JP2010164797A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To form an image suppressive in color smear, in an image forming apparatus which forms an image by using an intermediate transfer body and a plurality of image forming parts successively arranged along the intermediate transfer body. <P>SOLUTION: The image forming apparatus PR includes the intermediate transfer body 8, and the plurality of image forming parts Y, M, C and K successively 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, a dynamic friction coefficient of a photoreceptor in the downstream side image forming part is equal to or above a dynamic friction coefficient of a photoreceptor 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 dynamic friction coefficient μ(K) of the photoreceptor 1 in the most downstream side image forming part K is larger than a dynamic friction coefficient μ(C) of the photoreceptor in the upstream side image forming part C, that is, [μ(Y)≤μ(M)≤μ(C)<μ(K)] is held. <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 intermediate transfer member may flutter between the photosensitive members due to slack in the intermediate transfer member between the photosensitive members, or the intermediate transfer member may slip with respect to the photosensitive member. In addition, color misregistration may occur between the color toner images that are primarily transferred onto the intermediate transfer member, and the image quality may deteriorate.

  Regarding countermeasures against color misregistration, for example, Japanese Patent Laid-Open No. 2005-196007 discloses (1) Phase alignment between a plurality of photoconductors in a short time when rotation of the photoconductor is performed, and thereby a photoconductor in continuous image formation. Prevent color misregistration due to phase shift (speed difference) between them, and (2) phase alignment between multiple photoconductors when stopping the photoconductor, Reduces speed fluctuation due to phase alignment, reduces the speed difference between the photoconductor and the intermediate transfer body to further prevent color misregistration. (3) When the photoconductor is started and stopped, the intermediate transfer belt drive motor and each It is described that the color difference is prevented by reducing the speed difference between the intermediate transfer belt and the photoconductor and the speed difference between the photoconductors by changing and controlling the order of the photoconductor drive motors appropriately.

  Japanese Patent Laid-Open No. 2006-171334 detects the color misregistration amount of the toner image on the intermediate transfer member, and based on the detection result, the rotational speed of the downstream photoconductor is determined from the rotational speed of the other photoconductors. It is described to increase.

  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

  However, as described in JP-A-2005-196007, JP-A-2006-171334, and JP-A-2006-259551, the intermediate transfer member and the photosensitive member are merely controlled by controlling the rotational speed of the photosensitive member. If the toner image slips and the intermediate transfer member flutters, the color shift of the toner image on the intermediate transfer member cannot be suppressed.

  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. The toner image is developed 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 primary transfer toner image is an image forming apparatus that can be secondarily transferred to a recording medium by a secondary transfer unit, and the intermediate transfer member is moved between the photosensitive members due to a large slack in the intermediate transfer member portion between the photosensitive members. This may cause flapping or a large slip between the intermediate transfer member and the photoconductor. Color shift among the toner images are primarily transferred onto the intermediate transfer member occurs, image quality and to provide an image forming apparatus which can prevent the lowered through.

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 unit facing the photoconductor with the intermediate transfer member interposed therebetween. Is an image forming apparatus capable of performing secondary transfer onto a recording medium by a secondary transfer unit, and among the plurality of image forming units, on the upstream side of the most downstream image forming unit, between the adjacent image forming units on the downstream side dynamic friction coefficient with respect to the intermediate transfer member of the photosensitive member of the image forming portion of the upstream image forming section And a dynamic friction coefficient than the intermediate transfer member of the optical element, between the image forming portion of the most downstream side image forming unit One upstream, the dynamic friction coefficient with respect to the intermediate transfer member of the photosensitive member of the most downstream side image forming unit is upstream An image forming apparatus having a coefficient of dynamic friction with respect to an intermediate transfer member of a photoconductor of a side image forming unit is provided.

  In the image forming apparatus according to the present invention, the dynamic friction coefficient of the downstream image forming unit with respect to the intermediate transfer member between the adjacent image forming units upstream of the most downstream image forming unit among the plurality of image forming units. Is set to be equal to or greater than the dynamic friction coefficient of the photosensitive member of the upstream image forming unit with respect to the intermediate transfer member, and the most downstream image forming unit between the most downstream image forming unit and one upstream image forming unit. The dynamic friction coefficient of the photosensitive member with respect to the intermediate transfer member is set to be larger than the dynamic friction coefficient of the photosensitive member of the upstream image forming unit with respect to the intermediate transfer member.

  Accordingly, the intermediate transfer member portion between the adjacent photoconductors is pulled to the downstream side so that the occurrence of slack, and the occurrence of fluttering due to the slack, is suppressed, and the contact between each photoconductor and the intermediate transfer member. The slip of the intermediate transfer member with respect to the photosensitive member at the nip portion is suppressed, the color shift between the toner images on the intermediate transfer member is suppressed accordingly, and the image quality is 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, component tolerances on the circumference of the intermediate transfer member, elongation of the intermediate transfer member due to changes over time, and dimensional tolerances of the members supporting the intermediate transfer member (for example, belt form) The outer diameter tolerance of the roller that supports the intermediate transfer member), the intermediate transfer member and the support member may slip due to slippage between the intermediate transfer member and the support member. As a whole, the occurrence of color misregistration can be further suppressed.

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 primary-transferred onto the intermediate transfer member by a primary transfer unit 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 means, and a large slack is generated in an intermediate transfer member portion between the photosensitive members. The intermediate transfer member flutters between them, or a large slip is formed between the intermediate transfer member and the photosensitive member. And or cause, these by color shift occurs between the respective color toner images are primarily transferred onto the intermediate transfer member, the image quality can be provided an image forming apparatus which can prevent the lowered.

1 is a diagram schematically illustrating a configuration of an example of an image forming apparatus according to the present invention. FIG. 3 is a diagram illustrating a state where color misregistration is suppressed in the first embodiment. FIG. 10 is a diagram illustrating a state where color misregistration is suppressed in the second embodiment. FIG. 10 is a diagram illustrating a state in which color misregistration is suppressed in Example 3. It is a figure which shows the state by which the color shift is suppressed in Example 4. FIG. It is a figure which shows the state in which the color shift which cannot be permitted in the comparative example 1 has generate | occur | produced. It is a figure which shows the state in which the color shift which cannot be permitted in the comparative example 2 has generate | occur | produced.

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 by following the rotation, following the movement of the recording medium S fed into the nip portion as 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 dynamic friction coefficient of each photoconductor 1 with respect to the intermediate transfer belt 8 and the rotational speed of each photoconductor are any one of Examples 1 to 4 shown in Table 1 below. Accordingly, color misregistration between the color toner images transferred onto the transfer belt 8 is suppressed.

In the following description of the examples, etc.
μ (Y) is a coefficient of dynamic friction of the photoreceptor of the yellow image forming portion Y,
μ (M) is a coefficient of dynamic friction of the photoconductor of the magenta image forming unit M,
μ (C) is a coefficient of dynamic friction of the photoreceptor of the cyan image forming unit C,
μ (K) is a dynamic friction coefficient of the photosensitive member 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)
Photoconductor dynamic friction coefficient Photoconductor rotation speed
Example 1 μ (Y) <μ (M) <μ (C) <μ (K) V (Y) <V (M) <V (C) <V (K)
Example 2 μ (Y) <μ (M) <μ (C) <μ (K) V (Y) = V (M) = V (C) = V (K)
Example 3 μ (Y) = μ (M) = μ (C) <μ (K) V (Y) <V (M) <V (C) <V (K)
Example 4 μ (Y) = μ (M) = μ (C) <μ (K) V (Y) = V (M) = V (C) = V (K)
The photoreceptor dynamic friction coefficients of Examples 1 to 4 are collectively shown as follows:
μ (Y) ≦ μ (M) ≦ μ (C) <μ (K),
In summary of the photoconductor rotation speed,
V (Y) ≦ V (M) ≦ V (C) ≦ V (K).

Table 2 below shows specific examples of the dynamic friction coefficient and the rotational speed of the photoreceptor shown in Table 1.
(Table 2)
μ (Y) μ (M) μ (C) μ (K) V (Y) V (M) V (C) V (K)
Example 1 0.6 0.8 1.0 1.4 216 232 248 264
Example 2 0.6 0.8 1.0 1.0 216 216 216 216
Example 3 0.8 0.8 0.8 1.0 216 232 248 264
Example 4 0.8 0.8 0.8 1.0 216 216 216 216
Photoconductor rotation speed: mm / second

  In the printer PR of the type shown in FIG. 1, the dynamic friction coefficient of the photosensitive member and the rotational speed of the photosensitive member are set as shown in Table 2, and the others are used for detecting color misregistration of each color on the intermediate transfer belt 8 under the same image forming conditions. The image position formed by the black image forming unit K was used as a reference, and the yellow image shift amount, the magenta image shift amount, and the cyan image shift amount from the reference position were measured. .

The measurement results are shown in FIGS. 2 shows the results of Example 1, FIG. 3 shows the results of Example 2, FIG. 4 shows the results of Example 3, and FIG. 5 shows the results of Example 4.
2 to 5, the vertical axis represents the color misregistration amount [μm], and the horizontal axis represents the measurement position [mm].

For comparison, the dynamic friction coefficient of each photoconductor 1 with respect to the intermediate transfer belt 8 and the rotational speed of each photoconductor are set as in Comparative Examples 1 and 2 shown in Tables 3 and 4 below where the present invention is not applied. Images were formed in the same manner as in Examples 1 to 4, and the amount of color misregistration was measured. The measurement results are shown in FIGS. 6 shows the result of Comparative Example 1, and FIG. 7 shows the result of Comparative Example 2.
6 and 7, the vertical axis represents the color misregistration amount [μm], and the horizontal axis represents the measurement position [mm].

(Table 3)
Photoconductor dynamic friction coefficient Photoconductor rotation speed
Comparative Example 1 μ (Y) = μ (M) = μ (C) = μ (K) V (Y) = V (M) = V (C) = V (K)
Comparative Example 2 μ (Y)> μ (M) = μ (C)> μ (K) V (Y) = V (M) = V (C) = V (K)

(Table 4)
μ (Y) μ (M) μ (C) μ (K) V (Y) V (M) V (C) V (K)
Comparative Example 1 1.0 1.0 1.0 1.0 216 216 216 216
Comparative Example 2 1.4 1.0 1.0 0.8 216 216 216 216
Photoconductor rotation speed: mm / second

Such a dynamic friction coefficient in each example and each comparative example can be set by adjusting one or more of the surface energy, surface roughness, surface hardness and the like of the photoreceptor 1. Here, each dynamic friction coefficient was set by adjusting the surface energy.
In both the examples and the comparative examples, the amount of color misregistration was measured with a measuring instrument (Haydon Tribogear type 94) manufactured by Shinto Kagaku Co., Ltd.
Further, a resin belt (here, a polyimide belt) was used as the intermediate transfer belt 8, and the belt running speed was set to 216 mm / second.

  From these measurement results, the color friction between the color toner images transferred onto the belt 8 is suppressed by setting the dynamic friction coefficient of the photoconductor as in the present invention or by further setting the rotation speed of the photoconductor. I understand that I can do it.

  As can be seen from a comparison of FIGS. 2 to 5, the color shift can be most suppressed by sequentially increasing the dynamic friction coefficient and the rotational speed of the photoconductor in the downstream image forming unit as in the first embodiment. Recognize.

  In consideration of the cost, as in the fourth embodiment, only the dynamic friction coefficient of the photosensitive member of the image forming unit (here, the black image forming unit K) on the most downstream side is used as the dynamic friction coefficient of the photosensitive member of the other image forming unit. It can be seen that color misregistration can be suppressed only by setting a larger value.

  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 body, and capable of forming an image with suppressed color misregistration. Can be used to provide.

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 unit facing the photoconductor with the intermediate transfer member interposed therebetween. Is an image forming apparatus capable of performing secondary transfer onto a recording medium by a secondary transfer unit, and among the plurality of image forming units, on the upstream side of the most downstream image forming unit, between the adjacent image forming units on the downstream side The dynamic friction coefficient of the photosensitive member of the image forming unit with respect to the intermediate transfer member is The dynamic friction coefficient of the photoconductor with respect to the intermediate transfer member is equal to or greater than the dynamic friction coefficient of the photoconductor between the most downstream image forming portion and the upstream upstream image forming portion. An image forming apparatus having a coefficient of dynamic friction with respect to an intermediate transfer member of a photoconductor of a side image forming unit.   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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