JP4654729B2 - Image forming apparatus and transfer device used therefor - Google Patents

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a printer, and more particularly, to an image forming apparatus having a belt transfer system as a transfer apparatus for transferring an image formed on an image carrier onto a recording material, and The present invention relates to a transfer device used.

As an example of a conventional image forming apparatus, for example, an intermediate transfer type color image forming apparatus model adopting an electrophotographic method, each color component toner image formed on an image carrier such as a photosensitive drum is transferred to an intermediate transfer body ( For example, it is known that primary transfer is sequentially performed on an intermediate transfer belt), and a multi-color toner image primary-transferred onto the intermediate transfer member is transferred to a recording material in a batch (secondary) by a batch transfer device. Yes.
A typical embodiment of this type of batch transfer apparatus is a so-called roll transfer system (see, for example, Patent Document 1). For example, a transfer roll is disposed in pressure contact with the front side of an intermediate transfer belt as an intermediate transfer member, and a backup roll (usually a tension roll of the intermediate transfer belt is provided on the back side of the intermediate transfer belt facing the transfer roll). And a multi-color toner image on the intermediate transfer belt is collectively transferred to the recording material side by forming a transfer electric field between the transfer roll and the backup roll.

  Another typical embodiment of the batch transfer apparatus is a belt transfer system (see, for example, Patent Documents 2 and 3). This is because the transfer conveyance belt is stretched over a plurality of tension rolls, and any one of the tension rolls located on the upstream side functions as a transfer roll, and the transfer conveyance belt portion corresponding to the transfer roll is placed in the middle. Placed in pressure contact on the front side of the transfer belt, placed a backup roll on the back side of the intermediate transfer belt corresponding to this transfer roll, applied a transfer electric field between the transfer roll and backup roll, and positioned between the transfer roll and backup roll. The recording material guide surface by the transfer conveyance belt is disposed downstream of the transfer nip area. According to this aspect, since the recording material after transfer is guided and conveyed by the transfer conveyance belt, it is possible to effectively prevent the recording material from being poorly peeled as compared with the roll transfer method, and furthermore, the conveyance property of the recording material after peeling. Can be kept good.

JP 2000-75680 A (Embodiment of the Invention, FIG. 4) JP 2001-265128 A (Embodiment of the Invention, FIG. 1) JP 2002-189353 A (Embodiment of the Invention, FIG. 3)

By the way, in the roll transfer method described in Patent Document 1, the recording material is skewed at the transfer portion due to a manufacturing error of the transfer roll, an attachment posture error, an error in the tension of the intermediate transfer belt, and the like. Since there is a problem that the image on the material is inclined, in order to prevent this, an image parallelism adjusting mechanism is already provided.
This image parallelism adjusting mechanism eliminates the lead edge skew or the side edge skew of the recording material by changing the alignment of the transfer roll, and as a result, adjusts the inclination of the image on the recording material.
However, in the belt transfer systems described in Patent Documents 2 and 3, when the transfer roll alignment is adjusted in the same manner as the roll transfer system, it is difficult to adjust the inclination of the image on the recording material. A challenge has been found.

  When this factor was examined, in the belt transfer method, if the direction of travel of the intermediate transfer belt was adjusted by changing the alignment of the transfer roll, the direction of travel of the transfer conveyance belt also changed, resulting in recording before and after adjustment. There is a concern that the skew of the material will not be improved. Also, if the surface friction coefficient of the transfer / conveyance belt is reduced so that the direction of travel of the transfer / conveyance belt is not changed by adjusting the alignment of the transfer roll, the recording material will slip on the surface of the transfer / conveyance belt this time. It becomes difficult to adjust the inclination of the.

Such a technical problem is not limited to the above-described intermediate transfer type image forming apparatus. For example, a direct transfer type image forming apparatus in which an image such as a photosensitive belt is directly transferred to a recording material. Also occurs in the same manner.
The present invention has been made to solve the above technical problems, and an image forming apparatus capable of reliably adjusting the inclination of an image on a recording material at a transfer site while taking advantage of a belt transfer system. A transfer apparatus used for this is provided.

That is, according to the present invention, as shown in FIG. 1A, an image is provided with an image carrier 1 on which an image is carried, and a transfer device 4 that transfers the image on the image carrier 1 to a recording material 5. in forming apparatus, the transfer device 4, a plurality of tension rolls 6 (e.g. 6a, 6b) and the transfer conveyor belt 8 which is rotatably stretched, to at least the image bearing member 1 of the plurality of tension rolls 6 A surface portion that is in pressure contact with the back surface of the transfer conveyance belt 8 so as to sandwich the transfer conveyance belt 8 with the image carrier 1 by using the opposite tension roll 6a, and is in contact with the back surface of the transfer conveyance belt 8. An elastic transfer roll 7 for forming a transfer electric field composed of an elastic member having a lower hardness than the opposing image carrier 1 portion, and the elastic transfer roll 7 by making a difference in the amount of biting at both ends in the axial direction of the elastic transfer roll 7. This twist causes a twist A force is applied to the recording material 5 via a transfer conveyor belt 8, and an image parallelism adjusting mechanism 9 which enables adjusting the parallelism of the image with respect to the width direction orthogonal to the conveying direction of the recording material 5, the image parallel The degree adjusting mechanism 9 supports the elastic transfer roll 7 so as to be swingable with one end in the axial direction as a fulcrum, and allows the swinging free end of the elastic transfer roll 7 to move up and down, and further, the recording material 5 and the transfer conveyance belt 8. the friction coefficient mu _a between the _surfaces, the elastic transfer roll 7 surface, the friction coefficient between the transfer conveyance belt 8 back side case of the mu _B, and satisfies the relation of μ _{a <μ B.}

In such technical means, the image forming apparatus according to the present invention only needs to have a belt transfer type transfer device, regardless of whether it is a direct transfer type or an intermediate transfer type, and not only a color machine. Although it is also intended for a monochrome machine, it is particularly effective in a mode in which a portion of the image carrier 1 facing the transfer device 4 is a belt member.
Here, as a typical embodiment of the image carrier 1 whose portion facing the transfer device 4 is a belt member, an image forming carrier 2 on which an image is formed and carried, and an image on the image forming carrier 2 are recorded. Examples include a belt-like intermediate transfer body 3 that is held and conveyed intermediately before transferring to the material 5, and may be a multi-cycle type such as a so-called tandem type or a 4-cycle type. In the case of the tandem type, a plurality of image forming carriers 2 (for example, 2a to 2d) are disposed to face the intermediate transfer member 3, and the belt-like intermediate transfer member 3 has an appropriate number of stretches. It is stretched around the rolls 3a to 3c.

Moreover, although the two tension | tensile_strength roll 6 (for example, 6a, 6b) is shown by Fig.1 (a), it is not restricted to this, What is necessary is just two or more.
Furthermore, the elastic transfer roll 7 may be a single layer or multiple layers as long as the surface portion is made of an elastic member. Further, since it is used for forming a transfer electric field, it usually has conductivity.
The elastic transfer roll 7 may be provided separately from the tension roll 6, but the tension roll 6 (6 a in this example) facing at least the image carrier 1 among the plurality of tension rolls 6. It is preferable to use both. Thus, if the tension roll 6 (6a) of the transfer conveyance belt 8 is also used, not only the number of parts can be reduced, but also the elastic angle of the transfer transfer belt 8 can be set large. This twisting reaction force is easily applied to the recording material via the transfer conveyance belt 8.
Furthermore, as long as the transfer / conveying belt 8 is stretched around the stretch roll 6, an appropriate material such as resin or rubber can be used. The elastic transfer roll 7 and the stretch roll 6 adjacent thereto can be used. The portion of the transfer conveyance belt 8 positioned between the two is normally configured as a recording material conveyance surface.

Further, the image parallelism adjusting mechanism 9 only needs to have a function of adjusting the image parallelism, but the adjustment principle is based on changing the amount of biting in the axial direction of the elastic transfer roll 7. If necessary, it can be selected appropriately.
The image parallelism here refers to the degree of parallelism of the image with respect to the width direction of the recording material 5 as shown in FIG. 1B, for example, and one end in the width direction of a predetermined image forming region G on the recording material 5. This is indicated by a difference ΔL (= Lout−Lin) between the line image length Lout on the side and the line image length Lin on the other end side. In FIG. 1B, of the transfer nip area of the transfer device 4, the side closer to the user is the Out side (corresponding to the front side of the image forming apparatus), and the opposite side is the In side (the back of the image forming apparatus). Equivalent).
As a method for changing the amount of biting in the axial direction of the elastic transfer roll 7, the elastic transfer roll 7 is tilted toward the image carrier 1 to change the nip pressure, There is a mode in which the tension in the width direction is changed.

The adjustment principle of the image parallelism adjusting mechanism 9 according to the present invention will be described with reference to FIGS.
First, considering the comparative model shown in FIG. 2B (for example, assuming a roll transfer method using only the elastic transfer roll 7 ′), the amount of biting in the axial direction of the elastic transfer roll 7 ′ is changed. When the amount of biting is large (large amount of biting), the nip pressure is large, and when the elastic transfer roll 7 ′ starts to rotate, a deviation between the shaft 7a and the surface due to the rotation of the roll surface occurs. The amount of deviation depends on the magnitude of the nip pressure, and the amount of deviation due to the nip pressure difference at both axial ends (Out side, In side) of the elastic transfer roll 7 ′ causes the elastic transfer roll 7 ′ to be twisted. A torsional reaction force Rs ′ acts on a recording material not shown. This torsional reaction force Rs ′ acts on the elastic transfer roll 7 ′ with a smaller biting amount (small biting amount), and this torsional reaction force Rs ′ is assumed to give sensitivity to image parallelism.

In contrast, when the invention model shown in FIG. 2A is examined, when the transfer conveyance belt 8 is stretched, the elastic transfer roll 7 is locally elastically deformed by the tension of the transfer conveyance belt 8 (FIG. 2). (Refer to 7b in (a)). In this state, if the amount of biting in the axial direction of the elastic transfer roll 7 is changed, the difference in the amount of deviation (shift between the shaft 7a / surface) due to the nip pressure difference in the axial direction of the elastic transfer roll 7 generates a twist. However, the amount of twist is reduced by the elastic crushing deformation of the elastic transfer roll 7 due to the tension of the transfer conveyance belt 8. For this reason, the torsional reaction force Rs accompanying the twisting of the elastic transfer roll 7 acts on the smaller amount of biting of the elastic transfer roll 7 (small biting amount), but the twisting reaction force in the case of the comparative model shown in FIG. It becomes smaller than the force Rs ′. Therefore, in the inventive model, the sensitivity of the torsional reaction force Rs to the image parallelism is lower than that in the comparative model.
Therefore, in the present invention, the image parallelism adjusting mechanism 9 is based on changing the amount of biting in the axial direction of the elastic transfer roll 7 as shown in FIG. However, it is necessary to cause the torsional reaction force Rs to act on the recording material 5 via the transfer conveying belt 8 as shown in FIG. 3B. The twist reaction force Rs corrects the difference between the line image lengths Lin and Lout at both ends of the image forming region G on the recording material 5 so that the image parallelism of the tilted image G ′ can be adjusted. .

Further, as an aspect adopted in the present invention for realizing the image parallelism adjusting mechanism 9, the friction coefficient between the surface of the recording material 5 and the transfer conveyance belt 8 is μ _A , the surface of the elastic transfer roll 7 , the transfer conveyance belt. the friction coefficient between 8 backside when the mu _B, include embodiments to satisfy the relation of μ _{a <μ B.} According to this aspect, since the transfer conveyance belt 8 does not slip between the elastic transfer roll 7 before the speed of the recording material 5 changes, the torsional reaction force based on the difference in biting amount of the elastic transfer roll 7 is directly recorded. This is preferable in that the speed on both sides in the width direction of the material 5 can be changed.

Further, as a preferable twisting characteristic of the elastic transfer roll 7, a torque load 4 gf × due to a frictional force when a force corresponding to a transfer pressure is applied to the other end portion in a state where one end portion in the axial direction of the elastic transfer roll 7 is fixed. K ≧ 4 × 10 ⁻⁶ M ² −5 × 10 ⁻⁴ M + 1.97 × 10 where k is the amount of twist when 14 mm is added in the circumferential direction, and M is the surface hardness of Asuka C of the elastic transfer roll 7. ^-2 are satisfied. If such characteristics are provided, the elastic transfer roll 7 is preferable in that a sufficient twisting reaction force can be easily obtained for adjusting the image parallelism.

Furthermore, as a preferable elongation rate condition of the transfer / conveying belt 8, when the belt elongation rate of the transfer / conveying belt 8 is Bs (%), Bs ≦ 1.12. If this type of transfer / conveying belt 8 is used, the image parallelism adjusting mechanism 9 can easily adjust the image parallelism to zero.
Here, if the belt extension rate is too large, the transfer / conveying belt 8 absorbs the torsional deformation of the elastic transfer roll 7, which is not preferable because the sensitivity of the image parallelism adjusting mechanism 9 is difficult to be obtained.

  The present invention is not limited to the above-described image forming apparatus, but also covers the transfer device 4 itself used in the image forming apparatus.

According to the image forming apparatus of the present invention, on the premise of the aspect adopting the belt transfer system, the image parallelism adjusting mechanism is devised, and the elastic transfer is based on changing the amount of biting in the axial direction of the elastic transfer roll. Since the roll is twisted and this twisting reaction force is applied to the recording material via the transfer conveyance belt, the image parallelism on the recording material can be adjusted. In addition, the inclination of the image on the recording material at the transfer site can be reliably adjusted while making use of the transportability. For this reason, the image parallelism can always be adjusted to 0, and an image with a good image parallelism can be easily formed accordingly.
In particular, in the present invention, as the image parallelism adjusting mechanism, a swinging method using one axial end of the elastic transfer roll as a fulcrum is adopted, so that the amount of biting at the free swing end of the elastic transfer roll in the axial direction is adjusted. Thus, it is possible to give the elastic transfer roll a characteristic that it is easy to obtain a twisting reaction force sufficient to adjust the image parallelism, and the transfer conveyance belt is connected to the elastic transfer roll before the speed of the recording material is changed. Therefore, the torsional reaction force based on the difference in biting amount of the elastic transfer roll can directly change the speed on both sides in the width direction of the recording material.
Further, according to the transfer device used in such an image forming apparatus, it is possible to reliably adjust the inclination of the image of the recording material at the transfer site while taking advantage of the belt transfer method.

Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
Embodiment 1
FIG. 4 is an explanatory diagram showing the overall configuration of the first embodiment of the image forming apparatus to which the present invention is applied.
In the figure, the image forming apparatus is an intermediate transfer type tandem color image forming apparatus, for example, that forms toner images of four color components (in this embodiment, yellow, magenta, cyan, and black) by electrophotography. An image forming unit 20 (20a to 20d), an intermediate transfer belt 30 that sequentially transfers (primary transfer) each color component toner image formed by each image forming unit 20, and multiple transfer onto the intermediate transfer belt 30. And a batch transfer device 50 for batch transfer (secondary transfer) of the multicolor toner image to the recording material P.

  In the present embodiment, each of the image forming units 20 (20 a to 20 d) has a photosensitive drum 21, and a charging device 22 such as a corotron that charges the photosensitive drum 21 around the photosensitive drum 21. , An exposure device 23 such as a laser scanning device in which an electrostatic latent image is written on the charged photosensitive drum 21, and the electrostatic latent image written on the photosensitive drum 21 is visualized with each color component toner. A developing device 24, a primary transfer device 25 for transferring a toner image on the photosensitive drum 21 to the intermediate transfer belt 30, and a drum cleaner 26 for removing residual toner on the photosensitive drum 21 are provided. .

The intermediate transfer belt 30 is composed of an endless belt having a volume resistivity of about 10 ⁶ to 10 ¹⁵ Ω · cm in which, for example, vinyl chloride or polyimide is kneaded with carbon black or the like, and a plurality of (in this embodiment, 5) belts. It is stretched over the stretching rolls 31 to 35, and has a linear portion extending substantially linearly along the arrangement direction of the photosensitive drums 21 between the stretching rolls 31 to 32.
In this embodiment, the tension roll 31 is used as a drive roll driven by a drive motor (not shown), and the tension rolls 32 to 35 are used as driven rolls. The tension roll 33 is used as a steering roll for meandering regulation of the intermediate transfer belt 30 (for example, adopting a roll configuration that is tiltable with one axial end as a fulcrum), and the tension roll 34 is a batch transfer device 50 described later. Used as a backup roll.
Further, a belt cleaner 36 is provided on the surface side of the intermediate transfer belt 30 facing the stretching roll 31 in order to remove toner remaining on the intermediate transfer belt 30 after batch transfer onto the recording material P.

Further, in the present embodiment, the batch transfer apparatus 50 has a transfer conveyance belt 53 stretched between a plurality of (for example, two) stretch rolls 51 and 52 as shown in FIGS. 4 and 5, for example. . A belt cleaner 54 (for example, adopting a blade cleaning method) is disposed on the surface side of the transfer conveyance belt 53 facing the stretching roll 51.
Here, the transfer conveyance belt 53 is a semiconductive belt having a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm using a material such as chlorobrene, and one tension roll 51 is configured as an elastic transfer roll 55. The elastic transfer roll 55 is disposed in pressure contact with the intermediate transfer belt 30 via the transfer conveyance belt 53 at a predetermined transfer nip region n, and the tension roll 34 of the intermediate transfer belt 30 is disposed as a backup roll so as to face the tension. A conveyance path for the recording material P is formed from the position of the gantry roll 51 toward the other tension roll 52 position.

In this example, the elastic transfer roll 55 has a configuration in which a metal shaft 55a is covered with an elastic layer 55b in which urethane black rubber or EPDM is mixed with carbon black or the like.
Further, a transfer bias from a transfer bias power source 57 is applied to the tension roll (backup roll) 34 via a conductive power supply roll 56, while the elastic transfer roll 55 is grounded via a metal shaft 55a. Thus, a predetermined transfer electric field is formed between the elastic transfer roll 55 and the backup roll 34. The tension roll 52 is grounded so as to effectively prevent power storage on the transfer / conveyance belt 53, and considering the peelability of the recording material P at the downstream end of the transfer / conveyance belt 53. It is effective to make the tension roll 52 smaller in diameter than the tension roll 51 on the upstream side.

In particular, in the present embodiment, an image parallelism adjusting mechanism 70 for adjusting image parallelism (see [0011]) is provided.
As shown in FIGS. 5 and 6, the image parallelism adjusting mechanism 70 includes a biting amount adjusting mechanism 71 capable of variably adjusting the biting amount in the axial direction of the elastic transfer roll 55, the recording material P, and transfer conveyance. When the friction coefficient between the belt 53 surfaces A is μ _A and the friction coefficient between the surface of the elastic transfer roll 55 and the back surface of the transfer conveyance belt 53 is μ _B , it is set so as to satisfy the relationship of μ _A <μ _B It is. 6 corresponds to a cross section taken along line VI-VI in FIG. 5, and shows a state in which the recording material P is conveyed in the nip in the transfer nip region.

In this example, the biting amount adjusting mechanism 71 supports the elastic transfer roll 55 that is rotatably supported by the pair of bearing members 72 and 73 so that the elastic transfer roll 55 can swing freely with one end in the axial direction as a fulcrum 74. The movable free end can be moved up and down by an eccentric cam 75, and the eccentric cam 75 is driven and rotated by a predetermined amount by a motor 76, thereby adjusting the biting amount h on the swing free end side of the elastic transfer roll 55. Is.
At this time, the adjustment work by the biting amount adjustment mechanism 71 may be performed artificially, for example, by looking at a test pattern image in which the user checks the image parallelism, or the test pattern image is read by a scanner or the like. Accordingly, the image parallelism may be determined by a control device (not shown) and may be appropriately selected such as controlling the amount of biting by the biting amount adjusting mechanism.
In FIG. 6, reference numerals 77 and 78 denote bearing members that rotatably support the backup roll 34.

  Furthermore, in the present embodiment, the recording material conveyance system 80 feeds the recording material P stored in the supply tray 81 by the feed roll 82 and conveys it by a predetermined number of conveyance rolls 83 as shown in FIG. At the same time, after registration with the registration roll 84, it is sent to a batch transfer portion by the batch transfer device 50, and then transported to the fixing device 90 through the transport belt 85, and unfixed on the recording material P by the fixing device 90. The toner image is fixed.

Next, an image forming process of the image forming apparatus according to the present embodiment will be described.
Now, in each image forming unit 20 (20a to 20d), when image data of each color component is sent to the exposure device 23, an electrostatic latent image for each color component is formed on the photosensitive drum 21 of each image forming unit 20. Each color component toner image is formed by the developing device 24 that stores the corresponding color toner.
The color component toner images on the respective photosensitive drums 21 are sequentially primary transferred onto the intermediate transfer belt 30 by the primary transfer device 25 at the primary transfer portions where the respective photosensitive drums 21 and the intermediate transfer belt 30 are in contact with each other. The
Thereafter, each color component toner image primarily transferred onto the intermediate transfer belt 30 is conveyed to a batch transfer site (secondary transfer site), and the batch transfer device 50 applies the recording material P sent to the batch transfer site. Batch transfer.
At this time, the batch transfer device 50 sandwiches the recording material P in the transfer nip region between the intermediate transfer belt 30 and the transfer conveyance belt 53, and performs recording with a transfer electric field formed between the backup roll 34 and the elastic transfer roll 55. The color component toner images on the intermediate transfer belt 30 are collectively transferred to the material P.
Thereafter, the recording material P onto which each color component toner image has been transferred is peeled off from the intermediate transfer belt 30 by the electric field of the transfer conveyance belt 53 disposed on the downstream side of the transfer nip region, and on the recording material conveyance surface of the transfer conveyance belt 53. Held and conveyed, peeled off at the downstream end of the transfer and conveying belt 53 (natural peeling or peeling by a peeling member not shown), sent to the fixing device 90 via the conveying belt 85, and the fixing process of the unfixed toner image is performed. Made.
On the other hand, some residual toner remains on the intermediate transfer belt 30 after the batch transfer, but these residual toners are removed by the belt cleaner 36.

In such an image forming process, when the image on the recording material P is inclined, the image parallelism adjusting mechanism 70 performs image parallelism adjustment processing.
In this example, a test pattern image for checking the image parallelism on the recording material P is output, and the state of the image parallelism is determined from the test pattern image based on the user's own judgment or judgment by a control device (not shown). Then, based on the recognition result, a predetermined control signal may be sent to the bite amount adjustment mechanism 71 to adjust the bite amount h of the bite amount adjustment mechanism 71.
At this time, as shown in FIGS. 5 and 6, the control device (not shown) sends a control signal corresponding to the recognized image parallelism adjustment allowance to the motor 76 to rotate the eccentric cam 75 by a predetermined amount. Accordingly, the amount of biting h on the one end side in the axial direction of the elastic transfer roll 55 is adjusted.

In this state, if the amount of biting h on the one end side in the axial direction of the elastic transfer roll 55 (substantially equivalent to the amount of biting on the other end side in the axial direction of the elastic transfer roll 55) is appropriate, this biting amount. Along with h, the elastic transfer roll 55 is twisted.
Particularly, in this example, when the friction coefficient between the recording material P and the surface A of the transfer conveyance belt 53 is μ _A , and the friction coefficient between the surface of the elastic transfer roll 55 and the back surface of the transfer conveyance belt 53 is μ _B , μ _A Since the relationship of <μ _B is satisfied, the torsional reaction force Rs (see FIGS. 2 and 3) accompanying the twist of the elastic transfer roll 55 surely acts on the recording material P via the transfer conveyance belt 53. Accordingly, the speed on one end side of the recording material P is increased with the twist reaction force Rs. For this reason, the skew of the recording material P is corrected, and accordingly, the image parallelism on the recording material P is adjusted to be zero.

Example 1
This example uses a specific model of the image forming apparatus according to the embodiment, and examines a change in image parallelism when the biting amount h of the biting amount adjusting mechanism 71 is appropriately adjusted.
Hereinafter, the present example model and the comparative example model will be described (see FIG. 7B).
<Example model>
Intermediate transfer belt 30: formed with an appropriate amount of carbon black or the like in a polyimide resin so as to have a volume resistivity of 10 ⁶ to 10 ¹⁵ Ω · cm, and its thickness is set to 0.1 mm, for example.
Batch transfer device 50:
Transfer transfer belt 53:
A material obtained by dispersing conductive carbon black in chloroprene as a base material and having a surface coated with a PTFE-dispersed urethane emulsion having a thickness of 9 μm, has a volume resistivity of 10 ⁶ to 10 ¹² Ω · cm as a whole. Is 0.45 mm.
Elastic transfer roll 55:
A grounded roll having an elastic layer with a thickness of 10 mm in which conductive carbon black is blended with 28 mm in diameter, urethane foam rubber or EPDM.
Friction coefficients (here, static friction coefficients) between the recording material P, the transfer conveyance belt 53 and the elastic transfer roll 55 μ _A and μ _B :
μ _A <μ _B is satisfied, and μ _A is 0.32.
<Comparative model>
Except for the following friction coefficient relationship, it is the same as the example model.
Friction coefficients (here, static friction coefficients) between the recording material P, the transfer conveyance belt 53 and the elastic transfer roll 55 μ _A and μ _B :
μ _A ≧ μ _B is satisfied, and μ _A is 0.32.

In the example model and the comparative example model, when the bite amount h by the bite amount adjusting mechanism 71 is changed, in the example model, the image parallelism gradually changes to 0, but in the comparative model, The amount of change in image parallelism was small, and the image parallelism did not reach 0.
Therefore, it is understood that the example model has higher adjustment sensitivity of the image parallelism than the comparative example model. Here, since the example model and the comparative example model are the same except for the friction coefficient relationship, the adjustment sensitivity of the image parallelism is low in the comparative example model because the transfer conveyance belt is changed before the speed of the recording material is changed. While the image model slides between the elastic transfer rolls, the image model has high sensitivity for adjusting the image parallelism, and it slips between the transfer conveyance belt and the elastic transfer roll before the recording material speed changes. It is assumed that this is due to the absence of

Example 2
In this example, elastic transfer rolls manufactured by three different methods (hereinafter abbreviated as transfer rolls 1 to 3) are used, and the amount of roll twist when twisting is applied under a predetermined condition is plotted. The torsional characteristics of 1 to 3 were examined.
Here, each of the transfer rolls 1 to 3 will be described as follows.
Transfer roll 1: A roll having a diameter of φ28 in which conductive carbon black is blended with foamed urethane rubber and the blending ratio and foaming ratio are changed.
Transfer roll 2: A roll having a diameter φ28 in which conductive carbon black is blended with EPDM and the blending ratio is changed.
Transfer roll 3: A roll having a diameter of φ28, in which conductive carbon black is mixed with foamed urethane rubber, the blending ratio and the foaming ratio are changed, and a rubber layer made of EPDM having a thickness of 0.5 mm is provided on the surface.
The roll hardness and roll / belt friction coefficient (corresponding to the friction coefficient between the transfer rolls 1 to 3 and the transfer conveyance belt) of these transfer rolls 1 to 3 are shown in FIG.

Further, as shown in FIG. 8B, the twisting condition in this embodiment is that one end of the elastic layer flesh portion of the transfer rolls 1 to 3 is fixed and the other end of the elastic layer flesh portion is transferred pressure. It shall be twisted with torque load α (gf) × d (mm) due to frictional force when receiving a considerable force.
Here, as a specific example of the torque load, for example, when the total transfer load is 6000 gf, the transfer nip length is 300 mm, the transfer nip width is 6 mm, and the static friction coefficient between the transfer conveyance belt / transfer roll is 0.4, the total pressure is 6000 gf. / (300 × 6) mm ² , the frictional force acting at a position of 0.5 mm from the end of the transfer roll is (6000 × 0.5 × 0.4 / 300) = 4 gf. Therefore, the torque acting on the φ28 transfer roll is 4 gf × 14 mm.

The twist characteristics of the transfer rolls 1 to 3 are shown in FIG.
According to the figure, it is understood that if the hardness is the same, the transfer roll 1 has the smallest twist amount, and the transfer roll 2 and the transfer roll 3 have a larger twist amount. Therefore, when the transfer rolls 1 to 3 are used as the elastic transfer rolls, it can be said that the transfer rolls 2 and 3 can obtain a larger torsional reaction force than the transfer roll 1.

Example 3
In the present embodiment, each transfer roll manufactured in the second embodiment is mounted on the model of the first embodiment, the extension rate of the transfer conveyance belt 53 is changed, and the amount of biting in the transfer nip region of the transfer rolls 1 to 3 at each extension rate. And the parallelism inclination was measured.
The results are shown in FIG. In FIG. 10, the hardness of each of the transfer rolls 1 to 3 is Aska C 50 degrees, the horizontal axis is the elongation rate [%], and the vertical axis is the parallelism inclination, which is the image parallelism ΔL (FIG. 1). Reference) [unit: mm] / biting amount h [unit: mm].

In the figure, it is possible to adjust the image parallelism in a region where the parallelism inclination (which is usually a negative value because the speed of the recording material on the side where the amount of bite is large is slow) is 0.5 or more in absolute value. Was confirmed.
As a result, it is confirmed that the transfer roll 1 having a small twist characteristic (twist amount with respect to hardness) cannot adjust the image parallelism in a region where the transfer material of the transfer transport belt has a good elongation ratio of 0.5% or more. In other transfer rolls 2 and 3, it was confirmed that the transfer conveyance belt elongation rate was 1.12% or less and the image parallelism could be adjusted to zero. This result was not greatly influenced by the hardness of the transfer roll, and it was confirmed that the same tendency was observed for other hardnesses.

Based on the above results, if the elastic transfer roll has a twist characteristic higher than that of the transfer roll 2, a sufficient roll reaction force can be obtained for the roll alone to affect the speed of the recording material. The speed at both ends in the direction can be changed.
That is, it can be said that it is effective in adjusting the image parallelism if the twist amount of the elastic transfer roll is a value equal to or larger than the twist characteristic curve y of the transfer roll 2 shown in FIG.
Specifically, any material satisfying the following mathematical formula may be used.
k ≧ 4 × 10 ⁻⁶ M ² −5 × 10 ⁻⁴ M + 1.97 × 10 ⁻²
However, k is the twist amount of an elastic transfer roll, M is roll hardness (Asuka C hardness).
Further, according to FIG. 10, it is understood that the transfer / conveying belt needs to have an elongation rate of 1.12% or less. This is based on the fact that if the extension rate of the transfer conveying belt is too large, the torsional reaction force is absorbed by the transfer conveying belt and hardly acts on the recording material via the transfer conveying belt. If it is below, the torsional reaction force acts on the recording material without being absorbed by the transfer / conveying belt, and the speed at both ends in the width direction of the recording material can be changed.

(A) is explanatory drawing which shows the outline | summary of the image forming apparatus which concerns on this invention, and the transfer apparatus used for this, (b) is explanatory drawing which shows the concept of image parallelism. (A) is a schematic diagram which shows the generation | occurrence | production state of the torsional reaction force in an invention model, (b) is a schematic diagram which shows the generation | occurrence | production state of the torsional reaction force in a comparative model. (A) is explanatory drawing which shows the effect | action of the twist reaction force by an image parallelism adjustment mechanism, (b) is the plane schematic diagram. 1 is an explanatory diagram showing an overall configuration of Embodiment 1 of an image forming apparatus according to the present invention. FIG. 3 is an explanatory diagram showing details of a batch transfer device used in the first embodiment. It is explanatory drawing equivalent to the VI-VI line cross section in FIG. (A) is the graph which shows the relationship between the amount of biting h and image parallelism (DELTA) L in Example 1 and the comparative example 1 model, (b) is explanatory drawing which shows an Example model and a comparative example model. (A) is explanatory drawing which shows the roll hardness of a transfer roll 1-3 used in Example 2, 3, and a roll / belt friction coefficient, (b) is explanatory drawing which shows the load torque given to a transfer roll in Example 2. FIG. . In Example 2, it is explanatory drawing which shows the relationship between the hardness of the transfer rolls 1-3, and roll twist amount. In Example 3, it is explanatory drawing which shows the relationship between the expansion | extension rate of the transfer rolls 1-3, and a parallelism inclination.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 (2a-2d) ... Image formation carrier, 3 ... Intermediate transfer body, 3a-3c ... Stretching roll, 4 ... Transfer device, 5 ... Recording material, 6 (6a, 6b) ... Tension Stand roll, 7 ... elastic transfer roll, 8 ... transfer conveyance belt, 9 ... image parallelism adjustment mechanism

Claims (5)

In an image forming apparatus comprising an image carrier on which an image is carried and a transfer device for transferring an image on the image carrier to a recording material,
The transfer device includes a transfer conveyor belt which is rotatably stretched around a plurality of tension rolls,
Among the plurality of stretching rolls, at least the stretching roll that faces the image carrier is used as a pressure roller and is arranged in pressure contact with the back surface of the transfer conveyance belt so as to sandwich the transfer conveyance belt with the image carrier . and an elastic transfer roller for transferring electric field formation surface portion in contact with the rear surface is made of a low elastic member hardness than the image bearing member portion facing,
The elastic transfer roll is twisted by making a difference in the amount of biting at both ends in the axial direction of the elastic transfer roll, and this twisting reaction force is applied to the recording material via the transfer conveying belt, in the recording material conveying direction. An image parallelism adjustment mechanism capable of adjusting the parallelism of the image with respect to the orthogonal width direction ,
The image parallelism adjusting mechanism supports the elastic transfer roll in a swingable manner with one end in the axial direction as a fulcrum, and allows the free end of the elastic transfer roll to move up and down, and further between the recording material and the transfer conveyance belt surface. the friction coefficient mu _a, the elastic transfer roll surface, when the friction coefficient between the transfer conveyance belt back surface was μ _B, μ _{a <image} forming apparatus characterized by satisfying the relation of mu _B. The image forming apparatus according to claim 1.
In a state where one end of the elastic transfer roll in the axial direction is fixed, k is the amount of twist when a torque load of 4 gf × 14 mm is applied in the circumferential direction due to frictional force when receiving a force corresponding to the transfer pressure at the other end. When the Asuka C surface hardness of the elastic transfer roll is M,
k ≧ 4 × 10 ⁻⁶ M ² −5 × 10 ⁻⁴ M + 1.97 × 10 ⁻²
An image forming apparatus characterized by satisfying the above. The image forming apparatus according to claim 1.
If the belt extension rate of the transfer conveyance belt is Bs (%),
An image forming apparatus satisfying Bs ≦ 1.12. The image forming apparatus according to claim 1.
The image carrier includes an image forming carrier on which an image is formed and supported, and a belt-shaped intermediate transfer member that intermediately holds and conveys the image on the image forming carrier before being transferred to a recording material. An image forming apparatus. A transfer device used in the image forming apparatus according to any one of claims 1 to 4.

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