JP2012163706A - Developing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device that feeds developer that has formed a developer layer on a developing roller to an electrostatic latent image carrier on which an electrostatic latent image is formed, and thereby suppresses the occurrence of image failure such as streaks on an image to be formed in developing an electrostatic latent image to form an image, as well as an image forming apparatus.SOLUTION: A developing device applies potential difference between a developing roller 41 and a layer regulating member 12 that regulates the layer thickness of a developer layer formed on the developing roller 41 so as to suppress the occurrence of streaks due to deteriorated developer passing through the layer regulating member 12. The developing device changes potential difference to be applied in accordance with a deterioration state of developer and during a predetermined period initiated for image formation, and thereby suppresses the occurrence of white streaks caused by fusion of developer to the layer regulating member 12.

Description

  The present application relates to a developing device that develops an electrostatic latent image formed on an electrostatic latent image carrier with a developer, and an image forming apparatus including the developing device.

  In an electrophotographic image forming apparatus, for example, the surface of an electrostatic latent image carrier such as a photoconductor is charged, and an electrostatic latent image is formed by exposing the charged surface according to image information. A developing method for developing (visualizing) the electrostatic latent image is employed. In such a developing method, for example, a one-component developer using only toner without using a carrier is used as the developer.

  In such a developing device, a developing roller for developing the toner on the photosensitive member, a supplying roller for supplying the toner to the developing roller and removing the toner from the developing roller, and a supplying roller for supplying the developing roller to the developing roller. A toner layer regulating blade that regulates the thickness of the toner layer formed of toner is provided as a main component.

  In such a developing device, the stability of the toner layer is regarded as the biggest problem. In particular, when the operating time of the developing device becomes long, the deterioration of the toner proceeds due to factors such as friction between the toner layer regulating blade and the developing roller, which causes phenomena such as a change in charge amount and non-uniformity of the toner layer. To do. Therefore, it is important to reduce the pressure by the toner layer regulating blade to suppress toner deterioration. However, when the blade pressure is reduced, the toner deteriorates slightly and the fluidity is only slightly deteriorated. As a result, a streak is seen in the toner layer, and a streak is also generated in the image.

  For example, Patent Document 1 includes a bias applying unit that generates a potential difference between a developing roller and a layer regulating member that regulates the toner layer thickness on the developing roller, and variably controls the potential difference according to the number of latent image formations. A developing device is described. In Patent Document 1, variable control is performed in which the initial potential difference between the layer regulating member and the developing roller is reduced and the potential difference is gradually increased.

Japanese Patent Application Laid-Open No. 2000-221776

  However, as the potential difference is increased, an electric field is applied in the direction in which the toner adheres to the layer regulating member, so that the specific toner continues to adhere to the layer regulating member and easily induces toner fusion to the layer regulating member. Become. When the toner is fused to the layer regulating member, the toner hardly passes under the fused portion, and thus appears as a white stripe in the toner layer. There is a problem that such a white stripe in the toner layer becomes a white stripe in the image, leading to an image defect.

  The present invention has been made in view of such circumstances, and even when fluidity changes due to deterioration of the toner, while suppressing streaks due to toner slipping from the layer restricting member, the present invention can be applied to the layer restricting member. An object of the present invention is to provide a developing device and an image forming apparatus capable of suppressing the occurrence of white stripes due to toner fusion.

  The developing device according to the present invention forms a developer layer on the surface with the supplied developer, and supplies the developer of the developer layer to the electrostatic latent image carrier on which the electrostatic latent image is formed. And a layer regulating member that regulates the layer thickness of the developer layer formed on the developing roller, and is formed on the electrostatic latent image carrier to form an image on the image forming medium. In a developing device that develops a latent image with a developer, a potential difference applying unit that applies a potential difference between the layer regulating member and the developing roller, a potential difference applied by the potential difference applying unit is changed according to the deterioration state of the developer, and And changing means for changing during a predetermined period triggered by image formation.

  In the present invention, the developer is prevented from slipping through by providing a potential difference between the layer regulating member and the developing roller. In addition, the potential difference to be applied is changed in accordance with the deterioration state of the developer, and is also changed during a predetermined period triggered by image formation, thereby preventing the specific developer from being fused to the layer regulating member. .

  The developing device according to the present invention is characterized in that the changing unit changes the positive / negative of the potential difference during a predetermined period after image formation.

  In the present invention, by reversing the positive / negative of the potential difference, a repulsive force is generated between the layer regulating member and the developer to prevent the specific developer from being fixed to the layer regulating member. Prevents developer fusing.

  In the developing device according to the present invention, the potential difference between the developer charged on the developing roller and the layer regulating member is smaller on the downstream side in the rotation direction of the developing roller than the closest position of the developing roller and the layer regulating member. Features.

  In the present invention, the developer is prevented from forming a developer layer after passing through the layer regulating member due to the developer adhering to the layer regulating member on the downstream side of the layer regulating member.

  In the developing device according to the present invention, the layer regulating member has a plate shape with a conductive support member to which a voltage is applied from the potential difference applying unit, and is supported by the conductive support member on one side and the other side. The elastic member is in contact with the developer, and the elastic member is thicker on the downstream side in the rotation direction of the developing roller than the closest position to the developing roller.

  In the present invention, since the elastic member becomes thicker on the downstream side, the electric force for attracting the developer becomes smaller on the downstream side than the closest position between the elastic member and the developing roller, and the developer is prevented from adhering to the layer regulating member. Suppress.

  The developing device according to the present invention further includes means for acquiring the number of images formed by the image forming means for forming an image on an image forming medium with the developed developer, and the changing means develops the acquired number of images. As an index indicating the deterioration state of the agent, the potential difference is changed as the number of images increases.

  In the present invention, by controlling the potential difference based on the developer deterioration state using the number of formed images, for example, the cumulative value of the number of formed images as an index, the occurrence of streaks can be suppressed with simple control.

  The developing device according to the present invention further comprises means for obtaining the number of times that the developer is regulated by the layer regulating member, and the changing means uses the obtained number of times of regulation as an index indicating the deterioration state of the developer. It is characterized in that the potential difference is changed so as to increase as the number of times of restriction is increased.

  In the present invention, for example, in a system that does not replenish toner as a developer, the potential difference is controlled based on the number of times of restriction based on the knowledge that the average number of passes through the layer restriction member and the deterioration state of the toner are highly correlated. By doing so, the generation of streaks can be suppressed with simple control.

  The developing device according to the present invention is characterized in that the changing unit changes the potential difference during a period from image formation on the image forming medium to image formation on the next image forming medium. .

  In the present invention, even when images are continuously formed, it is possible to prevent the developer from being fused to the layer regulating member.

  The developing device according to the present invention is characterized in that the changing means changes the potential difference different from that during image formation during a certain period after the image is formed on the image forming medium.

  In the present invention, the developer is prevented from being solidified and fused after the image formation by applying a potential difference for peeling the developer from the layer regulating member during a certain period after the image formation.

  The developing device according to the present invention is characterized in that the layer regulating member is formed of an insulating material at a portion in contact with the developer.

  In the present invention, by using an insulating material, it is possible to prevent the attractive force of the layer regulating member against the developer from becoming too strong, and to suppress fusion.

  An image forming apparatus according to the present invention includes the developing device described above and means for forming an image on an image forming medium with a developer developed by the developing device.

  In the present invention, the generation of white stripes due to the fusion of the developer to the layer regulating member is suppressed while the stripes caused by the developer slipping from the layer regulating member are suppressed.

  The developing device and the image forming apparatus according to the present invention are provided between a developing roller that supplies toner to the electrostatic latent image carrier and a layer regulating member that regulates the layer thickness of the developer layer formed on the developing roller. The potential difference to be applied is changed according to the deterioration state of the developer and is changed during a predetermined period triggered by image formation. As a result, an image defect in which streaks are formed in the formed image by preventing the specific developer from fusing to the layer regulating member by changing the potential difference under a predetermined condition while preventing the developer from slipping through. It is possible to suppress the occurrence of the occurrence of excellent effects.

  Further, in the present invention, repulsive force is generated between the layer regulating member and the developer by reversing the potential difference between positive and negative, and the specific developer is prevented from being fixed to the layer regulating member. There are excellent effects such as prevention of fusion of the developer and suppression of image defects.

  Furthermore, in the present invention, for example, a layer regulating member having a conductive support member and an elastic member made of an insulating material is used, and the elastic member is disposed downstream of the closest position between the elastic member and the developing roller. The potential difference with the developing roller is made small. Thereby, it is possible to reduce the attractive force with respect to the developer on the downstream side, suppress the adhesion of the developer to the layer regulating member, and suppress the occurrence of image defects.

  Furthermore, in the present invention, by controlling the potential difference based on the deterioration state of the developer, it is possible to suppress the occurrence of streaks and prevent the occurrence of image defects with simple control. .

  Furthermore, in the present invention, by changing the potential difference between image formations, it is possible to prevent the developer from fusing to the layer regulating member and suppress the occurrence of image defects even when images are continuously formed. It has excellent effects such as being possible.

  Furthermore, in the present invention, by applying a potential difference that peels off the developer from the layer regulating member during a certain period after image formation, the developer is prevented from solidifying and fusing after image formation, and image defects It is possible to suppress the occurrence of the occurrence of excellent effects.

1 is a schematic diagram illustrating a configuration example of a main part of an image forming apparatus according to Embodiment 1 of the present invention. 1 is a schematic diagram illustrating a configuration example of a developing device according to a first embodiment of the present invention. It is the schematic which shows the structural example of the layer control member with which the developing device which concerns on Embodiment 1 of this invention is provided. FIG. 6 is a schematic diagram illustrating a region in which a toner layer on a developing roller has a layer thickness regulated by a layer regulating member. It is explanatory drawing which shows the condition where slip-through occurred. 6 is a graph showing a change in potential difference provided by a layer regulating member provided in the developing device according to the first embodiment of the present invention. 6 is a graph showing a change in potential difference provided by a layer regulating member provided in the developing device according to the first embodiment of the present invention. It is a graph which shows the change of the electric potential difference given by the layer control member with which the developing device concerning Embodiment 2 of the present invention is provided. 10 is a graph showing the relationship between the number of image formations and the average number of blade passages in the developing device according to Embodiment 3 of the present invention. It is a graph which shows the change of the electric potential difference given by the layer control member with which the developing device concerning Embodiment 3 of the present invention is provided. It is a graph which shows the change of the electric potential difference given by the layer control member with which the developing device concerning Embodiment 3 of the present invention is provided. It is a graph which shows the change of the electric potential difference given by the layer control member with which the developing device concerning Embodiment 4 of the present invention is provided. It is a graph which shows the change of the electric potential difference given by the layer control member with which the developing device concerning Embodiment 4 of the present invention is provided.

  Hereinafter, the present invention will be described in detail with reference to the drawings illustrating embodiments thereof.

Embodiment 1 FIG.
FIG. 1 is a schematic diagram illustrating a configuration example of a main part of an image forming apparatus according to Embodiment 1 of the present invention. In FIG. 1, reference numeral 100 denotes an image forming apparatus employing an electrophotographic system such as a copying machine, a laser printer, or a digital multifunction machine. In FIG. 1, the main components of the image forming apparatus 100 are schematically illustrated.

  The image forming apparatus 100 displays an image based on image data such as image data transmitted from various terminal devices such as a PC (Personal Computer) connected via a network and image data read by a document reading device such as a scanner. And has a function of forming on an image forming medium. Image formation by the image forming apparatus 100 forms an electrostatic latent image based on image data on an electrostatic latent image carrier, develops the electrostatic latent image by supplying a developer, and forms an image on a sheet P or the like. This is done by transferring the image onto a medium to form an image.

  In the following description, an example will be described in which the image forming process is applied to a non-magnetic one-component developing method using a one-component developer consisting only of toner as a developer. However, the developing method is not limited to this. For example, a developing method using a two-component developer having toner and carrier may be used. Further, although the image forming apparatus 100 that forms a color image is illustrated, the present invention can be applied to a dedicated machine for monochrome images.

  The image forming apparatus 100 includes a supply unit 20 that supplies paper P, a conveyance unit 30 that conveys the supplied paper P, and an image that forms an image by transferring a toner image based on image data to the conveyed paper P. A forming unit 40 and a fixing unit 50 that fixes the formed image on the paper P are provided.

  The supply unit 20 includes a supply tray that supplies the paper P, and supplies the paper P placed on the supply tray to the transport unit 30.

  The conveying unit 30 includes a driving roller 31, a driven roller 32, and a conveying belt 33, and the endless conveying belt 33 is stretched between the driving roller 31 and the driven roller 32. When the driving roller 31 rotates, the conveyance belt 33 is operated in the direction indicated by the arrow Z in FIG. 1, and the paper P supplied from the supply unit 20 is conveyed to the fixing unit 50 via the image forming unit 40. . In the conveyance process, an image by the image forming unit 40 is formed on the paper P.

  The image forming unit 40 includes image forming stations 40Y, 40M, 40C, and 40B for yellow image, magenta image, cyan image, and black image, and each color based on the image data is conveyed on the sheet P to be conveyed. Transfer the image. Details of the image forming unit 40 will be described later.

  The fixing unit 50 includes a heating roller 51 and a pressure roller 52, and receives the paper P conveyed by the conveying unit 30 at a fixing nip portion where these abut against each other. The image is fixed on the paper P by thermocompression with respect to the image transferred to the paper P at the fixing nip portion.

  Next, the image forming unit 40 will be described in detail. In the image forming unit 40, the image forming stations 40Y, 40M, 40C, and 40B are supplied from the supply unit 20 to the fixing unit 50, the yellow image forming station 40Y, the magenta image forming station 40M, the cyan image forming station 40C, and the black image forming station. Stations 40B are arranged in this order. In other words, the image forming apparatus 100 is a tandem system in which images of the respective colors are transferred onto the paper P by the image forming stations 40Y, 40M, 40C, and 40B that are continuously provided. Then, the image forming stations 40Y, 40M, 40C, and 40B for the respective colors form yellow, magenta, cyan, and black toner images based on the image data corresponding to the respective colors, and transfer the toner images onto the paper P.

  These color image forming stations 40Y, 40M, 40C, and 40B have substantially the same configuration except for the type of toner. Therefore, the reference numerals for the components included in each of the image forming stations 40Y, 40M, 40C, and 40B in FIG. 1 are described only for the yellow image forming station 40Y. The reference numerals for the components of the other image forming stations 40M, 40C, and 40B refer to the yellow image forming station 40Y, and the description thereof is omitted.

  Note that the image forming station unit 40 of the present embodiment has been described with respect to a configuration in which images of four colors of yellow, magenta, cyan, and black are formed. However, the present invention is not particularly limited to these four colors. For example, a six-color toner image may be formed by adding light cyan (LC) and light magenta (LM) having the same hue as cyan and magenta and lower densities.

  Each of the image forming stations 40Y, 40M, 40C, and 40B includes a photoreceptor 41 as an electrostatic latent image carrier on which an electrostatic latent image is formed on the surface. Each photoconductor 41 has a substantially cylindrical drum shape and is rotatably supported. The photoconductor 41 is controlled to be driven to rotate in a predetermined direction indicated by an arrow R in the drawing by a driving unit and a control unit (not shown). . Each photoreceptor 41 has a photosensitive material such as OPC (Organic Photoconductor) on the side surface of the cylinder, that is, the surface in the circumferential direction.

  Each photoconductor 41 is arranged above the conveyor belt 33 so that the conveyance direction and the axial direction of the rotation axis are perpendicular to each other so as to transfer the toner image onto the paper P conveyed by the conveyance unit 30. Yes. Further, a charging device 42, an exposure device 43, a developing device 1, a transfer roller 44, and a cleaning device 46 are arranged around each photoconductor 41 along the circumferential direction.

  The charging device 42 is a charging means for uniformly charging the circumferential surface of the photoconductor 41 to a predetermined potential, and is disposed above the photoconductor 41 and close to the outer peripheral surface thereof. In this embodiment, a mode in which a contact roller type charging roller is used will be described. However, other types of charging devices such as a charger type, a brush method, and an ion emission charging method may be used. .

  The exposure device 43 is disposed on the downstream side of the charging device 42 in the rotation direction of the photoconductor 41 and close to the outer peripheral surface of the photoconductor 41. The exposure device 43 irradiates the circumferential surface of the photoreceptor 41 charged by the charging device 42 with laser light and exposes it based on image data output from an image processing unit (not shown). The surface of the body 41 has a function of writing an electrostatic latent image corresponding to image data.

  Each exposure apparatus 43 receives image data corresponding to yellow, magenta, cyan, or black according to each image forming station 40Y, 40M, 40C, 40B, so that static corresponding to the corresponding color is obtained. Each electrostatic latent image is formed. As the exposure device 43, a device such as a laser scanning unit (LSU) provided with a laser irradiation unit and a reflection mirror, a writing device (for example, a writing head) in which light emitting elements such as EL and LED are arranged in an array, and the like are used. Can do.

  The developing device 1 is disposed on the downstream side of the exposure device 43 in the rotation direction of the photoconductor 41 and close to the outer peripheral surface of the photoconductor 41. The developing device 1 has a developing roller 10 as a developer carrying member that carries toner as a developer, and rotatably supports the developing roller 10. The developing roller 10 is disposed so as to be close to the photoconductor 41, and an area close to the photoconductor 41 is a development area for supplying the toner to be carried to the photoconductor 41. The developing roller 10 is rotated by a driving unit and a control unit (not shown), so that the carried toner is conveyed to the developing region and is supplied to the photoreceptor 41. When the developing device 1 supplies toner to the photoconductor 41, the electrostatic latent image formed on the surface of the photoconductor 41 is developed by the exposure device 43 to form a toner image (visible image).

  Each developing device 1 contains yellow, magenta, cyan, or black toner according to the image formation at each image forming station 40Y, 40M, 40C, 40B. These toners include toner charged to the same polarity as the surface potential of the charged photoreceptor 41. The polarity of the surface potential of the photoconductor 41 and the charge polarity of the toner to be used may be positive or negative, but in the present embodiment, the following description will be made assuming that the polarity is negative.

  The transfer roller 44 is disposed below the conveyance belt 33 and faces the transfer roller 44 via the conveyance belt 33. The transfer roller 44 has a function of transferring the toner image formed on the photoconductor 41 onto the surface of the paper P conveyed by the conveying belt 33, and has a polarity opposite to the charging polarity of the toner, that is, the main image. In the embodiment, a positive (plus) bias voltage is applied.

  The cleaning device 46 is disposed on the downstream side of the transfer roller 44 in the rotation direction of the photoconductor 41 and close to the outer peripheral surface of the photoconductor 41. The cleaning device 46 has a function of removing and collecting the toner remaining on the outer peripheral surface of the photoreceptor 41 after the toner image is transferred onto the paper P.

  In the image forming apparatus 100 configured as described above, the toner images of the respective colors are sequentially applied to the paper P when the paper P transported by the transport unit 30 passes through the image forming stations 40Y, 40M, 40C, and 40B. Transcribed. As a result, the toner images of the respective colors are superimposed and transferred onto the paper P, and a desired full-color toner image is formed on the paper P. The paper P onto which the toner image has been transferred in this manner is subjected to a toner image fixing process by the fixing device 40 and then sent to a paper discharge tray (not shown).

  Next, a configuration example of the developing device 1 will be specifically described. FIG. 2 is a schematic diagram illustrating a configuration example of the developing device 1 according to Embodiment 1 of the present invention. The developing device 1 provided in each of the image forming stations 40Y, 40M, 40C, and 40B of the image forming unit 40 includes the supply roller 11, the layer regulating member 12, the potential difference applying unit 13, and the variable potential difference applying unit 14 in addition to the developing roller 10 described above. , A potential difference changing unit 15, an operation state acquiring unit 16, and a time measuring unit 17.

  The developing device 1 is arranged so that the built-in developing roller 10 and the photoconductor 41 are close to each other through a developing region. A developing area for supplying toner from the developing roller 10 to the photoreceptor 41 is a gap called a developing gap, and is held at 150 to 500 μm by a gap holding material (not shown). The developing roller 10 rotates counterclockwise in FIG. 2 as indicated by an arrow R10, and supplies the carried toner to a photoconductor 41 that rotates clockwise as indicated by an arrow R. The developing roller 10 is formed of a material such as aluminum having a surface roughness Ra of about 0.3 to 0.6 μm.

  The supply roller 11 has a cylindrical shape and is rotatably supported by a rotation shaft portion located at the center axis. The supply roller 11 rotates counterclockwise as shown by an arrow R11 to develop toner. Supply to roller 10. At the nip portion where the supply roller 11 and the developing roller 10 are in contact, both rollers are pressed, and toner is supplied from the supply roller 11 to the developing roller 10 at the nip portion. Since the supply roller 11 is configured by using a polyurethane foam formed in a columnar shape around a metal shaft serving as a rotation shaft portion, a biting of 0.2 to 1.0 mm occurs in the nip portion. The supply roller 11 is supplied with toner by an agitation roller that agitates the inside of the toner tank provided in the developing device 1 and conveys the agitated toner.

  The toner supplied from the supply roller 11 to the developing roller 10 forms a toner layer on the surface of the developing roller 10. The layer regulating member 12 has a function of regulating the thickness of the toner layer formed on the surface of the developing roller 10 at a constant level.

  FIG. 3 is a schematic diagram illustrating a configuration example of the layer regulating member 12 included in the developing device 1 according to Embodiment 1 of the present invention. FIG. 3 is an enlarged view of the developing roller 10 and the layer regulating member 12 shown in FIG. The layer regulating member 12 includes a conductive support member 12a having an elongated book plate shape and an elastic member 12b having a plate shape and formed of an insulating material having elasticity. One end of the conductive support member 12a is fixed to the housing of the developing device 1, and the conductive support member 12a is fixed to the other end. The conductive support member 12a is supported by the conductive support member 12a on one side, and contacts the toner carried on the developing roller 10 on the other side. The conductive support member 12a is a book board formed using a metal such as phosphor bronze or SUS having a thickness of about 0.08 to 0.20 mm, for example. The elastic member 12b is formed in a plate shape using an elastic rubber such as urethane having a thickness of about 1 to 2 mm. Note that the elastic member 12b is molded so that its thickness is increased on the downstream side in the rotation direction of the developing roller 10 from the closest position to the developing roller 10.

  As shown in FIG. 3, the elastic member 12 b is thicker on the downstream side in the rotation direction of the developing roller 10 than the nip portion that is the closest position to the developing roller 10. By molding into such a shape, as will be described later, when a voltage that causes a potential difference between the developing roller 10 and the conductive support member 12a of the layer regulating member 12 is applied, it is downstream of the nip portion. On the side, the potential difference between the developing roller 10 and the surface of the elastic member 12b becomes small. As a result, it is possible to suppress toner accumulation on the downstream side and maintain toner uniformity.

  In addition, by forming the elastic member 12b using an insulating material, the force for electrically attracting toner becomes weaker than when the elastic member 12b is formed using a conductive material. Therefore, it is possible to suppress toner fusion to the layer regulating member 12.

  Returning to FIG. 2, the potential difference applying unit 13 applies a potential difference Vd to the developing roller 10, the supply roller 11, and the conductive support member 12 a of the layer regulating member 12 with other members such as the photoreceptor 41. It is a power supply. The potential difference applying unit 13 includes a power source that applies a voltage and an attached circuit thereof, or a circuit that controls a voltage applied from the outside. In the example of FIG. 2, the same potential is applied to the developing roller 10 and the supply roller 11, but a constant potential difference may be provided between the developing roller 10 and the supply roller 11. When a negative potential is applied to the supply roller 11 side, the negatively charged toner is easily transferred to the developing roller 10 side, so that the amount of toner supplied from the supply roller 11 to the developing roller 10 is increased. On the other hand, when a positive potential is applied to the supply roller 11 side, negatively charged toner is easily transferred from the developing roller 10 to the supply roller 11 side, so that the toner is peeled off from the developing roller 11 more. When the supply roller 11 has insufficient toner peeling ability and a ghost appears in the image, it is effective in reducing the ghost.

  The variable potential difference applying means 14 has a function of generating a potential difference ΔVb between the developing roller 10 and the supply roller 11 and the conductive support member 12a of the layer regulating member 12, and a power source for applying voltage and its associated circuit, Or it is comprised by the circuit which controls the voltage applied from the outside. Note that the potential difference given by the variable potential difference applying means 14 is not constant but variable.

  The potential difference changing unit 15 is a mechanism such as a circuit or a program that changes the voltage applied by the variable potential difference applying unit 14. The potential difference changing unit 15 applies the variable potential difference based on information such as the image formation status obtained from the operation status acquisition unit 16, the operation status such as the number of sheets formed, the number of toner restrictions, and various elapsed times obtained from the timing unit 17 The potential difference given by the means 14 is changed.

  The potential difference applying unit 13, the variable potential difference applying unit 14, the potential difference changing unit 15, the operation state acquiring unit 16, and the timing unit 17 may be provided in each of the image forming stations 40Y, 40M, 40C, and 40B. You may make it provide as a mechanism of one circuit, a program, etc. which are used in common with all the image forming stations 40Y, 40M, 40C, and 40B. Further, in the case of mounting as one mechanism that is used in common, it may be arranged outside the housing of the developing device 1 in the image forming apparatus 100 instead of being incorporated in the housing of the developing device 1. Further, for example, when the operation status is detected by a mechanism arranged outside the housing of the developing device 1, a mechanism that is incorporated in the housing of the developing device 1 and receives a detected operation status or a command based on the detected operation status is operated. You may make it consider it as a mechanism, such as the acquisition means 16.

  In the developing device 1 configured as described above, the toner conveyed by the supply roller 11 is rubbed against the developing roller 10 at the nip portion, whereby the toner is pumped up to the developing roller 10 to form a toner layer. When the toner layer formed on the developing roller 10 passes through the elastic member 12b of the layer regulating member 12, the layer thickness is regulated by the pressure applied through the conductive support member 12a of the layer regulating member 12, It will be charged again. The toner that has passed through the elastic member 12 b of the layer regulating member 12 is developed on the photoconductor 41 according to the voltage applied to the developing roller 10 and the latent image potential on the photoconductor 41, and the surface of the photoconductor 41 is exposed. Visualize the electrostatic latent image.

  Here, streaks of the toner layer due to toner slipping, which is one of the problems to be solved by the present invention, will be described. This phenomenon is completely different from the toner fusion to the layer regulating member. In addition, although the said description differs from this invention, the same code | symbol shall be attached | subjected about the structure similar to this invention for convenience. However, it is a code for convenience only, and does not indicate that streaks of the toner layer are generated in the present invention.

  FIG. 4 is a schematic diagram illustrating a region where the layer thickness of the toner layer on the developing roller 10 is regulated by the layer regulating member 12. In FIG. 4, a state in which three toner layers are present is simply illustrated. A constant pressure Fc is applied from the layer regulating member 12 to the developing roller 10 side. Further, the developing roller 10 has an uneven surface, and a force Fr that moves the toner in the lower layer along the rotation direction R10 is applied. When the fluidity of the toner is very good and the force acting between the toners can be regarded as zero, only the lowermost toner contacting the developing roller 10 is carried by the force Fr from the developing roller 10. Then, the toner of the uppermost layer in contact with the layer regulating member 12 is not separated from the layer regulating member 12 due to the frictional force with the layer regulating member 12. Therefore, toner does not slip through.

  However, in reality, the force between the toners cannot be zero, and a certain amount of force is applied. Therefore, the lowermost layer toner and the intermediate layer toner that are in contact with the developing roller 10 are accompanied by the rotation of the developing roller 10. It passes through the layer regulating member 12. When the toner is deteriorated, a phenomenon occurs in which the external additive attached to the toner is peeled off from the toner or buried in the toner. When such a phenomenon occurs, the force between the toners becomes very large. For this reason, the lowermost layer toner pulls the intermediate layer toner, and the intermediate layer toner pulls the uppermost layer toner. When the uppermost toner exceeds the frictional force acting on the layer regulating member 12, the uppermost toner slips through.

  FIG. 5 is an explanatory diagram showing a situation where slip-through has occurred. The upper part of FIG. 5 shows the surface of the layer regulating member 12 that contacts the toner layer. In the layer regulating member 12 shown in the upper part of FIG. 5, the upper side is the upstream side, and the lower side is the downstream side. The lower part of FIG. 5 shows the distribution of the pressure Fc (hereinafter referred to as blade pressure) applied from the layer regulating member 12 to the developing roller 10 as a graph. In the graph in the lower part of FIG. 5, the horizontal axis corresponds to the position in the horizontal direction of the layer regulating member 12 shown in the upper part of FIG. In the upper part of FIG. 5, the arrows indicate the moving direction of the toner that passes through the layer regulating member 12. In particular, the hatched arrows indicate the moving direction of the toner in a region that becomes a slip-through portion through which the toner passes.

  As shown in the lower part of FIG. 5, the blade pressure is reduced in the vicinity of the slip-through part where the uppermost toner shown in the upper part of FIG. Further, when the blade pressure is reduced at the slip-through portion, the contact area is reduced, so that the blade pressure at both ends shown as the horizontal direction in the upper part of FIG. A portion where the blade pressure is low has a thick toner layer, and a portion where the blade pressure is high has a thin toner layer. Since such a pressure state is likely to become normal, once the streaks of the toner layer are generated, they remain without disappearing. In order to suppress such a phenomenon, it is effective to increase the blade pressure. However, when the blade pressure is increased, the stress applied to the toner is also increased, and the deterioration of the toner progresses, so that the fluidity of the toner is abruptly deteriorated and the charge amount is also reduced.

  In the present invention, such a problem is solved by applying a voltage to the conductive support member 12a of the layer regulating member 12 in accordance with the deterioration state of the toner. FIG. 6 is a graph showing a change in potential difference given by the layer regulating member 12 included in the developing device 1 according to Embodiment 1 of the present invention. In FIG. 6, the horizontal axis indicates the number of images to be formed, and the vertical axis indicates the change in applied voltage. Note that the change in the applied voltage shown on the vertical axis is a change in the potential difference applied by the variable potential difference applying unit 14, and is an arbitrary unit (au) potential difference in which the value at the start of image formation is zero. It is shown as ΔV. As shown in FIG. 6, the potential difference between the layer regulating member 12 and the conductive support member 12a is increased by increasing the potential difference ΔV as the number of images formed increases. With this setting, even if the toner deteriorates as the number of image formations increases and the fluidity deteriorates, the attractive force to attract the toner to the layer regulating member 12 side increases, so that the layer regulation can be achieved without increasing the blade pressure. The frictional force by the member 12 is increased, and the toner can be prevented from slipping through.

  The developing device 1 acquires the number of images formed by the operation status acquisition unit 16. Then, the developing device 1 uses the acquired number of formed images as an index indicating the deterioration state of the toner, and controls the variable potential difference applying unit 14 by controlling the potential difference changing unit 15 based on the acquired number of formed images, thereby setting the potential difference ΔV. change. By such control, it is possible to control the applied voltage according to the deterioration state of the toner having the number of image formations shown in FIG. 6, and the toner can be prevented from slipping through.

  However, if the potential difference between the layer regulating member 12 and the developing roller 10 becomes too large, an electric field is applied in the direction in which the toner adheres to the layer regulating member 12, so that the specific toner continues to adhere to the layer regulating member 12 and the layer regulation It becomes easy to induce the fusion of the toner to the member 12. The portion where the toner is fused to the layer regulating member 12 becomes difficult for the toner to pass under the layer regulating member 12 and appears as a streak in the toner layer. The toner layer streak becomes a white streak of the image, resulting in an image defect. Therefore, as shown in FIG. 6, the potential difference is changed according to the toner deterioration state, and the potential difference is changed during a predetermined period triggered by image formation.

  FIG. 7 is a graph showing a change in potential difference provided by the layer regulating member 12 included in the developing device 1 according to Embodiment 1 of the present invention. In FIG. 7, the horizontal axis represents time and the vertical axis represents the change in applied voltage, and the relationship is shown. The change in the applied voltage shown on the vertical axis is the changeable potential difference ΔVb applied by the variable potential difference applying unit 14. A period indicated as T1 in FIG. 7 indicates a period during which image formation is performed on an image forming medium such as paper P. Therefore, the potential difference during the period shown as T1 in FIG. 7 is not constant, and changes according to the deterioration state of the toner as shown in FIG. However, since the degree of the change is smaller than the change in the potential difference ΔVb shown in FIG. 7, it is shown as in FIG.

  As shown in FIG. 7, in the first embodiment, the potential difference periodically changes, and the positive / negative of the potential difference is periodically reversed. Note that the absolute value of the potential difference is not necessarily the same before and after inversion. Before the start of image formation, the potential difference Vd by the potential difference applying unit 13 is set to zero, and a positive potential difference is given during the image forming period indicated as T1. As described above, the potential difference ΔV in the period T1 changes according to the deterioration state of the toner using the number of formed images as an index as shown in FIG. After the image formation, a negative potential difference that is a reverse bias is given for a certain period of time shown as T2 in FIG. 7, and a repulsive force is generated between the layer regulating member 12 and the charged toner. Since the developing roller 10 also rotates during this period, the toner adhering to the layer regulating member 12 is pulled away, and the toner at the position facing the layer regulating member 12 can be replaced with new toner. Thereby, it is possible to prevent the toner from being fused to the layer regulating member 12 and to suppress the occurrence of image defects.

  The developing device 1 acquires the image formation status and the elapsed time by the operation status acquisition unit 16 and the timing unit 17. Then, the developing device 1 controls the variable potential difference applying unit 14 by controlling the potential difference changing unit 15 based on the acquired image forming situation and time so that the positive / negative of the potential difference during a predetermined period after the image formation is reversed. The potential difference ΔVb is changed. Such control makes it possible to control the applied voltage in accordance with the image forming state shown in FIG. 7, and to prevent toner fusing and to suppress the occurrence of image defects.

Embodiment 2. FIG.
The second embodiment is a mode in which the voltage is changed in response to image formation without inverting the applied voltage in the first embodiment. In addition, about the component similar to Embodiment 1, the code | symbol similar to Embodiment 1 is attached | subjected, Embodiment 1 shall be referred and the description is abbreviate | omitted. Since main components in the second embodiment are the same as those in the first embodiment, the description is omitted with reference to FIGS. 1 to 3 and the description thereof shown in the first embodiment.

  FIG. 8 is a graph showing a change in potential difference given by the layer regulating member 12 included in the developing device 1 according to Embodiment 2 of the present invention. In FIG. 8, the horizontal axis represents time and the vertical axis represents the change in applied voltage, and the relationship is shown. In the first embodiment, a voltage in the reverse direction is applied. However, when the fluidity of the toner is deteriorated, there is a case where it is not necessary to change the potential difference until the reverse direction is reached. The second embodiment corresponds to such a situation, and as shown in FIG. 8, a potential difference different from the period shown as T1 during image formation is given in a certain period shown as T2 after image formation. It is.

  The developing device 1 acquires the image formation status and the elapsed time by the operation status acquisition unit 16 and the timing unit 17. Then, the developing device 1 controls the variable potential difference applying unit 14 by controlling the potential difference changing unit 15 based on the acquired image forming status and time, and changes the potential difference ΔVb during a predetermined period after the image formation. Such a control makes it possible to control the applied voltage in accordance with the image forming state shown in FIG. 8, and in a situation where the fluidity of the toner is deteriorated, toner fusing is prevented and image defects are prevented. Occurrence can be suppressed.

Embodiment 3 FIG.
The third embodiment is a form in which the potential difference is changed based on the average number of blade passages in the first embodiment. In addition, about the structure similar to Embodiment 1, the code | symbol similar to Embodiment 1 shall be attached | subjected, Embodiment 1 shall be referred and the description is abbreviate | omitted. Since main components in the third embodiment are the same as those in the first embodiment, the description is omitted with reference to FIGS. 1 to 3 and the description thereof shown in the first embodiment.

  FIG. 9 is a graph showing the relationship between the number of formed images and the average number of blade passages in the developing device 1 according to Embodiment 3 of the present invention. FIG. 9 shows the relationship with the number of processed sheets on the horizontal axis and the average number of blade passages on the vertical axis. The number of processed sheets indicates the number of sheets P that are image forming media on which images are formed. The average blade passage number is an index indicating how many times the toner stored in the developing device 1 has passed through the layer regulating member 12 on average. In FIG. 9, in a system that does not continuously replenish toner, the printing rate indicating the ratio of the image area formed on the image forming surface of the paper P using 100 g of toner is 1%, 3%, and 5%. The relationship between the number of processed sheets and the average number of blade passages when 10% is shown is shown. It is assumed that the toner amount after passing through the layer regulating member 12 is 0.55 mg / cm 2, the toner consumption during solid printing is 0.5 mg / cm 2, and the image forming surface of the paper P is 210 mm × 297 mm. .

  Since the average number of times of blade passage has a correlation with the change in toner fluidity, the average number of times of blade passage can be used as an indicator of toner deterioration in a system that does not supply toner as shown in FIG. As shown in FIG. 9, the average number of blade passages can be obtained from the number of processed sheets and the printing rate.

  10A and 10B are graphs showing changes in the potential difference provided by the layer regulating member 12 included in the developing device 1 according to Embodiment 3 of the present invention. In FIGS. 10A and 10B, the horizontal axis represents the average number of times of blade passage, and the vertical axis represents the change in applied voltage. Note that the change in the applied voltage shown on the vertical axis is a change in the potential difference applied by the variable potential difference applying means 14, and an arbitrary unit (au) where the value at the start of derivation of the average blade passage number is zero. .) Is shown as a potential difference ΔV. In the third embodiment, the average blade passage number is obtained, and the changeable potential difference ΔV is increased according to the obtained average blade passage number. As shown in FIG. 10A, the potential difference ΔV may be increased in proportion to the increase in the number of times of passing through the average blade, and the initial change is reduced as shown in FIG. You may make it enlarge. Since the average number of times of blade passage increases only during image formation, the change in the potential difference ΔV shown in FIGS. 10A and 10B is the period T1 during which the image formation shown in FIG. 7 is performed in the first embodiment. Changes.

  In the developing device 1, the operation state acquisition unit 16 acquires the image formation state, and obtains the average blade passage number based on the acquired image formation state. Then, the developing device 1 uses the obtained average blade passage number as an index indicating the deterioration state of the toner, and controls the variable potential difference applying unit 14 by controlling the potential difference changing unit 15 based on the average blade passage number, so that the potential difference ΔV is obtained. change. Such control makes it possible to control the applied voltage in accordance with the image forming state shown in FIG. 7, and to prevent toner fusing and to suppress the occurrence of image defects.

Embodiment 4 FIG.
In the fourth embodiment, the potential difference is changed at a different timing from the first embodiment. In addition, about the component similar to Embodiment 1, the code | symbol similar to Embodiment 1 is attached | subjected, Embodiment 1 shall be referred and the description is abbreviate | omitted. Since main components in the fourth embodiment are the same as those in the first embodiment, the description is omitted with reference to FIGS. 1 to 3 shown in the first embodiment and the description thereof.

  FIG. 11 is a graph showing a change in potential difference given by the layer regulating member 12 included in the developing device 1 according to Embodiment 4 of the present invention. In FIG. 11, the horizontal axis represents time, and the vertical axis represents the change in applied voltage, showing the relationship. The change in the applied voltage shown on the vertical axis is the changeable potential difference ΔVb applied by the variable potential difference applying unit 14. A period indicated as T1 in FIG. 11 indicates a period during which image formation is performed on an image forming medium such as paper P. Note that the potential difference in the period T1 is not constant, and changes according to the deterioration state of the toner as shown in FIG. 6 of the first embodiment and FIGS. 10A and 10B of the third embodiment. However, since the degree of the change is smaller than the change of the potential difference ΔVb shown in FIG. 11, it is shown as in FIG.

  As shown in FIG. 11, in the fourth embodiment, the potential difference periodically changes with the image formation as a trigger, and the positive / negative of the potential difference is reversed. Note that the absolute value of the potential difference is not necessarily the same before and after inversion. Before the start of image formation, the potential difference Vd by the potential difference applying unit 13 is set to zero, and a positive potential difference is given during image formation shown as T1. As described above, the potential difference ΔV in the period T1 changes according to the deterioration state of the toner. During the period from the image formation on the image forming medium to the image formation on the next image forming medium, the so-called inter-paper interval T2, a negative potential difference serving as a reverse bias is given, and the layer regulating member A repulsive force is generated between the toner 12 and the charged toner.

  When the potential difference is changed at the end of image formation, if a continuous image formation continues for a long time, the constant potential state continues, so that the specific toner continues to adhere to the layer regulating member 12 and the toner fusion May cause wearing. When the potential difference is changed between the papers T2, the potential difference is changed every time even when continuous image formation is performed. Therefore, the repulsive force can be stably generated regardless of the continuous state, and the layer regulating member 12 It is possible to prevent the toner from fusing to the surface and suppress the occurrence of image defects.

  FIG. 12 is a graph showing a change in potential difference given by the layer regulating member 12 included in the developing device 1 according to Embodiment 4 of the present invention. FIG. 12 shows a configuration in which the potential difference is changed not only in the paper interval T2 but also in a certain period T4 after the end of image formation in the potential difference control as shown in FIG. It goes without saying that even when the control shown in FIG. 12 is performed, the same effect as that obtained when the control shown in FIG. 11 is performed can be obtained.

  The developing device 1 acquires the image formation status by the operation status acquisition unit 16 and controls the variable potential difference applying unit 14 by the control of the potential difference change unit 15 based on the acquired image formation status to change the potential difference ΔVb. By such control, it is possible to control the applied voltage in accordance with the image forming state shown in FIG. 11 or FIG. 12, and it is possible to prevent the occurrence of image defects by preventing toner fusion.

  The first to fourth embodiments only exemplify a part of the myriad forms of the present application, and settings of various member configurations, material selection, control conditions, and the like are appropriately designed according to the intended use. Is possible. Also, the first to fourth embodiments may be combined as appropriate, rather than being executed individually.

DESCRIPTION OF SYMBOLS 1 Developing device 10 Developing roller 11 Supply roller 12 Layer regulating member 12a Conductive support member 12b Elastic member 13 Potential difference applying means 14 Variable potential difference applying means 15 Potential difference changing means 16 Operation status obtaining means 17 Timing means 20 Supplying section 30 Conveying section 31 Driving Roller 32 Followed roller 33 Conveying belt 40 Image forming unit 40Y, 40M, 40C, 40B Image forming station 41 Photoconductor 42 Charging device 43 Exposure device 44 Transfer roller 46 Cleaning device 50 Fixing unit 51 Heating roller 52 Pressure roller 100 Image forming device P paper

Claims (10)

A developer layer is formed on the surface by the supplied developer, and a developer roller for supplying the developer of the developer layer to the electrostatic latent image carrier on which the electrostatic latent image is formed, and formed on the developer roller An electrostatic latent image formed on the latent electrostatic image bearing member with a developer so as to form an image on the image forming medium. In the developing device,
A potential difference applying means for providing a potential difference between the layer regulating member and the developing roller;
A developing device comprising: a changing unit that changes a potential difference given by the potential difference applying unit in accordance with a deterioration state of the developer and changes during a predetermined period triggered by image formation.   The developing device according to claim 1, wherein the changing unit changes the potential difference so that the sign of the potential difference is reversed during a predetermined period after image formation.   The potential difference between the developer charged on the developing roller and the layer regulating member is smaller on the downstream side in the rotation direction of the developing roller than the closest position of the developing roller and the layer regulating member. The developing device according to 1. The layer regulating member is
A conductive support member to which a voltage is applied from the potential difference applying means;
It has a plate shape, has an elastic member that is supported by a conductive support member on one side and is in contact with the developer on the other side,
The developing device according to claim 3, wherein the elastic member is thicker on the downstream side in the rotation direction of the developing roller than a position closest to the developing roller. Means for obtaining the number of images formed by image forming means for forming an image on an image forming medium with the developed developer;
5. The change means according to claim 1, wherein the change means changes the potential difference to increase with an increase in the number of images using the acquired number of images as an index indicating the deterioration state of the developer. The developing device according to 1. Means for obtaining the number of times the developer is regulated by the layer regulating member;
6. The change unit according to claim 1, wherein the changing means changes the potential difference to increase with an increase in the number of times of restriction, using the obtained number of times of restriction as an index indicating the deterioration state of the developer. The developing device according to any one of the above.   7. The change unit according to claim 1, wherein the changing unit changes the potential difference during a period from when an image is formed on an image forming medium to when an image is formed on the next image forming medium. The developing device according to any one of the above.   8. The change unit according to claim 1, wherein the change unit changes the potential difference to be different from that during image formation during a certain period after the image is formed on the image forming medium. Development device.   The developing device according to claim 1, wherein the layer regulating member is formed of an insulating material at a portion in contact with the developer. A developing device according to any one of claims 1 to 9,
An image forming apparatus comprising: means for forming an image on an image forming medium with a developer developed by the developing device.

Images