JP2006030778A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To stably ensure the prevention of image mis-registration caused by image stretch or shrink in the secondary transfer part of an intermediate transfer system, and the ability to convey a recording material regardless of a recording material type. <P>SOLUTION: An image forming apparatus includes: one or more image carriers 1 on which toner images of their respective colors are formed and held; an intermediate transfer body 2 onto which the toner images of the respective colors on the corresponding image carriers 1 are intermediately transferred and held; and a batch transfer device 4 by which the toner images of the respective color toner images on the intermediate transfer body 2 are transferred to a recording material 3 in batch. The batch transfer device 4 has a plurality of rolls 5a and 5b, and a transfer conveyance belt 6 rotatably stretched around the rolls 5a and 5b. The roll 5a located upstream of the roll 5b is used as a transfer roll. The transfer roll (roll 5a) is disposed in firm contact with the intermediate transfer body 2 via the transfer conveyance belt 6. The back of the transfer conveyance belt 6 and the contact face B of the transfer roll (roll 5a) are in slidable contact with each other such that one slides against the other. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printer that employs an electrophotographic system, an electrostatic recording system, or the like, and in particular, records after an image formed on an image carrier is once transferred to an intermediate transfer body. The present invention relates to an improvement in an intermediate transfer type image forming apparatus that performs batch transfer onto a material.

Conventionally, as an intermediate transfer type image forming apparatus of this type, each color component toner image formed on a photoconductor or the like is sequentially primary transferred to an intermediate transfer body, and a multicolor toner image on the intermediate transfer body is transferred to a secondary transfer apparatus ( A device that performs batch transfer onto a sheet by a batch transfer apparatus) is known.
In this type of image forming apparatus, there is a problem in that the sheet as a recording material from the intermediate transfer member is poorly peeled and the paper is not easily transported after peeling.
First, the sheet peeling failure will be described. The sheet as a recording material is charged to pass through the nip region between the transfer roll and the intermediate transfer member at the secondary transfer portion, and is easily drawn toward the intermediate transfer member. . For this reason, even if the leading edge of the paper is peeled off from the intermediate transfer member, the paper conveyance state after the nip area is again not along the paper guide (the guide guide installed after the paper peeling) depending on the type of paper. A situation in which it is adsorbed by the intermediate transfer member is likely to occur.
Also, in recent years, the use frequency of special paper such as coated paper coated with a coating layer on the paper surface has increased, and these special papers tend to have poorer peelability, and the paper can be peeled off from the intermediate transfer member. However, there is a problem that trouble such as paper jam is likely to occur.

Japanese Patent Laid-Open No. 10-319741 (Embodiment of the Invention, FIG. 1)

In response to such a problem, the applicant of the present invention uses a transfer roll instead of a transfer roll in order to keep the paper peelable from the intermediate transfer body at the secondary transfer outlet well and to stabilize the transportability of the paper to the fixing device. A transfer conveyance belt system using a transfer belt was proposed (for example, see Patent Document 1).
Certainly, with this transfer conveyance belt system, the effect of the transfer electric field at the secondary transfer site is eliminated even with thin paper coated paper, etc., and the effect of suppressing paper jamming on the intermediate transfer member and winding jam on the transfer roll There is.

Furthermore, in recent years, an image forming apparatus such as a copying machine or a printer using an electrophotographic system has been increasingly used in a commercial printing field (for example, a light printing industry). Therefore, in such a market, higher accuracy of image registration is required, and it is necessary to further reduce image misalignment (image registration misalignment) on the front and back during double-sided printing due to image expansion and contraction at the transfer portion. .
Such image registration misalignment is particularly noticeable in an embodiment in which the transfer roll includes an elastic layer, and in this case, the cause is as follows.
The transfer roll surface is the same as the surface transfer speed of the intermediate transfer body in a state where there is a difference in the transfer nip pressure in the roll axis direction due to the dimensional tolerance and mounting position tolerance of the transfer roll that transfers the toner image from the intermediate transfer body to the paper. The surface of the transfer roll tries to move along the surface of the intermediate transfer body by following the rotation at high speed. However, since the shaft of the transfer roll itself is a rigid body, distortion due to the twist of the transfer roll occurs in the roll axis direction. End up. The reaction force due to this distortion acts on the paper as a drag (resistance force) that hinders paper conveyance. As a result, a difference occurs in the sheet speed in the roll axis direction, resulting in an image shift (image registration shift).

This image registration misalignment cannot be resolved only by the technique described in Patent Document 1 described above.
Accordingly, the inventors of the present invention have determined that the transfer amount of the transfer roll and the backup roll (the belt of the transfer roll in the form of the belt member as an intermediate transfer member) so that the image registration deviation is within an allowable range for each image forming apparatus. A proposal has been made of a method of finely adjusting and optimizing an alignment position in a twist direction with respect to an opposing roll disposed oppositely via a member (see, for example, Japanese Patent Application No. 2003-034986).

However, even if such a method is adopted, distortion accumulation on the roll cannot be completely prevented, and when using paper other than the paper used when optimizing the image registration, Registration misalignment may occur, and it is necessary to perform optimization in accordance with the paper to be used each time. Therefore, there is a technical problem that adjustment itself is complicated and a sufficient effect cannot be obtained.
In addition, as described above, such a technical problem is remarkable in the aspect in which the transfer roll includes an elastic layer. However, even in the aspect in which the transfer roll is a rigid roll, for example, the axial dimension is small. It can occur in different cases as well.
The present invention provides an image forming apparatus capable of stably performing image registration misalignment prevention and conveyance of a recording material due to expansion and contraction of an image at a secondary transfer site in an intermediate transfer method, regardless of the recording material type. There is to do.

  That is, according to the present invention, as shown in FIG. 1, one or a plurality of image carriers 1 on which each color component toner image is formed and supported, and each color component toner image on this image carrier 1 is transferred and supported intermediately. In the image forming apparatus, the batch transfer device 4 includes a plurality of rolls, and the batch transfer device 4 that batch-transfers each color component toner image on the intermediate transfer member 2 onto the recording material 3. 5a and 5b, and a transfer conveyance belt 6 that is rotatably stretched around the rolls 5a and 5b. Among the plurality of rolls 5a and 5b, a roll 5a positioned upstream in the recording material conveyance direction is used as a transfer roll. The transfer roll (roll 5a) is disposed in pressure contact with the intermediate transfer member 2 via the transfer conveyance belt 6, and the contact surface B between the back surface of the transfer conveyance belt 6 and the transfer roll (roll 5a) is configured to be slidable. Special It is an.

In such technical means, the image forming method of the image forming apparatus that is the subject of the present application may be appropriately selected, such as an electrophotographic method, an electrostatic recording method, etc. In order to form a color image, a multi-cycle method (for example, four-cycle method) using one image carrier 1 may be used, or a tandem method using a plurality of image carriers 1 or the like. The aspect of this may be sufficient.
The intermediate transfer member 2 may be either a belt shape or a drum shape, but a belt shape is preferred from the viewpoint of layout flexibility.

Furthermore, the batch transfer device 4 according to the present invention shows two rolls 5a and 5b in FIG. 1, but is not limited to this mode. For example, three or more rolls are linear or non-linear. It can be arranged in a shape.
Further, the transfer roll (roll 5a) may be either elastic or rigid, but from the viewpoint of ensuring a wide nip width during transfer, an embodiment in which an elastic layer is provided on the surface is preferable. At this time, the transfer conveyance belt 6 can be driven by the intermediate transfer body 2, and the intermediate transfer body 2 and the transfer conveyance belt 6 move at the same speed, so that a speed difference from the recording material 3 to be conveyed occurs. Therefore, it is possible to further suppress image registration misalignment.
Further, the transfer / conveying belt 6 may be either elastic or rigid, but is preferably elastic from the viewpoint of reducing reaction force due to distortion of the transfer roll (roll 5a) and reducing transmission of force to the recording material 3. . By using the transfer / conveying belt 6 as an elastic material, the reaction force due to the distortion of the transfer roll (roll 5a) can be absorbed by the elastic material, and the transmission of force to the recording material 3 can be reduced, thereby reliably preventing image registration displacement. Will be able to.

In the present invention, the contact surface B between the back surface of the transfer conveyance belt 6 and the transfer roll (roll 5a) is configured to be slidable so that the transfer conveyance belt 6 Slip occurs between the transfer roll (roll 5a), and does not affect the conveyance speed of the recording material 3, thereby preventing image registration displacement.
At this time, the contact surface A between the surface of the transfer conveyance belt 6 and the recording material 3 may be nipped, and usually does not slip. Even if the contact surface A slips slightly, since the intermediate transfer member 2 and the recording material 3 are nipped, the conveyance speed of the recording material 3 is not affected. For this reason, this aspect is also included in this case.

In the present invention, focusing on the contact surface B between the transfer conveyance belt 6 and the transfer roll (roll 5a), as shown in FIG. 2, the contact surface B is in sliding contact (example in FIG. 2A). And the case where no sliding contact is made (example in FIG. 2B).
As shown in FIGS. 2A and 2B, when it is assumed that a sheet conveyance resistance force (hereinafter referred to as drag) α due to the distortion of the roll 5a is generated, in the case of sliding contact as shown in FIG. The drag α is not transmitted to the transfer / conveying belt 6 due to the sliding action on the contact surface B between the transfer / conveying belt 6 and the roll 5a, and the recording material 3 is not affected. On the other hand, when the sliding contact does not occur as in (b), the drag force α is not slid on the contact surface B between the transfer conveyance belt 6 and the roll 5a, and both act integrally, so the drag force α is This is transmitted to the recording material 3 via the transfer conveyance belt 6, and the speed of the recording material 3 is reduced, resulting in image registration displacement.
Therefore, in the present invention, the effect of the drag α is reduced by the sliding action on the contact surface B between the transfer conveyance belt 6 and the roll 5a, and image registration displacement can be prevented.

Further, the static friction coefficient mu _B of the contact surface B of the static friction coefficient mu _A and the transfer conveyance belt 6 back surface of the contact surface A of the recording material 3 and the transfer conveyance belt 6 surface and the transfer roll (roll 5a) μ _A> μ _B is preferably set so as to satisfy _B , and even if drag α due to distortion of the transfer roll (roll 5a) is generated, sliding (sliding) occurs on the contact surface B between the transfer conveyance belt 6 and the transfer roll (roll 5a). Contact) is likely to occur and does not affect the conveyance speed of the recording material 3, so that image registration misalignment can be prevented.

In the present invention, from the viewpoint of reducing the static friction coefficient μ _B of the contact surface B between the back surface of the transfer conveyance belt 6 and the transfer roll (roll 5a), it is preferable to provide a back surface coating layer on the back surface of the transfer conveyance belt 6. A typical embodiment of the back coat layer is a fluorine resin layer.

In the embodiment of the intermediate transfer belt in which the intermediate transfer member 2 is an endless belt in the present invention, an intermediate transfer belt (corresponding to the intermediate transfer member 2) is held at a position facing the transfer roll (roll 5a). It is preferable that the opposing roll is provided so that the Asker C hardness on the surface of the transfer roll (roll 5a) is less than the Asker C hardness on the surface of the opposing roll. The hardness of the transfer roll (roll 5a) is preferably By making it smaller, the nip area between the two can be formed reliably, the transport speed of the transfer transport belt 6 driven by the moving speed of the intermediate transfer belt can be stabilized, and image registration displacement can be prevented. Moreover, stable transfer can be performed by securing the transfer nip area.
Furthermore, in this case, by setting the Asker C hardness of the surface of the transfer roll (roll 5a) to 5 degrees or more and less than 50 degrees, more preferably 20 degrees or more and 40 degrees or less, reaction force can be generated even when distortion due to roll deformation accumulates. As a result, the force transmitted to the recording material 3 is reduced, and the influence on the image registration deviation is suppressed. Further, by ensuring a wide nip area, stable transferability and transportability can be obtained. If the surface of the transfer roll is less than 5 degrees Asker C hardness, the transfer roll is greatly deformed by the tension of the transfer conveyance belt 6 stretched around the transfer roll (roll 5a), and stable conveyance cannot be performed. On the other hand, image registration shift occurs at 50 degrees or more.

According to the present invention, as a batch transfer apparatus, a plurality of rolls and a transfer conveyance belt that is rotatably stretched around the rolls are provided, and a roll positioned upstream in the recording material conveyance direction among the plurality of rolls is a transfer roll. The transfer roll is arranged in pressure contact with the intermediate transfer member via the transfer conveyance belt, and the contact surface between the transfer conveyance belt back surface and the transfer roll can be slidably contacted. Without having a complicated adjustment mechanism such as roll alignment at the next transfer site, it is possible to stably prevent registration displacement due to image expansion and contraction and running performance of the recording material regardless of the recording material type.
Further, since the recording material immediately after the transfer is conveyed by the belt, it is not necessary to provide a guide member such as a recording material guide immediately after the transfer, and it is possible to effectively avoid a situation where the recording material is caught by the guide member even in a low humidity environment. . For this reason, it is possible to always maintain good releasability of the recording material from the intermediate transfer member without being affected by the type of the recording material, and to stabilize the transportability of the recording material to the fixing device.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 3 is an overall configuration diagram of a color image forming apparatus (for example, a color copying apparatus) to which the present invention is applied.
In the figure, an image forming apparatus includes a document reading device 10 that reads a document 12 on a platen 11, and an image (toner) in each of four color components (black, yellow, magenta, cyan in this embodiment) by, for example, electrophotography. An image forming unit 20 (20a to 20d) that forms an image), an intermediate transfer belt 30 that sequentially transfers (primary transfer) each color component image formed by each image forming unit 20, and an intermediate transfer belt 30 A batch transfer device 50 that batch-transfers (secondary transfer) the transferred superimposed image to a sheet (recording material) 100, a fixing device 70 that fixes the batch-transferred image on the sheet 100, and a sheet 100 at a batch transfer site. And a paper transport system 80 for supplying the paper.

  In the present embodiment, the document reading apparatus 10 includes, for example, a light source 13 that is disposed below the platen 11 and irradiates light on the surface of the document 12, and a CCD that converts reflected light from the surface of the document 12 into an electrical signal. The photoelectric conversion element 14, an appropriate number of mirrors 15 that form a path for guiding the reflected light from the surface of the document 12 to the photoelectric conversion element 14, and the reflected light from the surface of the document 12 are coupled on the imaging surface of the photoelectric conversion element 14. And an imaging lens 16 for imaging.

  Each image forming unit 20 (20a to 20d) has a photosensitive drum 21, and a charging device 22 such as a corotron for charging the photosensitive drum 21 is charged around each photosensitive drum 21. A laser scanning device in which an electrostatic latent image (mainly image data read by the photoelectric conversion element 14 or electrostatic latent image based on image data taken from another recording medium) is written on the photosensitive drum 21 The exposure device 23, the developing device 24 for developing the electrostatic latent image written on the photosensitive drum 21 with each color component toner, and the transfer roll for transferring the toner image on the photosensitive drum 21 to the intermediate transfer belt 30. And a drum cleaner 26 from which residual toner on the photosensitive drum 21 is removed.

Furthermore, the intermediate transfer belt 30 is composed of, for example, a film-like endless belt having a volume resistivity of about 10 ⁹ to 10 ¹² Ω · cm, in which conductive carbon black is kneaded with polyimide resin. The four support rolls 31 to 34 are provided between the support rolls 31 and 32. The linear rolls 30a extend substantially linearly along the arrangement direction of the photosensitive drums 21 between the support rolls 31 and 32. The support roll 34 is arranged farthest downward with respect to the support roll 33, and further, the support roll 33 is placed outside the straight line connecting the support rolls 32, 34 so that the angle formed by the support rolls 32, 33, 34 is an acute angle. They are arranged.

In this embodiment, the support roll 31 is used as a drive roll driven by a belt drive motor (not shown), the support roll 32 is used as a driven roll, and the support roll 33 is an intermediate transfer belt. 30 is used as a meander-restricting correction roll (steering roll: provided so as to be tiltable with one end in the axial direction as a fulcrum) in a direction substantially perpendicular to the moving direction of 30, and a support roll 34 as will be described later. Used as a backup roll.
A belt cleaner 35 for removing residual toner on the intermediate transfer belt 30 after the secondary transfer is retractable with respect to the intermediate transfer belt 30 on the surface side of the intermediate transfer belt 30 facing the support roll 31. Is provided.

Furthermore, in the present embodiment, the batch transfer apparatus 50 is a semiconductive transfer having a volume resistivity of 10 ⁶ to 10 ¹⁰ Ω · cm stretched between a plurality of (for example, two) rolls 51 and 52. For example, one roll 51 is used as a transfer roll and pressed against the intermediate transfer belt 30 via the transfer belt 53, and the intermediate transfer belt 30 is disposed on the back side of the intermediate transfer belt 30 facing the transfer roll 51. A backup roll 34 also serving as a tension roll is disposed, and the transfer belt 53 is disposed toward the fixing nip region of the fixing device 70 along the conveyance direction of the sheet 100.
In the present embodiment, a predetermined transfer bias (not shown) is applied to the backup roll 34, while the transfer roll 51 is grounded, and a predetermined transfer gap is provided between the transfer roll 51 and the backup roll 34. A transfer electric field is formed. The roll 52 is grounded.

And the transfer roll 51 in this Embodiment is comprised with what provided the electroconductive foaming urethane layer whose Asker C hardness is 35 degree | times as an elastic layer around the metal shaft. On the other hand, the backup roll 34 includes a conductive urethane rubber layer having an Asker C hardness of 70 degrees around the metal shaft. Therefore, in this embodiment, the hardness of the transfer roll 51 is smaller than the hardness of the backup roll 34.
And in the opposing site | part (secondary transfer site | part) of the transfer roll 51 and backup roll 34 in this Embodiment, as shown in FIG. 4, the backup roll 34 bites into the transfer roll 51 side, Each of the pressures is set so that the bite amount D becomes a target of 0.9 mm.

  Further, as shown in FIG. 5, the transfer belt 53 in the present embodiment includes a base material 53a in which a conductive agent such as conductive carbon black is blended with an elastic material of chloroprene rubber having a thickness of 300 to 600 μm, and a back surface (transfer) On the roll 51 side), a back coat layer 53b is formed by applying 5 to 15 μm of a modified fluororesin paint using urethane as a modified resin. The back surface coating layer 53b reduces the frictional resistance at the contact portion between the transfer roll 51 and the transfer belt 53.

Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described with reference to FIG.
Now, when image data of each color component image (black, yellow, magenta, cyan) read by the document reading device 10 is sent to the exposure device 23 of each image forming unit 20 (20a to 20d), each image formation is performed. An electrostatic latent image for each color component is formed on the photosensitive drum 21 of the unit 20, and each color unfixed toner image is formed by the developing device 24 that stores the corresponding color toner.
The unfixed toner image of each color component is reverse to the charged polarity of the toner with respect to the base material of the intermediate transfer belt 30 by the primary transfer device 25 at the primary transfer portion where each photosensitive drum 21 and the intermediate transfer belt 30 are in contact. By applying a voltage of polarity, primary transfer is performed by sequentially overlapping the surface of the intermediate transfer belt 30.
The unfixed toner image primarily transferred to the intermediate transfer belt 30 in this way is conveyed to a secondary transfer portion facing the conveyance path of the paper 100 as a recording material as the intermediate transfer belt 30 rotates. .

At the secondary transfer site, the batch transfer device 50 is pressed by the transfer roll 51 pressed against the backup roll 34 disposed in the space in the intermediate transfer belt 30 via the semiconductive transfer belt 53 and the intermediate transfer belt 30. The paper 100 unloaded at a predetermined timing from the paper tray 82 (paper transport system 80) by the feed roll 81 (paper transport system 80) passes through a predetermined number of transport rolls 83 (paper transport system 80) and the intermediate transfer belt 53. It is sandwiched between the belt 30.
Here, when a voltage having the same polarity as the charging polarity of the toner is applied to the backup roll 34 (alternatively, a voltage having a polarity opposite to the charging polarity of the toner may be applied to the transfer roll 51), the backup roll The unfixed toner image held on the intermediate transfer belt 30 is electrostatically transferred to the paper 100 at the secondary transfer site by a transfer electric field formed between the transfer roller 34 and the transfer roll 51.
Then, the transferred paper 100 is peeled off from the intermediate transfer belt 30 by the electric field of the transfer belt 53 disposed on the downstream side in the paper conveyance direction, held on the conveyance surface of the transfer belt 53 and conveyed, and downstream of the transfer belt 53. The sheet is peeled off from the transfer belt 53 by a sheet peeling member (not shown) and sent to the fixing device 70 to fix the unfixed toner image.
On the other hand, with respect to the intermediate transfer belt 30 in which the transfer of the unfixed toner image to the paper 100 is completed, the residual toner is removed by the belt cleaner 35.

  In the present embodiment, since the hardness of the transfer roll 51 is smaller than the hardness of the backup roll 34, stable transfer can be performed while maintaining a predetermined transfer nip width for transfer, and a holocharacter. Will not be generated. Further, since the backup roll 34 side is harder than the transfer roll 51, fluctuations in the rotational speed of the intermediate transfer belt 30 are suppressed, and image quality troubles do not occur, and the transfer roll 51 side is further softened. The sheet 100 is self-stripped along the elastic deformation trajectory of the transfer roll 51 and is easily peeled off from the intermediate transfer belt 30.

  Here, the behavior of the contact surface between the transfer belt 53 and the transfer roll 51 in the present embodiment will be described with reference to FIGS. 6 (a), 6 (b), and 6 (c). Assuming that the amount of biting into the transfer roll 51 provided with the elastic layer 51b on the metal shaft 51a is different in the axial direction (small biting amount on the front side and large biting amount on the rear side), the transfer belt 53 is thin. In some cases, the amount of biting is determined by the biting state of the backup roll 34 with respect to the elastic layer 51 b of the transfer roll 51. (A) is a perspective view of the transfer roll, (b) is a relationship between the backup roll 34 and the transfer roll 51 at a portion where the amount of biting is small (Front side), and (c) is a portion where the amount of biting is large (Rear side) The relationship between the backup roll 34 and the transfer roll 51 in FIG.

In this context, the surface speed of the intermediate transfer belt 30 (see FIG. 4) is a surface speed v ₁₀ of the backup roll 34, the surface velocity v ₁₀ equals the surface speed of the elastic layer 51b of the transfer roll 51 .
On the other hand, assuming that the effective radius of the transfer roll 51 is r ₁₁ when the biting amount is small and r ₁₂ when the biting amount is large, the angular velocities at the respective effective radii are ω ₁₁ = v ₁₀ / r ₁₁ , ω ₁₂ = v _10. / R ₁₂ , and ω ₁₁ <ω ₁₂ from the relationship r ₁₁ > r ₁₂ . However, since the angular velocity at the metal shaft 51a is uniform regardless of the amount of biting, the difference between the angular velocities ω ₁₁ and ω ₁₂ affects only the elastic layer 51b of the transfer roll 51 and causes the twist in the elastic layer 51b. Connected.
This torsion becomes a torsional reaction force to the transfer belt 53 (see FIG. 4) as shown in FIG. 6A, which leads to a force (drag) that hinders paper conveyance.
In the present embodiment, since the back surface coating layer 53b (see FIG. 5) is provided on the back surface of the transfer belt 53, slip occurs on the contact surface between the transfer belt 53 and the transfer roll 51, and distortion on the transfer roll 51 side ( The twist of the elastic layer 51b in this embodiment is not transmitted to the transfer belt 53 side, and does not affect the sheet conveyance. As a result, image registration misalignment can be suppressed.

Next, in this embodiment, the point that an elastic member is used as the transfer belt 53 will be described.
FIG. 7 shows the state of the transfer site, and it is assumed that the backup roll 34 and the transfer roll 51 are attached with the amount of biting shifted in the roll axis direction. In this example, the amount of biting on the rear side of the transfer roll 51 is larger than that on the front side.
Here, in the case where an elastic member is used as the transfer belt 53, the transfer belt 53 itself causes a torsional reaction force (which leads to a drag force to return the sheet in the direction opposite to the conveyance direction) due to the distortion of the transfer roll 51. Therefore, the sheet 100 is stably conveyed without affecting the conveyance speed of the sheet 100. Further, in the present embodiment, the sheet 100 is transported more stably by sliding on the contact surface between the transfer belt 53 and the transfer roll 51.
On the other hand, when the transfer belt 53 is not elastic, the drag due to the distortion of the transfer roll 51 is not absorbed by the transfer belt 53, but the drag is transmitted to the paper 100. Therefore, the conveyance performance of the paper 100 in the roll axis direction is impaired, and as a result, image registration misalignment may occur. However, in this embodiment, the sliding due to the distortion of the transfer roll 51 is not transmitted to the paper 100 by sliding on the contact surface between the transfer belt 53 and the transfer roll 51, so that the paper 100 is transported stably. become.

In the present embodiment, the shift in the amount of biting of the transfer roll 51 due to the mounting accuracy between the backup roll 34 and the transfer roll 51 has been described. For example, the diameter at both ends of the transfer roll 51 depends on the processing accuracy of the transfer roll 51. Even in such a case, since slip occurs on the contact surface between the transfer roll 51 and the transfer belt 53, the drag generated by each distortion is eliminated, and smooth conveyance of the paper 100 is ensured. Become.
In other words, when a deviation occurs in the nip width in the rotation axis direction due to design tolerances or the like, even if distortion accumulates on the transfer roll 51 installed inside the transfer belt 53 and drag occurs, the transfer belt back surface and the transfer belt are transferred. Since slippage occurs on the surface of the roll 51 and does not affect the conveyance speed of the paper 100, image registration displacement can be prevented.
Furthermore, in this embodiment, since the transfer belt 53 is used, the sheet posture at the transfer outlet can be stabilized, and the running failure of the sheet 100 can be prevented.
In this embodiment, since the transfer belt 53 is provided with semiconductivity, the electrostatic sheet suction force due to charge accumulation can be reduced, and the posture stability of the sheet 100 is further improved. .

Embodiment 2
FIG. 8 shows a second embodiment of an image forming apparatus to which the present invention is applied.
In the same figure, unlike the first embodiment, the image forming apparatus has one photosensitive drum 101 and an intermediate transfer belt 110 disposed in contact with the photosensitive drum 101, and a photosensitive member is disposed around the photosensitive drum 101. A charging device 102 that charges the drum 101, an exposure device 103 that writes an electrostatic latent image for each color component, and a plurality of developing units that store toner of each color component are mounted, and are intermittently disposed facing the photosensitive drum 101. A rotary type developing device 104 that visualizes an electrostatic latent image with a corresponding toner; a primary transfer device 105 such as a transfer roll that transfers each color component toner image on the photosensitive drum 101 to an intermediate transfer belt 110; A drum cleaner 106 for removing residual toner on the drum 101 is provided.
Further, the intermediate transfer belt 110 is stretched around, for example, three rolls 111 to 113, and a batch transfer device 120 having a configuration substantially similar to that of the first embodiment is disposed at a position corresponding to the roll 113. Reference numeral 114 denotes a belt cleaner that removes residual toner on the intermediate transfer belt 110.

The batch transfer device 120 includes a semiconductive transfer belt 123 having a volume resistivity of 10 ⁶ to 10 ¹⁰ Ω · cm stretched between a plurality of (for example, two) rolls 121 and 122, for example, The roll 121 is used as a transfer roll in pressure contact with the intermediate transfer belt 110 via the transfer belt 123, and is also used as a tension roll for the intermediate transfer belt 110 on the back side of the intermediate transfer belt 110 facing the transfer roll 121. And a transfer bias (not shown) that forms a transfer electric field for batch transfer is applied between the transfer roll 121 and the backup roll 113 and is fixed along the conveyance direction of the paper 100. The transfer belt 123 is disposed toward the fixing nip region of the apparatus 130.

Therefore, according to the present embodiment, the respective color component toner images are sequentially formed on the photosensitive drum 101, sequentially transferred to the intermediate transfer belt 110, and then the multiple colors on the intermediate transfer belt 110 are transferred by the batch transfer device 120. An image forming process is performed in which the toner images are collectively transferred onto the paper 100. Note that the behavior of the paper 100 after batch transfer is substantially the same as in the first embodiment.
In particular, in the present embodiment, the toner image formed on the photosensitive drum 101 is secondarily transferred after being sequentially superimposed on the intermediate transfer belt 110 at the same position, so that the final color is not fixed. Until the toner image is primarily transferred to the intermediate transfer belt 110, the transfer belt 123 and the transfer roll 121 of the batch transfer device 120 are held away from the intermediate transfer belt 110 with the roll 122 on the downstream side in the conveying direction of the transfer belt 123 as the rotation axis. It is necessary to.
When the entire unfixed toner image on the intermediate transfer belt 110 has passed the secondary transfer position, the transfer belt 123 is pressed against the backup roll 113 via the intermediate transfer belt 110 and has the same rotational speed as the intermediate transfer belt 110. The secondary transfer process is performed by moving at a speed.

  Further, also in the present embodiment, as in the first embodiment, a back surface coating layer is applied to the back surface side of the transfer belt 123 so that the contact surface between the transfer roll 121 and the transfer belt 123 becomes slippery. Yes. For this reason, the present embodiment has the same effects as those of the first embodiment.

Comparative Example In this comparative example, the relationship between the image parallelism and the biting amount difference was evaluated and confirmed in order to confirm the effect of the image registration deviation of the present case.
Here, the image parallelism is defined as follows.
FIG. 9 shows a portion of the transfer post nip. When a rectangular image is transferred to a sheet, if a difference occurs in the sheet speed between the front side and the rear side, the length of the sheet in the traveling direction (progresses per predetermined time). The length is different between the front side and the rear side.
When the lengths on the front side and _rear side of the A3 size paper after transfer are L _front and L _rear , respectively, the parallelism of the image is expressed by the following equation.
Image parallelism ≡L _front -L _rear
On the other hand, the biting amount difference indicates a difference between the front side and the rear side of the biting amount shown in FIG.
Biting amount difference = Front side biting amount-Rear side biting amount

Here, for example, “difference in biting amount +0.2, image parallelism −1.0” means that when the biting amount on the front side is 0.2 mm larger, the image on the front side is contracted by 1.0 mm compared to the rear side. It shows that there is.
The present inventors assume that the image parallelism allowable value (target value) is ± 0.4 mm or less as a level at which image registration deviation does not become a problem even if the image is expanded or contracted at the transfer portion. .

FIG. 10 shows the result in this comparative example, and it is understood that the image parallelism is greatly influenced by the difference in the amount of biting. When the biting amount difference is 0.4 mm, the image parallelism is about 1.5 mm. To reduce the image parallelism to an allowable value (target value) of 0.4 mm or less, the biting amount difference is about 0.1 mm or less. The need to come out.
It is very difficult to realize this with an actual apparatus configuration, and it has been difficult to achieve good image parallelism.

Example 1
This example was evaluated by the configuration of the first embodiment in the same manner as the above-described comparative example.
As shown in FIG. 11, the obtained relationship between the image parallelism and the bite amount difference in the present example is within ± 0.1 mm within the range where the bite amount difference is ± 0.5 mm. Compared with the comparative example, a significant improvement effect was confirmed.
With this difference in biting amount, the image forming apparatus can be realized without much trouble, and the usefulness of this case was confirmed.

Example 2
In this example, the relationship between the Asker C hardness of the transfer roll and the image registration deviation in the configuration of the first embodiment is evaluated and confirmed.
In this embodiment, the Asker C hardness of the transfer roll is set to five levels of 5, 20, 35, 40, 50, and 70 degrees. At this time, the Asker C hardness of the backup roll is set to two levels of 58 degrees and 70 degrees. Confirmed. The difference in biting amount was evaluated as 0.5 mm.
The results were the same regardless of the hardness of the backup roll, and the results shown in FIG. 12 were obtained.
If the roll hardness of the transfer roll is 5, 20, 35, and 40 degrees, the image registration deviation (evaluated by the image parallelism as in the comparative example and the allowable value is ± 0.4 mm or less) is 50 degrees without any problem. It was confirmed that image registration misalignment becomes a problem at 70 degrees. Incidentally, it was confirmed that the image parallelism is a more preferable level of ± 0.2 mm or less at 20, 35, and 40 degrees.
Thereafter, the present inventors conducted further detailed studies on the roll hardness of the transfer roll, and confirmed that image registration misalignment would not be a problem if the Asker C hardness was 5 degrees or more and less than 50 degrees. .

1 is an explanatory diagram illustrating a configuration of an image forming apparatus according to the present invention. (A) is explanatory drawing which shows the effect | action in the case of sliding contact by this invention, (b) is an explanatory view which shows the effect | action in the case of no sliding contact as a comparison. 1 is an explanatory diagram showing an overview of an image forming apparatus according to Embodiment 1. FIG. FIG. 3 is an explanatory diagram illustrating a biting state according to the first embodiment. 3 is an explanatory diagram illustrating a transfer belt according to Embodiment 1. FIG. FIG. 2 is an explanatory diagram illustrating an operation due to distortion of the transfer roll in Embodiment 1, where (a) is a perspective view of the transfer roll, (b) is a state where the amount of biting is small, and (c) is a state where the amount of biting is large. . FIG. 4 is an explanatory diagram illustrating an elastic action of the transfer belt according to the first embodiment. 5 is an explanatory diagram of an image forming apparatus according to Embodiment 2. FIG. It is explanatory drawing which shows image parallelism. It is explanatory drawing which shows the result of a comparative example. It is explanatory drawing which shows the result of Example 1. FIG. FIG. 6 is an explanatory diagram showing the results of Example 2.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Intermediate transfer body, 3 ... Recording material, 4 ... Batch transfer apparatus, 5a, 5b ... Roll, 6 ... Transfer conveyance belt, A, B ... Contact surface

Claims (7)

One or a plurality of image carriers on which each color component toner image is formed and supported, an intermediate transfer member on which each color component toner image on this image carrier is transferred and supported, and each color component toner on this intermediate transfer member In an image forming apparatus comprising a batch transfer device that batch-transfers an image onto a recording material,
The batch transfer apparatus has a plurality of rolls and a transfer conveyance belt that is rotatably stretched around the rolls.
Among the plurality of rolls, a roll positioned on the upstream side in the recording material conveyance direction is used as a transfer roll, and the transfer roll is disposed in pressure contact with the intermediate transfer member via a transfer conveyance belt,
An image forming apparatus, wherein a contact surface between a back surface of a transfer conveyance belt and the transfer roll is slidable. The image forming apparatus according to claim 1.
That the transfer conveyor belt surface and the static friction coefficient mu _A of the contact surface of the recording material and the transfer conveyance belt back surface and the static friction coefficient mu _B of the contact surface of the transfer roll is set to satisfy μ _A> μ _B An image forming apparatus. The image forming apparatus according to claim 1.
Provide at least an elastic layer on the transfer roll surface,
An image forming apparatus, wherein the transfer conveyance belt is driven by an intermediate transfer member. The image forming apparatus according to claim 1.
An image forming apparatus, wherein the transfer / conveying belt is made of an elastic material. The image forming apparatus according to claim 1,
An image forming apparatus comprising a back surface coating layer for reducing a static friction coefficient between the back surface and the surface of the transfer roll on the back surface of the transfer conveyance belt. The image forming apparatus according to claim 1, wherein the intermediate transfer member is an endless belt.
In the position facing the transfer roll, provided with an opposing roll that sandwiches and opposes the intermediate transfer belt,
An image forming apparatus, wherein the Asker C hardness of the transfer roll surface is set to be less than the Asker C hardness of the opposite roll surface. The image forming apparatus according to claim 6.
An image forming apparatus having an Asker C hardness of 5 to 50 degrees on the surface of the transfer roll.

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