JP2018045224A - Developing device and magnet for development with two-component developer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To facilitate peeling from a developer carrier of a two-component developer used for development by adjusting a magnetic force pattern with a simple configuration so as to obtain two peeling regions.SOLUTION: A magnet is grooved throughout in a lengthwise direction thereof so that a first magnetic force region where an absolute value of a magnetic force component in a normal direction of a developer carrier is not more than 1[nN] is formed on a surface of the developer carrier below a third maximal peak position and above a second maximal peak position with respect to a rotation direction of the developer carrier and a second magnetic force region where the absolute value of the magnetic force component in the normal direction of the developer carrier is not more than 1[nN] is formed on the surface of the developer carrier below a first maximal peak position and above the third maximal peak position with respect to the rotation direction of the developer carrier.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a developing device for developing an electrostatic latent image and a magnet for two-component development.

  The developing device includes a developing sleeve as a rotatable developer carrying member carrying a two-component developer containing a non-magnetic toner and a magnetic carrier. Inside the developing sleeve, a magnet for two-component development having a plurality of magnetic poles and carrying the two-component developer on the surface of the developing sleeve is fixedly disposed. A two-component developer carried on the surface of the developing sleeve (hereinafter simply referred to as a developer) is a region where development is performed on an electrostatic latent image on the surface of a photosensitive drum as an image carrier. Area). When the developer carried on the surface of the developing sleeve is used for development in the development area, the toner in the developer is consumed, and the toner concentration in the developer is lowered.

  The developer that has been subjected to development and has a reduced toner concentration forms a repulsive magnetic field between the magnetic poles of the same polarity of the magnet, and a magnetic force region (the absolute value of the magnetic force in the normal direction of the developing sleeve is 1 [nN] or less ( It is conveyed to the peeling area. The developer that has been subjected to development in the development area and has a reduced toner concentration acts to separate from the development sleeve in the separation area. The developer separated from the developing sleeve in the peeling region is collected in the developing container. The developer collected in the developing container is agitated with the developer already present in the developing container, so that the toner concentration becomes uniform.

  When the developer used for development is not sufficiently detached from the developing sleeve, the developer having a lowered toner concentration is used again for development in the developing region as the developing sleeve rotates. As a result, the toner density in the developer used for development becomes uneven, which may cause image defects. This is particularly a problem when forming a solid image. Therefore, it is necessary to sufficiently release the developer that has been subjected to development and has a reduced toner concentration from the developing sleeve.

  In the developing device of Patent Document 1, a rotatable stripping roller having a magnet body therein is disposed in the vicinity of a developer stripping magnetic pole (hereinafter referred to as a stripping pole) of a developer carrying member. Has been. In this developing device, the developer carried on the developer carrying member is attracted to the peeling roller side by the magnetic pole inside the peeling roller. Thereby, the stripping property of the developer in the vicinity of the stripping pole is improved.

JP 2002-148921 A

  In recent years, the developing device has been downsized, and the diameter of the developing sleeve has been reduced accordingly. When the diameter of the developing sleeve is small, the magnet inside the developing sleeve is smaller than when the diameter of the developing sleeve is large. As a result, since the section from the magnetic pole to the magnetic pole in the rotation direction of the developing sleeve is shortened and the peeling area is narrowed, the developer used for the development tends to be difficult to separate from the developing sleeve.

  When a configuration in which a new magnet is added from the outside in the vicinity of the stripping pole like the stripping roller described in Patent Document 1, a space for arranging a new magnet outside the developing sleeve is required. This increases the size of the device.

  On the other hand, even if the peeling area is narrow, if there are two peeling areas, the developer used for development can go through two peeling steps, so that the developer used for development is developed. It tends to peel off from the sleeve. Therefore, the developer is stripped near the stripping pole by adjusting the magnetic pattern near the stripping pole so that two stripping areas can be obtained without arranging a new magnet outside the developing sleeve. It is desirable to achieve both improvement in performance and downsizing of the apparatus.

  The present invention has been made in view of the above problems. The object of the present invention is to facilitate the separation of the two-component developer subjected to development from the developer carrying member by adjusting the magnetic pattern so that two separation regions can be obtained with a simple configuration. Another object is to provide a developing device or a magnet for two-component development.

In order to achieve the above object, a developing apparatus according to an aspect of the present invention has the following arrangement. That is,
A developer carrier that is rotatably provided and carries a developer containing toner and a magnetic carrier for developing an electrostatic latent image formed on the image carrier;
The first magnetic pole and the first magnetic pole are arranged adjacent to the first magnetic pole with respect to the rotation direction of the developer carrier, and are disposed in the same manner as the first magnetic pole. A magnet for generating a magnetic field for separating the developer that has passed through the development region facing the image carrier from the surface of the developer carrier,
In a developing device comprising:
The magnet is provided with a groove over the entire length of the magnet so as to satisfy the following (1) to (3). (1) The first magnetic pole of the first magnetic pole with respect to the rotation direction of the developer carrier. The magnetic flux density of the normal direction component of the developer carrier of the second magnetic pole and the downstream side of the first maximum peak position where the magnetic flux density of the normal direction component of the developer carrier is a maximum is the maximum. The surface of the developer carrier upstream of the second maximum peak position becomes a third maximum peak position where the magnetic flux density of the normal direction component of the developer carrier is a maximum,
(2) On the surface of the developer carrier on the downstream side of the first maximum peak position and the upstream side of the third maximum peak position in the rotation direction of the developer carrier, the developer carrier The magnetic flux density of the normal component of the body has a minimum peak position where the magnetic flux density is minimum, and the magnetic flux density of the normal direction component of the developer carrier at the minimum peak position is the development at the first maximum peak position. Greater than 30% and less than 95% of the magnetic flux density of the normal component of the agent carrier,
(3) On the surface of the developer carrier on the downstream side of the third maximum peak position and on the upstream side of the second maximum peak position in the rotation direction of the developer carrier, the developer carrier A first magnetic force region having an absolute value of a magnetic force of a normal direction component of the body of 1 [nN] or less is formed, and is downstream of the first maximum peak position in the rotation direction of the developer carrier and the first A second magnetic field region having an absolute value of a magnetic force of a normal direction component of the developer carrier of 1 [nN] or less is formed on the surface of the developer carrier upstream of the maximum peak position of 3. It is characterized by that.

In order to achieve the above object, a magnet for two-component development according to one embodiment of the present invention has the following configuration. That is,
A magnet for two-component development arranged fixedly inside a rotatable developer carrier,
A first magnetic pole;
A second magnetic pole disposed adjacent to the first magnetic pole with respect to the rotation direction of the developer carrier, and having the same polarity as the first magnetic pole;
With
The magnet is provided with a groove over the entire length of the magnet so as to satisfy the following (1) to (3). (1) The first magnetic pole of the first magnetic pole with respect to the rotation direction of the developer carrier. The magnetic flux density of the normal direction component of the developer carrier of the second magnetic pole and the downstream side of the first maximum peak position where the magnetic flux density of the normal direction component of the developer carrier is a maximum is the maximum. The surface of the developer carrier upstream of the second maximum peak position becomes a third maximum peak position where the magnetic flux density of the normal direction component of the developer carrier is a maximum,
(2) On the surface of the developer carrier on the downstream side of the first maximum peak position and the upstream side of the third maximum peak position in the rotation direction of the developer carrier, the developer carrier The magnetic flux density of the normal component of the body has a minimum peak position where the magnetic flux density is minimum, and the magnetic flux density of the normal direction component of the developer carrier at the minimum peak position is the development at the first maximum peak position. Greater than 30% and less than 95% of the magnetic flux density of the normal component of the agent carrier,
(3) On the surface of the developer carrier on the downstream side of the third maximum peak position and on the upstream side of the second maximum peak position in the rotation direction of the developer carrier, the developer carrier A first magnetic force region having an absolute value of a magnetic force of a normal direction component of the body of 1 [nN] or less is formed, and is downstream of the first maximum peak position in the rotation direction of the developer carrier and the first A second magnetic field region having an absolute value of a magnetic force of a normal direction component of the developer carrier of 1 [nN] or less is formed on the surface of the developer carrier upstream of the maximum peak position of 3. It is characterized by that.

  According to the present invention, the two-component developer subjected to development is promoted to be peeled off from the developer carrier by adjusting the magnetic force pattern so that two peeling regions can be obtained with a simple configuration. be able to.

1 is a cross-sectional view illustrating a configuration of an image forming apparatus according to a first embodiment. 1 is a schematic diagram illustrating a configuration of a developing device according to a first embodiment. 1 is a cross-sectional view illustrating a configuration of a developing device according to a first embodiment. It is a schematic diagram which shows the structure of the magnet which concerns on 1st Embodiment. It is a figure which shows distribution of Br and Fr in the structure of the magnet which concerns on 1st Embodiment. It is a figure which shows the relationship between a non-magnetic band width and a density | concentration fall. It is a figure which shows distribution of Br and Fr in the structure of the magnet which concerns on 2nd Embodiment. It is a figure which shows distribution of Br and Fr in the vicinity of a peeling pole. It is a figure which shows distribution of Br and Fr in the structure of the conventional magnet.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments do not limit the present invention according to the claims, and all the combinations of features described in the present embodiments are not necessarily essential to the solution means of the present invention. . The present invention can be implemented in various applications such as printers, various printing machines, copiers, FAX machines, and multifunction machines.

[First Embodiment]
(Configuration of image forming apparatus)
First, the configuration of the image forming apparatus according to the first embodiment of the present invention will be described with reference to the cross-sectional view of FIG.

  As shown in FIG. 1, the image forming apparatus includes an endless intermediate transfer belt (ITB) 62 as an intermediate transfer member, and the upstream side of the rotation direction of the intermediate transfer belt 62 (the direction of arrow R2 shown in FIG. 1). Four image forming portions P (Pa, Pb, Pc, Pd) are provided on the downstream side.

  In the first embodiment, a tandem type, an intermediate transfer system, and a full color printer will be described as an example of the image forming apparatus. However, a single drum type / tandem type, a direct transfer system / intermediate transfer system, and a full color printer / monochrome printer are used. Any combination may be used.

  Each of the image forming portions P (Pa, Pb, Pc, Pd) forms toner images of respective colors of Y (yellow), M (magenta), C (cyan), and Bk (black). The image forming unit P (Pa, Pb, Pc, Pd) includes a rotatable photosensitive drum 1 (1A, 1B, 1C, 1D) as an image carrier. In the first embodiment, a drum-shaped organic photoreceptor is described as an example of the photoreceptor drum 1 (1A, 1B, 1C, 1D). However, an inorganic photoreceptor such as an amorphous silicon photoreceptor may be used. Alternatively, a belt-shaped photoconductor may be used. Further, the charging method, the developing method, the transfer method, the cleaning method, and the fixing method are not limited to the methods described below.

  Each of the photosensitive drums 1 (1A, 1B, 1C, 1D) is rotationally driven in a rotational direction (in the direction of arrow R1 shown in FIG. 1) at a predetermined process speed. Around the photosensitive drum 1 (1A, 1B, 1C, 1D), along the rotation direction of the photosensitive drum 1, a charger 2 (2A, 2B, 2C, 2D) as a charging unit, a latent image forming unit As an exposure apparatus 3 (3A, 3B, 3C, 3D). Further, around the photosensitive drum 1 (1A, 1B, 1C, 1D), along the rotation direction of the photosensitive drum 1, a developing device 4 (4A, 4B, 4C, 4D) as a developing unit, primary transfer. A primary transfer roller 61 (61A, 61B, 61C, 61D) is disposed as a means. Further, around the photosensitive drum 1 (1A, 1B, 1C, 1D), a photosensitive member as a photosensitive member cleaner for collecting toner remaining on the photosensitive drum 1 without being primarily transferred to the intermediate transfer belt 62. A cleaning device 8 (8A, 8B, 8C, 8D) is provided.

  Each of the developing devices 4 (4A, 4B, 4C, 4D) is detachable from the image forming apparatus. Each of the developing devices 4 (4A, 4B, 4C, 4D) has a developing container that contains a developer. The details of the developing device 4 will be described later with reference to FIGS.

  The photosensitive drum 1 (1A, 1B, 1C, 1D) is formed with a photosensitive layer having a negative polarity on the outer peripheral surface of the aluminum cylinder. The charger 2 (2A, 2B, 2C, 2D) charges the surface of the photosensitive drum 1 (1A, 1B, 1C, 1D) to a uniform negative polarity dark portion potential Vd [V]. Subsequently, the exposure apparatus 3 (3A, 3B, 3C, 3D) scans the laser beam with a rotating mirror, and an electrostatic image of the image is formed on the surface of the charged photosensitive drum 1 (1A, 1B, 1C, 1D). Write (electrostatic latent image). Each of the developing devices 4 (4A, 4B, 4C, 4D) develops an electrostatic latent image using a developer, and forms a toner image on each surface of the photosensitive drum 1 (1A, 1B, 1C, 1D). Form.

  The intermediate transfer belt 62 is stretched around a primary transfer roller 61 (61A, 61B, 61C, 61D), a tension roller 65, a secondary transfer counter roller 63, and a tension roller 66.

  Each of the primary transfer rollers 61 (61A, 61B, 61C, 61D) presses the inner surface of the intermediate transfer belt 62, and between the photosensitive drum 1 (1A, 1B, 1C, 1D) and the intermediate transfer belt 62. A toner image transfer portion is formed on each. This transfer portion is a primary transfer nip portion T1 (T1a, T1b, T1c, T1d) as a primary transfer portion. Then, by applying a positive DC voltage to the primary transfer roller 61 (61A, 61B, 61C, 61D), a negative toner image carried on the photosensitive drum 1 (1A, 1B, 1C, 1D) is formed. Primary transfer is performed on the intermediate transfer belt 62.

  The secondary transfer counter roller 63 also serves as a driving roller. As the secondary transfer counter roller 63 rotates, the intermediate transfer belt 62 rotates in the rotation direction (arrow R2 direction). The rotational speed of the intermediate transfer belt 62 is set to be approximately the same as the rotational speed (process speed) of each of the photosensitive drums 1 (1A, 1B, 1C, 1D).

  A secondary transfer roller 64 as a secondary transfer unit is disposed at a position corresponding to the secondary transfer counter roller 63 on the surface of the intermediate transfer belt 62. The intermediate transfer belt 62 is sandwiched between the secondary transfer counter roller 63 and the secondary transfer roller 64. Thus, a secondary transfer nip portion T2 as a secondary transfer portion is formed between the secondary transfer roller 64 and the intermediate transfer belt 62.

  Further, a belt cleaner 67 as an intermediate transfer body cleaner for collecting toner remaining on the intermediate transfer belt 62 without being secondarily transferred to the recording material at a position corresponding to the tension roller 66 on the surface of the intermediate transfer belt 62. Are in contact.

  A recording material (for example, a sheet of paper or transparent film) used for image formation by the image forming unit P (Pa, Pb, Pc, Pd) is stored in a state of being stacked on a feeding cassette as a sheet storage unit. Has been. Then, the recording material taken out from the feeding cassette by the pickup roller is separated one by one by the separation roller and fed to the registration roller. The registration roller sends the recording material to the secondary transfer nip T2 in time with the toner image on the intermediate transfer belt 62.

  A fixing device 7 having a fixing portion and a pressure portion is disposed downstream of the secondary transfer nip portion T2 in the recording material conveyance direction. Further, a discharge tray for loading the recording material discharged outside the apparatus is disposed downstream of the fixing device 7 in the recording material conveyance direction. The recording material to which the toner image has been transferred is heated and pressurized by the fixing device 7 so that the toner image is fixed on the surface of the recording material. Then, the recording material having the toner image fixed on the surface is discharged to a discharge tray.

(Configuration of developing device)
Next, the configuration of the developing device 4 will be described with reference to the schematic diagram of FIG. 2 and the cross-sectional view of FIG.

  The developing device 4 includes a developing container 44 that stores a developer. In the developing container 44, a developing sleeve 41 as a developer carrying member for carrying a developer (two-component developer) and development as a developer regulating member for regulating the amount of developer carried on the surface of the developing sleeve 41 are provided. A blade 43 is disposed.

  The developing blade 43 serves to form a thin layer of developer on the surface of the developing sleeve 41. The developing blade 43 may be a developing blade formed by resin molding using a resin material or a developing blade using a metal material such as SUS.

  In the first embodiment, the developing sleeve 41 is made of aluminum which is a nonmagnetic material. The developing sleeve 41 may be made of stainless steel as long as it is a nonmagnetic material. In the first embodiment, the diameter of the developing sleeve 41 is set to 18 mm (φ18) or less in order to reduce the size of the developing device 4.

  Inside the developing sleeve 41, a magnet 42 (magnet for two-component development) as magnetic field generating means having a plurality of magnetic poles is fixedly disposed along the circumferential direction of the developing sleeve 41. In the first embodiment, the magnet 42 includes a plurality of mag pieces (a first magnet part 42a, a second magnet part 42b, a third magnet part 42c, a fourth magnet part 42d, and a fifth magnet part 42e).

  The developing sleeve 41 rotates counterclockwise around the outer periphery of the magnet 42 (in the direction of arrow R41 shown in FIG. 3). The magnet 42 has a width (hereinafter referred to as a developer carrying region) on which the developer is carried on the developing sleeve 41 in the axial direction of the rotation axis of the developing sleeve 41 (hereinafter referred to as the longitudinal direction of the developing sleeve 41). Is substantially the same as the width in the longitudinal direction.

  In the developing container 44, a developing chamber 44a and a stirring chamber 44b are arranged side by side in the horizontal direction. The developing container 44 is provided with a partition wall 47 for partitioning the developing chamber 44a and the stirring chamber 44b. The developer separated from the developing sleeve 41 is collected in the developing chamber 44a. The developer collected in the developing chamber 44a is supplied again to the developing sleeve 41 in the developing chamber 44a.

  In the longitudinal direction of the developing sleeve 41, an opening is provided in the developing chamber 44a at a position corresponding to a region of the developing sleeve 41 facing the photosensitive drum 1 (hereinafter referred to as a developing region). The developing sleeve 41 is rotatably disposed in the opening so that a part of the developing sleeve 41 is exposed.

  A first conveying screw 45a as a first developer conveying member that stirs and conveys the developer in the developing chamber 44a is rotatably provided in the developing chamber 44a. The agitating chamber 44b is rotatably provided with a second conveying screw 45b as a second developer conveying member that conveys and conveys the developer in the agitating chamber 44b. The second conveying screw 45b agitates and conveys the developer supplied by the developer replenishing mechanism (hopper) for replenishing the developer and the developer already present in the stirring chamber 44b. Each of the first conveying screw 45a and the second conveying screw 45b conveys the developer in the opposite direction, and circulates the developer in the developer container 44 through the developer circulation path.

  As shown in FIG. 2, the developer conveyed by the first conveying screw 45a is transferred from the developing chamber 44a to the stirring chamber 44b via the communication portion 46a. The developer transported by the second transport screw 45b is transferred from the stirring chamber 44b to the developing chamber 44a via the communication portion 46b.

  The developer accommodated in the developing container 44 is a two-component developer in which a negatively charged nonmagnetic toner and a magnetic carrier are mixed. The non-magnetic toner is obtained by encapsulating a colorant, a wax component or the like in a resin such as polyester or styrene, and pulverizing or polymerizing it. The magnetic carrier is obtained by applying a resin coat to the surface layer of a core made of resin particles kneaded with ferrite particles or magnetic powder.

(Development process)
Next, a process (development process) in which development is performed on the electrostatic latent image on the surface of the photosensitive drum 1 will be described.

  The surface of the photosensitive drum 1 is uniformly charged by the charger 2 to a charging potential (dark portion potential) Vd [V]. Thereafter, a portion corresponding to the image portion on the surface of the photosensitive drum 1 is exposed by the exposure device 3 to be an exposure potential (bright portion potential) Vl [V]. A DC voltage or a voltage obtained by superimposing an AC voltage on the DC voltage is applied to the developing sleeve 41. When the DC component voltage of the developing sleeve 41 is Vdc, the absolute value | Vdc−Vl | of the difference between the DC component voltage of the developing sleeve 41 and the exposure potential is referred to as Vcont. By this Vcont, an electric field for carrying toner to the image portion on the surface of the photosensitive drum 1 is formed. The absolute value | Vdc−Vd | of the difference between the DC component voltage Vdc of the developing sleeve 41 and the charging potential Vd is referred to as Vback. By this Vback, an electric field that pulls the toner from the surface of the photosensitive drum 1 toward the developing sleeve 41 is formed.

  When the diameter of the developing sleeve 41 is reduced as the developing device 4 is reduced in size, the magnet 42 inside the developing sleeve 41 is reduced as compared to the case where the diameter of the developing sleeve 41 is large. As a result, the section from the magnetic pole to the magnetic pole in the rotation direction of the developing sleeve 41 is shortened and the peeling area is narrowed, so that the developer used for development tends to be difficult to separate from the developing sleeve.

  A case will be considered where a new magnet 42 is added from the outside in the vicinity of a magnetic pole (stripping pole) for separating the developer carried on the surface of the developing sleeve 41 from the developing sleeve 41. When such a configuration is adopted, a space for arranging a new magnet outside the developing sleeve 41 is required, leading to an increase in the size of the apparatus. Therefore, in the developing device 4 using the developing sleeve 41 having a small diameter, the magnetic pattern in the vicinity of the stripping pole is adjusted without arranging a new magnet outside the developing sleeve 41, so that the vicinity of the stripping pole is adjusted. It is desirable to achieve both improvement in developer peelability and downsizing of the apparatus.

  In the first embodiment, the stripping is performed by adjusting the magnetic force pattern in the vicinity of the magnetic pole (stripping pole) for separating the developer carried on the surface of the developing sleeve 41 from the developing sleeve 41 with a simple configuration. This improves the peelability of the developer in the vicinity of the electrode. Details will be described below.

  The configuration of the magnet 42 according to the first embodiment will be described with reference to the schematic diagram of FIG. In the first embodiment, as shown in FIG. 3, the fifth magnet part 42e disposed downstream of the fourth magnet part 42d in the rotation direction of the developing sleeve (R41 shown in FIG. 4) includes the magnet 42. A groove portion 48 is provided over the entire region in the longitudinal direction.

  The stripping pole made by the fifth magnet part 42b has two maximum values N3 and N4 of the same polarity. Of the two maximum values, the maximum value on the upstream side is N3 pole, and the maximum value on the downstream side is N4 pole.

  The developer is peeled off by a peeling area formed between the peeling pole N4 and the magnetic pole (pumping pole) N1 that has the same polarity as the peeling pole N4 and attracts the developer to the developing sleeve 41. The In addition, in the first embodiment, since the stripping poles have the same maximum value of the N3 pole and the N4 pole, it is difficult for the developer to exist between the two poles (the developer is not developed). A pre-peeling region is formed which has a weak force attracted to the sleeve 41.

  First, the force with which the developer is attracted to the developing sleeve 41 will be described. The force with which the developer is attracted to the developing sleeve 41 is represented by a magnetic attractive force Fr obtained by the following equation (Equation 1).

In the formula, μ is the magnetic carrier permeability, μ ₀ is the vacuum magnetic permeability, and b is the magnetic carrier radius. Br is a normal direction component of the developing sleeve 41 in the magnetic flux density. F. W. Using a magnetic field measuring instrument “MS-9902” (trade name) manufactured by BELL, Br was measured with the distance between the probe, which is a member of the measuring instrument, and the surface of the developing sleeve 41 being about 100 μm.

  Bθ is obtained from the following formula (Formula 2) using the value of Br measured by the above method.

  Using the value of Br measured in this way, Bθ can be derived and Fr can be calculated.

  FIG. 5 shows a relationship between Br and Fr indicated by the magnet 42 according to the first embodiment.

  Fr is calculated assuming that the relative permeability of the magnetic carrier is 5 and the radius of the magnetic carrier is 20 μm. In the figure, the angle of the horizontal axis is 0 ° in the vertical upward direction, and the rotation direction of the developing sleeve 41 is the positive direction.

  Focusing on Br indicated by a solid line in FIG. 5, there is a region where Br is small between the N4 pole (stripping pole) and the N1 pole (pumping pole). This is due to the repulsive force generated by the repulsive magnetic field formed between the N4 pole and the N1 pole. In this region, Fr indicated by a dotted line in FIG. 5 is also small. Fr represents the force in the normal direction of the developing sleeve 41 among the forces acting on the magnetic carrier. Therefore, the force that attracts the magnetic carrier toward the center of the developing sleeve 41 is expressed by a negative value of Fr. That is, in the region where the Fr existing between the N4 pole and the N1 pole is small, the force at which the developer is attracted to the developing sleeve 41 does not work, and this region becomes the peeling region.

  Further, at Br upstream of the rotation direction of the developing sleeve 41 with respect to the peeling region, there is a maximum peak position of the N3 pole where the Br of the N3 pole is maximum, and a maximum peak position of the N4 pole where the Br of the N4 pole is maximum. doing. Further, in the rotation direction of the developing sleeve 41, there is a minimum peak position at which Br is minimized immediately downstream of the maximum peak position of the N3 pole and immediately upstream of the maximum peak position of the N4 pole. And in the area | region which has two maximum values of N3 pole and N4 pole in a maximum peak position, Fr has fallen between N3 pole and N4 pole. This is caused by the repulsive action between the N3 pole and the N4 pole. In this region, the developer is difficult to be carried on the developing sleeve 41. That is, this area is a preliminary peeling area because the developer is peeled from the developing sleeve 41 prior to the peeling area.

  In the first embodiment, in order to enhance the preliminary peeling effect in the preliminary peeling region, the ratio of the magnitude of the minimum value between the N3 pole and the N4 pole to the magnitude of the maximum value of the N3 pole is more than 30%. The magnetic force pattern in the vicinity of the stripping pole is adjusted so as to be larger than 95%.

  In order to set the ratio of the magnitude of the minimum value between the N3 pole and the N4 pole to the magnitude of the maximum value of the N3 pole to 30%, the following is set. That is, the size of the cross-sectional area of the groove portion 48 is set to 22.2% with respect to the sum of the cross-sectional area of the magnet portion 42e and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41. From another viewpoint, the size of the cross-sectional area of the groove portion 48 is set to 5.6% with respect to the sum of the cross-sectional area of the entire magnet 42 and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41. The

  On the other hand, in order to set the ratio of the magnitude of the minimum value between the N3 pole and the N4 pole to the magnitude of the maximum value of the N3 pole as 95%, the following setting is made. That is, the size of the cross-sectional area of the groove portion 48 is set to 1.6% with respect to the sum of the cross-sectional area of the magnet portion 42e and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41. From another viewpoint, the size of the cross-sectional area of the groove portion 48 is set to 0.4% with respect to the sum of the cross-sectional area of the entire magnet 42 and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41. The

  Therefore, in order to make the ratio of the minimum value between the N3 pole and the N4 pole to the maximum value of the N3 pole larger than 30% and smaller than 95%, it is set as follows. The That is, the size of the cross-sectional area of the groove portion 48 with respect to the sum of the cross-sectional area of the magnet portion 42e and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41 is larger than 1.6% and 22.2%. Is set smaller. From another viewpoint, the size of the cross-sectional area of the groove portion 48 with respect to the sum of the cross-sectional area of the entire magnet 42 and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41 is more than 0.4%. It is set to be larger than 5.6%.

  On the other hand, if the magnitude of the minimum value between the N3 pole and the N4 pole is made too small relative to the magnitude of the maximum value of the N3 pole, the preliminary peeling effect increases, but the N3 pole, the N4 pole, and the N1 pole There is a concern that the balance of repulsive force between the two will be lost and the peeled area will be narrowed.

  Therefore, in order to sufficiently release the developer from the developing sleeve 41 in each of the preliminary peeling area and the peeling area, the minimum between the N3 pole and the N4 pole with respect to the maximum value of the N3 pole. The ratio of the magnitudes of the values is more preferably larger than 50% and smaller than 95%.

  In order to set the ratio of the magnitude of the minimum value between the N3 pole and the N4 pole to the magnitude of the maximum value of the N3 pole to 50%, the following setting is made. That is, the size of the cross-sectional area of the groove portion 48 is set to 15.8% with respect to the sum of the cross-sectional area of the magnet portion 42e and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41. From another viewpoint, the size of the cross-sectional area of the groove 48 is set to 4.0% with respect to the sum of the cross-sectional area of the entire magnet 42 and the cross-sectional area of the groove 48 in the cross-section orthogonal to the rotation axis of the developing sleeve 41. The

  Therefore, in order to make the ratio of the magnitude of the minimum value between the N3 pole and the N4 pole to the magnitude of the maximum value of the N3 pole, more preferably, more than 50% and less than 95%, Is set as follows. That is, the size of the cross-sectional area of the groove portion 48 relative to the sum of the cross-sectional area of the magnet portion 42e and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41 is greater than 1.6% and 15.8%. Is set smaller. From another viewpoint, the size of the cross-sectional area of the groove portion 48 with respect to the sum of the cross-sectional area of the entire magnet 42 and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41 is more than 0.4%. It is set to be larger than 4.0%.

  In the first embodiment, the ratio of the magnitude of the minimum value between the N3 pole and the N4 pole to the magnitude of the maximum value of the N3 pole is set to 70% as follows. That is, the size of the cross-sectional area of the groove portion 48 was set to 9.5% with respect to the sum of the cross-sectional area of the magnet portion 42e and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41. From another viewpoint, the size of the cross-sectional area of the groove portion 48 is set to 2.4% with respect to the sum of the cross-sectional area of the entire magnet 42 and the cross-sectional area of the groove portion 48 in the cross section orthogonal to the rotation axis of the developing sleeve 41. .

  That is, a certain amount of developer is peeled off in the preliminary peeling region located upstream in the rotation direction of the developing sleeve 41 with respect to the peeling region formed between the N4 pole and the N1 pole. Further, the developer that could not be peeled off in the preliminary peeling region is conveyed to the peeling region as the developing sleeve 41 rotates, and is peeled off in the peeling region. Since the peeling process in the preliminary peeling area and the peeling process in the peeling area can be performed twice, the peeling defect in which the developer used for the development is not sufficiently detached from the developing sleeve 41 is suppressed.

  Further, in order to obtain two peeling regions such as a peeling step in the preliminary peeling region and a peeling step in the peeling region, in order to obtain such two peeling regions, Fr in the vicinity of the N4 pole is It needs to be large to some extent. The absolute value of Fr forming a so-called peeling region where the developer used for development is stably peeled from the developing sleeve 41 is 1 [nN] or less, but the absolute value of Fr is 10 [nN] or less. If so, the peeling of the developer from the developing sleeve 41 starts to be performed. Therefore, in order to obtain two separation regions stably, the absolute value of Fr in the vicinity of the N4 pole is 10 [nN] or more (at this time, the Fr at the maximum peak position of the N4 pole where Br is maximum). The absolute value must be 10 [nN] or more. Therefore, in order to set the absolute value of Fr near the N4 pole to 10 [nN] or more, the following conditions must be satisfied.

  First, on the downstream side of the N3 pole maximum peak position where the N3 pole Br becomes maximum in the rotation direction of the developing sleeve 41 and on the upstream side of the N1 pole maximum peak position where the N1 pole Br becomes maximum, It has a maximum peak position of the N4 pole where Br is a maximum. Second, there is a minimum peak position (also referred to as a minimum point) at which Br is minimized on the downstream side of the maximum peak position of the N3 pole and the upstream side of the maximum peak position of the N4 pole in the rotation direction of the developing sleeve 41. That is. Third, Br at the maximum peak position of the N4 pole is 120 of Br at the minimum peak position downstream of the maximum peak position of the N3 pole and upstream of the maximum peak position of the N4 pole in the rotation direction of the developing sleeve 41. % Or more.

  Therefore, in the first embodiment, Br at the maximum peak position of the N4 pole is 27.3 [mT], and is downstream of the maximum peak position of the N3 pole and upstream of the maximum peak position of the N4 pole in the rotation direction of the developing sleeve. The minimum peak position Br on the side was 18.4 [mT]. That is, in the first embodiment, Br at the maximum peak position of the N4 pole is set to a minimum peak downstream of the N3 pole maximum peak position and upstream of the N4 pole maximum peak position in the rotation direction of the developing sleeve 41. The size is about 150% of Br at the position.

  As a comparative example, a magnet 42 in which the groove portion 48 is not formed in the fifth magnet portion 42e is used. FIG. 9 shows a distribution of Br and Fr in the configuration of the magnet 42 of the comparative example. As a comparative example, FIG. 9 shows the distribution of Br and Fr in a configuration in which the fifth magnet portion 42e that creates the stripping pole is not provided with the groove portion 48 and the stripping pole has only one maximum value N3.

  In the comparative example, the stripping pole has one maximum value N3. The magnetic pole created by the fifth magnet portion 42e does not have a minimum point (minimum peak position), and the maximum value is only one of the N3 poles. In the comparative example, even if attention is paid to Fr on the upstream side in the rotation direction of the developing sleeve 41 with respect to the peeling region, the Fr does not decrease as shown in the first embodiment, and the developer is peeled only in the peeling region. Is called.

  In order to confirm the effect of the first embodiment, a solid image of A4 is obtained in each of the case where the configuration of the magnet 42 according to the first embodiment is used and the case where the configuration of the magnet 42 according to the comparative example is used. The decrease in image density when 10 sheets were continuously fed was measured. The density value is measured using a reflection spectral densitometer 500 series (trade name) manufactured by X-Rite, and is an average value of 10 values in the main search direction at the center of the output image in the sub-scanning direction. did.

  When the difference between the reflection density values of the first and tenth sheets is Δ, Δ = 0.22 when the configuration of the magnet 42 according to the comparative example is used. When the configuration of the magnet 42 is used, Δ = 0.02, which is greatly improved.

  The width of the magneticless band (region where the absolute value of Br is 5 mT or less) in the comparative example and the first embodiment is about 42 °, and the separation region where Fr becomes small (Fr is −1 nN or more) The width of the region, in other words, the magnetic force region in which the absolute value of Fr is 1 nN or less is about the same. From this, it can be said that the peeling action of the developer in both peeling areas is equivalent. In other words, this reduction in density can be improved by providing a preliminary peeling region prior to the peeling region, so that the two peeling steps of the peeling step in the preliminary peeling region and the peeling step in the peeling region can be performed. For this reason, the peeling defect in which the developer provided for development does not sufficiently separate from the developing sleeve 41 is suppressed.

Similarly to the first embodiment, the difference Δ between the reflection density values of the first sheet and the tenth sheet when the width of the coercive band is changed in the configuration in which the preliminary separation region is provided is shown. Is shown in FIG.
As shown in FIG. 6, when the width of the coercive force band is less than 40 °, a decrease in density occurs. At 35 °, Δ = 0.21, and a non-negligible level of decrease in density was observed. This indicates that the developer that could not be peeled off in the preliminary peeling region was not peeled off in the peeling region. For this reason, in order to improve the peelability of the developer, the width of the peeling region is preferably 35 ° or more, and more preferably 40 ° or more.

[Second Embodiment]
In the first embodiment, as shown in FIG. 5, the maximum value N3 and the maximum value N4 are substantially the same. On the other hand, in the second embodiment, by adjusting and optimizing the magnetic force pattern in the vicinity of the stripping pole so that the maximum value N3 is larger than the maximum value N4, in the preliminary peeling region. The effect of removing the developer from the developing sleeve 41 is further enhanced.

  In the first embodiment, as shown in FIG. 5, when the change in Fr is observed, Fr rises again on the downstream side in the rotation direction of the developing sleeve 41 from the preliminary peeling region. This is mainly Fr produced by the N4 pole attractive force. If this portion has a large Fr, when the developer is transported from the N3 pole to the preliminary peeling area, the amount of developer attracted to the N4 pole without being peeled in the preliminary peeling area increases. Therefore, from this viewpoint, it is preferable that Fr near the N4 pole is small. There are two ways to weaken Fr near the N4 pole.

  The first method is to reduce the N4 pole Br. It can be seen from Equations 1 and 2 that Fr is reduced by reducing the absolute value of Br. However, simply reducing the N4 pole Br increases the preliminary peeling effect, but the repulsive force balance between the N3 pole, the N4 pole, and the N1 pole may be lost and the peeling area may be narrowed. is there.

  Further, as described above in the first embodiment, in order to obtain two peeling regions stably, the absolute value of Fr in the vicinity of the N4 pole needs to be 10 [nN] or more. For this purpose, Br at the maximum peak position of the N4 pole is 120 of the minimum peak position Br downstream of the N3 pole maximum peak position and upstream of the N4 pole maximum peak position in the rotation direction of the developing sleeve 41. % Or more is necessary.

  Therefore, while maintaining the balance of repulsive force between the N3 pole, the N4 pole, and the N1 pole, Br at the maximum peak position of the N4 pole is 120% or more of Br at the minimum peak position between the N3 pole and the N4 pole. It is required to reduce the Fr in the vicinity of the N4 pole while keeping the magnitude of. Therefore, the Br at the maximum peak position of the N4 pole is set so that Br at the maximum peak position of the N4 pole is 120% or more of the minimum peak position Br between the N3 pole and the N4 pole. What is necessary is just to enlarge Br of the maximum peak position of N3 pole, setting it as minimum necessary Br. At this time, the magnitude of Br at the maximum peak position of the N3 pole is made larger than the magnitude of Br at the maximum peak position of the N4 pole.

  In the second method, as shown in Equation 1, it can be seen that Fr increases as the change in Br becomes steeper. Therefore, in order to reduce Fr, the minimum point (minimum peak position) between the N3 pole and the N4 pole is set to the N3 pole side (upstream in the rotation direction of the developing sleeve 41), and Br near the N4 pole is set. You should smooth out the changes.

  In accordance with the above two policies, the shape and position of the groove portion 48 provided in the fifth magnet portion 42e is changed from the first embodiment, and as shown in Table 1, the values of Br of the N3 pole and the N4 pole, The position of the minimum point was adjusted.

  Compared with the first embodiment, the second embodiment increases the N3 pole Br and decreases the N4 pole Br. Further, in the first embodiment, the position of the local minimum point is substantially at the center position between the N3 pole and the N4 pole, whereas in the second embodiment, the N3 pole side (upstream in the rotation direction of the developing sleeve 41). ) About 7 °.

  A diagram showing the distribution of Br and Fr in the configuration of the magnet 42 according to the second embodiment is shown in FIG. FIG. 8 is an enlarged view of the periphery of the stripping pole (in the range of 40 ° to 100 ° in the rotation direction of the developing sleeve 41). FIG. 8A uses the configuration of the magnet 42 according to the first embodiment. On the other hand, FIG. 8B shows the configuration of the magnet 42 according to the second embodiment.

  In the second embodiment, as shown in FIG. 8B, the value of Fr near the N4 pole is increased (the force attracting the developing sleeve 41 is decreased). Specifically, in each of FIG. 8A and FIG. 8B, the maximum value of Fr in the vicinity of the N4 pole indicated by the triangular point is −16.5 × 10 nN in the first embodiment. In the second embodiment, it is −12.9 nN.

  Thus, by optimizing the relationship between the N3 pole and N4 pole Br and the minimum point (minimum peak position) between them, Fr in the vicinity of the N4 pole can be reduced. Thereby, in 2nd Embodiment, the amount of peeling by a preliminary | backup peeling area | region increases, and peeling defect is further suppressed.

(Other embodiments)
The present invention is not limited to the above embodiment, and various modifications (including organic combinations of the embodiments) are possible based on the spirit of the present invention, and these are excluded from the scope of the present invention. is not.

  In the above embodiment, as illustrated in FIG. 1, the image forming apparatus configured to use the intermediate transfer belt 62 as an image carrier has been described as an example, but the present invention is not limited thereto. It is also possible to apply the present invention to an image forming apparatus configured to perform transfer by bringing a recording material into direct contact with the photosensitive drum 1 (1A, 1B, 1C, 1D) in order. In that case, the photosensitive drum 1 (1A, 1B, 1C, 1D) constitutes a rotatable image carrier that carries a toner image.

  In the above embodiment, as shown in FIG. 3, the developing sleeve 41 rotates counterclockwise (in the direction of arrow R41 shown in FIG. 3), and the developing blade 43 is disposed below the developing sleeve 41. The developing device 4 having the above configuration has been described as an example, but is not limited thereto. The present invention can also be applied to the developing device 4 configured such that the developing sleeve 41 rotates clockwise and the developing blade 43 is disposed above the developing sleeve 41.

  In the above-described embodiment, as illustrated in FIG. 3, the developing device 4 having the configuration in which the developing chamber 44a and the stirring chamber 44b are arranged side by side in the horizontal direction is described as an example. I can't. It is also possible to apply the present invention to the developing device 4 having a configuration in which the developing chamber 44a and the stirring chamber 44b are arranged side by side with respect to the direction of gravity.

4 Developing Device 41 Developing Sleeve 42 Magnet 42e Magnet Part 44 Developer Container 48 Groove Part

Claims (10)

A developer carrier that is rotatably provided and carries a developer containing toner and a magnetic carrier for developing an electrostatic latent image formed on the image carrier;
The first magnetic pole and the first magnetic pole are arranged adjacent to the first magnetic pole with respect to the rotation direction of the developer carrier, and are disposed in the same manner as the first magnetic pole. A magnet for generating a magnetic field for separating the developer that has passed through the development region facing the image carrier from the surface of the developer carrier,
In a developing device comprising:
The magnet is provided with a groove over the entire length of the magnet so as to satisfy the following (1) to (3). (1) The first magnetic pole of the first magnetic pole with respect to the rotation direction of the developer carrier. The magnetic flux density of the normal direction component of the developer carrier of the second magnetic pole and the downstream side of the first maximum peak position where the magnetic flux density of the normal direction component of the developer carrier is a maximum is the maximum. The surface of the developer carrier upstream of the second maximum peak position becomes a third maximum peak position where the magnetic flux density of the normal direction component of the developer carrier is a maximum,
(2) On the surface of the developer carrier on the downstream side of the first maximum peak position and the upstream side of the third maximum peak position in the rotation direction of the developer carrier, the developer carrier The magnetic flux density of the normal component of the body has a minimum peak position where the magnetic flux density is minimum, and the magnetic flux density of the normal direction component of the developer carrier at the minimum peak position is the development at the first maximum peak position. Greater than 30% and less than 95% of the magnetic flux density of the normal component of the agent carrier,
(3) On the surface of the developer carrier on the downstream side of the third maximum peak position and on the upstream side of the second maximum peak position in the rotation direction of the developer carrier, the developer carrier A first magnetic force region having an absolute value of a magnetic force of a normal direction component of the body of 1 [nN] or less is formed, and is downstream of the first maximum peak position in the rotation direction of the developer carrier and the first A second magnetic field region having an absolute value of a magnetic force of a normal direction component of the developer carrier of 1 [nN] or less is formed on the surface of the developer carrier upstream of the maximum peak position of 3. A developing device. 2. The developing device according to claim 1, wherein an absolute value of a magnetic force of a normal direction component of the developer carrying member at the third maximum peak position is 10 [nN] or more. The magnetic flux density of the normal component of the developer carrier at the third maximum peak position is 120% or more of the magnetic flux density of the normal component of the developer carrier at the minimum peak position. The developing device according to claim 1 or 2. The magnetic flux density of the normal direction component of the developer carrier at the first maximum peak position is larger than the magnetic flux density of the normal direction component of the developer carrier at the third maximum peak position. The developing device according to any one of claims 1 to 3. The ratio of the cross-sectional area of the groove portion to the sum of the cross-sectional area of the magnet and the cross-sectional area of the groove portion in a cross section perpendicular to the rotation axis of the developer carrier is greater than 0.4% and smaller than 5.6%. The developing device according to claim 1, wherein A magnet for two-component development arranged fixedly inside a rotatable developer carrier,
A first magnetic pole;
A second magnetic pole disposed adjacent to the first magnetic pole with respect to the rotation direction of the developer carrier, and having the same polarity as the first magnetic pole;
With
The magnet is provided with a groove over the entire length of the magnet so as to satisfy the following (1) to (3). (1) The first magnetic pole of the first magnetic pole with respect to the rotation direction of the developer carrier. The magnetic flux density of the normal direction component of the developer carrier of the second magnetic pole and the downstream side of the first maximum peak position where the magnetic flux density of the normal direction component of the developer carrier is a maximum is the maximum. The surface of the developer carrier upstream of the second maximum peak position becomes a third maximum peak position where the magnetic flux density of the normal direction component of the developer carrier is a maximum,
(2) On the surface of the developer carrier on the downstream side of the first maximum peak position and the upstream side of the third maximum peak position in the rotation direction of the developer carrier, the developer carrier The magnetic flux density of the normal component of the body has a minimum peak position where the magnetic flux density is minimum, and the magnetic flux density of the normal direction component of the developer carrier at the minimum peak position is the development at the first maximum peak position. Greater than 30% and less than 95% of the magnetic flux density of the normal component of the agent carrier,
(3) On the surface of the developer carrier on the downstream side of the third maximum peak position and on the upstream side of the second maximum peak position in the rotation direction of the developer carrier, the developer carrier A first magnetic force region having an absolute value of a magnetic force of a normal direction component of the body of 1 [nN] or less is formed, and is downstream of the first maximum peak position in the rotation direction of the developer carrier and the first A second magnetic field region having an absolute value of a magnetic force of a normal direction component of the developer carrier of 1 [nN] or less is formed on the surface of the developer carrier upstream of the maximum peak position of 3. A magnet characterized by that. The magnet according to claim 6, wherein an absolute value of a magnetic force of a normal direction component of the developer carrying member at the third maximum peak position is 10 [nN] or more. The magnetic flux density of the normal component of the developer carrier at the third maximum peak position is 120% or more of the magnetic flux density of the normal component of the developer carrier at the minimum peak position. The magnet according to claim 6 or 7. The magnetic flux density of the normal direction component of the developer carrier at the first maximum peak position is larger than the magnetic flux density of the normal direction component of the developer carrier at the third maximum peak position. The magnet according to any one of claims 6 to 8. The ratio of the cross-sectional area of the groove portion to the sum of the cross-sectional area of the magnet and the cross-sectional area of the groove portion in a cross section perpendicular to the rotation axis of the developer carrier is greater than 0.4% and smaller than 5.6%. The magnet according to any one of claims 6 to 9, wherein:

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