JP2011022307A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device in which occurrence of history of development is suppressed regardless of repeated image formation, and to provide an image forming apparatus using the developing device. <P>SOLUTION: The developing device includes: a toner attracting member in contact with a developer on a developer carrier; and a power source for applying a bias voltage for forming an electric field in the direction where toner in the developer is attracted to the toner attracting member between the developer carrier and toner attracting member, to the toner attracting member. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention uses a hybrid developing device that forms a toner layer on a toner carrier using a developer containing a carrier and toner, and develops a latent image on the image carrier using the formed toner layer, and the same. The present invention relates to an image forming apparatus.

  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.

  In the one-component development method, the toner is generally charged by passing the toner through a regulating portion formed by a toner carrier and a regulation plate pressed against the toner carrier, and a desired toner thin layer can be obtained. Therefore, it is advantageous in terms of simplification, miniaturization, and cost reduction of the apparatus. On the other hand, the deterioration of the toner is likely to be promoted due to the strong stress of the regulating portion, and the charge acceptability of the toner is likely to be lowered. Further, since the regulating member that is a charge imparting member to the toner and the surface of the toner carrier are contaminated with the toner and the external additive, the charge imparting property to the toner is also lowered, so that the toner charge amount is further lowered and the fogging is caused. The life of the developing device is short.

  On the other hand, in the two-component development method, since the toner is charged by frictional charging by mixing with the carrier, the stress applied to the carrier surface is small, and the carrier surface area is large, so that the toner is relatively resistant to contamination by toner and external additives. It is strong and advantageous for extending the life of the developer. 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 formed by the developer, so that a magnetic brush mark is generated on the developed image. Have the problem of doing. 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, as a general problem of the hybrid development system, there is a phenomenon 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 a bias for supplying toner from the developer carrier to the toner carrier is applied to the opposite portion (toner supply and recovery region) between the developer carrier and the toner carrier that supplies toner to the toner carrier. However, since the operation of collecting the development residual toner on the toner carrier onto the developer carrier is also performed at the same opposing portion, the bias in the toner supply direction at the opposing portion is Recovery is hindered and recovery capability is insufficient. Therefore, there is a difference between the portion with a large amount of residual toner on the toner carrier and the portion with a small amount of toner even after the toner is supplied to the toner carrier, and in the next development process, it appears as a density difference on the image and a development history is generated. .

  In order to solve this problem, in Patent Document 2, a developer carrying body that supplies toner to a toner carrying body and a developer carrying body that collects development residual toner on the toner carrying body are separately arranged, and each development is performed. There has been proposed a method for reliably collecting the development residual toner on the toner carrier by setting the bias applied to the agent carrier in the toner supply direction and the collection direction.

JP-A-5-150636 JP-A-10-319708

  However, in the method of Patent Document 2, a development history is not initially generated, but there is a problem that a development history is generated while image formation is repeated. As a result of intensive studies on this problem, the following was found. Due to the toner recovery voltage applied to the developer carrying member for collecting toner, the residual toner developed from the toner carrying member and the toner separated from the carrier in the developer are carried by the developer carrying toner. It moves to the vicinity of the surface of the body and accumulates as a toner layer while repeating image formation. Since the accumulated toner is charged, the electric field in the collecting direction is weakened in the toner collecting area (the area in which the development residual toner on the toner carrying body is collected by the collecting developer carrying body), and the toner collecting ability Will go down. For this reason, it was found that the recovery capability that was initially sufficient does not last for a long period of time, and development history (ghost) occurs with repeated image formation, which is a problem. In addition, since two developer carriers are used, there is a problem that the developing device becomes large.

  Therefore, in view of the above problems, an object of the present invention is to provide a developing device that suppresses the development history even when image formation is repeated, and an image forming device using the developing device.

  The problems of the present invention can be solved by the following means.

1. A toner carrier for carrying and conveying toner on the surface and developing a latent image on the image carrier;
A developer containing the toner and a carrier is carried and conveyed on the surface, the toner is supplied from the developer to the toner carrier in a region facing the toner carrier, and the toner carrier after development A developer carrying member for collecting the toner from the surface of
A developing device comprising:
A toner attracting member in contact with the developer on the developer carrier on the upstream side in the transport direction of the developer in the facing region;
A power source for applying a bias voltage to the toner attracting member for forming an electric field in a direction to attract the toner contained in the developer between the developer attracting member and the toner attracting member; And a developing device.

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

3. A regulating member for regulating the amount of the developer on the surface of the developer carrying member;
A power source for applying a bias voltage to the regulating member for forming an electric field in a direction in which the toner in the developer is attracted to the regulating member between the developer carrying member and the regulating member. 3. The developing device as described in 1 or 2 above.

4). The developer carrier has a fixed magnetic pole inside,
4. The developing device according to any one of 1 to 3, wherein the toner attracting member is disposed at a position facing the fixed magnetic pole.

5. The developer carrier has a fixed magnetic pole inside,
The toner attracting member is disposed at a position facing between the magnetic pole at a position where the developer carrying body and the toner carrying body face each other and a magnetic pole adjacent to the magnetic pole. 4. The developing device according to any one of 3 above.

  6). An image forming apparatus comprising: an image carrier; and the developing device according to any one of 1 to 5 for developing a latent image on the image carrier.

  According to the developing device of the present invention, the toner attracting member is brought into contact with the developer on the developer carrying member for supplying the toner, and the voltage for attracting the toner to the toner attracting member from the developer carrying member to the toner attracting member side. Is applied, the toner in the developer is unevenly distributed on the surface of the developer, and the uneven distribution of the toner can improve the toner supply performance in the toner supply / recovery region facing the toner carrier. Since the toner supply performance is improved, the toner supply bias applied to the developer carrying member can be lowered. When the toner supply bias is reduced, the recovery performance of the development residual toner in the toner supply / recovery area is improved. Therefore, it is possible to provide a developing device that can obtain a stable and good image that is not affected by the development history, and an image forming apparatus that uses the developing device.

1 is a schematic cross-sectional view of an image forming apparatus used in the present embodiment. It is the schematic which shows the structure of the image development apparatus in case a magnet roller has 5 poles. 5 is an image chart and a print image for explaining a development history (ghost). FIG. 6 is an enlarged view of a facing portion when a developer carrying member and a toner carrying member are rotated in the same direction. FIG. 6 is a diagram illustrating a change in a value obtained by measuring a potential of a toner layer on a toner carrying member between a toner supply region and a developing region after passing through a toner supply region for each number of times of passing through the toner supply region when no toner attracting member is provided. FIG. 4 is a cross-sectional view schematically showing a state of a developer on a sleeve of a developer carrying member and a state of toner movement in an electric field direction before and after passing through a toner attracting member. FIG. 6 is a diagram illustrating a change in a value obtained by measuring a potential of a toner layer on a toner carrying member between a toner supply region and a development region after passing through the toner supply region for each number of times of passing through the toner supply region when a toner attracting member is provided. FIG. 6 is a diagram schematically showing a difference in relationship between a toner supply potential difference (Vb2−Vb1) and a toner supply amount to a toner carrier with and without a toner attracting member. FIG. 6 is a diagram schematically showing a state of a contact nip portion between a toner attracting member and a developer on a developer carrying sleeve. It is an enlarged view which shows the state which the film member which provided the magnetic member in contact with the developer on the back. It is an enlarged view which shows the state which the film member which provided the discontinuous magnetic member which consists of a plurality on the back is contacting the developer. It is an enlarged view which shows the state which the film member which provided the lining member on the back is in contact with the developer. It is an enlarged view which shows the state which the film member which made the loop shape by fixing both ends contact | abutted with the developing agent.

An embodiment of the present invention will be described 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. This image forming apparatus is a printer that performs image formation by transferring a toner image formed on an image carrier (photoconductor) 1 to a transfer medium P such as paper by an electrophotographic method. This image forming apparatus has an image carrier 1 for carrying an image, and a charging member 3 as a charging unit for charging the image carrier 1 and an image carrier around the image carrier 1. A developing device 2 that develops an electrostatic latent image on the image 1, a transfer roller 4 for transferring a toner image on the image carrier 1 to a transfer medium P, and a cleaning blade 5 for removing residual toner on the image carrier 1 Are arranged in order along the rotation direction A of the image carrier 1.

  The image carrier 1 is charged by the charging member 3 and then exposed by an exposure device 6 equipped with a laser emitter or the like at the position E in the figure, and an electrostatic latent image is formed on the surface thereof. . The developing device 2 develops the electrostatic latent image into a toner image. The transfer roller 4 transfers the toner image on the image carrier 1 to the transfer medium P, and then discharges it in the direction of arrow C in the figure. The cleaning blade 5 removes the residual toner on the image carrier 1 after the transfer with its mechanical force. The image carrier 1, the charging member 3, the exposure device 6, the transfer roller 4, the cleaning blade 5 and the like used in the image forming apparatus may arbitrarily use a known electrophotographic technique. For example, although a charging roller is shown in the drawing as the charging means, 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.

  The developing device 2 includes a developer 23 containing a carrier and toner, a developer tank 17 for storing the developer 23, a developer carrier 13 for carrying and transporting the developer 23 supplied from the developer tank 17 on the surface, A toner carrier 24 that is disposed opposite to the agent carrier 13, is supplied with only toner from the developer carrier 13 in the supply region 9, and develops the electrostatic latent image formed on the image carrier 1. It becomes. Further, a regulating member 16 for regulating the amount of developer carried and conveyed on the surface of the developer carrying body 13, and the developer carrying body 13 that is regulated by the regulating member 16 and reaches the supply region 9. A toner attracting member 41 for contacting the upper developer and attracting toner in the developer to the vicinity of the surface of the developer layer is provided.

Further, the developing device 2 includes a toner carrier bias power source 31 that supplies a developing bias voltage Vb2 to the toner carrier 24, a developer carrier bias power source 32 that supplies a toner supply bias voltage Vb1 to the developer carrier 13, A toner attracting bias power source 33 that supplies the toner attracting bias voltage Vb3 to the toner attracting member 41 is provided.
(Developer composition)
The developer 23 used in the present embodiment includes toner and a carrier for charging the toner.

<toner>
The toner is not particularly limited, and a commonly used known toner can be used. The binder resin contains a colorant or, if necessary, a charge control agent or a release agent, and is added externally. 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 manufacturing such a toner, it can be manufactured by a publicly known method, for example, 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.

  Further, as the colorant, known ones that are generally used 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, or the like can be used, and it is generally preferable to use 2 to 20 parts by mass with respect to 100 parts by mass of the binder resin.

  Moreover, as a charge control agent, a well-known thing can be used. Examples of charge control agents for positively chargeable toners include nigrosine dyes, quaternary ammonium salt compounds, triphenylmethane compounds, imidazole compounds, and polyamine resins. Examples of charge control agents for negatively chargeable toners include metal-containing azo dyes such as Cr, Co, Al, and Fe, salicylic acid metal compounds, alkylsalicylic acid metal compounds, and calixarene compounds. In general, the charge control agent is preferably used at a ratio of 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin.

  Moreover, as a mold release agent, the well-known thing 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 kinds, and generally used at a ratio of 0.1 to 10 parts by mass with respect to 100 parts by mass of the binder resin. Is preferred.

  In addition, as the external additive, publicly known publicly known materials can be used, and as an external additive (fluidizing agent) for improving fluidity, for example, inorganic materials such as silica, titanium oxide, and aluminum oxide are used. Fine particles and resin fine particles such as acrylic resin, styrene resin, silicone resin, and fluororesin can be used, and it is particularly preferable to use one that has been hydrophobized with a silane coupling agent, a titanium coupling agent, silicon oil, or the like. Such a fluidizing agent is added at a ratio of 0.1 to 5 parts by mass with respect to 100 parts by mass of the toner. The number average primary particle size of the external additive is preferably 10 to 100 nm.

  Further, as the external additive, particles having the opposite polarity to the toner (reverse polarity particles) may be used. The reverse polarity particles preferably used are appropriately selected depending on the charging polarity of the toner. For example, when the toner is negatively charged by the carrier, the opposite polarity particles are positively charged particles that are positively charged in the developer. Also, for example, when the toner is positively charged by the carrier, the reverse polarity particles are negatively charged particles that are negatively charged in the developer. By incorporating reverse polarity particles in a two-component developer and accumulating reverse polarity particles in the developer with durability, the chargeability of the carrier is reduced due to the spent of the toner or post-treatment agent on the carrier. However, since the reverse polarity particles can charge the toner to the normal polarity, the chargeability of the carrier can be effectively compensated, and as a result, the deterioration of the carrier can be suppressed. When a negatively chargeable toner is used as the toner, fine particles having positive chargeability are used as the reverse polarity particles. For example, inorganic fine particles such as strontium titanate, barium titanate, and alumina, acrylic resin, benzoguanamine resin, and nylon resin are used. Fine particles composed of thermoplastic resin such as polyimide resin and polyamide resin or thermosetting resin can be used, and a positive charge control agent imparting positive charge property can be contained in the resin, or a nitrogen-containing monomer You may make it comprise the copolymer of these. Here, as the positive charge control agent, for example, a nigrosine dye, a quaternary ammonium salt, or the like can be used, and as the nitrogen-containing monomer, 2-dimethylaminoethyl acrylate, 2-acrylic acid 2- Diethylaminoethyl, 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 thermoplastic resins such as thermoplastic resins or thermosetting resins can be used, and a negative charge control agent that imparts negative chargeability to the resin can be contained, or fluorine-containing acrylic monomers and fluorine-containing methacrylates can be used. You may make it comprise the copolymer of a system monomer. Here, as said negative charge control agent, a salicylic acid type, a naphthol type chromium complex, an aluminum complex, an iron complex, a zinc complex etc. can be used, for example.

  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 parts by mass with respect to 100 parts by mass of toner.

<Career>
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. Although it is not limited to this as a carrier particle size, 15-100 micrometers is preferable.

  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. Charging characteristics such as 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 for 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 in an amount of 50 to 90% by mass in the magnetic resin carrier.

  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 can be fixed to the surface of the binder type carrier by, for example, mixing the magnetic resin carrier and the fine particles uniformly and adhering the fine particles to the surface of the magnetic resin carrier. 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 copolymers, acrylic resins, 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, a surface treatment or 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, similarly to a binder-type carrier, positive or negatively chargeable fine particles are fixed to the carrier surface. 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 toner ratio is 3 to 50% by mass, preferably 6 to 30% by mass with respect to the total amount of the toner and the carrier. ing.
(Configuration of developing device)
FIG. 1 is a schematic view of a cross section of the image forming apparatus used in this embodiment.

  A configuration example and an operation example of a developing device used in the present embodiment will be described with reference to FIG.

  The developer tank 17 is formed by a casing 20, and normally contains mixing and agitating members 18 and 19 for mixing and agitating the developer therein and supplying the developer to the developer carrier 13.

  An ATDC sensor 21 for detecting the toner concentration is preferably disposed at a position of the casing 20 facing the mixing and agitating member 19.

  The developing device 2 normally has a replenishing unit 15 for replenishing the developer tank 17 with toner that is consumed by the image carrier 1. In the replenishment unit 15, replenishment toner 22 sent from a hopper (not shown) that stores replenishment toner is replenished into the developer tank 17.

  The developing device 2 also has a regulating member 16 for thinning the developer for regulating the amount of developer on the developer carrying member 13. The developer carrier 13 is usually composed of a fixedly arranged magnet roller 26 and a rotatable sleeve roller 27 containing the magnet roller 26, and a toner supply bias for supplying toner to the toner carrier 24 during image formation. Vb1 is applied by the developer carrier bias power source 32. The sleeve roller 27 may have various coatings on its surface. The magnet roller 26 has a plurality of magnetic poles.

  FIG. 2 is a schematic diagram showing the configuration of the developing device in the case where the magnet roller has five poles as an example. Among these magnetic poles, the main magnetic pole N1 is a facing portion facing the toner carrier 24 (toner supply / recovery area: toner supply / recovery area, the toner carrier rotation direction upstream side of the toner carrier rotation direction, and the downstream side of toner recovery area. (Referred to as region 9).

  Further, magnetic poles S <b> 2 and S <b> 3 having the same polarity that generate a repulsive magnetic field for separating the developer 23 on the sleeve roller 26 are disposed at positions facing the inside of the developer tank 17.

  Between the regulating member 16 and the toner supply area 8, the toner attracting member 41 is opposed to the developer carrier 24 in order to make the toner unevenly distributed near the surface of the developer layer conveyed to the toner supply area 8. Is provided. 1 and 2 exemplify a film member as the toner attracting member, but the shape is not limited to this as long as it is a conductive member capable of applying a bias. For example, a plate member, a rotating member such as a roller or a brush, a wire It may be a shaped member. As shown in FIGS. 1 and 2, when the toner attracting member 41 is a film member, a toner peeling bias Vb4 is applied by a power source 34 via a holding electrode 42 that holds the film member in the longitudinal direction.

  In addition, it is desirable that a separate measure is provided so that the toner attracting member (film member) 41 contacts the developer 24 layer with a stable pressure. When the contact pressure is weakened, the toner attracted to the toner attracting member 41 is not scraped off by the developer 24 and accumulates, and the attracting electric field to the toner attracting member 41 may be weakened. A method for stabilizing the contact force is not particularly limited. For example, a member that reinforces the stiffness of the film may be provided on the back side of the surface where the toner attracting member 41 contacts the developer. Further, a magnetic member 43 may be provided, and a force that attracts the magnetic member 43 by a magnetic pole disposed inside the developer carrier 24 may be used. Further, the stiffness of the film may be increased by fixing the free end of the film to form a loop. By these measures, the film-like toner attracting member can come into contact with the layer of the developer 24 with a stable pressure.

  The toner carrier 24 is disposed so as to face the developer carrier 13 and the image carrier 1, and a developing bias Vb2 for developing the electrostatic latent image on the image carrier 1 is a bias power source for the toner carrier. 31 is applied.

The toner carrier 24 may be made of any material as long as the voltage can be applied. 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, polysulfone 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.
(Developer operation)
The operation of the developing device 2 shown in FIG. 1 will be described in detail. The developer 23 in the developer tank 17 is mixed and agitated by the rotation of the mixing and agitating members 18 and 19 and is frictionally charged. At the same time, the developer 23 is circulated and conveyed in the developer tank and supplied to the sleeve roller 27 on the surface of the developer carrier 13. Is done.

  The developer 23 is held on the surface side of the sleeve roller 27 by the magnetic force of the magnet roller 26 inside the developer carrier 13, and is rotated together with the sleeve roller 27 so as to face the developer carrier. 16, the passing amount is regulated.

  Next, the developer 23 is conveyed to the toner attracting member 41, and an electric field formed based on a potential difference between the toner supply bias Vb2 applied to the developer carrying member 13 and the toner attracting bias Vb3 applied to the toner attracting member 41 is as follows. The toner in the developer 23 is moved to the vicinity of the surface of the developer 23 and is unevenly distributed.

  Thereafter, the developer is conveyed to the toner supply region 8 facing the toner carrier 24. In the toner supply region 8, the developer spike is formed by the magnetic force of the main magnetic pole N <b> 1 of the magnet roller 26, but the toner concentration at the tip of the spike is high due to the effect of the toner attracting member 41. In FIG. 2, the installation position of the toner attracting member 41 faces the magnetic pole S <b> 1 in front of the main magnetic pole N <b> 1 of the magnet roller 26. In this case, since an electric field is formed at the developer spike, the toner can be unevenly distributed.

  On the other hand, the installation position of the toner attracting member 41 is not limited to this, and may be installed between the poles of the magnetic poles N1 and S1, for example. In this case, since the uneven distribution of toner is generated at a position close to the toner supply unit, there is an advantage that it is easy to maintain a state where the toner concentration at the tip end portion is high.

  In addition, a power supply for applying a bias voltage to the regulating member 16 for forming an electric field in a direction to attract the toner in the developer to the regulating member 16 side between the developer carrier 13 and the regulating member 16 may be provided. preferable. In this way, in addition to the toner attracting member 41, the regulating member 16 can also cause the toner to be more unevenly distributed on the surface of the developer on the developer carrier 13. The uneven distribution of toner can be increased more stably.

  The toner that is unevenly distributed at the tip end of the spike is caused by the electric field formed based on the potential difference between the developing bias Vb2 applied to the toner carrier 24 and the toner supply bias Vb1 applied to the developer carrier 13 to the toner carrier 24 side. Supplied to. Normally, the toner supply bias Vb1 applied to the developer carrier 13 is applied with only a DC voltage or a bias obtained by superimposing an AC voltage on the DC voltage, and a DC electric field, Alternatively, an electric field in which an alternating electric field is superimposed on a DC electric field is formed.

  At this time, the toner supply bias Vb1 for obtaining a desired supply amount is set lower because the toner concentration at the tip of the developer spike in the toner supply region 8 is higher than when the toner attracting member 41 is not provided. can do.

  The toner layer supplied to the toner carrier 24 is conveyed to the development region 7 as the toner carrier 24 rotates, and is generated by a development electric field formed by the development bias Vb2 and the latent image potential on the image carrier 1. The latent image is developed into a visible image. Various known biases can be applied as the developing bias Vb2, but normally a bias obtained by superimposing an AC voltage on a DC voltage is applied.

  The development method may be a reversal development method or a regular development method.

  The toner layer (development residual toner) remaining on the toner carrier 24 after the toner is consumed in the development region 7 is further conveyed to the toner collection region 9 facing the developer carrier 13 by the rotation of the toner carrier 24. Is done. In the toner collection area 9, the development residual toner is collected by the mechanical and electrical toner collection action by the developer on the developer carrier 13.

  At this time, as will be described in detail later, in the toner recovery area 9, the toner supply bias Vb1 acts in the direction of inhibiting the recovery. Accordingly, the potential difference between the toner supply bias Vb1 and the development bias Vb2 can be reduced as compared with the case where the toner attracting member 41 is not provided, so that the recovery of the development residual toner to the developer carrier 13 side in the toner recovery region 9 is further promoted. Is done.

  Here, in FIG. 1, the rotation directions of the developer carrier 13 and the toner carrier 24 are set in the same direction, but they can be set in the reverse direction.

  In the hybrid development system, it is possible to collect development residual toner as much as possible, and reduce the density of the developed and undeveloped portions of the toner as much as possible, and then supply the next toner to reduce development history (ghost). It is important to suppress.

  In the opposite portion (toner supply / recovery region) between the developer carrier 13 and the toner carrier 24, first, the toner in the developer 23 on the developer carrier 13 is supplied to the toner carrier 24 in the toner supply region 8. The Therefore, the toner density of the developer 23 that has moved to the toner recovery area 9 decreases, and a counter charge occurs in the carrier in the developer 23. By this counter charge, the development residual toner is electrically collected by the developer 23 on the developer carrier 13 in the toner collection area 9.

  Further, when the rotation directions of the developer carrier 13 and the toner carrier 24 are set to the same direction as shown in FIG. 1, the opposing portions of the developer carrier 13 and the toner carrier 24 rotate in the counter direction. Therefore, the relative speed increases, and mechanical recovery by the developer 23 having a low toner density on the developer carrier 13 (the contact probability between the developer on the developer carrier 13 and the development residual toner increases, And is collected by frictional charging with the carrier. Therefore, setting the rotation direction of the developer carrier and the toner carrier to a counter is advantageous from the viewpoint of collecting the development residual toner, and is preferable because it leads to suppression of development history (ghost).

  Note that the toner supply region 8 and the toner recovery region 9 in the facing portion (toner supply / recovery region) of the developer carrier 13 and the toner carrier 24 are not clearly distinguishable. The toner is supplied mainly in the toner supply area 8 on the upstream side in the rotation direction of the developer carrier 13 of the opposing portion, and the toner is recovered mainly in the toner collection area 9 on the downstream side of the rotation direction of the developer carrier 13 in the opposite portion. In fact, it is thought that both supply and recovery are mixed.

The developer on the developer carrier 13 that has passed through the toner collection area 9 is conveyed toward the developer tank 17 as the sleeve rotates, and the repulsion provided at a position corresponding to the developer collection area 14 of the magnet roller 26. It is peeled from the developer carrier 13 by the same-polarity portions S2 and S3 that generate a magnetic field, and is collected into the developer tank 17. When a supply control unit (not shown) provided in the supply unit 15 detects from the output value of the ATDC sensor 21 that the toner concentration in the developer 23 has become equal to or lower than the minimum toner concentration for ensuring image density, it is not shown. The replenishing toner 22 stored in the hopper by the toner replenishing means is supplied into the developer tank 17 through the toner replenishing section 15.
(Recovery performance in the toner recovery area and effect of the toner attracting member)
The toner collection performance in the toner collection area 9 and the effect of the toner attracting member 41 will be described in detail.

  First, the development history (ghost) will be described, and then the toner supply, recovery capability and bias setting by the developer carrier will be described.

<About development history>
The development history (ghost) will be described with reference to FIG.

  FIG. 3A is an example of an image chart used for detecting a ghost. A solid image area 52 and a halftone image area 53 are arranged as shown in the figure on a white background 51 which is a background area. FIG. 3B 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 (ghost) is the following phenomenon.

  As shown in the image chart of FIG. 3A, after printing a high-contrast image (high-contrast image) in which the solid image area 52 is arranged on the white background 51, a halftone image area that is a halftone image such as gray An image pattern followed by 53 is printed. Then, in the output print image, as shown in FIG. 3B, a pattern of a high-contrast image printed on the upstream side that did not exist in the original image chart appears in the halftone image area 53. . In FIG. 3B, a ghost pattern 54, which is a development history, is seen in the halftone image area 53 that is printed one cycle after the toner carrier of the solid image area 52. That is, assuming that the circumferential speed v1 of the image carrier 1, the circumferential length L of the toner carrier 24, and the circumferential speed v2 of the toner carrier 24 in the rotation direction of FIG. 1, the toner carrier cycle T = L × v1 / v2. A ghost appears at the position.

  Such a phenomenon is caused by the following.

  On the toner carrier immediately after developing the latent image corresponding to the high-contrast image, a portion of the toner image corresponding to the print image pattern that hardly consumed toner remains as a development residual toner layer. For this reason, in the toner collection area 9, the development residual toner is not sufficiently collected and remains in a pattern, and when toner is supplied in the toner supply area 8, a printed image pattern is formed on the toner carrier. Accordingly, uneven thickness of the toner layer occurs.

  When the latent image is developed with the toner carrier having the uneven thickness of the toner layer, the development characteristics change due to the uneven thickness of the toner layer occurs, and the uneven density corresponding to the pattern printed in advance on the next printed image. (Ghost) is generated. The density unevenness due to the development characteristic change is particularly noticeable and conspicuous in the halftone image area after the high contrast 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 developer carrier>
The toner supply, recovery capability and bias setting by the developer carrier 13 will be described with reference to FIG. 4 taking the case where the toner attracting member 41 is not provided as an example.

  Each bias voltage applied to each of the developer carrier 13 and the toner carrier 24 may be a DC voltage or a voltage obtained by superimposing an AC voltage on a DC voltage. An explanation will be given using the average value of the 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 averaged value (the same applies hereinafter).

  FIG. 4 is an enlarged view of the facing portion when the developer carrier 13 and the toner carrier 24 are rotated in the same direction. In this case, the opposing portions of the developer carrier 13 and the toner carrier 24 rotate in the counter direction. In order to supply toner from the developer on the developer carrier 13 to the toner carrier 24, a potential difference (Vb2-Vb1: also referred to as toner supply potential difference) is set between the developer carrier 13 and the toner carrier 24. Has been.

  In the toner supply region 8, the amount of toner supplied from the developer carrier 13 to the toner carrier 24 depends on the magnitude of the toner supply potential difference (Vb2-Vb1). Due to the influence of the counter charge generated on the carrier in the developer 23 later, it is possible to supply an amount of toner sufficient to fill in all potential differences with one toner supply (only after passing the toner supply region 8 once). Can not. This is because in the toner supply region 8, the toner at the tip portion of the developer head tends to move away from the carrier to the toner carrier 24 due to the toner supply potential difference (Vb 2 −Vb 1). It is considered that some toner is generated because the toner is pulled back to the carrier side due to the counter charge generated at the time.

  FIG. 5 shows a case where a solid image of one rotation of the toner carrier 24 is developed and an image in which a plurality of white background portions of the toner carrier 24 are continuously developed passes through the toner supply region 8 and reaches the development region 7. FIG. 6 is a diagram showing values obtained by measuring the potential of the toner layer on the toner carrier 24 during each interval for each number of passages (toner supply times) that have passed through the toner supply region 8.

  The potential Vtd of the toner layer is a value obtained by measuring the potential Vtd of the toner layer on the developer carrier 13 by setting a probe of a surface potentiometer (Model 344 manufactured by TREK) between the toner supply region 8 and the development region 7. is there.

  Thus, the potential of the toner layer on the toner carrier 24 after developing the solid image approaches the value of the toner supply potential difference (Vb2−Vb1) every time the toner supply region 8 is passed. Since the toner layer potential Vtd and the thickness of the toner layer are in a substantially proportional relationship, the amount of toner consumed in the solid image cannot be supplied by one toner supply in the toner supply region 8, and the desired amount of toner can be supplied. It can be seen that the toner layer thickness cannot be formed on the surface of the toner carrier 24.

  On the other hand, in the toner collection area 9, the undeveloped toner 50 on the toner carrier 24 has a mechanical rubbing force by the developer 23 on the sleeve 27 of the developer carrier 13 and a counter possessed by the carrier after toner supply. In response to an electrical attraction force due to charging, a force (a force in the collecting direction) collected on the developer carrier 13 side is received. However, there is a toner supply potential difference (Vb2-Vb1) between the developer carrier 13 and the toner carrier 24, and the toner layer potential due to the remaining toner 50 (potential acting in the direction of decreasing the toner supply potential difference) is taken into consideration. Even so, an electric field in the direction (supply direction) that impedes recovery to the developer carrier 13 acts on the remaining toner 50. Due to the electric field in the direction that inhibits the collection (supply direction), the force in the toner collection direction in the toner collection area 9 is reduced. For this reason, the undeveloped toner 50 cannot be sufficiently collected, and the remaining toner 50 moves to the toner supply area 8 and is supplied with toner.

  That is, in the development area 7, the development residual toner on the toner carrier 24 corresponding to the white background is transported to the toner collection area 9 in a state where almost no toner is consumed. Since the force is reduced, the undeveloped toner is conveyed to the toner supply area 8 in a state where the toner is not sufficiently collected. On the other hand, since the development residual toner on the toner carrier 24 corresponding to the solid image portion is almost consumed in the development area 7, even if it is not sufficiently collected in the toner collection area 9, there is almost no toner layer. The toner is conveyed to the toner supply area 8.

  Therefore, toner is supplied from the toner supply region 8 in a state where the thickness of the toner layer on the toner carrier 24 is different between the portion corresponding to the solid image portion and the portion corresponding to the white background portion. However, as shown in FIG. 5, the toner amount sufficient to fill the toner supply potential difference (Vb2−Vb1) cannot be supplied only by passing the toner supply region 8 once, and the difference in the toner layer thickness remains. In this state, the toner is conveyed to the developing area 7 and developed. In the development process, if the toner layer thickness on the toner carrier 24 is different, it appears as a density difference on the image and a development history (ghost) occurs.

<Effect of toner attracting member>
Next, a case where a toner attracting member is arranged will be described.

  FIG. 6 is a cross-sectional view schematically showing the state of the developer on the sleeve 27 of the developer carrying member and the state of toner movement in the electric field direction before and after passing through the toner attracting member 41. A toner attracting bias Vb3 is applied to the toner attracting member 41.

  FIG. 6A schematically shows the state of adhesion of the toner in the developer immediately before passing through the toner attracting member 41, and the toner 45 is dispersed almost uniformly on the surface of the carrier 46 particles. Yes.

  On the other hand, FIG. 6B schematically shows the toner attracting member 41 and the adhesion state of the toner in the developer that is passing and after passing, and a part of the toner 45 is near the surface of the developer 23 ( The toner is moved to the toner attracting part 41 side), and the toner is unevenly distributed. This is because the electric field generated by the toner contained in the developer 23 on the sleeve 27 of the developer carrier 13 by the voltage Vb3 applied to the toner attracting member 41 and the voltage Vb1 applied to the developer carrier 13. This is a result of being attracted to the surface side of the developer 23 by receiving the action of (toner attracting electric field). At this time, a counter charge is generated in the carrier 46 in the vicinity of the conductive sleeve 27 from which the toner 45 has moved from the surface, but charge injection or discharge from the conductive sleeve 27 occurs because the distance from the conductive sleeve is short. It is easy to eliminate the counter charge as soon as the charge is removed. Therefore, it can be considered that a large amount of toner 45 unevenly distributed on the surface of the developer after passing through the toner attracting member 41 is not supplied with the counter charge of the carrier 46 and is easily supplied to the toner carrier 24 in the toner supply region 8.

  FIG. 7 shows a case in which the toner attracting member 41 is provided, and the toner is developed when an image in which a plurality of white background portions of the toner carrier 24 are continuous after the solid image of one rotation of the toner carrier 24 is developed. 9 is a graph showing values obtained by measuring the potential of the toner layer on the toner carrier 24 between the toner supply member 8 and the toner attracting member 41 after passing through the supply region 8 for each number of passes (toner supply times) passing through the toner supply region 8. is there.

  The potential Vtd of the toner layer is a value obtained by measuring the potential Vtd of the toner layer on the developer carrier 13 by setting a probe of a surface potential meter (Model 344 manufactured by TREK) between the toner supply region 8 and the toner attracting member 41. It is.

  Compared to the case where the toner attracting member 41 of FIG. 5 is not provided, the toner layer potential Vtd1 of the first rotation immediately after the development of the solid image becomes a value substantially close to the toner supply potential difference (Vb2-Vb1), and the subsequent toner It can be seen that the layer potential is almost the same value even if the number of passes through the toner supply region 8 is overlapped. This is because the toner layer potential Vtd and the thickness of the toner layer are approximately proportional to each other, and therefore, after the solid image is consumed, the amount of toner consumed by the solid image is supplied almost immediately after passing through the toner supply region 8 for the first time. It can be seen that the desired toner layer thickness is formed. From this, it can be considered that in the toner supply region 8, the counter charge of the carrier is small and the toner is easily supplied.

  FIG. 8 is a diagram schematically showing the difference between the toner supply potential difference (Vb2−Vb1) and the toner supply amount to the toner carrier 24 with and without the toner attracting member 41. It is. After the solid image for one rotation of the toner carrier 24, the amount of toner adhering (toner supply amount) on the toner carrier 24 after passing through the toner supply region 8 once is measured in the case of the presence or absence of a drawing member. It is the result.

  From this figure, when the toner attracting member 41 is provided, the toner supply potential difference (Vb2−Vb1) for obtaining a desired toner supply amount can be reduced by ΔV compared to the case where the toner attracting member 41 is not provided. . The fact that the toner supply potential difference (Vb2-Vb1) can be reduced can weaken the electric field in the direction (supply direction) that impedes the collection of the development residual toner in the toner collection area 9, and can improve the collection performance. When the collection performance is improved, the difference between the area with a large amount of development residual toner and the area with a small amount of developed toner can be reduced. That is, in the toner collection area 9, the amount of residual toner can be sufficiently collected regardless of the amount of toner consumption in the development area, and toner can be supplied in the toner supply area 8 with no development history. it can.

  By having the toner attracting member 41 in this way, the toner recovery performance can be improved and the toner supply performance can be improved. Therefore, the history of residual toner can be eliminated by passing the toner supply / recovery area once, and the development history (ghost) can be prevented from occurring on the next image.

  Further, when the toner attracting member 41 is installed in the vicinity of the magnetic pole in the magnet roller 26, the rising of the developer 23 occurs almost parallel to the direction of the electric field. It travels through the magnetic brush chain formed with the ears and easily moves to the surface of the developer carrier 13. Thereafter, before the spikes in the toner supply area 8 fall once, the developer is disturbed and the developer is disturbed. However, the uneven distribution of the toner is not eliminated by one fall of the spikes, and even in the toner supply area 8 at the tip of the spikes. There is a high density toner.

  Further, when the toner attracting member 41 is installed between the pole S1 and the main magnetic pole N1 in the magnet roller 26, the ears of the developer 23 are tilted almost perpendicular to the electric field direction. Although the attracting effect by the toner attracting member is slightly reduced, it is advantageous because the toner can be supplied in a state where the toner is unevenly distributed near the surface because the time required for forming the spikes in the toner supply region 8 is short.

  Further, when the magnetic member 43 is provided on the back surface of the toner attracting member 41, the magnetic member 43 is attracted by the magnetic pole of the magnet roller 26, the contact pressure against the developer 23 is stabilized, and the direction of the ears is changed to the electric field. Therefore, the effect of attracting the toner toward the toner attracting member 41 is promoted.

  Here, there is a concern that a toner layer is formed on the surface of the toner attracting member 41 as a result of the toner in the developer 23 being attracted to the toner attracting member 41 side by the toner attracting potential difference (Vb3−Vb1). In this case, when the toner layer on the toner attracting member 41 is increased by the repeated operation, the toner attracting potential difference (Vb3−Vb1) is canceled by the toner layer potential on the surface of the toner attracting member 41, and the effective toner attracting potential difference is reduced. It is thought that it will end.

  However, in practice, a toner layer is hardly formed on the surface of the toner attracting member 41, and a toner attracting electric field acts stably.

  FIG. 9 schematically shows the state of the contact nip between the toner attracting member 41 and the developer 23 on the sleeve 27 of the developer carrying member. Even if the toner 45 is attracted to the toner attracting member 41 side by the toner attracting electric field, the toner 23 is scraped off due to the rubbing force by the developer 23, and the toner layer accumulates on the surface of the toner attracting member 41. Absent.

  Thus, since the toner layer does not accumulate on the surface of the toner attracting member 41, the potential of the toner layer is not increased by repeated operation, and is limited to almost zero or extremely small level, thereby stabilizing the toner attracting potential difference. Can be maintained.

  From the above, at least the toner attraction potential difference (Vb3−Vb1) may be set to a negative value when using positively charged toner and to a positive value when using negatively charged toner. Further, the electric field between the toner attracting member 41 and the developer carrier 13 is preferably an oscillating electric field.

  By making the electric field between the toner attracting member 41 and the developer carrier 13 an oscillating electric field, the toner in the developer 23 can be reliably attracted to the toner attracting member 41 side.

<Configuration and material of toner attracting member>
As described above, the toner attracting member 41 according to this embodiment includes
(A) forming a toner attracting potential difference for attracting toner in the developer 23 on the sleeve 27 of the developer carrying member 13 toward the toner attracting member 41; and
(B) The toner adhering to the surface of the toner attracting member 41 due to the toner attracting potential difference is scraped off by the magnetic brush of the developer 23, and the surface of the toner attracting member 41 is kept clean.
Is required.

  The material of the toner attracting member 41 is not particularly limited as long as an electric field can be formed between the toner attracting member 41 and the developer carrying member 13, and can be used even with conductivity such as metal. An insulating coating such as a resin may be provided on the surface.

  In addition, the effect of obtaining the contact position of the toner attracting member 41 with the developer layer can be obtained anywhere between the regulating member 16 and the toner supply region 8. preferable. By doing so, the magnetic brush of the developer is raised, and the toner attracting electric field not only facilitates the movement of the toner in the developer toward the toner attracting member 41 but also adheres to the toner attracting member 41. It is possible to increase the rubbing force when the developer scrapes off the toner. More preferably, it is desirable to be between the main magnetic pole N1 of the magnet body inside the developer carrier 13 and the position of the magnetic pole S1 adjacent to the main magnetic pole N1, or in the vicinity of the position of the adjacent magnetic pole S1. By setting the contact position between the main magnetic pole N1 and the adjacent magnetic pole S1 (between the poles), it is possible to advantageously maintain the toner uneven distribution state until reaching the toner supply region. Further, by setting the magnetic brush near the position of the magnetic pole S1 adjacent to the main magnetic pole N1, the magnetic brush of the developer is raised, and the toner in the developer can easily move to the toner attracting member 41 side by the toner attracting electric field. In addition, it becomes possible to increase the rubbing force when the developer scrapes off the toner adhering to the toner attracting member 41.

  Further, when the toner attracting member 41 is brought into contact with the developer side by the magnetic attraction force of the magnetic member 43, the effect of improving the stability of the contact pressure of the toner attracting member 41 is also obtained. Further, a developer bridge is formed between the developer carrying member 13 and the magnetic material, and the toner attached to the toner attracting member 41 can be efficiently scraped off.

The toner attracting member 41 can have various shapes such as a plate-like member, a rotating member, and a wire-like member, but it is more preferable to use a film-like 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 time for the toner in the developer to move in the developer layer to the film member side by the toner attracting electric field formed between the developer carrier 13 and the film member. Secured and can be used in smaller electric fields and when the system speed is high.

  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 as the toner attracting member 41 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 Film made of resin, polysulfone resin, polyetherketone resin, vinyl chloride resin, vinyl acetate resin, silicone resin, fluorine resin, etc., rubber film made of silicone rubber, urethane rubber, nitrile rubber, natural rubber, isoprene rubber, etc. However, it is not limited to these.

  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). It is preferable to use a material having chargeability (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 electric 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 carrying member 13, and can be used even with conductivity such as metal, or like a resin film. Even an insulating material can be used by forming an electrode by metal 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 developer carrier 13. 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 such a 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 42 to which a bias is applied, and the holding method may be cantilever support with one end as a free end, or may be both end support with both ends fixed. Further, the film member may be held on the holding electrode as a cylindrical sleeve structure.

  For the contact of the film member fixed to the holding electrode with the developer layer, the elastic restoring force of the film member may be used, or the shape or member that assists the restoring force may be devised. It is preferable to use a magnetic attraction force to the magnetic poles.

  By devising shapes and members that support elastic restoring force for the contact of film members, and by using magnetic attraction, creep deformation occurs in film members even in long-term use and long-term storage in high-temperature and high-humidity environments. It is difficult to change the contact pressure of the film member to the developer layer. Since there is little change in the contact pressure of the film member to the developer layer, there is little decrease in the rubbing force due to the developer on the developer carrier 13, and the toner adhering to the surface of the film member can be removed stably. And there is no fear of impairing the effect of the film member.

  In particular, when the film member is brought into contact with the developer carrier 13 by magnetic attraction, there is no risk of a decrease in contact pressure due to creep deformation of the film member, and a stable contact pressure is maintained over a long period of time. can do.

  The film member can be easily brought into contact with the developer carrying member 13 by a magnetic attractive force by providing the magnetic member 43 on the back side of the film member brought into contact with the developer.

  FIG. 10 is an enlarged view of a state in which the magnetic member 43 is provided on the back surface of the film member 41 with one end held by the holding electrode 42 and the other end being a free end, and in contact with the developer 23. By providing the magnetic member 43 on the back surface of the film member 41, the magnetic member 43 is attracted to the developer carrier 13 side by the magnetic attraction force by the magnetic field formed by the magnetic pole of the developer carrier 13 via the film member 41. It is possible to ensure the contact pressure of the film member 41 against the developer layer 24.

  Here, the film member 41 is brought into contact with the developer layer 23 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. 10, the film member 41 and the magnetic member 43 are not bonded, and the magnetic member 43 is configured to be movable in the normal direction of the developer carrier 13 by a guide provided on the housing side plate. Development that passes between the film member 41 and the developer carrier 13 by making one end of the film member 41 a free end and allowing the magnetic member 43 to move independently without being bonded to the film member 41. Even if the amount of the developer fluctuates, it is preferable that the film member 41 can always contact the surface of the developer with a constant pressure following the amount of the developer.

  Further, FIG. 11 shows a case where the magnetic member 43 is not a continuous body but a discontinuous body (particle shape in the drawing) with respect to the circumferential direction and the longitudinal direction of the developer carrier 13. By doing in this way, even if the magnetic member 43 is fixed to the film member 41, the flexibility of the film is not impaired, and the contact force by the magnetic attractive force can be secured. Similarly, if a film-like member in which magnetic particles are dispersed is used as the magnetic member 43, the magnetic member itself has flexibility. The nip width 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 itself by dispersing the magnetic particles in the film member 41.

  FIG. 12 is an enlarged view of a state in which a backing member 44 is provided on the back surface of the film member 41 with one end held by the holding electrode 42 and the other end is a free end and in contact with the developer 23. The backing member is a member that reinforces the stiffness of the contact surface of the film member 41, and a thick film or the like can be used. Such a backing member 44 may be used to prevent fluctuations in the contact pressure of the film member 41 on the developer layer 24.

  FIG. 13 is an enlarged view of a state where both ends of the film are in contact with the developer 23 in a loop shape with the holding electrodes 42 fixed. By adopting such a configuration, the stiffness of the film may be increased.

  As described above, in the developing device and the image forming apparatus according to the present embodiment, the toner attracting member 41 that contacts the developer carrier 13 after passing through the regulating member 16 is provided, and the toner is attracted by applying a bias voltage. An electric field is formed in the direction of drawing to the member 41. Accordingly, the toner in the developer is unevenly distributed on the developer surface, and the toner supply bias in the toner supply region 8 is improved, so that the toner supply bias can be lowered, and the toner recovery property in the toner recovery region 9 is improved. Since this can be realized, a high-quality image that does not cause a ghost problem can be obtained over a long period of time.

  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.

DESCRIPTION OF SYMBOLS 1 Image carrier 2 Developing device 3 Charging member 4 Transfer roller 5 Cleaning blade 6 Exposure device 7 Development area 8 Toner supply area 9 Collection area 13 Developer carrier 14 Developer collection area 15 Toner replenishment part 16 Restriction member 17 Developer tank 18, 19 Mixing and stirring member 20 Developer housing 21 ATDC sensor 22 Replenished toner 23 Developer 24 Toner carrier 26 Magnet roller 27 Sleeve roller 31 Bias power source for toner carrier 32 Bias power source for developer carrier 33 Toner attracting bias power source 41 toner attracting member, film member 42 holding electrode 43 magnetic member 44 backing member 45 toner 46 carrier 50 undeveloped toner 51 white background 52 solid image area 53 halftone image area 54 ghost pattern

Claims (6)

A toner carrier for carrying and conveying toner on the surface and developing a latent image on the image carrier;
A developer containing the toner and a carrier is carried and conveyed on the surface, the toner is supplied from the developer to the toner carrier in a region facing the toner carrier, and the toner carrier after development A developer carrying member for collecting the toner from the surface of
A developing device comprising:
A toner attracting member in contact with the developer on the developer carrier on the upstream side in the transport direction of the developer in the facing region;
A power source for applying a bias voltage to the toner attracting member for forming an electric field in a direction to attract the toner contained in the developer between the developer attracting member and the toner attracting member; And a developing device. The developing device according to claim 1, wherein the toner attracting member is a film member. A regulating member for regulating the amount of the developer on the surface of the developer carrying member;
A power source for applying a bias voltage to the regulating member for forming an electric field in a direction in which the toner in the developer is attracted to the regulating member between the developer carrying member and the regulating member. The developing device according to claim 1 or 2, characterized in that The developer carrier has a fixed magnetic pole inside,
4. The developing device according to claim 1, wherein the toner attracting member is disposed at a position facing the fixed magnetic pole. 5. The developer carrier has a fixed magnetic pole inside,
2. The toner attracting member is disposed at a position facing a magnetic pole between a position where the developer carrying body and the toner carrying body face each other and a magnetic pole adjacent to the magnetic pole. 4. The developing device according to any one of items 1 to 3. An image forming apparatus comprising: an image carrier; and the developing device according to claim 1 for developing a latent image on the image carrier.

Images