JP2011039268A - Transfer apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transfer apparatus and an image forming apparatus having excellent transfer efficiency and preventing meandering of transfer image and a transfer belt. <P>SOLUTION: The transfer apparatus includes an intermediate transfer belt 8 having an elastic layer and configured to carry a toner image, a secondary transfer roller 12 having an elastic layer and configured to transfer the toner image carried on the intermediate transfer belt 8 onto a transfer material 15 at a secondary transfer nip 11c formed in contact with the intermediate transfer belt 8, and an intermediate transfer belt driving roller 9 configured to be brought into pressure-contact with the secondary transfer roller through the intermediate transfer belt 8. The secondary transfer nip includes a pressure-contact nip 11a formed when the secondary transfer roller is brought into pressure-contact with the intermediate transfer belt driving roller, and a contact nip 11b formed by winding the intermediate transfer belt around the secondary transfer roller. In a secondary transfer part 11, a contact nip width W of the contact nip 11b in a direction orthogonal or substantially orthogonal to a virtual line δ that connects the center of rotation 12c of the secondary transfer roller and the center of rotation 9a of the intermediate transfer belt driving roller, is smaller than 1/2 of a pressure-contact nip width W of the pressure-contact nip 11a in the same direction. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

The present invention relates to a transfer apparatus and an image forming apparatus that transfer an image carried on a transfer belt to a transfer material using a transfer belt having an elastic layer and a transfer roller having an elastic layer.

Conventionally, in an electrophotographic image forming apparatus using a liquid developer, transfer efficiency of an image carried on a transfer belt to a transfer material such as transfer paper becomes a problem. In particular, when transferring an image carried on a transfer belt and overlaid with a plurality of colors onto a transfer material, a decrease in transfer efficiency becomes a problem.

Therefore, image formation is performed using a transfer long nip including a pressure nip in which the transfer roller is pressed against the transfer belt, and a winding nip formed by winding the transfer belt around the transfer roller and formed much longer by the pressure nip. An apparatus has been proposed (see, for example, Patent Document 1). In this image forming apparatus, in the transfer long nip, the transfer material is pressed against the image on the transfer belt, and the time during which the transfer bias acts is increased, thereby increasing the transfer efficiency.

JP 2001-166611 A.

However, when the transfer long nip is used, if the winding nip is long, the image transferred onto the transfer material may be dragged during transfer. A possible cause of this image shift is a change in the belt surface speed at the transfer long nip. In general, the surface layer of the transfer roller is formed to be softer than the backup roller of the transfer roller, so that the surface of the transfer roller is recessed in the pressure nip, and the surface of the transfer belt on the side carrying the image extends along this recess. Bend. Further, at the winding nip, the surface of the transfer belt bends in the direction of compression along the outer peripheral surface of the transfer roller. As described above, since the bending direction of the surface of the transfer belt is different at the transfer nip, the surface speed of the transfer belt changes between the pressure nip and the winding nip. When the winding nip becomes longer, the change in the surface speed of the transfer belt becomes larger, so that image misalignment is likely to occur.

In addition, since the elastic layer of the transfer belt is compressed by the pressure load at the pressure nip, the actual length of the belt in the pressure nip is shortened. On the other hand, since no pressure contact load is applied to the transfer belt at the winding nip, the elastic layer of the transfer belt hardly deforms. For this reason, a difference occurs in the surface speed of the transfer belt between the pressure nip and the winding nip.

Further, when the transfer long nip is used, both the contact area between the transfer belt and the transfer roller and the contact area between the transfer belt and the transfer material are increased. For this reason, the transfer belt meanders due to the difference in the pressure load in the direction perpendicular or almost perpendicular to the transfer material moving direction, the position of the transfer material at the transfer nip (position different from the predetermined position), or the posture of the transfer material (skew). It becomes easy to do.

The present invention has been made in view of such circumstances, and an object of the present invention is to provide a transfer that can suppress transfer image misalignment and suppress meandering of the transfer belt while obtaining good transfer efficiency. An apparatus and an image forming apparatus are provided.

In order to solve the above-described problem, in the transfer device and the image forming apparatus according to the present invention, the transfer nip is formed by the pressure nip formed by the pressure contact between the transfer roller and the backup roller via the transfer belt, and the backup roller. It includes a contact nip formed by contact between the unrolled transfer belt and the transfer roller, and is formed as a transfer long nip that is longer than the transfer nip formed only by the pressure nip. Therefore, better transfer efficiency can be obtained compared to transfer using only the pressure nip.

Further, when the pressure nip protrudes toward the transfer roller, the transfer roller has a radius larger than that of the backup roller, so that the transfer belt can be easily guided from the end of the pressure nip to the backup roller. Thereby, the contact nip width of the contact nip can be reduced, and the bending in the compression direction of the surface of the transfer belt along the outer peripheral surface of the transfer roller can be more effectively suppressed.

Further, the contact nip width at which the transfer belt contacts the transfer roller is made smaller than the pressure nip width. This reduces the amount of contact of the transfer belt that contacts the transfer roller,
The transfer belt hardly bends in the direction compressed along the outer peripheral surface of the transfer roller. Therefore, since the bending direction of the surface of the transfer belt hardly changes at the transfer nip, the change in the surface speed of the transfer belt is suppressed between the pressure nip and the contact nip. As a result, it is possible to suppress the deviation of the image transferred to the transfer material during transfer. In particular, when the contact nip width is made smaller than half of the pressure nip width, the bending direction of the surface of the transfer belt at the transfer nip does not change further. Therefore, the change in the surface speed of the transfer belt can be more reliably suppressed between the pressure nip and the contact nip, and the image shift can be further effectively suppressed.

Further, the transfer belt that has passed through the pressure nip is guided in a direction orthogonal or substantially orthogonal to a virtual straight line connecting the rotation center of the transfer roller and the rotation center of the backup roller. This makes it possible to stabilize the moving direction of the transfer belt that has passed through the pressure nip. Therefore, it is possible to reliably form the contact nip by suppressing the fluctuation in the moving direction of the transfer belt that has passed through the press nip, and to make the contact nip width smaller than the press nip width more reliably. .

Furthermore, the moving speed of the transfer belt can be stabilized by configuring the backup roller with a transfer belt driving roller and driving the transfer belt with the transfer belt driving roller in the transfer portion. Thereby, the moving speed of the transfer material at the transfer nip can be stabilized, and it is possible to make it difficult for image transfer of the transfer image to occur.

Furthermore, even when the transfer nip is a transfer long nip, the width of the transfer nip in the transfer material moving direction can be made sufficiently shorter than that of the image forming apparatus described in Patent Document 1 described above. That is, both the contact area between the transfer belt and the transfer roller and the contact area between the transfer belt and the transfer material can be reduced. As a result, the difference in the pressing load in the direction orthogonal or almost orthogonal to the moving direction of the transfer material, the position of the transfer material at the transfer nip (position different from the predetermined position), or the posture of the transfer material (skew) The impact can be reduced. Therefore, meandering of the transfer belt can be effectively suppressed.
Thus, according to the transfer device and the image forming apparatus according to the present invention, it is possible to suppress the shift of the transferred image and to suppress the meandering of the transfer belt while obtaining good transfer efficiency.

Further, a transfer material gripping member is disposed on the transfer roller. Since the image carried on the transfer belt is transferred to the transfer material while the transfer material is held by the transfer material holding member, the transfer material can be reliably peeled off from the transfer belt after transfer.

Furthermore, a nozzle hole through which air flows is disposed in the transfer roller. When the air outside the transfer roller flows through the nozzle holes and flows into the transfer roller, the transfer material is adsorbed by the transfer roller. In this way, the image carried on the transfer belt is transferred to the transfer material in a state where the transfer material is adsorbed to the transfer roller by the nozzle hole, so that the transfer material can be reliably peeled off from the transfer belt after transfer. . Further, after the transfer, the air inside the transfer roller flows through the nozzle hole and flows out of the transfer roller, so that the transfer material can be easily peeled off from the transfer roller.

1 is a diagram schematically and partially showing a first example of an embodiment of an image forming apparatus according to the present invention. (A) is the elements on larger scale of the secondary transfer part of the 1st example, (b) is the elements on larger scale of the secondary transfer nip in (a). (A) And (b) is a figure explaining the measuring method of a secondary transfer nip. FIG. 3 is a view similar to FIG. 1, showing a second example of the embodiment of the image forming apparatus according to the present invention. It is the elements on larger scale similar to FIG. 2A which show the secondary transfer part of the 2nd example. 3 shows a third example of an embodiment of the image forming apparatus of the present invention, (a) is a partially enlarged view of a secondary transfer portion similar to FIG. 2 (a), (b) is a VB-VB line in (a). FIG. FIG. 9 is a partial enlarged view of a secondary transfer unit similar to FIG. 2A, showing a fourth example of an embodiment of an image forming apparatus of the present invention.

Hereinafter, embodiments for carrying out the present invention will be described with reference to the drawings.
FIG. 1 is a diagram schematically and partially showing a part of a first example of an embodiment of an image forming apparatus according to the present invention, and FIG. 2A is a partially enlarged view of a secondary transfer portion of the first example. FIG. 2B is a partially enlarged view of the secondary transfer nip in FIG.

The image forming apparatus 1 of the first example performs image formation using a liquid developer containing toner particles and a carrier liquid. As shown in FIG. 1, the image forming apparatus 1 includes yellow (Y), magenta (
M), photoreceptor 2 which is a latent image carrier that carries cyan (C) and black (K) latent images.
Y, 2M, 2C, 2K. Each of the photoconductors 2Y, 2M, 2C, and 2K is arranged in tandem horizontally or substantially horizontally. Here, in each of the photoreceptors 2Y, 2M, 2C, and 2K, 2Y represents a yellow photoreceptor, 2M represents a magenta photoreceptor, 2C represents a cyan photoreceptor, and 2K represents a black photoreceptor. Similarly, for the other members, the reference numerals of the members are Y,
Each color member is represented with M, C and K.

Charging units 3Y, 3M, 3C, and 3K are provided around the photoreceptors 2Y, 2M, 2C, and 2K, respectively. Further, from the charging units 3Y, 3M, 3C, and 3K, the photoreceptors 2Y, 2M, respectively.
, 2C, 2K in turn toward the rotation direction α, the exposure units 4Y, 4M, 4C, 4K which are image writing units in order.
Further, developing units 5Y, 5M, 5C, and 5K, primary transfer units 6Y, 6M, 6C, and 6K as transfer devices, and photosensitive member cleaning units 7Y, 7M, 7C, and 7K are disposed. Each exposure unit 4Y, 4M, 4C,
In 4K, latent images are written on the photosensitive members 2Y, 2M, 2C, and 2K, respectively. Each developing unit 5Y,
5M, 5C, and 5K respectively develop the latent images carried on the respective photoreceptors 2Y, 2M, 2C, and 2K with toner of a liquid developer to form a toner image that is a developer image.

The image forming apparatus 1 also includes an endless intermediate transfer belt 8 that is an image bearing member as well as a transfer belt. The intermediate transfer belt 8 is disposed above the photoreceptors 2Y, 2M, 2C, and 2K. The intermediate transfer belt 8 is pressed against the photoreceptors 2Y, 2M, 2C, and 2K at the primary transfer portions 6Y, 6M, 6C, and 6K. The primary transfer portions 6Y, 6M, 6C, and 6K transfer the toner images of the respective colors carried on the photosensitive members 2Y, 2M, 2C, and 2K on the intermediate transfer belt 8 while superimposing them on the intermediate transfer belt 8, respectively. As a result, a full-color toner image is carried on the intermediate transfer belt 8.

Although not shown, the intermediate transfer belt 8 is formed on a surface of the elastic layer, such as a flexible base layer such as a resin, an elastic layer such as a rubber layer formed on the surface of the base material layer, and the like. 3 with surface layer
It is formed on a relatively soft elastic belt having a layer structure. In that case, the base material layer is located on the inner peripheral side, and the surface layer is located on the outer peripheral side. As an example of the intermediate transfer belt 8, for example, a resin such as a polyimide resin can be used as the base layer, and a rubber layer such as a urethane rubber can be used as the elastic layer, and a fluorine resin can be used as the surface layer. Or a fluororubber-based material can be used. Of course, the intermediate transfer belt 8 is not limited to this. The intermediate transfer belt 8 is stretched around an intermediate transfer belt drive roller 9 and an intermediate transfer belt tension roller 10 to which a driving force of an intermediate transfer belt drive motor (not shown) is transmitted. The intermediate transfer belt 8 is rotated in the rotation (movement) direction β in a state where a tension is applied.
Note that the arrangement order of members such as photoconductors corresponding to the respective colors Y, M, C, and K is not limited to the example shown in FIG. 1 and can be arbitrarily set.

A secondary transfer unit 1 serving as a transfer device is disposed on the intermediate transfer belt 8 on the side of the intermediate transfer belt driving roller 9.
1 is provided. The secondary transfer unit 11 includes a secondary transfer roller 12, a stretching roller 13, and a secondary transfer roller cleaning unit 14.

As shown in FIGS. 1 and 2A, the secondary transfer roller 12 includes a base material 12a and a base material 1.
And an elastic layer (for example, a rubber layer) 12b made of an elastic member disposed on the outer peripheral surface of 2a. This elastic layer 12b forms an electric resistance layer. As the base material 12a, for example, an iron metal material can be used. The elastic layer 12b includes the intermediate transfer belt 8 described above.
The same elastic material as the elastic layer such as urethane rubber can be used. In that case, the thickness of the elastic layer 12 b of the secondary transfer roller 12 is larger than the thickness of the elastic layer of the intermediate transfer belt 8.

Further, the radius R ₁ (mm) of the outer peripheral surface of the elastic layer 12b of the secondary transfer roller 12 is set larger than the radius R ₂ (mm) of the intermediate transfer belt drive roller 9 (R ₁ > R ₂ ). Further, in the image forming apparatus 1 of the first example, the thickness (μm) of the elastic layer of the intermediate transfer belt 8 is set smaller than the radius R ₂ (mm) of the intermediate transfer belt driving roller 9. The secondary transfer roller 12 rotates in the rotation direction γ during the image forming operation.

The secondary transfer roller 12 is provided with an elastic layer 1 by a biasing force of a biasing means such as a spring (not shown).
2b is pressed against the intermediate transfer belt driving roller 9 via the intermediate transfer belt 8. As a result, as shown in FIGS. 2A and 2B, a pressure nip 11 a is formed between the intermediate transfer belt 8 and the elastic layer 12 b of the secondary transfer roller 12. At this time, the intermediate transfer belt driving roller 9 functions as a backup roller against the pressing of the secondary transfer roller 12. In this case, since the thickness of the elastic layer 12b of the secondary transfer roller 12 is larger than the thickness of the elastic layer of the intermediate transfer belt 8, the intermediate transfer belt 8 and the intermediate transfer belt drive roller 9 are elastic layers of the secondary transfer roller 12. The elastic layer 12b side is recessed in an arc shape so as to bite into 12b. That is,
The pressure nip 11a has a shape that is curved and protrudes in an arc shape on the elastic layer 12b side of the secondary transfer roller 12.

Further, the tension roller 13 is disposed in the moving direction β of the intermediate transfer belt 8 from the intermediate transfer belt driving roller 9. The portion 8a of the intermediate transfer belt 8 that has passed through the pressure nip 11a is wound around the stretching roller 13 and moved to the secondary transfer roller 12 side. At this time, the portion 8 a of the intermediate transfer belt 8 is at the intersection of the virtual straight line δ connecting the rotation center 9 a of the intermediate transfer belt drive roller 9 and the rotation center 12 c of the secondary transfer roller 12 and the outer peripheral surface of the intermediate transfer belt 8. Guided in the tangential direction ε (that is, the direction orthogonal to the virtual straight line δ). That is, the moving direction β of the portion 8a of the intermediate transfer belt 8 is the tangential direction ε. A portion 8 of the intermediate transfer belt 8 that passes through the pressure nip 11 a and is not wound around the intermediate transfer belt driving roller 9.
a partially contacts the elastic layer 12 b of the secondary transfer roller 12. As a result, a contact nip 11 b is formed between the intermediate transfer belt 8 and the elastic layer 12 b of the secondary transfer roller 12.
The contact nip 11b is formed continuously at the end of the press nip 11a (the end of the press nip 11a on the rear side in the intermediate transfer belt moving direction β). Pressure nip 11a and contact nip 1
1b constitutes a secondary transfer nip 11c for secondary transfer of the toner image carried on the intermediate transfer belt 8 onto a transfer material 15 such as transfer paper.

In the secondary transfer nip 11 c, the transfer material 15 that passes through the pressure nip 11 a is interposed between the intermediate transfer belt drive roller 9 and the elastic layer 12 b of the secondary transfer roller 12.
It is pinched together. Further, the transfer material 15 passing through the contact nip 11 b is sandwiched between the intermediate transfer belt 8 separated from the intermediate transfer belt driving roller 9 and the elastic layer 12 b of the secondary transfer roller 12. The transfer material 15 that has passed through the contact nip 11b moves away from the intermediate transfer belt 8, is wound around the elastic layer 12b of the secondary transfer roller 12, and finally moves away from the elastic layer 12b.

Accordingly, the position p _{1 at which} the intermediate transfer belt 8 is separated from the intermediate transfer belt drive roller 9.
And the position p ₂ where the transfer material 15 is separated from the intermediate transfer belt 8 are different in the tangential direction ε. Specifically, the position p ₁ is closer to the near side in the movement direction β of the intermediate transfer belt 8 than the position p ₂ .

As shown in FIG. 2B, in the secondary transfer nip 11c, the distance (that is, the pressure nip width) in the moving direction β of the intermediate transfer belt 8 of the pressure nip 11a is set to W ₁ (mm), and the contact nip 11c is contacted. The distance in the movement direction β of the intermediate transfer belt 8 at the nip 11b (that is, the contact nip width) is W ₂ (mm). That is, the moving direction β of the intermediate transfer belt 8 in the secondary transfer nip 11c.
Is the distance W ₁ (mm) of the pressure nip 11a.
) And the distance W ₂ (mm) of the contact nip 11b. 2B, for convenience of description, the secondary transfer nip width W (mm), the pressure nip width W ₁ (mm), and the contact nip width W ₂ (
mm) is shown as the tangential direction ε, but in practice these nip widths are both
This is the width of the intermediate transfer belt 8 in the moving direction. In the image forming apparatus 1 of the first embodiment, the contact nip width W ₂ (mm) is set to be smaller than half of the press nip width W ₁ (mm) (i.e., W ₂ <W _1/2) . The contact nip width W ₂ is set larger than the thickness of the elastic layer of the intermediate transfer belt 8. The contact nip width W ₂ (mm) is not necessarily the pressure nip width W ₁ (
It is not necessary to be smaller than half of (mm), and it is only necessary to set it to be smaller than the pressure nip width W ₁ (mm) (W ₂ <W ₁ ). However, the contact nip width W ₂ (mm) is reduced to the pressure nip width W ₁ (m
In order to more effectively suppress the bending of the intermediate transfer belt 8 at the contact nip 11b, it is preferable to make it smaller than half of m).

Here, the secondary transfer nip width W (mm) and the pressure nip width of the secondary transfer nip 11c are set to W ₁ (
mm) and a method for measuring the contact nip width W ₂ (mm). As shown in FIG. 3A, first, the intermediate transfer belt 8 is moved to the intermediate transfer belt driving roller 9 and the stretching roller 13.
Wrap around. Next, the same tension as in the normal use state is applied to the intermediate transfer belt 8 by a belt tension applying mechanism (not shown). Next, a two-part curable silicone rubber for mold making is applied to the portion of the secondary transfer roller 12 where the measurement nip is formed. In this embodiment, exafine (injection type) (manufactured by GC Corporation) can be used as the two-component curable silicone rubber. Next, the two-component curable silicone rubber of the secondary transfer roller 12 is pressed against the belt driving roller 9 through the intermediate transfer belt 8 with a pressure contact force during normal use to form a deformed portion in the two-component curable silicone rubber. . Then, after the two-component curable silicone rubber is cured, the width of the nip forming portion is measured using a caliper in a state where the nip forming portion, which is a thinned portion of the deformed portion, is flattened on a flat surface. The measured width of the nip forming portion is the secondary transfer nip width W (mm) including the pressure nip width W ₁ (mm) and the contact nip width W ₂ (mm). Next, as shown in FIG. 3B, the tension of the intermediate transfer belt 8 is sufficiently loosened,
The intermediate transfer belt 8 is wound around the intermediate transfer belt drive roller 9 more than the state where the tension is applied. Next, in the same manner as described above, the secondary transfer roller 12 has 2
Applying liquid curable silicone rubber and pressing the secondary transfer roller 12 against the intermediate transfer belt drive roller 9 with the pressing force during use to form a deformed part (corresponding to the pressure nip) in the two liquid curable silicone rubber To do. At this time, the intermediate transfer belt 8 is wound around the intermediate transfer belt driving roller 9 side from the pressure nip outlet (end end of the pressure nip in the moving direction of the transfer material) and is not wound around the secondary transfer roller 12 side. So there is no contact nip.
After the two-component curable silicone rubber is cured, the width of the nip forming portion is measured using a caliper in a state where the nip forming portion which is a thinned portion of the deformed portion is flattened on a flat surface. The measured width of the nip forming portion is the pressure nip width W ₁ (mm). Then, the contact nip W ₂ (mm) (= W−W ₁ ) is obtained from the measured secondary transfer nip width and the pressure nip width W ₁ .

As described above, the secondary transfer nip width includes the pressure nip width W ₁ (mm) and the contact nip width W ₂ (mm).
Therefore, it is formed as a long transfer long nip as compared with the transfer nip having only the pressure nip width W ₁ (mm). However, since the contact nip width W ₂ (mm) is limited to be smaller than the pressure nip width W ₁ (mm), the contact nip width in the image forming apparatus described in Patent Document 1 is larger than the pressure nip width. It is extremely small compared to.

Furthermore, as shown in FIG. 1, the image forming apparatus 1 includes a gate roller 16 that feeds the transfer material 15 toward the secondary transfer nip 11 c. The gate roller 16 feeds the transfer material 15 in the direction ζ of the secondary transfer nip 11c. Then, during the image forming operation, the secondary transfer roller 12 rotates in the rotational direction γ when the intermediate transfer belt 8 moves in the moving direction β, and a transfer bias is applied to the secondary transfer roller 12 at the secondary transfer nip 11c. The toner image transferred to 8 is transferred to the transfer material 15 fed from the gate roller 16.

The transfer mechanism in the secondary transfer unit 11 configured in this way is assumed as follows. That is, the elastic layer of the intermediate transfer belt 8 is deformed by the pressure load at the pressure nip 11 a, so that the surface of the intermediate transfer belt 8 follows the unevenness of the surface of the transfer material 15. As a result, the adhesion between the toner image carried on the intermediate transfer belt 8 and the transfer material 15 is enhanced. And
In the state where the adhesion between the toner image and the transfer material 15 is increased, an electric field is formed by the secondary transfer bias in the pressure nip 11a, so that the toner image carried on the intermediate transfer belt 8 is
It is effectively transferred onto the surface of the transfer material 15 having irregularities.

By the way, when the toner image carried on the intermediate transfer belt 8 is transferred to the surface of the transfer material 15 by the secondary transfer nip 11c including only the pressure nip 11a, the toner adhered to the convex portion on the surface of the transfer material 15 Is relatively easy to peel off from the intermediate transfer belt 8, but the toner adhering to the concave portion on the surface of the transfer material 15 is less likely to peel from the intermediate transfer belt 8 than the toner adhering to the convex portion of the transfer material 15. The reason is considered as follows. When the contact nip 11b is not formed, the transfer material 15 is peeled off from the intermediate transfer belt 8 at the exit of the pressure nip 11a (the end of the pressure nip 11a in the moving direction of the transfer material 15). At this time, a relatively large physical adhesive force exists between the intermediate transfer belt 8 and the toner and between the transfer material and the toner due to the pressure applied by the press nip 11a. In the vicinity of the outlet of the press nip 11a, the pressure is suddenly released, and the deformation of the elastic layer of the intermediate transfer belt 8 is recovered. Then, in the concave portion of the transfer material 15, a minute gap tends to be generated between the concave portion of the transfer material 15 and the intermediate transfer belt 8, so that the cohesive force between the toners positioned in the concave portion of the transfer material 15 becomes small. . On the other hand, since there is a large physical adhesion force between the intermediate transfer belt 8 and the toner in the vicinity of the outlet of the press nip 11a, the cohesive force between the toners causes the physical force between the intermediate transfer belt 8 and the toner. The toner film is broken in the film under the negative adhesion force. As a result, a part of the toner located in the concave portion of the transfer material 15 adheres to the transfer material 15, but the remaining toner remains attached to the intermediate transfer belt 8, and it is considered that toner transfer residue occurs.

In the secondary transfer portion 11 of the first example, the contact nip 11b is formed following the pressure nip 11a, so that the secondary transfer nip 11c is a transfer long nip. This contact nip 11
In b, the intermediate transfer belt driving roller 9 and the secondary transfer roller 1 through the intermediate transfer belt 8 are used.
2 is eliminated. Therefore, while the transfer material 15 is passing through the contact nip 11 b, almost no pressure is applied to the toner sandwiched between the transfer material 15 and the intermediate transfer belt 8. For this reason,
The physical adhesion between the intermediate transfer belt 8 and the toner image carried on the intermediate transfer belt 8 is alleviated. In addition, a transfer current is generated by the secondary transfer bias in the pressure nip 11a, but the intermediate transfer belt 8 and the transfer material 15 are charged by the transfer current, and thus an electric field also exists in the contact nip 11b. That is, while the transfer material 15 is passing through the contact nip 11b,
An electric field acts on the toner in a state where the physical adhesion between the intermediate transfer belt 8 and the toner is relaxed. As a result, when the intermediate transfer belt 8 and the transfer material 15 are peeled off, the toner adhering to the concave portion on the surface of the transfer material 15 is affected by the electric field and the cohesive force between the toner adhering to the convex portion adjacent to the concave portion. As a result, peeling from the intermediate transfer belt 8 is facilitated. Thus, the toner adhering to the concave portion of the transfer material 15 is also relatively easily peeled off from the intermediate transfer belt 8 by the contact nip 11b formed subsequent to the pressure nip 11a, so that it is considered that the transfer efficiency is improved.

The secondary transfer roller cleaning unit 14 removes the liquid developer attached to the elastic layer 12b of the secondary transfer roller 12 with a cleaning member such as a cleaning blade. The liquid developer removed by the cleaning member is collected in a liquid developer container.

The transfer material 15 onto which the toner image has been transferred by the secondary transfer unit 11 is conveyed to a conventionally known fixing unit (not shown). Then, the toner image transferred to the transfer material 15 is fixed by being heated and pressed by the fixing unit. The transfer material 15 on which the toner image is fixed is accommodated in a waste transfer material tray (not shown).

According to the image forming apparatus 1 of the first example, the secondary transfer nip 11c includes the pressure nip 11a and the contact nip 11b, and is formed as a transfer long nip that is longer than the transfer nip including only the pressure nip. Therefore, better transfer efficiency can be obtained as compared with transfer using only the pressure nip 11a.

Further, the contact nip width W ₂ (mm) at which the intermediate transfer belt 8 that is not wound around the intermediate transfer belt drive roller 9 contacts the secondary transfer roller 12 is half of the pressure nip width W ₁ (mm).
Made smaller. As a result, the contact amount of the intermediate transfer belt 8 that contacts the secondary transfer roller 12 is reduced, so that the intermediate transfer belt 8 hardly bends in the direction of compression along the outer peripheral surface of the secondary transfer roller 12. Accordingly, since the bending direction of the surface of the intermediate transfer belt 8 hardly changes at the secondary transfer nip 11c, the pressure nip 11a and the contact nip 11 are not changed.
With b, the change in the surface speed of the intermediate transfer belt 8 is suppressed. As a result, it is possible to suppress the deviation of the image transferred to the transfer material 15 during the secondary transfer.

Further, when the pressure nip 11 a has a shape protruding toward the secondary transfer roller 12, the radius R ₁ (mm) of the secondary transfer roller 12 is made larger than the radius R ₂ (mm) of the intermediate transfer belt drive roller 9. Thus, the tension roller 13 can easily guide the intermediate transfer belt 8 from the end of the press nip 11a to the intermediate transfer belt driving roller 9 side. Thereby, the contact nip width W ₂ (mm) can be reduced, and the bending of the surface of the intermediate transfer belt 8 along the outer peripheral surface of the secondary transfer roller 12 in the compression direction can be further effectively suppressed.

Furthermore, when the pressure nip 11a has a shape protruding toward the secondary transfer roller 12, the thickness (mm) of the elastic layer 12b of the secondary transfer roller 12 is made larger than the contact nip width W ₂ (mm). Similarly, the tension roller 13 can easily guide the intermediate transfer belt 8 from the end of the press nip 11a to the intermediate transfer belt driving roller 9 side. As a result, the contact nip width W
₂ (mm) can be reduced, and the bending of the surface of the intermediate transfer belt 8 along the outer peripheral surface of the secondary transfer roller 12 in the compression direction can be more effectively suppressed.

Further, when the pressure nip 11a has a shape protruding to the secondary transfer roller 12 side, the thickness of the elastic layer of the intermediate transfer belt 8 is made smaller than the contact nip width W ₂ (mm). 13 makes it easy to guide the intermediate transfer belt 8 from the end of the press nip 11a to the intermediate transfer belt drive roller 9 side. Thereby, the contact nip width W ₂ (mm) can be reduced, and the bending of the surface of the intermediate transfer belt 8 along the outer peripheral surface of the secondary transfer roller 12 in the compression direction can be further effectively suppressed.

Furthermore, even if the secondary transfer nip 11c is a transfer long nip, the width of the secondary transfer nip 11c in the moving direction of the transfer material 15 can be made sufficiently shorter than that of the image forming apparatus described in Patent Document 1. . That is, both the contact area between the intermediate transfer belt 8 and the secondary transfer roller 12 and the contact area between the intermediate transfer belt 8 and the transfer material 15 can be reduced. As a result, the difference in pressure contact load in the direction orthogonal or almost orthogonal to the moving direction of the transfer material 15, the position of the transfer material 15 in the secondary transfer nip 11c (a position different from the predetermined position), or the posture (skew) of the transfer material 15 ) To the intermediate transfer belt 8 can be reduced. Therefore, meandering of the intermediate transfer belt 8 can be effectively suppressed.

Furthermore, by arranging the stretching roller 13 in the moving direction β of the intermediate transfer belt 8 from the intermediate transfer belt driving roller 9, it is possible to stabilize the moving direction β of the intermediate transfer belt 8 that has passed through the press contact nip 11a. It becomes. Accordingly, the wobbling in the moving direction β of the intermediate transfer belt 8 that has passed through the press nip 11a can be suppressed, and the contact nip 11b can be reliably formed, and the contact nip width W ₂ (mm) can be set to the press nip width W. _It can be more reliably realized to be smaller than half of ₁ (mm).

Further, in the secondary transfer unit 11, the intermediate transfer belt 8 is driven by the intermediate transfer belt driving roller 9.
Is driven, the moving speed of the intermediate transfer belt 8 can be stabilized. Thereby, the moving speed of the transfer material 18 in the secondary transfer nip 11c can be stabilized, and it is possible to make it difficult for image transfer of the transfer image to occur.

Thus, according to the image forming apparatus 1 of the first example, it is possible to suppress the shift of the transfer image while obtaining good transfer efficiency, and to suppress meandering of the intermediate transfer belt 8.
Other configurations and other functions and effects of the image forming apparatus 1 of the first example are the same as those of a conventionally known tandem type image forming apparatus using a liquid developer.

FIG. 4 is a view similar to FIG. 1 showing a second example of the embodiment of the image forming apparatus of the present invention, and FIG. 5 is a partially enlarged view of the secondary transfer portion similar to FIG. .
As shown in FIGS. 4 and 5, in the image forming apparatus 1 of the second example, unlike the first example, the elastic layer 12b is not provided on the entire circumference of the base material 12a. That is, the image forming apparatus 1 of the second example includes a concave portion 1 disposed between both ends of the elastic layer 12b in the circumferential direction of the secondary transfer roller.
7 In this case, the length of the elastic layer 12b in the circumferential direction of the secondary transfer roller is larger than the size in the direction of the transfer material 15 in which the size of the transfer material 15 used in the image forming apparatus 1 in the transfer material moving direction is the maximum size. It is set to be long.

In the recess 17, a gripper 18 as a transfer material gripping member, a gripper support portion 19 as a transfer material gripping member receiving member on which the gripper 18 is seated, and a peeling claw 20 as a transfer material peeling member are disposed. Although not shown, a predetermined number of grippers 18 are arranged along the axial direction of the secondary transfer roller 12, and each gripper 18 is formed in a comb-teeth shape. The gripper support portions 19 are disposed corresponding to the grippers 18, and the peeling claws 20 are disposed between the comb teeth of the gripper 18 and outside the comb teeth located at both ends.

Each gripper 18 sandwiches the leading end portion 15a of the transfer material 15 with the gripper support portion 19 and rotates in the rotational direction η from this gripping position and the leading end portion 15a of the transfer material 15 as shown in FIG.
It is provided so that it can rotate integrally with the release position shown in FIG. Each peeling nail 2
5 is the retracted position shown in FIG. 5 where the tip is located in the recess 17 and the rear surface of the transfer material 15 on which the toner image is transferred by linearly moving in the direction θ from the retracted position and protruding the tip outside the recess 17. The toner image is provided so as to be movable between a protruding position (not shown) where the toner image transfer surface is peeled off from the outer peripheral surface of the secondary transfer roller 12.

Then, immediately before the concave portion 17 reaches the secondary transfer nip 11c, the gripper 18 rotates toward the gripper support portion 19 and is fed to the leading end portion of the transfer material 15 fed from the gate roller 16 in the feeding direction ζ. 15 a is gripped between the gripper support portion 19 and the gripper support portion 19. Then, the toner image carried on the intermediate transfer belt 8 is transferred to the transfer material 15 in the secondary transfer nip 11 c with the gripper 18 holding the leading end 15 a of the transfer material 15. Further, the transfer material 15 that has passed through the secondary transfer nip 11 c is reliably peeled off from the intermediate transfer belt 8 by gripping the leading end portion 15 a of the transfer material 15 by the gripper 18. Thereafter, the gripper 18 rotates in a direction away from the gripper support portion 19 to release the grip of the leading end portion 15 a of the transfer material 15.
Further, the release claws 20 are protruded to the protruding position at the same time as the gripper 18 releases the transfer material. Thereby, the back surface of the transfer material 15 protrudes from each peeling claw 20. Thus, the transfer material 15 is peeled from the secondary transfer roller 12. Thereafter, each peeling claw 20 returns to the retracted position in the recess 17. The operations of the gripper 18 and the peeling claw 20 are controlled by a gripper control cam and a peeling claw control cam (not shown) as the secondary transfer roller 12 rotates.

According to the image forming apparatus 1 of the second example, the front end portion 15 of the transfer material 15 by the gripper 18.
Since the toner image carried on the intermediate transfer belt 8 is transferred to the transfer material 15 while holding a, the transfer material 15 can be reliably peeled off from the intermediate transfer belt 8 after the transfer. Further, since the back surface of the transfer material 15 protrudes from the outer peripheral surface by the peeling claw 20, the transfer material 15 can be reliably peeled off from the outer peripheral surface of the elastic layer 12b of the secondary transfer roller 12 after transfer.
Other configurations and other functions and effects of the image forming apparatus 1 of the second example are the same as those of the image forming apparatus of the first example.

6A and 6B show a third example of the embodiment of the image forming apparatus of the present invention. FIG. 6A is a partially enlarged view of a secondary transfer portion similar to FIG. 2A, and FIG. It is sectional drawing which follows the VB-VB line.
As shown in FIGS. 6A and 6B, in the image forming apparatus 1 of the third example, the base material 12a of the secondary transfer roller 12 is formed in a cylindrical shape. One end of the cylindrical base 12a is closed by a disk-shaped end wall 12a ₁ having a rotating shaft 12d. The other end side of the substrate 12a is partially closed by an annular end wall 12a ₂ having a rotating shaft 12e. The rotation shaft 12e of the other end with formed in a cylindrical shape, the axial direction of the air suction part connection hole 12f that penetrates the end wall 12a ₂ and the rotary shaft 12e is provided. Although not shown, the suction part connection hole 12f is selectively connected to an air supply part such as an air pump or an air blower and an air suction part via a switching valve.

Further, the secondary transfer roller 12 is provided with a predetermined number of air flow nozzle holes 12g penetrating the cylindrical portion of the substrate 12a and the elastic layer 12b. These air flow nozzle holes 12 g are arranged along the axial direction of the secondary transfer roller 12. In that case, the air flow nozzle holes 12g are arranged in a line along the axial direction of the secondary transfer roller 12 as shown in the drawing. The air flow nozzle holes 12g are not limited to this, and a plurality of rows can be arranged along the axial direction of the secondary transfer roller 12 in the circumferential direction. Thus, when providing the air flow nozzle holes 12g in a plurality of rows in the circumferential direction, they can be arranged in a staggered manner.

In the image forming apparatus 1 of the third example configured as described above, each air flow nozzle hole 12g
Just before reaching the secondary transfer nip 11c, the switching valve is set so that the air suction part is connected to the air suction part connection hole 12f, and the air suction part is operated. Thereby, the air inside the base material 12a is sucked through the air suction portion connection hole 12f, and the inside of the base material 12a becomes a negative pressure. Then, air in the vicinity of the outside in the air flow nozzle hole 12g forming portion of the secondary transfer roller 12 is sucked into the base material 12a through each air flow nozzle hole 12g, and an air flow is generated. In this state, when the transfer material 15 is fed from the gate roller 16 and the leading end portion 15a of the transfer material 15 reaches the air flow nozzle hole 12g forming portion of the secondary transfer roller 12,
The leading end portion 15a of the transfer material 15 is sucked by the airflow flowing through each air flow nozzle hole 12g and is adsorbed to the elastic layer 12b of the secondary transfer roller 12.

The toner image carried on the intermediate transfer belt 8 in the secondary transfer nip 11c is transferred to the transfer material 1 in a state where the leading end portion 15a of the transfer material 15 is adsorbed by each air flow nozzle hole 12g.
5 is transferred. Further, the transfer material 15 that has passed through the secondary transfer nip 11c is reliably peeled off from the intermediate transfer belt 8 by the leading end portion 15a of the transfer material 15 being adsorbed by each air flow nozzle hole 12g. Thereafter, the operation of the air suction unit is stopped, and the suction of the leading end portion 15a of the transfer material 15 is completed. When the leading end portion 15a of the transfer material 15 reaches the peeling position where the transfer material 15 is peeled off from the secondary transfer roller 12, the air supply unit is activated and the switching valve is switched so that the air supply unit is connected to the air suction unit connection hole. 12f. Then, positive pressure air is supplied to the inside of the base material 12a, and the positive pressure air flows out from the nozzle hole 12g to the outside of the base material 12a to generate an air flow. The transfer material 15 is easily peeled from the secondary transfer roller 12 by this air flow.

According to the image forming apparatus 1 of the third example, the toner image carried on the intermediate transfer belt 8 is transferred to the transfer material 15 in a state where the leading end portion 15a of the transfer material 15 is sucked by each air flow nozzle hole 12g. Therefore, it is possible to reliably peel the transfer material 15 from the intermediate transfer belt 8 after transfer. Further, since the suction of the transfer material 15 by the air flow nozzle holes 12g is completed after the transfer, the transfer material 15 can be easily peeled from the outer peripheral surface of the elastic layer 12b of the secondary transfer roller 12.
Other configurations and other functions and effects of the image forming apparatus 1 of the third example are the same as those of the image forming apparatus of the first example.

FIG. 7 is a partially enlarged view of a secondary transfer unit similar to FIG. 2A, showing a fourth example of the embodiment of the image forming apparatus of the present invention.
In the first example of the above-described embodiment, the moving direction β of the portion 8a of the intermediate transfer belt 8 is the tangential direction ε.
However, as shown in FIG. 7, in the image forming apparatus 1 of the fourth example, the moving direction β of the portion 8a of the intermediate transfer belt 8 is set to the direction from the tangential direction ε toward the intermediate transfer belt drive roller 9 side. Yes. That is, the stretching roller 13 moves the portion 8 a of the intermediate transfer belt 8 to the secondary transfer roller 1.
2 is partially contacted, but is guided to the intermediate transfer belt driving roller 9 side as compared with the first example. Thereby, the width W ₂ (mm) of the contact nip 11b can be made smaller than in the first example.
Other configurations and other operational effects of the image forming apparatus 1 of the fourth example are the same as those of the image forming apparatus of the first example.

The transfer device and the image forming apparatus of the present invention are not limited to the examples of the above-described embodiments. For example, the image forming apparatus of each example described above is a four-color image forming apparatus.
A monochromatic image forming apparatus may be used. In short, the present invention can be modified in various ways within the scope of the matters described in the claims.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2Y, 2M, 2C, 2K ... Photoconductor, 5Y, 5M, 5C, 5K ... Developing part, 6Y
, 6M, 6C, 6K ... primary transfer unit, 8 ... intermediate transfer belt, 9 ... intermediate transfer belt drive roller, 9a ... rotation center of intermediate transfer belt drive roller, 11 ... secondary transfer unit (transfer device), 11
a ... pressure contact nip, 11b ... contact nip, 11c ... secondary transfer nip, 12 ... secondary transfer roller, 12a ... base material, 12b ... elastic layer, 12c ... rotation center of the secondary transfer roller, 12f ... air suction part connection Holes, 12 g, air flow nozzle holes, 13, stretching rollers, 15, transfer material, 17
... concave portion, 18 ... gripper, W ₁ ... pressure nip width, W ₂ ... contact nip width, R ₁ ... secondary transfer roller radius, R ₂ ... intermediate transfer belt drive roller (backup roller) radius

Claims (8)

A transfer belt having an elastic layer and carrying an image;
A transfer roller having an elastic layer and transferring the image carried on the transfer belt to a transfer material at a transfer nip formed in contact with the transfer belt;
While being in pressure contact with the transfer roller via the transfer belt, a backup roller having a diameter smaller than the diameter of the transfer roller;
Have
The transfer nip portion includes a press nip formed by press contact between the transfer roller and the backup roller via the transfer belt, and the transfer belt and the transfer roller that are not wound by the backup roller. A contact nip formed by contact,
The transfer apparatus, wherein the transfer belt that has passed through the press-contact nip is rotated in a direction orthogonal or substantially orthogonal to a virtual straight line connecting the rotation center of the transfer roller and the rotation center of the backup roller. A latent image carrier on which a latent image is formed;
A developing unit for developing the latent image with a developer;
A transfer belt having an elastic layer and onto which an image developed by the developing unit is transferred;
A transfer roller having an elastic layer and transferring the image transferred to the transfer belt to a transfer material at a transfer nip formed in contact with the transfer belt;
While being in pressure contact with the transfer roller via the transfer belt, a backup roller having a diameter smaller than the diameter of the transfer roller;
A fixing unit for fixing the image transferred to the transfer material;
Have
The transfer nip portion includes a pressure nip formed by pressure contact between the transfer roller and the backup roller, and a contact nip formed by contact of the transfer belt not wound around the backup roller with the transfer roller. Including
The image forming apparatus, wherein the transfer belt that has passed through the pressure nip is rotated in a direction orthogonal or substantially orthogonal to a virtual straight line connecting a rotation center of the transfer roller and a rotation center of the backup roller. The image forming apparatus according to claim 2, wherein the transfer roller has a recess and a transfer material gripping member that grips the transfer material in the recess. The image forming apparatus according to claim 3, wherein the transfer roller has a nozzle hole that selectively performs adsorption or peeling of the transfer material by an air current. The image forming apparatus according to claim 2, wherein a distance of the contact nip in the rotation direction of the transfer belt is smaller than a distance of the pressure nip in the rotation direction. The image forming apparatus according to claim 5, wherein a distance of the contact nip is smaller than a half of a distance of the pressure nip. 6. The image forming apparatus according to claim 2, wherein a tension roller that forms the contact nip is disposed while the transfer belt is wound in a rotation direction of the transfer belt. The image forming apparatus according to claim 2, wherein the backup roller is a transfer belt driving roller that drives the transfer belt.

Images