JP5550422B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to a configuration of a guide unit that conveys a sheet to a transfer unit.

  Conventionally, in an image forming apparatus such as a copying machine, a printer, or a facsimile, a transfer unit that transfers a toner image formed on an image carrier such as a photosensitive drum or a secondary transfer belt to a sheet, and the sheet is conveyed to the transfer unit. A sheet conveying device is provided. Here, when a toner image is transferred onto a sheet in a transfer unit including an image carrier and a transfer roller that is pressed against the image carrier, the behavior of the sheet in the transfer unit affects the transfer state.

  For example, when the distance between the registration roller and the transfer portion is short, the sheet may suddenly change its posture when the trailing edge passes through the registration roller with the sheet reaching the transfer portion. In this case, there is a problem that a scatter image at the transfer portion or an image blur due to a shock when passing through the registration roller occurs.

  For this reason, various proposals have been made to stabilize the behavior of the sheet. For example, a guide portion is provided between the transfer portion and the registration roller, and the toner is stably transferred onto the sheet by allowing the sheet to enter the transfer portion while regulating the behavior by the guide portion. Yes.

  Here, as a countermeasure against the scattered image at the transfer unit, in order to transport the sheet to the transfer nip in a state in which the sheet is stabilized in potential, the guide unit is configured to guide the sheet from the image carrier side to the transfer nip as much as possible. Is effective. For this reason, as a configuration of the guide portion, the conveyance surface is arranged at a position facing the image carrier, that is, a position where the lower transfer guide, which is a guide member on the transfer roller side, is traveled to the image carrier as much as possible. .

  However, when the lower transfer guide is disposed at such a position, the sheet is bent between the transfer portion and the registration roller until the trailing edge of the sheet passes through the registration roller after the sheet reaches the transfer portion. Be transported. As a result, particularly when a thick sheet is conveyed, the sheet jumps due to the waist of the bent sheet at the moment when the rear end passes through the nip of the registration roller, and the sheet is blurred at the transfer nip portion, and image blurring occurs. In other words, when taking measures against scattered images, image blur occurs due to shock at the moment of passing through the nip of the registration roller. Thus, at present, it is difficult to achieve both of the countermeasures against the image that is scattered and the image blur due to the shock at the moment of passing through the nip of the registration roller (hereinafter referred to as “registration loss shock”).

  Therefore, conventionally, as a countermeasure against both scattered image splattering and registration loss shock, there is a configuration in which the lower transfer guide is configured to be rotatable in a direction substantially perpendicular to the sheet conveying direction (see Patent Document 1). In this case, the lower transfer guide is disposed so as to travel to the upper transfer guide side with respect to the tangent line between the image carrier and the transfer roller, and the lower transfer guide is rotated by the waist of the sheet. ing. With such a configuration, in the case of a thick sheet that is susceptible to shock, the amount of rotation of the guide is increased, so that the bending of the sheet is reduced, the shock is less likely to occur, and the missed registration shock is reduced. In addition, a thin sheet which is not easily shocked is advantageous in terms of transfer scattering because the amount of rotation of the guide is small.

JP 2000-229748 A

  By the way, in such a conventional image forming apparatus, when the lower transfer guide and the transfer unit are close to each other, there is a concern about leakage of a high transfer voltage applied to the transfer unit during transfer. For this reason, the material of the lower transfer guide is limited to an insulating material, and for example, a resin guide is used as the lower transfer guide.

  Here, when the lower transfer guide is a resin guide and is configured to rotate with the waist of the sheet, the sheet passes while pressing the lower transfer guide with a strong force. The surface becomes sharpened. In order to prevent this, a polyethylene sheet or the like is attached to the guide surface of the resin guide. However, when a polyethylene sheet or the like is attached in this way, the surface roughness of the polyethylene sheet becomes small and the surface becomes smooth due to long-term use, and the contact area with the conveyed sheet increases. If the contact area with the sheet increases in this manner, abnormal charging due to friction with the sheet is likely to occur, and as a result, an abnormal image is generated.

  Accordingly, the present invention has been made in view of such a situation, and an object of the present invention is to provide an image forming apparatus capable of preventing the occurrence of abnormal charging in the guide portion even after long-term use. It is.

The present invention provides an image carrier that carries a toner image, a transfer roller that is in pressure contact with the image carrier, and that forms a transfer unit that transfers the toner image to a sheet together with the image carrier, and a sheet that is placed on the transfer unit. In the image forming apparatus including the guide unit for guiding, the guide unit is disposed on the side of the image carrier, the first guide member disposed on the side of the image carrier, and the guide surface for guiding the sheet is the image carrier. And a flexible second guide member positioned on the image carrier side with respect to the tangent of the pressure contact portion of the transfer roller, and an adhesive portion bonded to the second guide member, the adhesive portion being the second an insulating porous sheet attached to the second guide member is adhered to a region other than the guide surface of the guide member, is characterized in that example Bei a.

  By attaching a porous insulating sheet to the guide surface that guides the sheet of the second guide member that constitutes the guide part that guides the sheet to the transfer part as in the present invention, abnormal charging in the guide part can be achieved even when used for a long period of time. Can be prevented.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. The principal part enlarged view of the said image forming apparatus. FIG. 3 is a view for explaining a porous sheet provided in a pre-transfer lower guide provided in the image forming apparatus. The figure which shows the area | region of the lower guide before transfer at the time of sticking the said porous sheet with a double-sided tape.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, 1 is an image forming apparatus, and 2 is an image forming apparatus main body (hereinafter referred to as an apparatus main body). The image forming apparatus 1 includes an image reading unit 60 provided in an upper part of the apparatus main body 2, an image forming unit 2A disposed below the image reading unit 60, and a sheet feeding unit that supplies sheets to the image forming unit 2A. A feeding device 2B is provided. Further, a sheet conveying device 3 that conveys the sheet fed from the sheet feeding device 2B to the image forming unit 2A, a fixing unit 19 and the like are provided.

  In the present embodiment, the sheet conveying device 3 conveys the sheet to the image forming unit 2A and forms an image on the second surface opposite to the sheet on which the image is formed on the first surface by the image forming unit 2A. The sheet is conveyed again to the image forming unit 2A. Further, the sheet conveying apparatus 3 includes a reversing path 41 that is a sheet conveying path for conveying the sheet to the image forming unit 2A again.

  Here, the image reading section 60 reads a document (not shown) set on the document glass 53 with the pressure plate 52 opened. The image forming unit 2A includes a photosensitive drum 11 that is an image carrier, and a developing device 13 that develops the electrostatic latent image formed on the photosensitive drum with toner to form a toner image on the photosensitive drum. Yes. In addition, the image forming unit 2A includes a transfer roller 25 that forms a transfer unit that presses the photosensitive drum 11 and transfers a toner image onto a sheet, and a laser scanner 5 that forms an electrostatic latent image on the photosensitive drum. I have.

  The sheet feeding device 2B separates the sheet feeding cassette 2a for storing the sheet, the sheet feeding roller 2b for feeding the sheet stored in the sheet feeding cassette 2a, and the sheet fed by the sheet feeding roller 2b one by one. And a separation roller pair 2c. When the sheet feeding cassette 2a is set in the apparatus main body 2, the sheet is raised in the sheet feeding cassette by a lifter motor (not shown) so that the sheet can be fed.

  Next, an image forming operation in the image forming apparatus 1 having such a configuration will be described.

  In the case of forming an image on a sheet, first, an original is set on the original glass 53, and thereafter, when the copy button is pressed, the original image is read by the image reading unit 60, and the read original image is electrically converted by the image processing unit. It is converted into a signal and transmitted to the laser scanner 5. Next, laser light corresponding to image information is irradiated from the laser scanner 5 to the photosensitive drum 11 whose surface is uniformly charged by the charging roller 33, and an electrostatic latent image is formed on the photosensitive drum 11. . Thereafter, the electrostatic latent image is developed by the developing device 13 and visualized as a toner image.

  Here, the toner for developing the electrostatic latent image reaches the developing unit 13 from the toner supply device 14, reaches the developing sleeve 30 while being stirred inside, and is supplied from the developing sleeve 30 to the photosensitive drum 11. Note that after the toner image is transferred onto the sheet, the toner remaining on the photosensitive drum 11 is removed by the cleaning member 23 in contact with the photosensitive drum 11 and is accommodated in a waste toner container (not shown) by the conveying screw 24. Thereafter, the photosensitive drum 11 from which the residual toner has been removed is exposed to the pre-exposure unit 29, whereby the charging unevenness remaining on the surface is erased. Then, the photosensitive drum 11 from which the charging unevenness has been eliminated is uniformly charged by the charging roller 33, and is prepared for the next latent image formation.

  Further, in parallel with the toner image forming operation, the sheet feeding roller 2b rotates and is stored in the sheet feeding cassette 2a, and the sheet surface is raised by a lifter motor (not shown) to feed out a sheet that can be fed. . Thereafter, the fed sheets are separated one by one by the separation roller pair 2 c and then conveyed to the registration roller pair 4 provided in the sheet conveying device 3, and the skew correction is performed by the registration roller pair 4.

  Next, the sheet subjected to the skew correction by the registration roller pair 4 is transferred to a transfer portion constituted by the photosensitive drum 11 and the transfer roller 25 in synchronization with the rotation of the photosensitive drum 11 by the registration roller pair 4. Be transported. The toner image is transferred to the sheet by applying a voltage having a polarity opposite to that of the toner image to the transfer roller 25 at the transfer portion. Here, the sheet is detected by a sensor (not shown) when traveling toward the registration roller pair 4, and a control unit (not shown) aligns the sheet with the position of the toner image in accordance with a detection signal from the sensor. The registration roller pair 4 is driven so as to feed in a timely manner.

  Next, the sheet on which the toner image is transferred is conveyed to the fixing unit 19, and the sheet is heated and pressed in the fixing unit 19, whereby the toner image is permanently fixed on the sheet. In the case where an image is formed only on the first surface after the toner image is fixed in this way, the sheet passes through the discharge sensor 51 by the reversing roller pair 21 rotating in the normal direction, and then the in-cylinder discharge port. 27 is discharged. As a result, the image forming apparatus 1 ends the single-sided copying operation of the sheet.

  On the other hand, in the case of double-sided printing in which an image is also formed on the second side, the sheet with the image formed on one side passes through the fixing unit 11 and is then switched back by the reverse roller pair 21 and passes through the reverse path 41. To do. Further, the skew is corrected again by the registration roller pair 4 and conveyed to the transfer portion. Then, an image is formed on the opposite surface at the transfer portion, and then the sheet is conveyed in the same manner as in the single-sided copying operation, passes through the discharge sensor 51, and is discharged to the in-body discharge port 27.

  By the way, upstream of the transfer portion constituted by the photosensitive drum 11 and the transfer roller 25 in the sheet conveying direction, as shown in FIG. 2, a pre-transfer upper guide constituting a guide portion for guiding the sheet S to the transfer portion T. 55 and a pre-transfer lower guide 53 are provided. Here, in order to prevent scattered images, the sheet S does not collide with the photosensitive drum 11 as much as possible when entering the transfer nip 26 that is a nip portion (pressure contact portion) between the photosensitive drum 11 and the transfer roller 25. Thus, it is necessary to enter from the photosensitive drum side.

  Therefore, the registration roller pair 4 is configured such that the tangent line of the roller nip 56 of the registration roller pair 4 is directed toward the upper guide 55 before transfer. As a result, after the sheet S passes through the registration roller pair 4, it comes into contact with the pre-transfer upper guide 55, and enters the transfer nip 26 from the photosensitive drum side by the pre-transfer upper guide 55.

  Even after the leading edge of the sheet enters the transfer nip 26, the sheet S needs to enter the transfer nip 26 as close to the photosensitive drum 11 as possible. Therefore, the pre-transfer lower guide 53 provided on the transfer roller side opposite to the pre-transfer upper guide 55 that is the first guide member provided on the photosensitive drum side (image carrier side) is provided on the transfer nip 26. The tangent line is configured to protrude to the photosensitive drum side. The tangent line of the transfer nip 26 is at an angle of 55 degrees with respect to the horizontal line in order to stabilize sheet conveyance between the transfer portion T and the fixing portion.

  Here, the pre-transfer lower guide 53 which is a flexible second guide member is installed in the vicinity of the transfer roller 25 to which a high voltage is applied, and therefore needs to have an insulating property. For this reason, in the present embodiment, at least the pre-transfer lower guide 53 among the pre-transfer lower guide 53 and the pre-transfer upper guide 55 is formed of resin.

  Next, the sheet conveying operation between the registration roller pair 4 and the transfer unit T of the image forming apparatus 1 having such a configuration will be described. The sheet S fed from the sheet feeding cassette 2 a is first subjected to skew correction by the registration roller pair 4 and then conveyed in the tangential direction of the roller nip 56 by the registration roller pair 4. Here, as described above, the tangent line of the roller nip 56 is directed toward the pre-transfer upper guide 55, and thereafter, the sheet S collides with the transfer upper guide 55, and the transfer upper guide 55 to the pre-transfer lower guide 53. Along the transfer nip 26.

  Next, the sheet S is conveyed along the tangent line of the transfer nip 26. As described above, the pre-transfer lower guide 53 protrudes toward the photosensitive drum 11. For this reason, when the sheet S is nipped in both the roller nip 56 and the transfer nip 26, the sheet S is pressed against the conveyance surface (guide surface) of the pre-transfer lower guide 53 as shown in FIG. The strong sheet S passes while pushing down the lower transfer guide 53 with a strong force. At this time, the sheet S does not contact the pre-transfer upper guide 55.

  Here, even if the sheet S passes through the lower pre-transfer guide 53 with a strong force as described above, the transfer surface of the lower transfer guide 53 is not scraped, for example, on the transfer surface of the lower transfer guide 53. The insulating sheet is fixed with double-sided tape or the like. However, in such a configuration, since the lower transfer guide 53 is insulative as described above, when the insulating sheet is rubbed strongly by the sheet S, the insulating sheet is triboelectrically charged. In addition, the surface roughness of the insulating sheet is reduced by long-term use, the surface area is increased, and abnormal charging is caused by the sheet being rubbed strongly, resulting in an image defect.

  For this reason, in this Embodiment, the porous insulating sheet which has slidability and insulation is employ | adopted as an insulating sheet. Here, in the case of a porous insulating sheet having both slidability and insulating properties, when strongly rubbed by the sheet S, the portion 54b without the hole 54a of the porous insulating sheet 54 shown in FIG. The portion of the hole 54a does not change. For this reason, an increase in surface area due to long-term use can be reduced, and surface roughness can be secured. Therefore, as a result, the configuration is less likely to cause abnormal charging.

  In the present embodiment, as the porous insulating sheet 54, a polyethylene insulating sheet and a sheet having a porosity of about 25% to 43% with countless holes 54a of about 17 μm is used. . Moreover, since the hole 54a of the porous sheet 54 has a hole diameter of 17 μm, the sheet does not get caught.

  As described above, by using the porous insulating sheet 54 as the insulating sheet as in the present embodiment, the surface property can be maintained even if the porous insulating sheet 54 is scraped by long-term use. , It will not cause abnormal charging. As a result, it is possible to take measures against scattered images and image defects due to abnormal charging.

  In the present embodiment, the porous insulating sheet 54 is attached to the resin guide with a double-sided tape. Here, for example, when the environment is hot and humid, the adhesive of the double-sided tape may ooze out from the countless holes 54a of the porous insulating sheet 54 to the transport surface (guide surface) side. And when an adhesive oozes out to the conveyance surface side in this way, a sheet | seat will be caught by an adhesive and there exists a possibility that a conveyance defect may arise.

  For this reason, in order to prevent conveyance failure even if the adhesive oozes out, the pasting area of the lower transfer guide 53 to which the porous insulating sheet 54 is bonded via the double-sided tape is provided. A region other than the guide surface where the sheet does not contact is preferable. For example, the sheet does not contact the range indicated by the arrow on the back side 53b of the conveyance surface 53a for guiding the sheet of the lower transfer guide 53 shown in FIG. 4 and the range indicated by the arrow on the upstream portion 53c on the conveyance surface side. For this reason, the porous insulating sheet 54 (adhesive portion thereof) may be bonded and fixed to this region with a double-sided tape. Thereby, it is possible to stably fix the porous insulating sheet 54 and to prevent the adhesive from seeping out. That is, by making the adhesive area of the double-sided tape an area where the conveyance sheet is not in contact, it is possible to prevent conveyance failure due to the double-sided tape oozing out to the conveyance surface side.

  In the above description, an image forming apparatus having a configuration in which a photosensitive drum is used as an image carrier that carries a toner image, and the sheet is conveyed to a transfer unit that transfers the toner image formed on the photosensitive drum. Although described as an example, the present invention is not limited to this. For example, an image forming apparatus configured to primarily transfer a toner image formed on a photosensitive drum to an intermediate transfer belt, and transport the sheet to a secondary transfer unit that secondarily transfers the toner image transferred to the intermediate transfer belt. Can be applied.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Image forming apparatus main body, 2A ... Image forming part, 3 ... Sheet conveying apparatus, 11 ... Photosensitive drum, 25 ... Transfer roller, 53 ... Lower guide before transfer, 53a ... Conveying surface, 54 ... Porous insulating sheet, 55 ... upper guide before transfer, S ... sheet, T ... transfer section

Claims (1)

An image carrier that carries a toner image, a transfer roller that is in pressure contact with the image carrier and that forms a transfer unit that transfers the toner image to the sheet together with the image carrier, and a guide unit that guides the sheet to the transfer unit In an image forming apparatus comprising:
The guide portion is
A first guide member disposed on the image carrier side;
A flexible second guide member disposed on the transfer roller side and having a guide surface for guiding the sheet positioned on the image carrier side with respect to a tangent line between the image carrier and the press contact portion of the transfer roller;
A porous insulating sheet attached to the second guide member by attaching the adhesive portion to a region other than the guide surface of the second guide member; an image forming apparatus characterized in that e Bei.

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