JP2018054647A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image defect caused by paper powder even when a sheet containing a large amount of paper powder is used.SOLUTION: A paper powder removing roller pair applied with voltage is provided on a sheet conveyance path upstream of a transfer part. One of the paper powder removing roller pair has a roller surface layer that is made of a foaming member in order to charge paper powder on a sheet to have an appropriate polarity and remove the paper powder from the sheet.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer.

  In electrophotographic image forming apparatuses such as copying machines and printers, paper fibers or fillers such as calcium carbonate, talc, kaolin, titanium dioxide, and aluminum hydroxide may be detached from the sheet and cause various problems. There is. In the following, paper dust is a paper powder or filler that has been separated from the sheet. Paper dust on the image transfer surface (front surface) of the sheet may adhere to an image carrier such as a photosensitive member or an intermediate transfer belt in a transfer portion, which may cause image flow or poor cleaning of the image carrier. Further, the paper dust on the back surface of the sheet adheres to the pressure roller of the fixing device downstream of the transfer unit, and may cause fixing failure.

  In view of this, a method has been proposed in which a roller pair to which a voltage is applied is provided upstream of the transfer unit to remove charged paper dust and reduce the amount of paper dust attached to the image carrier (Patent Document 1). In addition, a method has been proposed in which a charging unit is provided upstream of the transfer unit, and the paper powder is charged with a polarity such that it is difficult to move to the transfer unit, thereby reducing the amount of paper dust attached to the image carrier (Patent Document 2). ).

JP 2006-27761 A JP 2002-169384 A

  However, in the transfer unit that applies a voltage to transfer the toner image from the image carrier to the sheet, the paper powder may be charged by the voltage application in the transfer unit.

  Therefore, as in Patent Document 1, even if only paper dust charged to the opposite polarity to the image carrier is collected upstream of the transfer unit, the paper dust is charged to the image carrier in the opposite polarity to the image carrier in the transfer unit. May stick. Also, as in Patent Document 2, in the method of charging paper dust to a polarity that does not adhere to the image carrier upstream of the transfer unit, the paper powder is charged to a polarity that easily adheres again to the image carrier and adheres to the image carrier. May end up. Therefore, in order to reduce the amount of paper dust adhering to the image carrier in the transfer unit, it is necessary to remove paper dust to the maximum extent upstream of the transfer unit.

  Accordingly, an object of the present invention is to propose a configuration capable of obtaining a high paper dust removal effect upstream of the transfer unit in view of the fact that paper powder is charged in the transfer unit.

In order to solve the above problems, an image forming apparatus according to the present invention includes:
A transfer portion for transferring a toner image to a sheet;
First voltage applying means for applying a voltage to the transfer portion;
A pair of rollers provided upstream of the transfer unit in the conveyance direction of the sheet and rotating and conveying the sheet;
Second voltage applying means,
The roller pair (40) includes a removal roller (41) and a counter roller (42) whose surface layer (42a) is made of a foam member,
The surface of the removal roller (41) is smoother than the surface layer (42a),
The second voltage applying means (47) applies a voltage to at least one of the removing roller (41) and the counter roller (42).

  According to the image forming apparatus of the present invention, the paper dust removing roller pair in which a voltage is applied to the paper conveyance path upstream of the transfer unit is provided. By making one roller surface layer of this paper dust removing roller pair into a foamed member, it is possible to charge to a polarity suitable for removing the paper dust on the sheet and remove it from the sheet.

Sectional view of a color copying machine to which the first embodiment is applied The figure showing the structure of the secondary transfer part and paper dust removal roller pair vicinity of the color copying machine to which the 1st Example was applied. The figure showing the state change of the paper dust near the paper dust removal roller pair of the color copying machine to which the first embodiment is applied In the color copying machine to which the first embodiment is applied, a method for applying a voltage to a pair of paper dust removing rollers, which compares the amount of paper dust removed when the surface layer of the opposing roller is a foam member and when the surface layer is smooth It is a figure showing the state change of paper dust. The figure showing the structure of the secondary transfer part and paper dust removal roller pair vicinity of the color copying machine to which the 2nd Example was applied. The figure showing the voltage application method to a paper dust removal roller pair in the color copying machine to which the 2nd Example was applied. The figure showing the structure of the paper dust removal roller of the color copying machine to which the 3rd Example was applied.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the Example described below demonstrates this invention exemplarily, Comprising: The dimension of the component described below, a material, a shape, its relative arrangement, etc. have no specific description. As long as the scope of the present invention is not limited thereto.

[Example]
Image Forming Apparatus The entire apparatus of the present invention will be schematically described with reference to the entire image forming apparatus shown in FIG.

  The sheet S, which is a transfer material, is stored so as to be stacked on a lift-up device 11 included in the paper feeding device 10 and is fed by the paper feeding unit 12 in accordance with the image forming timing of the image forming apparatus 1. . Here, the paper feeding means 12 includes a system using frictional separation by a paper feed roller or the like, a system using separation adsorption by air, and the like. In FIG. 1, an air paper feeding system is taken as an example. The sheet S sent out by the paper feeding unit 12 passes through a transport path of the transport unit 20 and is transported to the registration unit 30.

  The registration unit 30 performs skew feeding correction and timing correction, and the paper dust on the sheet S is removed by the paper dust removing roller pair 40. A detailed description of the paper dust removing roller pair 40 will be described later. Then, the sheet S that has passed through the paper dust removing roller pair 40 is sent to the secondary transfer unit 58. The secondary transfer portion 58 is a toner image transfer nip portion to the sheet S formed by the substantially opposed secondary transfer inner roller 53 and secondary transfer outer roller 54. A reverse secondary transfer voltage is applied to the secondary transfer outer roller 54. Thereby, an electric field in a direction in which the toner is moved to the sheet S is formed, and the toner image is transferred to the sheet S.

  An image forming process that is sent to the secondary transfer unit 58 at the same timing as the conveyance process of the sheet S to the secondary transfer unit 58 described above will be described.

  The image forming unit 90 mainly includes a photoconductor 91, an exposure device 93, a developing device 92, a primary transfer device 55, a photoconductor cleaner 95, and the like. The exposure device 93 emits light based on the image information signal sent to the photosensitive member 91 that rotates counterclockwise whose surface is uniformly charged by a charging unit (not shown), and appropriately reflects the reflecting unit 94 and the like. A latent image is formed via. Then, a developing voltage is applied to the developing device 92 to generate a potential difference from the photosensitive member 91, and a precharged toner image (not shown) is moved on the photosensitive member 91 in the developing device 92 to form a latent image. Visualize. In this embodiment, it is assumed that the toner is negatively charged.

  Thereafter, electrostatic force is applied by the primary transfer device 55 by applying a predetermined pressure and transfer voltage, and the toner image is transferred onto the intermediate transfer belt 50. Thereafter, the transfer residual toner slightly remaining on the photoconductor 91 is collected by the photoconductor cleaner 95 and is prepared for the next image formation again.

  In the case of FIG. 1, the image forming unit 90 described above includes four sets of yellow (Y) 90, magenta (M) 96, cyan (C) 97, and black (Bk) 98. Of course, it is not limited to four colors, and the order of colors is not limited to this.

  Next, the intermediate transfer belt 50 will be described. The intermediate transfer belt 50 is stretched by rollers such as a drive roller 52, a tension roller 51, and a secondary transfer inner roller 53, and is conveyed and driven in the direction of arrow B in the drawing. Therefore, the image forming process of each color processed in parallel by the above-described Y, M, C, and Bk image forming apparatuses is performed at the timing of superimposing on the upstream toner image primarily transferred onto the intermediate transfer belt. As a result, a full-color toner image is finally formed on the intermediate transfer belt 50 and conveyed to the secondary transfer unit 58.

  As described above, the full-color toner image is secondarily transferred onto the sheet S in the secondary transfer unit 58 by the sheet conveying process and the image forming process described above. Thereafter, the sheet S is conveyed to the fixing device 60 by the pre-fixing conveyance unit 61. The fixing device 60 melts and fixes the toner on the sheet S by applying a predetermined pressing force by a substantially opposing roller or belt and a heating effect by a heat source. The sheet S having a fixed image obtained in this manner is discharged directly onto the discharge tray 111 by the branch transfer device 110, or is transferred to the reverse transfer device 70 when double-sided image formation is required. Is selected.

Next, a conveying operation when double-sided image formation is required will be described. The sheet S sent to the reverse conveying device 70 is switched back and forwards by a switchback operation, and is conveyed to the duplex conveying device 80. Thereafter, the sheets are merged from the re-feeding path of the conveyance unit 20 at the same timing as the sheet S of the subsequent job conveyed from the sheet feeding device 10, and are similarly sent to the secondary transfer unit 58. Since the image forming process is the same as that of the first side, the description is omitted. A series of image forming processes by the image forming apparatuses described above are completed, and the next image forming operation is prepared.

(2) Paper dust removal mechanism <Example 1>
Next, an example of a paper dust removing mechanism in the present embodiment will be described in detail. FIG. 2 shows a schematic diagram of the paper dust removing mechanism. In the following description, the surface of the sheet S on which the toner image is transferred is defined as the surface of the sheet S.

  In the present invention, in order to reduce the amount of paper dust adhering to the intermediate transfer belt 50, the paper dust on the surface side of the sheet S is removed by the paper dust removing roller pair 40 to which voltage is applied upstream from the secondary transfer portion 58. It has a configuration. The pair of removal rollers 40 includes a removal roller 41 that contacts the surface of the sheet S and a counter roller 42 that contacts the back surface of the sheet S. The outer diameter of the removing roller 41 is φ20 [mm], and the material is desirably low in electrical resistance. In this embodiment, stainless steel is used.

In the counter roller 42, a surface layer 42a made of a foam member having an average foam diameter of about 350 [μm] is formed around a core metal 42b made of SUM. The counter roller 42 has an outer diameter of φ24 [mm], the thickness of the surface layer 42a is 6 [mm], the material is NBR + conductive EPDM, and the electrical resistance is 2.0 × 10 ⁷ to 4.4 between the surface layer 42a and the core metal 42b. 0 × 10 ⁷ [Ω], Asker C hardness is about 28 °. The pair of removal rollers 40 is pressure-contacted at about 2.3 [kgf / cm]. The second voltage application unit 47 applies a voltage of about 3.4 [kV], which is substantially the same as the voltage applied to the transfer unit 58 by the first voltage application unit 59 to the counter roller 42. This is for the purpose of preventing a current from leaking from the transfer section 58 through the sheet S and causing image defects.

  Further, the surface of the removing roller 41 needs to be smoother than the surface layer 42 a of the counter roller 42. Further, the conveyance guide and the conveyance roller that are in contact with each other while the sheet S is sandwiched between the pair of removal rollers 40 are insulated members or varistors (applied voltage) in order to prevent current from leaking from the pair of removal rollers 40 through the sheet S. (With appropriate varistor voltage). Here, the reason why the surface layer 42a of the facing roller 42 is a foamed member will be described.

  FIG. 3 is a diagram showing a change in the state of paper dust in the vicinity of the sandwiching portion when a positive voltage is applied to the opposing roller 42. Upstream of the pair of removal rollers 40, on the sheet S, there are paper powder 44 charged to the positive electrode, paper powder 45 charged to the negative electrode, or paper powder 46 not charged. These paper powders are charged when they are rubbed with a conveyance roller or a conveyance guide, or when the sheets S are separated at the time of paper feeding. Next, in the vicinity of the nipping portion where the sheet S is nipped by the paper dust removing roller pair 40, discharge is generated from both the removing roller 41 and the opposing roller 42 to the paper dust 44 to 46 and the sheet S. A positive discharge is generated from the counter roller 42 side, and a negative discharge is generated from the removal roller 41. At this time, the discharge generated in the sheet S sandwiching portion is greatly affected by the surface properties of the removing roller 41 and the opposing roller 42.

  In general, when a discharge occurs between objects, a spatial gap is required between the objects, and when there is no gap, no discharge occurs. On the contact surface between the facing roller 42 and the sheet S, the surface layer 42a of which is a foam member, a large amount of gaps (gap that can be discharged) are formed between the sheet S and the facing roller 42, and electric discharge occurs between the sheet S and the sheet S. It occurs actively. Therefore, when the surface layer 42a of the counter roller 42 is a foamed member, the sheet S and the paper powders 44 to 45 are charged by electric discharge as compared with the case where the surface layer 42a is smooth. In this case, since a positive voltage is applied to the opposing roller 42, a positive charge is applied to the sheet S and the paper dust.

  Positive discharge from the opposite roller 42 side occurs more positively than negative discharge from the removal roller 41 side. As a result, the charge applied to the sheet S and the paper dust is total in the downstream of the sandwiching portion. The sheet S and the paper dust are positively charged. Therefore, the paper dust 44 receives a force for detaching from the sheet S due to the electric field generated in the clamping unit, moves to the removal roller 41, and is removed from the surface of the sheet S.

FIG. 4 is a graph comparing the amount of paper dust removed between the facing roller 42 whose surface layer 42a is a foamed member and a roller whose surface layer is smooth and made of a non-foamed member. A roller made of a non-foamed member uses a SUM core, and has an outer diameter of about φ24 [mm], the surface layer material is epichlorohydrin + conductive EPDM, the thickness of the surface layer is 6 [mm], and the electrical resistance. Is 2.0 × 10 ^{7 to} 4.0 × 10 ⁷ [Ω] between the surface layer and the core metal, and the Asker C hardness is about 26 °.

  The voltage applied to the rollers is about 3.4 [kV], and the pressure contact load of the roller pair 40 is about 2.3 [kgf / cm]. As shown in FIG. 4, the use of a foamed member roller resulted in more removal of paper dust. This is because, as described above, a gap is formed by the foamed member, discharge is easily performed, and the sheet S is more charged than when a roller made of a non-foamed member is used.

  In order to stably remove paper dust from the sheet S over a long period of time, it is desirable to provide a cleaning means for collecting the paper dust attached to the removing roller 41. In this embodiment, as shown in FIG. 1, the scraper 43 b is brought into contact with the surface of the removing roller 41. The scraper 43b has a thin plate shape, and the paper powder adhering to the surface of the roller is removed by pressing the tip of the scraper 43b against the removing roller 41. The scraper 43b is fixed to the paper dust collection box 43a, and the removed paper dust is accumulated in the paper dust collection box 43a. In addition to the method using the scraper 43b, the cleaning roller or the cleaning brush may be brought into pressure contact with the removing roller 41 for cleaning.

  In this embodiment, since the voltage applied to the secondary transfer portion 58 and the removing roller pair 40 is the same, the first voltage applying means 59 and the second voltage applying means 47 can be used together, and the cost is reduced. A desired effect can be realized. In this embodiment, an example of an intermediate transfer type image forming apparatus is shown. However, it is obvious that the same effect can be obtained for a direct transfer type image forming apparatus.

<Example 2>
Next, an image forming apparatus to which the second embodiment of the present invention is applied will be described with reference to FIG. In the following description of the present embodiment, description of the same contents as in the first embodiment will be omitted.

  In this embodiment, the distance L between the secondary transfer portion 58 and the removal roller pair 40 is longer than the length of the sheet S, as shown in FIG. In this case, since the voltage applied to the secondary transfer unit 58 does not leak to the removal roller pair 40 through the sheet S, any voltage is applied to the removal roller pair 40 regardless of the voltage applied to the secondary transfer unit 58. A voltage can be applied. FIG. 6 illustrates a method for applying a voltage to the removal roller pair 40.

  As shown in FIG. 6A, when positive polarity is applied to the removal roller 41 side, negative charges are applied to the sheet S and paper dust from the opposing roller 42. Contrary to the reason described above, the sheet S and the paper dust are negatively charged downstream of the holding roller pair 40 sandwiching portion, and the negatively charged paper dust 45 moves to the removal roller 41 side and is removed. Further, in FIGS. B (b) and (c), paper dust can be removed for the same reason.

  In this case, a conveyance roller pair 48 is required between the removal roller pair 40 and the secondary transfer unit 58. The conveyance roller pair 48 is formed of an insulating member or is grounded via a varistor.

  In this embodiment, an optimum voltage for removing paper dust can be applied to the paper dust removing roller pair 40 regardless of the voltage applied to the secondary transfer section 58, and the paper dust removing ability can be further enhanced. .

<Example 3>
In the first embodiment and the second embodiment, the configuration for removing the surface of the sheet S is shown, but in this embodiment, the configuration for removing the paper dust on the back side of the sheet S will be described with reference to FIG. . In order to remove the back surface side of the sheet S, as shown in FIG. 7, a removal roller 41 is disposed on the back surface side of the sheet S, an opposing roller 42 made of a foam member is disposed on the front surface side, and a voltage is applied to the roller pair. It can be realized by doing. Other voltage application conditions / methods and configurations are the same as those in the first and second embodiments.

  In this embodiment, it is possible to remove paper dust on the back side of the toner transfer surface. Therefore, it is possible to avoid the occurrence of fixing failure due to paper dust adhering to the pressure roller of the fixing device 60.

40 Removal roller pair, 41 Removal roller, 42 Opposing roller, 42a Surface layer, 42b Core metal, 43 Cleaning means, 43a Paper dust collection box, 43b Scraper, 44 Paper powder charged to positive electrode, 45 Charged to negative electrode Paper powder, 46 Uncharged paper powder, 47 Second voltage application means, 50 Intermediate transfer belt, 54 Secondary transfer outer roller, 58 Secondary transfer section, 59 First voltage application means

Claims (6)

A transfer section (58) for transferring the toner image to the sheet (S);
First voltage applying means (59) for applying a voltage to the transfer portion (58);
A roller pair (40) provided upstream of the transfer section (58) in the conveyance direction of the sheet (S) and rotating and conveying the sheet (S);
Second voltage applying means (47),
The roller pair (40) includes a removal roller (41) and a counter roller (42) whose surface layer (42a) is made of a foam member,
The surface of the removal roller (41) is smoother than the surface layer (42a),
The image forming apparatus (1), wherein the second voltage applying means (47) applies a voltage to at least one of the removing roller (41) and the opposing roller (42). The removal roller (41) contacts the toner image transfer surface side of the sheet (S), and the opposing roller (42) contacts the back surface side of the toner image transfer surface of the sheet (S). The image forming apparatus (1) according to claim 1. The removing roller (41) is in contact with the back surface side of the toner image transfer surface of the sheet (S), and the counter roller (42) is in contact with the toner image transfer surface side of the sheet (S). The image forming apparatus (1) according to claim 1. The image forming apparatus (1) according to any one of claims 1 to 3, further comprising a cleaning unit (43) that removes deposits attached to the removal roller (41). The length of the sheet conveyance path between the roller pair (40) and the transfer section (58) is shorter than the length of the sheet (S), and the transfer section (58) and the removal roller (41) or the facing The image forming apparatus (1) according to any one of claims 1 to 4, wherein the voltage applied to at least one of the rollers (42) is the same. The image forming apparatus (1) according to any one of claims 1 to 5, wherein the second voltage applying means (59) also serves as the first voltage applying means (47).