JP2009244596A - Developing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device in which deterioration of developer is less likely to occur. <P>SOLUTION: The developing device 13 has a developing tank 19, a developing roller 89, and a blade member 101. The developing roller 89 includes a developing sleeve 20 that bears developer on the peripheral face 20a, and a magnetic member 21 disposed inside the developing sleeve 20 so as to be immovable. The magnetic member 21 includes an S1 pole that generates a magnetic field for attracting developer in the developing tank 19 to the peripheral face 20a, and an N1 pole that generates in a developing area a magnetic field for bearing the developer. The blade member 101 regulates the layer thickness of developer on the peripheral face 20a. In addition, the blade member 101 is disposed in the area where the magnetic fields of both the S1 pole and N1 pole are distributed and in the area where the magnetic flux density in the direction of a normal line relative to the peripheral face 20a is greater than that in the direction of a tangent line relative to the peripheral face 20a. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a developing device provided in an electrophotographic image forming apparatus.

  In an electrophotographic image forming process, an electrostatic latent image is formed by exposing a photosensitive member charged to a uniform potential with light according to image information, and the formed electrostatic latent image is developed by a developing device. Develop to make visible image. As a method for developing an electrostatic latent image, there are a one-component developing method using a magnetic one-component developer or a non-magnetic one-component developer and a two-component developing method using a two-component developer including a toner and a carrier. .

  In the two-component development method, toner is supported on the surface of a carrier by mixing and stirring magnetic particles called a carrier and the toner and charging them by friction. Then, on the surface of the developing roller containing a plurality of magnets, a spike (magnetic brush) made of a carrier carrying toner is formed, and the toner contained in the spike is transferred from the developing roller to the electrostatic latent image on the photoreceptor. develop. The two-component development method is used more frequently than the one-component development method, although the structure of the apparatus is slightly more complicated, but the toner potential setting is relatively easy and the high-speed compatibility and stability are excellent.

  In a developing device that uses a two-component developer, the plurality of magnets arranged inside the developing roller includes a magnet that functions as a pumping pole and a magnet that functions as a release pole. The pumping pole (attracting pole) is a magnetism generating means for pumping (attracting) the developer in the developing tank onto the surface of the developing roller, and the releasing pole is the magnetism generating for releasing (separating) the developer from the surface of the developing roller. Means.

  The developer pumped on the surface of the developing roller by the pumping pole is carried to the developing area by the rotation of the developing roller. At this time, the developer on the surface of the developing roller is regulated to a certain amount by a regulating member (doctor blade). Thereby, the amount of the developer conveyed to the development area is adjusted appropriately. The developer on the surface of the developing roller passes through the developing area and is released from the developing roller by the release pole. The developer released from the developing roller is accommodated in a stirring / conveying section (location where the developer is stirred and conveyed) in the developing tank.

  By the way, in recent years, in the industry of image forming apparatuses such as electrophotographic copying machines and printers, there is a strong demand for a high-speed small-sized machine that requires a large number of copies and prints per unit time and requires a small installation space. For this reason, it is necessary to design the developing tank so that it can be installed in a limited space. It is essential to reduce the developer storage space, use a small-diameter developing roller, and rotate the developing roller at high speed.

  However, in an image forming apparatus that rotates the developing roller at a higher speed than in the past for downsizing, when repeated image formation is performed, the developer is mixed, stirred, pumped, regulated, and released for a long time. Repeatedly, the developer is subjected to significant loads such as mechanical stress and thermal stress.

  Here, the developer is considered to receive the most mechanical stress when being held on the surface of the developing roller. This is because the developer on the surface of the developing roller is subjected to a large mechanical stress by colliding with the regulating member. That is, surplus developer that cannot pass through DG (doctor gap) by colliding with the regulating member is mechanically stressed by being scraped from the surface of the developing roller by the regulating member.

  In addition, if the developer immediately after being released from the surface of the developing roller by the release pole is immediately pumped up onto the developing roller, only a part of the developer will be used repeatedly, and mechanically repeatedly. You will be stressed.

  Furthermore, when the developer continues to be subjected to mechanical stress for a long time as described above, the developer deteriorates. Specifically, when the stress is continued, the temperature of the developer rises, and a phenomenon that the toner component locally adheres to the carrier occurs. As a result, frictional charging between the toner and the carrier is less likely to occur locally, and the charge amount of the developer as a whole is reduced. At the same time, the number of contact between the toner and the carrier is reduced due to the decrease in the fluidity of the developer, thereby deteriorating the charging ability and causing problems (toner scattering, fogging) in the formed image. Further, fusion between the toner and the carrier occurs, causing problems of developability and density reduction, and it becomes difficult to output a solid image with uniform density.

On the other hand, there is Patent Document 1 below as a prior art for the purpose of suppressing the deterioration of the developer. Japanese Patent Application Laid-Open No. 2003-228688 discloses a technique for storing developer remaining on the developing roller after development into the developing chamber by magnetic repulsion between the taking-in pole N3 and the pumping pole N2 disposed on the downstream side of the taking-in pole N3. It is disclosed. Patent Document 1 suggests that this technique makes it difficult for the developer remaining on the developing roller after development to be restrained by the pumping electrode N2 as it is, thereby suppressing deterioration of the developer.
Japanese Patent Laid-Open No. 10-39613 (Publication date: February 13, 1998)

  However, in the technique disclosed in Patent Document 1, the doctor blade (regulating member) and the pumping pole are separated from each other, and almost all of the magnetic field generated from the pumping pole contributes to the pumping of the developer. An excessive amount of developer is pumped up on the surface of the developing roller by the pumping pole, and a large amount of developer stays on the upstream side of the blade and repeatedly collides with the blade, which causes deterioration of the developer. There was a problem that was promoted.

  The present invention has been made in view of the above problems, and an object thereof is to provide a developing device and an image forming apparatus in which the developer hardly deteriorates.

  If it is possible to suppress an excessive amount of developer from being attracted to the surface of the developing roller by the pumping electrode, it is considered that the deterioration of the developer can be suppressed. Therefore, measures to weaken the magnetic force of the pumping pole can be considered. However, in order to suppress the amount of developer attracted to the surface of the developing roller, the magnetic force of the pumping pole must be excessively weakened. When the magnetic force of the pumping pole is excessively weakened, the amount of developer attracted to the surface of the developing roller is reduced. Stabilization becomes impossible, developer conveyance failure occurs, and image quality unevenness occurs in the developed toner image. Therefore, there is a need for a measure that can suppress an excessive amount of developer from being attracted to the surface of the developing roller without excessively weakening the magnetic force of the pumping pole.

  Therefore, in the present invention, in order to achieve the above object, a developing tank for storing the developer, a sleeve for carrying the developer on the outer peripheral surface, and a magnetic member provided non-rotatingly inside the sleeve are provided. And a developing roller that conveys the developer on the outer peripheral surface to a developing region in a gap between the outer peripheral surface and the photosensitive member by rotation of the sleeve, and a blade member that regulates the layer thickness of the developer on the outer peripheral surface. In the developing device, the magnetic member includes a first magnetic pole that generates a magnetic field for attracting the developer in the developing tank to the outer peripheral surface, and the first magnetic pole on the downstream side in the rotation direction with respect to the first magnetic pole. A second magnetic pole disposed adjacent to the magnetic pole and generating a magnetic field for supporting in the developing region, and the blade member includes both the magnetic field of the first magnetic pole and the magnetic field of the second magnetic pole. Area where magnetic field is distributed Wherein the magnetic flux density in the normal direction of the magnetic flux with respect to the outer circumferential surface there is is arranged in a region larger than the magnetic flux density in the tangential direction of the magnetic flux with respect to the outer peripheral surface.

  According to the configuration of the present invention, the blade member is disposed in the distribution region of the magnetic field (magnetic field for attracting the developer in the developing tank to the outer peripheral surface of the sleeve) generated from the first magnetic pole. Therefore, in the configuration of the present invention, the range of the magnetic field that contributes to the attraction of the developer to the outer peripheral surface out of the entire range of the magnetic field generated from the first magnetic pole can be made narrower than the conventional configuration. This makes it possible to reduce the amount of developer attracted from the developing tank to the sleeve without excessively weakening the magnetic force itself of the first magnetic pole, and to collide (scratch) the blade member with the rotation of the sleeve. And the deterioration of the developer can be suppressed.

  Furthermore, in the configuration of the present invention, the blade member is not only disposed in a region where the magnetic field of the first magnetic pole is distributed, but also both the magnetic field of the first magnetic pole and the magnetic field of the second magnetic pole. In which the magnetic flux density in the normal direction to the outer peripheral surface is larger than the magnetic flux density in the tangential direction to the outer peripheral surface. Therefore, it is possible to suppress an excessive amount of the developer attracted from the developing tank to the sleeve outer peripheral surface while attracting the developer necessary and sufficient for the development processing to the sleeve outer peripheral surface.

  In the developing device of the present invention, in addition to the above configuration, the magnetic field of the first magnetic pole is generated in the developing tank from the downstream side to the upstream side in the rotation direction of the sleeve in the developing tank. The formed downstream region, the intermediate region, and the upstream region are arranged in this order, and the magnetic member includes a third magnetic pole disposed upstream of the first magnetic pole in the direction of rotation and the first magnetic pole. A fourth magnetic pole disposed upstream of the rotation direction and downstream of the rotation direction of the third magnetic pole, the third magnetic pole for separating the developer from the outer peripheral surface. A magnetic field is generated in the upstream region, and the fourth magnetic pole generates a magnetic field in the intermediate region that suppresses the developer in the developing tank from being attracted to the outer peripheral surface. To do.

  As a result, in the developing tank, the developer in the developing tank is between the downstream area where the developer is attracted to the sleeve and the upstream area where the developer carried on the sleeve is returned to the developing tank. An intermediate region, which is a region that is restrained from being attracted to the sleeve, is disposed, and the downstream region and the upstream region are separated from each other. Therefore, the developer returned from the sleeve to the developing tank in the upstream region is not immediately attracted to the sleeve in the downstream region. Thereby, it is possible to suppress only a part of the developer from being repeatedly used, and it is possible to suppress the deterioration rate of the developer.

  On the other hand, in the conventional developing device, the downstream area and the upstream area are adjacent to each other, so that the developer dropped from the sleeve near the boundary between the downstream area and the upstream area is attracted to the sleeve immediately after dropping. As a result, only part of the developer is repeatedly used, and only part of the developer deteriorates immediately.

  Moreover, in order to suppress the developer in the developing tank from being attracted to the outer peripheral surface in the intermediate region, the peak value of the magnetic flux density generated from the fourth magnetic pole needs to be 30 mT or less. If the peak value is too small, a repulsive magnetic force is hardly generated in the third magnetic pole. If the repulsive magnetic force is not generated, the developer on the outer peripheral surface is hardly separated in the upstream region, and the same developer is continuously carried on the sleeve, and the deterioration of the developer is promoted. In order to generate the repulsive magnetic force, the fourth magnetic pole needs to have the same polarity as the third magnetic pole, and the peak value of the magnetic flux density generated from the fourth magnetic pole needs to be at least 10 mT or more. Therefore, in the developing device of the present invention, in addition to the above configuration, the third magnetic pole and the fourth magnetic pole have the same polarity, and the peak value of the magnetic flux density of the magnetic flux generated from the fourth magnetic pole is 10 mT or more. It is preferable to make it 30 mT or less.

  On the other hand, if the magnetic force of the first magnetic pole is too weak, the developer in the developing tank cannot be stably attracted to the outer peripheral surface of the sleeve, causing a developer conveyance failure and stabilizing the image quality of the developed toner image. It becomes difficult. In order to stably attract the developer in the developing tank to the outer peripheral surface of the sleeve, the magnetic flux density of the magnetic flux generated from the first magnetic pole needs to be at least 30 mT. On the other hand, if the magnetic force of the first magnetic pole is too strong, the amount of developer attracted to the outer peripheral surface of the sleeve becomes excessive, and the developer scraped off by the blade member in the gap between the outer peripheral surface and the blade member. As a result, the amount of the toner increases, excessive stress is applied to the developer, and the deterioration of the developer is promoted. In other words, the magnetic flux density of the magnetic flux generated from the first magnetic pole needs to be 60 mT or less in order to make the amount of the developer scraped off by the blade member appropriate and prevent the developer from being excessively stressed. . Therefore, in the developing device of the present invention, in addition to the above configuration, the peak value of the magnetic flux density of the magnetic flux generated from the first magnetic pole is preferably 30 mT or more and 60 mT or less.

  Furthermore, a straight line that is perpendicular to the rotational axis of the sleeve and connects the rotational shaft and the end of the blade member on the outer peripheral surface side is defined as a first straight line, and is a straight line that is perpendicular to the rotational axis. A straight line connecting the rotation axis and a position where the magnetic flux density of the magnetic flux generated from the first magnetic pole reaches a peak value is defined as a second straight line. When the second straight line is located closer to the development area than the first straight line, a magnetic field for attracting the developer in the developer tank to the outer peripheral surface of the sleeve (that is, the peak of the magnetic flux density of the first magnetic pole). ) Occurs not in the developing tank but between the developing area and the blade member, and the minimum amount of developer cannot be attracted to the sleeve. It cannot be formed, and uneven conveyance is likely to occur.

  On the other hand, when the first straight line is positioned closer to the development area than the second straight line, or when the first straight line and the second straight line coincide with each other, the first straight line is attracted to the sleeve. There is no problem that the amount of the developer is less than the required amount. However, when the first straight line is located closer to the development area than the second straight line, or when the first straight line and the second straight line coincide with each other, the first straight line If the acute angle formed by the second straight line exceeds 5 °, the amount of developer attracted to the outer peripheral surface of the sleeve becomes excessive, and the blade member is scraped off at the gap between the outer peripheral surface and the blade member. As a result, the amount of the developer to be increased increases, excessive stress is applied to the developer, and the deterioration of the developer is promoted.

Therefore, it is preferable that the blade member and the developing roller are set so as to satisfy the following conditions 1 and 2.
Condition 1: The first straight line is located closer to the development area than the second straight line, or the first straight line and the second straight line are coincident with each other.
Condition 2: The acute angle formed by the first straight line and the second straight line is 0 ° to 5 °.

  In the developing device of the present invention, in addition to the above configuration, a plurality of grooves extending in a direction parallel to the rotation axis of the sleeve are formed on the outer peripheral surface of the sleeve, and the groove is formed by a plane perpendicular to the rotation axis. The cross section when the sleeve is cut is preferably V-shaped. As a result, the developer adhering to the outer peripheral surface of the sleeve can easily follow the rotation of the sleeve, and the conveyance of the developer by the developing roller can be optimized.

  Furthermore, in the developing device of the present invention, if the distance between the grooves adjacent to each other is shorter than 0.70 mm, the amount of developer held on the outer peripheral surface of the sleeve becomes excessive, and this developer amount is suppressed. In order to achieve this, it is necessary to set a narrow gap (doctor gap) between the outer peripheral surface and the blade member. When the doctor gap is narrowed, the stress applied to the developer increases and the deterioration of the developer is promoted. On the other hand, when the interval between the grooves adjacent to each other is longer than 0.42 mm, unevenness due to the formation of grooves on the outer peripheral surface in the image after printing occurs. Therefore, in the developing device of the present invention, in addition to the above configuration, it is preferable that the interval between the grooves adjacent to each other is 0.70 mm to 1.42 mm.

  Further, in the developing device of the present invention, if the depth of the groove is shorter than 0.05 mm, it becomes difficult for the developer on the outer peripheral surface of the sleeve to follow the rotation of the sleeve, and the developer transport performance by the developing roller. Decreases. On the other hand, when the depth of the groove is longer than 0.08 mm, the amount of developer held on the outer peripheral surface of the sleeve becomes excessive, and in order to suppress the amount of developer, the outer peripheral surface and the It is necessary to design the gap between the blade member (doctor gap) narrow. When the doctor gap is narrowed, the stress applied to the developer increases and the deterioration of the developer is promoted. Therefore, in the developing device of the present invention, in addition to the above configuration, the depth of the groove is preferably 0.05 mm to 0.08 mm.

  Furthermore, in the developing device of the present invention, when the angle of the bottom of the V-shaped groove is larger than 110 °, the developer easily slips on the outer peripheral surface of the rotating sleeve, and the developer transport performance by the developing roller is improved. Decreases (conveying force in the rotational direction decreases). On the other hand, when the angle becomes smaller than 70 °, the magnetic brush (developing of the developer) formed on the outer peripheral surface of the sleeve is reduced, and a groove is formed on the outer peripheral surface in the printed image. The resulting unevenness occurs. Therefore, in the developing device of the present invention, in addition to the above configuration, the angle of the bottom of the V-shaped groove is preferably 70 ° to 110 °.

  In the developing device of the present invention, in addition to the above configuration, the blade member preferably includes a nonmagnetic member and a magnetic member. According to this configuration, the amount of the developer carried on the outer peripheral surface of the sleeve can be suppressed even when the doctor gap is set wider, and the deterioration of the developer can be further suppressed as compared with a blade member made of only a nonmagnetic member. Is possible.

  Further, in the developing device of the present invention, in addition to the above-described configuration, a region in which the developer is accommodated in the developing tank is located below the developing region, and the developing roller is disposed in the developing tank. It is preferable that the developer is set to be transported to the developing region so as to draw up the developer from the lower side to the upper side. According to this configuration, since the developer is transported from the lower side to the upper side in the vertical direction, the developer that is sufficiently accumulated in the lower part is set to be transported to the developing area by a necessary minimum amount. It becomes easy to carry out, and it becomes possible to make it difficult to produce a conveyance defect.

  Further, when a one-component developer made of magnetic toner is used, if the magnetic force of the first magnetic pole is weakened, the friction between the toner particles and between the toner and the blade member is reduced, so that the charge amount of the toner is reduced and the graininess is decreased. Deterioration of image quality occurs due to deterioration. However, when a two-component developer composed of toner and a magnetic carrier is used, even if the magnetic force of the first magnetic pole is weakened, there is almost no decrease in the charge amount of the toner due to the reduction in friction, and image quality is unlikely to deteriorate. Therefore, in the developing device of the present invention, the developer is preferably composed of toner and a magnetic carrier.

  Further, in the image forming apparatus provided with the developing device of the present invention, it is possible to reduce the stress applied by the developer, and it is possible to obtain a stable image even when aging (durable use) is performed.

  As described above, in the developing device of the present invention, the blade member is a region in which both the magnetic fields of the first magnetic pole and the magnetic field of the second magnetic pole are distributed, and is normal to the outer peripheral surface. The magnetic flux density is arranged in a region larger than the magnetic flux density of the magnetic flux in the tangential direction with respect to the outer peripheral surface.

  As a result, the amount of the developer attracted from the developing tank to the outer peripheral surface of the sleeve can be reduced, so that the amount of the developer colliding with the blade member (scratched off) by the rotation of the sleeve can be suppressed. Deterioration can be suppressed.

  An image forming apparatus including a developing device according to an embodiment of the present invention will be described. FIG. 1 is a diagram illustrating an internal configuration of the image forming apparatus according to the present exemplary embodiment.

  The image forming apparatus 100 is an electrophotographic printer and includes a photosensitive drum 10. Further, around the photosensitive drum 10, a charging device 11, an exposure device 12, a developing device 13, a transfer device 14, a cleaning device 15, and a static elimination device 16 are arranged in this order along the rotation direction of the photosensitive drum 10. Yes.

  As shown in FIG. 1, the photoconductor drum (photoconductor) 10 includes a base material made of a metal drum such as aluminum, and an organic optical semiconductor (OPC) or amorphous silicon formed in a thin film on the outer peripheral surface of the base material. It consists of a photoconductive layer such as (a-Si).

  The charging device 11 is a device that uniformly charges the surface of the photosensitive drum 10. The charging device 11 may be a corona charger, a charging roller, or a charging brush made of a charging wire such as a tungsten wire, a metal shield plate, or a grit plate.

  The exposure device 12 scans light on the uniformly charged photosensitive drum 10 to write an electrostatic latent image on the photosensitive drum 10. The exposure apparatus 12 may be a laser scanning unit (LSU) or an LED (Light Emitting Diode) array.

  The developing device 13 visualizes (develops) the electrostatic latent image by supplying a developer to the electrostatic latent image written on the photosensitive drum 10 by the exposure device 12. The developing device 13 will be described in detail later.

  The transfer device 14 releases a transfer bias for transferring an image visualized on the photosensitive drum 10 onto a recording medium (paper). The transfer device 14 may be the transfer roller shown in FIG. 1, or a charging brush or a corona charger.

  The cleaning device 15 removes the developer remaining on the photosensitive drum 10 after the transfer and enables a new image to be recorded on the photosensitive drum 10. The neutralizing device 16 is for neutralizing the surface of the photosensitive drum 10.

  The recording medium on which the image is transferred by the transfer device 14 is conveyed to the fixing device 17. In the fixing device 17, the image on the recording medium is fixed by heat and pressure, thereby completing the printing of the image on the recording medium.

  Next, the flow of the image forming process executed by the image forming apparatus 100 described above will be described. The surface of the photosensitive drum 10 is first uniformly charged by the charging device 11, and then the light exposure according to the image information is performed by the exposure device 12 to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum 10 is developed by a developing device by a developing electric field (a bias power source provided in the developing device 13 is not shown) formed between the photosensitive drum 10 and the developing device 13. The toner contained in the developer in 13 is supplied to become a toner image, which is visualized. This toner image is transferred onto the recording medium by the transfer device 14 and fixed by the fixing device 17. After the toner image is transferred, the toner remaining on the photosensitive drum 10 is removed by a cleaning device 15 (for example, a cleaning blade). The portion of the photosensitive drum 10 from which the toner has been removed is then uniformly charged again by the charging device 11, and the above-described process is repeated.

  Next, the developing device 13 of this embodiment will be described in detail. FIG. 2 shows a configuration example of a main part of the developing device 13. FIG. 2 is a schematic view of the developing device 13 as seen from the end side in the longitudinal direction (axial direction) of the developing roller 89.

  As shown in FIG. 2, the developing device 13 includes a developing tank 19 that contains a developer, a developing roller 89 that carries the developer in the developing tank 19, and a blade that regulates the amount of developer carried on the developing roller 89. A member 101, a first agitation conveyance member 28 and a second agitation conveyance member 29 for agitating and conveying the developer inside the developing tank 19, and a sensor 34 for detecting the amount of the developer inside the developing tank 19 are provided. .

  The developer in this embodiment is a two-component developer including a magnetic carrier made of magnetic particles and toner as components. In this embodiment, toner having an average particle diameter of 6.2 μm and a magnetic carrier having an average particle diameter of 50 μm are used, but each average particle diameter is not limited to these values.

  As shown in FIG. 2, the developing roller 89 faces the photosensitive drum 10, is arranged so that the axis of the developing roller 89 and the axis of the photosensitive drum 10 are parallel, and is supported by the frame of the developing tank 19. ing. The developing roller 89 has a developing sleeve 20 and a magnetic member 21.

  The developing sleeve (sleeve) 20 is a cylindrical member that rotates in a direction indicated by a rotation direction 102. In addition, since the developing device 13 of the present embodiment is a pumping developing system, the developing sleeve 20 is configured such that the portion exposed from the developing tank 19 rotates from below to above. Further, the developing sleeve 20 moves in the same direction as the photosensitive drum 10 in a developing region that is a gap between the photosensitive drum 10 and the developing sleeve 20 (the rotation direction is opposite to that of the photosensitive drum 10). . The developing device 13 of the present embodiment employs the pumping development method, but is not limited to this method.

  The magnetic member 21 is a cylindrical member that is fixed to the inner peripheral side of the developing sleeve 20 and generates a magnetic field. The developer in the developing tank 19 is attracted to the outer peripheral surface 20a of the developing sleeve 20 by the magnetic field of the magnetic member 21, and a magnetic brush in which the developer is linked in a spike shape is formed on the outer peripheral surface 20a. Thus, the developer is carried on the developing sleeve 20 in the form of a magnetic brush.

  As the developing sleeve 20 rotates, the developer carried on the outer peripheral surface 20a of the developing sleeve 20 is conveyed to the developing area. In the developing area, toner having a charge in the developer forming the magnetic brush is transferred to the photosensitive drum 10 in accordance with the potential difference between the developing roller 89 and the photosensitive drum 10. As a result, the electrostatic latent image on the photosensitive drum 10 is developed and a toner image is formed. Details of the developing sleeve 20 and the magnetic member 21 will be described later.

  The blade member 101 is installed so that its edge portion faces the outer peripheral surface 20a of the developing sleeve 20 with a gap, and the amount of developer on the outer peripheral surface 20a is regulated by scraping off the developer on the outer peripheral surface 20a. To do.

  The gap between the blade member 101 and the outer peripheral surface 20a of the developing sleeve 20 is referred to as a doctor gap (hereinafter referred to as DG). The set value of DG is appropriately adjusted depending on the developer conditions, the developing roller 89 conditions, and the like.

However, when the amount of developer per unit area of the outer peripheral surface 20a of the developing sleeve 20 in the development region is defined as the transport amount, the rear end density is excessive when the transport amount is excessive (especially 90 mg / cm ² or more). An increase (image defect) occurs. Here, as shown in FIG. 5, the rear end density increase means a phenomenon in which the density increases at the boundary on the rear end side in the paper conveyance direction among the boundary between the solid image and the non-printed area. This is because toner is successively consumed by the electrostatic latent image (solid image) passing through the development area, but the electrostatic latent image is located upstream of the rear end of the electrostatic latent image in the rotational direction of the photosensitive drum 10. This is because, since there is no image, extra toner is supplied near the rear end of the electrostatic latent image.

In the present embodiment, DG is set so that the transport amount is 60 mg / cm ² in order to suppress the rear end concentration increase.

  The blade member (doctor blade) 101 is a non-magnetic blade, and is fixed to the developing tank 19 or a fixing sheet metal (not shown) by screws or rivets. In the present embodiment, the fixing sheet metal or the like is fixed using a fixing screw, but the present invention is not particularly limited.

  Further, the nonmagnetic blade is not particularly limited as long as it is a metal having no magnetism. For example, as non-magnetic blades, SUS302, SUS303, SUS304, SUS304Cu, SUS304L, SUS304N1, SUS304J3, SUS305, SUS305J1, SUS309S, SUS310S, SUS316, SUS316L, SUS316N, SUS316F, SUS3US17, SUS3US34 Stainless steel, aluminum, copper and the like.

  Next, the inside of the developing tank 19 will be described. FIG. 3 is a schematic view of the inside of the developing tank 19 as viewed from above. The developing tank 19 is made of, for example, hard synthetic resin, and is a casing whose longitudinal direction is the axial direction of the developing roller 89 as shown in FIG. The developing tank 19 has a long side having a length substantially corresponding to the length L1 of the developing roller 89 in the axial direction. Further, the inside of the developing tank 19 is divided into two tanks by a partition wall member 25 extending in parallel with the longitudinal direction of the developing tank 19 (the same as the axial direction of the developing roller 89).

  One of the two tanks is a development area tank 23 and the other is an agitation area tank 24. The developing area tank 23 is a tank for agitating and conveying the developer and supplying it to the developing roller 89. The stirring area tank 24 is a tank for stirring toner supplied from the toner hopper 104 (see FIG. 2) with the developer and supplying the stirred developer to the developing area tank 23.

  Here, the partition wall member 25 is a wall disposed between the development area tank 23 and the agitation area tank 24, but is for completely blocking between the development area tank 23 and the agitation area tank 24. is not. That is, the first passage 26 and the second passage 27 that connect the developing region tank 23 and the agitation region tank 24 are formed at two positions on the partition wall member 25 at both ends in the longitudinal direction of the developing tank 19. Thereby, a part of the developer stored in the developing tank 19 can be moved from the developing area tank 23 to the stirring area tank 24, and conversely, from the stirring area tank 24 to the developing area tank 23. It becomes possible to move.

  In the developing tank 19, the developing roller 89, the first stirring / conveying member 28 that stirs and conveys the developer, and the second stirring so that the direction of the rotation axis is parallel to the longitudinal direction of the developing tank 19. A conveyance member 29 is rotatably provided. Specifically, the developing roller 89 and the first stirring / conveying member 28 are provided in the developing region tank 23, and the second stirring / conveying member 29 is provided in the stirring region tank 24. In the present embodiment, the first agitation and conveyance member 28 and the second agitation and conveyance member 29 are so-called screw members, and agitate and convey the developer in the developing tank 19 by rotating.

  The first agitating / conveying member 28 is in the vicinity of the developing roller 89 in the developing region tank 23 in the direction of the arrow 35 (the direction from one end A to the other end B of the developing tank 19). Transport. The second agitating and conveying member 29 moves the developer conveyed to the vicinity of the end B of the developing tank 19 by the first agitating and conveying member 28 to the agitating region tank 24 through the first passage 26 and conveys it in the direction of arrow 36. At the same time, it is conveyed along the partition wall member 25 in the direction of arrow 37 (direction from the end B toward the end A).

  The developer passes through the second passage 27 in the vicinity of the end A and is conveyed in the direction of the arrow 38 and is moved again by the first agitation and conveyance member 28. Therefore, in the developing tank 19, a developer circulation flow indicated by arrows 35, 36, 37, and 38 is formed by the first and second stirring and conveying members 28 and 29 and the partition wall member 25.

  The sensor 34 detects the toner concentration contained in the developer in the developing tank 19. As the sensor 34, a magnetic permeability sensor or a piezoelectric detection sensor can be used. According to these sensors, it is possible to detect the toner amount in the developer, in other words, the toner concentration which is the blending ratio of the magnetic carrier and the toner.

  As shown in FIGS. 2 and 3, the sensor 34 is located in the developing area tank 23 on the downstream side in the developer agitating and conveying direction, near the end B of the developing tank 19 and on the bottom surface of the developing area tank 23 ( It is attached to the wall material. Further, the sensor 34 is disposed so as to face the first stirring and conveying member 28. By attaching the sensor 34 at such a position, the sensor 34 can measure the toner concentration contained in the developer immediately after the toner is consumed by the developing roller 89.

  Further, in the developing device 13, a control unit (not shown) operates the toner hopper 104 (FIG. 2) in accordance with the toner density detection output, so that the toner is supplied to the stirring area tank 24. Therefore, in the developing device 13, the toner concentration of the developer in the developing tank 19 after the developing process is detected, and the developing tank 19 is replenished with toner so as to have an appropriate toner concentration. Thereby, the toner density of the developer is adjusted with high accuracy. The sensor 34 may be installed anywhere as long as the toner density can be properly detected.

  Next, an outline of processing for supplying toner from the toner hopper 104 to the developing tank 19 will be described with reference to FIG. The toner hopper 104 is a container member made of, for example, hard synthetic resin. The toner hopper 104 stores toner in the internal space, drives the internal toner supply roller 49 in accordance with an operation command from a control unit (not shown), and supplies the toner 50 to the developing tank 19.

  The toner replenishing roller 49 is provided directly above the stirring area tank 24 so that its outer periphery can rotate while being in sliding contact with the toner replenishing port 104a. The toner replenishing roller 49 is provided with a cylindrical porous elastic member such as urethane foam around a cored bar. The toner held by the porous elastic member of the toner replenishing roller 49 in the toner hopper 104 is dropped from the toner replenishing roller 49 by the sliding contact between the toner replenishing port 104 a and the toner replenishing roller 49 and replenished to the developing tank 19.

  The toner replenishing port 104 a of the toner hopper 104 is disposed above the second stirring / conveying member 29 in the stirring region tank 24. As a result, the toner 50 in the toner hopper 104 is replenished to the developing tank 19 so as to drop onto the second stirring and conveying member 29. In the stirring area tank 24, the developer replenished with the toner 50 is stirred according to the circulating flow (flow indicated by arrows 35 to 38) in the developing tank 19 described above.

  Next, the developing sleeve 20 included in the developing roller 89 will be described in detail. As shown in FIG. 2, the developing sleeve 20 faces the photosensitive drum 10 and is arranged so that its axial direction is parallel to the axial direction of the photosensitive drum 10, and is supported by the frame of the developing tank 19. ing.

  The developing sleeve 20 is a cylindrical member that is rotatably provided around the magnetic member 21 and is made of a nonmagnetic material. In this embodiment, the developing sleeve 20 is designed to have an outer diameter of 18 mm. However, the outer diameter of the developing sleeve 20 is not limited to 18 mm, and may be changed according to various conditions. Good.

  Examples of the nonmagnetic material used for the developing sleeve 20 include SUS302, SUS303, SUS304, SUS304Cu, SUS304L, SUS304N1, SUS304J3, SUS305, SUS305J1, SUS309S, SUS310S, SUS316, SUS316L, SUS316J, SUS316J, SUS316J, SUS316J, SUS316J, SUS316J, SUS316J, Stainless steel such as SUS317F, SUS321, and SUS347, aluminum, copper, and the like are used.

  A plurality of linear grooves 20 b extending in a direction parallel to the rotation axis of the developing sleeve 20 are formed on the outer peripheral surface 20 a of the developing sleeve 20. Further, 60 grooves 20b are formed in the developing sleeve 20. The grooves 20b are arranged at regular intervals in the rotation direction of the developing sleeve.

  Further, as shown in FIG. 4, the groove 20 b has a V-shaped cross section when the developing sleeve 20 is cut along a plane perpendicular to the axial direction of the developing sleeve 20. The groove 20 b has a role of transporting the developer carried on the outer peripheral surface 20 a of the developing sleeve 20 following the rotation of the developing sleeve 20. Further, as shown in FIG. 4, the depth L of the groove 20b is 0.06 mm, and the distance d between the adjacent grooves 20b and 20b is 0.942 mm.

  Next, the magnetic member 21 included in the developing roller 89 will be described in detail. The magnetic member 21 is a cylindrical magnet roller that is non-rotatably disposed in the hollow portion (inner side) of the developing sleeve 20. The magnetic member 21 is composed of a plurality of permanent magnets, and the permanent magnets are arranged so as to be aligned along the circumferential direction, and form a cylindrical shape as a whole.

  The magnetic member 21 includes a magnet including an N1 pole disposed between the rotation shaft of the developing roller 89 and the developing region, and a magnet including an S2 pole adjacent to the N1 pole on the downstream side in the rotation direction 102 from the N1 pole. From the N1 pole, the magnet including the N3 pole adjacent to the S2 pole downstream of the S2 pole, the N2 pole adjacent to the N3 pole downstream of the N3 pole, and the N2 pole. And the magnet including the S1 pole adjacent to the N1 pole and the N2 pole on the upstream side in the rotation direction 102 and on the downstream side in the rotation direction 102 with respect to the N2 pole. The S1 pole and the S2 pole are each an S pole magnetic pole, and the N1 pole to the N3 pole are each an N pole magnetic pole.

  In the following description, as shown in FIG. 2, the interior of the developing tank 19 includes a downstream area 40 and an intermediate area 42 from the downstream side to the upstream side in the rotation direction 102 of the developing sleeve in the developing tank 19. And the upstream region 41 are arranged in this order. The S1 pole functions as a pumping pole (attracting pole) that forms a magnetic field for pumping (attracting) the developer in the developing tank 19 to the outer peripheral surface 20a of the developing sleeve 20 with respect to the downstream region 40. . The S1 pole is located on the upstream side in the rotation direction 102 of the developing sleeve 20 from the portion of the outer peripheral surface 20a of the developing sleeve 20 facing the blade member 101.

  The N1 pole is a developing pole that forms a magnetic field in the developing region so that the magnetic carrier contained in the developer attracted to the outer circumferential surface 20a of the developing sleeve 20 by the S1 pole is continuously attracted to the outer circumferential surface 20a even in the developing region. It functions as.

  The N3 pole functions as a release pole (separation pole) that forms a magnetic field for releasing (separating) the developer attached to the outer peripheral surface 20a of the developing sleeve 20 from the outer peripheral surface 20a with respect to the upstream region 41. Is. As a result, the developer remaining on the outer peripheral surface 20 a of the developing sleeve 20 after passing through the developing region falls from the outer peripheral surface 20 a to the developing tank 19 in the upstream region 41. Therefore, the developer is almost removed from the outer peripheral surface 20a of the developing sleeve 20 after passing through the upstream region 41.

  The N2 pole is a pumping regulation pole (attraction regulation pole) that forms a magnetic field for suppressing the developer in the developing tank 19 from being pumped (attracted) to the outer peripheral surface 20a of the developing sleeve 20 with respect to the intermediate region 42. ). Thus, the developer in the developing tank 19 is hardly attracted to the outer peripheral surface 20a of the developing sleeve 20 after passing through the upstream region 41 and before reaching the downstream region 40.

  With the configuration described above, the developer in the developing tank 19 is pumped up to the outer peripheral surface 20a of the developing sleeve 20 by the magnetic field formed in the S1 pole in the downstream region 40. The blade member 101 regulates the amount of developer carried on the outer peripheral surface 20 a of the developing sleeve 20. As a result, the amount of developer conveyed to the development area is adjusted.

  Next, the relationship between the distribution of magnetic flux around the developing roller 89 and the blade member 101 will be described. FIG. 6 is a view showing the distribution of magnetic flux around the developing roller 89. In FIG. 6, an area denoted by reference numeral 106 (area surrounded by a two-dot chain line) is a distribution of magnetic flux in the normal direction of the outer peripheral surface 20 a of the developing sleeve 20, and an area denoted by reference numeral 105 (one-dot chain line). (Region surrounded by) is a magnetic flux distribution in the tangential direction of the outer peripheral surface 20a of the developing sleeve 20.

  In the present specification, the magnetic flux in the normal direction means a magnetic flux formed between one magnetic pole and the other magnetic pole included in a single magnet. The tangential magnetic flux means a magnetic flux formed between a magnetic pole a included in a certain magnet a and a magnetic pole b included in a magnet b different from the magnet a and adjacent to the magnetic pole a. For example, in FIG. 6, the normal direction magnetic flux distributed in the region 106a is a magnetic flux formed between the S1 pole and the N pole (not shown) of the magnet having the S1 pole. Further, the magnetic flux in the tangential direction distributed in the region 105a is a magnetic flux formed between the S1 pole and the N1 pole.

  In FIG. 6, a position where the magnetic flux density of the tangential magnetic flux formed between the N1 pole and the S1 pole is equal to the magnetic flux density of the normal magnetic flux formed by the N1 pole is defined as a position D. To do. A straight line perpendicular to the rotation axis X of the developing sleeve 20 and connecting the rotation axis X and the position D is defined as L0.

  Further, in FIG. 6, a position E is a position where the magnetic flux density in the tangential direction formed between the N1 pole and the S1 pole is equal to the magnetic flux density in the normal direction formed by the S1 pole. A straight line that is perpendicular to the rotation axis X and connects the rotation axis X and the position E is defined as L3.

  In FIG. 6, a position where the magnetic flux density of the normal direction magnetic flux formed by the S1 pole is maximum is a position C, and is a straight line perpendicular to the rotation axis X and connecting the rotation axis X and the position C. Is L2. A straight line that is perpendicular to the rotation axis X and connects the edge portion of the blade member 101 and the rotation axis X is defined as L1.

  In the developing device 13 described above, L3 is arranged at a position where L0 is rotated by 60 ° in the direction opposite to the direction of the rotation direction 102 about the rotation axis X, and L0 is in the direction opposite to the direction of the rotation direction 102. L2 is arranged at a position rotated by 85 °.

  In this embodiment, it should be noted that the blade L1 is arranged at a position where L0 is rotated by 60 ° to 85 ° in the direction opposite to the direction of the rotation direction 102 with the rotation axis X as the rotation center. The member 101 is positioned. In other words, the blade member 101 is positioned so that L1 is arranged between L2 and L3.

  With such positioning, the magnetic flux density in the normal direction formed by the magnetic pole S1 is formed between the magnetic pole N1 and the magnetic pole S1 in the region where the magnetic field of the magnetic pole S1 and the magnetic field of the magnetic pole N1 are formed. The blade member 101 is disposed in a region higher than the magnetic flux density in the tangential direction. Thereby, in the downstream area 40, the pumping of the developer is restricted by the blade member 101, and the amount of the developer pumped up to the outer peripheral surface 20a of the developing sleeve 20 can be reduced. Therefore, the amount of developer colliding with the blade member 101 by the rotation of the developing sleeve 20 can be suppressed, and the deterioration of the developer can be suppressed.

  In FIG. 6, the blade member 101 is arranged in a region where the magnetic flux density of the normal direction magnetic flux formed by the S1 pole is lower on the downstream side than on the upstream side in the rotation direction 102. It can be said.

  In the present embodiment, the blade member 101 made of a nonmagnetic blade is used. However, instead of the blade member 101, a blade member 101a formed by stacking a nonmagnetic blade and a magnetic blade may be used. When the blade member 101a is used, the DG can be set widely even with a smaller transport amount than when the blade member 101a is not used.

  The blade member 101a is attached at the position indicated by reference numeral 101 in FIG. 2 so that the nonmagnetic blade is disposed on the developing region side and the magnetic blade is disposed on the downstream region 40 side. The blade member 101a is designed so that the gap between the nonmagnetic blade and the magnetic blade is 100 μm or less. Further, the magnetic blade is not particularly limited as long as it is a stainless steel having a nickel component ratio of 1% or less and a magnetic permeability of 500 H / m or less. For example, SUS403, SUS410, SUS410S, SUS416, SUS420J1, SUS420F, SUS410L, SUS430, SUS430F, SUS434, or the like is used.

  In this embodiment, the magnetic member 21 has five magnets. However, the magnetic member 21 includes the developing electrode, the pumping electrode, the release electrode, and the pumping restriction electrode. For example, the number of magnets contained is not limited to five. In addition, the thickness and width of each magnet contained in the magnetic member 21 are adjusted, and the conditions of the magnetizing process for each magnet contained in the magnetic member 21, the thickness of each magnet, and the width of each magnet are appropriately changed. Thus, it is possible to adjust the magnetic strength of each pole.

  As described above, the developing device 13 of this embodiment includes the developing tank 19 that stores the developer, the developing roller 89, and the blade member 101. Here, the developing roller 89 includes a developing sleeve 20 that carries the developer on the outer peripheral surface 20 a and a magnetic member 21 that is provided non-rotatingly on the inner side of the developing sleeve 20. The developer on the outer peripheral surface 20a is transported to the development region in the gap between the photosensitive drum 10 and 20a. The blade member 101 is disposed with a gap with respect to the outer peripheral surface 20a of the developing sleeve 20, and regulates the layer thickness of the developer on the outer peripheral surface 20a.

  Further, the magnetic member 21 includes an S1 pole (first magnetic pole) that generates a magnetic field in the developing tank 19 for attracting the developer in the developing tank 19 to the outer peripheral surface 20a, and a downstream side in the rotation direction 102 from the S1 pole. An N1 pole (second magnetic pole) is disposed adjacent to the S1 pole and generates a magnetic field in the developing region for supporting the developer on the developing sleeve. The blade member 101 is an area where both the magnetic field of the S1 pole and the magnetic field of the N1 pole are distributed, and the magnetic flux density of the magnetic flux in the normal direction relative to the outer peripheral surface 20a is tangential to the outer peripheral surface 20a. It is the structure arrange | positioned in the area | region larger than the magnetic flux density.

  According to this configuration, the blade member 101 is arranged in a distribution region of a magnetic field (magnetic field for attracting the developer in the developing tank 19 to the outer peripheral surface 20a) generated from the S1 pole. Therefore, in the configuration of the present invention, the range of the magnetic field that contributes to the attraction of the developer to the outer peripheral surface 20a out of the entire range of the magnetic field generated from the S1 pole can be made narrower than the conventional configuration. As a result, the amount of the developer attracted from the developing tank 19 to the developing sleeve 20 can be reduced without excessively weakening the magnetic force of the S1 pole, and the blades 101 collide with the rotation of the developing sleeve 20 (scraping). The amount of developer that is dropped off can be suppressed, and deterioration of the developer can be suppressed.

  And since it is not necessary to weaken the magnetic force of S1 pole excessively, the problem resulting from excessively weakening the magnetic force of S1 pole does not arise. Note that this problem is that if the magnetic force of the S1 pole is excessively weakened, the amount of developer attracted to the developing sleeve 20 becomes unstable, resulting in poor conveyance and image quality deterioration.

  Further, in the configuration of the present invention, the blade member 101 is not only disposed in the region where the S1 pole magnetic field is distributed, but also both the S1 pole magnetic field and the N1 pole magnetic field are distributed. The magnetic flux density in the normal direction with respect to the outer peripheral surface 20a is arranged in a region that is larger than the magnetic flux density in the tangential direction with respect to the outer peripheral surface 20a. Therefore, it is possible to suppress an excessive amount of developer attracted from the developing tank 19 to the outer peripheral surface 20a while attracting the developer necessary and sufficient for the developing process to the outer peripheral surface 20a.

  Further, in the developing tank 19 of the present embodiment, the downstream region 40, the intermediate region 42, and the upstream in which the magnetic field of the S1 pole is formed from the downstream side in the rotation direction of the developing sleeve 20 in the developing tank 19 toward the upstream side. Regions 41 are arranged in order. Further, the magnetic member 21 includes an N3 pole (third magnetic pole) disposed upstream of the S1 pole in the rotational direction 102, an upstream side of the rotational direction 102 relative to the S1 pole, and a downstream of the rotational direction 102 relative to the N3 pole. And an N2 pole (second magnetic pole) disposed on the side. The N3 pole generates a magnetic field in the upstream region 41 for separating the developer from the outer peripheral surface 20a, and the N2 pole is a magnetic field that suppresses the developer in the developing tank 19 from being attracted to the outer peripheral surface 20a. Is generated in the intermediate region 42.

  As a result, in the developing tank 19, there is a gap between a downstream area 40 where the developer is attracted to the developing sleeve 20 and an upstream area 41 where the developer carried on the developing sleeve 20 is returned to the developing tank 19. In addition, an intermediate region 42, which is a region where the developer in the developing tank 19 is suppressed from being attracted to the developing sleeve 20, is disposed, and the downstream region 40 and the upstream region 41 are separated from each other. Therefore, the developer returned from the developing sleeve 20 to the developing tank 19 in the upstream region 41 is not immediately attracted to the developing sleeve 20 in the downstream region 40. Thereby, it is possible to suppress only a part of the developer from being repeatedly used, and it is possible to suppress the deterioration rate of the developer.

  Further, in order to suppress the developer in the developing tank 19 from being attracted to the outer peripheral surface 20a in the intermediate region 42, the peak value of the magnetic flux density generated from the N2 pole needs to be 30 mT or less. If the value is too small, a repulsive magnetic force is hardly generated in the N3 pole adjacent to the N2 pole. If the repulsive magnetic force does not occur, the developer on the outer peripheral surface 20a is not easily separated in the upstream region 41, and the same developer is continuously carried on the developing sleeve 20 to promote the deterioration of the developer. . In order to generate the repulsive magnetic force at the N3 pole, it is necessary to make the N2 pole adjacent to the N3 pole the same polarity as the N3 pole and to set the peak value of the magnetic flux density of the N2 pole to at least 10 mT or more. Therefore, in the developing device 13, it is desirable that the N2 pole and the N3 pole have the same polarity, and the peak value of the magnetic flux density of the magnetic flux generated from the N2 pole is 10 mT or more and 30 mT or less. In addition, the magnetic flux density in this specification shall mean the absolute value of magnetic flux density.

  On the other hand, if the magnetic force of the S1 pole is too weak, the developer in the developing tank 19 cannot be stably attracted to the outer peripheral surface 20a of the developing sleeve 20, causing a developer conveyance failure, and the image quality of the developed toner image. It becomes difficult to stabilize. In order to stably attract the developer in the developing tank 19 to the outer peripheral surface 20a of the developing sleeve 20, the magnetic flux density of the magnetic flux generated from the S1 pole needs to be at least 30 mT. Further, if the magnetic force of the S1 pole is too strong, the amount of developer attracted to the outer peripheral surface 20a of the developing sleeve 20 becomes excessive, and the developer scraped off by the blade member 101 in the gap between the outer peripheral surface 20a and the blade member 101. As a result, the amount of the toner increases, excessive stress is applied to the developer, and the deterioration of the developer is promoted. In order to make the amount of the developer scraped off by the blade member 101 appropriate and prevent the developer from being excessively stressed, the magnetic flux density of the magnetic flux generated from the S1 pole needs to be 60 mT or less. Therefore, in the developing device 13, it is desirable that the peak value of the magnetic flux density of the magnetic flux generated from the S1 pole be 30 mT or more and 60 mT or less.

  Further, as shown in FIG. 6, a straight line that is perpendicular to the rotation axis X of the developing sleeve 20 and connects the rotation axis X and the end of the blade member 101 on the outer peripheral surface 20a side is L1 (first straight line). ) And a straight line that is perpendicular to the rotation axis X and connects the rotation axis X and the position C at which the magnetic flux density of the magnetic flux generated from the S1 pole reaches its peak value is defined as L2 (second line). If L2 is positioned closer to the development area than L1, the magnetic field for attracting the developer in the developing tank 19 to the outer peripheral surface 20a of the developing sleeve 20 (that is, the peak of the magnetic flux density of the S1 pole) is developed. It occurs not in the tank 19 but between the developing region and the blade member 101, and the minimum necessary developer cannot be attracted to the developing sleeve 20, and the magnetic brush (protruding) is uniformly formed in the developing sleeve 20. It cannot be formed with a length, and uneven conveyance tends to occur.

  On the other hand, when L1 is positioned closer to the development area than L2 as shown in FIG. 6, or when L1 and L2 coincide, the amount of developer attracted to the developing sleeve 20 is the required amount. The problem that it is less than does not occur. However, even in these cases, when the acute angle formed by L1 and L2 exceeds 5 °, the amount of developer attracted to the outer circumferential surface 20a of the developing sleeve 20 becomes excessive, and the outer circumferential surface 20a. In the gap between the blade member 101 and the blade member 101, the amount of the developer scraped off by the blade member 101 increases, excessive stress is applied to the developer, and the deterioration of the developer is promoted.

Therefore, it is preferable that the blade member 101 and the developing roller 89 are set so as to satisfy the following conditions 1 and 2.
Condition 1: L1 is positioned closer to the development area than L2, or L1 and L2 coincide.
Condition 2: The acute angle formed by L1 and L2 is 0 ° to 5 °.

  A plurality of grooves 20b extending in a direction parallel to the rotation axis of the developing sleeve 20 are formed on the outer peripheral surface 20a of the developing sleeve 20 of the present embodiment. The groove 20b preferably has a V-shaped cross section when the developing sleeve 20 is cut along a plane perpendicular to the rotation axis of the developing sleeve 20. As a result, the developer adhering to the outer peripheral surface 20a of the developing sleeve 20 can easily follow the rotation of the developing sleeve 20, and the developer transport by the developing roller 89 can be optimized.

  Further, in the developing sleeve 20, when the distance d between the adjacent grooves 20b and 20b is shorter than 0.70 mm, the amount of developer held on the outer peripheral surface 20a of the developing sleeve 20 becomes excessive, and this amount of developer is increased. In order to suppress this, it is necessary to set DG narrowly. When DG is narrowed, the stress applied to the developer increases, and the deterioration of the developer is promoted. On the other hand, if the distance d between the groove 20b and the groove 20b is longer than 0.42 mm, unevenness due to the formation of the groove 20b on the outer peripheral surface 20a occurs in the image after printing. Therefore, in the developing sleeve 20, it is preferable that the distance d between the adjacent grooves 20b and 20b is 0.70 mm to 1.42 mm.

  In the developing sleeve 20, if the depth L of the groove 20 b is shorter than 0.05 mm, it becomes difficult to cause the developer on the outer peripheral surface 20 a of the developing sleeve 20 to follow the rotation of the developing sleeve 20. The developer transport performance decreases. On the other hand, when the depth L of the groove 20b is longer than 0.08 mm, the amount of the developer held on the outer peripheral surface 20a of the developing sleeve 20 becomes excessive, and in order to suppress the amount of the developer, DG It is necessary to design narrowly. When DG is narrowed, the stress applied to the developer increases, and the deterioration of the developer is promoted. Therefore, in the developing sleeve 20, the depth of the groove 20b is preferably 0.05 mm to 0.08 mm.

  Further, in the developing sleeve 20, when the angle β of the bottom of the V-shaped groove 20b is larger than 110 °, the developer easily slips on the outer peripheral surface 20a of the rotating developing sleeve 20, and the developer roller 89 causes the developer to flow. The conveyance performance is reduced (the conveyance force in the rotation direction is reduced). On the other hand, when the angle β is smaller than 70 °, the magnetic brush (developing of the developer) formed on the outer peripheral surface 20a of the developing sleeve 20 is reduced, and the groove 20b is formed on the outer peripheral surface 20a in the printed image. Unevenness due to being present occurs. Therefore, in the developing sleeve 20, it is preferable that the angle β of the bottom of the V-shaped groove 20b is 70 ° to 110 °.

  Further, when using a blade member 101a composed of a nonmagnetic member and a magnetic member, it is carried on the outer peripheral surface 20a of the developing sleeve 20 even if the DG is set wider than the blade member 101 composed of only a nonmagnetic member. The amount of the developer can be suppressed, and the deterioration of the developer can be further suppressed.

  Furthermore, in the developing device 13 of the present embodiment, the region in the developing tank 19 where the developer is accommodated is located below the developing region, and the developing roller 89 causes the developer in the developing tank 19 to move downward. Is set so as to be transported to the developing area so as to be pumped upward from the top. Therefore, since the developer is conveyed from the lower side to the upper side in the vertical direction, it is easy to set so that the developer that is sufficiently accumulated in the lower part is transported to the developing area by a necessary minimum amount. It becomes possible to make it difficult for poor transport.

  When a one-component developer made of magnetic toner is used, if the magnetic force of the S1 pole is weakened, the friction between the toner particles and between the toner and the blade member is reduced, so that the charge amount of the toner is reduced and the graininess is improved. Degradation causes image quality degradation. However, when a two-component developer composed of toner and a magnetic carrier is used, even if the magnetic force of the S1 pole is weakened, there is almost no decrease in the charge amount of the toner due to the reduction in friction, and image quality is unlikely to deteriorate. Therefore, it is preferable to use a two-component developer composed of toner and a magnetic carrier for the developing device 13.

  Next, Experimental Example 1 and Experimental Example 2 performed on the developing device of the present embodiment will be described in detail.

[Experimental Example 1]
Experimental example 1 shows the optimum value of the magnetic flux density of the normal direction magnetic flux formed by the pumping restriction pole (N2 pole) and the optimum value of the magnetic flux density of the normal direction magnetic flux formed by the pumping pole (S1 pole). And the optimum position of the blade member 101. In Experimental Example 1, test printing is performed using the image forming apparatuses of Examples 1 to 3 and Comparative Examples 1 to 4 described below, and the image quality is compared.

The image forming apparatuses of Examples 1 to 3 and Comparative Examples 1 to 4 are all copiers (trade name: MX-7000N, manufactured by Sharp Corporation). In each of the image forming apparatuses of Examples 1 to 3 and Comparative Examples 1 to 4, the transport amount (the amount of developer per unit area of the outer peripheral surface 20a of the developing sleeve 20 in the developing region) is 60 mg / cm ² . DG is set so that

  In Experimental Example 1, initial image quality evaluation and durability evaluation were performed using the image forming apparatuses of Examples 1 to 3 and Comparative Examples 1 to 4. In the initial image quality evaluation, a solid image is first printed after the developer in the developing tank 19 is made new, and the image quality of the solid image is evaluated. In the solid image, when the image quality defect due to the unevenness due to the groove 20b or the conveyance failure occurred, “Initial image quality” in Table 1 below was set as “X”, and when there was no particular problem, “Initial image quality” was set as “◯”.

Furthermore, the durability evaluation was performed only for the examples or comparative examples in which the initial evaluation was. In durability evaluation, aging is performed to output 100,000 images with a printing rate of 1%, and solid images are printed during aging (50,000 sheets have elapsed) and after aging (100,000 sheets have elapsed). Evaluated. Specifically, it is confirmed whether density unevenness or white streaks have occurred in the solid image. If there is no problem, “Durability” in Table 1 below is set to ○, and density unevenness or white streaks have occurred. Indicates “durability” as x. Then, “durability” after aging (elapsed 100,000 sheets) was evaluated as acceptable in the comprehensive evaluation.
Example 1
The magnetic flux density (magnetic force) of the N1 pole was 125 mT, the magnetic flux density of the S1 pole was 45 mT, the magnetic flux density of the N2 pole was 20 mT, the magnetic flux density of the N3 pole was 42 mT, and the magnetic flux density of the S2 pole was 80 mT. In FIG. 6, if the straight line L2 is rotated by an angle α (see FIG. 6) about the rotation axis X in the direction of the rotation direction 102 by the angle α (see FIG. 6), it is assumed that the straight line L1 coincides with the straight line L1. Set to °.
(Example 2)
The same conditions as in Example 1 were used except that the magnetic flux density of the N2 pole was 10 mT, the magnetic flux density of the S1 pole was 30 mT, and α = 0 °.
(Example 3)
The conditions were the same as in Example 1 except that the magnetic flux density of the N2 pole was 30 mT, the magnetic flux density of the S1 pole was 60 mT, and α = 5 °.
(Comparative Example 1)
The conditions were the same as in Example 1 except that α = −2 °. That is, in Comparative Example 1, it is assumed that L1 is at a position where the straight line L2 is rotated by 2 ° in the direction opposite to the direction of the rotation direction 102 with the rotation axis X as the rotation center.
(Comparative Example 2)
The conditions were the same as in Example 1 except that α = 7 °.
(Comparative Example 3)
The same conditions as in Example 1 were used except that the magnetic flux density of the N2 pole was 35 mT, the magnetic flux density of the S1 pole was 65 mT, and α = 5 °.
(Comparative Example 4)
The same conditions as in Example 1 were used except that the magnetic flux density of the N2 pole was 5 mT, the magnetic flux density of the S1 pole was 25 mT, and α = 0 °.

The results of Experimental Example 1 are shown in Table 1. As shown in Table 1, in Examples 1 to 3, good images were obtained. On the other hand, in the comparative example 1, since the angle α is a negative value, the length of the magnetic brush (protruding) is not uniform on the outer peripheral surface 20a of the developing sleeve 20, and density unevenness occurs in the initial image. did. In Comparative Example 2, since the angle α is too large, the amount of the developer pumped up to the developing sleeve 20 becomes excessive, and the DG needs to be set extremely narrow when trying to adjust the transport amount to 60 mg / cm ^2. First of all, the developer was stressed by the influence, so the durability evaluation was rejected. In Comparative Example 4, there was no problem with the value of the angle α, but because the magnetic flux density of the N2 pole and S1 pole was too low, the developer was not sufficiently pumped up to the developing sleeve 20 and density unevenness occurred. In Comparative Example 3, there was no problem with the angle α, but because the magnetic flux densities of the N2 pole and S1 pole were too large, the developer deteriorated quickly, and the initial image was satisfactory, but failed in the durability evaluation.

[Experiment 2]
Experimental example 2 is an experiment for examining the optimum condition for the shape of the outer peripheral surface 20 a of the developing sleeve 20. In Experimental Example 2, test printing is performed using the image forming apparatuses of Example 1, Examples 4 to 11 and Comparative Examples 5 to 11 below, and image quality comparison is performed. The image forming apparatuses of Example 1, Examples 4 to 11 and Comparative Examples 5 to 11 are all copying machines (trade name: MX-7000N, manufactured by Sharp Corporation).

  In Experimental Example 2, initial image quality evaluation and durability evaluation were performed using the image forming apparatuses of Example 1, Examples 4 to 11, and Comparative Examples 5 to 11. The initial image quality evaluation in Experimental Example 2 is that after the developer in the developing tank 19 is made new, a solid image is printed first, the image quality of the solid image is confirmed, and further, the trailing edge density rises in the solid image. It is to evaluate whether or not. Specifically, when an image quality defect due to unevenness or conveyance failure due to the groove 20b occurs in the solid image, the “image quality defect” in Tables 2 and 3 is set to “x”. ○. Further, the solid image is visually confirmed, and when the rear end density increase occurs, the “rear end density increase” in Tables 2 and 3 is set as x, and when the rear end density increase does not occur, In Table 2 and Table 3, “rear end concentration increase” was marked with “◯”.

Furthermore, durability evaluation was carried out only for the examples or comparative examples in which both “image quality failure” and “rear end density increase” were ◯. In durability evaluation, aging is performed to continue outputting images with a printing rate of 1% up to 150,000 sheets, and solid images are printed during aging (50,000 sheets passed, 100,000 sheets passed) and after aging (150,000 sheets passed). Then, the image quality of this solid image was evaluated. Specifically, it is confirmed whether density unevenness or white streaks are generated in the solid image. If there is no problem, “durability” in Tables 2 and 3 is set to ○, and density unevenness and white streaks are generated. When it is, “durability” was set as “X”. And the thing of "durability" at the time of 100,000 printing progress was made into the pass in comprehensive evaluation.
Example 1
In addition to the conditions described in Experimental Example 1, the shape of the groove 20b, the distance d between the grooves 20b and 20b, the depth L of the groove 20b, and the angle β of the groove 20b were defined as shown in Table 2 below. Moreover, the blade member 101 which consists only of a nonmagnetic blade was used.
Example 4
The conditions were the same as in Example 1 except that the distance d was 1.42 mm.
(Example 5)
The conditions were the same as in Example 1 except that the distance d was 0.70 mm.
(Example 6)
The conditions were the same as in Example 1 except that the depth L was 0.05 mm.
(Example 7)
The conditions were the same as those in Example 1 except that the depth L was 0.08 mm.
(Example 8)
The conditions were the same as in Example 1 except that the distance d was 0.70 mm, the depth L was 0.08 mm, and the angle β was 110 °.
Example 9
The conditions were the same as in Example 1 except that the distance d was 1.42 mm, the depth L was 0.05 mm, and the angle β was 70 °.
(Example 10)
The same conditions as in Example 1 were used except that a blade member 101a composed of a magnetic blade and a nonmagnetic blade was used, the depth L was 0.08 mm, and the angle β was 110 °.
Example 11
The conditions were the same as those in Example 1 except that a blade member 101 composed of a magnetic blade and a nonmagnetic blade was used.
(Comparative Example 5)
The conditions were the same as in Example 1 except that the distance d was 1.45 mm and the angle β was 65 °.
(Comparative Example 6)
The conditions were the same as in Example 1 except that the distance d was 0.66 mm and the angle β was 115 °.
(Comparative Example 7)
The conditions were the same as in Example 1 except that the depth L was 0.04 mm and the angle β was 65 °.
(Comparative Example 8)
The conditions of Example 1 except that the depth L was 0.09 mm, the angle β was 115 °, and the transport amount (the amount of developer per unit area of the outer peripheral surface 20a of the developing sleeve 20 in the developing region) was 70 mg / cm ^2. Was the same.
(Comparative Example 9)
The conditions were the same as in Example 1 except that the depth L was 0.09 mm, the angle β was 115 °, and the transport amount was 80 mg / cm ² .
(Comparative Example 10)
The conditions were the same as those in Example 1 except that the distance d was 1.45 mm, the depth L was 0.04 mm, the angle β was 65 °, and the transport amount was 50 mg / cm ² .
(Comparative Example 11)
The conditions of Comparative Example 6 were the same except that the transport amount was 90 mg / cm ² by spreading DG.

  The results of Experimental Example 2 are shown in Table 2 and Table 3 below. As shown in Table 2, Examples 1 and 4 to 11 can maintain good image quality until 100,000 sheets are printed, and Examples 10 and 11 using the blade 101a are 150,000 sheets. Good image quality was maintained until printing.

  On the other hand, in the comparative example 5, since the interval d and the angle β are inappropriate, unevenness due to the groove 20b occurred. In Comparative Example 6, the initial image passed, but because the DG was narrow, the developer was easily stressed, and the durability was rejected. In Comparative Example 7, the groove 20b was too shallow, resulting in poor developer conveyance, and the solid image was rough due to poor conveyance. In Comparative Example 8, the initial image passed, but because the DG was narrow, the developer was easily stressed and failed in durability. In Comparative Example 9, the angle β was too large, the developer transportability deteriorated, and the solid image was rough due to poor transport. In Comparative Example 10, unevenness due to the groove 20b occurred. In Comparative Example 11, since the carry amount was large, the trailing edge density increased in the initial image, which was unacceptable.

  The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope shown in the claims, and the embodiments can be obtained by appropriately combining the respective technical means disclosed in the above-described embodiments. The form is also included in the technical scope of the present invention.

  The developing device of the present invention is suitable for an electrophotographic printing apparatus.

1 is a schematic diagram illustrating a main part of an image forming apparatus including a developing device according to an embodiment of the present disclosure. It is a schematic diagram which shows the principal part of the developing device of this embodiment. It is a schematic diagram which shows the inside of the developing tank in the developing device shown in FIG. FIG. 4 is a diagram illustrating a groove formed in the developing sleeve, and is a diagram illustrating a cross section of the groove when the developing sleeve is cut along a plane perpendicular to the axial direction of the developing sleeve. It is explanatory drawing which shows a rear end density | concentration raise. FIG. 6 is a diagram showing a distribution of magnetic flux formed around a developing roller.

Explanation of symbols

10 Photosensitive drum (photosensitive member)
13 Developing Device 19 Developing Tank 20 Developing Sleeve (Sleeve)
20a
20b groove 21 magnetic member 40 downstream area 41 upstream area 42 intermediate area 89 developing roller 100 image forming apparatus 101 blade member S1 pole (first magnetic pole)
N1 pole (second magnetic pole)
N3 pole (third magnetic pole)
N2 pole (4th magnetic pole)
L1 (first straight line)
L2 (second straight line)

Claims (13)

A developer tank containing a developer;
A sleeve that carries the developer on the outer peripheral surface and a magnetic member that is provided non-rotatingly on the inner side of the sleeve, and the rotation of the sleeve causes the developing region in the gap between the outer peripheral surface and the photosensitive member to A developing roller for transporting the developer;
In a developing device comprising a blade member that regulates the layer thickness of the developer on the outer peripheral surface,
The magnetic member is adjacent to the first magnetic pole for generating a magnetic field for attracting the developer in the developing tank to the outer peripheral surface, and the first magnetic pole downstream of the first magnetic pole in the rotation direction. And a second magnetic pole for generating a magnetic field for supporting in the developing region,
The blade member is a region in which both the magnetic field of the first magnetic pole and the magnetic field of the second magnetic pole are distributed, and the magnetic flux density of the magnetic flux in the normal direction to the outer peripheral surface is a tangential direction to the outer peripheral surface The developing device is arranged in a region larger than the magnetic flux density of the magnetic flux. In the developing tank, a downstream area, an intermediate area, and an upstream area in which the magnetic field of the first magnetic pole is formed are arranged in order from the downstream side to the upstream side in the rotation direction of the sleeve in the developing tank. ,
The magnetic member includes a third magnetic pole disposed upstream of the first magnetic pole in the direction of rotation, an upstream side of the first magnetic pole in the direction of rotation and the rotation of the third magnetic pole relative to the third magnetic pole. A fourth magnetic pole disposed downstream of the direction,
The third magnetic pole generates a magnetic field in the upstream region for separating the developer from the outer peripheral surface, and the fourth magnetic pole is that the developer in the developing tank is attracted to the outer peripheral surface. The developing device according to claim 1, wherein a magnetic field to be suppressed is generated in the intermediate region. The third magnetic pole and the fourth magnetic pole have the same polarity,
The developing device according to claim 2, wherein a peak value of a magnetic flux density of the magnetic flux generated from the fourth magnetic pole is 10 mT or more and 30 mT or less.   4. The developing device according to claim 1, wherein a peak value of a magnetic flux density of the magnetic flux generated from the first magnetic pole is 30 mT or more and 60 mT or less. A straight line that is perpendicular to the rotational axis of the sleeve and connects the rotational shaft and the end of the blade member on the outer peripheral surface side is a first straight line that is perpendicular to the rotational axis. And when the straight line connecting the rotational axis and the position where the magnetic flux density of the magnetic flux generated from the first magnetic pole becomes the peak value is the second straight line,
5. The developing device according to claim 1, wherein the blade member and the developing roller are set so as to satisfy the following conditions 1 and 2: 5.
Condition 1: The first straight line is located closer to the development area than the second straight line, or the first straight line and the second straight line are coincident with each other.
Condition 2: The acute angle formed by the first straight line and the second straight line is 0 ° to 5 °. A plurality of grooves extending in a direction parallel to the rotation axis of the sleeve are formed on the outer peripheral surface of the sleeve,
The developing device according to claim 5, wherein the groove has a V-shaped cross section when the sleeve is cut by a plane perpendicular to the rotation axis.   The developing device according to claim 6, wherein an interval between the grooves adjacent to each other is 0.70 mm to 1.42 mm.   The developing device according to claim 6, wherein the groove has a depth of 0.05 mm to 0.08 mm.   The developing device according to claim 6, wherein an angle of a bottom portion of the V-shaped groove is 70 ° to 110 °.   The developing device according to claim 1, wherein the blade member includes a nonmagnetic member and a magnetic member.   An area in which the developer is accommodated in the developing tank is located below the developing area, and the developing roller reaches the developing area so as to pump up the developer in the developing tank from the lower side to the upper side. The developing device according to claim 1, wherein the developing device is conveyed.   The developing device according to claim 1, wherein the developer includes toner and a magnetic carrier.   An image forming apparatus comprising the developing device according to claim 1.

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