JP5446240B2 - Transfer device and image forming apparatus having the same - Google Patents

Description

  The present invention relates to a transfer device and an image forming apparatus including the transfer device.

JP 2004-333521 A

  2. Description of the Related Art Conventionally, color image forming apparatuses such as color copying machines and color printers to which electrophotography is applied include a plurality of colors corresponding to each color such as yellow (Y), magenta (M), cyan (C), and black (K). A primary transfer device that includes an image forming unit and that is sequentially formed on the photosensitive drum of each image forming unit is temporarily transferred in multiple layers onto an endless intermediate transfer belt by a primary transfer device disposed opposite to each photosensitive drum. After that, the toner images of each color transferred in a multiple manner onto the intermediate transfer belt are collectively transferred onto a recording medium by a secondary transfer device, and then these toner images are heated and pressed to form a recording medium. 2. Description of the Related Art A so-called intermediate transfer type image forming apparatus configured to form a color image by fixing on top is known (for example, see Patent Document 1).

  Here, Patent Document 1 discloses an image forming apparatus in which a charge removal member is disposed in a prenip region upstream of a secondary transfer portion where a secondary transfer roll and an intermediate transfer belt are in contact with each other.

  An object of the present invention is to provide a transfer device capable of suppressing gap discharge in the vicinity of the upstream side of the transfer portion, and an image forming apparatus including the transfer device.

The transfer device according to claim 1 is a rotatable endless intermediate transfer belt on which a toner image is primarily transferred on a surface thereof, and a secondary transfer portion that is in pressure contact with the intermediate transfer belt. A next transfer roll;
An opposing roll disposed opposite to the secondary transfer roll across the intermediate transfer belt,
A secondary transfer electric field is formed by a potential difference between the secondary transfer roll and the counter roll,
A tension roll is provided inside the intermediate transfer belt on the upstream side of the counter roll, and the tension roll and the counter roll have an endless shape having a smaller volume resistivity than the intermediate transfer belt. opposed belts are passed over, and the, in the region between the tension roll the opposing roll, the opposing belt is arranged so as to be in close contact with the inner surface of the intermediate transfer belt, further, the The entry position of the recording medium into the secondary transfer portion is set inside an area where the opposed belt and the intermediate transfer belt are in close contact with each other.

According to a second aspect of the present invention, in the configuration of the first aspect , the inner surface of the intermediate transfer belt and the surface of the stretching roll are in surface contact along the rotation direction of the intermediate transfer belt. It is characterized by.

According to a third aspect of the present invention, in the transfer device according to the first or second aspect , the intermediate transfer belt contains a conductive polymer and / or an ion conductive conductive agent as a conductive agent, and has a volume resistance. The rate is 10 ¹⁰ to 10 ¹⁴ Ω · cm, whereas the volume resistivity of the facing belt is 10 ⁸ to 10 ¹³ Ω · cm.

An image forming apparatus according to a fourth aspect includes the transfer apparatus according to any one of the first to third aspects and an image forming unit that forms an image on a recording medium.

According to the first aspect of the present invention, gap discharge in the vicinity of the upstream side of the secondary transfer portion can be suppressed, and the occurrence of scaly image defects can be effectively prevented.

According to the second aspect of the present invention, the contact state between the opposing belt and the intermediate transfer belt can be stably maintained.

According to the third aspect of the present invention, with respect to the intermediate transfer belt formed of a material that easily generates electric discharge, the opposed belt that can stably suppress gap discharge between the opposed roll and the intermediate transfer belt. Can be provided.

According to the fourth aspect of the present invention, any of the above transfer devices can be suitably applied to an image forming apparatus.

  An embodiment of the present invention will be described below with reference to the drawings.

  First, a schematic configuration of an image forming apparatus to which the present invention can be applied will be described with reference to FIG. Here, FIG. 1 is a schematic diagram showing a schematic configuration of a tandem type color electrophotographic copying machine to which the present invention is applicable. Although this tandem type color electrophotographic copying machine is provided with an image reading device, the image forming device is not provided with an image reading device and is based on image data output from a personal computer (not shown) or the like. It may be a color printer, a facsimile, or the like that forms an image.

  In FIG. 1, reference numeral 1 denotes a main body of a tandem type color electrophotographic copying machine. The color electrophotographic copying machine main body 1 has an image reading device (IIT) for reading an image of a document 2 at an upper portion on one end side thereof. : Image Input Terminal) 4, and the color electrophotographic copying machine main body 1 includes image data output from the image reading device 4 or a personal computer (not shown), or a telephone line or LAN. Image processing apparatus (IPS: Image Processing System) 12 that performs predetermined image processing on the image data sent via the image data, and image data that has been subjected to image processing predetermined by the image processing apparatus 12 Based image output device (IOT: Image Output Terminal) 100 and is disposed.

  In the image reading device 4, an image of the original document 2 pressed onto the platen glass 5 by the platen cover 3 or an original document automatically conveyed by an automatic document conveying device (not shown) is read. The image reading device 4 illuminates a document 2 placed on a platen glass 5 with a light source 6, and reflects a reflected light image from the document 2 from a full-rate mirror 7, half-rate mirrors 8 and 9, and an imaging lens 10. The image reading element 11 made of a CCD or the like is scanned and exposed through a reduction optical system, and the image material 11 reflects the color material reflected light image of the original 2 by a predetermined dot density (for example, 16 dots / mm). ).

  The color material reflected light image of the document 2 read by the image reading device 4 is subjected to image processing as, for example, document reflectance data of three colors of red (R), green (G), and blue (B) (8 bits each). The image processing device 12 sends the reflectance data of the document 2 in advance such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color / moving editing, etc. Defined image processing is performed.

  The image data that has been subjected to predetermined image processing by the image processing apparatus 12 as described above is four colors of yellow (Y), magenta (M), cyan (C), and black (K) (8 bits each). As described below, yellow (Y), magenta (M), cyan (C), and black (K) image forming units 13Y, 13M, The images are sent to 13C and 13K exposure devices 14Y, 14M, 14C, and 14K, and the exposure devices 14Y, 14M, 14C, and 14K use laser light LB in accordance with the original color material gradation data of a predetermined color. Exposure is performed.

  Inside the tandem color electrophotographic copying machine main body 1, as described above, four image forming units 13Y, 13M, yellow (Y), magenta (M), cyan (C), and black (K) are provided. 13C and 13K are arranged in parallel at regular intervals in the horizontal direction.

  These four image forming units 13Y, 13M, 13C, and 13K are all configured in the same manner, and are roughly classified as photosensitive drums as image carriers that are rotationally driven at a predetermined speed along the direction of arrow A. 15 and a scorotron 16 as a charger for uniformly charging the surface of the photosensitive drum 15, and a laser beam corresponding to the image information of each color is scanned and exposed on the surface of the photosensitive drum 15 to form an electrostatic latent image. For example, a developing device 17 for developing the electrostatic latent image formed on the photosensitive drum 15, and a drum cleaning device 18 for removing transfer residual toner remaining on the surface of the photosensitive drum 15 after the transfer. Has been.

  In the present embodiment, the photosensitive drum 15 is formed by forming an organic photosensitive layer on the surface of a metal thin cylindrical drum. The charger 16 discharges the photosensitive drum 15 to charge the photosensitive drum 15 to a predetermined potential.

  The exposure device 14 modulates the semiconductor laser 19 according to the original color material gradation data, and emits a laser beam LB from the semiconductor laser 19 according to the gradation data. The laser beam LB emitted from the semiconductor laser 19 is deflected and scanned by the rotary polygon mirror 22 through the reflection mirrors 20 and 21, and the image is held again through the reflection mirrors 20 and 21 and the plurality of reflection mirrors 23 and 24. Scanning exposure is performed on the photosensitive drum 15 as a body.

  From the image processing apparatus 12, the exposure apparatuses 14Y, 14M, 14C, and 14K of the image forming units 13Y, 13M, 13C, and 13K for each color of yellow (Y), magenta (M), cyan (C), and black (K) are provided. The image data (raster data) of each color is sequentially output to the laser beam LB emitted according to the image data from the exposure devices 14Y, 14M, 14C, and 14K, and the photosensitive drums 15Y, 15M, 15C, and 15K. The surface is exposed to scanning to form an electrostatic latent image. The electrostatic latent images formed on the photosensitive drums 15Y, 15M, 15C, and 15K are respectively yellow (Y), magenta (M), cyan (C), and cyan by the corresponding developing devices 17Y, 17M, 17C, and 17K. It is developed as a toner image of each color of black (K).

  In the present embodiment, the toner has a property of being negatively charged, and a binder resin such as polyester or styrene acrylic is obtained by a suspension polymerization method, an emulsion aggregation coalescence method, a dissolution suspension method, or the like. A so-called spherical toner having a shape factor of about 100 to 140 is used. The carrier is a fine particle obtained by coating a magnetic material with a semiconductive material, and the toner is charged by stirring and mixing with the toner in the developing device 17.

  Each color of yellow (Y), magenta (M), cyan (C), and black (K) sequentially formed on the photosensitive drums 15Y, 15M, 15C, and 15K of the image forming units 13Y, 13M, 13C, and 13K. The unfixed toner images are sequentially transferred while being superimposed on the surface of the intermediate transfer belt 25 in the primary transfer portion where the photosensitive drums 15Y, 15M, 15C, and 15K are in contact with the intermediate transfer belt 25 as an intermediate transfer member. Is done. Semiconductive primary transfer rolls 26Y, 26M, 26C, and 26K as transfer members are disposed on the back surface side of the intermediate transfer belt 25 in the primary transfer portion, and these primary transfer rolls 26Y, 26M, and 26C are disposed. , 26K, the intermediate transfer belt 25 comes into contact with the surfaces of the photosensitive drums 15Y, 15M, 15C, 15K. The primary transfer rolls 26Y, 26M, 26C, and 26K are applied with a voltage having a polarity opposite to the charged polarity of the toner, and unfixed toner images of the respective colors formed on the photosensitive drums 15Y, 15M, 15C, and 15K are obtained. Then, each is sequentially electrostatically attracted onto the intermediate transfer belt 25 to form a full-color image. The transfer residual toner on the surfaces of the photosensitive drums 15Y, 15M, 15C, and 15K is cleaned by the drum cleaning devices 18Y, 18M, 18C, and 18K.

  The intermediate transfer belt 25 is fixed between a drive roll 27, a driven roll 28, a tension roll 29, a driven roll 30, a backup roll 31 that is an opposing roll for secondary transfer, and an idle roll 32. In the direction of arrow B in synchronism with the rotation of the photosensitive drums 15Y, 15M, 15C, and 15K, by a drive roll 27 that is stretched by a special drive motor (not shown) with excellent constant speed characteristics (not shown). Are circulated at a predetermined speed.

  When a single color image is formed, only the desired color image forming units 13Y, 13M, 13C, and 13K are operated, and a desired single color unfixed toner image is formed on the intermediate transfer belt 25.

  In this way, the unfixed toner images of the respective colors of yellow (Y), magenta (M), cyan (C), and black (K) that have been primary-transferred multiple times on the intermediate transfer belt 25 are intermediate transfer belt 25. Is rotated to the secondary transfer unit facing the conveyance path of the recording paper (recording medium) P, and an unfixed toner image is transferred from the intermediate transfer belt 25 to the recording paper P in the secondary transfer unit. Next transferred.

  The recording paper P is fed from one of the paper trays 39, 40, 41 by a feed roll 42, transported to a registration roll 47 by a paper transport path 46 having a plurality of transport rolls 43, 44 and temporarily stopped. . Next, the recording paper P is conveyed by the registration roll 47 at a predetermined timing, and is guided to the secondary transfer portion via the guide member 49 and is interposed between the secondary transfer roll 33 and the intermediate transfer belt 25. It is caught. Further, on the back side of the intermediate transfer belt 25 in the secondary transfer portion, a backup roll 31 that is opposed to the secondary transfer roll 33 and a metal roll (not shown) that contacts the backup roll 31 are disposed. In the present embodiment, a secondary transfer electric field is generated using the secondary transfer roll 33 as a counter electrode by applying a voltage (normal transfer bias) having the same polarity as the charging polarity of the toner to the metal roll. The secondary transfer roll 33 is cleaned by a brush roll (not shown).

  Then, the recording paper P onto which the unfixed toner image has been transferred is peeled off from the intermediate transfer belt 25, and then sent to the fixing device 37 by the paper transport belts 35 and 36 as the two transfer material transporting means. The toner image is fixed and discharged onto a discharge tray 38 provided outside the apparatus main body 1. The intermediate transfer belt 25 that has finished the secondary transfer of the unfixed toner image is configured such that residual toner is removed by a belt cleaning device 48 located downstream of the secondary transfer portion.

  Next, the configuration of the secondary transfer apparatus 300 according to the present embodiment will be described with reference to FIGS. Here, FIG. 2 is a schematic diagram showing the configuration of the secondary transfer apparatus 300 according to the present embodiment, and FIG. 3 is a diagram showing the inner side of the intermediate transfer belt 25 of the secondary transfer apparatus 300 according to the present embodiment. It is a sectional side view which shows a structure.

  As shown in FIGS. 2 and 3, the secondary transfer apparatus 300 according to the present embodiment includes a rotatable secondary transfer roll 33 configured to be in pressure contact with the toner holding surface side of the intermediate transfer belt 25. The secondary transfer roll 33 is provided with a backup roll 31 as an opposing roll disposed so as to face the intermediate transfer belt 25. Further, a tension roll 310 having a diameter substantially the same as that of the backup roll 31 is provided inside the intermediate transfer belt 25 in the vicinity of the upstream side of the backup roll 31, and the tension roll 310 and the backup roll 31 are also provided. Between the two, an endless counter belt 325 is wound. In the present embodiment, the counter belt 325 is driven by the intermediate transfer belt 25 to rotate in the same direction as the intermediate transfer belt 25, and the counter belt 325 is rotatably stretched. The roll 310 is grounded.

  In addition, a metal power supply roll SR is disposed in contact with the surface of the backup roll 31 inside the opposed belt 325. The power supply roll SR is connected to a secondary transfer bias power source (not shown) as a bias application unit, and by applying a secondary transfer bias (negative polarity in the present embodiment) having the same polarity as the toner, A secondary transfer electric field is formed between the backup roll 31 and the grounded secondary transfer roll 33 using the backup roll 31 as a counter electrode, and the unfixed toner image on the intermediate transfer belt 25 is secondarily transferred onto the recording paper P. It has become.

  Further, in the present embodiment, a cleaning roll 325 </ b> C for cleaning dirt attached to the surface of the facing belt 325 is disposed outside the facing belt 325 near the tension roll 310. Reference numeral 300H denotes a housing that accommodates these components.

Here, the secondary transfer roll 33 according to the present embodiment is made of a urethane rubber tube having carbon dispersed on the surface, the inside is made of foamed urethane rubber having carbon dispersed therein, and further a fluorine coating is applied to the roll surface. The resistance is 10 ⁶ to 10 ¹⁰ Ω and the roll diameter is 28 mm, and the hardness is set to 30 ° (Asuka C), for example. On the other hand, the backup roll 31 is a tube of EPDM and NBR blend rubber in which carbon is dispersed on the surface, the inside is made of EPDM rubber, the surface resistivity is 10 ⁷ to 10 ¹⁰ Ω / □, and the roll diameter is 28 mm. The hardness is set to 70 ° (Asuka C), for example.

  By the way, in the secondary transfer apparatus 300 configured as described above, a secondary transfer electric field is generated by the potential difference between the backup roll 31 and the secondary transfer roll 33 when performing the secondary transfer. The electric field affects not only the secondary transfer nip region (the region where the secondary transfer roll 33 is pressed against the intermediate transfer belt 25) but also the pre-nip region near the upstream side of the secondary transfer nip region. Specifically, in the vicinity of the upstream side of the secondary transfer nip region where the secondary transfer roll 33 and the backup roll 31 are opposed to each other with the intermediate transfer belt 25 interposed between the backup roll 31 and the inner surface of the intermediate transfer belt 25. When a gap discharge occurs between the backup roll 31 and the intermediate transfer belt 25 in the formed wedge-shaped gap, the toner on the intermediate transfer belt 25 enters (rushes into) the secondary transfer nip region. The image is transferred to the immediately preceding recording sheet P, and a scaly image defect occurs on the surface of the recording sheet P.

  In particular, when a spherical toner having a small shape factor is used as the toner, the transferability is good, but there is a high possibility that the toner is disturbed on the intermediate transfer belt 25 or the recording paper P by a slight electric field change due to discharge or the like. This will cause image defects. Further, when the intermediate transfer belt 25 in which electric conduction is mainly performed by ionic conduction is used, an excessive charge due to discharge is compared with a belt having the same volume resistivity where electric conduction is mainly carried out by electronic conduction. Are likely to accumulate in the intermediate transfer belt 25, and the possibility that the toner is disturbed on the intermediate transfer belt 25 or the recording paper P by a slight change in electric field is further increased, and the above-described scaly image defects are likely to occur.

  Therefore, in the secondary transfer apparatus 300 according to the present embodiment, as described above, the counter belt 325 is disposed opposite to the inner side of the intermediate transfer belt 25 in the vicinity of the upstream side of the secondary transfer nip region, and the counter belt 325 is backed up. The roll 31 is placed between the grounded stretch roll 310 and the opposed surface of the opposed belt 325 is disposed in close contact with the inner surface of the intermediate transfer belt 25.

Here, as the intermediate transfer belt 25 according to the present embodiment, a suitable material containing a conductive agent made of a conductive polymer in a resin such as polyimide or polyamide is used, and its volume resistivity is 10 ¹⁰ to 10 ¹⁴ Ω. -It forms so that it may become cm, and the thickness is set, for example to 0.1 mm. In addition, instead of the ion conductive conductive agent, various conductive polymers may be included in the resin.

On the other hand, the facing belt 325 according to the present embodiment is formed of the same material as the intermediate transfer belt 25 and has the same width. Further, the volume resistivity of the opposing belt 325 is formed to be 10 ⁸ to 10 ¹³ Ω · cm, and is set to be smaller than the volume resistivity of the intermediate transfer belt 25. As described above, by setting the volume resistivity of the opposed belt 325 in close contact with the intermediate transfer belt 25 to be smaller than that of the intermediate transfer belt 25, the discharge between the backup roll 31 and the intermediate transfer belt 25 is effectively suppressed. can do.

  Further, the intermediate transfer belt 25 according to the present embodiment is disposed so as to always overlap the stretching roll 310. That is, as schematically shown in FIG. 2, the inner side of the tangent line at the contact point N2 between the intermediate transfer belt 25 and the stretching roll 310 (the contact point when the intermediate transfer belt 25 and the stretching roll 310 are in point contact). (Upper side in the drawing) the intermediate transfer belt 25 is wound around the stretching roll 310 so as to be positioned (θ> 0). Thus, the intermediate transfer belt 25 is overlapped with the stretching roll 310 and stretched (stretching so that the inner surface of the intermediate transfer belt 25 and the surface of the stretching roll 310 are in surface contact). The contact state between the opposing belt 325 and the intermediate transfer belt 25 can be stably maintained.

  Note that the distance at which the opposing belt 325 and the intermediate transfer belt 25 are in close contact (the contact length along the rotation direction of the intermediate transfer belt 25, and the contact point when the intermediate transfer belt 25 and the secondary transfer roll 33 are in point contact. The distance L2 between N1 and the contact N2 is defined as a rush position T at which the intermediate transfer belt 25 intersects the direction in which the recording paper P enters (rushes) into the secondary transfer portion. When the distance from N1 is L1, it is preferable to set so as to satisfy L2> L1. Thus, by setting the distance L2 at which the opposing belt 325 and the intermediate transfer belt 25 are in close contact with each other, the gap discharge between the backup roll 31 and the intermediate transfer belt 25 in the area where the recording medium enters (enters) is stabilized. Can be suppressed.

  In the secondary transfer apparatus 300 according to the present embodiment configured as described above, the counter belt 325 having a smaller volume resistivity than the intermediate transfer belt 25 is backed up in the vicinity of the upstream side of the secondary transfer unit. Between the backup roll 31 and the intermediate transfer belt 25, the roll 31 is placed between the grounded stretching roll 310 and the opposite surface thereof is in close contact with the inner side of the intermediate transfer belt 25. It is possible to remove excessive charges existing on the back surface of the intermediate transfer belt 25 in the wedge-shaped gap formed in the above, and to stably suppress discharge between the backup roll 31 and the intermediate transfer belt 25 in the region. . Thereby, it is possible to effectively suppress the occurrence of scaly image defects and contribute to the improvement of image quality.

  In the above-described embodiment, the secondary transfer device 300 has been described as an example. However, the present invention is not limited to such a configuration. For example, a similar opposing belt 325 is used as a primary transfer roll. 26 may be applied. Specifically, a tension roll provided with the primary transfer roll 26 is provided in the vicinity of the upstream side of the primary transfer portion, and a similar facing belt 325 is hung between the tension roll and the primary transfer roll 26. By disposing the facing belt 325 so as to be in close contact with the inner side of the intermediate transfer belt 25, it is possible to suppress gap discharge in the vicinity of the upstream side of the primary transfer portion and suppress toner scattering.

1 is a schematic configuration diagram illustrating a tandem type image forming apparatus to which the present invention is applicable. It is a schematic diagram for demonstrating the structure of the secondary transfer apparatus which concerns on this Embodiment. FIG. 3 is a side cross-sectional view illustrating a configuration inside an intermediate transfer belt of a secondary transfer apparatus according to the present embodiment.

Explanation of symbols

  1: Image forming device, 13Y, 13M, 13C, 13K: Image forming unit, 14Y, 14M, 14C, 14K: Exposure device, 15Y, 15M, 15C, 15K: Photosensitive drum, 16Y, 16M, 16C, 16K: Charging device , 17Y, 17M, 17C, 17K: Development device, 18Y, 18M, 18C, 18K: Drum cleaning device, 25: Intermediate transfer belt, 26Y, 26M, 26C, 26K: Primary transfer roll, 27: Drive roll, 31: Backup Roll: 33: Secondary transfer roll, 35, 36: Paper transport belt, 37: Fixing device, 38: Discharge tray, 39, 40, 41: Paper tray, 47: Registration roll, 48: Belt cleaning device, 49: Guide Member, 300: secondary transfer device, 300H: housing, 310: tension roll, 325: pair Belt, 325C: cleaning roll, N1: the secondary transfer position, P: recording paper, SR: feed roll

Claims (4)

An endless intermediate transfer belt that is rotatably formed on the surface of which a toner image is primarily transferred;
A secondary transfer roll that forms a secondary transfer portion in pressure contact with the intermediate transfer belt;
An opposing roll disposed opposite to the secondary transfer roll across the intermediate transfer belt,
A secondary transfer electric field is formed by a potential difference between the secondary transfer roll and the counter roll,
A tension roll is provided inside the intermediate transfer belt on the upstream side of the counter roll, and the tension roll and the counter roll have an endless shape having a smaller volume resistivity than the intermediate transfer belt. And the counter belt is disposed in close contact with the inner surface of the intermediate transfer belt in a region between the tension roll and the counter roll. The transfer apparatus, wherein the recording medium enters the secondary transfer portion at a position inside an area where the opposed belt and the intermediate transfer belt are in close contact with each other .   The transfer apparatus according to claim 1, wherein an inner surface of the intermediate transfer belt and a surface of the stretching roll are in surface contact along a rotation direction of the intermediate transfer belt. The intermediate transfer belt contains a conductive polymer and / or an ion conductive conductive agent as a conductive agent and has a volume resistivity of 10 ¹⁰ to 10 ¹⁴ Ω · cm. The transfer device according to claim 1, wherein the volume resistivity is 10 ⁸ to 10 ¹³ Ω · cm.   An image forming apparatus comprising: the transfer device according to claim 1; and an image forming unit that forms an image on a recording medium.

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