JP3843988B2 - Image forming apparatus - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a digital copying machine or a printer that employs an electrophotographic method, and more particularly to an image forming apparatus that secondarily transfers a toner image formed on an intermediate transfer member onto a recording medium. .

JP 2000-112190 A JP-A-10-216992

2. Description of the Related Art Conventionally, as an image forming apparatus such as a digital copying machine or a printer that employs the above-described electrophotographic method, a plurality of toner images such as yellow (Y), magenta (M), cyan (C), and black (K) are formed. An image forming unit is provided, and toner images of each color formed by the image forming units such as yellow (Y), magenta (M), cyan (C), and black (K) are sequentially superimposed on the intermediate transfer belt. There is a configuration in which a color image is formed by performing primary transfer in a combined state and then performing secondary transfer and fixing on the recording paper collectively from the intermediate transfer belt.
In such an image forming apparatus, as shown in FIGS. 11 and 12, yellow (Y), magenta (M), cyan (C), black (K), and the like primary-transferred multiple times onto the intermediate transfer belt 100. When the toner image is collectively transferred onto the recording paper 101, the recording paper 101 is synchronized with the toner image on the intermediate transfer belt 100 and the pre-secondary shoots 103 and 104 are moved by the registration roll 102. Accordingly, the backup roll 105 and the secondary transfer roll 106 are configured to be conveyed to the secondary transfer unit 107 that is in pressure contact with each other via the intermediate transfer belt 100.

  However, the above prior art has the following problems. That is, in the case of the conventional image forming apparatus, as shown in FIGS. 11 and 12, when the leading end of the recording paper 101 enters the secondary transfer unit 107, the secondary transfer unit 107 is impacted by the impact of the paper entry. The position of the paper 101 located upstream of the recording paper 101 is disturbed, and the toner image secondarily transferred to the vicinity of the leading edge of the recording paper 101 is disturbed.

In the case of the conventional image forming apparatus, as shown in FIGS. 11 and 12, the pre-secondary transfer chutes 103 and 104 positioned upstream of the secondary transfer unit 107 are disposed at the rear end of the recording paper 101. When the sheet passes, the trailing edge of the sheet 101 rebounds due to the stiffness (rigidity) of the sheet itself, causing a problem in that image disturbance occurs due to contact with the surface of the intermediate transfer belt 100. The image disturbance due to the rebound of the trailing edge of the sheet is more likely to occur as the sheet is thicker. This is because the paper that is stiffer has a larger jumping force and easily disperses the toner on the intermediate transfer belt.

  More specifically, in the case of the conventional image forming apparatus, when the thick paper 101 enters the nip portion of the secondary transfer portion 107, the amount of biting of the secondary transfer roll 106 increases by the thickness of the paper 101, and the nip is increased. The amount will also increase. Since the pressing force F at which the secondary transfer roll 106 is pressed against the backup roll 105 is sufficiently larger than the increased nip force, the abutting portion is not separated and the amount of biting is constant. For this reason, the thick paper 101 is warped due to the increased nip force, and the rebound force when leaving the pre-secondary transfer chute 104 is increased, which causes a problem that the toner on the intermediate transfer belt 100 is scattered. In particular, the secondary transfer portion 107 where the secondary transfer roll 106 and the backup roll 105 are pressed against each other has a convex shape on the side of the secondary transfer roll 106 and a concave shape on the side of the backup roll 105 depending on the relationship of the surface hardness of the roll. When the nip portion is set to be formed, the rear end of the recording sheet 101 is deformed so as to warp toward the intermediate transfer belt 100 in accordance with the shape of the nip portion. As a result, the rebound force at the time of leaving the toner increases by one, and the problem that the toner on the intermediate transfer belt 100 is scattered occurs remarkably.

Accordingly, the present invention has been made to solve the above-described problems of the prior art, and the object of the present invention is when a recording medium such as recording paper enters the secondary transfer portion, Provided is an image forming apparatus capable of preventing a toner image from being disturbed by rebounding by the stiffness of the recording medium after the trailing end has passed a guide member that guides the recording medium to the secondary transfer unit. There is to do.
The object of the present invention is not to attach the secondary transfer roll to the image forming apparatus main body, but to attach the secondary transfer roll by attaching it to a member formed separately from the image forming apparatus main body. An object of the present invention is to provide an image forming apparatus having an improved degree of freedom.

In order to achieve the above object, the invention described in claim 1
An intermediate transfer belt stretched between a plurality of rolls;
A secondary transfer unit that secondary-transfers the toner image primarily transferred to the intermediate transfer belt onto a sheet by a secondary transfer roll;
A guide unit for guiding the sheet to the secondary transfer unit;
In an image forming apparatus having
The secondary transfer roll is rotatably attached to a support frame configured separately from the frame on the image forming apparatus main body side, and the secondary transfer roll attaches the support frame to the image forming apparatus main body side. The spring is pressed against the backup roll fixed to the frame on the image forming apparatus main body side where the intermediate transfer belt is stretched, and the rotating shaft of the secondary transfer roll abuts against the frame on the image forming apparatus main body side. Installed in the state
When the recording medium having a basis weight equal to or less than the first basis weight enters the secondary transfer portion, the abutting force that abuts the secondary transfer roll against the frame on the image forming apparatus main body side enters the secondary transfer portion. When a recording medium having a grammage greater than the second grammage and entering the secondary transfer portion is larger than the force by which the abutment portion of the secondary transfer roll is separated from The image forming apparatus is characterized by being set small .

In addition, the invention described in claim 2
An intermediate transfer belt stretched between a plurality of rolls;
A secondary transfer unit that secondary-transfers the toner image primarily transferred to the intermediate transfer belt onto a sheet by a secondary transfer roll and a backup roll;
A guide unit for guiding the sheet to the secondary transfer unit;
In an image forming apparatus having
The backup roll is attached in a state where the position is fixed to the frame on the image forming apparatus main body side ,
The secondary transfer roll is rotatably attached to a support frame configured separately from the frame on the image forming apparatus main body side, and the secondary transfer roll attaches the support frame to the image forming apparatus main body side. The spring is pressed against the backup roll that stretches the intermediate transfer belt, and the rotating shaft of the secondary transfer roll is attached in a state of abutting the frame on the image forming apparatus main body side,
When the recording medium having a basis weight equal to or less than the first basis weight enters the secondary transfer portion, the abutting force that abuts the secondary transfer roll against the frame on the image forming apparatus main body side enters the secondary transfer portion. When a recording medium having a grammage greater than the second grammage and entering the secondary transfer portion is larger than the force by which the abutment portion of the secondary transfer roll is separated from The image forming apparatus is characterized by being set small .

Furthermore, the invention described in claim 3 is the image forming apparatus according to claim 1 or 2 , wherein the first basis weight is 80 gsm .

According to a fourth aspect of the present invention, in the image forming apparatus according to the first or second aspect, the second basis weight is 160 gsm .

  Further, in the invention described in claim 5, the sheet is transported along the side surface of the image forming apparatus and fed to a secondary transfer portion which is a press-contact portion between the secondary transfer roll and the backup roll. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.

According to the present invention, when a recording medium such as recording paper enters the secondary transfer portion, or after the rear end of the recording medium passes through the guide member that guides the recording medium to the secondary transfer portion, It is possible to provide an image forming apparatus capable of preventing the toner image from being disturbed by rebounding with the strength of the stiffness.
According to the present invention, the secondary transfer roll is not attached to the image forming apparatus main body, but is attached to a member configured separately from the image forming apparatus main body. An improved image forming apparatus can be provided.

Embodiments of the present invention will be described below with reference to the drawings.
Embodiment 1
FIG. 2 shows a tandem digital color printer as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 shows a tandem type digital color copying machine as an image forming apparatus according to Embodiment 1 of the present invention.

  2 and 3, reference numeral 1 denotes a main body of a tandem type digital color printer and copying machine. In the case of a digital color copying machine, as shown in FIG. An automatic document feeder (ADF) 3 that automatically conveys the documents one by one and a document reading device 4 that reads an image of the document 2 conveyed by the automatic document feeder 3 are provided. The document reader 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 composed of a CCD or the like is scanned and exposed through a reduction optical system, and the color material reflected light image of the document 2 is formed at a predetermined dot density (for example, 16 dots / mm) by the image reading element 11. It is supposed to read.

  The color material reflected light image of the document 2 read by the document reading device 4 is, for example, IPS (red (R), green (G), blue (B) (8 bits each) as document reflectance data of three colors. (Image Processing System) 12, and the IPS 12 performs predetermined corrections such as shading correction, position shift correction, brightness / color space conversion, gamma correction, frame deletion, color / moving editing, etc. on the reflectance data of the document 2. Image processing is performed. The IPS 12 also performs predetermined image processing on image data sent from a personal computer or the like.

  The image data that has been subjected to the predetermined image processing by the IPS 12 as described above is also four colors of yellow (Y), magenta (M), cyan (C), and black (K) (each 8 bits) by the IPS 12. As described below, the image forming units 13Y, 13M, 13C, and 13K for each color of yellow (Y), magenta (M), cyan (C), and black (K) are converted. The ROS (Raster Output Scanner) 14 is used, and the ROS 14 serving as the image exposure apparatus performs image exposure with the laser beam LB in accordance with document reproduction color material gradation data of a predetermined color.

  By the way, inside the tandem type digital color printer and the copying machine main body 1, as shown in FIGS. 2 and 3, four colors of yellow (Y), magenta (M), cyan (C), and black (K) are provided. The two image forming units 13Y, 13M, 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 roughly divided, a photosensitive drum 15 as an image carrier that is rotationally driven at a predetermined speed, and the photosensitive drum. A charging roll 16 for primary charging that uniformly charges the surface of 15, and an ROS 14 as an image exposure device that forms an electrostatic latent image by exposing an image corresponding to a predetermined color on the surface of the photosensitive drum 15. And a developing unit 17 for developing the electrostatic latent image formed on the photosensitive drum 15 with toner of a predetermined color, and a cleaning device 18 for cleaning the surface of the photosensitive drum 15.

  As shown in FIGS. 2 and 3, the ROS 14 is configured in common to the four image forming units 13Y, 13M, 13C, and 13K, and uses four semiconductor lasers (not shown) to reproduce the color reproduction gradation material for each color. The laser beams LB-Y, LB-M, LB-C, and LB-K are emitted from these semiconductor lasers according to the gradation data. Of course, the ROS 14 may be individually configured for each of a plurality of image forming units. The laser beams LB-Y, LB-M, LB-C, and LB-K emitted from the semiconductor laser are irradiated to the rotary polygon mirror 19 through an f-θ lens (not shown), and deflected by the rotary polygon mirror 19. Scanned. The laser beams LB-Y, LB-M, LB-C, and LB-K deflected and scanned by the rotary polygon mirror 19 are scanned obliquely from below on the photosensitive drum 15 through a plurality of reflection mirrors (not shown). Exposed.

  As shown in FIG. 2, the ROS 14 scans and exposes an image on the photosensitive drum 15 from below. Therefore, the ROS 14 includes four image forming units 13Y, 13M, 13C, and 13K located above. There is a possibility that toner or the like may fall from the developing unit 17 and be contaminated. Therefore, the periphery of the ROS 14 is hermetically sealed by a rectangular parallelepiped frame 20, and four laser beams LB-Y, LB-M, LB-C, and LB-K are placed on the upper portion of the frame 20, Transparent glass windows 21Y, 21M, 21C, and 21K as shield members are provided for exposure on the photosensitive drums 15 of the image forming units 13Y, 13M, 13C, and 13K. And these glass-made windows 21Y, 21M, 21C, and 21K are members located on the uppermost side in the optical path along the laser beam LB of the ROS 14 as the image exposure apparatus.

  From the IPS 12, the image of each color is provided to the ROS 14 provided in common to the image forming units 13Y, 13M, 13C, and 13K of each color of yellow (Y), magenta (M), cyan (C), and black (K). Data is sequentially output, and the laser beams LB-Y, LB-M, LB-C, and LB-K emitted from the ROS 14 in accordance with the image data are scanned and exposed on the surface of the corresponding photosensitive drums 15 to statically. An electrostatic latent image is formed. The electrostatic latent images formed on the photosensitive drum 15 are respectively developed in yellow (Y), magenta (M), cyan (C), and black (K) colors by developing units 17Y, 17M, 17C, and 17K. Developed as a toner image.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images sequentially formed on the photosensitive drums 15 of the image forming units 13Y, 13M, 13C, and 13K are as follows. On the intermediate transfer belt 25 disposed over the image forming units 13Y, 13M, 13C, and 13K, the images are transferred in multiple by the primary transfer roll 26. The intermediate transfer belt 25 is wound around the drive roll 27 and the backup roll 28 with a constant tension, and is driven by a drive roll 27 that is rotationally driven by a dedicated drive motor with excellent constant speed (not shown). The circuit is circulated at a predetermined speed in the direction of the arrow. As the intermediate transfer belt 25, for example, a flexible synthetic resin film such as PET is formed in a band shape, and both ends of the synthetic resin film formed in a band shape are connected by means such as welding, thereby endless A belt-shaped one is used.

  The yellow (Y), magenta (M), cyan (C), and black (K) toner images transferred onto the intermediate transfer belt 25 in a multiple manner are transferred to the backup roll 28 by a secondary transfer roll 29. The transfer sheet 30 that has been secondarily transferred onto the transfer sheet 30 by the pressure contact force and electrostatic force and onto which the toner images of these colors have been transferred is conveyed to a fixing device 31 positioned above. The secondary transfer roll 29 is in pressure contact with the side of the backup roll 28, and secondary-transfers each color toner image onto a transfer sheet 30 conveyed from below to above. The transfer paper 30 onto which the toner images of the respective colors have been transferred is subjected to a fixing process with heat and pressure by a fixing device 31 and then discharged onto a discharge tray 33 provided on the upper portion of the main body 1 by a discharge roll 32. The

  As shown in FIGS. 2 and 3, the transfer sheet 30 has a predetermined size from a sheet feeding cassette 34, and is fed via a sheet conveying path 37 by a sheet feeding roller 35 and a pair of sheets separating and conveying rollers 36. Once conveyed to the registration roll 38, it is stopped. The transfer paper 30 supplied from the paper feed cassette 34 is sent to the secondary transfer position of the intermediate transfer belt 35 by a registration roll 38 that rotates at a predetermined timing.

  In the digital color printer and the copying machine, when full-color double-sided copying is performed, the transfer sheet 30 on which an image is fixed on one side is not directly discharged onto the discharge tray 33 by the discharge roll 32 but is illustrated. The conveyance direction is switched by the switching gate not to be conveyed, and the sheet is conveyed to the duplex conveyance unit 40 via the sheet conveyance roller pair 39. Then, in this double-sided conveyance unit 40, the transfer sheet 30 is conveyed again to the registration roll 38 with the front and back sides of the transfer paper 30 being reversed by a pair of conveyance rollers (not shown) provided along the conveyance path 41. After the image is transferred and fixed on the back surface of the transfer paper 30, it is discharged onto the discharge tray 33.

  2 and 3, 44Y, 44M, 44C, and 44K supply toners of predetermined colors to the developing devices 17 of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Each toner cartridge is shown.

  FIG. 4 shows the image forming units of the digital color printer and the copying machine.

  The four image forming units 13Y, 13M, 13C, and 13K of yellow, magenta, cyan, and black are all configured similarly as shown in FIG. 4, and these four image forming units 13Y. , 13M, 13C, and 13K, as described above, yellow, magenta, cyan, and black toner images are sequentially formed at predetermined timings. As described above, the image forming units 13Y, 13M, 13C, and 13K for the respective colors are provided with the photosensitive drums 15, and the surfaces of these photosensitive drums 15 are uniformly formed by the charging rolls 16 for primary charging. Charged. Thereafter, the surface of the photosensitive drum 15 is scanned and exposed to an image forming laser beam LB emitted from the ROS 14 according to the image data, and an electrostatic latent image corresponding to each color is formed. The laser beam LB scanned and exposed on the photosensitive drum 15 is set so as to be exposed at a predetermined inclination angle α from an obliquely lower position slightly to the right side from directly below the photosensitive drum 15. The electrostatic latent image formed on the photosensitive drum 15 is converted into yellow, magenta, cyan, and black colors by the developing roll 17a of the developing unit 17 of each image forming unit 13Y, 13M, 13C, and 13K. The visible toner images are developed with toner, and these visible toner images are sequentially transferred in multiple onto the intermediate transfer belt 25 by the charging of the primary transfer roll 26.

  Residual toner, paper dust, and the like are removed from the surface of the photosensitive drum 15 after the toner image transfer process by the cleaning device 18 to prepare for the next image forming process. The cleaning device 18 includes a cleaning blade 42, and the cleaning blade 42 removes residual toner, paper dust, and the like on the photosensitive drum 15. Further, the surface of the intermediate transfer belt 25 after the toner image transfer process is finished, as shown in FIGS. 2 and 3, the residual toner and paper dust are removed by the cleaning device 43, and the next image forming process. Prepare for. The cleaning device 43 includes a cleaning brush 43a and a cleaning blade 43b. The cleaning brush 43a and the blade 42 remove residual toner, paper dust, and the like on the intermediate transfer belt 25.

  By the way, in this embodiment, a paper tray, a conveyance path for conveying the paper fed out from the paper tray along the side surface of the image forming apparatus, an intermediate transfer belt stretched around a plurality of rolls, An image having a secondary transfer unit that collectively transfers a toner image primarily transferred to the intermediate transfer belt onto a sheet by a secondary transfer roll, and a guide unit that guides the sheet to the secondary transfer unit. In the forming apparatus, the secondary transfer roll is configured to be attached to a support frame configured separately from the main body of the image forming apparatus.

  A backup roll is disposed so as to face the secondary transfer roll via the intermediate transfer belt.

  Further, in this embodiment, the secondary transfer roll is configured to be pressed against the side of the backup roll.

  In this embodiment, the sheet is transported along the side surface of the image forming apparatus and is fed to a secondary transfer portion which is a pressure contact portion between the secondary transfer roll and the backup roll. It is configured.

  That is, in this embodiment, as shown in FIGS. 1 and 5, among the plurality of rolls that support the intermediate transfer belt 25 so as to be able to circulate, secondary transfer is performed to the backup roll 28 via the intermediate transfer belt 25. Pre-secondary transfer chutes 51 and 52 as guide members for guiding the recording medium 30 conveyed by the resist roll 38 to the secondary transfer unit 50 are disposed on the upstream side of the secondary transfer unit 50 in contact with the roll 29. Has been. In this embodiment, the surface layer of the backup roll 28 is set to have a higher hardness than the surface layer of the secondary transfer roll 29, and the secondary roll where the backup roll 28 and the secondary transfer roll 29 are in pressure contact with each other. In the transfer unit 50, the secondary transfer roll 29 side is deformed so as to have a concave shape.

Further, as shown in FIG. 6, the position of the backup roll 28 is fixed to a frame 53 on the printer main body 1 side, and the secondary transfer roll 29 uses the rotation shaft 29 a of the secondary transfer roll 29 as a frame 53. In this state, the secondary transfer roll 29 is urged toward the backup roll 28 by a predetermined pressing force F through a support frame 54 that rotatably supports the secondary transfer roll 29. A nip portion is formed between the secondary transfer roll 29 and the backup roll 28 over a predetermined width. Note that a peeling member 56 for peeling the recording paper is provided in a separated state at the exit of the nip portion of the secondary transfer portion.

  The pre-secondary transfer chutes 51 and 52 are made of, for example, a pair of plate members made of metal or synthetic resin, and the pre-secondary transfer chutes 51 and 52 made of the pair of plate-like members are formed on the recording paper 30. It is arrange | positioned so that the surface side and the back surface side may be opposed. The pre-secondary transfer shoots 51 and 52 are not necessarily provided over the entire width of the recording paper 30 and may be provided at positions where the recording paper 30 can be stably guided.

Of the pre-secondary transfer chutes 51 and 52 formed of the pair of plate-like members, the pre-secondary transfer chute 52 located on the back side (secondary transfer roll side) of the recording paper 30 is shown in FIGS. As shown in FIG. 5, the base end portion 52a linearly extending over a predetermined length along the conveyance direction of the registration roll 38 and the base end portion 52a are integrally connected to the tip end of the intermediate transfer portion. The intermediate portion 52b is bent toward the belt 25 by a relatively small angle, and the curved front end portion 52c is bent from the front end of the intermediate portion 52b toward the secondary transfer roll 29 again.

  On the other hand, among the pre-secondary transfer chutes 51 and 52 formed of the pair of plate-like members, the pre-secondary transfer chute 51 located on the surface side (intermediate transfer belt side) of the recording paper 30 is fed with the resist roll 38. A base end portion 51a that extends shortly to the vicinity of the surface of the resist roll 38 along the direction, an intermediate portion 51b that is inclined to the intermediate transfer belt 25 side by an angle of about 45 degrees with respect to the base end portion 51a, and A front end 51c that is bent again from the front end of the intermediate portion 51b toward the secondary transfer roll 29 is provided.

  The tip 51c of the pre-secondary transfer chute 51 is set to have an angle of 40 degrees or less with the intermediate transfer belt 25, about 20 degrees in the illustrated example. It is configured to be spaced apart.

  As shown in FIGS. 1 and 5, the pre-secondary transfer chute 52 for bending the recording paper 30 conveyed by the registration roll 38 toward the intermediate transfer belt 25 is provided on the pre-secondary transfer chutes 51 and 52. The first bent portion 57 is formed by the intermediate portion 52b, and the recording paper 30 bent to the intermediate transfer belt 25 side by the first bent portion 57 is bent to the secondary transfer roll 29 side. A second bent portion 58 is formed by the tip 51 c of the pre-secondary transfer chute 51. Therefore, the pre-secondary transfer shoots 51 and 52 are provided with bent portions 57 and 58 for bending the recording medium 30 into a substantially S shape.

  As a result, the recording paper 30 conveyed by the registration roll 38 is conveyed linearly along the base end portions 51a, 52a of the pre-secondary transfer chutes 51, 52 as shown in FIG. It strikes against the intermediate portion 52b of the pre-secondary transfer chute 52 on the back surface side that forms one bent portion 57, and is conveyed while being bent toward the intermediate transfer belt 25 side. Thereafter, the recording paper 30 bent toward the intermediate transfer belt 25 abuts against the front end portion 51c of the pre-secondary transfer chute 51 on the surface side forming the second bent portion 58, and bends toward the secondary transfer roll 29. Then, it is transported to the secondary transfer section 50 along the front end portions 51c and 52c of the pre-secondary transfer chutes 51 and 52 arranged substantially in parallel.

  With the above configuration, in the image forming apparatus according to this embodiment, when a recording medium such as a recording sheet enters the secondary transfer unit as described below, the rear end of the recording medium uses the second recording medium. After passing through the guide member that guides to the next transfer portion, it is possible to prevent the toner image from being disturbed by rebounding due to the stiffness of the recording medium.

  That is, in this embodiment, as shown in FIGS. 2 to 4, the toner images of yellow, magenta, cyan, black and the like sequentially transferred onto the intermediate transfer belt 25 are moved along with the movement of the intermediate transfer belt 25. Are conveyed to the secondary transfer unit 50. Then, as shown in FIG. 1, the toner image moved to the secondary transfer unit 50 is synchronized with the toner image on the recording paper 30 conveyed by the registration roll 38 by the secondary transfer roll 29. Secondary transferred.

  At that time, the recording paper 30 is conveyed to the secondary transfer section 50 by the registration roll 38, but the recording paper 30 is guided by the pre-secondary transfer chutes 51 and 52. As shown in FIGS. 1 and 7, the pre-secondary transfer shoots 51 and 52 are provided in the middle of the pre-secondary transfer chute 52 that bends the recording paper 30 conveyed by the resist roll 38 toward the intermediate transfer belt 25. A first bent portion 57 is formed by the portion 52b, and the recording paper 30 bent to the intermediate transfer belt 25 side by the first bent portion 57 is bent to the secondary transfer roll 29 side. A second bent portion 58 is formed by the tip portion 51 c of the pre-transfer chute 51.

  Therefore, the recording paper 30 conveyed by the resist roll 38 is conveyed linearly along the base end portions 51a and 52a of the pre-secondary transfer chutes 51 and 52, and then forms the first bent portion 57. It strikes against the intermediate portion 52b of the pre-secondary transfer chute 52 on the back surface side, and is conveyed while being bent toward the intermediate transfer belt 25 side. Thereafter, the recording paper 30 bent toward the intermediate transfer belt 15 abuts against the front end portion 51c of the pre-secondary transfer chute 51 on the surface side that forms the second bent portion 58, and is bent toward the secondary transfer roll 29. Then, it is transported to the secondary transfer section 50 along the front end portions 51c and 52c of the pre-secondary transfer chutes 51 and 52 arranged substantially in parallel.

  Therefore, the recording paper 30 conveyed to the secondary transfer section 50 by the pre-secondary transfer shoots 51 and 52 is bent toward the intermediate transfer belt 25 by the first bent section 57 as shown in FIG. Thereafter, the second bent portion 58 is bent to the secondary transfer roll 29 side, and as a result, stiffness (rigidity) is weakened and a curl (down curl) on the secondary transfer roll 29 side is formed.

  Therefore, the recording paper 30 is weak in stiffness (rigidity), the impact when entering the nip portion of the secondary transfer portion 50 is reduced, and image disturbance is less likely to occur. Further, when the recording paper 30 passes through the pre-secondary transfer shoots 51 and 52, the paper 30 is down-curled by the second bent portion 58, so that the rear edge of the paper is the intermediate transfer belt as shown in FIG. The force that rebounds up to 25 is reduced, and toner scattering can be reduced.

  In this embodiment, the recording paper 30 is conveyed along the pre-secondary transfer chute 51 on the image side, that is, the pre-secondary transfer chute 51 on the side close to the intermediate transfer belt 25. For this reason, the recording paper 30 enters the secondary transfer portion at a shallower angle than along the pre-secondary transfer chute 52 on the secondary transfer roll 29 side. As a result, it is possible to reduce the impact of the paper entry and the impact when the rear edge of the paper leaves the pre-secondary transfer chute 51. Further, since the leading edge of the sheet is along the pre-secondary transfer chute 51, the leading edges of the sheet are aligned and easily come into contact with the intermediate transfer belt 25, and image disturbance at the leading edge of the sheet is reduced.

  Further, in this embodiment, the first bent portion 57 that bends toward the intermediate transfer belt 25 is provided on the pre-secondary transfer chute 52 that is located upstream of the secondary transfer portion 50, so that the first bent portion is provided. The recording paper 30 that has passed through 57 enters the secondary transfer section 50 along the pre-secondary transfer chute 51 on the side opposite to the secondary transfer roll 29, that is, on the image surface side. For this reason, the effect of weakening the stiffness of the paper and the effect of reducing the paper entry angle can be obtained.

  Furthermore, in this embodiment, in the pre-secondary transfer chutes 51 and 52 located upstream of the secondary transfer unit 50, the first and second bent portions 57 and 58 in which the recording paper 30 bends in opposite directions to each other. Therefore, the stiffness of the recording paper 30 is weakened, and the impact when the recording paper 30 enters the secondary transfer portion 50 can be further weakened than the above-described action. Further, since the orientation of the recording sheet 30 is changed to the secondary transfer roll 29 side by the tip 51c of the pre-secondary transfer chute 51 just before the secondary transfer, the secondary is formed along the chute 51 on the image surface side described above. The image is conveyed to the transfer unit 50 and image disturbance at the leading end and the trailing end of the paper 30 can be prevented.

  In addition, when the recording paper enters the secondary transfer portion in a substantially horizontal direction, the paper receives a downward force due to gravity, and the leading edge of the paper is relatively stable. On the other hand, as shown in FIG. 1, when the recording paper 30 enters the secondary transfer unit 50 facing substantially upward in the vertical direction, the leading edge of the paper is relatively likely to vary because there is no gravity assist.

  For this reason, by adopting the above configuration, the sheet 30 is placed along the pre-secondary transfer chute 51 on the intermediate transfer belt 25 side when the recording sheet 30 is conveyed substantially upward in the vertical direction. The variation at the tip can be suppressed, and a greater effect can be obtained.

Embodiment 2
9 and 10 show the second embodiment of the present invention. The same reference numerals are given to the same parts as those in the first embodiment, and in this second embodiment, the secondary transfer is performed. In a configuration in which the amount of biting of the roll with respect to the backup roll is set to be constant, when a recording medium having a basis weight of 80 gms or less enters the secondary transfer portion with an abutting force against the secondary transfer roll against the opposing member In addition, when a recording medium having a basis weight of 160 gms or more, which is greater than the force with which the abutting portion of the secondary transfer roll is separated, enters the secondary transfer portion, the abutting portion of the secondary transfer roll is separated. It is configured to be set smaller than the force to be applied.

That is, in this embodiment, as shown in FIGS. 9 and 10, the backup roll 28 is rotatably disposed in a state where the position is fixed to the frame 53 on the printer body 1 side, and the secondary transfer is performed. The roll 29 is rotatably disposed on a support frame 54 for supporting the secondary transfer roll 29. The secondary transfer roll 29 is urged toward the backup roll 28 by a spring 55 through a support frame 54 with a predetermined pressing force F ′, and the rotating shaft 29a of the secondary transfer roll 29 is moved to the main body side. It is arranged in a state where it abuts against the frame 53.

  By the way, the pressing force F ′ of the spring 55 that urges the secondary transfer roll 29 toward the backup roll 28 when the recording medium 30 having a basis weight of 80 gms or less enters the secondary transfer portion 50. When the recording medium 30 with a grammage of 160 gms or more enters the secondary transfer portion 50, the abutting portion of the secondary transfer roll 29 is separated from the force by which the abutting portion of the transfer roll 29 is separated. It is set smaller than the force.

  In the above configuration, in this embodiment, as shown in FIG. 9, the recording medium 30 having a pressing force F ′ for pressing the secondary transfer roll 29 against the backup roll 28 with a basis weight of 160 gms or more is the secondary transfer section 50. Is set to be smaller than the force by which the abutting portion of the secondary transfer roll 28 is separated when entering the secondary transfer roll 28, so that a thick paper having a basis weight of 160 gms or more enters the secondary transfer portion 50 as the recording medium 30. The secondary transfer roll 29 is not brought into contact with the backup roll 28. For this reason, the curling of the sheet 30 due to the nip force of the secondary transfer unit 50 is reduced, so that the rear end of the sheet 30 does not hit the intermediate transfer belt 25 strongly when it leaves the pre-secondary transfer chutes 51 and 52. The occurrence of image disturbance can be prevented.

  In this embodiment, as shown in FIG. 10, the recording medium 30 having a pressing force F ′ that presses the secondary transfer roll 29 against the backup roll 28 and having a basis weight of 80 gms or less enters the secondary transfer unit 50. Sometimes, the force of separating the abutting portion of the secondary transfer roll 29 is set to be larger, so even if a thin paper having a basis weight of 80 gms or less enters the secondary transfer portion 50 as the recording medium 30. The secondary transfer roll 29 is favorably subjected to secondary transfer without leaving the abutment against the backup roll 28. In addition, in the case of a thin paper having a basis weight of 80 gms or less, the stiffness is weak, so that the paper 30 is not warped by the nip force of the secondary transfer unit 50, and the rear end of the paper 30 leaves the pre-secondary transfer chute 51. In some cases, the intermediate transfer belt 25 is not strongly abutted, and the occurrence of image disturbance can be prevented.

  Other configurations and operations are the same as those of the above-described embodiment, and thus description thereof is omitted.

FIG. 1 is a block diagram showing a main part of an image forming apparatus according to Embodiment 1 of the present invention. FIG. 2 is a block diagram showing a tandem digital color printer as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 3 is a block diagram showing a tandem type digital color copying machine as an image forming apparatus according to Embodiment 1 of the present invention. FIG. 4 is a configuration diagram illustrating the image forming unit. FIG. 5 is a block diagram showing a main part of the image forming apparatus according to Embodiment 1 of the present invention. FIG. 6 is a block diagram showing the main part of the image forming apparatus according to Embodiment 1 of the present invention. FIG. 7 is an explanatory view showing the operation of the image forming apparatus according to Embodiment 1 of the present invention. FIG. 8 is an explanatory view showing the operation of the image forming apparatus according to Embodiment 1 of the present invention. FIG. 9 is a block diagram showing a main part of an image forming apparatus according to Embodiment 2 of the present invention. FIG. 10 is a block diagram showing a main part of an image forming apparatus according to Embodiment 2 of the present invention. FIG. 11 is a block diagram showing a main part of a conventional image forming apparatus. FIG. 12 is a block diagram showing a main part of a conventional image forming apparatus.

Explanation of symbols

25: intermediate transfer belt, 28: backup roll, 29: secondary transfer roll, 30: recording medium, 51: recording medium, 51, 52: chute before secondary transfer (guide member), 57: first bent portion, 58: Second bent portion.

Claims (5)

An intermediate transfer belt stretched between a plurality of rolls;
A secondary transfer unit that secondary-transfers the toner image primarily transferred to the intermediate transfer belt onto a sheet by a secondary transfer roll;
A guide unit for guiding the sheet to the secondary transfer unit;
In an image forming apparatus having
The secondary transfer roll is rotatably attached to a support frame configured separately from the frame on the image forming apparatus main body side, and the secondary transfer roll attaches the support frame to the image forming apparatus main body side. The spring is pressed against the backup roll fixed to the frame on the image forming apparatus main body side where the intermediate transfer belt is stretched, and the rotating shaft of the secondary transfer roll abuts against the frame on the image forming apparatus main body side. Installed in the state
When the recording medium having a basis weight equal to or less than the first basis weight enters the secondary transfer portion, the abutting force that abuts the secondary transfer roll against the frame on the image forming apparatus main body side enters the secondary transfer portion. When a recording medium having a grammage greater than the second grammage and entering the secondary transfer portion is larger than the force by which the abutment portion of the secondary transfer roll is separated from An image forming apparatus characterized by being set small . An intermediate transfer belt stretched between a plurality of rolls;
A secondary transfer unit that secondary-transfers the toner image primarily transferred to the intermediate transfer belt onto a sheet by a secondary transfer roll and a backup roll;
A guide unit for guiding the sheet to the secondary transfer unit;
In an image forming apparatus having
The backup roll is attached in a state where the position is fixed to the frame on the image forming apparatus main body side ,
The secondary transfer roll is rotatably attached to a support frame configured separately from the frame on the image forming apparatus main body side, and the secondary transfer roll attaches the support frame to the image forming apparatus main body side. The spring is pressed against the backup roll that stretches the intermediate transfer belt, and the rotating shaft of the secondary transfer roll is attached in a state of abutting the frame on the image forming apparatus main body side,
When the recording medium having a basis weight equal to or less than the first basis weight enters the secondary transfer portion, the abutting force that abuts the secondary transfer roll against the frame on the image forming apparatus main body side enters the secondary transfer portion. When a recording medium having a grammage greater than the second grammage and entering the secondary transfer portion is larger than the force by which the abutment portion of the secondary transfer roll is separated from An image forming apparatus characterized by being set small . The image forming apparatus according to claim 1, wherein the first basis weight is 80 gsm. The image forming apparatus according to claim 1, wherein the second basis weight is 160 gsm. " 5. The sheet according to claim 1, wherein the sheet is transported along a side surface of the image forming apparatus and is fed to a secondary transfer unit that is a press-contact portion between the secondary transfer roll and a backup roll. The image forming apparatus according to any one of the above.

Images