JP2016188885A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can prevent scattering of toner from a sheet to which a toner image is transferred.SOLUTION: An image forming apparatus 1 comprises: a transfer member 9 that forms a transfer nip 17 with an image carrier 6 carrying a toner image and transfers the toner image from the image carrier 6 to a sheet while holding and conveying the sheet at the transfer nip 17; a transfer voltage application part 21 that applies a transfer voltage having an opposite polarity to that of the toner image to the transfer member 9; a separation member 23 that eliminates electricity from the sheet to which the toner image is transferred to separate the sheet from the image carrier 6 or transfer member 9; and a separation voltage application part 35 that applies a separation voltage having the same polarity as that of the toner image to the separation member 23. The image forming apparatus further includes detection means 39 that detects the charging polarity of the sheet to which the toner image is transferred, and reduces the separation voltage to be applied from the separation voltage application part 35 to the separation member 23 on the basis of the charging polarity of the sheet detected by the detection means 39.SELECTED DRAWING: Figure 2

Description

  The present invention relates to an image forming apparatus that forms an image by transferring a toner image from an image carrier to a sheet.

  In an image forming apparatus such as a printer, a toner image formed on a photosensitive drum is transferred from the photosensitive drum to a sheet at a transfer nip formed between the photosensitive drum and a transfer roller, and the toner image is transferred. The sheet is conveyed to the fixing device, and the toner image is fixed on the sheet in the fixing device.

  In the transfer nip, the toner image is transferred to the paper by applying a voltage (transfer voltage) having a polarity opposite to that of the toner image to the transfer roller. At this time, a separation member is provided on the downstream side of the transfer nip in order to prevent the sheet charged to the opposite polarity to the toner image by the transfer voltage from being wound around the photosensitive drum or the transfer roller. A voltage having the same polarity as the toner image (separation voltage) is applied to the separation member.

  Here, when the paper is separated from the photosensitive drum and the transfer roller, the paper may be charged to a potential having a predetermined polarity. When the polarity of the charged paper is the same as that of the toner image, if a separation voltage having the same polarity as that of the toner image is further applied to the paper from the separation member, the charging potential of the paper rises and the paper and the toner image are electrostatically repelled. As a result, toner scattering may occur.

  In addition, when the sheet on which the toner image is transferred is guided to the fixing device while being charged, if the sheet is in contact with or close to a member formed of a conductive material such as a conveyance guide, a discharge is generated between the sheet and the conductive member. There is a problem that toner scattering occurs.

  In order to solve this problem, Japanese Patent Application Laid-Open No. H10-228667 measures the height of the sheet conveyed from the transfer nip to the fixing device, and controls the separation voltage according to the interval between the separation member and the sheet, thereby appropriately adjusting the sheet. An image forming apparatus configured to be able to remove static electricity is disclosed.

JP 2008-216468 A

  However, although the image forming apparatus described in Patent Document 1 can give a constant charge eliminating action regardless of the difference between the separation member and the sheet, the charged state of the sheet itself is not taken into consideration. There is a possibility that toner scattering due to charging of the toner cannot be suppressed.

  SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide an image forming apparatus capable of preventing toner scattering from a sheet on which a toner image is transferred.

  In order to achieve the above object, an image forming apparatus according to the present invention forms a transfer nip with an image carrier that carries a toner image, and the image carrier from the image carrier to the paper while nipping and conveying the paper in the transfer nip. A transfer member that transfers the toner image; a transfer voltage applying unit that applies a transfer voltage of a polarity opposite to the toner image to the transfer member; and the image carrier that discharges the paper onto which the toner image has been transferred. Or a separation member that separates the sheet from the transfer member, and a separation voltage application unit that applies a separation voltage having the same polarity as the toner image to the separation member, and the sheet on which the toner image is transferred It has a detection means for detecting the charging polarity, and is configured to reduce the separation voltage applied to the separation member from the separation voltage application section based on the charging polarity of the paper detected by the detection means. Special To.

  By adopting such a configuration, a separation voltage according to the charging polarity of the paper can be applied to the separation member, so that electrostatic repulsion between the toner image and the paper can be suppressed and toner scattering can be prevented. it can.

  In the image forming apparatus according to the aspect of the invention, when the charging polarity of the paper detected by the detecting unit is determined to be the same as that of the toner image, the separation voltage is applied from the separation voltage application unit to the separation member. It may be configured to be stopped.

  By adopting such a configuration, it is possible to prevent the paper from being charged to the same polarity as the polarity of the toner image, so that toner scattering can be suppressed.

  In the image forming apparatus according to the aspect of the invention, the image forming apparatus further includes a conductive guide portion provided on the downstream side of the separation member in the conveyance direction of the paper so as to face the paper, and the detection unit is provided in the guide portion. And an ammeter that measures a current flowing from the sheet guided along the guide to the guide unit, and the charging polarity of the sheet is determined based on a polarity of a current value measured by the ammeter. good.

  By adopting such a configuration, it is possible to detect the charging polarity of the sheet on which the toner image is transferred by a simple method.

  According to the present invention, since the separation voltage is applied to the separation member based on the charging polarity of the paper onto which the toner has been transferred, the paper can be appropriately discharged and toner scattering can be suppressed.

FIG. 2 is a cross-sectional view schematically illustrating the internal structure of the printer according to the embodiment of the invention. FIG. 3 is a diagram schematically illustrating a conveyance path from a transfer nip to a fixing device in a printer according to an embodiment of the present invention. 3A and 3B are diagrams illustrating a separation member in a printer according to an embodiment of the present invention, in which FIG. 3A is a front cross-sectional view of the separation member, and FIG. 3B is a plan view of the separation plate. 6 is a graph showing a relationship between a charging potential of a sheet and a separation voltage in a printer according to an embodiment of the present invention. FIGS. 5A and 5B are diagrams schematically illustrating a process of separating a sheet after passing through the transfer nip. FIG. 5A illustrates a process in which the sheet is separated from the photosensitive drum, and FIG. 5B illustrates a process in which the sheet is separated from the transfer roller. Show the process.

  Hereinafter, an image forming apparatus according to an embodiment of the present disclosure will be described with reference to the drawings.

  First, an overall configuration of a printer 1 as an image forming apparatus will be described with reference to FIG. FIG. 1 is a schematic diagram showing an outline of a printer according to an embodiment of the present invention. In the following description, the front side of the page in FIG. 1 is the front side (front side) of the printer 1, and the left and right directions are the printer. The direction when 1 is viewed from the front is used as a reference.

  The printer 1 includes a substantially rectangular parallelepiped housing 2 having a hollow portion. Inside the housing 2, a paper feed cassette 3 that stores paper is detachably mounted below. A paper feeding device 4 that feeds paper from the paper feeding cassette 3 is provided on the upper right side of the paper feeding cassette 3.

  An image forming unit 5 is provided above the sheet feeding device 4. The image forming unit 5 is rotatably provided with a photosensitive drum 6 (image carrier). Around the photosensitive drum 6, a charging device 7, a developing device 8, a transfer roller 9, and a cleaning device 10 are provided. Are arranged along the rotation direction of the photosensitive drum 6 (see the arrow X in FIG. 1). The developing device 8 is connected to the toner container 11. Further, an exposure unit 12 composed of a laser scanning unit (LSU) is provided on the left side of the image forming unit 5.

  A fixing device 13 is provided above the image forming unit 5, and a paper discharge unit 14 is provided on the left side of the fixing device 13. The paper discharge unit 14 faces a paper discharge tray 15 formed on the upper surface of the housing 2.

  Further, inside the housing 2, paper is conveyed from the paper feeding device 4 to the paper discharge unit 14 through the transfer nip 17 and the fixing device 13 formed between the photosensitive drum 6 and the transfer roller 9. A path 18 is provided.

  Next, an image forming operation of the printer 1 having such a configuration will be described. After the surface of the photosensitive drum 6 is charged by the charging device 7, exposure corresponding to image data is performed on the photosensitive drum 6 by laser light (see arrow P) from the exposure device 12, and the photosensitive drum 6 is exposed. An electrostatic latent image is formed on the surface. The electrostatic latent image is developed into a toner image by the developing device 8. The toner remaining on the photosensitive drum 6 is removed by the cleaning device 10.

  On the other hand, the sheet fed from the sheet feeding cassette 3 to the conveying path 18 by the sheet feeding device 4 is conveyed to the transfer nip 17 in synchronization with the above-described image forming operation, and is transferred onto the photosensitive drum 6 at the transfer nip 17. The toner image is transferred to the paper. The sheet on which the toner image has been transferred is conveyed downstream in the conveyance path 18 and enters the fixing device 13, and the toner image is fixed on the sheet in the fixing device 13. The paper on which the toner image is fixed is discharged from the paper discharge unit 14 to the paper discharge tray 15.

  Next, the transfer nip 17 will be described with reference to FIG. FIG. 2 is a diagram schematically showing a conveyance path from the transfer nip to the fixing device.

  The transfer nip 17 is formed between the photosensitive drum 6 and the transfer roller 9 as described above. The transfer roller 9 includes a roller main body and a rotation support shaft, is rotatably supported by being pressed against the photosensitive drum 6, and conveys the sheet conveyed along the conveyance path 18 to the downstream side. The roller body is formed of a material having a rough surface shape such as a foam material (for example, a rubber material such as EPDN or NDR added with a foaming agent such as ADCA). A transfer voltage power source 21 to which a voltage (transfer voltage) having a polarity opposite to that of the toner is applied is connected to the transfer roller 9. By applying a transfer voltage having a polarity opposite to that of the toner to the transfer roller 9, the toner is electrostatically transferred from the surface of the photosensitive drum 6 to the sheet.

  In the conveyance path 18 from the transfer nip 17 to the fixing device 13, a separation member 23 and a conveyance guide 25 are arranged in order from the downstream side in the conveyance direction.

  The separating member will be described with reference to FIG. 3A is a side sectional view of the separating member, and FIG. 3B is a plan view of the separating plate.

  The separating member 23 is disposed on the transfer roller 9 side of the transport path 18 on the downstream side of the transfer nip 17 in the transport direction. The separation member 23 includes a separation plate 31 provided along the width direction of the paper, a clamping member 32 that sandwiches the separation plate 31, and a guide portion 33 that guides the paper closer to the conveyance path than the separation plate 31. .

  As shown in FIG. 3B, the separation plate 31 is a rectangular plate-like conductive member that is long in the paper width direction, and includes a plurality of needle-like electrodes 31a along the side edge on the conveyance path side. Is formed. As shown in FIG. 2, a separation voltage power source 35 (separation voltage application unit) to which a voltage (separation voltage) having the same polarity as the toner is applied is connected to the separation plate 31. As described above, a transfer voltage having a polarity opposite to that of the toner is applied to the transfer roller 9, and the sheet is charged with a polarity opposite to that of the toner. A separation voltage having the same polarity as the toner is applied from the separation voltage power source 35 to the separation plate 31 in order to separate the sheet from the photosensitive drum 6 and stabilize the conveyance of the sheet.

  The sandwiching member 32 is made of an insulating material, and is sandwiched from above and below so that the needle-like electrode 31a of the separation plate 31 faces the conveyance path 18 side, as shown in FIG. The guide portion 33 is a plate-like member extending along the conveyance path 18, and extends in the conveyance path 18 side from the tip of the needle electrode 31 a of the separation plate 31, and a plurality of guide parts 33 are arranged along the width direction of the sheet. ing. The guide unit 33 guides the paper along the transport path 18 while preventing contact between the paper and the separation plate 31.

  As illustrated in FIG. 2, the transport guide 25 is disposed on the transfer roller 9 side of the transport path 18 on the downstream side of the separation member 23 in the transport direction. The conveyance guide 25 is a member that is long in the width direction of the sheet and is formed of a sheet metal material provided along the conveyance direction. The transport guide 25 is provided with a plurality of ribs 38 extending along the transport direction at predetermined intervals along the paper width direction. The ribs 38 are made of an insulating material, and prevent contact between the paper and the conveyance guide 25. An ammeter 39 is connected to the transport guide 25, and the amount of current flowing into the transport guide 25 is measured.

  The transfer voltage power source 21 connected to the transfer roller 9, the separation voltage power source 35 connected to the separation plate 31, and the ammeter 39 connected to the transport guide 25 are electrically connected to the control unit 40. The controller 40 controls the transfer voltage applied from the transfer voltage power source 21 to the transfer roller 9 so that a predetermined transfer current flows during toner transfer. Further, the control unit 40 controls the value of the separation voltage applied from the separation voltage power supply 35 and the presence / absence of application of the separation voltage. Furthermore, data relating to the polarity of the inflow current value measured by the ammeter 39 is transmitted to the control unit 40.

  Next, a method for controlling the separation voltage applied from the separation voltage power source 35 to the separation plate 31 in the control unit 40 will be described.

  First, the relationship between the sheet charging potential and the separation voltage will be described with reference to the graph of FIG. The vertical axis of the graph represents the surface potential (V) of the paper after passing through the separating member 23, and the horizontal axis represents the transfer current (−μA) flowing from the transfer roller 9 to the photosensitive drum 6. The black squares in the graph indicate the case where the separation voltage is applied to the initial transfer roller, and the white squares in the graph indicate the case where the separation voltage is not applied to the initial transfer roller. A black circle indicates a case where a separation voltage is applied to the transfer roller after the 600K printing test, and a white circle indicates a case where no separation voltage is applied to the transfer roller after the 600K printing test.

  In this example, the case where the toner is positively charged will be described. That is, a positive separation voltage (+3000 V) is applied to the separation plate 31 from the separation voltage power source 35. In each of the above-described conditions, the sheet potential shows the same tendency regardless of the value of the transfer current, so that the sheet potential hardly depends on the transfer voltage.

  In the initial state of the transfer roller 9, as shown by the white square, when no separation voltage is applied, a transfer voltage having a polarity opposite to that of the toner, that is, a negative transfer voltage is applied to the transfer roller 9 in the transfer nip. The paper is charged to -4000V to -3000V. Therefore, as shown by the black square, by applying a separation voltage having the same polarity as the toner, that is, a positive polarity, to the separation plate 31, the charge amount of the sheet becomes near zero, and the sheet is almost discharged. Recognize.

  On the other hand, after the 600K printing test, when the separation voltage is applied to the transfer roller 9 as usual, the sheet is charged to about +6000 V as shown by the black circle, and it can be seen that the sheet is not discharged.

  Therefore, in this embodiment, the application of the separation voltage to the transfer roller 9 was stopped after the 600K printing test. Then, as indicated by the white circles, the charging potential of the paper was +4000 V to +4500 V, and the potential decreased by 1500 V to 2000 V compared to when a separation voltage was applied.

  As described above, the charging polarity of the sheet after passing through the transfer nip 17 is different between the initial state of the transfer roller 9 and the state after the end of the 600K printing test. Specifically, in the initial state, the toner is charged with a polarity opposite to that of the toner, and is charged with the same polarity as that of the toner after completion of the printing test. The reason is considered as follows.

  When the transfer roller 9 formed of a material having a rough surface shape is used, the sheet that has passed through the transfer nip 17 at the initial stage of use when the surface shape is rough, as shown in FIG. More likely to wind around the photosensitive drum 6. On the other hand, after the 600K printing test, the surface of the transfer roller 9 is smoothed by abrasion, so that the paper that has passed through the transfer nip 17 is more transferred than the photosensitive drum 6 as shown in FIG. 9 tends to wrap around.

  In consideration of such a tendency and the graph of FIG. 4, the charging polarity of the sheet on which the toner image is transferred changes depending on the surface state of the transfer roller 9, and when separated from the photosensitive drum 6, the toner It can be said that it has a characteristic that it is easily charged to the opposite polarity to the image and is easily charged to the same polarity as the toner image when separated from the transfer roller 9.

  Such a charging polarity of the paper affects the electrostatic attraction between the toner image and the paper. That is, when the toner image and the paper have the same polarity, there is a problem that the toner image and the paper are electrostatically repelled and the toner is likely to be scattered.

  Therefore, as can be seen from the result after the 600K printing test, when the paper is charged with the same polarity as the toner, applying a separation voltage with the same polarity as the toner may increase the electrostatic repulsion between the toner and the paper. There is. Therefore, the charging polarity of the sheet is detected, and when the detected charging polarity is the same as that of the toner, the control unit 40 controls the separation voltage power source 35 so that the separation voltage is not applied to the separation plate 31.

  In the present embodiment, the charging polarity of the sheet is detected by measuring the current flowing into the conveyance guide 25 from the sheet conveyed along the conveyance guide 25 with the ammeter 39. That is, data relating to the polarity of the amount of current measured by the ammeter 39 is sent to the control unit 40. The control unit 40 determines that the charging polarity of the sheet is negative when the polarity of the current amount is negative, and that the charging polarity of the sheet is positive when the polarity of the current amount is positive. At this time, for example, the current values sampled continuously at a predetermined sampling period are averaged to determine the polarity of the average value. Then, when it is determined that the charging polarity of the paper is the same as the charging polarity of the toner, control is performed so that the application of the separation voltage from the separation voltage power source 35 to the separation plate 31 is stopped. As a result, for example, as indicated by a white circle in the graph, the charging potential of the sheet is reduced by about 1500 V to 2000 V compared to the case where the separation voltage is applied.

  As described above, according to the present invention, when the paper is charged to the same polarity as the polarity of the toner, the separation voltage is not applied to the separation plate 31 to prevent the charging potential of the paper from increasing. Can do. Accordingly, electrostatic repulsion between the paper and the toner can be suppressed, and toner scattering after toner transfer can be suppressed. In the present embodiment, the case where the separation voltage applied from the separation voltage power source 35 to the separation plate 31 is 0, that is, the case where the application of the separation voltage is stopped is also included in the reduction of the separation voltage.

  As another method for detecting the charging polarity of the paper, a method in which a surface potential meter is installed on the surface on the transport path side of the transport guide 25 and the surface potential of the paper is measured with the surface potential meter can be used. . However, it is preferable to use the ammeter 39 because the configuration and control are simple.

  In the present embodiment, the positively charged toner has been described. However, a negatively charged toner can have the same configuration.

  Note that the above description of the embodiment of the present invention describes a preferred embodiment of the image forming apparatus according to the present invention, and thus may have various technically preferable limitations. The technical scope of the present invention is not limited to this embodiment unless specifically described to limit the present invention. Furthermore, the constituent elements in the embodiments of the present invention described above can be appropriately replaced with existing constituent elements, and various variations including combinations with other existing constituent elements are possible. The description of the embodiment of the present invention is not intended to limit the content of the invention described in the claims.

1 Printer (image forming device)
6 Photosensitive drum (image carrier)
9 Transfer roller (transfer member)
17 Transfer nip 21 Transfer voltage power supply (transfer voltage application part)
23 Separating member 25 Conveyance guide (guide part)
35 Separation voltage power supply (separation voltage application unit)
39 Ammeter (detection means)

Claims (3)

A transfer member that forms a transfer nip with an image carrier that carries a toner image, and transfers the toner image from the image carrier to the paper while nipping and conveying the paper in the transfer nip;
A transfer voltage applying unit that applies a transfer voltage of a reverse polarity to the toner image to the transfer member;
A separation member that neutralizes the sheet on which the toner image has been transferred and separates the sheet from the image carrier or the transfer member;
A separation voltage application unit that applies a separation voltage having the same polarity as the toner image to the separation member;
With
Separation applied to the separation member from the separation voltage application unit based on the charge polarity of the paper detected by the detection means, having detection means for detecting the charge polarity of the paper to which the toner image has been transferred An image forming apparatus configured to reduce a voltage.   When the charging polarity of the paper detected by the detection unit is determined to be the same as that of the toner image, the application of the separation voltage from the separation voltage application unit to the separation member is stopped. The image forming apparatus according to claim 1. A conductive guide portion provided on the downstream side of the separating member in the transport direction of the paper so as to face the paper;
The detecting means has an ammeter for measuring a current flowing from the paper guided along the guide portion into the guide portion, and charging the paper based on a polarity of a current value measured by the ammeter. The image forming apparatus according to claim 1, wherein the polarity is determined.

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