JP2007264342A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing a defective image due to irregularities in a toner image on a photoreceptor drum, toner-dropping and toner-scattering caused by the soiling on a guide member by the toner by maintaining a guide member for guiding a paper sheet to a transfer position in an image forming part in the predetermined potential. <P>SOLUTION: The surface guide member 24 is provided integrally on the bottom surface of a non-conductive housing 18b for a developing apparatus 18, and a CR circuit where a capacitor 29 and a resistance 30 are connected in parallel is provided between the surface guide member 24 and a bias apply part 26. The same bias as a developing bias applied on the developing roller 18a is applied on the surface guide member 24 through the CR circuit. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more particularly to a guide member for guiding a sheet to a transfer position on the surface of a photosensitive drum as an image carrier.

  In conventional image forming apparatuses such as copying machines, printers, and facsimile machines using an electrophotographic system, a charging process for uniformly charging the surface of the photosensitive drum as an image carrier, and the surface of the photosensitive drum is exposed to electrostatic. An exposure process for forming a latent image, a development process for developing an electrostatic latent image with toner (developer) to form a toner image, a transfer process for transferring the toner image on the photosensitive drum to a sheet, and a transfer process to the sheet An image is formed through a fixing process for fixing the toner image.

  In such an electrophotographic system, the transfer process for transferring the toner image onto the paper is an important process for determining the quality of the image formed on the paper. In order to perform optimal image formation, the surface of the photosensitive drum Therefore, it is necessary to transport the paper properly to the transfer position. Therefore, in an image forming apparatus using an electrophotographic system, a pair of pre-transfer guides that guide both sides of a sheet upstream of the transfer position in order to guide the sheet conveyed from the pair of registration rollers to the transfer position to a better position. By arranging the guide, high transfer performance is secured.

  Here, in order to enhance the effect of regulating the paper position, the tip of the guide member may be brought close to the vicinity of the transfer position. However, when the gap between the transfer position and the tip of the guide member approaches 2 mm or less, the guide is caused by the transfer bias. The member is charged, and the toner image on the photosensitive drum is scattered in the direction opposite to the rotation direction of the photosensitive drum, or the toner on the photosensitive drum is transferred to the guide member and accumulated on the guide member. In such a case, the phenomenon that the rear end portion of the formed image is scattered or the toner accumulated on the pre-transfer guide falls on the paper transported due to the impact of the paper transport, etc. May produce images.

Therefore, in Patent Document 1, toner transfer to the conductive member is prevented by applying the same bias as that of the developing roller provided in the developing device to the conductive member that is a guide member attached to the housing of the developing device. In addition, by using a paper or OHP sheet that has been subjected to a surface treatment that tends to have an electric charge, the paper can be transported to a transfer position so as not to contact the conductive member. In order to prevent toner adhesion, there has been proposed a method for preventing a transfer failure caused by abnormal charging of a sheet by a bias applied to a conductive member.
JP 2000-275986 A

  However, as described in Patent Document 1, in the method in which the sheet conveyed to the transfer position is variable between a path that contacts the conductive member and a path that does not contact the conductive member, an extra mechanism must be added. There is a disadvantage of not becoming. In addition, if a paper that has absorbed moisture in a high humidity environment contacts a conductive member to which a development bias is applied, the transfer current may leak through the paper, resulting in a transfer failure.Conversely, the transfer bias is set to a constant voltage. When the electric field is not weakened, the transfer bias flows along the sheet to the conductive member, and the developing bias causes a voltage drop, which may reduce the developing efficiency. Further, the conductive member may be charged with a polarity opposite to that of the toner and contaminated with the toner due to the influence of the paper exposed to the transfer electric field even in a high humidity environment.

  In the present invention, in view of the above-described circumstances, the guide member that guides the paper to the transfer position of the image forming unit is maintained at a predetermined potential, so that the toner image on the photosensitive drum is disturbed or the guide member is contaminated with toner. An object of the present invention is to provide an image forming apparatus capable of preventing image defects caused by toner dropping or toner scattering due to toner.

  To achieve the above object, the present invention provides a photosensitive drum as an image carrier, a developing device for forming a toner image on the surface of the photosensitive drum, and an alternating current component superimposed on a direct current component in the developing device. A bias applying unit that applies a developing bias, a transfer roller for transferring a toner image formed on the surface of the photosensitive drum to a sheet, and a sheet to a transfer position formed by the photosensitive drum and the transfer roller. A pair of pre-transfer guides configured by a front guide member that guides the front surface of the paper and a back guide member that is provided at a position facing the front guide member across the paper transport path and guides the back surface of the paper; In the image forming apparatus, the surface guide member is formed of a conductive material, and the development applied from the bias application unit to the development device through a CR circuit. Bias and the bias is characterized by being applied to the surface guide member.

  The present invention also provides a photosensitive drum as an image carrier, a developing device that forms a toner image on the surface of the photosensitive drum, and a bias that applies a developing bias in which an alternating current component is superimposed on a direct current component to the developing device. An application unit; a transfer roller for transferring a toner image formed on the surface of the photosensitive drum to the paper; and a paper surface for guiding the paper to a transfer position formed by the photosensitive drum and the transfer roller. An image forming apparatus comprising: a front surface guide member that guides the paper; and a pair of pre-transfer guides that are provided at positions facing the front surface guide member across the paper conveyance path and configured to guide the back surface of the paper. The surface guide member is formed of a conductive material, and the same bias as the developing bias applied to the developing device is applied from the bias applying unit through a half-wave rectifier circuit. Scan is characterized by being applied to the surface guide member.

  According to the present invention, in the image forming apparatus having the above configuration, a separating member having a volume resistance value at least equal to or greater than the volume resistance value of the sheet is integrally provided on the sheet conveyance path side of the surface guide member. And the paper to be transported are separated from each other.

  According to the present invention, in the image forming apparatus configured as described above, a conductive member is provided at least on a portion of the isolation member that contacts the paper, and the conductive member is grounded.

  According to the present invention, in the image forming apparatus configured as described above, the surface guide member is provided integrally with a housing of the developing device.

  According to the first configuration of the present invention, the bias is directly applied from the bias applying unit by applying the same bias as the developing bias applied to the developing device to the surface guide member through the CR circuit from the bias applying unit. Compared to the case, the voltage drop of the developing bias does not easily occur and the developing efficiency does not decrease. Further, the AC component of the developing bias is transmitted to the surface guide member by the capacitor component, and the DC component is a potential difference between the developing bias and the transfer bias, the resistance component, and the sheet resistance from the time when the sheet enters the transfer position. Since the AC voltage is maintained at a value close to the developing bias, the toner adhesion to the surface guide member can be prevented.

  Further, according to the second configuration of the present invention, the same bias as the developing bias applied to the developing device is applied from the bias applying unit to the surface guide member through the half-wave rectifier circuit, thereby directly from the bias applying unit. Compared with the case where a bias is applied, a voltage drop of the developing bias hardly occurs and the developing efficiency does not decrease. In addition, by grounding the surface guide member via a Zener diode, a voltage having a polarity opposite to that of the photosensitive drum can be leaked, and only a voltage having the same polarity as that of the photosensitive drum can be applied to the surface guide member. Since the member can always be maintained in the same polarity as the photosensitive drum, it is possible to prevent the toner on the photosensitive drum from transferring to the surface guide member.

  According to the third configuration of the present invention, in the image forming apparatus having the first or second configuration, the surface guide member and the paper to be conveyed have a volume resistance value at least equal to or higher than the volume resistance value of the paper. By isolating with the separating member, the bias applied to the front surface guide member does not interfere with the transfer bias via the paper, so that it is possible to prevent the occurrence of transfer failure.

  Further, according to the fourth configuration of the present invention, in the image forming apparatus having the third configuration, the conductive member is provided at least in a portion that contacts the sheet of the separating member, and the conductive member is grounded. Even if the separating member rubs against the paper to be transported, it will not be charged, and the paper will be attracted to the separating member, resulting in a paper jam, or when the toner image is transferred to the paper, the toner image will be disturbed and image formation failure may occur. Is prevented.

  According to the fifth configuration of the present invention, in the image forming apparatus having any one of the first to fourth configurations, the surface guide member is provided integrally with the housing of the developing device, thereby being incorporated in the image forming apparatus. Therefore, the number of components and the arrangement space can be reduced, and the image forming apparatus can be reduced in size and cost. Further, when the paper is jammed, the developing device and the surface guide member can be integrally removed, so that maintenance is facilitated.

  Hereinafter, a first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram showing the overall configuration of the image forming apparatus according to the present embodiment. In this embodiment, a laser beam printer is exemplified as an example of the image forming apparatus. However, it goes without saying that the present invention can be applied to a copying machine, a facsimile machine, or the like other than the printer.

  As shown in FIG. 1, the image forming apparatus 1 includes a paper feed cassette 2 that accommodates paper P stacked on the lower part of the main body. Above this paper feed cassette 2 is formed a paper transport path 4 that extends substantially horizontally from the main body right side surface portion to the main body left side surface portion and further extends upward to the paper discharge portion 3 formed on the upper surface of the main body. The pickup roller 5, feed roller 6, intermediate conveyance roller 7, registration roller pair 8, pre-transfer guide 9, image forming unit 10, image fixing unit 11, and discharge roller pair 12 are sequentially arranged along the sheet conveyance path from the upstream side. Is arranged.

  The paper feed cassette 2 includes a paper stacking plate 13 whose rear end in the paper transport direction is rotatably supported on the bottom surface of the paper feed cassette 2, and a bias that biases the front end of the paper stacking plate 13 upward. A biasing means 14 is provided so that the stacked paper P is pressed against the pickup roller 5. A retard roller 15 is disposed in front of the paper feed cassette 2 so as to be in pressure contact with the feed roller 6. When a plurality of sheets are simultaneously fed by the pickup roller 5, The sheet P is rolled by the feed roller 6 and the retard roller 15, and only the uppermost sheet is conveyed.

  Then, the paper P that is rolled by the feed roller 6 and the retard roller 15 is conveyed to the registration roller pair 8 by the intermediate conveyance roller 7, and the timing is adjusted by the registration roller pair 8 and supplied to the image forming unit 10. Will be. At this time, the sheet P is guided to the better transfer position described later by being guided by the pre-transfer guide 9 on both sides.

  The image forming unit 10 forms a predetermined toner image on the paper P by an electrophotographic process, and is an image carrier that is rotatably supported in a predetermined direction (direction indicated by an arrow A in FIG. 1). A photosensitive drum 16 and a charging device 17, a developing device 18, a cleaning device 20, and a transfer device disposed so as to face the photosensitive drum 16 with the paper transport path 4 interposed therebetween. The laser scanning unit (LSU) 21 is disposed above the roller 19 and the photosensitive drum 16. These devices and units are configured to be detachable from the device main body in order to facilitate maintenance work.

  As the photosensitive drum 16, for example, a cylindrical aluminum core having a surface formed with an amorphous silicon layer can be suitably used, and the photosensitive drum 16 is rotationally driven by a driving device (not shown). The charging device 17 is arranged so that the charging roller 17a contacts the photosensitive drum 16. When the photosensitive drum 16 rotates, the charging roller 17a contacts the surface of the photosensitive drum 16 and rotates. At this time, by applying a predetermined voltage to the charging roller 17a from a power source (not shown), the surface of the photosensitive drum 16 is uniformly charged. Further, the charging device 17 is provided with a brush roller 17b in contact with the charging roller 17a to remove external toner additive, paper dust and the like adhering to the surface of the charging roller 17a. As the charging roller 17a, for example, an ionic charging roller mainly composed of epichlorohydrin can be used.

  Next, an electrostatic latent image is formed on the photosensitive drum 16 by the laser beam from the laser scanning unit (LSU) 21 based on the input image data. A jumping development method is used for the developing device 18, and a developing bias in which an AC component is superimposed on a DC component is applied from a bias applying unit 26 (see FIG. 2) to a developing roller 18 a provided in the developing device 18. As a result, toner adheres to the electrostatic latent image, and a toner image is formed on the surface of the photosensitive drum 16, and the transfer roller 19 causes the toner image on the surface of the photosensitive drum 16 to be transferred to the photosensitive drum 16 and the transfer roller. 19 is transferred to the paper P supplied to the transfer position formed in the nip portion with the paper 19.

  The paper P on which the toner image is transferred is conveyed from the image forming unit 10 toward the image fixing unit 11. The image fixing unit 11 is disposed on the downstream side of the image forming unit 10 in the sheet conveying direction, and the sheet P on which the toner image is transferred in the image forming unit 10 is a heating roller 22 provided in the image fixing unit 11. The toner image that is sandwiched and heated by the pressure roller 23 pressed against the heating roller 22 is fixed.

  The paper P on which image formation has been performed in the image forming unit 10 and the image fixing unit 11 is discharged to the paper discharge unit 3 by the discharge roller pair 12. On the other hand, the toner remaining on the surface of the photosensitive drum 16 after the transfer is removed by the cleaning device 20. Then, the photosensitive drum 16 is charged again by the charging device 17, and thereafter image formation is performed in the same manner.

  Next, the pre-transfer guide 9 provided in the image forming apparatus 1 will be further described with reference to FIG. FIG. 2 is a schematic diagram showing a main part of the image forming apparatus according to the first embodiment of the present invention. The sheet P to be transported is expressed as a surface on which toner is transferred at the transfer position as a front surface and a surface contacting the transfer roller 19 as a back surface.

  The pre-transfer guide 9 is a conveyance guide for guiding the paper P conveyed to the transfer position by the registration roller pair 8 to a better position of the transfer position, and a surface guide member 24 that guides the surface of the paper P. The rear surface guide member 25 is provided at a position facing the front surface guide member 24 across the paper conveyance path 4 and guides the rear surface of the paper P. The front surface guide member 24 and the rear surface guide member 25 are rectangular plate-like members having substantially the same width as the width of the photosensitive drum 16, and are arranged so that the long side direction is orthogonal to the paper transport direction. .

  Further, the front surface guide member 24 is formed to be greatly curved in the short side direction, and is arranged so that only the front edge in the paper transport direction is close to the back surface guide member 25, and the paper P is the pre-transfer guide 9. It enters from the rear end side and is guided to the transfer position by the front surface guide member 24 and the back surface guide member 25. Further, the front surface guide member 24 is integrally provided on the lower surface of the non-conductive housing 18b of the developing device 18 disposed above the sheet conveying path 4, thereby reducing the size of the main body of the image forming apparatus 1. In addition, the maintenance at the time of paper jam can be easily performed. In order to guide the paper P to a better position, the distance between the surface guide member 24 and the photosensitive drum 16 is preferably set to 1 to 3 mm.

  The surface guide member 24 is formed of a conductive material such as SUS, and the development bias applied to the developing roller 18a from the bias application unit 26 in order to prevent toner adhesion to the surface guide member 24. The same bias is applied. In addition, an isolation member 27 made of an insulating material is attached to the front surface guide member 24 on the side of the paper conveyance path 4, whereby a bias applied to the front surface guide member 24 is transferred via the paper P to a transfer bias. So that it does not interfere with. For the separating member 27, for example, an insulating polyethylene sheet can be suitably used.

  Furthermore, a conductive member 28 is attached to a portion of the separating member 27 that contacts the paper P so as not to contact the surface guide member 24. By grounding the conductive member 28, the separating member 27 is Even if the sheet P is rubbed with the conveyed sheet P, the sheet P is not charged, and the sheet P is attracted to the separating member 27 to cause a paper jam, or when the toner image is transferred to the sheet P, the toner image is disturbed to cause an image defect. Is prevented. For the conductive member 28, for example, a conductive polyethylene sheet can be suitably used. Further, the conductive member 28 may be grounded via a resistor or a Zener diode.

  In the first embodiment, a CR circuit in which a capacitor 29 and a resistor 30 are connected in parallel is provided between the surface guide member 24 and the bias applying unit 26. Through this CR circuit, the surface guide is provided. A bias is applied to the member 24. In this way, by applying a bias to the surface guide member 24 through the CR circuit, compared to the case where the bias is directly applied from the bias applying unit 26, a voltage drop of the developing bias hardly occurs and the developing efficiency does not decrease. .

  Further, the AC component of the developing bias is transmitted to the surface guide member 24 by the capacitor component, and the DC component is a potential difference between the developing bias and the transfer bias and the resistance component and the sheet from the time when the sheet P enters the transfer position. The voltage determined by the partial pressure with the P resistance is maintained. Further, the surface guide member 24 and the paper P are insulated by the separating member 27, and the DC voltage becomes substantially equal to the DC component of the developing bias. In this case, an electric field in which the toner is transferred from the surface guide member 24 toward the photosensitive drum 16 is maintained, and the AC voltage is maintained at a value close to the developing bias, so that the effect of preventing toner adhesion to the surface guide member 24 is high.

  In order to confirm the effect of the first embodiment of the present invention, SUS sheet metal is used as the surface guide member 24, the capacitance of the capacitor 29 is 47 pF, the resistance value of the resistor 30 is 50 MΩ, and the surface potential of the photosensitive drum 16 is set. Using the image forming apparatus 1 in which the developing bias applied from the bias applying unit 26 at 270 V is a voltage obtained by superimposing a DC voltage of +170 V on a frequency of 2.5 kHz, a peak-to-peak voltage of 1.5 kVpp, and an AC voltage of Duty 55%. A paper passing test is performed in a low humidity environment (temperature 23 ° C., humidity 50%) and a high temperature high humidity environment (temperature 32 ° C., humidity 80%), and the toner on the surface guide member 24 and the quality of the formed image are visually checked. And observed.

  Further, as Comparative Example 1, the isolation member 27 and the conductive member 28 are not affixed to the surface guide member 24, and further, the development bias is not applied to the surface guide member 24 from the bias applying unit 26, and the resistance is simply 100 MΩ. As a comparative example 2, as in Comparative Example 2, the bias applying unit is not attached to the surface guide member 24 without attaching the isolation member 27 and the conductive member 28 to the surface guide member 24 and without grounding the surface guide member 24. A configuration in which a developing bias was directly applied from No. 26 was also subjected to a paper passing test under the same conditions.

  As a result of the test, in Comparative Example 1, the toner was deposited on the surface guide member 24 only by printing several high-density patterns, and the toner dropped on the paper due to the impact during paper conveyance, resulting in an abnormal image. . Further, the toner image on the photoconductive drum 16 is scattered in the direction opposite to the rotation direction of the photoconductive drum 16, and an image defect occurs due to the disturbance of the toner image on the photoconductive drum 16. In Comparative Example 2, neither toner contamination nor abnormal images associated therewith occurred in the low humidity environment. However, in the high temperature and high humidity environment, the development bias and the transfer bias interfere with each other through the paper P, and the development efficiency and transfer The image density is reduced due to the reduction in efficiency, and the voltage of the surface guide member 24 is lowered to cause an image defect due to toner contamination.

  However, in the first embodiment of the present invention, the potential of the surface guide member 24 is maintained at a DC voltage of 162 V and an AC voltage of 1.24 kVpp in a low humidity environment, and toner contamination of the surface guide member 24 and abnormal images associated therewith are generated. The image quality of the formed image was good. Even in a high-temperature and high-humidity environment, the potential of the surface guide member 24 was maintained at a DC voltage of 166 V and an AC voltage of 1.25 kVpp, and good image quality was obtained without causing toner contamination and image defects resulting therefrom. .

  Next, a second embodiment of the present invention will be described with reference to FIG. FIG. 3 is a schematic diagram showing a main part of the image forming apparatus according to the second embodiment of the present invention. In addition, the same code | symbol is attached | subjected to the part which is common in FIG.1 and FIG.2 of 1st Embodiment, and description is abbreviate | omitted.

  In the second embodiment, the surface guide member 24 and the bias applying unit 26 are connected via a capacitor 29, and the surface guide member 24 is grounded via a Zener diode 31, so that the surface guide member 24 and the bias applying unit 26 are connected. And a bias is applied to the surface guide member 24 through the half-wave rectifier circuit.

  Thus, by applying a bias to the surface guide member 24 through the half-wave rectifier circuit, compared to the case where the bias is directly applied from the bias applying unit 26, a voltage drop of the developing bias hardly occurs, and the developing efficiency is lowered. There is no. Further, by grounding the surface guide member 24 via the Zener diode 31, a voltage having a polarity opposite to that of the photosensitive drum 16 is leaked, and only a voltage having the same polarity as that of the photosensitive drum 16 is applied to the surface guide member 24. In addition, since the surface guide member 24 can always be maintained in the same polarity as the photosensitive drum 16, the toner on the photosensitive drum 16 can be prevented from transferring to the surface guide member 24.

  In order to confirm the effect of the second embodiment of the present invention, the capacitance of the capacitor 29 is 47 pF, the Zener voltage of the Zener diode 31 is 330 V, the surface potential of the photosensitive drum 16 is 270 V, and the development is applied from the bias applying unit 26. Using the image forming apparatus 1 in which the bias is a voltage obtained by superimposing a DC voltage of +170 V on a frequency of 2.5 kHz, a peak-to-peak voltage of 1.5 kVpp, and a duty of 55%, a paper passing test is performed in the same manner as in Example 1. The surface guide member 24 was visually observed for toner contamination and the quality of the formed image.

  As a result of the test, in the second embodiment of the present invention, the potential of the surface guide member 24 is maintained at a DC voltage of 177 V and an AC voltage of 310 Vpp in a low humidity environment, and toner contamination of the surface guide member 24 and image defects due to this occur. The image quality of the formed image was good. Even in a high-temperature and high-humidity environment, the potential of the surface guide member 24 was maintained at a DC voltage of 166 V and an AC voltage of 310 Vpp, and good image quality was obtained without causing toner contamination and image defects resulting therefrom.

  As described above, according to the configuration of the first embodiment or the second embodiment of the present invention, even when the surface guide member 24 that guides the paper to the transfer position is arranged close to the transfer position, the transfer bias causes Since the surface guide member 24 is not charged and the toner on the photosensitive drum 16 is not transferred to and accumulated on the surface guide member 24, an abnormal image due to toner contamination of the surface guide member 24 is prevented. Can do. Further, by separating the front guide member 24 and the paper P by the separating member 27, even when the paper P absorbs moisture and has a low resistance, the development efficiency and the transfer efficiency are reduced due to the interference between the transfer bias and the development bias. It can be avoided.

  In addition, this invention is not limited to the said embodiment, A various change is possible in the range which does not deviate from the meaning of this invention. For example, in the above-described embodiment, the surface guide member 24 is integrally provided on the lower surface of the housing 18b of the developing device 18, but the surface guide member 24 may be directly installed on the frame of the main body of the image forming apparatus 1. Further, the separating member 27 is stuck on the front surface guide member 24 to separate the front surface guide member 24 and the paper P. However, since the paper P is usually very high resistance, the separating member 27 is not necessarily required. However, since the paper P may absorb moisture and have a low resistance in a high humidity environment, it is preferable to isolate the surface guide member 24 and the paper P by the separating member 27.

  Further, the separating member 27 can be formed of a conductive material as long as it can prevent the developing bias applied to the front surface guide member 24 from interfering with the transfer bias via the paper P. That is, it is only necessary that the separating member 27 has a volume resistance value that is equal to or greater than the volume resistance value of the paper P in an environment where the image forming apparatus 1 is used. Further, it is preferable to attach a conductive member 28 to the portion of the separating member 27 that contacts the paper P and to ground it. However, since the amount of charge of the separating member 27 due to friction with the paper P is very small, A configuration without the member 28 is also possible.

  INDUSTRIAL APPLICABILITY The present invention can be used in image forming apparatuses such as copying machines, printers, and facsimiles. More specifically, the present invention is used as a pre-transfer guide for guiding paper to a transfer position on the surface of a photosensitive drum as an image carrier. can do.

FIG. 1 is a schematic configuration diagram showing an overall configuration of an image forming apparatus according to the present invention. FIG. 2 is a schematic diagram showing a main part of the image forming apparatus according to the first embodiment of the present invention. These are the schematic diagrams which show the principal part of the image forming apparatus of 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 9 Guide before transfer 16 Photosensitive drum 18 Developing apparatus 18a Developing roller 18b Housing 19 Transfer roller 24 Front surface guide member 25 Back surface guide member 26 Bias application part 27 Separating member 28 Conductive member 29 Capacitor 30 Resistor 31 Zener diode

Claims (5)

A photosensitive drum that is an image carrier, a developing device that forms a toner image on the surface of the photosensitive drum, a bias applying unit that applies a developing bias in which an alternating current component is superimposed on a direct current component to the developing device, and A transfer roller for transferring a toner image formed on the surface of the photosensitive drum to a sheet; and a surface guide for guiding the surface of the sheet for guiding the sheet to a transfer position formed by the photosensitive drum and the transfer roller. An image forming apparatus comprising: a pair of pre-transfer guides configured by a back surface guide member that is provided at a position facing the front surface guide member across the member and the paper transport path and guides the back surface of the paper;
The surface guide member is made of a conductive material, and the same bias as the developing bias applied to the developing device is applied to the surface guide member from the bias applying unit through a CR circuit. Forming equipment. A photosensitive drum that is an image carrier, a developing device that forms a toner image on the surface of the photosensitive drum, a bias applying unit that applies a developing bias in which an alternating current component is superimposed on a direct current component to the developing device, and A transfer roller for transferring a toner image formed on the surface of the photosensitive drum to a sheet; and a surface guide for guiding the surface of the sheet for guiding the sheet to a transfer position formed by the photosensitive drum and the transfer roller. An image forming apparatus comprising: a pair of pre-transfer guides configured by a back surface guide member that is provided at a position facing the front surface guide member across the member and the paper transport path and guides the back surface of the paper;
The surface guide member is made of a conductive material, and the same bias as the developing bias applied to the developing device is applied to the surface guide member from the bias applying unit through a half-wave rectifier circuit. Image forming apparatus.   A separation member having at least a volume resistance value equal to or greater than the volume resistance value of the sheet is integrally provided on the sheet conveyance path side of the surface guide member, and the surface guide member and the sheet to be conveyed are separated from each other. The image forming apparatus according to claim 1, wherein the image forming apparatus is an image forming apparatus.   The image forming apparatus according to claim 3, wherein a conductive member is provided on at least a portion of the separating member that contacts the paper, and the conductive member is grounded.   The image forming apparatus according to claim 1, wherein the surface guide member is provided integrally with a housing of the developing device.

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