JP2017072820A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of transfer failure and a tailed image and prevent dirt on a guide member.SOLUTION: An image forming apparatus comprises: an image carrier that carries a toner image; transfer means that transfers the toner image carried on the image carrier to a recording medium; voltage application means that applies voltage to the transfer means; and guide means that guides the recording medium to the transfer means, and includes a first area with which the recording medium can be in contact and having conductivity where the potential difference from the transfer means is smaller than the potential difference between the transfer means and a portion of the image carrier carrying the toner image, a second area providing a voltage having the same polarity as that of a toner to the portion of the image carrier carrying the toner image, and an insulating layer interrupting the conduction between the first area and second area. The guide member has the first area, the insulating layer, and the second area arranged in this order from the image carrier side to a side with which the recording medium is in contact, and an end of the insulating layer projects toward the image carrier from the tip of the first area.SELECTED DRAWING: Figure 3

Description

  The present invention relates to an image forming apparatus having a guide member for guiding a conveyed recording medium to a transfer area.

  In an image forming apparatus using an electrophotographic process such as a copying machine, a printer, a facsimile machine, etc., an electrostatic charge obtained by irradiating laser light on a photosensitive drum uniformly charged in advance based on image information. The latent image is developed with toner supplied from a developing device. The toner image on the photosensitive drum is transferred to a recording medium by a transfer roller, and then heated and fixed to form an image on the recording medium.

  By the way, it is known that when a recording medium is conveyed to a transfer area (transfer nip) formed by the photosensitive drum and the transfer roller, the image quality is improved by bringing the recording medium into contact with the photosensitive drum. Yes.

  As described above, since the contact of the recording medium with the photosensitive drum has an influence on the image quality, the contact position of the recording medium with the photosensitive drum is often defined by the guide member. The end of the guide member is used as a guide to the photosensitive drum, and is disposed in the immediate vicinity of the photosensitive drum.

  In such a configuration, a transfer failure occurs due to the transfer current flowing from the transfer region to the guide member via the recording medium being transferred.

  In Patent Document 1, in order to prevent the transfer current from flowing in, a conductive member to which a bias is applied and a transfer guide member in which an insulator is attached to the surface of the conductive member are disclosed.

Japanese Patent Laid-Open No. 10-260595

  However, when the insulator (dielectric material) is provided on the sheet passing surface of the conductive member in this way, the insulator is frictionally charged by contact with the recording medium. This charging causes a potential difference between the photosensitive drum and the transfer guide member. Due to this potential difference, the untransferred toner on the photosensitive drum is attracted to and attached to the transfer guide member, and the toner attached to the transfer guide member adheres to the end of the recording medium guided by the transfer guide member, etc. Toner contamination occurs. Furthermore, when the recording medium itself is charged to the opposite polarity to the untransferred toner by frictional charging, the untransferred toner adheres to the recording medium upstream from the nip between the photosensitive drum and the transfer device, and a trailing image is generated. .

  The present invention has been made in view of the above-described problems, and an object of the present invention is to prevent the occurrence of a trailing image and toner contamination while preventing a transfer failure.

  In order to achieve this object, an image forming apparatus of the present invention includes an image carrier that carries a toner image, a transfer unit that transfers the toner image carried on the image carrier to a recording medium, and a voltage applied to the transfer unit. A voltage application means for applying a voltage to the transfer means, and the potential difference between the transfer means and the transfer means is a potential difference between the transfer means and the portion carrying the toner image on the image carrier. A first region having a smaller conductivity, a second region for applying a voltage having the same polarity as the toner to a portion of the image carrier that carries the toner image, the first region, and the second region And an insulating layer for blocking conduction in the area of the first area, the guide means from the image carrier side to the side in contact with the recording medium, the first area, the insulating layer, Arranged in the order of the second region, the insulating layer The end of the projection protrudes from the tip of the first region toward the image carrier so as to block toner flying from the image carrier toward the tip of the first region toward the image carrier. It is characterized by that.

  According to the present invention, it is possible to prevent the occurrence of a trailing image and toner contamination while preventing transfer failure.

1 is a diagram schematically illustrating an image forming apparatus according to an embodiment of the present invention. 2 is a block diagram illustrating a configuration of a high-pressure control unit for supplying high pressure to each unit of the image forming apparatus according to the exemplary embodiment of the present invention. FIG. It is a figure which shows the structure of the upper guide before transcription | transfer of embodiment of this invention, and its periphery. It is a figure which shows the structure of the upper guide before transfer of the comparative example 1, and its periphery. It is a figure which shows the structure of the upper guide before transfer of the comparative example 2, and its periphery. It is the graph which compared the effect in paper passage transition of the embodiment of the present invention with comparative examples 1 and 2. It is a figure which shows arrangement | positioning of the photoconductor drum of embodiment of this invention, and the pre-transfer upper guide.

(Example 1)
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In addition, the component described in the following embodiment is an illustration to the last, and is not the meaning which limits the scope of the present invention only to them.

<Schematic configuration of image forming apparatus>
FIG. 1 is a diagram schematically illustrating an image forming apparatus 100 according to an embodiment of the present invention.

  The recording medium 16 in the recording medium cassette 17 is fed by the rotation of the sheet feeding roller 15 and is conveyed by the conveying roller pair 8. Further, the recording medium 16 is supplied to the nip between the transfer roller 5 and the photosensitive drum 1 in accordance with the toner image formed on the photosensitive drum 1 (image carrier) by the registration roller pair 10.

  When the recording medium 16 is supplied to the nip between the transfer roller 5 (transfer member) and the photosensitive drum 1, the recording medium 16 is moved by the pre-transfer lower guide 20 and the pre-transfer upper guide 180 (guide member). Guided.

  Formation of the toner image on the photosensitive drum 1 is performed as follows. First, the surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. The surface of the charged photosensitive drum 1 is exposed by an exposure device 3 (exposure means) to form a latent image. Toner is attached to the latent image from the developing device 4, and the latent image is developed as a toner image.

  The toner image on the photosensitive drum 1 is transferred onto the recording medium 16 by the transfer roller 5, and the toner remaining on the photosensitive drum 1 without being completely transferred onto the recording medium 16 is removed by the cleaner 7. On the other hand, the recording medium 16 onto which the toner image has been transferred is separated from the photosensitive drum 1 by the separation static elimination needle 6 and the action of the curvature of the photosensitive drum 1. With the first unfixed toner image carried on the surface of the recording medium 16, it is conveyed to the fixing device 14, and the toner image is fixed by the pressure roller 11 and the fixing film 12. Thereafter, the recording medium 16 is discharged by the paper discharge roller 13.

  Next, the operation of the image forming apparatus will be described in the order of charging, exposure, transfer, transfer, fixing, and cleaning.

  The (charging) charging roller 2 is in contact with the photosensitive drum 1. A predetermined DC voltage (DC charging method) or a voltage obtained by superimposing a predetermined DC voltage and a predetermined AC voltage (AC + DC charging method) is applied as a charging bias to the charging roller 2 through a metal shaft. As a result, the surface of the photosensitive drum 1 that is rotationally driven at a predetermined speed is uniformly contact-charged to a predetermined polarity and potential. In the present embodiment, the surface of the photosensitive drum 1 is charged to −500V.

  (Exposure) The charged surface of the photosensitive drum 1 is subjected to image exposure by the exposure device 3 based on the image information, and an electrostatic latent image is formed. In the present embodiment, the exposure is performed by scanning exposure of a semiconductor laser (wavelength 780 nm), but exposure by an LED array may be used.

  (Development) The electrostatic latent image on the photosensitive drum 1 formed by exposure is developed by the developing device 4. The developing device 4 has a developing sleeve. A developing bias (AC + DC charging method) in which a predetermined DC voltage and a predetermined AC voltage are superimposed is applied to the developing sleeve from a high-voltage power supply unit so that toner adheres to the electrostatic latent image on the photosensitive drum 1 and electrostatic latent image. Is developed as a toner image.

  (Transfer) The toner image developed on the photosensitive drum 1 is rotationally moved to the nip portion with the transfer roller 5 by the rotational driving of the photosensitive drum 1. The recording medium 16 accommodated in the recording medium cassette 17 is conveyed by the paper feed roller 15 and the conveying roller pair 8 in accordance with this timing, and conveyed to the transfer nip portion between the photosensitive drum 1 and the transfer roller 5. The Then, at a timing when the recording medium 16 is conveyed to the transfer nip portion, a predetermined DC voltage having a polarity opposite to that of the developer or a voltage obtained by superimposing a predetermined DC voltage and a predetermined AC voltage is applied to the transfer roller 5. As a result, the toner images attached to the photosensitive drum 1 are sequentially electrostatically transferred to the recording medium 16. In this embodiment, the toner has a negative polarity, and a positive DC voltage corresponding to the opposite polarity is applied to the transfer roller 5. In this embodiment, a contact transfer roller system that contacts the photosensitive drum 1 is used. However, an intermediate transfer belt system in which a toner image is transferred to a transfer belt and then transferred to a recording medium 16 may be used.

  (Fixing) The recording medium 16 that electrostatically carries the toner image is conveyed to the fixing device 14. The fixing device 14 includes a heating member that heats the toner, a fixing film 12 that is a cylindrical rotating body that includes the heating member, and a pressure roller 11 that pressurizes the fixing film 12. The recording medium 16 on which the toner is fixed is discharged to a paper discharge tray.

  (Cleaning) On the other hand, toner remaining on the surface of the photosensitive drum 1 without being transferred to the recording medium 16 is removed by a cleaning blade of the cleaner 7.

  By repeating the above operations, image formation is performed one after another.

<Configuration of high-pressure control unit>
FIG. 2 is a block diagram illustrating a configuration of a high-pressure control unit for supplying high pressure to each unit of the image forming apparatus 100.

  As shown in the figure, the separation high voltage circuit 24 is a circuit for supplying a high voltage to the separation static elimination needle 6. The transfer high voltage circuit 25 (first voltage applying means) is a circuit for supplying a high voltage to the transfer roller 5. The upper guide high voltage circuit 26 (second voltage applying means) is a circuit for supplying a high voltage to the pre-transfer upper guide 180.

  The memory 21 stores high-pressure data supplied to the separation static elimination needle 6, the transfer roller 5, and the pre-transfer upper guide 180. The CPU 22 refers to the high voltage value data referenced from the memory 21 and transfers it to the high voltage controller 23 so that the outputs of the transfer high voltage circuit 25, the separation high voltage circuit 24, and the upper guide high voltage circuit 26 can be changed. It has become.

<Configuration of upper guide before transfer>
FIG. 3 is a view showing the configuration of the pre-transfer upper guide 180 and its surroundings.

  As shown in the figure, the pre-transfer upper guide 180 guides the pre-transfer recording medium 16 so as to come into contact with a predetermined position of the photosensitive drum 1 when being supplied to the transfer nip. The pre-transfer upper guide 180 is configured by providing an insulating member 182 (insulating layer) between a conductive member 181 (first conductive member) and a conductive member 183 (second conductive member). ing. A high voltage having the same polarity as the toner is supplied from the upper guide high voltage circuit 26 to the conductive member 181 on the side close to the photosensitive drum 1. On the other hand, the conductive member 183 provided on the side far from the photosensitive drum 1 and in contact with the recording medium 16 is grounded.

  (Electric potential of the photosensitive drum 1) The photosensitive drum 1 is uniformly charged by the charging roller 2 to a white portion potential (Vd) = − 500V. An exposure device 3 is exposed based on the image information, and an electrostatic latent image is formed so that a portion where an image is formed has a black portion potential (VL) = − 200V. Then, the negative (minus) toner adheres to the black portion potential (VL) = − 200 V, whereby the electrostatic latent image is developed.

(Apply voltage to upper guide before transfer)
If the developed negative toner adheres to the pre-transfer upper guide 180 before the developed negative toner is transferred to the surface of the photosensitive drum 1, toner contamination occurs on the recording medium 16 guided by the pre-transfer upper guide 180. In order to prevent this toner contamination, a negative bias having the same polarity as the negative toner is applied to the conductive member 181 of the pre-transfer upper guide 180. In the present embodiment, the upper guide high voltage circuit 26 applies −700 V, which has an absolute value larger than the white portion potential (Vd) and the black portion potential (VL) of the photosensitive drum 1, to the pre-transfer upper guide 180. Yes. That is, a force in the direction of the photosensitive drum 1 is applied to the negative toner by an electric field formed between the conductive member 181 and the black portion potential (VL) of the photosensitive drum 1. This makes it difficult for toner to adhere to the pre-transfer upper guide 180.

(Applying voltage to the transfer roller)
In this embodiment, a positive bias (VT) of +500 V is applied to the transfer roller 5 so that a force from the black portion potential (VL) portion of the photosensitive drum 1 toward the transfer roller 5 is applied to the negative toner. With this bias, the negative toner on the photosensitive drum 1 is transferred onto the recording medium 16.

  On the other hand, since the conductive member 183 which is a member of the sheet passing surface of the pre-transfer upper guide 180 is grounded, 0V is applied. In general, it is possible to apply a predetermined potential without grounding the conductive member 183. Therefore, the potential of the conductive member 183 is generally (VC). When the potential difference (VT−VL) between the transfer roller 5 and the black portion potential of the photosensitive drum 1 becomes smaller than the potential difference (VT−VC) between the transfer roller 5 and the conductive member 183, transfer from the transfer roller 5 is performed. The current is transmitted through the recording medium 16 and leaks to the conductive member 183 of the pre-transfer upper guide 180. As a result, the transfer current from the transfer roller 5 to the photosensitive drum 1 is insufficient, and a transfer failure occurs in which the negative toner cannot be transferred onto the recording medium 16. Therefore, the transfer current is prevented from leaking to the conductive member 183 via the recording medium 16 so that (VT−VL)> (VT−VC). Thereby, it is possible to prevent the occurrence of transfer failure.

  When the conductive member 183 is grounded, VC = 0V, so (VT−VL)> (VT), that is, VL <0. That is, it is sufficient if VL is a negative potential.

  In this embodiment, VC = 0V and VL = −200V.

  Even when the voltage applied to the photosensitive drum 1 and the transfer roller 5 is changed due to a change in the temperature and humidity environment, control is performed so that the state of (VT−VL)> (VT−VC) is maintained. .

  In this embodiment, −700 V is applied to the conductive member 181 by the upper guide high-voltage circuit 26, and the conductive member 183 is grounded to 0 V. Therefore, the conductive member 183 has a positive potential compared to the conductive member 181, and there is a concern that the negative toner on the photosensitive drum 1 jumps over the conductive member 181 and directly adheres to the conductive member 183. There is. For this reason, in the present embodiment, the insulating member 182 has an end portion closer to the photosensitive drum 1 of the upper pre-transfer guide 180 than the respective end portions 181a and 183a of the conductive member 181 and the conductive member 183. The end portion 182a is configured to protrude. It is possible to prevent the negative toner from adhering directly to the conductive member 183 by the protruding end portion 182a of the insulating member 182.

  Providing the conductive member 183 on the sheet passing surface (contact surface) of the pre-transfer upper guide 180 prevents frictional charging due to contact between the recording medium 16 and the pre-transfer upper guide 180, and occurs when the recording medium 16 is charged. The trailing image can be prevented.

  Further, −700 V is applied to the conductive member 181 by the upper guide high-voltage circuit 26 and the conductive member 183 is grounded. Therefore, the conductive member 181 and the conductive member 183 need to be insulated. There is. In this embodiment, the conductive member 181 and the conductive member 183 are insulated by the insulating member 182, but may be insulated by an air layer.

  FIG. 4 is a diagram illustrating the configuration of the pre-transfer upper guide and its surroundings in Comparative Example 1.

  As shown in the drawing, instead of the pre-transfer upper guide 180 having the configuration shown in FIG. 3 of the present embodiment, a pre-transfer upper guide 210 is provided, and −700 V is supplied. Other configurations are the same as those of the first embodiment. In Comparative Example 1, a transfer current flows from the transfer nip to the pre-transfer upper guide 210 via the recording medium 16 being transferred, and transfer failure occurs.

  FIG. 5 is a diagram illustrating a configuration of the upper guide before transfer and the periphery thereof in Comparative Example 2.

  As shown in the drawing, instead of the pre-transfer upper guide 180 having the configuration shown in FIG. 3 of the present embodiment, an pre-transfer upper guide 310 is provided, and −700 V is supplied. The pre-transfer upper guide 310 includes a conductive member 311 and an insulating member 312, and −700 V is supplied to the conductive member 311. Other configurations are the same as those of the first embodiment. In this comparative example 2, since the insulating member 312 is disposed on the sheet passing surface of the pre-transfer upper guide 310, the insulating member 312 contacts the recording medium to be conveyed, and the recording medium itself is caused by frictional charging due to the contact. Charge. As a result, the toner on the photosensitive drum 1 adheres to the charged recording medium 16 upstream of the transfer nip, thereby generating a trailing image.

  On the other hand, in the configuration as shown in this embodiment, the leakage of the transfer current is prevented by satisfying the relationship of potential (VT−VL)> (VT−VC), and transfer failure can be prevented. Since no frictional charging occurs, it is possible to prevent a trailing image.

  FIG. 6 is a graph comparing the effects of the paper passage transition of this embodiment with Comparative Examples 1 and 2.

  The horizontal axis indicates the number of sheets to be passed, and the vertical axis indicates a value obtained by converting the trailing distance in the trailing image into a numerical value.

  When the tail becomes 7 or more, the tail image can be recognized and becomes NG level. In Comparative Example 2, since the insulating member 312 is attached to the sheet passing surface, the insulating member 312 and the recording medium 16 are frictionally charged as the number of sheets passing increases, and the recording medium 16 is positively charged. Gets worse. In Comparative Example 1, since a minus bias is applied to the pre-transfer upper guide 210 made of a conductive member, the degree of tail deterioration is smaller than that of Comparative Example 2.

  In this embodiment, since the grounded conductive member 183 is provided on the sheet passing surface of the pre-transfer upper guide 180, the recording medium 16 is not charged and the trailing does not reach the NG line.

  In the configuration shown in Patent Document 1, a guide member having a configuration in which an insulator is attached to the entire surface of the conductive member is used. As described above, when the insulator is attached to the entire surface of the conductive member, the toner on the photosensitive drum 1 is attached to the guide member by charging the insulating member on the surface of the photosensitive drum. It becomes easy. In this embodiment, a conductive member 181 is provided on the surface of the upper guide 180 before transfer on the side of the photosensitive drum 1, and toner adhesion due to charging of the insulating member hardly occurs.

  As described above, in this embodiment, it is possible to prevent toner contamination of the guide member while preventing the transfer failure and the trailing image.

  In this embodiment, the case where the photosensitive drum 1 is used as the image carrier has been described. However, an intermediate transfer belt may be used as the image carrier. The same applies to other embodiments.

(Example 2)
Next, a second embodiment for adjusting the protruding amount of the insulating member 182 with respect to the conductive member end 183a will be described with reference to FIG. In addition, what was comprised similarly to the said 1st Embodiment attaches | subjects the same member name even if the same code | symbol or a code | symbol differs, and abbreviate | omits description.

  FIG. 7 is a view showing the arrangement of the photosensitive drum 1 and the pre-transfer upper guide 180 according to the embodiment of the present invention.

If the protruding amount L of the insulating member 182 with respect to the conductive member end 183a is too large, the tip of the insulating member 182 contacts the surface of the photosensitive drum 1 and disturbs the toner image.
Therefore, as shown in FIG. 7, the closest point from the conductive member 183 on the circumference of the photosensitive drum 1 is A, the length of the line segment AB formed with the conductive member end 183a as B is D, and D The protrusion amount L is set so that> L. As a result, the tip of the insulating member 182 can be prevented from contacting the surface of the photosensitive drum 1.

  On the other hand, if the protruding amount L is too small, the negative toner cannot be prevented from adhering to the conductive member 183. This is because depending on the thickness of the conductive member 183, the insulating member 182 may block the negative toner flying from the photosensitive drum 1 due to the electric lines of force generated by the potential difference between the conductive member end 183 a and the photosensitive drum 1. It is because it becomes impossible.

  Therefore, as shown in FIG. 7, the angle between the line segment AB and the end face of the conductive member 183 is θ, the length of the line segment AB is D, the thickness of the insulating member 182 is d, and L ≧ d × The protruding amount L of the insulating member 182 is set so as to be tan θ. Thereby, adhesion of negative toner to the conductive member 183 can be prevented.

  As described above, in this embodiment, by adjusting the protruding amount L of the insulating member 182 with respect to the conductive member end portion 183a, the toner image on the photosensitive drum 1 is disturbed or negative toner adheres to the conductive member 183. Can be prevented.

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 3 ... Exposure apparatus 5 ... Transfer roller 16 ... Recording medium 22 ... CPU
25 ... Transfer high voltage circuit 26 ... Upper guide high voltage circuit 100 ... Image forming apparatus 180 ... Pre-transfer upper guide 181 ... Conductive member 181a ... End 182 ... Insulating member 182a ... End 183 ... Conductive member 183a ... End

Claims (5)

An image carrier for carrying a toner image;
Transfer means for transferring the toner image carried on the image carrier to a recording medium;
Voltage application means for applying a voltage to the transfer means;
The recording medium is guided to the transfer means, and the recording medium is in contact with the transfer means so that the potential difference between the transfer means and the transfer means is lower than the potential difference between the image carrier and the first toner image. A second region that applies a voltage having the same polarity as the toner to a portion of the image carrier that carries the toner image, and an insulation that blocks conduction between the first region and the second region. A guiding means comprising a layer;
Have
The guide means is arranged in the order of the first area, the insulating layer, and the second area from the image carrier side to the side where the recording medium comes into contact.
The end portion of the insulating layer is more directed toward the image carrier than the front end of the first region so as to block toner flying from the image carrier toward the front end portion on the image carrier side of the first region. An image forming apparatus that protrudes.   The amount of protrusion of the insulating layer with respect to the second conductive member from the end on the side close to the image carrier is L, and the recording medium is in contact with the second conductive member on the side close to the image carrier. A straight line connecting an end portion on the contact surface side to the closest point of the second conductive member on the surface of the image carrier, and an end surface of the second conductive member on the side close to the image carrier. Is defined as θ, the thickness of the second conductive member is d, and the distance between the image carrier and the second conductive member is D, L is D> L ≧ d × tan θ. The image forming apparatus according to claim 1, wherein: Voltage applying means for applying a voltage having the same polarity as that of the toner to the first conductive member;
Exposure means for exposing the image carrier to form an electrostatic latent image on the image carrier;
The first conductive member such that a force in a direction toward the image carrier is applied to the toner by an electric field between a portion of the image carrier exposed by the exposure unit and the first conductive member. Control means for applying a voltage to
The image forming apparatus according to claim 1, further comprising:   The image forming apparatus according to claim 1, wherein the second conductive member is grounded.   The control means determines a potential difference between the transfer means and a portion of the image carrier exposed by the exposure means based on a potential difference between the transfer means and a contact surface of the guide means on which the recording medium contacts. The image forming apparatus according to claim 3, wherein the image forming apparatus is also made larger.

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