JP2010085491A - Image forming apparatus - Google Patents

Abstract

An image forming apparatus capable of preventing the occurrence of image blanking due to frictional charging between a recording material and an insulating member and outputting a good image.
A pre-transfer guide 20 for guiding a recording material 101 toward a transfer portion in which a transfer member 119 is disposed includes an upper transfer guide 116 positioned on the printing surface side of the recording material 101, and the recording material 101. The upper transfer guide 116 is provided with a sheet member 118 having a free end on the downstream side in the recording material conveyance direction, and the upper transfer guide 116 is made of an insulating member. The sheet member 118 is made of a conductive member.
[Selection] Figure 2

Description

  The present invention relates to an image forming apparatus using an electrophotographic system such as a laser beam printer, a copying machine, and a facsimile.

  In an electrophotographic image forming apparatus, a charging unit, an exposing unit, a developing unit, and the like are provided around an electrophotographic photosensitive member as an image carrier. Then, after the photosensitive member is charged by the charging unit, exposure is performed by the exposing unit to form an electrostatic latent image on the surface of the photosensitive member and developed by the developing unit. Thereafter, the developed toner image is transferred onto a recording material by a transfer unit, and further fixed by a fixing unit, and the image-formed recording material is discharged to a discharge unit.

  As a transfer means of such an image forming apparatus, there are a corona charging transfer system in which a corona charger is disposed facing a photoconductor, and a roller transfer system in which a transfer roller is brought into contact with the photoconductor to form a transfer nip portion. is there. Then, the recording material is conveyed from the paper feeding unit to the transfer unit via a pair of conveying rollers that are conveying means. In the transfer unit, the toner image on the photosensitive member is transferred to the recording material by applying a transfer bias voltage to the transfer member. At this time, in order to accurately transfer the toner image on the surface of the photoreceptor onto the recording material and obtain a good image, it is necessary to guide the recording material conveyed from the conveying roller pair to a good position on the transfer portion. . For this purpose, a pre-transfer guide for guiding the recording material conveyed from the pair of conveying rollers to a good position of the transfer unit is provided on the upstream side of the transfer unit in the recording material conveyance direction. It consists of a lower guide.

  A sheet member is fixed to the upper transfer guide disposed on the printing surface side of the recording material by adhesion. When the recording material is released from the guide of the pre-transfer guide, the rear end of the recording material jumps up, and the recording material may be displaced from a predetermined contact position with the photosensitive drum due to the shock of the jumping up, and the image may be distorted. The sheet member is a member that suppresses the jumping of the recording material and prevents the impact caused by the splash from being transmitted to the transfer region (see Patent Document 1).

The material of the sheet member is preferably an elastic member that absorbs vibrations at the trailing edge of the recording material, and preferably has a smooth surface and rigidity in order to prevent the leading edge of the recording material from being caught. For example, a synthetic resin film such as PET, polyimide or polyethylene, or a rubber material whose surface is coated with PTFE, PFA, FEP, polyimide, polyamideimide, PEEK, PES, PPS or the like is preferable.
JP-A-5-257395

  However, the above conventional example has the following problems.

  When an insulating sheet member (insulating member) is provided on the transfer upper guide, the recording material is rubbed against the insulating sheet member when the recording material is conveyed to the transfer portion along the pre-transfer guide. The sheet member is frictionally charged at the contact portion with the recording material. At the frictionally charged portion, discharge occurs in the vicinity of the transfer portion, and the polarity of the toner attached to the photosensitive member is reversed. Then, since the toner on the photosensitive member whose polarity is reversed is not transferred to the recording material, white spots occur in the image transferred to the recording material. The white spots in the image due to the discharge between the recording material and the photosensitive member are likely to occur particularly in a low temperature and low humidity environment. Further, it is likely to occur in a recording material having a smooth surface and high resistance.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to prevent the occurrence of white spots due to frictional charging between the recording material and the insulating member and to output a good image. An image forming apparatus is provided.

The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention comprises an image carrier that carries an image to be formed on a recording material, a transfer member that transfers a toner image on the image carrier to the recording material, and a transfer member that is a recording material. In an image forming apparatus comprising: a pre-transfer guide for guiding toward the transfer unit; and a transport unit that transports a recording material to the pre-transfer guide.
The pre-transfer guide is composed of a transfer upper guide positioned on the printing surface side of the recording material and a transfer lower guide positioned on the non-printing surface side of the recording material,
The transfer upper guide is provided with a sheet member having a free end on the downstream side in the recording material conveyance direction,
In the image forming apparatus, the transfer upper guide is formed of an insulating member, and the sheet member is formed of a conductive member.

  According to the present invention, the triboelectric charge amount of the recording material is reduced by imparting conductivity to the sheet member provided in the upper transfer guide. Thereby, discharge between the recording material and the image carrier can be prevented, and a good image can be obtained.

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

Example 1
A first embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus.

  In this embodiment, the image forming apparatus 100 includes a paper feed tray 102 on which recording materials 101 such as postcards and thin large paper are stacked. The recording material 101 loaded on the paper feed tray 102 is separated and transported one by one by the paper feed roller 103 and the paper feed pad 104, passes through the paper feed guide 105, and reaches the transport rollers 106 and 107 as transport means. To do. At this time, the conveyance rollers 106 and 107 temporarily stop rotating, the leading edge of the conveyed recording material 101 follows the position of the registration mechanism unit 108, and the skew of the recording material 101 is corrected.

  The image forming apparatus 100 also includes a drum-shaped electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 109 as an image carrier. The photosensitive drum 109 is driven in the direction of the arrow by a motor (not shown). Rotate. The photosensitive drum 109 includes a conductive substrate 110 made of aluminum or the like, and a photosensitive layer 111 made of CGL (charge generation layer) and CTL (charge transport layer) laminated on the conductive substrate 110. Yes. A charging roller 112 is disposed in pressure contact with the photosensitive drum 110, and the surface of the photosensitive drum 109 is uniformly charged by the charging roller 112. Thereafter, the exposure L from the laser irradiation unit irradiates the photosensitive layer 111 of the photosensitive drum 109, and an electrostatic latent image is formed on the photosensitive drum 109. A developing device 113 for developing the electrostatic latent image is provided on the downstream side in the rotation direction of the photosensitive drum 109 from the position where the photosensitive layer 111 is irradiated with the exposure L. The developing device 113 has a rotating developing sleeve 114, and developer (toner) 115 is supplied from the developing sleeve 114 to the photosensitive drum 109. When the electrostatic latent image formed on the photosensitive drum 109 comes to a position facing the developing sleeve 114, the toner 115 is supplied to the electrostatic latent image from the developing sleeve 114, and the toner image (visible image) is applied to the photosensitive drum 109. ) 115a is formed.

  On the other hand, the transport rollers 106 and 107 start to rotate at a timing synchronized with the moving speed of the toner image 115 a formed on the photosensitive drum 109. As the rotation starts, the recording material 101 whose skew has been corrected by the registration mechanism unit 108 is sandwiched between the upper transfer guide 116 and the lower transfer guide 117 constituting the pre-transfer guide 20 from the transport rollers 106 and 107. And reaches the photosensitive drum 109.

  The upper transfer guide 116 is positioned on the printing surface side of the recording material 101, that is, the side to which the toner image 115a of the photosensitive drum 109 is transferred, and the lower transfer guide 117 is on the printing surface side of the recording material 101. Is located on the opposite non-printing side.

  When the conveyance state of the recording material 101 is not stable, such as a large amount of bounce or vibration in the conveyance path from the conveyance rollers 106 and 107 to the photosensitive drum 109, the sheet member 118 fixed to the transfer upper guide 116 is used for the recording material 101. Bounce and vibration can be reduced. The operation of the sheet member 118 will be described later.

  The recording material 101 that has reached the photosensitive drum 109 is transferred with the toner image 115 a on the photosensitive drum 109 at a transfer nip N formed by a pressure contact portion between the photosensitive drum 109 and a transfer roller (transfer member) 119. A cleaning device 121 having a cleaning blade 120 is disposed downstream of the transfer nip N in the rotation direction of the photosensitive drum 109, and the toner remaining on the photosensitive drum 109 after the transfer is scraped off by the cleaning blade 120. .

  On the other hand, the recording material 101 onto which the toner image 115 a has been transferred passes through the conveyance guide 122 and is conveyed to the fixing device 123. The fixing device 123 includes two rollers 124 and 125 which are pressed against each other, and melt and fix the toner image 115a on the recording material 101 by heat and pressure. Thereafter, the recording material 101 is discharged from the paper discharge roller 126 onto the tray 127, and one printing cycle is completed.

  Here, with reference to FIG. 2, the configuration and operation of the transfer upper guide 116 and the sheet member 118 in this embodiment will be described. FIG. 2 is a cross-sectional view schematically showing the vicinity of the sheet member 118.

  The conveying rollers 106 and 107 are in pressure contact with springs (not shown) at the ends. The conveyance roller 106 is made of a POM (polyoxymethylene) material having a smooth surface. The outer diameter of the roller is made uniform by increasing the central portion (inner side) in the axial direction of the roller and decreasing both end sides (outer sides). The transport roller 107 is configured by winding a rubber material around a metal shaft. The outer diameter has an effect on the paper conveyance speed for conveying the recording material 101 to the transfer area. In this embodiment, the roller paper conveyance speed converted from the roller diameter and the rotation speed is set to 100% of the process speed. On the other hand, both the transfer roller 119 and the conveyance roller 107 are set to 101.3%.

  The upper transfer guide 116 and the lower transfer guide 117 constituting the pre-transfer guide 20 are connected to the main body 100A of the image forming apparatus 100, and both are formed of an insulated ABS resin. In addition, a plurality of ribs are set up in the longitudinal direction so that papers of various sizes and stiffness can be conveyed without problems.

  When a metal is used as the material of the transfer upper guide 116, when an image is formed on a recording material that has been left to absorb moisture in a high humidity environment, the transfer current leaks from the transfer upper guide 116 along the recording material. Transfer failure occurs. For this reason, it is necessary to ground through a resistance of at least several hundred MΩ, but not only an extra space is required, but also the cost is increased.

  In addition, when metal is used, there is difficulty in workability, so that a complicated shape such as a rib cannot be given, and the plate is used in a flat state. A metal guide member used in a flat state cannot have a sufficient function as a guide member for a recording material. For this reason, in this embodiment, by using an insulating resin member that is excellent in moldability and capable of forming ribs flexibly with a mold, escape of transfer current is prevented and paper conveyance is stabilized.

  A sheet member 118 is fixed to the upper surface of the transfer upper guide 116 by adhesion. The sheet member 118 is a member that suppresses the jump of the recording material 101 and prevents the impact due to the jump from being transmitted to the transfer region. The sheet member 118 is disposed on the upper surface of the upper transfer guide 116 so as to protrude further downstream in the recording material conveyance direction than the upper transfer guide 116. An adhesive tape 130 for fixing to the upper surface of the transfer upper guide 116 is attached to the back side of the width w1 in the transport direction of 15 mm and the upstream side width w1 = 5 mm. Further, the downstream width w2 = 10 mm is not fixed to the transfer upper guide 116 but is a free end, and can be elastically curved by contact with the recording material 101. Further, the downstream width (that is, the amount of protrusion) a = 7 mm protrudes from the transfer upper guide 116 to the conveyance path in a tension-free manner.

  FIG. 3A shows a state in which the post end of the postcard 101a passes through the conveying rollers 106 and 107 when the postcard 101a is passed as the recording material 101 having a large jump. Similarly, FIG. 3B shows a state immediately after the rear end portion of the postcard 101a passes through the conveying rollers 106 and 107. FIG.

  As shown in FIGS. 3A and 3B, when a thick paper having a strong stiffness and a large jump is passed like a postcard 101a, the recording material 101 is transferred with the momentum that has passed through the conveying rollers 106 and 107. Around the end of the upper guide 116, it jumps greatly upward. However, even when the trailing edge of the recording material jumps up immediately after the conveyance roller, the impact due to the jumping up can be absorbed by the sheet member 118 provided on the upper surface of the transfer upper guide 116. Therefore, even when a thick thick paper like a postcard 101a is passed, the transfer member such as the photosensitive drum 109 and the transfer roller 119 and the recording material (postcard) 101a being transferred are vibrated by the impact of the jumping up. And image blurring at the transfer, latent image, and development positions can be prevented.

  However, if the overhanging amount a of the sheet member 118 is too large, the impact absorbing effect is enhanced, but the curled thin paper is likely to be caught at the leading end, and the conveyance resistance is abnormally high, resulting in conveyance failure. There is a fear. In the present embodiment, as described above, the protruding amount a of the sheet member 118 from the transfer upper guide 116 is 7 mm.

  If the thickness t of the sheet member 118 is too thick, the conveyance resistance due to contact with the recording material 101 increases, which may cause conveyance failure. On the other hand, if it is too thin, the impact of the recording material 101 may not be absorbed. The thickness t of the sheet member 118 is preferably 100 to 150 μm, and the sheet member 118 in this example has a thickness t of 125 μm.

  Next, the position where the sheet member 118 is attached in the longitudinal direction will be described with reference to FIG. FIG. 4 is a diagram showing the positional relationship of the sheet member 118 in the longitudinal direction.

  As shown in FIG. 4, the sheet member 118 is fixed at a symmetrical position with respect to the longitudinal direction with respect to the paper center P. This longitudinal position is preferably provided at a symmetrical position in consideration of the skew caused by the conveyance resistance. The size L1 indicates the size (100 mm) of the postcard 101a, and the size L2 indicates the size (216 mm) of the LTR (letter paper) 101b, which is the maximum sheet passing width of the image forming apparatus of this embodiment. Further, the longer the length in the longitudinal direction, the greater the effect of absorbing the impact, but the conveyance resistance becomes large. In this embodiment, the longitudinal length L of the sheet member 118 is 220 mm.

  Two types of materials for the sheet member 118 were prepared. One is a biaxially stretched polyester film ("Polyester film mirror S" manufactured by Toray, trade name) that is electrically insulating. The other is a film (Toray's "High Beam CH22": trade name) in which indium tin oxide (Indium Tin Oxide = ITO) or the like is sputtered on the surface of the polyester film to impart conductivity to the surface layer.

  Then, 10 sheets generated at this time were printed on the two kinds of sheet members 118 by passing 10 recording materials continuously under a low temperature and low humidity environment (15 ° C./10% Rh). The total number of image blanks on all recording materials was counted.

The recording material 101, the surface of surface resistance with high EW-100,64g / m ² in an easy CLC-SK that was charged with smooth, and 80 g / m ² recycled paper. The results are shown in Table 1.

  When the polyester film mirror S, which is an insulating film, was used as the sheet member 118, many white spots occurred near the rear end of the recording material 101. This is because, after the recording material 101 passes through the conveying rollers 106 and 107, the end portion of the recording material 101 bounces up and is frictionally charged with the upper transfer guide 116 and the sheet member 118, so that the photosensitive drum 109 is discharged near the transfer nip N.

  On the other hand, when the high beam CH22 having conductivity on the surface layer, that is, a sheet member having a conductive layer formed on the surface of the insulating film was used as the sheet member 118, no white spots occurred. This is because the recording material 101 rubs against the upper transfer guide 116 and is frictionally charged, but immediately after contact with the sheet member 118 imparted with conductivity, the charge is eliminated. This is because the triboelectric charge amount does not become so large as to reach discharge. Since the sheet member 118 does not rub against the recording material strongly, there is almost no charge accumulation during friction, and only the recording material is neutralized by imparting conductivity. Further, since the sheet member 118 is provided with conductivity, it is attached to the insulating upper transfer guide 116, so that the transfer current does not escape and there is no need for high resistance grounding. The high beam CH22 has a surface resistance of about 300Ω / □ by conducting conductive processing on the surface of the polyester film. However, since the base material has a thickness of 125 μm, the impact of the original recording material is intended. It has been confirmed that the effect of absorbing is not changed.

  As described above, the transfer upper guide 116 is formed of an insulating member, and the conductive layer is formed on the surface of the sheet member 118 provided on the transfer upper guide 116, thereby reducing the triboelectric charge amount of the recording material. Therefore, discharge between the recording material and the photosensitive drum 109 can be prevented, and a good image can be output.

  Further, the sheet member 118, which is a conductive member, is affixed to the insulating upper transfer guide 116 and is not electrically grounded, so that no transfer current escape occurs. Further, since there is no need for high resistance grounding, it is possible to reduce the size and cost of the device.

  Furthermore, when resin is used as the material of the upper transfer guide 116, it can be molded flexibly, so that complicated shapes such as ribs can be added, and more advanced functions can be added to stabilize paper conveyance. Can do.

Example 2
A second embodiment of the image forming apparatus according to the present invention will be described with reference to FIG.

  In this embodiment, the image forming apparatus is a color laser printer 100 as shown in FIG. That is, in this embodiment, the image forming apparatus 100 has a plurality of photosensitive drums 1 as first image carriers, and sequentially multiplexes them on the intermediate transfer belt 6 as a second image carrier. This is a four-drum type (in-line type) printer that transfers and obtains a full-color print image.

  More specifically, the image forming apparatus 100 includes a plurality of image forming units P (PY, PM, PC, PBk) in the present embodiment. Each image forming unit P has the same configuration, and a charging unit 2, a developing unit 4, and a cleaning unit 5 are arranged around the photosensitive drum 1. Further, an intermediate transfer belt 6 is disposed below each image forming portion P (PY, PM, PC, PBk).

The intermediate transfer belt 6 is an endless belt, is suspended by a driving roller 10, a tension roller 11, and a secondary transfer counter roller 12, and rotates at a process speed of 115 mm / sec in the direction of the arrow in the figure. The driving roller 10, the tension roller 11, and the secondary transfer counter roller 12 are support rollers that support the intermediate transfer belt 6. The driving roller 10 and the secondary transfer counter roller 12 have a diameter of 24 mm, and the tension roller 11 has a diameter of 16 mm. It has a configuration. As the material of the intermediate transfer belt 6, polyimide, polyamide, polycarbonate (PC), polyvinylidene fluoride (PVDF), polytetrafluoroethylene polymer (PTFE), or the like is used. The intermediate transfer belt 6 of this embodiment is made of polyimide whose resistance is adjusted with carbon black, has a volume resistivity of 1 × 10 ⁸ Ω · cm, a thickness of 70 μm, an inner peripheral length of 700 mm, and a longitudinal direction ( The width in the direction perpendicular to the moving direction is 250 mm.

  Four photosensitive drums 1 of each image forming portion P are arranged in series in the moving direction of the intermediate transfer belt 6 corresponding to each color. The photosensitive drum 1 of the yellow image forming unit PY having the yellow developing device (developing unit) 4 is uniformly charged to a predetermined polarity and potential by the primary charging roller (charging unit) 2 during the rotation process. Next, by receiving image exposure 3 by an image exposure unit (not shown), an electrostatic latent image corresponding to the first color (yellow) component image of the target color image is formed.

  Next, the electrostatic latent image is developed by the first developer (yellow developer) 4 with yellow toner as the first color. The yellow image formed on the photosensitive drum 1 enters the primary transfer nip portion with the intermediate transfer belt 6. In the primary transfer nip portion, a voltage applying member (primary transfer roller) 7 as a transfer unit is brought into contact with and contacted with the back side of the intermediate transfer belt 6. A bias is applied to the voltage applying member 7 from a primary transfer bias power source 7 a to transfer a yellow image onto the intermediate transfer belt 6.

  Similarly, magenta, cyan, and black images are formed by the magenta, cyan, and black image forming units PM, PC, and PBk having developing units for magenta, cyan, and black, respectively. Each toner image is biased to the corresponding voltage applying member 7 from the primary transfer bias power supplies 7b, 7c, and 7d, and sequentially transfers magenta, cyan, and black colors onto the intermediate transfer belt 6 at each port.

  The four color toner images on the intermediate transfer belt 6 pass through the contact nip portion between the intermediate transfer belt 6 and the secondary transfer roller 8 by the secondary transfer bias applied from the secondary transfer bias power source 8a. A batch transfer is performed on the recording material 101. The secondary transfer roller 8 serving as a transfer member uses a semiconductive sponge mainly composed of NBR hydrin rubber as an elastic layer, and has an outer diameter of 18 mm and a core metal diameter of 6 mm.

  The recording material 101 on which the four-color toner images are secondarily transferred is introduced into the fixing device 123, where the four-color toners are melted and mixed and fixed to the recording material 101 by heating and pressurizing, and a full-color print is printed. An image is formed. Thereafter, the recording material 101 is discharged from the paper discharge roller 126 onto the tray 127, and one printing cycle is completed.

  The secondary transfer residual toner remaining on the surface of the intermediate transfer belt is charged to a polarity opposite to that of the photosensitive drum 1 by a cleaning roller (cleaning means) 9. The cleaning roller 9 is brought into contact with the surface of the intermediate transfer belt 6, and the secondary transfer counter roller 12 is used as a counter pole, and a bias power source 9 a applies a cleaning bias having a predetermined polarity to the cleaning roller 9, thereby performing the secondary transfer. The remaining toner is charged to a predetermined polarity. The secondary transfer residual toner charged to the reverse polarity on the intermediate transfer belt 6 is electrostatically attracted and transferred to the photosensitive drum 1 at and near the contact portion of the intermediate transfer belt 6 with the photosensitive drum 1. After being removed from the intermediate transfer belt 6, it is collected in the waste toner container 5.

  In the image forming apparatus 100 according to the present exemplary embodiment, the recording material 101 stacked and stored in the paper feed cassette 99 is fed by the paper feed roller 103 and sent to the nip portion of the transport roller pairs 106 and 107 serving as transport means. . Next, the recording material 101 is sent to a contact nip portion NT between the intermediate transfer belt 6 and the secondary transfer roller 8 by a pair of conveying rollers 106 and 107.

  Here, with reference to FIGS. 6A, 6 </ b> B, and 6 </ b> C, the configuration and operation of the upper transfer guide 116 and the sheet member 118 constituting the pre-transfer guide 20 in this embodiment will be described. FIG. 6 is a cross-sectional view schematically showing the vicinity of the sheet member 118. 6B is a cross-sectional view of the transfer upper guide and the sheet member, and FIG. 6C is a diagram illustrating a positional relationship in the longitudinal direction of the sheet member.

  The conveying rollers 106 and 107 are in pressure contact with springs (not shown) at the ends. The transport roller 106 is made of a POM material having a smooth surface. The outer diameter of the roller 106 is made larger on the inner side in the axial direction and smaller on the outer side, so that the pressure is made uniform. The transport roller 107 is configured by winding a rubber material around a metal shaft. The outer diameter has an effect on the paper transport speed for transporting the recording material 101 to the transfer area. In this embodiment, the paper transport speed of the roller converted from the roller diameter and the rotational speed is set to be equal to the process speed. The recording material 101 is set so as not to form a loop before the secondary transfer.

  The upper transfer guide 116 and the lower transfer guide 117 that constitute the pre-transfer guide 20 are connected to the main body 100A of the image forming apparatus 100, and both are molded of insulating PC + ABS resin. In addition, a plurality of ribs are set up in the longitudinal direction so that papers of various sizes and stiffness can be conveyed without problems.

  The upper transfer guide 116 is located on the printing surface side of the recording material 101, that is, the side on which the toner image on the intermediate transfer belt 6 is secondarily transferred, and the lower transfer guide 117 is printed on the recording material 101. It is located on the non-printing surface side opposite to the surface side.

  A sheet member 118 is fixed to the upper surface of the transfer upper guide 116 by adhesion. The sheet member 118 is disposed on the upper surface of the upper transfer guide 116 so as to protrude further downstream in the recording material conveyance direction than the upper transfer guide 116. Also, an adhesive tape 130 for fixing to the upper surface of the transfer upper guide 116 is pasted on the back side of the width w1 in the transport direction of 11 mm and the width w1 = 4 mm on the upstream side. Further, the downstream side width w2 = 7 mm is not fixed to the transfer upper guide 116 but is a free end, and can be elastically curved by contact with the recording material. Further, the width on the downstream side, that is, the overhang amount a = 3 mm, overhangs from the transfer upper guide 116 to the conveyance path in a tension-free manner. The thickness t of the sheet member 118 was 100 μm, and the length L in the longitudinal direction was 220 mm.

  In this embodiment, three types of materials for the sheet member 118 were prepared. One is a biaxially stretched polyester film ("Polyester film mirror S" manufactured by Toray, trade name) that is electrically insulating. The other is a film (Toray's “High Beam CH22”: trade name) in which indium tin oxide (Indium Tin Oxide = ITO) or the like is sputtered on the surface of the polyester film to impart conductivity to the surface layer. Still another is an ultra-high molecular weight polyethylene film (Nitto Denko “No. 440”: trade name) which is a polyethylene-based synthetic resin film.

  In the case of this example, when the polyester film mirror S was used as the sheet member 118, the following problems occurred.

  That is, when the recording material 101 is conveyed along the pre-transfer guide 20 to the nip portion NT of the secondary transfer roller 8, the recording material 101 rubs against the insulating resin transfer upper guide 116 and the insulating sheet member 118. To do. As a result, the transfer upper guide 116 and the sheet member 118 are frictionally charged at the contact portion with the recording material 101. When the recording material 101 is frictionally charged, a discharge occurs between the recording material and the intermediate transfer belt 6, and the polarity of the toner attached to the intermediate transfer belt 6 is reversed. Then, since the toner on the intermediate transfer belt 6 whose polarity is reversed is not secondarily transferred to the recording material 101, white spots in the image occur.

  Further, when the high beam CH22 used in the first embodiment is used, the image forming apparatus 100 of the present embodiment has a longer product life than the first embodiment. The problem was that the layer would wear out. For this reason, although there was no problem in the initial performance, there was a problem that white spots of the image occurred after passing about 50,000 sheets.

Therefore, in this embodiment, as the material of the sheet member 118, an ultra high molecular weight polyethylene film (No. 440 manufactured by Nitto Denko) is used, and by imparting conductivity to the film itself, the volume resistivity is 10 ³ Ω. -It adjusted so that it might become about cm. As a result, the conductivity can be maintained throughout the durability, so that the durability performance is improved and no problem occurs even when about 100,000 sheets are passed.

  As described above, the frictional charge amount of the recording material is reduced by configuring the transfer upper guide 116 with an insulating member and the sheet member 118 provided on the transfer upper guide 116 with a conductive material. Therefore, discharge between the recording material and the image carrier can be prevented, and a good image can be output. In particular, in an image forming apparatus having a long product life, conductivity can be maintained even if it is worn by rubbing against the recording material 101, so that the performance after durability is good.

  Further, since the conductive sheet member is affixed to the insulating transfer guide and is not electrically grounded, no transfer current escape occurs. Further, since there is no need for high resistance grounding, it is possible to reduce the size and cost of the device.

  Furthermore, when resin is used as the material of the upper transfer guide 116, it can be molded flexibly, so that complicated shapes such as ribs can be added, and more advanced functions can be added to stabilize paper conveyance. Can do.

Example 3
A third embodiment of the image forming apparatus according to the present invention will be described.

  The image forming apparatus according to the present embodiment illustrated in FIG. 7 can automatically print on both sides of a recording material by attaching the automatic duplex unit 200 to the image forming apparatus 100 according to the second embodiment. Therefore, in the present embodiment, the same reference numerals are given to members / portions common to the second embodiment, and the description thereof will be omitted.

  The operation of the automatic duplex unit 200 including the reverse feeding unit will be described.

  The transport path of the fixed recording material 101 is selectively switched by the switching flapper 201 depending on whether the single-sided printing or the double-sided printing selected in advance.

  When single-sided printing is selected, the fixed recording material 101 is conveyed toward the discharge roller pair 126 by the switching flapper 201 and is directly discharged onto the discharge tray 127.

  When duplex printing is selected, the sheet is conveyed by the switching flapper 201 toward the paper discharge roller pair 126. The paper discharge roller pair 126 also functions as a switchback roller pair during double-sided printing, and after the recording material is conveyed toward the paper discharge tray 127, the timing at which the rear end of the recording material passes through the fixing unit 123. Simultaneously with the reverse rotation, the switching flapper 201 is switched to transport the recording material toward the reverse transport path 202. The duplex conveying roller pair 203 conveys the recording material 101 to the refeed roller pair 204. The recording material 101 re-fed by the re-feed roller pair 204 joins the re-feed conveyance path 205 in an inverted state, and is conveyed again to the registration roller pairs 106 and 107. The recording material conveyance and toner image transfer after the registration roller pairs 106 and 107 are the same as in the above-described single-sided printing.

  In the automatic double-sided printing, the recording material 101 that has once passed through the fixing device 123 has high resistance because the contained water evaporates. That is, during the secondary transfer of the second side, the resistance is higher than that of the first side. For this reason, the triboelectric charge amount when the recording material 101 rubs against the upper transfer guide 116 and the sheet member 118 constituting the pre-transfer guide 20 increases, and image whiteout is likely to occur. When the insulating polyester film mirror S was used as the sheet member 118, when the automatic double-sided printing was performed, an image blank with a poor level occurred on the second side. Therefore, the sheet members of Example 1 and Example 2 were tried, but no significant improvement effect was observed with respect to the image blank on the second side. That is, even when the high beam CH22 and the ultra-high molecular weight polyethylene film were used, slight image blanking occurred on the second and subsequent surfaces when automatic printing was performed on both sides automatically.

  Therefore, in this embodiment, SUS, which is a metal, is used as the material of the sheet member 118. Since the capacitance of the metal is large and it is difficult to charge itself, and the electric resistance is almost zero, the neutralization effect of the recording material 101 is extremely large. The thickness was set to 20 μm so that the rigidity was almost the same as the thickness of the polyester film of 100 μm.

  Also, as shown in FIG. 8, the sheet member 118 is divided into three parts in the longitudinal direction, and formed by three members having a longitudinal width of 80 mm at both ends and a central part of 50 mm so that the conveyance resistance is reduced. Arranged.

  In the gap portion g between the sheet members, the neutralization effect is lost, and when the gap is opened by 5 mm or more, a blank image is generated in the gap portion g. Therefore, in this embodiment, the gap g is 5 mm. Arranged to be. With this configuration, even if a metal having high rigidity is used, the effect as an impact absorbing plate is not impaired.

Then, 10 sheets of recording material 101 are continuously passed on both sides of the sheet member 118 made of SUS under a low temperature and low humidity environment (15 ° C./10% Rh), and a halftone is printed. The total number of white spots on the second surface on all the 10 recording materials was counted. The recording material 101, the surface of surface resistance with high EW-100,64g / m ² in an easy CLC-SK that was charged with smooth, and 80 g / m ² recycled paper. Table 2 shows the results of a comparative experiment with the case of using the ultrahigh molecular weight polyethylene film employed in Example 2.

  From this result, when an ultra-high molecular weight polyethylene film was used as the sheet member 118, white spots were observed in the vicinity of the rear end of the recording material on the second and subsequent surfaces of the fifth and subsequent sheets although they were minor. However, it has been found that when the material of the sheet member 118 is SUS, white spots are not generated and there is a significant improvement effect.

  As described above, since the sheet member 118 provided on the transfer upper guide 116 is made of metal, the frictional charge amount of the recording material is reduced, so that the discharge between the recording material and the image carrier can be prevented. A good image can be output. In addition, in an image forming apparatus having a long product life, there is no wear due to rubbing against the recording material, and the conductivity can be maintained, so that the performance after durability is good.

  Further, even in an image forming apparatus capable of automatic double-sided printing, it is possible to completely prevent white spots on the second side where the resistance of the recording material is high. Further, since the metal sheet member 118 is attached to the insulating transfer upper guide 116 and is not electrically grounded, no transfer current escape occurs. Further, since there is no need for high resistance grounding, it is possible to reduce the size and cost of the device.

  Furthermore, when resin is used as the material of the upper transfer guide 116, it can be molded flexibly, so that complicated shapes such as ribs can be added, and more advanced functions can be added to stabilize paper conveyance. Can do.

1 is a schematic configuration diagram of a first embodiment of an image forming apparatus according to the present invention. It is sectional drawing which shows the outline of the sheet | seat member vicinity in Example 1 of this invention. FIG. 3A is a schematic diagram showing the behavior of the paper when the thick paper is passed in the vicinity of the sheet member, and FIG. 3A is a diagram showing a state where the paper is nipped and conveyed by the conveyance roller, and FIG. These are figures which show the state immediately after the rear end of paper passed the conveyance roller. It is a figure which shows the positional relationship of the longitudinal direction of the sheet | seat member in Example 1 of this invention. It is a schematic block diagram of the 2nd Example of the image forming apparatus which concerns on this invention. FIG. 6A is a cross-sectional view schematically illustrating the vicinity of a sheet member in Example 2 of the present invention, FIG. 6A is a diagram illustrating a state where paper is nipped and conveyed by a conveyance roller, and FIG. FIG. 6C is a cross-sectional view of the transfer upper guide and the sheet member, and FIG. 6C is a diagram illustrating a positional relationship in the longitudinal direction of the sheet member. It is a schematic block diagram of the 3rd Example of the image forming apparatus which concerns on this invention. It is a figure which shows the positional relationship of the longitudinal direction of the sheet | seat member which concerns on Example 3 of this invention.

Explanation of symbols

1 Photosensitive drum (first image carrier)
2 Charging roller (charging means)
3 Exposure 4 Developer (Developing means)
5 Cleaning device (cleaning means)
6 Intermediate transfer belt (second image carrier)
7 Primary transfer roller 8 Secondary transfer roller (transfer member)
12 Secondary transfer counter roller 20 Pre-transfer guide 101 Recording material 106, 107 Conveying roller pair (conveying means)
109 Photosensitive drum (image carrier)
116 Transfer upper guide 117 Transfer lower guide 118 Sheet member 119 Transfer roller (transfer member)

Claims (5)

An image carrier that carries an image to be formed on a recording material, a transfer member that transfers a toner image on the image carrier to the recording material, and guides the recording material toward a transfer portion where the transfer member is disposed. An image forming apparatus comprising: a pre-transfer guide for conveying; and a conveying unit that conveys a recording material to the pre-transfer guide.
The pre-transfer guide is composed of a transfer upper guide positioned on the printing surface side of the recording material and a transfer lower guide positioned on the non-printing surface side of the recording material,
The transfer upper guide is provided with a sheet member having a free end on the downstream side in the recording material conveyance direction,
The image forming apparatus, wherein the transfer upper guide is made of an insulating member, and the sheet member is made of a conductive member.   The image forming apparatus according to claim 1, wherein the sheet member is formed by forming a conductive layer on an insulating film surface.   The image forming apparatus according to claim 2, wherein the insulating film of the sheet member is a polyester film.   The image forming apparatus according to claim 1, wherein the sheet member is a polyethylene-based synthetic resin film.   The image forming apparatus according to claim 1, wherein the sheet member is made of metal.

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