JP2007072144A - Magnetic carrier, toner charging method, and contact type development method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve a longer lifetime with a simple configuration and to maintain higher image quality for a long period in high speed stirring and high speed developing. <P>SOLUTION: The two-component developer is composed by using a magnetic carrier 5A including a single core material 5AA formed by using microballoons etc., a resin binder 5AB dispersed with magnetic powder 5AC formed by using any among at least magnetite, hematite, ferrite, iron powder, etc., and a resin binder 5AB covering the surface of the core material 5AA. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a magnetic carrier for electrophotographic development constituting a two-component developer for developing a latent image formed on an image carrier provided in an image forming apparatus or the like, and toner charging for charging toner using this magnetic carrier The present invention relates to a method and a contact-type developing method for developing a latent image formed on an image carrier using a two-component developer containing the magnetic carrier.

  An image forming apparatus using a two-component developer composed of a magnetic carrier and a toner is generally classified as a two-component developing system, and is particularly used for a high-speed machine, a full-color printer, and a copying machine. In the two-component development system, first, the magnetic carrier and the toner are stirred and mixed in the developing device to charge the toner, and the toner is adhered around the particles of the magnetic carrier by charging. In this state, the magnetic carrier is magnetically attracted to the outer peripheral surface of the developing sleeve containing the magnet. Thereby, a magnetic brush made of a magnetic carrier and toner is formed on the outer peripheral surface of the developing sleeve.

  Thereafter, the developing sleeve is rotated, and the magnetic brush to which the developing bias is applied is conveyed to an approach position or a contact position on the surface of the photosensitive drum on which the electrostatic latent image is formed. Thereby, the toner in the magnetic brush is electrostatically attracted to the electrostatic latent image, and the electrostatic latent image is developed.

  In the conventional dry two-component development method, magnetic particles such as iron powder and ferrite are used as a magnetic carrier. In these magnetic carriers, the resistance value and the like are not suitable for use, and there are problems such as insufficient toner charging capability and a decrease in toner charging capability due to contamination of the carrier surface. As means for solving this problem, a means for coating (coating) the surface of the magnetic carrier with a resin or the like has been generally employed.

  However, even a magnetic carrier having a structure with coding has a problem of disturbing a toner image due to a strong magnetic force due to a strong magnetic force, and cannot sufficiently cope with a high image quality. In addition, in the case of a magnetic carrier in which a magnetic core made of a metal-based core material is coated with a resin as described above, when the resistance of the internal magnetic core is low, a part of the coated resin is worn or peeled off, etc. However, there is a problem in that the toner image formed on the surface of the photoconductive drum is defective because the carrier rising due to the magnetic carrier adhering to the surface of the photoconductive drum increases.

  In addition, there is a carrier having a small particle diameter and lower magnetization than a general magnetic carrier. This low-magnetization carrier having a small particle diameter has a dense magnetic head of the carrier formed on the outer peripheral surface of the developing sleeve, whereby an image with good dot reproducibility can be obtained. However, when the magnetization is lowered, the force to keep the carrier on the developing sleeve is reduced, so that the carrier tends to increase.

  On the other hand, there is a so-called magnetic powder dispersed binder type carrier in which magnetic powder is dispersed in a resin binder. This magnetic dispersion type carrier is generally higher in resistance and lighter than the magnetic carrier having the above-described magnetic core, and the magnetic force can be changed by changing the amount of the dispersed magnetic powder. have. Magnetic powder-dispersed binder-type carrier can be soft developed with little deterioration when used in a two-component developer due to its light weight, and with low stress during development, but is sufficient for high-speed stirring and high-speed development The service life has not been extended.

  Although the deterioration of the two-component developer occurs due to various causes, the magnetic carrier is mainly caused by the spent due to the adhesion of the toner and the change of the surface layer such as wear and peeling of the coating member. The spent or the coating member is worn or peeled off due to stress applied to the two-component developer during stirring. In particular, the progress of deterioration tends to be quicker during high-speed operation.

  In order to reduce the stress at the time of stirring, it is effective to reduce the carrier density and reduce the weight, but in order to reduce the carrier rise, it is necessary to obtain a certain degree of high saturation magnetization. Therefore, it is difficult to reduce the weight more than the current state. Thus, some conventional magnetic carriers have a structure using a hollow spherical particle ferrite as the magnetic carrier (see, for example, Patent Document 1). In addition, there is a configuration in which a coating of a magnetic material such as nickel is formed on the surface of a hollow substance such as a carbon microballoon (see, for example, Patent Document 2). Further, there is a configuration in which a cavity is provided inside a binder-type carrier to reduce the weight compared to the conventional one (for example, see Patent Document 3). Also, there is a configuration in which the surface of a core material having a relatively small specific gravity such as aluminum powder or resin particles is covered with a plating film of a magnetic material such as nickel (for example, see Patent Document 4).

  However, in the configuration of Patent Document 1, since the ferrite of hollow spherical particles is used as a magnetic carrier, it is a configuration using only a conventional ferrite although it is hollow, and is insufficient in terms of weight reduction. . Also, such a special structure of ferrite is not suitable for mass production. In the configuration of Patent Document 2, since a magnetic material film is formed by plating or the like, the conductivity increases when the magnetic material film is exposed on the surface, and the charge imparting characteristics and development characteristics for charging the toner vary. There is a problem of doing.

  The configuration of Patent Document 3 enables further weight reduction as compared with a conventional binder-type carrier, but is not sufficient in terms of strength and durability. In the configuration of Patent Document 4, the plating film is exposed on the surface, so that the conductivity is high, and there is a problem that the charge imparting characteristics for charging the toner and the charging stability are poor. Moreover, since it is necessary to form a plating film on the surface of the core material, it is not suitable for mass production.

  In addition, in the carrier of the structure of patent document 2 and 4, since the film is formed by plating etc., the surface of a film will become smooth. Therefore, the resin coat layer formed on the surface of the coating has no durability and is easily peeled off.

Therefore, some carriers in recent years have a structure in which a layer made of magnetic powder is formed around a resin core and then a resin is coated by polymerization (see, for example, Patent Document 5). Moreover, there exists a thing of the structure containing 2 or more space | gap in the binder resin which disperse | distributed magnetic powder (for example, refer patent document 6).
JP-A-57-177160 JP 63-143564 A JP-A-3-89253 JP 59-142557 A Japanese Patent No. 3293700 Japanese Patent No. 2993622

  However, in the configuration of Patent Document 5 described above, the strength can be relatively increased, but the material selection range is narrow because it is limited to a special manufacturing method and the coating layer is formed by polymerization. There is a problem that a suitable resin cannot be selected for charging the toner. Moreover, since the inside is filled with the resin core material, there is a limit to weight reduction.

  Moreover, in the structure of the above-mentioned patent document 6, when it has two or more voids, the particle shape tends to be indefinite, and particularly when it has a large hollow, the influence becomes remarkable. The irregularly shaped magnetic carrier particles have a problem in durability because the force is applied non-uniformly, and the development characteristics such as rising of the carrier are also adversely affected.

  An object of the present invention is to provide a magnetic carrier that can achieve a long life with a simple structure and can maintain high image quality over a long period of time even in high-speed stirring and high-speed development.

  In order to solve the above problems, the present invention has the following configuration.

(1) a single core material having a hollow shape;
A resin binder in which magnetic powder is dispersed, the resin binder covering the surface of the core material.

  In this configuration, the surface of a single core material having a hollow shape is covered with a resin binder in which magnetic powder is dispersed. Therefore, since the core material is formed in a hollow shape, the bulk density and the like are reduced. In addition, since only a single cavity is formed in the interior, the particle shape does not become indeterminate, and the agitation force is not applied unevenly during agitation. Will never be faster.

(2) particle size is 17Myuemu～63myuemu, apparent density, characterized in that a ^{0.8g / cm 3 ~1.9g / cm 3} .

  In this configuration, the magnetic carrier is formed within the range of the particle size value and the apparent density value that prevent the occurrence of brush streaks in the toner image. The particle size and apparent density define the mass of the magnetic carrier. If the mass is large, the toner image formed on the image carrier is scraped off by the magnetic spikes of the magnetic carrier formed on the developing sleeve, and brush streaks are generated. To do.

  Further, the particle size and the apparent density are appropriate values, the weight of the magnetic carrier is not too heavy, the bulk density and the like are reduced, and the toner can be more easily stirred than before, and the torque at the time of stirring is also reduced. For this reason, since the stress applied by the stirring of the toner is reduced, the progress of the deterioration becomes slower than the conventional one. In addition, since the stirring performance is improved, the change in the charge amount due to the variation in the toner concentration is reduced.

(3) The saturation magnetization is 30 emu / g to 100 emu / g, and the volume resistance is 1.0 × 10 ¹¹ Ω · cm to 1.0 × 10 ¹⁵ Ω · cm.

  In this configuration, the magnetic carrier is formed within the range of the saturation magnetization value and the volume resistance value that prevent the generation of the magnetic carrier. Saturation magnetization is necessary for attracting the magnetic carrier to the outer periphery of the developing sleeve by a magnetic force in the developing device. Further, when the volume resistance is increased, electric charges are not injected from the developing sleeve during development, and the carrier rising where the magnetic carrier is developed on the image carrier is prevented.

(4) The particle size is 17 μm to 64 μm, the apparent density is 0.8 g / cm ^{3 to} 1.9 g / cm ³ , and the volume resistance is 1.0 × 10 ¹¹ Ω · cm to 1.0 × 10 ^15. It is Ω · cm.

  In this configuration, the magnetic carrier is formed within the range of the particle size value, the apparent density value, and the volume resistance value that prevent the occurrence of toner fog. In other words, the magnetic carrier is formed within the above-mentioned range where the toner is easily charged uniformly. This is because the toner fog is caused by non-charged toner or reverse-charged toner adhering to the non-image portion of the latent image as a major factor. The particle size and the apparent density improve the stirring performance, and the higher the volume resistance, the easier it is to charge, so the charging ability to charge the toner to the opposite polarity during stirring is improved.

  (5) The magnetic powder is composed of one or more of magnetite, hematite, ferrite, and iron powder.

  In this configuration, it is composed of at least one of magnetite, hematite, ferrite, and iron powder, which has a high volume resistance and is suitable for increasing the volume resistance of the magnetic carrier itself.

(6) In a toner charging method for a two-component developer in which a toner for developing a latent image formed on an image carrier is stirred and charged with a magnetic carrier.
The magnetic carrier is a magnetic carrier for electrophotographic development according to any one of (1) to (5).

  In this configuration, the toner constituting the two-component developer is stirred and charged with the magnetic carrier described in any one of (1) to (5).

  (7) The toner weight concentration ratio (T / D) when stirring the toner is 10% to 25%, where T is the weight of the toner and D is the sum of the weight of the toner and the weight of the magnetic carrier. It is characterized by being.

  In this configuration, the toner is constantly stirred by the magnetic carrier within a range of T / D 10% to 25% where the change amount of the toner specific charge due to the change in toner concentration in the two-component developer is small.

(8) In a contact developing method of a two-component developer comprising a toner and a magnetic carrier for developing a latent image formed on an image carrier,
The magnetic carrier is a magnetic carrier for electrophotographic development according to any one of (1) to (5).

  In this configuration, the two-component developer comprising the toner carried on the developer carrying member and the magnetic carrier described in any one of (1) to (5) contacts the surface of the image carrying member, and only the toner Is electrostatically attracted to the latent image formed on the surface of the image carrier, and development is performed. At this time, the magnetic carrier remains in the developer carrying member (adsorbed) by the magnetic force.

  (9) The toner weight concentration ratio (T / D) when stirring the toner is 10% to 25%, where T is the weight of the toner and D is the sum of the weight of the toner and the weight of the magnetic carrier. It is characterized by being.

  In this configuration, the toner after being stirred and charged by the magnetic carrier within the range of T / D 10% to 25% where the amount of change in the toner specific charge due to the change in the toner concentration in the two-component developer is small is used for development. .

  According to the present invention, the following effects can be obtained.

  (1) By covering the surface of a single core material having a hollow shape with a resin binder in which magnetic powder is dispersed, the particle shape can be made into a fixed shape with a simple configuration while reducing weight. Since it is possible to prevent the progress of the deterioration only at this point, it is possible to achieve a longer life than in the past.

(2) a 17μm~63μm particle size, the apparent density by the ^{0.8g / cm 3 ~1.9g / cm 3} , while maintaining the development of high quality by preventing the occurrence of brush streaks, stirring The torque at the time can be reduced and the life can be extended compared with the conventional case. Further, the toner can be uniformly charged.

(3) The saturation magnetization is set to 30 emu / g to 100 emu / g, and the volume resistance is set to 1.0 × 10 ¹¹ Ω · cm to 1.0 × 10 ¹⁵ Ω · cm to prevent the carrier from rising. While maintaining high image quality development, it is possible to achieve a longer life than in the past.

(4) The particle size is 17 μm to 64 μm, the apparent density is 0.8 g / cm ^{3 to} 1.9 g / cm ³ , and the volume resistance is 1.0 × 10 ¹¹ Ω · cm to 1.0 × 10 ¹⁵ Ω · By setting the thickness to cm, it is possible to prevent the occurrence of toner fog and maintain high-quality development, and to achieve a longer life than conventional ones.

  (5) By dispersing magnetic powder composed of one or more of magnetite, hematite, ferrite, and iron powder in a resin binder, it is easy to achieve a desired volume resistance while making saturation magnetization a desired value. A carrier can be formed.

  (6) By charging the toner by stirring with the magnetic carrier having a long life as described in any one of (1) to (5), the charge rising and uniform chargeability of the toner can be improved over a long period of time. Can be improved.

  (7) The toner / magnetic carrier can be used in a wide range of T / D 10% to 25%. In addition, when the toner is stirred with the magnetic carrier, it is possible to charge the toner in a state where the amount of change in the toner specific charge due to the change in the toner concentration in the two-component developer is small. It can be improved further.

  (8) By developing the latent image formed on the image carrier using a two-component developer composed of the toner and the magnetic carrier according to any one of (1) to (5), a long period of time can be obtained. It is possible to maintain high-quality development by preventing the occurrence of carrier rise and toner fog.

  (9) The toner after stirring and charging with a magnetic carrier within a range of T / D 10% to 25%, which is a toner concentration higher than that normally used, is used for development, so that a high toner concentration and a specific toner charge can be obtained. It is possible to use toner in a stable state, and it is possible to cope with high speed and to achieve high image quality.

  FIG. 1 is an enlarged view showing a partial configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 includes a photosensitive drum (corresponding to the image carrier of the present invention) 10, a developing device 20, and the like, and transfers the toner image formed based on the image data onto the sheet, thereby transferring the image onto the sheet. Form.

  The developing device 20 includes a stirring roller 21 and a developing sleeve 22 in a developing tank 20A, and an electrostatic latent image formed on the surface of the photosensitive drum 10 using the two-component developer 5 accommodated in the developing tank 20A. Develop the image. The agitation roller 21 conveys the magnetic carrier 5A and the toner 5B constituting the two-component developer 5 to the developing sleeve 22 while being agitated and mixed by rotation. At this time, the toner 5B is charged by stirring and mixing with the magnetic carrier 5A, and is conveyed to the developing sleeve 22 in a state of being attached to the periphery of the magnetic carrier 5A.

  The developing sleeve 22 includes a magnet inside a rotatable roller, and forms a magnetic brush by magnetically adsorbing a magnetic carrier with the toner 5B attached to the outer peripheral surface thereof. The developing sleeve 22 is connected to a developing bias power source (not shown). The developing bias power source applies a developing bias voltage to the two-component developer 5 on the outer peripheral surface of the developing sleeve 22.

  Further, the developing sleeve 22 conveys the two-component developer 5 in a state where a developing bias is applied to the developing region Y facing the photosensitive drum 10 with a gap by rotation. At this time, the toner 5B is electrostatically attracted to the electrostatic latent image formed on the surface of the photosensitive drum 10 in the development area Y to form a toner image. The photosensitive drum 10 transfers the toner image formed on the surface thereof to a sheet. The gap provided between the photosensitive drum 10 and the developing sleeve 22 is formed at an interval such that the two-component developer 5 conveyed on the outer peripheral surface of the developing sleeve 22 contacts the surface of the photosensitive drum 10. Yes.

  FIG. 2 is a sectional view showing the structure of the magnetic carrier 5A according to the embodiment of the present invention. The magnetic carrier 5A includes a spherical core material 5AA having a hollow shape, and a resin binder 5AB covering the surface of the core material 5AA. Resin binder 5AB contains magnetic powder 5AC in a dispersed state. Thereby, a bulk density etc. can be reduced and a particle shape can be made into a fixed shape with a simple structure, aiming at weight reduction. In addition, since only a single cavity is formed in the interior, the particle shape does not become indeterminate, and the agitation force is not applied unevenly during agitation. Can be prevented. As a result, it is possible to achieve a longer life than in the past.

Ferromagnetic particles are used as the magnetic powder that can be used in the present invention. The ferromagnetic particles are not particularly limited, but ferrite, magnetite and hematite having a volume resistance of 1.0 × 10 ⁵ Ω · cm or more are preferably used. When the volume resistance is less than 10 ⁵ Ω · cm, the electric resistance as the magnetic powder fluctuates due to durability, or the electric resistance of the magnetic carrier 5A itself decreases, so the toner used for development on the photosensitive drum 10 This is because there may occur problems such as fluctuations in image density due to fluctuations in the amount of toner and adhesion of the magnetic carrier 5A to the photosensitive drum 10 due to the injected charge from the developing sleeve 22.

  Examples of magnetic powders other than ferrite include iron oxides such as hematite and magnetite, ferromagnetism metals such as iron, nickel and cobalt, and alloys and compounds thereof. A powder resistance measuring device was used for measuring the volume resistance of the magnetic carrier 5A of the present invention. Specifically, a cylindrical cell is filled with a magnetic component, a circular upper electrode and a lower electrode are arranged in contact with the filled magnetic powder, a voltage is applied between these electrodes, and a current that flows at that time is applied. Was measured to determine the specific resistance (volume resistance) ρ (Ω · cm). In the above measuring method, since the magnetic powder 5AC is a powder, a change occurs in the filling rate, and the volume resistance may change accordingly.

The measurement conditions of the specific resistance in the present embodiment were a contact area S between the filled magnetic powder and the electrode = about 3.2 cm ² , a thickness = about 1 mm, an upper electrode load of 500 g, and an applied voltage of 500V. The magnetic powder 5AC used in the present invention has a primary particle diameter of 0.05 to 5 μm, preferably 0.1 to 1 μm as a volume average diameter.

  Further, as the ferromagnetic fine particles, spinel ferrite such as γ-iron oxide, and magnetoplanar such as spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Zn, Mg, Cu, etc.). Bite-type ferrite and iron or alloy fine particle powder having an oxide layer on the surface can also be used. The shape of the ferromagnetic fine particles may be any of granular, spherical and acicular.

  In particular, when high magnetization is required, a ferromagnetic fine particle powder such as iron can be used. However, in consideration of chemical stability, magnet branbite such as spinel ferrite and barium ferrite including magnetite and gamma iron oxide are used. It is preferable to use ferromagnetic fine particle powder of type ferrite.

  As the binder resin used for the resin binder 5AB, a material having an appropriate chargeability may be selected from those conventionally known as binder resins for magnetic powder-dispersed binder type carriers. For example, as an addition polymerization resin, styrene System, acrylic system, olefin system, diene system, acrylonitrile system, acrylic amide system, vinyl acetate system and halogenated olefin system each or copolymer, polyester system, aramide system and silicone system as polycondensation system Examples of the polymer and the polyaddition type epoxy polymer and polyurethane polymer can be listed.

  Among these binder resins, use of a crosslinkable polymer is preferable because impact resistance as a magnetic powder-dispersed binder type carrier is increased and durability is further improved. Here, when the binder resin is a vinyl polymer, the cross-linkable polymer is cross-linked with a compound mainly having two or more polymerizable double bonds as a cross-linking agent. Moreover, the following are raised as a crosslinking agent used in this case. For example, aromatic divinyl compounds such as vinylbenzene, divinylnaphthalene and their derivatives, diethine glycol methacrylate, diethylene glycol acrylate, triethylene glycol methacrylate, trimethylolpropane trimethacrylate, allyl methacrylate, t-butylaminoethyl methacrylate, tetraethylene Diethylenic carboxylic esters such as glycol dimethacrylate, 1,3-butanediol dimethacrylate, all divinyl compounds such as N, N-divinylaniline, divinyl ether, divinyl sulfide, divinyl sulfone, and three or more vinyl groups Are selected alone or as a mixture and are added in the range of 0.005% to 20% based on the total monomer weight.

  Further, typical monomers used for forming the vinyl polymer as described above include styrene, p-chlorostyrene, vinyl naphthalene, for example, ethylene series such as ethylene, propylene, butylene, isobutylene and the like. Unsaturated monoolefins, for example, vinyl esters such as vinyl chloride, vinyl bromide, vinyl fluoride, vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate, vinyl formate, vinyl malariate, vinyl caproate, etc. For example, methyl acrylate, ethyl acrylate, acrylic acid-n-butyl, isobutyl acrylate, dodecyl acrylate, acrylic acid-n-octyl, acrylic acid-2-chloroethyl, phenyl acrylate, methyl-α-chloroacrylate, Methyl methacrylate, ethyl methacrylate, methacrylate Ethylenic monocarboxylic acids such as butyl acid and esters thereof, for example, ethylenic monocarboxylic acid substitution products such as acrylonitrile, methacrylonitrile, acrylamide, etc., ethylenic compounds such as dimethyl maleate, diethyl maleate, dibutyl maleate, etc. Dicarboxylic acids and substituted products thereof, for example, vinyl ketones such as vinyl methyl ketone, vinyl hexyl ketone, methyl isoprophenyl ketone, etc., vinyl ethers such as vinyl methyl ether, vinyl isobutyl ether, vinyl ethyl ether, etc., for example, vinylidene chloride, Vinylidene halides such as vinylidene chlorofluoride, for example, N-vinyl compounds such as N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole and N-vinyl pyrrolidone There is a thing. The polymer used in the present invention is produced by addition polymerization of one or more of these monomers and the above-mentioned crosslinking agent. The expression addition polymerization includes, for example, a free radical polymerization method, an anionic polymerization method and It includes well-known polymerization methods such as cationic polymerization.

  When the binder resin is polyester, a crosslinked polyester obtained by polycondensation of a trihydric or higher polyhydric alcohol or a trivalent or higher polyvalent carboxylic acid with another monomer is preferably used. Here, examples of the trihydric or higher polyhydric alcohol include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, steaming, 1,2,4-butanetriol, 1,2,5-pentatriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, 1,3 , 5-trihydroxymethylbenzene and others. Examples of the trivalent or higher polyvalent carboxylic acid include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 1,2,4-cyclohexanetricarboxylic acid, 2,5,7. -Naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxyl Examples include propane, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, acid anhydrides thereof, and the like.

  Examples of other monomers include alcohols such as ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4- Diols such as butenediol, 1,4-bis (hydroxymethyl) cyclohexane, etherified bisphenols such as bisphenol A, hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A, and other two Valent alcohol monomer. Examples of the carboxylic acid include maleic acid, fumaric acid, mesaconic acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, malonic acid. And anhydrides of these acids, dimers of lower alkyl esters and linolenic acid, and other divalent organic acid monomers.

An example of the crosslinkable binder resin described above is a polymer resin polymerized to some extent at the raw material resin stage before manufacturing the magnetic powder dispersed binder type carrier, but the magnetic powder dispersed binder type of the present invention. When manufacturing the magnetic carrier 5A for electrophotographic development, it is possible to give sufficient hardness and durability by coating with a low to medium molecular weight resin and then crosslinking by a method such as heating. In that case, a crosslinking agent that undergoes a crosslinking reaction with the resin may be added to obtain a crosslinkable binder resin. The resin used in this case is selected from, for example, a copolymer composed of two or more monomers including a monomer having a crosslinkable functional group in the side chain.

  Examples of the monomer having a crosslinkable functional group in the side chain include a monomer having an organic acid in the side chain (for example, acrylic acid, methacrylic acid, itaconic acid, fumaric acid, etc.), and a hydroxy group in the side chain. Monomer having (for example, 2-hydroxyethyl acrylate, 2-hydroxyethyl methacrylate, 4-hydroxybutyl acrylate, 4-hydroxybutyl methacrylate, o-, m- or p-hydroxystyrene, o-, m- or p- Hydroxyphenyl methacrylate, 2-hydroxyethyl vinyl ether, etc.), monomers having an epoxy group in the side chain (for example, glycidyl acrylate, glycidyl methacrylate), monomers having an imino group in the side chain (for example, acrylamide, methacrylamide, N-ethylacrylamide, N-ethylmethacrylamide N-hexylacrylamide, N-hexylmethacrylamide, N-cyclohexylacrylamide, N-phenylacrylamide, N-nitrophenylacrylamide, N-methylolacrylamide, N-methylolmethacrylamide, N- (4-hydroxyphenyl) acrylamide, N- (4-hydroxyphenyl) methacrylamide, N- (4-hydroxynaphthyl) methacrylamide, ureidoethyl acrylate, ureidoethyl methacrylate, ureidoethyl vinyl ether, methacryloyl dicyanamide, etc.), monomers having an aziridinyl group in the side chain (For example, 2- (1-aziridinyl) ethyl acrylate, 2- (1-aziridinyl) ethyl methacrylate, etc.), maleic anhydride, polyethylene glycol It can be exemplified dimethacrylate.

  Other monomers that can be used together with the monomer having a crosslinkable functional group in the formation of the above crosslinkable polymer include, for example, styrenes such as styrene, α-methylstyrene, chlorostyrene; acrylic acid Methyl, ethyl acrylate, propyl acrylate, butyl acrylate, amyl acrylate, hexyl acrylate, octyl acrylate, 2-chloroethyl acrylate, acrylic acid-N, N-dimethylaminoethyl, methyl methacrylate, methacrylic acid (Meth) acrylic acid alkyl esters such as ethyl, propyl methacrylate, butyl methacrylate, amyl methacrylate, hexyl methacrylate, octyl methacrylate, 2-chloroethyl methacrylate, methacrylic acid-N, N-dimethylaminoethyl; Ethyl vinyl ether, 2-c Vinyl ethers such as roethyl vinyl ether, propyl vinyl ether, butyl vinyl ether, octyl vinyl ether, phenyl vinyl ether; vinyl esters such as vinyl acetate, vinyl chloroacetate, vinyl butyrate, vinyl benzoate; methyl vinyl ketone, ethyl vinyl ketone, propyl vinyl Vinyl ketones such as ketone, butyl vinyl ketone and phenyl vinyl ketone; olefins such as ethylene, propylene, isobutene, butadiene and isoprene; nitrogen-containing compounds such as n-vinylpyrrolidone, N-vinylcarbazole and 4-vinylpyridine; acrylonitrile; And vinyl nitriles such as methacrylonitrile; fluorine-containing compounds represented by the following general formula (1); One or more of these monomers can be used in appropriate combination.

In the formula (1), R represents a hydrogen atom or a methyl group, X represents an oxygen atom, a COO group or a CO group, and _Rf represents a fluoroalkyl group.

  It is also possible to add materials having other functions to the resin. Examples of such additives include CCA and CCR for charge control, titanium oxide and carbon black for resistance adjustment, silica for fluidity securing, etc., and adjusting the amount to be added as necessary. Thus, a function can be added to the magnetic carrier 5AC.

  As the material of the hollow core material 5AA, either organic particles or inorganic particles can be used. As the organic particles, foamed rubber such as urethane, hollow resin particles formed of phenol resin, polyvinylidene chloride, epoxy resin, urea resin or the like are used. As the inorganic particles, hollow glass microballoons such as glass balloons, silica balloons, and shirasu balloons, carbon microballoons, and the like can be used.

  These hollow particles can be used by mixing those formed from the beginning, and those prepared during the process can also be used. Considering the function as the magnetic carrier 5AC, it is preferable that the strength or rigidity is high to some extent so that the magnetic carrier 5AC is not easily broken.

  As a manufacturing method of the hollow magnetic carrier 5A, a coating layer in which magnetic powder 5AC is dispersed in a polymer solution in which a hollow particle (core material 5AA) is used as a core and a resin is dissolved in an organic solvent is used. It is possible to apply by this method. In addition, by dispersing and suspending hollow particles in a liquid in which magnetic powder is dispersed in a monomer and then performing polymerization, it is possible to create particles having a coating layer in which magnetic powder is dispersed in resin binder 5AB. It is.

By first selecting the size and particle size distribution of the hollow particles, it is possible to control the approximate particle size of the finally produced magnetic carrier 5A, and the coating thickness of the hollow particles is It is possible to use a coating layer having a particle size of about 2% to 200%, more preferably about 0.5 μm to 10 μm. In order to be suitably used as the magnetic carrier 5A, a certain degree of magnetization is required, and the saturation magnetization is preferably designed to be about 20 emu / g to 200 emu / g at 10 ³ Oe.

  The two-component developer 5 includes a magnetic carrier 5A and a toner 5B. The toner weight concentration ratio indicating the mixing ratio of the magnetic carrier 5A and the toner 5B is T / D (toner weight / (toner weight + carrier weight). It becomes.

  It is desirable that the charge amount of the toner 5B be as constant as possible because it relates to the image density during development. The specific charge Q / M (toner charge amount / toner weight) is used as an index for evaluating the toner charge amount. It is preferable that the change in the toner specific charge (Q / M) is small, but it is generally known that the toner specific charge (Q / M) changes with the change in T / D. In order to keep (Q / M) constant, it is necessary to precisely control the T / D in the developing tank 20A. T / D is used in a range of approximately 1 to 10%, and usually 3 to 8%.

  T / D holding control is performed by a control unit (not shown) based on T / D detected by a magnetic sensor (not shown) provided in the developing device 20.

The charging ability varies depending on the compatibility between the magnetic carrier 5A and the toner 5B, their conductivity, the stirring speed, and the like, but it is preferable to charge them as uniformly as possible in order to improve the image quality. In order to achieve uniform charging, the stirring performance of the developing device 20 and the fluidity of the two-component developer 5 are affected. Therefore, by reducing the particle density and bulk density of the magnetic carrier 5A, the flow of the two-component developer 5 is reduced. Thus, the agitation efficiency is increased, the torque during agitation is reduced, the stress on the two-component developer 5 is reduced, and the deterioration of the two-component developer can be suppressed. Therefore, the bulk density is preferably 3.0 g / cm ³ or less, and particularly preferably 1.5 g / cm ³ or less.

  In this embodiment, a contact developing method is used in which development is performed by bringing the two-component developer 5 conveyed on the outer peripheral surface of the developing sleeve 22 into contact with the surface of the photosensitive drum 10 in the developing region Y. A non-contact developing method in which the two-component developer 5 conveyed on the outer peripheral surface of the developing sleeve 22 in the region Y is brought close to the surface of the photosensitive drum 10 may be used.

  In the contact development method, when the development speed is increased, brush streaks are generated due to the toner image of the magnetic carrier 5A scraping off the toner image.

  The developing speed is about 20 mm / min and the peripheral speed of the photosensitive drum 10 is about 100 mm / s, and about 80 mm / min and the peripheral speed of the photosensitive drum 10 is about 350 mm / s. When the two-component developer using the magnetic carrier 5A of the present invention is used, the apparent density of the magnetic carrier 5A is light, so that there is an advantage that scraping by the magnetic carrier 5A is reduced and image deterioration does not occur. In the present embodiment, the apparent density is obtained using the volume occupied by the magnetic carrier 5A itself and the volume of the hollow portion of the core material 5AA as the volume for density calculation.

  As a problem of improving the image quality, there is a carrier rising that the magnetic carrier 5A is developed on the surface of the photosensitive drum 10. When this carrier rise occurs, the image portion of the formed electrostatic latent image is developed by the magnetic carrier 5A, causing toner loss, and the image quality is greatly deteriorated. A measure for avoiding this phenomenon is to securely hold the magnetic carrier 5A on the outer peripheral surface of the developing sleeve 22, but for this purpose, saturation magnetization of the magnetic carrier 5A or on the outer peripheral surface of the developing sleeve 22 is required. It is necessary to set the magnetic flux density optimally.

Another problem with high image quality is a phenomenon that the electrostatic latent image formed on the surface of the photosensitive drum 10 is disturbed. This phenomenon occurs due to the flow of current through the magnetic carrier 5 </ b> A to the surface of the photosensitive drum 10 due to the developing bias and the contact between the magnetic carrier 5 </ b> A and the photosensitive drum 10. Therefore, this phenomenon that is dependent on the volume resistivity and the developing bias such as a magnetic carrier 5AC, to increase the volume resistivity of the magnetic carrier 5A to usually about ^{10 10 Ω · cm~10 13 Ω ·} cm It is possible to reduce the occurrence of the phenomenon.

  As the development electric field (development bias), any of a DC bias, an AC bias, and an AC bias on which a DC component is superimposed can be used. As a problem when developing the electrostatic latent image, there is a toner fog of the toner 5B. The cause of this phenomenon is various, but a major factor is mainly the portion where the non-charged toner 5B or the reversely charged toner 5B adheres to the non-image portion. Therefore, it is necessary to reliably charge the toner 5B, and it is effective to charge the toner 5B uniformly by precisely controlling the toner concentration in the two-component developer 5 and devising a stirring mechanism for the two-component developer. is there.

  Hereinafter, the present invention will be described more specifically using Examples 1 to 5 and Comparative Examples 1 to 8 of the present invention. Unless otherwise specified, “parts” represents “parts by weight”.

Example 1
Glass bubbles K46 (manufactured by 3M) was prepared as a microballoon for the core material, dispersed in water, and the hollow particles broken using a specific gravity difference were removed, followed by drying. When the particle size of the microballoon particles was measured by a laser diffraction scattering method, the average particle size was 58.1 μm.

  Next, in 180 parts of ethyl acetate, 20 parts of the polyester resin was mixed at a ratio of 150 parts of magnetite as a magnetic material to obtain a magnetic powder-dispersed resin liquid in which the magnetic powder was dispersed in the resin liquid. Thereafter, the magnetic powder-dispersed resin solution is applied to the surface of the microballoon by spraying using a fluidized bed method, and then heated to dry. By repeating this operation, a hollow magnetic carrier in which magnetic powder was dispersed around the microballoon was obtained.

  The particle size of the obtained magnetic carrier was measured by a laser diffraction scattering method. Moreover, after melt | dissolving the resin of the obtained magnetic carrier using a solvent, only the magnetite was isolate | separated and the weight was measured and the quantity of magnetic powder was calculated | required. From these measurement results, the structural characteristics of the obtained carrier particles are shown in FIG. Further, FIG. 4 shows the measurement results of the apparent density, saturation magnetization, and volume resistance of the obtained magnetic carrier. The apparent density was measured using AccuPick 1330 (manufactured by Shimadzu Corporation), and the saturation magnetization was measured using a vibrating sample magnetometer (VSM). The volume resistance was measured using a powder resistance measuring instrument.

  To the obtained magnetic carrier, a toner having a particle size of 6.5 μm was mixed so that the toner weight concentration ratio (T / D) was 10%, 20%, and 25%, thereby preparing a two-component developer. . After the two-component developer was stirred for 5 minutes to charge the toner, various characteristics of charging were measured with a Faraday gauge to determine the toner specific charge (Q / M). In addition, a life test was performed by idling the developing device 20 corresponding to 300,000 sheets using the two-component developer. The measurement results are shown in FIG. Contamination (spent) on the carrier surface due to toner particles and wax was evaluated by reducing the carrier charge amount and SEM observation, and coat peeling and wear were evaluated based on the amount of change by measuring volume resistance.

  Next, image quality in development and the like was evaluated using this two-component developer. This two-component developer was put into a developing tank and developed using the photosensitive drum 10. By observing the toner image on the photoconductive drum 10, the carrier rising, the toner fog, and the circumferential stripe (brush stripe) in the toner image formed on the latent image were visually evaluated. The photosensitive drum 10 and the developing sleeve 22 were rotated in the same direction at a circumferential speed ratio of 1: 2, and the circumferential speed of the photosensitive drum 10 was set to 350 mm / s. Regarding the evaluation of the carrier rise and the brush streak, the toner weight concentration ratio (T / D) was set to 10%, and the toner fog was evaluated in addition to this when T / D was 20% or 25%. These results are shown in FIG.

(Example 2)
In Example 2, a magnetic carrier having the same configuration was formed by the same method as in Example 1 except that a microballoon having an average particle diameter of 33.5 μm was used as the core material, and the process was carried out as shown in FIGS. Measurements and evaluations similar to those of the magnetic carrier of Example 1 were performed.

(Example 3)
In Example 3, a magnetic carrier having the same configuration is formed by the same method as in Example 1 except that 30 parts of magnetite is added to the magnetic powder-dispersed resin solution, and the process is performed as shown in FIGS. Measurements and evaluations similar to those of the magnetic carrier of Example 1 were performed.

Example 4
In Example 4, a magnetic carrier having the same configuration was formed by the same method as in Example 1 except that the magnetic powder charged into the magnetic powder-dispersed resin solution was changed to 100 parts of iron powder instead of magnetite. As shown in FIG. 6, the same measurement and evaluation as the magnetic carrier of Example 1 were performed.

(Example 5)
In Example 5, a magnetic carrier having the same configuration was formed by the same method as in Example 1 except that a microballoon having an average particle diameter of 14 μm was used as the core material. As shown in FIGS. Measurements and evaluations similar to those of the magnetic carrier were performed.

(Comparative Example 1)
In Comparative Example 1, a magnetic carrier was formed in the same manner as in Example 1 except that the amount of magnetite charged into the magnetic powder-dispersed resin solution was 280 parts, and as shown in FIGS. Measurements and evaluations similar to those of the magnetic carrier of Example 1 were performed.

(Comparative Example 2)
In Comparative Example 2, a magnetic carrier having the same configuration was formed by the same method as in Example 1 except that 10 parts of the magnetite charged into the magnetic powder-dispersed resin solution was used. As shown in FIGS. Measurements and evaluations similar to those of 1 magnetic carrier were performed.

(Comparative Example 3)
Comparative Example 3 is the same as in Example 1 except that the same microballoon as in Example 2 is used as the core material, and 10 parts of magnetite is used in the magnetic powder-dispersed resin solution as in Comparative Example 1. The magnetic carrier having the structure as described above was formed, and the same measurement and evaluation as the magnetic carrier of Example 1 were performed as shown in FIGS.

(Comparative Example 4)
A mass obtained by mixing magnetite as a magnetic powder at a ratio of 85 parts with respect to 15 parts of polyester resin, heating and kneading to disperse the magnetic powder in a resin binder, pulverizing with a jet mill, and classifying to about 60 μm Thus, a magnetic powder-dispersed magnetic carrier in which magnetic powder was dispersed in a resin binder was obtained. About the obtained magnetic carrier, as shown in FIGS. 3-6, the same measurement and evaluation as the magnetic carrier of Example 1 were performed.

(Comparative Example 5)
In Comparative Example 5, a magnetic carrier having the same configuration was formed by the same method as in Example 1 except that polyester resin particles were used as the core material instead of the microballoon, and as shown in FIGS. Measurements and evaluations similar to those of 1 magnetic carrier were performed.

(Comparative Example 6)
In Comparative Example 6, a magnetic carrier coated with a plating film was obtained by applying a plating film to a microballoon by the following method.

  After dispersing 100 parts of the same microballoon as in Example 1 in a 0.1 molar aqueous solution of hydrochloric acid (400 parts), the broken microballoon was separated and removed, and then taken out and washed with ion-exchanged water to disperse the core particles. A dispersion was obtained.

  The obtained dispersion is put into a plating coater having a stirrer, thermometer, oxidizer solution, dropping funnel, heating device, and nitrogen gas introduction tube, and the nitrogen is substituted, and the ferrous chloride solution 160 is added to 100 parts of the dispersion. Parts, 80 parts of nickel chloride solution and 300 parts of ammonium acetate solution were added and heated to 65 ° C. with sufficient stirring and mixing. Thereafter, the pH was adjusted to 7.0 with aqueous ammonia while continuing stirring, and 220 parts (solid content 22 parts) of sodium nitrite solution was added dropwise to this solution over 1 hour. During the dropping and reaction, nitrogen gas was introduced and stirred, and the liquid temperature was kept at 65 ° C. and pH 7.0 to 7.2 to obtain plated film particles having a magnetic plating film on the surface of the microballoon.

  5 parts of a silicone resin solution (manufactured by Shin-Etsu Chemical Co., Ltd.) was dissolved in 45 parts of toluene, and the resulting plated film particles were sprayed using a fluidized bed and then dried to obtain a magnetic carrier. About the obtained magnetic carrier, as shown in FIGS. 3-6, the same measurement and evaluation as the magnetic carrier of Example 1 were performed. The thickness of the plating film was determined by calculation from the difference between the initial microballoon particle diameter and the plating film particle diameter.

(Comparative Example 7)
In Comparative Example 7, a magnetic carrier having the same configuration was formed by the same method as in Example 1 except that a microballoon having an average particle size of 92 μm was used as the core material. As shown in FIGS. Measurements and evaluations similar to those of the magnetic carrier were performed.

(Comparative Example 8)
In Comparative Example 8, a magnetic carrier having the same configuration was formed by the same method as in Comparative Example 1 except that 280 parts of iron powder was used instead of magnetite as the magnetic powder charged into the magnetic powder-dispersed resin solution. As shown in FIG. 6, the same measurement and evaluation as the magnetic carrier of Example 1 were performed.

  Based on the results shown in FIGS. 3 to 6 in Examples 1 to 5 and Comparative Examples 1 to 8 described above, for each of the evaluation results of the phenomenon such as carrier rise, together with the measured values of the items that are the factors, FIGS. As shown in FIG.

  FIG. 7 shows the evaluation results of the carrier rise and the factors thereof. From the comparison between Example 1 and Comparative Example 3, it can be seen that the carrier with a large saturation magnetization has a large force attracted onto the developing sleeve 22 by a magnetic force, so that the carrier rising is suppressed. Further, comparing Example 1 and Comparative Example 6 having similar particle diameters and saturation magnetizations, it can be seen that the volume resistance has an effect on the carrier rise. This is because, when the volume resistance is high, the developing device 20 is likely to be charged with a polarity opposite to that of the toner 5B during agitation. Therefore, when the toner 5B is electrostatically adsorbed to the photosensitive drum 10, the magnetic carrier is opposite in polarity. This is because it is prevented from repelling and adsorbing to the photosensitive drum 10.

From the results shown in FIG. 7, when the saturation magnetization is set to 30 emu / g to 100 emu / g and the volume resistance is set to 1.0 × 10 ¹¹ Ω · cm to 1.0 × 10 ¹⁵ Ω · cm, the occurrence of carrier rise It is possible to achieve a longer life than that of the prior art while maintaining high-quality development.

  FIG. 8 shows the evaluation results of brush stripes and the relationship between the factors. As for the brush streaks, Example 3 having a small apparent density, the other Examples 1, 2, 4 and 5 had favorable results, and Comparative Example 4 having a large apparent density had the worst results. The particle diameter and the apparent density define the mass of the magnetic carrier 5A. However, if the mass is large, the toner image formed on the photosensitive drum 10 is easily scraped off by the magnetic spikes of the magnetic carrier 5A formed on the developing sleeve 22. This is because brush streaks are generated, but conversely, if it is small, the toner image is difficult to be scraped off even when touched, and brush streaks are unlikely to occur.

From the results shown in FIG. 8, maintaining the 17μm~63μm particle size, the apparent density by the ^{0.8g / cm 3 ~1.9g / cm 3} , the development of high quality by preventing the occurrence of brush streaks it can. Further, since the particle size and the apparent density become appropriate values and the weight of the magnetic carrier 5A is not too heavy, the bulk density and the like are reduced, and the toner 5B can be more easily stirred than before, and the torque at the time of stirring is also increased. Reduced. For this reason, the stress applied by the stirring of the toner 5B can be reduced, so that the life can be extended.

FIG. 9 shows the amount of change (difference) in toner specific charge (Q / M) and its factors. The toner specific charge (Q / M) due to the toner weight concentration (T / D) is mainly affected by the particle size and apparent density, that is, mass, and the amount of change is small for Example 2 and Comparative Example 3 where the particle size is small. It has become. Further, when Example 3 and Comparative Example 1 having substantially the same particle diameter are compared, the smaller apparent density results in less change in the toner specific charge (Q / D). A good result for Example 1-5 according to the present invention, by a 17μm~63μm particle size, the apparent density and ^{0.8g / cm 3 ~1.9g / cm 3} , the occurrence of brush streaks The toner 5B can be uniformly charged while preventing it.

  FIG. 10 shows the relationship between the evaluation results of toner fog and the factors. Regarding the toner fog on the photosensitive drum 10, cases where the toner weight concentration ratio (T / D) is 10%, 20%, and 25% were evaluated. The results of Example 2 and Comparative Example 3 having a small particle size were excellent. Further, as can be seen from the result of Comparative Example 7, which had the worst evaluation, the larger the particle size, the higher the toner density ratio (T / D), the more the toner fog tends to increase. Moreover, although Example 1 and Comparative Example 4 have different results in spite of substantially the same particle diameter and volume resistance, this is because the apparent density also influences although not shown. The toner fog is caused by the non-charged toner 5B and the reversely charged toner 5B adhering to the non-image portion of the latent image as a major factor, and can be prevented by uniformly charging the toner 5B. This is because the density also improves the stirring performance as described above. Further, since the volume resistance is easily increased as the volume resistance is increased, the charging ability for charging the toner 5B to the opposite polarity during stirring is improved.

From the results shown in FIG. 10, the particle size is 17 μm to 64 μm, the apparent density is 0.8 g / cm ^{3 to} 1.9 g / cm ³ , and the volume resistance is 1.0 × 10 ¹¹ Ω · cm to 1.0 ×. By setting it to 10 ¹⁵ Ω · cm, it is possible to prevent the occurrence of toner fog and maintain high-quality development, and to achieve a longer life than in the past.

  FIG. 11 shows the relationship between spent and durability evaluation results related to developer deterioration and factors thereof. Regarding spent, it is considered that the apparent density and bulk density are affected, and Comparative Example 4 having the largest apparent density gave the worst results. The magnetic carriers of Examples 1 to 5 according to the present invention have good results.

  Regarding the durability, the magnetic powder-dispersed carrier had almost no problem. In Comparative Example 6 covering the outside of the plating layer having the conventional configuration, a decrease in volume resistance due to peeling of the coat was observed. Therefore, it turns out that durability is improving rather than before.

  FIG. 12 shows the results of comprehensive evaluation of the magnetic carriers of Examples 1 to 5 and Comparative Examples 1 to 8 based on the measurement results and evaluation results shown in FIGS. From this result, the evaluation results of the magnetic carrier 5A according to the present invention in Examples 1 to 5 are good, and if the magnetic carrier 5A according to the present invention is used, the carrier rise and the like are prevented, and the high image quality and high speed are supported. It is possible to provide a two-component developer satisfying the durability.

1 is an enlarged view showing a partial configuration of an image forming apparatus according to an embodiment of the present invention. It is sectional drawing which shows the structure of the magnetic carrier which concerns on embodiment of this invention. It is a figure which shows the kind (composition) of a carrier particle. It is a figure which shows the kind (physical property) of a carrier particle. It is a figure which shows the evaluation result of the various characteristics of a two-component developer. It is a figure which shows the evaluation result of the image quality of a toner image. It is a figure which shows the relationship between the evaluation result of career rise, and the factor of career rise. It is a figure which shows the relationship between the evaluation result of a brush stripe, and the factor of a brush stripe. FIG. 6 is a diagram illustrating a relationship between a change amount (difference) in toner specific charge (Q / M) and factors thereof. FIG. 6 is a diagram illustrating a relationship between a toner fog evaluation result and a toner fog factor. It is a figure which shows the relationship between the evaluation of developer deterioration, and the factor of developer deterioration. It is a figure which shows the result of comprehensive evaluation in Examples 1-5 and Comparative Examples 1-8.

Explanation of symbols

5-component developer 5A-magnetic carrier 5AA-core material 5AB-resin binder 5AC-magnetic powder 10-photosensitive drum 20-developing device 21-stirring roller 22-developing sleeve

Claims (9)

A single core material having a hollow shape;
A magnetic carrier for electrophotographic development, comprising: a resin binder in which magnetic powder is dispersed, the resin binder covering the surface of the core material. Particle size is 17Myuemu～63myuemu, magnetic carrier for an electrophotographic developer according to claim 1, the apparent density is equal to or is ^{0.8g / cm 3 ~1.9g / cm 3} . 2. The electrophotography according to claim 1, wherein the saturation magnetization is 30 emu / g to 100 emu / g, and the volume resistance is 1.0 × 10 ¹¹ Ω · cm to 1.0 × 10 ¹⁵ Ω · cm. Magnetic carrier for development. The particle size is 17 μm to 64 μm, the apparent density is 0.8 g / cm ^{3 to} 1.9 g / cm ³ , and the volume resistance is 1.0 × 10 ¹¹ Ω · cm to 1.0 × 10 ¹⁵ Ω · cm. The magnetic carrier for electrophotographic development according to claim 1, wherein:   The magnetic carrier for electrophotographic development according to claim 1, wherein the magnetic powder is composed of one or more of magnetite, hematite, ferrite, and iron powder. In a toner charging method for a two-component developer in which a toner for developing a latent image formed on an image carrier is stirred and charged with a magnetic carrier.
A toner charging method, wherein the magnetic carrier is a magnetic carrier for electrophotographic development according to any one of claims 1 to 5.   The toner weight concentration ratio (T / D) when stirring the toner is 10% to 25%, where T is the weight of the toner and D is the sum of the weight of the toner and the weight of the magnetic carrier. The toner charging method according to claim 6. In a contact developing method of a two-component developer comprising a toner and a magnetic carrier for developing a latent image formed on an image carrier,
The contact developing method according to claim 1, wherein the magnetic carrier is a magnetic carrier for electrophotographic development according to claim 1.   The toner weight concentration ratio (T / D) when stirring the toner is 10% to 25%, where T is the weight of the toner and D is the sum of the weight of the toner and the weight of the magnetic carrier. The contact-type developing method according to claim 8.

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