JP2016095435A - Transfer device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an intermediate transfer device including a primary transfer belt whose service life is prolonged and an image forming apparatus including the intermediate transfer device.SOLUTION: A primary transfer unit 34 for transferring a toner image includes an endless primary transfer belt 340 which is arranged opposite to a photoreceptor drum, a driving roller 341 which rotationally drives the primary transfer belt 340, and primary transfer rollers 343Y to 343B which hold the primary transfer belt 340 together with the photoreceptor drum and to which a voltage is applied to transfer the toner image carried by the photoreceptor drum to the primary transfer belt 340. The primary transfer belt 340 is configured so that the conductive performance of a non-transfer area 340b located outside in a width direction substantially orthogonal to the rotational direction of the primary transfer belt 340 is higher than that of a transfer area 340a at least used for transferring the toner image.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a transfer device having a transfer belt used for transferring a toner image and an image forming apparatus including the transfer device.

  In an electrophotographic image forming apparatus, an electrostatic latent image formed on the surface of a photosensitive drum is developed (toner image) by a developing device, transferred to a sheet by a transfer device, and then heated by a fixing device. The sheet is fixed by applying pressure. In such an image forming apparatus, a primary transfer apparatus having a primary transfer belt that carries a toner image formed on the surface of a photosensitive drum by being primarily transferred and transported for secondary transfer to a sheet. An image forming apparatus including the image forming apparatus is known.

  Here, the primary transfer belt described above is formed so as to have a uniform thickness in the entire region. However, when viewed locally, the thickness of the primary transfer belt slightly changes by a ripple difference of 2 to 3 μm. For example, the width direction perpendicular to the toner image conveyance direction (hereinafter simply referred to as “width direction”). It is often inclined to.

  Thus, if the thickness of the primary transfer belt is uneven in the width direction, the applied current that flows through the primary transfer belt when a voltage is applied to the primary transfer roller is inevitably concentrated on a thin portion with low electrical resistance. End up. When such local charge concentration occurs, dielectric breakdown due to energization deterioration proceeds in the concentrated portion. Occurrence of dielectric breakdown of the primary transfer belt is unavoidable as long as voltage is applied, but a local decrease in electrical resistance (resistance difference) due to dielectric breakdown occurred in the transfer area of the primary transfer belt. In this case, image defects such as white streaks, white spots, and black spots may occur. As a result, the primary transfer belt must be replaced, resulting in a problem that the life of the primary transfer belt is shortened.

  For this, an image forming apparatus is disclosed in which the thickness of both end portions in the width direction of the primary transfer belt is made thinner than the thickness of the center portion in the width direction (see, for example, Patent Document 1).

JP 2013-148648 A

  However, in the image forming apparatus described in Patent Document 1, since the thickness of the primary transfer belt is gradually reduced from the central portion toward both ends, current deterioration due to charge concentration in the transfer region of the primary transfer belt. May occur. When energization deterioration occurs in the transfer region, the primary transfer belt must be replaced, and as a result, the life of the primary transfer belt may be shortened. The same applies to a secondary transfer belt that applies a voltage to secondary transfer a toner image carried by the primary transfer belt onto a sheet.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a transfer device having a transfer belt that suppresses the deterioration of energization in the transfer region and extends the life, and an image forming apparatus including the transfer device.

  The present invention is a transfer device for transferring a toner image carried by an image carrier by applying a voltage, and rotating the endless transfer belt disposed opposite to the image carrier and the transfer belt. The transfer belt is sandwiched between the driving means and the image carrier, and a voltage is applied so that a toner image carried by the image carrier is transferred between the transfer belt or the image carrier and the transfer belt. A transfer roller for transferring to a sheet conveyed therebetween, wherein the transfer belt is located outside of at least a transfer region used for transferring a toner image in a width direction substantially orthogonal to a rotation direction of the transfer belt. The non-transfer area is configured to have high conductivity performance.

  According to the present invention, a transfer having a transfer belt that suppresses the deterioration of energization in the transfer region by reducing the thickness outside the transfer region in the width direction rather than the thickness of the transfer region, thereby enabling a long life. An image forming apparatus including the apparatus and the transfer apparatus can be provided.

1 is a cross-sectional view schematically showing a printer according to a first embodiment of the present invention. FIG. 2 is a front view of a primary transfer unit and a secondary transfer unit according to the first embodiment. FIG. 3 is a perspective view of the primary transfer unit shown in FIG. 2. It is sectional drawing which shows typically the primary transfer belt which concerns on 1st Embodiment. It is a figure which shows the film thickness of the primary transfer belt which concerns on 1st Embodiment. It is sectional drawing which shows typically the primary transfer belt which concerns on 2nd Embodiment. It is sectional drawing which shows typically the primary transfer belt which concerns on 3rd Embodiment. It is sectional drawing which shows typically the primary transfer belt which concerns on 4th Embodiment. It is sectional drawing which shows typically the primary transfer belt which concerns on 5th Embodiment.

  An image forming apparatus including a transfer device having a transfer belt according to an embodiment of the present invention will be described with reference to the drawings. An image forming apparatus according to an embodiment of the present invention is an electrophotographic image forming apparatus including a transfer device having a transfer belt used for transferring a toner image, such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these. . In the following embodiments, as an example of a transfer device, a laser beam printer (hereinafter referred to as “printer”) including a primary transfer unit having a primary transfer belt to which a toner image formed on a photosensitive drum is primarily transferred. Will be described.

<First Embodiment>
A printer 100 according to the first embodiment will be described with reference to FIGS. 1 to 5. First, a schematic configuration of the printer 100 will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing a configuration of a printer 100 according to the first embodiment of the present invention. FIG. 2 is a front view of the primary transfer unit 34 and the secondary transfer unit 35 according to the first embodiment. FIG. 3 is a perspective view of the primary transfer unit 34 shown in FIG.

  As shown in FIG. 1, the printer 100 includes a sheet feeding unit 10 that feeds sheets, a manual feeding unit 20 that can manually feed sheets, and a sheet feeding unit 10 or a manual feeding unit 20. An image forming unit 30 that forms an image on the fed sheet, a sheet discharge unit 40 that discharges the sheet on which the image is formed to the outside of the apparatus, and a control unit 50 that controls them are provided.

  The sheet feeding unit 10 includes a feeding sheet stacking unit 11 that stacks and accommodates sheets, and a separation feeding unit 12 that separates and feeds the sheets stacked on the feeding sheet stacking unit 11 one by one. . The feeding sheet stacking unit 11 includes an intermediate plate 14 that rotates about a rotation shaft 13, and the intermediate plate 14 rotates to lift the sheet upward when the sheet is fed (FIG. 1). 2). The separation feeding unit 12 includes a pickup roller 15 that feeds the sheet lifted to the intermediate plate 14, and a separation pad 16 that is in pressure contact with the pickup roller 15.

  The manual feeding unit 20 includes a manual tray 21 on which sheets can be stacked, and a separation feeding unit 22 capable of feeding while separating the sheets stacked on the manual tray 21 one by one. The manual feed tray 21 is rotatably supported by the printer main body 101. When manually feeding the sheet, the manual feed tray 21 can be rotated to stack sheets (a state indicated by a two-dot chain line shown in FIG. 1). The separation feeding unit 22 includes a feeding roller 23 that feeds sheets stacked on the manual feed tray 21, and a separation pad 24 that is in pressure contact with the feeding roller 23.

  The image forming unit 30 includes four process cartridges (toner image forming apparatuses) 31Y to 31B for forming yellow (Y), magenta (M), cyan (C), and black (B) images, and a photosensitive drum described later. An exposure device 32 that exposes the surfaces of 310Y to 310B, a transfer unit 33 that transfers the toner images formed on the surfaces of the photosensitive drums 310Y to 310B to the sheet, and a fixing that fixes the unfixed toner image transferred to the sheet. Part 37.

  Each of the four process cartridges 31Y to 31B is configured to be detachable from the printer main body 101, and is replaceable. Since the four process cartridges 31Y to 31B have the same configuration except that the color of the image to be formed is different, the configuration of the process cartridge 31Y that forms a yellow (Y) image will be described to explain the process cartridge 31M. Description of ~ 31K is omitted. The alphabet (Y, M, C, B) added at the end of the code indicates the respective colors (yellow, magenta, cyan, black).

  The process cartridge 31Y includes a photosensitive drum 310Y as an image carrier, a charging roller 311Y that charges the photosensitive drum 310Y, a developing device 312Y that develops an electrostatic latent image formed on the photosensitive drum 310Y, and a photosensitive drum. And a cleaner unit 313Y that removes toner remaining on the surface of the body drum 310Y. The developing device 312Y includes a developing device main body 314Y that develops an electrostatic latent image and a toner cartridge 315Y that supplies toner to the developing device main body 314Y. The toner cartridge 315Y is configured to be detachable from the developing device main body 314Y. When the stored toner runs out, the toner cartridge 315Y can be removed from the developing device main body 314Y and replaced.

  The exposure device 32 includes a light source 320 that emits laser light, and a plurality of mirrors 321 that guide the laser light to the photosensitive drums 310Y to 310B.

  As shown in FIGS. 1 and 2, the transfer unit 33 performs primary transfer to the primary transfer unit (transfer device) 34 to which the toner images formed on the photosensitive drums 310 </ b> Y to 310 </ b> B are primarily transferred, and to the primary transfer unit 34. A secondary transfer unit 35 for secondary transfer of the toner image to the sheet.

  The primary transfer unit 34 is configured to be detachable from the printer main body 101 and is replaceable. As shown in FIGS. 2 and 3, the primary transfer unit 34 includes a primary transfer belt (transfer belt) 340 that carries and conveys toner images formed on the photoconductive drums 310 </ b> Y to 310 </ b> B, and a primary transfer belt 340. A driving roller (driving means) 341 and a driven roller 342 for rotationally driving the toner, primary transfer rollers (transfer rollers) 343Y to 343B for primarily transferring the toner images formed on the photosensitive drums 310Y to 310B to the primary transfer belt 340, And a cleaner unit 36 for removing toner remaining on the primary transfer belt 330.

  The primary transfer belt 340 is formed in an endless shape, and is stretched around the driving roller 341 and the driven roller 342. Further, the primary transfer belt 340 is disposed to face the photosensitive drums 310Y to 310B. The primary transfer belt 340 will be described in detail later.

  The driving roller 341 and the driven roller 342 are rotatably supported by the frames 344 and 345, and are transferred to the primary transfer belt 340 by rotating the primary transfer belt 340 in the direction of arrow A shown in FIGS. The toner image is moved toward the secondary transfer unit 35. Further, as shown in FIG. 3, the axial lengths of the roller surfaces 341a and 342a of the driving roller 341 and the driven roller 342 are in the width direction (hereinafter simply referred to as “the direction of the toner image” of the primary transfer belt 340). It is formed so as to be shorter than the length in the width direction) and longer than the length in the width direction of the transfer region 340a used for transferring the toner image on the primary transfer belt 340.

  The transfer area here is an area corresponding to the toner image forming area on the photoconductive drums 310Y to 310B, and the toner image forming area on the photoconductive drums 310Y to 310B here is capable of forming a toner image. Area (printing area).

  The primary transfer rollers 343Y to 343B are rotatably supported by the frames 344 and 345 on the back side opposite to the toner image carrying surface (front surface) of the primary transfer belt 340, and each process cartridge 31Y to 31B is supported from the back side. The primary transfer belt 340 can be pressed against the photosensitive drums 310Y to 310B. In the present embodiment, the primary transfer rollers 343Y to 343B are configured to contact and separate from the photosensitive drums 310Y to 310B by rotation of a roller transfer cam mechanism (not shown).

  Further, the primary transfer rollers 343Y to 343B are connected to a voltage application unit (not shown) provided in the printer main body 101 and configured to be able to apply a voltage. By applying a voltage to the primary transfer rollers 343Y to 343B, an applied current flows to the photosensitive drums 310Y to 310B via the primary transfer belt 340, and the toner images formed on the photosensitive drums 310Y to 310B are transferred to the primary transfer belt. 340 is primarily transferred.

  Note that the axial lengths of the roller surfaces 343a of the primary transfer rollers 343Y to 343B (the lengths of the pressure contact regions 340c in the axial direction) are the roller surfaces 341a of the driving roller 341 and the driven roller 342, as shown in FIG. It is shorter than the length in the axial direction of 342a and longer than the length in the width direction of the transfer region 340a of the primary transfer belt 340.

  The secondary transfer unit 35 is configured to be detachable from the printer main body 101 and is replaceable. The secondary transfer unit 25 includes an endless secondary transfer belt 350, a driving roller 351 and a driven roller 352 that rotate the secondary transfer belt 350, and a driving roller for the primary transfer unit 34. And a pressing roller 353 that presses toward 341.

  The secondary transfer belt 350 is formed of general polyimide, and is imparted with conductivity by adding a carbon conductive material. Further, the secondary transfer belt 350 is stretched around a driving roller 351 and a driven roller 352 and is disposed so as to face the driving roller 341 via the primary transfer belt 340.

  The driving roller 351 and the driven roller 352 are rotatably supported by the frame 354, and rotate the secondary transfer belt 350 in the direction of arrow B shown in FIG. The pressing roller 353 is rotatably supported by the frame 354 on the back surface (the surface opposite to the surface in contact with the primary transfer belt 340) of the secondary transfer belt 350, and the primary transfer unit 34 is supported by a biasing spring 355. The drive roller 341 is urged. As a result, the primary transfer belt 340 and the secondary transfer belt 350 are sandwiched between the pressing roller 353 and the driving roller 341.

  The drive roller 341 is connected to a voltage application unit (not shown) provided in the printer main body 101, and a secondary transfer is performed via the primary transfer belt 340 by applying a voltage to the drive roller 341 at a predetermined timing. An applied current flows toward the belt 350, and the toner image carried by the primary transfer belt 340 is transferred to the conveyed sheet.

  The fixing unit 37 includes a heating roller 370 that heats the sheet, and a pressure roller 371 that presses against the heating roller 370. The sheet discharge unit 40 includes a discharge roller 41 that can rotate forward and backward, and a driven roller 42 that is in pressure contact with the discharge roller 41 and rotates following the discharge roller 41.

  The control unit 50 includes a CPU that drives and controls the sheet feeding unit 10, the manual feeding unit 20, the image forming unit 30, and the sheet discharge unit 40, and a memory that stores various programs and various information. The control unit 50 controls the operations of the sheet feeding unit 10, the manual feeding unit 20, the image forming unit 30, and the sheet discharge unit 40 by using them, and forms an image on the sheet.

  Next, an image forming operation (image forming control by the control unit 50) of the printer 100 configured as described above will be described. In the present embodiment, description will be made using an image forming operation for forming an image on the sheet S stacked on the feeding sheet stacking unit 11 based on image information input from an external PC.

  When image information is input from the external PC to the printer 100, the exposure device 32 irradiates the photosensitive drums 310Y to 310B with laser light based on the input image information. At this time, the photosensitive drums 310Y to 310B are pre-charged by the charging rollers 311Y to 311B, and an electrostatic latent image is formed on the photosensitive drums 310Y to 310B by being irradiated with laser light. Thereafter, the electrostatic latent images are developed by the developing devices 312Y to 312B, and yellow (Y), magenta (M), cyan (C), and black (B) toner images are formed on the photosensitive drums 310Y to 310B. The

  The toner images of the respective colors formed on the photosensitive drums 310Y to 310B are sequentially superimposed and transferred onto the transfer area 340a of the primary transfer belt 340 rotating in the arrow A direction by applying a voltage to the primary transfer rollers 343Y to 343B. The four-color toner images (full-color toner images) that are superimposed and transferred are conveyed to the secondary transfer unit 35 by the primary transfer belt 340.

  In parallel with the image forming operation described above, the sheets stacked on the feeding sheet stacking unit 11 are fed to the sheet conveying path 102 one by one by the separation feeding unit 12. Then, the skew is corrected by the registration roller pair 103 on the downstream side of the sheet conveyance path 102, and at the timing when the toner image carried on the primary transfer belt 340 is conveyed to the secondary transfer unit 35, the secondary transfer unit 35. It is conveyed toward. The toner image carried by the primary transfer belt 340 is transferred to the sheet conveyed to the secondary transfer unit 35 by applying a voltage to the drive roller 341. The sheet onto which the toner image has been transferred is heated and pressed by the fixing unit 37 so that the toner image is melted and fixed, and is discharged to the outside by the discharge roller 41. The sheets discharged outside the apparatus are stacked on a discharge sheet stacking unit 104 provided on the upper surface of the printer main body 101.

  When images are formed on both surfaces (first surface and second surface) of the sheet, the sheet on which the image is formed on the first surface (front surface) is discharged before being discharged to the discharge sheet stacking unit 104. The roller 41 is rotated in the reverse direction and conveyed to the double-sided conveyance path 105, and is conveyed again to the image forming unit 30 via the double-sided conveyance path 105. Then, similarly to the first surface, an image is formed on the second surface (back surface) and discharged outside the apparatus.

  Next, the primary transfer belt 340 described above will be described in more detail with reference to FIG. FIG. 4 is a cross-sectional view schematically showing the primary transfer belt 340 according to the first embodiment.

  The primary transfer belt 340 is formed of polyimide. By using polyimide, the primary transfer belt 340 has high mechanical strength, excellent heat resistance and insulation performance, and excellent chemical resistance. Moreover, the expansion coefficient with respect to heat is low as an organic substance, and an error due to expansion can be made small even when used at a high temperature.

  Further, carbon black (carbon conductive material) is added to the primary transfer belt 340, and conductivity is imparted by adding carbon black. The additive for imparting conductivity to the primary transfer belt 340 is not limited to carbon black as long as it can reduce the resistance, but fine particles are preferable. Carbon black has a relatively small particle size of 3 to 500 μm, and can flow a current stably. Examples of the additive other than carbon black include carbon nanotubes.

  As shown in FIG. 4, in the primary transfer belt 340, the thickness of the non-transfer area 340b located on both sides in the width direction of the transfer area 340a is thinner than the thickness of the transfer area 340a. In the present embodiment, the non-transfer area 340b extends from the front side (the side where the toner image is transferred) and the back side (the side opposite to the side where the toner image is transferred) to the outside in the width direction (end). And gradually getting thinner. The non-transfer area 340b may be configured to be thinner than the transfer area 340a by gradually decreasing one of the front side and the back side toward the outside.

  The average thickness of the non-transfer area 340b of the primary transfer belt 340 is preferably in the range of 4 to 30% of the thickness of the transfer area 340a, and more preferably in the range of 4 to 10%. In the present embodiment, the non-transfer area 340b is formed to be 4 to 5 μm thinner than the transfer area 340a having a thickness of 60 μm ± 4 μm. For example, when considering that the unevenness of thickness formed when manufacturing the primary transfer belt 340 having a thickness of about 60 μm is usually about 2 to 3 μm, a larger difference (4 to 5 μm) is obtained. By providing, it is possible to provide a portion with low electrical resistance without affecting the mechanical strength of the primary transfer belt 340.

  As described above, the printer 100 according to the first embodiment is formed such that the thickness of the non-transfer area 340b of the primary transfer belt 340 in the primary transfer unit 34 is thinner than the thickness of the transfer area 340a. . Therefore, the non-transfer area 340b has an electric resistance smaller than that of the transfer area 340a, and an applied current that flows through the primary transfer belt 340 when a voltage is applied to the primary transfer rollers 343Y to 343B easily flows to the non-transfer area 340b. Thereby, local energization deterioration easily occurs in the non-transfer area 340b, and the energization deterioration in the transfer area 340a is suppressed. As a result, the life of the primary transfer belt 340 is extended, and the life of the primary transfer belt 340 can be extended.

  Further, the film thickness difference between the transfer area 340a and the non-transfer area 340b is formed to be larger than the film thickness difference formed when the primary transfer belt 340 is manufactured. For this reason, even when the primary transfer belt 340 having a film thickness difference is used, it is possible to suppress the deterioration of energization in the transfer region 340a, and the life of the primary transfer belt 340 can be extended.

  For example, as shown in FIG. 5, since the thickness of the conventional primary transfer belt (before improvement) decreases from the F side to the R side in the width direction, the current concentrates on the portion of the M frame, Energization deterioration is likely to occur in the portion of the M frame. Since the portion of the M frame is in the transfer area (printing area), the image quality is gradually affected when the energization is gradually deteriorated. On the other hand, in the primary transfer belt (after improvement) according to the first embodiment, the thickness of the N frame portion on the R (rear) side and F (front) side in the width direction is locally thin. That is, the unevenness of the unevenness is large. Therefore, the current is concentrated on this portion, but the current is not concentrated in the transfer area (printing area). As a result, energization deterioration of the transfer area (print area) is suppressed.

Second Embodiment
Next, a printer 100A according to a second embodiment of the present invention will be described with reference to FIGS. FIG. 6 is a cross-sectional view schematically showing a primary transfer belt 340A according to the second embodiment.

  The printer 100A according to the second embodiment is different from the first embodiment in the shape of the primary transfer belt. Therefore, the difference from the first embodiment, that is, the shape of the primary transfer belt will be mainly described here, and the other components are denoted by the same reference numerals as those of the first embodiment, and the description thereof is omitted. .

  As shown in FIG. 6, in the primary transfer belt 340A, the thickness of the non-pressure contact region 340d located on both sides in the width direction of the pressure contact region 340c is smaller than the thickness of the pressure contact region 340c. In the present embodiment, the non-pressure contact region 340d extends from the front surface side (side to which the toner image is transferred) and the back surface side (side opposite to the surface to which the toner image is transferred) to the outside in the width direction (end portion). And gradually getting thinner. The non-pressure contact region 340d may be configured to be thinner than the pressure contact region 340c by gradually decreasing one of the front surface side and the back surface side toward the outside.

  Further, the average thickness of the non-pressure contact area 340d of the primary transfer belt 340 is preferably in the range of 4 to 30% of the thickness of the pressure contact area 340c, and more preferably in the range of 4 to 10%. In this embodiment, the non-pressure contact region 340d is formed to be 4 to 5 μm thinner than the pressure contact region 340c having a thickness of 60 μm ± 4 μm. For example, when considering that the unevenness of thickness formed when manufacturing the primary transfer belt 340 having a thickness of about 60 μm is usually about 2 to 3 μm, a larger difference (4 to 5 μm) is obtained. By providing, it is possible to provide a portion with low electrical resistance without affecting the mechanical strength of the primary transfer belt 340.

  As described above, the printer 100A according to the second embodiment is formed such that the thickness of the non-pressure contact area 340d of the primary transfer belt 340 in the transfer portion 33 is thinner than the thickness of the pressure contact area 340c. Therefore, the applied current is more likely to flow through the non-pressure contact region 340d located on the outer side in the width direction than the transfer region 340a, and the energization deterioration in the transfer region 340a is suppressed. For example, in the primary transfer belt 340 according to the present embodiment, the non-pressure contact region 340d is positioned on the outer side by about 5 mm from the transfer region 340a with respect to a length of about 330 mm in the width direction. Therefore, it is possible to more reliably suppress an unnecessary applied current from flowing to the transfer region 340a in a state where the energization stability to the transfer region is sufficiently kept. As a result, the life of the primary transfer belt 340 is extended, and the life of the primary transfer belt 340 can be extended.

<Third Embodiment>
Next, a printer 100B according to a third embodiment of the present invention will be described with reference to FIG. FIG. 7 is a cross-sectional view schematically showing a primary transfer belt 340B according to the third embodiment.

  A printer 100B according to the third embodiment is different from the first embodiment in the shape of the primary transfer belt. Therefore, the difference from the first embodiment, that is, the shape of the primary transfer belt will be mainly described here, and the other components are denoted by the same reference numerals as those of the first embodiment, and the description thereof is omitted. .

  As shown in FIG. 7A, in the primary transfer belt 340B, more conductive material is added to the non-transfer areas 340b located on both sides in the width direction of the transfer area 340a than in the transfer area 340a. In the present embodiment, more carbon black is added than in the transfer region 340a.

  Thus, in the printer 100B according to the third embodiment, more conductive material is added to the non-transfer area 340b than to the transfer area 340a. Therefore, the non-transfer area 340b has an electric resistance smaller than that of the transfer area 340a, and an applied current that flows through the primary transfer belt 340 when a voltage is applied to the primary transfer rollers 343Y to 343B easily flows to the non-transfer area 340b. . Thereby, local energization deterioration easily occurs in the non-transfer area 340b, and the energization deterioration in the transfer area 340a is suppressed. As a result, the life of the primary transfer belt 340 is extended, and the life of the primary transfer belt 340 can be extended.

  Further, when the electrical resistance of the non-transfer area 340b is made smaller than that of the transfer area 340a by reducing the thickness of the non-transfer area 340b, the mechanical strength of the primary transfer belt 340 may be weakened. By adding more conductive material than 340a to the non-transfer area 340b to reduce the electric resistance, the electric resistance of the non-transfer area 340b can be reduced without reducing the thickness of the non-transfer area 340b. . That is, the electrical resistance can be reduced without reducing the mechanical strength of the primary transfer belt 340.

  For example, as shown in FIG. 7B, in the primary transfer belt 340B ′, more conductive material is added to the non-pressure contact region 340d located on both sides in the width direction of the pressure contact region 340c than the pressure contact region 340c. Thus, the electric resistance of the non-pressure contact region 340d may be smaller than that of the transfer region 340a.

<Fourth embodiment>
Next, a printer 100C according to a fourth embodiment of the present invention will be described with reference to FIGS. FIG. 8 is a cross-sectional view schematically showing a primary transfer belt 340C according to the fourth embodiment.

  A printer 100C according to the fourth embodiment is different from the first embodiment in the shape of the primary transfer belt. Therefore, the difference from the first embodiment, that is, the shape of the primary transfer belt will be mainly described here, and the other components are denoted by the same reference numerals as those of the first embodiment, and the description thereof is omitted. .

  As shown in FIG. 8, in the primary transfer belt 340C, concave portions 346 having a thickness smaller than the thickness of the transfer region 340a are formed in the non-pressure contact regions 340d located on both sides in the width direction of the pressure contact region 340c. Yes. In the present embodiment, the concave portion 346 is formed on the surface side of the non-pressure contact region 340d. The concave portion 346 may be formed on the back side of the non-pressure contact region 340d.

  As described above, in the printer 100C according to the fourth embodiment, the concave portion 346 is formed in the non-pressure contact region 340d. Therefore, an applied current that flows through the primary transfer belt 340 when a voltage is applied to the primary transfer rollers 343Y to 343B easily flows into the concave portion 346 of the non-transfer area 340b. Thereby, local energization deterioration easily occurs in the non-transfer area 340b, and the energization deterioration in the transfer area 340a is suppressed. As a result, the life of the primary transfer belt 340 is extended, and the life of the primary transfer belt 340 can be extended.

<Fifth Embodiment>
Next, a printer 100D according to a fifth embodiment of the present invention will be described with reference to FIGS. FIG. 9 is a cross-sectional view schematically showing a primary transfer belt 340D according to the fifth embodiment.

  A printer 100D according to the fifth embodiment is different from the first embodiment in the shape of the primary transfer belt. Therefore, the difference from the first embodiment, that is, the shape of the primary transfer belt will be mainly described here, and the other components are denoted by the same reference numerals as those of the first embodiment, and the description thereof is omitted. .

  As shown in FIG. 9, in the primary transfer belt 340D, the thickness of the non-pressure contact region 340d located on both sides in the width direction of the pressure contact region 340c is made thinner than the thickness of the pressure contact region 340c, and a conductive member 347 is attached. Yes. In the present embodiment, the non-pressure contact region 340d has a surface side that gradually becomes thinner toward the outside, and a conductive member 347 is attached to the back side.

  As the conductive member 347, a metal tape such as Alpet, a conductive brush such as Sandalon, a conductive nonwoven fabric, or the like can be used.

  Thus, in the printer 100D according to the fifth embodiment, the thickness of the non-pressure contact region 340d is made thinner than the thickness of the pressure contact region 340c, and the conductive member 347 is attached. For this reason, the electric resistance of the non-pressure contact area 340d is smaller than that of the pressure contact area 340c, and an applied current that flows through the primary transfer belt 340 when a voltage is applied to the primary transfer rollers 343Y to 343B easily flows to the non-pressure contact area 340d. Thereby, local energization deterioration is likely to occur in the non-pressure contact area 340d, and energization deterioration in the transfer area 340a is suppressed. As a result, the life of the primary transfer belt 340 is extended, and the life of the primary transfer belt 340 can be extended.

  Further, when the electric resistance of the non-pressure contact region 340d is made smaller than that of the transfer region 340a by reducing the thickness of the non-pressure contact region 340d, the mechanical strength of the primary transfer belt 340 may be weakened. By attaching 347, the electrical resistance of the non-pressure contact region 340d can be made smaller than that of the transfer region 340a without reducing the mechanical strength.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to embodiment mentioned above. In addition, the effects described in the embodiments of the present invention only list the most preferable effects resulting from the present invention, and the effects of the present invention are not limited to those described in the embodiments of the present invention.

  For example, in this embodiment, the transfer device has been described using a primary transfer unit, but the present invention is not limited to this. The transfer device can be used for the secondary transfer unit 35 by using, for example, a secondary transfer belt 350 as a transfer belt, a primary transfer belt 340 as an image carrier, and a pressing roller 353 as a transfer roller.

  Further, the present invention may be configured to use a primary transfer belt that selectively combines the differences of the primary transfer belt according to each embodiment.

100 printer (image forming apparatus)
31Y to 31B Process cartridge (toner image forming apparatus)
34 Primary transfer unit (transfer device)
35 Secondary transfer unit 310Y to 310B Photosensitive drum (image carrier)
340 Primary transfer belt (transfer belt)
340a Transfer area 340b Non-transfer area 341 Drive roller (drive means)
343Y to 343B Primary transfer roller (transfer roller)
350 Secondary transfer belt

Claims (11)

A transfer device for applying a voltage to transfer a toner image carried by an image carrier,
An endless transfer belt disposed opposite to the image carrier;
Drive means for rotationally driving the transfer belt;
The transfer belt is sandwiched between the image carrier and a voltage is applied, whereby the toner image carried by the image carrier is conveyed between the transfer belt or the image carrier and the transfer belt. A transfer roller for transferring to the sheet,
The transfer belt is configured such that at least a transfer region used for transferring a toner image has higher conductivity in a non-transfer region located outside the width direction substantially orthogonal to the rotation direction of the transfer belt. ,
A transfer device characterized by that. In the transfer belt, the thickness of the non-transfer area is thinner than the thickness of the transfer area.
The transfer device according to claim 1. The non-transfer area of the transfer belt gradually decreases in thickness toward the outside in the width direction.
The transfer device according to claim 2. More conductive material is added to the non-transfer area of the transfer belt than the transfer area.
The transfer device according to claim 1, wherein In the transfer belt, the thickness of the non-pressure contact region located outside the roller surface in the axial direction of the transfer roller is smaller than the thickness of the pressure contact region in contact with the roller surface,
The transfer device according to claim 1. The non-pressure contact area of the transfer belt gradually decreases in thickness toward the outside in the width direction.
The transfer device according to claim 5, wherein: A conductive member is disposed in the non-pressure contact area of the transfer belt.
The transfer apparatus according to claim 5 or 6, wherein More conductive material is added to the non-pressure contact area located outside the roller surface in the axial direction of the transfer roller of the transfer belt than the pressure contact area contacting the roller surface,
The transfer device according to claim 1, wherein The non-pressure contact region located outside the roller surface in the axial direction of the transfer roller of the transfer belt has a concave portion thinner than the thickness of the pressure contact region in contact with the roller surface,
The transfer device according to claim 1, wherein The non-transfer area of the transfer belt has a larger unevenness in the thickness direction than the transfer area,
The transfer apparatus according to claim 1, wherein A toner image forming apparatus for forming a toner image;
The transfer device according to claim 1, which transfers a toner image formed by the toner image forming device.
An image forming apparatus comprising: