JP5422227B2 - Developing device and image forming apparatus including the same - Google Patents

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, and a printer, and an image forming apparatus including the developing device, and in particular, uses a two-component developer composed of a magnetic carrier and toner, and carries toner. The present invention relates to a developing device that develops an electrostatic latent image on an image carrier while holding only toner charged on the body.

  Conventionally, as a development method using dry toner in an image forming apparatus using an electrophotographic process, a one-component development method using no carrier and a two-component developer charging a nonmagnetic toner using a magnetic carrier are used. In addition, a two-component development system is known in which an electrostatic latent image on an image carrier (photoconductor) is developed by 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. On the other hand, the toner is charged by the charge roller, and the elastic regulating blade is used on the development roller. In order to regulate the layer thickness, the toner additive adheres to the charge roller, the charging ability is lowered, and it is difficult to stably maintain the charge amount of the toner. In addition, toner may adhere to the regulating blade, resulting in non-uniform layer formation and 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 (toner supply member) is used to transfer the developer onto a developing roller (toner carrier) installed in a non-contact manner with respect to the image carrier (photoconductor). In this case, a non-magnetic toner is transferred onto the developing roller while leaving the magnetic carrier on the magnetic roller to form a thin toner layer, and an electrostatic latent image on the image carrier (photoconductor) is formed by an AC electric field. A developing method for adhering toner has been proposed.

  In the case of the above developing method, if a toner consumption area and a non-consumption area are generated on the developing roller, a variation in the toner adhesion state and the toner potential difference occurs on the developing roller. However, there is a problem that a phenomenon that appears as an afterimage (ghost) during the next development, that is, a so-called hysteresis phenomenon is likely to occur. Therefore, after passing through the portion facing the image carrier (development nip), a thin toner layer that has not been used for development is sufficiently collected using a magnetic brush on the magnetic roller, and new toner is placed on the development roller. It is necessary to form a thin layer.

  By the way, with the recent demand for higher image quality, the toner has become smaller in particle size, and the carrier needs to be smaller in diameter. When a small-diameter carrier is used, the magnetic brush formed on the magnetic roller becomes soft, and at the same time, so-called carrier pulling, in which the carrier moves from the magnetic roller to the developing roller, easily occurs. Then, the carrier that has moved onto the developing roller adheres to the electrostatic latent image, causing white spots in the image. For this reason, it becomes difficult to form a long magnetic brush, and the toner scraping force from the surface of the developing roller by the magnetic brush tends to be reduced, and the toner recoverability tends to deteriorate.

  Further, in order to cope with an increase in the image processing speed, the increase in the peripheral speed of the photosensitive member is also remarkable. Accordingly, it is necessary to increase the rotation speed of the developing roller and magnetic roller in the developing device. Here, the rotating sleeve used for the magnetic roller is mainly made by blasting the pipe material to give the surface roughness, so when the developer transport speed increases, the developer slips on the rotating sleeve. As a result, a sufficient amount of developer cannot be supplied to the developing roller.

  Therefore, as a configuration for solving the above-described problem, Patent Document 1 discloses that a developer filling density in a region where a toner carrier (developing roller) and a developer carrier (magnetic roller) are opposed to each other is a predetermined amount or more. A developing device set in such a manner is disclosed.

Japanese Patent Laid-Open No. 10-123841

  However, according to the description in Patent Document 1, since the distance between the developing roller and the magnetic roller is large, it is presumed that a carrier having a relatively large particle diameter is used. For this reason, it has been difficult to directly apply the developing device using a carrier having a small diameter.

  When a small-diameter carrier is used, the contact of the magnetic brush formed on the magnetic roller with the developing roller becomes soft and it becomes difficult to form a long magnetic brush. For this reason, the toner scraping force from the surface of the developing roller tends to be reduced and the toner recoverability tends to deteriorate, and when a solid image is printed, a density difference may occur depending on the number of rotations of the developing roller, or ghost (history development). There was a problem that occurred. Further, there is a possibility that carrier pulling or developer leakage may occur depending on the amount of developer on the magnetic roller and the magnetic force between the magnetic roller and the developing roller.

  SUMMARY OF THE INVENTION In view of the above problems, the present invention provides a developing device capable of obtaining a good image over a long period of time without causing solid image density unevenness, ghosting, carrier pulling, and developer leakage, and image formation including the same. An object is to provide an apparatus.

In order to achieve the above object, the present invention provides a toner carrier that is disposed so as to face the image carrier in a non-contact manner, a toner supply member that forms a toner layer on the toner carrier using a magnetic brush, and the toner A fixed magnet body having a plurality of magnetic poles including a main pole disposed in the vicinity of the toner supply member and the toner carrier, and disposed in the supply member so as to face the main pole in the toner carrier; In the developing device having the toner carrier side magnetic pole disposed on the resin, the toner carrier has an alumite layer formed on an outer peripheral surface made of aluminum or an aluminum alloy, and a resin containing a resistance adjusting agent on the surface of the alumite layer. A coating layer is formed, and a plurality of grooves extending in the axial direction are formed on the outer peripheral surface of the toner supply member, and the developer existing amount on the toner supply member is A 0~40mg / cm ^2, is characterized in that the magnetic force of the main pole than 100 mT, and the magnetic force difference between the main electrode and the toner bearing member pole is above 50 mT.

  According to the present invention, in the developing device configured as described above, a closest distance between the toner carrier and the toner supply member is 0.2 mm to 0.5 mm.

  According to the present invention, in the developing device configured as described above, the main electrode is disposed in the vicinity of the closest portion between the toner carrier and the toner supply member in the vicinity of the downstream side in the rotation direction of the toner supply member. The carrier-side magnetic pole is arranged in the vicinity of the upstream side in the rotation direction of the toner carrier.

  In the developing device configured as described above, the peripheral speed of the toner supply member is 400 mm / second or more, and the peripheral speed difference between the toner supply member and the toner carrier is 80 mm / second or more. It is said.

  According to the present invention, in the developing device configured as described above, the resin coat layer is mainly composed of urethane or acrylic resin.

  According to the present invention, in the developing device configured as described above, the resistance adjusting agent contains carbon or titanium oxide.

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

  According to the first configuration of the present invention, the amount of the developer present on the toner supply member is set to a predetermined amount, and the magnetic force difference between the main pole of the toner supply member and the magnetic pole on the toner carrier side is defined. Even when a developer composed of toner and carrier is used, the developing device can suppress ghosting and carrier pulling without deteriorating the toner supply property to the toner carrier and the toner recovery property from the toner carrier.

  According to the second configuration of the present invention, in the developing device having the first configuration, the closest distance between the toner carrier and the toner supply member is set to 0.2 mm to 0.5 mm, so that the toner It is possible to achieve both improvement of the toner recovery from the body and suppression of developer leakage.

  According to the third configuration of the present invention, in the developing device having the first or second configuration, the main electrode is positioned in the rotation direction of the toner supply member with respect to the closest portion between the toner carrier and the toner supply member. By arranging the magnetic pole on the toner carrier side in the vicinity of the upstream side in the rotation direction of the toner carrier, the scraping force of the toner on the upstream side in the rotation direction of the toner carrier is strengthened. The scraping power at is weakened. Therefore, it is possible to improve the performance of forming a new toner thin layer while efficiently collecting the residual toner on the toner carrier.

  According to the fourth configuration of the present invention, in the developing device having any one of the first to third configurations, the peripheral speed of the toner supply member is 400 mm / second or more, and the toner supply member, the toner carrier, By setting the peripheral speed difference of 80 mm / second or more, a high-speed printing is possible, and a developing device capable of suppressing deterioration in toner recoverability and occurrence of carrier pulling can be obtained.

  According to the fifth configuration of the present invention, in the developing device having any one of the first to fourth configurations, when the coat layer contains urethane or acrylic resin as a main component, positively charged toner is used. In addition, the chargeability of the toner with the resin material becomes close, and a coat layer with good toner releasability can be formed.

  According to the sixth aspect of the present invention, in the developing device having any one of the first to fifth aspects, the resin coat layer contains a resistance adjusting agent containing carbon or titanium oxide. The residual charge on the surface of the layer can be adjusted appropriately.

  Further, according to the seventh configuration of the present invention, by mounting the developing device having any one of the first to sixth configurations, density unevenness, ghost, carrier pulling, and developer leakage from the developing device can be prevented. Thus, the image forming apparatus can obtain a good image over a long period of time without being generated.

Schematic showing the overall configuration of an image forming apparatus equipped with the developing device of the present invention Side surface sectional view showing the configuration of the developing device of the present invention The figure which shows an example of the bias waveform applied to a developing roller and a magnetic roller Side surface sectional drawing of the developing roller used for the image development apparatus of this invention Cross-sectional enlarged view of the developing roller Sectional drawing which shows the positional relationship of the main pole in a magnetic roller, and the developing roller side magnetic pole in a developing roller

  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.

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

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

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

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

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

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

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

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

  FIG. 2 is a side sectional view showing a configuration of a developing device used in the image forming apparatus of the present invention. 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 simply referred to as a developer) is accommodated, and the developing container 20 is divided into a first wall and a second wall by a partition wall 20a. The first and second agitating chambers 20b and 20c are divided into agitating chambers 20b and 20c, and a toner (positively charged toner) supplied from a toner container (not shown) is mixed with a carrier and agitated and charged. The stirring screw 21a and the second stirring screw 21b are rotatably arranged.

  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, a magnetic roller 22 is disposed in the developing container 20 above the second stirring screw 21b, and the developing roller 20 is disposed 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 1 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.

  Note that a toner concentration sensor (not shown) is disposed in the developing container 20 so as to face the first stirring screw 21a, and the toner supply port 20d is supplied from the supply device according to the toner concentration detected by the toner concentration sensor. The toner is supplied into the developing container 20 via

  The magnetic roller 22 includes a non-magnetic rotating sleeve 22a and a fixed magnet body 22b having a plurality of magnetic poles (here, five poles) contained in the rotating sleeve. The developing roller 23 is composed of a non-magnetic developing sleeve, and the magnetic roller 22 and the developing roller 23 are opposed to each other at a facing position (opposing position) with a predetermined gap.

  Further, a spike cutting blade 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 spike cutting blade 25 rotates in the rotational direction of the magnetic roller 22 (clockwise in the figure). Around the opposite position between the developing roller 23 and the magnetic roller 22. A slight gap (gap) is formed between the front end of the spike cutting blade 25 and the surface of the magnetic roller 22.

  The developing roller 23 includes a cylindrical developing sleeve 23a and a developing roller side magnetic pole 23b fixed in the developing sleeve 23a. The developing roller side magnetic pole 23b is different in polarity from the opposing magnetic pole (main pole) 35 of the fixed magnet body 22b.

  The developing roller 23 is connected to a first bias circuit 30 that applies a DC voltage (hereinafter referred to as Vslv (DC)) and an AC voltage (hereinafter referred to as Vslv (AC)). A second bias circuit 31 for applying a voltage (hereinafter referred to as Vmag (DC)) and an alternating voltage (hereinafter referred to as Vmag (AC)) is connected. The first bias circuit 30 and the second bias circuit 31 are grounded to a common ground.

  A voltage variable device 33 is connected to the first bias circuit 30 and the second bias circuit 31, and Vslv (DC), Vslv (AC) applied to the developing roller 23 and Vmag (DC) applied to the magnetic roller 22. ), Vmag (AC) can be varied.

  As described above, the first stirring screw 21a and the second stirring screw 21b circulate in the developing container 20 while the developer is being stirred to charge the toner, and the second stirring screw 21b causes the developer to move to the magnetic roller 22. Be transported. Since the spike cutting magnetic pole 37 of the fixed magnet body 22 b faces the spike cutting blade 25, the spike cutting blade 25 is made of a non-magnetic material or a magnetic material having a different polarity from the spike cutting magnetic pole 37. A magnetic field is generated in a direction attracting the gap between the tip of the sleeve and the rotating sleeve 22a.

  Due to this magnetic field, a magnetic brush is formed between the ear cutting blade 25 and the rotating sleeve 22a. When the thickness of the magnetic brush on the magnetic roller 22 is regulated by the cutting blade 25 and then moves to a position facing the developing roller 23, the magnetic field attracted by the main pole 35 of the fixed magnet body 22b and the developing roller side magnetic pole 23b. Therefore, the magnetic brush contacts 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 thickness of the toner layer on the developing roller 23 varies depending on the resistance of the developer and the rotational speed difference 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. 3 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. 3A, the developing roller 23 has a combined waveform Vslv (solid line) in which a rectangular wave Vslv (AC) having a peak-to-peak value of Vpp1 superimposed on Vslv (DC) is a first bias circuit. 30 applied. 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 circuit 31.

  Accordingly, 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 separated from the surface of the developing roller 23 by a horizontal (roller circumferential direction) magnetic field generated by the magnetic poles of different polarities adjacent to the main pole 35, and used for development. The toner remaining without being collected is collected from the developing roller 23 onto the rotating sleeve 22a. When the rotating sleeve 22a further rotates, a magnetic field repelled by the adjacent magnetic poles of the same polarity adjacent to the fixed magnet body 22b is applied, so that the toner separates from the rotating sleeve 22a in the developing container 20. Then, after being stirred and transported by the second stirring screw 21b, a magnetic brush is again formed on the rotating sleeve 22a as a two-component developer that is uniformly charged with an appropriate toner concentration, and transported to the pan blade 25. The

  4 is a side sectional view of the developing roller used in the developing device of the present invention, and FIG. 5 is an enlarged sectional view of the developing roller (a sectional view taken along the line AA ′ in FIG. 4). The developing roller 23 has an alumite layer (aluminum oxide film) 40 formed on the outer peripheral surface of an aluminum or aluminum alloy developing sleeve 23a, and the surface of the alumite layer 40 is coated with a silicon-modified polyurethane resin or an acrylic resin. Layer 41 is laminated. The developing roller side magnetic pole 23b in the developing sleeve 23a is not shown.

  Next, a method for manufacturing the developing roller 23 will be described. First, an aluminum or aluminum alloy cylinder is finished into a developing sleeve 23a having a predetermined outer diameter by cutting, polishing, or the like, and then anodized in an aqueous acid solution to form an alumite layer 40 on the surface. The alumite layer 40 is an aggregate of hexagonal columnar cells having a fine hole in the center, and the bottom surface of the fine hole serves as an interface (barrier layer) with the aluminum substrate. The alumite layer 40 prevents the occurrence of leakage when a developing bias is applied to the developing roller 23.

  If the alumite layer 40 is too thick, the resistance of the entire developing roller becomes large and it becomes necessary to apply a high-voltage developing bias. On the other hand, if the alumite layer 40 is too thin, the alumite layer cannot be formed uniformly and a leak may occur. Therefore, the layer thickness of the alumite layer 40 is preferably about 15 μm to 20 μm.

  Then, the coat layer 41 is formed on the surface of the alumite layer 40 by spraying, dipping, roll coating or the like. The coat layer 41 suppresses the toner supplied onto the developing sleeve 23a from sticking to the alumite layer 40. Further, since the mechanical stress applied to the developer by the coat layer 41 is less than that on the metal surface, improvement in toner recoverability from the developing roller 23 and prevention of developer deterioration when the developer conveyance amount is increased. Both can be achieved.

  Examples of the material of the coating layer 41 include urethane resin, acrylic resin, melamine resin, silicon resin, fluorine resin, and the like. However, the resin material of the positively charged toner is close to the chargeability, and the urethane resin having good toner releasability, Acrylic resin is preferred. Among these, the use of a silicon-modified polyurethane resin in which a part of carbon of the urethane resin is replaced with silicon is preferable because the hygroscopic property of the urethane resin is improved and the change in the charging characteristics of the coat layer 41 with respect to the environmental change is suppressed.

The coating layer 41 contains a conductive material having a dielectric constant of 10 or more as the resistance adjusting agent 43 to adjust the volume resistance value of the coating layer 41 and suppress resistance unevenness. Examples of the resistance adjusting agent 43 include carbon black and fiber-shaped potassium titanate. As a result, it is possible to stabilize the charged state of the toner layer and improve the releasability during toner recovery. The volume resistance value of the coat layer 41 is preferably about 10 ⁴ to 10 ⁸ Ω which can appropriately retain the residual charge on the surface of the developing roller 23.

  In the present invention, in order to suppress the slip of the developer on the rotating sleeve 22a when supplying the developer from the magnetic roller 22 to the developing roller 23, a number of grooves extending in the axial direction on the outer peripheral surface of the rotating sleeve 22a. (Knurl shape) is formed. As a result, the developer can be stably supplied to the facing portion between the developing roller 23 and the magnetic roller 22, and a uniform toner thin layer can be formed on the developing roller 23.

When the developer existing amount on the magnetic roller 22 is less than 20 mg / cm ² , the toner thin layer cannot be stably formed on the developing roller 23, and the toner recoverability from the developing roller 23 is also reduced. On the other hand, when the developer existing amount exceeds 40 mg / cm ² , the developer density at the closest portion between the developing roller 23 and the magnetic roller 22 may increase, and developer (carrier) leakage from the developing device may occur. is there. Therefore, the width, depth, number, etc. of the grooves formed in the rotating sleeve 22a may be set so that the developer existing amount on the magnetic roller 22 is 20 to 40 mg / cm ² .

  Note that, when the developer existing amount on the magnetic roller 22 increases, the carrier existing amount increases accordingly, and carrier pulling easily occurs. Further, developer leakage is likely to occur. Therefore, by setting the main pole 35 of the fixed magnet body 22b to 100 mT or more, which is stronger than a general setting (60 to 80 mT), carrier pulling to the developing roller 23 side and developer leakage are prevented and the magnetic roller 22 is prevented. The toner collecting power to the side can also be improved. In particular, in order to prevent carrier pulling, it is preferable to increase the magnetic force difference between the main pole 35 and the developing roller side magnetic pole 23b, which is the opposite magnetic pole, so that the magnetic force on the magnetic roller 22 side is set relatively strong.

  If the difference in magnetic force between the main pole 35 and the developing roller side magnetic pole 23b is small, the magnetic brush is formed too strongly, and the developer and toner are likely to deteriorate. In addition, since the magnetic roller 22 and the developing roller 23 are counter-rotated at the opposed portions, if the magnetic difference between the main pole 35 and the developing roller side magnetic pole 23b is small, the magnetic brush dividing point is too far from the developing roller 23. In some cases, sufficient toner recovery power cannot be obtained. Specifically, the magnetic force difference between the main pole 35 and the developing roller side magnetic pole 23b is set to 50 mT or more.

  Here, as shown in FIG. 6, the main pole 35 of the fixed magnet body 22 b is arranged closer to the downstream side in the rotation direction of the magnetic roller 22 than the closest portion R between the magnetic roller 22 and the developing roller 23, and the developing roller side When the magnetic pole 23b is arranged closer to the upstream side in the rotation direction of the developing roller 23 than the closest portion R, a magnetic brush is formed between the main pole 35 and the developing roller side magnetic pole 23b. As a result, the scraping power of the toner on the upstream side in the rotation direction of the developing roller 23 is strengthened, and the remaining toner that is not used for development can be preferentially collected. In contrast, since the scraping force at the closest portion R is weakened, a uniform thin toner layer can be formed on the developing roller 23 at the closest portion R.

  When the closest distance between the developing roller 23 and the magnetic roller 22 exceeds 0.5 mm, the developer density at the closest portion R decreases, so the carrier existence rate also decreases, and the toner recoverability from the developing roller 23 decreases. To do. Also, carrier pulling is likely to occur. On the other hand, when the closest distance is less than 0.2 mm, the developer density at the closest portion R becomes too high, so that the developer cannot pass through the closest portion R, and developer leakage is likely to occur. Therefore, the closest distance between the developing roller 23 and the magnetic roller 22 is preferably set to 0.2 to 0.5 mm.

  Further, as the peripheral speed of the magnetic roller 22 increases, and as the peripheral speed difference between the magnetic roller 22 and the developing roller 23 increases, the contact time of the magnetic brush with the developing roller 23 is shortened. The carrier pulling is likely to occur. According to the configuration of the present invention, by defining the developer existing amount on the magnetic roller 22 and the magnetic force between the magnetic roller and the developing roller, the peripheral speed of the magnetic roller 22 is 400 mm / second or more. Even in a high-speed machine having a difference in peripheral speed of 80 mm / second or more, excellent toner supply performance and recovery performance can be maintained, and generation of ghost and carrier pulling can be effectively suppressed.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in each of the embodiments described above, the developing device using positively charged toner whose charging direction is positive (plus side) is described as an example. However, the developing device using negatively charged toner whose charging direction is negative (minus side). The same applies to the above.

  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.

  Using the testing machine shown in FIG. 1 equipped with the developing device of the present invention shown in FIG. 2, the distance between the magnetic roller and the developing roller, the presence or absence of a knurled shape on the surface of the magnetic roller, the amount of magnetic brush on the magnetic roller (Developer transport amount), image density of solid image and carrier adhesion (carrier pulling) when the magnetic force of the main pole and the developing roller side magnetic pole was changed were compared. Further, the developer leakage that occurs when the developer transport amount increases excessively was also confirmed. The test was performed in a cyan image forming portion Pa including the photosensitive drum 1a and the developing device 3a.

The test machine conditions were a printing speed of 40 sheets / minute, a photosensitive drum peripheral speed of 200 mm / sec, and a drum surface potential of 300 V for the white background potential (V0) and 20 V for the image portion potential (VL). The developing roller has a 15 μm alumite layer formed on the outer peripheral surface, and a developing roller side magnetic pole is formed with a magnetic roller in a developing sleeve having a diameter of 20 mm in which a coating layer made of a silicon-modified polyurethane resin having a volume resistivity of 10 ⁷ Ω is laminated. The roller was disposed at a position of 14 ° upstream of the contact point in the rotation direction, and the peripheral speed of the developing roller was set to a peripheral speed ratio of 1.5 (forward rotation on the facing surface) with respect to the photoreceptor. The gap between the photoconductor and the developing roller was 0.15 mm.

  In the case of a magnetic roller having a knurled shape, the magnetic roller is arranged in a sleeve having a diameter of 20 mm so that the main pole of the fixed magnet body is at a position of 5 ° on the downstream side in the rotation direction from the closest contact point with the developing roller. Eighty grooves having a depth of 0.08 mm were formed in the axial direction on the outer peripheral surface of the sleeve. The peripheral speed of the magnetic roller was set to a peripheral speed ratio of 1.5 (counter rotation on the facing surface) with respect to the developing roller.

As the developer, a two-component developer comprising a positively charged toner having an average particle size of 6.8 μm, a specific gravity of 1.2, a volume resistivity of 10 ¹² Ω, a saturation magnetization of 40 emu / g, and a coated ferrite carrier having an average particle size of 35 μm. Used, the mixing ratio of toner to carrier (T / C) was set to 12% by weight.

  The voltage application conditions to the developing roller were Vslv (DC) = 100 V, Vpp of Vslv (AC) was 1500 V, the frequency was 3 kHz, and Duty = 45%. The voltage application conditions to the magnetic roller were Vmag (DC) = 300 V, Vmag (AC) Vpp of 1700 V, frequency = 3 kHz, and Duty = 60%.

  As an evaluation method, a reflection densitometer (Spectro Eye, manufactured by Gretag Macbeth Co., Ltd.) was used to measure the image density (ID; image density) at the leading edge of the solid image on the first and second developing rollers, and the difference in measured values. Was less than 0.08, and x was 0.08 or more. Further, the developer leakage from the developing device was visually observed, and the case where there was no leakage was indicated as ◯, and the case where leakage was observed was indicated as ×. In addition, the presence or absence of carrier adhesion to the solid image was visually observed, and the case where carrier adhesion was not recognized was evaluated as ◯ and the case where carrier adhesion was observed as x. The evaluation results are shown in Table 1.

As is apparent from Table 1, the magnetic brush amount is 20 to 40 mg / cm ² using a knurled magnetic roller, the closest distance between the magnetic roller and the developing roller is 0.2 to 0.5 mm, the main pole In the first to fourth aspects of the present invention in which the magnetic force is 100 mT or more and the magnetic force difference between the main pole magnetic force and the developing roller side magnetic pole is 50 mT or more, the difference in image density between the solid images at the first and second rounds of the developing roller is the same. It was as small as less than 0.08. In addition, developer leakage from the developing device and carrier adhesion to a solid image were not observed.

On the other hand, in Comparative Example 1 using a magnetic roller having no knurled shape, the developer cannot be stably supplied to the facing portion between the developing roller and the magnetic roller, and the solid image density on the second circumference of the developing roller is lowered As a result, the difference in image density between the solid images at the first and second rounds of the developing roller was 0.08 or more. Further, in Comparative Example ² in which the magnetic brush amount on the magnetic roller was 50 mg / cm ² , the developer density at the closest portion between the developing roller and the magnetic roller increased, and the developer leaked from the developing device.

  In Comparative Example 3 in which the distance between the magnetic roller and the developing roller exceeds 0.5 mm, the developer density at the closest portion between the developing roller and the magnetic roller decreases, so the solid image density on the second circumference of the developing roller decreases, The difference in image density between the first and second rounds of the developing roller was 0.08 or more. In addition, since the main electrode attracts the carrier, the carrier adhesion also occurs.

  In Comparative Example 4 in which the main pole magnetic force is less than 100 mT, a toner thin layer cannot be stably formed on the developing roller because the toner recoverability from the developing roller is reduced, and the solid image density on the second round of the developing roller Decreased. In addition, since the main electrode attracts the carrier, the carrier adhesion also occurs.

  From the above results, a magnetic roller having a knurled shape is used, and the closest distance between the magnetic roller and the developing roller, the developer conveyance amount of the magnetic roller, the main magnetic pole force in the magnetic roller, and the magnetic force of the developing roller side magnetic pole are predetermined. It was confirmed that the occurrence of density unevenness, carrier adhesion, and developer leakage can be effectively suppressed by setting to this range. Here, the test was performed in the cyan image forming portion Pa, but it has been confirmed that similar results can be obtained in the magenta, yellow, and black image forming portions Pb to Pd.

  The above embodiment is merely an example of the present invention, and the drum surface potential, conditions for applying voltage to the developing roller and the magnetic roller, and the like can be appropriately set according to the specifications of the apparatus and the usage environment.

INDUSTRIAL APPLICABILITY The present invention can be used in a developing device that develops an electrostatic latent image on an image carrier by holding only the charged toner on the toner carrier using a toner supply member, and is made of aluminum or an aluminum alloy. A toner carrier in which an alumite layer is formed on the outer peripheral surface of the carrier and a coat layer made of a resin material containing a resistance adjusting agent is formed on the surface of the alumite layer, and a plurality of grooves extending in the axial direction are formed on the outer peripheral surface. The formed toner supply member is used, the developer existing amount at the closest part between the toner carrier and the toner supply member is 20 to 40 mg / cm ² , the magnetic force of the main electrode is 100 mT or more, and the main electrode and the toner The difference in magnetic force with the carrier-side magnetic pole is 50 mT or more.

  As a result, even when a developer composed of a small-diameter toner and a carrier is used, the toner supply property to the toner carrier and the toner recovery property from the toner carrier are not deteriorated. A developing device that does not cause developer leakage can be provided. In particular, even in a high-speed machine in which the peripheral speed of the toner supply member is 400 mm / second or more and the difference in peripheral speed between the toner supply member and the toner carrier is 80 mm / second or more, carrier pulling and reduction in toner recovery can be effectively suppressed. . At this time, by setting the closest distance between the toner carrier and the toner supply member to be 0.2 mm to 0.5 mm, both improvement of toner recovery from the toner carrier and suppression of developer leakage can be easily achieved. be able to.

  In addition, the main pole is disposed in the vicinity of the downstream side in the rotation direction of the toner supply member, and the magnetic pole on the toner carrier side is disposed in the vicinity of the upstream side in the rotation direction of the toner carrier with respect to the closest portion between the toner carrier and the toner supply member. Therefore, it is possible to improve the performance of forming a new toner thin layer while efficiently collecting the residual toner on the toner carrier.

  In addition, since a coating layer mainly composed of urethane or acrylic resin is formed and a resistance adjusting agent containing carbon or titanium oxide is included in the coating layer, particularly when a positively charged toner is used, good toner releasability In addition, a coating layer having charge persistence can be formed.

1a to 1d Photosensitive drum (image carrier)
3a to 3d Developing device 21a First stirring screw 21b Second stirring screw 22 Magnetic roller (toner supply member)
22a Rotating sleeve 22b Fixed magnet body 23 Developing roller (toner carrier)
23a Developing sleeve 23b Developing roller side magnetic pole 25 Ear cutting blade 30 First bias circuit 31 Second bias circuit 33 Voltage variable device 35 Main pole 37 Ear cutting magnetic pole 40 Anodized layer 41 Coat layer 43 Resistance adjusting agent 100 Image forming apparatus Pa to Pd image forming unit

Claims (5)

A toner carrier that is disposed to face the image carrier in a non-contact manner;
A toner supply member that forms a toner layer on the toner carrier using a magnetic brush formed of a two-component developer containing a magnetic carrier and toner;
A fixed magnet body having a plurality of magnetic poles including a main pole disposed in the toner supply member and disposed in the vicinity of the toner supply member and the toner carrier;
A toner carrier-side magnetic pole disposed in the toner carrier so as to face the main pole;
In a developing device having
The toner carrier has an alumite layer having a thickness of 15 μm to 20 μm formed on the outer peripheral surface made of aluminum or an aluminum alloy, and a volume resistance value of 10 ⁴ made of a silicon-modified polyurethane resin containing a resistance adjusting agent on the surface of the alumite layer. -10 ⁸ Ω coat layer is formed,
A number of axially extending grooves are formed on the outer peripheral surface of the toner supply member,
The developer present amount on the toner supply member is 20 to 40 mg / cm ² ;
The magnetic force of the main pole is 100 mT or more, and the magnetic force difference between the main pole and the toner carrier side magnetic pole is 50 mT or more;
A developing device, wherein a closest distance between the toner carrier and the toner supply member is 0.2 mm to 0.5 mm.   The main pole is disposed in the vicinity of the downstream side in the rotational direction of the toner supply member with respect to the closest portion between the toner carrier and the toner supply member, and the magnetic pole on the toner carrier side is disposed upstream in the rotational direction of the toner carrier. The developing device according to claim 1, wherein the developing device is disposed in the vicinity of the side.   The peripheral speed of the toner supply member is 400 mm / second or more, and the peripheral speed difference between the toner supply member and the toner carrier is 80 mm / second or more. Development device. The developing device according to claim 1 , wherein the resistance adjuster contains carbon or titanium oxide . An image forming apparatus on which the developing device according to claim 1 is mounted .

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