JP2012083568A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device with a simple structure capable of preventing a guide member for guiding a recording medium to a transfer part from being contaminated with toner and the recording medium from being contaminated by adhesion of toner adhered to the guide member.SOLUTION: During rotation of an image carrier, while the recording material P exists on the lower guide member 22, a voltage whose polarity is opposite to the normal charging polarity of toner is applied to the lower guide member 22 from a lower guide member voltage applying means 14. While the recording medium P does not exist on the lower guide member 22, a voltage is not applied, or a voltage whose polarity is the same as the normal charging polarity of toner is applied to the lower guide member 22 from the lower guide member voltage applying means 14.

Description

  The present invention relates to an image forming apparatus that employs an image forming process such as an electrophotographic system or an electrostatic recording system.

  2. Description of the Related Art Conventionally, image forming apparatuses such as copying machines and printers using an electrophotographic system have been widely used. An electrophotographic image forming apparatus forms an image by the following image forming process. That is, an electrophotographic photosensitive member (photosensitive drum) generally in the form of a drum is uniformly charged with a charger while rotating at a predetermined process speed. An electrostatic latent image is formed on the photosensitive drum by irradiating the surface of the charged photosensitive drum with light carrying image information. The electrostatic latent image formed on the photosensitive drum is developed using toner as a developer to form a visible image (toner image) on the photosensitive drum. This toner image is transferred to a recording material such as recording paper in the transfer area to obtain a recorded image.

  The recording material is conveyed while being sandwiched between the conveying roller pair, and is guided by the guide member to reach the toner image transfer portion. Then, the toner on the photosensitive drum is transferred onto the recording material at this transfer portion. Here, a configuration is known in which the guide member is made of a conductive material such as metal and a constant voltage is applied by a power source or the like.

  There are the following two purposes for applying a voltage to the guide member. First, by applying a voltage having a polarity opposite to that of the toner, the transfer current is prevented from flowing into the guide member. Further, by applying a voltage having the same polarity as that of the toner, the toner adheres to the guide member and the recording material is thereby prevented from being contaminated by the toner.

  In addition, the following has been proposed as an attempt to prevent the transfer current from flowing into the guide member and the adhesion of toner. Patent Document 1 proposes that the guide member is divided into a plurality of parts in a direction orthogonal to the recording material conveyance direction, and the portion to which the voltage is applied is changed depending on the size of the recording material. Patent Document 2 proposes that a plurality of guide members be provided in the conveyance direction of the recording material so that the generated voltages are different between those near the transfer portion and those far from the transfer portion. Patent Documents 3 and 4 propose that temperature / humidity detection means is provided in the image forming apparatus, and the voltage generated in the guide member is turned on / off and the voltage value is adjusted by the output value. ing.

Japanese Patent No. 3322024 JP 63-210978 A Japanese Patent No. 3073931 Japanese Patent No. 3581525

  However, as described in Patent Document 1 and Patent Document 2, a configuration in which a plurality of guide members are provided in a direction orthogonal to the recording material conveyance direction or in the conveyance direction inevitably complicates the apparatus. Further, as described in Patent Document 3 and Patent Document 4, the configuration in which the voltage generated in the guide member is controlled in accordance with the output value of the temperature / humidity detecting means may cause complication of the apparatus.

  Accordingly, an object of the present invention is to prevent the toner from adhering to the guide member that guides the recording material to the transfer portion with a simple configuration, and the toner adhering to the guide member adheres to the recording material. It is an object of the present invention to provide an image forming apparatus capable of preventing contamination of the image.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to a rotatable image carrier that carries toner, transfer means for transferring toner on the rotating image carrier to a recording material at a transfer portion, and a recording material to the transfer portion. A conveying unit that conveys, and a guide unit that guides the recording material conveyed to the transfer unit by the conveying unit on the upstream side of the transfer unit in the conveying direction of the recording material, the recording unit moving toward the transfer unit A guide unit having a lower guide member formed of a conductive material disposed on the lower side; and a lower guide member voltage applying unit for applying a voltage to the lower guide member, and during rotation of the image carrier While the recording material is present on the lower guide member, a voltage having a polarity opposite to the normal charging polarity of the toner is applied from the lower guide member voltage applying means to the lower guide member. Recording material Between standing the city is an image forming apparatus and applying the lower guide member voltage or from the application member no voltage is applied to the lower guide member or the normal charging polarity voltage of the same polarity of the toner.

  According to another aspect of the present invention, a rotatable image carrier that carries toner, a transfer unit that transfers toner on the rotating image carrier to a recording material in a transfer unit, and recording on the transfer unit A conveying unit that conveys the material, and a guide unit that guides the recording material conveyed to the transfer unit by the conveying unit on the upstream side of the transfer unit in the conveying direction of the recording material, and recording toward the transfer unit A guide means having a lower guide member formed of a conductive material disposed on the lower side of the material, and a lower guide member voltage applying means for applying a voltage to the lower guide member, and a conveying direction in the transfer unit When an image is formed on the first recording material whose width in the direction orthogonal to the maximum value at which the toner can be transferred by the transfer portion, the upper guide member There is a recording material in During this time, a voltage having a polarity opposite to the normal charging polarity of the toner is applied from the lower guide member voltage applying means to the lower guide member, and while the recording material is not present on the lower guide member, the lower guide member No voltage is applied from the member voltage application means to the lower guide member or a voltage having the same polarity as the normal charging polarity of the toner is applied, and the width in the direction perpendicular to the transport direction in the transfer unit is greater than the maximum value. When an image is formed on the second recording material having a small value, the recording material exists on the lower guide member while the recording material exists on the lower guide member during rotation of the image carrier. An image forming apparatus characterized by not applying a voltage from the lower guide member voltage applying means to the lower guide member or applying a voltage having the same polarity as the normal charging polarity of the toner. It is subjected.

  According to the present invention, the toner is prevented from adhering to the guide member that guides the recording material to the transfer portion with a simple configuration, and the recording material is soiled by the toner adhering to the guide member adhering to the recording material. Can be prevented.

1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram illustrating the vicinity of a transfer portion of an image forming apparatus according to an embodiment of the present invention. It is a sequence diagram of an image forming operation according to an embodiment of the present invention. FIG. 10 is a sequence diagram of another example of the image forming operation according to the embodiment of the present invention. 1 is a schematic control block diagram of an image forming apparatus according to an embodiment of the present invention. 6 is a schematic diagram illustrating the vicinity of a transfer portion of an image forming apparatus of Comparative Example 1. FIG. 10 is a sequence diagram of an image forming operation according to Comparative Example 2. FIG. FIG. 6 is a schematic diagram illustrating the vicinity of a transfer portion of an image forming apparatus according to another embodiment of the present invention. It is a sequence diagram of an image forming operation according to another embodiment of the present invention. FIG. 6 is a schematic control block diagram of an image forming apparatus according to another embodiment of the present invention. FIG. 10 is a sequence diagram of an image forming operation according to still another embodiment of the present invention. FIG. 11 is a flowchart of processing for selecting a sequence of image forming operations according to the type of recording material in still another embodiment of the present invention. FIG. 10 is a sequence diagram of another example of an image forming operation according to still another embodiment of the present invention.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
1. FIG. 1 is a schematic diagram illustrating a schematic configuration of an image forming apparatus 100 according to the present exemplary embodiment. The image forming apparatus 100 according to the present exemplary embodiment is a laser beam printer using an electrophotographic method.

  The image forming apparatus 100 includes a paper feed tray 11 on which recording paper or the like is stacked as the recording material P. The recording material P loaded on the paper feed tray 11 is separated and conveyed one by one by the paper feed roller 9, passes through a paper feed guide (not shown), and reaches the transport roller (registration roller) 10. To do. The conveyance roller 10 temporarily stops rotating when the recording material P arrives. As a result, the leading edge of the recording material P that has been conveyed follows the position of the registration mechanism, and the skew of the recording material P is corrected. The conveyance roller 10 is a conveyance unit that conveys the recording material P to the transfer unit N.

  Further, the image forming apparatus 100 includes a drum-shaped electrophotographic photosensitive member, that is, the photosensitive drum 1 as a rotatable image carrier that carries a toner image. The photosensitive drum 1 is rotationally driven in the direction of arrow A in the figure by a main motor (not shown) as a driving means. The photosensitive drum 1 has a conductive substrate made of aluminum or the like, and a photosensitive layer made of CGL (charge generation layer) and CTL (charge transport layer) laminated on the conductive substrate. The photosensitive drum 1 in this embodiment has a cylindrical shape with a diameter of 30 mm. By rotating the photosensitive drum 1 at a speed of 150 rpm, the process speed becomes 235.6 mm / sec, and an image can be formed and output on 40 A4-sized recording materials P per minute.

  Note that the maximum value (hereinafter referred to as “maximum usable width”) of the width of the recording material P that can form and output an image in the image forming apparatus 100 of the present embodiment in the direction orthogonal to the transport direction is as follows. It is the width (210 mm) of A4 size at the time of vertical feed (a transport direction in which the longitudinal direction is the transport direction). Further, the image forming apparatus 100 according to the present exemplary embodiment transports the recording material P toward the center in a direction orthogonal to the transport direction.

  A charging roller 2 as a charging unit is disposed in pressure contact with the photosensitive drum 1. The charging roller 2 rotates following the photosensitive drum 1. The surface of the photosensitive drum 1 is uniformly charged by the charging roller 2. During the charging operation, a charging bias that is a DC voltage of the charging polarity (negative polarity in this embodiment) of the photosensitive drum 1 is applied to the charging roller 2 from a charging bias power source (not shown) as charging voltage application means. Is done. Thereafter, a laser beam L corresponding to the image information is irradiated to the photosensitive layer of the charged photosensitive drum 1 from a laser irradiation unit of a laser scanner (exposure apparatus) 3 as an exposure unit, and the photosensitive drum 1 is statically exposed. An electrostatic latent image (electrostatic image) is formed. A developing device 4 as a developing unit is disposed on the downstream side in the rotation direction of the photosensitive drum 1 with respect to the position where the laser beam L is irradiated to the photosensitive layer (exposure portion). The developing device 4 has a developing sleeve that rotates as a developer carrying member, and toner that is a developer is supplied from the developing sleeve to the photosensitive drum 1. When the electrostatic latent image formed on the photosensitive drum 1 comes to a position (developing portion) G facing the developing sleeve of the developing device 4, toner is supplied to the electrostatic latent image from the developing sleeve, and the photosensitive drum A toner image (visible image) is formed on 1. During the developing operation, a developing bias in which a DC component and an AC component are superimposed is applied to the developing sleeve of the developing device 4 from a developing bias power source (not shown) as a developing voltage applying unit. In this embodiment, the developing device 4 has a charged polarity (negative polarity in this embodiment) of the photosensitive drum 1 in a portion (exposed portion) where the charge is attenuated by exposure on the uniformly charged photosensitive drum 1. A toner charged to the same polarity as that of the toner is attached (reversal development).

  On the other hand, the conveyance roller 10 starts rotating at a timing synchronized with the moving speed of the toner image formed on the photosensitive drum 1. Along with the start of the rotation, the recording material P whose skew has been corrected by the registration mechanism is sent out from the transport roller 10 to the pre-transfer guide means 20. The pre-transfer guide unit 20 guides the recording material P conveyed to the transfer unit N by the conveyance roller 10 on the upstream side of the transfer unit N in the conveyance direction of the recording material P. As will be described in detail later, the pre-transfer guide means 20 has a metal plate-shaped pre-transfer upper guide 21 and a pre-transfer lower guide 22. The recording material P reaches the photosensitive drum 1 through a region sandwiched between the pre-transfer upper guide 21 and the pre-transfer lower guide 22.

  When the recording material P reaches the photosensitive drum 1, the toner image on the photosensitive drum 1 is transferred at a transfer portion (transfer nip) N that is a pressure contact portion between the photosensitive drum 1 and the transfer roller 5. The transfer roller 5 is a transfer unit that transfers the toner on the rotating image carrier onto the recording material P at the transfer portion N. During the transfer operation, the transfer roller 5 is supplied with a DC voltage having a polarity opposite to the normal charging polarity (negative polarity in the present embodiment) of the toner from a transfer vice power supply (not shown) as a transfer voltage application unit. A bias is applied. A cleaning device 6 as a cleaning unit is disposed downstream of the transfer unit N in the rotation direction of the photosensitive drum 1. The cleaning device 6 has a cleaning blade that contacts the surface of the photosensitive drum 1 as a cleaning member. By this cleaning blade, the toner (transfer residual toner) remaining on the photosensitive drum 1 after the transfer is scraped off and collected.

  The recording material P onto which the toner image has been transferred passes through a conveyance guide (not shown) and is conveyed to a fixing device 7 as a fixing unit. The fixing device 7 has two rollers that are pressed against each other, and the recording material P is sandwiched and conveyed between the rollers, so that the toner image on the recording material P is transferred to the recording material P by heat and pressure. To melt and fix. Thereafter, the recording material P is discharged to the outside of the image forming apparatus 100 by the paper discharge roller 8, and one printing cycle is completed.

2. Pre-transfer guide means The pre-transfer guide means 20 will be further described. FIG. 2 is a schematic diagram illustrating the vicinity of the transfer portion N of the image forming apparatus 100 according to the present exemplary embodiment.

  In the present embodiment, the pre-transfer guide unit 20 includes a pre-transfer upper guide 21 that is an upper guide member formed of a conductive material disposed on the upper side of the recording material P facing the transfer portion N. The pre-transfer guide unit 20 includes a pre-transfer lower guide 22 that is a lower guide member formed of a conductive material disposed below the recording material P toward the transfer portion N.

  More specifically, the pre-transfer upper guide 21 is a guide member that is disposed above the gravitational direction among the two guide members of the pre-transfer guide means 20 that regulate the moving path of the recording material P. . The pre-transfer upper guide 21 has a length (longitudinal length) along the longitudinal direction (rotation axis direction) of the photosensitive drum 1 and a length along the conveyance direction of the recording material P (short direction length). A plate-like member made of a metal as a conductive material.

  The pre-transfer lower guide 22 is a guide member that is disposed below the gravitational direction among the two guide members of the pre-transfer guide unit 20 that regulate the moving path of the recording material P. The pre-transfer lower guide 22 has a length (longitudinal length) along the longitudinal direction (rotation axis direction) of the photosensitive drum 1 and a length along the conveyance direction of the recording material P (short direction length). A plate-like member made of a metal as a conductive material. In this embodiment, the pre-transfer lower guide 22 constitutes a conductive portion of the pre-transfer guide unit 20 whose potential is changed by applying a voltage.

  The pre-transfer upper guide 21 and the pre-transfer lower guide 22 are disposed to face each other, and form a region through which the recording material P passes therebetween. In this embodiment, the interval between the pre-transfer upper guide 21 and the pre-transfer lower guide 22 is narrowed toward the downstream side in the conveyance direction of the recording material P. This makes it easy to guide the recording material P to the transfer portion N. Further, a portion within a predetermined range from the upstream end in the transport direction of the recording material P of the pre-transfer upper guide 21 and the pre-transfer lower guide 22 becomes closer to the upstream in the transport direction of the recording material P. Each is bent so that it becomes wider. As a result, the recording material P can be easily received in the area sandwiched between the two. Further, the pre-transfer upper guide 21 and the pre-transfer lower guide 22 have their respective ends on the downstream side in the transport direction of the recording material P on the surface of the photosensitive drum 1 so that the recording material P can be properly guided to the transfer portion N. And placed close to each other.

  As shown in FIG. 2, a power source (a pre-transfer lower guide bias power source) 14 as a lower guide member voltage applying unit for applying a voltage to the lower pre-transfer guide 22 is connected to the lower pre-transfer guide 22. A resistor (a pre-transfer lower guide resistor) 13 is connected between the power source 14 and the pre-transfer lower guide 22. This is because when the recording material P absorbs moisture in a high humidity environment and the electrical resistance of the recording material P is low, the current of the lower transfer guide 22 flows into the upper guide 21 before transfer, thereby causing the upper guide 21 before transfer. This is to prevent the toner from adhering due to a change in the potential of the toner. In this embodiment, a resistor 13 having a resistance of 100 MΩ was connected.

  The power source 14 can apply a pre-transfer lower guide bias, which is a DC voltage having a polarity (positive in this embodiment) opposite to the normal charging polarity of the toner, to the lower transfer guide 22.

  As will be described in detail later, in this embodiment, during the rotation of the photosensitive drum 1, while the recording material P exists on the pre-transfer lower guide 22 (on the lower guide member), the regular toner is supplied from the power source 14. A pre-transfer lower guide bias having a polarity opposite to the charging polarity is applied. During the rotation of the photosensitive drum 1, while the recording material P is not present on the pre-transfer lower guide 22, no voltage is applied from the power source 14 to the pre-transfer lower guide 22 or the same as the normal charging polarity of the toner. A polar (negative polarity in this embodiment) voltage is applied. The presence of the recording material P on the pre-transfer lower guide 22 is a range from the upstream end position of the pre-transfer lower guide 22 to the downstream end position in the direction along the conveyance direction of the recording material P. In addition, it means that at least a part of the recording material P exists. Also, the absence of the recording material P on the pre-transfer lower guide 22 means that the position of the downstream end from the position of the upstream end of the pre-transfer lower guide 22 in the direction along the conveyance direction of the recording material P. The recording material P does not exist in the range up to.

3. Application of Voltage to Lower Guide Before Transfer FIG. 3 is a sequence diagram of an image forming operation in this embodiment. Reference numerals given in the sequence of FIG. 3 represent timings described below. FIG. 3 is a sequence diagram of an image forming operation particularly when no voltage is applied from the power source 14 to the pre-transfer lower guide 22 while the recording material P is not present on the pre-transfer lower guide 22.

  As shown in FIG. 3, when the image forming apparatus 100 receives a print signal (T1), the main motor starts rotating (T3). The main motor drives the photosensitive drum 1, and when the main motor starts rotating, the photosensitive drum 1 starts rotating, and when the main motor stops rotating, the rotating of the photosensitive drum 1 stops. At the same time, the polygon motor inside the laser scanner 3 starts to rotate (T5). After the rotation of the polygon motor rises, the recording material P is fed by rotating the paper feed roller 9 (T11). Further, a charging bias is applied to the photosensitive drum 1 via the charging roller 2 (T13). After the photosensitive drum 1 is charged to a constant potential, exposure with a laser is performed according to the image pattern (T7). When the electrostatic latent image formed on the photosensitive drum 1 by laser exposure reaches the developing portion G, a developing bias is applied to the developing sleeve of the developing device 4 (T17), and toner is supplied from the developing sleeve. And developed as a toner image. When the toner image formed on the photosensitive drum 1 reaches the transfer portion N, a transfer bias is applied to the transfer roller 5 (T21), and the toner image is transferred from the photosensitive drum 1 to the recording material P. Is transcribed.

  By the way, when the photosensitive drum 1 rotates, an air flow is generated inside the image forming apparatus 100. The air flow from the developing part G to the transfer part N is indicated by a dotted line in FIG. This air flow is generated by the movement of the air around the photosensitive drum 1 as the photosensitive drum 1 rotates. That is, after the air flow is generated along the photosensitive drum 1 up to the vicinity of the transfer portion N, the air flow is rebounded by the transfer portion N and passes over the pre-transfer guide means 20. Thereafter, the air flow is diffused inside the image forming apparatus 100. At this time, the toner existing on the photosensitive drum between the developing portion G and the transfer portion N is blown off by the air flow and becomes scattered toner, which contaminates the pre-transfer guide means 20. In addition, this toner may get into the inside of the image forming apparatus 100 by riding on the air flow, and may cause problems by entering the laser scanner 3.

  Therefore, in this embodiment, when the leading end of the recording material P in the transport direction reaches the position of the end of the upstream pre-transfer lower guide 22 in the transport direction of the recording material P (T25), the pre-transfer lower guide 22 Application of a lower guide bias before transfer to is started. In this example, a +1 kV DC bias was applied as the pre-transfer lower guide bias. In addition, the application of the pre-transfer lower guide bias to the pre-transfer lower guide 22 is such that the rear end in the conveyance direction of the recording material P passes through the position of the end of the lower pre-transfer guide 22 on the downstream side in the conveyance direction of the recording material P. Is stopped (T26). When the leading end of the next recording material P in the transport direction reaches the position of the upstream end of the pre-transfer lower guide 22 (T27), the application of the pre-transfer lower guide bias to the pre-transfer lower guide 22 is started again. Is done.

  In this way, while the recording material P is present on the pre-transfer lower guide 22, the toner scattered in the vicinity of the transfer portion N is applied before the transfer by applying the pre-transfer lower guide bias having a polarity opposite to that of the toner. It is attracted to the recording material P by the potential of the lower guide 22. As a result, the scattered toner does not contaminate the inside of the image forming apparatus 100, adheres to the recording material P to an inconspicuous extent, and is discharged out of the image forming apparatus 100. Further, while the recording material P is not present on the pre-transfer lower guide 22, the pre-transfer lower guide bias is turned OFF. This prevents toner from adhering to the pre-transfer guide means 20.

  In the sequence of FIG. 3, T8 is the end timing of exposure by the laser when forming an image on the first recording material P. Further, T14 is the application bias application finish timing at the time of image formation on the first recording material P. Also, T18 is the timing for finishing the application of the developing bias when forming an image on the first recording material P. Also, T22 is the timing for ending application of the transfer bias when forming an image on the first recording material P. T2 is the reception timing of a print signal when an image is formed on the second recording material P. T4 is the stop timing of the main motor that has been continuously driven during image formation on a plurality of recording materials P. T6 is the stop timing of the scanner motor that has been continuously driven during image formation on a plurality of recording materials P. T9 and T10 when the second image is formed are the same timing as T7 and T8 when the first image is formed. Also, T12 when the second image is formed is the same timing as T11 when the first image is formed. Also, T15 and T16 when the second image is formed are the same timing as T13 and T14 when the first image is formed. T19 and T20 when the second image is formed are the same timings as T17 and T18 when the first image is formed. Also, T23 and T24 when the second image is formed are the same timing as T21 and T22 when the first image is formed. T28 when the second image is formed is the same timing as T26 when the first image is formed.

  Alternatively, while the recording material P is not present on the pre-transfer lower guide 22, a voltage having the same polarity as the normal charging polarity of the toner (negative polarity in this embodiment) is supplied from the power source 14 to the pre-transfer lower guide 22. May be applied. Thereby, it is possible to further prevent the toner from adhering to the pre-transfer lower guide 22. Further, during this period, even if a voltage having the same polarity as the normal charging polarity of the toner is applied to the pre-transfer lower guide 22, no transfer failure occurs due to the transfer current flowing into the pre-transfer lower guide 22. Further, during this period, since there is no toner image on the photosensitive drum 1, even if a voltage having the same polarity as the normal charging polarity of the toner is applied to the lower guide 22 before transfer, the voltage causes the electrostatic force of the toner. It will be scattered and will not pollute the aircraft.

  FIG. 4 shows a sequence of image forming operations when a voltage having the same polarity as the normal charging polarity of toner is applied from the power source 14 to the lower pre-transfer guide 22 while the recording material P is not present on the lower pre-transfer guide 22. FIG. In the sequence of FIG. 4, the same reference numerals are given to the same timing as that of the sequence shown in FIG. In this case, at T26, the polarity of the voltage applied from the power source 14 to the lower guide 22 before transfer is changed from positive polarity (opposite polarity to the normal charging polarity of the toner) to negative polarity (same polarity as the normal charging polarity of the toner). ). Thereafter, at T27, the polarity is switched again from the negative polarity to the positive polarity.

4). Control Mode FIG. 5 shows a schematic control mode of the image forming apparatus 100 of the present embodiment. In the present embodiment, the operation of the image forming apparatus 100 is comprehensively controlled by the CPU 31 that is a central element of control of the control unit 30 included in the image forming apparatus 100. In connection with the present embodiment, the CPU 31 forms an image for forming a toner image on the recording material P, which includes the photosensitive drum 1, the charging roller 2, the laser scanner 3, the developing device 4, the transfer roller 5, and the like. The means 50 is controlled. Further, the CPU 31 controls the power supply 14 that applies a voltage to the pre-transfer lower guide 22. In accordance with image information sent from the external device 200 such as a personal computer, information instructing image forming conditions such as the type of the recording material P, the CPU 31 follows a program stored in the ROM 32, data stored in the RAM 33, and the like. Control the image forming operation. The CPU 31 is connected to an operation unit 40 provided in the image forming apparatus 100, and information indicating an image forming condition such as information specifying the type of the recording material P is input from the operation unit 40. There is.

  In this embodiment, the power source 14 has a positive voltage output unit as a voltage output unit. The power source 14 has an ON / OFF switch as means for switching ON / OFF of the voltage output from the positive voltage output unit. Then, the CPU 531 controls ON / OFF of voltage application from the power supply 14 to the pre-transfer lower guide 22 according to the above-described sequence. The CPU 31 determines the position of the recording material P based on a signal from a sensor that detects the position of the recording material P provided in the conveyance path of the recording material P, the setting of the conveying operation of the conveying means of the recording material P, and the like. By grasping it, the timing of applying the voltage to the pre-transfer lower guide 22 can be obtained.

  Alternatively, as described above, a voltage having the same polarity as the normal charging polarity of the toner can be applied to the lower pre-transfer guide 22 while the recording material P is not present on the lower pre-transfer guide 22. . In this case, the power supply 14 has a positive voltage output as a first voltage output unit and a negative voltage output unit as a second voltage output unit. Further, in this case, the power supply 14 has a polarity changeover switch as means for switching whether the voltage is output from either the first voltage output unit or the second voltage output unit. The power source 14 has an ON / OFF switch as a means for switching ON / OFF of the voltage output from each of the first and second voltage output units. Then, the CPU 31 controls the switching of the polarity of the voltage applied from the power source 14 to the pre-transfer lower guide 22 and ON / OFF of the voltage application according to the above-described sequence.

5. Evaluation test 5-1. In this example, 500 halftone images with a printing rate of 25% were continuously output using the image forming apparatus 100 of this example. As the recording material P, A4 size paper was used for vertical feeding. As a result, although some contamination due to toner was observed on the pre-transfer upper guide 21, no toner adhered to the pre-transfer lower guide 22, and no contamination due to toner was observed on the output recording material P. .

  Further, the printing pattern was switched to a horizontal line image with a 2% printing rate, and 150,000 sheets were continuously output. As a result, no further contamination of the pre-transfer guide means 20 due to the toner was observed, and other problems due to the toner entering the laser scanner 3 did not occur.

  The above result is a result when the pre-transfer lower guide bias is turned off while the transfer material P is not present on the pre-transfer lower guide 22, but during this period, the pre-transfer lower guide having the same polarity as the toner is used. Similar results were obtained when a bias was applied. When the pre-transfer lower guide bias having the same polarity as the toner is applied during this period, the effect of preventing the toner from adhering to the pre-transfer lower guide 22 tends to be higher.

5-2. Comparative Example 1
In this comparative example, as shown in FIG. 6, the voltage application mechanism to the pre-transfer lower guide 22 is omitted from the image forming apparatus 100 of the first embodiment. For convenience, in this comparative example, elements having functions and configurations corresponding to those of the present embodiment will be described with the same reference numerals.

  Using the image forming apparatus 100 of this comparative example, 500 halftone images with a printing rate of 25% were continuously output as in the case of Example 1. As the recording material P, A4 size paper was used for vertical feeding. As a result, the stain due to the toner occurred at the leading end of the 200th and subsequent recording materials P in the transport direction. When the pre-transfer guide means 20 was observed after the end of continuous output, toner adhesion was observed at the downstream end of the pre-transfer upper guide 21. In this comparative example, since the amount of scattered toner adhering to the pre-transfer upper guide 21 is increased as compared with the case of Example 1, it can be considered that the end portion of the pre-transfer upper guide 21 is contaminated with toner. Then, it is considered that the contamination due to the toner is manifested as the contamination of the recording material P due to the toner by scraping the front end portion of the recording material P in the conveyance direction.

  In the same manner as in Example 1, the print pattern was switched to a horizontal line image with a 2% printing rate, and 150,000 sheets were continuously output. As a result, the density when the halftone image was output again after continuous output was lowered. This is because the amount of scattered toner inside the image forming apparatus 100 increases, so that the scattered toner also enters the laser scanner 3 and contaminates the laser, polygon mirror, etc., and reaches the surface of the photosensitive drum 1. This is thought to be because the exposure amount decreased.

5-3. Comparative Example 2
In this comparative example, the image forming apparatus 100 according to the first embodiment is modified such that the pre-transfer lower guide bias is continuously applied even when the transfer material P does not exist on the pre-transfer lower guide 22. For convenience, in this comparative example, elements having functions and configurations corresponding to those of the present embodiment will be described with the same reference numerals.

  FIG. 7 is a sequence diagram of an image forming operation in this comparative example. In the sequence of FIG. 7, the same reference numerals are given to the same timing as that of the sequence of FIG.

  As shown in FIG. 7, the sequence of the image forming operation in this comparative example is substantially the same as that of the image forming apparatus 100 of the first embodiment. However, in this comparative example, the pre-transfer lower guide bias started to be applied at T25 is continuously applied even when the recording material P is not on the pre-transfer lower guide 22, and the operation of the image forming apparatus 100 (rotation of the main motor). ) Is stopped (T29).

  Using the image forming apparatus 100 of this comparative example, 500 halftone images with a printing rate of 25% were continuously output as in the case of Example 1. As the recording material P, A4 size paper was used for vertical feeding. As a result, the back surface of the recording material P was smeared with toner. When the inside of the image forming apparatus 100 is observed at this time, it is considered that toner is deposited on the downstream end of the pre-transfer lower guide 22 and this toner adheres to the back surface of the recording material P.

6). Effect In this embodiment, while the recording material P is present on the pre-transfer lower guide 22, by applying a pre-transfer lower guide bias having a polarity opposite to that of the toner, the toner scattered in the vicinity of the transfer portion N is It is attracted to the recording material P by the potential of the lower guide 22 before transfer. As a result, the scattered toner does not contaminate the inside of the image forming apparatus 100, adheres to the recording material P to an inconspicuous extent, and is discharged out of the image forming apparatus 100. Since the scattered toner is discharged to the outside of the image forming apparatus 100 one after another by the recording material P, the amount of toner adhering to one recording material P is very small, and there is no practical problem. In this way, the scattered toner is discharged to the outside of the image forming apparatus 100 one after another by the recording material P, so that it is possible to prevent the toner from adhering and accumulating on the pre-transfer lower guide 22. On the other hand, when a voltage having a polarity opposite to the normal charging polarity of the toner is applied to the lower guide 22 before transfer while the recording material P is not present on the lower guide 22 before transfer, the toner is directly attracted to the lower guide 22 before transfer. . As a result, toner accumulates on the pre-transfer lower guide 22, which leads to contamination of the recording material P by the toner. Therefore, in this embodiment, while the recording material P is not present on the pre-transfer lower guide 22, the pre-transfer lower guide bias is turned off or a voltage having the same polarity as the toner is applied. Accordingly, it is possible to prevent the toner from adhering to the pre-transfer guide means 20 and to prevent the recording material P from being contaminated by the toner.

  Here, in order to prevent toner adhesion to the pre-transfer lower guide 22, a voltage having the same polarity as the toner may be applied to the pre-transfer lower guide 22 while the recording material P exists on the pre-transfer lower guide 22. Conceivable. However, when a voltage having the same polarity as the toner is applied to the pre-transfer lower guide 22 as described above, the toner may be scattered by receiving an electrostatic force due to the voltage, and the inside of the apparatus may be contaminated. In particular, there may be problems such as mirror contamination due to toner entering the laser scanner, and image density reduction due to a decrease in the amount of laser light. As described above, according to this embodiment, this is not the case.

Example 2
Another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of this embodiment are the same as those of the first embodiment. Accordingly, elements having the same or corresponding functions and configurations as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, the pre-transfer guide means 20 applies a voltage not only to the pre-transfer lower guide 22 but also to the pre-transfer upper guide 21. That is, in the present embodiment, the pre-transfer upper guide 21 also constitutes a conductive portion whose potential is changed by application of a voltage in the pre-transfer guide means 20. However, in this embodiment, unlike the pre-transfer lower guide 22, a voltage having the same polarity as the normal charging polarity of the toner is applied to the pre-transfer upper guide 21.

  FIG. 8 is a schematic diagram showing the vicinity of the transfer portion N of the image forming apparatus 100 of the present embodiment. As shown in FIG. 8, as in the first embodiment, the lower power guide 22 before transfer is connected to a first power source (lower guide bias power source before transfer) 14 as a lower guide member voltage applying unit. A first resistor (a pre-transfer lower guide resistor) 13 is connected between the first power source 14 and the pre-transfer lower guide 22. In the present embodiment, the pre-transfer upper guide 21 is connected to a second power source (pre-transfer upper guide bias power source) 16 as an upper guide member voltage applying unit for applying a voltage to the pre-transfer upper guide 21. Yes. Further, a second resistor (pre-transfer upper guide resistor) 15 is connected between the second power source 16 and the pre-transfer upper guide 21. Similar to the first resistor 13, the second resistor 15 is for preventing the current of the pre-transfer upper guide 21 from flowing into the pre-transfer lower guide 22. In this embodiment, the second resistor 15 is the second resistor 15. As 15, a 100 MΩ type was connected.

  The second power supply 16 can apply a pre-transfer upper guide bias, which is a DC voltage having the same polarity as the normal charging polarity of toner, to the pre-transfer upper guide 21.

  FIG. 9 is a sequence diagram of the image forming operation in this embodiment. In the sequence of FIG. 9, the same reference numerals are given to the same timing as that of the sequence of FIG.

  As shown in FIG. 9, the sequence of the image forming operation in this embodiment is substantially the same as that of the image forming apparatus 100 of the first embodiment. However, in this embodiment, application of the pre-transfer upper guide bias to the pre-transfer upper guide 21 is started when the operation of the image forming apparatus 100 (rotation of the main motor) is started (T30). In this example, a DC bias of −1 kV was applied as the upper guide bias before transfer. The pre-transfer upper guide bias is continuously applied while the image forming apparatus 100 is operating, and is stopped when the operation of the image forming apparatus 100 (rotation of the main motor) stops (T31).

  As described in the first embodiment, a voltage having the same polarity as the normal charging polarity of the toner may be applied to the pre-transfer lower guide 22 while the recording material P is not present on the pre-transfer lower guide 22. Similarly to the pre-transfer lower guide bias, the pre-transfer upper guide bias may be applied while the transfer material P is present on the pre-transfer lower guide 22 and may not be applied while it is not present. That is, in this embodiment, during the rotation of the photosensitive drum 1, at least as long as the recording material P exists on the pre-transfer lower guide 22, a voltage having the same polarity as the normal charging polarity of the toner is applied to the pre-transfer upper guide 21. Apply. Further, while the photosensitive drum 1 is rotating, a voltage having the same polarity as the normal charging polarity of the toner is applied to the pre-transfer upper guide 21 even when the recording material P is not present on the pre-transfer lower guide 22. You may have a period. Typically, as in the present embodiment, the pre-transfer upper guide bias is applied even when the transfer material P is not present on the pre-transfer lower guide 22, and the image forming apparatus 100 scatters in the meantime. It is possible to better prevent the toner existing on the lower guide 22 before transfer.

  FIG. 10 shows a schematic control mode of the image forming apparatus 100 of the present embodiment. The control mode shown in FIG. 10 is the same as the control mode of the image forming apparatus 100 of the first embodiment shown in FIG. However, in this embodiment, in addition to controlling the first power supply 14 that applies a voltage to the pre-transfer lower guide 22, the second power supply 16 that applies a voltage to the pre-transfer upper guide 21 is controlled.

  In the present embodiment, the second power supply 16 has a negative voltage output unit as a voltage output unit. The second power supply 16 has an ON / OFF switch as means for switching ON / OFF of the voltage output from the negative voltage output unit. Then, the CPU 31 controls ON / OFF of voltage application from the second power supply 16 to the pre-transfer upper guide 21 according to the above-described sequence. The control of the first power supply 14 is the same as the control of the power supply 14 in the first embodiment.

  Using the image forming apparatus 100 of this example, 500 halftone images having a printing rate of 25% were continuously output as in the case of Example 1. As the recording material P, A4 size paper was used for vertical feeding. As a result, the recording material P was not smudged with toner. Further, when the inside of the image forming apparatus 100 was observed, almost no toner was found on the lower guide 22 before transfer and the upper guide 21 before transfer.

  Further, as in Example 1, the print pattern was switched to a horizontal line image with a print rate of 2%, and 150,000 sheets were continuously output. As a result, no further contamination of the pre-transfer guide means 20 due to the toner was observed, and other problems due to the toner entering the laser scanner 3 did not occur.

  The above result is a result when the pre-transfer lower guide bias is turned off while the transfer material P is not present on the pre-transfer lower guide 22, but during this period, the pre-transfer lower guide having the same polarity as the toner is used. Similar results were obtained when a bias was applied. When the pre-transfer lower guide bias having the same polarity as the toner is applied during this period, the effect of preventing the toner from adhering to the pre-transfer lower guide 22 tends to be higher.

  As described above, according to the present embodiment, while the recording material P exists on the pre-transfer lower guide 22, the pre-transfer lower guide bias having a polarity opposite to that of the toner is applied so that the scattered toner is removed. The toner is deposited on P so as not to be noticeable, and is discharged out of image forming apparatus 100. Further, while the recording material P does not exist on the pre-transfer lower guide 22, the toner is prevented from adhering to the pre-transfer guide means 20 by turning off the pre-transfer lower guide bias. In this embodiment, a voltage having the same polarity as that of the toner is applied to the pre-transfer upper guide 21 in order to prevent the toner from adhering to the pre-transfer upper guide 21. Thus, even when a voltage having the same polarity as the toner is applied to the pre-transfer upper guide 21, while the recording material P exists on the pre-transfer lower guide 22, the scattered toner is recorded by the potential of the pre-transfer lower guide 22. Attracted to P. For this reason, the toner is scattered by receiving the electrostatic force due to the voltage having the same polarity as the toner, and the inside of the apparatus is not contaminated, and effectively works to prevent the toner from adhering to the pre-transfer upper guide 21. The resistors 13 and 15 prevent current from flowing from the pre-transfer upper guide 21 to the pre-transfer lower guide 22. In this embodiment, even when the recording material P is not present on the pre-transfer lower guide 22, the toner having the same polarity as the toner is applied to the pre-transfer upper guide 21, thereby supplying the toner to the pre-transfer upper guide 21. Can be better prevented. During this period, there is no toner image on the photosensitive drum 1. Therefore, even if a voltage having the same polarity as the toner is applied to the upper guide 21 before transfer, the toner is scattered by electrostatic force due to the voltage, and the inside of the apparatus is not contaminated. Works effectively to prevent adhesion.

Example 3
Another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the second embodiment. Accordingly, elements having the same or corresponding functions and configurations as those of the image forming apparatus of the second embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In the present embodiment, as in the second embodiment, a voltage can be applied to the pre-transfer upper guide 21 and the pre-transfer lower guide 22 in the pre-transfer guide unit 20. In this embodiment, however, the voltage applied to the pre-transfer lower guide 22 passes through the pre-transfer guide means 20 in other words, according to the size of the recording material P used for forming and outputting an image. It is changed according to the size of the recording material P.

  More specifically, the image forming apparatus 100 according to the present exemplary embodiment can form and output images on a plurality of types of recording materials P having different widths in the direction orthogonal to the conveyance direction in the image forming apparatus 100.

  As described above, the maximum usable width of the image forming apparatus 100 according to the present exemplary embodiment is the width (210 mm) at the time of A4 size vertical feeding. Further, the image forming apparatus 100 according to the present exemplary embodiment transports the recording material P toward the center in a direction orthogonal to the transport direction. Therefore, when using a recording material P having a width narrower than the maximum usable width (for example, longitudinal feeding of A5 size paper, postcard, envelope, etc.), when the recording material P exists on the lower guide 22 before transfer. In addition, an area outside the width of the recording material P on the surface of the lower recording guide 22 on the recording material P side is exposed.

  Therefore, in this embodiment, when the recording material P whose width is smaller than the maximum usable width is used as the recording material P, the pre-transfer lower guide bias is not applied to the pre-transfer lower guide 22.

  That is, when the width of the recording material P is narrower than the maximum usable width and the lower guide bias before transfer is applied as in the first or second embodiment, the recording material P adheres to the recording material P having the maximum usable width and is out of the machine. The scattered toner to be discharged may adhere to the pre-transfer lower guide 22. Then, when a recording material P having a larger width (for example, the recording material P having the maximum usable width) is used, the toner of the lower guide 22 before transfer adheres to the end in the width direction of the recording material P. Sometimes. Therefore, in this embodiment, as described above, when the recording material P having a width smaller than the maximum usable width is used, the pre-transfer lower guide bias is not applied.

  FIG. 11 is a sequence diagram of the image forming operation when the recording material P having a width smaller than the maximum usable width is used. In the sequence of FIG. 11, the same reference numerals are given to the same timing as that of the sequence shown in FIG.

  As shown in FIG. 11, the sequence of the image forming operation in this case is substantially the same as that of the image forming apparatus 100 of the second embodiment. However, this embodiment is different from the second embodiment in that the pre-transfer lower guide bias is not applied to the pre-transfer lower guide 22.

  FIG. 12 shows a schematic flow of a process of selecting a voltage application mode for the pre-transfer guide unit 20 during the image forming operation according to the type of the recording material P. When receiving the print signal, the CPU 31 of the control unit 30 reads a signal indicating the type of the recording material P input from the operation unit 40 or the external device 200 (step 1), and the recording material P to be used has a maximum usable width. It is determined whether or not the recording material P is (step 2). If it is determined that the recording material P has the maximum usable width, the image forming operation is started according to the sequence shown in FIG. 9 (applying the lower guide bias before transfer and the upper guide bias before transfer) (step 3). On the other hand, when it is determined that the recording material P has a width narrower than the maximum usable width, the image forming operation is started according to the sequence shown in FIG. 11 (only the upper guide bias before transfer is applied) (step 4).

  The control mode of the image forming apparatus 100 of the present embodiment is the same as the control mode of the image forming apparatus 100 of the first embodiment shown in FIG. However, in this embodiment, the CPU 31 executes a process of selecting an image forming operation sequence depending on the type of the recording material P as shown in FIG.

  Alternatively, when the recording material P having a width smaller than the maximum usable width is used, a voltage having the same polarity as the normal charging polarity of the toner may be applied as the lower guide bias before transfer. FIG. 13 is a sequence diagram of the image forming operation in that case. In the sequence of FIG. 13, the same reference numerals are given to the same timing as that of the sequence of FIG. In the example of FIG. 13, when the operation of the image forming apparatus 100 (rotation of the main motor) starts, application of the pre-transfer upper guide bias having the same polarity as the normal charging polarity of the toner to the pre-transfer lower guide 21 is started. (T32). For example, a DC bias of −1 kV can be applied as the pre-transfer lower guide bias. The pre-transfer lower guide bias is continuously applied while the image forming apparatus 100 is operating, and is stopped when the operation of the image forming apparatus 100 (rotation of the main motor) stops (T33). The pre-transfer lower guide bias having the same polarity as the normal charging polarity of the toner applied to the pre-transfer lower guide 22 is transferred onto the transfer material P on the pre-transfer lower guide 22 in the same manner as shown in FIG. The voltage may be applied while it is present and may not be applied while it is not present.

  Using the image forming apparatus 100 of the present embodiment, as a recording material (second recording material) P having a width smaller than the maximum usable width, A5 size paper is vertically fed (a conveyance method in which the longitudinal direction is the conveyance direction). ), 500 halftone images with a printing rate of 25% were continuously output. As a result, the contamination by the toner on the pre-transfer guide means 20 was not noticeable. After that, as the recording material (first recording material) P having the maximum usable width, A4 size paper was used for vertical feeding (conveying method in which the longitudinal direction is the conveying direction) and an image was output. The material P was not soiled by the toner.

  This is thought to be due to the following usage. That is, when the recording material P having a width smaller than the maximum usable width is used, since the width of the printing area on the photosensitive drum 1 is narrow, the amount of scattered toner is relatively reduced. Therefore, when the recording material P having a width smaller than the maximum usable width is used, it is considered that the contamination due to the toner inside the image forming apparatus 100 can be reduced to some extent without applying the lower guide bias before transfer.

  The above results are the results when the lower guide bias before transfer is turned off when the recording material P having a width smaller than the maximum usable width is used. Similar results were obtained even when a polar voltage was applied. When the pre-transfer lower guide bias having the same polarity as the toner is applied, the effect of preventing the toner from adhering to the pre-transfer lower guide 22 tends to be higher.

  As described above, in this embodiment, when an image is formed on the first recording material in which the width in the direction orthogonal to the conveyance direction in the transfer unit N is the maximum value at which the toner can be transferred by the transfer unit N. The image formation is performed in the same sequence as described in the first and second embodiments. On the other hand, when an image is formed on the second recording material in which the width in the direction perpendicular to the transport direction in the transfer portion N is smaller than the maximum value, the following is performed. That is, during the rotation of the photosensitive drum 1, both the recording material P is present on the pre-transfer lower guide 22 and the recording material P is not present on the pre-transfer lower guide 22. No voltage is applied, or a voltage having the same polarity as the normal charging polarity of the toner is applied. As a result, when an image is formed on the recording material P having the maximum usable width, the pre-transfer lower guide bias having the reverse polarity to the toner and the pre-transfer upper guide bias having the same polarity as the toner are applied to the pre-transfer guide unit 20. Toner adhesion can be prevented. On the other hand, when an image is formed on a recording material P having a width smaller than the maximum usable width, the amount of scattered toner is relatively small, so the lower guide bias before transfer is set to OFF or the same polarity as the toner. The toner is prevented from being actively attracted to the exposed portion of the pre-transfer lower guide 22.

  In this embodiment, when the recording material P having the maximum usable width is not used as the recording material P, the lower guide bias before transfer is not applied. However, the present invention is not limited to such an embodiment, and when a recording material P having a predetermined width or less narrower than the maximum usable width is used, the pre-transfer lower guide bias may not be applied. Good.

  Further, in this embodiment, the present embodiment is applied in a configuration in which an upper guide bias before transfer can be applied as in the second embodiment. As a result, toner adhesion to the pre-transfer upper guide 21 can be prevented better. However, if desired, the present embodiment may be applied to a configuration in which only the pre-transfer lower guide bias can be applied as in the first embodiment.

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Charging roller 3 Laser scanner 4 Developing device 5 Transfer roller 6 Cleaning device 10 Conveyance roller (registration roller)
14 Pre-transfer lower guide bias power supply (first power supply)
16 Pre-transfer upper guide bias power supply (second power supply)
20 Pre-transfer guide means 21 Pre-transfer upper guide 22 Pre-transfer lower guide

Claims (6)

A rotatable image carrier that carries toner, a transfer unit that transfers toner on the rotating image carrier to a recording material in a transfer unit, a conveyance unit that conveys the recording material to the transfer unit, and the conveyance Guide means for guiding the recording material conveyed to the transfer unit by means on the upstream side of the transfer unit in the conveyance direction of the recording material, and a conductive material disposed below the recording material toward the transfer unit A guide means having a lower guide member formed by: and a lower guide member voltage applying means for applying a voltage to the lower guide member,
While the image carrier is rotating, while the recording material is present on the lower guide member, a voltage having a polarity opposite to the normal charging polarity of the toner is applied to the lower guide member from the lower guide member voltage applying unit. While the recording material is not present on the lower guide member, no voltage is applied to the lower guide member from the lower guide member voltage application means or a voltage having the same polarity as the normal charging polarity of the toner is applied. An image forming apparatus. The guide means further includes an upper guide member formed of a conductive material disposed on the upper side of the recording material facing the transfer portion, and the image forming apparatus further includes an upper guide for applying a voltage to the upper guide member. Having a member voltage applying means,
During the rotation of the image carrier, at least as long as the recording material exists on the lower guide member, a voltage having the same polarity as the normal charging polarity of the toner is applied to the upper guide member from the upper guide member voltage applying unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is applied.   Further, during the rotation of the image carrier, while the recording material is not present on the lower guide member, the upper guide member voltage application means applies the same polarity as the normal charging polarity of the toner to the upper guide member. The image forming apparatus according to claim 2, further comprising a period for applying a voltage. A rotatable image carrier that carries toner, a transfer unit that transfers toner on the rotating image carrier to a recording material in a transfer unit, a conveyance unit that conveys the recording material to the transfer unit, and the conveyance Guide means for guiding the recording material conveyed to the transfer unit by means on the upstream side of the transfer unit in the conveyance direction of the recording material, and a conductive material disposed below the recording material toward the transfer unit A guide means having a lower guide member formed by: and a lower guide member voltage applying means for applying a voltage to the lower guide member,
When an image is formed on the first recording material in which the width in the direction perpendicular to the transport direction in the transfer unit is the maximum value at which the transfer unit can transfer toner, While the recording material is present on the lower guide member, a voltage having a polarity opposite to the normal charging polarity of the toner is applied from the lower guide member voltage applying means to the lower guide member. In the absence of the recording material, a voltage is not applied from the lower guide member voltage application means to the lower guide member or a voltage having the same polarity as the normal charging polarity of the toner is applied.
When an image is formed on the second recording material in which the width in the direction perpendicular to the conveyance direction in the transfer unit is smaller than the maximum value, the lower guide member is rotated while the image carrier is rotating. No voltage is applied from the lower guide member voltage applying means to the lower guide member or during the normal charging polarity of the toner both during the presence of the recording material and on the lower guide member An image forming apparatus that applies a voltage having the same polarity as that of the image forming apparatus. The guide means further includes an upper guide member formed of a conductive material disposed on the upper side of the recording material facing the transfer portion, and the image forming apparatus further includes an upper guide for applying a voltage to the upper guide member. Having a member voltage applying means,
During the rotation of the image carrier, at least as long as the recording material exists on the lower guide member, a voltage having the same polarity as the normal charging polarity of the toner is applied to the upper guide member from the upper guide member voltage applying unit. The image forming apparatus according to claim 4, wherein the image forming apparatus is applied.   Further, during the rotation of the image carrier, while the recording material is not present on the lower guide member, the upper guide member voltage application means applies the same polarity as the normal charging polarity of the toner to the upper guide member. The image forming apparatus according to claim 5, further comprising a period during which a voltage is applied.

Images