JP2005189432A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus with which electric discharging of a separating means along the width direction of a paper guide is made uniform to prevent occurrence of insulation destruction of an image carrying body, a recording medium is properly separated from the image carrying body and no injury caused by the separating means occurs for a worker during maintenance or the like. <P>SOLUTION: An electric discharge separating section holder 23 is provided with an upstream side wall section 27 which is separately positioned to a sheet transporting direction upstream side from a separating needle 17 and a downstream side wall section 28 which is separately positioned to a sheet transporting direction downstream side from the separating needle 17. Let "a" (mm) be a shortest distance between the separating needle 17 and the upstream side wall section 27 and "b" (mm) be a shortest distance between the separating needle 17 and the downstream side wall section 28. Then, the sizes of "a" and "b" are determined by a≥1.5 and b≥1.5 and also 4≥a+b≥3. Moreover, let "c" (mm) be a shortest distance of the line connecting the tip of the upstream side wall section 27 and the tip of the downstream side wall section 28. Then, the tip of the separating needle 17 is constituted to satisfy 0≤c≤2. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to an image forming apparatus that facilitates charge-separation separation of a sheet-like recording medium after transfer of a toner image from an image carrier. .

  In general, image forming apparatuses such as electrophotographic copying machines, printers, facsimiles, etc. visualize the electrostatic latent image formed on the surface of an image carrier such as a photosensitive drum or an intermediate transfer member as a toner image by developing means. The toner image formed on the surface of the image carrier is transferred to a sheet-like recording medium (copy paper, plastic film, etc.), and then the recording medium is separated from the surface of the image carrier by a separating means. The recording medium separated from the carrier is sent to the fixing unit, and the fixing unit fixes the toner image on the recording medium. Then, the fixed recording medium is conveyed to a discharge tray, an intermediate tray for duplex printing, and the like. ing.

  As the separation means of such an image forming apparatus, for example, a static elimination separation type as shown in FIG. 6 (see, for example, Patent Document 1), or a static elimination separation type as shown in FIG. 2) and the static elimination separation type shown in FIG. 8 (for example, see Patent Document 3). Among them, the separating means 100 and 101 shown in FIG. 6 and FIG. 7 have the upstream side wall portions 104 and 105 positioned on the upstream side in the recording medium conveyance direction and the downstream side wall positioned on the downstream side in the recording medium conveyance direction. A plurality of separation needles 102 and 103 are arranged in a direction orthogonal to the recording medium conveyance direction (hereinafter abbreviated as a paper passing width direction). Further, the separating means 108 shown in FIG. 8 has a form in which the upstream side wall portions 104 and 105 and the downstream side wall portions 106 and 107 shown in FIGS. 6 and 7 are scraped off, and the separation needle 110 is greatly exposed. It is to be held in the state.

  Among the separating units 100, 101, and 108 of such an image forming apparatus, the separating units 100 and 108 disclosed in Patent Documents 1 and 3 have a predetermined timing after the toner image is transferred to the recording media 111 and 112. When the separation voltage is applied to the separation needles 102 and 110, a corona discharge is generated between the separation needles 102 and 110 and the image carriers 113 and 114, and the recording medium 111 is transferred by the transfer rollers 117 and 118. , 112 is removed, and the recording medium 111, 112 is separated from the image carrier 113, 114 by its own strength or its own weight.

  In addition, the separating unit 101 disclosed in Patent Document 2 discharges an excessive charge from the back surface side of the recording medium 115 to the grounded separation needle 103 side, and the recording medium 115 is charged by the transfer operation by the transfer roller 120. Is to be removed.

  Even when the separating means 101 as disclosed in Patent Document 2 known in the past is used, if the recording medium 115 itself is stiff, the recording medium 115 and the image carrier It was possible to carry out the charge removal separation with 116 well.

  However, in recent years, printing on both sides of a recording medium is increasing from the viewpoint of effectively using resources and protecting the environment. When printing on both sides of such a recording medium, there is a possibility that the recording medium 115 cannot be separated from the image carrier 116 with the separating means 101 as disclosed in Patent Document 2 of the related art. Here, as a mode of printing on both sides of the recording medium 115, after printing on one side of the recording medium 115, a double-sided printing unit or the like is used, and the recording medium 115 printed on one side is turned upside down. In addition to double-sided printing in which printing is continuously performed on the other side that is not printed, copy paper or the like after single-sided printing is reused as the recording medium 115, and the recording medium 115 to be reused is reused. There is also an aspect in which printing is performed on an unprinted surface.

  That is, when performing such double-sided printing, the curl (curvature deformation) of the recording medium 115 such as copy paper is likely to be larger than the curl of the recording medium 115 only for single-sided printing. Is easily wound around the image carrier 116 side such as a photosensitive drum (when curled toward the image carrier 116 side), it is separated from the image carrier 116 as much as the curl increases. The recording medium 115 is wound up to the image carrier 116 side, and there is a possibility of causing problems such as jam (paper jam).

  In order to solve such a problem, for example, in the separation unit 100 of Patent Document 1, a voltage having a polarity opposite to the transfer current is applied to the separation needle 102, and a corona between the separation needle 102 and the image carrier 113 is used. It is effective to discharge the recording medium 111 by discharging to increase the separation efficiency of the recording medium 111 from the image carrier 113.

Japanese Patent Laid-Open No. 9-218623 JP-A-8-137358 Japanese Patent Application Laid-Open No. 8-114989

  However, in the separation means 100 of Patent Document 1, if the upstream side wall portion 104 and the downstream side wall portion 106 are formed of an insulating resin, the insulating resin is generated by corona discharge generated between the separation needle 102 and the image carrier 113. The upstream side wall portion 104 and the downstream side wall portion 106 made of the product may be charged, and the electric field around the plurality of separation needles 102 (the electric field in the sheet passing width direction) may become uneven depending on the position in the sheet passing width direction. At this time, when the applied voltage to each separation needle 102 is increased to obtain the desired separation performance of the recording medium 111, abnormal discharge occurs between the separation needle 102 and the image carrier 113, and the photosensitive member. There is a risk of dielectric breakdown of the image carrier 113 such as a drum.

  On the other hand, a structure in which the upstream side wall portion 104 and the downstream side wall portion 106 in the separating means 100 of Patent Document 1 are greatly scraped off, as in the separating means 108 of Patent Document 3, that is, as shown in FIG. Is exposed and the discharge of the plurality of separation needles 110 in the paper passing width direction is made uniform, the operator's finger may come into contact with the tip of the separation needle 110 during maintenance or the like, resulting in injury.

  Accordingly, the present invention makes it possible to make the discharge in the sheet passing width direction of the separating means uniform to prevent dielectric breakdown of the image carrier, and to satisfactorily separate the recording medium from the image carrier. In addition, an image forming apparatus is provided that is not injured by the separating means.

  An image forming apparatus according to a first aspect of the present invention includes the configurations (A) to (C). That is, the image forming apparatus of the present invention comprises (A). An image carrier that carries and rotates a toner image; and (B). Transfer means for applying a transfer current to a sheet-like recording medium passing between the image carrier and transferring the toner image to the recording medium; and (C). When a separation voltage is applied to a plurality of separation needles positioned downstream of the transfer unit in the recording medium conveyance direction and perpendicular to the recording medium conveyance direction, the image carrier and the separation are separated. Separating means for discharging between the needles and discharging the recording medium charged by the transfer means to separate it from the image carrier. Among these, the said separating means has the discharge separation part holder which accommodates the said separation needle in an inside. An upstream side wall portion in which the discharge separation unit holder is located farther upstream than the separation needle in the recording medium transport direction, and a downstream side wall portion located farther downstream in the recording medium transport direction than the separation needle And have. Further, when the shortest distance between the separation needle and the upstream side wall is a (mm) and the shortest distance between the separation needle and the downstream side wall is b (mm), a ≧ 1.5, b ≧ 1 And the dimensions of the a and the b are determined so that 4 ≧ a + b ≧ 3. The tip of the separation needle is configured to satisfy 0 ≦ c ≦ 2, where c (mm) is the shortest distance between a line connecting the tip of the upstream side wall and the tip of the downstream side wall. Yes.

  An image forming apparatus according to a second aspect of the invention is characterized by the separation needle according to the first aspect of the invention. That is, the separation needle is characterized in that it protrudes from the edge of the plate-shaped separation electrode portion on the image carrier side so that the cross-sectional shape orthogonal to the recording medium conveyance direction is substantially triangular. .

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect of the present invention, the image carrier is formed of amorphous silicon.

  According to the present invention, the discharge in the sheet passing width direction of the separating means can be made uniform, and the dielectric breakdown of the image carrier can be effectively prevented. Moreover, according to the present invention, the recording medium can be satisfactorily discharged and separated from the image carrier, and the high-quality image can be formed without disturbing the image before fixing. Furthermore, according to the present invention, it is possible to effectively prevent an operator from being injured by the separation needle of the separation means during maintenance or the like.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 shows a schematic configuration of an image forming apparatus 1 according to the present embodiment. In FIG. 1, a photosensitive drum (image carrier) 2 rotates in a direction indicated by an arrow A in FIG. 3, the surface is uniformly charged, and laser light is irradiated by the exposure unit 5 that operates based on a control signal from the control unit 4, and an electrostatic latent image is formed on the surface, and then the developing unit 6 is formed on the surface. Thus, toner as a developer is supplied, and the electrostatic latent image is visualized as a toner image.

  A sheet-like recording medium (copy paper, plastic film or the like, hereinafter simply referred to as a sheet) 12 fed from the paper feed trays 7 and 8 by the paper feed rollers 10 and 11 is transferred to the photosensitive drum 2 by the registration rollers 13. And a transfer roller (transfer means) 14 to a transfer position P. The transfer roller 14 applies a transfer bias having a polarity opposite to that of the toner to the sheet 12, thereby transferring the toner image attached to the surface of the photosensitive drum 2 (in this embodiment, the photosensitive drum 2 and the transfer roller 14). The nip portion) P is transferred to the sheet 12. Note that the toner remaining on the surface of the photosensitive drum 2 without being transferred to the sheet 12 is removed by the cleaning unit 15. Further, as the photosensitive drum 2, an amorphous silicon type is used.

  Separating means 16 is arranged at a predetermined position downstream of the transfer position P in the sheet conveying direction. As will be described in detail later, the separation means 16 applies a separation voltage to a separation needle (separation electrode portion) 17 to generate a corona discharge between the separation drum 16 and the photosensitive drum 2, and thereby removes the sheet 12 from the photosensitive member The charge is separated from the drum 2. Further, a separation claw 18 is provided around the photosensitive drum 2 and between the separation unit 16 and the cleaning unit 15 to separate and separate the sheet 12 that could not be separated by the separation unit 16 from the surface of the photosensitive drum 2. Is arranged.

  The sheet 12 from which the charge is removed from the photosensitive drum 2 by the separating unit 16 is sent to the fixing unit 20 and heated and pressurized by the fixing unit 20 to fix the toner. Then, the sheet sent out from the fixing unit 20 is discharged to the paper discharge tray 22 by the paper discharge roller 21 and is stacked on the paper discharge tray 22.

  FIG. 2 shows details of the separating means 16. In FIG. 2, the separation means 16 has a separation needle 17 held in a discharge separation portion holder 23. The discharge separation unit holder 23 includes a transfer housing 24 that rotatably supports the transfer roller 14, a plate-like spacer 25, and a conveyance guide 26. The discharge separation unit holder 23 has a spacer 25 attached to the upstream side wall 27 of the transfer housing 24, and a substantially plate-shaped separation electrode 30 is sandwiched between the spacer and the downstream side wall 28 of the transport guide 26. It comes to hold in.

  The separation electrode unit 30 is formed of a conductive material (for example, SUS304), and at least the sheet passing width direction dimension of the largest sheet among the sheets 12 used for printing (perpendicular to the conveyance direction of the sheet 12). In the length direction). A plurality of separation needles 17 project from the edge of the separation electrode portion 30 on the photosensitive drum 2 side in the sheet passing width direction (see FIG. 3). The separation needle 17 has a substantially triangular shape when viewed in the paper passing direction (see FIG. 3), and converges toward the photosensitive drum 2 side, and between the tip and the photosensitive drum 2. Discharge occurs. Further, the tip of the separation needle 17 is v = 0.05 to 0 on the upper side in the vertical direction (substantially downstream in the sheet conveying direction) from the rotation center of the photosensitive drum 2 when the diameter of the photosensitive drum 2 is 1. 0.06 (preferably, v = 0.507) and h = 0.18 to 0.27 (preferably h = 0.21) in the horizontal direction from the surface of the photosensitive drum 2. ).

  The conveyance guide 26 is formed with a plurality of ribs 31 extending in the sheet conveyance direction in accordance with the dimension in the sheet conveyance width direction of the sheet 12 (size of the postcard, B5, A4, B4, A3, etc.) (FIG. 3). reference). The ribs 31 of the conveyance guide 26 can support the sheets 12 of various sizes that are conveyed (used for printing) so that the sheet 12 does not come into contact with the separation needle 17. As shown in FIG. 3, the rib 31 of the conveyance guide 26 is engaged with a notch 32 between the separating needles 17 and 17, and a plurality of (four pieces) are provided at intervals of W1 in the sheet passing width direction. ) The number of separation needles 17 that are arranged in the dimension W2a from both ends of the first group WA of the separation needles 17 that are continuous (the tip of the separation needle 17) and that are continuous (multiple) at intervals of the dimension W1 in the sheet passing width direction. From the both ends of the second group WB (the tip of the separation needle 17), it is arranged in the dimension of W2b. Here, W2a and W2b are set to 1 to 4 mm.

  Next, in the present embodiment, how the discharge in the sheet passing width direction of the separating needle 17 of the separating means 16 is made uniform to prevent dielectric breakdown of the photosensitive drum 2, and the sheet 12 is removed from the photosensitive drum 2. The condition will be specifically described as to whether or not the operator can be well separated and the operator has not been injured by the separating needle 17 of the separating means 16 at the time of jam processing or the like.

  First, FIG. 4 is a view showing the relationship between the upstream side wall portion 27 and the downstream side wall portion 28 and the separation needle 17. That is, in FIG. 4, the separation needle 17 has a shortest distance from the upstream side wall portion 27 in the positional relationship with the upstream side wall portion 27 and the downstream side wall portion 28, and the shortest distance from the downstream side wall portion 28. The distance is b (mm), and the shortest distance between the line L1 connecting the tip of the upstream side wall 27 and the tip of the downstream side wall 28 and the tip (tip of the separation needle 17) is shown as c (mm).

  Next, the table of FIG. 5 shows the results of measuring the above-mentioned dimensions a, b, and c and measuring the safety at the time of jam processing, the separation of the sheet from the photosensitive member, and the situation of black spots due to dielectric breakdown. Show. In addition, the dimension of W1 of FIG. 3 was 4 mm.

  Here, the safety shown in the table of FIG. 5 is evaluated based on whether or not the operator's finger enters between the upstream side wall portion and the downstream side wall portion during the jam processing, and the upstream side wall portion 27 and the downstream side wall portion 28 are evaluated. If the finger does not enter between the upper side wall portion 27 and the downstream side wall portion 28, the operator may be injured. ing.

  The separation shown in the table of FIG. 5 was transferred when the transferred sheet 12 collided with the separation claw 18 and the toner image transferred to the sheet 12 had claw marks on the separation claw 18. Since the toner image is disturbed, it is evaluated as x. When the nail mark of the separation claw 18 does not adhere to the toner image transferred to the sheet 12, the evaluation is o.

  In addition, the dielectric breakdown shown in the table of FIG. 5 is evaluated as ◎ when the discharged electrode is 80% or more, and when the discharged electrode is 60% or more and less than 80%, Evaluation is ◯. In these evaluations ◎ and ○, black spots associated with dielectric breakdown do not occur in the image. In addition, when the number of discharged electrodes is 30% or less, black spots associated with dielectric breakdown may be conspicuously generated in the image. Further, when the discharged electrode exceeds 30% and less than 60%, a black spot due to dielectric breakdown may occur in the image, and thus the evaluation is Δ. Thus, the dielectric breakdown shown in the table of FIG. 5 also means discharge efficiency. The amorphous silicon photosensitive drum 2 used in the present embodiment has a protective layer on its surface that also serves as charge holding. The protective layer of the photosensitive drum 2 has a thickness of about 1 μm and a withstand voltage of several hundred volts. Therefore, dielectric breakdown is likely to occur compared to an organic photoreceptor drum having a large film thickness, and a highly accurate design is required. In such a photosensitive drum 2, when the protective layer is broken, the charged charge cannot be held on the surface, so that the toner adheres to the portion where the charged charge cannot be held and is unnecessary on the image. It is generally known that black spots occur.

  As shown in the table of FIG. 5, the image forming apparatus 1 according to the present embodiment satisfies the conditions of a ≧ 1.5 and b ≧ 1.5, 4 ≧ a + b ≧ 3, and 2 ≧ It was confirmed that if a configuration satisfying the condition of c ≧ 0 is adopted, desired effects can be obtained with respect to safety, separability and dielectric breakdown. In the comparative example, any one of safety, separability, and dielectric breakdown (discharge efficiency) was evaluated as x, which was judged inappropriate.

  In addition, since the present embodiment has a configuration in which the substantially triangular separation needles 17 are integrally formed on the plate-shaped separation electrode portion 30, compared to the case where the separation needles 17 are formed separately one by one, The number of points can be reduced and the number of assembly steps can be reduced.

  An embodiment of the present invention will be described with reference to FIG. In this embodiment, the diameter D of the amorphous silicon photosensitive drum 2 is 40 mm, and the diameter d of the transfer roller 14 is 21.5 mm. Then, the transfer roller 14 is inserted into the photosensitive drum 2 side by about 0.2 mm so that a nip portion P is generated between the transfer roller 14 and the photosensitive drum 2, and this nip portion P is the transfer position. It becomes. The transfer roller 14 is formed of a material having an electrical resistance of 7.0 (log Ω) and a rubber hardness (Asuka C) of 35 ° (for example, EPDM blended with conductive carbon black or the like).

  Also, the angle α formed by the line L3 connecting the rotation center of the photosensitive drum 2 and the rotation center of the transfer roller 14 with respect to the horizontal line L2 in FIG. 2 is 30 degrees, and the angle θ at which the sheet 12 enters the nip portion P is 60 degrees. It has become. The tip of the separation needle 17 is positioned at v = 2.29 mm in the vertical direction from the rotation center of the photosensitive drum 2 and is positioned at h = 7.43 mm in the horizontal direction from the surface of the photosensitive drum 2. Yes.

  The linear velocity of the photosensitive drum 2 is 180 mm / sec, the surface potential at the developing position of the photosensitive drum 2 is 250 V, the transfer output is 50 μA (constant current), and the separation output applied to the separation needle 17 is 10 μA (constant current). ), About 3 KV. The developing bias is applied with a direct current of 150 V and an alternating current of 1.7 KV · 3 KHz.

  Moreover, the relationship between the upstream side wall 27 and the downstream side wall 28 and the separation needle 17 is such that the dimension a shown in FIGS. 4 and 5 is 2 mm, b is 2 mm, a + b = 4 mm, and c is 0 mm. Moreover, W1 of FIG. 3 was 4 mm.

  The image forming apparatus 1 according to the present embodiment configured as described above can make the discharge in the sheet passing width direction of the separating needle 17 of the separating unit 16 uniform, and can effectively prevent the dielectric breakdown of the amorphous silicon photosensitive drum 2. Can be prevented. In addition, according to the image forming apparatus 1 of the present embodiment, the sheet 12 can be well discharged and separated from the photosensitive drum 2, and a high-quality image can be formed without disturbing the image before fixing. . Furthermore, according to the image forming apparatus 1 of the present embodiment, it is possible to effectively prevent an operator from being injured by the separation needle 17 of the separation unit 16 during maintenance or the like. That is, according to the present embodiment, it is possible to provide the image forming apparatus 1 that is capable of forming a high-quality image that is excellent in safety and separability, and that does not cause a dielectric breakdown. In addition, a present Example is an example of this invention, Comprising: It is not limited to this.

  The present invention can be widely applied to an image forming apparatus such as an electrophotographic copying machine, a printer, a facsimile machine, and a multifunction machine of these.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows the relationship with a separating means, a photoreceptor drum, and a transfer roller. It is the figure which looked at the shape of the separation needle of a separation means from the direction along the sheet conveyance direction, and is a front view of the separation needle. It is a figure which shows the positional relationship of an upstream side wall part and a downstream side wall part, and a separation needle. It is a figure which shows an experimental result. It is a partial block diagram of an image forming apparatus showing a first conventional example. It is a partial block diagram of an image forming apparatus showing a second conventional example. It is a partial block diagram of the image forming apparatus which shows a 3rd prior art example.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 2 ... Photosensitive drum (image carrier), 12 ... Sheet (recording medium), 14 ... Transfer roller (transfer means), 16 ... Separation means, 17 ... Separation needle, 33 …… Discharge separation part holder, 27 …… Upstream side wall part, 28 …… Downstream side wall part, 30 …… Separation electrode part

Claims (3)

An image carrier that carries and rotates a toner image;
Transfer means for applying a transfer current to the sheet-like recording medium passing between the image carrier and transferring the toner image to the recording medium;
When a separation voltage is applied to a plurality of separation needles positioned downstream of the transfer unit in the recording medium conveyance direction and perpendicular to the recording medium conveyance direction, the image carrier and the separation are separated. Separating means for discharging between the needles and discharging the recording medium charged by the transfer means to separate it from the image carrier;
In an image forming apparatus comprising:
The separation means has a discharge separation part holder for accommodating the separation needle therein,
An upstream side wall portion that is located farther upstream in the recording medium transport direction than the separation needle, and a downstream side wall portion that is located farther downstream in the recording medium transport direction than the separation needle. Have
When the shortest distance between the separation needle and the upstream side wall is a (mm) and the shortest distance between the separation needle and the downstream side wall is b (mm), a ≧ 1.5, b ≧ 1.5 And the dimensions of the a and the b are determined so that 4 ≧ a + b ≧ 3.
The tip of the separation needle is configured to satisfy 0 ≦ c ≦ 2, where c (mm) is the shortest distance between a line connecting the tip of the upstream side wall and the tip of the downstream side wall. An image forming apparatus.   The separation needle is formed to protrude from an edge of the plate-shaped separation electrode portion on the image carrier side so that a cross-sectional shape perpendicular to the recording medium conveyance direction is a substantially triangular shape. The image forming apparatus according to 1.   The image forming apparatus according to claim 1, wherein the image carrier is formed of amorphous silicon.

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