JP7527226B2 - Image forming device - Google Patents

Description

The present invention relates to image forming devices such as copiers, multifunction machines, facsimile machines, and printers.

Figure 12 is a schematic cross-sectional view showing an example of a transfer section in a conventional image forming device 100X.

As shown in FIG. 12, a conventional image forming apparatus 100X includes an endless transfer belt 1X, a drive roller 2X, a pre-transfer roller 3X, a pair of registration rollers 4X, 4X, and a pre-transfer guide member 5X (guide member).

The driving roller 2X contacts the inside of the transfer belt 1X and rotates the transfer belt 1X. The pre-transfer roller 3X contacts the inside of the transfer belt 1X and is provided immediately upstream of the driving roller 2X in the moving direction M of the transfer belt 1X below the driving roller 2X. In other words, the pre-transfer roller 3X contacts the inside of the transfer belt 1X and is provided immediately upstream of the driving roller 2X in the moving direction M of the transfer belt 1X. The pair of registration rollers 4X, 4X transport the recording sheet P toward the corresponding area α1 of the transfer belt 1X corresponding to the pre-transfer roller 3X. The pre-transfer guide member 5X guides the recording sheet P sent from the pair of registration rollers 4X, 4X. In the image forming device 100X, the toner image Ta formed on the transfer belt 1X is transferred to the recording sheet P. The conventional image forming device 100X also includes a transfer roller 6X. The transfer roller 6X faces the driving roller 2X via the transfer belt 1X.

In such a conventional image forming device 100X, the following problems may occur when the recording sheet P is fed to the transfer belt 1X.

Figures 13A to 13C are cross-sectional views to explain the inconvenience of the rear end P2 of the recording sheet P becoming soiled with toner T.

As shown in FIG. 13A, toner or other deposits 7X may adhere to the surface 3Xa of the pre-transfer roller 3X and/or the inner surface 1Xa of the transfer belt 1X as image formation is repeated. This increases the static friction coefficient between the surface 3Xa of the pre-transfer roller 3X and the inner surface 1Xa of the transfer belt 1X. As a result, the surface 3Xa of the pre-transfer roller 3X and the inner surface 1Xa of the transfer belt 1X repeatedly stick to and separate from each other in the area where the static friction coefficient of the deposits 7X has increased, causing the pre-transfer roller 3X to vibrate. This causes the toner T of the toner image Ta on the transfer belt 1X to fall onto the pre-transfer guide member 5X, and the toner T adheres to the upper end 5Xa of the pre-transfer guide member 5X.

As shown in FIG. 13B, the rear end P2 of the recording sheet P bounces and collides with the corresponding area α1 on the transfer belt 1X. This causes the toner T of the toner image Ta on the transfer belt 1X to fall onto the pre-transfer guide member 5X, and the toner T adheres to the upper end 5Xa of the pre-transfer guide member 5X.

As shown in Figures 13A and 13B, when the toner T of the toner image Ta on the transfer belt 1X falls onto the pre-transfer guide member 5X, the rear end P2 of the recording sheet P scrapes off the toner T adhering to the upper end 5Xa of the pre-transfer guide member 5X, and becomes contaminated with the scraped off toner T, as shown in Figure 3C.

Figure 14 is a cross-sectional view illustrating the inconvenience of the leading edge P1 of the recording sheet P colliding with the corresponding area α1 on the transfer belt 1X, causing a defective image.

As shown in FIG. 14, when the leading edge P1 of the recording sheet P enters the corresponding area α1 on the transfer belt 1X, the pre-transfer roller 3X vibrates. This causes the exposure device (not shown) to vibrate, resulting in image defects due to exposure blur (laser light writing blur).

These issues become particularly noticeable when using a recording sheet with a large basis weight, such as cardboard, as the recording sheet P.

JP 2013-3374 A

In relation to these points, Patent Document 1 discloses an image forming device that includes a photosensitive drum on whose surface an electrostatic latent image is formed, a developing roller that deposits toner onto the photosensitive drum, a collecting roller that collects toner that scatters or spills from the developing roller, and a control unit that drives and rotates the collecting roller when no recording paper is present in the area below the collecting roller.

However, the configuration of Patent Document 1 does not address issues such as toner stains on the trailing edge of the recording sheet when the recording sheet is fed to the transfer belt and image defects.

The present invention aims to provide an image forming device that can effectively prevent toner stains on the trailing edge of a recording sheet and image defects when the recording sheet is fed to a transfer belt.

In order to solve the above problems, the present invention provides the following first and second image forming apparatuses.
(1) First aspect of the image forming apparatus
An image forming apparatus according to a first aspect of the present invention includes an endless transfer belt, a drive roller that contacts the inner side of the transfer belt and rotates the transfer belt, a pre-transfer roller that contacts the inner side of the transfer belt and is provided immediately upstream of the drive roller in the direction of movement of the transfer belt, a pair of registration rollers that transport a recording sheet toward an area of the transfer belt corresponding to the pre-transfer roller, and a guide member that guides the recording sheet sent from the pair of registration rollers, and transfers a toner image formed on the transfer belt to the recording sheet, and the guide member is suspended between the drive roller and the pre-transfer roller. the first edge portion being located on a virtual extension line extended in the suspension direction of the transfer belt, a second edge portion being located on a virtual tangent line from the downstream side in the rotation direction of the pre-transfer roller that passes through a roller nip portion where the pair of registration rollers abut against each other or on the opposite side of the virtual tangent line to the rotation axis of the pre-transfer roller and closer to the pair of registration rollers than the first edge portion, and a recess between the first edge portion and the second edge portion that is recessed inward from a line connecting the first edge portion and the second edge portion, and the recess in the guide member is provided with a second wall portion that is connected to the second edge portion and extends horizontally .
(2) Image forming apparatus according to the second aspect
According to a second aspect of the present invention, an image forming apparatus includes an endless transfer belt, a drive roller that contacts the inner side of the transfer belt and rotates the transfer belt, a pre-transfer roller that contacts the inner side of the transfer belt and is provided immediately upstream of the drive roller in the direction of movement of the transfer belt, a pair of registration rollers that transport a recording sheet toward an area of the transfer belt corresponding to the pre-transfer roller, and a guide member that guides the recording sheet sent from the pair of registration rollers, and transfers a toner image formed on the transfer belt to the recording sheet, and the guide member guides the recording sheet toward the area of the transfer belt that is suspended between the drive roller and the pre-transfer roller. The present invention is characterized in that the guide member has a first edge portion located on a virtual extension line extended in the suspension direction, a second edge portion located on a virtual tangent line from the downstream side in the rotation direction of the pre-transfer roller that passes through a roller nip portion where the pair of registration rollers abut against each other, or on the opposite side of the virtual tangent line to the rotation axis of the pre-transfer roller, and closer to the pair of registration rollers than the first edge portion, and a recess between the first edge portion and the second edge portion that is recessed inward from a line connecting the first edge portion and the second edge portion, and the guide member has a film that inclines diagonally downward from the second edge portion toward the first edge portion, and the film forms part of the recess.

This invention makes it possible to effectively prevent toner stains on the trailing edge of a recording sheet and image defects when the recording sheet is fed to the transfer belt.

1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present invention, as viewed from the front. 2 is a schematic cross-sectional view showing an enlarged view of a pre-transfer guide member and its surrounding area shown in FIG. 1 . 3 is a schematic cross-sectional view showing, in a further enlarged scale, the image forming apparatus shown in FIG. 2 with a secondary transfer device removed. 11 is an enlarged view showing a state in which the rear end of a recording sheet abuts against a first edge portion of a pre-transfer guide member and its vicinity; FIG. 11 is an enlarged view showing a state in which the recording sheet abuts against a second edge portion of the pre-transfer guide member; FIG. 11 is a schematic cross-sectional view for explaining that the inclination of the imaginary extension line is different between a state in which the transfer belt is curved along the secondary transfer roller by the pre-transfer roller and a state in which the transfer belt is not curved. FIG. FIG. 11 is a schematic cross-sectional view showing an enlarged view of a part of a pre-transfer guide member in an image forming apparatus according to a second embodiment. FIG. 11 is a schematic cross-sectional view showing an enlarged view of a part of a pre-transfer guide member in an image forming apparatus according to a third embodiment. FIG. 11 is a schematic cross-sectional view showing an enlarged view of a part of a pre-transfer guide member in an image forming apparatus according to a third embodiment. FIG. 11 is a schematic cross-sectional view showing an enlarged view of a part of a pre-transfer guide member in an image forming apparatus according to a fourth embodiment. FIG. 11 is a schematic cross-sectional view showing an enlarged view of a part of a pre-transfer guide member in an image forming apparatus according to a fourth embodiment. 5 is a schematic cross-sectional view showing a state in which the pre-transfer guide member according to the first embodiment is covered with a material having the same charge polarity as that of toner. FIG. FIG. 11 is a schematic cross-sectional view showing an enlarged portion of a pre-transfer guide member according to a reference example. FIG. 11 is a schematic cross-sectional view showing an example of a transfer unit in a conventional image forming apparatus. 10A and 10B are schematic cross-sectional views for explaining the inconvenience that the trailing edge of a recording sheet is stained with toner. 10A and 10B are schematic cross-sectional views for explaining the inconvenience that the trailing edge of a recording sheet is stained with toner. 10A and 10B are schematic cross-sectional views for explaining the inconvenience that the trailing edge of a recording sheet is stained with toner. FIG. 14 is a schematic cross-sectional view for explaining a problem in which the leading edge of a recording sheet collides with a corresponding area on a transfer belt, causing a defective image.

The following describes an embodiment of the present invention with reference to the drawings. In the following description, identical parts are given the same reference numerals. Their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

<Overall Configuration of Image Forming Apparatus>
1 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention, as viewed from the front. In the figure, the symbol X indicates a width direction (depth direction), the symbol Y indicates a left-right direction perpendicular to the width direction X, and the symbol Z indicates a top-bottom direction.

The image forming device 100 includes an image reading device 10 and an image forming device main body 110, which includes an image forming section 101 and a sheet conveying system 102.

The image forming section 101 includes an exposure device 1 (exposure unit), a development device 2 (development unit), a photoconductor drum 3, a photoconductor cleaning device 4, a charging device 5, a primary transfer belt device 6 (primary transfer belt unit), and a fixing device 7 (fixing unit). The sheet transport system 102 includes a paper feed tray 8 and a discharge tray 9.

The primary transfer belt device 6 includes an endless transfer belt 61, a drive roller 62, a driven roller 63, a pre-transfer roller 64, a tension roller 65, and a primary transfer roller 66. The drive roller 62 and the driven roller 63 are suspended on the transfer belt 61. The pre-transfer roller 64 is in contact with the inner side of the transfer belt 61 and is provided immediately adjacent to the upstream side of the driven roller 63 in the moving direction M of the transfer belt 61. The tension roller 65 is in contact with the inner side of the transfer belt 61 and is provided immediately adjacent to the downstream side of the driven roller 63 and immediately adjacent to the upstream side of the pre-transfer roller 64 in the moving direction M of the transfer belt 61. The primary transfer rollers 66 are in contact with the inner side of the transfer belt 61 and are provided at positions corresponding to the respective photosensitive drums 3.

In addition, a pre-transfer guide member 12 (12A) is provided between the pair of registration rollers 15, 15 and the transfer belt 61. The pre-transfer guide member 12 (12A) guides the recording sheet P sent from the pair of registration rollers 15, 15.

An original placement glass 11 is provided on the top of the image forming device main body 110, and an image reading device 10 for reading an image of an original (not shown) is provided below the original placement glass 11. The original placement glass 11 is an original placement table on which an original is placed. The image of the original read by the image reading device 10 is sent to the image forming device main body 110 as image data, and an image formed based on the image data in the image forming device main body 110 is formed (printed) on a recording sheet P such as recording paper.

The image data handled by the image forming device 100 corresponds to a color image using multiple colors (in this example, the colors black (K), cyan (C), magenta (M), and yellow (Y)). Therefore, the developing device 2, photoconductor drum 3, photoconductor cleaning device 4, charging device 5, and primary transfer roller 66 are each set in multiple units (four units in this example) to form multiple types of images (four types in this example) corresponding to each color, and these constitute multiple (four in this example) image forming stations Pa to Pd.

In the image forming apparatus 100, when forming an image (printing), a recording sheet P is supplied from a paper feed tray 8, and the recording sheet P is conveyed to a pair of registration rollers 15, 15 by a conveying roller 14 provided along a main conveying path R. Next, the recording sheet P is conveyed by a secondary transfer roller 13a of a secondary transfer device 13 at a timing to align the toner image on a transfer belt 61 that is moved in a circulating manner in a moving direction M in a primary transfer belt device 6, and the toner image is transferred onto the recording sheet P. After that, the recording sheet P is passed through a fixing nip between an area of a fixing belt 73 heated by a heating roller 72 in a fixing device 7 corresponding to a fixing roller 71 and a pressure roller 74, whereby the unfixed toner on the recording sheet P is melted and fixed by heat, and the recording sheet P is discharged onto a discharge tray 9 via a conveying roller 16 and a discharge roller 17. In this way, the image forming apparatus 100 completes a series of printing operations. Note that the configuration for performing double-sided printing in the image forming apparatus 100 is not shown in the figures, and its description will be omitted.

(About this embodiment)
FIG. 2 is an enlarged schematic cross-sectional view showing the pre-transfer guide member 12A and its surrounding area shown in FIG.

As shown in FIG. 2, the image forming apparatus 100 according to this embodiment includes a transfer belt 61, a drive roller 62, a pre-transfer roller 64, a pair of registration rollers 15, 15, and a pre-transfer guide member 12A (an example of a guide member).

The drive roller 62 contacts the inside of the transfer belt 61 and rotates the transfer belt 61. The pre-transfer roller 64 contacts the inside of the transfer belt 61 and is provided immediately upstream of the drive roller 62. In other words, the pre-transfer roller 64 contacts the inside of the transfer belt 61 and is provided immediately upstream of the drive roller 62 in the moving direction M of the transfer belt 61. In detail, the pre-transfer roller 64 contacts the inside of the transfer belt 61 and is provided immediately upstream of the drive roller 62 in the moving direction M of the transfer belt 61 below the drive roller 62. The pair of registration rollers 15, 15 transport the recording sheet P toward the area of the transfer belt 61 corresponding to the pre-transfer roller 64 (hereinafter referred to as the corresponding area α1). The pre-transfer guide member 12A guides the recording sheet P sent from the pair of registration rollers 15, 15. In the image forming device 100, the toner image Ta formed on the transfer belt 61 is transferred to the recording sheet P in the transfer area α2 that corresponds to the lower side of the drive roller 62 on the transfer belt 61.

Figure 3 is a schematic cross-sectional view showing the image forming apparatus 100 shown in Figure 2 with the secondary transfer device 13 removed, in a further enlarged manner. Figure 4 is an enlarged view showing the state in which the rear end P2 of the recording sheet P abuts against the first edge portion 121 of the pre-transfer guide member 12A and its vicinity. Also, Figure 5 is an enlarged view showing the state in which the recording sheet P abuts against the second edge portion 122 of the pre-transfer guide member 12A.

In this embodiment, the pre-transfer guide member 12A has a first edge portion 121, a second edge portion 122, and a recess 123.

The first edge portion 121 is located on a virtual extension line β1 extended in the suspension direction of the transfer belt 61 suspended between the drive roller 62 and the pre-transfer roller 64. The second edge portion 122 is located on a virtual tangent β2 from the pre-transfer roller 64 that passes through the roller nip portion RN, which is the position where the pair of registration rollers 15, 15 abut against each other, or on the opposite side of the rotation axis γ2 side of the pre-transfer roller 64 from the first edge portion 121 to the pair of registration rollers 15, 15 from the virtual tangent β2. In detail, the second edge portion 122 is located on a virtual tangent β2 of the pre-transfer roller 64 that passes through the intersection δ1 between the first virtual straight line β3 that passes through the rotation axes γ1, γ1 of the pair of registration rollers 15, 15 and the roller nip portion RN of the pair of registration rollers 15, 15, or on the opposite side of the rotation axis γ2 side of the pre-transfer roller 64 from the virtual tangent β2 (in this example, on the virtual tangent β2). The recess 123 is between the first edge portion 121 and the second edge portion 122 and recesses inward from the line connecting the first edge portion 121 and the second edge portion 122.

According to this embodiment, the recess 123 in the pre-transfer guide member 12A is recessed between the first edge portion 121 and the second edge portion 122. Therefore, even if toner T falls onto the pre-transfer guide member 12A, the toner T can be made to fall into the recess 123 (see FIG. 4), and thus adhesion of the toner T to the upper end portion 12a of the pre-transfer guide member 12A can be suppressed. This makes it possible to effectively prevent the rear end P2 of the recording sheet P from being soiled by the toner T.

In addition, since the first edge portion 121 of the pre-transfer guide member 12A is located on the imaginary extension line β1 of the transfer belt 61 between the drive roller 62 and the pre-transfer roller 64, even if the trailing end P2 of the recording sheet P bounces, it abuts against the first edge portion 121 and its vicinity (see FIG. 4), and the momentum of the bounce of the trailing end P2 of the recording sheet P can be reduced by the first edge portion 121 and its vicinity. This eliminates or suppresses the impact force of the trailing end P2 of the recording sheet P on the corresponding area α1 of the transfer belt 61. Therefore, it is possible to effectively prevent the toner T of the toner image Ta on the transfer belt 61 from falling onto the pre-transfer guide member 12A, and further suppress the adhesion of the toner T to the upper end portion 12a of the pre-transfer guide member 12A.

In addition, the second edge portion 122 of the pre-transfer guide member 12A is located on the imaginary tangent β2 or on the opposite side of the imaginary tangent β2 to the rotation axis γ2 side of the pre-transfer roller 64, so that the path of the recording sheet P sent from the pair of registration rollers 15, 15 can be changed by the second edge portion 122 so that it moves from the corresponding area α1 on the transfer belt 61 toward the transfer belt 61 between the drive roller 62 and the pre-transfer roller 64 (see FIG. 5). Therefore, it is possible to prevent the leading edge P1 of the recording sheet P from entering the corresponding area α1, and it is possible to suppress vibration of the pre-transfer roller 64 and, ultimately, vibration of the exposure device 1. This makes it possible to effectively prevent the occurrence of image defects due to exposure blurring (laser light writing blurring).

These are particularly effective when using a recording sheet with a large basis weight, such as cardboard, as the recording sheet P.

Figure 6 is a schematic cross-sectional view illustrating that the inclination of the imaginary extension line β1 differs when the transfer belt 61 is curved along the secondary transfer roller 13a by the pre-transfer roller 64 and when it is not curved.

In this embodiment, the image forming device 100 is equipped with a secondary transfer roller 13a (an example of a transfer roller) that faces the drive roller 62 via the transfer belt 61.

Here, the imaginary extension line β1 includes a first imaginary extension line β1a (see the two-dot chain line in FIG. 6) of the transfer belt 61 between the drive roller 62 and the pre-transfer roller 64 in a state where the transfer belt 61 is not curved along the secondary transfer roller 13a by the pre-transfer roller 64, and a second imaginary extension line β1b (see the one-dot chain line in FIG. 6) of the transfer belt 61 between the drive roller 62 and the pre-transfer roller 64 in a state where the transfer belt 61 is curved along the secondary transfer roller 13a by the pre-transfer roller 64. That is, the first imaginary extension line β1a and the second imaginary extension line β1b have different inclinations depending on the amount of curvature by which the transfer belt 61 is curved along the secondary transfer roller 13a by the pre-transfer roller 64, so the first edge portion 121 is located within the range between the first imaginary extension line β1a and the second imaginary extension line β1b, including on the first imaginary extension line β1a and the second imaginary extension line β1b.

By doing this, the first edge portion 121 can be positioned in an appropriate position even in an image forming device 100 equipped with a secondary transfer roller 13a. This can provide the effect of suppressing adhesion of toner T to the upper end portion 12a of the pre-transfer guide member 12A.

In order to improve the transferability of the toner image Ta to the recording sheet P by the secondary transfer roller 13a, it is necessary to ensure the length of the transfer nip portion TN between the transfer belt 61 and the secondary transfer roller 13a in the circumferential direction W.

In this regard, in the present embodiment, the pre-transfer roller 64 passes through the intersection δ2 between the second imaginary line β4 and the transfer nip portion TN of the transfer belt 61 and the secondary transfer roller 13a, and intersects with the third imaginary line β5, which is a line perpendicular to the second imaginary line β4, or is located closer to the secondary transfer roller 13a than the third imaginary line β5. Here, the second imaginary line β4 is a line passing through the rotation axis γ3 of the drive roller 62 and the rotation axis γ4 of the secondary transfer roller 13a.

By doing so, the amount of curvature of the transfer belt 61 along the secondary transfer roller 13a can be increased, thereby ensuring the length of the transfer nip portion TN between the transfer belt 61 and the secondary transfer roller 13a in the circumferential direction W. Therefore, while improving the transferability of the toner image Ta to the recording sheet P by the secondary transfer roller 13a, it is possible to effectively prevent the occurrence of toner T stains and image defects at the rear end P2 of the recording sheet P when the recording sheet P is fed to the transfer belt 61.

However, inconveniences may occur depending on the angle θ (see FIG. 3) between the virtual extension line β1 and the fourth virtual straight line β6 (see FIG. 3) passing through the first edge portion 121 and the second edge portion 122. For example, if the angle θ is smaller than 120 degrees, the first edge portion 121 may go too far downward, and the rear end P2 (see FIG. 4) of the recording sheet P may not abut against the first edge portion 121. In that case, the first edge portion 121 cannot reduce the momentum of the jump of the rear end P2 of the recording sheet P. On the other hand, if the angle θ is greater than 130 degrees, the second edge portion 122 may be too far away from the transfer belt 61, so that the leading edge P1 of the recording sheet P may move toward the corresponding area α1 side of the transfer belt 61. In that case, the leading edge P1 of the recording sheet P may be more likely to enter the corresponding area α1. Also, if the angle θ is greater than 130 degrees, the second edge portion 122 may go too far downward. This makes it easier for the trailing edge P2 of the recording sheet P to scrape off the toner T that has accumulated in the recess 123 of the pre-transfer guide member 12A, and the trailing edge P2 of the recording sheet P becomes stained with toner T.

Therefore, in this embodiment, it is preferable that the angle θ is 120 degrees to 130 degrees (125 degrees in this example).

By setting the angle θ to 120 degrees or more, it is possible to prevent the first edge portion 121 from going too far downward, thereby making it easier for the rear end P2 of the recording sheet P to abut against the first edge portion 121 and its vicinity. Therefore, the first edge portion 121 can easily reduce the momentum of the bounce of the rear end P2 of the recording sheet P. In addition, by setting the angle θ to 130 degrees or less, it is possible to prevent the second edge portion 122 from moving too far away from the transfer belt 61, thereby reducing the possibility that the leading end P1 of the recording sheet P will enter the corresponding area α1 of the transfer belt 61. In addition, by setting the angle θ to 130 degrees or less, it is possible to prevent the second edge portion 122 from going too far downward, thereby making it harder for the rear end P2 of the recording sheet P to scrape off the toner T accumulated in the recess 123 of the pre-transfer guide member 12A, and thus it is possible to suppress the contamination of the rear end P2 of the recording sheet P with the toner T.

In this embodiment, the pre-transfer guide member 12A is provided with an inclined surface 12b (see Figures 4 to 6) that is connected to the second edge portion 122 and inclines diagonally downward toward the first edge portion 121.

This ensures that the leading edge P1 of the recording sheet P is guided reliably along the inclined surface 12b to the second edge portion 122.

In this embodiment, the recess 123 in the pre-transfer guide member 12A has a first wall portion 124a (see Figures 4 to 6) that is connected to the first edge portion 121 and aligned along the vertical direction V.

By doing this, even if the toner T of the toner image Ta falls onto the first wall portion 124a and comes into contact with the first wall portion 124a, the first wall portion 124a is aligned along the vertical direction V, so it is possible to make it difficult for the toner T to adhere to the first wall portion 124a. This makes it possible to further suppress adhesion of the toner T to the upper end portion 12a of the pre-transfer guide member 12A.

Second Embodiment
FIG. 7 is a schematic cross-sectional view showing an enlarged view of a part of a pre-transfer guide member 12B in an image forming apparatus 100 according to the second embodiment.

The image forming apparatus 100 according to the second embodiment is similar to the image forming apparatus 100 according to the first embodiment, except that a pre-transfer guide member 12B is provided instead of the pre-transfer guide member 12A in the image forming apparatus 100 according to the first embodiment. The following description will focus on the differences.

In the second embodiment, the recess 123 in the pre-transfer guide member 12B has a first wall portion 124b that is connected to the first edge portion 121 and slopes diagonally downward on the side opposite to the second edge portion 122.

By doing this, even if the toner T of the toner image Ta falls onto the first wall portion 124b, the first wall portion 124b is inclined diagonally downward on the side opposite the second edge portion 122, so the toner T can be prevented from coming into contact with the first wall portion 124b, and the toner T can be prevented from adhering to the first wall portion 124b. This can further suppress the adhesion of the toner T to the upper end portion 12a of the pre-transfer guide member 12B. In addition, the momentum of the bounce of the rear end P2 of the recording sheet P can be further reduced by the first wall portion 124b inclined diagonally downward on the side opposite the second edge portion 122.

In the image forming apparatus 100 according to the first and second embodiments, the recess 123 in the pre-transfer guide member 12B has a second wall portion 125 that is connected to the second edge portion 122 and aligned in the horizontal direction.

By doing this, the toner T that falls onto the pre-transfer guide member 12B can be stored in the second wall portion 125, and therefore the second wall portion 125 can act as a collector for the toner T.

In the first embodiment, the first wall portion 124a and the second wall portion 125 are perpendicular to each other. In the second embodiment, the first wall portion 124b and the second wall portion 125 intersect at an acute angle.

Third Embodiment
8A and 8B are schematic cross-sectional views showing enlarged views of a part of a pre-transfer guide member 12C in an image forming apparatus 100 according to a third embodiment.

The image forming apparatus 100 according to the third embodiment is similar to the image forming apparatus 100 according to the first and second embodiments, except that a pre-transfer guide member 12C is provided instead of the pre-transfer guide members 12A and 12B in the image forming apparatus 100 according to the first and second embodiments. The following description will focus on the differences.

The pre-transfer guide member 12C shown in FIG. 8A is the pre-transfer guide member 12A according to the first embodiment, with a recessed portion 126 provided in the second wall portion 125. The pre-transfer guide member 12C shown in FIG. 8B is the pre-transfer guide member 12B according to the second embodiment, with a recessed portion 126 provided in the second wall portion 125.

In the example shown in FIG. 8A, the recess 126 is recessed in the vertical direction V along the first wall 124a. In the example shown in FIG. 8B, the recess 126 is recessed diagonally downward along the first wall 124b on the side opposite to the second edge 122.

As shown in Figures 8A and 8B, the second wall portion 125 of the pre-transfer guide member 12C according to the third embodiment has a recessed portion 126 that is recessed below the second edge portion 122.

By doing so, the toner T that falls onto the pre-transfer guide member 12C can be further collected by the recessed portion 126, thereby improving the amount of collected toner T. Furthermore, when the recessed portion 126 is provided in the second wall portion 125 of the pre-transfer guide member 12B according to the second embodiment, the amount of collected toner T can be improved compared to when the recessed portion 126 is provided in the second wall portion 125 of the pre-transfer guide member 12A according to the first embodiment.

Fourth Embodiment
9A and 9B are schematic cross-sectional views showing, in an enlarged manner, a part of a pre-transfer guide member 12D in an image forming apparatus 100 according to a fourth embodiment.

The image forming apparatus 100 according to the fourth embodiment is similar to the image forming apparatus 100 according to the first to third embodiments, except that a pre-transfer guide member 12D is provided instead of the pre-transfer guide members 12A, 12B, and 12C in the image forming apparatus 100 according to the first to third embodiments. The following description will focus on the differences.

The pre-transfer guide member 12C shown in FIG. 9A is the pre-transfer guide member 12A according to the first embodiment, with a film 127 provided instead of the second wall portion 125. The pre-transfer guide member 12C shown in FIG. 9B is the pre-transfer guide member 12B according to the second embodiment, with a film 127 provided instead of the second wall portion 125.

The pre-transfer guide member 12D according to the fourth embodiment is provided with a film 127 (a resin film in this example) that slopes diagonally downward from the second edge portion 122 toward the first edge portion 121. In the pre-transfer guide member 12D, the film 127 forms part of the recess 123. The film 127 is provided on the sloped surface 12b. Here, examples of materials for the resin film include a resin material having rigidity, such as a mixed resin (PC-ABS alloy resin) of polycarbonate resin (PC) and acrylonitrile butadiene styrene (ABS) resin.

In the fourth embodiment, a part of the recess 123 can be easily formed using a simple member such as the film 127. In addition, the toner T that falls onto the pre-transfer guide member 12D can be collected on the upper side of the film 127, thereby improving the amount of toner T that can be collected.

In the example shown in FIG. 9A, the lower end 124a1 of the first wall portion 124a is aligned along the vertical direction V. However, this is not limited to this, and the lower end 124a1 may be curved toward the film 127. Also, in the example shown in FIG. 9B, the lower end 1241 of the first wall portion 124b is curved toward the film 127. However, this is not limited to this, and the lower end 124a1 may be inclined linearly.

In the first to fourth embodiments, the pre-transfer guide members 12A to 12D may be formed from a material having the same charge polarity as the toner T of the toner image Ta, or may be coated with a material having the same charge polarity as the toner T.

Figure 10 is a schematic cross-sectional view showing how the pre-transfer guide member 12A according to the first embodiment is coated with a material having the same charge polarity as the toner T.

As shown in FIG. 10, at least the upper end 12a of the pre-transfer guide member 12A (for example, the first edge portion 121 and its periphery, the first wall portion 124a, the second wall portion 125, and the second edge portion 122 and its periphery) is covered with a material 128 having the same polarity as the charge polarity of the toner T, in this example, a tape-like member made of a fluororesin (negatively charged material) such as polytetrafluoroethylene (PTFE). Note that the pre-transfer guide members 12B to 12D according to the second to fourth embodiments may be covered with a material having the same polarity as the charge polarity of the toner T.

This allows the pre-transfer guide members 12A-12D to be charged with the same polarity as the toner T, thereby preventing the toner T from adhering to the upper end portions 12a of the pre-transfer guide members 12A-12D.

Examples of materials with the same polarity as the negative charge polarity of toner T include polytetrafluoroethylene (PTFE), polyethylene, polystyrene, etc. Examples of materials with the same polarity as the positive charge polarity of toner include polyamide resin, glass material, etc.

[Example]
Next, the toner T contamination at the rear end P2 of the recording sheet P was evaluated for the pre-transfer guide member 12A of the first embodiment shown in Figure 4 and the pre-transfer guide member 12D of the fourth embodiment shown in Figure 9A with and without the recess 123, and these are described below along with a reference example.

Figure 11 is a schematic cross-sectional view showing an enlarged portion of the pre-transfer guide member 12E according to the reference example.

The pre-transfer guide member 12E shown in FIG. 11 does not have a recess 123 between the first edge portion 121 and the second edge portion 122, but has an inclined surface 129 that is linearly connected to the first edge portion 121 and the second edge portion 122.

(Evaluation conditions)
In the embodiment, the image forming apparatus 100 shown in Fig. 1 was used. The image forming apparatus 100 had already printed about 107,000 sheets, and toner T and other deposits were attached to the surface 64a (see Fig. 3) of the pre-transfer roller 64 and the inner surface 61a (see Fig. 3) of the transfer belt 61. Therefore, in the image forming apparatus 100, the pre-transfer roller 64 vibrates, and the toner T of the toner image Ta on the transfer belt 61 is likely to fall onto the pre-transfer guide members 12A, 12D, and 12E.

The experiment was carried out in an environment of room temperature 25° C. and humidity 45%, using a black solid original in monochrome mode, and double-sided printing of 50 sheets was carried out continuously on SW paper (basis weight 70 g/m ² ).

As a result, in the pre-transfer guide member 12E of the reference example shown in FIG. 11, there was a lot of toner T contamination at the rear end P2 of the recording sheet P. This is thought to be because when the inclined surface 129 is present, the toner T tends to accumulate on the inclined surface 129, causing the rear end P2 of the recording sheet P to become contaminated with toner T.

In contrast, in the pre-transfer guide member 12A according to the first embodiment shown in FIG. 4 and the pre-transfer guide member 12D according to the fourth embodiment shown in FIG. 9A, a recess 123 is provided, so there is no or only a small amount of accumulated toner T on the path of the trailing end P2 of the recording sheet P, and therefore the staining of the trailing end P2 of the recording sheet P with toner T is extremely slight.

The present invention is not limited to the above-described embodiment, but can be embodied in various other forms. Therefore, the embodiment is merely illustrative in all respects and should not be interpreted in a restrictive manner. The scope of the present invention is indicated by the claims, and is not restricted in any way by the text of the specification. Furthermore, all modifications and changes within the equivalent scope of the claims are within the scope of the present invention.

100 Image forming apparatus 12 Pre-transfer guide member (an example of a guide member)
12A to 12E Pre-transfer guide member 121 First edge portion 122 Second edge portion 123 Recess 1241 Lower end portion 124a First wall portion 124a1 Lower end portion 124b First wall portion 125 Second wall portion 126 Recess portion 127 Film 128 Material 129 having the same charge polarity as that of toner Inclined surface 12a Upper end portion 12b Inclined surface 13a Secondary transfer roller 15 Pair of registration rollers 61 Transfer belt 62 Drive roller 64 Pre-transfer roller 8 Paper feed tray M Movement direction P Recording sheet P1 Leading edge P2 Trailing edge RN Roller nip portion T Toner TN Transfer nip portion Ta Toner image V Vertical direction W Circumferential direction α1 Corresponding area (area of transfer belt corresponding to pre-transfer roller)
α2 Transfer area β1 Imaginary extension line β1a First imaginary extension line β1b Second imaginary extension line β2 Imaginary tangent β3 First imaginary straight line β4 Second imaginary straight line β5 Third imaginary straight line β6 Fourth imaginary straight line γ1 Rotation axis γ2 Rotation axis γ3 Rotation axis γ4 Rotation axis δ1 Intersection δ2 Intersection θ Angle

Claims (10)

An endless transfer belt;
a drive roller that contacts the inner side of the transfer belt and rotates the transfer belt;
a pre-transfer roller that is in contact with the inner side of the transfer belt and is provided immediately upstream of the drive roller in the moving direction of the transfer belt;
a pair of registration rollers for conveying a recording sheet toward a region of the transfer belt corresponding to the pre-transfer roller;
a guide member that guides the recording sheet fed from the pair of registration rollers, and the toner image formed on the transfer belt is transferred to the recording sheet,
the guide member has a first edge portion located on a virtual extension line extended in a suspension direction of the transfer belt suspended between the drive roller and the pre-transfer roller, a second edge portion located on a virtual tangent line from a downstream side in a rotation direction of the pre-transfer roller that passes through a roller nip portion at which the pair of registration rollers abut against each other or on the opposite side of the virtual tangent line to the rotation axis side of the pre-transfer roller and closer to the pair of registration rollers than the first edge portion, and a recessed portion between the first edge portion and the second edge portion that is recessed inward from a line connecting the first edge portion and the second edge portion ,
The image forming apparatus according to claim 1, wherein the recess in the guide member includes a second wall portion that is connected to the second edge portion and extends along a horizontal direction. 2. The image forming apparatus according to claim 1 ,
The image forming apparatus according to claim 1, wherein the second wall portion is provided with a recessed portion recessed below the second edge portion. An endless transfer belt;
a drive roller that contacts the inner side of the transfer belt and rotates the transfer belt;
a pre-transfer roller that is in contact with the inner side of the transfer belt and is provided immediately upstream of the drive roller in the moving direction of the transfer belt;
a pair of registration rollers for conveying a recording sheet toward an area of the transfer belt corresponding to the pre-transfer roller;
a guide member that guides the recording sheet fed from the pair of registration rollers, and the toner image formed on the transfer belt is transferred to the recording sheet,
the guide member has a first edge portion located on a virtual extension line extended in a suspension direction of the transfer belt suspended between the drive roller and the pre-transfer roller, a second edge portion located on a virtual tangent line from a downstream side in a rotation direction of the pre-transfer roller that passes through a roller nip portion at which the pair of registration rollers abut against each other or on the opposite side of the virtual tangent line to the rotation axis side of the pre-transfer roller and closer to the pair of registration rollers than the first edge portion, and a recessed portion between the first edge portion and the second edge portion that is recessed inward from a line connecting the first edge portion and the second edge portion,
The image forming apparatus, wherein the guide member includes a film that is inclined diagonally downward from the second edge portion toward the first edge portion, and the film constitutes a part of the recess. 4. The image forming apparatus according to claim 1 ,
a transfer roller facing the drive roller across the transfer belt,
an image forming apparatus characterized in that the imaginary extension line includes a first imaginary extension line of the transfer belt between the drive roller and the pre-transfer roller when the transfer roller is not curved along the drive roller by the transfer roller, and a second imaginary extension line of the transfer belt between the drive roller and the pre-transfer roller when the transfer roller is curved along the drive roller by the transfer roller, and the first edge portion is located within a range between the first imaginary extension line and the second imaginary extension line, including on the first imaginary extension line and the second imaginary extension line. 5. The image forming apparatus according to claim 4 ,
the pre-transfer roller passes through an intersection of a second imaginary line passing through the rotational axis of the drive roller and the rotational axis of the transfer roller and the transfer nip portion of the transfer roller, and intersects with a third imaginary line perpendicular to the second imaginary line, or is located on the transfer roller side of the third imaginary line. 6. The image forming apparatus according to claim 1 ,
an angle between the virtual extension line and a fourth virtual straight line passing through the first edge portion and the second edge portion is 120 degrees to 130 degrees; 7. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the guide member is provided with an inclined surface that is connected to the second edge portion and inclined obliquely downward toward the first edge portion. 8. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the recess in the guide member includes a first wall portion that is connected to the first edge portion and extends in a vertical direction. 8. The image forming apparatus according to claim 1,
The image forming apparatus according to claim 1, wherein the recess in the guide member includes a first wall portion that is connected to the first edge portion and inclines obliquely downward on a side opposite to the second edge portion. 10. The image forming apparatus according to claim 1 ,
an image forming apparatus, characterized in that the guide member is formed of a material having the same polarity as the charge polarity of the toner of the toner image, or is coated with a material having the same polarity as the charge polarity of the toner.

Images