JP2010020172A - Electrophotographic two-component developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the following problems: in an environment in which a two-component developer is subjected to thermal and mechanical stress with time and in the main unit of a copying machine, fluidity of the developer deteriorates significantly and density unevenness of an output image occurs; and in printing on many sheets, the fluidity of the developer deteriorates, density unevenness due to insufficient conveyance occurs and an obtained output image degrades significantly. <P>SOLUTION: There is provided an electrophotographic two-component developer satisfying an expression (1): 10.4≤log((C/B)/(A×T))≤17.9, wherein A represents the wax material content (wt.%) of a toner therein; T represents toner concentration (wt.%) of the two-component developer; B represents volume resistance (Ωcm) of a carrier core material; and C represents a volume resistance (Ωcm) of a carrier. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a two-component developer for electrophotography, and more specifically, 2 for revealing an electrostatic latent image formed by an image forming apparatus represented by a copying machine or a printer using an electrophotographic method. It relates to a component developer.

  In an image output device using electrophotographic technology such as a printer or a copying machine, a developer for developing a latent electrostatic image formed on an image carrier and forming a visible image is used. Conventionally, a two-component developer composed of toner and carrier and a one-component developer composed of toner alone have been used as the developer. Among these developing methods using a developer, a magnetic brush developing method using a two-component developer is widely used because it is superior in image quality and high-speed printing compared to other developing methods.

  An image forming apparatus using a magnetic brush developing system includes a developer carrier that carries a two-component developer and an image carrier on which an electrostatic latent image is formed. Further, the developer carrying member includes a cylindrical metal sleeve and a magnet roller provided therein. The magnet roller has a plurality of permanent magnets as magnetic field generating means, and each permanent magnet is arranged so that the N pole and the S pole are alternately arranged.

  In such an image forming apparatus, a visible image is formed on the image carrier by the following method. First, the two-component developer is carried on the surface of the metal sleeve in the developer carrier, and only the metal sleeve is rotated while the magnet roller is fixed. As a result, the two-component developer is transported to the development area facing the image carrier on which the electrostatic latent image is formed. Then, by a developing electric field applied between the developer carrier and the image carrier, only the charged toner is electrostatically adsorbed to the image carrier to form a visible image.

  The toner contained in the two-component developer is mixed and stirred with a carrier in a developing unit including a developer carrier. As a result, the toner comes into contact with the carrier and is frictionally charged. As an electrophotographic technique using such properties of toner, there is dry two-component development. In dry two-component development, the electrostatic force of the frictionally charged toner is used to electrically handle the toner to form an image. In dry two-component development, control of the toner charge amount is important. The charge amount of the toner is determined by various requirements on the image forming system, and it is desirable for the stability of the system that the value is stable.

  Also, in recent copying machines and printers, there is a tendency that high image quality and high speed of printing are regarded as important. At this time, the stability of the developer is particularly important. That is, in order to achieve high image quality, it is necessary to dispose a predetermined amount of toner at a predetermined location. In electrophotographic technology, electrostatic force is used for toner handling. Therefore, in order to overcome other external forces such as adhesion force and move the toner using the electrostatic force generated by the electric field, it is required to maintain the toner charge amount higher than a certain level. In addition, since the number of printed sheets increases as the machine speeds up, the demand for maintenance is increasing. Therefore, there is a need for a developer that operates stably over a long period of time.

  In particular, when considering the lifetime of the developer, among the known carriers, a coated carrier in which a carrier core material is coated with a resin is excellent. For this reason, various types of coated carriers have been developed. The coated carrier is required to charge the toner and maintain the charging performance of the toner for a long period of time. For that purpose, it is an important issue that the chargeability and fluidity of the toner operate stably in addition to the impact resistance, wear resistance, and environment resistance of the coated carrier.

  In order to solve such a problem, various coated carriers have been proposed. For example, Patent Document 1 describes that a coated carrier having a hard coating layer can be obtained by coating a melamine resin on the surface of a carrier core material and curing it. However, this carrier cannot prevent the toner component from adhering to the carrier surface (contamination).

  As a solution to the contamination of the toner component on the carrier surface, for example, Patent Document 2 proposes to coat the surface of the carrier core material with a silicone resin. However, the carrier coated with a silicone resin is insufficient to prevent contamination of the toner component as a result, since its surface wears with time.

  On the other hand, in order to improve the fixing releasability of the developer with the toner, it is necessary to control the molecular weight distribution of the binder resin contained in the toner and to disperse the wax resin having high releasability in the toner. Furthermore, the color toner retains the color developability in color superposition when the binder resin dissolves at a fixed fixing temperature. Therefore, in the color toner, it is necessary to lower the softening point of the resin by lowering the molecular weight of the binder resin.

  As a result, there are very low molecular weight components in the toner. Further, the toner contains a low melting point wax. Therefore, when it is attempted to improve the fixing and releasing of the developer with the toner, there arises a new problem that the fluidity of the toner is lowered due to the influence of the low melting point wax existing on the toner surface. In recent years, the diameter of toner particles has been reduced as an effort to improve image quality. The reduction in the diameter of the toner particles is also a factor that lowers the fluidity of the toner. Further, when the toner particles are reduced in size, the fluidity of the two-component developer that is a mixture with the carrier also decreases.

  As a method for solving such a problem, for example, a technique disclosed in Patent Document 3 has been proposed. Patent Document 3 discloses a two-component developer containing a toner having an external additive and a carrier. The external additive contains both silica treated with silicone oil and titanium oxide surface treated with a silane coupling agent containing fluorine. The carrier is formed of spherical magnetic particles, and the surface thereof is coated with a silicone resin in which an aminosilane coupling agent is dispersed.

  Further, examples of the toner having excellent low-temperature fixability include a toner using a polyester resin as a binder resin. The polyester resin has an advantage that a resin having a low softening point can be easily obtained although the glass transition point is high. Therefore, a toner using a polyester resin as a binder resin has good wettability to a sheet to be fixed such as paper when heated and melted, and can be fixed at a lower temperature.

  However, some polyester resins that have been widely used in the past have a low temperature at which an offset phenomenon occurs during the fixing process. The offset phenomenon is a phenomenon in which a part of the toner image adheres to the surface of the heating roller and is transferred to cause a stain on the next fixing sheet. Therefore, it is difficult to obtain a toner using a polyester resin as a binder resin in a wide fixing temperature range. As a solution to this problem, increasing the amount of coating resin on the carrier has been studied. However, an increase in the amount of coating resin on the carrier leads to an increase in the resistance of the carrier, which may cause image quality degradation.

  Furthermore, it is conceivable to improve the low-temperature fixability by using a toner containing a low melting point wax material. However, if the toner only contains a wax material, when the toner is pulverized, the wax interface is exposed on the toner surface, and the fluidity of the toner is deteriorated. The increase in the amount of toner that contaminates (spents) the carrier surface makes it difficult to maintain the charging performance. On the other hand, if the wax dispersion in the toner is made finer, there is a problem that the offset region becomes narrow because the wax is reduced on the surface at the time of toner fixing.

  In Patent Document 4, a developer having good toner fluidity is realized by controlling the amount of exposed wax X on the toner surface and the amount of wax Y contained in the toner.

Patent Document 5 uses a wax having a penetration of 5 to 12 dmm and a melt viscosity of 15 cps or less at 130 ° C. as a polyethylene wax contained in a toner, and a volume at an applied voltage of 10 ³ V / cm as a carrier. An electrostatic charge image developer using a carrier having a resistance of 10 ⁵ Ωcm to 10 ¹² Ωcm is described. As a result, an electrostatic charge image developer excellent in toner powder flowability and aggregation resistance (blocking resistance) is realized.
Japanese Patent Laid-Open No. 2-79862 (published on March 20, 1990) JP 61-204643 A (published September 10, 1986) JP 11-38670 A (published February 12, 1999) JP-A-9-319158 (published on December 12, 1997) Japanese Patent Laid-Open No. 10-123755 (published on May 15, 1998)

  Recently, many copiers have a printer function added, and the number of copies and prints is small, and the developer agitation time tends to increase with respect to the number of copies and prints.

  In the oilless toner in which the wax is dispersed, the wax is dispersed in order to ensure fixing releasability. Therefore, when thermal stress is applied to the two-component developer containing oilless toner, the wax oozes out on the toner surface and the wax adheres to the carrier surface. Furthermore, the inside of the copying machine is in a high temperature environment due to heat from the drive unit and the fixing device. With this heat, the developer was confirmed to have a temperature increase of about 10 to 20 ° C. The wax that has oozed out on the toner surface due to this temperature rise remains on the toner surface and the carrier surface even after being left standing. For this reason, when the copying machine main body is operated again, the wax easily contaminates the carrier surface. As a result, in the developer, the charging performance to the toner is lowered and the fluidity is lowered. As a result, image quality degradation occurs and the developer life is extremely shortened.

  In particular, when the fluidity of a two-component developer composed of a toner and a carrier deteriorates, the two-component developer aggregates in the developing unit including the developer carrying member. This aggregation reduces the ability of the two-component developer to be conveyed to the image carrier.

  The two-component developers disclosed in Patent Literatures 1 to 5 improve the toner fluidity and anti-aggregation property and realize stable toner fixing. However, considering the fluidity of the two-component developer composed of toner and carrier, sufficient fluidity has not been obtained. That is, with the conventional two-component developer, it has been difficult to ensure both the fluidity of the developer during development and the fixing stability of the toner.

  The present invention has been made in view of the above-described problems in the prior art, and the object thereof is to maintain toner fixability and at the same time have good flowability of a developer composed of a toner and a carrier. An object of the present invention is to provide a two-component developer for electrophotography that can withstand long-term use.

  The present inventors have studied and studied a two-component developer in order to improve the above-described problems in the prior art. As a result, the deterioration of the developer fluidity causes the wax contained in the toner to flow out to the carrier. It was found that it is caused by (adhering). And it discovered that adhesion of this wax was influenced by the resin coating state of the carrier surface. And, by setting the ratio of the toner wax internal addition amount and the toner concentration with respect to the developer and the volume resistance change rate before and after the resin coating of the carrier particles to a specific ratio, the flowability of the developer is good. At the same time, the inventors have found that a developer that can withstand long-term use can be provided, and have reached the present invention. That is, by adopting the following configuration of the present invention, the above problem has been successfully solved.

That is, the electrophotographic two-component developer of the present invention comprises a toner and a carrier in order to solve the above problems, and the toner contains a binder resin, a colorant and a wax material. In the two-component developer, the carrier has a carrier core material and a resin coating layer in which the surface of the carrier core material is coated with a resin, and the wax material content with respect to the toner is A (wt%). When the toner concentration relative to the two-component developer is T (% by weight), the volume resistance of the carrier core material is B (Ωcm), and the volume resistance of the carrier is C (Ωcm), the following formula (1)
10.4 ≦ log ((C / B) / (A × T)) ≦ 17.9 (1)
It is characterized by satisfying.

  In the above configuration, B corresponds to the volume resistance before the resin coating layer is formed on the carrier core material. On the other hand, C corresponds to the volume resistance after the resin coating layer is formed on the carrier core material. Therefore, C / B indicates the volume resistance change rate before and after the resin coating of the carrier particles. A × T represents the wax content relative to the two-component developer for electrophotography.

According to the above configuration, the volume resistivity change rate (C / B) before and after the resin coating of the carrier particles and the wax content (A × T) with respect to the two-component developer for electrophotography are expressed by the following formula (1).
10.4 ≦ log ((C / B) / (A × T)) ≦ 17.9 (1)
Designed to meet. By setting in this way, it is possible to realize a developer that has good developer fluidity and can withstand long-term use.

  Further, the toner is subjected to thermal and mechanical stress, and the wax resin is locally present on the surface. According to the above configuration, it is possible to reduce the adhesion to the carrier and maintain the fluidity of the developer even for such toner. Further, it is possible to prevent image quality deterioration by maintaining the developer charging performance and fluidity, and to maintain toner fixability.

  In the two-component developer for electrophotography of the present invention, the carrier core material is composed of magnetic particles, and the resin coating layer is formed by attaching an aminosilane-based coupling agent to the surface of the carrier core material, and then a silicone resin solvent. It is preferable that it consists of a resin cured material coated and cured. Thus, after the aminosilane coupling agent is attached to the surface of the carrier core material, the resin coating state on the carrier surface suitable for reducing the adhesion of wax can be realized by coating the silicone resin solvent. it can.

  In the two-component developer for electrophotography of the present invention, the average particle diameter of the carrier is preferably in the range of 35 μm to 55 μm. By setting the average particle diameter of the carrier within such a range, adhesion to the surface of the latent electrostatic image bearing member can be suppressed, and furthermore, the occurrence of fog can be suppressed.

  In the two-component developer for electrophotography of the present invention, the wax material content A with respect to the toner is preferably in the range of 3 wt% to 7 wt%. By setting the wax material content A to the toner within such a range, it is possible to prevent the toner from adhering to the fixing roller and to prevent a decrease in developer fluidity due to thermal and mechanical stress. .

  From the above, the present inventors combined the amount of wax contained in the toner with the carrier having a silicone resin coating layer on the surface of the carrier core material, thereby improving fluidity and reducing the toner spent on the carrier surface. In addition, it was possible to realize a developer having a long life, excellent charging stability, and excellent offset resistance during fixing.

As described above, the two-component developer for electrophotography of the present invention has a carrier core material and a resin coating layer in which the surface of the carrier core material is coated with a resin, and contains a wax material for toner. The rate is A (% by weight), the toner concentration with respect to the two-component developer for electrophotography is T (% by weight), the volume resistance of the carrier core material is B (Ωcm), and the volume resistance of the carrier is C (Ωcm). ), The following formula (1)
10.4 ≦ log ((C / B) / (A × T)) ≦ 17.9 (1)
It is the composition which satisfies.

  Therefore, it is possible to realize a developer that has good flowability of the developer and can withstand long-term use.

  An embodiment of the present invention will be described with reference to FIGS. 1 and 2 as follows.

  The developer 1 according to this embodiment is a two-component developer including an electrophotographic toner 3 and a magnetic carrier 2. The electrophotographic toner 3, the magnetic carrier 2, and the two-component developer 1 will be described in this order.

(Electrophotographic toner 3)
The electrophotographic toner 3 forms an image by adhering to a medium such as paper, and includes a binder resin and a colorant as essential components. Further, the electrophotographic toner may contain a charge control agent, a release agent, a fluidity improver, and the like in addition to the above essential components. Further, two or more types of external additives having different particle diameters are added to the electrophotographic toner 3. In the present embodiment, the fluidity improver described later is used as the external additive 3a.

  The binder resin is a so-called wax, and is an additive that functions as a paste when fixing the toner to the paper surface. Such a 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.

  Here, 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, polyoxyp Pyrene- (2.4) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene- (3.3) -2,2-bis (4-hydroxyphenyl) propane, and derivatives thereof. Can be mentioned.

  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, cyclohexanedicarboxylic acid, orthophthalic acid, isophthalic acid, terephthalic acid and other dibasic acids, trimellitic acid, trimethic acid, pyromellitic acid and other acids and their anhydrides and lower alkyl esters From the viewpoint of heat-resistant aggregation, terephthalic acid or its lower alkyl ester is preferred.

  Here, the acid value of the polyester resin constituting the electrophotographic toner 3 is preferably in the range of 5 to 30 mgKOH / g. When the acid value is less than 5 mgKOH / g, the charging characteristics of the resin are lowered, and the charge control agent is hardly dispersed in the polyester resin as described later. This may adversely affect the charge amount stability of repeated development due to rising of the charge amount or continuous use of the electrophotographic toner 3. In addition, when the acid value exceeds 30 mgKOH / g, it becomes easy to adsorb moisture, and under environmental conditions, for example, under high humidity, the charge rising is reduced and adversely affects the charge amount stability. For example, under low humidity, The charging stability is adversely affected, for example, the charging performance is high and the development amount is reduced.

  As the colorant, various colorants can be used depending on the desired color, such as a yellow toner colorant, a magenta toner colorant, a cyan toner colorant, and a black toner colorant. Can be mentioned.

  Specifically, as a colorant for yellow toner, for example, C.I. I. Pigment yellow 1, C.I. I. Pigment yellow 5, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 15, C.I. I. Azo pigments such as CI Pigment Yellow 17; inorganic pigments such as yellow iron oxide and ocher; 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, 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. As the colorant for black toner, an appropriate carbon black may be appropriately selected from the various carbon blacks exemplified above according to the design characteristics of the electrophotographic 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. Further, as the colorant, two or more of the same color may be used, or one or more of the different colors may be used.

  The form of the colorant is not limited as long as it can be colored. For example, it is 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, a resin that is the same type as the binder resin of the electrophotographic toner 3 or that has good compatibility with the binder resin of the electrophotographic toner 3 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.

  The amount of the colorant used is not particularly limited, but is preferably 5 to 20 parts by weight with respect to 100 parts by weight of the 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 electrophotographic toner 3.

  The charge control agent is added for the purpose of controlling the triboelectric charging property of the electrophotographic toner 3. As the charge control agent, those for positive charge control or negative charge control commonly used in this field can be used. Examples of charge control agents for controlling positive charge include nigrosine dyes, basic dyes, quaternary ammonium salts, quaternary phosphonium salts, aminopyrines, pyrimidine compounds, polynuclear polyamino compounds, aminosilanes, nigrosine dyes and derivatives thereof, triphenylmethane Derivatives, guanidine salts, amidine salts and the like can be mentioned. 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, metal salts of naphthenic acid, metal salts of salicylic acid and its derivatives (metals are metal Chromium, zinc, zirconium, etc.), boron compounds, fatty acid soaps, long-chain alkyl carboxylates, resin acid soaps, and the like. Among these exemplary charge control agents, boron compounds are particularly preferred as containing no heavy metals. Further, the charge control agent for controlling positive charge and the charge control agent for controlling negative charge may be properly used according to the respective applications. Moreover, a charge control agent may be used individually by 1 type, and may use 2 or more types together as needed. The amount of the charge control agent used is not particularly limited and can be appropriately selected from a wide range. Preferably, it is 0.5 to 3 parts by weight with respect to 100 parts by weight of the binder resin.

  The release agent is for improving the peelability between the paper and the fixing roller when the toner is fixed on the paper. As such a releasing agent, those commonly used in this field can be used, for example, petroleum wax such as paraffin wax and derivatives thereof, 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 (such as low molecular weight polyethylene wax) and derivatives thereof, carnauba wax and derivatives thereof, rice wax and derivatives thereof, candelilla wax And their derivatives, plant waxes such as wood wax, animal waxes such as beeswax and spermaceti, synthetic fat waxes such as fatty acid amides and phenol fatty acid esters, long chain carboxylic acids and 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. Preferably, the amount is 0.2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  The fluidity improver is used as the external additive 3a. For example, the effect is exerted by adhering to the surface of the electrophotographic toner 3. As the fluidity improver, those commonly used in this field can be used, and examples thereof include silicon oxide, titanium oxide, silicon carbide, aluminum oxide, and barium titanate. A fluidity improver can be used individually by 1 type, or can use 2 or more types together. The amount of the fluidity improver used is not particularly limited, but is preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the electrophotographic toner 3.

  Hereinafter, an example of a method for producing the electrophotographic toner 3 will be described, but the method for obtaining the electrophotographic toner 3 according to the present embodiment is not limited to this production method.

  First, the toner raw material excluding the fluidity improver is mixed by a mixer such as a Henschel mixer, a super mixer, a mechano mill, or a Q-type mixer. The obtained raw material mixture is melt-kneaded at a temperature of about 70 to 180 ° C. by a kneader such as a twin-screw kneader, a single-screw kneader, or a continuous two-roll kneader. Then, the melted and kneaded product of the toner raw material is cooled and solidified. After cooling and solidifying, the melted and kneaded material of the toner raw material is coarsely pulverized by a cutter mill, a feather mill or the like, and then finely pulverized by an air flow type jet mill, a fluidized bed type jet pulverizer or the like. These fine powder pulverizers pulverize toner particles by colliding toner particles with each other by colliding an air flow containing toner particles from a plurality of directions. Such a pulverizer is commercially available, for example, from Hosokawa Micron Corporation. As a result, the non-magnetic electrophotographic toner 3 having a specific particle size distribution can be produced.

  The particle diameter of the electrophotographic toner 3 is not particularly limited, but the average particle diameter is preferably in the range of 5 to 7 μm in order to improve the output image quality. Further, as necessary, the produced electrophotographic toner 3 may be adjusted in particle size such as classification. The fluidity improver as the external additive 3a is added to the electrophotographic toner 3 thus produced by a known method. The manufacturing method of the electrophotographic toner 3 is not limited to the above.

(Magnetic carrier 2)
The magnetic carrier 2 is a resin composition containing a charge control agent and conductive fine particles on the surface of a carrier core material (magnetic core particle, magnetic core material) 2a in consideration of imparting a sufficient charge to the toner. A carrier on which a covering layer 2b made of a material is formed is preferable.

  As the carrier core material 2a, those commonly used in this field can be used. Examples of the material include magnetic metals such as iron, copper, nickel and cobalt, and magnetic metal oxides such as ferrite and magnetite. When the carrier core material 2a is a magnetic material as described above, a magnetic carrier 2 suitable for a two-component developer used in the magnetic brush development method can be obtained. The volume average particle diameter of the carrier core material 2a is preferably in the range of 25 to 150 μm, and the volume average particle diameter is particularly preferably in the range of 25 to 90 μm. In the present specification, the volume average particle diameter is a value measured using a particle size measuring device (trade name: Microtrac MT3000, manufactured by Nikkiso Co., Ltd.).

  Further, the coating layer 2b is coated on the surface of the carrier core material 2a. The resin composition (coating resin composition) constituting the coating layer 2b is a composition in which a charge control agent having the same components as the charge control agent contained in the electrophotographic toner 3 and conductive fine particles are contained in the resin. It is a thing.

  It does not specifically limit as resin contained in the resin composition for coating | cover, A well-known thing can be used. However, the use of the silicone resin leads to better results from the viewpoint that both releasability with the electrophotographic toner 3 and adhesion with the carrier core material 2a can be achieved.

  The silicone resin is not particularly limited, and a silicone resin commonly used in this field can be used, but a crosslinkable silicone resin is preferable. The cross-linked silicone resin is a known silicone resin that is cured by crosslinking between hydroxyl groups bonded to Si atoms or a hydroxyl group and a group -OX by a heat dehydration reaction, a room temperature curing reaction, or the like, as shown in the following chemical formula.

  As the crosslinkable silicone resin, 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. There is no need to heat in order to cure the room temperature curable silicone resin. However, it is preferable to heat at 150 to 280 ° C. in order to shorten the curing time of the room temperature curable silicone resin.

  Among the cross-linked silicone resins, a silicone resin in which the monovalent organic group represented by R in the chemical formula is a methyl group is preferable. The crosslinked silicone resin in which R is a methyl group has a dense crosslinked structure. Therefore, when the coating layer 2b is formed using this cross-linked silicone resin, the magnetic carrier 2 having good water repellency and moisture resistance can be obtained. However, if the cross-linked structure becomes too dense, the resin coating layer tends to become brittle, so selection of the molecular weight of the cross-linked silicone resin is important.

  Moreover, it is preferable that the weight ratio (Si / C) of silicon and carbon in the crosslinkable silicone resin is in the range of 0.3 to 2.2. When Si / C is less than 0.3, the hardness of the coating layer 2b may be reduced, and the life of the magnetic carrier 2 may be reduced. On the other hand, when Si / C exceeds 2.2, the charge imparting property of the magnetic carrier 2 to the electrophotographic toner 3 is likely to be affected by the temperature change, and the coating layer 2b may become brittle.

  When a cross-linked silicone resin is used as the resin of the coating resin composition, a commercially available product can be used. Examples of commercially available cross-linked silicone resins include 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, and KR3093 (all trade names, manufactured by Shin-Etsu Chemical Co., Ltd.). Moreover, a crosslinking type silicone resin may be used individually by 1 type, and may use 2 or more types together.

  As the charge control agent contained in the coating layer 2b, the same charge control agent as that contained in the electrophotographic toner 3 is preferably used.

  Therefore, a charge control agent for positive charge control or negative charge control may be used as the charge control agent for the magnetic carrier 2 in accordance with the charge control agent contained in the electrophotographic toner 3. Examples of charge control agents for controlling positive charge include nigrosine dyes, basic dyes, quaternary ammonium salts, quaternary phosphonium salts, aminopyrines, pyrimidine compounds, polynuclear polyamino compounds, aminosilanes, nigrosine dyes and derivatives thereof, triphenylmethane Derivatives, guanidine salts, amidine salts and the like can be mentioned. Also, 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 charge control agents, boron compounds are particularly preferable because they do not contain heavy metals. Moreover, a charge control agent may be used individually by 1 type, and may use 2 or more types together as needed. 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 resin contained in the coating resin composition.

  As the conductive particles, for example, conductive carbon black, oxides such as conductive titanium oxide and tin oxide are used. Moreover, carbon black etc. are suitable at the point which expresses electroconductivity with a small addition amount. However, for the color toner, there is a concern that carbon is detached from the coating layer 2b of the magnetic carrier 2. In this case, conductive titanium oxide doped with antimony is used as the conductive particles. Further, the amount of the conductive particles used is not particularly limited and can be appropriately selected from a wide range, but is preferably 10 parts by weight or less with respect to 100 parts by weight of the resin contained in the coating resin composition.

  Further, the magnetic carrier 2 may contain a silane coupling agent for the purpose of adjusting the charge amount of the electrophotographic toner 3. More specifically, a silane coupling agent having an electron donating functional group is preferably used. Specific examples of the silane coupling agent include amino group-containing silane coupling agents. A conventionally well-known thing can be used as an amino group containing silane coupling agent, For example, what is represented by the following general formula (a) can be used.

(Y) nSi (R) m (a)
(In the formula, m Rs are the same or different and each represents an alkyl group, an alkoxy group or a chlorine atom. N Ys are the same or different and each represents a hydrocarbon group containing an amino group. Represents an integer of ˜3, where m + n = 4.)
In the general formula (a), examples of the alkyl group represented by R include a straight chain having 1 to 4 carbon atoms such as a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group. Examples thereof include a chain or branched alkyl group, and among these, a methyl group, an ethyl group, and the like are preferable. Examples of the alkoxy group include linear or branched alkoxy 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. Of 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 the following chemical formulas:
- _(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), or
-Ph-X
(Wherein, X is the same as 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
An amino group containing silane coupling agent may be used individually by 1 type, or may use 2 or more types together. The amount of the amino group-containing silane coupling agent used is appropriately selected from a range that gives sufficient charge to the electrophotographic toner 3 and does not significantly reduce the mechanical strength of the coating layer 2b. The amount of the amino group-containing silane coupling agent used is preferably 10 parts by weight or less, more preferably 0.01 to 10 parts by weight with respect to 100 parts by weight of the resin contained in the coating resin composition.

  The coating resin composition can contain other resins together with the silicone resin as long as the preferable characteristics of the coating layer 2b formed of the silicone resin (particularly the cross-linked silicone resin) are not impaired. 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.

  The resin composition for coating may contain a bifunctional silicone oil. Thereby, the moisture resistance of the coating layer 2b formed with a silicone resin (especially crosslinking type silicone resin), a mold release property, etc. can further be improved.

  The coating resin composition can be produced by mixing a predetermined amount of a silicone resin and an amino group-containing silane coupling agent. Moreover, you may manufacture by mixing an appropriate quantity of additives, such as resin (for example, bifunctional silicone oil) other than a silicone resin, as needed.

  As one form of the resin composition for coating | cover, the form of the solution which dissolved the component of the resin composition for coating | cover mentioned above in the organic solvent is mentioned. The organic solvent is not particularly limited as long as it can dissolve the silicone resin. Examples thereof include aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, ethers such as tetrahydrofuran and dioxane, higher alcohols, and a mixed solvent of two or more of these. If this solution resin composition for coating (hereinafter referred to as “coat resin solution”) is used, the coating layer 2b can be easily formed on the surface of the carrier core material 2a. Examples of a method for forming such a covering layer 2b include the following method. That is, first, a coating resin solution is applied to the surface of the carrier core material 2a to form a coating layer. Then, the organic solvent is volatilized and removed from the coating layer by heat drying. Further, the coating layer is heat-cured or simply cured at the time of heat-drying or after heat-drying. By these procedures, the coating layer 2b is formed on the surface of the carrier core material 2a, and the magnetic carrier 2 is manufactured.

  Examples of the method of applying the coating resin liquid onto the surface of the carrier core material 2a include, 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 film formation can be easily performed.

  Moreover, you may use a drying accelerator for the heat drying of the said application layer. As the drying accelerator, conventionally known ones can be used, for example, lead salts such as naphthyl acid and octyl acid, metal soaps such as iron salt, cobalt salt, manganese salt and zinc salt, and organic amines such as ethanolamine. Can be mentioned. A drying accelerator may be used individually by 1 type, and may use 2 or more types together.

  The coating layer is cured while selecting a heating temperature according to the type of silicone resin. For example, it is preferable to cure the coating layer by heating in the range of 150 to 280 ° C. Of course, when a room temperature curable silicone resin is used as the silicone resin, heating is not necessary. However, even in this case, the coating layer may be cured by heating in the range of 150 to 280 ° C. Thereby, the mechanical strength of the coating layer 2b to be formed can be improved and the curing time can be shortened.

  The total solid content concentration of the coating resin liquid is not particularly limited, and the film thickness of the coating layer 2b after curing is usually 5 μm or less, preferably 0.8, in consideration of the workability of application to the carrier core material 2a. What is necessary is just to adjust so that it may become about 1-3 micrometers.

  The magnetic carrier 2 thus obtained preferably has a high electrical resistance and a spherical shape, but the effect of the present invention is not lost even if it is conductive or non-spherical.

(Two-component developer 1)
The two-component developer 1 is produced by mixing an electrophotographic toner 3 and a magnetic carrier 2. The mixing ratio of the electrophotographic toner 3 and the magnetic carrier 2 is not particularly limited. However, considering that the two-component developer 1 is used in a high-speed image forming apparatus (40 sheets / min or more for A4 size images), the mixing ratio of the electrophotographic toner 3 and the magnetic carrier 2 is as follows: It only needs to be adjusted. That is, in the two-component developer 1 in which the volume average particle diameter of the magnetic carrier 2 / the volume average particle diameter of the electrophotographic toner 3 is 5 or more, the electrons with respect to the total surface area of the magnetic carrier 2 (the total surface area of all carrier particles). The ratio of the total projected area of the photographic toner 3 (the total projected area of all toner particles) (total projected area of toner / total surface area of carrier × 100) may be adjusted to be 30 to 70%.

  As a result, the electrophotographic toner 3 is stably maintained in a state of sufficiently good chargeability. Therefore, the two-component developer 1 including the electrophotographic toner 3 can form a high-quality image stably and for a long time even in a high-speed image forming apparatus. For example, the electrophotographic toner 3 with respect to the total surface area of the two-component developer 1 and the magnetic carrier 2 in which the volume average particle diameter of the electrophotographic toner 3 is 6.5 μm and the volume average particle diameter of the magnetic carrier 2 is 90 μm. The ratio of the total projected area of 30 to 70%. At this time, the mixing ratio of the electrophotographic toner 3 and the magnetic carrier 2 in the two-component developer 1 is about 2.2 to 5.3 parts by weight of the electrophotographic toner 3 with respect to 100 parts by weight of the magnetic carrier 2. It becomes the ratio to include. When high-speed development is performed using such a two-component developer 1, the electrophotographic toner 3 supplied to the developing tank of the developing device according to the transport amount of the electrophotographic toner 3 and the consumption amount of the electrophotographic toner 3. The supply amount of each becomes the maximum. However, the supply and demand balance of the electrophotographic toner 3 is not impaired. When the amount of the magnetic carrier 2 in the two-component developer 1 is greater than 2.2 to 5.3 parts by weight, the toner conveyance amount decreases, and desired development characteristics tend not to be obtained. On the other hand, when the amount of the magnetic carrier 2 is less than the above range, the charge amount of the electrophotographic toner 3 tends to be low, and fogging and development density become unstable, resulting in deterioration of image quality. Invite.

  In this embodiment, the total projected area of the electrophotographic toner 3 is calculated as follows. The specific gravity of the electrophotographic 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 relative to the weight of the electrophotographic toner 3 to be mixed is calculated, and the total number of toner electrophotographic toners 3 is calculated by assuming that the number of toners × the toner area (calculated assuming a circle). Similarly, the surface area of the magnetic carrier 2 is calculated from the weight of the carrier mixed based on the particle diameter obtained from Microtrac (trade name: Microtrac MT3000, manufactured by Nikkiso Co., Ltd.). The specific gravity of the magnetic carrier 2 at this time is 4.7. The mixing ratio (mixing ratio) is calculated by the total toner projected total area / carrier total surface area × 100 obtained above.

In the present invention, the two-component developer 1 has a wax material content with respect to the electrophotographic toner 3 as A (wt%), and the electrophotographic toner 3 concentration with respect to the two-component developer 1 as T (wt%). When the volume resistance of the core material 2a is B (Ωcm) and the volume resistance of the magnetic carrier 2 is C (Ωcm), the following formula (1)
10.4 ≦ log ((C / B) / (A × T)) ≦ 17.9 (1)
It is characterized by satisfying.

  Generally, the resistance value of the magnetic carrier 2 increases as the resin coating amount increases with respect to the carrier core material 2a. On the other hand, when the amount of wax contained in the electrophotographic toner 3 decreases, the developer conveyance rate (developer fluidity) increases. That is, as the amount of wax contained in the electrophotographic toner 3 increases, the amount of wax resin leaking to the surface of the electrophotographic toner 3 increases. As a result, the adhesion force between the particles increases, and the fluidity of the developer decreases.

  As shown in Examples described later, the present inventors have found that the developer conveyance rate is improved by increasing the amount of resin coating formed on the surface of the carrier core material 2a. On the other hand, the toner charge amount has been lowered with an increase in the resin coating amount.

  In general, the volume resistance value (C) of the magnetic carrier 2 is increased by coating the surface of the carrier core material 2a with a resin. In the present invention, the resistance value increase rate (C / B) is an index indicating the coating state of the coating layer 2b on the surface of the carrier core material 2a. The higher the resistance increase rate, the higher the coverage of the coating layer 2b with respect to the carrier core material 2a. That is, the increase in the resistance increasing rate indicates that the wax component contained in the electrophotographic toner 3 of the two-component developer 1 becomes difficult to adhere. On the other hand, if the rate of increase in resistance is too high, there is a problem that the ability to charge the electrophotographic toner 3 is reduced.

  In the two-component developer 1, the resistance value increase rate (C / B) and the wax component (A × T) contained in the electrophotographic toner 3 of the two-component developer 1 satisfy the above formula (1). Thus, the charging ability of the electrophotographic toner 3 is prevented from being lowered, and the wax component contained in the electrophotographic toner 3 is prevented from adhering to the magnetic carrier 3. This realizes a two-component developer that can maintain the fluidity of the developer and can produce a high-quality output image without causing toner scattering.

  The covering state of the covering layer 2b on the surface of the carrier core material 2a may be an arbitrary covering state as long as the resistance value increase rate (C / B) is set so as to satisfy the above formula (1). Good. Examples of the coating state of the coating layer 2b include a state where the coating layer 2b is coated so that the surface of the carrier core material 2a is exposed, and a state where the coating layer 2b covers the entire carrier core material 2a.

  In particular, when the coating layer 2b is coated such that the surface of the carrier core material 2a is exposed, a gap is formed by the coating layer 2b and the surface of the carrier core material 2a. The wax of the electrophotographic toner 3 has an affinity for the surface of the carrier core material 2a, but has a low affinity for the coating layer 2b. If the above formula (1) is satisfied, the exposure rate (gap) on the surface of the carrier core material 2a is appropriately set, and the wax of the electrophotographic toner 3 can be trapped.

(Developing device 20 and image forming apparatus)
The developing device 20 of the present embodiment performs development using the above-described two-component developer 1 of the present embodiment. As shown in FIG. 2, the developing device 20 includes a developing unit 10 that stores the two-component developer 1 and a developer carrier 13 that conveys the two-component developer 1 to the electrostatic latent image carrier 15. .

  A two-component developer 1 composed of a magnetic carrier 2 and an electrophotographic toner 3 is put in advance in the developing unit 10. The two-component developer 1 is stirred and charged by the stirring screw 12. A magnetic field generating means is disposed inside the developer carrier 13. The two-component developer 1 is transported to the developer carrier 13 by the magnetic field generated from the magnetic field generating means and held on the surface of the developer carrier 13. In this way, the two-component developer 1 held on the surface of the developer carrier 13 is regulated to a certain layer thickness by the developer regulating member 14, and the developer carrier 13 and the electrostatic latent image carrier 15 are It is conveyed to the development area formed in the adjacent area. An electric field due to a developing bias is formed between the developer carrier 13 and the electrostatic latent image carrier 15. By this electric field, the electrophotographic toner 3 of the two-component developer 1 on the developer carrier 13 is electrically attached to the electrostatic latent image pattern on the electrostatic latent image carrier 15. Thereby, the electrostatic latent image pattern on the electrostatic latent image carrier 15 is visualized.

  When an AC bias voltage is applied between the developer carrier 13 and the electrostatic latent image carrier 15, the development efficiency is improved by an AC electric field, and the image density from high image density to halftone is improved. A range is obtained stably.

  Further, consumption of the electrophotographic toner 3 is detected by the toner density sensor 16. When the electrophotographic toner 3 is consumed by development, the electrophotographic toner 3 is supplied from the toner hopper 17 by the consumed amount. The toner concentration sensor 16 detects that the toner concentration in the developing unit 10 has reached a predetermined specified toner concentration. The replenishment of the electrophotographic toner 3 from the toner hopper 17 is performed until the toner density sensor 16 detects that the specified toner density is reached. In this way, the density of the electrophotographic toner 3 contained in the two-component developer 1 in the developing unit 10 is kept substantially constant so as to be the toner density detected by the toner density sensor 16.

  As long as the image forming apparatus of the present embodiment includes the developing device 20, the configuration of a known electrophotographic image forming apparatus can be applied. The image forming apparatus according to the present embodiment includes, for example, an image carrier having a photosensitive layer capable of forming an electrostatic charge image on the surface, and a charging unit that charges the surface of the image carrier to a predetermined potential. An exposure means for irradiating a surface of the image carrier with signal light corresponding to image information to form an electrostatic charge image (electrostatic latent image) on the surface of the image carrier; A transfer means for transferring the toner image on the surface of the image carrier developed by supplying the toner 3 to the intermediate transfer body and then transferring it to the recording medium; and a fixing means for fixing the toner image on the surface of the recording medium to the recording medium; And a cleaning means for removing toner, paper dust and the like remaining on the surface of the image carrier after the transfer of the toner image to the recording medium, and a cleaning means for removing excess toner adhering to the intermediate transfer body. . Further, the image forming method of the present embodiment is performed using the image forming apparatus of the present embodiment having the developing device 20.

  When developing an electrostatic charge image, a developing process for visualizing the electrostatic charge image on the electrostatic latent image carrier 15 by a reversal development method is executed for each color of the toner, and the color is different on the intermediate transfer member. A multicolor toner image is formed by superimposing a plurality of toner images. In this embodiment, an intermediate transfer method using an intermediate transfer member is employed, but a configuration in which a toner image is directly transferred from an image carrier to a recording medium may be used.

  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. In Examples and Comparative Examples to be described later, measurement was performed using a two-component developer containing a toner (electrophotographic toner) and a carrier (magnetic carrier). First, a method for producing the toner and carrier used in this example and the comparative example will be described.

(Preparation of toner 3 for electrophotography)
First, each material shown in the following (A) to (D) was premixed with a Henschel mixer and then melt-kneaded with a twin-screw extrusion kneader. The kneaded product was coarsely pulverized with a cutting mill, then finely pulverized with a jet mill, and classified with an airflow classifier to produce toner base particles having an average particle size of 6.5 μm.
(A) Binder resin (T1) Polyester resin (acid value: 21 mgKOH / g)
Aromatic alcohol components: PO-BPA and EP-BPA
Acid components: fumaric acid and merit anhydride
87.5% by weight
(I) Pigment: Naphthol
5% by weight
(C) Wax: Nonpolar paraffin wax
6% by weight
(D) Charge control agent ... Product name: LR-147 (manufactured by Nippon Carlit Co., Ltd.)
1.5% by weight
97.8% by weight of the above prepared toner base particles, 1.2% by weight of silica hydrophobized with i-butyltrimethoxysilane having a volume average diameter of 100 nm, and silica fine particles hydrophobized with HMDS having a volume particle diameter of 12 nm 1.0% by weight was added, mixed with a Hensyl mixer, and externally added to prepare a cyan evaluation toner. Incidentally, LR-147 which is (E) a charge control agent used herein is a substance name "Boro bis (1.1-diphenyl-1 -oxo-acetyl) potassium Salt ", chemical formula is _C 28 _H 20 BKO ₆ expressed.

(Preparation of magnetic carrier 2)
The following amounts (parts) of silicone resin, conductive particles and toluene were stirred for 5 minutes with a three-one motor to prepare a coating resin solution. However, the conductive particles used in advance were dispersed in a toluene solvent using a dispersant. Moreover, what was melt | dissolved in the predetermined solution was used about the charge control agent. This coating resin solution was mixed with magnetic core particles (carrier core material 2a; ferrite core material) having a volume average particle diameter of 45 μm and 1000 parts by weight, and the mixture was added to a stirrer and mixed. Toluene was removed from the obtained mixture under reduced pressure and heating to form a coating layer on the surface of the magnetic core particles. This was heated at 200 ° C. for 1 hour to cure the coating layer to form a resin coating layer (coating layer 2b), which was passed through a 100-mesh sieve to produce a resin-coated carrier (magnetic carrier 2).
(A) Silicone resin ... Trade name: KR-240 (manufactured by Toray Dow Corning Co., Ltd.),
Product name: KR-251 (manufactured by Toray Dow Corning), and
Mixture of 20% silicone resin solution
100 parts by weight (B) conductive particles ... Product name: VULCANXC72 (manufactured by Cabot Corporation)
Conductive carbon black toluene dispersion, solid concentration 15% solution
5 parts by weight (C) charge control agent Product name: LR-147 (manufactured by Nippon Carlit Co., Ltd.)
Negative charge control agent, solution
20 parts by weight (D) coupling agent ... Product name: AY43-059 (manufactured by Toray Dow Corning Co., Ltd.)
100% solution
1 part by weight Next, measurement and evaluation methods in Examples and Comparative Examples described later will be described.

〔Evaluation test〕
(I: Measurement of transport amount of two-component developer 1)
The developing unit 10 was taken out from the developing device 20 shown in FIG. 2, and the transport amount of the two-component developer 1 in the developing unit 10 was measured. This transport amount is an index indicating the fluidity of the two-component developer 1 in the developing unit 10. As the developing unit 10, a developing unit taken out from a copying machine (Sharp Co., Ltd. MX-4500N) was used.

  First, the two-component developer 1 was prepared by mixing the magnetic carrier 2 and the electrophotographic toner 3 prepared in (Preparation of magnetic carrier 2) and (Preparation of electrophotographic toner 3). The produced two-component developer 1 was set in the developing unit 10, and the developing unit 10 was placed in a constant temperature layer maintained at a temperature of 52.5 ° C. Then, the developer carrier 13 was rotated at 430 rpm for one and a half hours, and the two-component developer 1 was stirred with the stirring screw 12. Thereafter, the amount of the two-component developer 1 conveyed to the developer carrier 13 by the stirring screw 12 was measured.

  Specifically, in order to obtain the amount of fall A of the two-component developer 1 in the developing unit 10 before entering the constant temperature bath, the developer carrier 13 is driven at 50 rpm, and the stirring screw 12 driven via a gear. The two-component developer 1 is dropped from the developer dropping hole while rotating. Then, the amount of developer that falls is measured. After the measurement, the developing unit 10 is placed in a thermostatic chamber having a temperature environment of 52.5 ° C., the developer carrier 13 is driven at a rotational speed of 430 rpm for 90 minutes, and mechanical stress is applied to the two-component developer 1 in the developing unit 10. Add Thereafter, the fall amount B of the two-component developer 1 is obtained in the same manner as before entering the thermostat.

  In this embodiment, for the two-component developer 1 in the developing unit 10, the ratio of the drop amount A before the introduction of the thermostat and the fall amount B after the introduction of the thermostat is defined as the developer conveyance rate. The developer conveyance rate is an index indicating the fluidity of the two-component developer that is accelerated and deteriorated.

  In addition, regarding the “developer conveyance rate” in the table, the evaluation criteria of “×”, “Δ”, “◯”, “◎” are as follows.

◎: Conveyance rate: 75% or more ○: Conveyance rate: 50% or more and less than 75% △: Conveyance rate: 30% or more and less than 50% X: Conveyance rate: less than 30% Conveyance rate of 30% or more is the image density and Although the image quality is significantly reduced, image output is possible. On the other hand, if the conveyance rate is less than 30%, the image cannot be output. On the other hand, when the conveyance rate is 50% or more, a slight decrease in image density occurs, but an output image is obtained. Further, when the conveyance rate is 75% or more, the image density and the image quality are almost the same as those before being put in the thermostatic chamber. Based on the relationship between the conveyance rate and the output image, the two-component developer 1 was classified according to the above evaluation criteria.

(II: measurement of charge amount of toner 3 for electrophotography)
The charge amount of the electrophotographic toner 3 was measured as follows.

  The two-component developer 1 on the surface of the developing sleeve disposed in the developing unit 10 was collected, and the charge amount was measured using a suction type charge amount measuring device (TREK: 210H-2A Q / M Meter). The measured value was used as the charge amount of the electrophotographic toner 3.

  Further, the toner charge amount measured in (II: measurement of charge amount of toner 3 for electrophotography) was evaluated based on the following evaluation criteria.

The evaluation criteria for toner chargeability are:
◎: Satisfies target charge amount and little change in charge amount over time ○: Satisfies target charge amount and decreases charge amount over time Δ: Less than target charge amount and little change in charge amount over time ×: Target The charge amount was lower than the charge amount and decreased with time.

  In this embodiment, the target charge amount in toner chargeability is set to 25 to 35 μC / g. This charge amount is obtained from a value that gives the best image quality in the process of the conventional model. Therefore, this is the specific charge amount necessary for ensuring the toner development amount and the toner transferability.

  Even if the charge amount is 20 μC / g, there is no problem without affecting the initial image quality. However, when the charge amount changes with time, there is an influence of toner fog due to insufficient charge amount. For this reason, in this embodiment, the charge amount is set as a target value.

(III: Measurement of resistance value in particles of magnetic carrier 2)
The electrical resistance value (volume resistance) of the particles of the magnetic carrier 2 is determined by using a bridge resistance measurement jig (distance 1 mm between opposed electrodes, measurement electrode area area 40 × 16 mm ² ) in a normal temperature / normal humidity environment. It was measured.

Specifically, first, the magnetic carrier 2 particles (resin-coated carrier particles; electrostatic latent image developing carrier particles) prepared in (Preparation of magnetic carrier 2) were measured separately using an electronic balance or the like as a measurement sample. Separated to 2 mg. And this measurement sample was inserted between the electrodes which a bridge resistance measurement jig | tool opposes, and the bridge | bridging of the magnetic carrier 2 was formed between counter electrodes using the magnet from the back side of this electrode. At this time, tapping was performed about 5 to 6 times in order to level the magnetic carrier 2 between the bridges. After uniformly leveling the magnetic carrier 2 between the bridges, the current value when a voltage generating an electric field strength of 1.5 × 10 ³ (V / cm) was applied was used with a digital electron meter (Advantest Corp .: R8340). The electrical resistance value (carrier resistance value) was calculated.

(IV: Measurement of resistance value of magnetic core particles alone (carrier core material 2a))
Using the carrier core material 2a as a measurement sample, it was set in a bridge resistance measurement jig in the same manner as (III: Measurement of resistance value in particles of magnetic carrier 2). Thereafter, the current value when a voltage generating an electric field intensity of 1 × 10 ³ (V / cm) is applied is measured and measured using a digital electron meter (Advantest: R8340), and the electric resistance value (core material resistance) Value).

(V: Volume average particle diameter)
About 1 to 5 mg of a measurement sample is added to 10 mL of a 0.1% pure aqueous solution of Triton X-100 (nonionic surfactant (chemical formula: C ₃₄ H ₆₂ O ₁₁ )), and 1 by an ultrasonic disperser. Dispersed for minutes. About 2 to 5 mL of this dispersion was added to 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.

(VI: Fixability and output image quality evaluation)
Using a digital color copying machine (Sharp Co., Ltd. MX-6000N) having the developing device 20, the fixing strength on the paper surface and image evaluation were performed. First, an electrophotographic toner 2 and a magnetic carrier 3 for evaluation of magenta color were prepared based on the above method. Then, the electrophotographic toner 2 for evaluation of magenta color and the magnetic carrier 3 were mixed at a ratio of 7:93 to prepare a two-component developer 1. Then, the two-component developer 1 was put into the developing device 20, and a test chart was printed using the developing device 20 and the digital color copying machine. Then, the image quality and the fixability of the printed test chart were determined by visual evaluation based on the following criteria.

  Judgment criteria for image quality evaluation were compared with output images using a standard developer of a commercially available digital color copying machine (Sharp Co., Ltd. MX-6000N), and image quality evaluation of the following items was performed.

・ High dot reproducibility (low toner scattering around the dot)
・ High line reproducibility (less variation in line width)
-Toner adhesion in non-image area (small amount of toner fog in background area)
Further, the comparison results were classified into the following four stages.

◎: Print quality with a higher image quality than internal standards ○: Print quality with the same level as internal standards △: Print quality with lower image quality than internal standards ×: Level almost impossible to print (VII; carrier adhesion)
First, the prepared two-component developer was put into the developing tank of the image forming apparatus, and a carrier bias was measured by applying a developing bias between the photosensitive member set on the test bench and the developing sleeve.

Specifically, after development, the number of carriers deposited on a certain area (37.8 cm ² ) on the photoreceptor corresponding to the non-image area was measured, and the quality of carrier deposition was evaluated. The evaluation criteria are “◎” for the case where the number of carrier attachments is less than 10 and good adhesion, and “○” for cases where the number of attachments is less than 10 and less than 20, and “20” for cases where adhesion is slightly. The defective one was designated as “x”.

  The measurement results in the examples and comparative examples will be described below.

Example 1
A magnetic carrier 2 was prepared according to the method described in (Preparation of Magnetic Carrier 2). However, the resin-coated carrier was prepared by changing the amount of the coating resin solution added to 1000 parts by weight of the magnetic core particles to 0.5 part, 0.75 part, 1 part, and 2 parts. Then, the resistance value of each resin-coated carrier was measured according to the method described in (III: Measurement of resistance value in particles of magnetic carrier 2). For the magnetic core particles used in Example 1, the resistance value was measured based on (IV: measurement of resistance value of magnetic core particles (carrier core material 2a) alone) before introducing the coating resin solution. .

  Further, an electrophotographic toner was prepared according to the method described in (Preparation of Electrophotographic Toner 3). However, toners 1 to 3 were prepared so that the wax content with respect to the toner would satisfy the following conditions.

Toner 1: Wax; 6.5%
Toner 2: Wax; 4.5%
Toner 3: Wax; 3.0%
A two-component developer 1 was prepared using the magenta evaluation toner prepared under the above conditions and the resin-coated carriers with different amounts of the coated resin solution prepared (different in volume resistance). Each produced two-component developer 1 is adjusted such that the toner concentration with respect to the two-component developer 1 is 7.2% by weight. For the two-component developer 1, the developer conveyance amount in the development unit was measured according to the above (I: Measurement of the conveyance amount of the two-component developer 1). Further, based on the above (VI: Fixability and output image quality evaluation), image quality deterioration due to offset at the time of fixing the output image was visually confirmed. In addition, regarding the fixability, a bending test was performed and a comprehensive evaluation of the output image quality was performed. Furthermore, carrier adhesion was evaluated according to the method described in (VII; carrier adhesion).

(Comparative Example 1)
A magnetic carrier 2 was prepared according to the method described in (Preparation of Magnetic Carrier 2). However, the amount of the coated resin solution added to 1000 parts by weight of the magnetic core particles was changed to 0.25 part and 2.5 parts to prepare a resin-coated carrier. Then, the resistance value of each resin-coated carrier was measured according to the method described in (III: Measurement of resistance value in particles of magnetic carrier 2). Further, for the magnetic core particles used in Comparative Example 1, the resistance value was measured based on (IV: measurement of resistance value of magnetic core particles (carrier core material 2a) alone) before introducing the coating resin solution. .

  In addition, using the toners 1 to 3 produced under the same conditions as in Example 1 and the resin-coated carriers having different amounts of the coated resin solution produced (different in volume resistance), the same as in Example 1 was used. A two-component developer 1 was prepared so as to have a toner concentration. In the same manner as in Example 1, the developer transport amount in the developing unit, output image quality evaluation, comprehensive evaluation, and carrier adhesion evaluation were performed.

Table 1 shows the measurement results of the carrier resistance value, the resistance increase rate, and the toner charge amount in each of the carriers 1 to 6 of Example 1 and Comparative Example 1. In Table 1, the resistance value of the resin-coated carrier is shown as “carrier resistance”. The “resistance increase rate” indicates an increase rate of the resistance value of the resin-coated carrier with respect to the resistance value of the magnetic core particles (resistance value of the magnetic core particles / resistance value of the resin-coated carrier). “Toner charge amount” indicates a result of evaluation based on the evaluation criteria of toner chargeability. “Resin coating amount” indicates the input amount of the coating resin solution to the magnetic core particles. In Table 1, “E + x (x is an integer)” means “× 10 ^x ”.

  As can be seen from Table 1, in the resin-coated carrier used in Example 1, the resistance increase rate of the resin-coated carrier is increased as the resin coating amount is increased.

  In the measurement according to (I: Measurement of transport amount of two-component developer 1), the developer transport rate increases as the amount of wax contained in the electrophotographic toner 3 decreases. That is, as the amount of wax contained in the toner increases, the amount of wax resin leaking to the toner surface increases. As a result, the adhesion between the particles is increased, and the fluidity of the developer is reduced. Further, it can be seen that the carrier after the resin coating improves the developer conveyance rate by increasing the amount of the resin coating formed on the surface of the carrier core material. On the other hand, the toner charge amount is reduced as the resin coating amount is increased. When the resin coating amount is 2.5 parts, the toner has little electrostatic holding power and toner scattering occurs, and the output image quality is also fogged due to toner scattering. Therefore, in order to maintain the charge amount of the toner and obtain an image quality free from toner scattering, the coating resin amount is preferably 2 parts by weight or less with respect to 1000 parts by weight of the magnetic core particles.

  Table 2 shows carrier adhesion evaluation and developer for the two-component developer prepared by mixing each of the carriers 1 to 6 of Example 1 and Comparative Example 1 and each of the toners 1 to 3 of Example 1. 5 is a table showing the results of evaluation of the transport amount (transport rate), image quality evaluation of the output image, and comprehensive evaluation based on these evaluations. Table 2 also shows values obtained by calculating conditional expression (1) “log ((C / B) / (A × T))” for each of the two-component developers.

  As can be seen from Table 2, among the two-component developers of Example 1, the two-component developer satisfying the following formula (1) is evaluated for carrier adhesion, evaluation of the developer conveyance amount (conveyance rate), The overall evaluation based on the image quality evaluation of the output image is “◯” or “◎”.

10.4 ≦ log ((C / B) / (A × T)) ≦ 17.9 (1)
In the formula (1), A is the wax content relative to the electrophotographic toner 2, B is the resistance value of the magnetic core particles, C is the resistance value of the resin-coated carrier, and T is This is the density of the electrophotographic toner 2 with respect to the two-component developer 1.

  Hereinafter, “C / B” in the above formula (1) will be described in more detail. “C / B” corresponds to “resistance increase rate” in Table 1.

First, in both Example 1 and Comparative Example 1, the resistance value (B) of the magnetic core particles alone under an electric field of 1.5 × 10 ³ V / cm is 1.37E + 07 (1.37 × 10 ⁷ ) Ωcm. Met. The resistance value (C) increases by coating the surface of the magnetic core particles with resin. The resistance value increase rate (C / B) is an index indicating the coating state of the resin on the surface of the carrier core material (magnetic core particles). The higher the resistance increase rate, the higher the resin coverage with respect to the carrier core material. That is, a high resistance increase rate indicates that the wax component contained in the toner of the two-component developer is difficult to adhere. On the other hand, if the rate of increase in resistance is too high, there is a problem that the ability to charge the toner decreases.

  As shown in Table 2, if the two-component developer in Example 1 is a two-component developer that falls within the range of the conditional expression (1), the above problem can be avoided. Further, the fluidity of the developer can be maintained, and toner output can be prevented without causing toner scattering.

(Example 2)
In this example, the surface of magnetic core particles as a carrier core material was coated with a coupling agent, and then a silicone resin as a coating resin was coated to prepare a resin-coated carrier.

  Specifically, an aminosilane coupling agent (trade name: AY43-059 (manufactured by Toray Dow Corning Co., Ltd.)) was used as the coupling agent.

  After coating the aminosilane coupling agent on the surface of the carrier core material, the coated carrier core material and a coating resin solution containing conductive fine particles are mixed to form a resin-coated carrier (referred to as carrier 7). Was made.

  For the resin-coated carrier of this example, the resistance value was measured based on the above (III: Measurement of resistance value of particles of magnetic carrier 2). As a result, although the amount of the coating resin is as small as 0.5 part, the magnetic carrier (carrier) whose volume resistance of the magnetic carrier does not use the aminosilane coupling agent is 0.5 part. The resistance value was higher than in 1).

  When the resin coating state of the surface of the carrier of this example was observed using an electron microscope, it was found that the coating resin covered the entire carrier core material with a thin film, and the carrier core material was hardly exposed.

  A two-component developer was prepared using the resin-coated carrier of this example and the toner 1 described in Example 1, and the developer in the developing unit was measured according to the above (I: Measurement of transport amount of two-component developer 1). The transport amount of the two-component developer is about 1.5 times that of the carrier 1 shown in Example 1, and the transport amount of the developer with a small amount of coating resin input. And high-quality image output can be obtained. Table 3 shows the evaluation results of the conveyance rate, output image, and fixability of the two-component developer. Table 3 also shows values calculated for conditional expression (1) “log ((C / B) / (A × T))” for each two-component developer.

(Example 3)
Magnetic core particles having different volume average particle diameters are prepared, and a resin-coated carrier (carriers 8 to 12) is prepared by coating each magnetic core particle with a resin by the method described in (Preparation of Magnetic Carrier 2). did. Then, for each resin-coated carrier using magnetic core particles having different volume average particle diameters, the toner 1 used in Example 1 and the carrier particles are mixed so that the toner concentration becomes 7.2% by weight. A component developer was prepared. Each two-component developer was evaluated according to the above (evaluation of carrier adhesion and background fog). The evaluation results are shown in Table 4.

  From Table 4, when the volume average particle diameter of the resin-coated carrier is 20 μm or less, the holding force of the resin-coated carrier by the mag roller included in the developer carrier is reduced, and the surface of the electrostatic latent image carrier is coated with resin. It turns out that a carrier becomes easy to adhere. Further, it can be seen that the mixing with the toner tends to be non-uniform, and the toner charge distribution is expanded, resulting in fogging. Therefore, it can be seen that by setting the volume average particle diameter of the resin-coated carrier to 25 to 60 μm, adhesion to the surface of the electrostatic latent image carrier can be suppressed, and furthermore, the occurrence of fogging can also be suppressed.

Example 4
A resin-coated carrier was prepared according to the method described in (Preparation of Magnetic Carrier 2).

  Further, an electrophotographic toner was prepared according to the method described in (Preparation of Electrophotographic Toner 3). However, toners 1 to 4 were prepared so that the wax content with respect to the toner would satisfy the following conditions.

Toner 1: Wax resin = 6.5%
Toner 2: Wax resin = 4.5%
Toner 3: Wax resin = 3.0%
Toner 4: Wax resin = 7.0%
A two-component developer 1 was prepared using the magenta evaluation toners 1 to 4 manufactured under the above conditions and the resin-coated carriers with different amounts of input of the prepared coating resin liquid (different in volume resistance). . Each produced two-component developer 1 is adjusted such that the toner concentration with respect to the two-component developer 1 is 7.2% by weight. For the two-component developer 1, the developer conveyance amount in the development unit was measured according to the above (I: Measurement of the conveyance amount of the two-component developer 1). Further, based on the above (VI: Fixability and output image quality evaluation), image quality deterioration due to offset at the time of fixing the output image was visually confirmed. In addition, regarding the fixability, a bending test was performed and a comprehensive evaluation of the output image quality was performed.

(Comparative Example 2)
In accordance with the method described in (Preparation of Electrophotographic Toner 3), an electrophotographic toner was prepared. However, toners 5 to 7 were prepared so that the wax content with respect to the toner would satisfy the following conditions.

Toner 5: Wax resin = 2.5%
Toner 6: Wax resin = 8.0%
Toner 7: Wax resin = 1.0%
In accordance with (I: Measurement of transport amount in developing unit), the transport amount of developer in the developing unit was measured, and comprehensive evaluation was performed in (VI: Fixability and output image quality evaluation). The carrier 3 in Table 1 was used as the carrier for forming the developer.

  For Example 4 and Comparative Example 2, the amount of wax in toners 1 to 7 in the developer, the transport rate of the developer, the output image, and the evaluation results of the fixability are shown in Table 5. The value of conditional expression (2) in Table 5 is the following expression (2) where A (wt%) is the wax material content relative to the toner and T (wt%) is the toner concentration relative to the two-component developer for electrophotography. ).

  D = −Log (A × T) (2)

  From Table 5, it was found that the toner of the electrophotographic developer used in this example is suitable to have a wax resin content of 4.5 wt% to 7 wt%. When the content of the wax resin with respect to the toner is 3% by weight or less, although not shown here, the toner adheres to the fixing roller side of the fixing device, and the toner image on the paper surface is deteriorated. Oops. Further, when the content of the wax resin with respect to the toner is more than 7% by weight, that is, under the condition where the D value in the formula (2) is less than 5.3, there is a possibility of affecting other processes. For example, in the development process, agitation is performed in the agitation unit in the development unit, so that thermal and mechanical stress is applied to the developer, which may cause a decrease in developer fluidity. As a result, the image density unevenness of the output image occurs, and the image is significantly deteriorated.

  Here, based on the results of Table 1, Table 2, and Table 5, the upper limit value and the lower limit value of the above formula (1) will be described in more detail.

(About the lower limit)
The resin film thickness coated on the surface of the carrier core material (magnetic core particles) is determined by the ratio between the resistance value B of the carrier core material and the resistance value C of the carrier particles after resin coating. The higher the resistance ratio (C / B), the thicker the resin film thickness. From the results of Table 1 (Table 1), if the resistance increase rate is 21 times or more and less than 2.82E + 06 times, it is possible to satisfy the carrier adhesion condition and the toner charging condition. Note that the amount of wax and the toner concentration (toner 1) contained in the toner at this time are 6.5% and 7.2%, respectively.

Here, taking the logarithm of the carrier resistance increase rate,
21 ≦ (C / B) ≦ 2.82E + 06 [A]
3.04 ≦ Ln (C / B) ≦ 14.85
Thus, it can be seen that if the above conditions are satisfied, carrier adhesion and toner charging are improved.

(About the upper limit)
In the contents described in Table 5 of Example 4, the amount of wax present in the developer mass (the sum of the toner mass and the carrier mass) is assumed. The amount of wax in the developer is expressed by the following formula: 0.0018 <(A × T) <0.00576 (b)
Can be expressed as Taking the logarithm (-Ln) of equation (b),
5.2 <−Ln (A × T) <6.3
It becomes. Here, looking at the relationship between the amount of wax contained in the developer and the rate of increase in carrier resistance, the wax resin has a low affinity with the surface of the silicone resin film, so it is difficult to exist on the surface.

  Therefore, since the fact that the resin film exists on the surface is realized as the increase rate of the carrier resistance is higher, if the ratio of the resistance increase rate and the amount of wax is obtained, the resin film adheres on the silicone resin film. You can see the amount of wax covered.

  If the ratio of the formula (A) and the formula (B) is taken and further logarithmically displayed, the following formula is obtained.

ln ((C / B) / (A × T)) = ln (C / B) − (− ln (A × T))
= Ln (C / B) + ln (A × T)
= [(3.04-14.85) + (5.2-6.3)]
For each of the above formulas, considering each condition range:
Lower limit: ln ((C / B) / (A × T)) = 8.24 (3.04 + 5.2)
Upper limit value: ln ((C / B) / (A × T)) = 21.15 (14.85 + 6.3)
It becomes. Therefore, the numerical range of ln ((C / B) / (A × T) is expressed by the following formula: 8.24 <ln ((C / B) / (A × T)) <21.15.
It becomes the range shown in. Furthermore, from the results of Example 1, specifically, the following formula (1)
10.4 ≦ ln ((C / B) / (A × T)) ≦ 17.9 (1)
If it satisfies, it will be more suitable.

  From the above results, the following can be understood.

The wax material content with respect to the electrophotographic toner 3 is A (wt%), the electrophotographic toner 3 concentration with respect to the two-component developer 1 is T (wt%), and the volume resistance of the carrier core material 2a is B (Ωcm). When the volume resistance of the magnetic carrier 2 is C (Ωcm), the following formula (1)
10.4 ≦ log ((C / B) / (A × T)) ≦ 17.9 (1)
By using a two-component developer that satisfies the following conditions, the following effects can be obtained.

  In other words, even under an environment where the main body of the copier or the like is subjected to thermal or mechanical stress, the flowability of the developer is not significantly reduced, and unevenness in the density of the output image does not occur, and stable even when printing many parts. Thus, a high-quality image can be output.

  The present invention is not limited to the above-described embodiments, and various modifications can be made within the scope shown in the claims. That is, embodiments obtained by combining technical means appropriately modified within the scope of the claims are also included in the technical scope of the present invention.

  The two-component developer using the resin-coated carrier particles of the present invention can be suitably used in image forming apparatuses such as electrophotographic copying machines, printers, and fax machines.

FIG. 2 is a schematic diagram illustrating a toner and a carrier included in a developer according to an exemplary embodiment of the present invention. 1 is a schematic diagram illustrating a developing device according to an embodiment of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developer 2 Carrier 2a Carrier core material 2b Coating layer 3 Toner 3a External additive 10 Developing unit 12 Stirring screw 13 Developer carrying member 14 Developer regulating member 15 Electrostatic latent image carrying member 16 Toner density sensor 17 Toner hopper

Claims (4)

In a two-component developer for electrophotography comprising a toner and a carrier, wherein the toner contains a binder resin, a colorant and a wax material,
The carrier has a carrier core material and a resin coating layer in which a resin is coated on the surface of the carrier core material,
The wax material content with respect to the toner is A (wt%), the toner concentration with respect to the two-component developer for electrophotography is T (wt%), the volume resistance of the carrier core material is B (Ωcm), and the volume of the carrier When the resistance is C (Ωcm), the following formula (1)
10.4 ≦ log ((C / B) / (A × T)) ≦ 17.9 (1)
An electrophotographic two-component developer characterized by satisfying: The carrier core material is made of magnetic particles,
2. The electrophotographic 2 according to claim 1, wherein the resin coating layer is made of a resin cured product obtained by attaching an aminosilane coupling agent to the surface of the carrier core material and then coating and curing a silicone resin solvent. Component developer.   The two-component developer for electrophotography according to claim 1 or 2, wherein an average particle diameter of the carrier is in a range of 35 µm to 55 µm.   The two-component developer for electrophotography according to any one of claims 1 to 3, wherein the wax material content A with respect to the toner is in the range of 3 wt% to 7 wt%.

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