JP2015152781A - image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can provide good cleanability for an intermediate transfer body, and can reduce the waiting time until the output of images can be started after paper jam or calibration.SOLUTION: An image forming apparatus 100 includes: an image carrier 1; an intermediate transfer body 8; a contact member 21 that contacts the intermediate transfer body 8 on the downstream of a secondary transfer part N2 in the direction of movement of the intermediate transfer body 8 and scrapes off a toner on the intermediate transfer body 8 along with the movement of the intermediate transfer body 8; a charging member 23 that charges the toner on the intermediate transfer body 8 on the upstream of a primary transfer part N1 and downstream of the contact member 21 in the direction of movement of the intermediate transfer body 8; an opposing member 10 that is arranged at a position opposite to the contact member 21 and charging member 23 across the intermediate transfer member 8; and a power source 60 that applies voltage to the opposing member 10.

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic system or an electrostatic recording system.

  2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus, for example, there is an intermediate transfer type image forming apparatus that secondarily transfers a toner image primarily transferred from a photosensitive member to an intermediate transfer member to a recording material and outputs an image. As the intermediate transfer member, an endless belt-like intermediate transfer belt is widely used.

  As a cleaning method for the toner (secondary transfer residual toner) remaining on the intermediate transfer body after the secondary transfer process, there are a blade cleaning method and an electrostatic cleaning method.

  In the blade cleaning method, as described in Patent Document 1, a cleaning blade is brought into contact with an intermediate transfer member, and secondary transfer residual toner is physically scraped off by the cleaning blade. Although this cleaning method can be expected to have good cleaning properties at low cost, it is easily affected by the unevenness of the surface of the intermediate transfer member, and the secondary transfer residual toner in the vicinity of the unevenness passes through the cleaning blade, so that good cleaning properties are achieved. May not be maintained.

  On the other hand, since the electrostatic cleaning method is a cleaning method using static electricity, it is less susceptible to the unevenness of the surface of the intermediate transfer member than the blade cleaning method. Specifically, in the electrostatic cleaning method, the secondary transfer residual toner is charged at the time of development by a charging unit to which a voltage is applied, which is provided downstream of the secondary transfer unit in the moving direction of the intermediate transfer member. Is charged to the opposite polarity. Thereafter, the secondary transfer residual toner charged to the opposite polarity is typically reversely transferred from the intermediate transfer member to the photosensitive member in the next primary transfer step, and collected by a cleaning unit that cleans the photosensitive member. The Therefore, this method is also called a simultaneous transfer cleaning method.

  In Patent Document 2, a conductive brush (conductive brush) and a conductive brush are used to uniformly disperse the secondary transfer residual toner on the intermediate transfer member and suppress image defects by performing uniform charging. An electrostatic cleaning method using a roller (conductive roller) has been proposed. Specifically, a DC voltage is applied to the conductive brush arranged on the upstream side in the moving direction of the intermediate transfer member, and the secondary transfer residual toner on the intermediate transfer member is mechanically scattered and primary recovered. And charged. Further, the secondary transfer residual toner that has passed through the conductive brush is charged by a roller disposed on the downstream side in the same direction. As a result, the secondary transfer residual toner on the intermediate transfer member can be uniformly charged with only a DC voltage without using an AC voltage, and electrostatic cleaning can be achieved.

JP 2009-288481 A JP 2009-205012 A

  However, in the above-described conventional cleaning method in which the toner is primarily collected by the conductive brush, the time for discharging the toner primarily collected to the conductive brush after printing (hereinafter also referred to as “discharge time”) is used. Necessary. Therefore, there may be a case where the waiting time until the next image output (printing) can be started (hereinafter also referred to as “print start waiting time”) becomes long.

  In particular, a large amount of toner remains on the intermediate transfer member after a jam (paper jam) occurs after the toner image is primarily transferred to the intermediate transfer member or after calibration (adjustment operation). In the calibration, control is performed in which an image pattern formed on the intermediate transfer member is detected and fed back to an image writing position, density at the time of image formation, or the like. When a large amount of toner on the intermediate transfer member passes through the conductive brush, more toner is primarily collected in the conductive brush (between the brush fibers). For this reason, since a discharge time for discharging the toner is required, the print start standby time may be long. Thus, in an image forming apparatus that employs electrostatic cleaning, it is desired to reduce the discharge time as much as possible.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of obtaining good cleaning performance of an intermediate transfer member and reducing standby time.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to an image carrier that carries a toner image and a rotatable toner image that is primarily transferred from the image carrier in a primary transfer portion to a transfer material in a secondary transfer portion. An intermediate transfer member for secondary transfer, and a toner on the intermediate transfer member in contact with the intermediate transfer member downstream of the secondary transfer portion in the moving direction of the intermediate transfer member and accompanying the movement of the intermediate transfer member A contact member that scrapes off the toner, a charging member that charges the toner on the intermediate transfer body upstream of the primary transfer portion and downstream of the contact member in the moving direction of the intermediate transfer body, An image forming apparatus comprising: a facing member disposed at a position facing the contact member and the charging member across an intermediate transfer member; and a power source for applying a voltage to the facing member.

  According to the present invention, good cleaning properties of the intermediate transfer member can be obtained, and the waiting time can be reduced.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention. It is a schematic diagram of the vicinity of the belt cleaner in one Example of this invention. It is a schematic diagram of the electroconductive brush in one Example of this invention. It is a schematic diagram for demonstrating the measuring method of the resistance value of a conductive fiber and a conductive brush. It is a schematic diagram which shows the electric current path of the electroconductive brush and intermediate transfer belt in one Example of this invention. FIG. 5 is a schematic diagram for explaining an equivalent circuit of a current path of a conductive brush and an intermediate transfer belt in an embodiment of the present invention. FIG. 6 is a schematic diagram for explaining a difference in how toner adheres to a conductive brush due to a difference in resistance value of the conductive brush. FIG. 6 is a schematic diagram for explaining generation of slipping toner due to unevenness on the surface of an intermediate transfer belt. It is a schematic diagram for demonstrating the effect of the voltage application to an opposing member. It is a graph for demonstrating a discharge threshold value.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. FIG. 1 is a schematic sectional view of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type image forming apparatus (laser beam printer) that employs an intermediate transfer method that can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units PY, PM, PC, and PK as a plurality of image forming units. The first, second, third, and fourth image forming units PY, PM, PC, and PK form yellow (Y), magenta (M), cyan (C), and black (K) images, respectively.

  In this embodiment, the configurations and operations of the image forming units PY, PM, PC, and PK are substantially the same except that the color of the toner used is different. Therefore, when it is not necessary to distinguish between them, Y, M, C, and K at the end of a symbol representing an element for any color are omitted, and the elements will be described collectively.

  The image forming unit P includes a drum-type (cylindrical) electrophotographic photosensitive member (photosensitive member), that is, a photosensitive drum 1 as an image carrier that supports a toner image. The photosensitive drum 1 is rotationally driven in the direction of arrow R1 in the figure. Around the photosensitive drum 1, the following means are arranged along the rotation direction. First, a charging roller 2 that is a roller-shaped charging member as a charging unit is disposed. Next, an exposure device (laser unit) 3 as an exposure means (image writing means) is arranged. Next, a developing device 4 as a developing unit is arranged. Next, a primary transfer roller 5 which is a roller-shaped primary transfer member as a primary transfer unit is disposed. Next, a drum cleaner 6 as a photosensitive member cleaning means is disposed. The developing device 4 includes a developing roller 41 as a developer carrying member and a toner container 42 that stores toner as a developer. The drum cleaner 6 includes a drum cleaning blade 61 as a cleaning member and a waste toner container 62.

  Further, an endless belt-like intermediate transfer belt 8 as a movable intermediate transfer member is disposed so as to face each photosensitive drum 1 of each image forming unit P. The intermediate transfer belt 8 is an example of an intermediate transfer body that is rotatable and secondarily transfers a toner image primarily transferred from the image carrier in the primary transfer portion to a transfer material in the secondary transfer portion. . The intermediate transfer belt 8 is stretched by a driving roller 9 and a tension roller 10, and rotates (circulates) in the direction of arrow R2 in the drawing when the driving roller 9 is driven to rotate. On the inner peripheral surface side of the intermediate transfer belt 8, the primary transfer roller 5 is disposed at a position facing each photosensitive drum 1 of each image forming portion P. The primary transfer roller 5 is urged (pressed) toward the photosensitive drum 1 via the intermediate transfer belt 8, and a primary transfer portion (primary transfer nip) N1 where the intermediate transfer belt 8 and the photosensitive drum 1 are in contact with each other. Is formed. On the outer peripheral surface side of the intermediate transfer belt 8, a secondary transfer roller 11 that is a roller-like secondary transfer member as a secondary transfer unit is disposed at a position facing the driving roller 9. The secondary transfer roller 11 is biased (pressed) toward the driving roller 9 via the intermediate transfer belt 8, and a secondary transfer portion (secondary transfer portion) where the intermediate transfer belt 8 and the secondary transfer roller 11 are in contact with each other. Transfer nip) N2 is formed. Further, on the outer peripheral surface side of the intermediate transfer belt 8, a belt cleaner 52 as an intermediate transfer member cleaning unit is disposed at a position facing the tension roller 10. The intermediate transfer belt unit 50 is configured by the intermediate transfer belt 8, the drive roller 9, the tension roller 10, the belt cleaner 52, and the like.

  In this embodiment, in each image forming unit P, the photosensitive drum 1, the charging roller 2, the developing device 4, and the drum cleaner 6 as process means acting on the photosensitive drum 1 integrally constitute a process cartridge 7. ing. The process cartridges 7Y, 7M, 7C, and 7K are detachable from the apparatus main body 110 of the image forming apparatus 100, respectively. In this embodiment, the process cartridges 7Y, 7M, 7C, and 7K have substantially the same configuration, and the toners contained in the toner containers 42Y, 42M, 42C, and 42K are yellow, magenta, cyan, and black. The toner is different.

  At the time of image formation, the outer peripheral surface of the rotating photosensitive drum 1 has a predetermined polarity (negative polarity in this embodiment) by a charging roller 2 to which a charging bias having a predetermined polarity (negative polarity in this embodiment) is applied. It is charged to the potential. Thereafter, the surface of the charged photosensitive drum 1 is exposed by the laser unit 3 based on the image signal. As a result, an electrostatic latent image (electrostatic image) is formed on the photosensitive drum 1.

  The electrostatic latent image is developed (visualized) as a toner image by the developing device 4 using toner as a developer. At this time, a developing bias having a predetermined polarity (negative polarity in this embodiment) is applied to the developing roller 41. In this embodiment, a toner image is formed on the photosensitive drum 1 by image exposure and reversal development. That is, the toner charged with the same polarity as the charging polarity of the photosensitive drum 1 is attached to the exposed portion on the photosensitive drum 1 where the absolute value of the potential is reduced by being exposed after being uniformly charged. A toner image is formed. In this embodiment, the toner used for development is negatively charged. That is, the toner charge polarity (regular charge polarity) during development is negative.

  The toner image formed on the rotating photosensitive drum 1 as described above is contacted with the photosensitive drum 1 at the primary transfer portion N1 on the intermediate transfer belt 8 rotating at a substantially constant speed with the photosensitive drum 1. Is transferred (primary transfer). At this time, a primary transfer bias power source (high voltage power source) 51 serving as a primary transfer bias application unit is applied to the primary transfer roller 5 from a polarity opposite to the toner charging polarity during development (in this embodiment, positive polarity). The primary transfer bias is applied.

  For example, when forming a full-color image, toner images formed on the photosensitive drums 1Y, 1M, 1C, and 1K of the first, second, third, and fourth image forming units PY, PM, PC, and PK are sequentially Are transferred onto the intermediate transfer belt 8 so as to be superimposed on each other. Then, with the four color toner images overlapped, the intermediate transfer belt 8 is conveyed to the secondary transfer portion N2 by rotation.

  On the other hand, the recording material S such as a recording sheet fed from the feeding / conveying device 12 is conveyed by the registration roller pair 16 to the secondary transfer portion N2. The feeding / conveying device 12 includes a feeding roller 14 that feeds the recording material S from the cassette 13 that stores the recording material S, and a transport roller pair 15 that transports the fed recording material S. Then, the recording material S conveyed from the feeding / conveying device 12 is conveyed to the secondary transfer portion N2 by the registration roller pair 16 so as to be synchronized with the toner image on the intermediate transfer belt 8.

  The toner image on the intermediate transfer belt 8 is transferred (secondary transfer) onto the recording material S that is nipped and conveyed between the intermediate transfer belt 8 and the secondary transfer roller 11 in the secondary transfer portion N2. The At this time, a secondary transfer bias power source (high voltage power source) 53 serving as a secondary transfer bias application unit is applied to the secondary transfer roller 11 from a polarity opposite to the toner charging polarity during development (positive polarity in this embodiment). The secondary transfer bias is applied.

  The recording material S to which the toner image is transferred is conveyed to a fixing device 17 as a fixing unit. The recording material S is nipped and conveyed by a fixing film 18 and a pressure roller 19 included in the fixing device 17 to be heated and pressurized, and a toner image is fixed on the surface thereof. The recording material S on which the toner image is fixed is discharged to the outside of the apparatus main body 110 by the discharge roller pair 20.

  The toner remaining on the surface of the photosensitive drum 1 after the primary transfer process (primary transfer residual toner) is cleaned by the drum cleaner 6. That is, the primary transfer residual toner is scraped off from the rotating photosensitive drum 1 by the drum cleaning blade 61 disposed in contact with the photosensitive drum 1 and collected in the waste toner container 62.

  The toner remaining on the surface of the intermediate transfer belt 8 after the secondary transfer process (secondary transfer residual toner) is cleaned by the action of the belt cleaner 52. As will be described in detail later, the belt cleaner 52 includes a belt cleaning blade 21, a conductive brush 23, and a waste toner container 22. Most of the secondary transfer residual toner is scraped from the moving intermediate transfer belt 8 by the belt cleaning blade 21 disposed on the upstream side in the moving direction (conveying direction) of the intermediate transfer belt 8, and is stored in the waste toner container 22. Collected. Further, a small amount of toner that has passed through the belt cleaning blade 21 (hereinafter also referred to as “passing toner”) is charged with toner during development by the conductive brush 23 disposed on the downstream side in the moving direction of the intermediate transfer belt 8. It is charged with the opposite polarity to the polarity. The charged secondary transfer residual toner is transferred to the photosensitive drum 1Y in the next primary transfer process in at least one of the plurality of image forming portions P, in the first image forming portion PY in this embodiment. Reverse transcription (transfer). Thereafter, the secondary transfer residual toner attached to the photosensitive drum 1Y is removed and collected by the drum cleaner 6Y together with the primary transfer residual toner. The cleaning of the toner on the intermediate transfer belt 8 will be described in detail later.

  In addition to forming an image to be transferred to the recording material S and outputting the image, the image forming apparatus 100 corrects a color shift (positional deviation) of a toner image formed by each image forming unit P (for control). Calibration for forming patches on the intermediate transfer belt 8 is performed. Therefore, in the image forming apparatus 100, a color misregistration detection sensor 27, which is an optical sensor as a detection unit, is installed so that toner on the intermediate transfer belt 8 can be detected in the vicinity of the drive roller 9. More specifically, the color misregistration detection sensor 27 is downstream of the primary transfer unit N1K of the fourth image forming unit PK and upstream of the secondary transfer unit N2 in the moving direction of the intermediate transfer belt 8. The intermediate transfer belt 8 is disposed so as to face the driving roller 9. The color misregistration detection sensor 27 detects a calibration toner pattern formed on the intermediate transfer belt 8. Based on the detection result, the toner image formation timing in each image forming unit P is adjusted. The toner pattern (residual toner) detected by the color misregistration detection sensor 27 is cleaned in the same manner as the secondary transfer residual toner. Calibration is executed at the time of non-image formation at a predetermined timing (for example, when the number of formed images reaches a predetermined number). In addition, the following is mentioned at the time of non-image formation. There are times when the image forming apparatus is turned on multiple times before a predetermined preparatory operation is performed for raising the fixing temperature such as when the power is turned on or when the image forming apparatus is returned from the sleep mode. In addition, there is a pre-rotation period in which a predetermined preparation operation is executed from when an image forming signal is input to when an image corresponding to image information is actually written. In addition, there is a corresponding paper interval between recording materials during continuous image formation. There is also a post-rotation time in which a predetermined organizing operation (preparation operation) is executed after the image formation is completed.

  Further, the image forming apparatus 100 is provided with a control board 25 on which an electric circuit for controlling the image forming apparatus 100 is mounted. On the control board 25, a CPU 26 as a control unit (control means) is mounted. The CPU 26 controls the drive source (not shown) related to the conveyance of the recording material S, the drive source (not shown) of the intermediate transfer belt 8 and each image forming unit P, the control related to image formation, and the control related to failure detection. For example, the operations of the image forming apparatus 100 are collectively controlled.

2. Next, the configuration relating to primary transfer and secondary transfer in this embodiment will be described in more detail.

  The intermediate transfer belt 8 is constituted by an endless belt obtained by adding a conductive agent to a resin material to impart conductivity. The intermediate transfer belt 8 is stretched around two axes of a drive roller 9 and a tension roller 10, and a tension of a total pressure of 100 N is applied by the tension roller 10.

As the intermediate transfer belt 8, an endless belt having a thickness of 70 μm formed of a polyimide resin having a volume resistivity adjusted to 1 × 10 ¹⁰ Ω · cm by mixing carbon as a conductive agent was used. The electrical characteristics of the intermediate transfer belt 8 are electronic conductivity characteristics and are characterized by small fluctuations in electrical resistance values with respect to temperature and humidity in the atmosphere. The range of the volume resistivity of the intermediate transfer belt 8 is preferably in the range of 1 × 10 ⁹ to 10 ¹¹ Ω · cm from the viewpoint of transferability. If the volume resistivity is lower than 1 × 10 ⁹ Ω · cm, transfer failure may occur due to transfer current escape under a high temperature and high humidity environment. On the other hand, if the volume resistivity is higher than 1 × 10 ¹¹ Ω · cm, transfer failure may occur due to abnormal discharge in a low temperature and low humidity environment.

  Here, the volume resistivity of the intermediate transfer belt 8 is obtained by the following measuring method. That is, using Hiresta-UP (MCP-HT450) manufactured by Mitsubishi Chemical Co., Ltd., using UR as the measurement probe, setting the room temperature at the time of measurement to 23 ° C., the room humidity to 50%, the applied voltage 250 V, and the measurement time 10 sec. Measure under the following conditions.

In this embodiment, polyimide resin is used as the material of the intermediate transfer belt 8, but the material of the intermediate transfer belt 8 is not limited to this. For example, as long as it is a thermoplastic resin, the following other materials may be used. Examples thereof include materials such as polyester, polycarbonate, polyarylate, acrylonitrile-butadiene-styrene copolymer (ABS), polyphenylene sulfide (PPS), polyvinylidene fluoride (PVdF), polyethylene naphthalate (PEN), and mixed resins thereof. .

The primary transfer roller 5 is configured by coating a core metal of a nickel-plated steel rod having an outer diameter of 6 mm with a foamed elastic layer so as to have an outer diameter of 12 mm, and has an electric power of 1 × 10 ⁶ to 1 × 10 ⁹ Ω. The one having resistance was used. The primary transfer roller 5 is brought into contact with the photosensitive drum 1 with an applied pressure of 9.8 N via the intermediate transfer belt 8, and is rotated following the rotation of the intermediate transfer belt 8. Further, when the toner on the photosensitive drum 1 is primarily transferred to the intermediate transfer belt 8, a 1500 V DC voltage (primary transfer bias) is applied to the primary transfer roller 5.

The secondary transfer roller 11 is configured by covering a cored bar of a nickel-plated steel rod having an outer diameter of 8 mm with a foamed elastic layer so as to have an outer diameter of 18 mm, and an electric power of 1 × 10 ⁷ to 1 × 10 ⁹ Ω. The one having resistance was used. The secondary transfer roller 11 is brought into contact with the intermediate transfer belt 8 with a pressing force of 50 N, and is driven to rotate as the intermediate transfer belt 8 rotates. Further, when the toner on the intermediate transfer belt 8 is secondarily transferred to the recording material S such as paper, a DC voltage (secondary transfer bias) of 2500 V is applied to the secondary transfer roller 11.

3. Configuration of Belt Cleaner As described above, the waiting time for the start of printing for the cleaning of the intermediate transfer belt 8 in the conventional cleaning method becomes longer because it takes time to discharge the toner primarily collected by the conductive brush. is there.

  In this embodiment, in order to reduce the print start waiting time, the belt cleaner 52 is generally configured as follows. That is, the belt cleaning blade 21 is disposed on the upstream side in the moving direction of the intermediate transfer belt 8, the conductive brush 23 is disposed on the downstream side, and a predetermined voltage is applied to the tension roller 10. Then, most of the toner on the intermediate transfer belt 8 is scraped off by the belt cleaning blade 21, and a small amount of slipping toner is charged by the conductive brush 23. Details will be described below.

  FIG. 2 is a schematic diagram showing in more detail the vicinity of the belt cleaner 52 in the present embodiment. The belt cleaner 52 has a belt cleaning blade 21 that is a blade-like member that contacts the intermediate transfer belt 8 as a cleaning member on the upstream side in the moving direction of the intermediate transfer belt 8. The belt cleaning blade 21 contacts the intermediate transfer member 8 downstream of the secondary transfer portion N2 in the moving direction of the intermediate transfer member 8 and scrapes off the toner on the intermediate transfer member as the intermediate transfer member 8 moves. It is an example. The belt cleaner 52 is a brush-like member that contacts the intermediate transfer belt 8 as a charging unit that charges the toner on the intermediate transfer belt 8 downstream of the belt cleaning blade 21 in the moving direction of the intermediate transfer belt 8. A certain conductive brush 23 is included. The conductive brush 23 is an example of a charging member that charges the toner on the intermediate transfer body upstream of the primary transfer portion N1 and downstream of the contact member 21 in the moving direction of the intermediate transfer body 8. In particular, the conductive brush 23 as a charging member is in contact with the intermediate transfer member 8. The belt cleaning blade 21 and the conductive brush 23 are pressed toward the tension roller 10 via the intermediate transfer belt 8. The tension roller 10 constitutes a counter roller that is an example of a counter member disposed at a position facing the contact member 21 and the charging member 23 with the intermediate transfer member 8 interposed therebetween. In particular, the tension roller 10 as the facing member is one of a plurality of rollers that stretch the intermediate transfer belt 8 that is an endless belt. The belt cleaning blade 21 and the conductive brush 23 are supported by the waste toner container 22.

  The belt cleaning blade 21 is a plate-like member made of an elastic material. In this embodiment, a plate-like member made of urethane as an elastic rubber material is used as the belt cleaning blade 21. The belt cleaning blade 21 has a predetermined length in each of a longitudinal direction arranged along a direction substantially orthogonal to the moving direction of the intermediate transfer belt 8 and a short direction substantially orthogonal to the longitudinal direction. It is a substantially rectangular plate-like member having a predetermined thickness in plan view. The belt cleaning blade 21 is pressed against the intermediate transfer belt 8 in the counter direction with a pressure of about 0.49 N / cm. That is, the belt cleaning blade 21 has a free end side in the short direction substantially orthogonal to the longitudinal direction facing the upstream of the movement direction of the intermediate transfer belt 8 in the entire region in the longitudinal direction substantially orthogonal to the movement direction of the intermediate transfer belt 8. In this way, it is brought into contact with the intermediate transfer belt 8. The belt cleaning blade 21 has a free end edge portion on the intermediate transfer belt 8 side and / or a surface in a predetermined range on the fixed end portion side from the edge portion in contact with the surface of the intermediate transfer belt 8. Here, the linear pressure of the belt cleaning blade 21 is the total pressure of the contact pressure of the belt cleaning blade 21 against the intermediate transfer belt 8 per unit length of the belt cleaning blade 21. This linear pressure can be obtained by attaching a load converter to the intermediate transfer belt 8, pressing the belt cleaning blade 21 against the surface of the intermediate transfer belt 8, and measuring the load.

The conductive brush 23 is made of a conductive fiber. 3A and 3B are schematic views showing the conductive brush 23 in more detail. In this embodiment, the conductive fiber 23a constituting the conductive brush 23 is mainly composed of nylon, uses carbon as a conductive agent, and has a resistance value (electric resistance) per unit length of the conductive fiber 23a. Is 1 × 10 ⁵ Ω / cm and the single yarn fineness is 170T / 68F. The single yarn fineness in this case indicates that one yarn is composed of 68 filament fibers, and the weight is 170 T (decitex: the weight for a length of 10,000 m is 170 g).

  Here, the resistance value of the conductive fiber 23a is obtained by the following measuring method. That is, as shown in FIG. 4 (a), a conductive fiber 23a to be measured is stretched by two metal rollers 33 having a diameter of 10 mm (D) and spaced by a distance of 10 mm (D), and a weight of 100 g on one side. At 34, load is applied to both ends. In this state, a voltage of 200 V is applied from the power source 31 to the conductive fiber 23 a via one metal roller 33, and the current value at that time is read by an ammeter 32 connected to the other metal roller 33. Then, the resistance value (Ω / cm) of the conductive fiber 23a per 10 mm (1 cm) is calculated.

The range of the resistance value of the conductive fiber 23a is preferably in the range of 1 × 10 ³ to 10 ⁷ Ω / cm from the viewpoint of charging the slipping toner. Details will be described later.

  As shown in FIGS. 3A and 3B, the conductive brush 23 as an assembly of the conductive fibers 23a as described above is electrically conductive with a base fabric 23d formed of insulating nylon in this embodiment. It is comprised by making the weave fiber 23a into a brush shape. Then, the base fabric 23d is bonded to the support 23e, which is a SUS (stainless steel) sheet metal having a thickness of 1 mm as a metal, with a conductive adhesive as a fixing means. The conductive fibers 23 woven into the base fabric 23d are in electrical contact with the support 23e under the base fabric 23d. In this embodiment, the conductive brush 23 is electrically grounded (connected to the ground) via the support 23e.

In this embodiment, the resistance value (electric resistance) Rb [Ω] of the conductive brush 23 is 1 × 10 ³ Ω. The density of the conductive fibers 23a of the conductive brush 23 is 100 kF / inch ² . The length X of the conductive fiber 23a (represented by the vertical distance from the plane of the base fabric 23d to the tip position of the conductive fiber 23a) X is 5 mm. The longitudinal width L of the conductive brush 23 (the length between the ends of the conductive fibers 23a in the direction substantially orthogonal to the moving direction of the intermediate transfer belt 8) L is 225 mm. Further, the short width of the conductive brush 23 (the length between the ends of the conductive fiber 23a in the direction along the moving direction of the intermediate transfer belt 8) W is 5 mm. Note that five rows of the conductive fibers 23a are planted in the moving direction of the intermediate transfer belt 8. Further, the front end position of the conductive brush 23 is fixedly disposed so as to have an intrusion amount of about 1.0 mm with respect to the surface of the intermediate transfer belt 8. Thereby, the conductive brush 23 rubs the surface of the moving intermediate transfer belt 8 (having a peripheral speed difference with respect to the surface of the intermediate transfer belt 8).

  Here, the resistance value Rb [Ω] of the conductive brush 23 is obtained by the following measurement method. That is, as shown in FIG. 4B, the conductive brush 23 to be measured is brought into contact with a metal roller 35 having a diameter of 30 mm with an intrusion amount of 1.0 mm, and a voltage of 200 V is supplied from the power source 36 to the conductive brush 23. Apply to. Then, the current value at that time is read by an ammeter 37 connected to the metal roller 35, and the resistance value [Ω] of the conductive brush 23 is calculated.

About the resistance value Rb of the conductive brush 23, in the conductive brush 23 using the conductive fiber 23a in the above-described resistance value range (1 × 10 ³ to 10 ⁷ Ω / cm), Rb = 1 × 10 ¹ to The range is 10 ⁵ Ω.

  The amount of penetration of the conductive brush 23 into the intermediate transfer belt 8 (or the metal roller 35) is represented by the following distance. That is, the tip of the conductive fiber 23a and the intermediate transfer belt 8 in the center position in the moving direction of the intermediate transfer belt 8 or the like in the contact area between the conductive brush 23 and the intermediate transfer belt 8 or the like. The distance along the normal direction between the surface and the like.

Based on the volume resistivity of the intermediate transfer belt 8 described above, the configuration of the conductive brush 23, and the resistance value Rb, the resistance value (electric resistance) of the intermediate transfer belt 8 at the portion where the intermediate transfer belt 8 and the conductive brush 23 are in contact with each other. ) Ri [Ω] is obtained as follows. That is, as described above, the area of the portion where the intermediate transfer belt 8 and the conductive brush 23 are in contact is approximately 5 mm × 225 mm from the short width W 5 mm and the long width L 225 mm of the conductive brush 23. The thickness of the intermediate transfer belt 8 is 70 μm. Therefore, the resistance value Ri of the intermediate transfer belt 8 at the portion where the intermediate transfer belt 8 and the conductive brush 23 are in contact is 1 × 10 ⁸ Ω · m × 70 × 10 ⁻⁶ m / (5 × 10 ⁻³ m ×). 225 × 10 ⁻³ m) = 6.2 × 10 ⁶ Ω.

The resistance value Ri of the intermediate transfer belt 8 is in the range of Ri = 6.2 × 10 ^{5 to} 6.2 × 10 ⁷ Ω when the intermediate transfer belt 8 in the volume resistivity range described above is used.

  A predetermined voltage is applied to the tension roller 10 facing the conductive brush 23 from a toner charging voltage power source (high voltage power source) 60 as a toner charging voltage applying unit. Accordingly, the toner on the intermediate transfer belt 8 can be easily removed by the belt cleaning blade 21. As a result, a discharge is generated between the conductive brush 23 and the intermediate transfer belt 8, and the slipping-through toner is charged.

4). Electrostatic Cleaning Next, the method for cleaning the toner on the intermediate transfer belt 8 in this embodiment will be described in more detail.

  Most of the toner on the intermediate transfer belt 8, such as secondary transfer residual toner, is mechanically scraped off by a belt cleaning blade 21 disposed on the upstream side in the moving direction of the intermediate transfer belt 8 to the waste toner container 22. It is collected (A in FIG. 2). In this embodiment, a negative voltage (DC voltage) having the same polarity as the charging polarity of the toner at the time of development (that is, the toner of the toner image formed on the photosensitive drum 1) is applied from the high voltage power source 60 to the tension roller 10. Applied. With reference to FIG. 9, the effect of applying a negative voltage to the tension roller 10 will be described.

  FIG. 9A is a diagram showing a case where no voltage is applied to the tension roller 10. A positive charge Ep injected into the intermediate transfer belt 8 when the toner T is primarily transferred in the primary transfer step exists in the intermediate transfer belt 8, and the positive charge Ep causes the toner T and the intermediate transfer belt 8 to be transferred. Electrostatic adhesion force is generated.

  FIG. 9B is a diagram illustrating a case where a negative voltage is applied to the tension roller 10. A negative charge En is injected from the tension roller 10 to the intermediate transfer belt 8. Due to the negative charge En injected into the intermediate transfer belt 8, an electrostatic repulsive force is generated between the toner T and the intermediate transfer belt 8. Therefore, when a negative voltage is applied to the tension roller 10, the electrostatic adhesion force of the toner T to the intermediate transfer belt 8 is reduced as compared with the case where only the positive charge Ep exists. Therefore, the belt cleaning blade 21 can easily scrape off the toner T mechanically.

  Here, since a lot of negatively charged toner remains on the intermediate transfer belt 8 after jamming and calibration, the cleaning performance by the belt cleaning blade 21 is improved by reducing the electrostatic adhesion force. be able to. The action of the belt cleaning blade 21 is not electrostatic recovery but mechanical scraping. Therefore, there is no need for the operation of discharging the primarily collected toner to the brush as in the conventional cleaning method. Therefore, the print start waiting time does not increase for that purpose.

  On the other hand, fine irregularities may be present on the surface of the intermediate transfer belt 8 due to the cause of manufacturing or the attachment of foreign matter. In the portion with minute irregularities, the adhesion between the belt cleaning blade 21 and the intermediate transfer belt 8 may not be sufficient, and slip-through toner that passes through the belt cleaning blade 21 is likely to occur (in FIG. 2). B). More specifically, slip-through toner is likely to occur at the base of the convex portion (FIG. 8A), the inside of the concave portion (FIG. 8B), and the like. Since the irregularities on the surface of the intermediate transfer belt 8 are minute, the height of the toner layer is usually about one layer.

  If the slip-through toner is left as it is, cleaning failure occurs. For this reason, the slip-through toner is charged by the conductive brush 23 disposed on the downstream side in the moving direction of the intermediate transfer belt 8, and in the present embodiment, it is reversely transferred to the photosensitive drum 1Y and collected in the first image forming unit PY. To do.

  Here, a roller-like member (conductive roller) can be used as a charging member as a charging unit for charging the toner on the intermediate transfer belt 8. However, a brush-like member (conductive brush) is more preferable in that it follows the unevenness of the surface of the intermediate transfer belt 8 flexibly.

  When passing through the conductive brush 23, the slip-through toner is charged to a positive polarity having a polarity opposite to the charging polarity of the toner during development by a negative voltage applied to the tension roller 10 from the high-voltage power supply 60. . Thus, a positive charge suitable for realizing electrostatic cleaning is imparted to the slip-through toner (C in FIG. 2). In order to apply a positive charge suitable for electrostatic cleaning almost uniformly to the toner, the negative voltage value applied to the conductive brush 23 is the absolute value of the discharge threshold (-1.5 to −2 kV) or higher.

  Here, the discharge threshold (discharge start voltage) is obtained as follows. FIG. 10 schematically shows the results of current measurement when the bias applied to the tension roller 10 is changed. The horizontal axis represents the applied voltage (V) (negative polarity in this example. The absolute value increases as it goes to the right), and the vertical axis represents the measured current (μA). This current is a current that flows between the conductive brush 21 and the intermediate transfer belt 8. As shown in FIG. 10, the voltage-current relationship between the conductive brush 23 and the intermediate transfer belt 8 increases substantially linearly until the applied voltage exceeds a predetermined value. However, the current increases rapidly from the vicinity of the predetermined value (in the present embodiment, -1.5 kV to -2 kV). This is presumably because the discharge starts between the surface of the conductive brush 23 and the surface of the intermediate transfer belt 8 and the current flowing between the conductive brush 23 and the intermediate transfer belt 8 increases rapidly. The voltage in the change region (the predetermined value) is called a discharge threshold (discharge start voltage).

  In this embodiment, the slip-through toner to which a positive charge is applied is reversely transferred to the photosensitive drum 1Y by the positive voltage applied to the primary transfer roller 6Y in the first image forming unit PY. Thereafter, the slip-through toner reversely transferred onto the photosensitive drum 1Y is collected by the drum cleaner 6Y. When the slip-through toner is a secondary transfer residual toner, after a positive charge is applied, it is reversely transferred to the photosensitive drum 1Y during the next primary transfer step (simultaneous transfer cleaning).

  As described above, in this embodiment, the belt cleaning blade 21 is arranged on the upstream side in the moving direction of the intermediate transfer belt 8, and a negative voltage is applied to the tension roller 10 to transfer the negative toner and the intermediate transfer belt. The electrostatic adhesion force with the belt 8 is reduced. Thereby, most of the toner on the intermediate transfer belt 8 can be scraped off by the belt cleaning blade 21, and the amount of slip-through toner can be sufficiently reduced. Therefore, it is not necessary to discharge the primarily collected toner to the brush as in the conventional cleaning method, and it is possible to reduce the print start waiting time.

  In some cases, after jamming or calibration, the amount of toner remaining on the intermediate transfer belt 8 increases, the amount of slip-through toner increases, and the height of the toner becomes higher than that of one toner layer. obtain. Even in such a case, the conductive brush 23 can be charged at the same time while physically passing through the toner to make it substantially higher. Therefore, it is possible to give a positive charge suitable for realizing electrostatic cleaning to the toner.

5. Next, a preferable range of the resistance value Rb of the conductive brush 23 in this embodiment will be described in detail.

  As shown in the schematic diagram of FIG. 5, in this embodiment, a current controlled to have a constant current of 10 μA is supplied to the conductive brush 23 by a high-voltage power supply 60. As a current path, a current flows from the conductive brush 23 to the tension roller 10 via the intermediate transfer belt 8.

The resistance value Rb of the conductive brush 23 is preferably sufficiently smaller than the resistance value Ri of the intermediate transfer belt 8. Here, in order to obtain the desired effect described in detail below, typically, when the resistance value Ri is 10 to 10,000,000 times the resistance value Rb, the resistance value Rb is the resistance value Ri. Smaller than that. More preferably, the resistance value Ri is 100,000 times to 10,000,000 times the resistance value Rb. As described above, in the present embodiment, Ri = 6.2 × 10 ^{5 to} 6.2 × 10 ⁷ Ω (≈1 × 10 ⁶ to 10 ⁸ Ω), and in this case, Rb = 1 × 10 ^1. A range of -10 ⁵ Ω is preferred.

  FIG. 6 shows the above-described current path as an equivalent circuit. The conductive brush 23 is regarded as a resistor 23b having a resistance value Rb [Ω], and the intermediate transfer belt 8 is regarded as a resistor 8b having a resistance value Ri [Ω]. The state in which a current is supplied from the high-voltage power supply 60 by constant current control of I [A] is shown.

  At this time, the potential difference Vb [V] applied to the resistor 23b indicating the conductive brush 23 is Vb = Rb × I, and the potential difference Vi [V] applied to the resistor 8b indicating the intermediate transfer belt 8 is Vi = Ri × I. The potential difference depends on the resistance value. As a result, as in this embodiment, when the resistance value Rb of the conductive brush 23 is sufficiently smaller than the resistance value Ri of the intermediate transfer belt 8 (Ri >> Rb), the potential difference Vb of the conductive brush 23 is set to the intermediate transfer belt. The potential difference Vi of 8 can be made sufficiently smaller.

  FIG. 7A schematically shows a state in which the passing-through toner is charged by the conductive brush 23 in this embodiment. Since a potential difference equal to or greater than the discharge threshold is generated from the power supply 60 between the conductive brush 23 and the tension roller 10, the slipping-through toner having both positive and negative polarities is positively charged by the discharge in the conductive brush 23. Be charged to the nature. Most of the negative slip-through toner is reversed in polarity by discharge in the conductive brush 23 and becomes positive. However, a part of the negative slip-through toner is electrostatically attached to the conductive brush 23. In this embodiment, since the potential difference Vb of the conductive brush 23 is small, toner adhesion can be concentrated only on the hair ends of the conductive fibers 23 a that are close to the intermediate transfer belt 8. As a result, the amount of toner adhering to the conductive brush 23 can be minimized, and the toner passing through the end of the life of the conductive brush 23 can be discharged without discharging the toner. Charging).

Here, if the resistance value Rb of the conductive brush 23 is lower than 1 × 10 ¹ Ω, a large current is likely to flow, and it becomes difficult to perform constant current control from the viewpoint of output accuracy of the high-voltage power supply 60. On the other hand, when the resistance Rb of the conductive brush 23 is higher than 1 × 10 ⁵ Ω, since the potential difference Vb of the conductive brush 23 is large, as shown in FIG. It will be collected to the base of the sexual fiber 23a. As a result, even when the belt cleaning blade 21 is arranged upstream to reduce the amount of slipping toner, the amount of slipping toner collected in the conductive brush 23 increases when the conductive brush 23 is near the end of its life. Therefore, the resistance value of the conductive brush 23 increases. If the voltage applied to the conductive brush 23 is increased by an amount corresponding to the increase in the resistance value, the output range limit of the high-voltage power supply 60 may be exceeded, and it becomes difficult to charge the slipping toner positively. Therefore, it is necessary to discharge the toner collected in the conductive brush 23, and the print start waiting time may be long.

  Next, the result of checking the difference in the amount of toner collected in the conductive brush 23 by changing the resistance value Rb of the conductive brush 23 will be described.

  Here, the toner to be removed on the intermediate transfer belt 8 is larger than the secondary transfer residual toner, and the amount of toner collected in the conductive brush 23 by the cleaning of the intermediate transfer belt 8 after calibration is confirmed. did. In each experiment, the configuration and operation of the image forming apparatus are substantially the same except that the resistance value Rb of the conductive brush 23 is different. The results are shown in Table 1.

In Experiment 1, the resistance value Rb of the conductive brush 23 is 1 × 10 ² Ω, the resistance value Ri of the intermediate transfer belt 8 is 1 × 10 ⁷ Ω, and the resistance value Rb is sufficiently smaller than the resistance value Ri (Rb << Ri). Therefore, when constant current control of 10 μA is performed by the high-voltage power supply 60, the potential difference Vb of the conductive brush 23 becomes (1 × 10 ² Ω) × (10 μA) = 0.001V, and the conductive brush 23 hardly drops in voltage. Accordingly, as shown in FIG. 7A, since the potential difference Vb of the conductive brush 23 is small, the toner adheres only to the hair ends of the conductive fibers 23a that are close to the intermediate transfer belt 8. As a result, it was not necessary to discharge the toner adhering to the conductive brush 23 throughout the lifetime of the conductive brush 23. Therefore, it is possible to sufficiently reduce the print start waiting time after calibration.

In Experiment 2, the resistance value Rb of the conductive brush 23 is 1 × 10 ³ Ω, the resistance value Ri of the intermediate transfer belt 8 is 1 × 10 ⁷ Ω, and the resistance value Rb is sufficiently smaller than the resistance value Ri (Rb << Ri). Therefore, when constant current control of 10 μA is performed by the high-voltage power supply 60, the potential difference Vb of the conductive brush 23 becomes (1 × 10 ³ Ω) × (10 μA) = 0.01 V, and the voltage is hardly dropped by the conductive brush 23. Thus, as in Experiment 1, it was not necessary to discharge the toner attached to the conductive brush 23 throughout the lifetime of the conductive brush 23. Therefore, it is possible to sufficiently reduce the print start waiting time after calibration.

In Experiment 3, the resistance value Rb of the conductive brush 23 was 1 × 10 ⁷ Ω, the resistance value Ri of the intermediate transfer belt 8 was 1 × 10 ⁷ Ω, and the resistance value Rb was equivalent to the resistance value Ri (Ri ≦ Rb). Therefore, when a constant current control of 10 μA is performed by the high voltage power supply 60, the potential difference Vb of the conductive brush 23 becomes as large as 100V. As a result, the force for electrostatically attracting the toner is increased, so that the toner adheres to the base of the conductive fiber 23a, and the toner discharging operation is necessary after the calibration. Therefore, there is a possibility that the print start waiting time after calibration becomes long. However, even in this case, since the toner collected in the conductive brush 23 can be reduced by the action of the belt cleaning blade 21, the print start waiting time required for the discharge of the toner from the conductive brush 23 is smaller than that in the prior art. It's short. Also in this case, it is not necessary to discharge the toner from the conductive brush 23 depending on the cleaning of the secondary transfer residual toner.

In Experiment 4, the resistance value Rb of the conductive brush 23 is 1 × 10 ⁸ Ω, the resistance value Ri of the intermediate transfer belt 8 is 1 × 10 ⁷ Ω, and the resistance value Rb is larger than the resistance value Ri (Ri ≦ Rb). ). Therefore, when the constant current control of 10 μA is performed by the high-voltage power supply 60, the potential difference Vb of the conductive brush 23 becomes as large as 1 kV. As a result, the force for electrostatically attracting the toner is increased in the same manner as in Example 3, so that the toner adheres to the root of the conductive fiber 23a, and the toner discharging operation is necessary after the calibration. Therefore, there is a possibility that the print start waiting time becomes long. However, even in this case, since the toner collected in the conductive brush 23 can be reduced by the action of the belt cleaning blade 21, the print start waiting time required for the discharge of the toner from the conductive brush 23 is smaller than that in the prior art. It's short.

  As described above, according to the present embodiment, the belt cleaning blade 21 is disposed on the upstream side, and the toner on the intermediate transfer belt 8 that is negatively charged by applying a negative voltage to the tension roller 10 and the intermediate transfer. The electrostatic adhesion force with the belt 8 is reduced. Thereby, the cleaning property with the belt cleaning blade 21 is improved, and most of the toner on the intermediate transfer belt 8 can be scraped off. Further, a small amount of slipping toner is charged by using a low resistance conductive brush 23 disposed on the downstream side. As a result, the amount of toner collected by the conductive brush 23 can be minimized, and typically, it is not necessary to discharge the toner, and the print start waiting time can be greatly reduced.

Other Embodiments Although the present invention has been described with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiment, the toner is not discharged from the brush. However, this may be performed, for example, after calibration. Even in this case, according to the present invention, it is possible to sufficiently reduce the frequency of toner discharge, the time required for toner discharge, and the like, thereby sufficiently reducing the print start standby time. For example, the toner discharging operation from the conductive brush may be performed as follows. That is, a negative polarity toner collected in the conductive brush is applied to the tension roller by applying a voltage having a polarity opposite to that during normal cleaning (positive polarity in the case of the above embodiment) from the high voltage power source. Transfer onto the transfer belt. For example, the toner discharged from the conductive brush is transferred from the intermediate transfer belt to the photosensitive drum by applying a voltage having a polarity opposite to that in the primary transfer process to the primary transfer roller of the first image forming unit. And collect with a drum cleaner.

  In the above-described embodiment, the counter member is one of a plurality of rollers that stretch the intermediate transfer belt. However, the present invention is not limited to this. The opposing member may be a roller provided separately from the roller for stretching the intermediate transfer belt. Further, the facing member is not limited to a roller-like member, and may be in contact with the intermediate transfer member and slid, for example, as long as it has the same action as the facing member in the above-described embodiment. It may be a member in any form such as a block shape or a plate shape.

  In the above-described embodiments, the intermediate transfer member is described as an intermediate transfer belt formed of an endless belt, but the present invention is not limited to this. For example, it may be an intermediate transfer drum formed into a drum shape by stretching a sheet made of the same material as that of the intermediate transfer belt in the above-described embodiment on a frame.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 5 Primary transfer roller 8 Intermediate transfer belt 11 Secondary transfer roller 21 Belt cleaning blade 23 Conductive brush 60 High voltage power supply

Claims (12)

An image carrier for carrying a toner image;
An intermediate transfer member, which is rotatable and for secondary transfer of a toner image primarily transferred from the image carrier in the primary transfer portion to a transfer material in the secondary transfer portion;
A contact member that contacts the intermediate transfer member downstream of the secondary transfer portion in the moving direction of the intermediate transfer member and scrapes off the toner on the intermediate transfer member as the intermediate transfer member moves;
A charging member that charges the toner on the intermediate transfer body upstream of the primary transfer portion and downstream of the contact member in the moving direction of the intermediate transfer body;
A facing member disposed at a position facing the contact member and the charging member across the intermediate transfer member;
A power source for applying a voltage to the opposing member;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the power source applies a voltage equal to or higher than a discharge threshold between the charging member and the intermediate transfer member to the facing member.   3. The image forming apparatus according to claim 1, wherein the power supply applies a voltage having the same polarity as a charging polarity of toner of a toner image formed on the image carrier to the facing member.   The image forming apparatus according to claim 1, wherein the contact member is a blade-shaped member.   The image forming apparatus according to claim 1, wherein the charging member is in contact with the intermediate transfer member.   The charging member charges the toner that has passed through a contact portion between the contact member and the intermediate transfer body while rubbing the intermediate transfer body as the intermediate transfer body moves. Item 6. The image forming apparatus according to Item 5.   The image forming apparatus according to claim 5, wherein an electric resistance of the charging member is smaller than an electric resistance of the intermediate transfer member at a portion where the charging member and the intermediate transfer member are in contact with each other. The electrical resistance of the charging member is 1 × 10 ¹ to 10 ⁵ Ω, and the electrical resistance of the intermediate transfer member at the portion where the charging member and the intermediate transfer member are in contact is 1 × 10 ⁶ to 10 ⁸ Ω. The image forming apparatus according to claim 7.   The image forming apparatus according to claim 1, wherein the charging member is a brush-like member.   The image forming apparatus according to claim 1, wherein the intermediate transfer member is an endless belt.   The image forming apparatus according to claim 10, wherein the facing member is one of a plurality of rollers that stretch the belt.   12. The image formation according to claim 1, wherein the toner charged by the charging member is transferred from the intermediate transfer member to the image carrier in the primary transfer portion. apparatus.

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