JP5247324B2 - Developing device and image forming apparatus using the same - Google Patents

Description

  The present invention relates to a developing device that visualizes an electrostatic latent image formed on the surface of an image carrier, and an image forming apparatus such as an electrophotographic copying machine, a laser printer, a facsimile, and a printing apparatus to which the developing device is applied.

  Conventionally, in this type of image forming apparatus, after uniformly charging the image carrier, image exposure is performed by analog exposure or a light source such as a semiconductor laser or LED, and an electrostatic latent image is formed on the image carrier. To do.

  Thereafter, the electrostatic latent image is visualized as a developer image by a developing device, and the developer image is transferred to a transfer material directly or via an intermediate transfer member. Then, the transfer material is separated, and a fixed image is output through a fixing device.

  In recent years, the speed of such an electrophotographic image forming apparatus has been increased. However, as a developing apparatus for increasing the speed, a development opportunity using a two-component magnetic brush is increased by using a plurality of developing sleeves. The thing which aimed at the increase is proposed (refer patent document 1).

  Further, a developing device having a plurality of miniaturized developing sleeves has been proposed (see Patent Document 2). Furthermore, a developing device having a developing sleeve using a plurality of two-component developments has been proposed (see Patent Documents 3 and 4).

  FIG. 10 shows a schematic configuration diagram of a developing device having a plurality of developing sleeves. In this developing device, the upstream developing sleeve 11 is rotatably positioned on the upstream side in the rotational direction R1 of the photosensitive drum 1, and the downstream developing sleeve 12 is rotatably disposed on the downstream side in the rotational direction R1 of the photosensitive drum 1. . In this case, the rotation direction R11 of the upstream developing sleeve 11 and the rotation direction R12 of the downstream developing sleeve 12 are the same. S1, S2, N1, and N2 indicate the magnetic poles of the upstream and downstream developing sleeves 11 and 12, respectively.

  FIG. 11 shows the flow of a two-component developer having a carrier. That is, the two-component developer is transferred from the upstream to the downstream in the vicinity of the two developing sleeves 11 and 12 and conveyed onto the circumference of the developing sleeves 11 and 12 facing the photosensitive drum 1.

  The two-component developer mainly needs to be transported because the toner is charged by the carrier. However, when a magnetic one-component developer whose development sleeve mainly contributes to charging is used, a stable thin film is formed on the development sleeve. It is necessary to use a layer coat to sufficiently charge the toner. For this reason, the flow of the developer in the downstream developing sleeve 12 is as shown by the arrow in FIG. 12, which is clearly different from the case where the two-component developer is used.

  In the figure, reference numeral 19 denotes a magnetic blade for coating the surface of the upstream developing sleeve 11 with a developer with a uniform layer thickness. Although the upstream developing sleeve 11 also serves as a developer layer thickness regulating member for the downstream developing sleeve 12 and is small in size and space-saving, it is difficult to uniformly coat the developer as in the case of two-component development using a carrier.

  In particular, although a developing device using a plurality of developing sleeves in a replenishment system that replenishes developer as needed is suitable for a high speed machine, durability and stability are required as a high speed developing apparatus. Therefore, it becomes difficult to coat the developer uniformly.

  In a developing device that uses a magnetic one-component developer and the upstream developing sleeve 11 also serves as a developer layer thickness regulating member of the downstream developing sleeve 12, the toner amount and toner density in the vicinity of the region Z (see FIG. 10) have the downstream developing sleeve 12. It is particularly sensitive to the toner amount and charge amount of the upper toner coat layer.

  Also, unlike the case of two-component developers, the state of zone Z changes when the power is turned on in the morning or when the power is turned on in the morning, or fluctuates in low temperature, low humidity environment, high temperature, high humidity environment, and causes defective coating or poor charging. . In severe cases, a toner lump may be formed in the region Z and the sleeve may be fused, or the coating may be uneven and uneven.

  Therefore, the N2 pole of the downstream developing sleeve 12 covers the maximum position of the normal direction magnetic force with the wall of the developing container, thereby maintaining the toner conveying force to the downstream developing sleeve 12 and excessive toner to the region Z. There has been proposed one that prevents pressure on the skin (see Patent Document 5).

  Further, in a high-speed machine, toner deterioration is likely to occur due to temperature rise and mechanical share accompanying high-speed rotation of a developing sleeve that is in durability. As a result, the density decreases in durability and the image quality deteriorates.

  For this reason, a developing device as shown in FIG. 13 has been proposed with an increase in the speed of the developing sleeve. That is, magnetic poles N2 and N3, which are repulsive poles, are provided in a portion of the downstream developing sleeve 12 that does not oppose the surface of the photosensitive drum 1, and the developing container 18 has all the normal positions of the magnetic poles N2 and N3 in the normal direction. By covering it, toner deterioration is reduced (see Patent Document 6).

  This has the effect of reducing the compression of the developer in the region Z by forming the repulsion pole, and the mechanical share in the toner layer thickness regulating portion is reduced.

  In such a multiple developing system in which the upstream developing sleeve 11 also serves as a developer layer thickness regulating member of the downstream developing sleeve 12, the toner image formed on the photosensitive drum 1 by the upstream developing sleeve 11 is further developed by the downstream developing sleeve 12. Is done. Therefore, the final image density is determined by the downstream development unit.

  That is, when the toner in the downstream developing sleeve 12 is deteriorated, the density becomes low as a result. In the region Z, the upstream developing sleeve 11 moves in the opposite direction to the downstream developing sleeve 12, so that the toner is particularly susceptible to mechanical share.

  Therefore, when the upstream and downstream developing sleeves 11 and 12 rotate at a high speed, the toner is significantly deteriorated and the density becomes low. Therefore, by forming a repelling pole in the downstream developing sleeve 12, about 60% of the toner on the downstream developing sleeve 12 is naturally peeled off from the downstream developing sleeve 12 between the repelling poles.

  As a result, the toner carried on the downstream developing sleeve 12 can be reduced, and since there is no follow-up, toner compression in the region Z can be reduced, toner deterioration is suppressed, and the density is maintained.

Japanese Patent Laid-Open No. 03-204084 Japanese Unexamined Patent Publication No. 03-5579 JP 09-80919 A JP 04-0669690 A JP 2003-255709 A JP 2005-258200 A

  However, in the conventional example, the toner is peeled off in the vicinity of zero gauss between the magnetic poles N2 and N3 which are the repulsive poles. In addition to the temperature rise due to the high-speed rotation of the upstream and downstream developing sleeves 11 and 12, toner deterioration is promoted by the mechanical share with the wall 20.

  For this reason, the toner coat on the downstream developing sleeve 12 may not be uniform and stable over a long period of time.

  The technical problem of the present invention has been made in view of the above circumstances, and a developing device capable of uniformly stabilizing a toner coat on a downstream developer carrying member over a long period of time, and image formation using the same A device is provided.

  In order to achieve the above object, a typical developing device according to the present invention includes a developing container for storing the developer and an image carrier on which a toner image is formed. An upstream developer carrying body and a downstream developer carrying body that rotate in the same direction on the upstream and downstream sides of the rotation direction of the body, and provided in the vicinity of the upstream and downstream developer carrying bodies, Agitating means for agitating the developer, and the upstream developer carrying member also serves as a developer layer thickness regulating member of the downstream developer carrying member, and the upstream and downstream developer carrying members. The first and second magnetic members having a plurality of magnetic poles are disposed on the body, and the first magnetic member has a first magnetic pole facing the developer carrier on the downstream side, and The second magnetic member has a second magnetic pole facing the image carrier and a surface facing the upstream developer carrier. And a fourth magnetic pole of the same polarity disposed downstream of the second magnetic pole and upstream of the third magnetic pole along the rotational direction of the downstream developer carrier. In the developing device having the fifth magnetic pole and the fifth magnetic pole, the stirring means is disposed at a position close to the upstream and downstream developer carriers, and the upstream of the fourth and fifth magnetic poles. The vicinity of the magnetic pole located on the side is covered with the wall of the developing container, and the upper end thereof is below the position where the magnetic flux density in the normal direction of the magnetic pole located upstream of the fourth and fifth magnetic poles is maximum. It is more than the position which becomes the half value of the magnetic flux density in the normal direction.

  A typical image forming apparatus according to the present invention includes: the developing device; an exposure unit that exposes the image carrier according to image information; a transfer unit that transfers the toner image to a transfer material; And a fixing device that fixes the toner image onto the transfer material onto which the toner image has been transferred.

  According to the present invention, the toner coat on the downstream developer carrier can be uniformly stabilized over a long period of time even in a high-speed machine.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a configuration diagram of a digital monochrome image forming apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a developing device in the image forming apparatus of FIG. It should be noted that the dimensions, materials and shapes, other relative arrangements, numerical values, and the like of the components described in the present embodiment are intended to limit the scope of the present invention only to those unless otherwise specified. Is not.

[Embodiment 1]
In FIG. 1, an image forming apparatus 100 performs image formation, and a reader unit 200 is connected or integrated. The reader unit 200 is a device that converts external information into an image signal. An image device or a personal computer that reads an external image document. Then, the luminance signal of the document image read by the image device and the image signal transferred from a personal computer or the like are transmitted to the image forming apparatus 100.

  The image forming apparatus 100 includes a photosensitive drum 1 as an image carrier, and an image forming process based on a charging process, a latent image forming process, a developing process, a transfer process, and a fixing process is performed.

  In the charging process, latent image forming process, and developing process, a toner image is formed on the photosensitive drum 1 based on image information from the reader unit 200. In the transfer step, the toner image is transferred from the photosensitive drum 1 to the transfer material P. In the fixing step, the toner image is fixed on the transfer material P.

  Specifically, the image forming apparatus 100 includes a charger 2 as a charging unit. In the charging process, the charger 2 applies a charging bias to uniformly apply the surface of the photosensitive drum 1 to a predetermined potential. Is charged. Further, the image forming apparatus 100 includes an exposure unit 3 of a laser writing unit that irradiates a laser beam L in accordance with image information from the reader unit 200 in a latent image forming process.

  In the charging process, the surface potential of the photosensitive drum 1 at the irradiated portion is changed and statically irradiated by irradiating the photosensitive drum 1 uniformly charged at a predetermined potential with the laser light L in the latent image forming process, that is, the exposure process. An electrostatic latent image is formed.

  The image forming apparatus 100 has a developing device 40 containing magnetic one-component toner as developing means, and this developing device 40 is provided with two developer carriers (developing sleeves) 41A and 41B that rotate in the same direction. ing. Then, the developer is transferred to the latent image portion formed on the photosensitive drum 1 by the developer carriers 41A and 41B, and a toner image is formed on the photosensitive drum 1.

  Such developer carriers 41A and 41B are arranged close to the photosensitive drum 1, and the developer carrier 41A is located on the upstream side in the rotation direction of the photosensitive drum 1, and the developer carrier 41B. Is located downstream of the photosensitive drum 1 in the rotational direction.

  The toner image formed on the photosensitive drum 1 by the developing device 40 is charged by the post charger 5 in order to perform efficient transfer, and is manifested by the transfer roller 61 as a transfer means in the transfer process. The toner image is transferred to an intermediate transfer belt 62 that is an intermediate transfer member.

  Then, the toner image transferred onto the intermediate transfer belt 62 is transferred onto a desired transfer material P by the transfer roller 63. The toner image formed on the transfer material P is fixed by a fixing device 7 as a fixing unit in a fixing process.

  In the above image forming process, the toner remaining on the photosensitive drum 1 is cleaned by the cleaner 81, and the toner remaining on the intermediate transfer belt 62 is cleaned by the cleaner 82. Then, after the previously formed toner image is removed, the next image formation is performed.

  The photosensitive drum 1 uses an a-Si photosensitive member having a diameter of 108 mm. This is a positively charged photoconductor (positive photoconductor) composed of a conductive drum substrate such as aluminum and a photosensitive layer (photoconductive layer) formed on the outer peripheral surface thereof. For example, a process of 800 mm / sec in the direction of the arrow It is rotationally driven at speed (circumferential speed).

  The charger 2 is a corona charger composed of two discharge wires and grid lines. When a predetermined voltage is applied to the discharge wires by a power source (not shown), a discharging operation is performed, and the photosensitive drum 1 The outer peripheral surface is uniformly charged in the range of about +200 to + 600V. In the present embodiment, the surface potential (charging potential) of the photosensitive drum 1 is set to + 500V.

  The image information is subjected to predetermined image processing by an image processing unit installed in the reader unit 200 and transferred to the exposure unit 3 in synchronization with the reading operation of the reader unit 200.

  The surface potential of the photosensitive drum 1 is exposed to a range of about +50 to +500 V by the laser light L emitted from the exposure unit 3. That is, the charged potential of the photosensitive drum 1 is lowered from +500 V by the laser light L. When negatively chargeable (negative) toner is used, a latent image is formed by a regular development method.

  The developer contained in the developing device 40 is a negatively chargeable magnetic one-component toner. The developer carriers 41A and 41B of the developing device 40 include magnets and are kept at a fixed distance from the photosensitive drum 1, respectively. Then, the developer is restrained while rotating in the direction of the arrow, and the developer moves onto the photosensitive drum 1 by a developing bias (not shown), so that an image with a desired density is formed.

  In the post charger 5, a bias is applied to the discharge wire, a discharge operation is performed by constant current control, and a current flows in the direction of the photosensitive drum 1. This increases the charge of the toner image, and assists in transferring the toner image formed on the photosensitive drum 1 to the intermediate transfer belt 62 during normal image formation. As a charging bias during normal image formation, an AC component (Vpp 1 to 5 kV) is superimposed on a DC component, and constant current control of about −100 to −200 μA is performed.

  The intermediate transfer belt 62 is an intermediate transfer member that is held flat over an area including the transfer portion of the photosensitive drum 1, and a toner image on the photosensitive drum 1 is transferred to the intermediate transfer belt 62.

  The intermediate transfer belt 62 can be circulated and moved by three rollers 64A, 64B, and 64C. The intermediate transfer belt 62 synchronizes with the rotation of the photosensitive drum 1, and the rotation speed (circumferential speed) of the photosensitive drum 1 during normal image formation. It circulates along the direction of the arrow at the same speed.

  As a primary transfer means for transferring the toner image formed on the photosensitive drum 1 onto the intermediate transfer belt 62, a transfer roller 61 is provided on the back side transfer portion of the surface of the intermediate transfer belt 62 facing the photosensitive drum 1. Yes.

The transfer roller 61 is composed of a central conductive support and an intermediate resistance elastic layer formed on the outer periphery thereof. The transfer roller 61 in the present embodiment is a conductive rubber roller having a resistance of 1 × 10 ⁷ Ω and a diameter of 16 mm.

  A predetermined primary transfer bias having a polarity opposite to that of the toner image, in the present embodiment, a positive bias is applied to the conductive support of the transfer roller 61 from a power source (not shown), and the photosensitive drum 1 is applied to the intermediate transfer belt 62. The toner image formed above is transferred.

  As a secondary transfer means for transferring the toner image transferred and carried on the intermediate transfer belt 62 to a desired transfer material P, a transfer roller 63 is provided on the front side of the intermediate transfer belt 62 facing the drive roller 64B.

The transfer roller 63 includes a central conductive support and an intermediate resistance elastic layer formed on the outer periphery thereof. The transfer roller 63 in the present embodiment is a conductive rubber roller having a resistance of 1 × 10 ⁸ Ω and a diameter of 24 mm.

  The transfer roller 63 is formed on the intermediate transfer belt 62 by applying a predetermined secondary transfer bias having a polarity opposite to that of the toner image from the power source (not shown) to the conductive support of the transfer roller 63. The transferred toner image is transferred onto the transfer material P.

  The transfer material P onto which the toner image has been transferred is conveyed to the fixing device 7. The toner image on the transfer material P is heat-fixed by heating and pressing the transfer material P at the fixing nip portion between the fixing roller 71 and the pressure roller 72 of the fixing device 7. Thereafter, the transfer material P on which the toner image is fixed is discharged to the outside, and a series of image formation ends.

  Next, the developing device 40 will be described in more detail. 2 to 4, the developing device 40 has a developing container 4 for storing a developer. The developer carriers 41 </ b> A and 41 </ b> B are close to the photosensitive drum 1 and are disposed at the opening of the developing container 4 along the rotation direction of the photosensitive drum 1.

  The developer carriers 41A and 41B are rotated in the same direction, and the developer carrier 41A located on the upstream side with respect to the rotation direction of the photosensitive drum 1 has its toner coat thickness regulated by the layer thickness regulating blade 42. The

  The developer container 4 includes toner agitating members 43A, 43B, 43C, and 43D as agitating means for agitating the toner in the developer container 4 and transporting the toner to the developer carrying bodies 41A and 41B. A toner amount detection sensor 44 for detecting the toner amount in the developing container 4 is provided.

  The toner (magnetic one-component toner) is a negative toner and has a weight average particle diameter of about 5.0 to 7.5 μm. The resin is made of at least one of styrene acrylic resin or polyester resin, contains about 60 to 90 parts by weight of a magnetic material, and has a relative permeability of about 1.5 to 2.0. Further, it contains about 0.5 to 1.5% (% by weight) of SiO 2 as an external additive.

  A toner replenishing container 45 that contains toner to be replenished in the developing container 4 is provided on the top of the developing container 4. When the toner amount detection sensor 44 detects that the amount of toner in the developing container 4 has decreased from a predetermined amount during development, the toner in the toner replenishing container 45 is replenished into the developing container 4.

  The toner supply is performed by rotating a magnet roller 46A provided at the supply port of the toner supply container 45 by a control signal from the control device 300.

  Toner replenishment attracts the toner in the toner replenishment container 45 to the surface of the magnet roller 46A by the magnetic force of the magnet roller 46A, and rotates the magnet roller 46A. The amount of toner carried on the surface of the magnet roller 46A is regulated by a predetermined gap (gap) between the magnet roller 46A and the toner regulating plate 43B arranged to face the magnet roller 46A.

  Then, a certain amount of toner carried on the surface of the magnet roller 46A is scraped off by the toner scraping plate 46C in contact with the magnet roller 46A and dropped into the developing container 4. As a result, the toner is supplied into the developing container 4, and the new and old toners are mixed and stirred by the toner stirring members 43A to 43D.

  The developer carriers 41A and 41B are films obtained by mixing phenolic resin, crystalline graphite, and carbon in a certain weight ratio ratio on surfaces of nonmagnetic members having a diameter of 32 mm and a diameter of 25 mm, respectively, and curing in a 150 ° C. environment. Is used.

  The thickness of the film was about 20 μm in order to form a stable and uniform film. In this case, the P / B ratio was ½, where B is the weight of the resin and P is the weight of the resin other than the resin (crystalline graphite + carbon).

  Further, a phenol resin containing about 20 parts of a quaternary ammonium salt was used in order to optimize the charging characteristics of the developer carriers 41A and 41B with respect to the toner. When added, the quaternary ammonium salt compound is uniformly dispersed in the phenol resin, and when the resin is heated and cured to form a coating, the phenol resin composition itself changes to a negatively charged substance. Therefore, if a developer carrying member having a coating layer formed using such a material is used, the developer can be charged slightly lower.

  A fixed magnet roller (first magnetic member) 47A having a plurality of magnetic poles (first magnetic poles) is fixedly arranged in the developer carrier 41A. Further, a fixed magnet roller (second magnetic member) 47B having a plurality of magnetic poles (second magnetic pole, third magnetic pole, fourth magnetic pole, and fifth magnetic pole) is also provided in the developer carrier 41B. It is fixedly arranged.

  That is, the magnetic poles N1, N2, N3, N4, S1, S2, S3, and S4 having a magnetic field pattern are arranged on the fixed magnet roller 47A in the developer carrier 41A. The fixed magnet roller 47B in the developer carrier 41B is provided with magnetic poles N1, N2, N3, S1, and S2 having a magnetic field pattern.

  The developer carriers 41A and 41B rotate at a speed of 50 to 150% with respect to the rotation speed (process speed) of the photosensitive drum 1, and between the developer carriers 41A and 41B and the photosensitive drum 1 at the development position. The gap is 150-400 μm. The coat thickness of the toner carried on the developer carrying member 41A by the magnetic force of the fixed magnet roller 47A is regulated by the layer thickness regulating blade 42.

  On the other hand, the toner carried on the developer carrier 41B by the magnetic force of the fixed magnet roller 47B has its coat thickness regulated by the developer carrier 41A. The gap between the developer carrier 41A and the developer carrier 41B is 200 to 400 μm.

  A developing bias in which a DC bias and an AC bias (Vpp 1 to 2 kV, frequency 1 to 4 kHz) are superimposed is applied to the developer carriers 41A and 41B from a developing bias power source (not shown). As a result, the toner is caused to fly toward the photosensitive drum 1 to develop the electrostatic latent image in a non-contact manner.

  Here, the relationship among the developer carriers 41A and 41B, the toner stirring member 43C, and the developing container wall 49 of the developing device 40 in this embodiment will be described in detail.

  The toner carried on the developer carrier 41A has its coating thickness regulated by the layer thickness regulating blade 42, whereas the toner carried on the developer carrier 41B has a coating thickness caused by the developer carrier 41A. Be regulated.

  Therefore, when the developer carrier 41A also serves as the toner layer thickness regulation of the developer carrier 41B as in Patent Documents 5 and 6, the toner behavior in the region Z has a great influence on the coatability of the developer carrier 41B. Effect. For this reason, the developer carrier 41B is provided with repulsive magnetic poles of the magnetic pole N2 (fourth magnetic pole) and the magnetic pole N3 (fifth magnetic pole), and the maximum magnetic force portion thereof is covered with the developing container wall 49 to the region Z. Conventionally, there has been a concept of limiting the amount of toner entering (FIG. 5).

  However, the configuration as shown in FIG. 5 has several problems, so that the coating property of the developer carrier 41B cannot be maintained over a long period when considering the high speed. If the repelling magnetic poles N2 and N3 are covered with the developer container wall 49 in order to limit the amount of toner entering the region Z, the developer accumulates in the region Y, and in addition to the temperature rise due to the high speed rotation of the developer carrier 41B, Deterioration of the agent is promoted by a mechanical share with the developing container wall 49.

  Further, since the stirrer does not enter the region Z at the position of the conventional stirrer member, there is a region where the toner does not move (dead zone), and the toner is likely to be aggregated.

  Therefore, the stirring member 43C is arranged at the closest position so that the gap between the developer carriers 41A and 41B is GA = GB. Further, by providing the developing container wall 49 only up to the vicinity of the N3 pole that is upstream of the repulsion electrode, the agent circulation is improved, and the coatability can be maintained for a long time.

  In the present embodiment, the gap between the stirring member 43C and the developer carriers 41A and 41B is about 1 to 10 mm, and the gap between the developer carrier 41B and the developer container wall 49 is about 1 to 5 mm.

  First, the position of the wall and the position of the stirring member with respect to the repulsive magnetic pole were examined. In this experiment, a magnet roller having a magnet pattern as shown in FIG. 6 was used for the developer carrier 41B on the downstream side, and coating properties, agent circulation, durability fluctuations, and environmental fluctuations were examined. The examination results are shown in FIG.

  The coatability is whether or not a predetermined toner layer is formed on the surfaces of the developer carriers 41A and 41B. The toner amount can be determined by sucking the toner amount of a certain area on the surfaces of the developer carriers 41A and 41B. Further, it means not only the amount but also the height and density of magnetic spikes formed on the developer carrier from the relationship between the magnetic force of the magnet roller and the relative magnetic permeability of the toner.

  The coatability of the developer carrier 41B is regulated by the magnetic force of the developer carrier 41A, the magnetic force of the developer carrier 41B, and the gap between the developer carriers 41A and 41B with respect to the conveyed toner. That is, it is determined by the relationship between the toner conveyance amount and the magnetic regulation force.

For this reason, if the toner conveyance amount is large or the toner amount cannot be sufficiently magnetically regulated, toner amount unevenness occurs in the rotation direction of the developer carrier. In this embodiment, the toner amount of the developer carrier 41B is set to a target value of about 0.5 to 1.0 mg / cm ² .

  Next, “agent circulation” will be described. The agent circulation is to suppress the pressure applied to the toner on the developer carrying member or the container wall and the pressure between the toners as much as possible, to increase the moving speed of the toner and to be stable with respect to time.

  In other words, if the toner stays at a certain location, packing occurs and the toner deteriorates. In this embodiment, the behavior of the toner was observed at three points in the regions X, Y, and Z. The point in the region X is whether or not the toner stays between the magnetic poles N3 and S2.

  The point in the area Y is whether the toner peeled off by the repulsive magnetic poles N2 and N3 is not retained. The point in the region Z is whether excessive toner has not invaded or toner cut from the developer carrier 41B by the developer carrier 41A does not stay.

  Next, “endurance fluctuation” will be described. What happens due to the endurance fluctuation includes a decrease in density due to toner deterioration and the generation of aggregates due to a decrease in fluidity. In addition to the temperature rise due to the high speed rotation of the developer carrier, if the mechanical share is received in the regions X, Y, Z, etc., the external additive is embedded in the toner, leading to a decrease in charging ability and fluidity.

  As a result, toner transportability is also reduced, leading to a decrease in the toner amount and toner charge amount on the developer carrier 41B, resulting in a decrease in developability and a decrease in density.

  Finally, “environmental changes” will be described. Examples of environmental fluctuations include blocking in a high temperature and high humidity environment, poor charging in a low humidity environment, and image unevenness due to toner coat unevenness.

  If the toner excessively enters the region Z, the toner is clogged and abrupt pressure is applied to the toner itself, so that the toner passes between the developer carriers 41A and 41B as a solid state, not as a powder. , Resulting in a non-uniform and uneven coat.

  In extreme cases, the developer carriers 41A and 41B will not rotate due to the resistance. This is called a blocking phenomenon. In addition, since toner is easily charged in a low-humidity environment, the chargeability and transportability differ depending on whether the toner being transported is circulating toner or stagnant toner, leading to electrostatic aggregation and uneven coating. Cheap.

  As a result of examination from the above viewpoint, in Experiment 0 as a conventional example, although the initial coatability was not a problem, the toner amount and the toner charge amount on the developing sleeve 41B were reduced due to durability.

  This is because the repelling magnetic poles N2 and N3 are covered with the developer container wall 49, and thus the toner that has been peeled off accumulates in the region Y, and the deterioration is promoted by the high-speed rotation of the developer carriers 41A and 41B. This is because. Further, since the stirring action does not reach the region Z, it has been found that blocking may occur when used as a dead zone in a high temperature and high humidity environment for a long period of time.

  In Experiment 1-1, the position of the developing container wall 49 was left as it was, and the position of the toner stirring member 43C was disposed at a position closest to the developer carriers 41A and 41B. As a result, although it improved for Experiment 0, sufficient results were not obtained. Although the agitation tends to be improved by arranging the stirring at such a position, the position of the developing container wall 49 is not sufficient as it is conventionally.

  In Experiment 1-2, the position of the developer container wall 49 was opened to the vicinity of the magnetic pole N3 upstream of the repulsive magnetic pole, and the position of the toner stirring member 43C was disposed at the position closest to the developer carriers 41A and 41B.

  With this configuration, the toner peeled off by the repulsive magnetic poles N2 and N3 in the region Y is circulated by the toner stirring member 43C, and new toner is supplied. There were no defects due to environmental changes.

  Therefore, the repulsive magnetic poles N2 and N3 are not covered with the developing container wall 49, and the effect obtained by circulating the toner peeled off by the repelling magnetic poles N2 and N3 through the toner stirring member 43C is obtained. Further, when the agent behavior near the N3 pole was observed, it was found that the toner was stripped between the zero Gauss band between the magnetic poles N2 and N3 and the maximum magnetic flux density position of the magnetic pole N3. Therefore, it is important that the upper end of the developing container wall 49 is not more than the maximum magnetic flux density position of the magnetic pole N3.

  In Experiment 1-3, the position of the toner stirring member 43C was the same as in Experiments 1-1 and 1-2, and the wall was positioned further upstream than the magnetic pole N3. Although there was no problem with the initial coatability, durability fluctuation and environmental fluctuation were worse than those of Experiment 1-2.

  When the behavior of the agent was confirmed, the stirrer effect was exhibited in the region Y and the region Z, but toner retention was observed in the region X.

  This is because the toner has entered a portion where the magnetic force between the magnetic poles N3 and S2 is small because there is no wall at a position where the magnetic force of the magnetic pole N3 does not reach. From this, in order to maintain the sealing property of the developing container wall 49 with respect to the region X, the upper end of the wall should be more than the range where the magnetic force of the magnetic pole N3 reaches, that is, the position where the magnetic force of the magnetic pole N3 becomes half value. all right.

  FIG. 8 shows the positional relationship between the developer container wall 49 and the repulsive magnetic poles N2 and N3 in terms of the magnetic flux density. It can be seen that a zero Gaussian band is formed by the repulsive magnetic poles N2 and N3.

  Thus, it is necessary to open the developing container wall 49 at least up to the maximum magnetic flux density position of the magnetic pole N3 so that the toner to be peeled off does not stay between the sleeve and the wall.

  Further, since the region X having a small magnetic force exists between the magnetic poles N3 and S2, the upper end of the developing container wall 49 should be at least at a position where the peak value of the magnetic pole N3 is at a half value or more so as not to stay in this portion. is there.

  From the above, the upper end of the developer container wall 49 is set to be equal to or lower than the maximum magnetic flux density position of the magnetic pole N3 and to a position where the magnetic flux density of the magnetic pole N3 is half the peak. The coatability of the developer carrier 41B could be maintained over a long period of time by setting the toner stirring member 43C to a position closest to the developer carriers 41A and 41B.

[Embodiment 2]
The second embodiment of the present invention will be specifically described below. In the present embodiment, the toner circulation property is improved by changing the diameter of the toner stirring member 43C with the same configuration as that of the first embodiment.

  An examination was made as to where the closest position should be by changing the diameter of the toner stirring member 43C without changing the relative position between the upper end of the developing container wall 49 and the magnetic pole N3. The result is shown in FIG.

  In Experiment 2-1, the diameter of the toner stirring member 43C is set to about the developer carrier 41B, and the closest position to the developer carrier 41B is between the magnetic poles N2 and N3. In this case, the stirring region in the region Y and the region Z was good agent circulation.

  In Experiment 2-2, the diameter is small, and the closest position to the developer carrier 41B is above the magnetic pole N2. In this case, although the stirring action in the region Z is achieved, the stirring action in the region Y is not sufficient, and the stagnation is caused.

  In a high temperature and high humidity environment, the toner stirs and adheres to the toner stirring member 43C, resulting in a meat dumpling. This is presumably because friction with the toner was promoted by the small diameter and high angular velocity. Therefore, it is not a good idea to reduce the diameter and increase the number of stirring members.

  In Experiment 2-3, the diameter of the toner stirring member 43C is set to be twice or more that of the developer carrier 41B, and the closest part to the developer carrier 41B is below the magnetic pole N3.

  In this case, although the stirring action to the region Y was good, the curvature was small due to the large diameter, and the stirring action to the region Z was not sufficient.

  From the above, it has been found that the stirring action on the region Y and the region Z can be maximized by setting the closest position of the toner stirring member 43C between the repulsive magnetic poles N2 and N3.

  Further, the position where the developing container wall 49 does not cover the region Y and covers the region X is optimal. That is, the upper end of the developing container wall 49 is equal to or lower than the position of the maximum magnetic flux density of the N3 pole on the upstream side of the repulsive pole and is equal to or higher than the half value.

  Further, the stirring member 43C is disposed at a position closest to the developer carriers 41A and 41B so as to exert an agitating action on the region Z, and the closest position to the developer carrier 41B is a magnetic pole N2-N3 where the toner tends to accumulate. It is good to put in between. As a result, the toner in the region Z and the region Y peeled off by the repulsive magnetic pole can be circulated efficiently, and deterioration can be prevented.

1 is a configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a configuration diagram of a developing device in the image forming apparatus shown in FIG. 1. FIG. 3 is an enlarged view of a main part of the developing device in FIG. 2. It is explanatory drawing of the image development apparatus of FIG. FIG. 4 is a diagram for explaining an optimum positional relationship among a magnetic pole position of a downstream developer carrying member, a developing container wall, and a toner stirring member. It is a figure explaining the pattern of the fixed magnet roller of a downstream developer carrier. It is a figure which shows the examination result of Embodiment 1. FIG. FIG. 6 is a diagram for explaining an optimum positional relationship between a magnetic pole position of a downstream developer carrier and a developing container wall. It is a figure which shows the examination result of Embodiment 2. It is a block diagram of the conventional developing device. 3 is a flowchart of a two-component developer having a carrier of a developing device. 3 is a flowchart of a one-component developer in the developing device. It is a block diagram of the other conventional developing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging device 3 Exposure means 5 Post-charging device 7 Fixing device
62 Intermediate transfer belt
40 Developer
41A, 41B Developer carrier
43A-43D Toner stirring member
47A, 47B Fixed magnet roller
49 Developer container wall N1-N4, S1-S4 magnetic pole

Claims (3)

A developer container for storing the developer and an upstream developer that is disposed in the vicinity of the image carrier on which the toner image is formed and rotates in the same direction on the upstream side and the downstream side in the rotational direction of the image carrier. The upstream developer carrier is provided with a carrier and a downstream developer carrier, and stirring means provided in the vicinity of the upstream and downstream developer carriers, and stirring the developer. The first and second magnetic members having a plurality of magnetic poles are disposed on the upstream and downstream developer carriers, which also serve as the developer layer thickness regulating member of the downstream developer carrier. The first magnetic member has a first magnetic pole facing the downstream developer carrier, and the second magnetic member has a second magnetic pole facing the image carrier and the upstream A third magnetic pole facing the developer carrier on the side and the rotation direction of the developer carrier on the downstream side In the downstream side of the pole, and the developing device having a fourth pole and the fifth pole of the third of the same polarity arranged on the upstream side of the pole,
The stirring means is disposed at a position close to the upstream and downstream developer carriers, and of the fourth and fifth magnetic poles up to the vicinity of the magnetic pole located on the upstream side of the developer container. Covered with a wall, the upper end of which is below the position where the magnetic flux density in the normal direction of the magnetic pole located on the upstream side of the fourth and fifth magnetic poles is maximum, and is half the normal direction magnetic flux density A developing device characterized by being at a position or more. The closest portion of the agitating means and the downstream developer carrier has a maximum magnetic flux density in the normal direction of the fourth magnetic pole and a maximum magnetic flux density in the normal direction of the fifth magnetic pole. The developing device according to claim 1, wherein the developing device is between the position and the position. The developing device according to claim 1, an exposure unit that exposes the image carrier according to image information, a transfer unit that transfers the toner image onto a transfer material, and the transfer onto which the toner image has been transferred. An image forming apparatus comprising: a fixing device that fixes the toner image on a material.

Images