JP2011186210A - Carrier for hybrid development, hybrid developing device, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier for hybrid development that prevents image memory by surely recovering residual toner on a developing roller in a hybrid developing system, to provide a hybrid developing device, and to provide an image forming apparatus. <P>SOLUTION: The carrier of a developer used in a hybrid development method has an average particle diameter of 20-40 μm and has a coefficient of variation A in number distribution of carrier core particles represented by formula A=Sn/D1×100 (Sn: standard deviation of number distribution and D1: number length average particle diameter (μm)) of 25-40. Furthermore, the carrier density per unit area becomes high since the carrier has low magnetic force and high electric resistance by setting the electric resistance of the carrier to 1×10<SP>12</SP>Ω or more and saturation magnetization to 30-45 Am<SP>2</SP>/kg under predetermined measurement conditions, and also has small diameter, thereby obtaining the carrier which physically and electrically improves recovery of the residual toner since scraping of the residual toner is improved. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a carrier used in a hybrid developing method, a hybrid developing device including a developer including the carrier and toner, and an image forming apparatus including the hybrid developing device.

  Conventionally, as a method for developing an electrostatic latent image formed on an image carrier, one component consisting only of toner, for an image forming apparatus such as a laser printer or a copying machine that records and forms a toner image using an electrophotographic process There are known a one-component development system using a system developer and a two-component development system using a two-component developer composed of a toner and a carrier.

  In the one-component development method, the toner is frictionally charged by passing the toner through a restriction region between the toner carrier and a restriction plate that presses against the toner carrier, and a toner thin layer having a desired thickness is formed on the outer peripheral surface of the toner carrier. This is advantageous in terms of simplification of the configuration of the developing device, miniaturization, and cost reduction. In addition, since a toner layer having a substantially constant thickness with an upper limit of tens of micrometers is formed on the toner carrier, the toner is held in a state where a minute gap is maintained between the toner carrier and the image carrier. By applying a strong electric field between the carrier and the image carrier, a high toner moving speed can be obtained and a high-definition image can be obtained.

  However, in the one-component development method, the deterioration of the toner is easily accelerated by the strong stress received in the regulation region, the toner charge amount is likely to decrease with the durability, and the regulation plate surface and the surface of the toner carrier are in contact with the toner and other external surfaces. Contamination with the additive deteriorates the charge imparting performance of the toner, resulting in problems such as fogging.

  On the other hand, the two-component development method is advantageous in terms of toner durability because the toner is subjected to friction charging by stirring and mixing the toner and the carrier, so that the stress received by the toner is small. Further, since the surface area of the carrier as a charge imparting member to the toner is larger than that of the toner particles, it is relatively resistant to contamination by the toner and other external additives, and is advantageous for extending the life of the developer. It is.

  However, the magnetic brush (sprouting) formed by the carrier on the developer conveying roller is 20 to 50 times as long as the thickness of the toner layer on the toner carrier in the one-component developing system, and is microscopic. From a general point of view, it is quite uneven. Therefore, in consideration of preventing current leakage, the electric field between the image carrier and the image carrier must be set to be weaker than in the case of the one-component development system, and at least a part of the magnetic brush is provided on the image carrier. It is necessary to set a gap between the image carrier and the image carrier. As a result, the speed at which the toner moves to the image carrier is slow. Further, since the toner on the image carrier is scraped off by the magnetic brush, the image quality is inferior to that of the one-component developing method.

  Therefore, in recent years, a hybrid development method combining the advantages of these development methods has been proposed. In the hybrid development system, only toner is selectively supplied to the outer peripheral surface of the developing roller from the developer including the toner and carrier held on the outer peripheral surface of the magnet body, and the toner held on the outer peripheral surface of the developing roller is used. The electrostatic latent image on the image carrier is developed (see, for example, Patent Document 1).

  Therefore, in the hybrid development method, it is necessary to control the flowability and chargeability of the toner at the same time as the two development processes are executed. However, since the stress received by the toner is small, the life of the toner can be extended. It is. Further, since the development on the image carrier is a one-component development system, it is advantageous for improving the image quality.

  Also, in the hybrid development system, there are general carriers such as magnetic particles such as ferrite, a coated carrier in which a resin film is simply provided on the surface of the magnetic particles, and a binder carrier in which magnetic powder is dispersed in a binder resin. used. The carrier serves to collect residual toner (toner not consumed for development) on the toner carrier in a toner supply / collection region between the developer carrier and the toner carrier. However, if the collection of residual toner by the carrier is insufficient, there are areas on the toner carrier where the toner that has not been consumed for development remains and areas where new toner is supplied after the toner is collected. A phenomenon in which an afterimage of an image created immediately before appears dark as a density difference on an image created thereafter (this phenomenon is called “image memory”) .) Occurs. Specifically, when the solid image is printed continuously and when the solid image is printed after passing through the blank paper, a density difference occurs in the former solid image. Further, for example, when a toner consumption region and a toner non-consumption region exist on the toner carrier, if a solid image or a halftone image is printed using the toner carrier in that state, the density of the printed image is It depends on.

  Therefore, as a developing device of the hybrid development system, a toner supply roller that supplies toner to the developing roller and a toner collecting roller that collects toner from the developing roller are provided, and the residual toner on the developing roller is collected by the toner collecting roller. A technique has been proposed (see, for example, Patent Document 2).

JP 2003-167441 A JP 2000-81778 A

  The technique disclosed in Patent Document 2 can suppress the image memory because the toner that has not been developed is reliably peeled off from the developing roller. However, since a great stress is applied to the toner during toner collection, there is a new problem that the toner deteriorates. Accordingly, the present invention has been made to solve such problems. The object of the present invention is to reliably collect the residual toner on the developing roller in the hybrid developing system and to store the image memory. It is to provide the technology to prevent.

  The carrier for hybrid development of the present invention forms a magnetic brush on the outer periphery of the developer conveying roller by toner and carrier in the developer, and the developer conveying roller and the developing roller while sliding the magnetic brush against the developing roller. This is a developer carrier used in a hybrid developing method in which only the toner is supplied to the developing roller using the potential difference between the two and the latent image on the latent image carrier is developed with the toner on the developing roller. The average particle diameter of the carrier is 20 to 40 μm, and the coefficient of variation A of the number distribution of carrier core particles represented by the following formula is 25 or more and 40 or less. A = Sn / D1 × 100 (Sn: number distribution standard deviation, D1: number length average particle diameter (μm))

Further, the carrier for hybrid development of the present invention is a developer carrying roller having a magnetic flux density of 1000 gauss, in which the carrier 5g is placed on the surface of the conductive sleeve, and the N pole and the S pole are alternately arranged in the conductive sleeve. Is set to 50 rpm, the electrode is disposed opposite to the conductive sleeve with a gap of 1 mm, and the electric resistance is 1 × 10 ¹² when a bias voltage of DC 500 V is applied by rotating the developer transport roller. It is preferable that it is Ω or more and the saturation magnetization is 30 to 45 Am ² / kg.

  The hybrid developing device of the present invention is characterized by including a developer containing toner and the carrier according to claim 1 or 2.

  An image forming apparatus according to the present invention includes the hybrid developing device according to claim 3.

  As is clear from the above description, according to the carrier for hybrid development of the present invention, the low magnetic force, the high electric resistance, and the small particle diameter, the carrier density per unit area is increased and the residual toner is scraped off. Property, that is, reset property is improved. As a result, the recoverability of residual toner is further improved physically and electrically in the toner recovery area. For this reason, there exists an effect that generation | occurrence | production of an image memory can be prevented over a long period of time.

1 is a configuration diagram illustrating an example of an image forming apparatus including a hybrid developing device according to an embodiment of the present invention. It is explanatory drawing of the image pattern for image memory evaluation in an experiment example, and an output image. It is a figure which shows the experimental conditions and experimental result of Experimental Examples 1-5 and Comparative Examples 1-4. It is a figure which shows one Embodiment of an electric field formation apparatus. FIG. 5 is a diagram illustrating a relationship between voltages supplied to the sleeve and the developing sleeve from the electric field forming device illustrated in FIG. 4. It is a figure which shows other embodiment of an electric field formation apparatus. It is a figure which shows the relationship of the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown in FIG. It is a figure which shows other embodiment of an electric field formation apparatus. It is a figure which shows the relationship between the voltage supplied to the sleeve and the image development sleeve from the electric field formation apparatus shown in FIG. It is a figure which shows other embodiment of an electric field formation apparatus. It is a figure which shows other embodiment of an electric field formation apparatus. It is the schematic for demonstrating the measuring method of the electrical resistance of a carrier.

  Hereinafter, the carrier for hybrid development according to the embodiment of the present invention will be described.

  The carrier for hybrid development of the present embodiment (hereinafter simply referred to as “carrier”) is a magnetic carrier (hereinafter referred to as “the carrier”) in which the surface of a magnetic material-dispersed resin core containing at least a magnetic material and a binder resin is coated with a coating material. A general carrier such as a magnetic carrier having a magnetic carrier core particle and a resin coating layer formed on the surface thereof (hereinafter referred to as “coated carrier”) is used. In addition, a magnetic carrier in which a core is formed by granulating magnetic powder and metal oxide powder and coated with a resin film is used.

  The binder type carrier is obtained by dispersing magnetic fine particles in a binder, and positive or negative chargeable fine particles can be fixed to the carrier surface, or a surface coating layer can be formed. The charging characteristics such as the polarity of the binder type carrier can be controlled by the type of the binder resin material, the chargeable fine particles and the surface coating layer.

  Examples of the binder resin used for the binder type carrier include vinyl resins typified by polystyrene resins, polyester resins, nylon resins, polyolefin resins, and other thermosetting resins.

  Magnetic fine particles of the binder type carrier include spinel ferrite such as magnetite and gamma iron oxide, spinel ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.), and iron oxide on the surface. Iron or its alloy particles containing can be used. The shape of the particles may be any of a granular shape, a spherical shape, and a needle shape. In particular, when high magnetization is required, it is preferable to use iron-based ferromagnetic fine particles. In consideration of chemical stability, it is preferable to use ferromagnetic fine particles of magnetoplumbite type ferrite such as spinel ferrite and barium ferrite containing magnetite and gamma iron oxide.

  The magnetic fine particles are suitably added to the magnetic resin carrier in an amount of, for example, 50 to 90% by weight. Thus, a magnetic resin carrier having a desired magnetization can be obtained by appropriately selecting the type and content of the ferromagnetic fine particles.

  Silicone resin, acrylic resin, epoxy resin, fluororesin, etc. are used as the surface coating material of the binder type carrier, and these resins are coated on the surface and cured to form a coating layer, thereby providing a charge imparting ability. Can be improved.

  For example, the charging fine particles or the conductive fine particles can be fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly, adhering the fine particles to the surface of the magnetic resin carrier, and then mechanically / thermally. It is carried out by applying impact and fixing the fine particles so as to be driven into the magnetic resin carrier. In this case, the fine particles are not completely embedded in the magnetic resin carrier, but are fixed so that a part thereof protrudes from the surface of the magnetic resin carrier.

  As the chargeable fine particles, organic or inorganic insulating materials are used. Specifically, in the organic system, organic insulating fine particles such as polysylene, styrene copolymer, acrylic resin, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof can be used. In the inorganic system, negatively charged inorganic fine particles such as silica and titanium dioxide, positively charged inorganic fine particles such as strontium titanate and alumina, and the like can be used.

  As for the charge level and polarity, a desired level of charge and polarity can be obtained by a material, a polymerization catalyst, a surface treatment, and the like.

  On the other hand, a coated carrier is a carrier core particle made of a magnetic material, and a resin coat is formed. Like a binder-type carrier, positively or negatively chargeable fine particles can be fixed on a carrier surface. Is possible. The charging characteristics such as the polarity of the coated carrier can be controlled by the type of the surface coating layer and the chargeable fine particles, and the same material as that of the binder-type carrier described above can be used. In particular, the same resin as the binder resin of the binder type carrier can be used as the coating resin.

  The carrier according to the present embodiment effectively prevents the occurrence of image memory, and from the viewpoint of improving image quality with respect to roughness, texture, carrier development, gradation, halftone reproducibility, toner scattering, etc. The particle size, the coefficient of variation of the number distribution of the carrier core particles (detailed later), the electric resistance of the carrier and the saturation magnetization of the carrier were set to the numerical ranges described below.

The carrier according to the present embodiment has an average carrier particle size of 10 to 50 μm, particularly 20 to 40 μm, and a variation coefficient A of the number distribution of carrier core particles represented by the following formula is set to 25 or more and 40 or less. In particular, when the average particle diameter of the carrier is less than 10 μm, carrier adhesion occurs, while when it exceeds 50 μm, carrier streaks occur and a uniform toner thin layer cannot be formed. Therefore, the carrier of the present embodiment has an average carrier particle size of 20 to 40 μm, and a carrier with a small particle size can be obtained by setting the variation coefficient A of the number distribution of carrier core particles to 25 to 40. The variation coefficient A of the number distribution of carrier core particles being 25 or more and 40 or less means that the number distribution is not a narrow distribution, but a distribution having a broad width to some extent.
A = Sn / D1 × 100 (Sn: number distribution standard deviation, D1: number length average particle diameter (μm))

  The average particle diameter of the carrier particles is measured by using a Coulter Multisizer 3 (manufactured by Beckman Coulter, Inc.) and obtaining a relative weight distribution by particle diameter with an 280 μm aperture tube.

The carrier of this embodiment, the electric resistance value of 1 × ^{10 12} Ω or more, preferably ^{1 × 10 12 Ω~1 × 10 14} Ω. When the electric resistance value of the carrier is less than 1 × 10 ¹² Ω, carrier adhesion occurs. When the electric resistance value exceeds 1 × 10 ¹⁴ Ω, the toner supply capability is lowered and the developability is deteriorated.

  The “electrical resistance value of the carrier” in the present specification is an electric resistance value (Ω) under a condition that the carrier actually forms a magnetic brush, and in detail is measured under the following conditions. Say.

As shown in FIG. 12, a rotatable developer conveying roller 302 containing a magnet body 301 and an electrode (electrode tube) 304 are arranged to face each other with a predetermined distance (1 mm), and 5 g of carrier is supplied onto the magnet body 301. Then, a magnetic field having a surface magnetic flux density on the developer conveying roller 302 of 1000 gauss is applied to couple the carriers in a chain shape, and a bias voltage of DC 500 V is applied from the power supply unit 305 to the magnet body 301. Then, the developer conveying roller 302 is rotated at a speed of 50 rotations per minute, and the current value flowing through the electrode tube 304 via the carrier on the developer conveying roller 302 connected in a chain is measured by an ammeter 306. Then, the electric resistance value of the carrier is calculated from the obtained current value based on the following equation.
R (Ω) = 500 / I (R: carrier electric resistance value, I: current value)

Moreover, as a magnetic characteristic of the carrier of this Embodiment, saturation magnetization is 20-80 Am < ² > / kg, Preferably it is 30-45 Am < ² > / kg. If the saturation magnetization value exceeds 80 Am ² / kg, magnetic condensation may occur and toner charging failure may occur. Further, when the saturation magnetization value is less than 20 Am ² / kg, carrier adhesion occurs.

  The saturation magnetization value of the carrier was measured using a DC magnetization characteristic automatic recording device (Yokogawa Hokushin Electric Co., Ltd .: TYPE-3257).

  As described above, the carrier according to the present embodiment has the average particle diameter of the carrier, the coefficient of variation of the number distribution of the carrier core particles (number distribution standard deviation / number length average particle diameter), electrical resistance, and saturation magnetization within the above ranges. By setting, since the magnetic resistance is low, the electric resistance is high, and the diameter is small, the carrier density per unit area is increased, the scraping property of the residual toner is improved, and the recoverability of the residual toner is physically and electrically improved. Further improvement. For this reason, generation | occurrence | production of an image memory can be prevented effectively and a stable image can be obtained over a long term.

  The mixing ratio of the carrier and the toner may be adjusted so as to obtain a desired toner charge amount, and the toner mixing ratio is selected in the range of 3 to 50% by weight with respect to the total amount of the toner and the carrier, A range of 6 to 30% by weight is particularly suitable.

[Available developers]
The toner is negatively or positively charged by frictional contact with the carrier, and contains at least a colorant and, if desired, additives such as a negative or positive charge control agent and a release agent in the binder resin.

  As the binder resin used in the toner, those conventionally used as a binder resin for toner in the field of toner can be used. For example, a styrene resin (monopolymer or copolymer containing styrene or a styrene substitution product). Polyester resin, epoxy resin, vinyl chloride resin, phenol resin, polyethylene resin, polypropylene resin, polyurethane resin, silicon resin and those arbitrarily mixed with these resins are exemplified. The binder resin preferably has a softening temperature in the range of about 80 to 160 ° C and a glass transition point in the range of about 40 to 75 ° C.

  As the colorant, materials known in the toner field are used. For example, carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultramarine blue, rose bengal, Lakey red etc. can be used. In general, the content of the colorant is preferably 2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  As the charge control agent, conventionally known materials can be used as the charge control agent in the field of toner. Examples include nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazole compounds, polyamine resins, and the like. Examples of negative charge control agents include metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkyl salicylic acid metal compounds, and curix arene compounds. The charge control agent is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  As the release agent, conventionally known materials can be used as the release agent in the field of toner. For example, polyethylene, polypropylene, carnauba wax, sazol wax, or a mixture obtained by appropriately combining them is exemplified. The release agent is preferably used at a ratio of 0.1 to 10 parts by weight with respect to 100 parts by weight of the binder resin.

  The toner is produced by a production method known in the toner field, for example, a dry method such as a pulverization method, or a wet granulation method such as an emulsion polymerization method or a suspension polymerization method. The average particle diameter of the toner is, for example, about 3 to 15 μm. The average particle diameter of the toner can be measured by the same method as the average particle diameter measurement of the core particles described above, except that a 100 μm aperture tube is used.

  A fluidizing agent that promotes fluidization may be added to the toner. As the fluidizing agent, for example, inorganic fine particles such as silica, titanium oxide and aluminum oxide, and resin fine particles such as acrylic resin, styrene resin, silicon resin and fluororesin can be used. In particular, it is preferable to use a silane coupling agent, a titanium coupling agent, and a fluidizing agent hydrophobized with silicon oil. The fluidizing agent is preferably added at a ratio of 0.1 to 5 parts by weight with respect to 100 parts by weight of the toner. The average primary particle size of these additives is preferably 10 to 100 nm.

  Furthermore, charged particles may be added to the toner for the purpose of improving the chargeability. The charged particles are appropriately selected according to the charging polarity of the toner, and particles charged to the opposite polarity to the charging polarity of the toner by frictional contact with the toner are used. Usually, the charging polarity of the toner is determined by frictional contact with the carrier. Particles that are charged to the opposite polarity are used. The average primary particle size of the charged particles is, for example, 100 to 850 nm.

  For example, when using toner that is negatively charged by frictional contact with the carrier, charged particles are particles that are positively charged by contact with the toner, and are usually charged positively by frictional contact with the carrier. Particles are used. Such particles include, for example, inorganic particles such as strontium titanate, barium titanate, magnesium titanate, calcium titanate, and alumina, thermoplastic resins such as acrylic resin, benzoguanamine resin, nylon resin, polyimide resin, polyamide resin, Or the particle | grains comprised with the thermosetting resin can be used. Note that a positive charge control agent that is positively charged by contact with the toner may be contained in the resin that constitutes the charged particles. As the positive charge control agent, for example, nigrosine dyes, quaternary ammonium salt compounds and the like can be used. The charged particles may be composed of a copolymer of nitrogen-containing monomers.

  Further, for example, in the case of a toner that is positively charged by frictional contact with a carrier, charged particles are particles that are negatively charged by contact with the toner, and are usually negatively charged by frictional contact with the carrier. Particles that are electrically charged are used. As such particles, for example, inorganic particles such as silica and titanium oxide, thermoplastic resins such as fluororesin, polyolefin resin, silicon resin, and polyester resin, or particles made of thermosetting resin can be used. In addition, a negative charge control agent that is negatively charged by contact with the toner may be contained in the resin constituting the charged particles. Examples of negative charge control agents that can be used include salicylic acid-based and naphthol-based chromium complexes, aluminum complexes, iron complexes, and zinc complexes. The charged particles may be a copolymer of a fluorine-containing acrylic monomer or a fluorine-containing methacrylic monomer. The content of the charged particles is not particularly limited as long as the object of the present invention is achieved. For example, 0.1 to 3 parts by weight is preferable with respect to 100 parts by weight of the toner.

  Next, a hybrid developing device and an image forming apparatus including a developer including a hybrid developing carrier according to an embodiment of the present invention will be described with reference to the accompanying drawings. In the following description, “upper part”, “lower part”, terms including those terms, “clockwise direction”, “counterclockwise direction” and the like are used for convenience, but these are for ease of understanding of the invention. Therefore, the technical scope of the present invention should not be limitedly interpreted by these terms.

[Schematic Configuration and Operation of Image Forming Apparatus]
Next, an image forming apparatus 100 according to an embodiment of the present invention will be described with reference to the accompanying drawings. As shown in FIG. 1, the image forming apparatus T is generally composed of a photosensitive drum 1, a charging unit 2, an exposure unit 3, a developing unit 4, a transfer unit 5, a cleaning unit 6, and the like. A series of operations including driving are controlled by a control unit (not shown). The detailed description of the developing device 4 will be described later.

  In the figure, a photosensitive drum (image carrier) 1 carrying an electrostatic latent image made of an organic photoreceptor is charged by, for example, a charging device 2 such as a scorotron, and an exposure device 3 having a laser writing device, an LED array, or the like. To write an electrostatic latent image. This electrostatic latent image is formed as a potential image based on the contrast with the high potential portion not exposed to light because the surface potential of the photosensitive drum 1 in the portion exposed to light is lowered. Next, the electrostatic latent image is visualized as a toner image by toner supplied from the developing device 4. Then, after the toner image is transferred to the recording medium P by the transfer unit 5, it is heated by a fixing device (not shown) and fixed on the recording medium P.

[Configuration of hybrid developing device]
The developing device 4 is a hybrid developing device. The developing device 4 has a housing 44. A part of the housing 44 forms a developer tank 45 in which a developer 46 containing toner, a carrier, and various additives described above is accommodated. The housing 44 also supports a developer stirring member, a developer carrier that holds the developer by magnetic force, and a toner carrier that holds only the toner of the developer.

  In the illustrated embodiment, the developer stirring member includes a first stirring and conveying screw 40a and a second stirring and conveying screw 40b. The developer carrier includes a developer conveyance roller 41 that carries and conveys the developer, and a regulation that regulates the amount of the developer conveyed by the developer conveyance roller 41 so as to face the developer conveyance roller 41 at a constant level. A member 43 is provided.

  The developer transport roller 41 includes a cylindrical sleeve 41a that is rotatably supported and a magnet body 41b that is fixed inside the sleeve 41a so as not to rotate. In the embodiment, the magnet body 41b includes a plurality of magnetic poles (N1, S1, N3, N2, S2) extending in the axial direction in a region (outer peripheral portion) facing the inner peripheral surface of the sleeve 41a. The toner carrier is rotatably supported so as to face the photosensitive drum 1 and the developer transport roller 41.

  The developing roller 42 is composed of, for example, a conductive roller made of aluminum that has been surface-treated. In addition, for example, polyester resin, polycarbonate resin, polyethylene resin, polyamide resin, polyimide resin, polysulfone resin, silicon resin, fluorine resin, or other conductive coatings such as aluminum, silicon rubber, urethane rubber Further, a rubber-coated structure such as nitrile rubber, natural rubber, or isoprene rubber may be used.

  As a coating material, a conductive agent may be added to the bulk or surface of the coating described above. Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent. Examples of the electronic conductive agent include carbon black such as ketjen black, acetylene black, and furnace black, metal powder, metal oxide fine particles, and the like, but are not limited thereto. Examples of the ionic conductive agent include chaotic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials, but are not limited thereto.

[Operation of hybrid developing device]
The operation of the developing device 100 will be described with reference to FIG. The developer 46 in the developer tank 45 is mixed and stirred by the rotational drive of the first stirring and conveying screw 40a and the second stirring and conveying screw 40b. The developer 46 is frictionally charged and simultaneously circulated and conveyed in the developer tank 45 and supplied to the sleeve 41 a on the surface of the developer conveying roller 41.

  The developer 46 supplied from the first agitating and conveying screw 40a to the developer conveying roller 41 is held on the outer peripheral surface of the sleeve 41a by the magnetic force of the magnetic pole N3 in the vicinity of the magnetic pole N3. The developer 46 held by the sleeve 41a forms a magnetic brush along the lines of magnetic force generated by the magnet body 41b, and is conveyed counterclockwise as the sleeve 41a rotates. The developer 46 held by the magnetic pole S <b> 1 in the region facing the regulating member 43 is regulated by the regulating member 43 into a thin layer having a predetermined thickness. The developer 46 formed in a thin layer is conveyed to a toner supply / recovery area (toner supply area 80, toner recovery area 81) where the developer conveying roller 41 and the developing roller 42 where the magnetic pole N1 is located are opposed to each other. .

  In the toner supply region 80 located on the upstream side in the rotation direction of the sleeve 41a in the toner supply / recovery region, only the toner adhering to the carrier is developed due to the presence of an electric field formed between the developing roller 42 and the sleeve 41a. Electrically supplied to the roller 42. The toner layer 200 held on the developing roller 42 is conveyed to a developing area formed with the photosensitive drum 1 as the developing roller 42 rotates, and is formed by a developing bias and a latent image potential on the photosensitive drum 1. The latent image is developed into a visible image by the developing electric field. The development method may be a reversal development method or a regular development method. In the toner collection area 81 located downstream in the rotation direction of the sleeve 41a, the toner on the developing roller 42 that has not contributed to the development is scraped off by a magnetic brush formed along the magnetic field lines of the magnetic pole N1. It is collected in the sleeve 60.

  The carrier is held on the outer peripheral surface of the sleeve 41a by the magnetic force of the magnet body 41b and does not move from the sleeve 41a to the developing roller. The carrier used in the present invention can retain a relatively large charge having a polarity opposite to the toner charging polarity after supplying the toner in the toner supply region 80 on the sleeve 41a, and is less likely to leak. For this reason, in the toner collection area 81, the carrier more effectively electrically sucks and collects the residual toner, thereby preventing the occurrence of an image memory.

[Electric field forming means]
In order to efficiently move the toner from the sleeve 60 to the developing roller 48 in the supply region 90, the developing roller 48 and the sleeve 60 are electrically connected to the electric field forming device 110. Specific examples of the power source are shown in FIGS.

4 includes a first power source 112 (corresponding to a second electric field forming unit) connected to the developing roller 48 and a second power source 114 (corresponding to the second electric field forming unit). Corresponding to first electric field forming means). The first power supply 112 has a DC power supply 118 connected between the developing roller 48 and the ground 116, and supplies a first DC voltage V _DC1 (for example, −200 volts) having the same polarity as the charging polarity of the toner. It is applied to the developing roller 48. The second power source 114 has a DC power source 120 connected between the sleeve 60 and the ground 116, and has the same polarity as the charging polarity of the toner and a second DC voltage V higher than the first DC voltage. _DC2 (eg, −400 volts) is applied to the sleeve 60. As a result, in the supply area 90, the negatively charged toner is electrically attracted from the sleeve 60 to the developing roller 48 due to the action of a DC electric field formed between the developing roller 48 and the sleeve 60. The At this time, the positively charged carrier is not attracted to the developing roller 48 from the sleeve 60. In the developing region 96, the negative toner held on the developing roller 48 is, as shown in FIG. 3B, the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L :−). It adheres to the electrostatic latent image portion based on the potential difference of 80 volts). At this time, the negative polarity toner adheres to the electrostatic latent image non-image portion due to a potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image non-image portion (V _H : −600 volts). There is nothing.

In the electric field forming apparatus 122 of FIG. 6 according to the second embodiment, the first power supply 124 (corresponding to the second electric field forming means) is provided between the developing roller 48 and the ground 126, similarly to the power supply of the first embodiment. The first DC voltage V _DC1 (for example, −200 volts) having the same polarity as the charging polarity of the toner is applied to the developing roller 48. The second power supply 130 (corresponding to the first electric field forming means) has a DC power supply 132 and an AC power supply 134 between the sleeve 60 and the ground 126. The DC power supply 132 applies a second DC voltage V _DC2 (for example, −400 volts) having the same polarity as the toner charging polarity and higher than the first DC voltage to the sleeve 60. As shown in FIG. 4B, the AC power supply 134 applies an _AC voltage VAC having a peak-to-peak voltage V _PP of, for example, 300 volts between the sleeve 60 and the ground 126. As a result, in the supply region 90, the negatively charged toner is electrically attracted from the sleeve 60 to the developing roller 48 due to the action of the pulsating electric field formed between the developing roller 48 and the sleeve 60. Is done. At this time, the positively charged carrier is held by the sleeve 60 by the magnetic force of the fixed magnet inside the sleeve 60 and is not supplied to the developing roller 48. In the developing region 96, the negative toner held on the developing roller 48 is caused by a potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L : −80 volts). Based on the electrostatic latent image portion.

In the electric field forming device 136 shown in FIG. 8, the first power supply 138 includes a DC power supply 142 and an AC power supply 144 between the developing roller 48 and the ground 140. The DC power supply 142 applies a first DC voltage V _DC1 (for example, −200 volts) having the same polarity as the toner charging polarity to the sleeve 60 and the developing roller 48. The AC power supply 144 applies an _AC voltage VAC having an amplitude (peak-to-peak voltage) _VP-P of, for example, 1,600 volts between the sleeve 60 and the developing roller 48 and the ground 146. The second power source 146 (corresponding to the first electric field forming means) has a DC power source 150 connected between the terminal 148 between the developing roller 48 and the AC power source 144 and the sleeve 60. The DC power supply 150 can output a predetermined DC voltage V _DC2 , and the anode is connected to the terminal 148 and the cathode is connected to the sleeve 60, whereby the sleeve 60 is biased to the negative polarity with respect to the developing roller 48. (See FIG. 5B). Accordingly, in the supply region 90, the negatively charged toner is electrically attracted from the sleeve 60 to the developing roller 48 due to the action of the pulsating electric field formed between the developing roller 48 and the sleeve 60. The In the developing region 96, the negative toner on the developing roller 48 is statically charged based on the potential difference between the developing roller 48 (V _DC1 : −200 volts) and the electrostatic latent image portion (V _L : −80 volts). It adheres to the electrostatic latent image portion.

The electric field forming device 152 shown in FIG. 10 is obtained by adding AC power sources 154 and 156 to the first power source 112 and the second power source 114, respectively, in the electric field forming device 110 of the first embodiment shown in FIG. 3A. The output voltages of the AC power supplies 154 and 156 are V _AC1 and V _AC2 . The voltages V _AC1 and V _AC2 may be the same or different. An electric field forming device 158 shown in FIG. 11 is obtained by adding an AC power source 160 to the first power source 112 in the power source of the embodiment shown in FIG. 3A. The output voltage of the AC power supply 160 is _{V AC.} Similarly to the electric field forming devices 110, 122, and 136, the electric field forming devices 152 and 158 of these forms also receive the action of the pulsating electric field formed between the developing roller 48 and the sleeve 60, and in the supply region 90. The negatively charged toner is supplied from the sleeve 60 to the developing roller 48, and the negatively charged toner is supplied from the developing roller 48 to the electrostatic latent image portion (V _L : −80 volts) in the developing region 96. Is supplied to the electrostatic latent image portion.

  The image quality was evaluated using the following developers (Examples 1 to 5 and Comparative Examples 1 to 4) in the above-described developing device and image forming apparatus.

Example 1
<Resin for carrier coat>
Polymerization is performed by a known emulsion polymerization method using CMHA (cyclohexyl methacrylate) / MMA (methyl methacrylate) / ST (styrene) = 45/45/10 (monomer weight ratio), and then washed with water and dried to obtain an average particle size. A resin particle a having a diameter of 100 nm (glass transition point Tg: 102 ° C., softening point Tm: 220 ° C.) was obtained.
-Production example of dry coat carrier In Examples 1 to 5 and Comparative Examples 1 to 4, the core material (Mn-Mg ferrite core particles) having physical properties shown in FIG. A coated carrier was produced according to the method described above. A 5 L Mn-Mg ferrite core particle having a coefficient of variation A of 40 shown in the following formula and a coating agent of 150 g are put into a 9 L Henschel mixer (manufactured by Mitsui Mining Co., Ltd.) capable of adjusting the temperature, and the product temperature is set to 90. The blade rotation speed is stirred at 200 rpm for 20 minutes while maintaining the temperature below ℃. Thereafter, the temperature of the blade is set to 200 rpm while the temperature-controlled oil is supplied to the jacket, the product temperature is raised to 115 ° C., and the temperature is maintained and stirred for another 15 minutes to coat the core particles with the coating agent. Thereafter, the carrier is stirred at a low speed until the product temperature becomes 70 ° C. or less, the particle diameter is 30 μm, the carrier having the electric resistance value of 1 × 10 ¹² Ω and the saturation magnetization of 35 Am ² / kg in the measurement conditions of the electric resistance value described above Particles were obtained.
A = Sn / D1 × 100 (Sn: number distribution standard deviation, D1: number length average particle diameter (μm))

(Example 2)
Carrier particles a having a particle size of 30 μm were obtained in the same manner as in Example 1 except that the number distribution coefficient of variation A was changed to 30 Mn—Mg ferrite core particles.

(Example 3)
Carrier particles C having a particle size of 30 μm were obtained in the same manner as in Example 1 except that the number distribution coefficient of variation A was changed to 25 Mn—Mg ferrite core particles.

Example 4
The number distribution coefficient of variation A was changed to 40 Mn—Mg ferrite core particles, the particle diameter was 30 μm by the same method as in Example 1, and the electric resistance value was 1 × 10 ^{11 under the} above-described measurement conditions of electric resistance value. A carrier particle D of Ω was obtained.

(Example 5)
Carrier particles A having a particle size of 30 μm and a saturation magnetization of 25 Am ² / kg were obtained in the same manner as in Example 1 except that the number distribution coefficient of variation A was changed to 40 Mn—Mg ferrite core particles.

(Comparative Example 1)
Carrier particles having a particle size of 20 μm were obtained in the same manner as in Example 1 except that the number distribution coefficient of variation A was changed to 40 Mn—Mg ferrite core particles.

(Comparative Example 2)
Carrier particles having a particle size of 50 μm were obtained in the same manner as in Example 1 except that the number distribution coefficient of variation A was changed to 40 Mn—Mg ferrite core particles.

(Comparative Example 3)
Carrier particles having a particle diameter of 30 μm were obtained in the same manner as in Example 1 except that the number distribution variation coefficient A was changed to 20 Mn—Mg ferrite core particles.

(Comparative Example 4)
Carrier particles having a particle size of 30 μm were obtained in the same manner as in Example 1 except that the number distribution variation coefficient A was changed to 45 Mn—Mg ferrite core particles.

A toner produced by the following method was used.
(Production of resin particles A)
First stage polymerization 8 g of sodium dodecyl sulfate and 3 L of ion-exchanged water are charged into a 5 L (liter) reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introducing device, and stirred at a stirring speed of 230 rpm in a nitrogen stream. The internal temperature was raised to 80 ° C. After heating, 10 g of potassium persulfate dissolved in 200 g of ion-exchanged water was added, the liquid temperature was again adjusted to 80 ° C., and the monomer mixture shown below was added dropwise over 1 hour, then at 80 ° C. Polymerization was carried out by heating and stirring for 2 hours to prepare resin particles. This is referred to as “resin particles (1H)”.
Styrene 480g
n-Butyl acrylate 250g
Methacrylic acid 68.0g
n-octyl-3-mercaptopropionate 16.0 g

Second stage polymerization A 5 L reaction vessel equipped with a stirrer, temperature sensor, cooling pipe and nitrogen introducing device was charged with a solution prepared by dissolving 7 g of polyoxyethylene (2) sodium dodecyl ether sulfate in 800 ml of ion-exchanged water at 98 ° C. After heating, 260 g of the resin particles (1H) and a solution obtained by dissolving the monomer solution shown below at 90 ° C. were added, and a mechanical disperser CLEARMIX (manufactured by M Technique Co., Ltd.) having a circulation path was added. Was mixed and dispersed for 1 hour to prepare a dispersion containing emulsified particles (oil droplets).
240g of styrene
125g of n-butyl acrylate
n-octyl-3-mercaptopropionate 1.5 g
190g polyethylene wax

  Next, an initiator solution in which 6 g of potassium persulfate was dissolved in 200 ml of ion-exchanged water was added to the dispersion, and the system was heated and stirred at 82 ° C. for 1 hour to obtain resin particles. This is referred to as “resin particles (1HM)”.

Third stage polymerization Furthermore, a solution prepared by dissolving 11 g of potassium persulfate in 400 ml of ion-exchanged water was added, and under a temperature condition of 82 ° C.,
Styrene 430g
n-Butyl acrylate 130g
Methacrylic acid 33g
n-octyl-3-mercaptopropionate 8 g
A monomer mixture consisting of was added dropwise over 1 hour. After completion of the dropping, polymerization was carried out by heating and stirring for 2 hours, and then cooled to 28 ° C. to obtain resin particles. This is referred to as “resin particle A”.

(Production of resin particles B)
A 5 L reaction vessel equipped with a stirrer, temperature sensor, cooling pipe and nitrogen introducing device was charged with 2.3 g of sodium dodecyl sulfate and 3 L of ion-exchanged water, and the internal temperature was adjusted to 80 rpm while stirring at a stirring speed of 230 rpm under a nitrogen stream. The temperature was raised to ° C. After heating, 10 g of potassium persulfate dissolved in 200 g of ion-exchanged water was added, the liquid temperature was again adjusted to 80 ° C., and the monomer mixture shown below was added dropwise over 1 hour, then at 80 ° C. Polymerization was carried out by heating and stirring for 2 hours to prepare resin particles. This is referred to as “resin particle B”.

Styrene 520g
210g of n-butyl acrylate
Methacrylic acid 68.0g
n-octyl-3-mercaptopropionate 16.0 g

(Preparation of colorant dispersion)
The mixture was dissolved in 90 g of sodium dodecyl sulfate and 1600 ml of ion exchange water with stirring. While stirring this solution, 420 g of carbon black “Regal 330R” (manufactured by Cabot Corp.) is gradually added, followed by dispersion treatment using a stirrer “Claremix” (manufactured by M Technique Co., Ltd.). A dispersion of agent particles was prepared. This is referred to as “colorant dispersion 1”. When the particle diameter of the colorant particles in the colorant dispersion 1 was measured using an electrophoretic light scattering photometer “ELS-800” (manufactured by Otsuka Electronics Co., Ltd.), it was 110 nm.

(Aggregation / fusion process)
In a 5 L reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introducing device, 300 g of the resin particle A in terms of solid content, 1400 g of ion-exchanged water, 120 g of the above “colorant dispersion 1”, polyoxyethylene (2 ) A solution in which 3 g of sodium dodecyl ether sulfate was dissolved in 120 ml of ion-exchanged water was added and the liquid temperature was adjusted to 30 ° C., and then the pH was adjusted to 10 by adding a 5 mol / L aqueous sodium hydroxide solution. Next, an aqueous solution in which 35 g of magnesium chloride was dissolved in 35 ml of ion-exchanged water was added over 10 minutes at 30 ° C. with stirring. After holding for 3 minutes, the temperature was raised, and the system was heated to 90 ° C. over 1 hour, and the particle growth reaction was continued while maintaining 90 ° C.

  In this state, the particle size of the associated particles was measured with “Coulter Multisizer 3” (manufactured by Beckman Coulter), and 260 g of the resin particles B were added when the median diameter on a volume basis reached 3.1 μm. Furthermore, the particle growth reaction was continued. When a desired particle size is reached, an aqueous solution in which 150 g of sodium chloride is dissolved in 200 ml of ion-exchanged water is added to stop particle growth, and further, FPIA is performed by heating and stirring at a liquid temperature of 98 ° C. as a fusion process. Fusion between particles was promoted until the circularity was 0.965 as measured by -2100. Thereafter, the solution was cooled to 30 ° C., hydrochloric acid was added to adjust the pH to 4.0, and stirring was stopped.

(Washing / drying process)
The particles produced in the aggregation / fusion process were solid-liquid separated with a basket-type centrifuge “MARK2 model number 60 × 40” (manufactured by Matsumoto Machinery Co., Ltd.) to form a wet cake of toner particles. The wet cake was washed with ion exchange water at 45 ° C. until the electric conductivity of the filtrate reached 5 μS / cm with the basket-type centrifuge, and then transferred to “flash jet dryer” (manufactured by Seishin Enterprise Co., Ltd.). Then, the toner particles were produced by drying until the water content became 0.5% by mass.

Toner 100 parts by weight of the toner particles having a volume average particle diameter of about 6.5 μm, 0.2 parts by weight of the first hydrophobic silica, 0.5 parts by weight of the second hydrophobic silica, and 0 of the hydrophobic titanium oxide .5 parts by weight and 2 parts by weight of strontium titanate having a number average particle size of 350 nm were subjected to surface treatment for 3 minutes at a rate of 40 m / sec using a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.), A chargeable toner was obtained.

  As the first hydrophobic silica used here, silica “# 13” (manufactured by Nippon Aerosil Co., Ltd.) having a number average primary particle size of 16 nm was subjected to surface treatment with hexamethyldisilazane (HMDS) as a hydrophobizing agent. It is a thing. The second hydrophobic silica is obtained by surface-treating silica “# 90” (manufactured by Nippon Aerosil Co., Ltd.) having a number average primary particle size of 20 nm with HMDS. Hydrophobic titanium oxide is obtained by surface-treating anatase-type titanium oxide having a number average primary particle size of 30 nm with isobutyltrimethoxysilane as a hydrophobizing agent in an aqueous wet process.

<Evaluation>
The negatively chargeable toner was mixed with the carriers obtained in Examples and Comparative Examples, and a developer in which the toner ratio in the developer was set to 8% was used. This toner ratio is the ratio of the total amount of toner, external additive and reverse polarity particles to the total amount of developer (the same applies hereinafter). The developer was mounted on an image forming apparatus (a modified version of bizhunb C350; manufactured by Konica Minolta Technologies, Inc.) incorporating a hybrid developing device of the form shown in FIG. A predetermined image was printed using this image forming apparatus and evaluated. The supply of toner is controlled based on the toner concentration of the developer.

Development conditions are as follows. The electric field forming apparatus employs the form shown in FIG. 11, and a DC voltage V _{DC2 of} −500 volts is applied to the conveying roller, and an AC voltage of DC voltage V _{DC1 of} −300 volts is applied to the developing roller. AC voltage frequency: 2 kHz, the amplitude _V P-P: 1,500 volts, minus the duty ratio (toner collecting duty ratio): 40%, plus a duty ratio (toner supply duty ratio): was 60% of the rectangular wave . The development gap 50 was set to 0.3 mm, the supply / recovery gap 56 was set to 0.6 mm, and the regulating portion was set so that the developer conveyance amount of the conveyance roller was 50 mg / cm ² . The charged potential (non-image portion) of the photoreceptor was −550 volts, and the potential of the electrostatic latent image (image portion) formed on the photoreceptor was −60 volts.

The developing roller 42 was an aluminum roller with an alumite treatment on the surface, and the gap formed between the developer conveying roller 41 and the developing roller 42 was set to 0.3 mm. Thus, the electric field in the toner supply direction formed between the developer conveying roller 41 and the developing roller 42 is 1000 V / 0.3 mm = 3.3 × 10 ⁶ V / m.

  The gap formed between the regulating member 43 and the developer conveying roller 41 was set to 0.4 mm so that the magnetic brush on the developer conveying roller 41 was slid onto the developing roller 42. The developer moving direction on the developer transporting roller 41 and the moving direction of the developing roller 42 are opposite to each other at the opposing portion. The background portion potential of the electrostatic latent image formed on the photosensitive drum 1 is −550 V, the image portion potential is −60 V, and the gap formed between the photosensitive drum 1 and the developing roller 42 is 0.15 mm. Set to.

(Image memory)
As shown in FIG. 2, an image pattern in which a solid area 90a and a half area 90b exist is output and printed, and evaluated based on the degree of occurrence of image memory in the printed image. Specifically, the evaluation was made according to the following criteria. The evaluation results are shown in FIG. The negative image is an image portion having a relatively low density that appears in the half area 90b. The positive image is an image portion having a relatively high density that appears in the half area 90b.
A: No negative / positive image was generated;
○: Some negative / positive images with a density difference of less than 0.03 were recognized, but there was no practical problem as a whole image;
Δ: Some negative / positive images having a density difference of less than 0.05 were recognized, but there was no practical problem as a whole image;
X: A negative / positive image with a density difference of 0.05 or more was recognized, and there was a practical problem as a whole image;

  The embodiments disclosed herein are illustrative and not limiting. The present invention is defined by the scope of the claims, rather than the scope described above, and is intended to include any modifications within the scope and meaning equivalent to the scope of the claims.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging means 3 Exposure means 4 Developing apparatus 5 Transfer means 6 Cleaning means 40a 1st stirring conveyance screw 40b 2nd stirring conveyance screw 41 Developer conveyance roller 41a Sleeve 41b Magnet body 42 Development roller 44 Housing 46 Developer 80 Toner supply area 81 Toner collection area
100 Image forming apparatus

Claims (4)

A magnetic brush is formed on the outer periphery of the developer transport roller by toner and carrier in the developer, and development is performed using the potential difference between the developer transport roller and the developing roller while sliding the magnetic brush against the developing roller. A carrier of a developer used in a hybrid development method in which only a toner is supplied to a roller and a latent image on a latent image carrier is developed with the toner on the developing roller, and the carrier has an average particle diameter of 20 to A carrier for hybrid development, which is 40 μm and has a variation coefficient A of the number distribution of carrier core particles represented by the following formula: 25 or more and 40 or less.
A = Sn / D1 × 100 (Sn: number distribution standard deviation, D1: number length average particle diameter (μm)) The carrier is
The carrier 5g is placed on the surface of the conductive sleeve, the rotation speed of the developer conveying roller having a magnetic flux density of 1000 gauss, in which the N pole and the S pole are alternately arranged in the conductive sleeve, is set to 50 rpm. The electrical resistance is 1 × 10 ¹² Ω or more when a bias voltage of DC 500V is applied by rotating the developer conveying roller while facing the conductive sleeve with a gap of 1 mm,
The carrier for hybrid development according to claim 1, wherein the saturation magnetization is 30 to 45 Am ² / kg.   A hybrid developing apparatus comprising a developer including toner and the carrier according to claim 1. An image forming apparatus comprising the hybrid developing device according to claim 3.