JP2012083646A - Image forming apparatus including conveyance belt - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that prevents the generation of unstable electrical field in a conveyance path from a transfer part to a fixing part to prevent the occurrence of an abnormal image such as background stains due to toner dust.SOLUTION: An image forming apparatus comprises: a conveyance belt that conveys a recording medium from a transfer part that transfers a toner image developed by an electrostatic photographic system on a recording medium by allowing the recording medium, which is held by a transfer nip, to be subjected to a transfer electrical field, to a fixing part that fixes an unfixed toner image carried by the recording medium. The surface resistance of the conveyance belt is set to be not more than the surface resistance of a transfer roller that holds a recording medium.

Description

  The present invention relates to a sheet conveying mechanism provided with a conveying belt used in an image forming apparatus such as a copying machine, a printer, and a facsimile, in particular, image transfer to a sheet (also referred to as a recording medium or a sheet material) fed from a sheet feeding unit. The present invention relates to a paper transport mechanism from a transfer section to a fixing section for fixing a transfer image on the paper.

  Electrostatic photography, in which toner is placed on an electrostatic latent image formed by exposing image information to the surface of the photoreceptor after it has been uniformly charged with static electricity and transferred and fixed, is widely used in current image forming apparatuses. Yes. In the color image forming apparatus, as disclosed in Japanese Patent Application Laid-Open No. H10-228707, an intermediate transfer belt is used to superimpose images formed with individual color toners, and a sheet is placed between the intermediate transfer belt and the secondary transfer roller. A transfer electric field (or transfer current) having a polarity opposite to that of the toner image is applied to the secondary transfer roller to form a transfer electric field in a direction in which the toner image is attracted to the paper side. A configuration for transferring from a transfer belt onto a sheet is known.

  Also, in an image forming apparatus developed for business use and called a high-end machine, plain paper, coated paper, etc. are used as a sheet material, and the sizes vary from A5 size to 13 × 19 inches. A wide variety of sheet materials such as 80 gram paper to 300 gram paper are used. For this reason, various sheet materials are required to be conveyed in the same manner from the transfer unit to the fixing unit. Therefore, a configuration is adopted in which a belt conveyance unit is disposed between the transfer unit and the fixing unit with a sufficient distance between the transfer unit and the fixing unit. In this case, for example, Japanese Patent Application Laid-Open No. 2004-260688 discloses a belt conveying unit that conveys a sheet material while sucking the sheet material onto a conveying belt in order to convey the sheet material from the transfer unit to the fixing unit in a stable state.

  However, the unfixed toner on the sheet material is easily affected by an unstable electric field in the conveyance path, and the toner may be scattered, resulting in a background stain or an abnormal image.

  An object of the present invention is to prevent the generation of an unstable electric field in the conveyance path from the transfer unit to the fixing unit, and to prevent abnormal images such as background stains due to toner dust.

  The above-mentioned problem is to fix the unfixed toner image carried on the recording medium from the transfer section that transfers the toner image visualized by the electrophotographic method to the recording medium sandwiched by the transfer nip by applying a transfer electric field. In the image forming apparatus provided with the conveyance belt for conveying the recording medium up to the recording medium, the problem is solved by setting the surface resistance of the conveyance belt to a value equal to or lower than the surface resistance of the transfer roller for nipping the recording medium.

  In the case of the intermediate transfer mode, an endless belt-shaped intermediate transfer body on which a toner image visualized by an electrostatic photography method is primarily transferred, and a toner image carrying surface of the intermediate transfer body facing the recording medium with a recording medium interposed therebetween. A secondary transfer roller and a counter roller located on the back side of the toner image carrying surface of the intermediate transfer member and forming a secondary transfer nip with the secondary transfer roller, and the secondary transfer roller and the counter roller between the secondary transfer roller In a secondary transfer device for forming a transfer electric field, and an image forming apparatus having a transport belt for transporting a recording medium from the secondary transfer device to a fixing device for fixing an unfixed toner image on the recording medium, the surface resistance of the transport belt Is set to a value equal to or lower than the surface resistance of the secondary transfer roller, the above-mentioned problem is solved.

  It is preferable that a roller for stretching the conveyor belt is grounded, or a grounded guide plate is provided on the back surface of the belt between the rollers for stretching the conveyor belt. It is more convenient if the surface roughness or the back surface roughness of the conveyor belt is 10 μm or less.

  According to the present invention, the surface resistance of the conveying belt that conveys the recording medium from the transfer unit to the fixing unit is set to a value that is equal to or less than the surface resistance of the transfer roller (secondary transfer roller in the case of the intermediate transfer mode) sandwiching the recording medium. By doing so, an unstable electric field is not generated during conveyance of the recording medium, and toner dust caused by scattering of the untransferred toner image on the recording medium can be suppressed, and a good image can be obtained. When the surface resistance of the conveying belt is large, the electric field strength between the toner on the recording medium and the transfer-side driven roller on the conveying belt is smaller than the electric field strength between the toner on the recording medium and the transfer roller. The toner acts on the recording medium in a state where the medium is interposed, and the adhesion between the recording medium and the belt is weakened. When the adhesion is weakened, the toner on the recording medium is easily displaced and easily scattered. However, by making the surface resistance of the conveying belt equal to or less than the surface resistance of the transfer roller sandwiching the recording medium, it is possible to suppress a decrease in electric field strength between the toner on the recording medium and the transfer side driven roller of the conveying belt stretcher. Because it becomes.

  If the roller that stretches the conveyor belt is grounded or a grounded guide plate is provided on the back of the belt between the rollers that stretch the conveyor belt, an unstable electric field may be generated during recording medium conveyance. Therefore, generation of toner dust can be suppressed. Further, when the surface roughness or back surface roughness of the conveying belt is 10 μm or less, the adhesion between the recording medium or the stretching roller and the belt is increased, and an unstable electric field is not generated during the conveyance of the recording medium. Generation can be suppressed.

1 is a schematic configuration diagram of a tandem indirect transfer type color electrophotographic copying machine. FIG. It is a detailed sectional view of a secondary transfer part. FIG. 3 is a schematic perspective view of a belt conveyance device to be disposed between a secondary transfer unit and a fixing device.

  FIG. 1 shows a color electrophotographic copying machine (hereinafter referred to as a copying machine) of a tandem type indirect transfer system which is an object of the present invention. The mechanism of the entire copying machine is basically the same as that conventionally known, and a predetermined device necessary for forming an image around the photosensitive member constituting the image forming means, for example, a charging means, exposure However, for the sake of brevity, the description will not be given for all of them, but those skilled in the art can easily understand the mechanism of the entire copying machine from the drawings. It is.

  In FIG. 1, an endless belt-like intermediate transfer belt 10 that is an intermediate transfer member is provided at the center of a copying apparatus main body 100. The intermediate transfer belt 10 has a base layer formed by combining, for example, a fluororesin having a small elongation or a rubber material having a large elongation with a material that is difficult to stretch, such as a canvas, and an elastic layer is provided thereon. The elastic layer is formed of, for example, fluorine-based rubber or acrylonitrile-butadiene copolymer rubber. The surface of the elastic layer is covered with a coat layer having good smoothness, which is formed by coating a fluorine resin, for example. Basically, the intermediate transfer belt 10 is wound around three support rollers 14, 15, 16 and further support rollers 70, 72 in the illustrated example, and can be rotated and conveyed in the clockwise direction in the figure. Yes.

  An intermediate transfer body cleaning device 17 for removing residual toner remaining on the intermediate transfer belt 10 after image transfer is provided at a position opposite to the auxiliary support roller 72. On the intermediate transfer belt portion stretched between the first support roller 14 and the second support roller 15, four image forming units 18 of black, yellow, magenta, and cyan are arranged along the conveyance direction. A tandem image forming apparatus 20 is provided in parallel. A primary transfer roller 62 for transferring the toner image formed on the photoreceptor 40 onto the intermediate transfer belt 10 is provided inside the belt of the tandem image forming apparatus 20 to form a primary transfer position.

  On the other hand, the third support roller 16 is a secondary transfer counter roller, and is opposed to the secondary transfer roller 23 with the intermediate transfer belt 10 interposed therebetween to form a secondary transfer nip and constitute a secondary transfer device 22. Yes. FIG. 2 is a detailed view of the secondary transfer roller 23 and the secondary transfer counter roller 16. The secondary transfer counter roller 16 functions as a repulsive roller. The repulsive roller 16 is connected to a constant current power source 13 that gives a constant current having the same polarity as the toner image, and the secondary transfer roller 23 is grounded.

The repulsive roller 16 is formed by laminating a resistance layer 16a on a cored bar 16b made of stainless steel or aluminum. The resistance layer 16a is made by dispersing conductive particles such as carbon or metal complex in polycarbonate, fluorine rubber, silicon rubber, or the like, or rubber such as NBR or EPDM, rubber of NBR / ECO copolymer, polyurethane semiconductive. Made of natural rubber. The volume resistance is 10 ⁶ to 10 ¹² [Ω], preferably 10 ⁷ to 10 ⁹ [Ω]. Further, a foam type having a hardness of 20 degrees to 50 degrees or a rubber type having a rubber hardness of 30 degrees to 60 degrees may be used. However, since it is in contact with the secondary transfer roller 22 via the intermediate transfer belt 10, it is non-contact even at a small contact pressure. A sponge type that does not produce a part is desirable.

The secondary transfer roller 23 is formed by laminating a resistance layer 23a made of conductive rubber or the like and a surface layer 23c on a metal core 23b made of stainless steel or aluminum. Further, the secondary transfer roller 23 is configured such that the surface resistance (resistance between the surfaces) is larger than the volume resistance (resistance between the core metal and the surface). In this example, the surface resistance of the secondary transfer roller is 10 ^6.5 Ω or more.

Returning to FIG. 1, on the left side of the secondary transfer device 22 in the figure, a belt transport device 101 that transports the paper and a fixing device 25 that fixes the transfer image on the paper are arranged. In FIG. 3 showing the details of the belt conveyance device 101, the sheet after the image transfer is carried on the conveyance belt 106 of the conveyance device 101 and conveyed to the fixing device. The conveying device 101 is provided with a driving shaft 104 and a driven shaft 103 for stretching and driving the conveying belt 106, and a guide plate 108 on the belt back surface between the two shafts, and each is grounded (not shown). The transport belt 106 is a base layer similar to a single-layer belt or intermediate transfer belt such as EPDM (ethylene / propylene / diene rubber), chloroprene, urethane, etc. For example, a combination of a stretchable fluororesin or a stretchable material such as canvas with a stretchable fluororesin. A base layer configured as described above is formed, and an elastic layer is provided thereon. The elastic layer is formed of, for example, fluorine-based rubber or acrylonitrile-butadiene copolymer rubber. The surface of the elastic layer is coated with, for example, a fluororesin and a smooth coat layer. The surface resistance (resistance between the surfaces) of the belt is set to be equal to or less than the surface resistance (resistance between the surfaces) of the secondary transfer roller. In this example, since the surface resistance of the secondary transfer roller is 10 ^6.5 Ω or more, the surface resistance of the belt is set to 10 ^6.5 Ω or less.

  Returning to FIG. 1 again, the fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 which is an endless belt. In the illustrated example, a paper reversing device 28 for reversing the paper for recording images on both sides of the paper is provided below the secondary transfer device 22 and the fixing device 25 in parallel with the tandem image forming device 20. Yes.

  When making a copy using such a copying machine, set the document on the document table 30 of the automatic document feeder (ADF) 400 or open the ADF 400 and set the document on the contact glass 32 of the scanner 300. Then close the ADF 400 and hold the document. When a start switch (not shown) is pressed, when a document is set on the ADF 400, after the document is transported and moved onto the contact glass 32, when the document is set on the other contact glass 32, the scanner 300 is immediately turned on. Driven, the first traveling body 33 and the second traveling body 34 travel. Then, the first traveling body 33 emits light from the light source, and the reflected light from the document surface is further reflected toward the second traveling body 34, reflected by the mirror of the second traveling body 34, and passed through the imaging lens 35. The document is placed in the reading sensor 36 and the original content is read.

  Further, when a start switch (not shown) is pressed, one of the support rollers 14, 15 and 16 is also rotationally driven by a drive motor (not shown) and the other two support rollers are driven to rotate, thereby causing the intermediate transfer belt 10 to rotate. Rotate and transport. At the same time, the photoconductors 40 are rotated by the individual image forming units 18 to form black, yellow, magenta, and cyan single-color images on the photoconductors 40, respectively. Then, along with the conveyance of the intermediate transfer belt 10, the single color images are sequentially transferred by the primary transfer roller 62 to form a composite color image on the intermediate transfer belt 10.

  When a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selected and rotated, and the paper is fed out from one of the paper cassettes 44 provided in the paper bank 43 in multiple stages. Then, the paper is separated one by one by the separation roller 45 and put into the paper feed path 46, transported by the transport roller 47, led to the paper feed path 48 in the copying machine main body 100, and abutted against the registration roller 49 and stopped.

  Then, the registration roller 49 is rotated in synchronization with the composite color image on the intermediate transfer belt 10, the sheet is fed between the intermediate transfer belt 10 and the secondary transfer device 22, and is transferred by the secondary transfer device 22. Record a color image on paper.

  The paper after the image transfer is transported by the transport device 101 and sent to the fixing device 25. The fixing device 25 applies heat and pressure to fix the transferred image, and then the path is switched by the switching claw 55 and the discharge roller. The paper is ejected at 56 and stacked on the paper ejection tray 57, or the path is switched by the switching claw 55 to enter the paper reversing device 28, where it is reversed and guided again to the transfer position, and the image is recorded also on the back surface. The paper is discharged onto the paper discharge tray 57 by the discharge roller 56.

  Tables 1 and 2 show the results of performing an average of 300,000 print tests using this copying machine and taking the average. In each test, the surface resistance of the secondary transfer roller and the conveyance belt was measured each time. The measuring method is a well-known method, and is disclosed in Patent Document 1, for example.

The surface resistance of the conveyor belt is two levels (10 ^7-8 Ω, 10 ^6-6.5 Ω) with respect to the surface resistance of 10 ^6.5-7 Ω of the secondary transfer roller. Toner dust was evaluated when the roughness of the front and back surfaces was 3 levels (5 μm, 10 μm, and 15 μm).

すべての条件においてトナーチリの発生率は通紙枚数の３０％以上であった。

Under all conditions, the generation rate of toner dust was 30% or more of the number of sheets passed.

上記の△は若干のトナーチリは見られたが、発生率は１０％未満を意味する。また○はトナーチリが未発生であった状態を意味する。

The above Δ means that some toner dust was observed, but the occurrence rate was less than 10%. Further, ◯ means a state where toner dust has not occurred.

  In the illustrated embodiment, primary transfer and secondary transfer are performed using an intermediate transfer belt, and repulsive transfer is performed at the time of secondary transfer. However, the present invention is not limited to these methods. The present invention is also applied to a case where an image is directly transferred from a photosensitive member to a recording medium and is sent to a fixing unit, or to an attractive bias transfer.

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 13 Constant current power supply 14, 15, 16, 70, 72 Support roller 17 Intermediate transfer body cleaning device 20 Tandem image forming device 22 Secondary transfer device 23 Secondary transfer roller 25 Fixing device 26 Fixing belt 27 Pressure roller Reference Signs List 40 Photosensitive member 62 Primary transfer roller 101 Belt conveying device 103 Drive shaft 104 Drive shaft 106 Conveying belt 108 Guide plate

JP 2007-32817 A JP 2000-272778 A

Claims (6)

  Recording from a transfer unit that applies a transfer electric field to a recording medium sandwiched in a transfer nip by a toner image visualized by an electrophotographic method, to a fixing unit that fixes an unfixed toner image carried on the recording medium An image forming apparatus comprising a transport belt for transporting a medium, wherein the surface resistance of the transport belt is set to a value equal to or less than the surface resistance of a transfer roller sandwiching a recording medium.   An endless belt-shaped intermediate transfer body to which a toner image visualized by an electrostatic photographic method is primarily transferred, a secondary transfer roller facing the toner image carrying surface of the intermediate transfer body with a recording medium interposed therebetween, A secondary transfer roller that is positioned on the back side of the toner image carrying surface of the intermediate transfer member and a counter roller that forms a secondary transfer nip, and that forms a secondary transfer electric field between the secondary transfer roller and the counter roller. In a secondary transfer device and an image forming apparatus having a transport belt for transporting a recording medium from the secondary transfer device to a fixing device for fixing an unfixed toner image on the recording medium, the surface resistance of the transport belt is determined by a secondary transfer roller. An image forming apparatus characterized in that the value is set to a value equal to or less than the surface resistance.   The image forming apparatus according to claim 1, wherein a roller that stretches the conveyance belt is grounded.   The image forming apparatus according to claim 1, wherein a grounded guide plate is provided on a back surface of the belt between the rollers that stretch the conveyance belt.   The image forming apparatus according to claim 1, wherein the conveyance belt has a surface roughness of 10 μm or less.   The image forming apparatus according to claim 1, wherein a back surface roughness of the conveyor belt is 10 μm or less.

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