JP4821133B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile, and more particularly to an intermediate transfer type image forming apparatus that transfers a toner image formed on an image carrier onto a recording medium via an intermediate transfer body. .

As an intermediate transfer type image forming apparatus, yellow (Y), magenta (M), cyan (C) and black (K) toner images are formed on one image carrier, and these are formed on the intermediate transfer body. It is generally known that the toner images of a plurality of colors are sequentially transferred onto the recording medium and then transferred onto the recording medium.
A so-called intermediate transfer belt in the form of a belt is widely used as the intermediate transfer member, and is arranged to face and contact an image carrier such as a photosensitive drum. A primary transfer device is provided in the facing area, and the toner images on the photosensitive drum are sequentially transferred. The secondary transfer device from the intermediate transfer belt to the recording medium includes, for example, a transfer roll disposed in contact with the intermediate transfer belt, and a backup roll disposed opposite to the transfer roll from the inside with the intermediate transfer belt interposed therebetween. What is provided is generally used. A transfer bias voltage is applied between the transfer roll and the backup roll, and the toner image on the intermediate transfer belt is transferred to a recording medium.

In such an image forming apparatus, when a toner image is formed on the photosensitive drum, images of the respective colors can be formed separately, and these toner images are transferred to the intermediate transfer belt under substantially the same conditions. can do. For this reason, an unstable factor at the time of image formation can be eliminated, and the occurrence of image disturbance and color misregistration at the time of multiple transfer can be effectively prevented.
However, such an intermediate transfer type image forming apparatus requires a secondary transfer apparatus in addition to the primary transfer apparatus, and it is necessary to arrange a member such as a transfer roll for each of them. This is one of the factors that make price reduction difficult.

Under such circumstances, Patent Document 1 proposes an image forming apparatus that integrates a primary transfer area and a secondary transfer area and performs primary transfer and secondary transfer in one transfer area.
In this image forming apparatus, the primary transfer and the secondary transfer are performed at the facing portion between the image carrier and the intermediate transfer member. The transfer means provided in this area generates a transfer electric field having a reverse polarity between the primary transfer from the image carrier to the recording medium or the intermediate transfer body and the secondary transfer from the intermediate transfer body to the recording medium. The primary transfer and the secondary transfer are realized by sharing one transfer means. That is, the toner image is transferred from the image carrier to the intermediate transfer member in order to superimpose a plurality of color toner images, and then the recording medium is fed to the opposite portion between the image carrier and the intermediate transfer member to perform intermediate transfer. The superimposed toner images are collectively transferred from the body to the recording medium. When a monochromatic toner image is formed, a recording medium can be inserted between the image carrier and the intermediate transfer member, and the toner image can be directly transferred from the image carrier to the recording medium.
With such a configuration, it is not necessary to provide a secondary transfer device separately from the primary transfer device around the intermediate transfer member, and the cost of the image forming apparatus can be reduced and the size can be reduced.
JP 2003-270965 A

However, the image forming apparatus described in Patent Document 1 has the following problems.
When forming a single color image, the toner image on the image carrier is directly transferred to the recording medium by primary transfer, whereas the toner image on which a plurality of colors are superimposed is primarily transferred to the intermediate transfer member. In the subsequent secondary transfer, the image is transferred from the intermediate transfer member onto the recording medium. For this reason, the surface of the recording medium on which the toner image is transferred is reversed between the single-color image and the multi-color image. This is not a problem when recording paper with no distinction between the front and back is used as the recording medium. However, when a recording medium with a clear front and back, such as coated paper, is used, the image transferred to the recording medium by primary transfer Either one of the images transferred to the recording medium by the secondary transfer is transferred to the back surface.

  Further, when the recording medium on which the toner image has been transferred is sent out to the paper discharge tray as it is, the recording medium on which the toner image has been transferred by primary transfer and the recording medium to which the toner image has been transferred via secondary transfer are used. Since the surface to which the toner is transferred is reversed, the recording medium with the toner image transferred to the upper surface (face-up) and the one with the toner image transferred to the lower surface (face-down) are mixed in the paper discharge tray. Will end up.

  Further, the recording medium on which the toner image is transferred is pressed against the surface of the fixing device on which the toner image is carried by pressing the heated fixing member, but the surface on which the toner image is carried is opposite. If recording media are mixed, fixing may not be performed properly. In other words, when the conventional fixing device is arranged, the recording medium on which the toner image is carried on the surface opposite to the surface on which the fixing member abuts cannot properly heat the toner image and is good. It becomes impossible to fix to. In addition, the guide member that guides the recording medium to the fixing device generally disturbs the unfixed toner image when it comes into contact with the surface on which the toner image is carried. Is provided so as to guide the recording medium. However, if there are mixed recording media having the toner image transferred surface on the opposite side, the guide member disturbs the toner image and a good image cannot be obtained.

  The present invention has been made in view of the above circumstances, and its purpose is to transfer a toner image to a recording medium by primary transfer from an image carrier and by secondary transfer from an intermediate transfer member. In both cases where the toner image is transferred from the opposite side of the recording medium, the toner image is appropriately transferred onto the surface of the recording medium. It is another object of the present invention to perform good fixing in any case, and to discharge the recording medium with the surface on which the toner image is carried being aligned.

In order to solve the above problems, the invention according to claim 1 is directed to an image carrier in which a latent image due to a difference in electrostatic potential is formed on an endless peripheral surface, and toner on the latent image on the image carrier. An image forming apparatus comprising: an image forming unit that forms a toner image by transferring; and an intermediate transfer member that is disposed so as to face the image carrier and onto which the toner image on the image carrier is transferred. A region where the image carrier and the intermediate transfer member face each other is a transfer unit, and the transfer unit is a primary transfer region for transferring a toner image on the image carrier to the intermediate transfer member or a recording medium. And a secondary transfer region in which the toner image once primary-transferred onto the intermediate transfer member is transferred to a recording medium, and the recording medium having the toner image transferred on one surface is transferred to the transfer unit a duplex transport path for retransmitting the upstream side, first the recording medium is the transfer section Anda front reversing portion transferring reversing the front and back sides of the recording medium before over to, the pre-transfer reversal unit, feeding the leading end of the recording medium in the conveying path for the duplex, the transfer by reversing the conveying direction Provided is an image forming apparatus which is to be conveyed to a printing unit.

  In this image forming apparatus, a region where the image carrier and the intermediate transfer member face each other serves as a transfer unit. In this transfer unit, primary transfer for transferring the toner image from the image carrier to the intermediate transfer member, and intermediate transfer Since the secondary transfer from the body to the recording medium can be performed, it is not necessary to provide a separate secondary transfer area as in the conventional apparatus. Thereby, the manufacturing cost of the image forming apparatus can be reduced and the apparatus can be downsized.

  The transfer unit can transfer toner images of a plurality of colors onto the intermediate transfer member and superimpose the toner images on the intermediate transfer member, and the monochrome image can be transferred to the toner on the image carrier as a primary transfer. The image can be transferred directly to a recording medium. Therefore, in a multi-color image, each color toner image can be accurately transferred onto the intermediate transfer member under the same conditions, and a good image can be obtained. In addition, since the toner image is transferred directly from the image carrier to the monochrome image, the time required to transfer it to the recording medium can be shortened, and efficient image formation can be achieved.

  As described above, a single color image is transferred from the image carrier to the recording medium, and a plurality of color images are transferred from the intermediate transfer body to the recording medium passing through the opposite portion of the image carrier. A toner image is transferred from the opposite side of the recording medium with a plurality of color images. When a recording medium with a clear front and back, such as coated paper, is fed into such a transfer unit, a single color image is transferred from the image carrier, and a plurality of color images are transferred from the intermediate transfer member. In either case, the front and back of the recording medium are reversed at the pre-transfer reversal portion. Therefore, even if the transfer direction is reversed between the single-color image and the multiple-color image, the surface of the recording medium can be sent to the transfer area in accordance with the transfer direction.

Further, in this image forming apparatus, the front and back of the recording medium can be easily reversed using the double-sided conveyance path. Therefore, it is not necessary to provide a new reversing device, and it is possible to cope with the case where the toner image is transferred from the opposite side of the recording medium as described above without significantly increasing the number of parts.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, after the recording medium passes through the transfer portion and the transferred toner image is fixed by the fixing device, the front and back sides of the recording medium are It has a post-transfer reversal part to be reversed.

  Since this image forming apparatus has a post-transfer reversal unit, the front and back of the recording medium on which the toner image is transferred and fixed can be reversed and discharged. Therefore, a recording medium on which a toner image is directly transferred from an image carrier as a primary transfer, and a recording medium on which a toner image is transferred from an intermediate transfer body via a secondary transfer are used. Can be discharged out of the apparatus by unifying the surface onto which the recording medium is transferred upward or downward. Therefore, even if a single-color image and a multi-color image are mixed, the recording surface is not ejected in a state where the image side is the front and the back are mixed, and the ejected recording medium Management becomes easier.

According to a third aspect of the present invention, in the image forming apparatus according to the second aspect, the post-transfer reversing unit feeds the recording medium from the leading edge to the double-sided conveying path, reverses the conveying direction, and discharges the recording medium. Shall be transported to

  In this image forming apparatus, a toner image is formed, and the fixed recording medium is reversed using the double-sided conveyance path. Therefore, even if recording media with the toner image transferred surface on the opposite side are mixed, the front and back of these recording media are reversed with a simple structure, and the surfaces on which the toner images are formed are aligned in one direction. Can be transported to the discharge port. Further, since there is no need to provide a separate reversing device, it is possible to cope with the case where the transfer direction of the toner image is opposite as described above with a small manufacturing cost.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the transfer portion is a primary transfer electric field for primary transfer, and the primary transfer electric field is reversed. It is assumed that a polar secondary transfer electric field is generated.

  In the transfer section of this image forming apparatus, the toner image can be transferred from the image carrier to the recording medium or from the intermediate transfer body to the recording medium by setting the polarity of the applied transfer bias voltage in the reverse direction. Therefore, it is not necessary to separately provide a transfer device for performing primary transfer and a transfer device for performing secondary transfer, and primary transfer and secondary transfer can be performed using the same transfer member.

According to a fifth aspect of the present invention, there is provided an image carrier in which a latent image due to a difference in electrostatic potential is formed on an endless peripheral surface, and toner is transferred to the latent image on the image carrier to form a toner image. An image forming unit, an intermediate transfer member disposed so as to face the image carrier, and to which a toner image on the image carrier is transferred; and provided in a region where the image carrier and the intermediate transfer member face each other. A transfer unit for transferring the toner image, a conveying device for feeding a recording medium to the transfer unit, and a fixing device for fixing the toner image transferred to the recording medium by heating and pressing the transfer unit to the recording medium. A transfer unit configured to transfer a toner image on the image carrier to the intermediate transfer member or a recording medium; and to transfer the toner image temporarily transferred onto the intermediate transfer member to the recording medium. A secondary transfer region, and the fixing device is heated. A heating member in contact with the recording medium carrying an unfixed toner image state, and a pressure member for pressing the recording medium to the heating member, the heating member and the pressing member, both It is an object of the present invention to provide an image forming apparatus which is supported so as to be able to be switched so that the position of the recording medium with respect to the conveyance path is reversed .

  In this fixing device, a heating member and a pressure member sandwich a recording medium carrying an unfixed toner image and heat-press the toner image. The position of the heating member and the pressure member is switched, and the heating member Can be brought into contact with the surface on which the toner image is transferred. Therefore, both the toner image directly transferred from the image carrier to the recording medium and the toner image transferred to the intermediate transfer body by the primary transfer and then transferred to the recording medium are applied to the surface on which the toner image is carried. The toner image can be heated sufficiently in contact with it, and a good fixed image can be obtained.

According to a sixth aspect of the present invention, there is provided an image carrier in which a latent image due to a difference in electrostatic potential is formed on an endless peripheral surface, and toner is transferred to the latent image on the image carrier to form a toner image. An image forming unit, an intermediate transfer member disposed so as to face the image carrier, and to which a toner image on the image carrier is transferred; and provided in a region where the image carrier and the intermediate transfer member face each other. A transfer unit for transferring the toner image formed thereon, a conveying device for feeding a recording medium to the transfer unit, a fixing device for fixing the toner image transferred to the recording medium by the transfer unit by heating and pressing, and a transfer device A transfer guide for guiding the transfer of the recording medium carrying the unfixed toner image, wherein the transfer unit transfers the toner image on the image carrier to the intermediate transfer body or the recording medium. Area and the toner once temporarily transferred onto the intermediate transfer member And a secondary transfer region that is transferred to the recording medium, and the conveyance guide is positioned so as to contact the surface of the recording medium on which the toner image is not transferred and guide the recording medium. An image forming apparatus that can be switched is provided.

  The conveyance guide contacts the surface of the recording medium and guides it to the fixing device, and switches the position to contact the opposite side of the surface on which the unfixed toner image is carried. The recording medium can be fed into the fixing device without disturbing the image. In other words, the toner image is carried between the case where the toner image is directly transferred from the image carrier to the recording medium, and the case where the toner image is transferred from the intermediate transfer member to the recording medium after being transferred to the intermediate transfer member. However, the conveyance guide changes its position and comes into contact with the surface on which no toner image is carried. Therefore, the recording medium can be sent to the fixing device without disturbing the unfixed toner image.

  As described above, according to the present invention, the area where the image carrier and the intermediate transfer member face each other is used as the toner image transfer portion, and the primary transfer from the image carrier to the recording medium or the intermediate transfer member, and the intermediate transfer Since the secondary transfer from the body to the recording medium can be performed, it is not necessary to separately set a secondary transfer area, and the manufacturing cost and the size of the image forming apparatus can be reduced. Further, since the monochrome image can be directly transferred from the image carrier to the recording medium as a primary transfer, the efficiency of image formation is improved.

  Further, the toner image is transferred from the image carrier to the recording medium directly by primary transfer, and the toner image is transferred to the recording medium by secondary transfer via the intermediate transfer member. The direction in which the toner is transferred is reversed, but since it has a pre-transfer reversal part, even when using a recording medium with a distinction between the front and back, the toner transfer side can be sent to the transfer part as the surface . The conveyance guide to the fixing device can guide the recording medium so as not to contact the surface on which the unfixed toner image is carried, and can feed the recording medium to the fixing device. Further, the fixing device reliably heats the surface on which the toner image has been transferred, thereby enabling good fixing.

  The recording medium on which the toner image is fixed has a single-color image directly transferred from the image carrier and a multi-color image transferred via the intermediate transfer member, the surface on which the toner image is carried is the upper side or the lower side. Although different, it is possible to reverse the front and back of the recording medium by the post-transfer reversing unit and discharge the sheets in an aligned state.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention. 2 to 7 are schematic views showing the functions and functions of the pre-transfer reversing unit, the post-transfer reversing unit, and the fixing device, which are characteristic parts of the image forming apparatus.
The image forming apparatus includes a cylindrical photosensitive drum 1 (image carrier), a charging device 2 that uniformly charges the surface of the photosensitive drum 1 around the photosensitive drum 1, and a photosensitive member. An exposure device 3 that irradiates image light onto the body drum 1 to form a latent image on the surface; a developing unit 4 that selectively transfers toner to the latent image on the photoreceptor drum 1 to form a toner image; An endless intermediate transfer belt 5 that is disposed so as to face the body drum 1 and is supported so that the circumferential surface thereof can rotate, and a cleaning device 6 that removes toner remaining on the photosensitive drum 1 after the toner image is transferred. And a static elimination exposure device (not shown) for neutralizing the surface of the photosensitive drum 1. An area where the photosensitive drum 1 and the intermediate transfer belt 5 face each other is a toner image transfer portion 8. ing.

The transfer unit 8 is configured to pull out the recording sheets P stored in the paper feed tray 12 one by one and send them to the transfer unit 8 through the paper feed conveyance path 19. A fixing device 10 is provided on the downstream side of the transfer unit 8 in the recording sheet conveyance direction to heat and pressurize the toner image and press-bond the toner image on the recording sheet, and further on the downstream side the recording sheet on which the toner image is fixed. Is provided.
In addition, a paper feed conveyance path 19 from the paper feed tray 12 to the transfer unit 8 is provided with a pre-transfer reversing unit 14 for reversing the front and back of the recording sheet, and also between the fixing device 10 and the paper discharge tray 11. A post-transfer reversing unit 15 for reversing the front and back of the recording sheet is provided. A double-sided conveyance path 13 is provided for conveying the recording sheet on which the toner image has been transferred and fixed from the downstream side of the fixing device 10 to the upstream side of the transfer unit 8 again.

The photosensitive drum 1 is provided with a photosensitive layer whose resistance value is lowered by light irradiation on the peripheral surface.
The developing unit 4 includes four developing devices 4a, 4b, 4c, and 4d that store toners of yellow, magenta, cyan, and black, and each is supported in close proximity to the photosensitive drum 1. . When a latent image corresponding to each color is sequentially formed, toner is transferred from the corresponding developing device to form a visible image.

The intermediate transfer belt 5 is a belt-like semiconductor, and is adjusted such that carbon is dispersed in a polyimide resin having a thickness of 100 [μm] and a volume resistivity is 10 ⁸ [Ωm]. There is a release layer in consideration of surface cleanability.
The intermediate transfer belt 5 is stretched around four tension rolls 5a, 5b, 5c, and 5d, and the tension transfer roll 5a positioned on the upstream side of the transfer unit 8 is driven to rotate, thereby causing intermediate transfer. The belt moves around, and the other tension rolls 5b, 5c, and 5d are all driven to rotate.

The transfer unit 8 is provided at a position where the intermediate transfer belt 5 and the photosensitive drum 1 face each other, and the transfer roll 9 faces the photosensitive drum 1 with the intermediate transfer belt 5 interposed therebetween, and the intermediate transfer belt 5. It arrange | positions so that the inner peripheral surface of may be contacted.
The transfer unit 8 performs, as primary transfer, transfer of a toner image from the photosensitive drum 1 to the intermediate transfer belt 5 or transfer to a recording sheet P fed between the photosensitive drum 1 and the intermediate transfer belt 5. Do. Further, as the secondary transfer, a toner image that is once transferred to the intermediate transfer belt 5 and overlaid with a plurality of colors is transferred to the recording sheet P.

The transfer roll 9 is formed of a material having elasticity at least near the surface. For example, foamed urethane, foamed acrylic, or foamed silicon is used as the elastic material. The member forming the peripheral surface of the transfer roll 9 needs to have conductivity in order to transfer the toner image, and the volume resistivity is preferably 10 ⁶ Ω · cm or less.
The transfer roll 9 is disposed so as to be in pressure contact with the intermediate transfer belt 5 and is driven to rotate. A power supply unit (not shown) is connected to the transfer roll 9, and a primary transfer bias voltage or a secondary transfer bias voltage is selected. Applied.

In the primary transfer, in order to transfer the toner on the photosensitive drum 1 to the intermediate transfer belt 5 or the recording sheet P, the primary transfer bias applied to the transfer roll 9 is a voltage having a polarity opposite to the charging polarity of the toner.
In the secondary transfer, it is necessary to transfer the toner on the intermediate transfer belt 5 to the recording sheet P all at once, so the secondary transfer bias applied to the transfer roll 9 is a voltage having the same polarity as the charging polarity of the toner. It is said.

The fixing device 10 includes a heating roll 10a having a built-in heating source, and a pressure roll 10b pressed against the heating roll 10a. These are arranged in parallel and pressed against each other to form a nip portion. ing. The recording sheet P to which the toner image has been transferred is fed into the nip portion, and is heated and pressed between the heated roll 10a and the pressure roll 10b that are rotationally driven. It is to be crimped to.
The entire fixing device is rotatably supported so that the positions of the heating roll 10a and the pressure roll 10b are opposite to the recording sheet fed into the nip portion. The unfixed toner is used in any transfer mode in which the toner image is directly transferred from the photosensitive drum 1 to the recording sheet P and is transferred to the recording sheet P via the intermediate transfer belt 5. The heating roll 10a can come into contact with the surface on which the image is carried.

  The heating roll 10a is formed by forming an elastic body layer such as a heat-resistant rubber on the peripheral surface of a metal core, and forming a release layer on the surface thereof. A halogen heater is incorporated as a heating source. ing. The pressure roll 10b is obtained by coating a metal cored bar with a surface release layer.

  The double-sided conveyance path 13 conveys a recording sheet having a toner image fixed on one side to the upstream side of the transfer unit 8 when a toner image is formed on both sides, and reverses the conveyance direction of the recording sheet. It is intended to be transported. As a result, the front and back of the recording sheet are reversed in the transfer unit 8 from the time when the transfer was performed first, and the recording sheet can be sent again to the transfer unit 8 to transfer the toner image to the back surface.

The pre-transfer reversing unit 14 is provided in the paper feed conveyance path 19 on the upstream side of the transfer unit 8 and reverses the front and back of the recording sheet using a part of the double-side conveyance path 13. A first gate 14a that switches the conveyance path of the recording medium, and a first reverse conveyance roll 14b that conveys the recording sheet at a portion where the first gate contacts the conveyance path 13 for both sides.
The first gate 14a has a substantially triangular shape as shown in FIG. 2, and can be rotated by a support shaft 14c. The recording sheet is guided in a predetermined direction along the recording sheet.
Further, the first reverse conveying roll 14 b is rotated to contact the recording sheet conveyed from the paper feed tray 12 by being rotationally driven, and conveys the recording sheet. The rotation direction is reversed to convey the recording sheet. Can be switched in the reverse direction.

The first gate 14a and the first reverse conveying roll 14b as described above function as follows. When the recording sheet P pulled out from the paper supply tray 12 by the paper supply roll 17 is sent to the transfer unit 8 in the same direction, the first gate 14a is set to the first position as shown in FIG. P is fed from the paper feed conveyance path 19 to the transfer unit 8. When the recording sheet is turned upside down and fed to the transfer section, the first gate 14a is set to the second position as shown in FIG. 3, and the recording sheet P pulled out from the sheet feeding tray 12 is conveyed for both sides from the leading edge. It is sent to the road 13. Then, in a state where the rear end passes through the portion facing the first gate 14a and is sandwiched between the first reverse transport rolls 14b, the rotation direction of the first reverse transport rolls 14b is reversed, as shown in FIG. Thus, the first gate 14a is switched to the third position. As a result, the recording sheet enters the paper feed conveyance path 19 from the rear end along the edge of the first gate 14a, and is fed into the transfer unit 8 with the front and back reversed.
The recording sheet sent from the downstream side of the fixing device via the duplex conveyance path 13 is fed by setting the first gate 14a to the third position as shown in FIG. It is sent from the conveyance path 19 to the transfer unit 8.

On the other hand, the post-transfer reversing unit 15 is provided in a conveyance path on the downstream side of the fixing device 10, has a substantially triangular second gate 15 a, and a second reversal conveyance roll 15 b near the entrance of the double-side conveyance path 13. have.
The second gate 15 a switches the conveyance path between a direction in which the recording sheet conveyed from the fixing device is fed from the leading edge to the duplex conveyance path 13 and a direction in which the recording sheet is conveyed to the paper discharge roll 16. Similar to the first reverse conveying roll 14b, the second reverse conveying roll 15b is rotated and abutted against the recording sheet to be conveyed, and the rotation driving direction is reversed to reverse the recording sheet conveying direction. It can be switched to.

The post-transfer reversal part functions as follows.
When the recording sheet sent from the fixing device is discharged to the discharge tray as it is, the second gate 15 a is set to the first position as shown in FIG. 5 and the recording sheet P is discharged by the discharge roll 16. It is sent out to the paper tray 11. When reversing the front and back of the recording sheet, the second gate 15a is set to the second position as shown in FIG. 6, and the leading edge of the recording sheet is moved from the leading edge to the double-sided conveyance path 13 along the edge of the gate. It is sent. And the rotation of the 2nd inversion conveyance roll 15b is reversed in the state where the rear end was pinched by the 2nd inversion conveyance roll 15a. As a result, the recording sheet is transported in the reverse direction and sent to the paper discharge roll 16, and the recording sheet is reversed and discharged onto the paper discharge tray 11.

  When the toner image is also transferred to the back surface of the recording sheet fed from the fixing device, the second gate 15a is set to the first position (the state shown in FIG. 5), and the recording sheet is conveyed to the paper discharge roll 16. Then, the leading end protrudes into the paper discharge tray 11. Then, the rotation direction of the discharge roll 16 is reversed while the rear end portion is held by the discharge roll 16, and the second gate 15a is switched to the third position as shown in FIG. Is fed into the double-sided conveyance path 13 by reversing the conveyance direction.

Next, the operation of the image forming apparatus will be described.
First, an operation when a monochrome image is formed will be described.
When a signal to start the image forming operation is input, the photosensitive drum 1 starts to rotate, and the surface of the photosensitive drum 1 is charged almost uniformly by the charging device 2. Subsequently, image light is irradiated from the exposure device 3 to form a latent image on the surface of the photosensitive drum 1 due to the difference in electrostatic potential. Then, the photosensitive drum 1 is moved to a position facing the developing unit 4d of the color (usually black in the case of a single color) for forming an image of the developing unit 4 by the rotation of the photosensitive drum 1, and the toner is transferred from the developing unit 4d to transfer the photosensitive drum A toner image is formed on 1.

  The toner image formed on the photosensitive drum 1 is conveyed to the transfer unit 8 facing the intermediate transfer belt 5 by the circumferential movement of the photosensitive drum 1. At this time, a positive transfer bias voltage is applied to the transfer roll 9 disposed inside the intermediate transfer belt 5 and facing the photosensitive drum 1, and a transfer electric field is formed between the transfer drum 9 and the photosensitive drum 1. ing. Then, the recording sheet P is fed into the transfer unit 8, and the negatively charged toner on the photosensitive drum 1 is electrostatically attracted to the recording sheet P, and the toner image is transferred onto the recording sheet P. The

  The recording sheet P is accommodated in the sheet feeding tray 12 with the front side facing up, and the recording sheet pulled out by the sheet feeding roll 17 passes through the sheet feeding / conveying path 19 as shown in FIG. When fed into the section 8, the surface faces the photosensitive drum 1, and the toner image is transferred to the surface.

The recording sheet P to which the toner image has been transferred is sent to the fixing device 10 where it is heated and pressurized, and the toner image is fused onto the recording sheet. At this time, since the surface of the recording sheet on which the toner image is transferred is on the photosensitive drum 1, the heating roll 10a is in a position in contact with the transfer surface of the recording sheet as shown in FIG. 10b is pressurized from the back side of the recording sheet toward the heating roll 10a. Thereby, the toner image is sufficiently heated and a good fixed image is obtained.
The fixed toner image is sent to the paper discharge roll 16 in the transport direction as it is, and is stored in the paper discharge tray 11 with the surface on which the toner image is formed facing down.

Next, the operation when a color image is formed will be described.
The surface of the photosensitive drum 1 is charged almost uniformly by the charging device 2, and then the image light of the first color separated from the exposure device 3 is irradiated and the surface of the photosensitive drum 1 is latentized by the difference in electrostatic potential. An image is formed. Then, when the photosensitive drum 1 rotates, the developing unit 4 moves to a position facing one developing device 4 a, and the first color toner is transferred from the developing device 4 a to form a toner image on the photosensitive drum 1. . This toner image is conveyed to a transfer unit 8 facing the intermediate transfer belt 5 and is primarily transferred onto the intermediate transfer belt 5. On the other hand, the toner remaining on the photosensitive drum 1 after the primary transfer is removed by the cleaning device 6, and then the surface of the photosensitive drum 1 is potentialally initialized by a static elimination exposure device (not shown), and again the charging device 2. Move to the opposite position. Thereafter, the toner is transferred from the other developing devices 4 b, 4 c, 4 d to the corresponding latent images in the developing unit 4, and similarly, second, third, and fourth color toner images are sequentially formed on the intermediate transfer belt 5. It is transcribed again.

  When the toner image on the intermediate transfer belt 5 is conveyed to the transfer unit 8 facing the photosensitive drum 1, the recording sheet is fed into the transfer unit 8. The full color toner image on the intermediate transfer belt 5 is secondarily transferred onto the recording sheet P by a transfer electric field formed between the transfer roll 9 and the photosensitive drum 1. At this time, a negative secondary transfer bias voltage is applied to the transfer roll 9 so that the negatively charged toner is transferred to the recording sheet.

  On the other hand, the recording sheet P fed into the transfer unit 8 needs to be conveyed with its surface facing down, that is, the side facing the intermediate transfer belt 5. For this reason, the recording sheet P stored in the paper feed tray 12 with the front side facing up is temporarily fed to the double-sided conveyance path 13 as shown in FIG. 3 by switching the first gate 14a. When the trailing end of the recording sheet reaches the first reverse conveying roll 14b provided immediately downstream of the first gate 14a, the rotation direction of the first reverse conveying roll 14b is reversed, and the recording sheet The feed direction is reversed and sent to the paper feed path 19 from the rear end. As a result, the front and back sides are reversed, and the transfer unit 8 transfers a full-color toner image from the intermediate transfer belt 5 to the surface.

  Thereafter, the recording sheet carrying the unfixed toner image is fed into the fixing device 10, but the surface on which the toner image is transferred is opposite to the transfer surface of the recording sheet on which the monochrome image is transferred. Therefore, in the fixing device 10, as shown in FIG. 6, the frame supporting the heating roll 10a and the pressure roll 10b rotates 180 degrees, and the positions of the heating roll 10a and the pressure roll 10b with respect to the transfer surface of the recording sheet are reversed. To do. As a result, the heating roll 10a is brought into contact with the full-color toner image secondarily transferred to the recording sheet, and is heated sufficiently so that appropriate thermocompression bonding is performed.

  The recording sheet that has passed through the fixing device 10 is not sent directly to the paper discharge roll 16, but is once sent from the leading edge to the duplex conveyance path 13 by switching the second gate 15a as shown in FIG. Then, in a state where the rear end is gripped by the second reverse transport roll 15 b, the rotational driving direction of the second reverse transport roll 15 b is reversed, sent from the rear end to the paper discharge roll 16, and sent to the paper discharge tray 11. . Therefore, the recording sheet is reversed and is stored in the paper discharge tray 11 with the surface on which the toner image is formed facing down. That is, the recording sheet on which the monochrome image is formed and the surface thereof are aligned and stored in the paper discharge tray 11.

The recording sheet discharged as described above has the front side facing down (face down) in the paper discharge tray. However, when the recording sheet is discharged with the front side facing up (face up), a monochrome image is formed. The recording sheet on which the front and back sides are reversed and the recording sheet on which the images of a plurality of colors are formed may be discharged as it is after being fixed.
In the above embodiment, the recording sheet in the paper feed tray 12 is stored with the surface facing up, but may be stored with the surface facing down. At this time, when forming a monochrome image, the cover of the recording sheet is reversed and sent to the transfer unit 8. However, when forming a plurality of colors, there is time to superimpose the toner images on the intermediate transfer belt, and the recording sheet is accommodated with the front side facing up, and the front and back are reversed when forming the toner images of a plurality of colors. This is desirable for efficient image formation.

8 and 9 are a schematic structural view showing an image forming apparatus according to an embodiment of the invention according to claim 6.
In this image forming apparatus, a conveyance guide 18 is provided in a conveyance path through which a recording sheet carrying an unfixed toner image passing through the transfer unit 8 is sent to the fixing device 10. As shown in FIG. 8, the conveyance guide comes into contact with the surface of the recording sheet facing the intermediate transfer belt 5 and guides it to the fixing device, and faces the photosensitive drum 1 as shown in FIG. It is possible to move to a position where it is in contact with the guided surface. The position can be switched between when the toner image is transferred from the photosensitive drum 1 to the recording sheet by primary transfer and when the toner image is transferred from the intermediate transfer belt 5.
Other configurations of this image forming apparatus are the same as those of the image forming apparatus shown in FIG.

  In such an image forming apparatus, the toner image is transferred to the recording sheet sent to the transfer unit 8 and conveyed to the fixing device 10 while carrying an unfixed toner image. At this time, when the toner image is transferred from the photosensitive drum 1 to the recording sheet by primary transfer, the conveyance guide 18 is in contact with the surface facing the intermediate transfer belt 5 as shown in FIG. To guide the recording sheet. Further, when the toner image is transferred from the intermediate transfer belt 5 by the secondary transfer, the conveyance guide 18 comes into contact with the surface facing the photosensitive drum 1 as shown in FIG. The position is switched to guide the device 10. Therefore, the conveyance guide 18 can be guided by contacting the surface of the recording sheet where the unfixed toner image is not carried, and the conveyance guide 18 can be prevented from disturbing the unfixed toner image.

FIG. 10 is a schematic configuration diagram showing, as a reference, an image forming apparatus using a fixing device having a different configuration .
The fixing device 20 included in the image forming apparatus includes a first heating roll 20a and a second heating roll 20b each having a heating unit, which are arranged in parallel and are in pressure contact with each other. The recording sheet onto which the toner image has been transferred is sandwiched between the first heating roll 20a and the second heating roll 20b, and heated and pressurized. Further, the temperature of each heater provided in the first heating roll 20a and the second heating roll 20b can be controlled. For example, the temperature of the first heating roll 20a is controlled to a predetermined temperature suitable for fixing, The two heating rolls 20b can be controlled to be supplementarily heated. Conversely, the temperature of the second heating roll 20b is controlled to a predetermined temperature suitable for fixing, and the first heating roll 20a can be supplementarily heated.

  In such an image forming apparatus, when the toner image is transferred from the photosensitive drum 1 to the recording sheet by primary transfer, the first heating roll 20a that contacts the surface on which the toner image is transferred is suitable for fixing. The predetermined temperature is controlled and the heater of the second heating roll 20b is energized and controlled to be turned off or supplementarily. When the toner image is transferred from the intermediate transfer belt 5 by secondary transfer, the second heating roll 20b is controlled to a predetermined temperature suitable for fixing, and the heater of the first heating roll 20a is turned off or The recording sheet is controlled to be heated supplementarily. Therefore, whether the toner image is transferred from the photosensitive drum 1 to the recording sheet or transferred to the recording sheet by secondary transfer after being transferred to the intermediate transfer belt 5, The toner image is appropriately heated, and a good fixed image can be obtained.

Note that the first heating roll 20a and the second heating roll 20b turn on the heaters of both heating rolls during the warm-up at the time of starting the image forming apparatus or returning from the standby state, and set the warm-up time. It can be shortened.
When the recording sheet is cardboard or the like, the recording sheet can be heated by the heaters of both the first heating roll 20a and the second heating roll 20b. This makes it possible to reliably fix the toner image even on a recording sheet such as thick paper.

FIG. 6 is a schematic configuration diagram illustrating an image forming apparatus that is an embodiment of the invention according to claims 1 to 5. FIG. 2 is a schematic diagram for explaining operations and functions of a pre-transfer reversing unit provided in the image forming apparatus shown in FIG. 1. FIG. 2 is a schematic diagram for explaining operations and functions of a pre-transfer reversing unit provided in the image forming apparatus shown in FIG. 1. FIG. 2 is a schematic diagram for explaining operations and functions of a pre-transfer reversing unit provided in the image forming apparatus shown in FIG. 1. FIG. 2 is a schematic diagram for explaining operations and functions of a post-transfer reversing unit provided in the image forming apparatus shown in FIG. 1. FIG. 2 is a schematic diagram for explaining operations and functions of a post-transfer reversing unit provided in the image forming apparatus shown in FIG. 1. FIG. 2 is a schematic diagram for explaining operations and functions of a post-transfer reversing unit provided in the image forming apparatus shown in FIG. 1. FIG. 7 is a schematic configuration diagram illustrating an image forming apparatus that is an embodiment of the invention according to claim 6; FIG. 9 is a schematic configuration diagram illustrating an operation of a conveyance guide included in the image forming apparatus illustrated in FIG. 8. FIG. 2 is a schematic configuration diagram showing an image forming apparatus using a fixing device having a different configuration as a reference .

1: Photosensitive drum, 2: Charging device, 3: Exposure device, 4: Development unit, 5: Intermediate transfer belt, 6: Cleaning device,
8: transfer unit, 9: transfer roll, 10, 20: fixing device, 10a ,: heating roll, 10b ,: pressure roll, 20a: first heating roll, 20b: second heating roll, 11: paper discharge tray, 12: Paper feed tray, 13: Double-sided conveyance path, 14: Pre-transfer reversing part, 14a: First gate, 14b: First reverse conveying roll, 14c: Support shaft, 15: Post-transfer reversing part, 15a: First 2 gate, 15b: 2nd reverse conveyance roll, 16: paper discharge roll, 17: paper feed roll, 18: conveyance guide, 19: paper feed conveyance path

Claims (6)

An image carrier in which a latent image due to a difference in electrostatic potential is formed on an endless peripheral surface;
An image forming unit that forms a toner image by transferring toner to a latent image on the image carrier;
An intermediate transfer member that is disposed so as to face the image carrier and onto which a toner image on the image carrier is transferred,
A region where the image carrier and the intermediate transfer member face each other is a transfer portion,
The transfer unit includes a primary transfer region for transferring a toner image on the image carrier to the intermediate transfer member or a recording medium, and a toner image that is temporarily transferred onto the intermediate transfer member to the recording medium. Including the next transfer area,
A double-sided conveyance path for retransmitting a recording medium having a toner image transferred on one side thereof to the upstream side of the transfer unit;
Anda front reversing portion transferring reversing the front and back sides of the recording medium before the recording medium is first passed through the transfer portion
The image forming apparatus, wherein the pre-transfer reversing unit feeds the leading end of the recording medium to the double-sided conveyance path, reverses the conveyance direction, and conveys the recording medium to the transfer unit . Passing the recording medium is the transfer unit, after the toner image transferred is fixed by the fixing device, according to claim 1, characterized in that it comprises a post-transcriptional reversing unit for reversing the front and back of the recording medium Image forming apparatus. The image forming apparatus according to claim 2, wherein the post-transfer reversing unit feeds the recording medium from the leading edge to the double-sided conveyance path, reverses the conveyance direction, and conveys the recording medium to a recording medium discharge port. apparatus. The said transfer part produces | generates the primary transfer electric field for primary transfer, and the secondary transfer electric field of the opposite polarity to the said primary transfer electric field , The Claim 1, 2 or Claim characterized by the above-mentioned. Item 4. The image forming apparatus according to Item 3 . An image carrier in which a latent image due to a difference in electrostatic potential is formed on an endless peripheral surface;
An image forming unit that forms a toner image by transferring toner to a latent image on the image carrier;
An intermediate transfer member that is arranged to face the image carrier and onto which a toner image on the image carrier is transferred;
A toner image transfer portion provided in a region where the image carrier and the intermediate transfer member face each other;
A transport device for feeding a recording medium to the transfer section;
A fixing device that heats and pressurizes the toner image transferred to the recording medium by the transfer unit and fixes the toner image on the recording medium,
The transfer unit includes a primary transfer region for transferring the toner image on the image carrier to the intermediate transfer member or the recording medium, and a secondary for transferring the toner image temporarily transferred onto the intermediate transfer member to the recording medium. Including a transcription region,
The fixing device includes a heating member that contacts a recording medium that holds an unfixed toner image in a heated state, and a pressure member that presses the recording medium against the heating member,
The image forming apparatus according to claim 1, wherein the heating member and the pressure member are supported so as to be switchable so that both of the positions of the heating member and the pressure member are reversed and the position of the recording medium with respect to the conveyance path is reversed. . An image carrier in which a latent image due to a difference in electrostatic potential is formed on an endless peripheral surface;
An image forming unit that forms a toner image by transferring toner to a latent image on the image carrier;
An intermediate transfer member that is arranged to face the image carrier and onto which a toner image on the image carrier is transferred;
A toner image transfer portion provided in a region where the image carrier and the intermediate transfer member face each other;
A transport device for feeding a recording medium to the transfer section;
A fixing device that heats and pressurizes the toner image transferred to the recording medium by the transfer unit and fixes the toner image on the recording medium;
A conveyance guide for guiding the conveyance of the recording medium carrying the transferred unfixed toner image,
The transfer unit includes a primary transfer region for transferring a toner image on the image carrier to the intermediate transfer member or a recording medium, and a toner image that is temporarily transferred onto the intermediate transfer member to the recording medium. Including the next transfer area,
The image forming apparatus, wherein the conveyance guide is capable of switching a position so as to guide the recording medium in contact with a surface of the recording medium on which the toner image is not transferred.

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