JP2012237911A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device capable of separating even a thin and weak recording sheet from a transfer belt by self stripping at a belt part corresponding to a separation roller without hindering transfer of a toner image, when the toner image is transferred to the recording sheet by a transfer belt type transfer unit.SOLUTION: An image forming device 100A (100B) includes a transfer belt type transfer unit 70A (70B) for transferring a toner image from an image carrier 8 to a recording sheet 11. The transfer unit 70A (70B) includes: a wrinkle generator for making difference of belt tension between a center part and at least one of side ends of a transfer belt 7 and generating a wrinkle at a part of the transfer belt 7 wound around a separation roller 12; and a wrinkle erasing roller 14 on which a part travelling from a transfer roller 71 to the separation roller 12 is stretched.

Description

  According to the present invention, a toner image corresponding to provided image information can be formed on an image carrier, the toner image can be transferred to a recording sheet by a transfer device, and can be fixed to the recording sheet by a fixing device. The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine in which two or more of these are combined.

  An image forming apparatus capable of forming a toner image corresponding to provided image information on an image carrier, transferring the toner image onto a recording sheet with a transfer device, and fixing the toner image onto the recording sheet with a fixing device. There are monochrome image forming apparatuses and color image forming apparatuses.

  In the monochrome image forming apparatus, an electrostatic latent image is formed on the electrostatic latent image carrier in accordance with the provided image information, the electrostatic latent image is developed to form a toner image, and the electrostatic latent image is formed. Generally, a toner image on an image carrier can be transferred to a recording sheet. In such an image forming apparatus, the transfer device is a transfer device for transferring the toner image on the electrostatic latent image carrier onto the recording sheet.

  In the color image forming apparatus, an electrostatic latent image is formed on an electrostatic latent image carrier that is a first image carrier in accordance with the provided image information, and the electrostatic latent image is developed to form a toner image. The toner image on the electrostatic latent image carrier is primarily transferred to an intermediate transfer member which is a second image carrier, and the toner image on the intermediate transfer member is secondarily transferred to the recording sheet. What you can do is common. In such an image forming apparatus, the transfer device is a transfer device for secondarily transferring the toner image on the intermediate transfer member onto the recording sheet.

  In any case, such a transfer device includes a transfer charger to which a transfer bias is applied and a transfer roller. However, a belt-type transfer device is also known.

  A belt-type transfer device is known that includes a transfer roller to which a transfer bias is applied, a separation roller, and a transfer belt that is wound around the transfer roller and the separation roller and is driven to rotate.

  In this type of transfer device, a transfer bias is applied to the transfer roller, whereby a recording sheet is electrostatically attracted to the transfer belt, and is carried into and passed through a toner image transfer area to transfer the toner image to the sheet. And the so-called curvature separation is performed from the transfer belt using the rigidity of the recording sheet by the separation roller so that the separation roller can be transferred to the fixing device.

By the way, regarding recording sheets, today, for example, even thin coated paper of about 60 g / m ² has been tried to be used as a recording sheet in an image forming apparatus.

  When a toner image is transferred from an image carrier onto such a thin recording sheet using the belt-type transfer device as described above, the thin recording sheet has a so-called low stiffness (small rigidity), so In addition, the state of being attracted to the transfer belt tends to be maintained even when conveyed to the position corresponding to the separation roller, and it is difficult to separate the curvature from the transfer belt at the position corresponding to the separation roller.

  For example, Japanese Patent Application Laid-Open No. 9-90770 discloses a groove for the separation roller, and a belt portion facing the groove is recessed toward the groove by the tension of the transfer belt. It has been proposed to reduce the adhesion to the transfer belt and improve the separation from the transfer belt.

JP-A-9-90770

  However, it is not easy to actually provide a groove that moderately decreases the adhesion of the recording sheet by recessing the transfer belt in the separation roller, and the separation roller structure is complicated and expensive.

Therefore, the present invention forms a toner image corresponding to the provided image information on an image carrier, transfers the toner image to a recording sheet by a transfer device, and fixes the toner image to the recording sheet by a fixing device. The transfer device includes a transfer roller, a separation roller, and a transfer belt that is wound around the transfer roller and the separation roller and is driven to rotate. By applying a transfer bias to the transfer roller, The recording sheet is electrostatically attracted to the transfer belt, and is carried into and passed through a toner image transfer area to transfer the toner image to the recording sheet, and the separation roller is used to separate the curvature from the transfer belt, and An image forming apparatus, which is a transfer device that enables transfer to a fixing device, and records a toner having a basis weight of about 80 g / m ^{2 when the} transfer device transfers a toner image onto the recording sheet. Even a recording sheet thinner than the paper can be separated from the transfer belt by the belt corresponding to the separation roller without causing any trouble in toner image transfer, and thus an image that can be imaged on a thin recording sheet. It is an object to provide a forming apparatus.

In order to solve the above problems, the present invention
A toner image corresponding to provided image information can be formed on an image carrier, the toner image can be transferred to a recording sheet by a transfer device, and fixed to the recording sheet by a fixing device. Includes a transfer roller, a separation roller, and a transfer belt that is wound around the transfer roller and the separation roller and is driven to rotate. By applying a transfer bias to the transfer roller, the recording sheet is The toner image is electrostatically attracted to the transfer belt, and is carried into and passed through a toner image transfer area to transfer the toner image onto the recording sheet. The separation roller can be separated from the transfer belt by the curvature, and transferred to the fixing device. An image forming apparatus that is a transfer device
The transfer device winds around at least the separation roller of the transfer belt with a difference in belt tension between the belt center in the belt width direction crossing the belt running direction of the transfer belt and at least one belt side end. A erasing roller that includes a wrinkle generating device that generates wrinkles extending in the running direction of the transfer belt at the hung portion, and stretches a portion of the transfer belt that runs from the transfer roller to the separation roller An image forming apparatus is provided.

According to the image forming apparatus of the present invention, the transfer device includes the wrinkle generating device, and the wrinkle generating device is applied to at least a portion of the transfer belt wound around the separation roller due to a tension difference in the belt width direction. Since wrinkles extending in the belt running direction are generated, the adhesion of the recording sheet to the portion of the transfer belt wound around the separation roller is lower than that without such wrinkles, even if the basis weight is 80 g / Even when the recording sheet is thinner than the recording paper of about m ^{2, the} curvature separation from the portion wound around the separation roller is improved.

  The wrinkle generating device generates the wrinkle at least on a portion of the transfer belt that is wound around the separation roller, and the transfer device travels from the transfer roller to the separation roller of the transfer belt. Since a erasing roller (in other words, a roller that stretches the transfer belt and eliminates wrinkles) is included, the portion of the transfer belt that contributes to the transfer of the toner image wound around the transfer roller Therefore, there is no problem in transferring the toner image from the image carrier to the recording sheet on the transfer belt.

  The wrinkle generating device generates the belt wrinkles with a difference in belt tension between a belt center portion in the belt width direction crossing the belt running direction of the transfer belt and at least one belt side end portion. . Furthermore, a belt tension difference is generated between the belt center portion in the belt width direction crossing the belt running direction of the transfer belt and at least one belt side end portion, thereby generating a belt width direction force on the belt. The above-described soot is generated by running while running.

  Therefore, the transfer belt may try to meander. Therefore, the wrinkle generator may include a mechanism for preventing meandering to generate wrinkles more reliably.

Some more specific examples of the wrinkle generator are listed below.
(1) The wrinkle generator includes a tension roller (in other words, a tension roller that applies tension to the belt) for stretching a portion of the transfer belt that travels from the separation roller to the transfer roller, and the tension A spring device that applies a belt tension force to each end of the roller, wherein the spring device provides a difference in the belt tension force between the two ends of the tension roller, and the belt tension force Can be granted.
(2) The wrinkle generating device includes the separation roller and a spring device that applies a belt tension force to each end of the separation roller, and the spring device stretches the belt between both ends of the separation roller. The belt tension can be applied with a difference in the tension.

(3) The separation roller also serves as a wrinkle generator, and the separation roller is formed in an inverted crown shape so that the belt tension is larger at both ends than at the center.
(4) The separation roller also serves as a wrinkle generator, and the separation roller has a belt tension at one end larger than that at the center and a belt tension at the other end smaller than the center. The outer diameter decreases from one end to the other end.
(5) A tension roller is provided for tensioning a portion of the transfer belt that travels from the separation roller to the transfer roller. The tension roller also serves as the wrinkle generator, and the tension roller The bridge roller is formed in a reverse crown shape so that the belt tension is larger at both ends than at the center.
(6) A tension roller is provided for tensioning a portion of the transfer belt that travels from the separation roller to the transfer roller. The tension roller also serves as the wrinkle generator, and the tension roller The gantry roller has a smaller outer diameter from one end to the other end so that the belt tension is greater at one end than at the center and the belt tension is less at the other end than at the center.

  In addition, the image forming apparatus according to the present invention may include a thin paper sheet detecting unit that detects a thin paper sheet having a predetermined thickness. In this case, the wrinkle generator includes the thin paper sheet detecting unit that detects the toner image. The belt tension may be different only when it is detected that the recording sheet to be transferred is the thin paper sheet.

  For example, when the wrinkle generator includes a spring device that applies a belt tension to each end of the tension roller or the separation roller as in the above-described wrinkle generators (1) and (2), An example in which the spring device and the like are as follows can be given.

  That is, the spring device includes a first spring that applies a belt tension to one end of the roller, a second spring that applies a belt tension to the other end of the roller, and the two springs. A spring force switching device capable of switching at least one belt tension force (spring force) from a first force that does not generate belt wrinkles to a second force for generating belt wrinkles, and a controller for the spring force switching device. The control unit applies the first force to the spring force switching device only when the thin paper sheet detecting unit detects that the recording sheet used for the toner image transfer is the thin paper sheet. Switch to 2 forces.

The image forming apparatus according to the present invention includes various types. For example,
(1) forming an electrostatic latent image on an electrostatic latent image carrier according to the provided image information, developing the electrostatic latent image to form a toner image, and forming the electrostatic latent image carrier; An image forming apparatus capable of transferring the toner image on the recording sheet, wherein the transfer apparatus is a transfer apparatus for transferring the toner image on the electrostatic latent image carrier to the recording sheet. ,
(2) forming an electrostatic latent image on an electrostatic latent image carrier which is a first image carrier in accordance with the provided image information, and developing the electrostatic latent image to form a toner image; Image formation in which the toner image on the electrostatic latent image carrier is primarily transferred to an intermediate transfer member that is the image carrier of Brother 2, and the toner image on the intermediate transfer member can be secondarily transferred to the recording sheet. And an image forming apparatus which is a transfer device for secondary transfer of the toner image on the intermediate transfer member onto the recording sheet.

As described above, according to the present invention, a toner image corresponding to provided image information is formed on an image carrier, the toner image is transferred to a recording sheet by a transfer device, and the recording sheet is transferred by a fixing device. The transfer device includes a transfer roller, a separation roller, and a transfer belt that is wound and rotated around the transfer roller and the separation roller, and applies a transfer bias to the transfer roller. Then, the recording sheet is electrostatically attracted to the transfer belt, and is carried into and passed through a toner image transfer area to transfer the toner image to the recording sheet, and is separated from the transfer belt by the separation roller. An image forming apparatus, which is a transfer device that allows curvature separation and transfer to the fixing device, and has a basis weight of 80 when transferring the toner image onto the recording sheet by the transfer device. / M at ² about a thin recording sheet from the recording sheet, it is possible to the curvature separated from the transfer belt by the corresponding belt portion to the separation roller without disturbing the toner image transfer, thus a thin recording sheet In addition, an image forming apparatus capable of forming an image can be provided.

1 is a diagram schematically showing a configuration of an example of an image forming apparatus according to the present invention. It is a figure which shows schematically the structure of the other example of the image forming apparatus which concerns on this invention. It is a figure which shows the example of the separation roller which also serves as the belt wrinkle generator of a belt system transfer apparatus, or a tension roller. FIG. 4A is a view showing another example of a separation roller or a stretching roller that also serves as a belt wrinkle generating device of a belt type transfer device, and FIG. 4B is a view showing an example of a belt meandering prevention mechanism. is there. It is a figure which shows the further another example of the belt wrinkle generator of a belt type transfer apparatus. It is a figure which shows the further another example of the belt wrinkle generator of a belt type transfer apparatus.

Embodiments of the present invention will be described below with reference to the drawings.
FIG. 1 shows an example of an image forming apparatus according to the present invention. An image forming apparatus 100A shown in FIG. 1 is a tandem full-color image forming apparatus, and is a so-called multi-function machine having a printer function, a facsimile function, and the like.

  The image forming apparatus 100 </ b> A includes an endless intermediate transfer belt 8. The transfer belt 8 is wound around a roller group including rollers 1, 2, 3, 72, and the like. The roller 1 is a driving roller that is rotationally driven by a driving unit (not shown). The roller 72 is a secondary transfer counter roller that faces a secondary transfer roller 71 of a secondary transfer device 70A described later.

  The intermediate transfer belt 8 is rotated clockwise X in FIG. The rollers 1, 2, 3, 72, etc. are driven to rotate by the belt.

  The secondary transfer device 70A is of the transfer belt type, and the endless transfer belt 7 is wound around the secondary transfer roller 71, the erasing roller 14, the separation roller 12, and the belt stretching roller 13, and a belt driving unit (not shown) is used. The belt 7 can be driven to rotate counterclockwise in the figure.

  A secondary transfer bias having a polarity opposite to the normal charging polarity of the toner can be applied to the secondary transfer roller 71 and, hence, the belt 7 from a power supply (not shown). As will be described later, the separation roller 12 is a roller for separating the curvature of the recording sheet 11 on which the toner image is secondarily transferred from the belt 7 using sheet rigidity.

  Both the erasing roller 14 and the stretching roller 13 are rollers (stretching rollers) that act to stretch the belt 7. The reason why the roller 14 is called an erasing roller will be clarified later.

  The erasing roller 14 stretches a portion of the transfer belt 7 that travels from the transfer roller 71 to the separation roller 12. The tension roller 13 stretches a portion of the transfer belt 7 that travels back from the separation roller 12 toward the transfer roller 71.

  A belt cleaner 91 that removes and cleans secondary transfer residual toner and the like on the belt 8 faces the portion of the belt 8 that is wound around the driving roller 1. The cleaner 91 has a cleaning blade 92 that contacts the belt 8.

  A fixing device 10 is disposed on the left side of the intermediate transfer belt 8 and the secondary transfer device 70A in the figure, a registration roller TR is disposed on the right side, and a supply unit CA for the recording sheet 11 is disposed below the fixing roller TR. ing.

  The fixing device 10 is not limited thereto, but here, as will be described later, between a heating roller 101 incorporating a heat source such as a halogen lamp heater, a fixing belt 103 wound around the fixing roller 102, and a backup roller 104. The toner image is fixed through the recording sheet 11 to which the toner image has been transferred.

  The recording sheets 11 to be used for image formation can be pulled out one by one from the sheet supply unit CA containing the recording sheets at a predetermined timing and supplied to the registration rollers TR.

  Between the roller 2 and the roller 3 around which the intermediate transfer belt 8 is wound, a yellow image forming unit Y, a magenta image forming unit M, and a cyan image are formed along the transfer belt 8 from the roller 2 side to the roller 3 side. The part C and the black image forming part K are arranged in this order.

  Each of the Y, M, C, and K image forming units forms an electrostatic latent image by an electrophotographic method and develops it to form a toner image.

  Each of the image forming units Y, M, C, and K includes a drum-type photoconductor 1a as an electrostatic latent image carrier, and a charger 2a, an image exposure device 3a, a developing device 4a, and the like around the photoconductor 1a. The cleaning devices 5a are arranged in this order. Further, a primary transfer roller 6 is arranged with respect to each photoconductor 1 with a belt 8 interposed therebetween.

  The photoconductor 1a in each image forming unit is a negatively chargeable photoconductor here, and is driven to rotate counterclockwise in FIG. 1 by a driving force transmitted from a photoconductor drive motor (not shown).

  The charger 2a in each image forming unit is charged with a charging voltage from a power supply (not shown) to charge the surface of the photoreceptor 1a.

  The image exposure device 3a performs image exposure on the photoconductor 1a in accordance with image information provided from an image reading device (not shown), a personal computer (not shown), a facsimile machine (not shown), and the like, thereby generating an electrostatic latent image. Can be formed.

  The developing device in each image forming unit is not limited to this, but in this example, a developing bias is applied to an electrostatic latent image formed on the photoreceptor 1a from a power source (not shown) using negatively chargeable toner. Can be reversed and developed with a developing roller.

  The primary transfer roller 6 is opposed to the photoconductor 1a with the transfer belt 8 in between, presses the belt 8 against the photoconductor 1a, and rotates as the belt runs. To the primary transfer roller 6, a primary transfer bias having a polarity opposite to the toner charging polarity for primary transfer of the toner image formed on the photoreceptor 1 a to the belt 8 can be applied from a power supply (not shown). .

According to the image forming apparatus 100A described above, an image can be formed using one or more of Y, M, C, and K image forming units.
Taking a case where a full color image is formed using all of the image forming portions Y, M, C, and K as an example, first, a yellow toner image is formed in the yellow image forming portion Y, and this is formed on the transfer belt 8 as a primary. Transcript.

  That is, in the yellow image forming portion Y, the photosensitive member 1a is rotationally driven in the counterclockwise direction in the figure, and the surface is uniformly charged to a predetermined potential by the charger 2a. Image exposure is performed, and an electrostatic latent image for yellow is formed on the photoreceptor 1a. The electrostatic latent image is developed by a developing roller to which a developing bias of a developing unit 4 a having yellow toner is applied to become a visible yellow toner image. The toner image is transferred onto the transfer belt 8 by the primary transfer roller 6. Next transferred. At this time, a primary transfer bias is applied to the primary transfer roller 6 from a power supply (not shown).

  Similarly, a magenta toner image is formed in the magenta image forming unit M and transferred to the transfer belt 8. A cyan toner image is formed in the cyan image forming unit C and transferred to the transfer belt 8. In the black image forming unit K. A black toner image is formed and transferred to the transfer belt 8.

  Yellow, magenta, cyan, and black toner images are formed at the timing when these toner images are transferred onto the intermediate transfer belt 8. Thus, the multiple toner images formed on the transfer belt 8 move toward the secondary transfer device 70 </ b> A by the rotation of the transfer belt 8.

  On the other hand, the recording sheet 11 is pulled out from the supply unit CA, supplied to the registration roller TR, and stands by.

  As described above, the recording sheet 11 waiting at the registration roller TR has a portion supported by the secondary transfer counter roller 72 of the transfer belt 8 and 2 in accordance with the multiple toner image sent by the intermediate transfer belt 8. The multiple toners are supplied to the nip portion of the belt 7 supported by the secondary transfer roller 71 of the secondary transfer device 70A and applied with a secondary transfer bias from a power supply (not shown). The image is secondarily transferred onto the recording sheet 11.

  Thereafter, the recording sheet 11 is passed through the fixing device 10 where the multiple toner images are fixed on the recording sheet 11 under heat and pressure. The recording sheet 11 continues to be discharged to the discharge tray T by the discharge roller R.

Transfer residual toner or the like remaining on the photosensitive member 1 in the primary transfer of the toner image to the belt 8 is cleaned by the cleaning device 5a of the image forming unit to prepare for the next image formation.
The secondary transfer residual toner remaining on the belt 8 by the secondary transfer is cleaned by the cleaner 91.
Each of these cleaned and removed toners is sent to a waste container by a conveying means (not shown).

  FIG. 2 shows another example of the image forming apparatus according to the present invention. An image forming apparatus 100B shown in FIG. 2 is obtained by replacing the secondary transfer apparatus 70A with a secondary transfer apparatus 70B in the image forming apparatus 100A of FIG. 1, and the other points are the same in configuration and action as the image forming apparatus 100A. Is shown. The same reference numerals as those of the device 100A are given to the same parts and parts as those of the device 100A.

  The basic configuration of the secondary transfer device 70B is obtained by omitting the tension roller 13 in the basic configuration of the secondary transfer device 70A. The other points are the same as the secondary transfer device 70A.

  The transfer devices 70A and 70B of the image forming apparatuses 100A and 100B described above apply a transfer bias to the secondary transfer roller 71, thereby electrostatically attracting the recording sheet 11 to the transfer belt 7 and transferring the toner image. The toner image on the intermediate transfer belt 8 is transferred to the sheet 11 by passing it through and transferred to the fixing device 10 by using the separation roller 12 to separate the curvature from the transfer belt 7 using the rigidity of the recording sheet. It is to make.

However, a toner image is transferred from the intermediate transfer body 8 to a recording sheet having a smaller basis weight than a recording sheet having a basis weight of about 80 g / m ² , for example, a thin paper coated sheet having a basis weight of about 60 g / m ² by using a transfer belt type transfer device. If it is attempted to do so, the thin recording sheet is so-called stiff (less rigid), so that the state where it is electrostatically attracted to the transfer belt is still maintained even if it is transported to the separation roller corresponding position. In some cases, it is difficult to separate the curvature from the transfer belt.

  Therefore, the transfer devices 70A and 70B of the image forming apparatuses 100A and 100B are provided between the belt center portion in the belt width direction crossing the belt traveling direction of the transfer belt 7 and at least one belt side end portion (here, both side end portions). A wrinkle generating device is included that generates a wrinkle extending in the running direction of the transfer belt 7 at least in a portion of the transfer belt 7 wound around the separation roller 12 by making a difference in belt tension. At the same time, the erasing roller 14 is used so that the secondary transfer of the toner image is not affected by the belt wrinkles. The roller 14 is a perfect circle roller having a uniform outer diameter as a whole.

As shown in FIG. 3, the separation roller 12 of the transfer devices 70 </ b> A and 70 </ b> B is formed in a reverse crown shape so that the belt tension is larger at both end portions 122 and 123 than at the center portion 121. It also serves as a generator.
The case where the outer diameter difference of the center part 121 of the roller 12 and each of the edge parts 122 and 123 shall be 2 mm or more and 5 mm or less can be illustrated.

Instead of forming the separation roller 12 in an inverted crown shape, as shown in FIG. 4A, the separation roller 12 has a belt tension at one end 122 greater than that at the center 121 and other than the center 121. The outer diameter may be gradually reduced from the one end portion 122 to the other end portion 123 so that the end portion 123 reduces the belt tension.
In this case, the case where the roller outer diameter difference between the roller one end and the other end is 2 mm or more and 5 mm or less can be exemplified.

  In the roller form as shown in FIG. 4A, the belt 7 is easy to meander so as to approach one end of the roller 12, and therefore, for example, a belt meandering prevention mechanism 120 may be provided as shown in FIG. 4B. . The belt meandering prevention mechanism 120 shown in FIG. 4B is not limited thereto, but in this example, the endless rib band b formed on the inner surface of the side end portion of the belt 7 and the rib band b are slidably fitted. It consists of a groove g of the roller 12. Although not shown, a belt meandering prevention mechanism using a steering roller as already known can be employed. Here, the “steering roller” means that the contact pressure with respect to the inner peripheral surface of the transfer belt 7 is uniform in the roller width direction (in other words, the roller rotation axis direction) or the end of one of the rollers. For example, the transfer belt 7 can be tilted around the rotation center set with respect to one of the roller ends so that the portion is larger (or smaller) than the other roller end. Can control the meandering.

The belt meandering prevention mechanism may be employed even when the separation roller 12 shown in FIG. 3 is employed.
When the belt meandering prevention mechanism is employed, the belt width direction movement limitation due to the belt tension difference in the belt width direction is ensured, and belt wrinkles are easily generated.

  The wrinkle generating device described above uses the separation roller 12. However, in the case of the transfer device 70A, instead of the separation roller 12, the stretching roller 13 is formed in an inverted crown shape like the separation roller 12 of FIG. May be. In this case, the case where the outer diameter difference of the center part of the roller 13 and each edge part shall be 2 mm or more and 5 mm or less can be illustrated.

In addition, the tension roller 13 has a belt tension at one end larger than that at the center of the roller and a belt tension at the other end smaller than that at the center, like the separation roller 12 in FIG. Thus, the outer diameter may be gradually reduced from one end to the other end. Also in this case, the case where the roller outer diameter difference between the one end portion and the other end portion of the roller 13 is 2 mm or more and 5 mm or less can be exemplified.
Further, a belt meandering prevention mechanism may be adopted for the tension roller 13 as well.

Further, in the transfer devices 70A and 70B, the wrinkle generating device shown in FIGS. 5 and 6 may be employed instead of the wrinkle generating device as described above.
5 includes a separation roller 12 and a spring device 12P that applies a belt tension force to each end of the separation roller 12. In this example, the spring device 12P supports the rotation bearing portions B1 and B2 at both ends of the separation roller 12 so that the belt tension is applied by the compression springs S1 and S2, and the tension applied by one spring S1. The force is set to be larger than the tension force applied by the other spring S2, and thus the belt tension force is applied by providing a difference in the belt tension force between both ends of the separation roller 12.
The case where the difference of the belt tension force given to the one end part of the roller 12 and the belt tension force given to the other end part shall be 2N or more and 10N or less can be illustrated.

  6 includes a separation roller 12 and a spring device 12Q that applies a belt tension force to each end portion of the separation roller 12. In this example, the spring device 12Q supports the rotary bearings B1 and B2 at both ends of the separation roller 12 so as to apply a belt tension force with compression springs S1 and S2. One spring S1 compresses the support Sp from the initial state when the solenoid SOL is on, and can apply a stronger belt tension to the roller end on the bearing part B1 side than the roller end on the bearing part B2 side. When the solenoid SOL is off, the springs S1 and S2 apply an equivalent belt tension to both ends of the roller 12.

In this example, the solenoid SOL is turned on and off based on an instruction from the control unit Cont that controls the operation of the image forming apparatus. An operation panel PA of the image forming apparatus is connected to the control unit Cont. The operation panel PA is equipped with a key for designating an image forming target sheet type, a numeric keypad for designating the number of images to be formed, a print start key for instructing start of image formation, a display for displaying various information, and the like.
In this example, when a thin recording sheet whose basis weight is less than or equal to a predetermined basis weight is designated as the image forming target sheet type on the operation panel PA, the part of the control unit Cont that recognizes this functions as a thin paper sheet detecting means. To do. When this detection means detects that the recording sheet 11 used for toner image transfer is a thin sheet having a basis weight of 80 g / m ² or less in this example, the controller Cont turns on the solenoid SOL to separate it. A difference is applied to the belt stretching force applied between both ends of the roller 12, thereby generating a belt tension difference in the belt width direction that generates wrinkles on the transfer belt 7. Also in this case, a case where the difference between the belt tension applied to one end of the roller 12 and the belt tension applied to the other end is set to 2N or more and 10N or less can be exemplified.
A cam mechanism that adjusts the spring force by displacing the support Sp instead of the solenoid SOL may be employed.

  5 and FIG. 6 uses the separation roller 12. However, in the case of the transfer device 70A, the tension roller 13 is replaced by the same wrinkle as in FIG. 5 and FIG. A generator may be employed. Also in these cases, a case where the difference between the belt tension applied to one end of the roller 13 and the belt tension applied to the other end is set to 2N or more and 10N or less can be exemplified.

  Further, when the wrinkle generator of the type shown in FIGS. 5 and 6 is employed, a belt meandering prevention mechanism may be employed.

  According to the image forming apparatuses 100 </ b> A and 100 </ b> B, the transfer devices 70 </ b> A and 70 </ b> B include the wrinkle generator, and the wrinkle generator is a portion of the belt 7 wound around at least the separation roller 12 due to a tension difference in the width direction of the belt 7. A wrinkle extending in the belt running direction is generated.

The adhesion of the recording sheet 11 to the portion of the transfer belt 7 wound around the separation roller 12 is lower than that without such wrinkles, and is thinner than the recording paper having a basis weight of about 80 g / m ^2. Even in the recording sheet 11, the curvature separation from the portion wound around the separation roller 12 is improved.

  The wrinkle generating device generates the wrinkles at least on the portion of the transfer belt 7 wound around the separation roller 12, but the transfer devices 70 </ b> A and 70 </ b> B travel from the transfer roller 71 of the transfer belt 7 toward the separation roller 12. Since the erasing roller 14 that stretches the portion to be stretched is included, wrinkles do not occur in the portion of the transfer belt 7 that contributes to the transfer of the toner image that is wound around the transfer roller 71, and therefore from the intermediate transfer body 8. There is no problem in transferring the toner image to the recording sheet 11 on the transfer belt 7.

  Next, the image forming apparatus 100A or 100B type image forming apparatus (Embodiments 1 to 8) and the image forming apparatus (Comparative Examples 1 to 2) adopting the comparative example transfer apparatuses 1 and 2 instead of the transfer apparatuses 70A and 70B. The evaluation results are shown in Table 1 below because the image quality of the toner image secondarily transferred to the recording sheet and the separability of the recording sheet from the transfer belt 7 of the transfer device were evaluated.

Evaluation of the separation property in the transfer device is as follows. When medium OK coated paper (Oji Paper Co., Ltd. basis weight 60.2 g / m ² ) is passed continuously in a low temperature and low humidity environment of 15 ° C. and 10% RH, paper jam occurs. If it was 3 or less, it was evaluated as “good”, and if it was more than 3, it was evaluated as “bad”.

  The image quality evaluation was evaluated as good “◯” for those that could be visually evaluated as having no image defect, and “x” for those that were not.

In any image forming apparatus, the transfer device
The transfer roller 71 has an outer diameter of 38 mm, the eraser roller 14 has an outer diameter of 10 mm,
The separation roller 12 has an outer diameter of 16 mm, and the stretching roller 13 (if any) has an outer diameter of 16 mm. The roller widths are all the same, and the transfer belt 7 has the same material, the same thickness, and the same width. The transfer voltage was also the same.
In addition, the following changes were made for each of the Examples and Comparative Examples.

Example 1: The image forming apparatus 100A is employed, and the transfer device 70A has a stretch
Different belt tensions were applied to each end of the roller 13 as shown in FIG. Low
The difference in belt tension between the two ends is 2N or more and 10N or less (4N in this example)
Set to.
Example 2: Adopting the image forming apparatus 100A and separating in the transfer apparatus 70A
The roller 12 is formed in an inverted crown shape as shown in FIG.
16mm) and the roller outer diameter difference between each end is 2mm or more and 5mm or less (this
In the example, it was set to 2 mm).
Embodiment 3: Employing the image forming apparatus 100A, and in the transfer apparatus 70A, stretching
The roller 13 is formed in a reverse crown shape as shown in FIG.
Set the roller outer diameter difference between 2 mm and 5 mm (2 mm in this example)
did.
The outer diameter of the roller central part is 16 mm.
Example 4: The image forming apparatus 100A is employed, and separation is performed in the transfer device 70A.
The roller 12 is formed in a tapered shape as shown in FIG.
The roller outer diameter difference was set to 2 mm or more and 5 mm or less (4 mm in this example).
The outer diameter of the roller central part is 16 mm.
Embodiment 5: The image forming apparatus 100A is employed, and the transfer device 70A has a stretch
The roller 13 is formed in a tapered shape as shown in FIG.
The roller outer diameter difference was set to 2 mm or more and 5 mm or less (4 mm in this example).
The outer diameter of the roller central part is 16 mm.
Example 6: The image forming apparatus 100B is employed and the transfer device 70B performs separation.
Different belt tensions were applied to each end of the roller 12 as shown in FIG. Low
The difference in belt tension between the two ends is 2N or more and 10N or less (4N in this example)
Set to.
Example 7: The image forming apparatus 100B is employed, and the transfer device 70B performs separation.
The roller 13 is formed in a reverse crown shape as shown in FIG.
The roller outer diameter difference between them was set to 2 mm to 5 mm (2 mm in this example)
.
The outer diameter of the roller central part is 16 mm.
Example 8: The image forming apparatus 100B is employed, and separation is performed in the transfer device 70B.
The roller 12 is formed in a tapered shape as shown in FIG.
The roller outer diameter difference was set to 2 mm or more and 5 mm or less (4 mm in this example).
The outer diameter of the roller central part is 16 mm.
Comparative Example 1: The image forming apparatus 100B is employed, and the transfer is performed in the transfer apparatus 70B.
There was no difference between the right and left of the belt 7 tension.
-Comparative example 2: Although it is set as the structure in any one of Examples 1-5, the erasing roller 14 was not provided.
.

Table 1
Separation quality
Example 1 ○ ○
Example 2 ○ ○
Example 3 ○ ○
Example 4 ○ ○
Example 5
Example 6 ○ ○
Example 7 ○ ○
Example 8
Comparative Example 1 × ○
Comparative Example 2 ○ ×

  As can be seen from the above evaluation results, in the image forming apparatus according to the present invention, even a thin recording sheet has good separability from the transfer belt 7 of the transfer devices 70A and 70B, and there is no problem in transferring the toner image.

  The image forming apparatus shown in FIG. 1 and FIG. 2 is a tandem type. However, in the present invention, for example, a cycle type (for example, four types) in which a plurality of developing units that perform development with assigned color toner are sequentially moved to a developing region. It can also be applied to a four-cycle color image forming apparatus equipped with a developing device.

  The present invention is an image forming apparatus that employs a belt-type toner image transfer device. When a toner image is transferred onto a recording sheet by the transfer device, the toner image transfer is hindered even with a thin and weak recording sheet. The present invention can be used to provide an image forming apparatus that can separate the curvature from the transfer belt at the belt portion corresponding to the separation roller.

100A, 100B Image forming apparatus Y Yellow image forming part M Magenta image forming part C Cyan image forming part K Black image forming part 1a Photoconductor 2a Charger 3a Image exposure device 4a Developer 5a Cleaning device 6 Primary transfer roller 8 Intermediate transfer Belt 1, 2, 3 Belt winding roller 72 Secondary transfer roller (secondary transfer counter roller)
70A, 70B Secondary transfer device 7 Transfer belt 71 Secondary transfer roller 12 Separating roller 13 Stretching roller 14 Erasing roller 121 Separating roller central portion 122, 123 Separating roller end portion P, Q Wrinkle generating device 12P, 12Q Spring device B1 , B2 Bearing part S1, S2 Spring Sp Spring support SOL Solenoid

Claims (11)

A toner image corresponding to provided image information can be formed on an image carrier, the toner image can be transferred to a recording sheet by a transfer device, and fixed to the recording sheet by a fixing device. Includes a transfer roller, a separation roller, and a transfer belt that is wound around the transfer roller and the separation roller and is driven to rotate. By applying a transfer bias to the transfer roller, the recording sheet is The toner image is electrostatically attracted to the transfer belt, and is carried into and passed through a toner image transfer area to transfer the toner image onto the recording sheet. The separation roller can be separated from the transfer belt by the curvature, and transferred to the fixing device. An image forming apparatus that is a transfer device
The transfer device winds around at least the separation roller of the transfer belt with a difference in belt tension between the belt center in the belt width direction crossing the belt running direction of the transfer belt and at least one belt side end. A erasing roller that includes a wrinkle generating device that generates wrinkles extending in the running direction of the transfer belt at the hung portion, and stretches a portion of the transfer belt that runs from the transfer roller to the separation roller An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the wrinkle generating device includes a meandering prevention mechanism that prevents meandering of the transfer belt.   The wrinkle generator includes a tension roller for stretching a portion of the transfer belt that travels from the separation roller to the transfer roller, and a spring device that applies a belt tension force to each end of the tension roller. 3. The image forming apparatus according to claim 1, wherein the spring device is capable of applying the belt tension force with a difference in belt tension force between both ends of the tension roller.   The wrinkle generating device includes the separation roller and a spring device that applies a belt tension force to each end portion of the separation roller, and the spring device generates a difference in belt tension force between both ends of the separation roller. The image forming apparatus according to claim 1, wherein the belt tensioning force can be applied.   3. The image forming apparatus according to claim 1, wherein the separation roller also serves as the wrinkle generating device, and the separation roller is formed in an inverted crown shape so that the belt tension is larger at both ends than at the center. .   The separation roller also serves as the wrinkle generator, and the separation roller has one end so that the belt tension is greater at one end than at the center and the belt tension is smaller at the other end than the center. The image forming apparatus according to claim 1, wherein the outer diameter decreases from the first end to the other end.   A tension roller is provided to stretch a portion of the transfer belt that travels from the separation roller to the transfer roller. The tension roller also serves as the wrinkle generator, and the tension roller is The image forming apparatus according to claim 1, wherein both end portions are formed in an inverted crown shape so as to increase belt tension at the center portion.   A tension roller is provided to stretch a portion of the transfer belt that travels from the separation roller to the transfer roller. The tension roller also serves as the wrinkle generator, and the tension roller is 3. The outer diameter from one end to the other end is reduced so that the belt tension is greater at one end than at the center and the belt tension is less at the other end than at the center. The image forming apparatus described.   The sheet generating device includes a thin paper sheet detecting unit that detects a thin paper sheet having a predetermined thickness, and the wrinkle generating device is configured such that the recording sheet used by the thin paper sheet detecting unit for the toner image transfer is the thin paper sheet. 5. The image forming apparatus according to claim 1, wherein a difference in the belt tension is provided only when this is detected.   According to the provided image information, an electrostatic latent image is formed on the electrostatic latent image carrier, the electrostatic latent image is developed to form a toner image, and the toner on the electrostatic latent image carrier 10. The image forming apparatus capable of transferring an image to the recording sheet, wherein the transfer apparatus is a transfer apparatus for transferring a toner image on the electrostatic latent image carrier to the recording sheet. The image forming apparatus according to claim 1. According to the provided image information, an electrostatic latent image is formed on an electrostatic latent image carrier, which is a first image carrier, and the electrostatic latent image is developed to form a toner image. An image forming apparatus capable of primarily transferring a toner image on an electrostatic latent image carrier to an intermediate transfer member which is a second image carrier, and secondarily transferring the toner image on the intermediate transfer member to the recording sheet. The image forming apparatus according to claim 1, wherein the transfer device is a transfer device for secondary transfer of the toner image on the intermediate transfer member to the recording sheet.

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