JP2012083389A - Resin coated carrier and two-component developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a resin coated carrier capable of stably charging a toner with an external additive having a large particle diameter externally added thereto for a long period of time, and to provide a two-component developer.SOLUTION: A resin coated carrier 2 is used together with a toner 3 to which a plurality of kinds of external additives 3a having different average primary particle diameters are externally added, in which at least one kind of external additive 3a in the plurality of kinds of external additives 3a has an average primary particle diameter of 50 nm or more. The carrier comprises a carrier core material 2a and a resin coating layer 2b formed on the surface of the carrier core material 2a. The resin coated layer 2b comprises a coating resin and charging assistant fine particles 2c. The charging assistant fine particles 2c form projections 2d in the resin coating layer 2b, comprise a specified ferrite, and have an average primary particle diameter which is larger than the maximum of the average primary particle diameters of the respective plurality of kinds of external additives 3a and which is 0.2 μm or more and 2.0 μm or less.

Description

  The present invention relates to a resin-coated carrier and a two-component developer.

  With the recent remarkable development of OA equipment, image forming apparatuses such as copying machines, printers, and facsimile machines that perform image formation using an electrophotographic system have become widespread.

  In an image forming apparatus using an electrophotographic system, an image is formed through, for example, charging, exposure, development, transfer, cleaning, static elimination, and fixing processes. In the charging process, the surface of the photoconductor to be rotated is uniformly charged by the charging device. In the exposure process, the charged photoconductor surface is irradiated with laser light by the exposure device, and an electrostatic latent image is formed on the surface of the photoconductor. Is done. Next, in the developing process, the electrostatic latent image on the surface of the photoconductor is developed by the developer charged by being stirred by the developing device, and a toner image is formed on the surface of the photoconductor. The toner image is transferred onto a transfer material by a transfer device. Thereafter, in the fixing step, the toner image is fixed on the transfer material by being heated by a fixing device. Further, the transfer residual toner remaining on the surface of the photoconductor after the image forming operation is removed by a cleaning device in a cleaning process and collected in a predetermined recovery unit, and the residual charge on the surface of the photoconductor after cleaning is removed in a static elimination process. In order to prepare for the next image formation, the charge is removed by the charge removal device.

  In an image forming apparatus using an electrophotographic system, a developer for developing an electrostatic latent image on the surface of a photoreceptor includes a one-component developer containing only toner and a two-component developer containing toner and carrier. Used. The two-component developer has a function separated from that of the toner and the carrier, and unlike the one-component developer, the toner does not have to have the function of the carrier. Therefore, the two-component developer is controlled more than the one-component developer containing only the toner alone. Characteristics are improved, and high-quality images are easily obtained.

  The carrier has two basic functions: a function of stably charging the toner to a desired charge amount and a function of transporting the toner to the photoreceptor. The carrier is stirred together with the toner in the developing tank, conveyed onto the magnet roller, forms a magnetic spike, passes through the regulating blade, returns to the developing tank again, and is repeatedly used. Therefore, the carrier is required to have a stable basic function, in particular, a function of charging the toner stably while being used continuously.

  In order to maintain such a carrier function, for example, a resin-coated carrier in which the surface of the carrier core material is coated with a resin component has been proposed. The resin-coated carrier can suppress generation of toner spent in which the toner component adheres to the surface of the resin-coated carrier, and can stably charge the toner.

  In recent years, in order to reduce the power consumption of the fixing device, a toner that can obtain a sufficient fixing strength even at a low fixing temperature is used. In such a toner, a resin material that is easily deformed by heat and pressure is used as a binder resin contained in the toner. When such a toner is used together with a resin-coated carrier, toner spent on the surface of the resin-coated carrier is likely to occur, resulting in a problem of destabilization of the charge amount of the toner.

  In order to solve such a problem, Patent Document 1 includes particles (alumina or silica) having a particle diameter larger than the thickness of the resin coating layer in the resin coating layer, and the resin coating layer protrudes from the resin coating layer. A resin-coated carrier having a portion formed therein is disclosed. According to the resin-coated carrier disclosed in Patent Literature 1, the strong impact on the binder resin caused by agitating the toner and the resin-coated carrier in the developing tank can be mitigated by the convex portions formed by the particles. Therefore, generation of toner spent on the surface of the resin-coated carrier can be suppressed.

JP 2001-188388 A

  In recent years, for the purpose of improving transferability, a toner to which an external additive having an average primary particle diameter of 50 nm or more and a large particle diameter is externally added is used. A two-component developer containing such a toner and a resin-coated carrier has a problem that the toner cannot be stably charged over a long period of time.

  The reason for this is that the stirring in the developing tank causes a large particle size external additive to adhere and embed in the resin coating layer of the resin coated carrier, preventing normal frictional charging between the toner and the resin coated carrier. This is because the charge imparting ability of the resin-coated carrier to the toner is reduced.

  Even when the resin-coated carrier disclosed in Patent Document 1 is used as a resin-coated carrier to be combined with a toner to which an external additive having a large particle size is externally added, the external additive having a large particle size is added to the resin-coated layer. If the toner adheres and is buried, the ability to impart charge to the toner may be reduced.

  An object of the present invention is to provide a resin-coated carrier and a two-component developer capable of stably charging a toner to which an external additive having a large particle size is externally added over a long period of time.

The present invention is a toner to which a plurality of types of external additives having different average primary particle sizes are externally added, and of the plurality of types of external additives, the average primary particle size of at least one type of external additive is A resin-coated carrier used with a toner of 50 nm or more,
A carrier core,
A resin coating layer formed on the surface of the carrier core material and having a convex portion;
The resin coating layer is
A coating resin;
The auxiliary auxiliary fine particles comprising the ferrite represented by the following general formula (1), the ferrite represented by the following general formula (2), or a mixture thereof, wherein the average primary particle size is the above-mentioned plurality of external additives Charge assisting fine particles that are larger than the maximum value of the average primary particle diameters in each of the above and 0.2 μm or more and 2.0 μm or less,
The convex portion is a resin-coated carrier formed by the charging auxiliary fine particles.
M ₁ O · Fe ₂ O ₃ (1)
(In the formula, M ₁ represents a metal element selected from Fe, Mn, Mg, and Zn.)
M ₂ O · 6Fe ₂ O ₃ (2)
(In the formula, M ₂ represents a metal element selected from Ba, Sr, and Pb.)

  In the invention, it is preferable that the resin coating layer further contains fine particles made of a nitrogen-containing organic substance.

In the invention, it is preferable that the coating resin is a cross-linked silicone resin.
In the invention, it is preferable that the carrier core material is porous ferrite having a plurality of pores on the surface, and the charging auxiliary fine particles are fitted into at least a part of the plurality of pores.

  The present invention also provides a toner to which the resin-coated carrier and a plurality of types of external additives having different average primary particle diameters are externally added, wherein at least one type of the external additives is selected from the plurality of types of external additives. And a toner having an average primary particle diameter of 50 nm or more.

  According to the present invention, the resin-coated carrier is a toner to which a plurality of types of external additives having different average primary particle sizes are externally added, and at least one of the plurality of types of external additives is added. It is used together with a toner having an average primary particle diameter of the agent of 50 nm or more, and includes a carrier core material and a resin coating layer formed on the surface of the carrier core material and having a convex portion. The resin coating layer includes a coating resin and charge assisting fine particles, and the convex portion is formed of the charge assisting fine particles. The charge assisting fine particles are composed of the ferrite represented by the general formula (1), the ferrite represented by the general formula (2), or a mixture thereof, and the average primary particle diameter is the same as that of the plurality of external additives. It is larger than the maximum value among the respective average primary particle diameters and is 0.2 μm or more and 2.0 μm or less.

  The charging auxiliary fine particles made of the ferrite represented by the general formula (1), the ferrite represented by the general formula (2), or a mixture thereof reduce the resistance value of the resin coating layer, and make the resin coating layer suitable. The resistance value can be adjusted. Projections are formed in the resin coating layer by such charge auxiliary fine particles, and the average primary particle diameter of the charge auxiliary fine particles is larger than the maximum value of the average primary particle diameters of the plurality of types of external additives, and When the size is 0.2 μm or more and 2.0 μm or less, even if the external additive having a large particle diameter is embedded in the resin coating layer, the convex portion formed of the charging auxiliary fine particles comes into contact with the toner, and the charging auxiliary fine particles are interposed via the charging auxiliary fine particles. As a result, the charge is transferred from the resin-coated carrier to the toner. As a result, the charge imparting ability of the resin-coated carrier to the toner can be stabilized. Such a resin-coated carrier can stably charge the toner for a long period of time.

  According to the invention, since the resin coating layer further contains fine particles made of a nitrogen-containing organic substance, the charge imparting ability of the resin-coated carrier to the toner can be further stabilized.

  According to the invention, the coating resin is a cross-linked silicone resin. When the coating resin is a cross-linked silicone resin, the charge assisting fine particles can be firmly held in the resin coating layer, so that the charge assisting fine particles are detached from the resin coating layer even when stirred in the developing tank for a long period of time. Can be suppressed. Accordingly, the charge imparting ability of the resin-coated carrier to the toner can be further stabilized over a long period of time.

  According to the invention, the carrier core material is porous ferrite having a plurality of pores on the surface, and the charge assisting fine particles are fitted into at least a part of the pores. As a result, the adhesion of the charge assisting fine particles to the carrier core material is enhanced, so that the charge assisting fine particles can be more firmly held in the resin coating layer, and the charge assisting fine particles are further prevented from being detached from the resin coating layer. can do.

  According to the invention, the two-component developer is a toner obtained by externally adding the resin-coated carrier of the invention and a plurality of types of external additives having different average primary particle sizes. Among the agents, since the toner contains at least one external additive having an average primary particle diameter of 50 nm or more, the toner can be stably charged over a long period of time. By forming an image using such a two-component developer, an image having a high image density and no fogging can be stably formed over a long period of time.

1 is a cross-sectional view schematically showing a configuration of a two-component developer 1 according to an embodiment of the present invention. It is the schematic which shows the structure of the measurement jig | tool 9 typically.

  FIG. 1 is a cross-sectional view schematically showing a configuration of a two-component developer 1 according to an embodiment of the present invention. The two-component developer 1 includes a toner 3 and a resin-coated carrier 2 that is an embodiment of the present invention. The toner 3 is obtained by externally adding an external additive 3a having an average primary particle diameter of 50 nm or more to the toner particles 3b. By externally adding the external additive 3a having an average primary particle diameter of 50 nm or more, the transferability of the toner 3 can be improved. A detailed configuration of the toner 3 will be described later.

<Resin coated carrier>
The resin-coated carrier 2 of the present embodiment includes a carrier core material 2a and a resin coating layer 2b.

(Carrier core)
As the carrier core material 2a, those commonly used in this field can be used, and examples thereof include magnetic metals such as iron, copper, nickel and cobalt, and magnetic metal oxides such as ferrite and magnetite toner. When the carrier core material 2a is a magnetic material as described above, a resin-coated carrier 2 suitable for a developer used in the magnetic brush development method can be obtained. Among these, ferrite is preferably used from the viewpoint that the resin-coated carrier 2 having excellent charging performance and durability and having saturation magnetization suitable for a full-color image forming apparatus can be realized.

  As the carrier core material 2a, porous ferrite having a plurality of pores formed on the surface is preferably used. Since the carrier core material 2a is porous ferrite, the charge auxiliary fine particles 2c described later or the fine particles made of a nitrogen-containing organic substance are partially fitted into the pores on the surface of the carrier core material 2a. The adhesion of 2c to the carrier core material 2a is enhanced, and the charging auxiliary fine particles 2c can be firmly held in the resin coating layer 2b, and the charging auxiliary fine particles 2c are prevented from being detached from the resin coating layer 2b. it can.

  The manufacturing method of the carrier core material 2a made of porous ferrite includes a weighing step, a mixing step, a pulverizing step, a granulating step, a calcining step, a firing step, a crushing step, and a classification step. .

[Weighing process, mixing process]
In this step, raw materials of the carrier core material 2a such as magnetic oxide are weighed and mixed to obtain a metal raw material mixture. When two or more kinds of magnetic oxides are used, the blending ratio of the two or more kinds of magnetic oxides is weighed so as to match the intended composition of the magnetic oxide.

  Next, resin particles are added to the metal raw material mixture. Examples of the resin particles added here include carbon-based resin particles such as polyethylene and acrylic. The carbon-based resin particles are burned in a calcining step described later, and a hollow structure is generated in the calcined powder by a gas generated during the burning.

  The volume average particle diameter of the resin particles is preferably 2 to 8 μm. Moreover, it is preferable that the addition amount of a resin particle is 0.1-20 wt% with respect to the whole quantity of the raw material of the carrier core material 2a. By adjusting the addition amount of the resin particles, the area average diameter of the pores formed on the surface of the obtained carrier core material 2a and the area ratio with respect to the total surface area of the carrier core material 2a can be controlled.

[Crushing process]
In this step, the metal raw material mixture and the resin particles are introduced into a pulverizer such as a vibration mill and pulverized to a volume average particle size of 0.5 to 2.0 μm, preferably 1 μm. Next, water, 0.5-2 wt% binder, and 0.5-2 wt% dispersant are added to the pulverized product to form a slurry having a solid content concentration of 50-90 wt%. Wet pulverize with a ball mill. Here, polyvinyl alcohol or the like is preferable as the binder, and ammonium polycarboxylate or the like is preferable as the dispersant.

[Granulation process]
In this step, the wet-pulverized slurry is introduced into a spray dryer, sprayed into hot air at 100 to 300 ° C. and dried to obtain a granulated powder having a volume average particle size of 10 to 200 μm. In consideration of the volume average particle diameter of the resin-coated carrier 2 produced by the present production method, the obtained granulated powder is adjusted in particle size by removing coarse particles and fine powder that deviate from the volume average particle diameter with a vibration sieve. Specifically, since the volume average particle diameter of the resin-coated carrier 2 is preferably 25 to 50 μm, it is preferable to adjust the volume average particle diameter of the granulated powder to 15 to 100 μm.

[Calcination process]
In this step, the granulated powder is put into a furnace heated to 800 ° C. to 1000 ° C. and calcined in the atmosphere to obtain a calcined product. At this time, a hollow structure is formed in the granulated powder by the gas generated by burning the resin particles.

[Baking process]
In this step, the calcined product in which the hollow structure is formed is put into a furnace heated to 1100 to 1250 ° C. and fired, and converted into a ferrite to obtain a fired product. If the firing temperature is high, iron oxidation proceeds and the magnetic force decreases, so that the residual magnetization of the carrier core material 2a can be adjusted, for example, by the firing temperature. The atmosphere at the time of firing is appropriately selected depending on the type of metal raw material such as magnetic oxide among the raw materials of the carrier core material 2a. For example, when the metal raw material is Fe and Mn (molar ratio 100: 0 to 50:50), the nitrogen atmosphere is used. When the metal raw material is Fe, Mn and Mg, a nitrogen atmosphere or an oxygen partial pressure adjusting atmosphere is preferable. When the metal raw material is Fe, Mn and Mg and the molar ratio of Mg exceeds 30%, the air atmosphere may be used. .

[Disintegration process, classification process]
In this step, the fired product obtained in the firing step is coarsely pulverized by hammer mill pulverization or the like, and then primary classified by an airflow classifier. Further, after aligning the particle size with a vibration sieve or an ultrasonic sieve, a non-magnetic component is removed by applying a magnetic separator, thereby obtaining a carrier core material 2a having voids inside and surface pores formed on the surface. .

The carrier core material 2a manufactured in this way is composed of a porous material in which voids are formed inside and a plurality of pores are formed on the surface, and the apparent density is 1.6-2. .2 g / cm ³ .

  The pores on the surface of the carrier core material 2a made of porous ferrite are preferably formed so that the total area thereof is 5 to 30% of the total surface area of the carrier core material 2a. Moreover, it is preferable that the said pore is formed so that the area average diameter may be set to 0.3-1.5 micrometers. When the area ratio of the pores is less than 5%, the carrier core material 2a having a sufficiently small apparent density cannot be obtained. In addition, when the area ratio of the pores exceeds 30% or the area average diameter exceeds 1.5 μm, the mechanical strength of the carrier core material 2a cannot be sufficiently obtained.

  Here, the area average diameter of the pores on the surface of the carrier core material 2a is the area percentage of the cumulative area with respect to all the pores in the cumulative area distribution obtained by integrating the pores formed on the surface of the carrier core material 2a from the small diameter side. The equivalent circle diameter is 50%.

  The pore area ratio P1 and the pore area average diameter are calculated as follows. First, the carrier core material 2a is photographed with a magnification of 1000 times by an electron microscope (trade name: VE-9500, manufactured by Keyence Corporation). Next, a region of 1/2 of the radius of the carrier core material 2a from the center of the carrier core material 2a is trimmed from the photograph, and image analysis software (trade name: A image-kun, manufactured by Asahi Kasei Engineering Co., Ltd.) By extracting and analyzing the outline of the pores on the surface of the carrier core material 2a, the total pore area and the area average diameter on the surface of the carrier core material 2a are calculated. Such an analysis is performed for 50 carrier core materials 2a, and the average value is defined as the pore total area and area average diameter of the surface of the carrier core material 2a. Then, the area of the trimmed region is defined as the total surface area of the carrier core material 2a, and the surface pore area ratio P1 is calculated.

(Resin coating layer)
The resin coating layer 2b is a layer formed on the surface of the carrier core material 2a, and includes a coating resin and charging auxiliary fine particles 2c. In the resin coating layer 2b, convex portions 2d are formed by the charging auxiliary fine particles 2c.

  The coating resin is not particularly limited, and a known resin can be used. However, it is preferable to use a resin containing a silicone resin from the viewpoint that both toner releasability and adhesion with the carrier core material 2a can be achieved.

  The silicone resin is not particularly limited, and those commonly used in this field can be used, but a cross-linked silicone resin is preferable. Since the coating resin is a crosslinkable silicone resin, the charge assisting fine particles 2c and the nitrogen-containing organic fine particles described later can be firmly held in the resin coating layer 2b. It is possible to suppress the charge assisting fine particles 2c and the nitrogen-containing organic fine particles from being detached from the layer 2b. Therefore, the charge imparting ability of the resin-coated carrier 2 to the toner 3 can be further stabilized over a long period of time. Further, since the releasability of the toner 3 from the resin-coated carrier 2 during development can be further improved, the developability can be further improved.

  The cross-linked silicone resin is a known silicone resin that is cured by crosslinking between hydroxyl groups bonded to Si atoms or hydroxyl groups and -OX groups by a heat dehydration reaction, a room temperature curing reaction, or the like, as shown in the following chemical formula.

  The cross-linked silicone resin is not particularly limited, and either a heat curable silicone resin or a room temperature curable silicone resin can be used. In order to crosslink the thermosetting silicone resin, it is necessary to heat the resin to about 200 to 250 ° C. Although heating is not required to cure the room temperature curable silicone resin, it is preferably heated at 150 to 280 ° C. in order to shorten the curing time.

  Among the cross-linked silicone resins, those in which the monovalent organic group represented by R is a methyl group are preferable. Since the crosslinkable silicone resin in which R is a methyl group has a dense crosslink structure, when the resin coating layer 2b is formed using such a crosslinkable silicone resin, a good resin coating such as water repellency and moisture resistance is obtained. Carrier 2 is obtained. However, if the cross-linked structure becomes too dense, the resin coating layer 2b tends to become brittle, so selection of the molecular weight of the cross-linked silicone resin is important.

  The weight ratio (Si / C) between silicon and carbon in the cross-linked silicone resin is preferably 0.3 to 2.2. If the weight ratio of silicon and carbon is less than 0.3, the hardness of the resin coating layer 2b may be reduced, and the life of the resin-coated carrier 2 may be reduced. When the weight ratio of silicon and carbon exceeds 2.2, the charge imparting property of the resin-coated carrier 2 to the toner 3 is likely to be affected by temperature changes, and the resin-coated layer 2b may be embrittled.

  As the cross-linked silicone resin, commercially available products can be used. For example, SR2400, SR2410, SR2411, SR2510, SR2405, 840RESIN, 804RESIN (all trade names, manufactured by Toray Dow Corning Co., Ltd.), KR271, KR272, KR274, KR216 , KR280, KR282, KR261, KR260, KR255, KR266, KR251, KR155, KR152, KR214, KR220, X-4040-171, KR201, KR5202, KR3093, KR240, KR350, KR400 (all trade names, Shin-Etsu Chemical Co., Ltd.) And TSR127B (trade name, manufactured by Momentive Performance Materials Japan GK). Among these, one type may be used alone, or two or more types of resins may be used in combination.

The resin coating layer 2b includes charging auxiliary fine particles 2c that form convex portions 2d on the resin coating layer 2b.
The charging auxiliary fine particles 2c are composed of ferrite represented by the following general formula (1), ferrite represented by the following general formula (2), or a mixture thereof.
M ₁ O · Fe ₂ O ₃ (1)
(In the formula, M ₁ represents a metal element selected from Fe, Mn, Mg, and Zn.)
M ₂ O · 6Fe ₂ O ₃ (2)
(In the formula, M ₂ represents a metal element selected from Ba, Sr, and Pb.)

  The auxiliary chargeable fine particles 2c made of the ferrite represented by the general formula (1), the ferrite represented by the general formula (2), or a mixture thereof reduce the resistance value of the resin coating layer 2b and The layer 2b can be adjusted to an appropriate resistance value. Moreover, even if the resin-coated carrier 2 is agitated for a long time in the developing tank and the resin-coated layer 2b is worn by forming the convex portions 2d on the resin-coated layer 2b by the charging auxiliary fine particles 2c as described above. On the surface of the resin-coated carrier 2, convex portions 2 d formed by the charging auxiliary fine particles 2 c remain.

  The average primary particle diameter of the auxiliary charging fine particles 2c is larger than the maximum value among the average primary particle diameters of the plurality of types of external additives 3a externally added to the toner particles 3b, and is 0.2 μm or more and 2.0 μm. It is as follows.

  Convex portions are formed on the resin coating layer by the particles represented by the ferrite represented by the general formula (1), the ferrite represented by the general formula (2), or particles other than the mixture thereof, for example, particles composed of alumina. When the external additive 3a having an average primary particle diameter of 50 nm or more is embedded in the resin-coated carrier, the charge-providing ability of the resin-coated carrier with respect to the toner 3 is reduced, but the charge-added fine particles 2c as described above are formed. Even if the resin-coated carrier 2 of this embodiment including the resin coating layer 2b having the convex portion 2d is stirred for a long time in the developing tank and the external additive 3a having a large particle diameter is buried in the resin coating layer 2b, Since the convex portion 2d formed of the charging auxiliary fine particles 2c comes into contact with the toner 3 and charges are transferred from the resin-coated carrier 2 to the toner 3 via the charging auxiliary fine particles 2c, the protrusion 2d is formed over a long period of time. The charge imparting ability to the toner 3 in the resin-coated carrier 2 can be stabilized.

  When the average primary particle diameter of the auxiliary charging fine particles 2c is equal to or smaller than the maximum value of the average primary particle diameters of the plurality of types of external additives 3a or smaller than 0.2 μm, the external additive 3a is used for a long period of use. When buried in the resin coating layer 2b, normal frictional charging between the toner 3 and the resin coated carrier 2 is hindered, and a decrease in the charge imparting ability of the resin coated carrier 2 to the toner 3 cannot be suppressed. When the volume average particle diameter of the charging auxiliary fine particles 2c exceeds 2.0 μm, the charging auxiliary fine particles 2c are easily detached from the resin coating layer 2b.

Among the ferrites represented by the above general formula (1), the ferrites represented by the above general formula (2), or a mixture thereof, the magnetite having a low resistance value among the ferrites (general formula) : FeO.Fe ₂ O ₃ ) can remarkably stabilize the charge imparting ability of the resin-coated carrier 2 to the toner 3. Further, in the case where ferrites containing alkaline earth metals such as barium ferrite (general formula: BaO.6Fe ₂ O ₃ ) and strontium ferrite (general formula: SrO.6Fe ₂ O ₃ ) are used as the auxiliary charging fine particles 2c, Due to its high electron donating property, the charge imparting ability of the resin-coated carrier 2 to the toner 3 can be more remarkably stabilized. In consideration of stabilizing the charge imparting ability of the resin-coated carrier 2 to the toner 3, the ferrite represented by the general formula (1) and the ferrite represented by the general formula (2) It is preferable to use the ferrite represented by the general formula (2).

The volume resistance value of the auxiliary charging fine particles 2c under an electric field of 1000 V / cm is preferably 1.0 × 10 ⁶ Ω / cm or more and 1.0 × 10 ¹² Ω / cm or less. When the volume resistance value of the auxiliary chargeable fine particles 2c under an electric field of 1000 V / cm is within the above range, the charge imparting ability of the resin-coated carrier 2 to the toner 3 can be further stabilized.

When the volume resistance value of the auxiliary chargeable fine particles 2c under an electric field of 1000 V / cm is less than 1.0 × 10 ⁶ Ω / cm, the resistance value of the resin-coated carrier 2 is remarkably reduced, and thus the carrier adheres to the photoreceptor. May increase. When the volume resistivity value of the charging auxiliary fine particles 2c under an electric field of 1000 V / cm exceeds 1.0 × 10 ¹² Ω / cm, the toner 3 can be stabilized even if the charging auxiliary fine particles 2c are contained in the resin coating layer 2b. It cannot be charged.

  Here, the volume resistance value of the auxiliary charging fine particles 2c under an electric field of 1000 V / cm is measured by a measuring jig 9 as shown in FIG. FIG. 2 is a schematic view schematically showing the configuration of the measuring jig 9. The measuring jig 9 includes a magnet 6, two aluminum electrodes 7, and a base (acrylic resin plate) 8. The distance between the electrodes 7 is 1 mm, and parallel plate electrodes having a size of 10 mm × 40 mm are formed. 200 mg of charging auxiliary fine particles 2c are inserted between the electrodes, and then a magnet 6 (surface magnetic flux density of 1500 gauss, magnet area of opposing part of 10 mm × 30 mm) is arranged so that the N pole and the S pole are opposed to each other. The fine particles 2c are held between the electrodes. The bridge resistance value is calculated by measuring the current value when the DC voltage is applied to this electrode 7 up to 800V in 1V step, and this value is set as the volume resistance value of the auxiliary charging fine particles 2c.

  The content of the charging auxiliary fine particles 2c is preferably 40 to 120 parts by weight with respect to 100 parts by weight of the solid content of the coating resin. When the content of the charging auxiliary fine particles 2c is less than 40 parts by weight, the charge imparting ability of the resin-coated carrier 2 with respect to the toner 3 cannot be sufficiently stabilized. When the content of the charging auxiliary fine particles 2c exceeds 120 parts by weight, the aggregation between the charging auxiliary fine particles 2c increases, and the aggregate of the resin-coated carriers 2 increases when the resin coating layer 2b is formed. The reason why the aggregates between the resin-coated carriers 2 increase when the aggregation between the charge-assisting fine particles 2c increases is not clear, but the aggregate of the charge-assistant fine particles 2c works to adhere the resin-coated carriers 2 to each other. This is presumed to be

(Nitrogen-containing organic fine particles)
The resin coating layer 2b preferably includes fine particles made of a nitrogen-containing organic material (hereinafter referred to as “nitrogen-containing organic fine particles”). When the resin coating layer 2b contains the nitrogen-containing organic fine particles together with the auxiliary charging fine particles 2c, the charge imparting ability of the resin-coated carrier 2 to the toner 3 can be further stabilized over a long period of time. The reason for this is not clear, but the nitrogen-containing organic fine particles have high electron donating properties, and the nitrogen-containing organic fine particles serve as a charge supply source to the charging auxiliary fine particles 2c. Conceivable.

  Examples of the resin constituting the nitrogen-containing organic fine particles include melamine resin and benzoguanamine resin.

  The content of the nitrogen-containing organic fine particles is preferably 15 to 60 parts by weight with respect to 100 parts by weight of the solid content of the coating resin. When the content of the nitrogen-containing organic fine particles is less than 15 parts by weight, it cannot sufficiently serve as a charge supply source to the auxiliary charging fine particles 2c. The effect of further stabilizing the charge imparting ability is not sufficiently exhibited. When the content of the nitrogen-containing organic fine particles exceeds 60 parts by weight, the aggregation between the nitrogen-containing organic fine particles increases, and the aggregate of the resin-coated carriers 2 increases when the resin coating layer 2b is formed. When the aggregation between the nitrogen-containing organic fine particles increases, the reason why the aggregate between the resin-coated carriers 2 increases is not clear, but the aggregate of the nitrogen-containing organic fine particles works to adhere the resin-coated carriers 2 to each other. This is presumed to be

  The average primary particle diameter of the nitrogen-containing organic fine particles is preferably 0.2 μm or more and smaller than the average primary particle diameter of the auxiliary charging fine particles 2c. When the average primary particle diameter of the nitrogen-containing organic fine particles is less than 0.2 μm, the toner cannot sufficiently serve as a charge supply source to the auxiliary charging fine particles 2c. The effect of further stabilizing the charge imparting ability with respect to 3 is not sufficiently exhibited. When the average primary particle size of the nitrogen-containing organic fine particles is equal to or larger than the average primary particle size of the charging auxiliary fine particles 2c, the convex portions formed by the nitrogen-containing fine particles become larger than the convex portions 2d formed by the charging auxiliary fine particles 2c. Therefore, the convex portion 2d formed by the charge assisting fine particles 2c is difficult to come into contact with the toner 3, and the charge imparting ability to the toner 3 cannot be stabilized.

(Conductive particles)
The resin coating layer 2b may contain conductive particles. By containing the conductive particles in the resin coating layer 2b, the charge imparting ability of the resin-coated carrier 2 to the toner 3 can be enhanced, and the toner 3 can be more stably charged over a long period of time.

  As the conductive particles, for example, conductive carbon black, oxides such as conductive titanium oxide and tin oxide are used. Carbon black or the like is suitable for developing conductivity with a small addition amount, but there is a concern that the color toner may be desorbed from the resin coating layer 2b of the resin-coated carrier 2. In this case, conductive titanium oxide doped with antimony may be used.

  The conductive particles can be used alone or in combination of two or more. Although the volume average particle diameter of the conductive particles is not particularly limited, it is preferably 0.02 to 2 μm, more preferably 0.02 to 1 μm. The volume average particle diameter is a value measured using a laser diffraction / scattering particle size measuring device (for example, LA-920 manufactured by Horiba, Ltd.).

  The content of the conductive particles in the resin coating layer 2b is not particularly limited, but is preferably 30 parts by weight or less, more preferably 1 part by weight or more and 30 parts by weight or less with respect to 100 parts by weight of the coating resin. If the content of the conductive particles exceeds 30 parts by weight with respect to 100 parts by weight of the coating resin, the conductive particles are likely to be lost from the resin coating layer 2b, which may affect the color image. Further, the mechanical strength of the resin coating layer 2b and the adhesion to the carrier core material 2a become insufficient, and the resin coating layer 2b may be peeled off to expose the carrier core material 2a. When the resin coating layer 2b is peeled and the carrier core material 2a is exposed, the charging performance is changed as compared with the initial resin-coated carrier 2, and the toner 3 may not be stably charged.

  By setting the content of the conductive particles to 30 parts by weight or less with respect to 100 parts by weight of the coating resin, the loss of the conductive particles from the resin coating layer 2b can be prevented and the influence on the color image can be suppressed. . Further, since the mechanical strength of the resin coating layer 2b and the adhesion to the carrier core material 2a can be improved, the resin-coated carrier 2 capable of charging the toner 3 stably for a long time is realized. Therefore, a developer capable of forming a high-quality image more stably is realized.

  If the content of the conductive particles is less than 1 part by weight with respect to 100 parts by weight of the coating resin, the effect of adding the conductive particles is not seen, and there is a possibility that sufficient charge cannot be imparted to the toner 3. . By setting the content of the conductive particles to 1 part by weight or more with respect to 100 parts by weight of the coating resin, the effect of adding the conductive particles can be expressed more reliably and sufficient charge can be imparted to the toner 3. .

(Silane coupling agent)
The resin coating layer 2b may contain a silane coupling agent in order to make the adjustment of the charge amount of the toner 3 easier. Among them, a silane coupling agent having an electron donating functional group is preferable, and an amino group-containing silane coupling agent is more preferable. A well-known thing can be used as an amino group containing silane coupling agent, For example, what is shown to following General formula (3) is mentioned.
(Y) nSi (R) m (Z) q (3)
(In the formula, m R and q Z represent the same or different alkyl group, alkoxy group or chlorine atom. N Y represents a hydrocarbon group containing the same or different amino group. M and n Each represents an integer of 1 to 3, provided that m + q + n = 4.)

In the general formula (1), examples of the alkyl group represented by R and Z include, for example, a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group. And a straight chain or branched chain alkyl group, and among these, a methyl group, an ethyl group, and the like are preferable. Examples of the alkoxy group represented by R and Z include straight chain or branched chain groups having 1 to 4 carbon atoms such as a methoxy group, an ethoxy group, a propoxy group, an isopropoxy group, a butoxy group, an isobutoxy group, and a tert-butoxy group. Among these, a methoxy group, an ethoxy group, and the like are preferable. Examples of the hydrocarbon group containing an amino group represented by Y include — (CH ₂ ) _a —X (wherein X represents an amino group, an aminocarbonylamino group, an aminoalkylamino group, a phenylamino group, or a dialkylamino group). A represents an integer of 1 to 4, and -Ph-X (wherein X is as defined above; -Ph- represents a phenylene group).

Specific examples of the amino group-containing silane coupling agent include the following.
H ₂ N (H ₂ C) ₃ Si (OCH ₃ ) ₃
H ₂ N (H ₂ C) ₃ Si (OC ₂ H ₅ ) _{3
H 2 N (H 2 C)} 3 Si (CH 3) (OCH 3) 2
_{H 2 N (H 2 C)} 2 HN (H 2 C) 3 Si (CH 3) (OCH 3) 2
H ₂ NOCHN (H ₂ C) ₃ Si (OC ₂ H ₅ ) ₃
H ₂ N (H ₂ C) ₂ HN (H ₂ C) ₃ Si (OCH ₃ ) _{3
H 2 N-Ph-Si (} OCH 3) 3 ( wherein -Ph- indicates a p- phenylene group.)
Ph-HN (H ₂ C) ₃ Si (OCH ₃ ) ₃ (wherein Ph- represents a phenyl group)
(H ₉ C ₄ ) ₂ N (H ₂ C) ₃ Si (OCH ₃ ) ₃

  The amino group-containing silane coupling agent can be used alone or in combination of two or more. The amount of the amino group-containing silane coupling agent is appropriately selected from a range that gives sufficient charge to the toner 3 and does not significantly reduce the mechanical strength of the resin coating layer 2b. It is 10 parts by weight or less, more preferably 0.01 parts by weight or more and 10 parts by weight or less with respect to 100 parts by weight of the composition of the layer 2b.

(Other additives)
When a crosslinkable silicone resin is used as the coating resin, the resin coating layer 2b contains other resins together with the crosslinkable silicone resin as long as the preferable characteristics of the resin coating layer 2b formed of the crosslinkable silicone resin are not impaired. Can do. Examples of other resins include epoxy resins, urethane resins, phenol resins, acrylic resins, styrene resins, polyamides, polyesters, acetal resins, polycarbonates, vinyl chloride resins, vinyl acetate resins, cellulose resins, polyolefins, and copolymers thereof. Examples thereof include resins and compounded resins. In addition, the resin coating layer 2b can contain a bifunctional silicone oil in order to further improve the moisture resistance, releasability and the like of the resin coating layer 2b formed of a cross-linked silicone resin.

  The layer thickness of the resin coating layer 2b is preferably 5 μm or less, and more preferably about 0.1 to 3 μm. With the resin coating layer 2b having such a layer thickness, the convex portions 2d can be formed on the resin coating layer 2b by the charging auxiliary fine particles 2c, and the separation of the charging auxiliary fine particles 2c from the resin coating layer 2b is suppressed. can do. The thickness of the resin coating layer 2b is the average value of the thickness of the resin coating layer 2b including the portion where the convex portion is formed by the charging auxiliary fine particles and the portion where the convex portion 2d is not formed by the charging auxiliary fine particle 2c. The measurement method will be described later.

(Method for producing resin-coated carrier)
The manufacturing method of the resin-coated carrier 2 includes a coating resin solution preparation step and a coating step.

[Coating resin solution preparation process]
In the coating resin solution preparation step, a coating resin solution is prepared. The coating resin solution can be prepared by dissolving or dispersing the raw material of the resin coating layer 2b in an organic solvent.

  The organic solvent is not particularly limited as long as it can dissolve the coating resin. For example, aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, and the like. Examples include alcohols, and mixed solvents of two or more of these. By using such a coating resin solution in the coating step described later, the resin coating layer 2b can be easily formed on the surface of the carrier core material 2a.

[Coating process]
In the coating step, the resin coating layer 2b is formed on the surface of the carrier core material 2a using a coating resin solution. The resin coating layer 2b is formed by attaching a coating resin solution to the surface of the carrier core material 2a to form a coating layer, volatilizing and removing the organic solvent from the coating layer by heating, and further heat-curing the coating layer during or after drying. It can be formed by curing. Thereby, the resin-coated carrier 2 is obtained.

  As a method for attaching the coating resin liquid to the surface of the carrier core material 2a, for example, an immersion method in which the carrier core material 2a is impregnated with the coating resin liquid, a spray method in which the coating resin liquid is sprayed on the carrier core material 2a, Examples thereof include a fluidized bed method in which a coating resin liquid is sprayed onto the carrier core material 2a in a state. Among these, the dipping method is preferable because the resin coating layer 2b can be easily formed.

  A drying accelerator may be used for drying the coat layer. Known drying accelerators can be used, and examples thereof include lead such as naphthylic acid and octylic acid, metal soap such as iron, cobalt, manganese and zinc salts, and organic amines such as ethanolamine. The drying accelerator is used by being contained in the coating resin solution.

  A curing catalyst may be used for curing the coat layer. Examples of the curing catalyst include organic titanium compounds such as ORGATICS TC-401, TC-750, and TC-100 (manufactured by Matsumoto Fine Chemical Co., Ltd.). The curing catalyst is used by being contained in the coating resin solution.

  Curing of the coat layer is performed while selecting a heating temperature according to the type of coating resin. For example, it is preferable to carry out by heating to about 150 to 280 ° C. When the coating resin is of a type that cures at room temperature, heating is not essential, but for the purpose of improving the mechanical strength of the resin coating layer 2b to be formed, shortening the curing time, etc. You may heat to about 150-280 degreeC.

[Fine particle addition process]
When porous ferrite is used as the carrier core material 2a, a fine particle addition step may be performed before the coating step.

  In the fine particle addition step, the carrier core material 2a made of porous ferrite is immersed in a fine particle dispersion liquid in which the charge auxiliary fine particles 2c or the nitrogen-containing organic fine particles are dispersed in an organic solvent, and heated with stirring (temperature: 80- 100 ° C.). Here, the organic solvent is not particularly limited as long as it does not dissolve the charging auxiliary fine particles 2c or the nitrogen-containing organic fine particles, and examples thereof include toluene. Thereafter, the organic solvent is volatilized and removed, so that the pores on the surface of the carrier core material 2a are blocked with the charge assisting fine particles 2c or the nitrogen-containing organic fine particles (the carrier core material with attached nitrogen-containing organic fine particles, the charge assisting fine particles). Adhesive carrier core material) is obtained. Thus, before forming the resin coating layer 2b, the resin coating layer 2b can be formed with a small amount of resin by closing the pores on the surface of the carrier core material 2a with the auxiliary charging fine particles 2c or the nitrogen-containing organic fine particles. it can.

  Note that, in this step, the charge assisting fine particles 2c and the nitrogen-containing organic fine particles are not used to block all the plurality of pores on the surface of the carrier core material 2a. There are irregularities on the surface of the carrier core material 2a due to the pores not blocked by either the fine particles 2c or the nitrogen-containing organic fine particles. Therefore, for example, when the resin coating layer 2b is formed on the surface of the carrier core material with attached nitrogen-containing organic fine particles in the coating step, some of the pores of the carrier core material 2a are previously blocked with nitrogen-containing organic fine particles. However, the auxiliary charging fine particles 2c are fitted into the remaining pores not covered with the nitrogen-containing organic fine particles. Therefore, in this step, even if some of the pores on the surface of the carrier core material 2a are blocked with nitrogen-containing organic fine particles, the remaining pores in which the charging auxiliary fine particles 2c are not blocked with nitrogen-containing organic fine particles in the coating step Therefore, the adhesion of the charge assisting fine particles 2c to the carrier core material 2a is increased.

  As the fine particles used in the fine particle addition step, nitrogen-containing organic fine particles are preferable to the charging auxiliary fine particles 2c. The nitrogen-containing organic fine particles have a greater effect of closing the pores on the surface of the carrier core material 2a, and the amount of the coating resin liquid can be reduced. This is because the nitrogen-containing organic fine particles have better dispersibility in a solvent such as toluene than the charging auxiliary fine particles 2c, and the pores on the surface of the carrier core material 2a can be uniformly filled.

  Further, in this step, the pores of the carrier core material 2a may be blocked with the charging auxiliary fine particles 2c and the nitrogen-containing organic fine particles. In that case, a fine particle dispersion in which the charging auxiliary fine particles 2c and the nitrogen-containing organic fine particles are dispersed in an organic solvent is attached to the carrier core material 2a, and the organic solvent is volatilized and removed.

<Toner>
A two-component developer 1 according to an embodiment of the present invention includes a resin-coated carrier 2 according to the present invention and an external additive 3a having an average primary particle diameter of 50 nm or more added to the toner particles 3b. Toner 3.

  Examples of the raw material for the toner particles 3b include a binder resin, a colorant, a release agent, and a charge control agent.

(Binder resin)
The binder resin is not particularly limited, and a known binder resin for black toner or color toner can be used. Examples thereof include polyester resins, polystyrene, styrene resins such as styrene-acrylic acid ester copolymer resins, acrylic resins such as polymethyl methacrylate, polyolefin resins such as polyethylene, polyurethane, and epoxy resins. Moreover, you may use resin obtained by mixing a raw material monomer mixture with a mold release agent and performing a polymerization reaction. Binder resin may be used individually by 1 type, and may use 2 or more types together.

  When a polyester resin is used as the binder resin, examples of the aromatic alcohol component for obtaining the polyester resin include bisphenol A, polyoxyethylene- (2.2) -2,2-bis (4-hydroxyphenyl) propane. , Polyoxyethylene- (2.0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene- (2.0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene -(2.2) -Polyoxyethylene- (2.0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene- (6) -2,2-bis (4-hydroxyphenyl) propane , Polyoxypropylene- (2.2) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene (2.4) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene - (3.3) such as 2,2-bis (4-hydroxyphenyl) propane and derivatives thereof.

  The polybasic acid component of the polyester resin includes succinic acid, adipic acid, sebacic acid, azelaic acid, dodecenyl succinic acid, n-dodecyl succinic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid. , Dibasic acids such as cyclohexanedicarboxylic acid, orthophthalic acid, isophthalic acid and terephthalic acid, acids having three or more bases such as trimellitic acid, trimetic acid and pyromellitic acid, and anhydrides and lower alkyl esters thereof. From the viewpoint of heat-resistant aggregation, terephthalic acid or its lower alkyl ester is preferred.

  Here, the acid value of the polyester resin is preferably 5 to 30 mgKOH / g. If the acid value is less than 5 mg KOH / g, the charging characteristics of the resin may be lowered, or the charge control agent may be difficult to disperse in the polyester resin. This may adversely affect the charge amount stability of repeated development due to rising of the charge amount and continuous use. When the acid value exceeds 30 mgKOH / g, the hygroscopicity due to the functional group resulting from the acid value is improved, and the charge amount may change due to a change in use environment, for example, the charge amount may decrease in a high temperature and high humidity environment. . Therefore, the above range is preferable. The acid value is measured according to a potentiometric titration method described in Japanese Industrial Standard (JIS) K0070-1992.

  The glass transition temperature (Tg) of the binder resin is not particularly limited and can be appropriately selected from a wide range. However, considering the fixability and storage stability of the toner 3 to be obtained, the glass transition temperature (Tg) may be 40 ° C. or higher and 80 ° C. or lower. preferable. When the temperature is less than 30 ° C., the storage stability becomes insufficient, so that the toner 3 is likely to be thermally aggregated inside the image forming apparatus, which may cause development failure. Further, the temperature at which the high temperature offset phenomenon starts to occur (hereinafter referred to as “high temperature offset start temperature”) is lowered. The high temperature offset phenomenon means that when toner 3 is fixed on a recording medium by heating and pressurizing with a fixing member such as a heating roller, the toner 3 is overheated, whereby the cohesive force of the toner particles 3b is changed between the toner 3 and the fixing member. This is a phenomenon in which the toner layer is divided below the adhesive strength of the toner, and a part of the toner 3 adheres to the fixing member and is removed. On the other hand, when the temperature exceeds 80 ° C., the fixing property is deteriorated, so that fixing failure may occur.

The softening temperature (T _1/2 ) of the binder resin is not particularly limited and can be appropriately selected from a wide range, but is preferably 150 ° C. or lower, and more preferably 60 ° C. or higher and 120 ° C. or lower. When the temperature is less than 60 ° C., the storage stability of the toner 3 is lowered, the toner 3 is likely to be thermally aggregated inside the image forming apparatus, and the toner 3 cannot be stably supplied to the image bearing member. Defects may occur. In addition, a failure of the image forming apparatus may be induced. If the temperature exceeds 120 ° C., the toner 3 is difficult to melt or soften when the toner 3 is fixed to the recording medium, so that the fixability of the toner 3 to the recording medium is lowered, and there is a possibility that fixing failure occurs.

  The molecular weight of the binder resin is not particularly limited and can be appropriately selected from a wide range. However, the weight average molecular weight (Mw) is preferably 5,000 or more and 500,000 or less. If it is less than 5,000, the mechanical strength of the binder resin is lowered, and the resulting toner particles 3b are easily pulverized by stirring or the like inside the developing device, and the shape of the toner particles 3b is changed. There is a risk of variation. On the other hand, if it exceeds 500,000, it becomes difficult to be melted, so that the fixability of the toner 3 is lowered, and there is a possibility that fixing failure occurs. Here, the weight average molecular weight of the binder resin is a value in terms of polystyrene measured by GPC.

(Coloring agent)
As the colorant, various colorants can be used according to a desired color, and examples thereof include a yellow toner colorant, a magenta toner colorant, a cyan toner colorant, and a black toner colorant. .

  Examples of the colorant for yellow toner include C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 5, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 15 and C.I. I. Pigment yellow 17, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 180, C.I. I. Organic pigments such as CI Pigment Yellow 185, inorganic pigments such as yellow iron oxide and ocher, C.I. I. Nitro dyes such as Acid Yellow 1, C.I. I. Solvent Yellow 2, C.I. I. Solvent Yellow 6, C.I. I. Solvent Yellow 14, C.I. I. Solvent Yellow 15, C.I. I. Solvent Yellow 19, and C.I. I. Examples thereof include oil-soluble dyes such as Solvent Yellow 21.

  Examples of the colorant for magenta toner include C.I. I. Pigment red 49, C.I. I. Pigment red 57, C.I. I. Pigment red 81, C.I. I. Pigment red 122, C.I. I. Solvent Red 19, C.I. I. Solvent Red 49, C.I. I. Solvent Red 52, C.I. I. Basic Red 10, C.I. I. Disperse Red 15 etc. are mentioned.

  Examples of the colorant for cyan toner include C.I. I. Pigment blue 15, C.I. I. Pigment blue 16, C.I. I. Solvent Blue 55, C.I. I. Solvent Blue 70, C.I. I. Direct Blue 25, C.I. I. Direct Blue 86 and the like can be mentioned.

  Examples of the colorant for black toner include carbon black such as channel black, roller black, disk black, gas furnace black, oil furnace black, thermal black, and acetylene black. From these various types of carbon black, an appropriate carbon black may be appropriately selected according to the design characteristics of the toner to be obtained.

  As the colorant, in addition to these pigments, a red pigment, a green pigment, or the like may be used. A coloring agent may be used individually by 1 type, and may use 2 or more types together. Two or more of the same color can be used, and one or more of the different colors can also be used.

  The colorant may be used in the form of a masterbatch. The master batch of the colorant can be produced in the same manner as a general master batch. For example, it can be produced by kneading a melt of a synthetic resin and a colorant to uniformly disperse the colorant in the synthetic resin, and then granulating the resulting melt-kneaded product. As the synthetic resin, the same kind as that of the toner binder resin or one having good compatibility with the toner binder resin is used. At this time, the use ratio of the synthetic resin and the colorant is not particularly limited, but is preferably 30 to 100 parts by weight with respect to 100 parts by weight of the synthetic resin. The master batch is granulated to a particle size of about 2 to 3 mm.

  Moreover, although the usage-amount of a coloring agent is not restrict | limited in particular, Preferably it is 5-20 weight part with respect to 100 weight part of binder resin. This is not the amount of the master batch but the amount of the colorant itself contained in the master batch. By using the colorant in this range, an image having a high image density and a very good image quality can be formed without impairing various physical properties of the toner.

(Release agent)
The release agent is added to impart releasability to the toner 3 when the toner 3 is fixed on the recording medium. Therefore, compared with the case where a mold release agent is not used, the high temperature offset start temperature can be increased and the high temperature offset resistance can be improved. In addition, the release agent can be melted by heating at the time of fixing the toner 3, the fixing start temperature can be lowered, and the high temperature offset resistance can be improved. As the release agent, those commonly used in this field can be used, for example, paraffin wax and derivatives thereof, petroleum wax such as microcrystalline wax and derivatives thereof, Fischer-Tropsch wax and derivatives thereof, polyolefin wax and derivatives thereof, Low molecular weight polypropylene wax and derivatives thereof, hydrocarbon-based synthetic waxes such as polyolefin polymer waxes (low molecular weight polyethylene wax and the like) and derivatives thereof, carnauba wax and derivatives thereof, rice wax and derivatives thereof, candelilla wax and derivatives thereof , Plant waxes such as wood wax, animal waxes such as beeswax and spermaceti, synthetic oil waxes such as fatty acid amides and phenol fatty acid esters, long chain carboxylic acids and their derivatives , Long chain alcohols and derivatives thereof, silicone polymers, such as higher fatty acids. Derivatives include oxides, block copolymers of vinyl monomers and waxes, graft modified products of vinyl monomers and waxes, and the like. The amount of the release agent used is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

(Charge control agent)
The charge control agent is added for the purpose of controlling the triboelectric charging property of the toner 3. As the charge control agent, a negative charge control agent commonly used in this field can be used. Examples of charge control agents for controlling negative charges include oil-soluble dyes such as oil black and spiron black, metal-containing azo compounds, azo complex dyes, naphthenic acid metal salts, metal complexes and metal salts of salicylic acid and its derivatives ( Examples of the metal include chromium, zinc, zirconium, etc.), boron compounds, fatty acid soaps, long-chain alkyl carboxylates, and resin acid soaps. Among these, a boron compound is particularly preferable as it does not contain a heavy metal. What is necessary is just to use a charge control agent properly according to a use. One charge control agent may be used alone, or two or more charge control agents may be used in combination as required. The amount of the charge control agent used is not particularly limited and can be appropriately selected from a wide range, but is preferably 0.5 to 3 parts by weight with respect to 100 parts by weight of the binder resin.

(Toner production method)
The method for producing the toner particles 3b is not particularly limited, and can be obtained by a known production method. The toner particles 3b can be produced, for example, by a melt kneading pulverization method. The melt-kneading pulverization method includes, for example, a mixing step, a melt-kneading step, a pulverizing step, and a classification step. According to the melt-kneading pulverization method, in the mixing step, a predetermined amount of each of a binder resin, a colorant, a release agent, a charge control agent, and other additives is dry-mixed to obtain a mixture. In the melt-kneading step, the mixture is melt-kneaded, and the resulting melt-kneaded product is cooled and solidified to obtain a solidified product. In the pulverization step, the solidified product is mechanically pulverized. In the classification step, the excessively pulverized toner particles and coarse toner particles are removed from the pulverized product obtained in the pulverization step with a classifier. Through these steps, the toner particles 3b can be manufactured.

  As a mixer used for dry mixing, for example, Henschel mixer (trade name, manufactured by Mitsui Mining Co., Ltd.), super mixer (trade name, manufactured by Kawata Co., Ltd.), mechano mill (trade name, manufactured by Okada Seiko Co., Ltd.), etc. Examples include a Henschel type mixing device, Ongmill (trade name, manufactured by Hosokawa Micron Corporation), hybridization system (trade name, manufactured by Nara Machinery Co., Ltd.), and Cosmo system (trade name, manufactured by Kawasaki Heavy Industries, Ltd.).

  The kneading is performed while stirring and heating to a temperature equal to or higher than the melting temperature of the binder resin (usually about 80 to 200 ° C., preferably about 100 to 150 ° C.). As a kneading machine, for example, a general kneading machine such as a twin-screw extruder, a triple roll, a lab blast mill can be used. More specifically, for example, a uniaxial or biaxial extruder such as TEM-100B (trade name, manufactured by Toshiba Machine Co., Ltd.), PCM-65 / 87 (trade name, manufactured by Ikegai Co., Ltd.), Needex ( Open roll type products such as trade name, manufactured by Mitsui Mining Co., Ltd.). Among these, an open roll type is preferable. Examples of the pulverization of the solidified product obtained by cooling the melt-kneaded product include a cutter mill, a feather mill, and a jet mill. For example, the solidified product is roughly pulverized with a cutter mill and then pulverized with a jet mill to obtain toner particles 3b having a desired volume average particle diameter.

  For the classification, a known classifier capable of removing excessively pulverized toner particles and coarse toner particles by classification by centrifugal force or classification by wind force can be used. For example, a swirling wind classifier (rotary wind classifier), etc. Can be used.

  The toner particles 3b are obtained by, for example, coarsely pulverizing the solidified product of the melt-kneaded product, turning the obtained coarsely pulverized product into an aqueous slurry, treating the resulting aqueous slurry with a high-pressure homogenizer, and pulverizing the resulting fine particles in an aqueous medium It can also be produced by heating and agglomerating and melting. The coarse pulverization of the solidified product of the melt-kneaded product is performed using, for example, a jet mill or a hand mill. By coarse pulverization, coarse powder having a particle size of about 100 μm to 3 mm is obtained. The coarse powder is dispersed in water to prepare an aqueous slurry. When dispersing the coarse powder in water, for example, an aqueous slurry in which the coarse powder is uniformly dispersed can be obtained by dissolving an appropriate amount of a dispersant such as sodium dodecylbenzenesulfonate in water. By treating this aqueous slurry with a high-pressure homogenizer, the coarse powder in the aqueous slurry is atomized, and an aqueous slurry containing fine particles having a volume average particle diameter of about 0.4 to 1.0 μm is obtained. The aqueous slurry is heated, the fine particles are aggregated, and the fine particles are melted and bonded to obtain toner particles 3b having a desired volume average particle diameter and average circularity. The volume average particle diameter and the average circularity can be set to desired values, for example, by appropriately selecting the heating temperature and heating time of the fine aqueous slurry. The heating temperature is appropriately selected from a temperature range not lower than the softening point of the binder resin and lower than the thermal decomposition temperature of the binder resin. When the heating time is the same, normally, the higher the heating temperature, the larger the volume average particle diameter of the toner particles 3b obtained.

  A commercial item is known as a high-pressure homogenizer. Examples of commercially available high-pressure homogenizers include microfluidizer (trade name, manufactured by Microfluidics), nanomizer (trade name, manufactured by Nanomizer), and optimizer (trade name, manufactured by Sugino Machine Co., Ltd.). Chamber type high pressure homogenizer, high pressure homogenizer (trade name, manufactured by Rannie), high pressure homogenizer (trade name, manufactured by Sanmaru Kikai Kogyo Co., Ltd.), high pressure homogenizer (trade name, manufactured by Izumi Food Machinery Co., Ltd.), NANO3000 (Trade name, manufactured by Mie Co., Ltd.).

  The toner particles 3b produced as described above may be spheroidized, and examples of the spheroidizing means include an impact spheronizing device and a hot air spheronizing device. As the impact spheroidizing device, a commercially available device can be used. For example, a faculty (trade name, manufactured by Hosokawa Micron Corporation), a hybridization system (trade name, manufactured by Nara Machinery Co., Ltd.), or the like is used. be able to. Or as a hot-air type | formula spheronization apparatus, what is marketed can also be used, for example, surface modification machine meteo olebo (brand name, Nippon Pneumatic Industry Co., Ltd. product) etc. can be used.

(External additive)
To the toner particles 3b thus obtained, an external additive 3a having an average primary particle diameter of 50 nm or more, preferably 0.1 μm or more and 0.2 μm or less is externally added. When the average primary particle diameter of the external additive 3a is less than 50 nm, transferability cannot be improved particularly in a color toner. When the average primary particle diameter of the external additive 3a exceeds 0.2 μm, the external additive 3a is easily detached from the toner particles 3b.

  As the external additive 3a, those commonly used in this field can be used, and examples thereof include silicon oxide, titanium oxide, silicon carbide, aluminum oxide, and barium titanate.

  In addition to the above, at least one kind of external additive 3a can be used in combination. The external additive 3a that can be used in combination is not particularly limited, and examples thereof include silicon oxide, titanium oxide, silicon carbide, aluminum oxide, and barium titanate. The average primary particle diameter of the external additive 3a that can be used in combination is preferably 5 to 30 nm. By using the external additive 3a having such a particle size in combination, the fluidity of the toner can be improved. If the average primary particle diameter of the external additive 3a that can be used in combination is less than 5 nm, it is difficult to uniformly disperse. If the average primary particle diameter of the external additive 3a that can be used in combination exceeds 30 nm, the effect of improving fluidity is not sufficient.

  Here, the average primary particle size of the external additive 3a is a particle size distribution measuring device using dynamic light scattering, such as DLS-800 (trade name, manufactured by Otsuka Electronics Co., Ltd.), Coulter N4 (trade name, Coulter Electronics). However, since it is difficult to dissociate the secondary aggregation of the particles after the hydrophobization treatment, a scanning electron microscope (SEM) or a transmission electron microscope (TEM) is used. It is preferable to directly obtain a photographic image obtained by a transmission electron microscope) by image analysis.

  The amount of the external additive 3a added is not particularly limited, but is preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the toner particles 3b. By setting the addition amount of the external additive 3a within such a range, it is possible to impart fluidity to the toner 3 and increase transfer efficiency. If the amount of the external additive 3a added is less than 0.1 parts by weight, the toner 3 cannot be provided with sufficient fluidity and the transfer efficiency cannot be increased. When the additive amount of the external additive 3a exceeds 3.0 parts by weight, the external additive 3a tends to adhere to the surface of the resin-coated carrier 2.

  The two-component developer 1 of the present invention can be obtained by mixing and stirring the toner 3 thus obtained with the resin-coated carrier 2 of the present invention.

  The mixing ratio of the resin-coated carrier 2 and the toner 3 is not particularly limited, but considering the use of the resin-coated carrier 2 and the toner 3 in a high-speed image forming apparatus capable of printing more than 40 sheets per minute with an A4 size image, The ratio of the volume average particle size of the resin-coated carrier 2 to the average particle size is preferably 5 or more and the coverage θ is about 50 to 75%. As a result, the chargeability of the toner 3 can be stably maintained in a sufficiently good state, and can be used as a suitable developer that can form a high-quality image stably and for a long period of time even in a high-speed image forming apparatus.

  The value of the coverage θ can be adjusted by the toner concentration in the developer. When the toner concentration in the developer is low (when coverage θ is less than 50%), the toner charge amount tends to increase. When the toner concentration is high (when coverage θ is greater than 75%), the toner charge amount Tend to decrease. Therefore, it is possible to adjust the charge amount to some extent using this phenomenon. However, when using a developer mounted on an actual machine, carrier adhesion becomes a problem due to an increase in the contact area between the carrier and the photoreceptor as the toner concentration is lowered. As the toner concentration is increased, toner scattering becomes more serious as the charge amount decreases.

  Specifically, regarding the relationship between the coverage θ and the toner concentration, the coverage θ is 50 when the volume average particle size of the toner 3 is 6.5 μm and the volume average particle size of the resin-coated carrier 2 is 40 μm. When it is set to ˜75%, about 6.9 to 10.4 parts by weight of toner 3 is contained with respect to 100 parts by weight of resin-coated carrier 2 in the developer. When high-speed development is performed with such a developer, the amount of toner consumed and the amount of toner supplied to the developing tank of the developing device are maximized in accordance with the consumption of toner 3, and the balance between supply and demand is not lost. When the toner 3 is more than about 6.9 to 10.4 parts by weight with respect to 100 parts by weight of the resin-coated carrier 2 in the developer, the charge amount tends to be lower and desired development characteristics can be obtained. In addition to the toner supply amount, the toner consumption amount is larger than the toner supply amount, and sufficient charge cannot be applied to the toner 3, thereby degrading the image quality. On the contrary, when the amount of the toner 3 is small, the charge amount tends to be high, and it becomes difficult for the toner 3 to be separated from the resin-coated carrier 2 by an electric field, resulting in deterioration of image quality.

  In this embodiment, the total projected area of the toner 3 is calculated as follows. The specific gravity of the toner 3 is set to 1.0, and calculation is performed based on the volume average particle diameter obtained with a Coulter counter (trade name: Coulter Counter Multisizer II, manufactured by Beckman Coulter, Inc.). That is, the number of toners in the toner weight to be mixed is calculated, and the number of toners × the toner area (calculated assuming a circle) is set as the total toner projected area. Similarly, the total surface area of the resin-coated carrier 2 is such that the carrier specific gravity is 4.7 and the carrier weight to be mixed based on the particle diameter obtained by Microtrac (trade name: Microtrac MT3000, manufactured by Nikkiso Co., Ltd.). To calculate the total surface area.

  Since the two-component developer of the present invention includes the resin-coated carrier 2 and the toner 3, the toner charge amount can be stabilized over a long period of time, the image density is high, and the image quality such as fogging is small. An image can be formed stably.

  Examples and comparative examples according to the present invention will be described below. The present invention is not limited to this example unless it exceeds the gist.

[Volume average particle diameter of carrier core material]
About 10 to 15 mg of a measurement sample is added to 10 ml of 5% aqueous solution of Emulgen 109P (manufactured by Kao Corporation, polyoxyethylene lauryl ether HLB 13.6), and the measurement sample is dispersed for 1 minute using an ultrasonic disperser. The measurement sample was dispersed in the aqueous solution. About 1 ml of this was filled in a predetermined part of Microtrac MT3000 (Nikkiso Co., Ltd.) and stirred for 1 minute to confirm that the scattered light intensity was stable and measured.

[Volume average particle diameter of toner]
20 ml of 1% aqueous solution (electrolyte) of sodium chloride (first grade) is put into a 100 ml beaker, 0.5 ml of alkylbenzene sulfonate (dispersant) and 3 mg of measurement sample are sequentially added thereto, and ultrasonic dispersion treatment is performed for 5 minutes. Went. To this, a 1% aqueous solution of sodium chloride (first grade) was added so that the total amount became 100 ml, and a sample subjected to ultrasonic dispersion treatment again for 5 minutes was used as a measurement sample. For this measurement sample, a Coulter Counter TA-III (trade name, manufactured by Coulter Co., Ltd.) was used, and measurement was performed under the conditions of an aperture diameter of 100 μm and a measurement target particle diameter of 2 to 40 μm on a number basis. The particle size was calculated.

[Apparent density of carrier core]
The apparent density of the carrier core material was measured according to JIS Z2504 2000.

[Average primary particle size of charge-assisting fine particles and nitrogen-containing organic fine particles]
Using an electron microscope (trade name: VE-9500, manufactured by Keyence Co., Ltd.), the primary particle diameter of 50 charging auxiliary fine particles was measured at a magnification of 10,000 times, and the average value of these was determined as the average of the charging auxiliary fine particles. The primary particle size was used. The average primary particle size of the nitrogen-containing organic fine particles was measured in the same manner.

[Average primary particle size of external additive]
Using an electron microscope (trade name: VE-9500, manufactured by Keyence Corporation), the primary particle diameters of 50 external additives were measured at a magnification of 10,000 times, and the average value of these was determined as the average of the external additives. The primary particle size was used.

[Layer thickness of resin coating layer]
Using a CP (cross section polisher, trade name: SM09020CP, manufactured by JEOL Ltd.), the cross section of the resin-coated carrier was observed, and the thickness of the resin-coated layer was measured at an average of 5 points per resin-coated carrier. Similarly, the thickness of the resin coating layer of ten resin-coated carriers was measured, and the average value of the thicknesses of the resin coating layers of a total of 50 points was taken as the layer thickness of the resin coating layer.

Example 1
[Coating resin solution preparation process]
1.0 part by weight of a cross-linked silicone resin (trade name: KR350, manufactured by Shin-Etsu Chemical Co., Ltd.) is dissolved in 12 parts by weight of toluene, and charged auxiliary fine particles (component: barium ferrite, average primary particle size: 0. 8 μm, volume resistivity: 1.0 × 10 ¹⁰ Ω / cm) 0.8 part by weight, nitrogen-containing organic fine particles (component: melamine resin, average primary particle size: 0.4 μm) 0.3 part by weight, conductivity Particles (trade name: VULCAN XC-72, manufactured by Cabot Corporation) 0.05 parts by weight, coupling agent (trade name: Z-6011, manufactured by Toray Dow Corning Co., Ltd.) 0.05 parts by weight, curing catalyst (product) Name: ORGATICS TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) 0.03 part by weight was internally added or dispersed to prepare a coating resin solution.

[Coating process]
The surface of 100 parts by weight of a carrier core material (Mn—Mg ferrite) having a volume average particle diameter of 40 μm was coated by an immersion method using 14.23 parts by weight of the coating resin solution. Then, after passing through a curing process at a curing temperature of 200 ° C. and a curing time of 1 hour, the resin-coated carrier of Example 1 was obtained by passing through a sieve having an opening of 150 μm.

(Example 2)
In the coating resin solution preparation step, charging auxiliary fine particles made of magnetite (average primary particle size: 0.3 μm, volume resistance value: 1.0 × 10 ⁸ Ω / cm) are replaced with 0 instead of charging auxiliary fine particles made of barium ferrite. .5 parts by weight, except that nitrogen-containing organic fine particles made of melamine resin having an average primary particle size of 0.2 μm were used instead of nitrogen-containing organic fine particles made of melamine resin having an average primary particle size of 0.4 μm. The resin-coated carrier of Example 2 was obtained in the same manner as Example 1.

(Example 3)
In the coating resin solution preparation step, instead of the charging auxiliary fine particles made of barium ferrite, the charging auxiliary fine particles made of Mn—Zn ferrite (average primary particle diameter: 1.9 μm, volume resistivity: 1.0 × 10 ⁹ Ω / cm ) Was used in the same manner as in Example 1 to obtain a resin-coated carrier of Example 3.

Example 4
A resin-coated carrier of Example 4 was obtained in the same manner as in Example 1 except that the nitrogen-containing organic fine particles were not used in the coating resin solution preparation step.

(Example 5)
[Weighing process, mixing process]
As a raw material for the carrier core material, finely pulverized Fe ₂ O ₃ and MgCO ₃ were prepared, weighed so that the molar ratio was Fe ₂ O ₃ : MgCO ₃ = 80: 20, and mixed to obtain a metal raw material mixture. Obtained. Polyethylene resin particles (trade name: LE-1080, manufactured by Sumitomo Seika Co., Ltd.) having a volume average particle diameter of 5 μm corresponding to 0.4 wt% with respect to all raw materials of the carrier core material, and poly corresponding to 1.5 wt% Prepare an aqueous solution in which an ammonium carboxylate-based dispersant, SN wet 980 equivalent to 0.05 wt% (wetting agent, manufactured by San Nopco Co., Ltd.), and polyvinyl alcohol (binder) equivalent to 0.02 wt% were added to water. did.

[Crushing process]
The metal raw material mixture was added to the aqueous solution and stirred to obtain a slurry having a concentration of 75 wt%. This slurry was wet pulverized by a wet ball mill and stirred for a while until the volume average particle diameter became 1 μm.

[Granulation process]
The slurry was sprayed with a spray dryer to obtain a dried granulated product having a volume average particle size of 10 to 200 μm. Coarse grains were separated from the granulated product using a sieve net having a mesh size of 61 μm.

[Calcination process]
The dried granulated product was calcined by heating at 900 ° C. in the atmosphere, and the resin particle component was decomposed to obtain a calcined product.

[Baking process]
The calcined product was calcined for 5 hours in a nitrogen atmosphere at 1160 ° C. to be converted into a ferritic product.

[Disintegration process, classification process]
The fired product was crushed with a hammer mill, fine powder was removed using an air classifier, and the particle size was adjusted with a vibrating screen having a mesh size of 54 μm to obtain a carrier core material made of porous ferrite. The obtained carrier core material had an apparent density of 2.00 g / cm ³ and an area average diameter of surface pores of 0.40 μm.

[Fine particle addition process]
Nitrogen-containing organic fine particles (component: melamine resin, average primary particle size: 0.40 μm) 0.6 parts by weight are added to 15 parts by weight of toluene, and stirred for 5 minutes with a three-one motor to contain nitrogen-containing organic fine particles in toluene. Were dispersed to obtain a nitrogen-containing organic fine particle dispersion.

  In this nitrogen-containing organic fine particle dispersion, 100 parts by weight of a carrier core material made of porous ferrite was immersed and stirred while heating. Thereafter, by removing the toluene by volatilization, nitrogen-containing organic fine particles were adhered to the surface of the carrier core material, and a nitrogen-containing organic fine particle-attached carrier core material having surface pores blocked with nitrogen-containing organic fine particles was obtained.

[Coating resin solution preparation process]
2.0 parts by weight of a cross-linked silicone resin (trade name: KR350, manufactured by Shin-Etsu Chemical Co., Ltd.) is dissolved in 15 parts by weight of toluene, and charged auxiliary fine particles (component: barium ferrite, average primary particle size: 0. 8 μm, volume resistivity: 1.0 × 10 ¹⁰ Ω / cm) 1.6 parts by weight, conductive particles (trade name: VULCAN XC-72, manufactured by Cabot Corporation) 0.10 parts by weight, coupling agent (product) Name: Z-6011, manufactured by Toray Dow Corning Co., Ltd.) 0.10 parts by weight, curing catalyst (trade name: Olga Chicks TC-401, manufactured by Matsumoto Fine Chemical Co., Ltd.) 0.06 parts by weight are internally added or dispersed. A coating resin solution was prepared.

[Coating process]
Using 10.86 parts by weight of the coating resin solution, the surface of 100.6 parts by weight of the nitrogen-containing organic fine particle adhered carrier core material was coated by a dipping method. Then, after passing through a curing process with a curing temperature of 200 ° C. and a curing time of 1 hour, the resin-coated carrier of Example 5 was obtained by passing through a sieve having an opening of 150 μm.

(Example 6)
In the coating resin solution preparation step, charging auxiliary fine particles made of strontium ferrite (average primary particle size: 1.0 μm, volume resistance value: 1.0 × 10 ¹⁰ Ω / cm) were used instead of the charging auxiliary fine particles made of barium ferrite. A resin-coated carrier of Example 6 was obtained in the same manner as Example 1 except that it was used.

(Comparative Example 1)
In the coating resin solution preparation step, a resin-coated carrier of Comparative Example 1 was obtained in the same manner as in Example 1 except that the charge assisting fine particles were not used.

(Comparative Example 2)
In the coating resin solution preparation step, instead of the charging auxiliary fine particles having an average primary particle diameter of 0.8 μm, charging auxiliary fine particles made of magnetite having an average primary particle diameter of 0.1 μm (volume resistance value: 1.0 × 10 ⁸ Ω) Other than using nitrogen-containing organic fine particles made of melamine resin having an average primary particle size of 0.2 μm instead of nitrogen-containing organic fine particles having an average primary particle size of 0.4 μm. In the same manner as in Example 1, a resin-coated carrier of Comparative Example 2 was obtained.

(Comparative Example 3)
In the coating resin solution preparation step, instead of the charging auxiliary fine particles having an average primary particle diameter of 0.8 μm, charging auxiliary fine particles made of magnetite having an average primary particle diameter of 3.0 μm (volume resistance value: 1.0 × 10 ⁷ Ω) / Cm), a resin-coated carrier of Comparative Example 3 was obtained in the same manner as in Example 1.

(Comparative Example 4)
Except that 0.8 parts by weight of alumina fine particles (average primary particle size: 1.0 μm, volume resistance value: 1.0 × 10 ¹⁵ Ω / cm) were used in the coating resin solution preparation step instead of the charging auxiliary fine particles. In the same manner as in Example 1, a resin-coated carrier of Comparative Example 4 was obtained.

(Comparative Example 5)
Other than using amorphous silica fine particles (average primary particle diameter: 1.1 μm, volume resistivity: 1.0 × 10 ¹⁵ Ω / cm) instead of charging auxiliary fine particles made of barium ferrite in the coating resin solution preparation step In the same manner as in Example 1, a resin-coated carrier of Comparative Example 5 was obtained.

  Table 1 shows the constituent components of the resin-coated carriers of Examples and Comparative Examples, and the layer thickness of the resin-coated layer. In addition, when a resin-coated carrier was produced in the same manner as in Examples 1 to 4 and 6 and Comparative Examples 1 to 5 except that the charging auxiliary fine particles and the nitrogen-containing organic fine particles were not used, the film thickness of the resin-coated carrier was When the resin-coated carrier is produced in the same manner as in Example 5 except that the charge auxiliary fine particles and the nitrogen-containing organic fine particles are not used, the thickness of the resin-coated carrier is 0.4 μm.

<Production of toner>
As binder resin, polyester resin (trade name: FC1494, manufactured by Mitsubishi Rayon Co., Ltd.) 87.5 parts by weight, colorant (CI Pigment Red 57: 1), 5 parts by weight, release agent (trade name: HNP11, Nippon Seiki Co., Ltd.) 6 parts by weight and a charge control agent (trade name: LR-147, Nippon Carlit Co., Ltd.) 1.5 parts by weight are premixed in a Henschel mixer and then mixed into a twin screw extruder kneader. And kneaded to obtain a kneaded product.

  The kneaded material was coarsely pulverized with a cutting mill, then finely pulverized with a jet mill, and classified with an air classifier to produce toner base particles having an average primary particle size of 6.5 μm.

  To this toner base particle 97.8% by weight, 1.2% by weight of silica having an average primary particle diameter of 0.1 μm hydrophobized with i-butyltrimethoxysilane, and an average primary particle diameter hydrophobized with HMDS By adding 1.0% by weight of 12 nm silica fine particles and mixing with a Henschel mixer and performing external addition treatment, a negatively chargeable toner (nonmagnetic magenta toner) was obtained. The maximum value of the average primary particle diameters of the plurality of external additives externally added to the toner is 0.1 μm.

<Preparation of two-component developer>
After the resin-coated carriers and toners of Examples and Comparative Examples were put into a resin cylindrical container at a weight ratio such that the ratio of the total projected area of the toner to the total surface area of the resin-coated carrier was 70%, both shafts were A two-component developer was prepared by mixing and stirring on a driving polybottle rotating base under the conditions of a rotation speed of 200 rpm for 1 hour.

<Evaluation>
The following evaluation was performed using the two-component developer.

[Life characteristics]
The two-component developer is set in a copying machine (trade name: MX-5000FN, color printing speed 50 ppm, monochrome printing speed 50 ppm, manufactured by Sharp Corporation), and an image with a printing rate of 5% is obtained at 50000 (50K) at room temperature and humidity. ) Printed. The charge stability of the two-component developer was evaluated using the charge amount of the two-component developer before and after printing 50K sheets. The charge amount of the two-component developer at the initial stage (before printing 50K sheets) and after printing 50K sheets was measured using a suction-type charge amount measuring device.

The evaluation criteria for the charging stability of the two-component developer are as follows.
○: Good. The difference between the initial charge amount and the charge amount after printing 50K sheets is 3 μC / g or less in absolute value.
Δ: Yes. The difference between the initial charge amount and the charge amount after printing 50K sheets is more than 3 μC / g and not more than 5 μC / g in absolute value.
X: Defect. The difference between the initial charge amount and the charge amount after 50K printing is larger than 5 μC / g in absolute value.

  Further, after printing 50K sheets, the image density of the image area and the whiteness of the non-image area were measured. The image density was measured with an X-Rite 938 spectrocolorimeter. For whiteness, tristimulus values X, Y, and Z were determined using an SZ90 type spectroscopic color difference meter manufactured by Nippon Denshoku Industries Co., Ltd.

The image density evaluation criteria are as follows.
○: Good. The image density is 1.4 or higher.
Δ: Yes. The image density is 1.3 or more and less than 1.4.
X: Defect. The image density is less than 1.3.

The evaluation criteria for whiteness are as follows.
○: Good. The value of Z is 0.5 or less.
Δ: Yes. The value of Z is more than 0.5 and 0.7 or less.
X: Defect. The value of Z exceeds 0.7.

[Comprehensive evaluation]
The evaluation criteria for comprehensive evaluation using the above evaluation results are as follows.
A: All the evaluation results of the above evaluations are “◯”.
○: The evaluation result of the above evaluation includes “Δ” but does not include “×”.
X: "x" is included in the evaluation result of the above evaluation.
The evaluation results are shown in Table 2.

  From Table 2, it can be seen that the resin-coated carriers of Examples 1 to 6 can maintain the charge imparting ability with respect to the toner for a long period of time, and can stably form an image having a high image density and no fogging.

  However, the resin-coated carrier of Example 2 had a slight decrease in charging stability because the average primary particle diameter of the charge assisting fine particles was relatively smaller than that of the other examples. In the resin-coated carrier of Example 3, since the average primary particle diameter of the charging auxiliary fine particles was relatively larger than that of the other examples, the charging stability was slightly lowered.

  Since the resin-coated carrier of Example 4 did not contain nitrogen-containing organic fine particles, the charging stability was slightly lowered.

  Since the resin-coated carrier of Comparative Example 1 and the resin-coated carrier of Comparative Example 4 did not contain the charge assisting fine particles, the results were poor.

  The resin-coated carrier of Comparative Example 2 had a poor result because the average primary particle diameter of the charging auxiliary fine particles was relatively smaller than that of the example. The resin-coated carrier of Comparative Example 3 had a poor result because the average primary particle size of the charging auxiliary fine particles was relatively larger than that of the example.

  Since the resin-coated carrier of Comparative Example 5 used silica having a resistance value higher than that of the charge assisting fine particles, the result was poor.

DESCRIPTION OF SYMBOLS 1 2 component developer 2 Resin coated carrier 2a Carrier core material 2b Resin coating layer 2c Charge auxiliary fine particle 2d Convex part 3 Toner 3a External additive 3b Toner particle

Claims (5)

A toner to which a plurality of types of external additives having different average primary particle sizes are externally added, and of the plurality of types of external additives, the average primary particle size of at least one type of external additive is 50 nm or more. A resin-coated carrier for use with toner,
A carrier core,
Formed on the surface of the carrier core material, including a resin coating layer having a convex portion,
The resin coating layer is
A coating resin;
The auxiliary auxiliary fine particles comprising the ferrite represented by the following general formula (1), the ferrite represented by the following general formula (2), or a mixture thereof, wherein the average primary particle size is the above-mentioned plurality of external additives Charge assisting fine particles that are larger than the maximum value of the average primary particle diameters in each of the above and 0.2 μm or more and 2.0 μm or less,
The resin-coated carrier, wherein the convex portion is formed by the charging auxiliary fine particles.
M ₁ O · Fe ₂ O ₃ (1)
(In the formula, M ₁ represents a metal element selected from Fe, Mn, Mg, and Zn.)
M ₂ O · 6Fe ₂ O ₃ (2)
(In the formula, M ₂ represents a metal element selected from Ba, Sr, and Pb.)   The resin-coated carrier according to claim 1, wherein the resin-coated layer further contains fine particles made of a nitrogen-containing organic material.   The resin-coated carrier according to claim 1, wherein the coating resin is a cross-linked silicone resin.   The carrier core material is porous ferrite having a plurality of pores on a surface, and the charging auxiliary fine particles are fitted into at least a part of the plurality of pores. The resin-coated carrier according to any one of the above.   A toner coated with the resin-coated carrier according to any one of claims 1 to 4 and a plurality of types of external additives each having a different average primary particle diameter, wherein the toner includes the plurality of types of external additives. And a toner having an average primary particle diameter of at least one external additive of 50 nm or more.

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