JP2008233756A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device using two-component developer and an image forming apparatus, wherein occurrence of a ghost is prevented, and good image formation can be achieved over a long period of time. <P>SOLUTION: The developing device including a toner carrier, a developer carrier for toner supply and a developer carrier for toner recovery is provided with a stirring means for stirring the developer on the developer carrier for toner recovery after recovering the toner from the toner carrier. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine using the electrophotographic system, and a developing device used therefor. In particular, the present invention relates to a developing device and an image forming apparatus that use a two-component developer composed of a carrier and a toner and develop an electrostatic latent image by holding only the toner on a toner carrier.

  Conventionally, in an image forming apparatus using an electrophotographic method, as a developing method of an electrostatic latent image formed on an image carrier, a one-component developing method using only toner as a developer and a two-component using a toner and a carrier Development methods are known.

  In the one-component development system, 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, thereby forming a desired toner thin layer and static. Develop the electrostatic latent image. For this reason, since the toner carrier and the image carrier are developed in close proximity, the dot reproducibility is excellent, and by forming a uniform toner thin layer, a magnetic brush found in the two-component development system is used. It is easy to obtain a uniform image without image unevenness. However, on the other hand, due to the strong stress in the regulating part, the toner surface is denatured and the charge acceptability is lowered, the toner regulating member and the surface of the toner carrier are contaminated by the adhesion of the toner and external additives, and the charge imparting property to the toner is reduced. This causes problems such as fogging due to poorly charged toner and contamination in the machine. As a result, there is a problem that the life of the developing device is shortened.

  On the other hand, in the two-component development system, the toner is charged by frictional charging by mixing with the carrier, so that stress is small and it is advantageous for toner deterioration. Furthermore, since the carrier as a charge imparting member to the toner has a large surface area, it is relatively resistant to contamination by the toner and external additives, and 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 formed by the developer, so that a magnetic brush mark is generated on the developed image. It has a problem. Furthermore, there is a problem that the carrier easily adheres to the image carrier and causes an image defect.

  As a development method that has the long life of the two-component development method using the two-component developer and solves the above-mentioned image defect problem, the two-component developer is supported on the developer carrier and the two-component development method is used. A so-called hybrid development system is disclosed in which only toner from a developer is supplied to a toner carrier and used for development (see, for example, Patent Document 1).

  In the hybrid development method, although the features of both one-component development and two-component development are combined, residual toner (development residual toner) that has not been used for development on the toner carrier is developed in the development history ( (Ghost) has a problem that appears on the image.

As a development system that solves this problem, a hybrid development system is proposed in which a recovery developer carrier that collects development residual toner after development from a toner carrier is provided (for example, Patent Documents 2 and 3). reference).
JP 59-172626 A JP-A-9-251237 JP 2005-157093 A

  However, in Patent Documents 2 and 3, since an electric field is applied to move the toner from the toner carrying member toward the developer collecting member for collecting toner, when passing through the toner collecting unit that is opposite to the toner carrying member. In other words, the toner is unevenly distributed on the surface of the developer carrying member for collecting the toner. Since the unevenly distributed toner is adsorbed to the surface of the toner collecting developer carrier by electrostatic force, it remains on the surface of the toner collecting developer carrier even if the developer is removed from the toner collecting developer carrier. Will remain. As a result, a layer of charged toner is formed on the surface of the developer carrying member for collecting toner by repeated use, and the electric field of the toner layer inhibits toner collection from the toner carrying member by the developer carrying member for collecting toner, The problem of ghosting arises. Further, when used in this state for a long period of time, the toner is filmed on the surface of the toner collecting developer carrying member, and toner collecting unevenness from the toner carrying member occurs, resulting in image noise. Further, in Patent Document 3, there is provided a retention preventing means for collecting the developer separated by the separation electrode for separating the developer on the developer carrier for collecting toner and returning it to the developer tank. The toner that is unevenly distributed on the surface of the developer carrying member for collecting toner cannot be removed even by the staying prevention means.

  The present invention relates to a developing device capable of forming a good image without ghosting and image noise over a long period of time, in a hybrid developing device using a two-component developer, in which toner does not stay on the surface of the developer carrying member for collecting toner. An object is to provide an image forming apparatus.

  The present invention has the following features in order to solve the above problems.

1.
A toner carrier for carrying toner for developing the electrostatic latent image;
A developer carrier for supply, which is disposed in proximity to the toner carrier, carries and conveys the developer including the toner and a carrier, and supplies the toner to the toner carrier;
A recovery developer carrier disposed near the toner carrier, carrying and transporting the developer, and collecting the toner remaining on the toner carrier after developing the electrostatic latent image;
In a developing device comprising:
A developing device comprising stirring means for stirring the developer on the collecting developer carrying member.

2.
The supply developer carrier and the recovery developer carrier are disposed close to each other, and the developer on the supply developer carrier is supplied to the toner carrier after the toner is supplied. 2. The developing device according to 1, wherein the developing device is moved onto a developer carrying member.

3.
The developing device according to claim 1 or 2, further comprising a developer tank, wherein the developer on the collecting developer carrying member is stirred by the stirring means and then transported to the developer tank. .

4).
The stirrer includes a stirrer disposed so as to come into contact with the developer on the recovery developer carrier and to press the developer toward the recovery developer carrier. 4. The developing device according to any one of 3 above.

5.
5. The developing device according to claim 4, wherein the agitation unit includes a voltage application unit that applies a voltage for attracting toner to the agitation member.

6).
The stirrer includes: an electrode disposed in non-contact with the developer on the recovery developer carrying member; and a voltage applying unit that applies a voltage for attracting toner to the electrode. The developing device according to claim 1.

7).
7. The developing device according to 5 or 6, wherein an alternating electric field is formed between the stirring member and the collecting developer carrying member.

8).
The image bearing member, an electrostatic latent image forming unit that forms an electrostatic latent image on the image bearing member, and any one of 1 to 7 for developing the electrostatic latent image on the image bearing member An image forming apparatus comprising: the developing device described above.

  According to the present invention, in a developing device including a toner carrier, a supply developer carrier, and a recovery developer carrier, development on the recovery developer carrier after the toner is collected from the toner carrier. A stirring means for stirring the agent. By this stirring means, the toner and the carrier separated on the recovery developer carrier can be stirred to prevent the toner layer from being formed on the recovery developer carrier. Further, toner filming can be prevented on the surface of the developer carrying member for recovery accompanying long-term use. Therefore, since the toner layer is not formed on the collecting developer carrier, it is possible to prevent the toner collecting electric field from being lowered by the toner layer and the toner filming on the surface of the collecting developer carrier in the long-term use. As a result, there is an effect that a developing device and an image forming apparatus capable of forming a good image for a long time without generating a ghost can be obtained.

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

  FIG. 1 shows 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 1, a transfer roller 4 for transferring a toner image on the image carrier 1, and a cleaning blade 5 for removing residual toner on the image carrier 1 include an image carrier. It arranges in order along the rotation direction A of the body 1.

  The image carrier 1 is charged by the charging member 3 and then exposed by an exposure device 30 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 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 D in the figure. The cleaning blade 5 removes the residual toner on the image carrier 1 after the transfer with its mechanical force. For the image carrier 1, the charging member 3, the exposure device 30, the transfer roller 4, the cleaning blade 5 and the like used in the image forming apparatus, a well-known electrophotographic technique may be arbitrarily used. 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.

  In the present embodiment, the developing device 2 includes a developer tank 16 that stores the developer 24, a supply developer carrier 11 that carries the developer 24 supplied from the developer tank on the surface, and transports the developer 24. Only the toner is supplied from the agent carrier 11 in the toner supply region 7, and passes through the toner carrier 25 for developing the electrostatic latent image formed on the image carrier 1 and the development region 6 and then on the toner carrier. It is characterized by comprising a recovery developer carrier 26 for recovering the remaining development residual toner in the toner recovery area 8 and a developer agitating means 29 arranged opposite to the recovery developer carrier. The developer after passing through the region 8 is stirred and mixed, and after the mixed state is improved, the developer is separated in the developer separation region 9 and returned to the developer tank 16.

  In the present embodiment, the developer 24 includes toner and a carrier for charging the toner.

The toner is not particularly limited, and a commonly used known toner can be used. The binder resin contains a colorant and, if necessary, a charge control agent, a release agent, etc. 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.

  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 at a ratio of 0.1 to 10 parts by mass with respect to 100 parts by mass of 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 parts by mass with respect to 100 parts by mass of the binder resin.

  Also, as the above external additives, publicly known ones can be used, and fluidity improvement, for example, inorganic fine particles such as silica, titanium oxide, aluminum oxide, acrylic resin, styrene resin, silicone resin In addition, resin fine particles such as a fluororesin can be used, and it is particularly preferable to use a resin 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 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 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, vinyl pyridine, N-vinyl carbazole, vinyl imidazole 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.

  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.

  In the developing device 2 shown in FIG. 1, the developer tank 16 is formed by a casing 19, and usually a mixing and stirring member that mixes and stirs the developer therein and supplies the developer to the supply developer carrier. 17 and 18 are stored. 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 normally has a replenishing unit 10 for replenishing toner in the developer tank 16 for the amount of toner consumed in the developing region 6. In the replenishment unit 10, replenishment toner sent from a hopper (not shown) that stores replenishment toner 23 is replenished into the developer tank 16.

  The developing device 2 includes a regulating member (regulating blade) 15 for thinning the developer for regulating the amount of developer on the supply developer carrier 11. The supply developer carrier 11 includes a magnet roller 13 that is fixedly arranged and a rotatable sleeve roller 12 that includes the magnet roller 13, and a toner supply bias for supplying toner to the toner carrier has a bias power source. 51 is applied. The magnet roller 13 has five magnetic poles N1, S1, N2, N3, and S2 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 recovery developer carrier 26 is composed of a magnet roller 28 that is fixedly arranged and a rotatable sleeve roller 27 that contains the magnet roller 28, and a recovery bias for recovering the development residual toner on the toner carrier. Is applied by the bias power source 52. The magnet roller 28 has five magnetic poles N4, S3, N5, S4 and N6 along the rotation direction C of the sleeve roller 27. Of these magnetic poles, the main magnetic pole S3 is disposed at the position of the toner supply region 7 facing the toner carrier 25, and generates a repulsive magnetic field for peeling off the developer 9 on the sleeve roller 27. The same polar parts N6 and N4 are arranged at positions facing the inside of the developer tank 16. On the downstream side of the main magnetic pole S3, on the upstream side of the same polar parts N6 and N4 where the developer 9 is peeled off, the developer on the recovery developer carrier 26 after the toner is collected from the toner carrier 25 Stirring means 29 for stirring is arranged. Further, in the developing device 2 of FIG. 1, in order to deliver the developer on the supply developer carrier 11 to the recovery developer carrier 26, S1 and N4 are connected to the supply developer carrier 11 and the recovery agent. Arranged at the opposing portion of the developer carrier 26. The toner carrier 25 is arranged to face the supply developer carrier 11, the recovery developer carrier 26, and the image carrier 1, and develops the electrostatic latent image on the image carrier 1. A developing bias is applied by a bias power source 53. The toner carrier 25 may be made of any material as long as the voltage can be applied. For example, an aluminum roller subjected to surface treatment may be used. 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.

  The operation of the developing device 2 shown in FIG. 1 will be described in detail.

  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 roller 13 inside the supply developer carrier 11, and rotates with the sleeve roller 12 so as to face the developing roller 11. The passage amount is regulated by the regulating member 15.

  Thereafter, the developer 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 roller 13, and are formed by the development bias applied to the toner carrier 25 and the toner supply bias applied to the supply developer carrier 11. The toner in the developer is supplied to the toner carrier 25 side by the force applied to the toner by the applied electric field.

  The toner layer supplied to the toner carrier 25 is transported to the developing region 6 as the toner carrier 25 rotates, and electrostatic latent is generated by an electric field formed by the developing 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 in which the toner is consumed in the developing area 6 is further conveyed to the toner collecting area 8 facing the collecting developer carrier 26.

  On the other hand, the remaining developer that has supplied the toner to the toner carrier 25 in the toner supply area 7 is conveyed to a portion opposite to the recovery developer carrier 26, and the magnetic pole S1 of the supply developer carrier 11 and the recovery developer. The developer carrier 26 is transported to the collection developer carrier 26 by a magnetic field formed by the magnetic pole N4 of the developer carrier 26, and delivered.

  The developer delivered to the collecting developer carrying member 26 rotates together with the sleeve roller 27 of the collecting developer carrying member 26 and is conveyed to the toner collecting region 8 facing the toner carrying member 25. In the toner collection area 8, the development residual toner on the toner carrier 25 is caused by an electrostatic force generated by an electric field formed by the development bias applied to the toner carrier 25 and the toner collection bias applied to the supply developer carrier 26. The toner is recovered from the toner carrier 25 to the recovery developer carrier 26 by the mechanical rubbing force of the developer spiked by the magnetic force of the main magnetic pole S3 of the recovery developer carrier. In this way, the developer on the supply developer carrier 11 that has passed through the toner supply region 7 and has a reduced toner concentration is transferred to the recovery developer carrier 26 disposed close to the supply developer carrier 11. By transferring and collecting the toner in the toner collection area, the development residual toner on the toner carrier 25 can be taken into the developer and collected more efficiently.

  Since the developer containing the toner collected on the collecting developer carrier 26 is in a state in which the toner and carrier are mixed by the electric field in the toner collecting area 8 and the toner is unevenly distributed on the surface of the sleeve roller. The mixture is agitated and mixed by agitation means 29 provided opposite to the developer.

  Thereafter, the toner is conveyed toward the developer tank 16, peeled off from the recovery developer carrier 26 by the repulsive magnetic fields of the magnet roller homopolar parts N 6 and N 4, and recovered into the developer tank 16. In this way, by returning the developer stirred by the stirring member 29 on the collecting developer carrier 26 to the developing tank, the toner and the carrier can be more evenly mixed to obtain a stable charged toner. it can.

  When a supply control unit (not shown) provided in the toner supply unit 10 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 ensuring image density, The replenishing toner 23 stored in the hopper by the toner replenishing means shown in the figure is supplied into the developer tank 16 through the toner replenishing unit 10.

  In FIG. 1, the supply developer carrier 11 and the recovery developer carrier 26 are arranged to face each other, and the developer supplied from the developer tank 16 onto the supply developer carrier 11 is supplied as the supply developer. It is regulated on the carrier 11, delivered from the supply developer carrier 11 to the recovery developer carrier 26, separated from the recovery developer carrier 26, and returned to the developer tank 16.

  However, the developer flow is not limited to this. For example, the developer may be transferred again from the recovery developer carrier 26 to the supply developer carrier 11 and then returned from the supply developer carrier 11 to the developer tank 16. Further, the developer is supplied to each of the supply developer carrier 11 and the recovery developer carrier 26, and after the amount of conveyance is regulated, the developer is conveyed to the toner supply region 7 and the toner collection region 8, and each developer carrier is supported. The developer may be separated from the body and returned to the developer tank (separate developer flows between the supply developer carrier 11 and the recovery developer carrier 26). That is, it is only necessary that the developer conveyed to the toner supply region 7 is a developer whose toner density is adjusted in the developer tank 16.

  Here, the operation of the toner stirring means 29 will be described. As shown in FIG. 2 (a), the developer on the developer carrying member that normally contains a magnet roller forms a magnetic brush by the magnetic field of the magnet roller in a state where toner adheres to the carrier surface. However, since the electrostatic force in the direction of moving the toner from the toner carrying member 25 toward the collecting developer carrying member 26 acts in the toner collecting region 8, the toner in the developer on the collecting developer carrying member 26 is also present. Further, it is moved to the surface of the developer carrier 26 for recovery. As a result, as shown in FIG. 2B, the toner is half-separated from the carrier and is unevenly distributed on the surface of the collecting developer carrier 26. In general, as a means for peeling the developer from the developer carrying member composed of a fixedly arranged magnet roller and a rotatable sleeve roller containing the magnet roller without applying a large stress to the developer, the same pole portion It is conceivable to use a magnetic force such as a repulsive magnetic field. However, in the configuration of the conventional developing device, since the toner and the carrier are separated in a state where the toner is unevenly distributed on the surface of the collecting developer carrier 26 as shown in FIG. Even if the carrier could be peeled off by a magnetic field, it was difficult to peel off the toner. Therefore, there is a problem that the toner remains on the surface of the collecting developer carrier 26 and the toner gradually accumulates on the surface of the collecting developer carrier 26 due to repeated use. When the toner accumulates, the toner collection electric field in the toner collection area 8 is hindered by the charge of the toner, so that the development residual toner on the toner carrier 25 is insufficiently collected. As a result, for example, as shown in FIG. When the half image portion H is printed after an image having a large density difference such that the black solid image portion E and the white portion W are alternately arranged, a development history (ghost) G appears on the image in the half image portion H. The effect of providing the collecting developer carrier 26 is reduced. Further, when used for a long period of time, the toner accumulated on the collecting developer carrier 26 gradually forms a film on the surface of the collecting developer carrier 26, and the recoverability is deteriorated due to charge-up of the filmed toner layer. In addition, vertical streak-like filming is likely to occur, and there is a problem that streaky density unevenness appears in the image.

  However, when the agitation means 29 according to the present invention is used, the separated toner and carrier can be agitated and mixed on the recovery developer carrier 26. The stirring means 29 peels off the toner unevenly distributed on the surface of the collecting developer carrier 26 from the surface of the collecting developer carrier 26 and mixes and stirs with the carrier-rich developer in the upper layer. As a result, only the carrier is not peeled off by the repulsive magnetic field, the toner and the carrier are peeled off together, and the developer can be reliably moved from the collecting developer carrier 26 to the developer tank 16.

  There are two methods for separating the toner unevenly distributed on the surface of the toner collection carrier 26 by the agitating means 29 and mixing the toner with the developer, such as a method of physically applying a shearing force or a method of applying an electrostatic force to the unevenly distributed toner. .

  For example, as shown in FIGS. 4A and 4B, as the stirring means 29, the developer on the recovery developer carrier 26 is brought into contact with the developer on the recovery developer carrier 26 side. Stirring members 291 and 292 arranged to press are used. The agitating member 291 is a plate-like member, and when the developer 9 passes between the agitating agent 291 and the sleeve roller 27, the agitating member 291 is pressed toward the collecting developer carrier 26 and is collected. The toner layer unevenly distributed on the surface of the toner is stressed. By doing so, the toner and developer on the surface of the collecting developer carrier 26 are agitated, and the unevenly distributed toner can be taken into the developer. Thereafter, the developer having taken in the unevenly distributed toner is conveyed to the developer tank 16 by the magnetic poles N6 and N4 arranged on the downstream side and having the same polarity. Therefore, the toner recovery capability in the toner recovery portion does not decrease, and toner filming on the recovery developer carrier 26 does not occur, and a good image can be formed over a long period of time. .

  The same effect as that of the stirring member 291 can be obtained by the stirring member 292 in which the shape of the stirring member 291 is a round bar. The stirring member 292 may be in a stationary state, as shown in the figure, in the counter direction (rotation direction in which the surfaces facing each other move in the opposite direction), or in the with direction (the surfaces facing each other in the same direction). Rotation direction).

  Further, as shown in FIGS. 5 (a) and 5 (b), the stirring members 291 and 292 are applied with a voltage by bias power sources 54 and 55 so that the stirring members 291 and 292 are disposed between the collecting developer carrier 26 and the stirring members 291 and 292. An electric field may be formed and the unevenly distributed toner may be peeled off from the surface of the collecting developer carrier 26. The unevenly distributed toner can be peeled and mixed more effectively by the stress and electrostatic force generated by the stirring members 291 and 292. When the toner is negatively charged, a voltage that is equal to or higher than the average value of the voltage applied to the recovery developer carrier is applied to the stirring member, and when the toner is positively charged, the recovery development is performed. A voltage that is equal to or lower than the average value of the voltage applied to the agent carrier is applied to the stirring member. Further, an alternating electric field may be formed between the collecting developer carrying member 26 and the stirring member. By applying such a voltage, the toner unevenly distributed on the surface of the collecting developer carrier 26 can be peeled off from the surface.

  Further, as shown in FIG. 6, as the stirring means, an electrode 293 arranged in non-contact with the developer on the collecting developer carrier 26 and a bias power source 56 for applying a voltage to the electrode 293 may be used. . When the toner is negatively charged, a voltage that is higher than the average value of the voltage applied to the recovery developer carrier 26 is applied to the electrode 293, and when the toner is positively charged, the recovery development is performed. A voltage having an average value lower than the average value of the voltage applied to the agent carrier 26 is applied to the electrode 293. Further, an alternating electric field may be formed between the collecting developer carrier 26 and the electrode 293.

  Furthermore, a stirring means may be used in which the electrode 293 that is not in contact with the developer on the recovery developer carrier 26 and the stirring members 291 and 292 are combined.

  By using the agitation means as described above, the toner unevenly distributed on the surface of the recovery developer carrier 26 is peeled and agitated, so that the reduction of the recovery electric field in the toner recovery portion 8 can be prevented. It is possible to prevent toner from filming on the surface of the developer carrier 26.

  An MFP bizhub C350 manufactured by Konica Minolta was remodeled as the image forming apparatus, and the developing apparatus having the configuration shown in FIG. 1 was used as the developing apparatus, and a printing durability test was performed under the following conditions.

  As the developer, a developer for MFP bizhub C350 manufactured by Konica Minolta was used. The toner concentration in the developer was 8%.

  The development gap between the image carrier and the toner carrier is 0.15 mm, the toner supply gap between the toner carrier and the supply developer carrier, the toner collection gap between the toner carrier and the recovery developer carrier, and supply The regulation gap between the developer carrying member for use and the regulating member was set to 0.35 mm. The voltage applied to the toner carrier is a rectangular wave voltage (average voltage -210 V) with an amplitude of 1.4 kV, a DC component of -350 V, a frequency of 2 kHz, and a duty ratio of 60%, and the voltage applied to the developer carrier for supply is DC- The voltage applied to 350 V and the developer carrier for collection was set to DC-50V. The background potential of the electrostatic latent image formed on the image bearing member was −550V, and the image portion potential was −60V.

The evaluation for confirming the effect of the present invention was performed by continuously printing 10 sheets of the chart shown in FIG. 3 with and without various stirring members, and developing history (ghost) of the 10th sheet. The occurrence state of was compared. The evaluation is performed by measuring the density of the black solid part and the white part of the half image part with a densitometer (X-Rite 310 manufactured by X-Rite). Is 0.05 to 0.1, and x is otherwise. Further, the state of toner filming on the collecting developer carrying member when 200,000 images with an image area ratio of 5% were printed was visually evaluated. The case where filming did not occur was indicated as ◯, and the case where filming occurred was indicated as x.
(Example 1)
As a stirring means, a polycarbonate plate (thickness 5 mm) was used for the stirring member 291 in the configuration of FIG. The interval between the collecting developer carrying member 26 and the stirring member 291 was set to 0.25 mm so that the stirring member 291 was in contact with the developer layer.
(Example 2)
As the stirring means, a rotating roller made of SUS was used for the stirring member 292 in the configuration of FIG. The interval between the collecting developer carrying member 26 and the stirring member 292 was set to 0.25 mm so that the stirring member 292 was in contact with the developer layer. In addition, the surface of the agitating member 292 was driven to rotate in the counter direction at the same speed as the surface of the recovery developer carrier 26 at the portion facing the recovery developer carrier 26.
(Example 3)
As a stirring means, an electrode 293 made of SUS was provided on the wall surface of the housing facing the recovery developer carrier 26 in the configuration of FIG. A voltage of DC 500 V was applied in a state where the distance between the collecting developer carrier 26 and the electrode 293 was about 1 mm and the developer on the collecting developer carrier 26 and the electrode 293 were not in contact with each other.
Example 4
As an agitation means, an aluminum roller having a surface anodized on the agitating member 292 in the configuration of FIG. 5B was used. The interval between the collecting developer carrier 26 and the stirring member 292 was set to 0.3 mm, and the stirring member 292 was brought into contact with the developer on the collecting developer carrier 26. The agitating member 292 was driven to rotate so that the surface of the agitating member 292 moved in the width direction at the same speed as the surface of the collecting developer carrier 26 at the portion facing the collecting developer carrier 26. A rectangular wave voltage having an amplitude of 1 kV, a DC component of −50 V, a frequency of 2 kHz, and a duty ratio of 50% was applied to the stirring member 292.
(Example 5)
As the stirring means, an aluminum plate (5 mm) whose surface was anodized was used for the stirring member 291 in the configuration of FIG. The interval between the collecting developer carrier 26 and the stirring member 291 was set to 0.25 mm, and the stirring member 291 was in contact with the developer on the collecting developer carrier 26. A rectangular wave voltage having an amplitude of 1 kV, a DC component of −50 V, a frequency of 2 kHz, and a duty ratio of 50% was applied to the stirring member 291.
(Example 6)
As an agitation means, an aluminum roller having a surface anodized on the agitating member 292 in the configuration of FIG. 5B was used. The interval between the collecting developer carrier and the stirring member 292 was set to 0.3 mm, and the stirring member 292 was in contact with the developer on the collecting developer carrier 26. The agitating member 292 was driven to rotate so that the surface of the agitating member 292 moved in the counter direction at the same speed as the surface of the collecting developer carrier 26 at the portion facing the collecting developer carrier 26. A rectangular wave voltage having an amplitude of 1 kV, a DC component of −50 V, a frequency of 2 kHz, and a duty ratio of 50% was applied to the stirring member 292.
(Comparative Example 1)
The developing device shown in FIG. 1 has a configuration in which no stirring means is provided.

  Table 1 shows the results of performing a printing durability test with the image forming apparatus using the developing devices having the configurations of Examples 1 to 6 and Comparative Example 1, and evaluating with the evaluation method.

  From the results shown in Table 1, by providing a stirring means for stirring the developer on the collecting developer carrying member after collecting the toner from the toner carrying member, the toner on the collecting developer carrying member can be used even after repeated use. It can be seen that the development history (ghost) due to the accumulation can be suppressed.

1 is a schematic configuration diagram illustrating a main part of an image forming apparatus and a developing device according to an embodiment of the present invention. FIG. 6 is a schematic diagram illustrating a state where toner is attached to a carrier surface on a magnet roller. It is the schematic which shows the image pattern of a printed image. It is the schematic which shows one Embodiment of the stirring means which concerns on this invention. It is the schematic which shows one Embodiment of the stirring means which concerns on this invention. It is the schematic which shows one Embodiment of the stirring means which concerns on this invention.

Explanation of symbols

1 Image carrier (photosensitive drum)
DESCRIPTION OF SYMBOLS 2 Developing apparatus 3 Charging apparatus 30 Exposure apparatus 4 Transfer roller 5 Cleaning blade 6 Development area 7 Toner supply part 8 Toner collection part 11 Supplying developer carrier 12, 27 Sleeve roller 13, 28 Magnet roller 15 Restriction member (regulation blade)
16 Developer tank 17, 18 Bucket roller 19 Casing 20 ATDC sensor 23 Replenished toner 24 Developer 25 Toner carrier 26 Recovery developer carrier 29 Stirring means 291, 292 Stirring member 293 Electrode 31 Conductive sleeve 32 Magnet roll 33 Bias Power supply 34 Cylindrical electrode 35 Condenser 51, 52, 53, 54, 55, 56 Bias power supply

Claims (8)

A toner carrier for carrying toner for developing the electrostatic latent image;
A developer carrier for supply, which is disposed in proximity to the toner carrier, carries and conveys the developer including the toner and a carrier, and supplies the toner to the toner carrier;
A recovery developer carrier disposed near the toner carrier, carrying and transporting the developer, and collecting the toner remaining on the toner carrier after developing the electrostatic latent image;
In a developing device comprising:
A developing device comprising stirring means for stirring the developer on the collecting developer carrying member. The supply developer carrier and the recovery developer carrier are disposed close to each other, and the developer on the supply developer carrier is supplied to the toner carrier after the toner is supplied. The developing device according to claim 1, wherein the developing device is moved onto a developer carrying member. 3. The developer tank according to claim 1, further comprising a developer tank, wherein the developer on the collecting developer carrier is stirred by the stirring unit and then conveyed to the developer tank. Development device. The agitation means includes an agitation member disposed so as to come into contact with the developer on the recovery developer carrier and to press the developer toward the recovery developer carrier. The developing device according to any one of 1 to 3. The developing device according to claim 4, wherein the agitation unit includes a voltage application unit that applies a voltage for attracting toner to the agitation member. 2. The agitation unit includes an electrode disposed in non-contact with the developer on the collecting developer carrying member, and a voltage applying unit that applies a voltage for attracting toner to the electrode. 4. The developing device according to any one of 3 above. The developing device according to claim 5, wherein an alternating electric field is formed between the stirring member and the collecting developer carrying member. The image bearing member, an electrostatic latent image forming unit that forms an electrostatic latent image on the image bearing member, and the electrostatic latent image on the image bearing member for developing the electrostatic latent image. An image forming apparatus.

Images