JP2008015277A - Developing device and image forming apparatus using same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device in which a two-component developer is picked off in a preferable state from a developer carrier and a degradation in the developer carrier and the developer is suppressed, and to provide an image forming apparatus using the same. <P>SOLUTION: The developing device includes a development housing 2 that is open opposite to an image carrier 1 carrying an electrostatic latent image and can house a two-component developer (developer) D containing a toner and a magnetic carrier, and a developer carrier 3 disposed opposing to the opening of the development housing 2 and capable of carrying and conveying the developer D, wherein the developer carrier 3 has a rotatable developing sleeve 3a and a magnet body 3b having magnetic poles of opposite polarities alternately arranged and fixed inside the developing sleeve 3a. The magnetic body 3b has such a magnetic force distribution that both of the normal component and the tangential component of the magnetic flux density between adjoining magnetic poles of opposite polarities decrease, and has a pick-off portion P where the developer D on the developing sleeve 3a can be released since the developer overcomes by the effect of gravity G and centrifugal force CF against the holding force by the magnetic force distribution. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a developing device used in an image forming apparatus such as a copying machine or a printer, and more particularly to a developing device using a two-component developer containing toner and a magnetic carrier and an improvement of an image forming apparatus using the developing device.

  In general, in a two-component developing method using a two-component developer containing toner and a magnetic carrier as a developing method used in an image forming apparatus such as an electrophotographic method, the developer remaining on the developing roll after development is picked off from the developing roll. For this reason, for types using magnetic poles of different polarity, there is a risk that the developer may be deteriorated if it is forced to peel using a peeling member. It has been. When such a repulsive magnetic pole is used, there is an advantage that pickoff can be achieved almost certainly if the developer reaches the repulsive magnetic field, but on the other hand, in the vicinity of the magnetic pole located upstream of the repelling magnetic pole in the developer conveying direction, A force that prevents the developer from entering the repulsive magnetic field acts on the developer. This is because the magnetic force in the tangential direction acts on the vicinity of the magnetic pole to prevent the developer from proceeding, and as a result, the stagnation of the developer tends to occur near the upstream magnetic pole.

  FIG. 14 shows an example of a conventional developing device, and a developing roll 103 is disposed at a position facing the photoconductor 101 at the opening of the developing housing 102 that opens facing the photoconductor 101. . The developing roll 103 is composed of a developing sleeve 104 that is rotatable on the surface and a magnet roll 105 that is fixedly arranged inside, and among the plurality of magnetic poles that are fixedly arranged in the magnet roll 105, two developing rolls that form a repulsive magnetic field. Repulsive magnetic poles 105a and 105b (in this example, for example, an S pole) are provided. Reference numeral 106 in the figure denotes a trimmer for regulating the layer thickness of the developer layer on the developing roll 103, and reference numeral 107 (107a, 107b) agitates and conveys the developer to give the developer a predetermined charge amount. In addition, the auger supplies the developer to the developing roll 103.

In the developing device having such a configuration, the developer supplied from the auger 107 onto the developing roll 103 is regulated in layer thickness by the trimmer 106 and then developed at a position where the developing roll 103 and the photoconductor 101 face each other. Is done. The residual developer that has been developed is transported on the developing roll 103 as it is rotated, and reaches the vicinity of the magnetic pole 105a. Here, the progress of the developer is hindered by the magnetic force in the tangential direction of the magnetic pole 105a, and the stagnation of the developer (a region indicated by symbol α in the figure) is generated at this portion.
Therefore, slippage between the developer and the developing roll 103 is likely to occur in this stagnation portion, and the surface of the developing roll 103 is worn and deformed, and deterioration of the developer is promoted.

  Such a phenomenon occurs particularly when a friction force with the surface of the developing roll is small, for example, when a carrier having a high sphericity or a resin dispersion carrier is used. In general, when a carrier with a high sphericity or a resin-dispersed carrier is used, the stress on the toner due to the smooth carrier surface is reduced and the life of the developer is extended compared to the case of using a normal magnetic carrier such as ferrite. However, as a result of the reduced frictional force between the developer and the developing roll, the stagnation of the developer described above is likely to occur, and as a result, the slip increases, and on the contrary, a magnetic material such as ferrite. The life of the developing roll and the developer is shortened compared to the case of using a carrier.

Japanese Patent Laid-Open No. 2-140775 (Example, FIG. 1)

  Therefore, as such a countermeasure, a method is assumed in which the developer is picked off from the developing roll without using a repulsive magnetic pole. Japanese Patent Application Laid-Open No. H10-228561 proposes a method of scattering the developer on the surface of the roll body using the centrifugal force of the roll body without using a repulsive magnetic pole. However, this roll body is not a development roll, but a conveyance roll that simply conveys the developer (in the patent document 1, a peeling roll). Further, the magnetic pole arrangement inside the conveyance roll is biased to one side, The developer is scattered from a place where it is not provided. For this reason, when such a magnetic pole arrangement is performed on the developing roll, the transportability of the developer as the developing roll is impaired, and the number of rotations of the developing roll itself is also required. Is even more difficult.

  The present invention has been made to solve such technical problems, and the two-component developer is favorably picked off from the developer carrier, and further, the deterioration of the developer carrier and the developer is suppressed. The developing device and an image forming apparatus using the same are provided.

  That is, as shown in FIG. 1, the present invention can accommodate a two-component developer (developer) D that opens opposite to an image carrier 1 on which an electrostatic latent image is carried and includes toner and a magnetic carrier. In a developing device including a developing housing 2 and a developer carrying member 3 that faces the opening of the developing housing 2 and can carry and transport the developer D, the developer carrying member 3 is rotatable development. A sleeve 3a and a magnet body 3b in which magnetic poles of different polarities are alternately fixed and arranged inside the developing sleeve 3a are provided. The magnet body 3b has a normal direction component of magnetic flux density between adjacent magnetic poles of different polarities. And a pick-off portion P having a magnetic force distribution in which both tangential components are attenuated, and the developer D on the developing sleeve 3a can overcome the holding force by the magnetic force distribution by the action of gravity G and centrifugal force CF and can be peeled off. It is characterized by having Than is.

  In such technical means, the developer carrier 3 may be any material that can carry the developer D. The developer carrier 3 has a magnet body 3b in which a plurality of magnetic poles are fixedly arranged, and can rotate to the outside. A developing sleeve 3a is provided. Further, the rotation direction of the developer carrier 3 (specifically, the developing sleeve 3a) and the image carrier 1 may be the same direction (With direction) at the opposite portion, or the opposite direction (Against direction). There is no problem.

  In the present invention, the pick-up part P of the developer D from the developer carrier 3 is provided between the adjacent magnetic poles m1 and m2 of the opposite polarity of the developer carrier 3, and the developer D is separated from the gravity G and the centrifugal force. By making the separation possible by the action of the force CF, it is possible to prevent the stagnation of the developer D in the vicinity of the magnetic pole located on the upstream side as in the case of using the repulsive magnetic pole, and the developer D and the developing sleeve 3a Slip can be suppressed. As a result, the life of the developer D and the developing sleeve 3a can be extended. Note that “the action of gravity G and centrifugal force CF overcomes the holding force due to the magnetic force distribution and the separation is possible” means that the magnetic force distribution between adjacent magnetic poles m1 and m2 of the magnet body 3b is the developing sleeve 3a. This means that the developer D has a small magnetic force that can surely be picked off from the developer D.

  Further, as a specific position where the pick-off portion P is set, straight lines connecting the surface of the developing sleeve 3a corresponding to each of the adjacent magnetic poles m1 and m2 of different polarities and the rotation center of the developing sleeve 3a are formed. It is preferable that the angle θ is 100 degrees or more, and the normal direction component and the tangential direction component of the magnetic flux density are set to be 20 mT or less.

Here, a state in which a force that hinders the entry of the developer into the pick-off portion when a conventional repulsive magnetic pole is used will be described. FIG. 2 shows a case where the repelling magnetic poles (S poles in this example) of the developer carrier are located in the vicinity, and the developer on the developer carrier is along the rotation direction of the developer carrier. As shown by the arrow A, it is conveyed toward a repulsive magnetic field (a magnetic field constituted by a repelling magnetic pole).
As indicated by the lines of magnetic force formed by the repulsive magnetic field (shown by dotted lines in the figure), there is a region β where there is no magnetic field line (becomes almost zero) between the repelling magnetic poles. Since the developer tends to line up along the lines of magnetic force, a force acts on the developer approaching the region β in the direction of moving from the region β toward the region having the lines of magnetic force. For this reason, the developer conveyed on the developer carrier tends to stay before the region β. However, the developer trying to stay is moved in the normal direction of the developer carrier, that is, in the direction of the arrow B because of the developer conveyed from behind. Therefore, in the vicinity of the magnetic pole located on the upstream side, the developer forms a wall extending in the normal direction. Further, this wall grows, but as it moves away from the developer carrying member, it falls down in the direction of arrow C (development of the developer occurs). Due to such movement of the developer, stagnation of the developer (indicated by α in the figure) occurs in the vicinity of the magnetic pole on the upstream side.
When stagnation is further increased by the developer conveyed from the rear, a part of the developer moves in the direction of the magnetic pole on the downstream side by cutting the weir (in the direction of arrow D), and from the developer carrier. It moves in the direction away (arrow E direction).

Compared to such an action, in the present invention, since the pick-off portion P is provided between the magnetic poles of different polarities, the occurrence of stagnation of the developer D can be suppressed.
Further, the present invention can also be configured in an aspect provided with a repulsive magnetic pole. In this case, as shown in FIG. 1, the opening is opposed to the image carrier 1 on which the electrostatic latent image is carried. And a developer housing 2 that can store a two-component developer (developer) D including toner and a magnetic carrier, and a developer carrier that is disposed facing the opening of the developer housing 2 and can carry and transport the developer D In the developing device, the developer carrier 3 includes a rotatable developing sleeve 3a and a magnet body in which a plurality of magnetic poles including a pair of adjacent magnetic poles of the same polarity are fixedly arranged inside the developing sleeve 3a. 3b, and the magnet body 3b has a pick-off portion P capable of separating the developer D on the developing sleeve 3a between the magnetic poles of the same polarity, and on the upstream side of the magnetic poles of the same polarity. Pickoff near the upstream magnetic pole It is sufficient to have a conveying permissible magnetic field acting in a direction to suppress the backflow to the developer D toward the P.

  As described above, the backflow is suppressed by the conveyance allowable magnetic field, so that it is possible to reduce the occurrence of stagnation of the developer in the vicinity of the upstream magnetic pole, and the developer D easily moves toward the pick-off portion P. Become. In addition, such a transfer allowable magnetic field is formed by greatly separating the repulsive magnetic poles or adding magnetic force adjustment.

  Further, as the transport allowable magnetic field, as shown in FIG. 3A, a straight line connecting the peak position of the normal direction component of the magnetic flux density by the upstream magnetic pole m3 and the rotation center of the developing sleeve 3a is defined as a reference line. Then, it is preferable to set the reference line to be deviated downstream in the developer conveyance direction with respect to a reverse flow region that leads to a behavior in which the developer D toward the pick-off portion P is partially conveyed and conveyed.

Here, this operation will be described in detail.
FIG. 3A schematically shows the magnetic field effect when the repulsive magnetic poles m3 and m4 are used in the present invention, the solid line indicates the normal direction component of the magnetic flux density, and the dotted line indicates the tangent of the magnetic flux density. The direction component is shown. In the present invention, the repulsive magnetic poles m3 and m4 are greatly separated from each other, or the magnetic force of the magnetic poles m3 and m4 is adjusted so that the reference line (indicated by the alternate long and short dash line) is from the backflow region (the boundary is indicated by the alternate long and two short dashed line). It is set to be on the downstream side. Therefore, in the vicinity of the upstream magnetic pole m3, the developer D is easily transported toward the pick-off part P, and the occurrence of stagnation is suppressed. This is because by arranging the repulsive magnetic poles m3 and m4 in this way, the magnetic lines of force due to the repulsive magnetic poles m3 and m4 are likely to spread toward each other, and the tangential direction of the magnetic flux density is also downstream of the upstream magnetic pole m3. It depends on the fact that the ingredients appear greatly.
On the other hand, as shown in FIG. 3B, for example, when the repulsive magnetic poles m3 and m4 are arranged close to each other, the reference line is positioned on the upstream side of the backflow region, and development is performed in the vicinity of the upstream magnetic pole m3. The backflow of the agent D is likely to occur. Therefore, stagnation of developer D is likely to occur. This is due to the fact that the tangential component of the magnetic flux density does not increase on the downstream side of the upstream magnetic pole m3 due to the magnetic field effect between the repulsive magnetic poles m3 and m4.

  Further, in the aspect using the repulsive magnetic poles m3 and m4, it is preferable to provide an auxiliary magnetic pole having a polarity different from that of the magnetic pole m3 and having a low magnetic flux density in the vicinity of the upstream and downstream sides of the upstream magnetic pole m3. Accordingly, it is possible to positively prevent the stagnation of the developer D in the vicinity of the upstream magnetic pole m3.

  As shown in FIG. 1, the pick-off portion P of the present invention is preferably provided at a position spaced above the developer D accommodated in the developing housing 2. Thus, the developer G can be effectively acted on by the gravity G and the centrifugal force CF, and a more effective pick-off can be performed.

  In the present invention, the magnetic carrier of the developer D to be used is not a conventional magnetic carrier in which a resin coating is applied to the surface of a magnetic material such as ferrite, but a magnetic material and a binder resin are dispersedly mixed. When using what has a structure, a more remarkable effect can be brought about. Here, “the structure in which the magnetic substance and the binder resin are dispersed and mixed” is not simply a resin coating on the surface of the magnetic substance as in the past. For example, the magnetic substance and the resin are dispersed and mixed and pulverized. Examples include classified materials, those prepared by a polymerization method, and materials prepared by impregnating a porous magnetic material with a resin.

The magnetic carrier in the present invention is preferably prepared by a polymerization method and has a shape factor (SF-2) of 115 or less. Thus, a magnetic carrier having a spherical shape and a small magnetization is used. Even if it does, it becomes possible to suppress the occurrence of stagnation of the developer D on the upstream side of the pick-off portion P of the developer D. Therefore, it is possible to extend the life of the developer D and the developing sleeve 3a while utilizing the low stress imparting property to the toner by using a carrier having high sphericity. The shape factor (SF-2) is calculated by the following equation (1), where L is the peripheral length of the projected image of the carrier particles and S is the projected area of the carrier particles.
Shape factor (SF-2) = (L ² / S) × {100 / (4π)} (1)

  Furthermore, as the developing sleeve 3a of the present invention, it is preferable that a process for maintaining the transportability of the developer D is performed on the outer peripheral surface thereof. As a specific process for improving the transportability of the developer D, The developing sleeve 3a is subjected to blasting so that the ten-point average roughness Rz is 10 μm or more and then subjected to a hard coating process such as Ta-C (Tetrahedral Amorphous Carbon), and the ten-point average roughness Rz is Examples include those that have been blasted so as to have an uneven surface of 20 μm or more, and those that have been subjected to groove processing (such as V-grooves) with a depth that is greater than the carrier diameter to be used.

  The present invention is not limited to the above-described developing device, but is also intended for an image forming apparatus using these developing devices.

According to the developing device of the present invention, the developer carrying member includes a rotatable developing sleeve, a magnet body in which magnetic poles of different polarities are alternately fixed and arranged inside the developing sleeve, and adjacent different polarities of the magnetic body. Pickoff part with small magnetic action that is set between the magnetic poles and attenuates both the normal direction component and the tangential direction component of the magnetic flux density by the magnet body so that the developer on the developing sleeve can be peeled off by the action of gravity and centrifugal force Therefore, it is possible to suppress the developer slip on the upstream side of the pick-off portion between the developer and the developing sleeve, and to extend the life of the developing sleeve and the developer. Further, since such a configuration is adopted, a resin-dispersed carrier having a high sphericity can be used favorably, the stress on the toner can be reduced correspondingly, and the life of the developer can be further extended. . Therefore, stable development characteristics can be maintained over a long period of time.
Furthermore, according to the developing device of another aspect of the present invention, the developer carrying member includes a rotatable developing sleeve and a plurality of magnetic poles including a pair of adjacent magnetic poles of the same polarity fixed inside the developing sleeve. And a normal direction component of magnetic flux density by the magnet body so that the developer on the developing sleeve can be peeled off by the action of gravity and centrifugal force. A pick-off portion having a small magnetic force action in which both tangential components are attenuated, and the upstream magnetic pole located upstream of the developer conveying direction among the same polarity magnetic poles suppresses the backflow with respect to the developer toward the pick-off portion. Since the conveyance allowable magnetic field acting in the direction is provided, the life of the developing sleeve and the developer can be extended. Therefore, stable development characteristics can be maintained over a long period of time.
Furthermore, an image forming apparatus having stable development characteristics over a long period can be realized by using the above-described developing device.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 4 shows an outline of an image forming apparatus including the first embodiment of the developing device to which the present invention is applied. In FIG. 4, reference numeral 21 rotates in the direction of the arrow, and an organic photoconductive layer is formed on the surface. The photosensitive member 21 is charged by a charger 22 such as a charging roll, and an electrostatic latent image is written by an exposure device 23 such as a laser writing device. . The written electrostatic latent image is formed as a potential image based on the contrast with the high potential portion not exposed to light, because the surface potential of the exposed portion of the photoreceptor 21 is lowered.

  In addition, the developing device 30 disposed opposite to the photosensitive member 21 contains a two-component developer (developer) including a toner that is colored particles and a magnetic carrier that carries and transports the toner in a developing housing 31. The developer is carried on a developing roll 32 as a developer carrying member, and a developing bias from a bias power source (not shown) is applied to the developing roll 32 so that the developing roll 32 side has a high potential portion of the electrostatic latent image. The image portion of the electrostatic latent image on the photosensitive member 21 is developed with the charged toner in the developer.

Further, a transfer device 24 is provided around the photoconductor 21, and this transfer device 24 is constituted by, for example, a transfer roll arranged in pressure contact with the photoconductor 21, and the toner on the photoconductor 21 by a bias power source (not shown). The toner image developed on the photoreceptor 21 is transferred to the recording material 26 by applying a transfer bias in a direction that attracts the image to the recording material 26 side. Further, the toner remaining on the photosensitive member 21 after the transfer is removed by, for example, a doctor blade type cleaner 25.
In this embodiment, the recording material 26 onto which the toner image on the photosensitive member 21 is transferred is conveyed to a fixing device 50, and the toner image on the recording material 26 is fixed by the fixing device 50. As the fixing device 50, for example, a heat roll method is adopted, which includes a heating roll 51 and a pressure roll 52, and a toner image is obtained by passing the recording material 26 between the heating roll 51 and the pressure roll 52. Is fixed to the recording material 26.

As shown in FIG. 5, the developing device 30 in the present embodiment has a developing housing 31 that opens toward the photoreceptor 21, and a developing roll 32 is disposed facing the opening of the developing housing 31. A layer thickness regulating member (trimmer) 33 that regulates the layer thickness of the developer on the developing roll 32 is provided below the developing roll 32 at a position close to the developing roll 32.
Further, behind the developing roll 32 in the developing housing 31, an auger 34 (34 a, 34 b) as a stirring member that charges the developer and supplies the developer to the developing roll 32 side while agitating and conveying the developer. ) Is provided. In the auger 34 according to the present embodiment, a supply auger 34a that mainly supplies developer to the developing roll 32 is disposed on the developing roll 32 side, and the supply auger 34a includes a part of the developing housing 31 behind the supply auger 34a. An admixing auger 34b for mainly mixing and stirring the developer is provided through the partition wall 31a.

  The developing roll 32 of the present embodiment is rotatably provided with a non-magnetic developing sleeve 32a blasted so that the surface has a predetermined roughness, and four magnetic poles are provided inside the developing sleeve 32a. A magnet roll 32b is provided as a fixedly arranged magnet body. Further, the magnetic pole in the magnet roll 32b is provided with an S1 magnetic pole as a developing magnetic pole at a position facing the photoconductor 21, and an N1 magnetic pole as a conveying magnetic pole in the vicinity of the uppermost portion of the developing roll 32 on the downstream side of the S1 magnetic pole, An S2 magnetic pole as a pick-up magnetic pole is disposed obliquely below and downstream of the N1 magnetic pole, and an N2 magnetic pole as a trimmer magnetic pole is disposed at a position substantially opposite to the trimmer 33. In the present embodiment, the angle formed by the straight lines drawn from the center of the developing roll 32 to the respective magnetic poles (N1 magnetic pole and S2 magnetic pole) is about 132 °.

Further, the trimmer 33 in the present embodiment fixes a nonmagnetic support 33a to the developing housing 31, and the surface of the nonmagnetic support 33a on the upstream side in the developer transport direction is in the normal direction of the developing roll 32. A magnetic thin plate 33b is mounted along the magnetic thin plate 33b, and the rising of the developer is effectively performed between the magnetic thin plate 33b and the N2 magnetic pole of the trimmer magnetic pole. A predetermined amount of developer layer is formed.
Furthermore, in the present embodiment, the developer in the developing housing 31 contains a developer amount such that the lowermost end of the developing roll 32 is in contact with the developer containing area, and N1 adjacent to the developing roll 32 is stored. The space between the magnetic pole and the S2 magnetic pole is positioned above the developer containing area.

  In particular, as the developer in the present embodiment, a two-component developer including a spherical carrier having a shape factor SF-2 of 105, which is made of a dispersion carrier (polymerization carrier) of a magnetic material and a resin, and toner is used. .

  Next, the operation of the developing device 30 will be described. In FIG. 5, the developer charged by the auger 34 is supplied onto the developing roll 32 by the action of the supply auger 34a and the action of the pickup magnetic pole (S2 magnetic pole) of the developing roll 32. The developer supplied to the developing roll 32 moves as the developing roll 32 rotates, and is regulated to a predetermined layer thickness by the trimmer 33. The developer restricted to the predetermined layer thickness is subjected to predetermined development by a developing bias (not shown) in a developing region that is a region where the developing roll 32 and the photosensitive member 21 are opposed to each other, and the toner in the developer flies. As a result, the electrostatic latent image on the photosensitive member 21 is visualized. The developer whose toner has been reduced after the development moves on the developing roll 32 as the developing roll 32 rotates, and is conveyed toward the magnetic pole S2 beyond the magnetic pole N1.

At this time, since the magnetic pole N1 and the magnetic pole S2 are provided at positions that are largely separated from each other, the magnetic flux density on the developing roll 32 (specifically, on the developing sleeve 32a) is near the developing roll 32. In both the normal direction and the tangential direction, both are smaller. FIG. 6 shows the magnetic flux density distribution of the developing roll 32 as an example, the solid line shows the normal direction component of the magnetic flux density, and the dotted line shows the tangential direction component of the magnetic flux density. Further, the concentric circles have an interval of 20 mT. As can be seen from this figure, between the magnetic pole N1 and the magnetic pole S2, a region where both the normal direction component and the tangential direction component are small (specifically, a region where the component is 20 mT or less) is the developer pick-off position. .
Therefore, as shown in FIG. 5, the developer in this vicinity has a weak magnetic attractive force toward the developing roll 32, and at the same time, centrifugal force due to the rotation of the developing roll 32 and the gravity of the developer itself are applied. Therefore, the developer easily separates (picks off) from the surface of the developing roll 32 in the direction of the arrow in the figure. In particular, in this embodiment, since the developer is not accommodated in this portion in the developing housing 31, pick-off is made more effective.
Then, the developer picked off from the developing roll 32 falls to a portion of the developing housing 31 where the developer is accommodated, and is again stirred and conveyed by the auger 34, whereby the developer is mixed and dispersed. Thus, the toner concentration in the developer is made uniform and predetermined charging is performed.
Further, it is possible to reduce the consumption of the driving torque that has conventionally been generated by the slip, and it is possible to obtain a secondary effect that the required torque in the developing device can be reduced.

  In this embodiment, since the magnetic pole N1 and the magnetic pole S2 are used as the magnetic poles before and after the pick-off position, for example, a force (magnetic force) that prevents the developer from entering the pick-off position as in the case of using a repulsive magnetic pole. Does not work. Therefore, the occurrence of stagnation of the developer is suppressed, the slip between the developer and the developing roll 32 is less likely to occur, and the shape of the surface of the developing roll 32 (specifically, the surface of the developing sleeve 32a) can be stabilized over a long period of time. Will be able to maintain. In addition, the life of the developer itself can be kept long. As a result, the development characteristics can be stabilized over a long period of time. In this embodiment, the stagnation of the developer that occurs in the conventional apparatus shown in FIG. 14 does not occur.

  In the present embodiment, the magnetic pole arrangement of the developing roll 32 is as shown in FIG. 5, but the magnetic pole arrangement is not limited to this, and may be appropriately selected. In addition, the angle formed by the magnetic poles adjacent to the pickoff position (in this example, the magnetic pole N1 and the magnetic pole S2) is 132 degrees. However, further investigation has revealed that if this angle is 100 degrees or more, good pickoff can be performed at the pickoff position It turned out to be.

Next, FIG. 7 shows a modified example of the developing device 30 of the present embodiment. The developing roll 32 is arranged substantially above the center of the supply auger 34a and the admixing auger 34b, and above the developing roll 32. The photoconductor 21 is provided. Further, the magnetic pole arrangement of the developing roll 32 is a structure in which the magnetic pole arrangement shown in FIG. The space between the magnetic pole N1 and the magnetic pole S2 is set above the developer accommodating area in the developing housing 31.
Even with such a configuration, the developer is favorably picked off at the pick-off position between the magnetic pole N1 and the magnetic pole S2 of the developing roll 32 as in the above-described embodiment. Therefore, it goes without saying that the same effects as those of the above-described embodiment can be obtained.

  In the present embodiment, an example in which the present invention is applied to a monochrome image forming apparatus having one developing device 30 has been described. However, the present invention is not limited to this. For example, the present invention is applied to a color image forming apparatus including a plurality of developing devices 30. It goes without saying that it is also possible.

Embodiment 2
FIG. 8 shows a second embodiment of the developing device 30 to which the present invention is applied. In the figure, the developing device 30 of the present embodiment is configured in substantially the same manner as the developing device 30 (see FIG. 5) of the first embodiment, but the magnetic pole arrangement of the developing roll 32 is different from that of the first embodiment. That is, in the present embodiment, repulsive magnetic poles (specifically, composed of magnetic poles N1 and N2) are provided, and the developer pick-off from the developing roll 32 is weak in magnetic force between the repelling magnetic poles. In addition, the centrifugal force and gravity are applied to the part. Components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

  The developing device 30 according to the present embodiment has a configuration in which the magnetic pole arrangement of the magnet roll 32b in the developing roll 32 has no pickup magnetic pole (magnetic pole S2) in the magnetic pole arrangement (see FIG. 5) of the first embodiment. Yes. Therefore, the developer in the developing housing 31 is supplied from the supply auger 34a to the developing roll 32 by the magnetic attractive force of the trimmer magnetic pole N2. Then, the developer supplied to the developing roll 32 is regulated in layer thickness by the trimmer 33, and after being developed in the developing region, it goes downward through the magnetic pole N1.

FIG. 9 shows the magnetic flux density distribution of the developing roll 32 as an example. Like FIG. 6, the solid line shows the normal direction component of the magnetic flux density, and the dotted line shows the tangential direction component of the magnetic flux density. As described above, when the repulsive magnetic pole (configured by the magnetic pole N1 and the magnetic pole N2) is used, a region where both the normal direction component and the tangential direction component of the magnetic flux density are small exists between the magnetic poles.
For example, by separating the magnetic pole N1 and the magnetic pole N2 from each other, the reference line connecting the peak position and the center (specifically, the rotation center of the developing sleeve) of the normal component of the magnetic pole N1 is downstream of the backflow region. Is set to be Therefore, the reverse flow of the developer near the magnetic pole N1 is suppressed, and the developer is easily transported to the pickoff position.
Similarly, the tangential component also appears largely downstream of the magnetic pole N1 in the tangential component, and this point does not greatly separate the repulsive magnetic pole (see FIG. 3B). Different. This also improves the developer transportability in the vicinity of the magnetic pole N1.

  In the present embodiment, since the magnetic flux density is distributed as described above, the developer that has reached the vicinity of the magnetic pole N1 is transported downstream as it is, and the stagnation of the developer in the vicinity of the magnetic pole N1. Occurrence of occurrence will be suppressed. The developer beyond the magnetic pole N1 has both a normal component and a tangential component small, and the developer is picked off from the developing roller 32 at a pick-off position where centrifugal force and gravity are effective. Therefore, if the repulsive magnetic poles are used as described above and the magnetic poles are separated from each other, for example, the developer slip is suppressed, and the same effect as in the first embodiment can be obtained.

  Here, for comparison, the magnetic flux density distribution of a conventional developing device of the type using a repulsive magnetic pole (see FIG. 14) will be described. FIG. 15 shows an example of the magnetic flux density distribution by the magnet roll 105 of the developing device shown in FIG. 14, in which the solid line shows the normal direction component and the dotted line shows the tangential direction component. As can be seen from the figure, although the tangential component between the repulsive magnetic poles is small, a large tangential component exists on the upstream side of the repelling magnetic pole located on the upstream side, while the tangential component is almost on the downstream side. There will be no. And the reference line by the magnetic pole S of an upstream magnetic pole is located upstream from a backflow area | region. Therefore, in this part, the developer trying to line up in the normal direction of the developing roll 103 in the direction of the normal of the developing roll 103 due to the effect of the normal direction component of the repelling magnetic pole located on the upstream side with respect to the traveling direction of the developer in the direction of the magnetic pole N on the upstream side. As a result, the developer tends to stagnate in this portion. On the other hand, in this embodiment, it is understood that the occurrence of such stagnation is suppressed.

Embodiment 3
FIG. 10 shows a third embodiment of a developing device 30 to which the present invention is applied. In the figure, the developing device 30 of the present embodiment is configured in substantially the same manner as the developing device 30 of the first embodiment, but the developer is picked off by a repulsive magnetic pole, and an auxiliary magnetic pole is provided in part. This is different from the developing device 30 of the first embodiment. Components similar to those in the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted here.

  The developing device 30 in the present embodiment is characterized by the magnetic pole arrangement of the magnet roll 32b in the developing roll 32. In the magnetic pole arrangement of the present embodiment, the magnetic pole N1 is the magnetic pole S3 in the magnetic pole arrangement of the first embodiment (see FIG. 5), and the angle from the center of the developing roll 32 is near each side of the magnetic pole S3. Two auxiliary magnetic poles N3 and N4 having a magnetic flux density within 30 [deg.] And less than half of the magnetic pole S3 are provided.

In this embodiment, by providing such a magnetic pole arrangement, the developer on the developing roll 32 is regulated in layer thickness by the trimmer 33, and after being developed in the developing region, the auxiliary magnetic pole N3 on the upstream side is provided. These magnetic pole positions are transported by the action of the magnetic pole S3 as the transport magnetic pole and the auxiliary magnetic pole N4 on the downstream side. The auxiliary magnetic poles N3 and N4 have a magnetic attractive force only in the vicinity of the magnetic pole, so that the developer on the developing roll 32 is easily transported as the developing roll 32 rotates.
Further, the magnetic pole S3 and the magnetic pole S2 constitute a repulsive magnetic pole. However, in this embodiment, since the auxiliary magnetic pole N4 is provided on the downstream side of the magnetic pole S3, the developer on the developing roll 32 is easily assisted. The developer stagnation can be suppressed in the vicinity of the magnetic pole S3 as the repulsive magnetic pole that is conveyed to the magnetic pole N4 side. For this reason, the developer can be easily conveyed into the repulsive magnetic field due to the reciprocal magnetic poles of the magnetic pole S3 and the magnetic pole S2, and the action of the repulsive magnetic field, centrifugal force, and gravity can be easily combined at the pick-off position. Then, the developer is peeled from the developing roll 32.

Therefore, even in the present embodiment, the same effect as in the first embodiment is obtained. At this time, if the repulsive magnetic poles S3 and S2 are arranged close to each other, the effects of the auxiliary magnetic poles N3 and N4 cannot be fully utilized, and the upstream repulsive magnetic pole (the magnetic pole S3 in this example) In the vicinity, the stagnation of the developer is caused.
Further, the auxiliary magnetic poles N3 and N4 of the present embodiment may have a magnetic field intensity that does not hinder the magnetic field action of the magnetic pole S3, and the magnetic flux density and arrangement may be appropriately selected.

Example 1
In this example, it was evaluated and confirmed how the wear state of the surface shape of the developing roll (particularly the developing sleeve) changes depending on the carrier used in the developing device having the configuration of the first embodiment. For comparison, an evaluation with a conventional developing device (see FIG. 14) was also performed.
The developing sleeve used had a 10-point average roughness Rz of the initial surface roughness of the aluminum surface of 23 μm.
Two types of carriers were used: a resin-dispersed carrier (shape factor SF-2 = 105) prepared by a polymerization method and a conventional ferrite carrier.
Evaluation was made by comparing the surface roughness of the developing sleeve after outputting 100 kpv of the paper with the initial surface roughness, and measuring ΔRz (change in 10-point average roughness) as sleeve wear. Usually, the surface of the developing sleeve is worn due to slip and the surface roughness becomes small, so ΔRz becomes a negative value.

As shown in FIG. 11, when a resin dispersion carrier is used, ΔRz varies greatly depending on the type of developing device. According to the present invention, ΔRz was 3 μm, but in the conventional developing device, ΔRz It was confirmed that a large wear of 15 μm occurred. On the other hand, when a normal ferrite carrier was used, almost no difference in the developing device was confirmed, and ΔRz was 7 to 8 μm.
This indicates that although the state of occurrence of developer stagnation varies greatly depending on the developing device, the degree of the effect of the slip phenomenon due to stagnation varies depending on the carrier used. In particular, the present invention was reconfirmed to be effective when using a resin-dispersed carrier.

  Here, by further changing the shape factor of the magnetic carrier, the same evaluation as described above was performed, and it was confirmed that a good result was obtained if the shape factor was 115 or less. In addition, as a magnetic carrier, a porous magnetic material (ferrite type, magnetite type, etc.) was impregnated with a resin, and a carrier with a uniform shape factor was evaluated in the same manner. It has been confirmed that the same effect can be obtained if it is 115 or less. Further, the ferrite fine powder was hardened into a spherical shape and then coated with a resin, and a carrier having a uniform shape factor was evaluated in the same manner. However, it was confirmed that the same effect can be obtained if the shape factor is 115 or less.

Example 2
The present embodiment is performed in order to confirm the deterioration state of the developer by a method substantially similar to that of the first embodiment.
In the evaluation, it was confirmed how the charge amount (evaluated by toner density × toner charge amount) possessed by the developer was lowered by repeated development, and the difference was measured as ΔTP.
The developing device and carrier used were the same as in Example 1. The test was performed by outputting 100 kpv paper.

As a result, as shown in FIG. 12, it was confirmed that the use of the resin-dispersed carrier caused less toner deterioration than the case of using a normal ferrite carrier. In particular, by using the developing device of the present invention, a significant improvement effect was confirmed over other combinations, and ΔTP was 10 (au), whereas a conventional developing device using a resin-dispersed carrier was used. It was confirmed that ΔTP was 60 when using, and ΔTP was 75-80 when using a ferrite carrier.
This indicates that the use of a resin-dispersed carrier reduces the stress on the toner and eliminates the stagnation of the developer, thereby significantly improving the deterioration of the developer.

Example 3
This example was carried out in order to evaluate and confirm how the surface property of the developing sleeve of the developing roll affects when the resin dispersion carrier is used in the developing device having the configuration of the first embodiment. . For comparison, evaluation with a conventional developing device (see FIG. 14) was also added.

The developing sleeve used was one having an Rz of 23 μm and 10 μm on the aluminum surface as an untreated product.
Further, a Ta-C coated product was obtained by coating the surface of an untreated product with a Ta-C thin film (tetrahedral amorphous carbon thin film) by FCVA technology (Filtered Cathodic Vacuum Arc Technology: NTI).
And it evaluated using the resin dispersion | distribution carrier (shape factor SF-2 = 105) produced by the polymerization method.
Evaluation was made in the same manner as in Example 1 by comparing the surface roughness of the developing sleeve after the paper was output at 100 kpv with the initial surface roughness and measuring ΔRz as sleeve wear.

As shown in FIG. 13, when the surface of the developing sleeve is not yet processed, ΔRz is greatly different between 23 μm and 10 μm, and ΔRz of the 23 μm product is 3 μm, whereas ΔRz is 10 μm. It became clear that when the surface roughness was 7 μm and the surface roughness was small, developer slip was likely to occur and the wear progressed.
It was also found that when Ta-C coating is applied to a 10 μm product, ΔRz can be reduced without causing wear by Ta-C coating, even if some developer slip occurs due to this hard coating film. However, it has been found that even when such a hard coat film is used, when it is combined with a conventional developing device, the advantage of the hard coat treatment cannot be utilized and the surface wear proceeds. It was understood that, as in the conventional developing device, when the stagnation of the developer occurs using the resin dispersion carrier, it leads to wear of the developing sleeve and it is difficult to ensure stable development characteristics. .
Therefore, the effectiveness of this case was confirmed again.

It is explanatory drawing which shows the outline | summary of the image development apparatus concerning this invention. It is explanatory drawing which shows an effect | action at the time of using a repulsion magnetic pole. (A) is explanatory drawing which shows the other aspect of the developer carrier used for the image development apparatus concerning this invention, (b) is explanatory drawing which shows the conventional aspect as a comparison. 1 is a schematic diagram illustrating an image forming apparatus using a developing device according to a first embodiment to which the present invention is applied. FIG. 2 is an explanatory diagram illustrating a developing device according to the first embodiment. 3 is an explanatory diagram illustrating a magnetic flux density distribution according to Embodiment 1. FIG. FIG. 10 is an explanatory diagram illustrating a modification of the developing device according to the first embodiment. FIG. 10 is an explanatory diagram of a developing device according to a second embodiment. 6 is an explanatory diagram showing a magnetic flux density distribution according to Embodiment 2. FIG. FIG. 10 is an explanatory diagram of a developing device according to a third embodiment. 3 is a graph showing the results of Example 1. 10 is a graph showing the results of Example 2. 10 is a graph showing the results of Example 3. It is explanatory drawing which shows an example of the conventional developing device. It is explanatory drawing which shows magnetic flux density distribution of the image development apparatus of FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Developing housing, 3 ... Developer carrier, 3a ... Developing sleeve, 3b ... Magnet body, P ... Pick off part, D ... Developer, G ... Gravity, CF ... Centrifugal force

Claims (11)

A developing housing that opens opposite to the image bearing member on which the electrostatic latent image is carried and can store a two-component developer containing toner and a magnetic carrier, and is disposed facing the opening of the developing housing and is a developer In a developing device comprising a developer carrying member capable of carrying and conveying
The developer carrier includes a rotatable developing sleeve and a magnet body in which magnetic poles of different polarities are alternately fixed and arranged inside the developing sleeve,
This magnet body has a magnetic force distribution in which both the normal direction component and the tangential direction component of the magnetic flux density are attenuated between adjacent magnetic poles of different polarities, and the developer on the developing sleeve is subjected to the action of gravity and centrifugal force. A developing device having a pick-off portion that can be peeled off by overcoming the holding force by the magnetic force distribution. The developing device according to claim 1,
The position where the pick-off part is set is that the angle formed by the straight lines connecting the developing sleeve surface corresponding to each of the adjacent magnetic poles and the rotation center of the developing sleeve is 100 degrees or more, and the normal direction component of the magnetic flux density and A developing device characterized in that a tangential component is set at a site of 20 mT or less. A developing housing that opens opposite to the image bearing member on which the electrostatic latent image is carried and can store a two-component developer containing toner and a magnetic carrier, and is disposed facing the opening of the developing housing and is a developer In a developing device comprising a developer carrying member capable of carrying and conveying
The developer carrier includes a rotatable developing sleeve and a magnet body in which a plurality of magnetic poles including a pair of adjacent magnetic poles of the same polarity are fixedly arranged inside the developing sleeve,
The magnet body has a pick-off portion that can peel off the developer on the developing sleeve between the magnetic poles of the same polarity, and a pick-off portion in the vicinity of the upstream magnetic pole located upstream of the magnetic poles of the same polarity. A developing device having a conveyance allowable magnetic field that acts in a direction to suppress a back flow with respect to the developer toward The developing device according to claim 3.
If the straight line connecting the peak position of the normal direction component of the magnetic flux density due to the upstream magnetic pole and the rotation center of the developing sleeve is defined as the reference line, the transport allowable magnetic field is partially reversed by the developer toward the pick-off portion. A developing device, wherein the reference line is set to be deviated toward the downstream side in the developer conveyance direction with respect to a reverse flow region that leads to the behavior of conveyance. The developing device according to claim 3.
A developing device characterized in that an auxiliary magnetic pole having a polarity different from that of the magnetic pole and a low magnetic flux density is further provided in the vicinity of the upstream and downstream sides of the upstream magnetic pole. The developing device according to claim 1 or 3,
The developing device according to claim 1, wherein the pick-off portion is provided at a position spaced above the developer contained in the developing housing. The developing device according to claim 1 or 3,
The developing device according to claim 1, wherein the magnetic carrier has a configuration in which a magnetic material and a binder resin are dispersed and mixed. The developing device according to claim 7.
A developing device, wherein the magnetic carrier is produced by a polymerization method and has a shape factor of 115 or less. The developing device according to claim 7.
A developing apparatus, wherein the magnetic carrier is a porous magnetic material impregnated with a resin and has a shape factor of 115 or less. The developing device according to claim 1 or 3,
The developing device, wherein the developing sleeve is subjected to a process for maintaining developer transportability on an outer peripheral surface thereof. An image carrier on which an electrostatic latent image is carried;
An image forming apparatus comprising the developing device according to claim 1.

Images