JP6455487B2 - Electrostatic latent image developing carrier and manufacturing method thereof - Google Patents

Description

  The present invention relates to a carrier for developing an electrostatic latent image and a method for producing the same.

  For example, a two-component developer including a carrier (specifically, a carrier for developing an electrostatic latent image) and a positively chargeable toner that is positively charged by friction with the carrier is known. As the carrier, a carrier (resin-coated carrier) containing a carrier core (for example, ferrite particles) and a resin layer coated on the surface of the carrier core can be used. For example, Patent Document 1 describes that a resin layer coated on the surface of a carrier core contains porous carbon black having predetermined physical properties.

JP-A-56-75659

  When the resin layer coated on the surface of the carrier core contains a conductive agent (for example, carbon black), if the content of the conductive agent in the resin layer increases, carrier development (the carrier moves to the toner carrier together with the toner) Phenomenon), and fogging easily occurs. On the other hand, when the content of the conductive agent in the resin layer is low, charge-up (a phenomenon in which the toner is excessively positively charged) easily occurs. Therefore, developability tends to decrease. The occurrence of such a problem becomes significant when continuous printing is performed.

  The present invention has been made in view of the above circumstances, and the object of the present invention is to prevent occurrence of carrier development and occurrence of fog and maintain high developability even when continuous printing is performed. An electrostatic latent image developing carrier is provided. Another object of the present invention is to provide a method for producing a carrier for developing an electrostatic latent image that can prevent occurrence of carrier development and occurrence of fog even when continuous printing is performed, and can maintain high developability. That is.

  The electrostatic latent image developing carrier according to the present invention includes a plurality of carrier particles including a carrier core having a concave portion on the surface, and a first coat layer and a second coat layer that cover the surface of the carrier core. The first coat layer and the second coat layer have a laminated structure in the order of the first coat layer and the second coat layer from the surface of the carrier core. The first coat layer contains a first resin, and the second coat layer contains a second resin. At least the second coat layer of the first coat layer and the second coat layer contains a conductive agent. The electric resistance of the second coat layer is lower than the electric resistance of the first coat layer. The first coat layer covers the entire surface of the carrier core. The second coat layer selectively covers a portion of the surface area of the first coat layer corresponding to the concave portion of the surface of the carrier core.

  The method for producing a carrier for developing an electrostatic latent image according to the present invention includes a first coating step of covering a surface of a carrier core having irregularities with a first coating layer containing a first resin, and a surface of the first coating layer. Including a second coating step of covering with a second coating layer containing a second resin, and a stirring step of stirring the carrier core covered with the first coating layer and the second coating layer. At least the second coat layer of the first coat layer and the second coat layer contains a conductive agent. The electric resistance of the second coat layer is lower than the electric resistance of the first coat layer. In the stirring step, in the surface region of the second coat layer, the second coat layer is scraped and the first coat layer is exposed at a portion corresponding to the convex portion of the surface of the carrier core.

  According to the present invention, even when continuous printing is performed, occurrence of carrier development can be prevented, occurrence of fogging can be prevented, and developability can be maintained high.

It is a figure which shows schematic structure of the two-component developer containing the carrier for electrostatic latent image development which concerns on embodiment of this invention. (A)-(c) is a figure for demonstrating the manufacturing method of the carrier for electrostatic latent image development which concerns on embodiment of this invention, respectively.

  An embodiment of the present invention will be described. Note that the evaluation results (for example, values indicating the shape or physical properties) regarding the powder (more specifically, toner base particles, external additives, toner, carrier, etc.) are averaged from the powder unless otherwise specified. This is the number average of the values measured for each of the average particles by selecting a significant number of such particles.

The number average particle diameter of the powder is the number average value of the equivalent circle diameter of primary particles (diameter of a circle having the same area as the projected area of the particles) measured using a microscope unless otherwise specified. . Moreover, the measured value of the volume median diameter (D ₅₀ ) of the powder is measured using a laser diffraction / scattering particle size distribution measuring device (“LA-750” manufactured by Horiba, Ltd.) unless otherwise specified. It is the value.

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. When the name of a polymer is expressed by adding “system” after the compound name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof. Acrylic and methacrylic are sometimes collectively referred to as “(meth) acrylic”. Further, acrylonitrile and methacrylonitrile may be collectively referred to as “(meth) acrylonitrile”.

[Two-component developer according to this embodiment]
The two-component developer according to this embodiment is positively charged positively by friction between the carrier according to this embodiment having the following configuration (specifically, a carrier for developing an electrostatic latent image) and the carrier. And toner. As described above, the two-component developer according to this embodiment includes the carrier according to this embodiment. Accordingly, when image formation is performed using the two-component developer according to the present embodiment, the occurrence of carrier development and the occurrence of fogging can be prevented and the developability can be maintained high even when continuous printing is performed.

[Carrier according to this embodiment]
The electrostatic latent image developing carrier according to the present embodiment includes a plurality of carrier particles including a carrier core having a concave portion on the surface, and a first coat layer and a second coat layer that cover the surface of the carrier core. The first coat layer and the second coat layer have a laminated structure in the order of the first coat layer and the second coat layer from the surface of the carrier core. The first coat layer contains a first resin, and the second coat layer contains a second resin. At least the second coat layer of the first coat layer and the second coat layer contains a conductive agent. The electric resistance of the second coat layer is lower than the electric resistance of the first coat layer. The first coat layer covers the entire surface of the carrier core. The second coat layer selectively covers a portion of the surface region of the first coat layer corresponding to the concave portion on the surface of the carrier core.

  The “part corresponding to the concave part on the surface of the carrier core” means a part located above the concave part on the surface of the carrier core. The following “convex portion on the surface of the carrier core” means a portion of the entire surface of the carrier core that is different from the concave portion on the surface of the carrier core. The following “part corresponding to the convex part on the surface of the carrier core” means a part located above the convex part on the surface of the carrier core. In the following, the conductive agent contained in the first coat layer may be referred to as “first conductive agent”, and the conductive agent contained in the second coat layer will be referred to as “second conductive agent”. There is a case.

  In the carrier according to the present embodiment, the first coat layer covers the entire surface of the carrier core, and the second coat layer corresponds to the concave portion of the surface of the carrier core in the surface region of the first coat layer. Selectively covering. Further, the electrical resistance of the second coat layer is lower than the electrical resistance of the first coat layer. For these reasons, in the carrier according to the present embodiment, the concave portion on the surface of the carrier core is covered with a coating layer having a lower resistance than the convex portion on the surface of the carrier core. Therefore, if image formation is performed using the two-component developer containing the carrier according to the present embodiment (two-component developer according to the present embodiment), the developability can be maintained high.

  Specifically, since the carrier according to the present embodiment is manufactured by a method described later, the uneven state on the surface of the carrier is easily affected by the uneven state on the surface of the carrier core. Thereby, in the carrier according to the present embodiment, the portion corresponding to the concave portion on the surface of the carrier core in the surface region of the carrier is likely to have a concave shape compared to the portion corresponding to the convex portion on the surface of the carrier core. . Therefore, in the two-component developer including the carrier according to the present embodiment (two-component developer according to the present embodiment), the toner is more than the portion corresponding to the convex portion on the surface of the carrier core in the surface area of the carrier. It becomes easy to gather in the site | part corresponding to the recessed part of the surface of a carrier core. Therefore, frictional charging between the carrier and the toner occurs preferentially in a portion corresponding to the concave portion on the surface of the carrier core in the surface region of the carrier rather than a portion corresponding to the convex portion on the surface of the carrier core. Become. In the carrier according to the present embodiment, since the concave portion on the surface of the carrier core is covered with a coating layer having a lower resistance than the convex portion on the surface of the carrier core, friction charging between the carrier and the toner in the surface area of the carrier is performed. It is possible to reduce the electrical resistance of the part where the preferential occurrence occurs.

  As described above, in the carrier according to the present embodiment, it is possible to suppress the electrical resistance of a portion of the surface area of the carrier where frictional charging between the carrier and the toner preferentially occurs. This stabilizes the ability of the carrier to charge the toner (hereinafter referred to as the charge imparting ability of the carrier), thus preventing the occurrence of charge-up. Therefore, if image formation is performed using the two-component developer containing the carrier according to the present embodiment, developability (for example, image density) can be maintained high.

  Further, in the carrier according to the present embodiment, the concave portion on the surface of the carrier core is covered with a coat layer having a lower resistance than the convex portion on the surface of the carrier core, so the convex portion on the surface of the carrier core is the surface of the carrier core. It is covered with a coat layer having a higher resistance than that of the concave portion. Accordingly, when image formation is performed using the two-component developer including the carrier according to the present embodiment, the occurrence of carrier development can be prevented and the occurrence of fog can be prevented.

  Specifically, in the carrier according to the present embodiment, the uneven state on the surface of the carrier is easily affected by the uneven state on the surface of the carrier core. Therefore, the part corresponding to the convex part on the surface of the carrier core in the surface area of the carrier tends to have a convex part shape as compared with the part corresponding to the concave part on the surface of the carrier core. Thus, in the two-component developer including the carrier according to the present embodiment (two-component developer according to the present embodiment), the contact between the toner and the carrier is in the concave portion of the surface of the carrier core in the surface area of the carrier. It is more likely to occur at a portion corresponding to the convex portion on the surface of the carrier core than a corresponding portion. In the carrier according to the present embodiment, the convex portion on the surface of the carrier core is covered with a coating layer having a higher resistance than the concave portion on the surface of the carrier core. It is possible to increase the electrical resistance of the site that occurs preferentially.

  As described above, in the carrier according to the present embodiment, it is possible to increase the electrical resistance of the portion of the surface area of the carrier where contact between the toner and the carrier occurs preferentially. Thus, it is possible to prevent the charge from moving from the toner side to the carrier side via the contact point between the toner and the carrier (charge leakage). Therefore, if image formation is performed using the two-component developer containing the carrier according to the present embodiment, the occurrence of carrier development can be prevented and the occurrence of fog can be prevented.

  As described above, when image formation is performed using the two-component developer containing the carrier according to the present embodiment, carrier development can be prevented, fogging can be prevented, and developability can be maintained high. . Here, in the carrier according to the present embodiment, the first coat layer and the second coat layer cover the surface of the carrier core having irregularities. Therefore, even when continuous printing is performed, the adhesion between the carrier core and the first coat layer can be ensured, so that deterioration of carrier characteristics can be prevented. Therefore, if image formation is performed using a two-component developer containing a carrier according to the present embodiment, the occurrence of carrier development and fogging can be prevented even when continuous printing is performed, and the developability is maintained high. it can.

  By the way, it has been studied to sequentially laminate two or more resin layers having different electric resistances on the surface of the carrier core. In this carrier under investigation, the entire surface of the carrier core is covered with the lower layer (resin layer), the entire lower surface is covered with the upper layer (resin layer), and the electrical resistance differs between the lower layer and the upper layer. Therefore, the surface layer of the carrier under consideration is composed of only a layer having a relatively high electrical resistance or only a layer having a relatively low electrical resistance. Here, the carrier characteristics are easily affected by the physical properties of the surface layer of the carrier. Therefore, it is difficult for the carrier under investigation to simultaneously realize prevention of carrier development, prevention of fogging, and prevention of deterioration of developability. On the other hand, in the carrier according to the present embodiment, the first coat layer (layer having a relatively high electrical resistance) covers the entire surface of the carrier core, whereas the second coat layer (the electrical resistance is relatively low). Layer) selectively covers a portion of the surface region of the first coat layer corresponding to the concave portion of the surface of the carrier core. Thereby, even when continuous printing is performed, it is possible to simultaneously prevent occurrence of carrier development, prevention of fogging, and prevention of deterioration of developability.

  In addition, as long as the above-described effect (the effect of preventing occurrence of carrier development and fogging and maintaining high developability even when continuous printing is performed), the second coat layer includes the first coating layer. Of the surface region of the coat layer, not only the portion corresponding to the concave portion on the surface of the carrier core, but also a portion of the portion corresponding to the convex portion on the surface of the carrier core may be further covered. For example, the coverage of the second coat layer may be 10% or less at a portion corresponding to the convex portion on the surface of the carrier core in the surface region of the first coat layer.

  Preferably, the content rate of the first conductive agent in the first coat layer is lower than the content rate of the second conductive agent in the second coat layer. Thereby, the electrical resistance of the second coat layer can be made lower than the electrical resistance of the first coat layer. Therefore, it becomes easy to obtain the above-described effects (effects that can prevent occurrence of carrier development and fogging and maintain high developability even when continuous printing is performed).

  The “content ratio of the first conductive agent in the first coat layer” means the ratio of the content (mass) of the first conductive agent to the content (mass) of the first resin in the first coat layer. Similarly, the “content ratio of the second conductive agent in the second coat layer” means the ratio of the content (mass) of the second conductive agent to the content (mass) of the second resin in the second coat layer. To do. “The content of the first conductive agent in the first coat layer is lower than the content of the second conductive agent in the second coat layer” means that the first conductive agent is not contained in the first coat layer. The case where two conductive agents are contained in the second coat layer is also included.

  More preferably, the first conductive agent and the second conductive agent are each carbon black, and the content of the first conductive agent in the first coat layer is 0 part by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the first resin. In addition, the content of the second conductive agent in the second coat layer is 4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the second resin. When the content of the first conductive agent (carbon black) in the first coat layer is 2 parts by mass or less with respect to 100 parts by mass of the first resin, the electrical resistance of the first coat layer can be effectively increased. Thereby, the electrical resistance of the first coat layer can be more effectively increased than the electrical resistance of the second coat layer. Therefore, if image formation is performed using such a two-component developer containing a carrier, the occurrence of carrier development can be further prevented even when continuous printing is performed, and the occurrence of fogging can be further prevented. .

  When the content of the second conductive agent (carbon black) in the second coat layer is 4 parts by mass or more with respect to 100 parts by mass of the second resin, the electric resistance of the second coat layer can be effectively suppressed. Thereby, the electrical resistance of the second coat layer can be effectively made lower than the electrical resistance of the first coat layer. Therefore, if image formation is performed using such a two-component developer containing a carrier, better developability can be obtained even when continuous printing is performed.

  When the content of the second conductive agent (carbon black) in the second coat layer is 10 parts by mass or less with respect to 100 parts by mass of the second resin, the content of the second conductive agent in the second coat layer is too high. Can be prevented. This effectively prevents charge leakage. Therefore, if image formation is performed using a two-component developer containing such a carrier, the occurrence of fog can be further prevented even when continuous printing is performed.

  In the carrier according to the present embodiment, preferably, the arithmetic average roughness of the surface of the carrier core (specifically, the arithmetic average roughness Ra specified by JIS (Japanese Industrial Standards) B0601-2013) is 0.3 μm or more. 2.0 μm or less. Thus, if image formation is performed using such a two-component developer containing a carrier, the adhesion between the carrier core and the first coat layer can be effectively ensured even when continuous printing is performed. Therefore, it is possible to effectively prevent the deterioration of the carrier characteristics. Therefore, if image formation is performed using such a two-component developer containing a carrier, even when continuous printing is performed, the occurrence of carrier development can be further prevented, and the occurrence of fog can be further prevented. Good developability can be obtained.

[Preferred structure of two-component developer]
The two-component developer according to this embodiment can have the following configuration, for example. FIG. 1 is a diagram showing a schematic configuration of a two-component developer according to this embodiment. The two-component developer shown in FIG. 1 includes a plurality of toner particles 30 and a plurality of carrier particles 40.

  The toner particles 30 include toner base particles 31 and external additives (a plurality of external additive particles 32) attached to the surface of the toner base particles 31. The external additive particles 32 may be inorganic particles (for example, silica particles) or resin particles.

  The carrier particle 40 includes a carrier core 41 having a concave portion on the surface, and a first coat layer 42 and a second coat layer 43 that cover the surface of the carrier core 41. The first coat layer 42 and the second coat layer 43 have a laminated structure in the order of the first coat layer 42 and the second coat layer 43 from the surface of the carrier core 41. The first coat layer 42 contains a first resin. The second coat layer 43 contains a second resin. At least the second coat layer 43 of the first coat layer 42 and the second coat layer 43 contains a conductive agent. The electric resistance of the second coat layer 43 is lower than the electric resistance of the first coat layer 42. The first coat layer 42 covers the entire surface of the carrier core 41. The second coat layer 43 selectively covers a portion of the surface region of the first coat layer 42 corresponding to the concave portion on the surface of the carrier core 41.

[Preferred production method of two-component developer]
The two-component developer shown in FIG. 1 can be easily produced according to the following method. First, carrier particles are produced according to the method shown in [Preferred production method of carrier] below. Subsequently, the toner particles and the produced carrier particles are mixed and stirred. At this time, the toner particles are preferably added in an amount of 1 to 20 parts by mass, more preferably 3 to 15 parts by mass, with respect to 100 parts by mass of the carrier particles. In addition, the toner particles and the carrier particles can be mixed and stirred using a mixer (for example, a ball mill, a Nauter mixer, or a rocking mixer). In this way, the two-component developer shown in FIG. 1 is obtained.

[Preferred manufacturing method of carrier]
The carrier particles can be easily manufactured by a method for manufacturing a carrier for developing an electrostatic latent image having the following configuration (hereinafter referred to as a preferable method for manufacturing a carrier).

  The method for producing a carrier for developing an electrostatic latent image includes a first coating step, a second coating step, and a stirring step. In the first coating step, the surface of the carrier core having irregularities is covered with a first coating layer containing a first resin. In the second coating step, the surface of the first coating layer is covered with a second coating layer containing a second resin. At this time, at least the second coat layer of the first coat layer and the second coat layer contains a conductive agent. Further, the electrical resistance of the second coat layer is lower than the electrical resistance of the first coat layer. In the stirring step, the carrier core covered with the first coat layer and the second coat layer is stirred. By this stirring, in the surface region of the second coat layer, the second coat layer is shaved and exposed to the first coat layer at a portion corresponding to the convex portion on the surface of the carrier core.

  With reference to FIG. 2A to FIG. 2C, an example of the “preferred manufacturing method of the carrier” will be described. First, as shown in FIG. 2A, a carrier core 41 having an uneven surface is prepared. A plurality of recesses P are formed on the surface of the carrier core 41. Subsequently, as shown in FIG. 2B, the surface of the carrier core 41 (the surface of the carrier core having irregularities) is covered with the first coat layer 42 containing the first resin (first coating step). Specifically, the first coat layer 42 completely covers the surface of the carrier core 41 (with a coverage of 100%). Subsequently, as shown in FIG. 2C, the surface of the first coat layer 42 is covered with a second coat layer 43a containing a second resin (second coating step). At this time, at least the second coat layer 43a of the first coat layer 42 and the second coat layer 43a contains a conductive agent. In addition, the electrical resistance of the second coat layer 43 a is lower than the electrical resistance of the first coat layer 42. Subsequently, the carrier core covered with the first coat layer 42 and the second coat layer 43a is stirred (stirring step). In this way, the carrier particles 40 shown in FIG. 1 are obtained.

(First coating step, second coating step)
Examples of the method for forming the first coating layer include a method of immersing the carrier core in the first coating liquid, or a method of spraying the first coating liquid onto the carrier core in the fluidized bed. While flowing the carrier core covered with the first coating liquid, heat treatment at a predetermined temperature (for example, a temperature selected from 200 ° C. to 300 ° C.) is performed for a predetermined time (for example, 30 minutes to 90 minutes). Time to be chosen). Thereby, the first coating liquid is cured (resinized) to form a first coating layer that covers the surface of the carrier core.

  The second coat layer may be formed by the same method as the first coat layer, or may be formed by a different method. The second coat layer may be formed on the surface of the first coat layer after the resin (first resin) in the first coat layer is cured. Or after making 1st resin and 2nd resin adhere to the surface of a carrier core in the state before each hardening, respectively, you may harden them simultaneously, for example by heating.

  In the present embodiment, the first coating liquid can be prepared by dissolving the first resin in the first solvent and dispersing the first conductive agent, or by dissolving the first resin in the first solvent. . Further, the second coating liquid can be prepared by dissolving the second resin in the second solvent and dispersing the second conductive agent.

  Preferably, the content rate of the first conductive agent in the first coating solution is set lower than the content rate of the second conductivity in the second coating solution. Thereby, since the content rate of the 1st electrically conductive agent in a 1st coat layer becomes lower than the content rate of the 2nd electrically conductive agent in a 2nd coat layer, the electrical resistance of a 2nd coat layer is more than the electrical resistance of a 1st coat layer. Also lower.

  More preferably, carbon black is used as the first conductive agent and the second conductive agent, and the first conductive agent (carbon black) is contained in an amount of 0 to 2 parts by mass with respect to 100 parts by mass of the first resin. One coating liquid is prepared, and a second coating liquid containing 4 parts by mass or more and 10 parts by mass or less of the second conductive agent (carbon black) with respect to 100 parts by mass of the second resin is prepared. Thereby, content of the 1st electrically conductive agent (carbon black) in a 1st coating layer will be 0 to 2 mass parts with respect to 100 mass parts of 1st resin. Further, the content of the second conductive agent (carbon black) in the second coat layer is 4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the second resin.

  As the first solvent and the second solvent, for example, one or more selected from the group consisting of methyl ethyl ketone and tetrahydrofuran can be used.

(Stirring process)
Subsequently, the carrier core covered with the first coat layer and the second coat layer is stirred using a mixing apparatus. By this stirring treatment, a physical impact is applied to the carrier core covered with the first coat layer and the second coat layer. Specifically, in the surface region of the second coat layer, the portion corresponding to the convex portion (between adjacent concave portions) on the surface of the carrier core (specifically, the portion of the carrier core in the surface region of the second coat layer). The carrier cores covered with the first coat layer and the second coat layer are likely to collide with each other at a portion located above the convex portion on the surface. As a result, the second coat layer is preferentially shaved at the portion (the portion corresponding to the convex portion of the surface of the carrier core in the surface region of the second coat layer), and the first coat layer is exposed. In this way, the carrier particles shown in FIG. 1 are obtained.

  In the obtained carrier particles, the second coat layer corresponds to the concave portion of the surface of the carrier core in the surface region of the first coat layer (specifically, the portion of the carrier core in the surface region of the first coat layer). A portion located above the concave portion on the surface is selectively covered. The surface of the carrier particles has a shape (unevenness) along the surface shape of the base (specifically, the unevenness of the surface of the carrier core).

  In a preferred method for producing a carrier, the arithmetic average roughness of the surface of the carrier core is preferably 0.3 μm or more and 2.0 μm or less. Thereby, the second coat layer is likely to remain in the portion corresponding to the concave portion on the surface of the carrier core in the surface region of the first coat layer by the stirring treatment in the stirring step. Therefore, if image formation is performed using such a two-component developer containing a carrier, better developability can be obtained even when continuous printing is performed.

  As the mixing device, for example, an FM mixer (manufactured by Nippon Coke Kogyo Co., Ltd.) can be used. The FM mixer includes a mixing tank with a temperature adjusting jacket, and further includes a deflector, a temperature sensor, an upper blade, and a lower blade in the mixing tank. When mixing the material (more specifically, powder or slurry, etc.) charged into the mixing tank using an FM mixer, the material in the mixing tank is swung in the vertical direction by rotating the lower blade. To flow. This causes convection of the material in the mixing tank. The upper blade rotates at a high speed and gives a shearing force to the material. The FM mixer applies a shearing force to the material, thereby allowing the material to be mixed with a strong mixing force.

  The stirring time is determined, for example, by producing a test carrier according to the above method. Specifically, first, a slight amount of colorants of different colors are mixed in the first coating liquid and the second coating liquid. In this way, the first coating liquid for test and the second coating liquid for test are prepared. Subsequently, in the above method, the “first coating liquid for test” is used instead of the “first coating liquid”, and the “second coating liquid for test” is used instead of the “second coating liquid”. A test first coat layer and a test second coat layer are sequentially formed on the surface. Subsequently, the carrier core covered with the test first coat layer and the test second coat layer is stirred. At this time, the carrier core (specifically, the first coating layer for testing and the first test layer for testing) was measured using a scanning electron microscope equipped with EDX (Energy Dispersive Micro Analysis of X-ray). The stirring process is performed while observing the carrier core covered with two coat layers. Then, the time point at which the first coating layer for testing is exposed at the portion corresponding to the convex portion of the surface of the carrier core in the surface area of the second coating layer for testing is defined as the end point of the stirring process, and stirring is started from the starting point of the stirring process. The time required until the end of the treatment is regarded as the stirring time.

  By observing the carrier with a scanning electron microscope equipped with EDX, the carbon (C) element derived from the first conductive agent and the second conductive agent can be confirmed. This confirms the magnitude relationship between the abundance of carbon element in the part corresponding to the concave part on the surface of the carrier core in the surface area of the carrier and the abundance of carbon element in the part corresponding to the convex part on the surface of the carrier core. it can. Therefore, it is possible to confirm whether or not the carrier according to this embodiment has been manufactured by observing the carrier manufactured with a scanning electron microscope equipped with EDX.

[Preferred examples of configurations of carrier particles and toner particles]
(Carrier particles)
As described above, the carrier particles contained in the carrier include a carrier core having a concave portion on the surface, and a first coat layer and a second coat layer that cover the surface of the carrier core.

(Career core)
The carrier core preferably contains a magnetic material. The carrier core may be magnetic material particles, or the magnetic material particles may be dispersed in the binder resin of the carrier core. Examples of magnetic materials contained in the carrier core include ferromagnetic metals (more specifically, iron, cobalt, nickel, or metals containing one or more of these metals), ferromagnetic metal oxides (more specifically, Includes ferrite or magnetite). Examples of the metal containing one or more of iron, cobalt, and nickel include one or more of iron, cobalt, and nickel, and copper, zinc, antimony, aluminum, lead, tin, bismuth, beryllium, Examples include alloys or mixtures with one or more of manganese, magnesium, selenium, tungsten, zirconium, and vanadium. As another example of the magnetic material contained in the carrier core, the above-mentioned ferromagnetic metal oxide, metal oxide of iron oxide, titanium oxide or magnesium oxide, nitride of chromium nitride or vanadium nitride, silicon carbide or tungsten carbide And a mixture with one or more of these carbides.

  The magnetic material contained in the carrier core is preferably ferrite or magnetite. Suitable examples of ferrite include magnetite (spinel ferrite), barium ferrite, Mn ferrite, Mn—Zn ferrite, Ni—Zn ferrite, Mn—Mg ferrite, Ca—Mg ferrite, Li ferrite, Cu—Zn ferrite, or Mn. -Mg-Sr ferrite.

  As a material for each carrier core, one type of magnetic material may be used alone, or two or more types of magnetic materials may be used in combination. A commercially available product may be used as the carrier core. Also, the carrier core may be made by pulverizing and firing the magnetic material. In the production of the carrier core, the saturation magnetization of the carrier can be adjusted by changing the amount of magnetic material added (particularly, the proportion of the ferromagnetic material). Further, in the production of the carrier core, the circularity of the carrier can be adjusted by changing the firing temperature.

  More preferably, in the carrier according to the present embodiment, the carrier core is a ferrite particle. Ferrite particles tend to have sufficient magnetism for image formation. Moreover, the ferrite particle produced by the general manufacturing method does not become a true sphere but tends to have moderate irregularities on the surface. Specifically, the arithmetic average roughness of the surface of the ferrite particles (specifically, the arithmetic average roughness Ra defined by JIS (Japanese Industrial Standards) B0601-2013) tends to be 0.3 μm or more and 2.0 μm or less.

The volume median diameter (D ₅₀ ) of the carrier core is preferably 30 μm or more and 100 μm or less. Thereby, better developability can be obtained. The volume median diameter (D ₅₀ ) of the carrier core is a value measured using a laser diffraction / scattering particle size distribution analyzer (“LA-700” manufactured by Horiba, Ltd.).

(First coat layer)
The first coat layer covers the entire surface of the carrier core. The first coat layer contains a first resin, and preferably further contains a first conductive agent.

(First resin)
The first resin is preferably one type selected from the group consisting of, for example, a silicone resin, an acrylic resin, a styrene-acrylic acid resin, a polyester resin, and a fluororesin.

(First resin: silicone resin)
The silicone-based resin has a siloxane bond “Si—O—Si” as a main chain and an organic group as a side chain. The methyl silicone resin has only methyl groups as side chain organic groups. The methylphenyl silicone resin has a methyl group and a phenyl group as side chain organic groups. The silicone-based resin has, for example, a structure represented by the following formula (1-1) or the following formula (1-2). N ₁₁ , n ₂₁ , and n ₂₂ in formula (1-1) and formula (1-2) each independently represent the number of repeating units (arbitrary number). In order for the silicone resin to have excellent durability, the main chains (siloxane bonds: Si—O—Si) of the silicone resin are preferably three-dimensionally connected.

In formula (1-1), R ₁₁ represents an organic group (more specifically, a methyl group or a phenyl group). R ₁₂ represents a hydrogen atom or an organic group (more specifically, a methyl group or a phenyl group). R ₁₁ and R ₁₂ may be the same or different from each other. Y ₁₁ represents the first terminal part, and Y ₁₂ represents the second terminal part. For example, an organosiloxy group (more specifically, a trimethylsiloxy group) is attached to the first terminal portion. For example, an organosilyl group (more specifically, a trimethylsilyl group) is attached to the second terminal portion.

In formula (1-2), R ₂₁ , R ₂₂ , and R ₂₃ each independently represents an organic group (more specifically, a methyl group or a phenyl group). R ₂₄ represents a hydrogen atom or an organic group (more specifically, a methyl group or a phenyl group). Y ₂₁ represents the first end, and Y ₂₂ represents the second end. For example, an organosiloxy group (more specifically, a trimethylsiloxy group) is attached to the first terminal portion. For example, an organosilyl group (more specifically, a trimethylsilyl group) is attached to the second terminal portion.

(First resin: Acrylic resin)
The acrylic resin is a polymer of one or more acrylic acid monomers. In order to synthesize an acrylic resin, for example, acrylic monomers as shown below can be preferably used.

  Preferable examples of the acrylic acid monomer include (meth) acrylic acid, (meth) acrylonitrile, (meth) acrylic acid alkyl ester, or (meth) acrylic acid hydroxyalkyl ester. Suitable examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, and (meth) acrylic. Examples include n-butyl acid, iso-butyl (meth) acrylate, or 2-ethylhexyl (meth) acrylate. Suitable examples of the (meth) acrylic acid hydroxyalkyl ester include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or (meth) acrylic. The acid 4-hydroxybutyl is mentioned.

(First resin: Styrene-acrylic acid resin)
The styrene-acrylic acid resin is a copolymer of one or more styrene monomers and one or more acrylic monomers. As the styrene monomer used for synthesizing the styrene-acrylic acid resin, the following styrene monomers can be suitably used. Moreover, as an acrylic acid-type monomer used in order to synthesize | combine a styrene-acrylic acid-type resin, the acrylic acid-type monomer as described in the said (1st resin: acrylic resin) can be used conveniently.

  Preferable examples of the styrenic monomer include styrene, alkylstyrene (more specifically, α-methylstyrene, p-ethylstyrene, or 4-tert-butylstyrene), p-hydroxystyrene, m-hydroxystyrene, Examples include vinyl toluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, or p-chlorostyrene.

(First resin: Polyester resin)
The polyester resin is obtained by polycondensation of one or more polyhydric alcohols and one or more polyhydric carboxylic acids. As the alcohol for synthesizing the polyester resin, for example, dihydric alcohols (more specifically, diols or bisphenols) or trihydric or higher alcohols as shown below can be preferably used. As the carboxylic acid for synthesizing the polyester resin, for example, divalent carboxylic acids or trivalent or higher carboxylic acids as shown below can be suitably used.

  Preferable examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 2-butene-1,4. -Diol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, or polytetramethylene glycol.

  Preferable examples of the bisphenol include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct, or bisphenol A propylene oxide adduct.

  Preferable examples of trihydric or higher alcohols include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butane. Triol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, or 1,3,5- Trihydroxymethylbenzene is mentioned.

  As preferable examples of the divalent carboxylic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid , Succinic acid, alkyl succinic acid (more specifically, n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, or isododecyl succinic acid), or alkenyl succinic acid (more specific N-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, or isododecenyl succinic acid).

  Preferred examples of the trivalent or higher carboxylic acid include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) Examples include methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, or empole trimer acid.

(First resin: Fluororesin)
Examples of the fluororesin include polyvinyl fluoride, polyvinylidene fluoride, polytetrafluoroethylene (PTFE), polytrifluoroethylene (more specifically, polychlorotrifluoroethylene), polyhexafluoropropylene, tetrafluoroethylene-hexa. A fluoropropylene copolymer (FEP (fluorinated-ethylene-propylene)) or a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) may be mentioned.

(First resin: content)
In the first coat layer, the first resin is preferably contained in an amount of 0.3 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the carrier core. If the first resin is contained in an amount of 0.3 parts by mass or more with respect to 100 parts by mass of the carrier core in the first coat layer, the occurrence of carrier development can be further prevented. In addition, if the first resin is contained in the first coat layer in an amount of 5 parts by mass or less with respect to 100 parts by mass of the carrier core, the occurrence of charge-up can be further prevented, so that even better developability can be obtained. More preferably, the first resin is included in the first coat layer in an amount of 0.5 parts by mass or more and 3 parts by mass or less with respect to 100 parts by mass of the carrier core.

(First conductive agent)
The first conductive agent may be a white conductive agent such as TiO ₂ or ZnO ₂ , but is preferably carbon black. Carbon black may be manufactured by any manufacturing method. For example, at least one selected from the group consisting of ketjen black, furnace black, channel black, acetylene black, and thermal black can be used.

(Second coat layer)
The second coat layer selectively covers a portion of the surface region of the first coat layer corresponding to the concave portion on the surface of the carrier core. The second coat layer contains a second resin and a second conductive agent.

(Second resin)
As the second resin, a resin described as a specific example of the first resin in the above (first coat layer) can be suitably used. The second resin may be a resin different from the first resin, but is preferably the same resin as the first resin. When the second resin is the same resin as the first resin, the heat treatment for the second coating liquid can be performed under the same conditions as the heat treatment conditions for the first coating liquid. Thereby, the carrier which concerns on this embodiment can be manufactured easily.

(Second resin: content)
In the second coat layer, the second resin is preferably contained in an amount of 0.3 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the carrier core. If the second resin is contained in the second coat layer in an amount of 0.3 part by mass or more with respect to 100 parts by mass of the carrier core, the occurrence of charge-up can be further prevented, so that even better developability can be obtained. In addition, if the second resin is contained in the second coat layer in an amount of 5 parts by mass or less with respect to 100 parts by mass of the carrier core, the leakage of charges can be further prevented, and thus the occurrence of fog can be further prevented. More preferably, the second resin is contained in the second coat layer in an amount of 0.5 parts by mass or more and 3 parts by mass or less with respect to 100 parts by mass of the carrier core.

(Second conductive agent)
The second conductive agent may be a white conductive agent such as TiO ₂ or ZnO ₂ like the first conductive agent, but is preferably carbon black. Carbon black may be manufactured by any manufacturing method. One or more selected from the group consisting of ketjen black, furnace black, channel black, acetylene black and thermal black can be used.

  The first conductive agent and the second conductive agent are preferably made of the same material. Thereby, a 1st electrically conductive agent and a 2nd electrically conductive agent will have the same electrical resistance value. Therefore, if the content ratio of the first conductive agent in the first coat layer is lower than the content ratio of the second conductive agent in the second coat layer, the electric resistance of the second coat layer is higher than the electric resistance of the first coat layer. Lower. However, as long as the first conductive agent and the second conductive agent have the same electrical resistance value, the first conductive agent and the second conductive agent may be made of different materials. Here, “the first conductive agent and the second conductive agent have the same electric resistance value” means that the electric resistance value of the first conductive agent in the bulk state and the electric resistance of the second conductive agent in the bulk state This means that the value is the same (for example, the electrical resistance value of the first conductive agent in the bulk state is 90% to 110% of the electrical resistance value of the second conductive agent in the bulk state).

(Toner particles)
The toner particles contained in the toner may include the toner base particles and the external additive as described above, or may not include the external additive. When the toner particles do not include an external additive, the toner base particles correspond to the toner particles.

  The toner particles may be toner particles without a shell layer (hereinafter referred to as non-capsule toner particles) or toner particles with a shell layer (hereinafter referred to as capsule toner particles). . Capsule toner particles can be produced by forming a shell layer on the surface of non-externally added non-capsule toner particles (toner core). The shell layer may consist essentially of a thermosetting resin, may consist essentially of a thermoplastic resin, or may contain both a thermoplastic resin and a thermosetting resin. .

  Non-capsule toner particles can be produced, for example, by a pulverization method or an aggregation method. In these methods, the internal additive is easily dispersed well in the binder resin of the non-capsule toner particles.

  In an example of the pulverization method, first, a binder resin, a colorant, a charge control agent, and a release agent are mixed. Subsequently, the obtained mixture is melt-kneaded using a melt-kneading apparatus (for example, a single-screw or twin-screw extruder). Subsequently, the obtained melt-kneaded product is pulverized and classified. Thereby, toner mother particles are obtained. When the pulverization method is used, the toner base particles can often be produced more easily than when the aggregation method is used.

  In an example of the aggregation method, first, these fine particles are aggregated in an aqueous medium containing fine particles of the binder resin, the release agent, and the colorant until a desired particle diameter is obtained. Thereby, aggregated particles containing the binder resin, the release agent, and the colorant are formed. Subsequently, the obtained aggregated particles are heated to unite the components contained in the aggregated particles. Thereby, toner mother particles having a desired particle diameter are obtained.

  When producing the capsule toner particles, the method for forming the shell layer is arbitrary. For example, the shell layer may be formed using any of an in-situ polymerization method, a submerged cured coating method, and a coacervation method.

(Non-capsule toner particles: toner mother particles)
The toner base particles contain a binder resin. The toner base particles may contain an internal additive (for example, a colorant, a release agent, a charge control agent, and a magnetic powder).

(Binder resin)
In the toner base particles, generally, the binder resin occupies most of the components (for example, 85% by mass or more). For this reason, it is considered that the properties of the binder resin greatly affect the overall properties of the toner base particles. In order to achieve both heat-resistant storage stability and low-temperature fixability of the toner, the toner base particles preferably contain a thermoplastic resin as a binder resin, and at least one of a styrene-acrylic acid resin and a polyester resin is used. It is particularly preferable to contain it.

  The styrene-acrylic acid resin is a copolymer of one or more styrene monomers and one or more acrylic monomers. As the styrene monomer used for synthesizing the styrene-acrylic acid resin, the styrene monomer described in the above (first resin: styrene-acrylic acid resin) can be suitably used. As the acrylic acid monomer used for synthesizing the styrene-acrylic acid resin, the acrylic acid monomer described in the above (first resin: acrylic resin) can be preferably used.

  The polyester resin is obtained by polycondensation of one or more polyhydric alcohols and one or more polyhydric carboxylic acids. As the alcohol used for synthesizing the polyester resin, diols, bisphenols or trihydric or higher alcohols described in the above (first resin: polyester resin) can be preferably used. Similarly, as the carboxylic acid used for synthesizing the polyester resin, the divalent carboxylic acid described in the above (first resin: polyester resin) or the trivalent or higher carboxylic acid can be preferably used.

(Coloring agent)
The toner base particles may contain a colorant. As the colorant, a known pigment or dye can be used according to the color of the toner. In order to form a high-quality image using toner, the amount of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

  The toner base particles may contain a black colorant. An example of a black colorant is carbon black. The black colorant may be a colorant that is toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

  The toner base particles may contain a color colorant such as a yellow colorant, a magenta colorant, or a cyan colorant.

  As the yellow colorant, for example, one or more compounds selected from the group consisting of condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds can be used. Examples of the yellow colorant include C.I. I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155 168, 174, 175, 176, 180, 181, 191, or 194), naphthol yellow S, Hansa yellow G, or C.I. I. Vat yellow can be preferably used.

  The magenta colorant is, for example, selected from the group consisting of condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. One or more compounds can be used. Examples of the magenta colorant include C.I. I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81: 1, 122, 144, 146, 150, 166, 169, 177 184, 185, 202, 206, 220, 221 or 254) can be preferably used.

  As the cyan colorant, for example, one or more compounds selected from the group consisting of a copper phthalocyanine compound, an anthraquinone compound, and a basic dye lake compound can be used. Examples of cyan colorants include C.I. I. Pigment blue (1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62, or 66), phthalocyanine blue, C.I. I. Bat Blue, or C.I. I. Acid blue can be preferably used.

(Release agent)
The toner base particles may contain a release agent. The release agent is used, for example, for the purpose of improving the fixing property or offset resistance of the toner. In order to improve the fixing property or offset resistance of the toner, the amount of the release agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

  Examples of the release agent include low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, or aliphatic hydrocarbon wax such as Fischer-Tropsch wax; oxidized polyethylene wax or a block thereof Oxides of aliphatic hydrocarbon waxes such as copolymers; plant waxes such as candelilla wax, carnauba wax, wood wax, jojoba wax, or rice wax; animal properties such as beeswax, lanolin, or whale wax Waxes; mineral waxes such as ozokerite, ceresin, or petrolatum; waxes based on fatty acid esters such as montanate ester wax or castor wax; fats such as deoxidized carnauba wax The wax portion of the ester or the whole was deoxygenated can be suitably used. One type of release agent may be used alone, or multiple types of release agents may be used in combination.

(Charge control agent)
The toner base particles may contain a charge control agent. The charge control agent is used, for example, for the purpose of improving the charge stability or charge rising property of the toner. The charge rising characteristic of the toner is an index as to whether or not the toner can be charged to a predetermined charge level in a short time.

  By adding a positively chargeable charge control agent (more specifically, pyridine, nigrosine, or a quaternary ammonium salt) to the toner base particles, the cationic property of the toner base particles can be increased. However, if sufficient chargeability is ensured in the toner, it is not necessary to add a charge control agent to the toner base particles.

(Magnetic powder)
The toner base particles may contain magnetic powder. Examples of magnetic powder materials include ferromagnetic metals (more specifically, iron, cobalt, nickel, or alloys containing one or more of these metals), ferromagnetic metal oxides (more specifically, ferrites). , Magnetite, or chromium dioxide), or a material subjected to ferromagnetization treatment (more specifically, a carbon material imparted with ferromagnetism by heat treatment) can be preferably used. In order to suppress elution of metal ions (for example, iron ions) from the magnetic powder, it is preferable to use the surface-treated magnetic particles as the magnetic powder. One type of magnetic powder may be used alone, or a plurality of types of magnetic powder may be used in combination.

(Non-capsule toner particles: external additive)
An external additive (specifically, a powder containing a plurality of external additive particles) may be adhered to the surface of the toner base particles. For example, the toner base particles (powder) and the external additive (powder) are stirred together, so that the external additive adheres (physically bonds) to the surface of the toner base particles with a physical force. The external additive is used, for example, to improve the fluidity or handleability of the toner. In order to improve the fluidity or handleability of the toner, the amount of the external additive (the total amount of these external additives in the case of using plural types of external additives) is 100 parts by mass of the toner base particles. On the other hand, it is preferable that they are 0.5 mass part or more and 10 mass parts or less. In order to improve the fluidity or handleability of the toner, the particle size of the external additive is preferably 0.005 μm or more and 1 μm or less.

  As the external additive particles, inorganic particles are preferable, and silica particles or metal oxide particles (more specifically, particles of alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, or barium titanate) are particularly preferable. preferable. However, particles of an organic acid compound such as a fatty acid metal salt (more specifically, zinc stearate) or resin particles may be used as the external additive particles. Moreover, you may use the composite particle which is a composite of a multiple types of material as external additive particle | grains. One type of external additive may be used alone, or a plurality of types of external additives may be used in combination.

  The external additive particles may be surface-treated. For example, when silica particles are used as the external additive particles, hydrophobicity and / or positive chargeability may be imparted to the surface of the silica particles by the surface treatment agent. Examples of the surface treatment agent include a coupling agent (more specifically, a silane coupling agent, a titanate coupling agent, or an aluminate coupling agent), or silicone oil (more specifically, dimethyl silicone oil). Can be suitably used.

  EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to the Example shown below.

  Examples of the present invention will be described. Table 1 shows carriers C-1 to C-10 according to Examples or Comparative Examples.

  In Table 1, “fluorine” means a fluororesin, and “silicone-based” means a silicone-based resin. “CB” means carbon black. “Conductive agent (CB)” indicates the content (unit: parts by mass) of the conductive agent with respect to 100 parts by mass of the resin.

  Hereinafter, the manufacturing method, evaluation method, and evaluation result of the carriers C-1 to C-10 will be described in order. In the evaluation in which an error occurs, a considerable number of measurement values with sufficiently small errors are obtained, and the arithmetic average of the obtained measurement values is used as the evaluation value.

[Production of toner]
(Preparation of toner base particles)
Using an FM mixer (“FM-10B” manufactured by Nippon Coke Industries Co., Ltd.), 100 parts by mass of polyester resin (“XPE258” manufactured by Mitsui Chemicals, Inc.) and polypropylene wax (“Biscol (registered trademark) manufactured by Sanyo Chemical Industries, Ltd.) ) 660P ") 5 parts by mass, 5 parts by mass of a colorant (" REGAL (registered trademark) 330R "manufactured by Cabot Corporation), and a quaternary ammonium salt (" BONTRON (registered trademark) P-51 "manufactured by Orient Chemical Co., Ltd.) ) 1 part by mass was mixed.

Subsequently, the obtained mixture was melt-kneaded using a twin-screw extruder (“PCM-30” manufactured by Ikegai Co., Ltd.). Subsequently, the obtained kneaded product was cooled and then pulverized using a pulverizer (“Turbo Mill” manufactured by Freund Turbo). Subsequently, the obtained pulverized product was classified using a classifier (“Elbow Jet EJ-LABO type” manufactured by Nippon Steel Mining Co., Ltd.). As a result, toner mother particles having a volume median diameter (D ₅₀ ) of 7 μm were obtained.

(External)
Subsequently, external addition was performed on the obtained toner base particles. Specifically, using FM mixer ("FM-10B" manufactured by Nippon Coke Industries Co., Ltd.), 100 parts by mass of the obtained toner base particles and conductive titanium oxide particles ("EC-100" manufactured by Titanium Industry Co., Ltd.) Substrate: TiO ₂ , coating layer: Sb-doped SnO ₂ film, number average primary particle size: about 0.36 μm) and 1 part by mass of hydrophobic silica particles (“AEROSIL (registered trademark) RA-” manufactured by Nippon Aerosil Co., Ltd.) 200H ", content: dry silica particles surface-modified with trimethylsilyl groups and amino groups, number average primary particle size: about 12 nm) 0.7 parts by mass were mixed (rotation speed: 3500 rpm, mixing time: 5 minutes). . In this manner, external additives (titanium oxide particles and silica particles) were attached to the surface of the toner base particles. As a result, a toner containing a large number of toner particles (non-capsule toner particles) was obtained.

[Manufacture of Carrier C-1]
(Preparation of career core)
A mixture of 40 parts by mass of MnO, 9 parts by mass of MgO, 50 parts by mass of Fe ₂ O ₃ and 1 part by mass of SrO was ground using a ball mill for 2 hours. Then, it baked at 1000 degreeC for 5 hours, and obtained the carrier core which consists of manganese-type ferrite (Mn-Mg-Sr ferrite). In the obtained carrier core, the saturation magnetization in an applied magnetic field of 3000 (10 ³ / 4π · A / m) was 65 Am ² / kg, and the volume median diameter (D ₅₀ ) was 40 μm.

(First coat)
Subsequently, methyl ethyl ketone and a tetrafluoroethylene / hexafluoropropylene copolymer (FEP) resin solution were mixed to obtain a first coating liquid. Subsequently, the carrier core obtained by the above-described procedure was put into a fluid coating apparatus, and the first coating liquid was sprayed toward the carrier core while fluidizing the carrier core. The amount of the first coating solution added was such that the amount of FEP was 2 parts by mass with respect to 100 parts by mass of the carrier core. The surface area of the carrier core was completely covered with the first coating solution (at a coverage of 100%). As a result, a first coated core (a carrier core covered with the first coating liquid) was obtained.

(Second coat)
Subsequently, methyl ethyl ketone, FEP resin solution, and carbon black were mixed to obtain a second coating solution. The obtained 2nd coating liquid contained 4 mass parts carbon black with respect to 100 mass parts of FEP resin solutions. Subsequently, the second coating liquid was sprayed toward the first coated core while flowing the first coated core using the fluidized coating apparatus. The amount of the second coating solution added was such that the amount of FEP was 2 parts by mass with respect to 100 parts by mass of the carrier core. Thereby, the surface area | region of the 1st coating core was completely covered with the 2nd coating liquid (at a coverage of 100%).

(Heat treatment)
Subsequently, the fluidized bed in the fluidized coating apparatus was subjected to heat treatment at a temperature of 280 ° C. for 1 hour to cure (resinize) the first coating liquid and the second coating liquid. As a result, a second coated core (a carrier core covered with the first coat layer and the second coat layer) was obtained. The first coat layer contained FEP (first resin: fluororesin). The second coat layer contained FEP (second resin: fluororesin) and carbon black (second conductive agent).

(Agitation treatment)
Subsequently, the obtained second coated core (powder) was put into an FM mixer (“FM-10B” manufactured by Nippon Coke Industries Co., Ltd.), and the rotation speed was 1200 rpm and the processing time was 10 minutes using the FM mixer. Stirring was performed under the conditions. By this stirring treatment, the second coat layer was shaved and exposed to the first coat layer in a portion of the surface region of the second coated core (powder) corresponding to the convex portion on the surface of the carrier core. As a result, a carrier (carrier C-1) containing a large number of carrier particles was obtained.

[Manufacture of Carrier C-2]
The method for producing carrier C-2 is the same as the method for producing carrier C-1, except that the content of carbon black in the second coating liquid is 10 parts by mass with respect to 100 parts by mass of the FEP resin solution. there were.

[Manufacture of Carrier C-3]
The method for producing carrier C-3 is the same as the method for producing carrier C-1, except that a coating liquid obtained by mixing methyl ethyl ketone, FEP resin solution and carbon black was used as the first coating liquid. Was the same. The used 1st coating liquid contained 2 mass parts carbon black with respect to 100 mass parts of FEP resin solutions.

[Manufacture of Carrier C-4]
The manufacturing method of carrier C-4 uses the first coating liquid used for manufacturing carrier C-3 as the first coating liquid, and the second coating liquid used for manufacturing carrier C-2 as the second coating liquid. Was the same as the method for producing carrier C-1.

[Manufacture of Carrier C-5]
The carrier C-5 is produced by using a thermosetting silicone resin solution (“SR2400” manufactured by Toray Dow Corning Co., Ltd., resin: methyl silicone resin, solvent: toluene, nonvolatile content: 50 mass%) instead of the FEP resin solution. It was the same as the manufacturing method of Carrier C-1, except that the first coating liquid was used to manufacture.

[Manufacture of Carrier C-6]
The carrier C-6 is produced by using a thermosetting silicone resin solution (“SR2400” manufactured by Toray Dow Corning Co., Ltd., resin: methyl silicone resin, solvent: toluene, nonvolatile content: 50% by mass) instead of the FEP resin solution. It was the same as the manufacturing method of carrier C-4, except that the first coating liquid was manufactured using it.

[Manufacture of Carrier C-7]
The method for producing carrier C-7 was the same as the method for producing carrier C-2, except that the stirring treatment was not performed on the second coated core.

[Manufacture of Carrier C-8]
The manufacturing method of Carrier C-8 was the same as the manufacturing method of Carrier C-4 except that the first coating liquid was sprayed after the second coating liquid was sprayed on the carrier core.

[Manufacture of Carrier C-9]
The manufacturing method of carrier C-9 was that the second coating liquid was not sprayed on the first coated core and that the obtained first coated core was not stirred. This was the same as the production method of Carrier C-3.

[Manufacture of Carrier C-10]
The carrier C-10 is produced by spraying the second coating liquid on the carrier core without spraying the first coating liquid, and the third coating core (covered only by the second coating layer). It was the same as the manufacturing method of carrier C-2 except that the stirring treatment was not performed on the carrier core).

[Preparation of two-component developer]
A toner (toner produced by the above-mentioned procedure) and a carrier (any one of the carriers C-1 to C-10 shown in Table 1) are mixed with a powder mixer (“Rocking Mixer (registered trademark)” manufactured by Aichi Electric Co., Ltd. ) ", Mixing method: container rotation rocking method), and mixed for 1 hour to prepare a two-component developer. The toner and the carrier were mixed at a mass ratio such that the ratio of the toner in the two-component developer was 10 mass%.

[Developer input]
The two-component developer prepared as described above was set in a multifunction machine (“TASKalfa 500ci” manufactured by Kyocera Document Solutions Inc., development method: touch-down development method). For example, a mixture (two-component developer) of toner (toner produced by the above-described procedure) and carrier C-1 was put into a housing portion of the developing device of the multifunction machine. In addition, the toner was put into the toner container, and the toner container into which the toner was put was attached to the multifunction machine.

[Evaluation method]
Evaluation methods for carriers C-1 to C-10 are as follows.

(Print life test)
Using a multi-function machine in which a two-component developer and toner are charged in accordance with the method described in [Loading Developer] above, a sample image for density measurement including a solid image portion and a blank portion (region without printing) is prepared. Printed. Next, in an environment of a temperature of 20 ° C. and a humidity of 50% RH, a printing durability test (hereinafter, referred to as “printing test”) in which 10,000 sample images of a printing rate of 1% are continuously printed on a recording medium (printing paper) using the above-described multifunction device. 1% printing durability). Subsequently, in the environment of a temperature of 20 ° C. and a humidity of 50% RH, a printing durability test (hereinafter referred to as “printing paper”) in which a sample image with a printing rate of 5% is continuously printed on a recording medium (printing paper) using the above-described multifunction machine. Described as 5% printing durability). The sample images for density measurement were also printed after the end of 1% printing and after the end of 5% printing.

(Image density, fog density)
Measure the image density (ID) and fog density (FD) of the sample images for density measurement printed at the beginning (before the start of 1% printing), at the end of 1% printing, and at the end of 5% printing. did.

  In the measurement of the image density (ID), using a Macbeth reflection densitometer (“RD914” manufactured by X-Rite), the reflection density (ID) of the solid part of the recording medium after printing (solid part of the formed sample image) is measured. : Image density).

In the measurement of fog density (FD), the reflection density of the blank portion of the recording medium after printing (the blank portion of the formed sample image) is measured using a color reflection densitometer (“R710” manufactured by Ihara Electronics Co., Ltd.). It was measured. Then, the fog density (FD) was calculated based on the following equation.
FD = (reflection density of blank area) − (reflection density of unprinted paper)

  When the image density (ID) is 1.3 or more, it is evaluated as ◎ (very good), when it is 1.0 or more and less than 1.3, it is evaluated as ◯ (good), and when it is less than 1.0. X (bad) was evaluated. If the fog density (FD) is 0.005 or less, it is evaluated as ◎ (very good), and if it exceeds 0.005 and 0.010 or less, it is judged as ◯ (good), and the fog density (FD) is 0. If it was over 010, it was judged as x (bad).

(Carrier development resistance)
Visually confirm the number of carrier particles (carrier particles transferred to the printed white paper portion) adhering to the printed white paper portion at the initial timing (first 1% printing) and after 5% printing did. The carrier development resistance was evaluated based on the number of carrier particles adhering to the printed paper blank. The number of carrier particles, if the zero / cm ² ◎ was evaluated as (very good), was evaluated as if 0 / cm ² ultra 0.25 / cm ² or less than a ○ (good), 0 When it was 25 pieces / cm ² or more, it was evaluated as x (bad).

[Evaluation results]
For each of the carriers C-1 to C-10, image density (at the end of initial 1% printing, 5% at the end of printing), fog density (at the end of initial 1% printing, 5% resistance) Table 2 shows the results of the evaluation of the end of printing) and the carrier development resistance (number of carrier particles attached to the blank portion of the printed material) (initially, 100,000th sheet with 5% printing durability).

  Each of the carriers C-1 to C-6 (carriers according to Examples 1 to 6) had the basic configuration described above. Specifically, in each initial state of Examples 1 to 6, the two-component developer was accommodated in the accommodating portion of the developing device. The two-component developer includes a carrier (a carrier for developing an electrostatic latent image) and a positively chargeable toner that is positively charged by friction with the carrier. The carrier particles contained in the carrier were provided with a carrier core and a first coat layer and a second coat layer covering the surface of the carrier core. The first coat layer and the second coat layer had a laminated structure in the order of the first coat layer and the second coat layer from the surface of the carrier core. The first coat layer contained the first resin. The second coat layer contained the second resin. At least the second coat layer of the first coat layer and the second coat layer contained a conductive agent, and the electric resistance of the second coat layer was lower than the electric resistance of the first coat layer. The first coat layer covered the entire surface of the carrier core. The second coat layer was partially scraped by the stirring treatment, and selectively covered a portion corresponding to the concave portion on the surface of the carrier core in the surface region of the first coat layer.

  As shown in Table 2, in each of the carriers C-1 to C-6, the image density was kept high even at the end of 5% printing durability, and the occurrence of fog was prevented. Further, the occurrence of carrier development was prevented even on the 100,000th sheet with a 5% printing durability. That is, in each of the carriers C-1 to C-6, even when continuous printing was performed, carrier development could be prevented, fogging could be prevented, and developability could be maintained high.

  Carriers C-7 and C-10 (carriers according to Comparative Examples 1 and 4) were inferior in evaluation of fog density and carrier development as compared with carriers C-1 to C-6. Specifically, in the evaluation of fog density, fog occurred at the end of 5% printing durability. Further, in the carrier development evaluation, carrier development occurred even in the initial stage. The reason why such a result is obtained is that, in the carriers C-7 and C-10, a low resistance layer is also formed in a portion corresponding to the convex portion on the surface of the carrier core in the surface area of the carrier. It was thought that it was.

  Carrier C-8 (carrier according to Comparative Example 2) was inferior in image density evaluation and carrier development evaluation as compared with Carriers C-1 to C-6. Specifically, in the evaluation of image density, the image density decreased at the end of 1% printing durability. Further, in the carrier development evaluation, carrier development occurred even in the initial stage. The reason why such a result was obtained is that, in the carriers C-1 to C-6 and the carrier C-8, the arrangement of the relatively high resistance layer and the arrangement of the relatively low resistance layer are mutually The reverse is conceivable.

  Carrier C-9 (carrier according to Comparative Example 3) was inferior in image density evaluation as compared with Carriers C-1 to C-6. Specifically, in the evaluation of image density, the image density decreased at the end of 1% printing durability. The reason why such a result was obtained is that in Carrier C-9, a high resistance layer was exposed even in a portion of the surface area of the carrier corresponding to the concave portion on the surface of the carrier core. It is done.

  The electrostatic latent image developing carrier according to the present invention can be used for forming an image in, for example, a copying machine, a printer, or a multifunction machine.

30 toner particles 31 toner mother particles 32 external additive particles 40 carrier particles 41 carrier core 42 first coat layer 43, 43a second coat layer

Claims (8)

A plurality of carrier particles comprising a carrier core having a recess on the surface, and a first coat layer and a second coat layer covering the surface of the carrier core;
The first coat layer and the second coat layer have a laminated structure in the order of the first coat layer and the second coat layer from the surface of the carrier core,
The first coat layer contains a first resin,
The second coat layer contains a second resin,
At least the second coat layer of the first coat layer and the second coat layer contains a conductive agent,
The electrical resistance of the second coat layer is lower than the electrical resistance of the first coat layer,
The first coat layer covers the entire surface of the carrier core,
The electrostatic latent image developing carrier, wherein the second coat layer selectively covers a portion of the surface area of the first coat layer corresponding to the concave portion of the surface of the carrier core.   2. The electrostatic latent image developing carrier according to claim 1, wherein the content of the conductive agent in the first coat layer is lower than the content of the conductive agent in the second coat layer. The conductive agent is carbon black,
The content of the conductive agent in the first coat layer is 0 part by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the first resin.
The electrostatic latent image developing carrier according to claim 1, wherein a content of the conductive agent in the second coat layer is 4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the second resin. .   The carrier for electrostatic latent image development according to any one of claims 1 to 3, wherein the arithmetic average roughness of the surface of the carrier core is 0.3 µm or more and 2.0 µm or less. A first coating step of covering the surface of the carrier core having irregularities with a first coating layer containing a first resin;
A second coating step of covering the surface of the first coating layer with a second coating layer containing a second resin;
A stirring step of stirring the carrier core covered with the first coat layer and the second coat layer;
Including
At least the second coat layer of the first coat layer and the second coat layer contains a conductive agent,
The electrical resistance of the second coat layer is lower than the electrical resistance of the first coat layer,
In the stirring step, in the surface region of the second coat layer, in the portion corresponding to the convex portion of the surface of the carrier core, the second coat layer is shaved to expose the first coat layer. A method for producing a carrier for developing an electrostatic latent image.   The method for producing a carrier for developing an electrostatic latent image according to claim 5, wherein the content of the conductive agent in the first coat layer is lower than the content of the conductive agent in the second coat layer. The conductive agent is carbon black,
The content of the conductive agent in the first coat layer is 0 part by mass or more and 2 parts by mass or less with respect to 100 parts by mass of the first resin.
The electrostatic latent image developing carrier according to claim 5 or 6, wherein the content of the conductive agent in the second coat layer is 4 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the second resin. Manufacturing method.   The method for producing a carrier for developing an electrostatic latent image according to any one of claims 5 to 7, wherein the arithmetic average roughness of the surface of the carrier core is 0.3 µm or more and 2.0 µm or less.

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