smaller than 10 μm, a phenomenon that the carrier adheres to the photosensitive member and flows out, that is, a so-called carrier rise is caused, and the toner amount in the developer cannot be controlled well by gradually decreasing the developer amount. The possibility increases. Further, in a severe case, the developer appears on the recording material. On the other hand, if the diameter is larger than 1 mm, when the toner of the developer is moved from the developing roller to the photosensitive member, 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 an iron powder carrier, 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.

(Coat material)
The carrier is configured to include a coating material. As the coating material, 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.

[Two-component developer]
The two-component developer according to the present invention can be produced by mixing the above-described toner and carrier with a mixer so as to have the above-described 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 the present invention is not limited to these Examples unless it exceeds the gist.

[ Reference example ]
In the reference example , the influence of the carrier coat amount of the carrier constituting the two-component developer (weight% of the coating material with respect to the weight of the core material) was examined.

(Example of toner production)
For 100 parts by weight of resin, 1.0 part of polyethylene (manufactured by Clariant Japan: PE130), 1.5 part of polypropylene (manufactured by Mitsui Chemicals: NP-505), a charge control agent (manufactured by Hodogaya Chemical Co., Ltd .: S) -34), 1 part of magnetite (manufactured by Kanto Denka Co., Ltd .: KBC-100), 5 parts of carbon black (manufactured by Cabot Corporation: 330R) as a colorant, and a super mixer (manufactured by Kawada Corporation: V- 20), and the obtained mixture was melt-kneaded by a biaxial kneader (Ikegai Iron Works Co., Ltd .: 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 of silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: R972) to the toner base particles.

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

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

( Reference Example 3 )
A two-component developer was produced in the same manner as in Reference Example 1 except that the carrier coat amount of the carrier was 4.1%.

( Reference Example 4 )
A two-component developer was produced in the same manner as in Reference Example 1 except that the carrier coat amount of the carrier was 2.2%.

[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 Reference Examples 1 and 2 and Reference Examples 3 and 4 , 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 evaluation results used in Table 1. “A” indicates that it is very excellent, “O” indicates that it is excellent, 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.
A: Image density is 1.33 or more.
○: 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 ( Reference Examples 1 and 2) using a carrier whose coating material is 5% by weight or more based on the weight of the core material has an image density even after printing 100,000 sheets. It was an excellent developer that could be maintained. However, the developer using the carrier whose coating material is less than 5% by weight with respect to the weight of the core material ( Reference Examples 3 and 4 ) has greatly reduced the image density after printing 100,000 sheets.

[ Example]
In the examples, the influence of the toner concentration in the two-component developer was examined.

(Example 1 )
In the above Reference Examples 1 and 2 and Reference Examples 3 and 4 , except that the pulverization conditions such as air pressure when the kneaded material is pulverized by a jet type pulverizer (made by Nippon Pneumatic Industry Co., Ltd .: IDS-2) are changed. 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 are obtained, and by adding 0.3 part of silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: R972), the toner specific gravity ρ _t is 1.2 and the specific surface area _St is A toner having 7810 cm ² / cm ³ was obtained.

8.0 wt% toner and coating amount obtained by the above production method is based on the weight of the core material, the average particle size of 70 [mu] m, the carrier density [rho _c is 4.8, the specific surface area _{S c} is 895cm ² / cm ^The two-component developer was obtained by stirring the spherical carrier No. ³ with a Nauta mixer (manufactured by Hosokawa Micron Corporation: VL-0) for 20 minutes so that the toner concentration becomes 5.0%.

At this time, k = 34.9, and the value of S _c ρ _t (100−X) / S _t ρ _c X is 0.54.

  In addition, the specific surface area was measured using the laser diffraction scattering type particle size distribution measuring apparatus (Horiba Ltd. make: LA-920).

(Example 2 )
8.0 wt% coating weight relative to the weight of the core material, the average particle size of 70 [mu] m, the carrier density [rho _c is 4.8, the specific surface area _{S c} is used profiled carrier is 1010 cm ² / cm ^3, two A two-component developer was produced in the same manner as in Example 1 except that the toner concentration in the component developer was 8.0%.

At this time, k = 30.9, and the value of S _c ρ _t (100−X) / S _t ρ _c X is 0.37.

(Example 3 )
A two-component developer was produced in the same manner as in Example 1 except that the toner concentration in the two-component developer was 3.8%.

At this time, k = 34.9, and the value of S _c ρ _t (100−X) / S _t ρ _c X is 0.73.

(Example 4 )
A two-component developer was produced in the same manner as in Example 1 except that the toner concentration in the two-component developer was 7.7%.

At this time, k = 34.9, and the value of S _c ρ _t (100−X) / S _t ρ _c X is 0.34.

(Example 5 )
A toner specific gravity ρ _{t is} obtained by externally adding 0.3 part of melamine fine particles (manufactured by Nippon Shokubai Co., Ltd .: Eposter S) instead of silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: R972) to the toner base particles produced in Example 1 . but 1.2, the specific surface area _{S t} to obtain toner is 7800cm ² / cm ^3.

8.0 wt% toner and coating amount obtained by the above production method is based on the weight of the core material, the average particle size of 70 [mu] m, the carrier density [rho _c is 4.8, the specific surface area _{S c} is 895cm ² / cm ^A two-component developer was obtained by stirring the spherical carrier No. ³ for 20 minutes with a Nauta mixer (manufactured by Hosokawa Micron Corporation: VL-0) so that the toner concentration was 5.0%.

At this time, k = 34.9, and the value of S _c ρ _t (100−X) / S _t ρ _c X is 0.55.

(Example 6 )
By adding 0.3 parts of titanium oxide fine particles (manufactured by Titanium Industry Co., Ltd .: STT-65C) instead of silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: R972) to the toner base particles produced in Example 1 , toner specific gravity is added. [rho _t is 1.2, the specific surface area _{S t} to obtain toner is 7805cm ² / cm ^3.

8.0 wt% toner and coating amount obtained by the above production method is based on the weight of the core material, the average particle size of 70 [mu] m, the carrier density [rho _c is 4.8, the specific surface area _{S c} is 895cm ² / cm ^A two-component developer was obtained by stirring the spherical carrier No. ³ for 20 minutes with a Nauta mixer (manufactured by Hosokawa Micron Corporation: VL-0) so that the toner concentration was 5.0%.

At this time, k = 34.9, and the value of S _c ρ _t (100−X) / S _t ρ _c X is 0.33.

(Comparative Example 1 )
A two-component developer was produced in the same manner as in Example 1 except that the toner concentration in the two-component developer was 8.0%.

At this time, k = 34.9, and the value of S _c ρ _t (100−X) / S _t ρ _c X is 0.33.

(Comparative Example 2 )
A two-component developer was produced in the same manner as in Example 1 except that the toner concentration in the two-component developer was 3.5%.

At this time, k = 34.9, and the value of S _c ρ _t (100−X) / S _t ρ _c X is 0.79.

[Evaluation methods]
For Examples 1-6 and Comparative Example 1, 2 in Table 2, we were subjected to environmental stability evaluation and image density evaluation below. 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)
After setting the two-component developer, the toner replenishment time after being allowed to stand for 17 hours under high temperature and high humidity (35 ° C., 85%) is measured. 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.
Δ: The value of white background fog is 1.0 or more and less than 1.5.
X: The value of white background fog is 1.5 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 1.33 or more.
○: Image density is 1.30 or more and less than 1.33.
X: The image density is less than 1.30.

As can be seen from Table 2, the values of S _c ρ _t (100-X) / S _t ρ _c X are 0.54 (Example 1 ), 0.37 (Example 2 ), and 0.73 (Example 3 ). ) And 0.34 (Example 4 ) are two-component developers having excellent environmental stability and image density, and S _c ρ _t (100-X) / S _t ρ _c X The two-component developer having a value of 0.33 (Comparative Example 1 ) does not have good environmental stability, and the value of S _c ρ _t (100-X) / S _t ρ _c X is 0.79 ( The developer of Comparative Example 2 ) does not have a good image density. Therefore, S _c ρ _t (100-X)
The value of / S _t ρ _c X is found to be preferably 0.34 or more and 0.75 or less, and the two-component developer satisfying the above formula (1) with the toner concentration is excellent in environmental stability and image density. I found out that it would be something.

In addition, the external additive is a two-component system using melamine fine particles (manufactured by Nippon Shokubai Co., Ltd .: Eposter S) or titanium oxide fine particles (manufactured by Titanium Industry Co., Ltd .: STT-65C) instead of silica fine particles (manufactured by Nippon Aerosil Co., Ltd .: R972). Even in the case of a developer, the value of S _c ρ _t (100-X) / S _t ρ _c X is a preferable range of 0.34 or more and 0.75 or less (Examples 5 and 6 ). It is a developer having excellent stability and image density.

Claims (3)

A two-component developer comprising a toner and a carrier,
The carrier is a core material coated with a coating material,
The coating material is 5% by weight or more and 20% by weight or less based on the weight of the core material,
Toner, toner concentration in the developer, meets the following formula, the specific gravity of the toner is 1.2, the specific gravity of the carrier is 4.8, the specific surface area of the toner 7800cm ² / cm ³ or more 7810Cm ² / cm ³ or less, a two-component developer, wherein the specific surface area of the carrier is less than 895cm ² / cm ³ or more 1010 cm ² / cm ^3.
100 / (0.75k + 1) ≦ X ≦ 100 / (0.34k + 1)
X = Toner concentration (% by weight)
k = Cover factor (k = S _t ρ _c / S _c ρ _t )
ρ _c = specific gravity of carrier
ρ _t = specific gravity of toner
S _c = specific surface area of the carrier (cm ² / cm ³ )
S _t = specific surface area of toner (cm ² / cm ³ )   The two-component developer according to claim 1, wherein the toner contains inorganic fine particles as an external additive.   The two-component developer according to claim 2, wherein the inorganic fine particles are silica.