JP2008233328A - Electrophotographic carrier and method for manufacturing the same, and image forming method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier for a developer and a method for manufacturing the carrier exhibiting the resistance and charging ability of the carrier always stable from starting the usage of the carrier even when the developer is used for a long period of time, and thereby, capable of stably forming a high-quality image without degrading development characteristics, and to provide an image forming method using the carrier. <P>SOLUTION: The electrophotographic carrier has a coating layer containing a resin and low resistance fine particles on the surface of a carrier core material and is characterized in that: the low resistance fine particles are made of at least one kind of compound selected from a group of compounds consisting of carbon black, magnetite, titanium black, zinc oxide and tin oxide; carbon black in the low resistance fine particles is added by 0.02 to 0.25 parts by mass with respect to 100 parts by mass of the carrier core material, and magnetite, titanium black, zinc oxide and tin oxide are added by 0.05 to 1.5 parts by mass; and the low resistance fine particles are present on the surface of the coating layer upon starting usage of the electrophotographic carrier. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an electrophotographic carrier, a method for producing the same, and an image forming method using the same.

  In an electrophotographic image forming method, generally, an electrostatic latent image is formed by irradiating a photoconductive layer with a light image corresponding to a document, and then an opposite polarity is formed on the electrostatic latent image. The electrostatic latent image is developed by attaching a colored fine powder called toner, and the toner image is transferred to a transfer material such as paper, if necessary, and then fixed by heat, pressure, solvent vapor, or the like. I'm getting things.

  In the process of developing the electrostatic latent image, the toner charged to a polarity opposite to that of the latent image is attracted by electrostatic attraction and adhered onto the electrostatic latent image (in the case of reverse development, the latent image is Toner having a charge of the same polarity as that of the toner). In general, there are roughly two methods for developing such an electrostatic latent image using toner, a method using a so-called two-component developer in which a small amount of toner is dispersed in a medium called a carrier and charging, and a carrier is used. There is a method using a so-called one-component developer in which the toner is used alone without using the toner.

  In general, carriers constituting the two-component developer are roughly classified into conductive carriers and insulating carriers. Oxidized or non-oxidized iron powder is usually used as the conductive carrier. However, in the developer containing this iron powder carrier as a component, the triboelectric chargeability with respect to the toner is unstable, and development is also possible. There is a problem that fogging occurs in a visible image formed by the agent. That is, when such a developer is used, toner particles adhere to the surface of the iron powder carrier particles with the use of the developer, so that the electrical resistance of the carrier particles increases, the bias current decreases, and the friction is reduced. As a result, the chargeability becomes unstable, and as a result, the image density of the visible image formed decreases and fogging increases.

  On the other hand, typical examples of the insulating carrier are carriers in which the surface of a carrier core material made of a ferromagnetic material such as iron, nickel, and ferrite is uniformly coated with an insulating resin. In the developer using this carrier, toner particles are fused to the surface of the carrier significantly less than in the case of a conductive carrier, so that it has excellent durability and a long service life. Suitable for the machine.

  Generally, the resistance of the core material used for the coated carrier is low, and the resistance of the material used for the resin coating layer (sometimes referred to simply as a coating layer) is high, so that the resistance of the carrier can be adjusted by coating the carrier surface. . Therefore, in order to adjust the resistance by the thickness of the coating layer, metal oxides such as carbon black (for example, see Patent Documents 1 and 2), tin oxide, titanium oxide, and zinc oxide in the coating layer (for example, Patent Documents). 3)) to adjust the resistance of the coating layer by adjusting the resistance of the coating layer to prevent the carrier from adhering to the edge of the development area at the time of high bias development and to the image area at the time of low bias development. A method for preventing the carrier from adhering has been proposed. However, when a large amount of such low-resistance fine particles are added, even if the initial carrier resistance is adjusted, the coating layer decreases due to friction and dropping during long-term use. However, there is a problem that the carrier gradually adheres to the image area.

In order to solve this problem, especially when only a small amount of low-resistance fine particles are added, the edge effect is high especially in the initial stage.For example, when an image having a halftone image and a solid image is printed, The halftone image is blanked out, and carrier adhesion occurs at the edge of the development area during high bias development.
Japanese Patent Laid-Open No. 56-126843 JP-A 62-45984 JP-A 64-35561

  The present invention has been made in view of the above technical situation, and since the developer life, the carrier resistance and the charging ability are closely related, the carrier resistance and the charging even when the developer is used for a long period of time. Highly durable electrophotographic carrier capable of stably forming a high-quality image without deterioration in development characteristics, and its manufacturing method, and an image using the same It is an object to provide a formation method.

  The above-described problem according to the present invention is solved by adopting the following configuration.

(1)
An electrophotographic carrier having a coating layer containing a resin and low-resistance fine particles on the surface of the carrier core, wherein the low-resistance fine particles are selected from a compound group consisting of carbon black, magnetite, titanium black, zinc oxide, and tin oxide Among the low-resistance fine particles, carbon black is 0.02 to 0.25 parts by mass with respect to 100 parts by mass of the carrier core material, and magnetite, titanium black, zinc oxide, and tin oxide are 0. An electrophotographic carrier characterized in that 0.05 to 1.5 parts by mass are added and the low-resistance fine particles are present on the surface of the coating layer at the start of use of the electrophotographic carrier.

(2)
An electrophotographic carrier according to (1), wherein a resin coating layer is formed on the surface of the carrier core material, followed by adding low-resistance fine particles, and mixing and stirring. Method.

(3)
An electrophotographic developer containing a toner and a carrier is supplied onto the developing sleeve, and the toner is supplied from the developing sleeve to the electrostatic latent image formed on the electrophotographic photosensitive member, developed, and visualized. In an image forming method for transferring and fixing a toner image onto a recording paper, the electrophotographic developer contains the electrophotographic carrier described in (1) as the carrier, and the developing sleeve and the electronic An image forming method, wherein the photographic photosensitive member is rotated so as to move in the same direction in a region (development region) where the photographic photosensitive member faces.

  By adopting the above configuration of the present invention, even when the developer is used for a long period of time, the resistance and charging ability of the carrier are stable from the beginning of the carrier use, and therefore, the development characteristics are not deteriorated and the high quality image is stably obtained. Can provide a highly durable electrophotographic carrier capable of forming a film, a method for producing the same, and an image forming method using the carrier.

  An electrophotographic carrier having a resin coating layer on the surface of a carrier core material, wherein low resistance fine particles are present on the surface of the carrier.

  That is, in the carrier of the present invention, the target resistance can be obtained without lowering the charging property by adding a small amount of the low-resistance fine particles by allowing the low-resistance fine particles to be present on the outermost surface. In addition, when used for a long time in an image forming apparatus, the carrier resistance decreases due to the wear of the coating resin layer, but increases as the low-resistance fine particles present on the outermost surface decrease together with the coating resin. The carrier resistance remains stable.

  The chargeability of the carrier is low because the initial carrier has many low-resistance fine particles on the outermost surface, but in reality the initial carrier is contaminated on the carrier surface by the toner and external additives and the film is depleted. Therefore, the toner is sufficiently charged and has no problem. The charge imparting property of the carrier used in the image forming apparatus is deteriorated due to contamination of the carrier surface by the toner and the external additive and depletion of the coating layer. Since the charge imparting property is improved together with the decrease, the charge imparting property of the carrier is stable. Accordingly, the carrier resistance and the charge imparting property of the carrier are stable both at the start of carrier use and at the time of printing use, and edges, carrier adhesion, and fog / toner scattering are extremely reduced throughout the entire use period.

  Hereinafter, the present invention and its components will be described in detail.

(Electrophotographic carrier)
The electrophotographic carrier of the present invention has a resin coating layer on the surface of the carrier core material, and the resin coating layer contains low-resistance fine particles on at least the surface thereof. The initial carrier resistance of the present invention is a value measured by resistance measurement described later in a carrier in which toner is separated from the developer at the start of use of the carrier.

The resistance (initial resistance) at the start of use of the carrier used in the present invention is preferably 5 × 10 ^{8 to} 3 × 10 ¹⁰ Ωcm, more preferably 8 × 10 ⁸ to 1 × 10 ¹⁰ Ωcm. When the carrier resistance is within the above range, the edge effect in which the image density in the central part of the solid image part is low and the edge part is dark is suppressed in actual shooting during initial use, and carrier adhesion and toner are maintained even after long-term use. It is because the effect which suppresses scattering can fully be exhibited.

(Measurement of carrier resistance)
The carrier resistance of the present invention is a resistance that is dynamically measured under developing conditions with a magnetic brush. The aluminum electrode drum having the same dimensions as the photosensitive drum is replaced with a photosensitive drum, carrier particles are supplied onto the developing sleeve to form a magnetic brush, and the magnetic brush is rubbed against the electrode drum. The resistance of the carrier particles was determined by the following equation by applying a voltage (500 V) between the two and measuring the current flowing between them.

DVR (Ωcm) = (V / I) × (N × L / Dsd)
DVR: Carrier resistance (Ωcm)
V: Voltage between developing sleeve and drum (V)
I: Measurement current value (A)
N: Development nip width (cm)
L: Development sleeve length (cm)
Dsd: Distance between developing sleeve and drum (cm)
In the present invention, the measurement is performed at V = 500 V, N = 1 cm, L = 6 cm, and Dsd = 0.6 mm.

  Hereinafter, each component will be described.

<Low resistance fine particles>
The low-resistance fine particles according to the present invention are carbon black (resistance value: 1 × 10 ⁻² to 1 × 10 ⁰ Ω · cm), magnetite (resistance value: 1 × 10 ⁰ to 1 × 10 ⁴ Ω · cm), titanium Black (resistance value: 1 × 10 ⁰ to 1 × 10 ⁴ Ω · cm), zinc oxide (resistance value: 1 × 10 ⁰ to 1 × 10 ⁴ Ω · cm), and tin oxide (resistance value: 10 ⁰ to 1) It is characterized in that at least one compound selected from the compound group consisting of × 10 ⁴ Ω · cm) is used as a constituent component.

  As an addition amount of the low resistance fine particles added to the carrier coating layer, when 100 parts by mass of the carrier core (core) is used, carbon black is 0.02 to 0.25 parts by mass, preferably 0.02 to 0.2 parts by mass, magnetite, titanium black, zinc oxide, and tin oxide are 0.05 to 1.5 parts by mass, and more preferably 0.1 to 1.2 parts by mass.

  The particle diameter of the low resistance fine particles is preferably in the range of 10 to 600 nm, more preferably 15 to 400 nm.

<Resin coating layer>
Suitable resins for forming the carrier coating layer of the present invention include polyolefin resins such as polyethylene, polypropylene, chlorinated polyethylene, and chlorosulfonated polyethylene; polyacrylates such as polystyrene and polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, and polyvinyl alcohol. Polyvinyl and polyvinylidene resins such as polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether and polybiliketones; copolymers such as vinyl chloride-vinyl acetate copolymers and styrene-acrylic acid copolymers; from organosiloxane bonds Silicone resin or its modified resin (for example, alkyd resin, polyester resin, epoxy resin, modified resin made of polyurethane, etc.); polytetrachloroethylene, polyfluoride Epoxy resins; amino resins such as formaldehyde resins - urea; polyamides;, polyvinylidene fluoride, fluorine resin such as poly chlorinated triflupromazine Lol ethylene polyester; polyurethane; polycarbonate. A particularly preferable resin in terms of preventing spent toner is polyacrylate resin or styrene-acrylic acid copolymer resin.

<< Method for producing resin coating layer >>
Specific methods for producing the coating layer include a wet coating method and a dry coating method. Each method is described in detail below.

As a wet coating method,
(1) Fluidized bed type spray coating method A coating solution in which a coating resin is dissolved in a solvent is spray coated on the surface of magnetic particles using a fluidized bed, and then dried to produce a coated layer. (2) Immersion Formula Coating Method A method in which magnetic particles are immersed in a coating solution in which a coating resin is dissolved in a solvent and then coated, and then dried to prepare a coating layer. (3) Polymerization Method A reactive compound is dissolved in a solvent. Examples of the method include a method of immersing magnetic particles in a coating solution and applying the coating, and then applying heat to perform a polymerization reaction to prepare a coating layer.

Dry coating method Resin particles are deposited on the surface of the particles to be coated, and then mechanical impact force is applied to melt or soften the resin particles deposited on the surface of the particles to be coated to fix the coating layer. It is a manufacturing method. Using a high-speed stirring mixer that can impart mechanical impact force to the carrier core material, resin, low-resistance fine particles, etc., without heating or under heating, the impact force is repeatedly applied to the mixture by high-speed stirring. A carrier fixed by dissolving or softening on the surface of the particles is produced. When heating, 60-125 degreeC is preferable. This is because when the heating temperature is excessive, aggregation of carrier particles tends to occur.

<Method to make low-resistance fine particles exist on the surface>
As a method of surface-treating low-resistance fine particles on the coated carrier, a mixer such as a turbula, ball mill, V-type or W-cone type, a high-speed air impact device such as a hybridization system, and a high-speed stirring and mixing used for the dry coating described above. In the machine, the coated carrier and at least one low-resistance fine particle are placed and mixed. For the purpose of securing charging properties, a third component such as a charge control agent may be added. As the inorganic substance, a substance having a resistance of 1 × 10 ⁻⁶ or more and a high positive charge property, such as strontium titanate, calcium titanate, and magnesium oxide is available. Examples of the organic substance include a compound composed of an azine compound, a quaternary ammonium salt, and triphenylmethane.

  In order to confirm the low-resistance fine particles present on the carrier surface, a photo of the carrier particle surface is taken with a scanning electron microscope (SEM) (1,000 to 10,000 times), and the state is visually observed. Can be done.

<Carrier core>
Examples of the carrier core material used in the present invention include iron powder, magnetite, various ferrite-based particles, or those obtained by dispersing them in a resin. Magnetite and various ferrite particles are preferred. As the ferrite, ferrite containing heavy metals such as copper, zinc, nickel, manganese, and light metal ferrite containing alkali metals and / or alkaline earth metals are preferable, and alkali metals and / or alkaline earth metals are particularly preferable. Light metal ferrite.

  The composition of the magnetic particles (carrier core material) includes an alkali metal such as Li and Na and / or an alkaline earth metal such as Mg, Ca, Sr, and Ba, and has the following composition. .

(M ₂ O) _x (Fe ₂ O ₃ ) _1-x or (MO) _x (Fe ₂ O ₃ ) _1-x
Further, a part of M ₂ O and / or Fe ₂ O ₃ may be substituted with an alkaline earth metal oxide. M represents the aforementioned alkali metal such as Li and Na and / or alkaline earth metal such as Mg, Ca, Sr and Ba. Further, x is 30 mole% or less, preferably 18 mole% or less, and the substituted alkaline earth metal and / or alkali metal oxide is preferably 1 to 10 mole%. More preferably, it is 3-15 mole%.

  The reason why this light metal ferrite or magnetite is preferable is not only the waste and environmental pollution problems that have become popular in recent years, but also the weight of the carrier itself can be reduced and the stress on the toner can be reduced. This is because it has the advantage of being able to.

The magnetic particle diameter is 10 to 100 μm, preferably 20 to 80 μm in volume average particle diameter. Further, the magnetization characteristic of the carrier itself is preferably 2.5 × 10 ^{−5 to} 10.0 × 10 ⁻⁵ Wb · m / kg in saturation magnetization.

  The volume average particle diameter of the magnetic particles is a volume-based average particle diameter measured by a laser diffraction particle size distribution measuring apparatus “HELOS” (manufactured by Sympatech) equipped with a wet disperser.

  The saturation magnetization is measured by “DC magnetization characteristic automatic recording device 3257-35” (manufactured by Yokogawa Electric Corporation).

(Manufacture of toner for electrophotography)
As the toner used in the present invention, those commonly used can be used without particular limitation. For example, a styrene-acrylic resin or a polyester resin can be used as the binder resin, and a conventionally used colorant can also be used as the colorant, and a release agent or charge control can be used as necessary. Agent is added.

  The production method may be a so-called pulverization method or a polymerization method, and in many cases, external additives such as silica fine particles are added after toner particle formation.

(Image forming method)
The carrier of the present invention is more effective in a developing system (forward developing system) in which the moving direction of the photosensitive drum and the developing sleeve is the same in the area where both are closest and face each other (so-called developing area). . In the forward developing system, the toner per unit time to the developing nip portion is compared with a developing system (reverse developing system) in which the moving direction of the photosensitive drum and the moving direction of the developer sleeve in the above region are opposite. This is because the edge effect is more likely to occur because the supply amount is small.

  Hereinafter, an example of an image forming apparatus which is a forward developing system will be described with reference to FIGS. FIG. 1 is a schematic cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention, and FIG. 2 is a schematic cross-sectional configuration diagram showing an example of a developing device of FIG.

  In FIG. 1, the image forming apparatus GS includes an image forming apparatus main body GH and an image reading apparatus YS.

  The image forming apparatus main body GH is called a tandem type color image forming apparatus, and includes a plurality of sets of image forming units 10Y, 10M, 10C, and 10K, a belt-like intermediate transfer member 6, a sheet feeding and conveying unit, and a fixing device 24. It consists of.

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a cleaning unit 8Y disposed around a photosensitive drum 1Y as an image carrier. The image forming unit 10M that forms a magenta (M) color image includes a photosensitive drum 1M as an image carrier, a charging unit 2M, an exposure unit 3M, a developing unit 4M, and a cleaning unit 8M. The image forming unit 10C that forms a cyan (C) color image includes a photosensitive drum 1C as an image carrier, a charging unit 2C, an exposure unit 3C, a developing unit 4C, and a cleaning unit 8C. The image forming unit 10K that forms a black (K) image includes a photosensitive drum 1K as an image carrier, a charging unit 2K, an exposure unit 3K, a developing unit 4K, and a cleaning unit 8K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported. Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred (primary transfer) by the transfer means 7Y, 7M, 7C, and 7K onto the rotating intermediate transfer body 6 and synthesized. A color image is formed. The recording paper P stored in the paper feeding cassette 20 is fed by the paper feeding means 21 and is conveyed to the transfer means 7A via the paper feeding rollers 22A, 22B, 22C, the registration rollers 23, etc. A color image is transferred to (secondary transfer). The recording paper P onto which the color image has been transferred is fixed by the fixing device 24, is sandwiched between the paper discharge rollers 25, and is placed on a paper discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the recording paper P by the transfer means 7A, the residual toner is removed by the cleaning means 8A from the intermediate transfer body 6 from which the recording paper P is separated by curvature.

  4Y, 4M, 4C, and 4K are developing units that contain a two-component developer composed of a toner having a small particle diameter and a carrier of yellow (Y), magenta (M), cyan (C), and black (K). Reference numerals 5Y, 5M, 5C, and 5K denote toner supply units that supply new toner to the developing devices 4Y, 4M, 4C, and 4K, respectively.

  An image reading device YS including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of the image forming apparatus main body GH. The document d placed on the document table of the automatic document feeder 201 is transported by a transport unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document image scanning exposure device 202, and the line image sensor CCD is scanned. Is read.

  The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, etc. in an image processing unit, and then image writing units (exposure means) 3Y, 3M, 3C. Send a signal to 3K.

  The automatic document feeder 201 includes automatic double-sided document conveying means. This automatic document feeder 201 can continuously read the contents of a large number of documents d fed from the document table and store them in the storage means (electronic RDH function). This is convenient when copying the contents of a large number of originals by the function or when transmitting a large number of originals d by the facsimile function.

  Note that a temperature / humidity sensor TS as an environmental condition detecting means for detecting environmental conditions is provided inside the image forming apparatus main body GH. In addition, a number counter for counting the number of copies connected to the development control unit is provided in the image forming apparatus main body GH.

  Next, the developing devices 4Y, 4M, 4C, and 4K are represented as the developing device 4, and the photosensitive drums 1Y, 1M, 1C, and 1K are represented as the photosensitive drum 1, and FIG. A developing device used in the image forming apparatus will be described below. In the following description, the two-component developer is also referred to as a developer. Also, the black filled arrow indicates the direction of supplying and transporting the two-component developer to the developer carrier, and the white arrow indicates the direction of peeling and collecting the two-component developer from the developer carrier. .

  The developing device 4 is composed of a developing device frame 40, a developing roller 41 as a developer carrying member, a magnetic field generating means (magnet roll) 42, a regulating means 43 made up of a scissor plate, a water wheel type supply means 44, and a screw. A stirring screw 45, 46 for carrying, a peeling roller 47, a peeling plate 48, a collecting means 49 including a screw, a toner concentration detection sensor TD, and the like.

  The electrostatic latent image is developed in the development region DR by the counterclockwise rotation of the peripheral speed Vp indicated by the arrow of the photosensitive drum 1 and the clockwise rotation of the peripheral speed Vs indicated by the arrow of the developing roller 41. A developing bias in which a DC bias having the same polarity as the polarity of the latent image is superimposed on the AC bias is applied to the developing roller 41 by a bias power source BS, and reversal development is performed.

  The developing roller 41 is disposed so as to face the photosensitive drum 1 carrying the electrostatic latent image, and is rotatably supported. The developing roller 41 rotates as indicated by an arrow to convey the developer to the developing region DR, and develops the developing roller 41. A developer layer necessary for development is formed by supporting the developer in the region DR.

  Hereinafter, the present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto. In the text, “part” means “part by mass”.

(Preparation of carrier 1)
100 parts by mass of carrier core material having a particle diameter of 35 μm and 2.5 parts by mass of acrylic resin are put into a high-speed agitating mixer, and the mixture is repeatedly agitated by applying high-speed agitation to the surface of the magnetic particles. To form.

  Next, 0.25 part by mass of carbon black (CB) (Mogul-L: manufactured by Cabot) (part by mass with respect to 100 parts by mass of the carrier core material) is added to the mixer, and the mixture is stirred at high speed. The low resistance fine particles were fixed on the surface of the magnetic particles on which the resin coating layer was formed by repeatedly applying an impact force to the surface.

(Production of carriers 2-3 and 6-17)
The manufacturing method of the carrier 1 was changed as shown in Table 1 described later.

(Preparation of carrier 4)
100 parts by weight of carrier core material having a particle diameter of 35 μm, 2.5 parts by weight of acrylic resin, C.I. B. (Mogul-L) 0.2 parts by mass is charged into a high-speed stirring mixer, and high-speed stirring is performed to repeatedly apply an impact force to the mixture. B. A resin coating layer containing was formed. When the surface of the carrier at this time was observed by SEM, C.I. B. Did not exist.

  Next, C.I. B. (Mogulu-L) 0.02 parts by mass (parts by mass with respect to 100 parts by mass of the carrier core material), the surface of the magnetic particles on which the resin coating layer is formed by repeatedly applying an impact force to the mixture by stirring at high speed The low-resistance fine particles were immobilized on the plate.

(Preparation of carrier 5)
100 parts by mass of carrier core material having a particle diameter of 35 μm and 2.5 parts by mass of acrylic resin are put into a high-speed agitating mixer, and the mixture is repeatedly agitated by applying high-speed agitation to the surface of the magnetic particles. To form.

  Next, C.I. B. (Mogul-L) 0.08 parts by mass (parts by mass with respect to 100 parts by mass of the carrier core material) and 0.08 parts by mass of magnesium oxide were added, and the mixture was stirred at high speed to repeatedly apply an impact force to the mixture. Low resistance fine particles and charge control particles were immobilized on the surfaces of the magnetic particles on which the particles were formed.

<Preparation of developer>
100 parts by mass of each carrier prepared above and 4 parts by mass of black toner were mixed with a stirrer to prepare “Developers 1 to 17”.

As the toner, a toner prepared by a polymerization method having a median diameter (D ₅₀ ) of 6.0 μm on a volume basis was used.

(Evaluation)
A developer and a toner cartridge are prepared using the carrier and Bk toner having the composition shown in Table 1, and a black toner single color pixel is prepared using a copying machine (8050: manufactured by Konica Minolta Business Technologies, Inc.) remodeled for experiments. An image with a rate of 10% (original image with character image 7%, human face photo, solid white image, solid black image divided into 1/4 each) is output to A4 quality fine paper (64 g / m ² ) The image quality was evaluated. In addition, the image quality evaluation after outputting 1 million sheets was performed at the initial stage.

(Toner charge measurement method)
Development when a developer is disposed between parallel plate (aluminum) electrodes, and the toner is developed under the conditions of a gap between electrodes of 0.5 mm, a DC bias of 1.0 KV, an AC bias of 4.0 KV, and 2.0 KHz. Efficiency was measured. The charge amount and mass of the developed toner were measured, and the charge amount per unit mass Q / m (μC / g) was defined as the charge amount.

  If the charge amount of the toner is −23 to 43 μC / g, it can be said that there is no problem.

(Carrier adhesion)
After outputting the 1st million prints, the imageless chart is developed, the number of carriers adhering to the surface of the photoconductor is counted by five visual field observations with a magnifier, and the average number of adhering carriers per 100 cm ² is the carrier adhering amount. did. The evaluation was as follows: 以下: 20 or less, ◯: 21 or more and less than 50, x: 50 or more, ◎, ◯ passed, and x rejected.

(Edge effect)
At the beginning of printing, an image having a solid image with an image density of 1.2 to 1.3 is printed at the rear of the solid halftone image with an image density of 0.5, and the halftone image near the boundary with the solid image is printed. Whether white spots occurred was evaluated.

◎: No whiteout ○: No whiteout, but the density is slightly reduced ×: Whiteout occurred However, ◎ and ○ were accepted levels.

(Cover)
The fog density is measured by first measuring and averaging the absolute image density at 20 locations using a Macbeth reflection densitometer “RD-918” for blank paper that has not been printed. Next, regarding the white background portion of the 1 millionth evaluation formed image, the absolute image density at 20 locations was similarly measured and averaged, and the value obtained by subtracting the white paper density from this average density was evaluated as the fog density. If the fog concentration is 0.010 or less, it can be said that fog is practically no problem.

◎: Less than 0.003 ○: 0.003 to less than 0.006 Δ: 0.006 to 0.010 or less ×: Value greater than 0.010

  As is clear from Table 2, the developer using the coated carrier of the present invention has a stable carrier resistance and chargeability even when used for a long period of time. Obtainable.

1 is a schematic cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus. FIG. 2 is a schematic cross-sectional configuration diagram illustrating an example of a developing device in FIG.

Explanation of symbols

1, 1Y, 1M, 1C, 1K Photosensitive drum 4, 4Y, 4M, 4C, 4K Developer 41 Developing roller 44 Supply means 45, 46 Stir screw 47 Stripping roller 49 Recovery means TD Toner density detection sensor

Claims (3)

An electrophotographic carrier having a coating layer containing a resin and low-resistance fine particles on the surface of the carrier core, wherein the low-resistance fine particles are selected from a compound group consisting of carbon black, magnetite, titanium black, zinc oxide, and tin oxide Among the low-resistance fine particles, carbon black is 0.02 to 0.25 parts by mass with respect to 100 parts by mass of the carrier core material, and magnetite, titanium black, zinc oxide, and tin oxide are 0. An electrophotographic carrier characterized in that 0.05 to 1.5 parts by mass are added and the low-resistance fine particles are present on the surface of the coating layer at the start of use of the electrophotographic carrier. 2. An electrophotographic carrier according to claim 1, wherein after forming a resin coating layer on the surface of the carrier core material, a low resistance fine particle is added, followed by mixing and stirring. Method. An electrophotographic developer containing a toner and a carrier is supplied onto the developing sleeve, and the toner is supplied from the developing sleeve to the electrostatic latent image formed on the electrophotographic photosensitive member, developed, and visualized. An image forming method for transferring and fixing a toner image on a recording paper, wherein the electrophotographic developer contains the electrophotographic carrier according to claim 1 as the carrier, and the developing sleeve and the electronic An image forming method, wherein the photographic photosensitive member is rotated so as to move in the same direction in an area (development area) where the photographic photoreceptor faces.

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