JP6324200B2 - Development device - Google Patents

Description

  The present invention relates to a developing device in which a magnet roller is disposed inside a developer carrier and an image forming apparatus using the developing device.

  In recent developing apparatuses, a two-component developing system in which a non-magnetic toner and a magnetic carrier are mixed and used as a developer is widely used. Since the two-component development system is excellent in the stability of the charge amount of toner, it is suitably used in high-speed image forming apparatuses and color image forming apparatuses.

  In an image forming apparatus using a two-component developer, a cylindrical magnet roller having a predetermined magnetic pattern is fixedly arranged inside a rotating cylindrical sleeve, and the developer is attached to the surface of the sleeve according to the magnetic pattern. Transport. The conveyed developer is made into a thin layer by a regulating blade adjacent to the developing sleeve, and then developed at the opposite portion of the photosensitive drum. The developer remaining on the developing sleeve after development is then separated from the developing sleeve and collected in the developing container 2.

  As a magnet roller, for example, there is a roller composed of five electrodes, a pumping electrode, a conveying electrode, a developing electrode, a collecting electrode, and a peeling electrode. In the case of a magnet roller having such an odd number of poles, the pumping pole and the peeling pole may be the same pole, and a low magnetic field region may be generated between the two poles. Due to the occurrence of this low magnetic field region, the recovery rate of the developer remaining on the developing sleeve after development is lowered, and the history after development remains after one round of the sleeve due to the unrecovered developer, causing image defects. There was fear.

  In order to prevent this, it is necessary to control the low magnetic field region to 10 mT or less on the sleeve surface, and it is necessary to flatten the region of 10 mT or less. Thereby, the recovery rate of the developer is improved.

  Patent Document 1 has a pole-like magnetic pole on the side surface having a substantially fan-shaped cross section between the same poles of the magnet roller 4 (region where the low magnetic field region is generated), and the inner peripheral surface is opposite to the side surface. Disposing a magnet piece.

  However, in the method of Patent Document 1, when a magnet piece is arranged for controlling a low magnetic field region, the magnetic characteristics of both end portions in the longitudinal direction of the magnet roller tend to increase. Then, at both ends of the low magnetic field region, the developer is not collected and goes outside, and the developer stays. Then, more developer is carried on the surface of the developing sleeve at a position corresponding to the longitudinal end surface of the magnet roller than at a position corresponding to the circumferential surface of the magnet roller.

  The developer staying in this way may leak out of the developing container and contaminate the image forming apparatus main body. Therefore, conventionally, as a countermeasure against developer leakage from the end of the developing sleeve, a configuration in which a magnetic plate or a magnet seal is disposed at the end of the developing sleeve and the magnetic ear is brought into contact with the sleeve and magnetically sealed has been adopted. (See Patent Document 2).

JP2002-50515 JP-A-2-262171

  However, in patent document 2, since a magnetic seal is required, it causes a cost increase correspondingly. In view of this, it is conceivable to improve the magnetic characteristics at the end of the developing sleeve to suppress developer leakage without using a magnetic seal.

  However, when the magnetic seal is not required, the developer leakage due to the developer staying at the end of the developing sleeve can be suppressed, but the gap between the developing sleeve and the developing container in the end portion of the developing sleeve can be suppressed. Therefore, there is a risk of toner scattering from the toner. This is because there is a region where the developer hardly exists in the low magnetic field region over the entire length of the developing sleeve. In addition, since the magnetic seal is not disposed at the end portion, a gap through which the scattered toner leaks is generated between the developing container and the developing sleeve at the end portion of the developing sleeve.

  As a countermeasure, when the clearance between the developing container and the developing sleeve is extremely narrowed to fill the gap, the developing container and the developing sleeve may come into contact with each other. As a result of the contact, deformation of the developing sleeve due to contact, aggregation of toner due to frictional heat generated at the time of contact, or the like may occur.

  An object of the present invention is to develop a toner that can suppress toner scattering while suppressing developer leakage due to the developer staying at the end of the developer carrier without providing a magnetic seal at the end of the developer carrier. Is to provide a device.

In order to achieve the above object, a typical configuration of the present invention includes an opening, a developer container that contains a developer including toner and a carrier, and the opening disposed in the image carrier. A developing rotator for carrying and transporting the developer toward a developing region for developing an electrostatic image, a fixed fixing unit disposed inside the developing rotator, a first magnetic pole, and a rotation direction of the developing rotator A second magnetic pole disposed adjacent to the first magnetic pole and having the same polarity as the first magnetic pole, and the developer that has passed through the developing region is peeled off from the surface of the developing rotor. In the developing device including a magnet for generating a magnetic field for the development, the development facing the end in the rotation axis direction of the developing rotator in a space formed between the developing container and the developing rotator. In the opposite area of the container, Characterized in that a formable electrodes an electric field to repel with that voltage is applied to the normal charge polarity of the toner is provided by.

  With the above configuration, a developing device capable of suppressing toner scattering while suppressing developer leakage due to developer staying at the end of the developer carrying member without providing a magnetic seal at the end of the developer carrying member. Can be provided.

FIG. 2 is a schematic explanatory diagram of an image forming apparatus using a developing device. FIG. 2 is a schematic configuration diagram of a developing device according to the first embodiment. The figure which showed the magnetic flux density of the cross-sectional direction of the magnetic field generation member in 1st Embodiment. The figure which showed the magnetic flux density of the longitudinal direction edge part vicinity in the low magnetic field area | region of a magnetic field generation member. Explanatory drawing of the magnet roller of 1st Embodiment. The figure which shows magnetic force distribution of the magnet roller of 1st Embodiment. Explanatory drawing of the periphery structure of the developing sleeve of 1st Embodiment. FIG. 6 is a schematic configuration diagram of a developing device according to a second embodiment. Explanatory drawing of the developing sleeve periphery structure of 2nd Embodiment. FIG. 10 is a schematic configuration diagram of a developing device according to a third embodiment. FIG. 10 is an enlarged view around a developing sleeve of a developing device according to a fourth embodiment. FIG. 10 is a longitudinal end view of a developing device according to a fourth embodiment. The schematic diagram explaining the effect of 4th Embodiment. Explanatory drawing of the periphery of the developing sleeve of the developing device of the fifth embodiment.

[First Embodiment]
A first embodiment of the present invention will be described. FIG. 1 is a schematic explanatory diagram of an image forming apparatus using a developing device.

  As shown in FIG. 1, in this embodiment, a plurality of drum cartridges are provided in parallel for four colors of yellow, magenta, cyan, and black in order to form toner images of each color. The drum cartridge has a photosensitive drum 28 (image carrier). A station for forming an image of each color is configured including the drum cartridge.

  The toner image formed on the photosensitive drum 28 of each station is primarily transferred onto the intermediate transfer belt 24, and then collectively transferred (secondary transfer) to a transfer material so that four colors are superimposed. Thereafter, the fixing device 25 performs pressure heating. Thereby, a full color image is obtained.

  In the following description, the numerals Y, M, C, and K are omitted and the numerals are simply shown, which are common to the yellow, magenta, cyan, and black drum cartridges in FIG.

  A toner image forming operation in each drum cartridge will be described. First, the surface of the photosensitive drum 28 having a diameter of 30 mm charged by the primary charger 21 is exposed by a laser irradiated from the exposure unit 22. Thereby, an electrostatic latent image is formed on the photosensitive drum 28.

  Next, the electrostatic latent image is developed by supplying toner from the developing device 1 (developing device) to obtain a toner image. The toner image is multiplex-transferred onto the intermediate transfer belt 24 by the primary transfer roller 23. The residual toner remaining on the photosensitive drum 28 after the transfer is removed by the cleaner 26.

  FIG. 2 is a schematic configuration diagram of the developing device according to the first embodiment. The developing device 1 according to the first embodiment will be described in detail with reference to FIG. The developing device 1 is used in a full-color image forming apparatus called a so-called tandem system.

  As shown in FIG. 2, the developing device 1 includes a developing container 2 that contains a two-component developer, and a developing sleeve 3 (developer carrier) having a diameter of 20 mm at the opening.

  The developer of the present embodiment is used in a two-component development system as a development system, and is a mixture of a negatively charged nonmagnetic toner and a magnetic carrier. The non-magnetic toner is obtained by encapsulating a colorant, a wax component and the like in a resin such as polyester or styrene acryl, and pulverizing or polymerizing the powder. The magnetic carrier is obtained by applying a resin coat to the surface layer of a core made of resin particles kneaded with ferrite particles or magnetic powder. The toner concentration in the developer in the initial state (weight ratio of toner contained in the developer) is 8% in this embodiment.

  The developing sleeve 3 is rotatably disposed inside the developing device 1. A part of the developing container 2 facing the photosensitive drum 28 is opened, and the developing sleeve 3 is arranged to be partially exposed from the opening (see FIG. 2).

  The developing sleeve 3 is made of a nonmagnetic material and includes a fixed magnet roller 4 (magnetic field generating member) having a plurality of magnetic poles. The developing sleeve 3 rotates in the direction of the arrow in the drawing, and conveys the developer adsorbed at the position of the drawing top pole N1 toward the blade 5.

  The developer spiked by the S1 pole is subjected to a shearing force by the blade 5 and its amount is regulated. When the developer passes through the gap between the developing sleeve 3 and the blade 5, a developer layer having a predetermined layer thickness is formed on the developing sleeve 3. The developer layer is carried and conveyed to a developing area facing the photosensitive drum 28, and is supplied to the electrostatic latent image formed on the surface of the photosensitive drum 28 in a state where magnetic spikes are formed by the N2 pole. Thereby, the electrostatic latent image is developed.

  After being subjected to development, the developer is peeled off from the developing sleeve 3 by a low magnetic field region between the peeling pole N3 (first magnetic pole) and the pumping pole N1 (second magnetic pole) adjacent to each other.

  The developing container 2 is divided into a developing chamber 11 (first developer accommodating chamber) and a stirring chamber 12 (second developer accommodating chamber) by a partition wall 15. The developing chamber 11 and the stirring chamber 12 have an inner diameter of φ30 mm and extend along the rotation axis direction of the developing sleeve 3. Both ends of the partition wall 15 do not reach the side walls in the longitudinal direction inside the developing container 2, thereby forming a communication portion that allows the developer to pass between the developing chamber 11 and the stirring chamber 12.

  The developing chamber 11 and the stirring chamber 12 are provided with a first screw 13 (first circulating and conveying member) and a second screw 14 (second circulating and conveying member) for circulating the developer between the developing chamber 11 and the stirring chamber 12. Have.

  The first screw 13 and the second screw 14 have a screw shaft diameter of φ8 mm, a screw blade diameter of φ20 mm, and a blade interval of 20 mm. The developing sleeve 3, the first screw 13, and the second screw 14 rotate at a speed of 400 rpm. By the rotation of the first screw 13 and the second screw 14, the developer is mixed and stirred while circulating in the developing container 2.

  The developing sleeve 3, the first screw 13, and the second screw 14 are connected and driven by gear trains (not shown), respectively, and rotate by receiving driving from a developing device driving gear (not shown).

  The partition wall 15 is close to the developing sleeve 3 in the vicinity of the non-magnetic band of the developing sleeve 3. After the developer on the developing sleeve 3 is peeled off at the N3 pole, it is accommodated in the developing chamber 11.

  Next, the characteristics of the magnet roller 4 in the present embodiment will be described with reference to FIGS. FIG. 3 is a diagram showing the magnetic flux density in the cross-sectional direction of the magnetic field generating member in the first embodiment.

  In general, in the case of a magnet roller composed of an odd number of magnetic pole peaks, the separation pole N3 (first magnetic pole) and the scooping pole N1 (second magnetic pole) have the same polarity. Low magnetic field region (minimum region G). Alternatively, a repulsive magnetic field may be generated due to the repulsive force between the two poles. In this embodiment, the separation pole N3 and the pumping pole N1 are magnetic poles that are the same and adjacent to each other, but an extremely small different pole may occur between the peeling pole N3 and the pumping pole N1. In this embodiment, including this case, the magnetic poles having the same polarity are adjacent to each other.

  When the magnetic field of the low magnetic field region or repulsive magnetic field is large, the peelability of the developer carried on the developer carrier after development is lowered, and the density is reduced by the developer that could not be peeled off from the developer carrier. There was a risk of image defects such as.

  Therefore, the magnet roller 4 of the present embodiment has a low magnetic field region in which the magnetic force measured on the circumferential surface substantially coincident with the outer circumferential surface of the developer carrier is 10 mT or less. In addition, the region where the magnetic force in the low magnetic field band of 10 mT or less is generated is flattened. Thereby, the peelability of the developer is improved. In addition to this, by defining the magnetic force distribution in the longitudinal direction of the magnet roller 4 in the low magnetic field region as follows, the wraparound of the developer outside the low magnetic field region is suppressed. As a result, the developer can be prevented from leaking without using a magnetic seal.

  FIG. 4 is a diagram showing the magnetic flux density in the vicinity of the end in the longitudinal direction in the low magnetic field region of the magnetic field generating member. FIG. 4A is a view showing a magnet according to this embodiment, and FIG. 4B is a view showing a magnet of a comparative example.

  Moreover, the magnet roller 4 prescribed | regulated the magnetic force characteristic of the longitudinal direction as follows. This will be described. First, in the circumferential direction of the developer carrier, a magnetic flux density distribution in the longitudinal direction of the developer carrier is defined in a low magnetic field region where the magnetic flux density is minimal between the peeling pole and the scooping pole. The regulation of the rising of the magnetic force at the end of the minimum region of the magnet roller 4 of the present embodiment is as follows.

  The magnetic force distribution in the longitudinal direction of the developer carrier at the position where the magnetic flux density in the low magnetic field region is minimum in the circumferential direction of the developer carrier is as follows. The difference between the maximum magnetic flux density in the range from the maximum position where the attenuation rate of the magnetic flux density is maximum to the position of 30 mm toward the center of the developer carrier and the magnetic flux density on the center side of the developer carrier from the above range is 3 mT or less. In addition, the absolute value of the magnetic flux density on the outer side in the longitudinal direction of the developer carrier from the maximum position is 3 mT or less.

  Further, the regulation of the magnetic reversal at the end of the magnet roller 4 is as follows. That is, when the same or opposite polarity of the magnetic field occurs in the magnetic field generation region in the direction opposite to the longitudinal center from the position at which the magnetic flux density decay rate is maximum at the longitudinal end of the magnetic field generation, the absolute value of the magnetic flux density The value is within 3 mT. Here, the magnetic flux density at the longitudinal center refers to the average value of the magnetic flux density in the inner region than the above end.

  Thus, if the magnetic characteristics are satisfied, the magnetic force distribution in the longitudinal direction of the low magnetic field region (repulsive magnetic field region) has the same magnetic characteristics. For this reason, it is possible to prevent the developer from leaking out due to the influence of the magnetic force at the end in the longitudinal direction in the low magnetic field region as in the prior art. On the other hand, in the circumferential direction of the magnet roller 4, except for between the separation pole and the drawing pole, basically, the developer is difficult to leak out from the end of the developer carrier because the magnetic force at the center of the developer carrier is high. It has become.

  In the measurement of the magnetic flux density in this embodiment, the measured value at a position 100 μm away from the surface of the developing sleeve is described as the magnetic force. Moreover, the measurement of the circumferential direction measured a total of three places near 2 cm center from the longitudinal center of the magnet roller 4, and both longitudinal ends. The measurement in the longitudinal direction was performed over the entire length of the developing sleeve 3.

  Next, the configuration and manufacturing method of the magnet roller 4 in this embodiment will be described in detail. FIG. 5 is an explanatory diagram of the magnet roller of the first embodiment. As shown in FIG. 5, the magnet roller 4 is composed of five magnet pieces.

  When the magnet roller 4 is manufactured, first, ferrite powder, NdFeB magnetic powder or the like is used as magnetic powder, and mixed with epoxy resin or nylon resin as binder. The kneaded product is formed into a rod shape with a substantially fan-shaped cross section, and then magnetized (a so-called bond magnet body), and the magnetic poles other than the pumping pole N1 and the peeling pole N3 shown in FIG. It is used for the magnet pieces constituting the pole N2 and the recovery pole S2. For each magnet piece, a magnetic powder and a binder may be appropriately selected according to the required characteristics.

  Further, magnetic anisotropic ferrite powder (anisotropic Sr ferrite, anisotropic Ba ferrite, etc.) is used as magnetic powder, and rubber (nitrile rubber, chloroprene rubber, silicone rubber, etc.) as a binder is mixed. The kneaded material is extruded in a magnetic field with a substantially fan-shaped cross section in a magnetic field, magnetized, and used as a magnet piece that becomes a scooping pole N1 and a separation pole N3 located on both sides of the gap.

  The orientation of the magnetization of the magnetic powder in this case is in the radial direction of the magnet pieces of the scooping pole N1 and the separation pole N3, as indicated by arrows in FIG. In other words, the radial direction is from the inner peripheral surface to the outer peripheral surface. In addition, in the vicinity of the side surface facing the gap between the magnet pieces of the upper and lower poles N1 and N3, the magnetization direction of the magnetic powder is along the side surface.

  However, the magnetization orientation of the magnetic powder may be in an angular range from a direction parallel to the side surface of the magnet piece to a direction parallel to the radial direction of the central portion of the magnet piece of the drawing pole N1 separation pole N3. Then, each magnet piece is bonded to the outer periphery of the shaft 7 so as to provide a gap between the pumping pole N1 and the peeling pole N3. The shaft 7 is usually a magnetic material such as iron.

  FIG. 6 is a diagram illustrating a magnetic force distribution of the magnet roller according to the first embodiment. A magnetization pattern when the surface magnetic force of the magnet roller 4 is measured in the circumferential direction, that is, along the circumferential surface corresponding to the cylindrical sleeve that houses the magnet roller 4 will be described with reference to FIG.

  FIG. 6A shows the magnetic force distribution in the circumferential direction (however, the surface magnetic flux density is measured clockwise (clockwise)). As shown in FIG. 6A, the magnetic force between the drawing pole N1 and the separation pole N3 can be reduced to 10 mT or less (7 mT or less in the illustrated example), and a flat pattern can be formed.

  FIG. 6B shows the magnetic force distribution in the longitudinal direction of the magnet roller 4 in the low magnetic field region in the gap portion between the drawing pole N1 and the separation pole N3. As shown in FIG. 6B, there is little variation in the magnetic force characteristics in the longitudinal direction, and the variation can be suppressed to 3 mT or less.

  In the present embodiment, the magnet roller 4 as described above is used, but the present invention is not limited to this. If it is a magnet which suppresses the rise of the magnetic force in the edge part of a magnet roller, what was manufactured with another manufacturing method may be used.

  FIG. 7 is an explanatory diagram of the peripheral structure of the developing sleeve according to the first embodiment. In this embodiment, as shown in FIG. 2 and FIG. 7 in the end region of the developing container 2, the curvature portion 31 of the developing container 2 and the end position of the developing sleeve 3 are at the normal charging polarity of the toner. An electrostatic seal member 32 (electric field forming member) capable of forming a repelling electric field is disposed. The electrostatic seal member 32 is preferably made of a material having a charge series charged to the same polarity as the toner and charged to a polarity higher than that of the toner. A bearing 33 is attached to the rotating shaft 6 of the developing sleeve 3 outside the developing sleeve 3.

  As shown in FIG. 7, the pasting area of the electrostatic seal member 32 is an end area outside the area of the developing sleeve 3 where the developer is conveyed. Further, the attachment area of the electrostatic seal member 32 is not covered with the magnet roller 4 in the longitudinal direction of the developing sleeve 3.

  The reason for this is as follows. That is, the developer is coated on the developing sleeve 3 in the region where the magnetic force of the magnet roller 4 is affected. For this reason, when the electrostatic seal member 32 and the developer come into contact with each other in the developer coating region, the electrostatic seal member 32 itself may be broken by the friction.

  The toner used in this embodiment is charged on the negative side (negative polarity). As the electrostatic seal member 32, a tape-shaped member having a thickness of 100 μm was used. The gap between the developing container 2 and the developing sleeve 3 is 1 mm. For this reason, even when a 100 μm tape is stretched, the developing sleeve 3 does not rub against the developing container 2.

  When the developer is put into the developing container 2, toner enters the installation area of the electrostatic seal member 32 first. As a result, the electrostatic seal member 32 is immediately charged to the negative side, so that the toner receives a repulsive electric field from the electrostatic seal member 32 having the same polarity between the electrostatic seal member 32 and the developing sleeve 3.

  On the other hand, the carrier in the developing container 2 is charged on the positive side (positive polarity). For this reason, the negatively charged toner is attracted by the carrier and returns to the developing container 2.

  As described above, the developer peeled off from the developing sleeve 3 in the low magnetic field region of the magnet roller 4 rises in the developing container 2. Then, the developer that has risen into the space S (see FIG. 13) between the developing sleeve 3 and the developing container 2 may be ejected from the gap between the containers.

  In the present embodiment, since the electrostatic seal member 32 is attached to the curvature portion 31, the toner receives a repulsive electric field from the electrostatic seal member 32 over time. For this reason, the developer returns into the developing container 2 without being ejected from the space S between the developing sleeve 3 and the developing container 2 to the outside.

  As a result, it is possible to suppress toner scattering from the end region of the developing sleeve 3, and it is possible to suppress problems such as scattering toner being placed in the output image over time.

[Second Embodiment]
A second embodiment of the present invention will be described. About the same structure as the above-mentioned, the same code | symbol is used and description is abbreviate | omitted. FIG. 8 is a schematic configuration diagram of a developing device according to the second embodiment.

  In this embodiment, as shown in FIG. 8, an electrostatic seal member capable of forming an electric field repelling the normal charging polarity of the toner on the entire circumference of the developing sleeve 3 in the end region of the developing sleeve 3. 32 (electric field forming member) is pasted. Thereby, the same effect as the above-mentioned embodiment can be acquired.

  As the electrostatic seal member 32, it is desirable to use a member having the property of being charged to the same polarity as the toner and having high charging characteristics, as in the above-described embodiment. Also in this embodiment, the electrostatic seal member 32 is a tape-shaped member having a thickness of 100 μm.

  FIG. 9 is an explanatory diagram of the peripheral structure of the developing sleeve according to the second embodiment. FIG. 9 shows the arrangement in the longitudinal direction in the end region of the developing sleeve 3. Also in this embodiment, the electrostatic seal member 32 is attached to the end region of the developing sleeve 3 where the magnet roller 4 does not exist. In the present embodiment, the electrostatic seal member 32 is pasted over the entire circumference of the developing sleeve 3 from the end of the developing sleeve 3 to an area of 12 mm.

  With the configuration of the present embodiment, toner scattering can be suppressed as in the above-described embodiment.

[Third Embodiment]
A third embodiment of the present invention will be described. About the same structure as the above-mentioned, the same code | symbol is used and description is abbreviate | omitted. FIG. 10 is a schematic configuration diagram of a developing device according to the third embodiment.

  In the first embodiment, the electrostatic seal member 32 is attached to the entire surface of the curved portion 31 of the developing container 2 facing the end region of the developing sleeve 3. On the other hand, in the present embodiment, as shown in FIG. 10, the developer is repelled from the normal charging polarity of the toner in the low magnetic field region between the peeling pole N3 and the upper electrode N1 where the developer is peeled off from the developing sleeve 3. An electrostatic seal member 32 (electric field forming member) capable of forming an electric field is installed. This is because toner scattering is likely to occur in a low magnetic field region.

  As a result, it is possible to effectively suppress toner scattering from the end portion. In the present embodiment, the separation pole N3 and the pumping pole N1 are magnetic poles that are the same and adjacent to each other, but an extremely small different pole may occur between the peeling pole N3 and the pumping pole N1. In this embodiment, including this case, the magnetic poles having the same polarity are adjacent to each other.

  The region where the electrostatic seal member 32 is installed is a region from a position where the magnetic flux density in the vertical direction of the separation pole N3 is maximized to a position where the magnetic flux density in the vertical direction of the pumping pole N1 is maximized.

  As a result, the tape attachment area can be narrowed, and toner scattering can be more efficiently suppressed.

[Fourth Embodiment]
A fourth embodiment of the present invention will be described. About the same structure as the above-mentioned, the same code | symbol is used and description is abbreviate | omitted. FIG. 11 is an enlarged view around the developing sleeve of the developing device according to the fourth embodiment. FIG. 11 shows a cross section perpendicular to the rotation axis of the developing sleeve 3 at the longitudinal end of the developing device 1.

  An electrode 16 (electric field forming member) capable of forming an electric field repelling the normal charging polarity of the toner is provided so as to cover the developing sleeve 3 in the curvature portion 31 of the developing container 2 at a position facing the developing sleeve 3. .

  The region where the electrode 16 is provided will be described in detail. FIG. 12 is a longitudinal end view of the developing device of the fourth embodiment. FIG. 12 shows a cross section parallel to the developing sleeve 3 axis at the longitudinal end of the developing device 1 as viewed from the side opposite to the photosensitive drum 28. FIG. 12 shows the end of one side of the developing device 1 in the longitudinal direction, but the other end (not shown) is reversed and has the same configuration, and thus the description thereof is omitted.

  In the present embodiment, the electrode 16 is provided in the entire region on the developing container 2 side facing the developing sleeve 3 with respect to the circumferential region. However, the present invention is not limited to this. The effect of the present embodiment can be obtained if it is provided at least in the vicinity of the low magnetic field region between the drawing pole N1 and the separation pole N3 of the magnet roller 4 so as to include a region where the developer is not carried. it can.

  As shown in FIG. 12, the region in the longitudinal direction of the electrode 16 is provided so as to include the end of the magnet roller 4 from the end of the developing sleeve 3.

  Note that the region is not limited to this region, and it is only necessary to provide at least a region on the developing sleeve 3 that overlaps the region on which the developer is carried in the longitudinal direction of the electrode 16. The longitudinal region may be freely set within a range not departing from the region. Therefore, when one end is set to overlap the developer carrying region, the other end is extended from the end of the developing sleeve 3. May be shortened.

  Next, the voltage applied to the electrode 16 will be described in detail. As shown in FIG. 12, the electrode 16 is connected to a voltage application power source 17. The voltage VA applied to the electrode 16 from the voltage application power source 17 is VA = −700V. Further, the voltage VA is applied while the developing device 1 is driven.

  The voltage VA is set so that the potential difference ΔV (= VA−VS) is the same as the charging polarity of the toner with respect to the voltage VS applied to the developing sleeve 3 facing the electrode 16. As a result, the scattering toner works to repel the electrode 16.

  In this embodiment, a negatively charged toner (negative polarity) is used. When the developing device 1 is driven, since a voltage of VS = −400V is applied to the developing sleeve 3, ΔV = −300V. In this case, since the electrode 16 exerts repulsive force on the scattered toner, the scattered toner can be prevented from leaking outside the developing device 1.

  The timing at which the voltage VA is applied to the electrode 16 and the magnitude of the voltage VA are not limited to those of the present embodiment. As described above, the purpose of applying the voltage VA is to apply a repulsive force to the toner. For this reason, you may set freely within the range which can acquire the effect of this embodiment.

  For example, even if ΔV = −300V, the repulsive force applied to the toner increases as the absolute value of ΔV increases. When the charge amount of the toner is large, the effect of sufficiently preventing scattering can be obtained even when ΔV is small. Therefore, ΔV may be changed each time depending on the developer used and the environment.

  Further, when positively charged (positive polarity) toner is used, the value of ΔV must also be set to a positive value. That is, the sign of ΔV is the most important, and it does not depend on the sign of the value of VA or VS itself as long as it matches the charging polarity of the toner.

  If the voltage VS applied to the developing sleeve 3 is obtained by superimposing AC on DC, VA or ΔV may be determined using the DC component or an average value obtained by adding the DC as VS.

  Further, the timing at which the voltage VA is applied to the electrode 16 is preferably applied at least while the developing device 1 is being driven. However, the present invention is not limited to this, and the voltage VA may be applied while the developing device 1 is stopped.

  Next, the effect of the electrode 16 will be described with reference to FIG. FIG. 13 is a schematic diagram for explaining the effect of the fourth embodiment, in which (a) is a cross-sectional view and (b) is a rear view. As shown in FIG. 13, a space S is created between the developing container 2 and the developing sleeve 3.

  The magnet roller 4 used in the present embodiment has a magnetic force in the low magnetic field region of 10 mT or less and a fluctuation in the magnetic force characteristic in the longitudinal direction is 3 mT or less. As shown in FIG. 13, a space S is generated between the developing container 2 and the developing sleeve 3.

  Here, an electrode 16 is provided near the space S, and a voltage having the same polarity as the charging polarity of the toner is applied to the electrode 16 from a voltage application power source 17. For this reason, it acts to repel toner. Then, the scattered toner is returned to the direction of the developer by the same polarity potential applied to the electrode 16 as shown in FIG. 13B.

  For this reason, even when the scattered toner drifting in the developing container 2 reaches the end of the developing sleeve 3 and is about to come out from the space S surrounded by the developing sleeve 3, the developing container 2, and the developer, the scattered toner Can be prevented from jumping out of the developing container 2.

[Fifth Embodiment]
A fifth embodiment of the present invention will be described. About the same structure as the above-mentioned, the same code | symbol is used and description is abbreviate | omitted. 14A and 14B are explanatory views of the periphery of the developing sleeve of the developing device of the fifth embodiment. FIG. 14A is a cross-sectional view of the developing sleeve 3, and FIG. 14B is a top view of the developing sleeve 3 in the longitudinal direction.

  As shown in FIG. 14, in the present embodiment, the opposite ends of the developing container 2 facing the end of the developing sleeve 3 are repelled from the normal charging polarity of the toner, as in the fourth embodiment. An electrode 16 (electric field forming member) capable of forming an electric field is disposed. A voltage application power source 17 that applies a voltage to the electrode 16 is disposed. In the present embodiment, the electrodes 16 at both ends are connected by new longitudinal electrodes 18.

  As shown in FIG. 14A, the longitudinal electrode 18 extends to the curvature portion 31 of the developing container 2 that faces the developing sleeve 3.

  In this way, when the electrodes 16 at both ends are connected by the longitudinal electrodes 18, all the openings of the developing container 2 where the scattered toner may come out are covered with the electrodes. Therefore, it is possible to more effectively suppress the scattered toner from jumping out of the developing container 2.

N1 ... upper electrode N3 ... peeling electrode S ... space 1 ... developing device 2 ... developing container 3 ... developing sleeve 4 ... magnet roller 32 ... electrostatic seal member

Claims (2)

A developer container having an opening and containing a developer containing toner and a carrier;
A developing rotator that is disposed in the opening and carries the developer toward a developing region for developing an electrostatic image formed on the image carrier;
The first magnetic pole and the first magnetic pole are arranged adjacent to the first magnetic pole with respect to the rotation direction of the developing rotary body and are the same polarity as the first magnetic pole. A magnet that has a second magnetic pole and generates a magnetic field for separating the developer that has passed through the developing region from the surface of the developing rotor;
In a developing device comprising:
In a space formed between said developer container and said developing rotary member, wherein the facing area of the developer container facing an end portion of the rotation axis direction of the developing rotary member, a voltage is applied by the voltage source a developing device, wherein a particular association capable of forming an electric field to repel against the regular charging polarity of the toner electrode is provided. The first magnetic flux density in the vertical direction of the second magnetic pole and the second magnetic pole is maximized on the downstream side of the first maximum peak position where the magnetic flux density in the vertical direction of the first magnetic pole is maximum with respect to the rotation direction of the developing rotator. A magnetic field region in which the absolute value of the magnetic flux density in the vertical direction is 10 [mT] or less is formed on the surface of the developing rotator upstream of the maximum peak position of 2;
The distribution of the magnetic flux density in the direction of the rotation axis of the developing rotator at the minimum peak position where the magnetic flux density is minimum in the magnetic field region is the rotation axis of the developing rotator from the maximum position where the attenuation rate of the magnetic flux density is maximum. The absolute value of the maximum magnetic flux density in the range up to the position of 30 mm toward the central portion in the direction, and the absolute value of the magnetic flux density on the central portion side in the rotation axis direction of the developing rotator from the range. The difference is 3 [mT] or less, and the absolute value of the magnetic flux density on the end side in the rotation axis direction of the developing rotator from the maximum position is 3 [mT] or less. Development device.

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