JP2005172937A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device in which uniform, steady electrification of developer supplied for the development of an electrostatic latent image can be ensured for a long time and whose structure is simple and inexpensive, and to provide an image forming apparatus for forming a steady and excellent image over a long time by providing the developing device. <P>SOLUTION: The developing device 3 includes: a developing roller 32 for developing an electrostatic latent image on a photoreceptor 1; a toner regulating member 34 which abuts on the developing roller 32 so as to form a thin layer of toner onto the developing roller and generate trivoelectricity in the toner; and a toner electrification film 36 which further electrifies the toner passed through the toner regulating member 34 before supplied to a developing area, film 36 being set smaller in the area of the contact of it with the developing roller 32 for a non-development period than a development period. The image forming apparatus is provided with the developing device. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a developing device and an image forming apparatus used in an electrophotographic image forming apparatus such as a copying machine or a printer.

  Conventionally, as a developing device used in an electrophotographic image forming apparatus, a rotatable developer carrier is opposed to an image carrier such as a photosensitive member, and the developer supplied to the developer carrier is used as a developer. It is known that a developer thin layer is formed on a developer carrying member regulated by a regulating member, and the developer thin layer is supplied to a developing region to develop an electrostatic latent image on the image carrier. Yes.

In the case of a one-component non-magnetic developing type developing device that uses a one-component non-magnetic developer as a developer, it is generally known that the developer is frictionally charged simultaneously with the restriction by the restriction member.
However, the friction charging by the developer regulating member does not sufficiently charge the developer, and the developer deteriorates by repeating the image, and the developer charged to a polarity opposite to the normal developer charging polarity increases. A phenomenon occurs in which this is transferred to a non-image portion on the image carrier (reversal fogging).

  Therefore, for example, as disclosed in Japanese Patent Application Laid-Open No. 2000-315014 and Japanese Patent Application Laid-Open No. 2001-34046, in the rotation direction of the developer carrier, upstream of the development region and more than the developer regulating member. The developer charging member (charging roller) provided on the downstream side makes the developer thin layer by the developer regulating member and also charges the developer by further charging the developer after being frictionally charged. A method of making it happen has been proposed. FIG. 6 shows a developing device disclosed in Japanese Patent Application Laid-Open No. 2000-315014.

  In FIG. 6, PC is a photosensitive member, D is a developing device, and the developing device D is a developer carrying member (developing roller in the illustrated example) dr that rotates in contact with the photosensitive member PC which is an image carrier, and a developing device therefor. The developer carrying member dr includes a supply roller sr for supplying the developer t, and a developer charging member (charging roller CR) is developed upstream of the developing region in contact with the photoreceptor PC in the rotation direction, and further developed on the upstream side. The agent regulating member B is disposed in contact. A developing bias is applied from the power source PWa to the developer carrying member dr, and a developer charging voltage is applied from the power source PWb to the developer charging member CR.

  According to this developing apparatus, in a state where the developer charging member CR is in pressure contact with the developer carrier dr, a voltage equal to or higher than the discharge start voltage is applied to the developer charging member CR to thereby develop the developer t on the developer carrier dr. Is discharged and charged.

  Further, the developing device disclosed in Japanese Patent Application Laid-Open No. 2001-34046 has the developer charging member (charging roller) CR shown in FIG. 6 separated from the developer carrier dr (not shown), and the developer. The charging member dr is configured to discharge and charge the developer on the developer carrier dr by applying a voltage equal to or higher than the discharge start voltage to the charging member dr.

JP 2000-315014 A JP 2001-34046 A

  However, in the case of the developing device disclosed in Japanese Patent Laid-Open No. 2000-315014, the developer is charged while the developer charging member (charging roller) CR is in pressure contact with the developer carrier dr. A load is applied to the developer thin layer that has passed through the restriction region by the agent restricting member, and the developer thin layer tends to be disturbed. Further, by repeating the image formation, the developer adheres to the developer charging member CR, and the charging ability of the member decreases. Accordingly, it is difficult to charge the developer uniformly and stably over a long period of time.

  Further, in the case of the developing device disclosed in Japanese Patent Application Laid-Open No. 2001-34046, the developer is charged with the developer charging member (charging roller) CR separated, so that the developer adheres to the developer charging member CR. However, since the discharge start voltage becomes high, an expensive high-voltage power supply is required, and the use of the high-voltage power supply increases the running cost.

  Accordingly, the present invention is a developing device used in an electrophotographic image forming apparatus, and the developer supplied to the development of the electrostatic latent image can be uniformly and stably charged over a long period of time. It is an object of the present invention to provide a developing device capable of obtaining a good developed image.

  Another object of the present invention is to provide such a developing device that has a simple structure and is inexpensive in terms of production cost and running cost.

  The present invention also relates to an electrophotographic image forming apparatus, which can stably and satisfactorily develop an electrostatic latent image formed on an image carrier over a long period of time, thereby stably providing a good image over a long period of time. It is an object of the present invention to provide an image forming apparatus capable of forming the image.

The present invention solves the above problems and provides the following developing device and image forming apparatus.
(1) Developing device A developer is brought into contact with an image carrier on which an electrostatic latent image is formed to develop the electrostatic latent image, and the developer carrier is pressed against the developer carrier via the developer. The development with respect to the developer carrying member, upstream of the development region formed by the developer regulating member, the image carrier and the developer carrying member facing the developer carrying member, in the rotational direction of the developer carrying member. A film-like developer charging member provided so as to be close to or in contact with the developer on the developer carrier on the downstream side in the rotation direction of the developer carrier from the pressure contact portion of the agent regulating member, During the development of the electrostatic latent image, a voltage for charging the developer on the developer carrying member is applied to the developer charging member so that the developer charging member is electrostatically adsorbed to the developer carrying member and the development is performed. When the developer is charged and not developed, the developer charging member and the developer A developing device in which a contact area with the carrier is set smaller than that during development.

  Here, “when non-development, the contact area between the developer charging member and the developer carrying member is set smaller than during development”, the developer charging member contacts the developer carrying member even during non-development. However, this includes not only the case where the contact area is set smaller than that during development, but also the case where the developer charging member is not in contact with the developer carrier.

(2) Image forming apparatus Image carrier, latent image forming means for forming an electrostatic latent image on the image carrier, and the above (for developing the electrostatic latent image formed on the image carrier ( An image forming apparatus comprising the developing device according to 1).

  According to the developing device of the present invention, when the electrostatic latent image formed on the image carrier is developed, the developer passes through the pressure contact portion of the developer regulating member to the developer carrier, so that the predetermined developer is obtained. A thin layer is triboelectrically charged, and the developer charging member to which a developer charging voltage is applied is more reliably charged by discharge charging and used for latent image development to form a good developed image. be able to.

  In addition, since the developer charging member is in the form of a film, the developer can be charged by contacting the developer on the developer carrying member with a wide area and low contact pressure. The developer can be charged in a state in which the disturbance of the developer layer is suppressed. Also in this respect, the developer can be reliably and uniformly charged.

  Further, the developer charging member is in the form of a film, and can be charged by contacting the developer on the developer carrying member over a wide area with a low contact pressure. Since the contact area between the developer charging member and the developer carrying member is set smaller than that during development, the developer is less likely to stay between them, and the developer significantly soils the developer charging member, Since it is possible to prevent the charging ability from being reduced due to fixing, the developer can be charged uniformly and stably in this respect as well.

  Further, since the developer charging member is in the form of a film, the contact area of the developer charging member to the developer carrying member can be controlled only by controlling the voltage applied to the member, and The contact area can be easily controlled at a low voltage. Therefore, the power supply cost and the running cost can be reduced to that extent. Further, since the developer charging member is in the form of a film, the production cost can be reduced.

  As a result, the developing device according to the present invention can uniformly and stably charge the developer supplied to the development of the electrostatic latent image over a long period of time, so that a good developed image can be obtained over a long period of time. Further, the structure is simple and the manufacturing cost and running cost are low.

  Since the image forming apparatus of the present invention employs such a developing device, the electrostatic latent image formed on the image bearing member can be stably and satisfactorily developed over a long period of time. An image can be formed.

  In the developing apparatus according to the present invention and the developing apparatus employed in the image forming apparatus according to the present invention, as an example in which the contact area between the developer charging member and the developer carrying member is set smaller than that during development in the non-development, Cases can be mentioned.

(1) The developer charging member is set in non-contact with the developer carrying member by stopping the voltage application to the developer charging member during non-development (in this case, for example, the elasticity of the film-like developer charging member) It can be made non-contact using the restoring force.)
(2) By controlling the potential difference between the developer carrying member and the developer charging member during non-development, the contact area between the developer charging member and the developer carrying member is made smaller than during development.
(3) Development is performed by setting the voltage applied between the developer charging member and the developer carrying member during non-development to be lower than the voltage applied between the developer charging member and the developer carrying member during development. The contact area between the developer charging member and the developer carrier is smaller than during development,
(4) When the charging potential of the image carrier is Va, the voltage applied to the developer carrier is Vb, and the voltage applied to the developer charging member is Vc, | Va−Vc | and | Vb during non-development −Vc | satisfies the condition of | Va−Vc | ≧ | Vb−Vc |, so that, for example, the developer charging member is separated from the developer carrier and positioned between the image carrier and the non-developing member. Or contact the image carrier.

  In the case of the image forming apparatus, the developer charging member may be brought into contact with the image carrier at the time of non-development.

  As described above, according to the present invention, the developing device used in the electrophotographic image forming apparatus can uniformly and stably charge the developer supplied to the development of the electrostatic latent image over a long period of time. Thus, it is possible to provide a developing device that can obtain a good developed image for a long period of time.

  In addition, according to the present invention, it is possible to provide such a developing device that has a simple structure and is inexpensive in terms of production cost and running cost.

  According to the present invention, there is also provided an electrophotographic image forming apparatus that can stably and satisfactorily develop an electrostatic latent image formed on an image carrier over a long period of time, thereby stably and satisfactorily over a long period of time. An image forming apparatus capable of forming an image can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 shows an example of an image forming apparatus according to the present invention.
<Image forming apparatus>
The image forming apparatus of FIG. 1 includes a drum-type photoreceptor 1 that is an example of an image carrier. Around the photoreceptor 1, a charger 2, a developing device 3, a transfer device 4, and a cleaning device 5 are arranged in this order. Further, an image exposure device 6 is provided above the developing device 3 so that the image exposure can be performed on the photosensitive member 1 from between the charger 2 and the developing device 3. A recording material supply cassette 7 is disposed below the photosensitive member 1. Further, a fixing device 8 is installed at the rear of the recording material conveyance path.

  In this example, the charger 2 is a charging roller to which a photoreceptor charging voltage is applied from a power source PW1, the transfer device 4 is a transfer roller to which a transfer voltage is applied from a power source PW4, and the cleaning device 5 is a photoreceptor 1. A cleaning blade 51 in contact with the toner, and a container 52 for storing toner and the like removed from the photosensitive member. The developing device 3 will be described in detail later. During image formation, each roller is driven to rotate in a predetermined direction by a driving unit (not shown).

  According to this image forming apparatus, the photosensitive member 1 is rotationally driven in the clockwise direction CW in the figure, the surface of the photosensitive member is charged to a predetermined potential by the charging roller 2, and the charged area is in accordance with image data from the image exposure device 6. The image is exposed to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 3 to be a visible toner image.

  On the other hand, the transfer sheet S, which is the recording material here, is pulled out from the recording material supply cassette 7 by the paper feed roller 71 and supplied to the transfer area in synchronization with the latent image on the photosensitive member 1, where transfer is performed. The toner image on the photosensitive member is transferred onto the paper S by the roller 4. The sheet S on which the toner image is transferred is conveyed to the fixing device 8, where the toner image is fixed under heat and pressure, and is discharged to the paper discharge tray 9. The toner remaining on the photoreceptor 1 after the toner image transfer is removed by the blade 51 of the cleaning device 5 and is prepared for the next image formation. The removed toner is stored in a waste toner container 52.

<Developing device>
The developing device 3 is an example of a developing device according to the present invention, and as a whole, is formed in a cartridge type that is detachable from the main body of the image forming apparatus. More specifically, the inside of the device case 30 that accommodates the one-component toner T is divided into two front and rear chambers by a partition wall 301. A rotary agitator 31 for supplying the toner T to the front chamber through the opening of the partition wall 301 while stirring the toner T is provided in the rear chamber containing the toner T. In the front chamber, a toner carrier (an example of a developer carrier) 32 in the form of a developing roller is rotatably disposed at a position that can face the photoreceptor 1. A toner supply roller 33 for supplying the toner T supplied from the agitator 31 to the developing roller 32 is disposed in contact with the developing roller 32 so as to be rotatable.

  Further, a toner regulating member (an example of a developer regulating member) 34 that regulates the layer thickness of the toner T supplied from the toner supply roller 33 is disposed in contact with the developing roller 32. The toner regulating member 34 regulates the layer thickness of the toner T on the developing roller 32 moving to the developing region to a predetermined thickness and frictionally charges the toner. Further, an electrode 34 is disposed on the upper side of the toner regulating member 34, and a toner charging film 36 is cantilevered on the electrode 34. The film 36 is an example of a developer charging member, and has flexibility.

  A developing bias voltage can be applied to the developing roller 32 from the power source PW2. In a state where the developing device cartridge is mounted on the image forming apparatus main body and the developing roller 32 is disposed at a position close to or in contact with the photosensitive member 1, the toner on the developing roller 32 is applied with the toner on the developing roller 32 by applying the developing bias voltage. The electrostatic latent image formed thereon can be visualized.

Further, a toner charging voltage can be applied to the toner charging film 36 from the power source PW3 via the electrode 34.
When the film 36 is not developed, no voltage is applied from the power source PW3. At the time of non-development where no voltage is applied from the power source PW3, as shown in FIG. 2A, the film 36 is placed in a position adjacent to the developing roller 32 without contacting with the developing roller 32 by its elastic restoring force. A voltage is applied from the power source PW3 when developing the electrostatic latent image on the photoconductor 1. During development, the voltage applied to the film 36 is a predetermined DC voltage that is equal to or higher than the discharge start voltage for the toner on the developing roller 32 and has the same polarity as the charging polarity of the toner.

  When a voltage is applied to the film 36 from the power source PW3 during development, the film 36 is electrostatically attracted to the developing roller 32 side due to a potential difference with the developing roller 32, and the film 36 is placed on the developing roller 32 as shown in FIG. The toner layer and the toner is charged by discharging.

The absolute value of the charge amount of the toner charged by the film 36 used for development is preferably about 20 μC / g to 60 μC / g.
Further, the toner conveyance amount of the developing roller is regulated by a toner regulating member 34 is preferably ² to 20 g / m ² about 2 g / m. If it is less than this, development failure will be caused, and if it is too much, charging by the film 36 will be insufficient and development failure will be caused.

  As described above, at the time of development, a predetermined voltage is applied to the film 36 from the power source PW3, so that the toner frictionally charged by the toner regulating member on the developing roller 32 can be discharged and charged more reliably. .

  Further, at the time of development, the toner charging film 36 can contact the toner on the developing roller 32 with a low contact pressure over a wide area to charge the toner, so that the disturbance of the toner thin layer on the developing roller 32 is suppressed. In this state, the toner can be charged. Also in this respect, the toner can be reliably and uniformly charged.

  Further, the toner charging film 36 can be charged by contacting the toner on the developing roller 32 in a wide area with a low contact pressure. Further, when the toner is not developed, the power supply PW3 is turned off. Since the electrostatic attraction force between the developing rollers 32 can be released and the film 36 can be separated from the developing roller 32, the toner hardly stays between the film 36 and the developing roller 32. Since it is suppressed that the charging ability is deteriorated due to remarkably fouling or adhering to the film 36, the toner can be reliably and uniformly charged in this respect as well.

  Further, the contact and separation of the film 36 with respect to the developing roller 32 can be controlled only by controlling the voltage applied to the toner charging film 36, and the control can be easily performed at a low voltage. Therefore, the power supply cost and the running cost can be reduced to that extent. In addition, the film 36 is inexpensive to manufacture.

  As a result, the developing device 3 can uniformly and stably charge the toner supplied to the development of the electrostatic latent image over a long period of time, so that a good image can be obtained over a long period of time. Further, the structure is simple and the manufacturing cost and running cost are low.

<Modification of developing device, particularly toner charging film>
Next, a modified example of the developer charging member (here, the toner charging film 36) will be described with reference to FIGS.
In the example shown in FIG. 3, in the configuration shown in FIGS. 1 and 2, the toner charging film 36 is provided in contact with the developing roller 32. At the time of development, as shown in FIG. 3B, due to the potential difference between the developing roller 32 and the film 36, the film 36 is further brought into close contact with the developing roller 32 by electrostatic adsorption force, and at the same time, the toner on the developing roller 32 is discharged and charged. .

  At the time of non-development, as shown in FIG. 3A, the potential difference generated between the developing roller 32 and the film 36 is reduced by setting the voltage applied to the toner charging film 36 to a voltage lower than that at the time of development. Thus, the electrostatic attraction force is reduced, thereby reducing the contact area (contact pressure) between the film 36 and the developing roller 32.

As a result, the toner staying at the contact portion between the film 36 and the developing roller 32 during development is likely to slip through, and thus the toner is fixed at the contact portion between the film 36 and the developing roller 32, or the image is disturbed due to the toner accumulation. It is suppressed. Further, since the contact area (contact pressure) with the developing roller 32 becomes small during non-development, the toner hardly adheres to the film 36 and the film 36 is less contaminated.
In this example, since the film 36 is not separated from the developing roller 32, the control is easy.

  In the example shown in FIG. 4, the toner charging film 36 is initially provided in light contact with the developing roller 32 or is disposed close to the developing roller. At the time of development, as shown in FIG. Due to the potential difference between the film 32 and the film 36, the film 36 is further brought into close contact with the developing roller 32 by electrostatic attraction, and at the same time, the toner on the developing roller 32 is discharged and charged.

  At the time of non-development, the potential difference between the film 36 and the surface potential of the photoreceptor 1 is made larger than the potential difference between the developing roller 32 and the film 36. Thus, at the time of non-development, as shown in FIG. 4A, the film 36 is electrostatically attracted to the photosensitive member 1 side, and the developing roller 32 and the film 36 are not in contact with each other.

As a result, the toner staying in the contact portion between the film 36 and the developing roller 32 at the time of development is removed, so that the toner adheres to the contact portion between the film 36 and the developing roller 32 or the image is disturbed due to toner accumulation. Absent. Further, since the toner is not attached to the developing roller 32 during non-development, the toner does not adhere to the film 36, and only the toner adheres to the film 36 at the time of development.
According to this example, the toner charging film 36 can be reliably brought into a non-contact state.

<Material of toner charging film>
Next, the toner charging film, the developing roller, and the toner will be further described.
(Toner charging film)
The toner charging film is a polymer film with adjusted conductivity. There is no restriction | limiting in particular for the polymer which comprises a film.
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 resin, silicone resin, fluorine resin, etc. And films made of rubber such as silicone rubber, urethane rubber, nitrile rubber, natural rubber, and isoprene rubber are not limited thereto.

  The thickness of the film is from 10 μm to 1 mm, more preferably from 10 μm to 200 μm. If it is too thin, the strength will be insufficient, and if it is too thick, streaky unevenness will occur in the toner layer, it will be difficult to uniformly contact the developer carrying member (here, the developing roller), or the nip will be difficult to make. The film may have a single layer structure or may have a structure of two or more layers as required.

In order to obtain an appropriate electric resistance, a conductive agent may be added to the bulk or surface of the film as necessary.
Examples of the conductive agent include an electronic conductive agent or an ionic conductive agent. Examples of the electronic conductive agent include 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, anionic compounds, nonionic compounds having an alkylene oxide group in the side chain, and other ionic polymer materials.

By adding the above conductive agent, the surface resistivity of the film is 10 ⁵ Ω / □ to 10 ¹² Ω / □, more preferably 10 ⁶ Ω / □ to 10 ¹⁰ Ω / □, and even more preferably 10 ^7. It is adjusted to Ω / □ to 10 ⁹ Ω / □. If the value falls below the lower limit described here, an excessive current may flow before reaching the discharge start voltage, and the discharge start voltage may not be reached. If the value exceeds the upper limit, the discharge start voltage increases excessively, which is not preferable. In the case of a film, since surface conduction is the main, control of surface resistivity is important.

The distance between the film electrode (here, the electrode 35 to which the film 36 is attached) and the nip portion between the film / toner carrier (here, the developing roller) is preferably 2 mm or more. However, if this distance is too large, the film is easily deformed when it is thin, which is not preferable. The distance is preferably about 3 cm or less. If it is too short, when the conductive agent is locally present, a conductive path is locally formed, and leakage is likely to occur. By increasing the distance to some extent, the current flowing on the surface of the film can be made more uniform. This is a great advantage compared to a material that conducts through a bulk such as a charging roller (since the thickness of the resistance layer of the charging roller is about several millimeters at the maximum). As a result, the resistance between the film electrode and the nip is 10 ⁵ Ω to 10 ⁹ Ω.

(Developer carrier (here, toner carrier)
Generally speaking, the toner carrier can be either a roll type or a belt type. The toner carrier in the developing device shown in FIG. 1 is in the form of a roll type developing roller.
As shown in FIG. 5A, the toner carrier (developing roller) 32 is provided with a base layer 322 on a cored bar 321 made of aluminum or the like, and further on the base layer 322. A surface layer 323 is provided.

The base layer 322 is made of a conductive rubber layer having a hardness of 50 degrees or less, and the thickness is preferably about 0.5 mm to 6 mm. The volume resistivity of the conductive rubber layer is preferably about 1 × 10 ³ Ω · cm to 1 × 10 ⁸ Ω · cm. Examples of the material for the conductive rubber layer include, but are not limited to, silicone rubber, urethane rubber, EPDM rubber, nitrile rubber, and fluorine rubber. And in order to provide electroconductivity, a conductive agent is mixed and an electrical resistance value is adjusted. As the conductive agent, the same conductive agent added to the film can be employed.

As the surface layer 323, a film of a nitrogen-containing resin such as a urethane resin, a polyamide resin, or a nitrile resin is preferable from the viewpoint of chargeability. The thickness is about 1 μm to 10 μm, more preferably about 5 μm to 30 μm. The surface resistivity of the surface layer is 1 × 10 ⁷ Ω / □ or more and 1 × 10 ¹² Ω / □ or less, more preferably 1 × 10 ⁸ Ω / □ or more and 1 × 10 ¹² Ω / □ or less. The total resistance of the toner carrier with the surface layer provided is preferably about 1 × 10 ⁴ Ω to 1 × 10 ⁸ Ω.

When the surface resistivity is less than 10 ⁷ Ω / □, there is local conduction to the toner carrier, and in the worst case, there is a risk of burning. If it exceeds 10 ¹² Ω / □, there is a risk of charge-up and ghosting.

  The arithmetic average surface roughness Ra of the surface layer is preferably 0.3 μm or more and 5 μm or less, and more preferably 0.7 μm or more and 3 μm or less. The method for adjusting the surface roughness Ra of the surface layer is not particularly limited, but it is common to add a roughness adjusting agent to the material forming the surface layer. As the roughness adjusting agent, fine particles of organic material such as acrylic resin and fine particles of inorganic material such as silica and alumina are preferable. Moreover, you may add crosslinking agents, such as an isocyanate compound, a methylol compound, an epoxy compound, to the material which forms a surface layer as needed. Furthermore, an adhesive layer such as a silane coupling agent or a polymer may be provided between the surface layer 323 and the base layer 322.

  An example of a belt-type toner carrier is shown in FIG. The toner carrier 32 ′ shown in FIG. 5B is of an endless belt type that is driven by carrying a conductive sponge roller (not shown) inside, and is used in place of the developing roller 32 described above. Can do.

  The toner carrier 32 ′ shown in FIG. 5B is configured by providing a surface layer 322 ′ on a base layer 321 ′. The base layer 321 ′ is a thin plate made of a synthetic resin or metal having a thickness of 10 μm to 1 mm, more preferably 100 μm to 300 μm. In the case of a metal, nickel or the like is used. When a synthetic resin is used, polyester, polyamide, polyethylene, polyimide, polycarbonate, or the like is used. In order to provide conductivity, a conductive agent is added as in the case of the toner carrier 32. The surface layer 322 ′ may be the same as the surface layer 323 of the toner carrier 32.

(toner)
The toner T used here is not particularly limited, and a publicly known toner that has been generally used can be used. Generally, a binder resin contains a colorant, a charge control agent, a release agent, and the like. In addition, a fluidizing agent or the like may be added if necessary.
Such a toner can also be produced by a known method that has been generally employed conventionally. For example, it can be produced by a pulverization method, an emulsion polymerization method, a suspension polymerization method, or the like.

  The binder resin used for the toner has a number average molecular weight (Mn) measured by gel permeation chromatography (GPC) in the range of 1000 to 15000, and a softening temperature in the range of 80 to 160 ° C. Moreover, it is preferable to use a glass transition point in the range of 50 ° C to 75 ° C.

  As the colorant, known materials that have been conventionally used can be used, such as carbon black, aniline black, activated carbon, magnetite, benzidine yellow, permanent yellow, naphthol yellow, phthalocyanine blue, first sky blue, Ultramarine blue, rose bengal, lake red, or the like can be used, and generally it is preferably used in a ratio of 2 to 20 parts by weight with respect to 100 parts by weight of the binder resin.

  As the charge control agent, known ones that have been conventionally used can be used, and examples thereof include organic compounds such as monoazo metal complexes, aromatic hydroxycarboxylic acid metal complexes, and aromatic dicarboxylic acid metal complexes. A metal complex, a chelate compound, etc. can be used, and it is preferable to use generally in the ratio of 1-10 weight part with respect to 100 weight part of said binder resin.

  As the mold release agent, known ones that have been generally used can be used, for example, polyethylene, polypropylene, carnauba wax, sazol wax, etc. can be used alone or in combination of two or more, In general, it is preferably used at a ratio of 1 to 8 parts by weight with respect to 100 parts by weight of the binder resin.

  As the fluidizing agent, known ones that have been conventionally used can be used. For example, inorganic fine particles such as silica, titanium oxide, aluminum oxide, acrylic resin, styrene resin, silicon resin, fluorine resin, etc. In particular, it is preferable to use a resin particle 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 3 parts by weight with respect to 100 parts by weight of the toner.

<Experimental example>
Next, experimental examples and comparative experimental examples will be described.
The toner carrier (developing roller) employed in the experimental examples and comparative experimental examples described below is as follows. That is,
An easy-adhesion-treated core metal with a diameter of 8 mm is fitted into a mold, and liquid silicone rubber whose conductivity is adjusted with carbon black is poured into the mold and around the core metal, followed by vulcanization at 130 ° C. for 2 hours. And molded. At this time, the rubber hardness was 30 degrees and the rubber thickness was 4 mm.

Next, this silicone rubber roller is corona-treated, treated with a silane coupling agent, and then a urethane resin coating liquid containing silica fine particles having a particle diameter of 5 μm as a roughness adjusting agent and carbon black as a conductive agent is applied to the outer periphery of the rubber layer. Was applied to form a surface layer. The film thickness of the surface layer was 15 μm. When the surface resistivity was measured with a resistivity meter Hiresta (manufactured by Mitsubishi Yuka Kabushiki Kaisha), it was 1 × 10 ⁹ Ω · cm, and the total resistance was 2 × 10 ⁶ Ω. The arithmetic average roughness Ra was measured with a surface roughness measuring machine (Surfcom 550 manufactured by Tokyo Seimitsu Co., Ltd.) and found to be 1.2 μm.

The toner carrier (developing roller) thus produced was set in the developing device having the configuration shown in FIG. 1, and this developing device was mounted on the image forming apparatus having the configuration shown in FIG. The following experimental examples 1 to 3 were used as toner charging films in the developing device.
A -1.2 kV voltage is applied to the charger 2 from the power supply PW1 for charging the photoconductor to uniformly contact and charge the surface of the photoconductor 1 to -600V, and a halftone image is obtained under the conditions of the following experimental example and comparative experimental example. Printed.

(Experimental example 1)
As a toner charging film, a solution obtained by adding 12 wt% of carbon black to polyurethane was applied onto a PET (polyethylene terephthalate) film with a bar coater, dried, and then peeled off from the PET film. The thickness was 25 μm and the surface resistivity was 1 × 10 ⁷ Ω / □.

This toner charging film was provided in the vicinity of the developing roller as shown in FIG. At the time of development, as shown in FIG. 2B, the toner charging film is attracted to the developing roller by the potential difference between the two. At this time, −200 V is applied as a developing bias from the power source PW2 to the developing roller so that the potential difference between the developing roller and the toner charging film is 800 V, and −1.0 kV is applied to the toner charging film from the power source PW3. did.
A thin toner layer having a toner conveyance amount of about 5 g / m ² and a toner charge amount of −25 μC / g to 45 μC / g could be stably formed on the developing roller.
Note that the power supply PW3 was turned off during non-development.

(Experimental example 2)
The same toner charging film as in Experimental Example 1 was used.
This toner charging film was provided in contact with the developing roller as shown in FIG. At the time of development, as shown in FIG. 3B, the toner charging film is strongly adsorbed to the developing roller by the potential difference between the two. At this time, −200 V is applied as a developing bias from the power source PW2 to the developing roller so that the potential difference between the developing roller and the toner charging film is 800 V, and −1.0 kV is applied to the toner charging film from the power source PW3. did.
A thin toner layer having a toner conveyance amount of about 5 g / m ² and a toner charge amount of −25 μC / g to 45 μC / g could be stably formed on the developing roller.
At the time of non-development, −300 V was applied to the toner charging film.

(Experimental example 3)
The same toner charging film as in Experimental Example 1 was used.
The toner charging film was provided close to the developing roller. At the time of development, as shown in FIG. 4B, the toner charging film is attracted to the developing roller by the potential difference between the two. At this time, −200 V is applied as a developing bias from the power source PW2 to the developing roller so that the potential difference between the developing roller and the toner charging film is 800 V, and −1.0 kV is applied to the toner charging film from the power source PW3. did.
A thin toner layer having a toner conveyance amount of about 5 g / m ² and a toner charge amount of −25 μC / g to 45 μC / g could be stably formed on the developing roller.
At the time of non-development, −200 V was applied to the toner charging film. As a result, the film contacted the photoreceptor 1 as shown in FIG.

(Comparative Example 1)
Instead of the toner charging film used in Experimental Examples 1 to 3, a charging roller (3 mm diameter stainless steel rod provided with a 1 mm thick conductive urethane layer. The surface resistivity is 1 × 10 ¹⁰ Ω / □) was used. A developing bias of −200 V was applied to the developing roller, and −1.7 kV was applied to the charging roller for charging the toner.
(Comparative Example 2)
In Experimental Examples 1 to 3, the same voltage as that during development was applied to the toner charging film even during non-development.

<Evaluation of charging uniformity of toner on developing roller and contamination of toner charging member>
The following table shows the charging uniformity of toner on the developing roller and the evaluation of toner charging member contamination.
The charging uniformity of the toner on the developing roller was evaluated by measuring the charging amount at five locations on the roller.
Toner charging member contamination was evaluated by tape-removing the contamination.

  In the following table, in the evaluation section for charging uniformity and charging member contamination, “◯” indicates that toner adhesion was hardly observed on the toner charging member, and that a good image was formed with good toner charging uniformity. Show. "X" indicates that a large amount of toner adheres to the entire toner charging member, the toner is fixed, and streak unevenness occurs frequently in the image. “Δ” indicates that the toner adheres to the front end portion of the toner charging member (film), the toner is partially fixed, and streak unevenness occurs in a part of the image.

Table Toner charging material Initial charge uniformity Charge uniformity after printing 5000 sheets
And Charging Member Dirt and Charging Member Dirt Experiment 1 Film ○ (Good) ○
Experimental Example 2 Film ○ (Good) ○
Experimental Example 3 Film ○ (Good) ○
Comparative Example 1 Charging roller ○ (Good) ×
Comparative Example 2 Film ○ (Good) △

  In Comparative Examples 1 and 2, the evaluation was performed under the same conditions as in Experimental Examples 1 to 3. As a result, in both Comparative Examples 1 and 2, toner accumulated or adhered to the contact portion between the developing roller and the toner charging member in the initial printing stage. Almost no toner stains were seen. However, toner accumulation (partially fixed) occurred as the number of printed sheets increased, and as a result, the toner layer on the developing roller was disturbed, resulting in streak unevenness. Further, a large amount of toner came to adhere to the toner charging member, and a decrease in charging performance was observed. In Experimental Examples 1 to 3 according to the present invention, a good state was maintained even after printing 5000 sheets.

  The developing device and the image forming apparatus of the present invention can be used to form a stable and good image for a long period of time in electrophotographic image formation.

1 is a diagram illustrating a schematic configuration of an example of an image forming apparatus according to the present invention. It is a figure which shows the operation state of one example of the film for toner charging in the developing device which concerns on this invention. It is a figure which shows the operation state of the other example of the film for toner charging in the developing device which concerns on this invention. It is a figure which shows the operation state of the further another example of the film for toner charging in the image development apparatus concerning this invention. FIG. 5A is a cross-sectional view of an example of a roller-type toner carrier, and FIG. 5B is a cross-sectional view of an example of a belt-type toner carrier. It is a figure which shows the example of a conventional image development apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photoconductor 2 Charger PW1 Photoconductor charging power supply 3 Developing device 30 Developing device case 31 Agitator 32 Developing roller (roller type toner carrier)
321 Core metal 322 Base layer 323 Surface layer 32 ′ Belt type toner carrier 321 ′ Base layer 322 ′ surface layer PW2 Developing bias power supply 33 Toner supply roller 34 Toner regulating member 35 Electrode 36 Toner charging film PW3 Toner charging power supply 4 Transfer device PW4 Transfer power supply 5 Cleaning device 51 Cleaning blade 52 Waste toner container 6 Image exposure device 7 Recording agent supply cassette 71 Paper feed roller S Paper 8 Fixing device 9 Paper discharge tray

Claims (7)

A developer carrier that develops the electrostatic latent image by bringing a developer into contact with the image carrier on which the electrostatic latent image is formed; and a developer regulating member that is pressed against the developer carrier via the developer. The developer regulating member is in pressure contact with the developer carrying member upstream of the developing region formed by the image carrier and the developer carrying member facing the image carrying member and in the rotational direction of the developer carrying member. A developer charging member in the form of a film provided on the downstream side in the rotation direction of the developer carrying member relative to the portion so as to be close to or in contact with the developer on the developer carrying member. At the time of development, a voltage for charging the developer on the developer carrying member is applied to the developer charging member so that the developer charging member is electrostatically adsorbed to the developer carrying member and the developer is charged. At the time of non-development, contact between the developer charging member and the developer carrier Developing apparatus is characterized in that the product is set smaller than the time of development. The developing device according to claim 1, wherein the developer charging member is brought into non-contact with the developer carrying member during non-development. The development according to claim 1 or 2, wherein a contact area between the developer charging member and the developer carrying member is made smaller than that during development by controlling a potential difference between the developer carrying member and the developer charging member during non-development. apparatus. The developer applied by lowering the voltage applied between the developer charging member and the developer carrying member during non-development than the voltage applied between the developer charging member and the developer carrying member during development. The developing device according to claim 1, wherein a contact area between the charging member and the developer carrying member is smaller than that during development. When the charging potential of the image bearing member is Va, the applied voltage to the developer bearing member is Vb, and the applied voltage to the developer charging member is Vc, | Va−Vc | and | Vb− at the time of non-development The developing device according to claim 1, wherein Vc | satisfies a condition of | Va−Vc | ≧ | Vb−Vc |. 6. The image carrier, latent image forming means for forming an electrostatic latent image on the image carrier, and developing the electrostatic latent image formed on the image carrier. An image forming apparatus comprising the developing device according to 1. The image forming apparatus according to claim 6, wherein the developer charging member is brought into contact with the image carrier during non-development.