JP5029555B2 - Developing device and image forming apparatus - Google Patents

Description

  The present invention uses a developer containing a carrier and toner, and supplies a toner carrier for supplying toner to the toner carrier, and a toner carrier for developing a latent image with the supplied toner. The present invention relates to a hybrid developing device provided with a toner collecting developer carrying member for collecting undeveloped toner from a toner carrying member, and an image forming apparatus using the same.

  Conventionally, as a developing method in an image forming apparatus using an electrophotographic method, a one-component developing method using only toner as a developer and a two-component developing method using toner and a carrier are known.

  The one-component development system is advantageous in terms of simplification, miniaturization, and cost reduction of the apparatus, but the deterioration of the toner is likely to be accelerated by the strong stress of the regulating part that charges the toner, and the charge acceptability of the toner is reduced. It's easy to do. Further, the toner regulating member and the surface of the toner carrying member are contaminated with the toner and the external additive, whereby the charge imparting property to the toner is also lowered, and as a result, the life of the developing device is shortened.

  In the two-component development system, the toner is charged by frictional charging by mixing with the carrier, so that the stress is small and it is advantageous for the deterioration of the toner. Furthermore, since the surface area of the carrier is large, it is relatively strong against contamination by toner and external additives, which is advantageous for extending the life.

  However, in the two-component development method, when developing the electrostatic latent image on the image carrier, the surface of the image carrier is rubbed with the magnetic brush of the developer, so that a magnetic brush mark may be generated. Furthermore, there is a problem that the carrier easily adheres to the image carrier and causes an image defect.

  As a development method that solves the problem of image defects while having the long-life characteristics of the two-component development method, the two-component developer is supported on the developer carrier, and only the toner from the two-component developer is changed to the toner carrier. A so-called hybrid development system that is supplied and used for development is disclosed (see Patent Document 1).

  However, the hybrid development system has a problem that undeveloped toner that has not been used for development on the toner carrier appears on the image as a development history (ghost) in the next development process. This is because priority is given to supplying a toner necessary for development to the toner carrying member by applying a bias to the developer carrying member, and thus the developer carrying member does not have sufficient ability to collect the development residual toner. doing.

  In recent years, in order to solve this problem, there has been proposed a method in which a developer collecting member for collecting toner is added and a voltage for collecting the development residual toner on the toner carrying member is applied in the hybrid developing method (see Patent Document 2). ). According to the technique described in Patent Document 2, the development residual toner on the toner carrying member can be reliably collected by the toner collecting developer carrying member, so that the problem of development history (ghost) does not occur in the initial stage.

  However, in this method, since a voltage for attracting the toner is always applied in the direction of the toner collecting developer carrier, residual toner collected from the toner carrier and toner separated from the carrier in the developer are removed. The toner moves to the surface of the developer collecting member for toner collection, and the toner is unevenly distributed.

  When the toner is unevenly distributed on the surface of the toner collecting developer carrier, the unevenly distributed toner remains on the surface of the toner collecting developer carrier when the developer is removed from the toner collecting developer carrier. To do. As a result, the toner is accumulated on the developer carrying member for collecting the toner by repeated use.

  Accumulation of charged toner obstructs the recovery electric field in the toner recovery area and lowers the toner recovery capability. For this reason, the recovery capability that was initially sufficient does not last for a long period of time, and ghosting becomes a problem as image formation is repeated.

In addition, when used for a long period of time, there is a problem that the accumulated toner is filmed on the surface of the toner collecting developer carrier.
JP-A-5-150636 JP-A-10-319708

  As described above, technical improvements have been made to cope with ghosting in the hybrid development method, but no technology that sufficiently satisfies the requirements has been proposed.

  The object of the present invention is to solve the above-mentioned problems, use a hybrid development system provided with a developer carrier for collecting toner, maintain the toner collecting ability, and do not generate development history (image memory, ghost). It is an object of the present invention to provide a developing device and an image forming apparatus that can obtain images of the above for a long time.

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

  1. A developer tank containing a developer containing toner and a carrier; a toner supply developer carrier for carrying and conveying the developer mixed and stirred in the developer tank to the surface; and the toner supply developer carrier A toner carrier for receiving and supplying the toner from the body to develop the latent image on the image carrier, and a developer carrier for collecting toner for collecting the development residual toner from the toner carrier. A toner release member that contacts the toner collecting developer carrier via the toner collecting developer layer on the toner collecting developer carrier, and a toner in the developer layer. A power source for applying a bias voltage to the toner peeling member for forming an electric field in a direction to separate the toner from the toner carrying developer carrying member, the toner peeling member carrying the toner collecting developer carrying A developing device, characterized in that the contact with the toner collecting developer carrier by the magnetic attraction force of the magnetic pole with the.

  2. 2. The developing device according to 1, wherein the toner peeling member is a film member.

  3. 3. The developing device according to 2, wherein the toner peeling member is provided with a magnetic member on the back side of the film member.

  4). 4. The developing device according to 3, wherein the magnetic member is a discontinuous body.

  5). 4. The developing device according to 3, wherein the magnetic member has flexibility.

  6). 3. The developing device according to 2, wherein the film member contains magnetic particles dispersedly.

  7). 7. The developing device according to claim 1, wherein the toner peeling member is disposed at a position facing a magnetic pole of the toner collecting developer carrier.

  8). An image forming apparatus comprising the developing device according to any one of 1 to 7.

  According to the present invention, the toner collection developer carrier can reliably collect the development residual toner on the toner carrier and can avoid accumulation of toner on the toner collection developer carrier. A stable toner layer is supplied on the body.

  Accordingly, it is possible to provide a developing device and an image forming apparatus that can obtain a high-quality image that maintains the toner recovery capability and does not cause a ghost problem over a long period of time.

  Embodiments of the present invention will be described below with reference to the drawings.

(Configuration and operation of image forming apparatus)
FIG. 1 shows a configuration example of a main part of an image forming apparatus according to an embodiment of the present invention. The schematic configuration and operation of the image forming apparatus will be described with reference to FIG.

  The image forming apparatus is a printer that performs image formation by transferring a toner image formed on an image carrier (photosensitive member) 1 to a transfer medium P such as paper by an electrophotographic method.

  The image forming apparatus includes an image carrier 1 for carrying an image. Around the image carrier 1, a charging member 3 for charging the image carrier 1 and an image carrier 1 are provided. A developing device 2 for developing an electrostatic latent image, a transfer roller 5 for transferring a toner image on the image carrier 1, and a cleaning blade 6 for removing residual toner on the image carrier 1 are provided on the image carrier 1. They are arranged in order along the rotation direction A.

  The image carrier 1 is charged by the charging member 3 and then exposed by an exposure device 4 equipped with a laser emitter or the like at the point E in the figure, and an electrostatic latent image is formed on the surface thereof. . The developing device 2 develops the electrostatic latent image to form a toner image. The transfer roller 5 transfers the toner image on the image carrier 1 to the transfer medium P, and then discharges it in the direction of arrow F in the figure. The cleaning blade 6 removes the residual toner on the image carrier 1 after the transfer with a mechanical force.

  The image carrier 1, the charging member 3, the exposure device 4, the transfer roller 5, the cleaning blade 6 and the like used in the image forming apparatus may arbitrarily use a known electrophotographic technique. For example, although a charging roller is shown as the charging member 3 in the figure, a charging device that is not in contact with the image carrier 1 may be used. Further, for example, there may be no cleaning blade.

  Next, a configuration example of the developing device 2 of the hybrid developing system according to the present embodiment will be described.

  The developing device 2 includes the following components. That is, a developer tank 16 that contains a developer 24 containing toner and a carrier, a toner supply developer carrier 11 that carries and conveys the developer 24 supplied from the developer tank 16 on the surface, and a toner supply development. The toner is supplied from the agent carrier 11 in the toner supply region 7, and develops the electrostatic latent image formed on the image carrier 1. After passing through the development region 8, the toner carrier 25 The toner collecting developer carrier 26 for collecting the undeveloped toner remaining in the toner collecting area 9 is provided.

  Further, a toner peeling member (film member) 41 that attracts the unevenly distributed toner on the surface of the toner collecting developer carrier 26 after passing through the toner collecting region 9 and separates it from the surface of the toner collecting developer carrier 26 is provided. Thus, the collected toner is returned to the developer tank 16 together with the developer separated in the developer separation region, and the toner layer on the toner carrier 25 can be always refreshed.

  Further, the developing device 2 includes a toner carrier bias power supply 31 that supplies a developing bias voltage Vb2 to the toner carrier 25, and a toner supply developer carrier that supplies the toner supply bias voltage Vb1 to the toner supply developer carrier 11. Bias power source 32, toner recovery bias carrier 33 that supplies toner recovery bias voltage Vb3 to toner recovery developer carrier 26, and toner release bias voltage Vb4 that supplies toner release bias voltage Vb4 to toner release member 41 A bias power supply 34 is provided.

  The detailed configuration and operation of the developing device 2 will be described later.

(Developer composition)
The configuration of the developer used in the developing device according to this embodiment will be described.

  The developer 24 used in the present embodiment includes toner and a carrier for charging the toner.

<Toner>
The toner is not particularly limited, and a known toner that is generally used can be used, and a colorant, a charge control agent, a release agent, and the like are contained in the binder resin, and external additives are added. What processed the agent can be used. The toner particle diameter is not limited to this, but is preferably about 3 to 15 μm.

  In producing such a toner, it can be produced by a publicly known method. For example, it can be produced using a pulverization method, an emulsion polymerization method, a suspension polymerization method or the like.

  The binder resin used in the toner is not limited to this. For example, styrene resin (monopolymer or copolymer containing styrene or a styrene-substituted product), polyester resin, epoxy resin, vinyl chloride Resins, phenol resins, polyethylene resins, polypropylene resins, polyurethane resins, silicone resins and the like can be mentioned. It is preferable to use those having a softening temperature in the range of 80 to 160 ° C. and those having a glass transition point in the range of 50 to 75 ° C., depending on the resin alone or the composite.

  Moreover, as a coloring agent, the publicly known well-known thing can be used, for example, carbon black, aniline black, activated carbon, magnetite, benzine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, ultra Marine blue, rose bengal, lake red and the like can be used, and it is generally preferable to use them in a proportion of 2 to 20% by mass with respect to the binder resin.

  As the charge control agent, known ones can be used. Examples of the charge control agent for positively chargeable toners include nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazoles. System compounds and polyamine resins. Examples of the charge control agent for negatively chargeable toners include metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkyl salicylic acid metal compounds, and curlyx arene compounds. In general, the charge control agent is preferably used in a proportion of 0.1 to 10% by mass with respect to the binder resin.

  In addition, as the above-mentioned mold release agent, known ones that are generally used can be used. For example, polyethylene, polypropylene, carnauba wax, sazol wax and the like can be used alone or in combination of two or more. In general, it is preferably used at a ratio of 0.1 to 10% by mass with respect to the binder resin.

  Also, as the above external additives, publicly known publicly known materials can be used. For example, inorganic fine particles such as silica, titanium oxide, aluminum oxide, acrylic resin, styrene resin, silicone resin, fluorine resin Resin fine particles such as silane coupling agent, titanium coupling agent, and silicone oil are preferably used. Such a fluidizing agent is added to the toner at a ratio of 0.1 to 5% by mass and used. The number average primary particle size of the external additive is preferably 10 to 100 nm.

  Further, as the external additive, reverse polarity particles having a chargeability opposite to that of the toner may be used. The reverse polarity particles preferably used are appropriately selected depending on the charging polarity of the toner.

  When a negatively chargeable toner is used as the toner, fine particles having positive chargeability are used as the opposite polarity particles. For example, inorganic fine particles such as strontium titanate, barium titanate, and alumina, acrylic resin, benzoguanamine resin, nylon ( Fine particles made of thermoplastic resin such as (registered trademark) resin, polyimide resin, polyamide resin or thermosetting resin can be used. Further, a positive charge control agent imparting positive chargeability may be contained in the resin, or a copolymer of nitrogen-containing monomers may be constituted.

  As the positive charge control agent, for example, nigrosine dye, quaternary ammonium salt and the like can be used, and as the nitrogen-containing monomer, 2-dimethylaminoethyl acrylate, 2-diethylaminoethyl acrylate, 2-Dimethylaminoethyl methacrylate, 2-diethylaminoethyl methacrylate, vinylpyridine, N-vinylcarbazole, vinylimidazole and the like can be used.

  On the other hand, in the case of using a positively chargeable toner, fine particles having negative chargeability are used as the reverse polarity particles. For example, in addition to inorganic fine particles such as silica and titanium oxide, fluorine resin, polyolefin resin, silicone resin, polyester resin Fine particles composed of a thermoplastic resin such as a thermosetting resin or the like can be used. Further, a negative charge control agent imparting negative chargeability may be contained in the resin, or a copolymer of a fluorine-containing acrylic monomer or a fluorine-containing methacrylic monomer may be constituted. Examples of the negative charge control agent include salicylic acid-based and naphthol-based chromium complexes, aluminum complexes, iron complexes, and zinc complexes.

  In addition, in order to control the chargeability and hydrophobicity of the reverse polarity particles, the surface of the inorganic fine particles may be surface treated with a silane coupling agent, a titanium coupling agent, silicone oil, etc. When imparting positive chargeability, surface treatment with an amino group-containing coupling agent is preferred, and when imparting negative chargeability, surface treatment with a fluorine group-containing coupling agent is preferred.

  The number average particle diameter of the reverse polarity particles is preferably 100 to 1000 nm. It is used by adding 0.1 to 10% by mass with respect to the toner.

<Carrier>
The carrier is not particularly limited, and a commonly used carrier can be used, and a binder type carrier, a coat type carrier, and the like can be used. The carrier particle size is not limited to this, but is preferably 15 to 100 μm.

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

  Examples of the binder resin used in the binder-type carrier include thermoplastic resins such as vinyl resins, polyester resins, nylon resins, polyolefin resins, and the like typified by polystyrene resins, and curable resins such as phenol resins. .

  Magnetic fine particles of the binder type carrier include spinel ferrite such as magnetite and gamma iron oxide, and magnets such as spinel ferrite and barium ferrite containing one or more metals other than iron (Mn, Ni, Mg, Cu, etc.). Plumbite type ferrite, iron or alloy particles having an oxide layer on the surface can be used. The shape may be granular, spherical, or needle-shaped. 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. A magnetic resin carrier having a desired magnetization can be obtained by appropriately selecting the type and content of the ferromagnetic fine particles. The magnetic fine particles are suitably added to the magnetic resin carrier in an amount of 50 to 90% by mass.

  Silicone resin, acrylic resin, epoxy resin, fluorine resin, 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 are fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly, adhering these fine particles to the surface of the magnetic resin carrier, and then mechanically and thermally. By applying a strong impact force 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, organic insulating fine particles such as polystyrene, styrene copolymer, acrylic resin, various acrylic copolymers, nylon, polyethylene, polypropylene, fluororesin, and cross-linked products thereof may be used as the organic type. Regarding the charge level and polarity, a desired level of charge and polarity can be obtained by a material, a polymerization catalyst, surface treatment, and the like. Further, as the inorganic type, negatively charged inorganic fine particles such as silica and titanium dioxide, and positively charged inorganic fine particles such as strontium titanate and alumina are used.

  On the other hand, a coated carrier is a carrier in which a carrier core particle made of a magnetic material is coated with a resin, and in a coated carrier, positive or negatively chargeable fine particles are fixed on the surface of the carrier as in a binder type carrier. it can. Charging characteristics such as polarity of the coat type carrier can be controlled by the type of the surface coating layer and the chargeable fine particles, and the same material as the binder type carrier can be used. In particular, the coating resin can be the same resin as the binder resin of the binder type carrier.

  The mixing ratio of the toner and the carrier may be adjusted so as to obtain a desired toner charge amount. The mixing ratio of the toner is 3 to 50% by mass, preferably 6 to 30% by mass with respect to the total amount of the toner and the carrier. Is suitable.

(Configuration and operation of developing device 2)
A detailed configuration example and operation example of the developing device 2 according to this embodiment will be described with reference to FIG.

<Device configuration>
The developer 24 used in the developing device 2 is composed of toner and carrier as described above, and is stored in the developer tank 16.

  The developer tank 16 is formed by a casing 19 and normally contains mixing and agitating members 17 and 18 therein. The mixing stirring members 17 and 18 mix and stir the developer 24 and supply the developer 24 to the toner supply developer carrier 11. An ATDC (Automatic Toner Density Control) sensor 20 for detecting the toner concentration is preferably disposed at a position of the casing 19 facing the mixing and agitating member 18.

  The developing device 2 usually has a replenishing unit 10 for replenishing the developer tank 16 with toner consumed in the developing area 8. In the replenishing unit 10, the replenishing toner 23 sent from a hopper (not shown) containing the replenishing toner 23 is replenished into the developer tank 16.

  The developing device 2 also has a regulating member (regulating blade) 15 for thinning the developer for regulating the amount of developer on the toner supply developer carrier 11.

  The toner supply developer carrier 11 includes a magnet body 13 that is fixedly arranged and a rotatable sleeve roller 12 that encloses the magnet body 13, and supplies toner to the toner carrier 25 during image formation. A toner supply bias Vb <b> 1 is applied by a toner supply developer carrier bias power supply 32.

  The magnet body 13 has five magnetic poles S1, N1, S2, S3, and N2 along the rotation direction B of the sleeve roller 12. Of these magnetic poles, the main magnetic pole N <b> 1 is disposed at the position of the toner supply region 7 facing the toner carrier 25.

  Similarly, the toner collecting developer carrier 26 is composed of a magnet body 28 that is fixedly arranged and a rotatable sleeve roller 27 that encloses the magnet body 28, and for collecting the development residual toner on the toner carrier 25. A toner recovery bias Vb3 is applied by a toner recovery developer carrier bias power source 33.

  The magnet body 28 has five magnetic poles N3, S4, N4, S5, and N5 along the rotation direction D of the sleeve roller 27. Of these magnetic poles, the main magnetic pole S4 is disposed at the position of the toner recovery region 9 facing the toner carrier 25.

  Further, homopolar portions N5 and N3 that generate a repulsive magnetic field for peeling off the developer 24 on the sleeve roller 27 are disposed at positions facing the inside of the developer tank 16.

  Between the toner collection area 9 and the developer separation area (the same polarity part) of the toner collection developer carrier 26, the unevenly distributed toner is attracted to the surface of the toner collection developer carrier after passing through the toner collection area 9. A toner peeling member (film member) 41 is provided, and a toner peeling bias Vb4 is applied by a power source 34 via a holding electrode 42. A magnetic member 43 for stabilizing the contact pressure of the toner peeling member (film member) 41 with the developer 24 is provided on the back surface of the toner peeling member (film member) 41 with the developer 24. Is provided.

  Further, in the developing device 2, in order to deliver the developer 24 on the toner supply developer carrier 11 to the toner collection developer carrier 26, each of the S2 pole and the N3 pole serves as a toner supply developer. The carrier 11 and the developer collecting member 26 for collecting toner are arranged at the opposing portions. The developer 24 is delivered and conveyed from the S2 magnetic pole side of the toner supply developer carrier 11 to the N3 magnetic pole side of the toner recovery developer carrier 26.

  The toner carrier 25 is disposed so as to face the toner supply developer carrier 11, the toner collection developer carrier 26, and the image carrier 1, and develops the electrostatic latent image on the image carrier 1. A developing bias Vb2 is applied by a toner carrier bias power source 31.

  The toner carrier 25 may be made of any material as long as the voltage can be applied, and examples thereof include an aluminum roller that has been subjected to a surface treatment such as alumite. In addition, on a conductive substrate such as aluminum, for example, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, porsulfone resin, polyether ketone resin, vinyl chloride resin, vinyl acetate You may use what gave resin coatings, such as resin, a silicone resin, a fluororesin, and rubber coatings, such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber. The coating material is not limited to this.

  Further, a conductive agent may be added to the bulk or surface of the coating. 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 kettin black, acetylene black, and furnace black, metal powder, and metal oxide fine particles, but are not limited thereto. Examples of the ionic conductive agent include cationic compounds such as quaternary ammonium salts, amphoteric compounds, and other ionic polymer materials. Furthermore, a conductive roller made of a metal material such as aluminum may be used.

<Operation of the device>
An example of the operation of the developing device 2 will be described in detail with reference to FIG.

  The developer 24 in the developer tank 16 is mixed and stirred by the rotation of the mixing and stirring members 17 and 18 and is frictionally charged. At the same time, the developer 24 is circulated and conveyed in the developer tank 16 to the sleeve roller 12 on the surface of the developer carrier 11. Supplied.

  The developer 24 is held on the surface side of the sleeve roller 12 by the magnetic force of the magnet body 13 inside the toner supply developer carrier 11 and rotates together with the sleeve roller 12 to be transferred to the toner supply developer carrier 11. The amount of passage is regulated by the regulating member 15 provided to face.

  Thereafter, the developer 24 is conveyed to the toner supply area 7 facing the toner carrier 25.

  In the toner supply region 7, developer spikes are formed by the magnetic force of the main magnetic pole N <b> 1 of the magnet body 13, and the development bias Vb <b> 2 applied to the toner carrier 25 and the toner supply bias applied to the toner supply developer carrier 11. The toner in the developer 24 is supplied to the toner carrier 25 side by the force applied to the toner by the supply electric field formed by Vb1.

  The toner layer supplied to the toner carrier 25 is transported to the development region 8 as the toner carrier 25 rotates, and is latentized by a development electric field formed by the development bias and the latent image potential on the image carrier 1. The image is developed into a visible image. The development method may be a reversal development method or a regular development method.

  The toner layer (development residual toner) on the toner carrier 25 that has consumed toner in the development area 8 is further conveyed to the toner collection area 9 facing the toner collection developer carrier 26 by the rotation of the toner carrier 25. Is done.

  On the other hand, the remaining developer 24 that has supplied the toner to the toner carrier 25 in the toner supply region 7 is conveyed to a portion facing the developer carrier 26 for collecting the toner, and the magnetic pole of the developer carrier 11 for toner supply is conveyed. The toner is transferred to the toner collecting developer carrier 26 by the magnetic field formed by the magnetic pole N3 of S2 and the toner collecting developer carrier 26.

  The developer 24 delivered to the toner collecting developer carrier 26 rotates and moves together with the sleeve roller 27 of the toner collecting developer carrier 26 and is conveyed to the toner collecting region 9 facing the toner carrier 25. Is done.

  In the toner recovery area 9, the electrostatic force applied to the toner by the recovery electric field formed by the development bias Vb2 applied to the toner carrier 25 and the toner recovery bias Vb3 applied to the toner recovery developer carrier 26, and the toner recovery The development residual toner moves from the toner carrying member 25 to the toner collecting developer carrying member 26 and is collected by the mechanical rubbing force of the developer 24 held on the developer carrying member 26.

  The toner collected on the toner collecting developer carrier 26 is collected in the developer 24 layer carried on the toner collecting developer carrier 26 by the action of the collecting electric field in the toner collecting area 9. The state is unevenly distributed near the surface of the developer carrying member (a toner layer is formed on the surface of the developer collecting member 26 for collecting toner).

  However, the toner collection bias Vb3 applied to the toner collection developer carrier 26 and the toner collection bias Vb3 applied to the toner collection member 26 in the contact area with the toner peeling member (film member) 41 in the process in which the developer 24 is conveyed toward the developer tank 16 The uneven distribution of the toner is eliminated by the force applied to the toner by the peeling electric field formed by the toner peeling bias Vb4 applied to the film member 41. Details of the uneven distribution of the toner and its elimination by the toner peeling member and the contact of the toner peeling member with the developer layer will be described later.

  Thereafter, the toner is transported together with the developer toward the developer tank 16, and is peeled off from the toner collecting developer carrier 26 by the repulsive magnetic field of the same polarity portions N <b> 5 and N <b> 3 of the magnet body 28 and into the developer tank 16. And recovered.

  When a supply control unit (not shown) detects from the output value of the ATDC sensor 20 that the toner concentration in the developer 24 has become equal to or lower than the minimum toner concentration for securing the image density, the toner supply means (not shown) puts the toner in the hopper. The stored supply toner 23 is supplied into the developer tank 16 through the toner supply unit 10.

<Developer flow>
In the configuration and operation example of the developing device 2, the developer flow was as follows.

  That is, the toner supply developer carrier 11 and the toner collection developer carrier 26 are arranged to face each other, and the developer 24 supplied from the developer tank 16 onto the toner supply developer carrier 11 is supplied with toner. The developer carrying body 11 is regulated, transferred from the toner carrying developer carrying body 11 to the toner collecting developer carrying body 26, separated from the toner collecting developer carrying body 26, and returned to the developer tank 16. I am doing so.

  However, the flow of the developer 24 is not limited to the above flow.

  For example, the developer 24 may be transferred again from the toner collecting developer carrier 26 to the toner supply developer carrier 11 and then returned from the toner supply developer carrier 11 to the developer tank 16. . In this case, the toner peeling member (film member) 41 may be provided after passing through the toner collection area 9 and before delivering the developer.

  Further, the developer 24 is supplied from the developer tank 16 to the toner carrier 11 for toner supply and the developer carrier 26 for toner recovery, respectively, and after the transport amount is regulated, the toner supply area 7 and the toner recovery area 9 to separate the developer 24 from each developer carrier and return it to the developer tank 16 (developers of the toner supply developer carrier 11 and the toner collection developer carrier 26). The flow may be separated). In this case, the toner peeling member (film member) 41 may be provided between the developer collection area 9 and the developer separation area after passing through the toner collection area 9.

  That is, the developer 24 transported to the toner supply region 7 may be a developer whose toner concentration is adjusted in the developer tank 16, and the toner peeling member (film member) 41 is the developer after passing through the toner recovery region 9. May be provided before the toner is removed from the toner collecting developer carrying member.

(Regarding problems in the toner recovery area and toner peeling member)
The problem of the toner collection capability in the toner collection area (toner accumulation on the surface of the developer carrying member for collecting toner) and details of the toner peeling member for preventing it will be described.

  First, the development history (ghost) will be described, then the toner supply, recovery capability and bias setting by the developer carrier will be described. Finally, the toner accumulation on the toner recovery developer carrier and the recovery capability will be reduced. The setting of the toner peeling member for preventing will be described.

<About Ghost>
The development history (also referred to as ghost or image memory) will be described with reference to FIG.

  FIG. 2A is an example of an image chart used for detecting a ghost. A black solid area 52 and a half image area 53 are arranged in the white portion 51 as the background area as shown in the figure. FIG. 2B is an example of a print image showing a state where a ghost is generated by printing in the print direction as shown in the image chart of FIG.

  The development history (image memory, ghost) is the following phenomenon.

  As shown in the image chart of FIG. 2A, a halftone image in which a halftone image area 53 such as gray continues to be printed after a high contrast image such as a black solid portion 52 is printed on a white background portion 51. Is output. Then, in the output print image, as shown in FIG. 2B, a pattern of a high-contrast image printed on the upstream side that does not exist in the original image chart appears in the halftone image area 53. . In FIG. 2B, a ghost pattern 54 is seen in the halftone image area 53 printed after one cycle of the toner carrier of the solid black portion.

  Such a phenomenon is caused by the following.

  Since the undeveloped toner layer corresponding to the print image pattern remains on the toner carrier immediately after printing the high-contrast image, if it is not sufficiently removed, the toner carrier after the subsequent toner supply to the toner carrier On the toner carrier, unevenness in the thickness of the toner layer corresponding to the printed image pattern remains.

  The development characteristic change due to the thickness unevenness of the toner layer causes density unevenness (ghost) corresponding to the previously printed pattern on the next print image. The density unevenness due to the development characteristic fluctuation is highly visible particularly in a halftone image.

  Therefore, it is necessary to sufficiently collect the development residual toner on the surface of the toner carrying member in order to suppress the occurrence of ghost.

<Toner supply, recovery capability and bias setting by each developer carrier>
This embodiment is a hybrid development system. In particular, in addition to a toner supply developer carrier that supplies toner to the toner carrier, a toner collection developer carrier is provided, and the development residual toner on the toner carrier is collected on the toner collection developer carrier. This is a hybrid development system of a toner supply / recovery function separation type in which voltage is applied.

  The toner supply, recovery capability and bias setting by the toner supply developer carrier and the toner recovery developer carrier will be described with reference to FIG.

  FIG. 3 shows the respective bias voltages applied to the toner supply developer carrier 11, the toner carrier 25, and the toner recovery developer carrier 26, and the toner layer accompanying the toner accumulation when no toner release member is provided. The potential is shown assuming that negatively charged toner is used.

  Each bias voltage applied to each of the toner supply developer carrier 11, the toner carrier 25, and the toner collection developer carrier 26 is a DC voltage, but an AC voltage is superimposed on the DC voltage. Although it may be a voltage, for the sake of simplicity, description will be made using an average value of the respective applied voltages. Here, the average value of the applied voltages is a voltage value if a DC bias is applied, and a DC component value if an AC superimposed bias is applied. For example, in the case of an asymmetric waveform such as a rectangular wave having a duty ratio, it is a time average (the same applies hereinafter).

  FIG. 3A shows an example of the relationship among bias voltages Vb1, Vb2, and Vb3 applied to the toner supply developer carrier 11, the toner carrier 25, and the toner collection developer carrier 26, respectively. .

  In this example, in order to supply toner from the developer on the toner supply developer carrier 11 to the toner carrier 25, a potential difference Vb2−Vb1 (toner between the toner supply developer carrier 11 and the toner carrier 25 is set. Supply potential difference) is set.

  Further, in order to collect the toner (development residual toner) that has not been used for the development on the toner carrier 25 on the toner collection developer carrier 26, the toner carrier 25 and the toner collection developer carrier 26 A potential difference Vb3-Vb2 (toner recovery potential difference) is set between them.

  First, only the toner supply from the toner supply developer carrier 11 to the toner carrier 23 will be considered.

  The amount of toner supplied from the toner supply developer carrier 11 to the toner carrier 25 depends on the magnitude of the toner supply potential difference Vb2−Vb1, and the toner supply amount gradually increases as the toner is repeatedly supplied. The maximum supply amount is an amount by which the toner layer potential Vtd due to the toner layer supplied onto the toner carrier 25 is substantially equal to the toner supply potential difference Vb2−Vb1 (see FIG. 3B).

  As described above, the toner amount on the toner carrier 25 varies depending on the toner supply history (the amount of toner on the toner carrier 25 before the toner supply, that is, the development history). Therefore, the toner carrier 26 is not provided. In this case, it is difficult to keep the toner amount on the toner carrier 25 constant, and the toner amount on the toner carrier 25 becomes uneven according to the development history, which causes image memory (ghost).

  Therefore, by providing a toner collecting developer carrier 26 and collecting at least a part of the development residual toner, it is possible to equalize the amount of toner on the toner carrier 25 before toner supply regardless of the development history. .

  For this reason, the recovery of the development residual toner on the toner carrier 25 to the toner collection developer carrier 26 is the potential difference Vb3-Vb2 (toner collection potential difference) between the toner carrier 25 and the toner collection developer carrier 26. In addition, the toner layer potential Vtd on the toner carrier 25 is also affected.

  That is, the potential difference Vb3− (Vb2 + Vtd) between the voltage Vb2 + Vtd obtained by adding the toner layer potential Vtd to the voltage Vb2 applied to the toner carrier 25 and the voltage Vb3 applied to the developer carrier 26 for collecting toner becomes an effective toner collection potential difference. .

  Therefore, if the voltage Vb3 applied to the toner collecting developer carrier 26 is a voltage in which Vb2 + Vtd−Vb3 is in the toner collecting direction, a toner collecting effect by electrostatic force can be obtained.

  For example, as shown in FIG. 3C, even if the applied voltage Vb3 to the toner collecting developer carrier 26 is in the direction of supplying the toner to the applied voltage Vb2 to the toner carrier 11, it is effective. Due to the difference in toner recovery potential, a part of the toner layer acts in the recovery direction, and an effect of leveling the development history (toner amount unevenness) on the toner carrier 25 before toner supply is obtained.

  Thus, the collection of the development residual toner from the toner carrier 25 to the toner collection developer carrier 26 in the toner collection area 9 depends on the effective toner potential difference. However, if the electric field in the collecting direction is too strong in the toner collecting area 9, the following problem occurs.

  That is, the toner recovered from the toner carrier 25 in the toner recovery region 9 and the toner separated from the carrier in the developer (rising) move to the surface of the developer carrier 26 for toner recovery, and the toner on the surface The occurrence of uneven distribution occurs.

<Toner accumulation on toner carrier for toner recovery and reduction in toner recovery capability>
FIG. 4 is a cross-sectional view showing the state of developer spikes by the magnetic poles of the toner collection developer carrier 26 and the movement of toner in the electric field direction in the toner collection area 9. With reference to FIG. 4, the uneven distribution and accumulation of toner on the surface of the toner collecting developer carrier 26 and the reduction of the collecting ability due to this will be described.

  In FIG. 4A, the rising of the developer 24 (magnetic brush) occurs substantially parallel to the direction of the recovery electric field (see the thick arrow in the center of the figure). A part of the toner collected on the toner collecting developer carrier 26 and the toner contained in the developer 24 on the toner collecting developer carrier 26 is subjected to the action of the toner collecting electric field, It travels along the magnetic brush chain formed with spikes by the magnetic poles and easily moves to the surface of the developer carrying member 26 for collecting toner.

  As a result, on the upstream side of the toner collection area 9, as shown in FIG. 4B, the toner 45 adhered to and dispersed on the surface of the carrier 46 particles is the downstream side after passing through the toner collection area 9. Then, as shown in FIG. 4C, a part of the toner 45 is separated from the carrier 46, and a toner layer unevenly distributed on the surface of the toner collecting developer carrier 26 is formed.

  In this way, the toner that has moved to the surface of the developer carrying member 26 for toner collection and is unevenly distributed is separated from the carrier. Therefore, when the developer 24 is conveyed along with the rotation of the developer carrier 26 for collecting the toner and returned to the developer tank 16 by the repulsive magnetic field of the same-polarity portions N5 and N3 of the magnet roll 28, the developer together with the carrier It does not return to the tank 16 but remains on the surface of the toner collecting developer carrier 26.

  The amount of toner remaining on the surface of the toner collecting developer carrier 26 gradually increases and accumulates by repeatedly performing the collecting operation. 3A, finally, as shown in FIG. 5, the toner layer potential Vtr on the toner collecting developer carrier 26 is set to the applied voltage Vb2 of the toner carrier 25. It increases until substantially equal to the value obtained by adding the toner layer potential Vtd on the body 25.

  The increase in the toner layer potential Vtr due to the accumulation of charged toner on the toner collecting developer carrier 26 indicates that the effective collecting potential difference Vb3 + Vtr− (Vb2 + Vtd) for toner collection by the toner collecting developer carrier 26. ) Will decrease.

  In particular, when the toner layer potential Vtr on the toner collecting developer carrier 26 increases to a state as shown in FIG. 5, the effective potential difference for collecting becomes zero.

  Accordingly, accumulation of charged toner on the surface of the toner collecting developer carrier 26 obstructs the collecting electric field in the toner collecting area 9 and lowers the toner collecting ability. For this reason, the recovery ability of the development residual toner, which was good until toner accumulation occurs, does not last for a long time, and ghosting becomes a problem as image formation is repeated.

  In this embodiment, in the toner collection area, the toner unevenly distributed on the surface of the toner collection developer carrier 26 is eliminated by providing a toner peeling member, and the above-described decrease in toner collection capability due to toner accumulation is suppressed. . The effect will be described below.

<Functional operation of toner release member>
6 and 7 show a toner supply developer carrier 11, a toner carrier 25, a toner collection developer carrier 26, and a toner release member when the toner release member (film member) 41 of the present invention is provided. The voltage applied to the (film member) 41 and the toner layer potential accompanying the toner moving by the respective potential differences are shown assuming that negatively charged toner is used as in FIG.

  6 and 7, as in FIG. 3, the toner is applied to the toner supply developer carrier 11, the toner carrier 25, the toner recovery developer carrier 26, and the toner peeling member (film member) 41. The voltage may be a DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage, but here, for simplicity, the description will be made using an average value of each applied voltage.

  FIG. 6A shows the voltages Vb1, Vb2, Vb3 applied to the toner supply developer carrier 11, the toner carrier 25, the toner recovery developer carrier 26 and the toner peeling member (film member) 41, respectively. An example of the relationship of Vb4 is shown.

  In this example as well, a toner supply potential difference Vb2-Vb1 for supplying toner from the developer on the toner supply developer carrier 11 to the toner carrier 25 is set. Further, a toner recovery potential difference Vb3−Vb2 is set for recovering the toner (development residual toner) that has not been used for development on the toner carrier 25 to the toner recovery developer carrier 26.

  In addition, in order to attract the toner layer unevenly distributed on the surface of the toner collecting developer carrying member to the toner peeling member (film member) 41 side, between the toner collecting developer carrying member 26 and the toner peeling member (film member) 41. Toner separation potential difference Vb4-Vb3 is set.

  The toner supply from the toner supply developer carrier 11 to the toner carrier 25 and the toner collection of the development residual toner on the toner carrier 25 to the toner recovery developer carrier 26 are the same as in FIG. Description is omitted.

  Let us consider a state in which a certain amount of toner layer (toner layer potential Vtr) is formed on the surface of the toner carrying developer carrying member as shown in FIG.

  The toner layer (toner layer potential Vtr) unevenly distributed on the surface of the toner collecting developer carrier 26 is attracted toward the toner peeling member (film member) 41 by the action of an effective toner peeling potential difference Vb4− (Vb3 + Vtr). To be resolved. Therefore, Vtr decreases, and the toner collection potential difference Vb3− (Vb2 + Vtd) between the toner carrying member 25 and the toner collecting developer carrying member 26 is caused by the toner layer formed on the surface of the toner collecting developer carrying member 26. It will not be canceled by the layer potential Vtr.

  Here, as shown in FIG. 7A, the toner layer (toner layer potential Vtr) on the surface of the toner collecting developer carrier 26 is changed to the toner peeling member (film member) 41 side by the toner peeling potential difference Vb4- (Vb3 + Vtr). As a result, the toner layer (toner layer potential Vtf) may be formed on the toner peeling member (film member) 41.

  That is, when the toner layer (toner layer potential Vtf) on the toner peeling member (film member) 41 is increased by the repetitive operation, the toner peeling potential difference Vb4− (Vb3 + Vtr) is canceled by the toner layer potential Vtf, and the effective toner peeling potential difference. Will be smaller.

  However, the toner layer (toner layer potential Vtf) is hardly formed on the toner peeling member (film member) 41 for the following reason.

  As shown in FIG. 8A, the moving speed of the developer 24 on the toner collecting developer carrier 26 is such that the developer 24 is attracted to the surface of the toner collecting developer carrier 26 by the magnetic force and moves. The moving speed of the surface (sleeve roller 27) of the toner collecting developer carrier 26 is almost equal (the speed difference does not occur at the interface between the toner collecting developer carrier 26 and the developer 24).

  Accordingly, the rubbing force does not act on the toner 45 layer formed on the surface of the toner collecting developer carrier 26, and the toner 45 layer cannot be removed using the developer 24.

  On the other hand, as shown in FIG. 8B, when the toner peeling member (film member) 41 is provided, the toner 45 is attracted to the toner peeling member (film member) 41 side by the toner peeling electric field, but the toner When attention is paid to the contact nip portion between the peeling member (film member) 41 and the developer 24 on the toner collecting developer carrier 26, the toner peeling member (film member) 41 is fixed while the development is performed. The agent 24 is in a state of moving with the rotation of the toner collecting developer carrier 26.

  As a result, even if a speed difference occurs at the interface between the toner peeling member (film member) 41 and the developer 24 and a toner 45 layer is formed on the film member 41 by the toner peeling electric field, the toner 45 Since the rubbing force by the developer 24 acts on the layer, the layer is scraped off, and the toner layer does not accumulate on the film member 41.

  As a result, as shown in FIG. 7B, the toner layer potential Vtf on the film member 41 does not increase by repeated operations, but is limited to almost zero or a very small level, thereby stabilizing the toner peeling potential difference. Can be maintained.

  From the above, at least the toner peeling potential difference Vb4− (Vb3 + Vtr) may be set to a negative value when the toner is positively charged and to a positive value when the toner is negatively charged. Further, the electric field between the film member 41 and the toner collecting developer carrier 26 is preferably an oscillating electric field.

  By making the electric field between the film member 41 and the toner collecting developer carrier 26 an oscillating electric field, it is possible to reliably attract the toner adhering to the surface of the toner collecting developer carrier 26 to the film member 41 side. It becomes.

(Toner layer state transition at each nip)
10 to 13 show the state of the toner layer on each member before and after passing through each nip when the toner peeling member (film member) 41 is provided. Here, the voltage setting of each member is an example, and is not necessarily limited thereto. FIG. 9 shows the main part of FIG. 1 extracted for reference.

  [1] Before and after the toner supply region 7, as shown in FIG. 10, no toner is present on the toner carrier 25 before passing through the nip. By passing through the nip, the developer carrier 11 for supplying toner is passed. Only the toner from the developer on the toner supply developer carrier 11 is supplied to the toner carrier 25 so as to fill the toner supply potential difference formed between the toner carrier 25 and the toner carrier 25.

  [2] Before and after the development area 8, the behavior differs between the image portion and the non-image (background) portion.

  In the image portion, as shown in FIG. 11A, the toner existing on the toner carrier 25 before passing through the nip passes through the nip, so that the image portions of the toner carrier 25 and the image carrier 1 are displayed. The image is developed from the toner carrier 25 to the image portion of the image carrier 1 so as to fill the development potential difference formed between the potential Vi and the amount of toner on the toner carrier 25 is reduced (in the figure, it is completely developed). ing).

  On the other hand, in the non-image portion, as shown in FIG. 11B, the toner existing on the toner carrier 25 before passing through the nip is non-imaged between the toner carrier 25 and the image carrier 1 even after passing through the nip. Due to the background potential difference formed with the part potential V 0, the toner carrier 25 cannot move to the non-image portion of the image carrier 1 and remains on the toner carrier 25.

  As a result, a development history is generated on the toner carrier 25 as a difference in the amount of residual toner.

  [3] Before and after the toner collection area 9, the behavior varies depending on whether or not there is a development history.

  When the development history is received, as shown in FIG. 12A, no toner is present on the toner carrier 25 (or less than the non-image area) before passing through the nip, and the nip is removed. Even if the toner passes through the toner carrier 25, the toner does not adhere to the toner carrier 25 due to the toner collection potential difference formed between the toner carrier 25 and the toner collection developer carrier 26 (the toner carrier after development). If the toner remains on the toner 25, the toner on the toner carrier 25 is collected by the toner collecting developer carrier 26).

  However, since the developer 24 is present on the toner collection developer carrier 26, a part of the toner in the developer adheres to the surface of the toner collection developer carrier 26 due to the difference in toner collection potential.

  On the other hand, if no development history has been received, as shown in FIG. 12B, the development residual toner existing on the toner carrier 25 before passing through the nip passes the toner carrier 25 and the toner when passing through the nip. The toner is recovered from the toner carrying member 25 to the toner collecting developer carrying member 26 so as to fill a toner collecting potential difference formed with the collecting developer carrying member 26.

  As a result, the development history based on the presence or absence of the development residual toner on the toner carrier 25 is reset, and the toner carrier 25 returns to the state before passing the nip of [1]. On the other hand, the influence of the development history on the toner carrying member 25 is transferred to the toner collecting developer carrying member 26 and remains as a difference in the amount of toner adhering to the surface of the toner collecting developer carrying member 26.

  [4] Before and after the toner peeling area 29, the toner does not stay on the toner peeling member (film member) 41, so that it is not affected by the amount of toner attached to the surface of the toner collecting developer carrier 26. As shown in FIG. 13, the toner adhering to the surface of the toner collecting developer carrier 26 before passing through the nip passes through the nip, so that the toner collecting developer carrier 26 and the toner peeling member (film The toner is peeled from the toner collecting developer carrier 26 toward the toner peeling member (film member) 41 so as to fill the toner peeling potential difference formed between the member 41 and the member.

  At the same time, the toner adhering to the toner peeling member (film member) 41 is rubbed by the developer 24 on the toner collecting developer carrier 26, so that it does not stay on the toner peeling member (film member) 41. Absent. In the developer separation area, the magnetic field is returned to the developer tank 16 by the repulsive magnetic field formed by the same magnetic poles N5 and N3 of the magnet body contained in the developer carrier 26 for collecting toner.

  As a result, the toner adhering to the surface of the toner collecting developer carrier 26 is reset, and the toner collecting developer carrier 26 returns to the state before passing through the nip of [3].

(Material and configuration of toner release member)
As described above, the toner peeling member (film member) 41 according to this embodiment includes
(A) forming a toner peeling potential difference for attracting the toner layer on the surface of the developer collecting member 26 for collecting toner to the toner peeling member (film member) 41; and
(B) Toner adhering to the toner peeling member (film member) 41 due to the toner peeling potential difference is scraped off by the magnetic brush of the developer 24, and contamination of the surface of the toner peeling member (film member) 41 is suppressed;
Is required.

A film-like member is preferably used as the toner peeling member. By using a film member,
・ A wide contact nip width with the developer can be easily secured.
・ A moderate and stable contact pressure to the developer can be secured.
The following advantages are obtained.

  By widening the contact nip width with the developer, the toner adhering to the surface of the developer carrying member for collecting toner is formed in the developer layer by the toner peeling electric field formed between the developer carrying member for collecting toner and the film member. Time for moving the film to the film member side is ensured, and use at a smaller electric field and high system speed are possible.

  By setting an appropriate contact pressure to the developer, the film member and the developer can be stably contacted, and the toner attracted to the film member can be reliably scraped off by the developer. . At the same time, even when the developer transport amount increases due to the environment and durability, it is possible to suppress the occurrence of a problem that the developer cannot stay through the film member contact portion and stay at the nip entrance.

  The material of the film member is not particularly limited, and phosphor bronze, metal thin film such as nickel or SUS, polyester resin, polycarbonate resin, acrylic resin, polyethylene resin, polypropylene resin, urethane resin, polyamide resin, polyimide resin, polysulfone resin, poly Examples include films made of resins such as ether ketone resins, vinyl chloride resins, vinyl acetate resins, silicone resins, fluororesins, and rubber films made of silicone rubber, urethane rubber, nitrile rubber, natural rubber, isoprene rubber, etc. It is not constrained by.

  Further, the film member may have a single layer structure, or may have a structure of two or more layers as necessary. From the viewpoint of scraping off the toner adhering to the film member by the rubbing force of the developer, it is preferable to use a material having a low surface energy (for example, using a fluororesin or a silicone resin), and further chargeability for removing the toner. It is preferable to use a material provided with (for example, a fluororesin for a negatively chargeable toner).

  The low surface energy and chargeability of the film member may be obtained by a film material, or may be controlled by adding a low surface energy material such as a silicone compound or a fluorine compound in the bulk or coating the film. good.

  Further, the adhesion force of the toner can be reduced also by the film surface roughness, and the arithmetic average surface roughness Ra of the developer contact surface of the film member is preferably 0.01 μm to 2 μm. If the surface roughness is too small, the adhesion between the film member and the toner will increase and scratching will not be easy, and if it is too large, the irregularities on the surface of the film member will act to resist rubbing by the developer. It will be a factor of removal failure.

  In order to obtain a desired film member surface roughness, a roughness adjusting agent may be added to the bulk or surface of the film member as necessary. Examples of the roughness adjuster include, but are not limited to, inorganic fine particles such as silica, titanium oxide, alumina, and calcium carbonate, and resin fine particles such as PMMA. Moreover, you may use electrically conductive agents, such as carbon black mentioned later, as a roughness regulator.

  The electrical resistance of the film member is not particularly limited as long as an electric field can be formed between the film member and the developer carrier for collecting toner, and can be used even with conductivity such as metal. Even an insulating material such as this can be used by forming an electrode by performing metal vapor deposition on the back surface.

  However, when the conductivity is high, it is necessary to set the toner peeling potential difference within a range where no leakage occurs between the film member and the toner collecting developer carrier. Further, when an insulating film is used, the insulating film is charged by friction between the insulating film and the developer, and there is a possibility that the toner peeling potential difference may be canceled, so that the range of material selection is narrowed.

From such a viewpoint, the film member resistance is preferably about 10 ⁴ to 10 ¹⁰ Ω / □. In order to obtain such an appropriate film member resistance, a conductive agent may be added to the bulk or surface of the resin film or rubber film as necessary. Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent.

  Examples of the electronic conductive agent include, but are not limited to, carbon black such as kettin black, acetylene black, and furnace black, metal powder, and metal oxide fine particles. Examples of the ionic conductive agent include, but are not limited to, cationic compounds such as quaternary ammonium salts, amphoteric compounds, and ionic polymer materials.

  Examples of the thickness of the film member include 5 μm or more and 1 mm or less, preferably 10 μm or more and 200 μm or less. If it is too thin, the strength will be insufficient, and if it is too thick, the contact pressure on the developer layer of the film member will become too large, depending on the elastic modulus of the film member and the length from the fulcrum of the film to the contact part. There is a risk that developer spills due to the clogging of the developer at the contact portion. Furthermore, there arises a problem that it is difficult to ensure a sufficient contact nip width with the developer.

  The film member is held by being fixed to a holding electrode to which a bias is applied, and the holding method may be cantilever support with one end as a free end, or may be end support with both ends fixed. Further, the film member may be held on the holding electrode as a cylindrical sleeve structure.

  The contact of the film member fixed to the holding electrode with the developer layer is performed using the magnetic attraction force on the magnetic pole of the developer carrying member for toner recovery rather than the elastic restoring force of the film member for the following reason. To do.

  That is, when the contact of the film member is performed by an elastic restoring force, the contact pressure of the film member is lowered when creep deformation occurs in the film member due to long-term use or long-term storage in a high-temperature and high-humidity environment. If the contact pressure of the film member decreases by a certain level or more, the rubbing force by the developer on the developer carrier for collecting toner is reduced, and it becomes difficult to remove the toner adhering to the surface of the film member. The effect of may be impaired.

  By abutting the film member with a magnetic attraction force to the toner collecting developer carrying member, there is no risk of a decrease in the contact pressure due to the creep deformation of the film member, and a stable contact pressure is maintained over a long period of time. Can be maintained.

  The film member can be easily brought into contact with the developer collecting member for collecting toner by providing the magnetic member 43 on the back side of the film member in contact with the developer.

  As shown in the enlarged view of the film member abutting portion in FIG. 14, the magnetic member 43 is provided on the back side of the film member 41, thereby forming the magnetic pole of the toner collecting developer carrier 26 via the film member 41. The magnetic member 43 is attracted to the toner collecting developer carrier 26 by the magnetic attractive force generated by the magnetic field. As a result, it is possible to ensure the contact pressure of the film member 41 on the developer layer 24 on the toner collection developer carrier 26.

  Here, the film member 41 is brought into contact with the developer layer 24 by the magnetic attractive force acting on the magnetic member 43 so that the flexibility that is a characteristic of the film member is not impaired. When the flexibility of the film member is impaired, not only the uniformity of the contact pressure of the film member to the developer is impaired, but also the contact nip width of the film member with the developer may be reduced.

  In the example of FIG. 14, the magnetic member 43 is not bonded to the film member 41, and the magnetic member 43 is configured to be movable in the normal direction of the surface of the developer carrying member for toner collection by a guide provided on the housing side plate. It is desirable to install the magnetic member in an independent movable state.

  Further, as shown in FIG. 15 (a) a cross-sectional view of the contact portion and (b) a top view of the film member, the magnetic member is not a continuous member but a circumferential direction and a longitudinal direction of the toner collecting developer carrier. On the other hand, when the magnetic member is fixed to the film member, the contact pressure by the magnetic attractive force can be ensured without losing the flexibility of the film even if the magnetic member is fixed to the film member.

  Similarly, if a film-like member in which magnetic particles are dispersed is used as the magnetic member, the magnetic member itself has flexibility, so that the contact pressure of the film member to the developer and the contact nip width due to magnetic attraction force. Can be secured at the same time. Similar effects can be obtained by stretching a wire-like flexible magnetic body on the back of the film.

  Furthermore, a magnetic attractive force may act on the film member 41 itself by adopting a configuration in which the magnetic particles are dispersed in the film member 41.

  The contact position of the film member with the developer layer is preferably in the vicinity of the magnetic pole position of the magnet body inside the toner collecting developer carrier. By setting the contact position in the vicinity of the magnetic pole position, the developer magnetic brush is raised, and the toner layer adhered to the surface of the developer carrying member for toner recovery by the toner peeling electric field can be easily moved to the film member side. In addition, it is possible to increase the rubbing force when the developer scrapes off the toner adhering to the film member.

  Furthermore, since the film member is brought into contact with the magnetic attractive force of the magnetic member, the effect of improving the stability of the contact pressure of the film member can also be obtained. Further, a developer bridge is formed between the developer carrying member for collecting toner and the magnetic feel, so that the toner adhering to the film member can be efficiently scraped off.

  As described above, the developing device and the image forming apparatus according to the present embodiment are provided with the toner peeling member that comes into contact with the toner collecting developer carrier via the developer layer after collecting the toner after passing through the toner collecting region. Then, a bias voltage is applied to form an electric field in a direction that separates the toner from the toner collecting developer carrier. As a result, the uneven distribution of toner on the surface of the toner collecting developer carrying member can be eliminated, a reduction in collecting ability due to toner accumulation can be suppressed, and a high-quality image free from ghost problems can be obtained over a long period of time.

  Further, the contact of the toner peeling member (film member) with the developer is performed by the magnetic attraction force of the magnetic pole of the developer carrier for collecting the toner, thereby suppressing the decrease in the contact pressure due to the creep deformation of the film member. And the above effect can be stably maintained.

  The result of having carried out in order to confirm an effect using the developing device concerning the embodiment mentioned above is described.

  As the developing device used, a developing device having a configuration corresponding to the developing device 2 was prepared. However, the film member as the toner peeling member according to the present invention and the magnetic member for stabilizing the contact pressure of the film member (used in the examples) and the magnetic member not provided (comparative example) Used).

  As the image forming apparatus, a bizhub C350, which is an MFP manufactured by Konica Minolta Business Technologies, Ltd., was modified and used with the developing device 2 having the configuration shown in FIG. The developer for bizhub C350 was also used as the developer. The polarity of the toner was negatively charged, and the toner concentration of the developer was 8%.

  In each developing device, the development gap between the image carrier and the toner carrier was 0.15 mm. The toner supply gap between the toner carrier and the toner supply developer carrier, the toner collection gap between the toner carrier and the toner collection developer carrier, and the gap between the toner supply developer carrier and the regulating member are 0 respectively. .35 mm.

  The voltage applied to the toner carrier was a rectangular wave voltage with an amplitude of peak to peak of 1.4 kV, a DC component of −350 V, a frequency of 4 kHz, and a duty ratio of 50%.

  The voltage applied to the toner supply developer carrier was DC-550V, and the voltage applied to the toner recovery developer carrier was DC-200V.

  The background potential of the electrostatic latent image formed on the image bearing member was −550V, and the image portion potential was −60V.

  In the examples and comparative examples described later, the image chart shown in FIG. 2A is continuously printed using the above-described image forming apparatus, and the development history (ghost) occurrence state depending on the number of printed sheets is initially set. In addition, comparison was made after standing for one week in a high temperature and high humidity environment (50 ° C., 80% RH).

  In FIG. 2B, an output image 54 indicates an example in which a ghost is generated, and a region 54 thinner than the half image portion 53 is generated at a position after one cycle of the black solid portion 52. The occurrence of ghost was evaluated by measuring the density of the region 54 corresponding to the black solid portion 52 and the half image portion 53 corresponding to the white solid portion 51.

  The development history (ghost) was evaluated by a densitometer (X-Rite 310 manufactured by X-Rite). The density of the areas corresponding to the black solid part and the white part of the printed half-image part is measured. If the density difference is 0.05 or less, the density difference is more than 0.05 (particularly good), and the density difference exceeds 0.05. In the case of 1 or less, Δ (good), and x (occurrence) in other cases.

  Also, in order to check whether toner has accumulated on the surface of the developer carrying member for collecting toner based on the printing history, the developing device is taken out according to the number of printed sheets, and is not separated with the carrier, but is separated from the same pole portion (from N5 pole). The surface potential of the toner layer adhering to the surface was measured between the N3 poles).

  When measuring the surface potential, the surface potential meter Model 344 manufactured by TREK was used, and the measurement was performed with the developer carrying member for collecting toner grounded. In the evaluation, when the absolute value of the measured toner layer potential is 10 V or less, it is evaluated as ◯ (particularly good), when it exceeds 10 V and is equal to or less than 100 V, Δ (good), and x (defective) otherwise.

<Example>
Using the developing device shown in FIG. 1, a film member 41 as a toner peeling member is provided so as to face the magnetic pole S5 of the developer carrying member 26 for collecting toner.

As the film member, a film having a thickness of 80 μm, in which carbon was dispersed in PTFE to make a film resistance of 10 ⁴ Ω / □, was used.

  The voltage applied to the film member was a rectangular wave voltage with an amplitude of peak to peak of 1.4 kV, a DC component of 0 V, a frequency of 4 kHz, and a duty ratio of 50%.

  As a magnetic member for contacting the film member with a magnetic attractive force, magnetic particles were fixed to the film member as shown in FIG. Carrier particles were used as the magnetic particles.

<Comparative example>
In Comparative Example 1, the magnetic member was removed from the developing device of the example. Further, Comparative Example 2 has a configuration in which the toner peeling member itself is removed from the developing device.

(Evaluation results)
Table 1 shows the evaluation results of Examples, Comparative Example 1, and Comparative Example 2.

  Table 1 shows the results after the initial stage and after leaving in a high-temperature and high-humidity environment.

  In the table, the presence and absence of the magnetic member of Example and Comparative Example 1 indicate the presence or absence of the magnetic member provided on the back surface of the film member as the toner peeling member described above (Comparative Example 2 has the toner peeling member itself). do not do).

  The “development history” is an evaluation based on the above criteria for determining the ghost occurrence status, and is evaluated for each number of printed sheets from the first sheet to the 1000th sheet.

  The “toner layer potential” is an evaluation based on the result of measuring the surface potential between the N3 and N5 poles on the surface of the developer carrying member for collecting toner, based on the above-mentioned criteria. It is evaluated by each number of printed sheets up to.

  As shown in Table 1, in the initial evaluation, the effect of the toner peeling member (film member) is obtained in both Example and Comparative Example 1 as compared with Comparative Example 2 without the toner peeling member. However, after leaving in a high temperature and high humidity environment, the effect of the toner peeling member differs between the example and the comparative example 1 depending on the presence or absence of the magnetic member.

  When the respective toner release members (film members) were removed after the evaluation of leaving in a high-temperature and high-humidity environment, creep deformation was generated in the curved shape of each film member. It was confirmed that toner adhered to the developer contact surface.

  From the above, it can be seen that by providing the magnetic member, the contact pressure of the toner peeling member (film member) can be secured even when creep deformation of the film member occurs.

  That is, in the developing device according to the present invention in which the toner peeling member is brought into contact with the magnetic attraction force, even when the film member is subjected to creep deformation due to leaving in a high temperature and high humidity environment, the surface of the toner carrying developer carrier Therefore, it is possible to maintain a state in which the amount of toner adhering to the surface of the toner carrying member is almost zero, thereby stabilizing the resetting property of the development residual toner on the toner carrier, and stably outputting a good image.

  As described above, the developing device and the image forming apparatus according to the present embodiment are provided with the toner peeling member that comes into contact with the toner collecting developer carrier via the developer layer after collecting the toner after passing through the toner collecting region. Then, a bias voltage is applied to form an electric field in a direction that separates the toner from the toner collecting developer carrier.

  As a result, even if toner is unevenly distributed and adhered to the surface of the toner collecting developer carrier due to the toner collecting electric field in the toner collecting region between the toner carrying member and the toner collecting developer carrier, the toner peeling member (film member) The toner can be peeled off, and the toner collection from the toner carrying member to the toner collecting developer carrying member can be stabilized.

  Further, since the toner peeling member (film member) is brought into contact with the developer by a magnetic attraction force, even when a flexible toner peeling member (film member) is used, the toner is left by being left in a high temperature and high humidity environment. It can suppress that a contact pressure falls by creep deformation of a peeling member (film member). In addition, it is possible to ensure both a wide contact nip width and a stable contact pressure due to the flexibility of the film.

  Therefore, the resetting property of the development residual toner on the toner carrier can be stably maintained, and stable and good image output without being affected by the development history can be achieved.

  In other words, the toner collection developer carrying member reliably collects the development residual toner on the toner carrying member, and a stable toner layer is always supplied onto the toner carrying member. As a result, it is possible to obtain a high-quality image over a long period of time, in which the toner recovery capability is maintained and the ghost problem does not occur.

  In addition, the above-mentioned embodiment is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

1 is a cross-sectional view illustrating a configuration example of a main part of a developing device 2 and an image forming apparatus including the same according to an embodiment of the present invention. (A) It is a figure which shows the chart for image development history evaluation. In addition, (b) an example of a ghost occurrence state during printing is shown. FIG. 5 is a diagram illustrating a relationship between a bias voltage applied to a toner supply developer carrier, a toner carrier, a toner collection developer carrier, and a toner layer potential accompanying toner accumulation. FIG. 4 is a cross-sectional view showing a state of rising of a developer by a magnetic pole of a toner carrier for collecting toner and a state of movement of toner in an electric field direction in a toner collecting area. FIG. 6 is a diagram illustrating a relationship between a toner supply developer carrier, a toner carrier, a bias voltage applied to a toner collection developer carrier, and a toner layer potential accompanying toner accumulation when toner is accumulated. . FIG. 6 is a diagram illustrating a relationship 1 regarding each bias voltage and a toner layer potential when a toner peeling member (film member) 41 is provided. FIG. 6 is a diagram showing a relationship 2 regarding each bias voltage and a toner layer potential when a toner peeling member (film member) 41 is provided. FIG. 6 is a diagram for explaining a toner layer adhesion state on a toner peeling member (film member). It is the figure which extracted and showed the principal part of FIG. FIG. 6 is a diagram illustrating a change in a toner layer on each member by passing through a toner supply region. FIG. 6 is a diagram illustrating a change in a toner layer on each member by passing through a development area. FIG. 6 is a diagram illustrating a change in a toner layer on each member due to passage through a toner recovery area. FIG. 6 is a diagram illustrating a change in a toner layer on each member by passing through a toner peeling area 29. 4 is an enlarged view showing a contact portion of a toner peeling member (film member) 41. FIG. FIG. 4 is a diagram illustrating an example in which a magnetic member of a toner peeling member (film member) 41 is a discontinuous body (magnetic particle).

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Development apparatus 3 Charging member 4 Exposure apparatus 5 Transfer roller 6 Cleaning blade 7 Toner supply area 8 Development area 9 Toner collection area 11 Toner supply developer carrier 12 Sleeve roller 13 Magnet body 16 Developer tank 24 Development Agent 25 Toner carrier 26 Toner recovery developer carrier 27 Sleeve roller 28 Magnet body 29 Toner peeling area 41 Toner peeling member (film member)
42 Holding electrode 43 Magnetic member

Claims (8)

A developer tank containing a developer including toner and a carrier;
A developer carrying member for supplying toner that carries the developer mixed and stirred in the developer tank to the surface; and
A toner carrier that receives and supplies the toner from the toner supply developer carrier and develops a latent image on the image carrier;
A toner collecting developer carrying member for collecting undeveloped toner from the toner carrying member,
A toner peeling member that comes into contact with the toner collecting developer carrier through the toner collected developer layer on the toner collecting developer carrier;
A power source for applying a bias voltage to the toner peeling member for forming an electric field in a direction to separate the toner in the developer layer from the toner collecting developer carrier.
The developing device according to claim 1, wherein the toner peeling member abuts on the toner collecting developer carrying member by a magnetic attractive force of a magnetic pole of the toner collecting developer carrying member. The developing device according to claim 1, wherein the toner peeling member is a film member. The developing device according to claim 2, wherein the toner peeling member is provided with a magnetic member on a back side of the film member. The developing device according to claim 3, wherein the magnetic member is a discontinuous body. The developing device according to claim 3, wherein the magnetic member has flexibility. The developing device according to claim 2, wherein the film member includes magnetic particles dispersed therein. The developing device according to claim 1, wherein the toner peeling member is disposed at a position facing a magnetic pole of the toner collecting developer carrier. An image forming apparatus comprising the developing device according to claim 1.

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