JP2008185735A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for obtaining stable images by suppressing toner scattering, reducing stress of collection toner, suppressing deterioration of toner, and maintaining stable development characteristics over a long period of time in the image forming apparatus provided with a touch-down development type developing device. <P>SOLUTION: The image forming apparatus having the touch-down development type developing device arranges a toner collection roller 14 for collecting scattering toner floating in the vicinity of a toner carrier 2 and a two-component developer carrier 1 in the downstream side of a rotating direction of the two-component developer carrier rather than the most proximate position of the two-component developer carrier 1 and the toner carrier 2 so as to block a gap between the two-component developer carrier 1 and a housing wall in the vicinity of the toner carrier. Arithmetic average roughness Ra of the surface of the toner collection roller is larger than that of the surface of the toner carrier and is 0.505-3.0 μm. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and in particular, using a two-component developer that charges a nonmagnetic toner using a magnetic carrier, The present invention relates to an image forming apparatus in which a magnetic brush is formed, a toner thin layer is formed on a developing roller by the magnetic brush, toner in the toner thin layer is ejected to an electrostatic latent image, and the latent image is developed.

Conventionally, in an electrophotographic image forming apparatus, as a developing method using a dry toner, a one-component developing method and a two-component developing method are known.
Since the one-component developing method does not include a carrier, the electrostatic latent image on the photosensitive member is not disturbed by the magnetic brush formed from the carrier and the toner, and is suitable for high image quality. However, in the one-component development method, it is difficult to stably maintain the charge amount of the toner. In the case of a color toner, since transparency is required, it must be a non-magnetic toner. For this reason, full-color image forming apparatuses often employ a two-component development system that uses a carrier as a medium for charging and transporting toner.

  As an image forming method using the two-component developing method, a toner thin layer is formed on a toner carrier with a magnetic brush formed on a developer carrier carrying a two-component developer, and the toner on the toner carrier There is known an image forming method by so-called touch-down development (also referred to as hybrid development) in which an electrostatic latent image on an electrostatic latent image carrier is developed and visualized by a thin layer. However, this development method combines a two-component development method and a one-component development method, and there is a difference between the proper charge amount of toner when developing an electrostatic latent image and the proper charge amount of toner when forming a thin toner layer. In some cases, the toner amount of the toner thin layer is small and an image density defect occurs, or a problem such as a development ghost due to a defective peeling of the toner thin layer that did not contribute to the development may occur. .

  One of the causes of the above problems is the influence of scattered toner. The toner scatters mainly in the developing device, such as when the toner is agitated in the housing and in the vicinity of the magnetic roller. The scattered toner generated in the developing device is scattered inside the electrophotographic apparatus including the electrostatic latent image carrier, the optical system device, the charging device, the transfer device, and the like. Cause image defects and malfunctions.

In order to solve such a problem, in Patent Document 1, a developer that is rotatably provided in a state of being opposed to and separated from the electrostatic latent image carrier is attached to the surface. It has been proposed to prevent toner scattering by using a scattering prevention member that prevents scattering to the outside, and a scraping means that scrapes off the developer adhered on the scattering prevention member. Patent Document 2 proposes a two-component developing method in which a collecting roller is provided in a housing opening of a developing device to collect scattered toner, and the toner is peeled off from the collecting roller and returned to the developing device. .
JP-A-8-137256 JP 2005-242194 A

  However, in Patent Document 1, the scraped developer is stressed by contact with the blade, and deterioration is promoted. In particular, the touch-down development method is susceptible to selective development. Accordingly, the external additive is detached or buried due to the stress caused by scraping with the blade, and the toner having changed charging characteristics is returned to the two-component developer container, thereby promoting toner scattering and selective development. Furthermore, it becomes difficult to form an image stably over a long period of time, such as an image density defect. In the touch-down development method, since the toner concentration of the two-component developer is high and the developer fluidity is poor, the developer is collected one after another when the magnetic brush is collected in the two-component developer container. Therefore, the air is pushed and compressed, and at the same time, the air loses its place and the toner is discharged to the outside together with the air, so that the toner is more easily scattered.

  In the touch-down development method, the ghost phenomenon is the most serious problem. To solve this problem, it is important to peel off the undeveloped toner adhering to the toner carrier with the two-component developer carrier. is there. However, as the process linear velocity increases, it is necessary to transport the toner necessary for developing a large number of electrostatic latent images to the toner carrier in a short time. Therefore, it is necessary to take measures such as increasing the toner concentration in the two-component developer. That is, after the toner layer is formed, the two-component developer collected in the two-component developer container has a higher toner concentration than at low speed. Also, the undeveloped toner peeling time on the toner carrier is shortened, and the two-component developer collected in the two-component developer container has a high toner concentration, which makes it more difficult to remove. . Further, toner scattering is likely to occur, and the scattered toner may adhere to the toner carrier, increasing the amount of collected toner, increasing toner scattering, and causing a ghost phenomenon due to poor peeling.

  Further, in Patent Document 2, when the toner is peeled off from the collecting roller that collects the scattered toner and returned to the developing device, it is necessary to provide a separate route for returning the toner. Since the toner is peeled off, the deterioration of the toner is promoted. Furthermore, in the touch-down development method, it is more difficult to collect scattered toner on a high-speed machine in which the drum linear speed is 180 mm / sec or more. Incidentally, as a guideline, the drum linear speed of 180 mm / sec is about 40 sheets / min at the A4 side, about 50 sheets / min at 250 mm / sec, and about 60 sheets / min at 340 mm / sec.

  An object of the present invention is to suppress toner scattering in an image forming apparatus including a touch-down developing type developing device and reduce the stress of collected toner, thereby suppressing toner deterioration and stable over a long period of time. An object of the present invention is to provide an image forming apparatus capable of maintaining development characteristics and obtaining a stable image.

As a result of intensive studies to solve the above-mentioned problems, the present inventor has achieved image quality stable for a long period of time by suppressing toner scattering and toner deterioration by an image forming apparatus having the following configuration. As a result, the present invention has been completed.
That is, the image forming apparatus of the present invention has the following configuration.

(1) A two-component developer carrying member that has a magnetic member disposed therein and magnetically holds a developer composed of a carrier and toner, and a toner thin layer on the surface of the two-component developer carrying member by transferring toner from the two-component developer carrying member An electrostatic latent image formed on the surface of the electrostatic latent image carrier by applying a developing bias to the toner carrier and / or the two-component developer carrier. An image forming apparatus for developing an image, comprising: a toner collecting roller for collecting scattered toner floating in the vicinity of the toner carrier and the two-component developer carrier; and the two-component developer carrier and the toner carrier. Arranged on the downstream side in the rotational direction of the two-component developer carrier from the closest position of the body and between the two-component developer carrier and the housing wall, the arithmetic average roughness Ra of the surface of the toner collecting roller But Wherein greater than the arithmetic average roughness Ra of the toner carrying member surface, and an image forming apparatus which is a 0.505～3.0Myuemu.
(2) The toner collecting roller is characterized in that a magnetic member having a polarity different from that of the magnetic member of the two-component developer carrying member is disposed inside the toner collecting roller so as to face the magnetic member of the two-component developer carrying member. The image forming apparatus according to (1).
(3) The arithmetic average roughness Ra on the surface of the toner collecting roller is 1.01 to 3.0 times the arithmetic average roughness Ra on the surface of the toner carrying member (1) or (2) The image forming apparatus described in 1.
(4) The image forming apparatus according to any one of (1) to (3), wherein a bias unit that applies a bias voltage for collecting the scattered toner is provided on the toner collecting roller.
(5) The image forming apparatus according to any one of (1) to (4), wherein a peripheral speed of the electrostatic latent image carrier is 180 mm / sec or more.

  According to the present invention, the arithmetic average roughness Ra of the toner collection roller surface is set larger than the arithmetic average roughness Ra of the toner carrier and set to a predetermined size. Since the toner collecting roller is disposed at a predetermined position, the scattered toner can be efficiently collected and toner scattering can be suppressed. Further, the toner collecting roller has a magnetic member having a polarity different from that of the magnetic member of the two-component developer carrying member disposed inside the toner collecting roller so as to face the magnetic member of the two-component developer carrying member. A magnetic brush layer is formed between the two-component developer carrying member, and the collected scattered toner can be returned to the two-component developer container without applying stress to the magnetic brush. As a result, toner deterioration is suppressed, and stable image quality can be obtained for a long time.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of an image forming apparatus of a touch-down development system according to an embodiment of the present invention. FIG. 2 is an explanatory diagram of a toner collection roller and a developer carrier for explaining the arrangement of magnetic members according to an embodiment of the present invention. FIG. 3 is a schematic configuration diagram showing a part of the developing means of FIG.

(Image forming device)
The image forming apparatus of the present invention forms a toner thin layer 9 on the developing roller 2 by using the two-component developer carried on the magnetic roller 1 by using the two-component developer comprising the magnetic carrier 4 and the toner 5, and photosensitive. This is an image forming apparatus based on a so-called touch-down development system that develops an electrostatic latent image formed on a body 3 (electrostatic latent image carrier). As shown in FIG. 1, the image forming apparatus includes the photoreceptor 3, and around the photoreceptor 3, a charging unit 8, an exposing unit 16, a developing unit 18, a primary transfer unit 22, and a secondary transfer unit 25. The fixing unit 26, the cleaning unit 24, and the like are disposed.

  Image formation by the image forming apparatus is performed as follows. That is, the surface of the photosensitive member 3 is uniformly charged by the charging unit 8, and the charged surface is exposed by the exposure unit 16 to form an electrostatic latent image. The obtained electrostatic latent image is developed as a toner image by attaching the toner 5 from the developing means 18. This toner image is transferred from the photoreceptor 3 onto the intermediate transfer belt 20 by a primary transfer roller 22 as a primary transfer unit. After the toner images of a plurality of colors are transferred on the intermediate transfer belt 20 in an overlapping manner, a secondary transfer roller 25 as a secondary transfer unit transfers the toner image to a transfer target conveyed from the paper feed cassette 27 to the secondary transfer position. Transfer the toner image. The transferred body is conveyed to a fixing roller 26 as a fixing unit, and after the toner image is fixed on the transferred body, it is discharged to, for example, a discharge tray (not shown). Undeveloped toner remaining on the surface of the photoreceptor 3 after the transfer is removed by the cleaning means 24.

  Examples of the photoreceptor 3 include inorganic photoreceptors such as selenium and amorphous silicon, and organic photoreceptors in which a single-layer or multilayer photosensitive layer containing a charge generating agent, a charge transport agent, a binder resin, and the like is formed on a conductive substrate. (OPC) and the like. Examples of the charging unit 8 include a scorotron system, a charging roller, and a charging brush. As for the exposure means 16, LED or a semiconductor laser is mentioned as exposure light. Moreover, as the cleaning means 24, for example, a doctor blade type or the like can be used, and known ones can be used.

  As shown in FIGS. 2 and 3, the developing means 18 has a sleeve-like shape in which a plurality of magnetic members M1 and M11 are fixed to an inner roller shaft R1, and the outer peripheral portions of the magnetic members M1 and M11 are rotated. The magnetic member M2 (two-component developer carrier) and a magnetic member M2 having a different polarity from the magnetic roller 1 are fixed to the inner roller shaft R2, and the outer periphery of the magnetic member M2 is rotated. A magnetic field is formed by the magnetic force of the different magnetic poles of the sleeve-like developing roller 2 (toner carrier) and the magnetic roller 1 and the developing roller 2, and the magnetic brush 6 formed on the magnetic roller 1 by this magnetic field The control blade 7 is configured to maintain a constant thickness and a toner recovery roller 14 (hereinafter also referred to as a recovery roller) for recovering scattered toner. Further, an alternating current (AC) bias power supply 11a and a direct current (DC: Vdc1) bias power supply 11b applied to the magnetic roller 1, and an alternating current (AC) bias power supply 12a and a direct current (DC: Vdc2) bias power supply 12b applied to the developing roller 2 are used. And. Further, a power source 13 that applies a direct current (DC: Vdc3) bias to the toner recovery roller 14 may be provided. Control means (not shown) for controlling these bias power supplies 11a, 11b, 12a, 12b and 13 is provided.

  The image forming apparatus of the present invention also includes a toner container (not shown) in which the toner 5 is stored and the toner 5 supplied from the toner container to the two-component developer storage unit 45 that stores the two-component developer. The two-component developer supplied to the stirring screw 44 from the stirring screw 40 through both ends of the partition plate 42 is communicated at both ends of the partition plate 42 and stirred with the carrier 4 to be charged. Supplied to the magnetic roller 1, the stirring screw 44 circulates the two-component developer from the other end side to the stirring screw 40 side, and the magnetic roller 1, the developing roller 2, the stirring screw 40, and the stirring screw 44. And a housing 46 in which is stored.

  As shown in FIG. 4, the image forming apparatus of the present invention forms a tandem (indirect transfer tandem system) color image in which four photoconductors 3A, 3B, 3C, and 3D are arranged on the intermediate transfer belt 20. It can use suitably for an apparatus. In this case, using the developing means 18 described above, the developing devices 18A, 18B, 18C, and 18D respectively containing magenta, cyan, yellow, and black toners electrostatically charge the photosensitive members 3A, 3B, 3C, and 3D. The latent image is visualized and a toner image is formed. The toner images visualized on the photoreceptors 3A, 3B, 3C, 3D are sequentially transferred onto the surface of the intermediate transfer belt 20 from the upstream photoreceptor 3A. The full-color image transferred onto the intermediate transfer belt 20 is transferred by the secondary transfer roller 25 to the transfer target conveyed from the paper feed cassette 27 and then fixed by the fixing roller 26. Is discharged.

  Here, as the generation source of the scattered toner, when the two-component developer on the magnetic roller 1 is mainly collected in the two-component developer container 45, the magnetic brush 6 is compressed, so that the magnetic brush 6 Since the air in between is repelled without entering the two-component developer accommodating portion 45, the toner 5 is also ejected from the two-component developer collecting portion 45 together with the air. In the touchdown development method, the magnetic roller 1 supplies toner 5 on the developing roller 2 near the position closest to the developing roller 2 to form a thin toner layer 9 and contributes to the development of the electrostatic latent image. The undeveloped toner on the developing roller 2 that has not been removed is peeled off and collected. This undeveloped toner has low adhesion to the carrier 4 (compared to the adhesion between the toner 5 and the carrier 4 in the two-component developer when the toner thin layer 9 is formed), and in the touch-down development method, the two-component developer Since the toner density in the inside is kept higher than that in the normal two-component developing method, the fluidity of the two-component developer is low, and the air between the magnetic brushes 6 is difficult to enter the two-component developer containing portion 45. Therefore, toner scattering is likely to occur. The scattered toner causes various image defects, operation defects, and the like, and particularly adheres to the surface of the developing roller 2 and is likely to cause a ghost phenomenon due to a peeling defect, which is one of the factors that hinder good image formation. It was.

(Toner recovery roller)
The toner collecting roller 14 according to the present invention is for collecting the scattered toner and returning it to the magnetic roller 1. As shown in FIG. 1, the photosensitive member 3, the developing roller 2, the magnetic roller 1, In the arrangement configuration of the agitating screws 40 and 44, a gap between the magnetic roller 1 and the wall of the housing 46 is provided on the downstream side in the rotation direction of the magnetic roller 1 with respect to the closest position of the magnetic roller 1 and the developing roller 2. The magnetic roller 1 is disposed so as to be closed.

  With this configuration, the toner moves in the direction of arrow A in FIG. 1 through the scattered toner floating in the vicinity of the developing roller 2 and the magnetic roller 1 and the gap on the lower side of the magnetic roller 1 to move inside the image forming apparatus. The scattered toner scattered on the toner can be collected by adhering to the surface of the toner collecting roller 14 by intermolecular force or electrostatic attraction.

  The collection roller 14 rotates in the circumferential direction. As a result, the scattered toner adhering to the surface of the collecting roller 14 can be peeled off in contact with the magnetic brush 6 formed on the magnetic roller 1 and returned to the magnetic roller 1 side.

  The toner recovery roller 14 has an arithmetic average roughness Ra on the surface larger than that of the developing roller 2 and is 0.505 to 3.0 μm, preferably 0.75 to 2.0 μm. If the arithmetic average roughness Ra of the surface of the toner collecting roller 14 is smaller than the developing roller 2, the scattered toner collecting force is smaller than that of the developing roller 2, and thus the scattered toner may be collected by the developing roller 2. The toner that is collected by the amount of scattered toner when it comes into contact with the magnetic brush 6 and peels off because the toner collected by the collecting roller 14 becomes worse and the scattered toner adheres to the developing roller 2. The amount increases and minute peeling failure occurs. As this accumulates, the highly charged toner 5 eventually accumulates on the developing roller 2 and may cause a ghost phenomenon, which makes it difficult to maintain stable image quality over a long period of time. . Further, when the arithmetic average roughness Ra of the surface of the toner collecting roller 14 is smaller than 0.505 μm, the collecting power and holding power of the scattered toner are not sufficient, and when it is larger than 3.0 μm, the recoverability to the magnetic brush 6 is improved. Insufficient toner is collected on the toner collecting roller 14. The arithmetic average roughness Ra on the surface of the developing roller 2 is preferably 0.5 to 1.0 μm.

  Further, the arithmetic average roughness Ra of the surface of the toner collecting roller 14 is preferably 1.01 to 3.0 times the arithmetic average roughness Ra of the surface of the developing roller 2. If the arithmetic average roughness Ra of the surface of the toner collecting roller 14 is within the above range, the adhesion with the toner is strengthened, and the scattered toner collecting ability is enhanced.

  As shown in FIG. 2, the toner collecting roller 14 includes a sleeve in which a magnetic member M3 is disposed and rotates on the outer periphery of the magnetic member M3. The magnetic member M3 is provided on a roller shaft R3 in the collecting roller 14, and is fixed and supported at a predetermined angle in the circumferential direction so as not to rotate. The position of the magnetic member M3 of the collecting roller 14 is preferably arranged on the upstream side in the rotation direction of the collecting roller 14 with respect to the line C connecting the center of the magnetic roller 1 and the center of the collecting roller 14. As shown in FIG. 2, the angle α is 1 to 6 °, preferably about 5 ° upstream. On the other hand, the drawing pole M1 of the magnetic roller 1 is preferably arranged on the upstream side in the rotation direction of the magnetic roller 1 with respect to the line C connecting the centers, and as shown in FIG. °, preferably about 5 ° upstream. If the angle α is less than 1 °, the carrier 4 may be attracted to the collecting roller, which is not preferable. On the other hand, if the angle α exceeds 6 °, the force to return the toner on the collecting roller 14 to the magnetic roller 1 side is too weak, and the toner may not be collected, which is not preferable. At this time, the magnetic member M3 of the collection roller 14 and the lead-in pole M1 of the magnetic roller 1 are arranged to face each other so that the polarities of the respective distal ends in the radial direction are different from each other. For example, in the example shown in FIG. 2, the magnetic member M3 of the collection roller 14 has an N pole, and the drawing pole M1 of the magnetic roller 1 has an S pole.

The collection roller 14 rotates in the circumferential direction, and the rotation direction is the same as the rotation direction of the magnetic roller 1 at the opposite position. And the peripheral speed of the said collection | recovery roller 14 has good 10-100 mm / sec, Preferably it is 20-70 mm / sec. When the circumferential speed of the collecting roller 14 is less than 10 mm / sec, the number of rotations is small and the amount of scattered toner collected is not preferable. On the other hand, if it exceeds 100 mm / sec, the collectability of the scattered toner is lowered, and it may be scattered again at the time of peeling of the adhered toner by the magnetic brush 6, which is not preferable. Furthermore, the carrier 4 may be pulled from the magnetic brush 6 carried on the magnetic roller 1, which is not preferable.
When the collecting roller 14 rotates within the above range, the scattered toner can adhere to and collect on the surface of the collecting roller 14, and the toner adhering to the surface of the collecting roller 14 is collected by the collecting roller 14 and the magnetic roller 1. It contacts with the magnetic brush 6 formed therebetween and is peeled off without being stressed, and can be returned to the magnetic roller 1 side. Further, it is possible to prevent the carrier from being pulled toward the toner collecting roller 14 side.

  The material of the rotating sleeve of the collecting roller 14 can be a metal such as aluminum or stainless steel. It is preferable that the surface is coated with anodized aluminum having a large specific surface area from the viewpoint of adhesion of scattered toner, and / or fluorine resin from the viewpoint of electrostatic adhesion (toner charging characteristics). Is positively charged). The magnetic member M3 is not particularly limited as long as it is a material that generates a magnetic force, but is preferably a magnet, for example, a rubber magnet that can be easily processed.

As shown in FIG. 2, the magnetic member M3 is arranged on the collecting roller 14 and the positional relationship with the magnetic pole M1 of the magnetic roller 1 is set as described above, so that the pulling pole M1 (S pole) of the magnetic roller 1 is set. Since there is a recovery roller 14 magnetic pole M3 (N pole) opposite to the magnetic pole, the magnetic roller 1 and the recovery roller 14 are located upstream of the position where the recovery roller 14 and the magnetic roller 1 are closest to each other. A magnetic field is formed between them, and a layer of the magnetic brush 6 is formed. The magnetic brush 6 is formed between the collection roller 14 and the magnetic roller 1 so as to be inclined to the downstream side in the rotation direction of the magnetic roller 1 as compared with the case where α = β = 0. After the toner is peeled off by the magnetic brush 6 with a mechanical force, the toner is easily conveyed downstream in the rotation direction of the magnetic roller 1. As a result, the collected toner is efficiently collected on the magnetic roller 1 side without stagnation. Further, since the magnetic brush 6 layer is formed between the collecting roller 14 and the magnetic roller 1, the effect of blocking the place of the scattered toner scattered from the paddle mixer 44 side to the developing roller 2 side of the magnetic roller 1 is also achieved. The toner can also be collected at the same time and returned to the magnetic roller 1 side.
In addition, since the recovery roller 14 and the magnetic roller 1 are rotated in the same direction in the circumferential direction at the opposed positions, the stress applied to the recovered toner is reduced, and deterioration of the recovered toner can be prevented.

The magnetic force (surface magnetic flux density) on the surface of the collection roller 14 in the radial direction of the magnetic member M3 disposed on the collection roller 14 is 30 to 70 mT, preferably 40 to 60 mT. At this time, the main pole M11 of the magnetic roller 1 is 70 to 100 mT, preferably 80 to 100 mT. The magnetic force (surface magnetic flux density) on the surface of the magnetic roller 1 in the radial direction of the drawing pole M1 is larger than the magnetic member M3 of the recovery roller 14 and smaller than the main pole M11 of the magnetic roller 1, 90 mT, preferably 70 to 90 mT.
By making the magnetic force of the magnetic member M3 of the collecting roller 14 smaller than the magnetic force of the pulling pole M1 of the magnetic roller 1, a large number of carriers 4 are drawn to the magnetic roller 1 side. Is efficiently collected by the magnetic roller 1 and the carrier 4 on the magnetic roller 1 is not taken to the collecting roller 14 side.

  The toner collecting roller 14 may be provided with bias means for applying a direct current bias voltage (DC: Vdc3) in order to collect the scattered toner. The bias unit applies a bias voltage Vdc3 applied to the toner recovery roller at a voltage lower or higher than the bias voltage Vdc1 applied to the magnetic roller 1 in accordance with the charging polarity of the toner to be used. For example, when a positively charged toner is used as the toner 5, the bias voltage Vdc 3 is applied so that the potential of the collection roller 14 is lower than the potential of the magnetic roller 1. As a result, the positively charged scattered toner is electrostatically attracted to the collection roller 14 having a lower potential than the magnetic roller 1, adheres to the surface of the collection roller 14, and is collected. Conversely, when negatively charged toner is used, the voltage may be applied so that the potential of the collection roller 14 is increased.

(Development method)
FIG. 3 schematically shows an example of the developing means according to the present invention. The developing method will be described below.
A magnetic brush 6 comprising a carrier 4 (magnetic particles) that is magnetically constrained by a fixed magnet contained in the magnetic roller 1 and a toner 5 that is charged and held on the surface of the carrier 4 is attached to the surface of the magnetic roller 1. It is rotated and conveyed to the developing roller 2. The surface of the magnetic roller 1 can be conveyed more smoothly by using a blasted or grooved surface.

  As shown in FIG. 3, a developing bias voltage 12 in which an alternating voltage (AC) 12a is superimposed on a direct current voltage (DC: Vdc2) 12b is applied to the developing roller 2, and a direct current voltage (DC: Vdc1) is applied to the magnetic roller 1. ) 11b is applied with a developing bias voltage 11 in which an alternating voltage (AC) 11a is superimposed. The magnetic brush 6 is formed on the magnetic roller 1. The magnetic brush 6 on the magnetic roller 1 is layer-regulated by a regulating blade 7 and conveyed by the potential difference between the magnetic roller 1 and the developing roller 2. Only the charged toner 5 of the magnetic brush 6 moves to the developing roller 2 to form a toner layer 9. Then, the electrostatic latent image on the photoreceptor 3 is developed by the toner layer 9 on the developing roller 2. The DC voltage Vdc is an area center voltage, and changes when the DUTY ratio is changed. In the present invention, the DUTY ratio is a duration T1 applied to the positive polarity side and a duration T2 applied to the negative polarity side in one cycle of the rectangular wave AC voltage, and the DUTY ratio (%) = [T1 / ( T1 + T2)] × 100. At this time, a voltage where the areas of the waveform rising to the positive polarity side and the waveform rising to the negative polarity side are equal to each other is called an area center voltage. A DC voltage may be superimposed as necessary, and when a DC voltage is superimposed, Vdc = DC voltage + immunocenter voltage. Vdc when no AC is applied is simply a DC voltage.

  The electrostatic latent image on the photoreceptor 3 can be formed using the exposure means 16 on the surface of the photoreceptor 3 charged to +250 to 800 V by the charging means 8. When an OPC photoconductor is used, +70 to 220 V is obtained in all exposures, and an amorphous silicon photoconductor provides a post-exposure potential of 10 to 50 V. For the exposure, either a semiconductor laser or an LED can be used.

  After the development is performed as described above, the developing roller 2 having the residual toner layer comes closest to the magnetic roller 1 having the developer layer at the facing position, and the mechanical force by the magnetic brush 6 at the facing position. As a result, the toner layer 9 on the developing roller 2 is scraped off. At the same time, the toner 5 is supplied from the developer layer on the magnetic roller 1 to the developing roller 2 side according to a potential difference (that is, an electric field) formed between the magnetic roller 1 and the developing roller 2.

  At the time of development, it is preferable to apply a bias condition of +300 to 500 V to the magnetic roller 1 and +100 V to the developing roller 2. The potential difference for forming the thin layer is appropriately 200 to 400 V, and may be adjusted according to the balance with the charge amount of the toner 5. By using feedback control or the like, the layer thickness of the toner thin layer 9 can be made constant to some extent.

  When the bias power supply 13 for applying a bias voltage to the toner collecting roller 14 is used, for example, when positively charged toner 5 is used, the collecting roller applied voltage (Vdc3) is lower than the potential of the magnetic roller 1 and The potential difference is preferably +50 to 150V. Within this range, the positively charged scattered toner in the vicinity of the magnetic roller 1 can be electrostatically attracted and adhered to the collecting roller 14, and the adhered scattered toner can be easily peeled off by the magnetic brush 6 and magnetized. It can be returned to the roller 1.

The AC conditions are as follows: V _PP (peak AC bias) = 0.1-2.0 kV, frequency = 2-4 kHz, DUTY ratio = 60-80% in the same period and opposite phase as the developing roller 2 in the magnetic roller 1 For the roller 2, V _PP = 1.0 to 2.0 kV, frequency = 2 to 4 kHz, and DUTY ratio = 20 to 40% are preferable. When V _PP is increased, a thin layer is formed more instantaneously, but on the other hand, the leak resistance is weakened and noise is generated. With respect to these points, it is preferable to increase the insulation by anodizing the surface of the magnetic roller 1 or the developing roller 2 because the margin is widened. The frequency may be adjusted by the charge amount of the toner 5.

As the toner 5, any of positively and negatively charged toners can be used. Preferably, positive charging is used. The volume average particle diameter is preferably 4.0 to 7.5 μm. If the thickness is less than 4.0 μm, the influence of non-electrostatic adhesion increases, and developability and recoverability deteriorate. If the thickness is greater than 7.5 μm, it is difficult to obtain a high-quality image such as smooth image quality. The charge amount of the toner 5 is preferably about 6 to 30 μC / g. If the charge amount is lower than this, the toner 5 will fly from the magnetic brush 6 and stain the periphery, and if it is higher than this, the thin layer formation will be weakened.
The toner volume average particle diameter can be measured using Multisizer III (manufactured by Beckman Coulter, Inc.) with an aperture diameter of 100 μm (measurement range: 2.0 to 60 μm).
The toner charge amount can be measured with a QM meter (manufactured by TREK, MODEL 210HS).

As the carrier 4, a known carrier can be used. Preferably, a carrier whose surface is coated with a resin using a ferrite core is preferably used. The carrier particle size (weight average particle size) is preferably 30 to 60 μm. If it is less than 30 μm, the holding force due to the magnetic force is weakened, so that carrier jumping or the like that causes the carrier 4 to move to the developing roller 2 and the collection roller 14 occurs, and if it exceeds 60 μm, the magnetic brush density is not appropriate, Further, the toner thin layer is not smoothly formed and the specific surface area is small, so that the toner recoverability is also lowered. Further, the saturation magnetization of the carrier 4 is preferably 35 to 90 emu / g. When the saturation magnetization is lower than 35 emu / g, the carrier 4 jumps remarkably, and when it is higher than 90 emu / g, the magnetic brush 6 becomes sparse and a uniform thin layer cannot be formed.
The saturation magnetization of the carrier 4 can be measured with a magnetic field of 79.6 kA / m (1 kOe) using “VSM-P7” manufactured by TOEI.

The gap between the magnetic roller 1 and the developing roller 2 is 200 to 600 μm, preferably 300 to 400 μm. The gap is the most effective factor for instantly forming a thin layer. If the width is wide, the efficiency is lowered, and problems such as development ghosts occur. On the other hand, if it is narrow, the magnetic brush 6 that passes through the blade gap cannot pass through the gap and the toner thin layer 9 is disturbed.
The gap between the magnetic roller 1 and the toner collection roller 14 is such that the magnetic brush 6 comes into contact with the collection roller 14 and should be smaller than the gap between the magnetic roller 1 and the developing roller 2 and is 150 to 500 μm. The thickness is preferably 200 to 300 μm.

By setting the distance between the magnetic roller 1 and the collection roller 14 to be equal to or less than the distance between the magnetic roller 1 and the developing roller 2, scattering toner generated from the periphery of the magnetic roller 1 is prevented from scattering to the developing roller 2 side. It becomes possible to do. Note that if the gap between the magnetic roller 1 and the collection roller 14 is narrowed, a leak occurs. Therefore, in order to suppress this leak, it is necessary to increase the insulation and provide resistance to the surface of the collection roller 14 by anodizing. It becomes. In that case, the electrical resistivity of the surface of the collection roller 14 is preferably 10 ⁷ to 10 ¹² Ω · m.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited only to a following example.

[Example 1]
The image forming apparatus of the present invention shown in FIG. 1 was produced according to the following specifications. The diameters of the sleeves of the photosensitive member 3, the developing roller 2, the magnetic roller 1, and the collecting roller 14 were 30 mm, 20 mm, 25 mm, and 10 mm, respectively, and aluminum was used.
The peripheral speed of each drum is as follows.
Photoconductor 3: 300 mm / sec
Developing roller 2: 450 mm / sec
Magnetic roller 1: 675mm / sec
Collection roller 14: 30 mm / sec

The magnetic force on the surface of each of the magnetic members of the developing roller 2 and the magnetic roller 11 in the radial direction was 45 mT for the S pole M2 of the developing roller 2 and 90 mT for the main pole M11 (N pole) of the magnetic roller 1.
Magnetic force measurement measured the magnetic force on the surface of the collection | recovery roller 14 and the magnetic roller 1 using Teslameter GX-100 (Nippon Electromagnetic Instrument Co., Ltd. product).

The arithmetic average roughness Ra of the surface of the toner collecting roller 14 and the surface of the developing roller 2 was 0.505 μm and 0.5 μm, respectively.
The surface roughness Ra was measured using SURFCOM 1500DX (manufactured by Tokyo Seimitsu Co., Ltd.) under the following conditions. Calculation standard: JIS-1994 standard, measurement type: roughness measurement, measurement length: 4.0 mm, cutoff wavelength: 0.8 mm, measurement speed: 0.3 mm / s, evaluation length: 4.0 mm.

Using the image forming apparatus prepared above, image formation was performed under the following conditions for image formation.
Photoconductor surface potential: + 310V
Q / m of toner in developer: 18 μC / g
Toner particle size (volume average particle size): 6.7 μm
Carrier particle size (weight average particle size): 55 μm
Distance between magnetic roller and developing roller: 350 μm
Distance between magnetic roller and collection roller: 250 μm
Developing roller applied voltage: Vdc2 = 100 V, V _PP = 1.6 kV, frequency f = 2.7 kHz, Duty ratio = 30%
Magnetic roller applied voltage: Vdc1 = 300 V, V _PP = 300 V in the same period and opposite phase as the developing roller, frequency f = 2.7 kHz, Duty ratio = 70%
Recovery roller applied voltage: Vdc3 = 200V

[Examples 2-5, Comparative Examples 1-3]
The arithmetic average roughness Ra of the surface of the toner collecting roller 14 and the developing roller 2 and the magnetic force between the collecting roller 14 and the magnetic roller 1 and between the developing roller 2 and the magnetic roller 1 were implemented except that the combinations shown in Table 1 were used. In the same manner as in Example 1, image forming apparatuses of Examples 2 to 5 and Comparative Examples 1 to 3 were produced.

(Evaluation)
In the evaluation, the image forming apparatus produced above was used to evaluate the collection property of the collected scattered toner to the two-component developer containing portion 45 by the collecting roller 14, toner scattering, and the ghost phenomenon. The evaluation method and evaluation criteria were used.
Regarding the recoverability of the scattered toner adhering on the recovery roller 14 to the two-component developer accommodating portion 45 by the magnetic brush 6, the toner concentration in the two-component developer composed of the carrier 4 and the toner 5 is approximately 7%, and the print density After 50% of 6% original output was output continuously, the toner adhesion amount M (mg / cm ² ) on the collecting roller 14 was measured and evaluated according to the following criteria.
The amount of collected toner adhering on the collecting roller 14 and the amount of scattered toner adhering to the member 47 described later were measured using a QM meter MODEL 210PS (manufactured by TREK).
A: M <0.01
○: 0.01 ≦ M ≦ 0.05
Δ: 0.05 <M ≦ 0.1
×: 0.1 <M
Toner scattering occurs on the inner wall portion of the member 47 when the member 47 (made of the same ABS resin as the housing) shown in FIG. 1 is modified to be detachable from the developing device 18 and 1000 originals with a printing rate of 6% are output. The amount of toner adhered per unit area was measured and evaluated according to the following criteria.
◎: less than ^{0.05mg / cm 2 ○: 0.05~0.1mg /} cm less than ² △: ^0.1~0.15mg / cm ² less than ×: 0.15mg / cm ² or more also, ghost phenomenon, After outputting 1000 originals with a printing rate of 6%, the image shown in FIG. 5 was output, and the obtained image was confirmed visually. However, FIG. 5 evaluates the image pattern. And it evaluated by the following criteria.
○: No ghost is seen.
Δ: Slightly ghost is seen.
X: A ghost is clearly seen.
The evaluation results are shown in Table 1.

As shown in Table 1, in Examples 1 to 5 within the scope of the present invention, the amount of residual toner on the collection roller 14 is small, and the two-component developer container 45 for the toner 5 on the collection roller 14 by the magnetic brush 6. The recoverability to was good. Further, the toner scattering amount is small, and the recoverability by the recovery roller 14 is good, and the toner scattering is suppressed. Furthermore, a good image was obtained without the occurrence of a ghost phenomenon.
On the other hand, in Comparative Examples 1 to 3 outside the scope of the present invention, in any case, at least the recoverability of the toner 5 on the recovery roller 14 into the two-component developer accommodating portion 45, the toner scattering amount, and the ghost phenomenon are at least. Either showed poor results.

1 is an explanatory diagram showing a schematic configuration of an image forming apparatus of a touchdown development system according to an embodiment of the present invention. FIG. 4 is an explanatory diagram of a toner recovery roller and a developer carrier for explaining the arrangement of magnetic members according to an embodiment of the present invention. It is a schematic block diagram which shows an example of the image development means of FIG. FIG. 2 is a schematic configuration diagram illustrating an example of a tandem color image forming apparatus using the developing unit illustrated in FIG. 1. It is a figure which shows an example of the ghost evaluation result by the image pattern in the Example of this invention, (A) shows the example in which the ghost did not generate | occur | produce, (B) shows the example in which the ghost generate | occur | produced.

Explanation of symbols

1 Two-component developer carrier (magnetic roller)
2 Toner carrier (developing roller)
3 Electrostatic latent image carrier (photoreceptor)
4 Carrier 5 Toner 6 Magnetic Brush 7 Regulating Blade 8 Charging Means 9 Toner Thin Layer 11a AC Power Supply 11b DC Power Supply 12a AC Power Supply 12b DC Power Supply 13 DC Power Supply 14 Toner Collection Roller 16 Exposure Means 22 Primary Transfer Means 24 Cleaning Means 25 Secondary Transfer Means 26 Fixing means

Claims (5)

A two-component developer carrying member that magnetically holds a developer composed of a carrier and toner by arranging a magnetic member inside, and a toner thin layer on the surface of the two-component developer carrying member by transferring toner from the two-component developer carrying member A toner carrier is provided at least in the housing, and a developing bias is applied to the toner carrier and / or the two-component developer carrier to develop the electrostatic latent image formed on the surface of the electrostatic latent image carrier. An image forming apparatus for performing
A toner collecting roller that collects the scattered toner floating in the vicinity of the toner carrier and the two-component developer carrier, the two-component developer from a position closest to the two-component developer carrier and the toner carrier; Arranged on the downstream side in the rotation direction of the carrier and between the two-component developer carrier and the housing wall, the arithmetic average roughness Ra of the surface of the toner collecting roller is the arithmetic average roughness of the surface of the toner carrier. An image forming apparatus characterized by being larger than Ra and 0.505 to 3.0 μm.   2. The toner collecting roller, wherein a magnetic member having a polarity different from that of the magnetic member of the two-component developer carrying member is disposed inside the toner collecting roller so as to face the magnetic member of the two-component developer carrying member. The image forming apparatus according to 1.   3. The image forming apparatus according to claim 1, wherein the arithmetic average roughness Ra of the surface of the toner collecting roller is 1.01 to 3.0 times the arithmetic average roughness Ra of the surface of the toner carrying member. .   The image forming apparatus according to claim 1, wherein a bias unit that applies a bias voltage for collecting the scattered toner is provided on the toner collecting roller.   The image forming apparatus according to claim 1, wherein a peripheral speed of the electrostatic latent image carrier is 180 mm / sec or more.

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