JP2011095350A - Developing apparatus and image forming apparatus including the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing apparatus capable of stably ensuring image quality over a long term by suppressing not only deterioration of developer but also deterioration of a surface of a developer carrier, and to provide an image forming apparatus including the same. <P>SOLUTION: Each of the developing apparatuses 3a to 3d is provided with a magnetic roller 22, a developing roller 23, a regulation blade 25 and a space adjusting device 27. The regulation blade 25 comes close to and separates from the magnetic roller 22 by the space adjusting device 27. When printing an image of a high printing rate, circumferential speed of the magnetic roller 22 is decreased, and also the regulation blade 25 is separated from the magnetic roller 22 to increase a developer amount on the magnetic roller 22. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device mounted on an image forming apparatus such as a copying machine, a facsimile machine, a printer, and the like, and particularly to an image forming apparatus provided with the same, using a two-component developer composed of a magnetic carrier and toner and charged. The present invention relates to a developing device that develops an electrostatic latent image on an image carrier by moving only toner.

  Conventionally, as a developing method using dry toner in an image forming apparatus using an electrophotographic process, a one-component developing method using no carrier and a non-magnetic toner using a magnetic carrier (hereinafter also simply referred to as a carrier) are used. There is known a two-component developing system that uses a two-component developer to be charged and develops an electrostatic latent image on a photosensitive member with a magnetic brush composed of toner and a carrier formed on a developing roller.

  The one-component development method is suitable for high image quality because the electrostatic latent image on the image carrier is not disturbed by the magnetic brush, but toner adheres to the regulating blade, resulting in non-uniform layer formation. It sometimes caused image defects.

  In the case of color printing in which color superposition is performed, since the color toner is required to be transparent, it needs to be a non-magnetic toner. Therefore, in a full-color image forming apparatus, a two-component development system in which toner is charged and conveyed using a carrier is often employed. 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 is disadvantageous in terms of image quality due to the influence of the magnetic brush described above.

  As one means for solving these problems, a magnetic roller (developer carrier) is used to place developer on a developing roller (toner carrier) placed in non-contact with the photosensitive member (image carrier). At the time of transfer, a non-magnetic toner is transferred onto the developing roller while leaving the magnetic carrier on the magnetic roller to form a toner thin layer (toner layer), and an electrostatic latent image on the photoreceptor is formed by an AC electric field. A developing method for adhering toner has been proposed.

  However, such a developing device has problems such as deterioration of a developer that has been subjected to thermal stress when driven for a long time, and toner being excessively charged and adhering to the developing roller (sleeve contamination). Further, the deterioration of the developer and the adhesion of the toner to the developing roller are also affected by the printing rate and the like.

  Therefore, in Patent Document 1, by controlling the amount of rotation of the agitating unit per unit operation time according to the printing rate, the image quality resulting from deterioration and deterioration of the developer due to stress in the developing device with enhanced agitation performance. A method of forming a high-quality image while preventing the degradation is disclosed.

  Further, in Patent Document 2, by changing the strength of the magnetic field generated in the regulating portion that regulates the developer amount on the surface of the developer carrying member, the stress on the toner is alleviated, and the toner life is extended. A method for forming a stable toner image is disclosed.

In Patent Document 3, the thickness of the toner carried on the toner carrying member is set to 6 μm to 15 μm, the first toner charge amount distribution of the toner, the toner carried on the developer carrying member, and the like. By setting the difference in the half-value width of the second toner charge amount number distribution to 0.8 (10 ⁻¹⁰ C / m) or less, image density defects, fogging, toner scattering, ghosting, etc. are suppressed, and over a long period of time. A method for maintaining stable and stable performance is disclosed.

JP 2006-235271 A JP 2006-208579 A JP 2009-31749 A

  However, in the method of Patent Document 1, although the stress of the developer at the time of stirring by the stirring means is reduced, the stress generated between the developer and the developing roller cannot be reduced, and the developer is sufficiently deteriorated. There is a possibility that it cannot be suppressed. Further, in the method of Patent Document 2, it is possible to reduce the stress on the toner, but there is a demand for further relaxation of the stress in order to further improve the image quality.

  On the other hand, in the method of Patent Document 3, the surface of the developing roller (toner carrier) is covered with a silicone-modified urethane resin to improve the toner releasability. When such a coating layer is provided, an external component of the toner may be deposited on the surface of the developing roller due to sliding from the magnetic brush formed on the magnetic roller during long-time driving. There is a possibility that image density may be lowered, or leakage may occur when an AC voltage is applied to the developing roller, causing image defects.

  In addition, in order to stably form an image by the two-component development method, it is necessary to keep a certain amount of toner moved from the magnetic roller onto the developing roller on the developing roller. When the adhesion between the toner and the developing roller is large, the image density may be lowered. In addition, such a problem increases as the resin fine particles are added as an external component to the toner, and is also affected by the printing rate.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention suppresses not only the developer but also the surface of the developer carrying member, and can stably ensure image quality over a long period of time, and an image forming apparatus having the same The purpose is to provide.

  In order to achieve the above object, the present invention uses a developer containing at least a toner and a carrier, and has a magnetic field generating member having a plurality of magnetic poles provided therein to supply the toner to the image carrier. A developing device provided with a body, an agitating and conveying member for agitating and conveying the developer carried on the developer carrying body, and a regulating member for regulating the amount of developer on the developer carrying body, When printing an image having a printing ratio equal to or higher than the first predetermined value, the peripheral speed of the developer carrier is reduced and the amount of developer carried on the developer carrier is increased. .

  According to the present invention, in the developing device having the above-described configuration, a toner carrier that carries the toner supplied from the developer carrier and supplies the toner to the image carrier is provided, and has a first predetermined value or more. When printing an image having a printing rate, a difference in peripheral speed between the developer carrier and the toner carrier is reduced.

  According to the present invention, in the developing device configured as described above, when a DC voltage and an AC voltage are applied to the toner carrier, and an image having a printing rate equal to or higher than the first predetermined value is printed, the frequency of the AC voltage is set. It is characterized by increasing.

  According to the present invention, in the developing device configured as described above, a resin coat layer is provided on the surface of the toner carrier.

  According to the present invention, in the developing device configured as described above, the developer amount is increased by increasing a distance between the regulating member and the developer carrier.

  According to the present invention, in the developing device configured as described above, the amount of the developer is increased by reducing the strength of a magnetic field generated between the regulating member and the magnetic pole closest to the regulating member. It is said.

  According to the present invention, in the developing device configured as described above, a DC bias and an AC bias are applied to the developer carrier, and the DC bias is applied when printing an image having a printing rate equal to or higher than the first predetermined value. It is characterized by being enlarged.

  According to the present invention, in the developing device configured as described above, when an image having a printing rate equal to or smaller than a second predetermined value smaller than the first predetermined value is printed, the rotational speed of the stirring and conveying member is reduced. It is said.

  According to the present invention, in the developing device configured as described above, a toner to which resin fine particles are externally added is used.

  The present invention also provides an image forming apparatus including the developing device having the above-described configuration.

  According to the first configuration of the present invention, when printing an image having a printing rate equal to or higher than the first predetermined value, the developer carrying member has a lower peripheral speed and a developer carried on the developer carrying member. By increasing the amount, the rubbing force between the developer carried on the developer carrying member and the developer carrying member is reduced, and the developer carrying in the developer carried on the developer carrying member is increased. The ratio of the developer that comes into contact with the body can be reduced. Thereby, not only the developer but also the deterioration of the developer carrying member can be suppressed, and the image quality can be stably secured over a long period of time.

  According to the second configuration of the present invention, in the developing device of the first configuration, a toner carrier that carries the toner supplied from the developer carrier and supplies the toner to the image carrier is provided. When printing an image having a printing ratio equal to or higher than the first predetermined value, the amount of toner on the toner carrier is increased and the magnetic brush is used by reducing the difference in peripheral speed between the developer carrier and the toner carrier. Since the rubbing force can be reduced, the deterioration of the toner on the toner carrier can be suppressed.

  According to the third configuration of the present invention, in the developing device having the second configuration, a DC voltage and an AC voltage are applied to the toner carrier, and an image having a printing rate equal to or higher than the first predetermined value is printed. In this case, since the movement of the toner from the toner carrier to the image carrier can be promoted by increasing the frequency of the alternating voltage, the rubbing force between the toner and the toner carrier is reduced, Developability can be improved.

  According to the fourth configuration of the present invention, in the developing device having the second or third configuration, the adhesion of the toner to the toner carrier is suppressed by providing the resin coat layer on the surface of the toner carrier. Therefore, it is possible to suppress the deterioration of the toner more effectively and prevent the occurrence of leakage between the toner carrier and the image carrier.

  According to the fifth configuration of the present invention, in the developing device having any one of the first to fourth configurations, the developer amount is increased by increasing the distance between the regulating member and the developer carrier. By doing so, the amount of developer on the developer carrying member can be surely increased, which is effective.

  According to the sixth configuration of the present invention, in the developing device having any one of the first to fourth configurations, the strength of the magnetic field generated between the regulating member and the magnetic pole closest to the regulating member is reduced. By reducing the amount, the amount of developer on the developer carrying member can be reliably increased by increasing the amount of developer, which is effective.

  Further, according to the seventh configuration of the present invention, in the developing device having any one of the first to sixth configurations, a DC bias and an AC bias are applied to the developer carrier, and the first predetermined value or more is applied. When printing an image with a printing rate of, it is possible to easily separate the developer from the developer carrier by increasing the direct current bias, thereby further suppressing deterioration of the developer and the developer carrier. Can do.

  According to the eighth configuration of the present invention, the developing device having any one of the first to seventh configurations prints an image having a printing rate equal to or smaller than a second predetermined value smaller than the first predetermined value. In this case, by reducing the rotation speed of the agitating / conveying member, it is possible to suppress the deterioration of the developer even in a state where the developer tends to stay on the developer carrying member.

  According to the ninth configuration of the present invention, in the developing device having any one of the first to eighth configurations, the toner adheres to the developer carrier by using the toner to which resin fine particles are externally added. Even in such a state, it is possible to suppress toner deterioration.

  Further, according to the tenth configuration of the present invention, the image forming apparatus including the developing device having any one of the first to ninth configurations makes it possible to stably ensure the quality over a long period of time. Can be formed.

1 is a schematic diagram illustrating an overall configuration of an image forming apparatus including a developing device according to a first embodiment of the present invention. Side surface sectional view which shows the structure of the image development apparatus concerning this embodiment. FIG. 3A is a partial side cross-sectional view showing the periphery of the regulating blade of the developing device according to the present embodiment, and FIG. 3A is a diagram showing a state when printing an image with a non-high printing rate, and FIG. ) Is a diagram showing the state when printing an image with a high printing rate The figure which shows an example of the bias structure applied to a magnetic roller and a developing roller The figure which shows an example of the bias waveform applied to a developing roller and a magnetic roller FIG. 6A is a partial side cross-sectional view illustrating the periphery of a regulating blade of a developing device according to a second embodiment of the present invention, and FIG. 6A is a diagram illustrating a state when printing an image with a non-high printing rate; FIG. 6B is a diagram showing a state when printing an image with a high printing rate. 1 is a block diagram illustrating an example of a control mechanism of an image forming apparatus including a developing device according to a first embodiment of the present invention. 6 is a flowchart illustrating an example of a control procedure of the image forming apparatus including the developing device according to the first embodiment of the invention. The figure which shows an example of the figure used for the evaluation of the ghost

  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 according to the present invention. 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.

  The image forming portions Pa to Pd are provided with photosensitive drums 1a, 1b, 1c, and 1d that carry visible images (toner images) of the respective colors, and are further driven by a driving unit (not shown). The intermediate transfer belt 8 that rotates clockwise is provided adjacent to the image forming portions Pa to Pd. The toner images formed on the photosensitive drums 1a to 1d are sequentially transferred onto the intermediate transfer belt 8 that moves while being in contact with the photosensitive drums 1a to 1d. The image is transferred onto P at a time, 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, the cyan, magenta, yellow, and black toner images on the photosensitive drums 1a to 1d are transferred to the intermediate transfer belt 8 by the primary 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 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 pair 12b to the secondary transfer roller 9 provided adjacent to the intermediate transfer belt 8 at a predetermined timing, and the 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 on only one side of the transfer paper P, the image is directly discharged onto the discharge tray 17 by the discharge roller pair 15.

  On the other hand, when images are formed on both sides of the transfer paper P, a part of the transfer paper P that has passed through the fixing unit 7 is once projected from the discharge roller pair 15 to the outside of the apparatus. Thereafter, the transfer paper P is distributed to the paper conveyance path 18 by the branching section 14 by rotating the discharge roller pair 15 in the reverse direction, and is re-conveyed to the registration roller pair 12b with the image surface reversed. Then, after the next image formed on the intermediate transfer belt 8 is transferred to the surface of the transfer paper P on which the image is not formed by the secondary transfer roller 9 and conveyed to the fixing unit 7 to fix the toner image. The paper is discharged from the discharge roller pair 15 to the discharge tray 17.

  FIG. 2 is a side sectional view showing the configuration of the developing device according to the first embodiment of the present invention, and FIG. 3 is a partial side sectional view showing the configuration around the regulating blade of the developing device according to the present embodiment. FIG. 3A is a diagram showing a state when an image with a non-high printing rate is printed, and FIG. 3B is a diagram showing a state when an image with a high printing rate is printed. . Here, the developing device 3a disposed in the image forming unit Pa of 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 also simply referred to as a developer) is accommodated. 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. An agitating screw (agitating and conveying member) 21a and a second agitating screw (agitating and conveying member) 21b are rotatably arranged.

  The toner is formed by using a binder containing a binder resin and a colorant as a base, and mixing the base and an external component. As external components, 0.8% by weight of resin fine particles made of polystyrene resin, 2% of hydrophobic famed silica, 1% of titanium oxide fine particles, and 0.1% of zinc stearate can be added. The type and amount of these external components can be appropriately set according to the characteristics of the toner, and are not particularly limited.

  Further, if the volume average particle diameter of the toner is reduced, it tends to be difficult to peel off the toner from the surface of the carrier or the developing roller 23. If the toner is increased, the image quality may not be sufficiently improved. Therefore, considering such a viewpoint, it is preferable to define the volume average particle diameter Dt of the toner in a range of, for example, 4.0 μm ≦ Dt ≦ 7.0 μm. In view of avoiding selective developability, it is preferable to suppress the spread of the particle size distribution so that the CV value in the toner particle size distribution is 25% or less.

As the carrier, a magnetite carrier, Mn ferrite, Mn-Mg ferrite, Cu-Zn, a resin carrier in which a magnetic material is dispersed in a resin, or the like can be used. It is. Considering the viewpoint of satisfactorily peeling off the toner from the magnetic brush, it is preferable that the volume resistivity of the carrier is 10 ⁶ Ωcm to 10 ¹³ Ωcm.

  Considering the viewpoint of forming a good magnetic brush with the toner, the weight average particle diameter of the carrier is preferably 50 μm or less. Further, the saturation magnetization of the carrier can be set to 65 emu / g, for example, and the mixing ratio T / C of the toner to the carrier can be set to 12% by weight, for example.

  Then, the developer is conveyed in the axial direction while being stirred by the first stirring screw 21a and the second stirring screw 21b, and is supplied to the first and second via a developer passage (not shown) formed in the partition wall 20a. It circulates between the stirring chambers 20b and 20c. In the illustrated example, the developing container 20 extends obliquely upward to the left, and a magnetic roller 22 is disposed above the first stirring screw 21 a in the developing container 20, and the developing is performed obliquely upward to the left of the magnetic roller 22. Rollers 23 are arranged opposite to each other. The developing roller 23 faces the photosensitive drum 1a on the opening side (left side in FIG. 2) of the developing container 20, and the magnetic roller 22 and the developing roller 23 rotate clockwise in the drawing.

  The developing container 20 is provided with a toner concentration sensor (not shown) facing the second stirring screw 21b, and a replenishing device (not shown) according to the toner concentration detected by the toner concentration sensor. Then, toner is supplied into the developing container 20 through the toner supply port 20d.

  The magnetic roller 22 includes a non-magnetic rotating sleeve 22a and a magnetic field generating member 22b that is disposed inside the rotating sleeve 22a and includes a magnet body having a plurality of magnetic poles. The rotating sleeve 22a rotates about the support shaft 22c, and the magnetic field generating member 22b is fixed to the inside of the rotating sleeve 22a so as not to rotate. The magnetic poles of the magnetic field generating member 22b are 5 main poles 35 consisting of S poles, regulation poles 36 consisting of N poles, separation poles 37 consisting of N poles, separation poles 38 consisting of S poles, and pumping poles 39 consisting of S poles. It is a pole configuration.

  In addition, a regulating blade (regulating member) 25 is attached to the developing container 20 along the longitudinal direction of the magnetic roller 22 (front and back direction in FIG. 2), and the regulating blade 25 rotates in the rotational direction of the magnetic roller 22 (see FIG. In the middle clockwise direction), it is positioned upstream of the position where the developing roller 23 and the magnetic roller 22 face each other. A slight gap (regulation gap) is formed between the tip of the regulation blade 25 and the surface of the magnetic roller 22.

  As shown in FIGS. 2 and 3, the regulation blade 25 is connected to an interval adjusting device 27 that adjusts the interval of the regulation gap by moving the regulation blade 25 close to and away from the magnetic roller 22. The distance adjusting device 27 is disposed at both ends of the regulating blade 25 in the longitudinal direction, and is composed of a solenoid coupled to the both ends.

  When the distance adjusting device 27 is operated, the restriction blade 27 comes close to the magnetic roller 22 as shown in FIG. 3A, and the distance between the restriction gaps is set to L1, and the solenoid stops. As shown in FIG. 3B, the regulating blade 25 is separated from the magnetic roller 22 so that the spacing of the regulating gap is set to L2 larger than L1. The distance adjusting mechanism 27 is not particularly limited as long as the distance between the restriction gaps can be adjusted by moving the restriction blade 25. For example, an eccentric cam and a pulse motor can be used.

  The developing roller 23 includes a cylindrical rotating sleeve 23a and a developing roller side magnetic pole 23b fixed in the rotating sleeve 23a, and the magnetic roller 22 and the developing roller 23 are predetermined at the facing position (opposing position). Are opposed to each other with a gap (development gap). The rotating sleeve 23a rotates about the support shaft 23c. The developing roller side magnetic pole 23b is composed of an N pole, and has a polarity different from that of the opposing main pole 35 of the magnetic field generating member 22b. The surface of the rotating sleeve 23a is coated with a silicon-modified urethane resin.

  FIG. 4 is a diagram illustrating an example of a bias configuration applied to the magnetic roller and the developing roller. As shown in FIG. 4, the developing roller 23 is connected to a first bias applying device 30 that applies a DC voltage (hereinafter referred to as Vslv (DC)) and an AC voltage (hereinafter referred to as Vslv (AC)). The magnetic roller 22 is connected to a second bias applying device 31 that applies a DC voltage (hereinafter referred to as Vmag (DC)) and an AC voltage (hereinafter referred to as Vmag (AC)). The first bias applying device 30 and the second bias applying device 31 are grounded to a common ground. The bias applied from the first and second bias applying devices 30 and 31 will be described later.

  As described above, the first stirring screw 21a and the second stirring screw 21b circulate the developer container 20 while the developer is being stirred to charge the toner, and the first stirring screw 21a causes the developer to move to the magnetic roller 22. Be transported. Since the regulation blade 25 of the magnetic field generating member 22b is opposed to the regulation blade 25, a nonmagnetic material or a magnetic material having a polarity different from that of the regulation pole 36 is used as the regulation blade 25, so that the tip of the regulation blade 25 and the rotating sleeve 22a A magnetic field in a direction attracting the gap is generated.

  Due to this magnetic field, a magnetic brush is formed between the regulating blade 25 and the rotating sleeve 22a. When the thickness of the magnetic brush on the magnetic roller 22 is regulated by the regulating blade 25 and then moves to a position facing the developing roller 23, a magnetic field attracted by the main pole 35 of the magnetic field generating member 22b and the developing roller side magnetic pole 23b is generated. Therefore, the magnetic brush comes into contact with the surface of the developing roller 23. Then, a toner thin layer is formed on the developing roller 23 by a potential difference ΔV between Vmag (DC) applied to the magnetic roller 22 and Vslv (DC) applied to the developing roller 23 and a magnetic field.

  The toner layer thickness on the developing roller 23 varies depending on the resistance of the developer and the difference in peripheral speed between the magnetic roller 22 and the developing roller 23, but can be controlled by ΔV. When ΔV is increased, the toner layer on the developing roller 23 is thickened, and when ΔV is decreased, the toner layer is thinned. The range of ΔV at the time of development is generally about 100V to 350V.

  FIG. 5 is a diagram illustrating an example of a bias waveform applied to the developing roller 23 and the magnetic roller 22. As shown in FIG. 5A, a first bias is applied to the developing roller 23 by a composite waveform Vslv (solid line) in which a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 is superimposed on Vslv (DC). Applied from device 30. Further, the magnetic roller 22 has a second combined waveform Vmag (broken line) in which Vmag (DC) has a peak-to-peak value of Vpp2 and a rectangular wave Vmag (AC) having a phase different from Vslv (AC). Applied from the bias applying device 31.

  Therefore, the voltage applied between the magnetic roller 22 and the developing roller 23 (hereinafter referred to as “MS”) is a composite waveform Vmag−Vslv having Vpp (max) and Vpp (min) as shown in FIG. Become. Note that Vmag (AC) is set so that the duty ratio is larger than Vslv (AC). Actually, an AC voltage having a partially distorted shape is applied instead of a complete rectangular wave as shown in FIG.

  The toner thin layer formed on the developing roller 23 by the magnetic brush is conveyed to a facing portion between the photosensitive drum 1 a and the developing roller 23 by the rotation of the developing roller 23. Since Vslv (DC) and Vslv (AC) are applied to the developing roller 23, the toner flies due to a potential difference with the photosensitive drum 1a, and the electrostatic latent image on the photosensitive drum 1a is developed. .

  When the rotating sleeve 22a further rotates clockwise, the magnetic brush is now separated from the surface of the developing roller 23 by the horizontal (roller circumferential direction) magnetic field generated by the different polarity peeling pole 37 adjacent to the main pole 35, and the developing roller 23a develops. The remaining toner that is not used for is collected from the developing roller 23 onto the rotating sleeve 22a.

  When the rotating sleeve 22 a further rotates, a magnetic field repelling is applied by the separation pole 38 of the magnetic field generating member 22 b and the scooping pole 39 having the same polarity, so that the developer separates from the rotating sleeve 22 a in the developing container 20. Then, after being stirred and transported by the first and second stirring screws 21a and 21b, a magnetic brush is again formed on the rotating sleeve 22a by the pumping pole 39 as a two-component developer that is uniformly charged with an appropriate toner concentration again. Then, it is conveyed to the regulating blade 25.

  Here, when printing an image with a high printing rate, toner is consumed from the magnetic roller 22 to the developing roller 23 and from the developing roller 23 to the photosensitive drum 1a, and from the first stirring chamber 20b so as to follow the toner consumption. It is necessary to supply toner onto the magnetic roller 22. Further, in order to sufficiently charge the toner replenished from the toner replenishing port 20d, for example, it is necessary to increase the rotational speed of the first and second agitating screws 21a and 21b.

  For this reason, the carrier and the toner are likely to deteriorate due to stress caused by stirring. When the developer deteriorates in this way, toner that is not sufficiently charged is carried on the magnetic roller 22. Further, when the developer carried on the magnetic roller 22 passes through the regulation gap between the magnetic roller 22 and the regulation blade 25, the developer slides on the surface of the magnetic roller 22 due to the restraining force caused by the magnetic field generated between them. Is done.

  Due to the rubbing force, the developer is stressed, and at the same time, the magnetic roller 22 is also stressed. Further, when toner that is insufficiently charged due to deterioration moves from the magnetic roller 22 to the developing roller 23 and is rubbed by the magnetic brush on the developing roller 23, the deterioration of the toner further proceeds.

  Therefore, in the present embodiment, when printing an image having a printing rate S equal to or greater than the first reference printing rate (first predetermined value) S1, the peripheral speed of the magnetic roller 22 is reduced and the developer on the magnetic roller 22 is developed. By increasing the amount, deterioration of the developer and the magnetic roller 22 was suppressed. Further, the amount of developer on the magnetic roller 22 is increased by separating the regulating blade 25 from the magnetic roller 22 by the spacing adjusting device 27 and increasing the spacing of the regulating gap.

  Since the developer is likely to deteriorate when the printing rate S is 8% or more, the first reference printing rate is 8%, and the printing rate S (S ≧ S1 = 8%) is 8% or more. High printing rate. Further, switching of the peripheral speed of the magnetic roller 22 and the interval of the regulation gap according to the printing rate S is controlled by the control unit 45 (see FIG. 7).

  As shown in FIG. 3A, when printing an image having a printing rate S of less than 8% (non-high printing rate), for example, the peripheral speed of the magnetic roller 22 is 600 rpm, the regulating blade 25 and the magnetic roller 22 Was set to L1 (here, 0.3 mm). Then, as shown in FIG. 3B, when printing an image with a high printing rate, the peripheral speed of the magnetic roller 22 is as small as 450 rpm, and the gap between the regulation gaps is as large as L2 (here, for example, 0.5 mm). Was set as follows. At this time, at the time of printing an image with a non-high printing rate and a high printing rate, for example, the rotation speed of the first and second stirring screws 21a and 21b was set to 300 rpm, and the peripheral speed of the developing roller 23 was set to 400 rpm.

  As described above, when printing an image with a high printing rate, the peripheral speed of the magnetic roller 22 is made smaller than when printing an image with a non-high printing rate, so that the developer and the magnetic roller 22 pass through the regulation gap. Stress due to the rubbing force generated between them can be reduced. In addition, the amount of developer on the magnetic roller 22 can be increased by increasing the interval of the regulation gap.

  Further, when printing an image with a high printing rate, the circumferential speed of the magnetic roller 22 is decreased from 600 rpm to 450 rpm, while at the time of printing an image with a non-high printing rate and a high printing rate, the circumferential speed of the developing roller 23 is It was set to 400 rpm without change. Thereby, the peripheral speed difference between the magnetic roller 22 and the developing roller 23 can be reduced.

  In addition, when printing an image with a high printing rate, Vmag (DC) applied to the magnetic roller 22 is increased. For example, Vmag (DC) is set to 280 V when printing an image at non-high printing, and Vmag (DC) is set to 300 V when printing an image with a high printing rate. At this time, when printing an image with a non-high printing rate and a high printing rate, for example, Vpp (Vmag2) of Vmag (AC) is 1800 V, the frequency is 4500 Hz, and the duty ratio is 70%.

  Further, when printing an image with a high printing rate, the frequency of Vslv (AC) applied to the developing roller 23 is increased. For example, when Vslv (DC) is set to 50 V, Vslv (AC) Vpp1 is set to 1100 V, and the frequency is set to 3000 Hz at the time of printing an image at non-high printing, Vslv (AC) is set at the time of printing a high printing rate image. Only the frequency was set to be as large as 4000 Hz. At this time, for example, the duty ratio of Vslv (AC) is set to 40% when printing an image with a non-high printing rate and a high printing rate.

  On the other hand, when printing an image with a low printing rate, the amount of toner remaining on the developing roller 23 without being used for development increases and stays on the developing roller 23, and the amount of residual toner collected by the magnetic roller 22 also increases. It increases and stays on the magnetic roller 22. For this reason, in the toner on the developing roller 23 and the developer on the magnetic roller 22, the proportion of toner deteriorated by more stress increases.

  Therefore, in the present embodiment, when printing an image having a printing rate S equal to or lower than the second reference printing rate (second predetermined value) S2 smaller than the first reference printing rate S1, the first and second stirring screws 21a, By reducing the rotation speed of 21b, the deterioration of the developer was suppressed. Here, the peripheral speed of the magnetic roller 22 is also reduced. Since the residual toner amount is likely to increase when the printing rate S is 3% or less, the second reference printing rate S2 is set to 3%, and the printing rate S of 3% or more (S ≦ S2 = 3%). Was set to a low printing rate.

  When printing an image with a printing rate S of more than 3% and less than 8% (normal printing rate), the peripheral speed of the magnetic roller 22 is 600 rpm and the rotational speeds of the first and second stirring screws 21a and 21b are the same as described above. Was set to 300 rpm. When printing an image with a low printing rate, the peripheral speed of the magnetic roller 22 was set to 450 rpm, and the rotational speeds of the first and second stirring screws 21a and 21b were set to 225 rpm. At this time, at the time of printing an image with a non-high printing rate and a high printing rate, for example, the interval of the regulation gap was set to 0.3 mm, and the peripheral speed of the developing roller 23 was set to 400 rpm.

  Thus, when printing an image with a low printing rate, the rotational speed of the first and second agitating screws 21a and 21b is made lower than when printing an image with a normal printing rate, so that the amount of developer on the magnetic roller 22 is reduced. As a result, the amount of toner moving to the developing roller 23 and the amount of residual toner collected from the developing roller 23 can be reduced. In addition, the stress applied to the developer by the stirring of the first and second stirring screws 21a and 21b can be reduced. Further, by reducing the peripheral speed of the magnetic roller 22, it is possible to reduce the rubbing force generated between the developer and the magnetic roller 22.

  As described above, in this embodiment, when printing an image with a high printing rate, the peripheral speed of the magnetic roller 22 is reduced and the amount of developer on the magnetic roller 22 is increased. The stress on the magnetic roller 22 can be reduced. Further, since the ratio of the developer that receives stress in the developer carried on the magnetic roller 22 is reduced, the stress on the developer can be reduced as a whole.

  Thereby, since deterioration of the developer and the magnetic roller 22 can be suppressed, it is possible to prevent occurrence of image defects such as image density variation, fogging, and ghost caused by the deterioration. In addition, the image quality can be secured stably over a long period of time. Further, since the amount of toner that moves from the magnetic roller 22 to the developing roller 23 also increases, it is possible to suppress the deterioration of the toner on the developing roller 23 and prevent the occurrence of image defects as will be described later.

  Here, since the developer amount on the magnetic roller 22 is increased by increasing the distance between the regulating blade 25 and the magnetic roller 22, the developer amount on the magnetic roller 22 can be reliably increased. Is. Further, as the developer amount on the magnetic roller 22 increases, the toner amount on the developing roller 23 also increases.

  In this embodiment, the developing roller 23 is provided in addition to the magnetic roller 22, and when printing a high printing rate image, the difference in peripheral speed between the magnetic roller 22 and the developing roller 23 is reduced. The rubbing force that the toner carried on the surface receives by the magnetic brush formed on the magnetic roller 22 can be reduced.

  Thereby, deterioration of the toner can be suppressed. Further, since only the peripheral speed of the magnetic roller 22 is changed without changing the peripheral speed of the developing roller 23 to reduce the difference in peripheral speed, the developability from the developing roller 23 to the photosensitive drum 1a depends on the printing rate S. Therefore, it is possible to prevent the occurrence of image defects.

  In addition, since the toner component such as a part of the toner and the externally added component can be prevented from being detached from the toner even when rubbed with the magnetic brush, the detached toner component is deposited on the developing roller 23 and developed. Leakage can be prevented from occurring between the roller 23 and the photosensitive drum 1a. Further, as the amount of developer on the magnetic roller 22 increases, the amount of toner on the developing roller 23 also increases, so that the proportion of the toner subjected to stress in the toner carried on the developing roller 23 decreases. As a result, the stress on the toner can be reduced as a whole, and the deterioration of the toner can be suppressed.

  Further, in the present embodiment, when printing an image with a high printing rate, Vmag (DC) applied to the magnetic roller 22 is increased, so that even if the toner on the magnetic roller 22 is insufficiently charged, the magnetic roller can be surely obtained. The toner can be separated from the toner 22 and moved to the developing roller 23. Since the developing roller 23 is used here, the amount of toner on the developing roller 23 can be increased, and toner deterioration on the developing roller 23 can be suppressed. Note that Vmag (DC) and Vmag (AC) applied to the magnetic roller 22 are not particularly limited to the above embodiment, and can be appropriately set according to the type of developer, other apparatus configuration, and the like. .

  Further, in the present embodiment, when printing an image with a high printing rate, the frequency of Vslv (AC) applied to the developing roller 23 is increased. Therefore, even if the toner on the developing roller 23 is insufficiently charged, the developing roller 23 From the toner to the photosensitive drum 1a can be promoted. Thereby, developability can be improved and occurrence of image defects such as fogging can be suppressed. Note that Vslv (DC) and Vslv (AC) applied to the developing roller 23 are not particularly limited to the above-described embodiment, and can be set as appropriate according to the type of toner and other apparatus configurations.

  In this embodiment, since the resin coat layer is provided on the surface of the developing roller 23, adhesion of toner to the developing roller 23 can be suppressed. Thereby, it is possible to more effectively suppress the deterioration of the toner and to prevent the occurrence of leakage between the developing roller 23 and the photosensitive drum 1a. In the present embodiment, since the toner to which resin fine particles are externally added is used, even when the toner is likely to adhere to the magnetic roller 22 and the developing roller 23, deterioration of the toner can be suppressed.

  In this embodiment, when printing an image with a low printing rate, the rotational speed of the first and second stirring screws 21a and 21b is reduced, so that the amount of residual toner collected from the developing roller 23 is reduced and the first And the stress which a developing agent receives by stirring of the 2nd stirring screws 21a and 21b can be reduced. Thereby, even if the toner is likely to stay on the magnetic roller 22, deterioration of the developer can be suppressed. In addition, since the peripheral speed of the magnetic roller 22 is reduced here, the frictional force generated between the developer and the magnetic roller 22 can be reduced, and the deterioration of the developer can be further suppressed.

  Although the peripheral speed of the developing roller 23 is not changed here, the deterioration of the toner on the developing roller 23 can be suppressed by reducing the peripheral speed of the developing roller 23. However, if the peripheral speed of the developing roller 23 is changed in accordance with the printing rate S, an image defect may occur. Therefore, the peripheral speed of the developing roller 23 is appropriately set according to the state of occurrence of the defect, the apparatus configuration, and the like. be able to.

  Further, since the amount of developer on the magnetic roller 22 is reduced, the amount of toner moving on the developing roller 23 and the amount of residual toner remaining on the developing roller 23 after development can be reduced. In this case, toner deterioration can be suppressed. Note that when printing an image with a low printing rate, the amount of toner consumed by development is small, and the amount of toner that follows the amount of toner consumed can be small. Therefore, the rotational speeds of the first and second agitating screws 21a and 21b are reduced. Even if it is smaller than when printing an image with a normal printing rate, the reduction in the rotational speed has little influence on the charging of the toner.

  In the present embodiment, when printing an image with a high printing rate, the interval between the regulating blades 25 is increased from L1 to L2. However, the intervals L1 and L2 are not particularly limited, and developability, It can be set as appropriate according to the degree of deterioration of the developer and other apparatus configurations. For example, if L2 is too small, the amount of developer on the magnetic roller 22 cannot be increased sufficiently, and the rubbing force may not be sufficiently reduced.

  On the other hand, if L2 is too large, the amount of developer on the magnetic roller 22 may increase excessively and image defects may occur. Therefore, for example, L2 can be appropriately set in consideration of such a viewpoint. The method for adjusting the developer amount on the magnetic roller 22 is not particularly limited to the regulation blade 25 of the present embodiment.

  FIG. 6 is a partial side cross-sectional view showing the periphery of the regulating blade of the developing device according to the second embodiment of the present invention, and FIG. 6A shows a state when printing an image with a non-high printing rate. FIG. 6B is a diagram illustrating a state when an image with a high printing rate is printed. Portions common to FIGS. 2 and 3 are denoted by common reference numerals, and description thereof is omitted.

  In the present embodiment, as shown in FIG. 6, the magnetic field generating member 22b disposed inside the magnetic blade 22 is rotatable about the support shaft 22c. Although not shown, the tip of the support shaft 22c is processed into a D-cut shape and is connected to a drive motor (not shown). The magnetic field generating member 22b rotates separately from the rotating sleeve 22a.

  When printing an image with a non-high printing rate, the restricting pole 36 is disposed at a normal position facing (closest to) the restricting blade 25 as shown in FIG. Then, when printing an image with a high printing rate, as shown in FIG. 6B, the magnetic field generating member 22b is rotated by a predetermined amount θ (here, 5 °) counterclockwise in the figure, and the regulation pole 36 is moved. It arrange | positions in the position shifted from the state of Fig.3 (a). Thereby, when printing an image with a high printing rate, the amount of developer on the magnetic roller 22 can be increased by reducing the strength of the magnetic field generated in the restriction gap.

  As the drive motor for rotating the magnetic field generating member 22b, a fine adjustment of the rotation amount (rotation angle) is required, and therefore, it is preferable to use a stepping motor that is driven and controlled using a drive waveform having a predetermined period. Further, as the amount of rotation of the magnetic field generating member 22b increases, the amount of displacement of the regulation pole 36 with respect to the regulation blade 25 also increases, and the strength of the magnetic field can be varied more greatly. The deviation amount of the separation electrode 37, the separation electrode 38, and the pumping pole 39 is also increased. For example, when the rotation amount of the magnetic field generating member 22b is large, the main pole 35 is greatly deviated from the original position, and the strength of the magnetic field at the position facing the photosensitive drum 1a is reduced, which may cause development problems.

  On the other hand, the smaller the rotation angle of the magnetic field generating member 22b, the smaller the change in the magnetic field, and there is a possibility that the effect of reducing the rubbing force received by the developer cannot be sufficiently obtained. Therefore, for example, the amount of rotation of the magnetic field generating member 22b can be appropriately set in consideration of this viewpoint, and the predetermined amount θ for rotating the magnetic field generating member 22b is preferably 2 ° or more and 10 ° or less, for example.

  As described above, in the present embodiment, the rotatable magnetic field generating member 22b is provided inside the magnetic roller 22, and the magnetic field generating member 22b rotates by a predetermined amount so that the restricting blade 25 and the restricting pole closest to the restricting blade 25 are provided. 36, the amount of developer carried on the magnetic roller 22 is increased by reducing the strength of the magnetic field generated between the magnetic roller 22 and the developer amount on the magnetic roller 22 can be reliably increased. It is effective. In addition, the amount of toner on the developing roller 23 can be increased reliably.

  Here, the magnetic field generating member 22b is rotated in the direction opposite to the rotating direction of the magnetic roller 22, but the rotating direction of the magnetic field generating member 22b may be appropriately set in consideration of the influence on other magnetic poles. . Since other configurations are the same as those of the first embodiment, description thereof is omitted.

  Next, the control mechanism of the image forming apparatus provided with the developing device according to the present invention will be described. FIG. 7 is a block diagram illustrating an example of a control mechanism of the image forming apparatus including the developing device according to the first embodiment. Portions common to FIGS. 1 to 3 are denoted by the same reference numerals and description thereof is omitted. The image forming apparatus 100 is an image forming unit Pa to Pd, a fixing unit 7, an image input unit 42, an AD conversion unit 43, a storage unit 44, a control unit 45, an operation panel 46, and a drive motor that drives each part of the apparatus. The motor 47 and the stirring motor 48 are included.

  When the image forming apparatus 100 is a copying machine, the image input unit 42 includes a scanning optical system equipped with a scanner lamp that illuminates the original during copying and a mirror that changes the optical path of reflected light from the original, and reflected light from the original. 1 is an image reading unit (not shown) including a condensing lens that collects and forms an image and a CCD that converts the imaged image light into an electrical signal. In the case of a printer as shown, it is a receiving unit that receives image data transmitted from a personal computer (not shown) or the like. An image signal input from the image input unit 42 is sent to the control unit 45, appropriately performs image processing such as gradation processing, and after being converted into a digital signal by the AD conversion unit 43, an image in the storage unit 44 described later It is sent to the memory 50. The image input unit 42 and the AD conversion unit 43 also have a function as a printing rate detection unit that detects a printing rate S of an image to be printed.

  The image forming sections Pa to Pd are composed of the photosensitive drums 1a to 1d, the charging units 2a to 2d, the exposure unit 4, the developing devices 3a to 3d, the primary transfer rollers 6a to 6d, and the like. Based on the image data stored in the memory 50, electrostatic latent images are formed on the photosensitive drums 1a to 1d.

  The storage unit 44 includes an image memory 50, a RAM 51, and a ROM 52. The image memory 50 stores an image signal input by the image input unit 42 and digitally converted by the AD conversion unit 43, and is stored in the control unit 45. Send it out. The RAM 51 and ROM 52 store an image processing program, processing contents, and the like of the control unit 45. The storage unit 44 also includes parameters that associate the image printing rate S with the circumferential speed of the magnetic roller 22 and the circumferential speed of the developing roller 23, the printing rate S, the first bias applying device 30, and the second bias applying device. 31 (see FIG. 4), the parameters relating the bias applied to the magnetic roller 22 and the developing roller 23, the printing rate S and the rotation speeds of the first and second stirring screws 21a, 21b (see FIG. 2). Associated parameters and the like are also stored.

  When the image forming apparatus 100 is a copying machine, the operation panel 46 includes an operation unit composed of a plurality of operation keys and a display unit (none of which is shown) that displays setting conditions, the state of the apparatus, and the like. In addition to setting the print size and other printing conditions by the user, for example, when the image forming apparatus 100 has a facsimile function, the facsimile transmission destination is registered in the storage unit 44, and the registered transmission destination is read out. It is also used for various settings such as rewriting and rewriting. When the image forming apparatus 100 is the printer shown in FIG. 1, the operation panel 46 is composed of an input unit displayed on a personal computer (not shown).

  The main motor 47 drives the photosensitive drums 1a to 1d, the primary transfer rollers 6a to 6d, the fixing unit 7 and the like according to a control signal from the control unit 45. The stirring motor 48 rotates the first and second stirring screws 21a and 21b, the magnetic roller 22 and the developing roller 23 (see FIG. 2) in the developing devices 3a to 3d in response to a control signal from the control unit 45. Instead of the stirring motor 48, a driving force can be transmitted from the main motor 47 by a clutch (not shown).

  The control unit 45 is, for example, a central processing unit (CPU), and in accordance with a set program, the image input unit 42, the image forming units Pa to Pd, the fixing unit 7, a main motor 47 that drives these, a stirring motor 48, and In addition to overall control of conveyance of the paper P from the paper cassette 16 (see FIG. 1), the image signal input from the image input unit 42 is subjected to scaling processing or gradation processing as necessary to obtain image data. Convert to The exposure unit 4 irradiates a laser beam based on the processed image data, and forms latent images on the photosensitive drums 1a to 1d.

  Further, the control unit 45 performs the peripheral speed of the magnetic roller 22, the peripheral speed of the developing roller 23, the driving of the interval adjusting device 27, the first and second biases based on the printing information of the image signal digitally converted by the AD conversion unit 43. It has a function of controlling the bias applied from the applying devices 30 and 31 and the rotational speed of the first and second stirring screws 21a and 21b.

  Next, the control operation of the image forming apparatus including the developing device according to the first embodiment will be described. FIG. 8 is a flowchart illustrating an example of a control procedure of the image forming apparatus including the developing device according to the first embodiment. The execution procedure of this control example will be described according to the steps in FIG. 8 with reference to FIGS. 2, 3, and 7.

  First, when printing (image formation) is started by the user, for example, as an initial condition, the controller 45 sets the peripheral speed of the magnetic roller 22 to 600 rpm, the peripheral speed of the developing roller 23 to 400 rpm, and the first and second stirring screws. The rotational speed of 21a, 21b is set to 300 rpm, the regulation gap is set to L1 (here 0.3 mm), Vmag (DC) applied to the magnetic roller 22 is set to 280 V, and the frequency of Vslv (AC) applied to the developing roller 23 is set to 3000 Hz. (Step S1).

  Next, when the image signal input from the image input unit 42 is converted into a digital signal by the AD conversion unit 43 and then output to the image memory 50, the digital signal in the image memory 50 is read to the control unit 45. Then, the control unit 45 calculates the printing rate S based on the digital signal (step S2). Next, it is determined whether or not the calculated printing rate S is equal to or higher than the first reference printing rate S1 (here, 8% or higher) (step S3).

  When the printing rate S is equal to or higher than the first reference printing rate S1 (S ≧ S1 = 8%), the control unit 45 applies the stirring motor 48, the interval adjusting device 27, and the first and second bias applying devices 30, 31 to each other. A control signal is transmitted, for example, the peripheral speed of the magnetic roller 22 is reduced (decreased) to 450 rpm (step S4), and the restriction blade 25 is separated from the magnetic roller 22 to set the gap of the restriction gap to L2 (here, 0.5 mm) (increase) (step S5), Vmag (DC) applied to the magnetic roller 22 is increased to 300 V (step S6), and the frequency of Vslv (AC) applied to the developing roller 23 is increased. The frequency is increased to 4000 Hz (step S7). Then, printing is started under the conditions set in steps S4 to S7 (step S8), and the process is terminated.

  On the other hand, if the printing rate S is less than the first reference printing rate S1 (S <S1 = 8%) in step S3, it is determined whether the printing rate S is equal to or less than the second reference printing rate S2 (here, 3%). (Step S9). When the printing rate S is equal to or lower than the second reference printing rate S2 (S ≦ S2 = 3%), a control signal is transmitted from the control unit 45 to the stirring motor 48, and the peripheral speed of the magnetic roller 22 is reduced to, for example, 450 rpm. Then, the difference in peripheral speed with the developing roller 23 is reduced (step S10), and the rotational speed of the first and second stirring screws 21a and 21b is reduced to, for example, 225 rpm (step S11). And after setting conditions in step S10 and step S11, it transfers to step S8, printing is started, and a process is complete | finished.

  On the other hand, if the printing rate S is greater than the second reference printing rate S2 (S> S2 = 3%) in step S9, the initial state is maintained, that is, the circumferential speed of the magnetic roller 22, the circumferential speed of the developing roller 23, the first The process proceeds to step S8 without changing the rotation speed of the second agitating screws 21a and 21b, the gap between the regulating gaps, the Vmag (DC) applied to the magnetic roller 22, and the Vslv (AC) applied to the developing roller 23. Then, printing is started and the process is terminated.

  In this control example, the example in which the regulating blade 25 is separated from the magnetic roller 22 is shown, but this is only an example, and the control operation is not particularly limited. In addition, for example, when the developing devices 3a to 3d shown in the second embodiment are used, the magnetic field generating member 22b is replaced with the regulation pole shown in FIG. 6A instead of increasing the regulation gap in step S5. What is necessary is just to rotate from the position which 36 opposes the control blade 25 to the position shown in the said FIG.6 (b).

  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, the circumferential speed of the magnetic roller 22, the circumferential speed of the developing roller 23, the gap of the regulation gap, the Vmag (DC) applied to the magnetic roller 22, the frequency of Vslv (AC) applied to the developing roller 23, the first and second The rotation speed of the stirring screws 21a and 21b, the rotation angle of the magnetic field generating member 22b of the magnetic roller 22, and the like are not particularly limited, and can be set as appropriate according to the apparatus configuration and the like.

  In each of the above embodiments, the main pole 35, the separation pole 38 and the pumping pole 39 are the S poles, and the regulation pole 36 and the peeling pole 37 are the N poles as the magnetic poles constituting the magnetic field generating member 22b of the magnetic roller 22. However, the main electrode 35, the separation electrode 38, and the top electrode 39 may be the N pole, and the regulation electrode 36 and the separation electrode 37 may be the S pole. In each of the above embodiments, the number of magnetic poles inside the magnetic roller 23 is five. However, the number of magnetic poles is not limited to five, and may be seven other. In the above embodiment, the control unit 45 is provided in the image forming apparatus 100. However, the control unit 45 may be provided in the developing devices 3a to 3d.

  In the above embodiments, the developing devices 3a to 3d using the developing roller 23 have been described. In addition, the developing roller 23 is not provided, the developer is carried on the magnetic roller 22, and the developing on the magnetic roller 22 is performed. Similarly, the present invention can also be applied to a developing device that moves only the toner from the agent onto the photosensitive drums 1a to 1d by the potential difference with the photosensitive drums 1a to 1d.

  Further, the present invention is not limited to the tandem type color printer shown in FIG. 1, and includes a developing device such as a digital or analog type monochrome copying machine, a monochrome printer, a rotary developing type color printer, a color copying machine, a facsimile, or the like. The present invention can be applied to various image forming apparatuses. Hereinafter, the effects of the present invention will be described in more detail with reference to examples.

Experimental example 1
The image forming apparatus 100 shown in FIG. 1 provided with the developing devices 3a to 3d according to the first embodiment shown in FIGS. 2 and 3 was used. As a toner, 2% of hydrophobic fumed silica Aerosil (registered trademark) R104 (manufactured by Nippon Aerosil), 1% of titanium oxide fine particles EC-100 (manufactured by Titanium Industry), and zinc stearate (manufactured by Kawamura Kasei) are used as toners. ) 0.1%, polystyrene resin fine particles (weight average molecular weight 280,000-320,000, average primary particle size: 0.07 μm, softening point 200 ° C. or higher) 0.8% externally added with an average particle size of 6.8 μm A positively charged toner was used, a coated ferrite carrier having a volume specific resistance of 10 ¹⁰ Ω, a saturation magnetization of 65 emu / g, and an average particle size of 45 μm was used as the carrier, and T / C was set to 12% by weight.

  As shown in Table 1, when printing an image with a printing rate S of less than 8% (non-high printing rate), the peripheral speed of the magnetic roller 22 is 600 rpm, the peripheral speed of the developing roller 23 is 400 rpm, and the first and first 2 The rotational speed of the stirring screw 21a, 21b is 300 rpm, the gap of the regulating gap by the regulating blade 25 is 0.3 mm, and the circumferential speed of the magnetic roller 22 is used when printing an image with a printing rate S of 8% or higher (high printing rate). Was controlled at 450 rpm, the rotation speed of the first and second agitating screws 21a and 21b was 225 rpm, and the gap between the regulating gaps was 0.5 mm, and printing was performed.

  The Vmag (DC) applied to the magnetic roller 22 is 280 V, the Vpp2 of Vmag (AC) is 1800 V, the frequency is 4500 Hz, the duty ratio is 70%, and the Vslv (DC) applied to the developing roller 23 is 50 V, Vslv ( AC) Vpp1 was 50 V, the frequency was 3000 Hz, and the duty ratio was 40%.

Experimental example 2
The image forming apparatus 100 shown in FIG. 1 provided with the developing devices 3a to 3d according to the second embodiment shown in FIG. 6 was used. As shown in Table 1, when printing an image having a printing rate S of 8% or more, the second magnetic field generating member 22b in the magnetic roller 22 is located upstream in the rotation direction of the magnetic roller 22 instead of increasing the gap of the regulation gap. Printing was performed in the same manner as in Experimental Example 1 except that the control was performed so as to rotate 5 ° toward (see FIG. 6B).

Experimental example 3
As shown in Table 1, when printing an image with a printing rate S of 8% or more, it is the same as in Experimental Example 1 except that printing is performed under the same conditions as printing an image with a printing rate S of less than 8%. Was printed.

Evaluation With respect to the above-described Experimental Examples 1 to 3, the evaluation was performed with respect to density maintenance, fogging, toner adhesion to the developing roller 23 (sleeve contamination), and ghost. Each evaluation method is as follows, and the evaluation results are shown in Table 2.

<Concentration maintenance>
After printing 5,000 test images with a printing rate S of 10%, the image density (ID) was measured using a spectroeye reflection densitometer (manufactured by Gretag Macbeth). When the difference between the solid image IDs is less than 0.15 between the first printed sheet and the 5000th sheet, ○, when the difference is 0.15 or more and 0.3 or less, Δ, when more than 0.3 X.

<Fog>
After printing 5000 test images with a printing rate S of 0.2%, and then printing 1000 test images with a printing rate S of 20%, print using a spectroeye reflection densitometer (manufactured by Gretag Macbeth). The fog density of the 1000th blank sheet was measured. Then, the case where the fog density is less than 0.009 is indicated by ◯, the case where the fog concentration is 0.009 or more and 0.015 or less is indicated by Δ, and the case where the fog density is more than 0.015 is indicated by ×.

<Stained sleeve>
After printing 20000 images with a printing rate S of 10%, the deposition resistance R on the surface of the developing roller 23 is measured with Hiresta UPMCP-HT450 (manufactured by Mitsubishi Chemical Analytech), and the deposition resistance value R0 before printing is measured. The ratio (R1 / R0) of the deposition resistance value R1 after printing 2000 sheets was calculated. A case where R1 / R0 is less than 10 is evaluated as ◯, a case where it is 10 or more and 100 or less is evaluated as Δ, and a case where it is more than 100 is indicated as ×.

<Ghost>
After printing 5000 test images with a printing rate S of 0.2%, as shown in FIG. 9, from a solid image consisting of a graphic F1 with a printing density of 100% and a graphic F2 having a size including the graphic F1. The half-images formed are sequentially printed from the downstream side of the transfer direction of the transfer paper P (in the direction of the arrow in FIG. 9) with an interval of one turn or more of the developing roller 23, and a spectroeye reflection densitometer ( Using Gretag Macbeth Co., Ltd.), the density of the portion that overlaps F1 and the portion that does not overlap in the graphic F2 was measured, and the density difference between the two was calculated.

  A case where the density difference is less than 0.10% is indicated by ◯, a case where the concentration difference is 0.10% or more and 0.20% or less is indicated by Δ, and a case where the density difference is more than 0.20% is indicated by ×. In the ghost evaluation, in both Experimental Example 1 and Experimental Example 2, a test image having a printing rate S of 0.2% was printed under the conditions for printing an image having a printing rate S of 8% or more. Moreover, the figure shown in FIG. 9 is only an example, and is not particularly limited.

  As shown in Table 2, when printing an image with a high printing rate of 8% or more, Experimental Example 1 in which the peripheral speed of the magnetic roller 22 was decreased and the interval of the regulation gap was increased, and the peripheral speed of the magnetic roller 22 In Example 2 in which the first magnetic field generating member 22b of the magnetic roller 22 was rotated while decreasing the density, the concentration maintaining property was good, and the occurrence of fogging and sleeve contamination was suppressed.

  Further, as shown in Experimental Example 1 and Experimental Example 2, the peripheral speed of the magnetic roller 22 is decreased, the developer amount on the magnetic roller 22 is increased, and the first and second stirring screws 21a and 21b are rotated. When the speed is reduced, a ghost is likely to occur. However, as a result of ghost evaluation, it was confirmed that no ghost was observed even in such a case. In Experimental Example 1 and Experimental Example 2, the rotational speeds of the first and second agitating screws 21a and 21b were also reduced, but no sleeve contamination or image failure due to insufficient charging was observed.

  On the other hand, in Experimental Example 3 in which the printing conditions were not changed when printing an image with a high printing rate, toner adhesion to the developing roller 23 was significant. In addition, although the fall of density maintenance and generation | occurrence | production of fog were recognized, it was an acceptable range.

Experimental Example 4
As shown in Table 3, when printing an image with a printing rate S of less than 8%, the circumferential speed of the magnetic roller 22 is 600 rpm, the rotation speed of the first and second stirring screws is 300 rpm, and the gap between the regulation gaps by the regulation blade 25 Is 0.3 mm, Vmag (DC) applied to magnetic roller 22 is 280 V, Vslv (AC) Vpp applied to developing roller 23 is 1100 V, frequency is 3000 Hz, and printing rate S is 8% or more when printing an image The peripheral speed of the magnetic roller 22 is 450 rpm, the rotational speed of the first and second stirring screws is 225 rpm, the gap between the regulation gaps is 0.5 mm, Vmag (DC) is 300 V, and the frequency of Vslv (AC) is 4000 Hz. Printing was performed in the same manner as in Experimental Example 1 except that the above control was performed.

Experimental Example 5
As shown in Table 3, when printing an image having a printing rate S of 8% or more, the circumferential speed of the magnetic roller 22 is set to 450 rpm, the first and second stirring screws 21a, while maintaining the gap of the regulation gap at 0.3 mm. , 21b was printed in the same manner as in Experimental Example 4 except that control was performed so that the rotation speed of 225 rpm was 225 rpm and Vmag (DC) was 300 V.

Experimental Example 6
As shown in Table 3, when printing an image having a printing rate S of 8% or more, the circumferential speed of the magnetic roller 22 is set to 450 rpm and the first and second stirring screws 21a are maintained with the gap of the regulation gap maintained at 0.3 mm. The printing was performed in the same manner as in Experimental Example 4 except that the control was performed so that the rotation speed of 21b was 225 rpm, Vmag (DC) was 300 V, and the frequency of Vslv (AC) was 4000 Hz.

Experimental Example 7
As shown in Table 3, when printing an image with a printing rate S of 8% or more, it is the same as in Experimental Example 4 except that printing is performed under the same conditions as printing an image with a printing rate S of less than 8%. Was printed.

Evaluation In the same manner as in Experimental Examples 1 to 3 described above, Experimental Example 4 to Experimental Example 7 were evaluated for concentration maintenance, fogging, sleeve contamination, and ghosting. In the ghost evaluation, in each of Experimental Examples 4 to 6, a test image having a printing rate S of 0.2% was printed under the conditions for printing an image having a printing rate S of 8% or more. The evaluation results are shown in Table 4.

  As shown in Table 4, when printing an image with a high printing rate of 8% or more, the peripheral speed of the magnetic roller 22 is reduced, the interval of the regulating gap is increased, and Vmag (DC) applied to the magnetic roller 22 In Experimental Example 4 in which the frequency of Vslv (AC) applied to the developing roller 23 was increased, the density maintenance was good, and fogging and sleeve contamination were also suppressed. In addition, no ghost was observed.

  Further, when printing an image with a high printing rate, in Example 5 in which the peripheral speed of the magnetic roller 22 was reduced and the Vmag (DC) applied to the magnetic roller 22 was increased while leaving the gap of the regulation gap unchanged. Although it was observed that it was in an acceptable range. On the other hand, the concentration maintenance was good and the occurrence of sleeve contamination and ghosting was suppressed.

  Further, when printing an image with a high printing rate, in addition to Experimental Example 5, in Experimental Example 6 in which the frequency of Vslv (AC) applied to the developing roller 23 is increased, the density maintenance is good, sleeve contamination, ghosting In addition to the occurrence of fog, the occurrence of fog was also suppressed. In addition, as a result of Experimental Example 5 and Experimental Example 6, it was found that when the frequency of Vslv (AC) applied to the developing roller 23 is increased, the generation of fog can be particularly effectively suppressed.

  Further, considering the results of Experimental Example 4 together with Experimental Examples 5 and 6, it was found that Experimental Example 4 tends to be more effective in suppressing the occurrence of fog and sleeve contamination than Experimental Example 5. Moreover, it turned out that the direction of Experimental example 4 has the tendency to be excellent in a density maintenance property rather than Experimental example 6. FIG. In Experimental Example 4, since the amount of developer on the magnetic roller 22 is increased, it is presumed that the deterioration of the developer can be suppressed more than in Experimental Example 5 and Experimental Example 6 when used for a longer period of time. In Experimental Examples 4 to 6, the rotational speeds of the first and second agitating screws 21a and 21b were also reduced, but no sleeve contamination due to insufficient charging or significant image defects were observed.

  On the other hand, in Experimental Example 7 in which the printing conditions were not changed when printing an image with a high printing rate, toner adhesion to the developing roller 23 was significant. In addition, although the fall of density maintenance and generation | occurrence | production of fog were recognized, it was an acceptable range.

Experimental Example 8
The image forming apparatus 100 shown in FIG. 1 provided with the developing devices 3a to 3d according to the first embodiment shown in FIGS. 2 and 3 was used. As shown in Table 5, when printing an image with a printing rate S exceeding 3% (normal printing rate), the peripheral speed of the magnetic roller 22 is 600 rpm, the peripheral speed of the developing roller 23 is 400 rpm, and the first and second The rotation speed of the agitating screws 21a and 21b is 300 rpm, the gap between the regulation gaps is 0.3 mm, and when printing an image with a printing rate of 3% or less (low printing rate), the peripheral speed of the magnetic roller 22 is 450 rpm and the developing roller 23 Control was performed so that the peripheral speed was 300 rpm, and the rotational speeds of the first and second stirring screws 21a and 21b were 225 rpm, and printing was performed.

  In addition, the used toner and carrier, Vmag (DC) and Vmag (AC) applied to the magnetic roller 22 and the developing roller 23, and Vslv (DC) and Vslv (AC) applied to the developing roller 23 are shown in Experimental Example 1. And the same.

Experimental Example 9
As shown in Table 5, when printing an image with a printing rate S of 3% or less, the circumferential speed of the developing roller 23 is 300 rpm, the first and second stirring screws 21a, while the circumferential speed of the magnetic roller 22 is maintained at 600 rpm. The printing was performed in the same manner as in Experimental Example 8 except that the control was performed so that the rotation speed of 21b was 225 rpm.

Experimental Example 10
As shown in Table 5, when printing an image with a printing rate S of 3% or less, the first and second agitating screws 21a are maintained while maintaining the peripheral speed of the magnetic roller 22 at 600 rpm and the peripheral speed of the developing roller 23 at 400 rpm. The printing was performed in the same manner as in Experimental Example 8 except that the control was performed so that the rotation speed of 21b was 225 rpm.

Experimental Example 11
As shown in Table 5, when printing an image with a printing rate of 3% or less, printing was performed in the same manner as in Experimental Example 8 except that printing was performed under the same conditions as printing an image with a printing rate of more than 3%. went.

Evaluation With respect to the above Experimental Examples 8 to 11, the above experiment was performed except that a test image with a printing rate S of 0.2% was printed for density maintenance, and a test image with a printing rate S of 2% was printed for sleeve contamination. In the same manner as in Example 1 to Experimental Example 3, evaluation was made on concentration maintenance, fogging, sleeve contamination, and ghost. The evaluation results are shown in Table 6.

  As shown in Table 6, when printing an image with a low printing rate of 3% or less, the peripheral speeds of the magnetic roller 22 and the developing roller 23 are reduced, and the difference between the peripheral speeds of the two is reduced. In Experimental Example 8 in which the rotational speeds of the two agitating screws 21a and 21b were reduced, the concentration maintenance was good and the occurrence of fogging and sleeve contamination was also suppressed. Moreover, although the occurrence of ghost was recognized, it was in an acceptable range.

  Further, when printing an image with a low printing rate, in Example 9 in which the peripheral speed of the developing roller 23 was decreased and the rotation speed of the first and second stirring screws 21a and 21b was decreased, the density maintaining property was good. In addition, the occurrence of fog and sleeve contamination was also suppressed. Moreover, although the occurrence of ghost was recognized, it was in an acceptable range.

  Further, when printing an image with a low printing rate, in Example 10 in which the rotation speeds of the first and second agitating screws 21a and 21b were reduced, the density maintenance was good, and fogging, sleeve contamination, and ghosting occurred. Was also suppressed. When printing an image at the time of low printing, the toner consumption is small and the amount of toner following the toner consumption is small. Therefore, the rotational speeds of the first and second stirring screws 21a and 21b are set to the normal printing rate image. Even when the printing speed was smaller than that during printing, the effect of the decrease in the rotational speed on the charging of the toner was small and the influence on the image was small.

  Further, comparing Experimental Example 8 to Experimental Example 10, Experimental Example 9 tends to be superior in Experimental Example 10 to maintain concentration and suppress the occurrence of sleeve contamination, and Experimental Example 8 is an experimental example. It tends to be superior to 9 in terms of concentration maintenance and fogging and sleeve suppression effects. In Experimental Example 8, since the peripheral speed of the magnetic roller 22 is reduced, it is assumed that the deterioration of the developer can be suppressed more than in Experimental Example 9 and Experimental Example 10 when the magnetic roller 22 is used for a longer period of time.

  On the other hand, in Experimental Example 11 in which the printing conditions were not changed when printing an image with a low printing rate, the occurrence of ghost was not observed, but not only the density maintenance was significantly reduced but also the sleeve contamination was significant. . Although fog was observed, it was within an acceptable range.

  The present invention reduces the peripheral speed of the developer carrying member and increases the amount of developer carried on the developer carrying member when printing an image having a printing ratio equal to or higher than the first predetermined value. .

  As a result, deterioration of not only the developer but also the developer carrier can be suppressed, and the image quality can be stably ensured over a long period of time, thereby improving the maintainability and reducing the burden on the operator. You can also. In addition, a toner carrier that carries toner supplied from a developer carrier and supplies toner to the image carrier is provided. When printing an image having a printing rate equal to or higher than a first predetermined value, By reducing the difference in peripheral speed with the toner carrier, it is possible to suppress toner deterioration on the toner carrier.

  In addition, when a DC voltage and an AC voltage are applied to the toner carrier and an image having a printing rate equal to or higher than the first predetermined value is printed, the frequency of the AC voltage is increased so that the toner and the toner carrier are not separated. The rubbing force can be reduced and the developability can be improved. Further, by providing a resin coat layer on the surface of the toner carrier, it is possible to more effectively suppress the deterioration of the toner and to prevent the occurrence of leakage between the toner carrier and the image carrier.

  Further, by increasing the distance between the regulating member and the developer carrying member, the developer amount on the developer carrying member can be reliably increased by increasing the developer amount. In addition, by reducing the strength of the magnetic field generated between the regulating member and the magnetic pole closest to the regulating member, the developer amount on the developer carrying member is reliably increased by increasing the developer amount. Can be made. Further, when a DC bias and an AC bias are applied to the developer carrying member to print an image having a printing rate equal to or higher than the first predetermined value, the developer and the developer carrying member are deteriorated by increasing the DC bias. Can be further suppressed.

  Further, when printing an image having a printing rate equal to or smaller than the second predetermined value smaller than the first predetermined value, the developer tends to stay on the developer carrying member by reducing the rotation speed of the stirring and conveying member. Even in the state, the deterioration of the developer can be suppressed. Further, by using the toner to which resin fine particles are externally added, it is possible to suppress the deterioration of the toner even when the toner is easily attached to the developer carrying member. Further, by using the image forming apparatus provided with the developing device, an image forming apparatus capable of forming an image having a stable and stable quality over a long period of time is obtained.

1a to 1d Photosensitive drum (image carrier)
3a to 3d Developing device 21a First stirring screw 21b Second stirring screw 22 Magnetic roller (developer carrier)
22a Rotating sleeve 22b Magnetic field generating member 23 Developing roller (toner carrier)
23a Rotating sleeve 23b Developing roller side magnetic pole 25 Restricting blade (regulating member)
DESCRIPTION OF SYMBOLS 30 1st bias application apparatus 31 2nd bias application apparatus 35 Main pole 36 Control pole 45 Control part 100 Image forming apparatus Pa-Pd Image formation part

Claims (10)

A developer containing at least a toner and a carrier is used,
A developer carrier for supplying toner to the image carrier having a magnetic field generating member having a plurality of magnetic poles provided therein;
An agitating and conveying member for agitating and conveying the developer carried on the developer carrying member;
A developing member provided with a regulating member for regulating the amount of developer on the developer carrying member,
When printing an image having a printing ratio equal to or higher than a first predetermined value, the peripheral speed of the developer carrier is reduced and the amount of developer carried on the developer carrier is increased. Development device. A toner carrier for carrying the toner supplied from the developer carrier and supplying the toner to the image carrier;
2. The developing device according to claim 1, wherein when an image having a printing ratio equal to or higher than the first predetermined value is printed, a difference in peripheral speed between the developer carrier and the toner carrier is reduced. A DC voltage and an AC voltage are applied to the toner carrier,
The developing device according to claim 2, wherein the frequency of the AC voltage is increased when an image having a printing rate equal to or higher than the first predetermined value is printed.   The developing device according to claim 2, wherein a resin coat layer is provided on a surface of the toner carrier.   The developing device according to claim 1, wherein the developer amount is increased by increasing a distance between the regulating member and the developer carrying member.   The amount of the developer is increased by reducing the strength of a magnetic field generated between the regulating member and the magnetic pole closest to the regulating member. Development device. A DC bias and an AC bias are applied to the developer carrier,
The developing device according to claim 1, wherein the DC bias is increased when an image having a printing rate equal to or higher than the first predetermined value is printed.   The rotational speed of the stirring and conveying member is reduced when printing an image having a printing rate equal to or smaller than a second predetermined value smaller than the first predetermined value. Development device.   The developing device according to claim 1, wherein a toner to which resin fine particles are externally added is used.   An image forming apparatus comprising the developing device according to claim 1.

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