JP2009244733A - Development device and image forming apparatus having it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a development device for preventing image inferiority without deteriorating printing efficiency in continuous printing, and to provide an image forming apparatus having it. <P>SOLUTION: When continuously performing development, a development remaining toner of a development roller 22 is collected on a magnetic roller 23, and after each development completion, a collection remaining toner amount Q is collected so that it is a first prescribed amount Q1. In each prescribed development interval T, the development device prevents increase of density of an edge part of a conveying direction of transfer paper P of a next page, image density transfer inferiority and adhesion of a toner to the development roller 22 by collecting the collection remaining toner amount Q so that it is a second prescribed amount Q2 smaller than Q1. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention uses a two-component developer composed of a magnetic carrier and a toner, holds only the charged toner on the developing roller, and can develop the electrostatic latent image on the image carrier in a non-contact manner, and The present invention relates to an image forming apparatus such as a copying machine, a facsimile, and a printer provided with the same.

  Conventionally, as a development method using dry toner in an image forming apparatus using an electrophotographic process, a one-component development method using no carrier and a two-component developer charging a nonmagnetic toner using a magnetic carrier are used. A two-component development system is known in which an electrostatic latent image on an electrostatic latent image carrier (photoconductor) is developed by a magnetic brush made of toner and carrier formed on a developing roller.

  The one-component development method is suitable for high image quality because the electrostatic latent image on the electrostatic latent image carrier is not disturbed by the magnetic brush, but the toner layer thickness on the developing roller is regulated by an elastic regulating blade. At the same time, since the toner is charged, the toner adheres to the regulating blade, resulting in non-uniform layer formation and image defects. Furthermore, it has been difficult to stably maintain the charging of the toner.

  In addition, a one-drum color superposition method that sequentially forms a plurality of color images on a photoconductor has been developed. By accurately superimposing toner on a photoconductor, a color image with little color misregistration can be formed. It can cope with image quality. Further, in recent years, a tandem method has been developed in which a plurality of photoconductors corresponding to toner colors are used, a color image is formed on the photoconductor in synchronization with conveyance of the transfer member, and color is superimposed on the transfer member. .

  While the tandem method is excellent in high speed, it is necessary to arrange the electrophotographic process members for each color side by side, which may increase the size of the apparatus. In order to avoid such an increase in size, there has been proposed a tandem type image forming apparatus in which an image forming unit that is made smaller by reducing the interval between the photosensitive members is arranged. In the case of color printing in which color superposition is performed in this way, the toner is required to be transparent, and therefore needs to be a non-magnetic toner.

  Therefore, full-color image forming apparatuses often employ a two-component development system that charges and conveys only toner that does not contain a carrier component. However, the two-component development method can maintain a stable charge amount for a long time and is suitable for extending the life of the toner, but the magnetic brush described above may affect the image quality.

  As one means for solving these problems, a magnetic roller is used to transfer the developer onto a developing roller installed in a non-contact manner with respect to the photosensitive member, and the toner is transferred onto the developing roller so as to transfer the non-magnetic toner. A developing system has been proposed in which a thin layer is formed and a toner image is formed by flying toner onto a latent image on a photoreceptor by an alternating electric field.

  According to this technology, the two-component development system as described above is adopted for the toner charging area in consideration of the extension of the life of the toner, and the subsequent development area is non-contact with the photoconductor for the purpose of improving the image quality. Since the one-component development method in which only the toner is ejected is adopted, the advantages of the one-component development method and the two-component development method can be utilized.

  However, in such a development method, there may be a case where development failure such as image density failure or image unevenness occurs. Therefore, a method for preventing such a decrease in development performance has been proposed.

For example, in Patent Document 1, in a developing method using a two-component developer, the image forming apparatus detects the data amount and the paper passing amount of each image to be printed, and the toner layer on the developing roll (roller) is detected at the end of development. By setting the interval between collection and replacement to the magnetic roll to be variable according to the printing rate determined by the above data amount and paper passing amount, development ghosts and selective development can be prevented without complicating the development device. In addition, a method is disclosed in which reliably charged toner is supplied to a developing roll and image nonuniformity does not occur even during continuous printing, and stable image quality is obtained for a long period of time.
JP 2003-280392 A

  However, if the development residual toner on the developing roller is almost completely collected by the magnetic roller after the development is completed, the density of the leading end of the recording medium to be developed next (on the next page) may vary. In such a case, the interval between pages is set long, and the toner supply time from the magnetic roller to the developing roller is lengthened to saturate the toner amount on the developing roller, thereby preventing fluctuations in the density of the leading edge of the next page. Can be considered.

  However, since the number of printouts per time decreases, it is necessary to increase the printing speed of the image forming apparatus in order to obtain the same printing efficiency. In particular, if the undeveloped toner is collected almost completely after each printing (after completion of development), the printing efficiency is greatly reduced. Further, if the toner collection is insufficient, the undeveloped toner adheres to the developing roller, and the adhered toner is charged up by charging such as friction, which may cause image defects.

  In view of the above problems, an object of the present invention is to provide a developing device and an image forming apparatus including the developing device capable of preventing image defects without reducing printing efficiency in continuous printing.

  In order to achieve the above object, the present invention uses a two-component developer containing at least a carrier and a toner, a toner carrier disposed opposite to the image carrier, and a toner using a magnetic brush on the toner carrier. A toner supply member that forms a thin layer, and developing a latent image on the surface of the image carrier from the toner carrier by applying a developing bias to the toner carrier and the toner supply member; In the developing device that collects the development residual toner on the toner carrying member on the toner supply member after the completion of development, when the development is continuously performed, the development residual toner is placed on the toner carrier after each development. The remaining amount of toner is collected so as to become the first predetermined amount, and the toner amount remaining on the toner carrier is set to a second predetermined amount smaller than the first predetermined amount at every predetermined development interval. It is characterized in that.

  According to the present invention, the developing device is characterized in that the second predetermined amount is equal to or less than a lower limit value that can be taken by the first predetermined amount.

In the present invention, the first predetermined amount is 0.3 mg / cm ² or more and 0.6 mg / cm ² or less, and the second predetermined amount is 0.3 mg / cm ² or less. It is said.

  According to the present invention, the toner carrier is allowed to fly from the toner carrier to the surface of the image carrier after the toner is collected at the predetermined development interval and before the next development is performed. It is characterized by a predetermined number of rotations.

  Further, the present invention provides a first bias applying unit that applies a first bias to the toner carrier, and is electrically connected to a ground common to the first bias applying unit. And a second bias applying means for applying a second bias superimposed on the first bias.

  The present invention is also an image forming apparatus provided with the developing device.

  According to the first configuration of the present invention, the electrostatic latent image on the surface of the image carrier is developed from the toner carrier by using a two-component developer and applying a development bias to the toner carrier and the toner supply member. In the developing device that collects the development residual toner on the toner carrying member on the toner supply member after the development is completed, when the development is continuously performed, the development residual toner is placed on the toner carrier on the toner carrying member after each development. A fixed amount of toner is collected so as to remain, and at a predetermined development interval, a second predetermined amount of toner smaller than the first predetermined amount can be collected on the toner carrier.

  In other words, after each development, it is possible to collect a larger amount of toner than after the completion of each development each time a predetermined development is completed while leaving the toner on the toner carrier appropriately. Thus, it is possible to prevent excessive toner from being supplied to the toner carrying member at the initial stage of the next development due to the excessive amount of toner collected to the toner supply member after each development. In addition, it is possible to prevent the amount of toner collected from being too small, so that a large amount of toner remains on the toner carrying member and fluctuations in toner supply to the image carrying member can be prevented. Therefore, it is possible to prevent an increase in the density of the leading edge of the recording medium in the next page and an image density transition failure of the recording medium.

  In addition, since the residual toner that has not been collected after the completion of each development can be further collected after each predetermined development, the toner on the toner carrier is reduced without lowering the printing efficiency, and the residual toner becomes the toner. It is possible to prevent adhesion to the carrier. Therefore, during continuous printing, it is possible to prevent the toner adhering to the toner carrier from being charged up due to friction or the like and causing image defects. Thus, in continuous printing, image defects can be prevented without reducing printing efficiency.

  Further, according to the second configuration of the present invention, in the developing device of the first configuration, the second predetermined amount is set to be equal to or lower than a lower limit value that can be taken by the first predetermined amount. Since a larger amount of residual toner that has not been collected after completion of each development can be collected, it is possible to further prevent the residual toner from adhering to the toner carrier.

According to the third configuration of the present invention, in the developing device of the second configuration, the first predetermined amount is 0.3 mg / cm ² or more and 0.6 mg / cm ² or less, and the second place By setting the fixed amount to 0.3 mg / cm ² or less, an appropriate amount of toner can be left on the toner carrying member after each development, and after the predetermined development interval, the toner is sufficient even under low temperature and low humidity conditions. Can be recovered. As a result, it is possible to more sufficiently prevent the increase of the tip end density, the image density transition, and the toner adhesion to the developing roller, and more sufficiently prevent the image defect.

  According to the fourth configuration of the present invention, in the developing devices having the first to third configurations, after the toner is collected at a predetermined development interval and before the next development is performed, the toner carrier. The toner amount on the toner carrier can be further stabilized by rotating the toner carrier at a predetermined number of revolutions without causing the toner to fly from the toner carrier to the surface of the image carrier. It can prevent that the front-end | tip part concentration falls by lack.

  According to the fifth aspect of the present invention, in the developing device having any one of the first to fourth aspects, the first bias applying unit that applies the first bias to the toner carrying member; A first bias applying means that is electrically connected to a common ground with the bias applying means and applies a second bias superimposed on the first bias is provided on the toner supply member. The AC component of the bias and the AC component of the second bias can be set independently without affecting each other. Therefore, the application conditions of the first and second biases can be easily set, and the residual toner amount after collecting the development residual toner can be easily adjusted.

  According to the sixth configuration of the present invention, an image forming apparatus including the developing device having any one of the first to fifth configurations described above prevents image defects without reducing printing efficiency. Image formation can be performed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view of an image forming apparatus on which the developing device of the present invention is mounted. Here, a tandem color image forming apparatus is shown. In the main body of the color image forming apparatus 100, four image forming portions Pa, Pb, Pc, and Pd are sequentially arranged from the upstream side in the transport direction (the right side in FIG. 1). These image forming portions Pa to Pd are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

  Photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors are disposed in the image forming portions Pa to Pd, and are formed on the photosensitive drums 1a to 1d. The transferred toner image is rotated clockwise in FIG. 1 by a driving means (not shown) and sequentially transferred onto the intermediate transfer belt 8 moving adjacent to each image forming unit, and then the secondary transfer roller 9. In this case, the toner image is transferred onto the transfer paper P at once, and further fixed on the transfer paper P in the fixing unit 7 and then discharged from the apparatus main body. An image forming process for each of the photosensitive drums 1a to 1d is executed while rotating the photosensitive drums 1a to 1d counterclockwise in FIG.

  The transfer paper P onto which the toner image is transferred is accommodated in a paper cassette 16 at the lower part of the apparatus, and is conveyed to the secondary transfer roller 9 via a paper feed roller 12a and a registration roller pair 12b. A sheet made of a dielectric resin is used for the intermediate transfer belt 8, and a belt in which both ends thereof are overlapped and joined to form an endless shape, or a belt without a seam (seamless) is used. A blade-shaped belt cleaner 19 for removing toner remaining on the surface of the intermediate transfer belt 8 is disposed on the downstream side of the secondary transfer roller 9.

  Next, the image forming units Pa to Pd will be described. There are chargers 2a, 2b, 2c, and 2d for charging the photosensitive drums 1a to 1d and image information on the photosensitive drums 1a to 1d around and below the photosensitive drums 1a to 1d that are rotatably arranged. The exposure unit 4 for exposing the toner, the developing devices 3a, 3b, 3c and 3d for forming toner images on the photosensitive drums 1a to 1d, and the developer (toner) remaining on the photosensitive drums 1a to 1d are removed. Cleaning units 5a, 5b, 5c and 5d are provided.

  When the image formation start is input by the user, first, the surfaces of the photosensitive drums 1a to 1d are uniformly charged by the chargers 2a to 2d, and then light is irradiated by the exposure unit 4 to each of the photosensitive drums 1a to 1d. An electrostatic latent image corresponding to the image signal is formed on the top. Each of the developing devices 3a to 3d is filled with a predetermined amount of cyan, magenta, yellow, and black toner by a replenishing device (not shown). The toner is supplied onto the photosensitive drums 1a to 1d by the developing devices 3a to 3d and electrostatically attached, whereby a toner image corresponding to the electrostatic latent image formed by exposure from the exposure unit 4 is formed. It is formed.

  After an electric field is applied to the intermediate transfer belt 8 at a predetermined transfer voltage, cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the intermediate transfer rollers 6a to 6d. Transcribed above. These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the toner remaining on the surfaces of the photosensitive drums 1a to 1d is removed by the cleaning units 5a to 5d in preparation for the subsequent formation of a new electrostatic latent image. The photosensitive drums 1a to 1d will be described later.

  The intermediate transfer belt 8 is stretched between an upstream conveyance roller 10 and a downstream drive roller 11, and the intermediate transfer belt 8 rotates clockwise as the drive roller 11 is rotated by a drive motor (not shown). When the rotation starts, the transfer paper P is conveyed from the registration roller 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and a full color image is transferred. The transfer paper P onto which the toner image is transferred is conveyed to the fixing unit 7.

  The transfer paper P conveyed to the fixing unit 7 is heated and pressurized by the fixing roller pair 13 so that the toner image is fixed on the surface of the transfer paper P, and a predetermined full color image is formed. The transfer paper P on which the full-color image is formed is distributed in the transport direction by the branching portion 14 that branches in a plurality of directions. When an image is formed only on one side of the transfer paper P, it is discharged as it is onto the discharge tray 17 by the discharge roller 15.

  On the other hand, when images are formed on both sides of the transfer paper P, the transfer paper P that has passed through the fixing unit 7 is distributed to the paper transport path 18 by the branching unit 14, and the secondary transfer roller 9 with the image surface reversed. Re-conveyed. Then, after the next image formed on the intermediate transfer belt 5 is transferred by the secondary transfer roller 9 to the surface of the transfer paper P where the image is not formed, and conveyed to the fixing unit 7 and the toner image is fixed. , And discharged to the discharge tray 17.

  As the photoreceptor drums 1a to 1d, an α-Si photoreceptor, OPC, or the like can be used. When an α-Si photosensitive member is used as the photosensitive material of the photosensitive drums 1a to 1d, it has a feature that the post-exposure potential on the surface is very low of 20V or less. The potential decreases, and the withstand voltage that leads to dielectric breakdown decreases. On the other hand, when latent images are formed, the charge density on the surfaces of the photosensitive drums 1a to 1d is improved, and the development performance tends to be improved.

  This characteristic is particularly prominent when the film thickness is 25 μm or less, more preferably 20 μm or less, in an α-Si photoreceptor having a dielectric constant as high as about 10. Further, when a positively charged OPC is used as the photosensitive drum 1a, the positively charged OPC (positive OPC) is stable in charging because ozone is hardly generated. In particular, a positive OPC having a single-layer structure is suitable for a system having a long life because a change in the photosensitive characteristic is small even when the film thickness changes due to long-term use and the image quality is stable.

  In order to increase the lifetime of the positive OPC, it is necessary to set the residual potential to 100 V or less. Therefore, it is particularly important to set the film thickness of the photosensitive layer to 25 μm or more and increase the amount of charge generation material added. is there. In particular, OPC having a single-layer structure is advantageous because a charge generating material is added to the photosensitive layer, and therefore the sensitivity change is small even when the photosensitive layer is reduced.

  Further, when the peripheral speed of the photosensitive drums 1a to 1d is set to 180 mm / sec or more, the process time for charging, exposing, developing, and neutralizing the photosensitive drums 1a to 1d is shortened, and printing of the image forming apparatus is performed at high speed. can do. However, since the developing nip time is short, it is necessary to further improve the developability, and it is important to reduce the adhesion force of the toner 26 to the developing roller 22.

  FIG. 2 is a side sectional view showing the structure of the developing device according to the present invention. Here, the developing device 3a disposed in the image forming unit Pa in FIG. 1 will be described, but the configuration of the developing devices 3b to 3d disposed in the image forming units Pb to Pd is basically the same, and thus described. Is omitted.

  As shown in FIG. 2, the developing device 3a includes a developing container 20 in which a two-component developer (hereinafter simply referred to as a developer) is accommodated, and the developing container 20 is divided into a first wall and a second wall by a partition wall 20a. The first and second agitating chambers 20b and 20c are divided into agitating chambers 20b and 20c, and a toner (positively charged toner) supplied from a toner container (not shown) is mixed with a carrier and agitated and charged. The stirring screw 21a and the second stirring screw 21b are rotatably arranged.

  The first and second stirring chambers are conveyed in the axial direction while being stirred by the first stirring screw 21a and the second stirring screw 21b, and are passed through a developer passage (not shown) formed in the partition wall 20a. Circulate between 20b and 20c. In FIG. 2, the developing container 3 a extends obliquely upward to the left, and a magnetic roller 23 (toner supply member) is disposed above the first stirring screw 21 a in the developing container 20.

  A developing roller 22 (toner carrier) is disposed oppositely to the upper left of the magnetic roller 23, and the developing roller 22 faces the photosensitive drum 1a on the opening side of the developing container 20 (left side in FIG. 2). The developing roller 22 and the magnetic roller 23 rotate clockwise in the figure. Note that a toner sensor (not shown) is disposed in the developing container 20 so as to face the second stirring screw 21b, and from the toner container through the toner supply port 20d according to the toner concentration detected by the toner sensor. Thus, the toner is supplied into the developing container 20.

  FIG. 3 is a schematic diagram showing a connection state of the first and second power sources in the developing device of the present embodiment. 4A shows the waveforms of the first and second biases applied to the developing roller and the magnetic roller used in this embodiment, and FIG. 4B shows the combined waveform of these. FIG. The developing device will be described in detail below with reference to FIGS.

  It is important to define the particle size distribution of the toner 26 in order to avoid selective developability. In general, the spread of the particle size distribution of the toner 26 is measured by, for example, a particle size distribution measuring device such as Multisizer III (manufactured by Beckman Coulter, Inc.) with an aperture diameter of 100 μm (measurement range: 2.0 to 60 μm). Is expressed by a ratio between the volume distribution average particle diameter and the number distribution average particle diameter. In order to prevent selective development, it is important to reduce the ratio. When the distribution is wide, toner 26 having a relatively small particle size is accumulated on the developing roller 22 during continuous printing, and developability is deteriorated.

  In addition, it is generally well known that the toner volume average particle diameter is reduced in order to improve the image quality. On the other hand, if the toner volume average particle diameter is reduced, the influence of van der Waals force becomes stronger. It is known that it becomes difficult to separate from the surface of the developing roller 22 or to peel off from the surface of the developing roller 22. Therefore, it is preferable to define the volume average particle diameter Dt of the toner 26 in the range of 4.0 μm ≦ Dt ≦ 7.0 μm.

  If Dt is less than 4.0 μm, the adhesive force is too strong, and the developability and the recoverability of toner from the developing roller may be reduced. Conversely, if it exceeds 7 μm, the reproducibility of one dot becomes difficult and it is difficult to achieve high image quality. The CV value in the number particle size distribution of the toner 26 is preferably 25.0% or less. When the CV value is more than 25.0%, the distribution of the particle size distribution is large and the selective developability becomes remarkable.

  The carrier 27 has a role of collecting undeveloped toner on the developing roller 22 and supplying toner thereafter. As the carrier 27, a magnetite carrier, a Mn ferrite, a Mn—Mg ferrite, a Cu—Zn, a resin carrier in which a magnetic material is dispersed in a resin, and the like can be used. It is also possible to process and use.

In order to peel off the toner 26 firmly and electrostatically adhered between the developing roller 22 and the magnetic roller 23 with the magnetic brush 28 and supply the toner 26 necessary for the development, the volume resistivity is 10 ⁶ Ωcm to 10 −10. It is preferable to use a carrier 27 in the range of ¹³ Ωcm. Further, by using the carrier 27 having a weight average particle diameter of 50 μm or less, the surface area of the carrier 27 can be increased and the number of contacts with the toner can be increased.

  The developing roller 22 carries a toner layer 29 of the toner 26 supplied from the magnetic brush 28, and causes the toner 26 to fly from the toner layer 29 to develop the electrostatic latent image on the photosensitive drum 1a. The surface of the developing roller 22 is composed of a sleeve made of uniform conductive aluminum, SUS, conductive resin coating, or the like.

  By coating the surface of the developing roller 22 with resin, a leak margin can be secured. By applying a fluororesin or urethane resin with good releasability of the toner 26 as such resin, leakage can be suppressed even when a thin α-Si photosensitive drum 1a having a thickness of 20 μm or less is used. It is possible to suppress problems such as black spots on the photosensitive drum 1a.

  In particular, when the toner 26 is positively charged, toner adhesion can be reduced by using a urethane resin having the same polarity, for example, a silicon-modified urethane resin. As a result, the toner can easily fly and the developing property can be improved, and the toner peeling property (recoverability) from the developing roller 22 to the magnetic roller 23 can be improved. However, the coating material and coating conditions can be appropriately set according to the characteristics of the toner, and are not particularly limited.

  A bias applied to the developing roller 22 is a first bias, and a bias applied to the magnetic roller 23 is a second bias. Connected to the shaft portion of the developing roller 22 is a first power source 30 including a DC power source 30a and an AC power source 30b, whereby a first bias is applied.

  The magnetic roller 23 is formed in a cylindrical shape that can rotate with a nonmagnetic metal material, and a plurality of fixed magnets are disposed inside the magnetic roller 23 to generate a magnetic brush 28 by a carrier 27 contained in the developer. The layer thickness of the brush 28 is regulated by the ear cutting blade 25. In addition to the first power source 30, the shaft portion is electrically connected to a common ground with the first power source 30, and a second power source 31 comprising a DC power source 31a and an AC power source 31b is connected. Yes. Thereby, the second bias is further superimposed on the first bias. Details of the first bias and the second bias will be described later.

  Then, the developer supplied from the toner container is circulated through the developing container 20 while being stirred by the first and second stirring screws 21a and 21b in the developing container 20, and the toner is charged by friction between the toner and the carrier. The developer is conveyed to the magnetic roller 23 by the second stirring screw 21b.

  A magnetic brush 28 is formed on the magnetic roller 23 by the developer, and the layer thickness of the magnetic brush 28 is regulated by the ear cutting blade 25. The magnetic brush 28 is in contact with or close to the developing roller 22 with a certain layer thickness. A toner layer (toner thin layer) is formed on the developing roller 22 by a potential difference formed between the magnetic roller 23 and the developing roller 22 by the bias. Further, the toner layer 29 is formed on the developing roller 22 and the undeveloped toner on the developing roller 22 is collected on the magnetic roller 23 by the potential difference between the developing roller 22 and the magnetic roller 23.

The thickness of the toner layer 29 on the developing roller 22 varies depending on the resistance of the toner, the rotational speed difference between the developing roller 22 and the magnetic roller 23, and the like, but is controlled by the potential difference ΔV between the developing roller 22 and the magnetic roller 23. Is possible. The toner layer 29 tends to be thicker by increasing ΔV and thinner by decreasing ΔV. Considering these, in order to obtain the thickness of the toner layer 29, the range of ΔV is preferably set to 100V to 350V.

  The toner on the developing roller 22 flies to the photosensitive drum 1a due to a potential difference formed between the developing roller 22 and the photosensitive drum 1a by the first bias, and forms an electrostatic latent image formed on the drum surface. The toner image is formed by being carried. In order to prevent scattering of the toner, it is preferable to apply the AC voltage from the first and second AC power supplies 30b and 31b immediately before the development.

  The development residual toner remaining on the developing roller 22 is not provided with a special device such as a scraping blade, and the magnetic brush 28 on the magnetic roller 23 comes into contact with the toner layer 29 on the developing roller 22. It is also collected by the brush effect caused by the difference in peripheral speed with the developing roller 22. The collected toner 26 is stirred by the stirring screw 21a (see FIG. 2), and the replacement of the toner 26 is promoted.

  At this time, since the width of the magnetic brush 28 corresponds to the width for collecting the toner 26 on the developing roller 22, the width of the developing roller 22 is made shorter than the width of the magnetic brush 28 to ensure that the toner 26 has not been collected. The area can be eliminated. As a result, the toner 26 adhering to the outside of the magnetic brush 29 area in the sleeve of the developing roller 22 is eliminated, and toner scattering at both ends of the developing roller 22 can be eliminated.

  As a method for promoting the replacement of the toner, the toner 26 on the developing roller 22 is collected by setting the rotation speed of the magnetic roller 23 to 1.0 to 2.0 times the speed of the developing roller 22. At the same time, toner set to an appropriate density can be supplied to the developing roller 22, and a uniform toner layer 29 can be formed.

In order to maintain a uniform image density, a potential difference ΔV between the developing roller 22 and the magnetic roller 23 before and after image formation, until the next image formation, and during non-image formation such as when the apparatus is started up.
By eliminating the potential and making the potential equipotential, it is possible to collect only the magnetic brush 28, and it is possible to collect the toner on the developing roller 22 to the magnetic roller 23 without imposing a burden on the toner.

  When α-Si is used as the photosensitive material of the photosensitive drum 1a, due to the above-described characteristics of the α-Si photosensitive member, when the film thickness of the photosensitive member is 25 μm or less, more preferably 20 μm or less, For example, development can be performed by setting Vdc1 of the first bias to 150 V or less, Vpp1 to 200 to 2000 V, and frequency to 1 to 5 kHz. When positive OPC is used as the photosensitive material, the first bias Vdc1 can be set to 400 V or less, more preferably 300 V or less, in order to prevent a strong electric field from being applied to the toner. In order to prevent leakage, it is preferable to set Vdc1 and Vpp1 so that the potential difference from the photosensitive drum 1a does not exceed 1500V.

  As shown in FIG. 4A, the first bias is applied to the DC voltage Vdc1 of the first DC power supply 30a, the peak-to-peak voltage (AC voltage) Vpp1, the duty ratio Dslv, and the frequency f of the first AC power supply 30b. And a synthesized waveform Vslv (solid line) on which a rectangular wave composed of is superimposed. The second bias is a composite in which a rectangular wave composed of the peak-to-peak voltage (AC voltage) Vpp2, the duty ratio Dmag, and the frequency f2 of the second AC power supply 31b is superimposed on the DC voltage Vdc2 of the second DC power supply 31a. It has a waveform Vmag (dashed line).

  The duty ratio Dslv indicates the duty ratio on the side (the same polarity side as the toner) that causes the toner 26 to fly from the developing roller 22 to the photosensitive drum 1a, and the duty ratio Dmag is the toner 26 from the magnetic roller 23 to the developing roller 22. The duty ratio on the side where the toner flies (the same polarity side as the toner) is shown. Next, the duty ratio will be described.

  FIG. 5 shows the developing roller 22 or the second bias when the first bias is applied when, for example, positively charged toner is used and the upper direction in the figure is a positive potential and the lower direction is a negative potential. The composite waveform of the magnetic roller 23 when applied is shown. At this time, assuming that the time during which the electric field for the toner flying from the developing roller 22 or the magnetic roller 23 is applied is a and the time during which the electric field for pulling the toner back to the developing roller 22 or the magnetic roller 23 is b, the duty ratio Dp Is represented by Dp = {a / (a + b)} × 100. That is, it is expressed as a percentage of the time during which a positive potential is applied with respect to the entire application time. When negatively charged toner is used, the duty ratio is Dp = {b / (a + b)} × 100.

  Next, a method for adjusting the first and second biases will be described with reference to FIGS. As described above, the first bias is a combined waveform Vslv having a DC voltage of Vdc1, an AC voltage Vpp1, a duty ratio of Dslv, and a frequency f. The second bias is a composite waveform Vmag having a DC voltage of Vdc2, an AC voltage of Vpp2, a duty ratio of Dmag, and a frequency f. The AC component of the second bias has the same frequency and opposite phase as the AC component of the first bias, and is set so that the duty ratio is larger than that of the first bias.

  Further, the frequency f of the first bias can be set to 1 to 5 kHz, for example, and can be equal to the frequency of the second AC bias, for example. However, the duty ratio and frequency are not particularly limited, and may be set as appropriate depending on the state of formation of the toner layer 29 on the developing roller 22 and the state of development of the electrostatic latent image on the photosensitive drum 1a. .

  As shown in FIG. 3, a first bias is applied to the developing roller 22. Further, since the second bias is applied to the magnetic roller 23 so as to overlap the first bias, the combined waveform Vmag-Vslv applied to the magnetic roller 23 is as shown in FIG. V (max) and V (min). However, since the first bias is canceled by the electric field between the developing roller 22 and the magnetic roller 23, only the second bias is applied between the magnetic roller 23 and the developing roller 22. At this time, only the first bias is applied between the developing roller 22 and the photosensitive drum 1a.

  As a result, even if the first power supply 30 and the second power supply 31 have different bias periods and duty ratios, the composite waveform of the bias formed between the developing roller 22 and the magnetic roller 23 is the second. The power supply 31 is not affected by the second bias of the power supply 31.

  On the other hand, the first power supply 30 can be superimposed on the second power supply 31. However, in such a configuration, the electric field between the developing roller 22 and the magnetic roller 23 is in a state where the second bias is canceled and only the first bias is applied, but between the developing roller 22 and the photosensitive drum 1a. Since the first bias and the second bias are applied, it becomes difficult to independently change the first and second biases, and it becomes difficult to make the developability uniform.

  Therefore, the first power supply 30 of the developing roller 22 and the second power supply 31 of the magnetic roller 23 are electrically connected to a common ground, and the first power supply 30 and the second power supply 31 are connected to the magnetic roller 23. It is preferable to use a connection configuration in which the two are superimposed.

  Also, as shown in FIG. 6, the first and second biases applied to the developing roller 22 and the magnetic roller 23 can be electrically connected to separate grounds. FIG. 6 is a schematic diagram showing a state in which the developing roller and the magnetic roller are electrically connected to separate grounds. FIG. 7A shows waveforms of the first and second biases applied to the developing roller and the magnetic roller when electrically connected to separate grounds, and FIG. 7B shows a combination of these. It is a model diagram which shows a waveform. In FIG. 7A, the duty ratio is different between Vslv (solid line) of the first power supply 30 and Vmag (broken line) of the second power supply 31, and the AC bias has the same period, the same frequency and the opposite phase as Vslv. Apply.

  However, if Dmag and Dslv are different in this configuration, the combined waveform between the developing roller 22 and the magnetic roller 23 is as shown in FIG. 7B, and the voltage Vi appears between Vmax and Vmin. Therefore, the application time of Vmax and Vmin is shortened by the application time of Vi, the time for forming the toner thin layer on the developing roller is shortened, and the recovery time of the undeveloped toner from the developing roller is also shortened. Becomes worse.

  When the setting of the first bias Vpp1 or the second bias Vpp2 is changed, Vpp2 is inevitably applied to the developing roller 22, and Vpp2 is inevitably applied to the magnetic roller 23. When Vpp2 is changed independently, it is difficult to set the bias because it affects each other.

  In the present embodiment, the bias of the first power supply 30 is applied to the developing roller 22, and the bias of the second power supply 31 is superimposed on the bias of the first power supply 30 and applied to the magnetic roller 23. The composite waveform of the bias formed between the developing roller 22 and the magnetic roller 23 becomes equal to the bias of the second power supply 31 and is not affected by the bias of the first power supply 31 applied to the developing roller 22.

  In addition, the first bias formed between the developing roller 22 and the photosensitive drum 1a is not affected by the bias of the second power supply 31, and is controlled only by the bias of the first power supply 30. The second bias and the second bias can be set independently of each other, and the voltage and duty ratio of each bias can be set. At this time, the collection of undeveloped toner from the developing roller 22 to the magnetic roller 23 depends only on the second bias.

  As described above, since the first power supply 30 and the second power supply 31 are superimposed on each other, the first bias and the second bias can be set independently. Detailed settings are possible.

  Accordingly, the first bias voltage and the duty ratio are set to be large to improve the developability, and the formation of the toner layer 29 on the developing roller 22 and the toner recovery from the developing roller 22 are favorably maintained. The bias voltage and the duty ratio of 2 can be set, and the bias balance between the developing roller 22 and the photosensitive drum 1a and between the developing roller 22 and the magnetic roller 23 can be easily achieved. .

  Further, when the first power supply 30 and the second power supply 31 are electrically connected to a common ground, as shown in FIG. 7B, they are different from the case where they are electrically connected to separate grounds. Vpp2 is not applied to the first bias. Therefore, the absolute values of Vmax and Vmin are smaller than in the case of FIG. 7B, and the electric field for moving the toner becomes weaker. Therefore, when electrically connected to a common ground, it is preferable to make Vpp1 of the first bias larger than when electrically connected to separate grounds.

  On the other hand, if the time applied to the developing roller 22 per unit time is lengthened, it may be difficult to collect the toner by the magnetic roller 23. Therefore, as described above, it is preferable to coat the surface of the developing roller 22 with, for example, a silicon-modified urethane resin.

  Then, the development residual toner on the developing roller 22 is collected so that the toner remains appropriately after each development in continuous printing, and more toner is collected after a predetermined development interval than after each development. It was. Hereinafter, after the development residual toner is collected from the developing roller 22 to the magnetic roller 23, the toner remaining on the development roller 22 is defined as a collection residual toner, and the amount thereof is defined as a collection residual toner amount Q (residual toner amount).

  That is, the development residual toner on the developing roller 22 is collected so that the recovery residual toner amount Q becomes the first predetermined amount Q1 after each development is completed, and the recovery residual toner amount Q is set at every predetermined development interval. The second predetermined amount Q2 smaller than Q1 is collected. Q1 is the amount of residual toner collected after toner collection performed after the end of the first development, and Q2 is the amount of residual toner collected after toner recovery performed for the first time after a predetermined development interval T has elapsed from the start of development. To do. The toner collection will be described.

  As described above, after the development is completed, the development residual toner on the developing roller 22 is collected by the magnetic roller 23 due to the potential difference between the developing roller 22 and the magnetic roller 23 caused by the application of the first and second biases. The Further, after the toner is collected, the magnetic brush 28 carries an amount of toner necessary for the next development.

  However, if the amount of toner collected from the developing roller 22 to the magnetic roller 23 is excessive after the completion of each development, the toner enters between the magnetic brushes 28 formed on the magnetic roller 23, and the collected toner is stored in the magnetic brush 28. In addition to being carried on the surface of the magnetic roller 23, it may be carried directly on the surface of the magnetic roller 23.

  In this case, the toner carried on the surfaces of the magnetic brush 28 and the magnetic roller 23 flies to the developing roller 22 at the time of the next development, so that the toner amount on the developing roller 22 is excessive until the toner amount on the roller is saturated. Toner is supplied. As a result, the density of the leading end of the transfer paper P on the next page (the rotation direction of the photosensitive drum 1a) becomes higher than the other portions of the transfer paper P.

  On the other hand, if the amount of toner collected from the developing roller 22 to the magnetic roller 23 is too small, the amount of residual toner collected may increase. In such a case, the amount of toner supplied from the developing roller 22 to the photosensitive drum 1a varies. Since it becomes easy, an image density transition occurs.

Accordingly, after each development is completed, the development residual toner is collected so that the collection residual toner amount Q becomes the first predetermined amount Q1, thereby increasing the image density at the front end in the transport direction on the transfer paper P of the next page and the image. It is possible to prevent density transition defects. In consideration of the above-mentioned problem that the amount Q of collected residual toner has on the formed image, the value Qx that Q1 can take can be set to 0.3 mg / cm ² or more and 0.6 / cm ² or less, for example.

By increasing Q1 to 0.3 mg / cm ² or more, the increase in the tip density can be sufficiently prevented. On the other hand, by setting the Q1 to 0.6 mg / cm ² or less, image density transition failure is sufficiently prevented. Can be prevented. Therefore, an appropriate amount of toner can be left on the developing roller 22. However, Q1 is not particularly limited as long as it can prevent the increase in the tip density and the image density transition failure, and can be appropriately set according to the image density, the type of transfer paper P, the printing speed, and the like.

  The method for evaluating the tip concentration is not particularly limited, but can be evaluated visually, for example. The evaluation method of the image density transition is not particularly limited, but can be evaluated by, for example, the reflection density transition. The transition of the reflection density can be evaluated, for example, by measuring the reflection density of the transfer paper P every minute after the start of development and setting the allowable fluctuation range to 1% or less.

  Further, even if the collection residual toner amount Q is set to Q1 in this way, if the collection residual toner after completion of each development adheres to the surface of the developing roller 22, the toner is charged up due to friction or the like, and an image such as image unevenness There is a risk of failure.

  In view of this, the development residual toner is collected such that the collection residual toner amount Q on the developing roller 22 becomes Q2 smaller than Q1 at every predetermined development interval T. By making Q2 smaller than Q1, it is possible to further collect the remaining toner after completion of each development. Thereby, it is possible to prevent the collection residual toner from accumulating on the developing roller 22 and adhering thereto. The method for evaluating the toner adhesion state is not particularly limited. For example, the evaluation can be performed based on ease of peeling when touched with eyes or fingers.

Further, by setting Q2 to be equal to or less than the lower limit value Qx (min) of Qx, it is possible to collect a larger amount of residual toner after completion of each development. Thereby, it is possible to further prevent the collection residual toner from adhering to the developing roller 22. Further, Q2 is preferably 0.3 mg / cm ² or less. By setting Q2 to 0.3 cm ² or less, toner adhesion can be sufficiently prevented even under low temperature and low humidity conditions.

However, Q2 is not particularly limited as long as it is smaller than Q1, and can be appropriately set according to the image density, the type of transfer paper P, the printing speed, and the like. The toner collection at each predetermined development interval T is also included in the present invention when Q2 is 0 mg / cm ^{2. In} this case, however, the toner is unavoidably placed on the developing roller 22 due to the toner collection capability. It is allowed to remain.

  Further, the predetermined development interval T can be set by, for example, the development driving time, and for example, the predetermined development interval T can be set once per minute. If the predetermined interval time T is small, the printing efficiency is lowered. If the predetermined interval time T is large, it may be difficult to adjust the collected residual toner amount Q to Q2. Therefore, the predetermined development interval T can be appropriately set in consideration of these factors, for example. In addition, the predetermined development interval T can be appropriately set according to the image density, the type of transfer paper P, the printing speed, and the like. For example, the predetermined development interval T is set to once every predetermined number of developments (predetermined number of printed sheets). You can also

  In the toner collection at every predetermined development interval T, when the collected residual toner amount Q becomes small, the toner supply amount to the photosensitive drum 1a is insufficient in the initial development immediately after, and the leading edge of the transfer paper P on the next page in the transport direction. There is a risk that the partial concentration may decrease. In such a case, after the toner is collected, for example, the developing roller 22 can be developed after being rotated by a predetermined number of rotations (idle operation) without causing the toner to fly to the photosensitive drum 1a.

  As a result, the amount of toner on the developing roller 22 can be further stabilized, so that the shortage of toner supply to the photosensitive drum 1a can be resolved and the decrease in the tip end portion density can be prevented. On the other hand, if it is rotated for a long time, the printing efficiency decreases. Therefore, the number of rotations can be set in consideration of these, for example, and can be set to about 2 to 4 rotations, for example.

  The method of adjusting the amount Q of collected residual toner to Q1 and Q2 can be performed by appropriately setting the application conditions of the first and second biases Vslv and Vmag.

  In this adjustment, for example, the first bias Vslv is not changed between development and non-development from the time of development, and the same polarity side as the toner (the toner is the magnetic roller 23) of the AC component Vpp2 of the second bias Vmag. The peak voltage value Vpp2 (max) on the side from the developing roller 22 toward the developing roller 22 can be changed by changing the amount of decrease from the developing time. Since the toner easily returns from the developing roller 22 to the magnetic roller 23 as Vpp2 (max) decreases during non-development, the amount of toner collected increases. Therefore, the remaining amount Q of collected toner on the developing roller 22 can be adjusted by appropriately changing the amount of decrease in Vpp2 (max).

  At this time, for example, the peak voltage value Vpp2 (min) on the side opposite in polarity to the toner (on the side where the toner returns from the developing roller 22 to the magnetic roller 23) can be constant during development and during non-development. Further, as Vpp2 (min) is decreased, the toner is more likely to return from the developing roller 22 to the magnetic roller 23, but the potential difference from Vslv is increased, and leakage between the magnetic roller 23 and the developing roller 22 is likely to occur. Become. Therefore, for example, Vpp2 (min) can be set in consideration of these. It is also possible to change both Vpp2 (max) and Vpp2 (min) from the time of development.

  In this way, for example, during non-development, by appropriately changing Vmag from the time of development, it is possible to adjust the recovered residual toner amount Q to be Q1 and Q2. However, the setting method is not particularly limited as long as the recovery residual toner amount Q can be set to Q1 and Q2. In addition, Vslv can be appropriately changed according to, for example, the amount of decrease in Vmag. Such application conditions can be set in advance by a preliminary experiment or the like.

  At this time, as shown in FIGS. 3 and 4, when Vslv and Vmag are electrically connected to a common ground and Vmag is superimposed on Vslv and applied to the magnetic roller 23, Vslv and Vmag affect each other. Therefore, it is easier to set the conditions for Vslv and Vmag when setting the collected residual toner amount Q to Q1.

  Next, the operation of the developing device of the present invention will be described with reference to FIGS. A magnetic brush 28 is formed on the magnetic roller 23 by the developer composed of the charged toner 26 and the carrier 27 shown in FIG. 3, and the magnetic brush 28 is layer-regulated by the earbrushing blade 25, as shown in FIG. A composite waveform Vmag of the second bias is applied, and a toner layer 29 of only toner 26 is formed on the developing roller 22 by a potential difference between the magnetic roller 23 and the developing roller 22.

  Next, the latent image exposed and formed on the photosensitive drum 1a is applied with the first bias composite waveform Vslv shown in FIG. 4A, and the toner 26 flies to the photosensitive drum 1a. The developed toner image is formed on the photosensitive drum 1a. Then, the toner image on the photosensitive drum 1 a is primarily transferred to the intermediate transfer belt 8, the toner image is secondarily transferred to the sheet conveyed to the intermediate transfer belt 8, fixed by the fixing unit 7, and discharged. .

  After each development, the development residual toner on the development roller 22 is peeled off by the second bias combined waveform Vmag shown in FIG. 4B so that the recovery residual toner amount Q on the development roller 22 becomes Q1. Collected in the magnetic roller 23. In addition, at the predetermined development interval T, after completion of the corresponding development, the development residual toner on the development roller 22 is peeled off and collected by the magnetic roller 23 so that the recovery residual toner amount Q on the development roller 22 becomes Q2.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above embodiment, the developing device using positively charged toner whose charging direction is positive (plus side) has been described as an example. However, the developing device using negatively charged toner whose charging direction is negative (minus side) is described. Is equally applicable. In that case, a negatively chargeable resin may be used as the coating material.

  Further, here, a tandem color image forming apparatus using an intermediate transfer belt has been described as an example, but the present invention is an image forming apparatus provided with a developing unit capable of developing by flying toner. The same applies to a tandem color image forming apparatus that directly transfers to a recording medium on a conveyor belt, a digital multifunction peripheral, an analog monochrome image forming apparatus, or another image forming apparatus such as a facsimile or a printer. Can do.

  Hereinafter, the present invention will be described in more detail with reference to examples.

  The developing devices 3a to 3d (see FIGS. 1 and 2) of the above-described embodiment are mounted on the tandem color image forming apparatus shown in FIG. 1, and a toner layer 29 is formed on the developing roller 22 under the following conditions. The toner was developed on the body drum 1a, transferred to the transfer paper P, and after the development was completed, the development residual toner on the developing roller 22 was collected on the magnetic roller 23.

  The number average particle diameter of the toner was 6 μm, the number average particle diameter of the carrier was 35 μm, and the toner charge amount was 15 μC / g. Α-Si was used as the photosensitive drum, and the surface potential was set to 350V. In addition, the gap between the photosensitive drums 1a to 1d and the developing roller 22 was 200 μm, and the gap between the developing roller 22 and the magnetic roller 23 was 320 μm. Further, the time required for one rotation of the developing roller 22 was set to 30 msec.

  Vdc1 is 100V, Vpp1 is 1.65kV (Vpp1 (max) is 925V, Vpp (min) is -725V), Vdc1 is VV1v of Vslv of the developing roller 22 at the time of development and after development, and the frequency is 4.%. The frequency was 5 kHz.

Further, among the Vmags of the magnetic roller 23 at and after the development, Vdc2 is 200 V, the duty ratio is 70%, the frequency is 4.5 kHz, and the Vpp2 of the magnetic roller 23 is appropriately changed by the method described above. As shown in Table 1, the amount of residual toner Q collected on the developing roller 22 after development is 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0,. 8. Adjusted to 0.9 mg / cm ² and collected the development residual toner. Note that the remaining amount Q of collected toner after the completion of the first development was set to each of the above conditions.

  Then, printing was performed under each of the above conditions, and the transition of the leading edge density and image density on the next page was examined. The results are shown in Table 1. In Table 1, the tip concentration was examined by visual inspection, and it was evaluated as “◯” when no density defect was observed, and “X” when observed. Further, the transition of the image density is determined by checking the reflection density of the transfer paper P on which the toner image is transferred every 1 minute from the start of development, and when the allowable fluctuation range of the reflection density is 0.1% or less, 0 X was over 1%.

As shown in Table 1, when the residual toner amount Q is 0.2 mg / cm ² or less, the tip density of the transfer paper P on the next page is increased, whereas when 0.3 mg / cm ² or more, the tip part is increased. No poor density was observed. Further, at 0.7 mg / cm ² or more, an image density transition failure was observed on the transfer paper P, whereas at 0.6 mg / cm ² or less, no image density transition failure was observed. As a result, it has been found that when the first predetermined amount Q1 is 0.3 mg / cm ² or more and 0.6 mg / cm ² or less, the tip density defect and the image density transition defect can be prevented.

Under the same conditions as in Example 1, Vpp2 of the magnetic roller 23 is appropriately changed by the above method, and the amount Q of collected residual toner on the developing roller 22 is shown in Table 2 at an interval of once per minute from the start of development. As shown, it is adjusted to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 mg / cm ^2, and development residual toner Was collected.

  Under each condition, the state of toner adhesion to the developing roller 22 after printing 1000 sheets was examined. Note that, after one minute has elapsed from the start of development, the residual toner amount Q after the first collection is set to the above-mentioned conditions. Further, after each toner was collected, the developing roller 22 was operated three and a half idle. Further, such recovery was performed under environmental conditions of a temperature of 10 ° C. and a humidity of 15% RH.

  The results are shown in Table 2. In Table 2, the adhesion state of the toner was observed, and the case where it was peeled off from the developing roller 22 when lightly rubbed with a finger was rated as “No”, and the case where it was not peeled was marked as “Poor”.

As a result, when the residual toner amount Q was 0.4 g / cm ² or more, adherence to the developing roller 22 was observed, but when 0.3 g / cm ² or less, adhesion was not recognized. Therefore, it has been found that the toner remaining on the developing roller 22 can be prevented by setting the recovery residual toner amount Q to 0.3 g / cm ² or less. Moreover, it turned out that adhesion | attachment can fully be prevented by collection | recovery once per minute. In addition, since the toner has high chargeability and good results are obtained in a low-temperature and low-humidity environment that easily adheres to the developing roller 22, a sufficiently good result can be obtained under high-temperature and high-humidity conditions. It is guessed.

From Example 1 and Example 2 described above, the development residual toner on the development roller 22 is transferred to the magnetic roller 23, and at the end of each development, the recovery residual toner amount Q is 0.3 mg / cm ² or more and 0.6 mg / cm ² or less ( Q1) is collected, and once every minute (predetermined development interval T), collection is performed so that the remaining toner amount Q is 0.3 g / cm ² or less (Q2) and smaller than Q1. Thus, it has been found that image defects can be prevented without lowering the printing efficiency.

  The present invention uses a two-component developer containing at least a carrier and a toner, a toner carrier disposed opposite to the image carrier, and a toner supply for forming a toner thin layer on the toner carrier using a magnetic brush A development bias is applied to the toner carrier and the toner supply member to develop an electrostatic latent image on the surface of the image carrier, and after the development is completed, the development residue on the toner carrier is developed. In the developing device that collects toner on the toner supply member, when the development is continuously performed, the amount of residual toner on the toner carrying member becomes a first predetermined amount after the completion of each development. The residual toner amount is recovered at a predetermined predetermined interval so that the residual toner amount becomes a second predetermined amount smaller than the first predetermined amount.

  As a result, after each development, it is possible to collect more toner than after the completion of each development, while leaving a suitable amount of toner on the toner carrier, and each time a predetermined development is completed. In this case, it is possible to prevent image defects without lowering the printing efficiency.

In addition, the first predetermined amount is set to 0.3 mg / cm ² or more and 0.6 mg / cm ² or less, and the second predetermined amount is set to 0.3 mg / cm ² or less, so that the toner is carried after completion of each development. An appropriate amount of toner can be left on the body, and after the predetermined development interval, the toner can be sufficiently collected even under low temperature and low humidity conditions. It is possible to prevent toner from adhering to the roller more sufficiently and to prevent image defects more sufficiently.

  Further, after the toner is collected at a predetermined development interval and before the next development is performed, the toner carrier is rotated at a predetermined number of revolutions without causing the toner to fly from the toner carrier to the surface of the image carrier. As a result, the amount of toner on the toner carrying member can be further stabilized, so that it is possible to prevent the lowering of the tip portion density due to insufficient toner supply to the image carrying member.

  Further, the first bias applying means for applying the first bias to the toner carrier and the ground common to the first bias applying means are electrically connected to the toner supply member, and the second bias is applied to the toner supply member. By applying a second bias applying unit that superimposes the bias of the first bias AC component and the second bias AC component independently of each other without affecting each other. Since it can be set, the residual toner amount after collecting the development residual toner can be easily adjusted.

  Further, by using the image forming apparatus provided with the developing device, it is possible to perform image formation in which image defects are prevented without reducing printing efficiency.

FIG. 1 is a schematic diagram illustrating an overall configuration of an image forming apparatus in which a developing device of the present invention is mounted. These are side surface sectional views which show the structure of the developing device of this invention. These are schematic diagrams showing the connection state of the first and second power sources in the developing device of the present embodiment. FIG. 4 is a schematic diagram showing waveforms of first and second biases applied to the developing roller and magnetic roller used in the present embodiment, and FIG. 4A is a diagram illustrating the first and second biases, respectively. FIG. 4B is a schematic diagram showing these combined waveforms. These are schematic diagrams showing a composite waveform of a developing roller when a first bias is applied or a magnetic roller when a second bias is applied. These are the schematic diagrams which show the state which connected the developing roller and the magnetic roller to the separate ground. FIG. 7 is a schematic diagram showing waveforms of first and second biases applied to the developing roller and the magnetic roller when electrically connected to separate grounds, and FIG. 7A shows the first and second waveforms. FIG. 7B is a schematic diagram showing these combined waveforms.

Explanation of symbols

Pa to Pd Image forming section 1a to 1d Photosensitive drum (image carrier)
3a to 3d Developing device 20 Developing container 21a First stirring screw 21b Second stirring screw 22 Developing roller (toner carrier)
23 Magnetic roller (toner supply member)
26 toner 27 carrier 28 magnetic brush 29 toner thin layer 30 first power source 30a first DC power source 30b first AC power source 31 second power source 31a second DC power source 31b second AC power source 100 image forming apparatus

Claims (6)

A two-component developer containing at least a carrier and a toner is used, and a toner carrier disposed opposite to the image carrier;
A toner supply member that forms a toner thin layer on the toner carrier using a magnetic brush, and
By applying a developing bias to the toner carrier and the toner supply member, an electrostatic latent image on the surface of the image carrier is developed from the toner carrier, and after development is completed, the development residual toner on the toner carrier In the developing device for collecting the toner in the toner supply member,
When continuously developing, the development residual toner is
After each development, the residual toner amount on the toner carrier is collected to become a first predetermined amount,
The developing device, wherein the residual toner amount is collected at a second predetermined amount smaller than the first predetermined amount at every predetermined development interval.   The developing device according to claim 1, wherein the second predetermined amount is equal to or less than a lower limit value that can be taken by the first predetermined amount. The first predetermined amount is 0.3 mg / cm ² or more and 0.6 mg / cm ² or less,
The developing device according to claim 2, wherein the second predetermined amount is 0.3 mg / cm ² or less.   After the toner is collected at each predetermined development interval and before the next development is performed, the toner carrier is rotated at a predetermined number of revolutions without causing the toner to fly from the toner carrier to the surface of the image carrier. The developing device according to claim 1, wherein First bias applying means for applying a first bias to the toner carrier;
A second bias applying unit that is electrically connected to a common ground with the first bias applying unit and that applies a second bias superimposed on the first bias to the toner supply member; The developing device according to claim 1, wherein:   An image forming apparatus comprising the developing device according to claim 1.

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