JP2010164798A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a dead space adjacent to a transfer nip part between an intermediate transfer body and a photoreceptor, and to suppress the splashing of toner from the dead space, in an image forming apparatus forming an image by using the intermediate transfer body and a plurality of image forming parts arranged along the intermediate transfer body. <P>SOLUTION: In the plurality of image forming parts Y, M, C and K arranged along the intermediate transfer body 8, between the adjacent image forming parts on a more upstream side than the most downstream side image forming part K, pressing force of a primary transfer roller 6 in the downstream side image forming part is equal to or above pressing force of the primary transfer roller 6 in the upstream side image forming part. Between the most downstream side image forming part K and the image forming part C on a more upstream side by one, the pressing force F(K) of the transfer roller in the most downstream side image forming part K is larger than pressing force F(C) of the transfer roller in the upstream side image forming part C, that is, [F(Y)≤F(M)≤F(C)<F(K)] is held in the image forming apparatus PR. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multifunction machine combining two or more of these.

  Various types of image forming apparatuses such as a copying machine, a printer, a facsimile machine, or a combination machine combining two or more of these are known. Among them, an intermediate transfer member and each color are assigned. An image forming apparatus having a plurality of image forming units capable of forming a toner image with toner is known.

  More specifically, the image forming apparatus includes: an intermediate transfer body that is rotationally driven; and a plurality of image forming units that are sequentially arranged from the upstream side to the downstream side in the running direction of the surface of the intermediate transfer body along the intermediate transfer body. The image forming unit includes a photosensitive member that is driven to rotate toward the intermediate transfer member, and forms an electrostatic latent image corresponding to the assigned color on the photosensitive member, and uses the assigned color toner for the electrostatic latent image. Development to form a toner image, and the toner image can be primarily transferred onto the intermediate transfer member by a primary transfer unit facing the photosensitive member with the intermediate transfer member interposed therebetween. The next transfer toner image is an image forming apparatus capable of secondary transfer to a recording medium by a secondary transfer unit.

  In this type of image forming apparatus, the toner image on the photosensitive member is primarily transferred onto the intermediate transfer member in a gap formed between the intermediate transfer member and the photosensitive member adjacent to the nip portion between the intermediate transfer member and the photosensitive member. The toner is scattered by the action of the electric field, which may reduce the image quality.

  In particular, toner scattering tends to occur when the assigned color toner image is primarily transferred to the intermediate transfer member in the downstream image forming unit between adjacent image forming units. This is because when the primary transfer toner image is already formed on the intermediate transfer member by the upstream image forming unit, the gap is wider than when there is no toner image, although the toner image is minute. Because.

  In addition, when slack occurs in the intermediate transfer member portion between the photoconductors, the gap adjacent to the nip portion between the intermediate transfer member and the photoconductor becomes larger, or the intermediate transfer member portion flutters due to the slackness, Again, toner scattering tends to occur mainly in front of the primary transfer nip portion on the downstream side.

  Looking at the prior art, regarding toner scattering, Japanese Patent Application Laid-Open No. 2008-76469 discloses that when a primary transfer toner image on an intermediate transfer member is secondarily transferred to a recording medium by a secondary transfer means, When the trailing edge moves away from the guide and enters the secondary transfer area, it is elastically restored to the intermediate transfer member side to touch the toner image on the intermediate transfer member, causing the toner to scatter or cause transfer deviation. In order to prevent this, the primary transfer toner image on the intermediate transfer member is transferred further downstream from the most downstream image forming unit but upstream from the position of the secondary transfer unit. It is described that pressing is performed by means for pressing to the side (for example, roller-type pressing means).

  Regarding the prevention of the looseness of the intermediate transfer member, for example, in Japanese Patent Laid-Open No. 2005-196007, (1) When the rotation of the photosensitive member is started, the phases of the plurality of photosensitive members are adjusted, thereby making it possible to perform photosensitive in the subsequent image formation. By preventing the occurrence of phase shift (speed difference) between bodies, or (2) by controlling the change of the order of the intermediate transfer belt drive motor and each photoreceptor drive motor at the time of starting and stopping of the photoreceptor, It describes the reduction of the speed difference between the intermediate transfer belt and the photoconductor, the speed difference between the photoconductors, and the like.

  Japanese Patent Laid-Open No. 2006-171334 detects the amount of color misregistration of a toner image on an intermediate transfer member, and based on the detection result, the rotational speed of a downstream photoconductor is made higher than the rotational speed of other photoconductors. It is described that the looseness of the intermediate transfer member is suppressed.

  Japanese Patent Laid-Open No. 2006-259551 discloses an image forming apparatus in which the intermediate transfer member described above is used as a recording medium carrier, the recording medium is supported on the intermediate transfer member, and each color toner image can be directly transferred to the recording medium. Based on the humidity in the image forming apparatus that affects the tension of the recording medium carrier, the operation of the driving means of each photoconductor and the driving means of the recording medium carrier is controlled, for example, each adjacent photoconductor In the meantime, it is described that the rotation speed of the downstream photoconductor is made larger than the rotation speed of the upstream photoconductor to prevent the recording medium carrier from slackening.

JP 2005-196007 A JP 2006-171334 A JP 2006-259551 A JP 2008-76469 A

However, as described in Japanese Patent Application Laid-Open No. 2008-76469, the intermediate transfer member and the photosensitive member are only exposed by pressing the toner image immediately before the secondary transfer further downstream from the most downstream image forming unit. The toner cannot be prevented from being scattered by the action of the primary transfer electric field in the gap formed between the intermediate transfer member and the photosensitive member adjacent to the nip portion with the member.
Further, as described in JP-A-2005-196007, JP-A-2006-171334, and JP-A-2006-259551, the intermediate transfer member and the photosensitive member can be obtained only by controlling the rotational speed of the photosensitive member. If the toner image slips and the intermediate transfer member flutters, the toner scattering cannot be prevented.

  Therefore, the present invention includes an intermediate transfer member that is rotationally driven, and a plurality of image forming units that are sequentially arranged from the upstream side to the downstream side in the running direction of the surface of the intermediate transfer member along the intermediate transfer member. Each image forming unit includes a photosensitive member that is rotated to face the intermediate transfer member, and forms an electrostatic latent image corresponding to the assigned color on the photosensitive member. A toner image is formed by developing the toner image, and the toner image can be primarily transferred onto the intermediate transfer member by a primary transfer member facing the photosensitive member with the intermediate transfer member interposed therebetween, The primary transfer toner image is an image forming apparatus capable of secondary transfer to a recording medium by a secondary transfer unit, and is adjacent to the nip portion between the intermediate transfer member and the photosensitive member and between the intermediate transfer member and the photosensitive member. The generated voids are suppressed to be small, and the toner image on the photosensitive member is primarily transferred onto the intermediate transfer member in the voids. And to provide an image forming apparatus which can prevent the toner scattered by the action of an electric field.

In order to solve the above problems, the present invention
An intermediate transfer member that is rotationally driven, and a plurality of image forming units that are sequentially arranged from the upstream side to the downstream side in the running direction of the surface of the intermediate transfer member along the intermediate transfer member. A photosensitive member that is driven to rotate toward the intermediate transfer member, and forms an electrostatic latent image corresponding to the assigned color on the photosensitive member, and develops the electrostatic latent image using the assigned color toner; A toner image is formed, and the toner image can be primarily transferred onto the intermediate transfer member by a primary transfer member facing the photoconductor with the intermediate transfer member interposed therebetween. Is an image forming apparatus that is secondarily transferred to a recording medium by a secondary transfer unit, and is downstream of adjacent image forming units upstream of the most downstream image forming unit among the plurality of image forming units. Intermediate transfer in the direction of the photoconductor by the primary transfer member facing the photoconductor of the side image forming unit The body pressing force is equal to or higher than the intermediate transfer member pressing force in the direction of the photosensitive member by the primary transfer member facing the photosensitive member of the upstream image forming unit, and the most downstream image forming unit and one upstream image forming thereof. Between the parts, the intermediate transfer member pressing force in the direction of the photosensitive member by the primary transfer member facing the photoreceptor of the most downstream image forming unit is caused by the primary transfer member facing the photoreceptor of the upstream image forming unit. An image forming apparatus having an intermediate transfer member pressing force in the direction of a photoconductor is provided.

  In the image forming apparatus according to the present invention, the primary transfer member that faces the photoreceptor of the downstream image forming unit between the adjacent image forming units on the upstream side of the most downstream image forming unit among the plurality of image forming units. The intermediate transfer member pressing force in the direction of the photoconductor is set to be equal to or higher than the intermediate transfer member pressing force in the direction of the photoconductor by the primary transfer member facing the photoconductor in the upstream image forming unit.

  Further, between the most downstream image forming unit and the upstream one image forming unit, an intermediate transfer member pressing force in the direction of the photosensitive member by the primary transfer member facing the photosensitive member of the most downstream image forming unit is generated. It is set to be larger than the pressing force of the intermediate transfer member in the direction of the photosensitive member by the primary transfer member facing the photosensitive member of the upstream image forming unit.

  Accordingly, the gap between the intermediate transfer member adjacent to the primary transfer nip portion between the photosensitive member and the intermediate transfer member in the downstream image forming unit between the adjacent image forming units is suppressed to be small, thereby The scattering of toner due to the primary transfer electric field in the air gap is suppressed, and as a result, the image quality can be improved accordingly.

  In the image forming apparatus according to the present invention, the rotation speed of the photosensitive member of the downstream image forming unit between the adjacent image forming units of the plurality of image forming units is the rotation speed of the photosensitive member of the upstream image forming unit. It is good also as above.

  By restricting the rotational speed of the photosensitive member in this way, it is possible to suppress the looseness of the intermediate transfer member portion between the photosensitive members by suppressing the looseness of the intermediate transfer member portion between the photosensitive members, and to suppress the flapping of the intermediate transfer member portion between the photosensitive members. Toner scattering can be suppressed, and the image quality as a whole can be further improved.

A typical example of the image forming apparatus according to the present invention is a tandem color image forming apparatus.
In any case, the intermediate transfer belt can be exemplified by an intermediate transfer belt.

  As described above, according to the present invention, the intermediate transfer member that is rotationally driven, and the plurality of image forming units that are sequentially arranged from the upstream side to the downstream side in the running direction of the surface of the intermediate transfer member along the intermediate transfer member. Each of the image forming units includes a photosensitive member that is rotationally driven to face the intermediate transfer member, and forms an electrostatic latent image corresponding to the assigned color on the photosensitive member. The image is developed with the toner of the assigned color to form a toner image, and the toner image is primarily transferred onto the intermediate transfer member by a primary transfer member facing the photosensitive member with the intermediate transfer member interposed therebetween. The primary transfer toner image can be secondarily transferred to a recording medium by a secondary transfer unit, and is an image forming apparatus that is adjacent to a nip portion between the intermediate transfer member and the photosensitive member. The gap formed between the photoconductor and the photoconductor is suppressed to be small, and the toner image on the photoconductor is formed in the gap. To between transfer member can suppress the toner scattered by the action of an electric field primary transfer, it is possible to provide an image forming apparatus capable of much improved image quality.

1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to the present invention. FIG. 6 is a diagram illustrating a state where toner scattering is suppressed as compared with the settings of Comparative Examples 1 and 2 according to the settings of Example 1 to Example 4. FIG. 6 is a diagram showing that toner scattering can be suppressed even when an intermediate transfer member having an elastic layer is employed.

Hereinafter, an example of an image forming apparatus according to the present invention will be described with reference to the drawings.
FIG. 1 schematically shows the configuration of an example PR of an image forming apparatus according to the present invention. The image forming apparatus PR is a tandem type full color printer.

  The printer PR includes a driving roller 81, a roller 82 facing the driving roller 81, and an endless intermediate transfer belt 8 wound around the rollers 83 and 84. The transfer belt 8 is rotated counterclockwise (arrow direction in the figure) CCW in the figure by a driving roller 81 driven by a belt driving unit (not shown).

  A cleaning device 85 for cleaning the secondary transfer residual toner, recording medium powder, and the like on the transfer belt 8 faces the roller 82. A secondary transfer roller 9 faces the driving roller 81 with the belt 8 therebetween. The toner or the like collected by the cleaning device 85 is sent to a waste container by a conveying means (not shown).

  The secondary transfer roller 9 is pressed against a portion of the intermediate transfer belt 8 supported by the drive roller 81 by a pressing unit (not shown), and forms a nip portion with the intermediate transfer belt 8. It can be rotated following the rotation or following the movement of the recording medium S fed into the nip portion as will be described later, or driven by a drive unit (not shown).

  A secondary transfer bias can be applied to the secondary transfer roller 9 from a power supply (not shown). In this example, the secondary transfer roller 9, the secondary transfer bias power source, and the like constitute secondary transfer means.

  A fixing device FX is disposed above the intermediate transfer belt 8 and the secondary transfer roller 9, a timing roller pair TR is disposed below, and a recording medium S such as recording paper is accommodated below the fixing device FX. The recording medium storage cassette 10 is disposed.

  The fixing device FX includes a fixing heating member (including but not limited to, a roller-type member) including a heat source such as a halogen lamp heater, and a pressure member (not limited thereto) that is in pressure contact with the fixing-heating member. ).

  The recording medium S accommodated in the recording medium accommodating cassette 10 can be pulled out one by one by the medium supply roller 101 and supplied to the timing roller pair TR.

  Between the rollers 83 and 84 around which the intermediate transfer belt 8 is wound, a yellow image is formed along the transfer belt 8 from the guide roller 83 closer to the opposing roller 82 toward the guide roller 84 closer to the drive roller 81. The part Y, the magenta image forming part M, the cyan image forming part C, and the black image forming part K are arranged in this order.

  Each of the image forming units Y, M, C, and K includes a drum-type photosensitive member 1 as an electrostatic latent image carrier, and a charger 2, an exposure device 3, a developing device 4 and the like around the photosensitive member. The cleaning devices 5 are arranged in this order.

  Further, the primary transfer member 6 is opposed to the photoreceptor 1 of each of the Y, M, C, and K image forming portions with the belt 8 interposed therebetween. In this example, the primary transfer member is a primary transfer roller, and can be driven and rotated by the belt 8.

  A primary transfer bias for primary transfer of the toner image formed on the photoreceptor 1 to the belt 8 can be applied to the primary transfer roller 6 from a power supply (not shown). In this example, the primary transfer roller 6, the primary transfer bias power source, and the like constitute primary transfer means.

  The exposure device 3 can perform image exposure by dot (point) exposure on the photosensitive member 1 by blinking of a laser beam in accordance with image information provided from a personal computer, an image reading device, a facsimile machine, etc. (not shown). .

The photoreceptor 1 in each image forming unit can be driven to rotate clockwise in the figure by a photoreceptor drive motor (not shown).
The charger 2 in each image forming unit is a scorotron charger in this example, and a charging voltage is applied from a power supply (not shown) at a predetermined timing. The charger 2 may be one using a charging roller.

  The developing device 4 in each image forming unit can reversely develop the electrostatic latent image formed on the photoreceptor 1 using a so-called two-component developer mainly composed of a magnetic carrier and toner. More specifically, the developing device 4 has a built-in magnet body and can develop a latent image with a developing sleeve 41 (in other words, a developing roller) in the form of a roller to which a developing bias is applied from a power supply (not shown).

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

  That is, in the yellow image forming portion Y, the photosensitive member 1 is rotated in the clockwise direction in the drawing, and the surface is uniformly charged to a predetermined potential by the charger 2, and the yellow region for the yellow image is transferred from the exposure device 3 to the charged area. Image exposure is performed, and a yellow electrostatic latent image is formed on the photoreceptor 1. This electrostatic latent image is developed by a developing sleeve 41 to which a developing bias of the developing device 4 having yellow toner is applied, and becomes a visible yellow toner image. The yellow toner image is primarily transferred onto the transfer belt 8 by the primary transfer roller 6. At this time, a primary transfer bias is applied to the primary transfer roller 6 from a power supply (not shown). At this time, the primary transfer roller 6 is pressed against the belt 8 by a roller pressing member (not shown) and is driven to rotate by the belt 8, so that the belt 8 and the photoreceptor 1 are in contact with each other.

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

Yellow, magenta, cyan, and black toner images are formed at the timing when these toner images are transferred onto the intermediate transfer belt 8.
Thus, the multiple toner image formed on the transfer belt 8 moves toward the secondary transfer roller 9 by the rotation of the transfer belt 8.

  On the other hand, the recording medium S is pulled out from the recording medium accommodating cassette 10 by the medium supply roller 101, supplied to the timing roller pair TR, and is on standby.

  Thus, the recording medium S waiting at the timing roller pair TR is supplied to the nip portion between the transfer belt 8 and the secondary transfer roller 9 in accordance with the multiple toner image sent by the intermediate transfer belt 8. . The multiple toner image is secondarily transferred onto the recording medium S by a secondary transfer roller 9 to which a secondary transfer bias is applied from a power supply (not shown).

  Thereafter, the recording medium S is passed through the fixing device FX, where the multiple toner images are fixed on the recording medium S under heat and pressure. The recording medium S is continuously discharged to the discharge tray DT by the discharge roller pair DR.

  In the primary transfer of the toner image to the belt 8, transfer residual toner or the like remaining on the photoreceptor 1 is cleaned by the cleaning device 5, and secondary transfer residual toner or the like remaining on the belt 8 by the secondary transfer is cleaned by the cleaning device 85. It is cleaned with. Each of these cleaned and removed toners is sent to a waste container by a conveying means (not shown).

  As described above, an image is formed. In the printer PR, the pressing force F of the intermediate transfer belt 8 in the direction of the photoconductor by the primary transfer roller 6 facing each photoconductor 1 is shown in Table 1 below. Set to any of Examples 1-4.

  Accordingly, the gap formed between the intermediate transfer member 8 and the photosensitive member 1 adjacent to the nip portion between the intermediate transfer member 8 and the photosensitive member 1 is suppressed to be small, and particularly on the downstream side between the adjacent image forming portions. It is possible to suppress the scattering of toner by suppressing the gap on the near side (upstream side) adjacent to the primary transfer nip portion formed between the photosensitive member 1 and the intermediate transfer member 8 to be small.

In the following description of the examples, etc.
F (Y) is the pressing force of the primary transfer roller 6 facing the photoreceptor 1 of the yellow image forming portion Y,
F (M) is the pressing force of the primary transfer roller 6 facing the photoreceptor 1 of the magenta image forming unit M,
F (C) is the pressing force of the primary transfer roller 6 facing the photoreceptor 1 of the cyan image forming section C,
F (K) is a pressing force of the primary transfer roller 6 facing the photosensitive member 1 of the black image forming portion K.

V (Y) is the rotational speed of the photoreceptor of the yellow image forming unit Y (in other words, the peripheral speed).
V (M) is the rotational speed of the photosensitive member of the magenta image forming unit M (in other words, the peripheral speed).
V (C) is the rotational speed of the photoreceptor of the cyan image forming section C (in other words, the peripheral speed).
V (K) is the rotational speed (in other words, peripheral speed) of the photosensitive member of the black image forming portion K.

(Table 1)
Transfer roller pressing force Photoconductor rotation speed
Example 1 F (Y) <F (M) <F (C) <F (K) V (Y) <V (M) <V (C) <V (K)
Example 2 F (Y) <F (M) <F (C) <F (K) V (Y) = V (M) = V (C) = V (K)
Example 3 F (Y) = F (M) = F (C) <F (K) V (Y) <V (M) <V (C) <V (K)
Example 4 F (Y) = F (M) = F (C) <F (K) V (Y) = V (M) = V (C) = V (K)
When the pressing force of the primary transfer roller 6 of Examples 1 to 4 is collectively shown,
F (Y) ≤ F (M) ≤ F (C) <F (K)
In summary of the photoconductor rotation speed,
V (Y) ≦ V (M) ≦ V (C) ≦ V (K).

Table 2 below shows specific examples of the pressing force and rotation speed of the primary transfer roller 6 shown in Table 1.
Here, the pressing force of the transfer roller 6 is the pressing force at the center of the primary transfer nip.
(Table 2)
F (Y) F (M) F (C) F (K) V (Y) V (M) V (C) V (K)
Example 1 5.452 5.854 6.256 6.792 216 218.16 220.32 222.48
Example 2 5.452 5.854 6.256 6.792 216 216 216 216
Example 3 5.452 5.452 5.452 6.256 216 218.16 220.32 222.48
Example 4 5.452 5.452 5.452 6.256 216 216 216 216
Pressing force: Unit [N]
Photoreceptor rotation speed: Unit [mm / sec]

  In the printer PR of the type shown in FIG. 1, the pressing force of the transfer roller 6 and the rotational speed of the photosensitive member are set as shown in Table 2, and a circular image is formed on the intermediate transfer belt 8 under the same image forming conditions. .

In image formation, the pressing force and rotation speed of each of Examples 1 to 4 are set.
Two-color superimposed image of yellow (Y) image and magenta (M) image,
Three-color superimposed image of Y, M and cyan (C) images,
Four-color superimposed images of Y, M, C, and black (K) were formed.

  Then, the outer peripheral length L is measured for each of the two-color superimposed image, the three-color superimposed image, and the four-color superimposed image, and the degree of circularity is obtained from the ratio of the outer peripheral length L ′ of the perfect circle calculated from the area, thereby scattering toner. evaluated. If (L ′ / L) = 1, the circularity is 1, and the formed superimposed image is a target perfect circle, which indicates that toner scattering is sufficiently suppressed.

  FIG. 2 shows the circularity of the two-color superimposed image, the three-color superimposed image, and the four-color superimposed image formed under the respective settings of Examples 1 to 4.

  For comparison, the pressing force of the transfer roller 6 and the rotational speed of the photosensitive member were set as shown in Table 3 below, and the pressing force and the rotational speed of the photosensitive member shown in Table 4 were set as specific examples.

(Table 3)
Transfer roller pressing force Photoconductor rotation speed
Comparative Example 1 F (Y) = F (M) = F (C) = F (K) V (Y) = V (M) = V (C) = V (K)
Comparative Example 2 F (Y)> F (M) = F (C)> F (K) V (Y) = V (M) = V (C) = V (K)

(Table 4)
F (Y) F (M) F (C) F (K) V (Y) V (M) V (C) V (K)
Comparative Example 1 5.452 5.452 5.452 5.452 216 216 216 216
Comparative Example 2 6.792 5.854 5.854 5.452 216 216 216 216
Pressing force: Unit [N]
Photoreceptor rotation speed: Unit [mm / sec]

  Under the settings of Comparative Example 1 and Comparative Example 2 shown in Table 4, a two-color superimposed image, a three-color superimposed image, and a four-color superimposed image are formed in the same manner as in Examples 1 to 4, Circularity was evaluated. The result is also shown in FIG.

  The image formation in each of the above example settings and comparative example settings was performed by using a resin belt (here, a polyimide belt) as the intermediate transfer belt 8 and setting the belt traveling speed to 216 mm / second.

  From the circularity evaluation shown in FIG. 2, the nip portion between the intermediate transfer member 8 and the photosensitive member 1 is set by setting the pressing force of the primary transfer roller as in the present invention, or further setting the rotational speed of the photosensitive member. It can be seen that the gap between the intermediate transfer member 8 and the photosensitive member 1 adjacent to each other can be suppressed to be small and toner scattering can be suppressed.

  The circularity evaluation shown in FIG. 2 was the case where the intermediate transfer belt 8 did not have an elastic layer as described above, but even when the intermediate transfer belt has an elastic layer on the photosensitive member side, There is a similar toner scattering suppression effect.

  A belt having an elastic rubber layer formed on the photoconductor side of the resin belt main body is employed as the intermediate transfer belt 8, and 3 as described above under the same settings as those in Examples 1 to 4 and Comparative Examples 1 and 2. Three types of color superimposed images were formed and their circularity was evaluated, and the results shown in FIG. 3 were obtained. From FIG. 3, it can be seen that even when the intermediate transfer belt has an elastic layer on the photoconductor side, the same toner scattering suppression effect is obtained.

  2 and 3, it can be seen that toner scattering can be suppressed most by increasing the transfer roller pressing force and the photosensitive member rotation speed in the downstream direction as in the first embodiment.

  In consideration of the cost, as in the fourth embodiment, the transfer roller pressing force at the most downstream image forming unit (here, the black image forming unit K) is set to be larger than that of the other image forming units. However, it can be seen that toner scattering can be suppressed.

  The image forming apparatus of FIG. 1 described above is a printer, but the present invention can be applied to any image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine combining two or more of these.

  The present invention is an image forming apparatus capable of forming an image using an intermediate transfer member and a plurality of image forming units sequentially arranged along the intermediate transfer member, and a primary transfer between the intermediate transfer member and a photosensitive member. The present invention can be used to provide an image forming apparatus that can suppress the gap adjacent to the nip portion to be small and suppress the scattering of toner due to the primary transfer electric field in the gap.

PR Printer Y Yellow image forming unit M Magenta image forming unit C Cyan image forming unit K Black image forming unit 1 Photoconductor 2 Charger 3 Image exposing device 4 Developing device 41 Developing sleeve 5 Cleaning device 6 Primary transfer roller 8 Intermediate transfer belt 81 Driving roller 82 Opposing rollers 83 and 84 Guide roller 83 Cleaning device 9 Secondary transfer roller 10 Recording medium supply cassette 101 Recording medium supply roller TR Timing roller pair FX Fixing device DR Recording medium discharge roller pair DT Recording medium discharge tray S Recording medium

Claims (3)

  An intermediate transfer member that is rotationally driven, and a plurality of image forming units that are sequentially arranged from the upstream side to the downstream side in the running direction of the surface of the intermediate transfer member along the intermediate transfer member. A photosensitive member that is driven to rotate toward the intermediate transfer member, and forms an electrostatic latent image corresponding to the assigned color on the photosensitive member, and develops the electrostatic latent image using the assigned color toner; A toner image is formed, and the toner image can be primarily transferred onto the intermediate transfer member by a primary transfer member facing the photoconductor with the intermediate transfer member interposed therebetween. Is an image forming apparatus that is secondarily transferred to a recording medium by a secondary transfer unit, and is downstream of adjacent image forming units upstream of the most downstream image forming unit among the plurality of image forming units. Intermediate transfer in the direction of the photoconductor by the primary transfer member facing the photoconductor of the side image forming unit The body pressing force is equal to or higher than the intermediate transfer member pressing force in the direction of the photosensitive member by the primary transfer member facing the photosensitive member of the upstream image forming unit, and the most downstream image forming unit and one upstream image forming thereof. Between the parts, the intermediate transfer member pressing force in the direction of the photosensitive member by the primary transfer member facing the photoreceptor of the most downstream image forming unit is caused by the primary transfer member facing the photoreceptor of the upstream image forming unit. An image forming apparatus having a pressure greater than an intermediate transfer member pressing force in a direction of a photosensitive member.   2. The image forming apparatus according to claim 1, wherein the rotation speed of the photosensitive member of the downstream image forming unit is equal to or higher than the rotation speed of the photosensitive member of the upstream image forming unit between adjacent image forming units of the plurality of image forming units.   3. The image forming apparatus according to claim 1, wherein the image forming apparatus is a tandem type color image forming apparatus.

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