Image forming apparatus

Abstract

To provide static eliminating means that stably eliminates the charged electric potential of a recording material even if the position of the recording material downstream of a secondary transfer unit is changed due to a change in the attitude of a belt surface upstream of the secondary transfer unit.SOLUTION: An image forming apparatus comprises: belt surface attitude changing means that can change the attitude of a belt surface upstream of a secondary transfer unit; a static eliminating member 31 that is arranged downstream of the secondary transfer unit; and a static eliminating support member 63 that supports the static eliminating member. The image forming apparatus changes a static eliminating bias applied to the static eliminating member 31 according to the attitude of the belt controlled by the belt surface changing means. Alternatively, the image forming apparatus changes the position of the static eliminating member to make constant the distance between a recording material and the static eliminating member.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to an electrophotographic apparatus using an electrophotographic process such as a copying machine, a printer, a facsimile machine, etc.

Background Art

[0002] In recent years, in image forming apparatuses using an electrophotographic method or the like, it has been demanded to form high-quality images on various recording materials. An image forming apparatus of an intermediate transfer system having an intermediate transfer belt which is an intermediate transfer member composed of an endless belt will be described as an example.

[0003] Recording materials with low surface smoothness are generally difficult to transfer the toner image on the intermediate transfer belt. When there are irregularities of several tens of micrometers or more on the surface of the recording material, for example, even in a configuration where a secondary transfer bias is applied while pressing with a secondary transfer member composed of a conductive rubber roller or the like, in the recessed portion of the recording material, the intermediate transfer belt and the recording material cannot sufficiently contact and voids are likely to be formed. Then, when a secondary transfer bias is applied, discharge may occur in the portion where the voids are formed. When the toner image on the intermediate transfer belt is subjected to discharge in the vicinity of a secondary transfer portion (secondary transfer nip) formed by the intermediate transfer belt and the secondary transfer member, the toner of the toner image is discharged or charged, and the charge amount distribution of the toner is broadened, resulting in impaired transferability. As a result, a part of the toner image on the intermediate transfer belt may not be properly transferred ("transfer omission"). Further, when the adhesion between the recording material and the intermediate transfer belt is impaired, the charge amount distribution of the toner on the intermediate transfer belt collapses due to the discharge received in the vicinity of the secondary transfer portion, and the number of toners that do not follow the electrostatic force acting on the secondary transfer portion increases, resulting in impaired transferability to the recording material.

[0004] To address these challenges, it is effective to provide a support member that holds the intermediate transfer belt in place from the inner circumferential surface to the outer circumferential surface near the upstream side of the secondary transfer section in the rotational direction of the intermediate transfer belt (Patent Document 1). By stabilizing the contact between the intermediate transfer belt and the recording material near the upstream side of the secondary transfer section with the above support member, discharge near the upstream side of the secondary transfer section is suppressed.

[0005] However, as mentioned above, if the intermediate transfer belt is held down by the support member near the upstream side of the secondary transfer section, the toner image may be distorted due to strong friction between the recording material and the intermediate transfer belt at the point where the support member is in contact with the inner surface of the intermediate transfer belt.

[0006] In other words, at the point where the support member is in contact with the inner surface of the intermediate transfer belt, the toner image is supported on the intermediate transfer belt. Because this toner image is supported on the intermediate transfer belt with relatively weak force, it is easily disturbed when force is applied. When the recording material and the intermediate transfer belt rub strongly at a point where the toner image is supported in this state, the toner image on the intermediate transfer belt is disturbed, causing the toner image on the recording material after transfer to be disturbed, resulting in "image distortion." This image distortion tends to occur more easily as the contact pressure between the recording material and the intermediate transfer belt near the upstream side of the secondary transfer section increases. Furthermore, when the intermediate transfer belt is held down by the support member, the contact pressure between the recording material and the intermediate transfer belt near the upstream side of the secondary transfer section increases compared to when there is no support member. Therefore, this image distortion is more likely to occur when the intermediate transfer belt is held down by the support member.

[0007] Furthermore, the contact pressure tends to increase as the basis weight of the recording material increases. This is because the rigidity of the recording material increases as the basis weight increases. Therefore, the image distortion described above tends to be more pronounced when forming an image on thick cardboard with a high basis weight.

[0008] Through our research, we have demonstrated that by controlling the orientation of the intermediate transfer belt surface using multiple positions of the support member placed near the upstream side of the secondary transfer section, we can satisfy the transfer performance requirements for various recording materials. [Prior art documents] [Patent Documents]

[0009] [Patent Document 1] Japanese Patent Publication No. 2007-57715 [Overview of the project] [Problems that the invention aims to solve]

[0010] On the other hand, when the optimal support member position is changed according to the recording material and the belt posture upstream of the secondary transfer section is controlled, differences occur in the paper discharge position and angle downstream of the secondary transfer. This difference is particularly pronounced in the high-rigidity cardboard range. As a result, when the distance between the static elimination needle placed downstream of the secondary transfer and the recording material is large, the static elimination effect on the paper's charge potential may be small, leading to the problem of image defects (toner scattering) occurring in the image formation process downstream of the transfer due to the recording material discharging between members with a potential difference.

[0011] With the recent expansion of supported media specifications, there is a demand for output across a wide range of materials, from thin paper with low rigidity to thick paper with high rigidity, and also for surface smoothness, as well as high-speed output. As a result, the required potential in the secondary transfer section increases in proportion to the production speed, and the above-mentioned challenges have become apparent.

[0012] The objective of the present invention is to propose an image forming apparatus that enables stable image formation even when the paper discharge position changes according to the belt position upstream of the secondary transfer section. [Means for solving the problem]

[0013] To achieve the above objective, the image forming apparatus according to claim 1 comprises a belt surface orientation changing means capable of changing the belt surface orientation upstream of the secondary transfer, a static elimination member 31 disposed downstream of the secondary transfer section, and a static elimination support member 63 that supports the static elimination member, wherein the static elimination bias applied to the static elimination member 31 is changed according to the belt orientation controlled by the belt surface changing means, or the position of the static elimination member is changed to keep the distance between the recording material and the static elimination member constant. [Effects of the Invention]

[0014] According to the present invention, by changing the voltage supplied to the static elimination member or the position of the static elimination member according to the position of the support member for adjusting the belt posture of the secondary transfer section and the recording material information, it is possible to stabilize the static elimination capability of the paper potential. [Brief explanation of the drawing]

[0015] [Figure 1] This is a schematic cross-sectional view of an image forming apparatus. [Figure 2] This is a schematic cross-sectional view of the vicinity of the secondary transfer region. [Figure 3] This is a schematic block diagram showing the control configuration of the main components of an image forming apparatus. [Figure 4] This is a schematic cross-sectional view illustrating the contact between the recording material and the belt upstream of the secondary transfer section. [Figure 5] This graph illustrates the difference in contact pressure between the recording material and the intermediate transfer belt due to differences in the position of the backup roller. [Figure 6] This graph illustrates the difference in recording material orientation downstream of secondary transfer due to differences in the position of the backup roller. [Figure 7] This is an explanatory diagram showing the paper potential measurement results downstream of the transport guide in Example 1. [Figure 8] This is a flowchart illustrating the control of Example 1. [Figure 9] This is a perspective view showing the secondary transfer outer roller and static elimination unit of Example 2. [Figure 10]It is a schematic cross-sectional view of the secondary transfer unit and the charge removal unit of Example 2. [Figure 11] It is an explanatory diagram showing the paper potential measurement results downstream of the transport guide in Example 2. [Figure 12] It is a flowchart of the control in Example 2. [Figure 13] It is a configuration explanatory diagram of the secondary transfer unit in Example 3. [Embodiment for Carrying out the Invention]

[0016] Hereinafter, embodiments will be given to specifically explain the present invention. Note that although these embodiments are examples of the best embodiments in the present invention, the present invention is not limited by these embodiments.

[0017] In this embodiment, only the main parts related to the formation / transfer of the toner image will be described, but the present invention can be implemented in various applications such as printers, various printing machines, copiers, FAX machines, multifunction machines, etc., by adding necessary devices, equipment, and housing structures.

[0018] [<Image Forming Apparatus and Image Forming Unit>] [Example 1] [Overall Configuration and Operation of the Image Forming Apparatus] FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a tandem type multifunction machine (having the functions of a copier, a printer, and a facsimile apparatus) that can form a full-color image using the electrophotographic method and adopts an intermediate transfer method.

[0019] The image forming apparatus 100 has a plurality of image forming sections, which are the first, second, third, and fourth image forming units UY, UM, UC, and UK, respectively, which form images of yellow (Y), magenta (M), cyan (C), and black (K). Elements having the same or corresponding functions or configurations in each image forming unit UY, UM, UC, and UK may be described collectively by omitting the Y, M, C, and K at the end of the symbols indicating that they are elements for one of the colors. The image forming unit U is composed of a photosensitive drum 101, a charging roller 102, an exposure device 103, a developing device 104, a primary transfer roller 105, a drum cleaning device 106, and the like, which will be described later.

[0020] The image forming unit U has a photosensitive drum 101, which is a rotatable drum-shaped (cylindrical) photoreceptor (electrophotographic photoreceptor), as a first image carrier. The photosensitive drum 101 is driven to rotate at a predetermined peripheral speed in the direction of arrow R1 in the figure. The surface of the rotating photosensitive drum 101 is uniformly charged to a predetermined potential of a predetermined polarity (negative polarity in this embodiment) by a charging roller 102, which is a roller-type charging member acting as a charging means. The charged surface of the photosensitive drum 101 is scanned and exposed by an exposure device (laser scanner) 103, which acts as an exposure means, and an electrostatic image (electrostatic latent image) is formed on the photosensitive drum 101. The electrostatic image formed on the photosensitive drum 101 is developed (visualized) by a developing device 104, which acts as a developing means, when toner is supplied as a developer, and a toner image (developer image) is formed on the photosensitive drum 101. In this embodiment, toner charged with the same polarity as the charging polarity of the photosensitive drum 101 (negative polarity in this embodiment) adheres to the exposure area (image area) on the photosensitive drum 101, where the absolute value of the potential has decreased after uniform charging treatment and exposure.

[0021] Opposite the four photosensitive drums 101 is an intermediate transfer belt 1, which is a rotatable intermediate transfer body composed of an endless belt and serves as a second image carrier. The intermediate transfer belt 1 is stretched and tensioned by a plurality of tension rollers: drive rollers 11, tension rollers 12, idler rollers 13, and secondary transfer inner rollers 14. The intermediate transfer belt 1 is driven by the drive rollers 11 and rotates (circulates) at a predetermined peripheral speed in the direction of arrow R2 in the figure. On the inner circumferential surface side of the intermediate transfer belt 1, a primary transfer roller 105, which is a roller-type primary transfer member serving as a primary transfer means, is arranged corresponding to each photosensitive drum 101. The primary transfer roller 105 is biased toward the photosensitive drum 101 via the intermediate transfer belt 1, forming a primary transfer section (primary transfer nip) T1 where the photosensitive drum 101 and the intermediate transfer belt 1 come into contact. As described above, the toner image formed on the photosensitive drum 101 is first transferred in the primary transfer section T1 onto the rotating intermediate transfer belt 1 by the action of the primary transfer roller 105.

[0022] During the primary transfer process, a primary transfer bias (primary transfer voltage), which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner (the charging polarity of the toner during development), is applied to the primary transfer roller 105 by a primary transfer power supply (high voltage power supply circuit) (not shown). For example, when forming a full-color image, the toner images of each color, Y, M, C, and K, formed on each photosensitive drum 101 are sequentially primary transferred in each primary transfer section T1 so as to be superimposed onto the intermediate transfer belt 1.

[0023] On the outer circumferential surface of the intermediate transfer belt 1, a roller-type secondary transfer member, the secondary transfer outer roller 2, is positioned opposite the secondary transfer inner roller 14 as a secondary transfer means. The secondary transfer outer roller 2 is biased toward the secondary transfer inner roller 14 via the intermediate transfer belt 1, forming a secondary transfer section (secondary transfer nip) T2 where the intermediate transfer belt 1 and the secondary transfer outer roller 2 come into contact. As described above, the toner image formed on the intermediate transfer belt 1 is secondarily transferred in the secondary transfer section T2 to a recording material (recording medium, sheet) P such as paper, which is held and transported between the intermediate transfer belt 1 and the secondary transfer outer roller 2 by the action of the secondary transfer outer roller 2. In this embodiment, during the secondary transfer process, a secondary transfer bias (secondary transfer voltage), which is a DC voltage with the opposite polarity (positive polarity in this embodiment) to the normal charging polarity of the toner, is applied to the secondary transfer outer roller 2 by a secondary transfer power supply (high voltage power supply circuit) 20.

[0024] The recording material P is fed out one sheet at a time from cassettes 7a to 7c, which serve as recording material storage units, by pickup rollers 8a to 8c, which serve as feeding members, and is transported by transport rollers (pairs of transport rollers) (not shown), which serve as transport members. Subsequently, the recording material P is transported to the secondary transfer unit T2 by a resist roller (pair of resist rollers) 5, which serve as transport members, in time with the toner image on the intermediate transfer belt 1. In the transport direction of the recording material P, a transport guide 6 is provided downstream of the resist roller 5 and upstream of the secondary transfer unit T2 to guide the recording material P to the secondary transfer unit T2. The transport guide 6 consists of a first guide member 61 that can contact the front surface of the recording material P (the surface on which the toner image is transferred immediately after passing through the transport guide 6), and a second guide member 62 that can contact the back surface of the recording material P (the surface opposite to the front surface). The first guide member 61 and the second guide member 62 are arranged opposite each other, and the recording material P passes between these two members. The first guide member 61 restricts the movement of the recording material P toward the intermediate transfer belt 1. The second guide member 62 restricts the movement of the recording material P toward the intermediate transfer belt 1.

[0025] The recording material P onto which the toner image has been transferred is transported to a fixing device 108, which serves as a fixing means. The fixing device 108 heats and pressurizes the recording material P carrying the unfixed toner image, thereby fixing (melting and solidifying) the toner image onto the recording material P. The recording material P with the fixed toner image is discharged (output) to the outside of the main body of the image forming apparatus 100 by discharge rollers (discharge roller pair) or the like (not shown).

[0026] Furthermore, toner that remains on the photosensitive drum 101 during the primary transfer process without being transferred to the intermediate transfer belt 1 (primary transfer residue toner) is removed and recovered from the photosensitive drum 101 by the drum cleaning device 106, which serves as a photoreceptor cleaning means. In addition, a belt cleaning device 107, which serves as an intermediate transfer body cleaning means, is positioned on the outer circumferential surface of the intermediate transfer belt 1, opposite the drive roller 11. Toner that remains on the intermediate transfer belt 1 without being transferred to the recording material P during the secondary transfer process (secondary transfer residue toner) and paper dust are removed and recovered from the intermediate transfer belt 1 by the belt cleaning device 107.

[0027] Here, the intermediate transfer belt 1 is preferably made of a resin such as polyimide or polyamide, or an alloy thereof, or various types of rubber, with an appropriate amount of an antistatic agent such as carbon black. In this embodiment, the intermediate transfer belt 1 is formed so that its surface resistivity is 1 × 10⁹ to 5 × 10¹³ Ω / □. In this embodiment, the intermediate transfer belt 1 is formed so that its thickness is, for example, 0.04 to 0.5 mm, in the form of an endless belt in the shape of a film. In this embodiment, as described above, the intermediate transfer belt 1 is stretched over the drive roller 11, tension roller 12, idler roller 13, and secondary transfer inner roller 14. The drive roller 11 is driven by a motor with excellent constant speed to circulate (rotate) the intermediate transfer belt 1. The tension roller 12 applies a constant tension to the intermediate transfer belt 1. The tension roller 12 is biased at both ends in the direction of its rotation axis by a biasing member (elastic member) called a compression spring (not shown) that acts as a biasing means, from the inner circumferential surface to the outer circumferential surface of the intermediate transfer belt 1. The idler roller 13 forms the surface of the intermediate transfer belt 1 near the upstream side of the secondary transfer section T2. ​​The secondary transfer inner roller 14 functions as an opposing member (counter electrode) of the secondary transfer outer roller 2. In this embodiment, the image forming apparatus 100 is configured so that the tension of the intermediate transfer belt 1 relative to the tension roller 12 is approximately 3 to 12 kgf.

[0028] Furthermore, the intermediate transfer belt 1 can be made of a single-layer or multi-layer resin-based material. Preferably, the intermediate transfer belt 1 has a thickness of 40 μm or more, a Young's modulus of 1.0 GPa or more, and a surface resistivity of 1.0 × 10⁹ to 5.0 × 10¹³ Ω / □.

[0029] In this embodiment, the primary transfer roller 105 is made of a metal roller formed from a metal material such as SUM or SUS. In this embodiment, the primary transfer roller 105 has a straight shape in the thrust direction (the outer diameter is approximately the same throughout almost the entire area in the direction of the rotation axis). In this embodiment, the outer diameter of the primary transfer roller 105 is approximately 6 to 10 mm.

[0030] In this embodiment, the secondary transfer roller 14 is constructed by providing an elastic layer (rubber layer) made of EPDM rubber on the outer circumference of a metal core (base material). In this embodiment, the secondary transfer roller 14 is formed to have an outer diameter of 20 mm and an elastic layer thickness of 0.5 mm. In this embodiment, the hardness of the elastic layer of the secondary transfer roller 14 is set to, for example, 70° (JIS-A). The secondary transfer roller 14 may also be composed of a metal roller made of a metal material such as SUM or SUS.

[0031] In this embodiment, the secondary transfer outer roller 2 is constructed by providing an elastic layer (rubber layer) made of NBR rubber or EPDM rubber containing conductive agents such as metal complexes and carbon on the outer circumference of a metal core (base material). In this embodiment, the outer diameter of the core of the secondary transfer outer roller 2 is 12 mm, and the thickness of the elastic layer is 6 mm, so that the outer diameter of the secondary transfer outer roller 2 is 24 mm. In this embodiment, the hardness of the elastic layer of the secondary transfer outer roller 2 is set to, for example, 28° (Asker C). In this embodiment, the secondary transfer outer roller 2 is spring-biased by a compression spring 21 (Figure 2), which is a biasing member (elastic member) as a biasing means, so as to contact the secondary transfer inner roller 14 with a predetermined pressure while sandwiching the intermediate transfer belt 1.

[0032] Here, from the viewpoint of properly forming the secondary transfer section T2, it is preferable that the secondary transfer outer roller 2 is biased toward the secondary transfer inner roller 14 via the intermediate transfer belt 1 by a biasing member. Also, from the viewpoint of properly forming the secondary transfer section T2, it is preferable that the hardness of the secondary transfer outer roller 2 (more specifically, the elastic layer constituting its surface) is smaller than the hardness of the secondary transfer inner roller 14 (more specifically, the elastic layer constituting its surface). For example, if the hardness of the secondary transfer inner roller 14 is 50 or more and 90 or less on the JIS-A hardness scale, it is preferable that the hardness of the secondary transfer outer roller 2 is 15 or more and 50 or less on the Asker C hardness scale.

[0033] In this embodiment, the image forming apparatus 100 performs image formation by rotating the intermediate transfer belt 1 at a peripheral speed of 400 mm / sec, regardless of the type of recording material P.

[0034] <Configuration of the secondary transfer section and configuration for changing the orientation of the transfer belt surface upstream of the secondary transfer> Figure 2 is a schematic cross-sectional view of the vicinity of the secondary transfer section T2 in this embodiment (a cross-section approximately perpendicular to the rotation axis direction of the secondary transfer inner roller 14). Here, regarding the arrangement of the tension rollers 11-14 of the intermediate transfer belt 1, the secondary transfer outer roller 2, and the backup roller 3 described later, upstream and downstream refer to the upstream and downstream in the rotation direction of the intermediate transfer belt 1, respectively, unless otherwise specified. Also, regarding the recording material P, the front and rear ends refer to the front and rear ends in the transport direction of the recording material P, respectively, unless otherwise specified. In this embodiment, the rotation axis directions of the tension rollers 11-14 of the intermediate transfer belt 1, the secondary transfer outer roller 2, and the backup roller 3 described later are approximately parallel.

[0035] In this embodiment, the core metal of the secondary transfer outer roller 2 is connected to the secondary transfer power supply 20. In this embodiment, the secondary transfer power supply 20 is a high-voltage power supply that can switch between constant voltage and constant current. In this embodiment, the core metal of the secondary transfer inner roller 14 is electrically grounded (connected to ground potential). In this embodiment, the secondary transfer inner roller 14 and the secondary transfer outer roller 2 form an electric field in the secondary transfer section T2 for transferring the toner image from the intermediate transfer belt 1 to the recording material P. In this embodiment, a secondary transfer bias with the opposite polarity to the normal charging polarity of the toner is applied to the secondary transfer outer roller 2, and the secondary transfer inner roller 14 is electrically grounded. Alternatively, a secondary transfer bias with the same polarity as the normal charging polarity of the toner may be applied to the secondary transfer inner roller 14, and the secondary transfer outer roller 2 may be electrically grounded.

[0036] Furthermore, a backup roller 3, composed of a roller-type member, is positioned near the upstream side of the secondary transfer inner roller 14, serving as a support member that contacts the inner circumferential surface of the intermediate transfer belt 1 and supports the intermediate transfer belt 1. More specifically, the backup roller 3 is positioned upstream of the secondary transfer inner roller 14 and downstream of the idler roller 13, so as to contact the inner circumferential surface of the intermediate transfer belt 1. The backup roller 3 is positioned adjacent to the secondary transfer inner roller 14 upstream of the secondary transfer inner roller 14, and adjacent to the idler roller 13 downstream of the idler roller (upstream roller) 13. In this embodiment, the backup roller 3 is a metal roller (made of SUS in this embodiment). The length of the backup roller 3 in the direction of its rotation axis is equivalent to the length of the intermediate transfer belt 1 in the width direction (a direction substantially perpendicular to the direction of surface movement), and the backup roller 3 contacts the intermediate transfer belt 1 over substantially the entire width. The backup roller 3 rotates in conjunction with the rotation of the intermediate transfer belt 1 while in contact with the intermediate transfer belt 1. In this embodiment, the outer diameter of the backup roller 3 is 8 mm.

[0037] Furthermore, in this embodiment, the image forming apparatus 100 has a moving mechanism (position variable mechanism) 4 as a moving means (position variable means) to move the backup roller 3 and make its position variable. The moving mechanism 4 is configured to include an eccentric cam, a solenoid, etc., as will be described later. And, as will be described later, the backup roller 3 is made movable in the out-of-plane direction of the intermediate transfer belt 1 by this moving mechanism 4. In this embodiment, the backup roller 3 is made slidable (reciprocating) in the above direction.

[0038] In this embodiment, the backup roller 3 is configured to press the intermediate transfer belt 1 from the inner circumferential surface side toward the outer circumferential surface side, thereby causing the intermediate transfer belt 1 to protrude toward the outer circumferential surface side. In other words, in this embodiment, the backup roller 3 is configured to be able to contact the intermediate transfer belt 1 with a predetermined amount of penetration. This amount of penetration is roughly the amount of penetration of the backup roller 3 into the surface (tensioned surface) of the intermediate transfer belt 1 formed when it is tensioned by the secondary transfer inner roller 14 and the idler roller 13. To further explain, in Figure 2, the common tangent line between the secondary transfer inner roller 14 and the idler roller 13 on the side around which the intermediate transfer belt 1 is wrapped is defined as the reference line L. Also, the tangent line of the intermediate transfer belt 1 in the region where the backup roller 3 contacts the intermediate transfer belt 1, which is approximately parallel to the reference line L, is defined as the support tangent line Ld. In this case, the distance X between the reference line L and the pressing part tangent Ld is defined as the amount of intrusion of the backup roller 3 into the intermediate transfer belt 1 (however, a positive value is used when the support part tangent Ld is outside the intermediate transfer belt 1 relative to the reference line L).

[0039] In this embodiment, the backup roller 3 is configured such that the penetration amount X is greater than 0 mm regardless of which position it is positioned in, as described later. However, it may also be configured to be positioned so that the penetration amount X is 0 mm. Although not limited to this, typically the penetration amount X is about 3 mm or less. If the penetration amount X is greater than 3 mm, the contact force between the backup roller 3 and the intermediate transfer belt 1 increases, which can cause the backup roller to deflect and the belt surface to become uneven in the direction of rotation.

[0040] Out-of-plane movement of the intermediate transfer belt 1 means that the distance traveled in the direction perpendicular to the reference line L is greater than the distance traveled in the direction parallel to the reference line L. In other words, the backup roller 3 only needs to be able to move in a way that changes the penetration amount X (see Figure 14). However, from the viewpoint of miniaturizing the device, the out-of-plane movement of the intermediate transfer belt 1 is preferably 5 times or more, more preferably 10 times or more, the distance traveled in the direction perpendicular to the reference line L is greater than the distance traveled in the direction parallel to the reference line L. In this embodiment, the backup roller 3 is movable in a direction approximately perpendicular to the reference line L. Note that being able to move in a direction approximately perpendicular to the reference line L includes not only cases where it is able to move in a perfectly perpendicular direction, but also cases where it is able to move in a direction that is deviated from the perpendicular direction by an error range (for example, about ±10°).

[0041] In this embodiment, the backup roller 3 is rotatably supported at both ends in the direction of the rotation axis by bearing members (not shown). In this embodiment, the moving mechanism 4 has an eccentric cam 41 as a switching member, an arm 42 as an operating member, and a tension spring 43 as a biasing member (elastic member) at both ends in the direction of the rotation axis of the backup roller 3. The moving mechanism 4 also has a drive unit 44 that drives the eccentric cams 41 at both ends in the direction of the rotation axis of the backup roller 3. The bearing members of the backup roller 3 are held in the main body of the image forming apparatus 100 or the housing of the unit including the intermediate transfer belt 1 so as to be able to slide in a direction substantially perpendicular to the reference line L. The eccentric cam 41 is held in the main body of the image forming apparatus 100 or the housing of the unit including the intermediate transfer belt 1 so as to be able to rotate.

[0042] The arm 42 is held by the main body of the image forming apparatus 100 or the housing of the unit including the intermediate transfer belt 1 so that it can rotate (oscillate) around the pivot center 42a. One end of the arm 42 engages with the bearing member of the backup roller 3, and the other end engages with the eccentric cam 41. The tension spring 43 biases the arm 42 to rotate in the direction that engages with the eccentric cam 41. The moving mechanism 4 rotates the eccentric cam 41 with the drive unit 44, and by rotating the arm 42, the backup roller 3 slides as shown by the solid and dashed lines in Figure 2. In this embodiment, the moving mechanism 4 is configured so that the backup roller 3 can be positioned at penetration depths X of 0.5 mm, 1.0 mm, 1.8 mm, and 2.5 mm, respectively.

[0043] In Figure 2, the inner roller centerline La is defined as a straight line passing through the rotation center of the secondary transfer inner roller 14 and approximately perpendicular to the reference line L. The backup roller centerline Lb is defined as a straight line passing through the rotation center of the backup roller 3 and approximately perpendicular to the reference line L. The backup roller centerline Lb is an example of a straight line passing approximately through the center of the belt in the direction of rotation of the contact area between the support member and the belt and approximately perpendicular to the reference line L. In this case, the distance between the inner roller centerline La and the backup roller centerline Lb is defined as the separation distance D of the backup roller 3 from the secondary transfer inner roller 14 (however, this is a positive value when the backup roller centerline Lb is upstream of the inner roller centerline La). In this embodiment, the separation distance D is 18 mm. Although not limited to this, typically the backup roller 3 is positioned so as to be able to contact the inner circumferential surface of the intermediate transfer belt 1 within 25 mm upstream from the area where the intermediate transfer belt 1 and the secondary transfer inner roller 15 are in contact.

[0044] Furthermore, in this embodiment, the secondary transfer outer roller 2 is positioned shifted (offset) upstream of the secondary transfer inner roller 14. Also, in this embodiment, the secondary transfer outer roller 2 contacts the secondary transfer inner roller 14 via the intermediate transfer belt 1. With this configuration, in this embodiment, the width of the secondary transfer section T2, which is the contact area between the secondary transfer outer roller 2 and the intermediate transfer belt 1, extends further upstream than the width of the contact area between the secondary transfer inner roller 14 and the intermediate transfer belt 1. In other words, the upstream end of the contact area between the secondary transfer outer roller 2 and the intermediate transfer belt 1 is located further upstream than the upstream end of the contact area between the secondary transfer inner roller 14 and the intermediate transfer belt 1. By positioning the secondary transfer outer roller 2 shifted upstream of the secondary transfer inner roller 14, the adhesion between the recording material P and the intermediate transfer belt 1 near the upstream side of the secondary transfer section T2 can be improved, thereby improving transfer performance.

[0045] In Figure 2, the inner roller centerline La is defined as a straight line passing through the rotation center of the secondary transfer inner roller 14 and approximately perpendicular to the reference line L. The outer roller centerline Lc is defined as a straight line passing through the rotation center of the secondary transfer outer roller 2 and approximately perpendicular to the reference line L. In this case, the distance between the inner roller centerline La and the outer roller centerline Lc is the shift amount Z of the secondary transfer outer roller 2 relative to the secondary transfer inner roller 14 (where Z is a positive value when the outer roller centerline Lc is upstream of the inner roller centerline La). In this embodiment, this shift amount Z is greater than 0 mm.

[0046] Furthermore, in this embodiment, the backup roller 3 is made of SUS, which is a conductive material (metallic material in this embodiment), as described above. This backup roller 3 can be electrically grounded (connected to ground potential (ground)) via a resistor such as a varistor. By electrically grounding the backup roller 3 via a resistor, it is possible to suppress the inflow of current into the backup roller 3 when a secondary transfer bias is applied to the secondary transfer outer roller 2, thereby preventing a shortage of transfer current. When using a varistor as a resistor, for example, if the applied voltage to the secondary transfer outer roller 2 is 0.5 to 8 kV and the surface resistivity of the intermediate transfer belt 1 is 1.0 × 10⁹ to 5.0 × 10¹³ Ω / □, it is preferable to use a varistor with a varistor voltage of 1.0 kV or higher. For example, in the configuration of this embodiment, the backup roller 3 can be electrically grounded via a varistor 32 with a varistor voltage of 1.5 kV.

[0047] <Secondary Transfer Downstream Static Elimination Configuration> Furthermore, the static elimination configuration in this embodiment will be explained using Figure 2. A static elimination needle 31, which is a means of eliminating static electricity from the recording material P, is arranged parallel to the axis of the secondary transfer roller 2 downstream of the secondary transfer roller 2 in the direction of movement (conveying direction) of the recording material P. The shape of the static elimination needle 31 is made by processing a thin sheet of SUS304 with a thickness of 0.2 mm into a sawtooth shape, with a pitch of 1 mm between adjacent sawtooths. The tip of the sawtooth is positioned to face the back surface of the recording material transfer surface, and the outer shape of the recording material transport guide 63 downstream of the transfer section protrudes beyond the tip of the static elimination needle, so that the recording material P and the static elimination needle are not in contact. A static elimination power supply 30 is connected to the static elimination needle 31. In this embodiment, since the charge polarity of the recording material after secondary transfer is negative, the static elimination power supply 30 is a high-voltage power supply that can change the voltage applied to the static elimination needle from 0V to 3kV.

[0048] <Control Mode> Figure 3 is a schematic block showing the control configuration of the main parts of the image forming apparatus 100 in this embodiment. The control unit 50, which serves as the control means, is composed of a CPU 51 as the arithmetic control means, which is the central element that performs arithmetic processing; a memory (storage medium) 52 such as ROM or RAM as the storage means; and an interface unit 53 that controls communication with external devices. The RAM, which is a rewritable memory, stores information input to the control unit 50, detected information, and calculation results, while the ROM stores the control program, a pre-determined data table, and the like. The CPU 51 and the memory 52 can transfer and read data from each other.

[0049] The control unit 50 is connected to various parts of the mechanism (engine) that forms an image on the recording material P through the image formation process described above.

[0050] In this embodiment, the control unit 50 is connected to, for example, a backup roller moving mechanism 4, a secondary transfer power supply 20, and a static elimination unit power supply 30. The control unit 50 controls the voltage output by the secondary transfer power supply 20 so that the current value detected by the current detection unit of the secondary transfer power supply 20 becomes a predetermined current value, thereby enabling constant current control of the bias applied from the secondary transfer power supply 20 to the secondary transfer outer roller 2. The control unit 50 can also control the bias applied by the static elimination unit power supply 30 to the static elimination needle 31 to a desired value. In this embodiment, when there is no recording material P in the secondary transfer unit T2, the secondary transfer voltage determined by applying a constant current controlled bias to the secondary transfer outer roller 2 is applied to the secondary transfer outer roller 2 with constant voltage control during image formation (secondary transfer).

[0051] Furthermore, the control unit 50 is connected to an operation unit (operation panel) 70 provided on the image forming apparatus 100. The operation unit 70 has a display unit as a display means for displaying information under the control of the control unit 50, and an input unit as an input means for inputting information to the control unit 50. In this embodiment, the operation unit 70 is configured to have a touch panel having the functions of a display unit and an input unit. In addition, the control unit 50 may be connected to an external device 200 such as an image reading device (not shown) provided on or connected to the image forming apparatus 100, or a personal computer that is communicatively connected to the image forming apparatus 100.

[0052] The control unit 50 can control each part of the image forming apparatus 100 to perform image formation based on image data input from an image reading device (not shown) or an external device, and information regarding image formation conditions such as the type of recording material P input from the operation unit 70 or an external device. The type of recording material P includes any information that can distinguish the recording material P, such as attributes based on general characteristics such as plain paper, cardboard, thin paper, glossy paper, coated paper, and embossed paper, as well as manufacturer, brand, product number, basis weight, thickness, and size.

[0053] <Position of backup roller and paper position downstream of secondary transfer section> Figure 4 shows the contact relationship between the recording material P and the intermediate transfer belt 1 upstream of the secondary transfer section T2 in this embodiment.

[0054] Figure 4 is a schematic cross-sectional view (a cross-section approximately perpendicular to the rotation axis direction of the secondary transfer roller 14) showing how the recording material P and the intermediate transfer belt 1 come into contact near the upstream side of the secondary transfer section T2.

[0055] In this embodiment, the transport speed of the recording material P being transported to the secondary transfer section T2 is set to be faster than the transport speed of the intermediate transfer belt 1. This is to prevent the transport speed of the recording material P from becoming slower than that of the intermediate transfer belt 1 due to wear of the resist roller 5 or changes in its outer diameter due to the operating environment. As a result, after the leading edge of the recording material P reaches the secondary transfer section T2, the recording material P takes a transport path that forms a loop between the secondary transfer section T2 and the resist roller 5. Therefore, as shown in Figure 4, the recording material P and the intermediate transfer belt 1 may come into contact near the position where the backup roller 3 contacts the inner circumferential surface of the intermediate transfer belt 1.

[0056] Figure 5 shows the relationship between the intrusion amount X of the backup roller 3 and the contact pressure between the recording material P and the intermediate transfer belt 1 at the position where the backup roller 3 is in contact with the inner surface of the intermediate transfer belt 1. Here, the above relationship was obtained by simulation using structural calculations assuming that cardboard with a thickness of 0.3 mm is used as the recording material P. In this case, the positions of the backup roller 3 were set to intrusion amounts X of 1.8 mm, 1.0 mm, and 0.5 mm, respectively. From Figure 5, it can be seen that the contact pressure decreases in the order of intrusion amount X = 1.8 mm, intrusion amount X = 1.0 mm, and intrusion amount X = 0.5 mm when the backup roller 3 is positioned.

[0057] Furthermore, it has been found that the greater the contact pressure between the recording material P and the intermediate transfer belt 1, the more likely the aforementioned "image distortion" is to occur, and conversely, if the contact between the recording material P and the intermediate transfer belt 1 is unstable, the aforementioned "transfer omissions" will occur. In addition, our studies have revealed that even with the same paper thickness and stiffness, the range of contact pressure at which "image distortion" and "transfer omissions" do not occur differs depending on the smoothness of the recording material P.

[0058] In this embodiment, for cardboard with a thickness of 0.3 mm or more, coated paper with high smoothness is less prone to "transfer failure," but if the contact pressure between the recording material P and the intermediate transfer belt 1 is high, "image distortion" is likely to occur. Therefore, the penetration amount X of the backup roller 3 is set to 0.5 mm. Conversely, for rough paper, embossed paper, etc., which have low smoothness, "transfer failure" is likely to occur if the contact pressure is low, so the penetration amount X is set to 1.8 mm or more. With these settings, it has been confirmed that all other aspects of image quality meet the target for each type of media.

[0059] As described above, even with cardboard of the same thickness and stiffness, the amount X that the backup roller 3 penetrates will differ. The orientation of the 0.3 mm thick cardboard after passing through the secondary transfer section T2 is determined from the simulation results described above and is shown in Figure 6.

[0060] The solid and dotted lines in Figure 6 represent the back surface of the recording material P (the surface opposite the static elimination needle 31). The position of the recording material P shown by the solid line is when the insertion depth X of the backup roller 3 is set to 0.5 mm. The position of the recording material P' shown by the dotted line is when the insertion depth X of the backup roller 3 is set to 1.8 mm. As can be seen from Figure 6, when the recording material P is pushed downward in the figure by the backup roller 3 in the upstream part of the secondary transfer, the cardboard, which has greater rigidity as a recording material, is positioned upward in the figure in the downstream part of the secondary transfer. Therefore, when passing the static elimination needle 31, the distance between the static elimination needle 31 and the recording material P will be a distance difference G shown in Figure 6, depending on the setting of the backup roller.

[0061] It is known that the static elimination effect on the charge potential of the recording material P decreases as the distance between the static elimination needle 31 and the recording material P increases. In this implementation, the static elimination unit power supply 30 is configured to supply the static elimination unit voltage to the static elimination needle 31 with a voltage opposite to the charge polarity of the recording material P.

[0062] Figure 7 shows the results of measuring the paper potential of 0.3 mm thick cardboard downstream of the recording material transport guide 63 (see Figure 2). When the distance between the recording material P and the static elimination needle 31 was large, the paper potential was -4 kV when the static elimination bias was 0 V. At this time, the toner scattered after transfer, and image defects occurred. In contrast, by setting the static elimination bias to 2 kV, the paper potential was reduced by approximately 50%. At this time, no image defects occurred. In other words, it was confirmed that even when the backup roller penetration amount X is 1.8 mm or more, setting the static elimination bias to 2 kV or more provides the same static elimination effect as when the penetration amount X is 0.5 mm.

[0063] <Control Flow> Figure 8 is a flowchart illustrating the general procedure for controlling a job in this embodiment. A job is a series of operations that form and output an image on one or more recording materials P. Here, we will explain as an example the case in which an operator, such as a user, causes the image forming apparatus 100 to execute a job by operating the operation unit 70. In this example, it is assumed that the type of recording material P used for image formation in a single job is the same. Note that Figure 8 shows a general outline of the control procedure focusing on changing the static elimination unit voltage value, and many other operations that are normally necessary to execute a job and output an image are omitted.

[0064] The control unit 50 acquires information regarding the recording material P to be used for image formation, which the operator specified on the operation unit 70 when starting a job (S101). This allows the control unit 50 to input information corresponding to the basis weight of the recording material P from the operation unit 70, which is used as an input means. In this case, the information corresponding to the basis weight of the recording material P is information that specifies the type of recording material P that correlates with the basis weight of the recording material P. When the operator registers the type of recording material P stored in each cassette, they may select from a list of types of recording material P (at least classified by basis weight) that is pre-stored in the memory 52 and displayed on the display unit of the operation unit 70.

[0065] The control unit 50 determines the position of the backup roller 3 based on the information about the recording material P acquired in S101 (S102). The memory 52 of the control unit 50 has pre-stored information on the position (penetration amount X) of the backup roller 3 according to the basis weight of the recording material P, as shown in Table 2 above. For example, if the operator sets it to "thick coated paper", the control unit 50 determines the position of the backup roller 3 to a penetration amount X = 0.5 mm. Also, for example, if the operator selects "thick rough paper (or low smoothness)", the control unit 50 determines the position of the backup roller 3 to a penetration amount X = 1.8 mm.

[0066] The memory 52 of the control unit 50 stores in advance the basis weight or brand of the recording material P and the static elimination bias setting value corresponding to the backup roller penetration amount X, and the static elimination unit voltage value is determined (S103).

[0067] When the operator presses the start button (not shown) on the operation unit 70 to input a job start instruction (S104), the control unit 50 moves the backup roller 3 to the position determined in S102 (S105). If the backup roller 3 is already in the desired position, the position of the backup roller 3 is not changed and it is sufficient to maintain that position. Next, the control unit 50 starts feeding the recording material P from the cassette (S106) and starts image formation. During image formation, the static elimination voltage determined in S103 is applied to the static elimination needle 31 (S107). After that, the control unit 50 determines whether the formation of all images for the job has been completed (S108). If it has not been completed, the process returns to S105; if it has been completed, the job is terminated.

[0068] Furthermore, if multiple types of recording material P are mixed in a single job, the position of the backup roller 3 can be changed between the sheets of paper. Accordingly, the static elimination unit voltage value can be changed.

[0069] Furthermore, the information regarding the type of recording material P selected by the operator may be, for example, pre-registered information regarding the brand name (manufacturer, product number, etc.) of the recording material P. In this case, the control unit 50 can obtain information regarding the basis weight of each brand of recording material P based on information that is pre-stored in the memory 52 or obtained at any time from an external storage means, for example, via a network. In addition, the operator may be able to input information regarding an index value correlated with the basis weight of the recording material P. In this case, the index value correlated with the basis weight is not limited to the basis weight itself, but may be the thickness corresponding to the basis weight. Alternatively, instead of basis weight and thickness, the operator may be able to input information indicating classifications of basis weight and thickness, such as thin paper, regular paper, and thick paper.

[0070] Furthermore, information regarding the recording material P used for image formation may be input via an external device 200, such as a personal computer, which is connected to the image forming apparatus 100 in a communicative manner. In this case, the operator can input information regarding the recording material P from the paper setting screen displayed on the display unit of the external device 200 by a printer driver installed on the external device 100. In this case, the interface unit 53 of the control unit 50 functions as an input means for inputting information corresponding to the basis weight and surface smoothness of the recording material P from the external device 200 to the control unit 50.

[0071] [Example 2] Figures 9 and 10 will be used to explain the static elimination section in Example 2. Figure 9 is a perspective view showing the secondary transfer outer roller and static elimination section in Example 2. Figure 10 is a schematic cross-sectional view of the secondary transfer section and static elimination section in Example 2. The belt surface attitude changing mechanism upstream of the secondary transfer section in Example 2 is the backup roller 3 moving mechanism 4 of Example 1, and the shape of the static elimination needle 31 is also the same as in Example 1, so an explanation will be omitted.

[0072] As shown in Figure 9, the secondary transfer outer roller 2 is attached to a transfer roller holder 60 having a recording material transport guide 62 upstream of the transfer via bearings 22 at both ends. Compression springs 21 attached to the bearings 22 spring-bias the roller so that it contacts the secondary transfer inner roller 14 with a predetermined pressure, sandwiching the intermediate transfer belt 1.

[0073] A static elimination needle 31, which is a means of eliminating static electricity from the recording material P, is positioned parallel to the axis of the secondary transfer roller 2 downstream of the secondary transfer roller 2 in the direction of movement (conveyance direction) of the recording material P. The static elimination needle 31 is held in place by adhesive to a metal holding member 311 and fixed to the recording material conveying guide 63 downstream of the transfer section.

[0074] The recording material transport guide 63 and the driven roller 633 protrude beyond the tip of the static elimination needle 31, so that the recording material P and the static elimination needle 31 are not in contact. In addition, in this embodiment, the static elimination plate is connected to the ground potential via the holding member 311.

[0075] The transport guide 63, which holds the static elimination needle 31, is attached by the engagement of guide arms 631 at both ends with the cylindrical portion of the bearing 22. The transport guide 63 is configured to be rotatable around the engagement point between the guide arms 631 and the bearing 22. The transport guide 63 is biased by a guide tension spring 632 so that the transport guide contact surface 634 abuts against the contact surface 621 of the transfer roller holder 60, thereby determining the positions of the static elimination needle 31 and the transport guide 63. (Figure 10a) The position where the transfer roller holder contact surface 621 and the transport guide contact surface 634 abut is defined as the first position.

[0076] A cam drive shaft 33 is positioned at the bottom of the transport guide 63 in Figure 10, and a guide eccentric cam 32 is attached to the cam drive shaft 33. The cam drive shaft 33 and the guide eccentric cam 32 are rotated via a drive gear 34 by the cam drive unit 35 shown in Figure 9.

[0077] In this embodiment, when the guide eccentric cam 32 is rotated 180 degrees, the outer shape of the guide eccentric cam 32 comes into contact with the transport guide 63, causing the static elimination needle 31 and the transport guide 63 to rotate and be positioned in the upper part of the figure as shown in Figure 10b. This position, where the static elimination needle 31 has moved 1.4 mm upward from the first position, is defined as the second position.

[0078] As described in Example 1, the position of the backup roller 3 affects the downstream orientation of the recording material P in the secondary transfer section. Also, as described, the static elimination effect decreases as the distance between the recording material P and the static elimination needle 31 increases. In this example, as shown in Figure 10a, when the penetration amount X of the backup roller 3 is 0.5 mm, the static elimination needle 31 and the transport guide 63 are in the first position. As shown in Figure 10b, when the penetration amount X of the backup roller 3 is 1.8 mm, the guide eccentric cam is driven so that the static elimination needle 31 and the transport guide 63 are in the second position.

[0079] Figure 11 shows the results of measuring the paper potential of 0.3 mm thick cardboard downstream of the recording material transport guide 63. When the backup roller penetration amount X is 1.8 mm, the position of the static elimination needle 31 and the transport guide 63 is set to the second position, and by setting the distance between the recording material P and the static elimination needle 31 to the same as when the penetration amount X is 0.5 mm, it was confirmed that the static elimination effect is equivalent. In this embodiment, the positions of the static elimination needle 31 and the transport guide 63 are set to the first and second positions, but there may be multiple positions depending on the shape and rotation angle of the guide eccentric cam.

[0080] <Control Flow> Figure 12 is a flowchart illustrating the general procedure for controlling a job in this embodiment. A job is a series of operations that form and output an image on one or more recording materials P. Here, we will explain as an example the case in which an operator, such as a user, causes the image forming apparatus 100 to execute a job by operating the operation unit 70. In this example, it is assumed that the type of recording material P used for image formation in a single job is the same. Note that Figure 12 shows a general outline of the control procedure focusing on the position change of the static elimination needle 31, and many other operations that are normally required to execute a job and output an image are omitted. In this embodiment, the control procedure determines the position of the static elimination needle 31 based on the recording material information and the backup roller position (S203). When an image formation start instruction is input from the operation unit 70 (S204), the backup roller position is changed, and the cam drive unit 35 is driven, changing the positions of the static elimination needle 31 and the transport guide 63 (S205). Subsequently, the recording material is fed (S206), image formation is performed (S207), and the process terminates after determining that image formation is complete (S208).

[0081] Furthermore, if multiple types of recording material P are mixed in a single job, the position of the backup roller 3 can be changed between the sheets of paper. Accordingly, the static elimination unit voltage value can be changed.

[0082] [Example 3] Figure 13 shows other configurations for changing the orientation of the intermediate transfer belt surface upstream of the secondary transfer section. A backup sheet 9 is in contact with the inner surface of the intermediate transfer belt 1 on the upstream side of the secondary transfer inner roller 14. The backup sheet 9 is also provided with a position-adjustable mechanism such as an eccentric cam and a solenoid, and in this embodiment, it is possible to move the position of the backup sheet 9 so as to change the amount of winding of the intermediate transfer belt 1 around the secondary transfer outer roller 2. The other configurations are the same as in Embodiment 1, so the same components are denoted by the same reference numerals as in Embodiment 1 and their descriptions are omitted.

[0083] The backup sheet 9 can be formed using, for example, a polyester resin such as PET resin. In this embodiment, the backup sheet 9 is composed of a plate-like member having a predetermined length in the longitudinal direction which is substantially parallel to the direction substantially perpendicular to the rotation direction of the intermediate transfer belt 1, and in the short direction which is substantially perpendicular to the longitudinal direction, and having a predetermined thickness. As an example, the thickness of the backup sheet 9 is 0.4 mm to 0.6 mm.

[0084] For example, when using a PET resin sheet as the backup sheet 9, if a PET resin sheet with low electrical resistance is used, current may flow through the backup sheet 9 when the secondary transfer voltage is applied to the secondary transfer outer roller 2, potentially causing transfer defects. Conversely, if a PET resin sheet with high electrical resistance is used, static electricity (triboelectric charging) may be generated due to friction between the backup sheet 9 and the intermediate transfer belt 1, causing the intermediate transfer belt 56 to adhere to the backup sheet 69 and hindering the rotation of the intermediate transfer belt 1. Therefore, it is preferable to use a PET resin sheet with medium electrical resistance (for example, a volume resistivity of 1 × 10⁵ to 1 × 10⁹ Ω·cm) as the backup sheet 9.

[0085] [Effects of using backup sheets] Compared to the configuration in which a backup roller is placed on the inner circumferential surface of the intermediate transfer belt upstream of the secondary transfer section (Examples 1 and 2), by placing the backup sheet 9 as a backup member, the sheet has elasticity, which has the effect of mitigating excessive contact pressure between, for example, the cardboard and the intermediate transfer belt 1, and furthermore, it is possible to avoid increasing the size of the device and raising initial costs. [Explanation of Symbols]

[0086] 1. Intermediate transfer belt P Transfer materials, paper, paper 2. Secondary transfer outer roller (secondary transfer member) 3. Backup roller (support member) 4. Moving mechanism (means for moving support members) 13 Idolaora 14. Secondary transfer internal roller (opposing member) 31 Static elimination needle (static elimination component) 32 Guide eccentric cam 35 Guide eccentric cam drive unit 63. Transport guide (static elimination support member)

Claims

1. (See Example 1) an image forming apparatus including a primary transfer section having a plurality of or a single image carrier, an endless intermediate transfer belt 1, and forming an image on the intermediate transfer belt by transferring toner from the image carrier onto the intermediate transfer belt; a secondary transfer section performing a secondary transfer step of transferring the image on the intermediate transfer belt to a recording material P; the secondary transfer section including a secondary transfer member 2, an opposing member 14 opposing the secondary transfer member for sandwiching and conveying the recording material via the intermediate transfer belt, belt surface attitude changing means (3, 4) capable of changing the belt surface attitude upstream of the secondary transfer, a static eliminator 31 arranged downstream of the secondary transfer section, and a static eliminator support member 63 supporting the static eliminator; The image forming apparatus is characterized in that the discharge conditions of the discharge member 31 can be changed in accordance with the belt posture controlled by the belt surface changing means.

2. (See Examples 1 and 3) 2. The image forming apparatus according to claim 1, wherein the belt surface changing means is a support member (3, 9) that contacts the intermediate transfer belt 1 from the inside upstream of the secondary transfer section in the recording material transport direction, the support member moving means 4, and a control means 50 that controls the moving means.

3. (See Example 1) 3. The image forming apparatus according to claim 1, further comprising a discharge output unit 30 that outputs a voltage to be applied to the discharge member, and the discharge conditions are changed by changing the applied voltage value of the discharge output unit in accordance with the belt posture controlled by the belt surface changing means.

4. (See Example 2) 3. The image forming apparatus according to claim 1, further comprising a discharge unit position changing means (32, 33, 35) for changing the position of the discharge support member 63, and the discharge unit position changing means changes the position of the discharge support member 63 in accordance with the belt posture controlled by the belt surface changing means.

5. (See Example 2) 5. The image forming apparatus according to claim 1, wherein the charge-eliminating support member is a guide member that guides the recording material downstream of the secondary transfer portion in the recording material conveyance direction.

6. (See Example 2) 5. The image forming apparatus according to claim 4, wherein the position of the charge removal support member 63 is changed by the charge removal unit position changing means in a direction in which the distance between the recording material and the charge removal member 31 becomes constant depending on the belt posture.

7. (See Example 1) 2. The image forming apparatus according to claim 1, wherein the support member is in the form of a roller, and is rotated by the movement of the intermediate transfer belt.

8. (See Example 3) 2. The image forming apparatus according to claim 1, wherein the support member is a sheet-like member made of a resin material.

Images