JP4497996B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus using an endless belt having an elastic layer as an intermediate transfer member.

  In an image forming apparatus such as a conventional copying machine or printer, an electrostatic recording method, an electrophotographic recording method, or the like is often used. For example, a toner image is formed on at least one photoconductive drum (image carrier), and the toner image is temporarily transferred onto the intermediate transfer member so that the toner images are sequentially overlapped, and then collectively onto a sheet. An intermediate transfer system that performs secondary transfer is known (see Patent Document 1). The intermediate transfer method has an advantage that stable image transfer to various sheets is possible compared to the multiple transfer method in which toner images of respective colors are sequentially transferred from the photosensitive drum to the sheet.

  A conventional intermediate transfer type image forming apparatus will be described with reference to FIG. The image forming apparatus shown in FIG. 4A includes a plurality of image forming units 90a to 90d, and forms toner images of respective colors on the photosensitive drums 91a to 91d. The toner image is primarily transferred onto the intermediate transfer belt 92 (intermediate transfer member) rotating in the direction of the arrow in a superimposed manner by primary transfer means 93a to 93d, and then secondarily transferred to the sheet all at once by the secondary transfer means 94. The toner image transferred to the sheet is permanently fixed by the fixing device 95.

  The intermediate transfer belt 92 is an endless belt member that is stretched around a plurality of rollers. The material is made of resin, and is usually formed of a film of resin material such as PVDF, polyimide, PET, or the like having a thickness of about 50 to 200 μm. Here, a cleaning device 96 is disposed downstream of the secondary transfer position in the rotation direction of the intermediate transfer belt 92. The cleaning device 96 includes an elastic blade 97, which cleans the transfer residual toner on the intermediate transfer belt 92 after the completion of the secondary transfer by scraping it off with the elastic blade 97 to prepare for the next image formation.

  Incidentally, an intermediate transfer belt is also known in which a rubber elastic layer is formed on the surface of a resin belt member (see Patent Document 2). In this case, the intermediate transfer belt has an elastic layer made of silicon rubber, urethane rubber or the like having a thickness of about 0.1 to 1 mm on the surface of a substrate such as PVDF, polyimide, or PET. According to the intermediate transfer belt formed of such a rubber elastic material, the nip formed by contact with the photosensitive drum is stabilized, and the image quality can be further stabilized. In addition, since the elastic layer is deformed and follows the surface of the sheet, the toner image can be stably transferred even when a sheet having an uneven surface is used.

  However, since the intermediate transfer belt having an elastic layer on the surface is softer than the resin intermediate transfer belt and inferior in wear resistance, an elastic blade 97 as shown in FIG. It cannot be cleaned. Therefore, as shown in FIG. 4B, there is a method of electrostatically removing toner using a cleaning device 98 provided with a fur brush 99 (see Patent Document 3).

JP 2000-293044 A JP 2000-369360 A JP 2000-229344 A

  However, an external additive such as a charge control agent added to the toner has a small particle size and a strong adsorbing force to the intermediate transfer belt. Therefore, depending on the cleaning device using the fur brush, it is difficult to completely remove it electrostatically, which may contaminate the intermediate transfer belt 92 and cause image defects.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus that can effectively remove toner and external additives attached on an intermediate transfer member having an elastic layer and can always form a high-quality image.

In order to solve the above problems, a typical configuration of an image forming apparatus according to the present invention includes an image carrier that carries a toner image and a rotatable intermediate transfer that carries a toner image transferred from the image carrier. A primary transfer unit that transfers the toner image to the intermediate transfer member, a secondary transfer unit that forms a secondary transfer unit that transfers the toner image on the intermediate transfer member to a recording material, and the intermediate transfer member. A brush member disposed downstream of the secondary transfer portion and upstream of the image carrier in the rotation direction of the image transfer member, and for removing transfer residual toner on the intermediate transfer body; A cleaning web disposed downstream of the brush member and upstream of the image carrier, contacting the intermediate transfer member to remove external additives added to the toner, and the cleaning web Inside In an image forming apparatus having a contact / separation unit for contacting / separating to a transfer body, when the image forming operation is interrupted due to an abnormality, the intermediate state is maintained while the cleaning web is separated from the intermediate transfer body. The transfer member is rotated to remove the toner on the intermediate transfer member, and when the toner density on the intermediate transfer member is reduced to a concentration that can be collected by the brush member, the cleaning webs separated from each other are removed from the intermediate transfer member. It is characterized by being brought into contact with a transfer body.

  According to the image forming apparatus of the present invention, the intermediate transfer member includes the first cleaning unit that performs cleaning using a fur brush and the second cleaning unit that performs cleaning using a web. Therefore, the secondary transfer residual toner and the external additive can be cleaned from the intermediate transfer member, and high-quality image formation is always possible.

  Further, according to the present invention, the second cleaning unit is provided with the separation / contact unit, and the intermediate transfer is performed when an amount (concentration) of toner exceeding the recovery capability of the first cleaning unit is supplied as in the case of jam recovery. Separate from the belt. As a result, it is possible to prevent toner filming from occurring in the nip between the intermediate transfer belt and the second cleaning unit, and high-quality image formation can always be achieved.

  Embodiments of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to the present embodiment.

  An image forming apparatus 1 shown in FIG. 1 is a color printer using an electrophotographic system, and has a plurality of image forming units 10a to 10d arranged in parallel. The image forming units 10a to 10d all have a common configuration, and form yellow, magenta, cyan, and black images, respectively. Photosensitive drums 11a to 11d as image bearing members are pivotally supported at the centers thereof and are driven to rotate by a driving means (not shown). The photosensitive drums 11a to 11d are given a uniform charge amount on the surface by a charging means (not shown), and then scanned and exposed by a laser beam modulated in accordance with the recording image signal by the laser scanner units 12a to 12d. As a result, an electrostatic latent image is formed. Further, the electrostatic latent image is visualized as a toner image by developing units 13a to 13d each containing developer of four colors of yellow, magenta, cyan and black (hereinafter referred to as toner). The toner images on the photosensitive drums 11a to 11d are transferred to the intermediate transfer belt 16 with a bias applied by primary transfer rollers 15a to 15d disposed at positions facing the intermediate transfer belt 16 (intermediate transfer body). Drum cleaning devices 14a to 14d are disposed downstream of the primary transfer positions of the photosensitive drums 11a to 11d, and the surfaces of the photosensitive drums 11a to 11d are cleaned by scraping off the toner with a cleaning blade. Through the process described above, image formation with each toner is sequentially transferred onto the intermediate transfer belt 16.

  The sheets S stored in the feeding unit 30 are held at a predetermined feeding position by the lifter plate 31 and fed one by one by the feeding / separating unit 32. Further, the sheet S is conveyed by the feeding / conveying unit 33, subjected to registration adjustment by the registration unit 34, and then conveyed to the secondary transfer unit in synchronization with the toner image on the intermediate transfer belt 16.

  In the secondary transfer portion, a bias is applied to the secondary transfer outer roller 35, and the toner image on the intermediate transfer belt 16 is transferred to the sheet S. Further, the sheet S is conveyed to the fixing unit 37 by the pre-fixing conveyance unit 36 and the toner image is fixed on the sheet S. Toner, external additives and the like remaining on the intermediate transfer belt 16 after the secondary transfer are removed by a first cleaning device 50 and a second cleaning device 60 described later.

  In the case of the single-sided printing process, the sheet S is conveyed by the discharge unit 38 and discharged to the discharge tray 39. In the case of the double-sided printing process, the sheet S is conveyed to the reversing unit 40, the front and back are reversed, and then conveyed again to the feeding and conveying unit 33 and the resist unit 34 via the double-sided conveying unit 41, and the back side image is transferred The toner is fixed and discharged to a discharge tray 39.

  Next, the intermediate transfer unit of the image forming apparatus 1 will be described in detail.

  The intermediate transfer belt 16 has a structure in which a resin endless belt is used as a base material and the surface thereof is covered with an elastic rubber layer. Resin materials such as polyimide, PET, and PVDF are used for the material of the base material. Further, silicon rubber, urethane rubber or the like is used as the material of the elastic layer. With this elastic layer, a stable transfer nip is formed in the primary transfer portion and the secondary transfer portion, and high-quality toner images can be transferred to various sheets.

  The intermediate transfer belt 16 is stretched around a tension roller 17, a driving roller 18, and a secondary transfer inner roller 19, and given tension is applied by the tension roller 17. The driving roller 18 is rotationally driven by a driving means (not shown), and the intermediate transfer belt 16 is driven in the direction of the arrow in FIG. In the vicinity of the intermediate transfer belt 16, toner patch reading means 20 for reading a density measurement patch is provided.

  The object of the present invention is to remove the toner and the external additive adhering to the intermediate transfer member having an elastic layer. However, as described in the above-mentioned problem of the present invention, the external additive such as a charge control agent added to the toner has a small particle size and a strong adsorption force to the intermediate transfer belt. For this reason, it is difficult to completely remove electrostatically depending on a cleaning device using a fur brush.

  Therefore, in the image forming apparatus 1 according to the present embodiment, in order to clean the intermediate transfer belt 16, a first cleaning device 50 (first cleaning means) using a fur brush and a second cleaning device using a web are used. 60 (second cleaning means). A cleaning web using a non-woven fabric or the like can effectively wipe off the external additive having the above characteristics. However, when the toner enters the nip between the intermediate transfer belt 16 and the cleaning web, the toner compressed in the nip is fixed to the intermediate transfer belt 16 to form a film. When this so-called filming occurs, the operational characteristics of the intermediate transfer belt 16 change, so that it is impossible to form an image as expected, resulting in an image defect.

  Therefore, as shown in the drawing, the first cleaning device 50 is disposed downstream of the secondary transfer position in the rotation direction of the intermediate transfer belt 16, and further downstream of the second cleaning position and upstream of the photosensitive drums 11a to 11d. A device 60 is arranged. That is, the first cleaning device 50 removes the toner first, and then the second cleaning device 60 removes the external additive. As a result, the surface of the intermediate transfer belt 16 is prevented from being contaminated, and high-quality image formation is always possible.

  FIG. 2 is a diagram for explaining the first and second cleaning means, and FIG. 3 is a diagram for explaining the operation of the second cleaning means. The first cleaning device 50 includes two sets of a fur brush 51, a counter roller 21, a bias roller 52, and a cleaning blade 53. The facing roller 21 is disposed on the inner surface side of the intermediate transfer belt 16, and a fur brush 51 is disposed on the outer surface side facing the roller. The fur brush 51 has conductive fibers implanted on the surface of the metal shaft, and is disposed at a position where the conductive fibers are in contact with the surface of the intermediate transfer belt 16, so that the fur brush 51 is in a counter direction with respect to the traveling direction of the intermediate transfer belt 16. It is driven to rotate (ie, the contact site advances in the opposite direction). Further, the metal bias roller 52 is disposed at a position in contact with the conductive fibers of the fur brush 51 and is driven to rotate in the forward direction with respect to the fur brush 51.

  A cleaning bias is applied to the bias roller 52 by a bias applying means (not shown), and the secondary transfer residual toner on the intermediate transfer belt 16 is electrostatically moved sequentially from the intermediate transfer belt 16 to the fur brush 51 and the bias roller 52. To do. The toner adhering to the surface of the bias roller 52 is scraped off by the cleaning blade 53. Cleaning biases having opposite polarities are applied to the two bias rollers 52. For this reason, the toner on the surface of the intermediate transfer belt 16 is electrostatically attracted to the fur brush 51 to which a positive or negative cleaning bias is applied regardless of the charging polarity, and is cleaned from the surface of the intermediate transfer belt 16.

  In the second cleaning device 60, a non-woven cleaning web 61 is wound around a web roller 63 from an attachment roller 62 and stretched around a take-up roller 64. The cleaning web 61 is brought into contact with the intermediate transfer belt 16 at a position facing the driving roller 18, and cleaning is performed by rubbing the surface of the intermediate transfer belt 16. The take-up roller 64 is rotationally driven by a driving means (not shown), and the cleaning web 61 is taken up, whereby new cleaning webs 61 are sequentially supplied to the contact portion of the intermediate transfer belt 16.

  The second cleaning device 60 is supported so as to be rotatable about a rotation center 65, and is configured to be rotatable by a contact / separation means 66 such as a solenoid. That is, the cleaning web 61 is brought into contact with the intermediate transfer belt 16 as shown in FIG. 2 or separated as shown in FIG. . In addition to the solenoid, the separation / contact means 66 may be driven using a motor, or may be configured to be separated and connected by parallel movement instead of rotation.

  Here, since the toner image supplied to the first cleaning device 50 at the time of normal image formation is a transfer residual toner after the secondary transfer, the toner image has a low density and can be substantially cleaned by the first cleaning device 50. However, sometimes, the first cleaning device 50 is supplied with untransferred high-density toner, and the toner concentration may exceed the recovery capability of the first cleaning device 50. This is because, unlike a blade cleaning method in which a nip is formed by a rubber blade and clogs toner, a cleaning method in which toner is electrostatically recovered using a fur brush has a limit on the recoverable toner concentration.

  For this reason, when high-concentration toner (mainly untransferred toner) is supplied, the first cleaning device 50 cannot completely clean the toner, and the toner that has passed through the first cleaning device 50 is removed from the second cleaning device. It will rush into 60. Then, as described above, the toner that has entered the nip between the intermediate transfer belt 16 and the cleaning web 61 is compressed in the nip, causing filming, which may cause image defects.

  Therefore, in this embodiment, when a toner image having a density exceeding the recovery capability is supplied to the first cleaning device 50, the control means (not shown) of the image forming apparatus 1 first operates the separation / contact means 66. Thus, the second cleaning device 60 is separated from the intermediate transfer belt 16. Then, the intermediate transfer belt 16 is driven to rotate, and the first cleaning device 50 is operated to collect the transfer residual toner. Further, by applying a bias having a polarity opposite to that at the time of image formation to the photosensitive drums 11a to 11d, the transfer residual toner that has passed through the first cleaning device 50 is transferred to the photosensitive drums 11a to 11d. The toner transferred onto the photosensitive drums 11a to 11d is collected by the drum cleaning devices 14a to 14d.

  The toner cleaning process by the first cleaning device 50 and the drum cleaning devices 14a to 14d is repeated according to the toner concentration. Then, after the toner concentration supplied to the first cleaning device 50 is reduced to a level that can be collected by the first cleaning device 50, the control means operates the separation / contact means 66 to rotate the second cleaning device 60. The cleaning web 61 is brought into contact with the intermediate transfer belt 16. Whether or not the toner concentration has been reduced to a level that can be collected by the first cleaning device 50 can be determined by the number of rotations of the intermediate transfer belt 16 relative to the first cleaning device 50. It can also be determined by detecting the actual toner density by using it.

  Examples of the case where a toner image having a density exceeding the recovery capability is supplied to the first cleaning device 50 includes a case where the operation is interrupted due to a jam or the like during image formation, or a case where a density measurement patch is formed. . When a jam occurs during the image forming operation, the image forming apparatus 1 stops the operation and displays a jam processing message to the user. When the user removes all sheets remaining in the machine such as jammed paper, the jam recovery operation is started. At this time, a toner image before the secondary transfer is attached on the intermediate transfer belt 16 from the primary transfer portion to the secondary transfer portion of each color. Note that the present invention is not limited to these cases, and if other high-concentration toners are supplied, the above-described control can provide the benefits of the present invention. In addition, a toner density detecting means (not shown) is arranged on the downstream side of the secondary transfer unit and the upstream side of the first cleaning device 50 to constantly monitor the toner density on the intermediate transfer belt 16, thereby controlling the cleaning as needed. It is also possible to carry out.

  With the above configuration, even when a large amount of untransferred toner is supplied to the first cleaning device 50 using a fur brush, the cleaning web 61 of the second cleaning device 60 and the intermediate transfer belt 16 It is possible to prevent a large amount of toner from entering between them, and to prevent toner filming on the intermediate transfer belt 16 from occurring.

  The present invention can be used in an image forming apparatus using an endless belt having an elastic layer as an intermediate transfer member.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure explaining the 1st and 2nd cleaning means. It is a figure explaining operation | movement of a 2nd cleaning means. It is a diagram illustrating a conventional intermediate transfer type image forming apparatus.

Explanation of symbols

S: Sheet 1 ... Image forming apparatus
10a to 10d Image forming unit
11a to 11d ... photosensitive drum
12a-12d ... Laser scanner unit
13a to 13d ... Development unit
14a-14d ... Drum cleaning device
15a to 15d ... Primary transfer roller
16 ... Intermediate transfer belt
17… Tension roller
18… Drive roller
19 ... Secondary transfer inner roller
20 ... Toner patch reading means
21… Opposite roller
30… Feeding unit
31 ... Lifter plate
32… Feed separation unit
33… Feeding and conveying unit
34… Registration unit
35 ... Secondary transfer outer roller
36… Conveyor unit before fixing
37… Fusing unit
38… discharge unit
39… discharge tray
40… Reversing unit
41… Double-sided transport unit
50 ... 1st cleaning device
51… Fur brush
52… Bias roller
53… Cleaning blade
60… second cleaning device
61… cleaning web
62… Mounting roller
63… Web Roller
64… take-up roller
65… center of rotation
66… Separation means
90a to 90d Image forming unit
91a to 91d ... photosensitive drum
92 ... Intermediate transfer belt
93a to 93d ... primary transfer means
94… Secondary transfer means
95 ... Fixing device
96… Cleaning device
97… Elastic blade
98… Cleaning device
99… Fur brush

Claims (4)

An image carrier that carries a toner image, a rotatable intermediate transfer member that carries a toner image transferred from the image carrier, a primary transfer unit that transfers the toner image to the intermediate transfer member, and the intermediate transfer A secondary transfer means for forming a secondary transfer portion for transferring the toner image on the body to a recording material; and a downstream side of the secondary transfer portion in the rotational direction of the intermediate transfer body and an upstream side of the image carrier. A brush member for removing transfer residual toner on the intermediate transfer member, and a downstream side of the brush member in the rotational direction and an upstream side of the image carrier, in contact with the intermediate transfer member, and a cleaning web for removing the external additive which is added to the toner, the image forming apparatus odor having a disjunction means for the disjunction of said cleaning web with respect to said intermediate transfer member ,
When returning after the image forming operation is interrupted due to an abnormality, the intermediate transfer member is rotated while the cleaning web is separated from the intermediate transfer member to remove the toner on the intermediate transfer member. An image forming apparatus, wherein the cleaning web that is separated is brought into contact with the intermediate transfer member when the toner concentration on the transfer member is reduced to a concentration that can be collected by the brush member.   A density detecting unit that detects a density of the toner image on the intermediate transfer body, and the density detecting unit detects the toner density on the intermediate transfer body at the time of a return operation; 2. The image forming apparatus according to claim 1, wherein the image forming apparatus is detected to have fallen to a minimum.   3. The image forming apparatus according to claim 2, wherein the density detection unit is disposed downstream of the secondary transfer unit and upstream of the brush member in the rotation direction.   4. The primary transfer unit is controlled so as to transfer the toner on the intermediate transfer member toward the image carrier during the toner removal operation. 5. Image forming apparatus.

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