JP2016038526A - Image formation device - Google Patents

Abstract

An image forming apparatus capable of suppressing a trailing edge blur image that occurs when a trailing edge of a recording material passes through a conveyance guide that guides a recording material conveyed to a transfer unit. An endless belt, a transfer member, a facing member, a transport guide, and a support member are provided, and the belt is stretched between a transfer portion and a support portion. In the image forming apparatus 100 that forms a surface, when the conveyance guide 32 has a virtual surface L that is a surface obtained by extending the stretched surface in the rotation direction of the belt 10, the recording material 6 is closer to the transfer member 10 than the virtual surface L. And a control section A that regulates the transport path of the recording material 6 and the end B of the recording material 6 in the transport direction of the recording material 6 from the control section A to the downstream side in the transport direction of the recording material 6 and is inclined so as to approach the virtual plane L. And an end B on the downstream side in the conveyance direction of the recording material 6 of the inclined guide portion 32a is separated from the belt 10 on the virtual surface L or on the belt 10 side of the virtual surface L. To be arranged. [Selection] Figure 2

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, or a facsimile apparatus using an electrophotographic system or an electrostatic recording system.

  2. Description of the Related Art Conventionally, for example, an image forming apparatus using an electrophotographic method uses an endless belt that carries and rotates a toner image. For example, in an intermediate transfer type image forming apparatus, a toner image is primarily transferred from a photosensitive member to an intermediate transfer belt, which is an intermediate transfer member composed of an endless belt, at a primary transfer unit. Then, the toner image is secondarily transferred from the intermediate transfer belt to a recording material such as paper in the secondary transfer portion, thereby forming a full color image or the like.

  In such an image forming apparatus, after the recording material is fed from the paper feed tray, the recording material is fed to the secondary transfer portion by a pair of registration rollers that correct skew feeding and adjust the feeding timing. In addition, a conveyance guide (guide member) is provided between the registration roller pair and the secondary transfer unit on the surface side (intermediate transfer belt side) of the recording material for the purpose of regulating the conveyance path of the recording material to the secondary transfer unit. ) Is often arranged. Such a conveyance guide is disposed so that the leading edge of the recording material is landed immediately before the secondary transfer portion or the secondary transfer portion for the following reason. That is, when the leading edge of the recording material is conveyed to a secondary transfer member such as a secondary transfer roller that forms a secondary transfer portion, the leading edge of the recording material thrusts into the secondary transfer member, thereby Tip edge contamination occurs. Further, when the recording material is conveyed to the surface side of the intermediate transfer belt, the toner image on the intermediate transfer belt is brought into contact with the recording material and the toner image on the intermediate transfer belt before the secondary transfer portion. Rubs and an image defect called “image rub” occurs.

  However, when such a conveyance guide is used, the following problems may occur due to a guide dropout shock that occurs when the trailing edge of the recording material passes through the conveyance guide. In other words, the rear end of the recording material that has passed through the conveyance guide is struck against the intermediate transfer belt, and the toner image on the intermediate transfer belt is disturbed by the impact, and an image called a “rear end blur image” near the rear end of the image. Defects may occur. In the rear-end blurred image, the stronger the recording material such as thick paper, the more shock is remarkable.

  For such a rear end blurred image, Patent Document 1 proposes the following method. That is, by projecting a sheet member having relatively low rigidity at the leading end of the guide plate, when the trailing end of the recording material passes through the sheet member, the distance between the intermediate transfer belt and the recording material is reduced by the bending of the sheet member. Shrink to relieve shock. Patent Document 2 proposes that the impact can be further reduced by changing the bending rigidity of the sheet member similar to the above in the conveying direction.

JP 2006-139168 A JP 2010-61060 A

  However, as a result of studies by the present inventors, it has been found that the conventional method as described above may not be able to sufficiently obtain the effect of suppressing the trailing edge blur image while suppressing image blurring.

  In other words, if the posture of the recording material before the trailing edge of the recording material passes through the conveyance guide is different from the posture after the trailing edge, the impact of the trailing edge of the recording material and the intermediate transfer belt cannot be suppressed, and the trailing edge Edge blur images may occur.

  On the other hand, the impact of the trailing edge of the recording material hitting the intermediate transfer belt can be suppressed by bringing the front end of the sheet member close to the surface of the intermediate transfer belt. However, if it is too close, the toner image on the intermediate transfer belt may rub against the sheet member due to the bending of the sheet material depending on the rigidity of the recording material.

  As described above, there is still a need for a new technique for suppressing the trailing edge blur image due to the guide missing shock that occurs when the trailing edge of the recording material passes through the conveyance guide.

  In the above, the conventional problem has been described in the case where the endless belt that carries and rotates with the toner image is an intermediate transfer belt. However, in order to transfer the toner image to a recording material by a transfer unit such as a photosensitive belt. The same problem can occur in other endless belts that rotate in the same manner.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of suppressing a trailing edge blur image that occurs when the trailing edge of a recording material passes through a conveyance guide that guides a recording material conveyed to a transfer unit. That is.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, according to the present invention, an endless belt that carries a toner image on its outer peripheral surface and rotates, and a transfer portion is formed in contact with the outer peripheral surface of the belt, and the transfer portion is sandwiched between the belt and the belt. And a transfer member that transfers the toner image from the belt to the recording material that is conveyed, an opposing member that contacts the inner peripheral surface of the belt and faces the transfer member via the belt, and is conveyed to the transfer unit. A conveyance guide that guides the recording material to be recorded from the belt-side surface side, and a support member that supports the inner peripheral surface of the belt at a support portion on the upstream side of the transfer portion in the rotation direction of the belt. In the image forming apparatus for forming the belt tension surface between the transfer portion and the support portion, the conveyance guide has a virtual surface defined by extending the tension surface in the belt rotation direction. , More than the virtual plane A restricting portion for restricting the recording material conveyance path on the imaging member side, and from the restriction portion to the downstream end in the recording material conveyance direction so as to approach the virtual surface as it goes downstream in the recording material conveyance direction. An end of the inclined guide portion on the downstream side in the recording material conveyance direction is separated from the belt on the virtual surface or on the belt side of the virtual surface. An image forming apparatus is arranged.

  According to the present invention, it is possible to suppress the trailing edge blur image that occurs when the trailing edge of the recording material passes through the conveyance guide that guides the recording material conveyed to the transfer unit.

1 is a schematic sectional view of an image forming apparatus in Embodiment 1. FIG. FIG. 3 is an enlarged cross-sectional view of the periphery of a secondary transfer portion in Embodiment 1. 3 is a schematic diagram illustrating a positional relationship of a conveyance guide in Embodiment 1. FIG. 3 is a schematic diagram illustrating a positional relationship of a conveyance guide in Embodiment 1. FIG. It is a cross-sectional enlarged view around the secondary transfer portion in a comparative example. It is a schematic diagram which shows the positional relationship of the conveyance guide in a comparative example. FIG. 6 is a schematic diagram illustrating the posture of a recording material before and after passing through a conveyance guide in a comparative example. FIG. 6 is a schematic diagram illustrating a posture of a recording material after passing through a regulation portion of a conveyance guide in Embodiment 1. 6 is a schematic diagram illustrating a positional relationship of a conveyance guide in a modification example of Embodiment 1. FIG. 10 is an enlarged cross-sectional view of the periphery of a secondary transfer portion T2 in Embodiment 2. FIG. It is a schematic diagram which shows the conveyance attitude | position of the thin paper in a comparative example. FIG. 10 is a schematic diagram illustrating a thin paper conveyance posture in the second embodiment.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. First, the overall configuration and operation of the image forming apparatus 100 according to an embodiment of the present invention will be described. FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a tandem type laser beam printer that employs an intermediate transfer method that can form a full-color image using an electrophotographic method.

  The image forming apparatus 100 includes first, second, third, and fourth image forming units (stations) PY, PM, PC, and PK as a plurality of image forming units. Each image forming unit PY, PM, PC, PK forms a toner image of each color of yellow (Y), magenta (M), cyan (C), and black (K). In this embodiment, the configurations and operations of the image forming units PY, PM, PC, and PK are substantially the same except that the color of the toner used is different. Therefore, hereinafter, unless there is a particular need for distinction, Y, M, C, and K at the end of a symbol representing an element for any color are omitted, and the elements will be described in a comprehensive manner. In this embodiment, the image forming unit P includes a photosensitive drum 1, a charging roller 2, an exposure device 5, a developing device 3, a primary transfer brush 14, and a cleaning device 4 which will be described later.

  The image forming apparatus 100 includes a photosensitive drum 1 that is a drum-shaped (cylindrical) electrophotographic photosensitive member (photosensitive member) as an image carrier. The photosensitive drum 1 is rotationally driven at a predetermined peripheral speed (process speed) in the direction of arrow R1 in FIG. The surface (outer peripheral surface) of the rotating photosensitive drum 1 is uniformly charged to a predetermined polarity and potential by a charging roller 2 which is a roller-shaped charging member as a charging unit. The charged surface of the photosensitive drum 1 is subjected to image exposure corresponding to the image information of the color components of each image forming portion P by an exposure device (laser scanner device) 5 as image exposure means. Thereby, an electrostatic latent image (electrostatic image) corresponding to the image information of the color component corresponding to each image forming unit is formed on the photosensitive drum 1. The electrostatic latent image formed on the photosensitive drum 1 is developed (visualized) as a toner image with a toner as a developer by a developing device 3 as a developing unit. The developing device 3 develops the electrostatic latent image with toner conveyed to a developing position which is a portion facing the photosensitive drum 1 by a developing roller 3a as a developer carrying member.

  Further, the image forming apparatus 100 includes an intermediate transfer belt 10 that is an intermediate transfer member disposed so as to face the photosensitive drums 1Y, 1M, 1C, and 1K of the image forming units PY, PM, PC, and PK. The intermediate transfer belt 10 is an example of an endless belt that carries a toner image on its outer peripheral surface and rotates. The intermediate transfer belt 10 is stretched by a driving roller 11 as a plurality of rollers (stretching rollers and support rollers), a tension roller 12 and a pre-transfer roller (auxiliary roller) 13. On the inner peripheral surface (back surface) side of the intermediate transfer belt 10, primary transfer brushes 14Y, 14M, which are brush-like primary transfer members serving as primary transfer means, are disposed at positions facing the photosensitive drums 1Y, 1M, 1C, 1K. 14C and 14K are arranged. The primary transfer brush 14 is urged (pressed) toward the photosensitive drum 1 via the intermediate transfer belt 10 to form a primary transfer portion (primary transfer nip) T1 where the intermediate transfer belt 10 and the photosensitive drum 1 are in contact with each other. . Further, on the outer peripheral surface (front surface) side of the intermediate transfer belt 10, a secondary transfer roller 15 that is a roller-like secondary transfer member as a secondary transfer unit is disposed at a position facing the drive roller 11. The secondary transfer roller 15 is urged (pressed) toward the driving roller 11 via the intermediate transfer belt 10, and a secondary transfer portion (secondary transfer nip) where the intermediate transfer belt 10 and the secondary transfer roller 15 come into contact with each other. ) T2 is formed. The secondary transfer roller 15 is an example of a transfer member that forms a transfer portion in contact with the outer peripheral surface of the belt and transfers a toner image from the belt to a recording material that is sandwiched and conveyed between the transfer portion and the belt. is there. The driving roller 11 is an example of a facing member that contacts the inner peripheral surface of the belt and faces the transfer member via the belt. The intermediate transfer belt 10 has a circumferential speed substantially the same as that of the photosensitive drum 1 in the direction of the arrow R2 in FIG. 1 in which the driving roller 11 moves in the same direction as the photosensitive drum 1 at the contact portion with the photosensitive drum 1. Is driven to rotate.

  Further, the pre-transfer roller 13 is disposed upstream of the secondary transfer portion T2 in the rotation direction of the intermediate transfer belt 10, and in the support portion S that is a portion where the intermediate transfer belt 10 is wound around the pre-transfer roller 13. The inner peripheral surface of the intermediate transfer belt 10 is supported. The pre-transfer roller 13 rotates following the rotation of the intermediate transfer belt 10. The pre-transfer roller 13 is intermediate to the recording material 6 upstream of the secondary transfer portion T2 in order to prevent image defects due to discharge from the intermediate transfer belt 10 to the recording material 6 upstream of the secondary transfer portion T2. They are arranged for the purpose of narrowing the gap between the surface of the transfer belt 10. The pre-transfer roller 13 is an example of a support member that supports the inner peripheral surface of the belt at a support portion upstream of the transfer portion in the rotation direction of the belt. The tension roller 12 is disposed downstream of the most downstream primary transfer portion T1K and upstream of the support portion S in the rotation direction of the intermediate transfer belt 10, and from the inner peripheral surface of the intermediate transfer belt 10 to the intermediate transfer belt. 10 is tensioned. The tension roller 12 is driven to rotate as the intermediate transfer belt 10 rotates.

  The toner image formed on the photosensitive drum 1 passes through the primary transfer portion T1 which is a contact portion between the photosensitive drum 1 and the intermediate transfer belt 10 and is subjected to the primary transfer voltage applied to the primary transfer brush 14 by the primary transfer voltage. Transfer (primary transfer) is performed on the outer peripheral surface of the intermediate transfer belt 10. For example, when forming a full-color image, yellow, magenta, cyan, and black toner images respectively formed on the photosensitive drum 1 of each image forming portion P are sequentially transferred onto the intermediate transfer belt 10 and transferred. A multiple toner image corresponding to the full color image is obtained. The primary transfer residual toner remaining on the surface of the photosensitive drum 1 after the primary transfer is removed from the photosensitive drum 1 by the cleaning device 4 and collected.

  On the other hand, in accordance with the timing at which the toner image on the intermediate transfer belt 10 reaches the secondary transfer portion T2, which is a contact portion between the intermediate transfer belt 10 and the secondary transfer roller 15, the recording material is transferred to the secondary transfer portion T2. 6 is conveyed. That is, in the feeding device 17 as a feeding unit, the uppermost recording material 6 placed on the feeding cassette 21 is fed out by the feeding roller 22. Thereafter, the recording material 6 is conveyed by a registration roller pair 16 that adjusts the skew correction and feeding timing of the recording material 6, and a secondary transfer unit by a conveyance guide 32 provided below the pre-transfer roller 13. Guided to T2. The registration roller pair 16 sandwiches and transports the recording material 6 by a transport unit (transport nip) U that is a contact portion of the rollers that are in pressure contact with each other. The conveyance guide 32 guides the recording material 6 to the secondary transfer portion T2 upstream of the secondary transfer portion T2 and in the vicinity of the pre-transfer roller 13 in the rotation direction of the intermediate transfer belt 10. The conveyance guide 32 guides the recording material 6 conveyed to the secondary transfer portion T2 from the front side (belt side surface side).

  The toner image on the intermediate transfer belt 10 is transferred to the surface of the recording material 6 (secondary transfer) by the secondary transfer voltage applied to the secondary transfer roller 15 in the process in which the recording material 6 passes through the secondary transfer portion T2. ) For example, when a full-color image is formed, the above-described multiple toner images on the recording material 6 are collectively transferred onto the recording material 6. Thereafter, the recording material 6 carrying the toner image is introduced into a fixing device 40 as fixing means, where it is heated and pressurized. Thereby, for example, four color toners are melted and mixed and fixed (fixed) to the recording material 6. Thereafter, the recording material 6 is discharged out of the main body of the image forming apparatus 100 as a printed matter.

2. Intermediate transfer belt, its stretching means, and secondary transfer roller Next, the intermediate transfer belt 10 in this embodiment, the driving roller 11, the tension roller 12 and the pre-transfer roller 13 constituting the stretching means, and the secondary The transfer roller 15 will be further described.

The intermediate transfer belt 10 has a two-layer structure of a base layer and a surface layer. The base layer is mainly composed of PEN (polyethylene naphthalate), and the surface layer is formed by coating the surface of the base layer with an acrylic resin. Is. The intermediate transfer belt 10 has a thickness of 65 μm and a volume resistivity of 1 × 10 ⁸ to 1 × 10 ¹¹ Ωcm. In this embodiment, PEN is used as the material of the base layer of the intermediate transfer belt 10, but the present invention is not limited to this. Examples thereof include materials such as polyimide resin, polyester, polycarbonate, polyarylate, acrylonitrile-butadiene-styrene copolymer (ABS), polyphenylene sulfide (PPS), and polyvinylidene fluoride (PVdF), and mixed resins thereof. In this embodiment, a belt having a two-layer structure is used as the intermediate transfer belt 10, but the present invention is not limited to the two-layer structure.

  The driving roller 11 is formed by coating an aluminum shaft having an outer diameter of 24 mm with EPDM (ethylene-propylene-diene terpolymer) having a thickness of 0.5 mm as an elastic layer. The tension roller 12 is an aluminum hollow shaft having an outer diameter of 20 mm. In this embodiment, the tension roller 12 applies a tension of 42 N on one side and 84 N in total pressure to the intermediate transfer belt 10 at both ends in the longitudinal direction. The pre-transfer roller 13 is a stainless steel hollow shaft having an outer diameter of 16 mm.

The secondary transfer roller 15 is an NBR (nitrile) having a thickness of 5 mm with a volume resistivity adjusted to 1 × 10 ⁶ to 1 × 10 ⁹ Ω · cm around a nickel-plated steel rod having an outer diameter of 6 mm. (Butadiene rubber) foamed sponge body is coated to an outer diameter of 16 mm. Further, the secondary transfer roller 15 is brought into contact with the intermediate transfer belt 10 with a pressure of 30 N, and is driven to rotate as the intermediate transfer belt 10 rotates.

3. Next, the configuration and positional relationship of the conveyance guide 32 in this embodiment will be described. FIG. 2 is an enlarged cross-sectional view of the periphery of the secondary transfer portion T2 in the image forming apparatus 100 of the present embodiment. 3 and 4 are schematic views showing the positional relationship of the conveyance guide 32. FIG. In the following description, the positional relationship and shape of each part are seen in a cross section substantially orthogonal to the rotation axis direction of the stretching means such as the driving roller 11 and the pre-transfer roller 13 as shown in FIG. 2 unless otherwise specified. Is the case. The conveyance direction of the recording material 6 that is sandwiched between the intermediate transfer belt 10 and the secondary transfer roller 15 and moves while being guided by the conveyance guide 32 in the secondary transfer portion T2 is also simply referred to as “conveyance direction”. The rotation direction of the intermediate transfer belt 10 is also simply referred to as “rotation direction”.

  First, the positional relationship between the conveyance path of the recording material 6 and the intermediate transfer belt 10 in this embodiment will be described. The end of the registration roller pair 16 on the downstream side in the conveyance direction of the conveyance unit U (hereinafter also referred to as “conveyance unit downstream end”) is denoted by Mr. Further, an end portion on the upstream side in the transport direction of the secondary transfer portion T2 (hereinafter also referred to as “transfer portion upstream end”) is referred to as M2. 2 is a tangent line (straight line) in FIG. 2 of the surface connecting the conveyance unit downstream end Mr and the transfer unit upstream end M2 which is the conveyance path of the recording material 6. Further, in FIG. 2, a virtual surface obtained by extending the stretched surface of the intermediate transfer belt 10 formed between the secondary transfer portion T2 and the support portion S of the intermediate transfer belt 10 by the pre-transfer roller 13 to the upstream side in the rotation direction. Let L be the tangent (straight line). The straight line M is the same as the tangent line of the conveyance unit (conveying nip) U of the registration roller pair 16. At this time, in this embodiment, the angle formed by the straight line M and the straight line L is 5 °, and the length of the straight line M is 38 mm. In order to suppress image blurring while sufficiently reducing the gap between the intermediate transfer belt 10 and the recording material 6 on the upstream side in the transport direction of the secondary transfer portion T2, the angle formed by the straight line M and the straight line L is It is preferably 1 ° or more and 10 ° or less, and more preferably 3 ° or more and 7 ° or less.

  Next, the configuration of the conveyance guide 32 in the present embodiment will be described. In this embodiment, the conveyance guide 32 is formed by molding a stainless steel sheet metal having a thickness of 1 mm. In this embodiment, the conveyance guide 32 extends over almost the entire area of the maximum width in the direction substantially orthogonal to the conveyance direction of the recording material P that can be used by the image forming apparatus 100. The transport guide 32 is positioned and fixed by a bottom metal plate 33 provided at a lower portion of the intermediate transfer belt 10 as a support means. An insulating member (not shown) is interposed between the bottom metal plate 33 and the conveyance guide 32. The conveyance guide 32 is electrically grounded via a 400 MΩ protective resistor (resistive element) (not shown). Thus, when the secondary transfer voltage is applied, the transfer current is prevented from escaping from the secondary transfer portion T2 through the recording material 6 and the conveyance guide 32 made of a metal that is a conductive material. Can do. Accordingly, it is possible to prevent the conveyance guide 32 from being overcharged and discharged due to friction between the recording material 6 and the conveyance guide 32 or transfer of charges between the charged recording material 6.

  In this embodiment, the conveyance guide 32 has a top portion A as a regulating portion that regulates the conveyance path of the recording material 6 on the secondary transfer roller 15 side (transfer member side) from the straight line L (virtual surface). Further, the conveyance guide 32 is inclined so as to approach the straight line L (virtual surface) from the top A to the downstream end B in the conveyance direction of the recording material 6 as it goes downstream in the conveyance direction of the recording material 6. It has a guide part 32a. At this time, the downstream end B of the inclined guide portion 32a in the conveyance direction of the recording material 6 is on the straight line L (on the virtual surface) or on the intermediate transfer belt 10 side of the straight line L (virtual surface). 10 and spaced apart. Further, in this embodiment, a registration roller pair 16 is provided that sandwiches and conveys the recording material 6 by a conveyance unit U on the upstream side of the conveyance guide 32 in the conveyance direction of the recording material 6. The top portion A of the transport guide 32 is arranged on a straight line M connecting the secondary transfer portion T2 and the transport portion U (on the surface connecting the secondary transfer portion T2 and the transport portion U). Furthermore, in this embodiment, the conveyance guide 32 has an entry guide portion 32b that is inclined so as to approach the straight line L (virtual surface) as it goes from the top A to the upstream side in the conveyance direction of the recording material 6. This will be described in more detail below.

  In this embodiment, the conveyance guide 32 is formed in a substantially V-shaped cross section (convex on the conveyance path side of the recording material 6) having one bent portion. And the top part (regulation part) A of the bent part is arranged on the straight line M. Here, the phrase “arranged on the straight line M” includes not only the case of being completely located on the straight line M, but also the case of being arranged close to the straight line M within an allowable error range. For example, an error of about ± 3 mm may be allowed. The position of the top portion A in the transport direction is arranged at a position where the distance from the transport portion downstream end Mr to the top portion A is 13 mm and the distance from the top portion A to the transfer portion upstream end M2 is 25 mm. Further, the length from the top A to the downstream end of the transport guide 32 in the transport direction (hereinafter also referred to as “guide downstream end”) B is 3 mm, and the guide downstream end B is arranged on the straight line L. The inclined guide portion 32a extends. Here, the phrase “arranged on the straight line L” includes not only the case of being completely located on the straight line L but also the case of being arranged close to the straight line L within an allowable error range. For example, an error of about ± 3 mm may be allowed.

  Next, the positional relationship of each member on the straight line L will be described. La, Lb, and Lc are intersections of the perpendicular line and the straight line L, respectively, which are dropped from the top A of the conveyance guide 32, the guide downstream end B, and the rotation center C of the pre-transfer roller 13 to the straight line L, respectively. In this case, the shape and arrangement of the conveyance guide 32 are set so that La, Lb, and Lc are arranged in this order from the upstream side in the conveyance direction. In this embodiment, the distance between the position La and the position Lb is 2 mm, and the distance between the position Lb and the position Lc is 6 mm.

4). Next, effects of the conveyance guide 32 in the present embodiment on the conveyance performance will be described.

  First, a comparative example used as a comparison target of this example will be described with reference to FIG. The image forming apparatus of the comparative example described below is the same as the present embodiment except for the shape and positional relationship of the conveyance guide. As the conveyance guide 34 of the comparative example, a sheet material 34b made of PET material having a thickness of 100 μm and a rigidity lower than that of the sheet metal 34a is formed on a stainless sheet metal 34a, and the tip of the sheet 34b protrudes 2 mm from the sheet metal 34a. What was affixed to was used. The leading end D of the sheet 34b of the conveyance guide 34 is located on a straight line M connecting the conveyance unit downstream end Mr and the transfer unit upstream end M2 as in the case of the present embodiment. The position of the sheet 34b in the conveying direction is 15 mm from the conveying unit downstream end Mr to the leading end D of the sheet 34b, and 23 mm from the leading end D of the sheet 34b to the transferring unit upstream end M2. It is arranged at the position. The distance between the leading end D of the sheet 34b and the straight line L is 1.7 mm.

In order to confirm the effect, a thick paper having a letter size (216 mm × 279 mm) and a basis weight of 163 g / m ² was used as the recording material 6. The rotation speed of the intermediate transfer belt 10 and the conveyance speed of the registration roller pair 16 are 50 mm / second. In addition, a single-color horizontal line image of 1 dot and 1 space was printed as an evaluation image in a range of a front margin of 5 mm, a left and right margin of 5 mm, and a rear end margin of 0 mm. Then, when 10 sheets were output continuously, the occurrence position of the trailing edge blur image from the trailing edge of the recording material 6 was confirmed. Table 1 shows the evaluation results of the comparative example and this example.

  In the comparative example, a trailing edge blur image was confirmed within a range of 6 mm from the trailing edge to the leading edge side of the recording material 6. On the other hand, in this embodiment, no trailing edge blur image occurred.

  The reason why the effect of suppressing the trailing edge blur image superior to that of the comparative example is obtained in the present embodiment is as follows. As shown in FIG. 7, in the case of the conveyance guide 34 of the comparative example, the posture of the recording material 6 before the trailing edge of the recording material 6 passes through the leading end D of the sheet 34b of the conveyance guide 34 is from the secondary transfer portion T2. The sheet 34b is bent in a bow shape (convex toward the intermediate transfer belt 10) toward the leading end D. When the rear end of the recording material 6 passes through the leading end D of the sheet 34b from the “recording material posture before rear end missing” in FIG. 7, the rear end of the recording material 6 is greatly displaced toward the intermediate transfer belt 10 side. . Then, when the position of the rear end of the recording material 6 rapidly changes to the “recording material posture after the trailing end” shown in FIG. 7, the vicinity of the rear end of the recording material 6 gives an impact to the intermediate transfer belt 10. As a result, the vicinity of the rear end of the recording material 6 rubs against the toner image on the intermediate transfer belt 10, thereby generating a rear end blur image. Further, as shown in FIG. 6, the intersections of the perpendicular line drawn from the front end portion D of the conveyance guide 34 and the rotation center of the pre-transfer roller 13 to the straight line L and the straight line L are Ld and Lc, respectively. . At this time, the position Ld is disposed upstream of the position Lc in the transport direction. Therefore, when the rear end of the recording material 6 passes through the front end portion D of the conveyance guide 34, the landing destination of the rear end on the surface of the intermediate transfer belt 10 is the upstream side in the rotation direction from the position Lc. 10 is a portion wound around the pre-transfer roller 13 (hereinafter also referred to as “winding portion”). As described above, if the landing point on the intermediate transfer belt 10 near the rear end of the recording material 6 is a winding portion, the amount of displacement of the rear end of the recording material 6 increases accordingly, and the impact at the time of landing increases. The trailing edge blur image is also likely to deteriorate. In the comparative example, the rear end blur image was confirmed particularly in the range corresponding to the wrapping portion (about 5 mm).

  On the other hand, in the present embodiment, as shown in FIG. 8, after the rear end of the recording material 6 passes through the top portion A of the conveyance guide 32, the slope of the inclined guide portion 32 a between the top portion A and the guide downstream end B is formed. Move along. Therefore, there is no sudden change in posture toward the intermediate transfer belt 10 near the rear end of the recording material 6. Further, the conveyance guide 32 of the present embodiment extends to a position where the guide downstream end B is in contact with the straight line L. Therefore, when the rear end of the recording material 6 moves away from the conveyance guide 32, the rear end portion of the recording material 6 is closer to the intermediate transfer belt 10 side than the straight line L, that is, the winding portion side of the intermediate transfer belt 10 around the pre-transfer roller 13. There is no displacement. That is, according to the conveyance guide 32 of the present embodiment, the rear end portion of the recording material 6 is slowly displaced toward the straight line L along the inclined guide portion 32a. Therefore, according to the present embodiment, it is possible to suppress the trailing edge blur image.

  In this embodiment, the shape and position of the transport guide 32 are set so that the distance between the position La and the position Lb is 2 mm, and the distance between the position Lb and the position Lc is 6 mm. On the other hand, when the distance between the position La and the position Lb is set to 0 mm, or the position Lb is set to be positioned upstream of the position La in the transport direction, the rear end of the recording material 6 causes the top portion A to be located. Since the slope after the passage is not formed, the trailing edge blur image is generated. Further, when the distance between the position Lb and the position Lc is set to 0 mm, or the position Lb is set to be located downstream of the position Lc in the transport direction, the guide downstream end B comes into contact with the intermediate transfer belt 10. End up. In this embodiment, the distance between the position Lb and the position Lc is set to 6 mm in order to provide a clearance between the guide downstream end B and the intermediate transfer belt 10 necessary for preventing this contact. In this way, in order to suppress the rear end blur image and prevent the contact downstream end B and the intermediate transfer belt 10 from contacting each other, La, Lb, and Lc are arranged in this order from the upstream side in the transport direction.

  In the present embodiment, the transport path of the recording material 6 is regulated by the top portion A of the transport guide 32 being arranged on the straight line M. For this reason, when the leading edge of the recording material 6 is conveyed toward the secondary transfer roller 15, the edge of the recording material 6 that is caused by the leading edge of the recording material 6 thrusting into the secondary transfer roller 15 can be suppressed. . Further, when the recording material 6 is conveyed to the surface side of the intermediate transfer belt 10, the recording material 6 and the toner image on the intermediate transfer belt 10 come into contact with each other before the secondary transfer portion T2, so Image rubbing caused by rubbing the toner image can also be suppressed.

  As described above, according to the present embodiment, it is possible to restrict the conveyance path of the recording material 6 fed from the registration roller pair 16 to the secondary transfer portion T2, and to suppress the trailing edge blur image due to the guide missing shock.

  In this embodiment, the guide downstream end B is arranged on the straight line L. However, as shown in FIG. 9, the guide downstream end B is located on the intermediate transfer belt more than the straight line L so that the inclined guide part (guide surface) 32 a formed between the top A and the guide downstream end B intersects the straight line L. You may arrange | position to the position close | similar to the pre-transfer roller 13 in 10 side. This also provides the same effect as in the present embodiment.

  In this embodiment, the conveyance guide 32 is provided with the entry guide portion 32b. As a result, the transfer material 6 can be conveyed more smoothly by guiding the tip of the transfer material 6 to the restricting portion A. However, this approach guide part 32b does not need to be provided from the viewpoint of suppressing the above-described rear end blur image. In addition, the conveyance guide 32 is not inclined from the restriction portion A to the upstream side in the conveyance direction as in the present embodiment, but has a shape having a portion extending from the restriction portion A in a direction substantially orthogonal to the straight line L. Also good.

  In the present embodiment, the inclined guide portion 32a of the conveyance guide 32 extends linearly so as to approach the straight line L as it goes downstream in the conveyance direction, but is not limited thereto. The inclined guide part 32a may have a curved surface such as a curved shape that is convex toward the straight line L.

Example 2
Next, another embodiment according to the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are substantially the same as those of the first embodiment. Therefore, elements having the same functions and configurations as those of the image forming apparatus of the first embodiment or corresponding to those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, the image forming apparatus 100 includes a back surface conveyance guide that guides the recording material 6 from the back surface side (the surface side on the transfer member side) on the upstream side in the conveyance direction of the secondary transfer portion T2. In the present embodiment, the conveyance guide 32 described in the first embodiment is referred to as a front surface conveyance guide with respect to the back surface conveyance guide. FIG. 10 is an enlarged sectional view of the periphery of the secondary transfer portion T2 in the present embodiment. The shape and positional relationship of the surface conveyance guide 32 of this embodiment are the same as those of the first embodiment.

  Next, the back surface conveyance guide 35 will be described. The back surface conveyance guide 35 is a mold member formed using polycarbonate and ABS. The back surface conveyance guide 35 regulates the entry path to the secondary transfer portion T2 at the leading end of the recording material 6 by guiding the recording material 6 from the back surface side upstream in the conveyance direction of the secondary transfer portion T2. That is, as shown in FIG. 10, the front end portion E as the back surface regulating portion of the back surface conveyance guide 35 is positioned upstream of the secondary transfer portion T2 on a straight line M connecting the conveyance portion downstream end Mr and the transfer portion upstream end M2. By being arranged on the side, the conveyance path at the front end of the recording material 6 is regulated by the back surface conveyance guide 35. In this embodiment, the front end E of the back surface conveyance guide 35 is arranged on the straight line M at a position 10 mm upstream from the transfer unit upstream end M2 in the conveyance direction.

  As described above, the back surface conveyance guide 35 guides the recording material 6 conveyed to the secondary transfer portion T2 from the surface side of the secondary transfer roller 15 on the downstream side in the conveyance direction of the recording material 6 relative to the front surface conveyance guide 32. To do. As will be described in detail later, the front end E that regulates the conveyance path of the recording material 6 in the back surface conveyance guide 35 is supported by the secondary transfer portion T2 and the pre-transfer roller 13 in the conveyance direction of the recording material 6. It arrange | positions between the parts S. Further, in this embodiment, the back surface conveyance guide 35 has a back surface entrance guide portion 35 a that is inclined so as to be separated from the intermediate transfer belt 20 as it goes upstream from the front end portion E in the conveyance direction of the recording material 6. In the present embodiment, the angle formed by the back surface intrusion guide portion (guide surface) 35a of the back surface transport guide 35 and the straight line M is 25 °.

Next, the results of comparing the effects of the recording material 6 with respect to the leading edge stain and the trailing edge blur image in the present example and the comparative example described in the first example will be described. Here, using a letter size (216 mm × 279 mm) at a basis weight 163 g / ^{m 2} cardboard and basis weight 60 g / ^{m 2} of thin paper, and outputs 10 sheets of the same evaluation image as in Example 1 each in a continuous recording material 6 And the occurrence position of the trailing edge blur image from the trailing edge of the recording material 6 was confirmed. Table 2 shows the evaluation results of the comparative example and this example. The tip edge contamination was marked with x when it occurred and ◯ when it did not.

  In the comparative example, the leading edge stain was generated on the thin paper, and the trailing edge blur image was generated in the range of 3 mm from the trailing edge on the thin paper and 6 mm from the trailing edge on the thick paper. On the other hand, in this embodiment, the leading edge stain and the trailing edge blur image did not occur on both the thin paper and the thick paper.

  The reason why the effect of suppressing the edge stain of the thin paper superior to that of the comparative example was obtained in the present example is as follows. As shown in FIG. 11, the recording material 6 fed from the registration roller pair 16 receives gravity in the downward direction in the figure. In the comparative example, when thick paper having a high stiffness is used as the recording material 6, the recording material 6 sent out from the registration roller pair 16 does not bend due to gravity and is tangent to the conveying portion (conveying nip) U of the registration roller pair 16. Along the straight line M to the secondary transfer portion T2. However, when thin paper with low stiffness is used, the recording material 6 bends in the direction of gravity, and the leading edge of the recording material 6 enters the secondary transfer roller 15 side from the straight line M. As a result, in the comparative example, the edge of the leading edge occurs with thin paper.

  On the other hand, in this embodiment as well, the recording material 6 fed from the registration roller pair 16 bends in the direction of gravity as in the comparative example, and the leading edge of the recording material 6 is conveyed from the straight line M to the secondary transfer roller 15 side. The However, in this embodiment, as shown in FIG. 12, the leading edge of the recording material 6 is guided by the back surface conveyance guide 35 arranged upstream of the secondary transfer portion T2, and after the return to the conveyance path of the straight line M, the secondary transfer is performed. Enter the part T2. Thereby, in the present embodiment, it is possible to suppress the edge edge contamination with thin paper. Also in this embodiment, as in the first embodiment, the rear end blur image can be suppressed by the surface conveyance guide 32.

  As described above, according to this embodiment, regardless of the stiffness of the recording material 6, the conveyance of the recording material 6 sent out from the registration roller pair 16 to the secondary transfer portion T <b> 2 is restricted to suppress the leading edge contamination, It is possible to suppress the rear end blur image due to the guide dropout shock.

  In the present embodiment, the position on the straight line M of the front end E of the back surface conveyance guide 35 is arranged at a position 10 mm upstream from the transfer section upstream end M2, but the present invention is not limited to this. As shown in FIG. 12, the position of the front end E of the back surface conveyance guide 35 is linear with the secondary transfer unit upstream end M2 and a perpendicular line N extending from the rotation center C of the pre-transfer roller 13 to the surface of the intermediate transfer belt 10. It can be arranged at any position between the intersection Mc with M. Such an arrangement is preferable for the following reason. In order to stabilize the distance between the recording material 6 and the stretched surface of the intermediate transfer belt 10 between the secondary transfer portion T2 and the support portion S before the leading end of the recording material 6 enters the secondary transfer portion T2. The tip E of the back surface conveyance guide 35 should be close to the transfer unit upstream end M2 on the straight line M. On the other hand, when the leading end E of the back surface transport guide 35 is disposed upstream of the position Mc in the transport direction, the front end of the recording material 6 passes through the front end portion E of the back surface transport guide 35 to the pre-transfer roller 13 of the intermediate transfer belt 10. There is a possibility of rushing into the winding part. As a result, the recording material 6 may enter the upstream side in the rotation direction of the intermediate transfer belt 10.

Others While the present invention has been described with reference to specific embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiment, the conveyance guide is formed by molding a sheet metal and has substantially the same cross-sectional shape in the entire region in the longitudinal direction, but is not limited thereto. The conveyance guide only needs to have the section having the cross-sectional shape described in the above-described embodiment, and may be constituted by a plurality of members divided in a direction substantially orthogonal to the recording material conveyance direction, for example. Further, for example, it may be configured by a member provided with ribs having the cross-sectional shapes described in the above-described embodiments at a plurality of locations in a direction substantially orthogonal to the recording material conveyance direction.

  In the above-described embodiments, the case where the endless belt is an intermediate transfer belt has been described. However, the present invention is not limited to this. For example, the present invention can be applied to any endless belt that carries and rotates a toner image transferred to a recording material in a transfer portion, such as a photosensitive belt, and the same effect as the above-described embodiment can be obtained. .

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 13 Roller before transfer 15 Secondary transfer roller 16 Registration roller 32 Conveyance guide 32a Inclination guide portion 32b Incoming guide portion A Top portion of conveyance guide (regulation portion)
B End of conveyance guide downstream in conveyance direction C Rotation center of pre-transfer roller L Extension line (imaginary surface) of tension surface of intermediate transfer belt
M Transfer material transport path

Claims (8)

An endless belt that carries a toner image on its outer peripheral surface and rotates;
A transfer member that contacts a peripheral surface of the belt to form a transfer portion, and transfers a toner image from the belt to a recording material that is sandwiched and conveyed between the belt and the transfer portion;
A facing member that contacts the inner peripheral surface of the belt and faces the transfer member via the belt;
A conveyance guide for guiding the recording material conveyed to the transfer section from the belt side surface;
A support member that supports an inner peripheral surface of the belt at a support portion on the upstream side in the rotation direction of the belt from the transfer portion;
Have
In the image forming apparatus for forming a stretched surface of the belt between the transfer unit and the support unit,
The transport guide includes a restricting portion that restricts a recording material transport path on the transfer member side of the virtual surface when a surface obtained by extending the stretched surface in the belt rotation direction is a virtual surface; And an inclined guide portion that is inclined so as to approach the virtual plane as it goes downstream in the recording material conveyance direction from the recording medium to the downstream end in the recording material conveyance direction, and the recording material of the inclination guide portion An image forming apparatus, wherein an end portion on the downstream side in the transport direction is disposed on the virtual surface or at a distance from the belt on the belt side with respect to the virtual surface.   It has a roller pair that sandwiches and conveys the recording material at a conveyance unit upstream of the conveyance guide in the conveyance direction of the recording material, and the regulation unit of the conveyance guide connects the transfer unit and the conveyance unit The image forming apparatus according to claim 1, wherein the image forming apparatus is disposed on a surface.   3. The image forming apparatus according to claim 1, wherein the conveyance guide has an entry guide portion that is inclined so as to approach the virtual plane from the regulation portion toward the upstream side in the conveyance direction of the recording material. .   The image forming apparatus according to claim 1, wherein the conveyance guide is formed of a conductive material and is electrically grounded through a resistance element. A back surface transport guide for guiding the recording material transported to the transfer unit from the surface side of the transfer member on the downstream side in the transport direction of the recording material from the transport guide;
5. The back surface regulating portion that regulates the conveyance path of the recording material in the back surface conveyance guide is disposed between the transfer portion and the support portion in the recording material conveyance direction. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 5, wherein the back surface conveyance guide includes a back surface entrance guide portion that is inclined away from the belt as it goes upstream from the back surface regulating portion in the recording material conveyance direction. .   The image forming apparatus according to claim 1, wherein the transfer member is a roller that is in pressure contact with the belt.   8. The belt according to claim 1, wherein the belt is an intermediate transfer member that conveys a toner image transferred from an image carrier in order to transfer the toner image to a recording material at the transfer unit. Image forming apparatus.

Images