Sheet transport device and image forming apparatus

Abstract

By using injection-molded transport guides, the occurrence of printing defects caused by water droplets adhering to the recording material is suppressed. [Solution] A sheet conveying device for conveying recording material, provided in an image forming apparatus having an image forming unit and a heating unit, comprising: a conveying unit and an injection-molded conveying guide 123 that forms a conveying path, having a curved portion 123b for forming a curved path in at least a part of the conveying path, wherein a plurality of ribs 123a are provided on the surface of the curved portion 123b that extend along the conveying direction of the recording material and guide the recording material, the plurality of ribs 123a include a first rib 123a1 and a second rib 123a2 adjacent to the first rib 123a1, and the second rib 123a2 is positioned offset from the first rib 123a1 in the width direction perpendicular to the conveying direction and in the conveying direction such that a gap is formed between the second rib 123a1 and the first rib 123a1.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus such as a printer, a copier, or a facsimile apparatus that uses an electrophotographic method or an electrostatic recording method, and a sheet conveying apparatus provided in the image forming apparatus for conveying a sheet-like recording material.

Background Art

[0002] Conventionally, in an image forming apparatus that forms an image on a recording material such as paper using toner by an electrophotographic image forming process, heat and pressure are applied to the paper on which the toner image is formed to fix the toner image on the paper. In such an image forming apparatus, due to the evaporation of moisture in the heated recording material, the air containing moisture flows to the sheet conveying apparatus that conveys the recording material, and the moisture in the air condenses, causing water droplets to adhere to the conveying path in the sheet conveying apparatus. Adhesion of water droplets to the recording material may cause various printing defects, such as image defects due to contamination of the toner image, paper jams or paper wrinkles due to deformation of the paper caused by water droplets, poor accommodation on the paper discharge tray, and damage to the paper itself. Therefore, Patent Document 1 discloses a configuration in which a water droplet holding shape is provided between a plurality of conveying ribs provided on the conveying path to suppress the fall of water droplets and reduce the amount of water droplets adhering to the recording material. However, when water droplets adhere to the conveying rib that extends long in the conveying direction of the recording material provided on the conveying path, a large amount of water droplets will adhere to the same position of the recording material from the conveying rib, which may cause printing defects such as image defects. On the other hand, for a configuration in which the conveying rib is arranged obliquely with respect to the conveying direction as disclosed in Patent Document 2, the water droplets adhering to the recording material are dispersed in the width direction of the recording material, so that the occurrence of printing defects can be suppressed.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

[0004] However, when the product is primarily manufactured by injection molding and the transport guide that constitutes the transport path is curved, it is difficult to manufacture the product by placing ribs diagonally to the transport direction on the curved portion of the transport guide due to mold constraints such as undercuts.

[0005] Therefore, the objective of the present invention is to suppress the occurrence of printing defects caused by water droplets adhering to the recording material by using an injection-molded transport guide. [Means for solving the problem]

[0006] To achieve the above objective, the sheet conveying device according to the present invention is An image forming apparatus having an image forming unit for forming an image on a sheet-shaped recording material and a heating unit for heating the recording material, wherein a sheet conveying device is provided for conveying the recording material, A transport unit for transporting the aforementioned recording material, A transport guide that forms a transport path through which the recording material is transported, comprising an injection-molded transport guide having a curved portion for forming a curved path in at least a part of the transport path, Equipped with, On the surface of the curved portion facing the recording material, a plurality of ribs are provided that extend along the transport direction of the recording material and guide the recording material. The plurality of ribs include a first rib and a second rib adjacent to the first rib, The second rib is characterized in that it is positioned offset from the first rib in the width direction perpendicular to the conveying direction and in the conveying direction, such that a gap is formed between the second rib and the first rib. [Effects of the Invention]

[0007] According to the present invention, by using an injection-molded transport guide, it is possible to suppress the occurrence of printing defects caused by water droplets adhering to the recording material. [Brief explanation of the drawing]

[0008] [Figure 1] This is a schematic cross-sectional view of an image forming apparatus according to the first embodiment. [Figure 2] This is a cross-sectional view of the fixing device and surrounding components according to the first embodiment. [Figure 3] This figure shows a separation guide according to the first embodiment. [Figure 4] This figure shows the paper output guide according to the first embodiment. [Figure 5] This figure shows the first transport guide according to the first embodiment. [Figure 6] This figure shows the second transport guide according to the first embodiment. [Figure 7] This figure shows the positional relationship of the ventilation holes according to the first embodiment. [Figure 8] This figure shows the transport path of the transported paper during single-sided printing according to the first embodiment. [Figure 9] This figure shows the transport path of the transported paper during double-sided printing according to the first embodiment. [Figure 10] This figure shows the transport path up to the formation of the second image according to the first embodiment. [Figure 11] This is a cross-sectional view of the fixing device and surrounding components according to the second embodiment. [Figure 12] These are a front view and a perspective view of the second transport guide according to the second embodiment. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments for implementing the present invention will be exemplarily described in detail with reference to the drawings. However, dimensions, materials, shapes, relative arrangements, etc. of the components described in the embodiments should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, the scope of the present invention is not intended to be limited to the following embodiments. Examples of image forming apparatuses to which the present invention is applicable include printers, copiers, etc. that utilize an electrophotographic method or an electrostatic recording method. Here, a case where the present invention is applied to a laser printer will be described.

[0010] <Example 1> (Description of the entire image forming apparatus) The image forming apparatus 100 according to Example 1 of the present invention will be described. FIG. 1 is a schematic cross-sectional view of the image forming apparatus 100 in this embodiment. The image forming apparatus 100 includes an image forming unit 11 that forms a toner image on a conveyance sheet S as a sheet-like recording material, a fixing unit 12 that fixes the toner image on the conveyance sheet S, and a sheet conveyance device 13 that conveys the conveyance sheet S. The sheet conveyance device 13 includes a plurality of conveyance guides that form a conveyance path and a conveyance unit that includes rollers and the like.

[0011] First, the image forming operation in the image forming unit 11 of the image forming apparatus 100 will be described. The photosensitive drum (image carrier) 101 provided in the image forming unit 11 is irradiated with laser light 102a by a laser scanner unit (optical scanning device) 102 according to image information instructed from an external device or the like, and an electrostatic latent image is formed. The electrostatic latent image formed on the photosensitive drum 101 is developed as a toner image using toner by a developing roller 110.

[0012] On the other hand, the conveyance sheet S stored in the paper feed stacking tray 109 is separated one by one by a separation unit including a paper feed roller 103 and fed to the image forming unit 11. Then, the conveyance sheet S is conveyed to a transfer nip portion N1 formed by the photosensitive drum 101 and a transfer roller 1C by a conveyance roller 104, and the toner image is transferred. The conveyance sheet S to which the toner image has been transferred is conveyed to the fixing unit 12 At the fixing nip portion N2 formed by the film unit 106 and the pressure roller 107, heating and pressing are performed, so that the toner image is fixed on the conveyance paper S. The conveyance paper S on which the toner image is fixed is discharged to the discharge tray 111 by the discharge roller 108.

[0013] In addition, the image forming apparatus 100 of the present embodiment is of a toner supply type in which the user supplies toner from the toner supply port 112. However, even in the case of a process cartridge replacement type in which the photosensitive drum, the developing roller, and the toner are integrated and replaced, the same configuration can be adopted.

[0014] Further, the above image forming apparatus is described by taking a monochrome laser printer using a single-color monochrome toner as a representative example. However, the application of the present invention is not limited to this, and it is also possible to apply it to a color laser printer such as a tandem type in which two or more color toners are transferred onto a recording material via an intermediate transfer belt to form an image.

[0015] (Overall Configuration of Fixing Unit 12) Details of the fixing unit 12, which is a heating unit for heating the conveyance paper S, will be described. FIG. 2 is a cross-sectional view showing the fixing unit 12 and peripheral members. The fixing unit 12 includes a film unit 106 in which a heater is provided in a cylindrical film, and a pressure roller 107. The film unit 106 and the pressure roller 107 are in contact with each other to form a fixing nip portion N2. An entrance guide 113 and a shutter 114 are provided on the upstream side in the conveyance direction of the conveyance paper S of the fixing unit 12. The shutter 114 is rotatably attached to the entrance guide 113 so that the user does not accidentally touch the film unit 106. The shutter 114 rotates in conjunction with the opening and closing of the rear door 115. When the rear door 115 is open, it rotates in the direction of arrow R to be in a closed state, preventing the user from touching the film unit 106 or the like.

[0016] A separation guide 116 and a paper discharge lower guide 117 are provided downstream of the fixing unit 12 in the transport direction. A paper discharge lower guide roller 120 is attached to the paper discharge lower guide 117, which guides the transport paper S transported from the fixing nip unit N2. Downstream of the separation guide 116 in the transport direction, a paper discharge upper guide 121 is provided opposite the paper discharge lower guide 117. The paper discharge upper guide 121, together with the paper discharge lower guide 117, forms a transport path to the paper discharge tray 111. A paper discharge roller 108 provided on the paper discharge upper guide 121, together with a paper discharge roller 122 provided opposite it, forms a paper discharge nip unit N3, and transports the transport paper S to the paper discharge tray 111.

[0017] Downstream of the separation guide 116 in the transport direction, a separate transport path is provided for transporting the paper S, which has finished fixing the first side in the fuser unit 12 during double-sided printing, back to the image forming unit 11, in addition to the transport path to the output tray 111. The transport path for double-sided printing is formed by the first transport guide 123 and the second transport guide 124, and includes a curved path in at least part of it. The first transport guide 123, which has a curved section for forming the curved path, is located above the fuser unit 12 and the separation guide 116.

[0018] Next, the configuration of the transport guides that form each transport path will be explained in detail. Figure 3(a) is a plan view of the separation guide 116, and Figure 3(b) is a perspective view of the separation guide 116. The separation guide 116 has transport ribs 116a on the surface facing the transported paper S. A paper discharge sensor 118 is attached to the separation guide 116 to detect the transported paper S immediately after it has passed through the fixing unit 12. Separation guide rollers 119 are also attached to the separation guide 116 to prevent the toner from the first side of the transported paper S from adhering to the transport ribs 116a provided on the separation guide 116 during double-sided printing.

[0019] When the transported paper S is heated in the fixing unit 12, the moisture contained in the transported paper S evaporates and mixes with the air, and condensation can occur, causing water droplets to adhere to the transport path. Since the heated air rises, water droplets are particularly likely to adhere to the transport path located above the fixing unit 12. Water droplets tend to adhere easily. If only a small amount of water droplets adhere from the transport rib to the transport paper, they evaporate quickly, preventing printing defects such as image defects. However, if the transport rib extends long along the transport direction, water droplets will continue to adhere to the same location in the width direction of the transport paper, resulting in a large amount of water droplets adhering and potentially causing printing defects. Therefore, in this embodiment, the transport rib 116a is positioned diagonally on the separation guide 116 at a predetermined angle with respect to the transport direction. Even if the transport rib is long in the transport direction, positioning it diagonally allows the water droplets adhering from the transport rib to the transport paper S to be dispersed in the width direction perpendicular to the transport direction. In other words, a large amount of water droplets do not adhere to the same location on the transport paper S in the width direction, thus suppressing the occurrence of printing defects due to water droplet adhesion compared to the case where the transport rib is positioned along the transport direction. In addition, the separation guide 116 is provided with ventilation holes 116b. The ventilation holes 116b allow the water vapor generated when the transport paper S is heated in the fixing unit 12 to flow upward along with the heated air, thereby suppressing the adhesion of water droplets to the separation guide 116.

[0020] Figure 4 is a plan view of the paper discharge guide 121. The paper discharge guide 121 has transport ribs 121a on the surface facing the transported paper S. The multiple transport ribs 121a are arranged diagonally with respect to the transport direction on the paper discharge guide 121, similar to the separation guide 116. Because the transport ribs 121a are arranged diagonally with respect to the transport direction, even if water droplets adhere to the transport ribs 121a, the water droplets that adhere from the transport ribs 121a to the transported paper S can be dispersed in the width direction.

[0021] Figure 5(a) is a plan view of the first transport guide 123 having a characteristic configuration of the present invention, and Figure 5(b) is a perspective view of the first transport guide 123. The first transport guide 123 has a curved portion 123b on the surface facing the transported paper S which is curved in a convex shape, and is located on the inner circumference side of the curved path in the transport path, forming a curved transport path for the transported paper S, which has finished fixing the image on the first surface, to be transported again to the image forming unit 11. Since water droplets can adhere to the first transport guide 123, it is preferable to arrange the transport ribs diagonally with respect to the transport direction, such as the separation guide 116 and the paper discharge guide 121, in order to suppress the occurrence of printing defects. The curved portion 123b is curved from the upstream side to the downstream side in the transport direction. However, in the first transport guide 123 manufactured by injection molding, it is extremely difficult to mold the transport ribs diagonally with respect to the transport direction on the curved portion 123b due to mold constraints such as undercuts. Furthermore, manufacturing curved conveyor guides with angled conveyor ribs using other methods such as machining is undesirable from a cost perspective.

[0022] On the other hand, as shown in Figure 5(a), the first transport guide 123 in this embodiment has a plurality of transport ribs 123a that extend along the transport direction and are discretely arranged with gaps between them. In other words, when the part of the first transport guide 123 that does not come into contact with the transported paper S is considered a non-contact part, the entire transport rib 123a is surrounded by the non-contact part. To put it another way, when the part of the first transport guide 123 that can come into contact with the transported paper S is considered a contactable part, there is no contactable part between adjacent transport ribs 123a. The length of each transport rib 123a in the transport direction is shorter than the length of the curved part 123b of the first transport guide 123 in the transport direction.

[0023] Multiple transport ribs 123a are discretely arranged on the curved section 123b from the upstream end 123b1 to the downstream end 123b2 in the transport direction. In addition, in the width direction perpendicular to the transport direction, multiple transport ribs 123a are discretely arranged from one end to the other of the paper-passing area W, which is the area through which the largest size of paper that can be passed by the image forming apparatus 100 passes, so that transport papers of different sizes can be transported appropriately. The range in which the transport ribs are placed within the paper-passing area on the transport guide can be appropriately changed considering the transportability of the paper.

[0024] Here, a plurality of transport ribs 1 are provided in close proximity to each other within region A shown in Figure 5(a). Focusing on 23a, the positional relationship of the conveying ribs 123a will be explained in detail. In this embodiment, multiple conveying ribs 123a are intermittently arranged within region A. Among the conveying ribs 123a within region A, the conveying rib located on the upstream side in the conveying direction will be called the first rib 123a1, and the rib adjacent to the first rib 123a1 in the width direction will be called the second rib 123a2, and the relationship between adjacent conveying ribs will be explained. In the conveying direction, the first rib 123a1 has a first upstream end and a first downstream end, and the second rib 123a2 has a second upstream end and a second downstream end. The first rib 123a1 and the second rib 123a2 have a second upstream end in the conveying direction. The first rib is positioned between the first upstream end and the first downstream end, and the first downstream end is positioned between the second upstream end and the second downstream end. In other words, when viewed from the width direction, the first rib 123a1 and the second rib 123a2 are positioned so that a portion of them overlap. By positioning them in this way, there is no gap in the transport direction between the first rib 123a1 and the second rib 123a2, so that the transported paper S can be transported properly. The transported paper S is transported in contact with at least one of the first rib 123a1 and the second rib 123a2. Furthermore, within region A, there is a third rib 123a3 located downstream of the second rib 123a2 in the transport direction, and a fourth rib 123a4 located downstream of the third rib 123a3 in the transport direction. The first rib 123a1, the second rib 123a2, the third rib 123a3, and the fourth rib 123a4 are arranged sequentially in the width direction. In the conveying direction, the third rib 123a3 has a third upstream end and a third downstream end, and the fourth rib 123a4 has a fourth upstream end and a fourth downstream end. The positional relationship between the second rib 123a2 and the third rib 123a3, and the positional relationship between the third rib 123a3 and the fourth rib 123a4, is the same as the positional relationship between the first rib 123a1 and the second rib 123a2. In addition, the downstream end of the first rib 123a1 is located upstream of the upstream end of the third rib 123a3. As described above, the first rib 123a1, the second rib 123a2, the third rib 123a3, and the fourth rib 123a4 are arranged from the upstream side to the downstream side in the conveying direction of the conveyed paper S.

[0025] The first transport guide 123 in this embodiment has a large number of transport ribs 123a arranged in the width direction in the same positional relationship as the region A described above. In other words, there are multiple first ribs 123a1, second ribs 123a2, third ribs 123a3, and fourth ribs 123a4. Note that the first ribs 123a1, second ribs 123a2, third ribs 123a3, and fourth ribs 123a4 arranged in areas other than region A on the curved section 123b do not need to be arranged in exactly the same positional relationship as in region A. For example, various modifications are possible as long as they do not interfere with the transport of the paper, such as providing second ribs 123a2 on both sides in the width direction relative to the first rib 123a1. The transport ribs 123a extend along the transport direction, and the curved section 123b curves from the upstream side to the downstream side in the transport direction. By adopting this configuration, when the first transport guide 123 is manufactured by injection molding, transport It is possible to form the rib 123a on the curved portion 123b. On the other hand, by arranging the multiple transport ribs 123a discretely in the width direction and the transport direction, it is possible to suppress the occurrence of printing defects caused by water droplets adhering to the recording material, as will be described later. The effect of suppressing the occurrence of printing defects caused by water droplets will be described in detail later. In addition, the length, shape, and arrangement position of the transport guide in the present invention are not limited to the configuration of this embodiment, and various changes are possible as long as they do not interfere with the transport of the transported paper. For example, although the region A of the first transport guide 123 is curved over the entire area in the transport direction, there may be a part that extends linearly in some places.

[0026] Figure 6(a) is a front view of the second transport guide 124, and Figure 6(b) is a perspective view of the second transport guide 124. Spurs (rollers, rotating bodies) 125 are attached to the second transport guide 124, which faces the first transport guide 123 in the transport path. In this embodiment, eight spurs 125 are provided on the second transport guide 124 so as to face the first transport guide 123, and each spur 125 is offset in the transport direction and width direction. Furthermore, the second transport guide 124 has a plurality of ventilation holes 124a. The ventilation holes 124a allow water vapor generated in the fixing section 12 to be discharged to the outside of the machine. The second transport guide 124 is also attached to the outer cover 1 It is attached to and secured to the 26.

[0027] Figure 7(a) is a plan view of the outer cover 126 covering the top surface of the image forming apparatus 100, as seen from the top, showing the positional relationship between the ventilation holes 126a of the outer cover 126 and the ventilation holes 124a of the second transport guide 124. Figure 7(b) is a cross-sectional view thereof. The outer cover 126 also has multiple ventilation holes 126a, similar to the second transport guide 124. As shown in Figure 7(a), when viewed from the top, the ventilation holes 126a of the outer cover 126 and the ventilation holes 124a of the second transport guide 124 are positioned offset from each other. By arranging the ventilation holes 126a of the outer cover 126 and the ventilation holes 124a of the second transport guide 124 in this way, foreign matter from the top surface is prevented from entering the image forming apparatus, while water vapor moves in the direction of arrow D shown in Figure 7(b) and is discharged outside the machine.

[0028] Downstream from the second transport guide 124 in the transport direction, a rear transport guide 115a is provided, which is integrally formed with the rear door 115 and faces the first transport guide 123. The first transport guide 123, the second transport guide 124, and the rear transport guide 115a guide the transport paper S, which has finished fixing the first side during double-sided printing, back to the image forming unit 11.

[0029] (Paper transport path during single-sided printing) The transport path of the transport paper S during single-sided printing will be explained using Figure 8. Figure 8(a) shows the transport of the transport paper S to the fuser nip section N2, Figure 8(b) shows the transport of the transport paper S to the discharge nip section N3, and Figure 8(c) shows the discharge of the transport paper S to the discharge tray 111.

[0030] First, the transported paper S fed from the paper feed tray 109 has an image transferred to it by the photosensitive drum 101 and transfer roller 105 in the transfer nip section N1 of the image forming unit 11. After that, the transported paper S is guided by the inlet guide 113 and transported to the fixing nip section N2 formed by the film unit 106 and pressure roller 107. In the fixing nip section N2, the toner transferred to the transported paper S is fixed by heating and pressurizing. After fixing, the transported paper S is guided by the separation guide 116 and the paper discharge guide 117 and transported to the paper discharge nip section N3. Even if water droplets adhere to the transport ribs 116a of the separation guide 116, since the transport ribs 116a are provided at an angle to the transport direction, the water droplets adhering to the transported paper S can be dispersed in the width direction, thereby suppressing the occurrence of printing defects.

[0031] The transported paper S is guided by the upper paper discharge guide 121 and transported to the paper discharge nip section N3 formed by the paper discharge roller 108 and the paper discharge roller 122. Even if water droplets adhere to the transport rib 121a of the upper paper discharge guide 121, since the transport rib 121a is provided at an angle to the transport direction, the water droplets adhering to the transported paper S can be dispersed in the width direction, thereby suppressing the occurrence of printing defects. At this time, the leading edge of the transported paper S has entered the paper discharge nip section N3, but the trailing edge is held in place by the fixing nip section N2. At this time, the transport speed of the paper discharge roller 108 is set to be faster than the transport speed of the pressure roller 107, so that the transported paper S is pulled in the transport direction. Due to the tension applied to the transported paper S, the transported paper S may rub strongly against the transport rib provided on the lower paper discharge guide 117. Therefore, by providing the paper discharge guide roller 120 on the paper discharge guide 117, the fixed image on the transport paper S is prevented from being peeled off by the transport ribs of the paper discharge guide 117. After the rear end of the transport paper S passes through the fixing nip section N2, the transport paper S is transported by the paper discharge roller 108 and paper discharge roller 122 of the paper discharge nip section N3 and discharged onto the paper discharge tray 111.

[0032] (Paper transport path during double-sided printing) The transport path of the transport paper S during double-sided printing will be explained using Figures 9 and 10. The transport path is the same as for single-sided printing until the image fixing of the first side is complete and the rear end of the transport paper S exits the fixing nip, so this explanation will be omitted. The transport path of the transport paper S after this point will be explained. Figure 9(a) Figure 9(b) shows the state after the transported paper S has passed through the fixing nip section N2, Figure 9(c) shows the transported paper S being transported as the paper discharge roller 108 rotates in the reverse direction, and Figure 9(c) shows the transported paper S passing through the paper discharge nip section N3 and traveling along a curved path.

[0033] The transport path described below describes how the transport paper S, after the image has been fixed to the first side, is transported back to the image forming unit 11 to transfer the image to the second side, which is the reverse side of the first side. After the transport paper S leaves the fixing nip section N2, when the trailing edge of the transport paper S passes the leading edge 123c of the first transport guide 123, the paper discharge roller 108 rotates in the reverse direction. When the paper discharge roller 108 rotates in the reverse direction, the trailing edge of the transport paper S (hereafter referred to as the leading edge of the second side) is guided and transported by the first transport guide 123, which forms a curved path. At this time, the transport paper S passes vertically above the transport rib 123a that protrudes from the first transport guide 123, which is located on the inner circumference side of the curved path, and is transported in a way that it rubs against the transport rib 123a. Then, any water droplets attached to the leading edge of the transport rib 123a of the first transport guide 123 are scraped off by the leading edge of the second side of the transport paper S. If the transport ribs, which are located on a curved section, extend long along the transport direction, a large amount of water droplets will adhere to the same position in the width direction at the leading edge of the transported paper. When a large amount of water droplets adhere to the transported paper in this way, the droplets do not evaporate completely before reaching the image forming section, and water droplets also adhere to the photosensitive drum. Since water droplet adhesion to the photosensitive drum is a cause of printing defects, it is important during double-sided printing to prevent water droplets adhering from the transport ribs to the transported paper from concentrating at the same position on the transported paper along the curved path.

[0034] In this embodiment, the first transport guide 123 has transport ribs 123a that extend short along the transport direction, which are discretely arranged in the transport direction and width direction such that there are gaps between the transport ribs 123a that extend along the transport direction. Therefore, even if water droplets adhere to the transport ribs 123a and the leading edge of the second side of the transported paper S scrapes off the water droplets, a large amount of water droplets will not concentrate and adhere to the same position in the width direction of the transported paper S. In other words, according to the present invention, the water droplets that adhere from the transport ribs to the transported paper are dispersed in the width direction and become small amounts, and evaporate before the transported paper re-enters the image fixing section, thus suppressing the adhesion of water droplets to the photosensitive drum. Furthermore, it is possible to suppress the occurrence of image defects due to toner image smudges caused by water droplet adhesion, and other printing problems such as paper jams due to paper deformation.

[0035] In the transport path for double-sided printing, the transported paper S is transported while being guided not only by the transport ribs 123a on the first transport guide 123 but also by the spurs 125 of the second transport guide 124. Furthermore, downstream of the second transport guide 124 in the transport direction, the transported paper S is transported toward the image forming unit 11, guided by the rear transport guide 115a which is integrally formed with the rear door 115. As mentioned above, the transport ribs 121a of the paper discharge guide 121 are arranged diagonally with respect to the transport direction, and the spurs 125 transport the transported paper S while rotating. In addition, multiple protrusions are formed on the surface of the spurs 125, and the tips of the protrusions come into contact with the transported paper S. Therefore, it is possible to suppress the accumulation of large amounts of water droplets concentrated in the same position on the transported paper S.

[0036] Figure 10 shows the transport path for double-sided printing, through which the transported paper S passes to the image forming unit 11, indicated by arrows. After being transported over the transport ribs 123a and the rear transport guide 115a, the transported paper S then enters the transport nip section N4 formed by the double-sided roller 128 and the double-sided transport roller 127, and is transported to the transport roller 104 by the rotation of the double-sided roller 128. Then, the transported paper S that has entered the image forming unit 11 has the second image formed by the photosensitive drum 101 and the transfer roller 105 in the transfer nip section N1, and is then transported to the fuser section 12. After the image is fixed in the fuser nip section N2 of the fuser section 12, the transported paper S is discharged onto the output tray 111 via the same path as in single-sided printing.

[0037] (Effects of the invention) With the above configuration, if water droplets adhere to the ribs provided on the curved portion of the transport guide, Even if moisture is present, it can disperse water droplets adhering to the transported paper in the width direction, thereby suppressing the occurrence of printing defects such as image defects caused by moisture adhering to the transported paper.

[0038] In this embodiment, the transport guide is configured to include transport ribs intermittently arranged among multiple transport ribs provided on the curved section. However, the present invention is not limited to the configuration shown in Figure 5. The arrangement of the transport ribs on the curved section may be regular or irregular, and various modifications are possible as long as they do not interfere with the transport of the paper.

[0039] Furthermore, in this embodiment, the present invention was applied only to the transport guide that constitutes the transport path for double-sided printing, located above the fixing unit, among the transport guides that make up the sheet transport device. However, the present invention is not limited to the transport guide described above, but can be applied to various transport guides. For example, the present invention can be applied not only to sheet transport devices installed inside image forming apparatuses as in this embodiment, but also to transport guides installed in sheet transport devices in paper discharge devices that can be attached externally to image forming apparatuses. The ease with which water droplets adhere to the transport ribs varies depending on the operating environment and the arrangement of each component. Therefore, by appropriately arranging the transport ribs on each transport guide according to the device configuration, an effective effect of suppressing the occurrence of printing defects can be obtained.

[0040] <Example 2> Next, the second transport guide 224 according to Example 2 will be described using Figures 11 and 12. In the configuration of Example 2, components similar to those in Example 1 are denoted by the same reference numerals and their descriptions are omitted. The second transport guide 224 in this example differs from that of Example 1 in that a nonwoven fabric is provided instead of spurs.

[0041] Figure 11 is a cross-sectional view showing the fixing section 12 and surrounding members in this embodiment. Figure 12(a) is a front view of the second transport guide 224 according to this embodiment, and Figure 12(b) is a perspective view of the second transport guide 224. Nonwoven fabric 225 is attached to the second transport guide 224 in six places, and in Figure 12, the nonwoven fabric 225 is shown with hatching for clarity.

[0042] (Paper transport path during double-sided printing) The transport path for the transported paper during single-sided printing in this embodiment is the same as in Embodiment 1. Furthermore, the transport path for the transported paper during double-sided printing in this embodiment is also the same as in Embodiment 1, except that the second transport guide 224 is equipped with a nonwoven fabric 225 as a moisture-absorbing material instead of spurs. The second transport guide 224 is provided with the nonwoven fabric 225 facing the first transport guide 123. In this embodiment, during double-sided printing, the transported paper S, after the image fixing of the first side has been completed, is guided by the nonwoven fabric 225 on the second transport guide 224, which is positioned opposite the first transport guide 123, as it proceeds along the transport path for double-sided printing.

[0043] (Effects of the invention) Because nonwoven fabric has the property of absorbing moisture, water droplets do not form beads on the nonwoven fabric as they do when they adhere to the transport ribs. Therefore, even if moisture evaporates due to the heating of the transport paper S in the fixing unit 12, it will not appear as water droplets on the nonwoven fabric 225, and a large amount of water droplets will not adhere from the nonwoven fabric 225 to the transport paper S, thereby suppressing the occurrence of printing defects due to water droplet adhesion to the transport paper. Even if a small amount of moisture adheres from the nonwoven fabric 225 to the transport paper S, the moisture on the transport paper will evaporate before the transport paper S re-enters the photosensitive drum 101, so printing defects due to water droplet adhesion to the transport paper will not occur. In addition, by placing the nonwoven fabric 225, if water droplets adhere to the transport paper S upstream of the second transport guide 224 in the transport direction, the nonwoven fabric 225 can be expected to wipe away the moisture on the transport paper S. In this embodiment, nonwoven fabric is used as the moisture absorbing material, but it is also possible to use a water-absorbing material such as a water-absorbing sponge.

[0044] With the above configuration, even if water droplets adhere to the transport ribs on the curved transport guide, the water droplets adhering to the transported paper can be dispersed in the width direction, and furthermore, water droplets that have adhered upstream of the transport guide in the transport direction can also be wiped away. Therefore, according to the present invention, even when there is a curved transport path, the occurrence of printing defects such as image defects caused by water droplets adhering to the transported paper can be suppressed.

[0045] In Example 1, only spurs were provided as rollers facing a curved transport guide within the transport path, and in Example 2, only nonwoven fabric was provided as a moisture-absorbing member. However, the application of the present invention is not limited to these. For example, both rollers and moisture-absorbing members may be provided facing the transport guide. The method of providing rollers, moisture-absorbing members, or both should be determined appropriately considering the manufacturing costs and manufacturing difficulties of each. [Explanation of symbols]

[0046] 11…Image forming unit, 12…Fixing unit (heating unit), 13…Sheet transport device, 100…Image forming device, 123…First transport guide (transport guide), 123a…Transport rib (rib), 123a1…First rib, 123a2…Second rib, 123b…Curved section, S…Transport paper (recording material)

Claims

[Claim 1] An image forming apparatus having an image forming unit for forming an image on a sheet-shaped recording material and a heating unit for heating the recording material, wherein a sheet conveying device is provided for conveying the recording material, A transport unit for transporting the aforementioned recording material, A transport guide that forms a transport path through which the recording material is transported, comprising an injection-molded transport guide having a curved portion for forming a curved path in at least a part of the transport path, Equipped with, On the surface of the curved portion facing the recording material, a plurality of ribs are provided that extend along the transport direction of the recording material and guide the recording material. The plurality of ribs include a first rib and a second rib adjacent to the first rib. A sheet conveying device characterized in that the second rib is positioned offset from the first rib in the width direction perpendicular to the conveying direction and in the conveying direction, such that a gap is formed between the second rib and the first rib.

Images