JP2004109760A - Transferring device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a transferring device that prevents a toner image from being disturbed, such as toner image disturbance caused by discharging in a gap between a recording medium and a belt-shaped image carrier and by the expansion and contraction of an image carrier surface and to provide an image forming apparatus. <P>SOLUTION: This transferring device and image forming apparatus is provided with a transferring roller 60 occupying the position that is at the upstream side of an area C where a counter roller 34 winds the image carrier 31 around itself in a running direction B of the image carrier 31 and where an angle formed between a line L1 connecting the rotation center O<SB>1</SB>of the transferring roller 60 with the rotation center O<SB>2</SB>of a counter roller 34 and a tangent L2 directed to an upstream side in the direction B at the most upstream point P in a contact area F between the transferring roller 60 in the direction B and the image carrier 31 is at about 90°. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a transfer device having a transfer roller positioned outside and inside an endless belt-shaped image carrier and a facing roller facing the transfer roller, and a copying machine, a facsimile machine having the transfer device and such an image carrier. The present invention relates to an image forming apparatus such as a printer.
[0002]
[Prior art]
An image forming apparatus such as a copying machine, a facsimile, and a printer has an image carrier such as a photoconductor and an intermediate transfer belt, and transfers a toner image formed on the image carrier by a transfer device that applies a voltage or the like. It has become. An intermediate transfer type image forming apparatus using an intermediate transfer belt includes a photoconductor on which a toner image corresponding to image information is formed, an endless intermediate transfer belt stretched over a plurality of rollers, and a photoconductor. And a secondary transfer device that transfers the toner image transferred onto the intermediate transfer belt onto a recording medium, and a primary transfer device that transfers the toner image onto the intermediate transfer belt. As a secondary transfer device, for example, as described in [Patent Literature 1], a device including a transfer roller in contact with the surface of an intermediate transfer belt and a facing roller inside the intermediate transfer belt is known. .
[0003]
This type of image forming apparatus has a problem in that when performing secondary transfer, image defects such as white spots occur due to discharge in a gap between the recording medium and the intermediate transfer belt. Therefore, as shown in FIG. 4, for example, in [Patent Document 2], a transfer roller 60 ′ is disposed on the upstream side in the running direction B of the intermediate transfer belt 31 with respect to the opposite roller 34, and the intermediate transfer belt 31 is By curving inward at a portion wound between the roller 34 and another roller, the recording medium is brought into close contact with the intermediate transfer belt 31 between the transfer roller 60 'and an image defect caused by electric discharge is prevented. Technology has been proposed.
[0004]
[Patent Document 1]
JP-A-9-090780
[Patent Document 2]
JP-A-10-133497
[0005]
[Problems to be solved by the invention]
However, in such an arrangement of the transfer roller 60 ', the intermediate transfer belt 31 is curved inward at a portion D wound around the opposing roller 34 and another roller, and then is wound around the opposing roller 34. The surface of the intermediate transfer belt 31 carrying the toner image is subjected to the action of contracting at the inner curved portion D and subsequently to the action of extending at the outer curved portion E because the curved portion E is curved outward. become. This means that the toner image held on the intermediate transfer belt 31 expands after contracting in the circumferential direction, and the expansion and contraction causes the toner to scatter and disturb the image.
[0006]
On the other hand, many image forming apparatuses using an intermediate transfer belt formed of a resin have conventionally been provided. However, an intermediate transfer belt formed of a resin generally has a high hardness and is used in a primary transfer section and a secondary transfer section. In particular, the toner image is particularly stressed at the central portion of the character, and a transfer failure called a character void phenomenon is likely to occur. Therefore, a layer made of an elastic material is provided on the intermediate transfer belt so that the surface of the transfer belt is deformed in accordance with the thickness of the toner image, and the concentration of stress on the toner image is reduced, thereby reducing the occurrence of missing characters in characters. There has been proposed a technique for improving the transfer failure of the image.
[0007]
However, when an intermediate transfer belt having such an elastic layer is used, the elastic layer is dragged by the elastic layer at the bending portion of the intermediate transfer belt because expansion and contraction in the circumferential direction is larger than that of a rigid layer such as resin. In this case, the belt surface expands and contracts more in the circumferential direction than a belt without an elastic layer. Further, an intermediate transfer belt having an elastic layer is generally thicker than an intermediate transfer belt having no elastic layer due to the thickness of the elastic layer. This also causes the belt surface to expand and contract. Therefore, when the intermediate transfer belt having the elastic layer is used, the toner image is likely to be disturbed due to the arrangement of the transfer roller.
[0008]
The present invention is directed to a method of forming a toner image such that an image defect such as a white spot is generated by a discharge in a gap between a recording medium and a belt-shaped image carrier and a toner image is disturbed due to expansion and contraction of the surface of the image carrier. An object of the present invention is to provide a transfer device and an image forming apparatus that prevent disturbance.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the invention according to claim 1 includes an opposing roller positioned inside the endless belt-shaped image carrier and wound around the endless belt-shaped image carrier, and positioned outside the endless belt-shaped image carrier. A transfer roller sandwiching the endless belt-shaped image carrier with the opposing roller, wherein the transfer roller has an endless belt-shaped image carrier in a running direction of the endless belt-shaped image carrier. A line connecting the rotation center of the transfer roller and the rotation center of the opposing roller at a position upstream of the winding area where the body is wound, and the transfer roller and the endless belt-shaped image carrier in the running direction. The endless belt-shaped image carrier at the most upstream point of the contact area with the tangent line toward the upstream side in the traveling direction occupies a position where the angle is approximately 90 °.
[0010]
According to a second aspect of the present invention, in the transfer device according to the first aspect, the transfer roller has an angle of 90 ° or less between a line connecting the most upstream point and the center of the opposite roller and the tangent. Occupy a position.
[0011]
According to a third aspect of the present invention, there is provided an image forming apparatus including the transfer device according to the first or second aspect, and an endless belt-shaped image carrier sandwiched between the opposed roller and the transfer roller.
[0012]
According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the endless belt-shaped image carrier has at least one elastic layer.
[0013]
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the endless belt-shaped image carrier has at least one base layer and at least one surface layer sandwiching the elastic layer. Features.
[0014]
According to a sixth aspect of the present invention, in the image forming apparatus of the fourth or fifth aspect, the thickness of the elastic layer is 0.1 mm to 0.5 mm.
[0015]
【Example】
FIG. 1 schematically shows a transfer apparatus to which the present invention is applied and an image forming apparatus having the same. The image forming apparatus is of a tandem type, is of an intermediate transfer type, is a well-known apparatus such as a copying machine, a facsimile, a printer, and forms a color image. The image forming apparatus 20 includes plain paper generally used for copying and the like, 90K paper such as an OHP sheet, a card, and a postcard, and a basis weight of about 100 g / m. ² It is possible to use as a sheet-shaped recording medium any of a considerable amount of thick paper and a so-called special sheet having a larger heat capacity than plain paper, such as an envelope.
[0016]
The image forming apparatus 20 is a copier main body 100 for forming an image, a paper feed table 200 on which the copier main body 100 is mounted, a scanner 300 mounted on the copier main body 100, and mounted on the scanner 300. And an ADF 400 as an automatic document feeder. The image forming apparatus 20 includes an image forming apparatus 21 having image forming units 21BK, 21Y, 21M, and 21C as image forming stations that form an image for each color, that is, a toner image, according to a document image in a copying machine main body 100. Have.
[0017]
The image forming apparatus 20 further includes a belt 31 serving as an intermediate transfer belt serving as an endless belt-shaped image carrier, which is disposed to face the image forming apparatus 21 and rotates clockwise in FIG. And a transfer device 63 that performs primary transfer from the image forming device 21 and a belt 31 that is disposed to face the roller 34 with the belt 31 interposed therebetween. And a transfer device 22 to which the present invention is applied, which has a secondary transfer including a belt 35 wound around a transfer roller 60 and a roller 61 located outside of the printer and the above-described roller 34 as an opposing roller. .
[0018]
The transfer roller 60 sandwiches the belt 31 between the transfer roller 60 and the roller 34. The transfer device 22 also has a function as a sheet conveying device that conveys the sheet on which the toner image has been transferred to the fixing device 1 described below. The roller 33 of the rollers 32, 33, and 34 is a driving roller that is driven to rotate by a motor (not shown), and the other rollers 32 and 34 are driven by the belt 31 that is driven by the roller 33 in the B direction. I do. The driving roller is not limited to the roller 33, and may be another roller.
[0019]
The image forming apparatus 20 further includes a cleaning device 64 for removing residual toner remaining on the belt 31 after the secondary transfer between the rollers 32 and 34, and a manual feeder disposed on a side of the copying machine main body 100. The tray 65, a paper feed roller 66 for feeding out a sheet serving as a recording medium on the manual feed tray 65, a separation roller 67 for separating the sheets sent from the manual feed tray by the paper feed roller 66 one by one, and a conveyance by the separation roller 67. The sheet fed from the sheet feeding table 200 or the manual feed tray 65 and the sheet feeding path 68 into which a single sheet has entered are supplied at the timing of image formation by the image forming units 21BK, 21Y, 21M, and 21C. And a registration roller 30 to be used.
[0020]
The image forming apparatus 20 further includes a fixing device 1 that fixes the sheet conveyed by the belt 35, on which the toner image is transferred and carries the toner image in the transfer area, and a portion below the transfer device 22 and the fixing device 1. And is disposed in parallel with the image forming apparatus 21 as a sheet reversing device for reversing the fixed sheet discharged from the fixing device 1 and conveying the sheet again to the transfer area to form images on both sides of the sheet. Reversing device 42, a switching claw 80 for switching between discharging the fixed sheet discharged from the fixing device 1 to the outside of the image forming device 20 main body and guiding the sheet to the reversing device 42, and transferring the sheet to the outside of the image forming device 20 main body. It has a paper discharge roller 44 for discharging and a paper discharge tray 43 as a sheet stacking unit for stacking the sheets conveyed and discharged by the paper discharge roller 44.
[0021]
The image forming device 21 is located at a position facing the belt 31 stretched between the rollers 32 and 33. The image forming units 21BK, 21Y, 21M, and 21C are arranged along the direction of arrow B at positions facing the belt 31 in this order, and perform development of each color of black, yellow, magenta, and cyan. Although the colors of the toners to be used are different, the configuration is substantially the same. Therefore, the configuration of the image forming unit 21C will be described as a representative of each of the image forming apparatuses 21BK, 21Y, 21M, and 21C.
[0022]
The image forming unit 21C includes a photosensitive drum 25C, which is an electrostatic latent image carrier as an image carrier, a charging device 27C, a developing device 26C, and a primary transfer that are sequentially arranged in the rotation direction A of the photosensitive drum 25C. Is a well-known configuration that has a transfer roller 28C and the like that constitute a transfer device 63 that performs exposure, and receives exposure light 29C between a charging device 27C and a developing device 26C. The electrostatic latent image carrier may have a belt shape instead of a drum shape.
[0023]
The image forming device 21 has a common exposure device 29 on its upper part for irradiating the exposure light 29BK, 29Y, 29M, 29C in each of the image forming units 21BK, 21Y, 21M, 21C. Further, the image forming apparatus 21 has cleaning devices 45BK, 45Y, 45M, and 45C as cleaning means in the image forming units 21BK, 21Y, 21M, and 21C, respectively. Each of the cleaning devices 45BK, 45Y, 45M, and 45C imparts lubricity to the photosensitive drums 25BK, 25Y, 25M, and 25C so that the transfer of each toner image is performed uniformly and favorably even when the superposition transfer is performed. A lubricating means (not shown) for applying the agent is provided.
[0024]
The paper feed table 200 is provided with a multi-stage paper bank 70 for supplying various sheets to a transfer area which is an area where the roller 34 provided in the copying machine main body 100 is opposed to the transfer roller 60 and the belt 35. Paper feed cassette 24 as a supplied sheet supply means, a paper feed roller 71 for feeding out the sheets stacked in the paper feed cassette 24, and a sheet fed from the paper feed cassette 24 by the paper feed roller 71 is separated one by one. Separation roller 36, a paper feed path 72 into which one sheet conveyed by the separation roller 36 enters, and a conveyance roller that conveys the sheet in the paper feed path 72 to a paper feed path 73 in the copier main body 100. 41.
[0025]
The scanner 300 has a contact glass 50 on which a document is placed and reads the document, a first traveling body 74 having a light source (not shown) and irradiating light to the document, and a reflected light from the document having a mirror (not shown). A traveling body 75 that further reflects the light, an imaging lens 76 that focuses the reflected light from the second traveling body 75, a reading sensor 77 that incorporates a CCD (not shown) that reads the light focused by the imaging lens 76, And a loading tray 51 for loading the read originals.
[0026]
The ADF 400 has a document table 49 on which documents conveyed to the contact glass 50 are stacked, and separates the documents placed on the document table one by one to separate the contact glass 50 provided on the scanner 300. The document that has been read upward on the contact glass 50 by the scanner 300 is further transported and loaded on the loading tray 51.
[0027]
The image forming apparatus 20 forms an image by a color separation and superimposition transfer method generally used in a full-color image forming apparatus. The scanner 300 includes a first traveling body, a second traveling body, an imaging lens 76, and the like. The original is read by reading image information light, which has been color-separated into three colors of blue, red, and green, via an optical system, with the reading sensor 77. Then, image processing is performed based on the intensity level of light detected by each CCD to create write image data to be developed in each of black, yellow, magenta, and cyan, and exposure is performed in accordance with the write image data. The device 29 irradiates the photosensitive drums 25BK, 25Y, 25M, and 25C with exposure light 29BK, 29Y, 29M, and 29C to perform optical writing.
[0028]
The fixing device 1 includes an endless fixing belt 17 as a sheet conveying member for conveying a sheet on which the toner is fixed, a heating roller 16 and a fixing roller 15 around which the fixing belt 17 is wound, and a fixing belt 17. A fixing roller disposed opposite to the fixing roller 15 and pressed against the fixing belt 17, and a heater as heating means (not shown) provided inside the heating roller 16. . The fixing device 1 may be a heat roller pair type fixing device instead of the belt fixing device.
[0029]
The registration roller 30 is grounded similarly to a general one, but a bias may be applied to remove paper dust from a sheet. In this case, for example, using a conductive rubber roller of a conductive NBR rubber having a diameter φ of 18 mm and a surface of 1 mm thick, the applied voltage is set to about −800 V on the toner transfer side of the sheet (front side) and about +200 V on the back side. A bias is applied. The electrical resistance of the conductive NBR rubber is desirably about 10E9 Ωcm in volume resistance of the rubber material.
[0030]
Generally, in the intermediate transfer method, paper dust is hard to move to the photosensitive drums 25BK, 25Y, 25M, and 25C. Therefore, it is not necessary to consider the transfer of paper dust, and the intermediate powder may be grounded. Further, the applied voltage is a DC bias, but an AC voltage having a DC offset component may be applied to more uniformly charge the sheet. Since the paper surface after passing through the biased registration roller 30 is slightly negatively charged, no voltage was applied to the registration roller 30 in the secondary transfer from the belt 31 to the sheet. Since the transfer environment changes as compared with the case, the transfer conditions may be changed.
[0031]
The belt 31 is formed by coating an elastic layer 81 made of a rubber with a thickness G of 0.1 to 0.5 mm and having high elongation, a base layer 82 sandwiching the elastic layer 81 and made of a low-elongation fluororesin, and a fluororesin. And a surface layer 83. Each of the elastic layer 81, the base layer 82, and the surface layer 83 has a single-layer structure, but may have at least a single-layer structure. The base layer 82 may be made of a material that does not easily stretch, such as canvas. The surface layer 83 has good smoothness, covers the elastic layer 81, and forms a surface with which the sheet abuts.
[0032]
Without the base layer 82, the belt 31 has nothing to suppress the expansion of the elastic layer 81, and is greatly deformed at the bent portion wound around the rollers 32, 33, 34, etc., and disturbs the toner image. When the toner image is not provided, the toner image is disturbed for the same reason as when the base layer 82 is not provided. In addition, since the surface energy of the surface on which the toner image is placed is large, the releasability of the toner image is poor, and the toner image is transferred from the belt 31 to the sheet. The above-mentioned configuration is adopted because the operation is not performed well.
[0033]
The reason why the thickness G of the elastic layer 81 is set to 0.1 to 0.5 mm is that if the thickness is less than 0.1 mm, the effect of the elasticity is reduced, the effect of reducing the stress concentration on the toner image is reduced, and the center of the character is lost. If the thickness is larger than 0.5 mm, the elongation in the circumferential direction of the surface layer 13 at the bent portion becomes large, which causes an image defect.
[0034]
As shown in FIG. 3, in the transfer device 22, the transfer roller 60 is moved in the B direction, which is the running direction of the belt 31, in order to prevent image defects such as white spots from occurring due to electric discharge in the gap between the sheet and the belt 31. In the above, the roller 34 is disposed at a position on the upstream side of the winding area C where the belt 31 is wound, and the belt 31 is bent inward to allow the sheet to be in close contact with the belt 31 to prevent such image defects. ing.
[0035]
However, when the transfer roller is disposed at the position indicated by reference numeral 60 'as shown in FIG. 4, the belt 31 is wound around the opposing roller 34 and another roller as described above. After being curved inward at the curved portion D, subsequently curved outward at the portion E wound around the opposing roller 34, the surface of the belt 31 carrying the toner image contracts at the curved inside portion D. The toner image held on the belt 31 is contracted in the circumferential direction and then stretched after being subjected to the action of extending in the outer curved portion E after receiving the toner. It becomes.
[0036]
Then, as shown in FIG. 2, when the belt 31 having the elastic layer 81 is used, the elastic layer 81 has a greater circumferential length at the bent portions D and E of the belt 31 than the base layer 82 with less expansion and contraction. Large expansion and contraction. Further, since the belt 31 has the elastic layer 81, the thickness G of the elastic layer 81 is thicker than that of the belt without the elastic layer 81. Has become. As described above, the belt 31 has the elastic layer 81 for preventing a character from missing in the center. For this reason, when the transfer roller is disposed at the position indicated by the reference numeral 60 'to prevent image defects. Disorder of the toner image is likely to occur.
[0037]
Therefore, as shown in FIG. 3, in the transfer device 22 to which the present invention is applied, the belt 31 having the elastic layer 81 is used, and the transfer roller 60 is wound around the upstream side of the region C in order to prevent image defects. In order to prevent the toner image from being disturbed due to the expansion and contraction of the belt 31 while being arranged at the position, ₁ And the rotation center O of the roller 34 ₂ Occupies a position where the angle α between the line L1 connecting the transfer roller 60 and the tangent L2 toward the upstream in the B direction at the most upstream point P in the B direction of the contact area F between the transfer roller 60 and the belt 31 is approximately 90 °. It is arranged as follows.
[0038]
With this arrangement, the belt 31 does not bend inward, so that the surface of the belt 31, that is, the surface on the side carrying the toner image does not shrink, and the toner image is prevented from being disturbed. Here, the angle α is set to approximately 90 °, but when the roller 60 is located further downstream in the direction B, the gap between the sheet and the belt 31 becomes large, and an image defect due to discharge in this gap occurs. Therefore, the transfer roller 60 occupies the above-described position, and the points P and O ₂ Are arranged so that the angle β between the line L3 connecting to the tangent line L2 and the tangent line L2 is 90 ° or less, thereby preventing such image defects.
[0039]
In FIG. 3, reference numeral 60 'denotes a conventional transfer roller position, and reference numeral O denotes a transfer roller position. ₃ Is the center of rotation of this conventional transfer roller, and L4 is O ₂ And O ₄ Indicates the angle between L2 and L4. 3, illustration of the belt 35 is omitted. The fact that the belt 35 is wound around the roller 60 does not affect the transfer because the roller 60 is disposed at the above-described position, but the surface of the belt 35 that is wound around the roller 60 is It may be considered that the roller 60 is disposed at the position described above.
[0040]
In the present embodiment, when the power of the image forming apparatus 20 is turned on, the image forming apparatus 20 is in a state in which good fixing can be performed, the startup is completed, and an image can be formed. Although image formation can be performed based on image information input from the outside, when an image is formed using a document, the document is placed on the document table 49 of the ADF 400 or the ADF 400 The ADF 400 is closed, the document is placed on the exposed contact glass 50, the ADF 400 is closed, the document is pressed, and a start switch (not shown) is pressed.
[0041]
When the original is placed on the ADF 400, the original is conveyed onto the contact glass 50, and immediately after the original is placed on the contact glass 50, the first traveling body 74 and the second traveling body Runs and reads the contents of the document. On the other hand, the belt 31 runs in conjunction with the pressing of the start switch, and the image forming apparatus 21 starts image formation. When a full-color image is formed, the toner images are sequentially transferred onto the belt 31 as described below, and after the toner images of all the colors are transferred, the toner images are collectively transferred onto the sheet. .
[0042]
In the case of forming a full-color image, when the operator performs a well-known operation of starting image formation, the photosensitive drum 25BK is charged by the charging device 27BK with the rotation of the photosensitive member 25BK in the direction A, and is exposed by the exposure light 29BK. An electrostatic latent image corresponding to the original image is formed, the electrostatic latent image is developed by the developing device 26BK, and the toner image formed on the photoconductor 25BK is transferred onto the belt 31 by the action of the electric field by the transfer roller 28BK. Next, the image is transferred and conveyed in the direction of arrow B.
[0043]
The toner remaining on the photoconductive drum 25BK after the transfer is scraped off by the cleaning device 45BK, so that the photoconductive drum 25BK is cleaned and used for the next charging. The belt 31 onto which the black toner has been transferred is conveyed in the direction of arrow B, and performs an image forming process similar to the above-described image forming process in the image forming unit 21BK while the belt 31 makes one rotation. , 21M, and 21C, the yellow, magenta, and cyan toner images are sequentially superimposed and transferred to appropriately synchronized positions, and all the toner images necessary for image formation are primarily transferred.
[0044]
On the other hand, when the start switch is pressed, one of the paper feed rollers 71 or the paper feed roller 66 in the paper feed table 200 is rotated according to the image forming conditions, and the corresponding paper feed cassette 24 or manual feed tray is rotated. Only one of the sheets placed on the sheet 65 collides with the registration roller 30 via the sheet feeding paths 72 and 73 or the sheet feeding path 68, and stops in a state where the sheet is abutted. The registration roller 30 rotates in synchronization with the timing at which the toner image on the belt 31 to which the primary transfer has been performed by the rotation of the belt 31 moves the abutted sheet to a transfer area, which is an area where the belt 31 and the roller 60 face each other. The toner image on the belt 31 is sent to the sheet sent to the transfer area, and is collectively secondarily transferred to the sheet.
[0045]
When a single-color image is formed, when the toner image of the color formed in the same manner as described above is primarily transferred to the belt 31, the toner image is conveyed to the registration roller 30 in the same manner as described above, and is transferred to the registration roller 30. Is secondary-transferred onto the sheet fed to the transfer area. In both the case of forming a full-color image and the case of forming a single-color image, since the belt 31 has the elastic layer 81, transfer failure is prevented both in the primary transfer and the secondary transfer, and When the roller 60 occupies the above-described position, discharge and disturbance of the toner image during the secondary transfer are prevented, and the state of the toner image on the sheet is extremely good.
[0046]
The sheet on which the toner image has been transferred is conveyed by the belt 35 and transferred to the fixing device 1. In the fixing device 1, while the sheet is conveyed by the movement of the fixing belt 2, the toner constituting the toner image is heated and pressed, and is fused and fixed on the sheet. Regardless of whether a full-color image or a single-color image is formed, the belt 31 after the secondary transfer of the toner image onto the sheet is cleaned by the cleaning device 64 to prepare for the next primary transfer. . The sheet after fixing is conveyed to the paper discharge roller 44 via the switching claw 80 and is stacked and stacked on the paper discharge tray 43, or is inverted by the reversing device 42 to form an image again and the paper discharge tray 43 is stacked and stacked.
[0047]
The transfer device 22 to which the present invention is applied and the image forming device 20 having the same have been described. The image formation is performed not only on the original image read by the image forming device, but also on the data input from the outside such as a personal computer. It can also be performed based on. The transfer to the belt 31 may be such that one color toner image is transferred every time the belt 31 makes one rotation, instead of transferring all the toner images of each color sequentially while the belt 31 makes one rotation. The transfer device 22 does not need to include the belt 35, but in this case, it is necessary to separately provide a unit for conveying the sheet on which the toner image has been transferred to the fixing device 1. The present invention is not limited to a secondary transfer device for transferring images from an intermediate transfer belt to a sheet, but is also applicable to a primary transfer device for transferring images from a belt-shaped photosensitive member to an intermediate transfer belt. The body includes an intermediate transfer belt, a photoreceptor belt and the like.
[0048]
【The invention's effect】
According to the present invention, an endless roller is located between the endless belt-shaped image carrier and the opposing roller that is wound around the endless belt-shaped image carrier and the endless roller that is located outside the endless belt-shaped image carrier. A transfer roller having a transfer roller sandwiching the belt-shaped image carrier, wherein the transfer roller is located in a winding area where the opposed roller is wound around the endless belt-shaped image carrier in a running direction of the endless belt-shaped image carrier. An upstream position, a line connecting the rotation center of the transfer roller and the rotation center of the opposing roller, and the most upstream point of the contact area between the transfer roller and the endless belt-shaped image carrier in the running direction. Occupies a position where the angle between the endless belt-shaped image carrier and the tangent toward the upstream side in the traveling direction is approximately 90 °, so that the recording medium is brought into close contact with the endless belt-shaped image carrier, and Arising Disturbance of the toner image due to image defects such as white spots due to electric discharge can be prevented, and the endless belt-shaped image carrier does not curve inward. It is possible to provide a transfer device that can prevent toner image disturbance and perform good transfer.
[0049]
If the transfer roller occupies a position where the angle between the line connecting the most upstream point and the center of the opposing roller and the tangent is 90 ° or less, the recording medium and the endless belt-shaped image carrier can be reliably connected. It is possible to provide a transfer device capable of more reliably preventing image defects such as white spots due to electric discharge caused by these gaps when brought into close contact.
[0050]
The present invention resides in an image forming apparatus having the transfer device according to claim 1 and an endless belt-shaped image carrier sandwiched between the opposing roller and the transfer roller. It is possible to provide an image forming apparatus having an image forming apparatus and capable of forming a high-quality image while preventing disturbance of a toner image.
[0051]
If the endless belt-shaped image carrier has at least one elastic layer, the surface of the endless belt-shaped image carrier is deformed according to the thickness of the toner image, thereby reducing stress concentration on the toner image. Thus, it is possible to provide an image forming apparatus capable of forming a high-quality image by preventing a transfer failure such as a decrease in the number of missing characters in a character.
[0052]
If the endless belt-shaped image carrier has at least one base layer and at least one surface layer sandwiching the elastic layer, the elastic layer provided for performing high-quality image formation may have an amount of expansion and contraction. Solves the problem that the toner image is disturbed by increasing the size of the toner image by suppressing the elongation of the elastic layer by providing the base layer and the surface layer. And the surface energy of the surface on which the toner image is placed can be reduced by the surface layer to improve the releasability of the toner image, and the toner image can be transferred well from the endless belt-shaped image carrier to the recording medium. Accordingly, it is possible to provide an image forming apparatus capable of forming a high-quality image.
[0053]
If the thickness of the elastic layer is from 0.1 mm to 0.5 mm, the effect of the elasticity of the elastic layer is reduced, the effect of reducing the concentration of stress on the toner image is reduced, and the effect of improving the hollow characters is reduced. It is possible to provide an image forming apparatus capable of forming a high-quality image without causing the occurrence of image defects due to an increase in the circumferential length of the bent portion in the circumferential direction.
[Brief description of the drawings]
FIG. 1 is a side view schematically showing a transfer device to which the present invention is applied and an image forming apparatus having the transfer device.
FIG. 2 is a side sectional view of an endless belt-shaped image carrier provided in the image forming apparatus shown in FIG.
FIG. 3 is a side view illustrating a positional relationship between a transfer roller and an opposing roller provided in the transfer device illustrated in FIG. 1 and an endless belt-shaped image carrier.
FIG. 4 is a side view showing a positional relationship between a transfer roller and an opposing roller provided in a conventional transfer device and an endless belt-shaped image carrier.
[Explanation of symbols]
20 Image forming apparatus
31 Endless belt image carrier
34 Opposing roller
60 Transfer roller
81 elastic layer
82 base layer
83 Surface
B Running direction of the endless belt-shaped image carrier
C Wrapping area
F Opposite area between transfer roller and endless belt-shaped image carrier
L1 Center of rotation O of transfer roller ₁ And the rotation center O of the opposing roller ₂ Line connecting to
L2 Tangent line of the endless belt-shaped image carrier at the most upstream point P toward the upstream side in the running direction of the endless belt-shaped image carrier
O ₁ Rotation center of transfer roller
O ₂ Rotation center of opposing roller
P The most upstream point of the facing area C between the transfer roller and the endless belt-shaped image carrier in the traveling direction B of the endless belt-shaped image carrier.
α Center of rotation of transfer roller O ₁ And the rotation center O of the opposing roller ₂ Between the line L1 connecting the endless belt-shaped image carrier at the most upstream point P and the tangent L2 toward the upstream side in the running direction of the endless belt-shaped image carrier.
β Angle between the most upstream point P and the tangent L2

Claims (6)

An endless belt-shaped image carrier is positioned between the opposed roller located inside the endless belt-shaped image carrier and around the endless belt-shaped image carrier, and the opposed roller located outside the endless belt-shaped image carrier. A transfer device having a transfer roller sandwiching the transfer roller,
The transfer roller is located at a position upstream of a winding area where the opposite roller is wound around the endless belt-shaped image carrier in the traveling direction of the endless belt-shaped image carrier, and is the same as the rotation center of the transfer roller. The line connecting the rotation center of the opposing roller and the endless belt-shaped image carrier at the most upstream point of the contact area between the transfer roller and the endless belt-shaped image carrier in the traveling direction are directed to the upstream side in the traveling direction of the endless belt-shaped image carrier. A transfer device characterized in that the transfer device occupies a position where an angle between the tangent and the tangent is approximately 90 °. 2. The transfer device according to claim 1, wherein the transfer roller occupies a position where an angle between a line connecting the most upstream point and the center of the opposing roller and the tangent is 90 ° or less. 3. Transfer device. An image forming apparatus comprising: the transfer device according to claim 1; and an endless belt-shaped image carrier sandwiched between the opposed roller and the transfer roller. 4. The image forming apparatus according to claim 3, wherein the endless belt-shaped image carrier has at least one elastic layer. 5. The image forming apparatus according to claim 4, wherein said endless belt-shaped image carrier has at least one base layer and at least one surface layer sandwiching said elastic layer. The image forming apparatus according to claim 4, wherein a thickness of the elastic layer is 0.1 mm to 0.5 mm.

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