JP2011048264A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus that more reliably prevents the occurrence of soiling in a back surface of paper. <P>SOLUTION: The image forming apparatus includes: an image carrier; an image forming section for forming, on the image carrier, a transfer toner image which is transferred to the paper and a between-sheets toner image which is not transferred to the paper; a transfer member which is arranged to form a transfer nip section with the image carrier and to which transfer bias is applied so that the transfer toner image is transferred to the paper when the paper is passed by the transfer nip section; a pre-transfer guide which is arranged in the vicinity of the transfer nip section and guides the paper to the transfer nip section; a measuring means for measuring electrical resistance of the paper; and a control section (29) for adjusting the period at which the between-sheets image reaches the transfer nip section based on the electrical resistance of the paper that is measured by the measuring means. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine and a printer using an electrophotographic method, and in particular, an image forming method in which a toner image formed on an image carrier is transferred to a sheet via an intermediate transfer member. It relates to the device.

  Conventionally, in color image forming apparatuses such as copying machines and printers using an electrophotographic method, toner images of cyan, magenta, yellow and black formed on a photosensitive drum are once superimposed on an intermediate transfer member other than paper. The color toner image is formed on the intermediate transfer member by sequential transfer (primary transfer) together, and finally the color toner image formed on the intermediate transfer member is collectively transferred to the paper to perform secondary transfer. Some are configured to form an image.

In the image forming apparatus configured as described above, when performing calibration such as image density, a correction patch image for each color is formed on the intermediate transfer member, and the correction patch image for each color is formed. Is detected by the detecting means. Then, image forming conditions such as a developing bias are corrected according to the detection result (see, for example, Patent Document 1).
Then, the correction patch image formed on the intermediate transfer member is removed from the intermediate transfer member by a predetermined cleaning method without being transferred onto the sheet, and the calibration is completed.

Incidentally, the secondary transfer process of transferring a toner image onto a sheet in an electrophotographic system is an important process for determining the quality of an image formed on the sheet. In this process, in order to perform optimal image formation, it is necessary to properly convey the sheet to a predetermined secondary transfer position.
Therefore, in order to guide the paper transported from the registration roller pair to the secondary transfer position to a better position, a pre-transfer guide that guides the paper upstream of the secondary transfer position is arranged, so that high secondary transfer is achieved. An image forming apparatus that ensures performance is known (for example, see Patent Document 2).

In the image forming apparatus disclosed in Patent Document 2, in order to guide the conveyed paper to a better secondary transfer position, the gap between the leading end of the pre-transfer guide and the intermediate transfer member is 0.5 mm. It is desirable to set it to a degree.
However, when the distance between the leading edge of the pre-transfer guide and the intermediate transfer member becomes small in this way, the toner of the correction patch image formed on the intermediate transfer member at the time of the above-mentioned calibration is transferred to the pre-transfer guide. In such a case, the toner adheres to the back surface of the paper conveyed during the image forming operation, and the back surface of the paper is soiled.

Therefore, in the image forming apparatus disclosed in Patent Document 3, a notch is provided at the leading edge of the pre-transfer guide on the downstream side in the sheet conveyance direction. The position of the notch is matched with the correction patch image forming position, thereby preventing the toner of the correction patch image from adhering to the pre-transfer guide.
According to this image forming apparatus, it is considered that the occurrence of stains on the back side of the sheet is surely prevented.

JP 2006-17911 A Japanese Laid-Open Patent Publication No. 2001-159836 JP 2008-26533 A

However, when a notch portion is formed in the pre-transfer guide, streaky stains may occur on the sheet corresponding to the notch portion depending on the type and state of the sheet.
The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an image forming apparatus in which the occurrence of stains on the back side of a sheet can be more reliably prevented.

  In order to achieve the above object, the present inventors have made various studies. As a result of this study, it was found that the charging of the guide before transfer, which is the cause of the backside contamination of the paper, has a correlation with the electrical resistance of the paper. The inventors have made further studies based on this knowledge, and based on the electrical resistance of the paper, by adjusting the time when the inter-paper toner image reaches the transfer nip, The present inventors have found that this is prevented and have come up with the present invention.

  Thus, in order to achieve the above object, according to one aspect of the present invention, an image carrier, and a transfer toner image transferred to paper and a paper-to-paper toner image not transferred to paper on the image carrier. An image forming portion to be formed and a transfer nip portion are formed together with the image carrier, and transfer is performed so that the transfer toner image is transferred to the paper when the paper passes through the transfer nip portion. A transfer member to which a bias is applied; a pre-transfer guide that is disposed in the vicinity of the transfer nip portion and guides the paper to the transfer nip portion; a measuring unit that measures an electric resistance of the paper; and the measuring unit An image forming apparatus comprising: a control device that adjusts a time at which the inter-paper toner image reaches the transfer nip portion based on the measured electric resistance of the paper. ).

According to the image forming apparatus of the first aspect, the control device determines the time when the inter-paper toner image reaches the transfer nip portion based on the electric resistance of the paper, thereby preventing the back side of the paper from being stained.
The higher the electrical resistance of the paper, the easier it is to charge the pre-transfer guide by sliding contact with the pre-transfer guide. The charged pre-transfer guide is easily contaminated with an inter-sheet toner image, and the pre-transfer guide stain adheres to the back surface of the paper to cause back contamination.

  In this image forming apparatus, the timing at which the inter-sheet toner image reaches the transfer nip is determined according to the electrical resistance of the paper, so the pre-transfer guide is charged or the pre-transfer guide is charged. When it is easy, the inter-paper toner image is prevented from passing near the pre-transfer guide. This prevents the pre-transfer guide from being soiled by the inter-paper donor image, thereby preventing the back of the paper from being soiled.

Preferably, the control device does not cause the image forming unit to form the inter-sheet toner image when the electric resistance of the paper measured by the measuring unit is higher than a threshold value.
According to the image forming apparatus of the present invention, when the electrical resistance is higher than the threshold value, the inter-paper toner image is not formed. Therefore, the pre-transfer guide due to the inter-paper toner image is reliably prevented and the back of the paper is stained. Is reliably prevented.

Preferably, when the electric resistance of the paper measured by the measuring unit is higher than a threshold value, the control unit passes the transfer nip part and then the inter-paper toner image on the transfer nip part. The time interval until the arrival of is extended (claim 3).
According to the image forming apparatus of the third aspect, the time interval from when the sheet passes near the pre-transfer guide to when the inter-sheet toner image reaches the vicinity of the pre-transfer guide is extended. Accordingly, even if the pre-transfer guide is slidably charged with the paper and charged, the time required for the pre-transfer guide to discharge is ensured before the inter-sheet toner image reaches the vicinity of the pre-transfer guide. As a result, while the inter-paper toner image is formed, the pre-transfer guide is prevented from being stained and the back of the paper is prevented from being stained.

Preferably, the measurement means includes a pair of volume resistance measurement electrodes for sandwiching the paper in the thickness direction and measuring the volume resistance of the paper.
According to the image forming apparatus of the fourth aspect, the volume resistance is measured as the electric resistance of the sheet by the pair of electrodes sandwiching the sheet in the thickness direction. By using the volume resistance as the electric resistance, the charging of the pre-transfer guide is reliably predicted, so the timing for the inter-sheet toner image to reach the transfer nip portion is accurately determined. As a result, the pre-transfer guide is reliably prevented from being soiled and the back surface of the paper is reliably prevented from being soiled.

Preferably, the pair of volume measuring electrodes is a pair of rollers that sandwich the paper.
According to the image forming apparatus of the fifth aspect, since the electrode is made of a roller, the electric resistance of the paper is measured with a simple configuration.

  According to the present invention, there is provided an image forming apparatus in which the occurrence of contamination on the back side of a sheet can be prevented more reliably.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a partial enlarged cross-sectional view schematically showing a periphery of a secondary transfer position (transfer nip portion) of the image forming apparatus shown in FIG. 1. FIG. 2 is a block diagram illustrating a functional configuration of a control device included in the image forming apparatus illustrated in FIG. 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present invention. Here, a four-drum tandem color image forming apparatus is shown. FIG. 2 is an enlarged schematic configuration diagram showing the periphery of the secondary transfer position of the image forming apparatus shown in FIG.

  As shown in FIG. 1, a paper feed unit 2 such as a paper feed cassette that accommodates a stack of stacked paper P is provided at the bottom of the image forming apparatus 1. A separation feeding unit 3 for feeding the stacked sheets P one by one from the uppermost sheet is provided at one end of the sheet feeding unit 2. A sheet conveying path 5 extending upward and reaching the discharge tray 4 formed on the upper surface of the main body is formed in the upper part of the separation feeding unit 3.

  Then, along this sheet conveying path 5, in order from the upstream in the sheet conveying direction, the separating roller unit 3, the conveying roller 6, and a conveying roller pair 8 comprising a conveying roller 7 that is pressed against and rotated by the conveying roller 6, A registration roller pair 11 composed of a driving roller 9 and a driven roller 10 that is in pressure contact with the driving roller 9 and is driven to rotate, a pre-transfer guide 12, a transfer roller 13, a fixing roller pair 14, and a paper discharge roller pair 15 are disposed.

  An intermediate transfer belt 16 as an image carrier is rotatably disposed on the right side of the transfer roller 13 in FIG. The intermediate transfer belt 16 is stretched between a driving belt roller 17 and a driven belt roller 18, and is driven to rotate clockwise in FIG. 1 by the driving belt roller 17.

  The drive belt roller 17 is in contact with a transfer roller 13 as a transfer member via the intermediate transfer belt 16, and this contact portion is a secondary transfer position, that is, a transfer nip portion. In addition, a sheet made of dielectric resin is used for the intermediate transfer belt 16, and a belt in which both end portions are overlapped and joined to each other to form an endless shape, or a belt without a seam (seamless) is preferably used.

  Below the intermediate transfer belt 16, four image forming units 20C, 20M, 20Y and 20K are arranged in the order from the right side in FIG. These image forming units 20C to 20K are provided corresponding to images of four different colors (cyan, magenta, yellow, and black), and cyan, magenta, and yellow are respectively performed by charging, exposure, development, and transfer processes. And a black image are sequentially formed.

These image forming units 20C to 20K have photosensitive drums 21C, 21M, 21Y and 21K for carrying visible images (toner images) of the respective colors, and the photosensitive drums 21C to 21K are rotatably arranged. ing.
Around each of the photosensitive drums 21C to 21K, a charger 22 for charging the photosensitive drums 21C to 21K, a developing unit 23 for forming a toner image on the photosensitive drums 21C to 21K, and the photosensitive drums 21C to 21K. A cleaning unit 24 that removes the developer remaining on the surface, and an intermediate transfer roller 25 that is in contact with the photosensitive drums 21C to 21K via the intermediate transfer belt 16 are disposed. Further, an optical scanning device 26 that exposes image information to each of the photosensitive drums 21C to 21K is disposed below the photosensitive drums 21C to 21K.

In the vicinity of the driven belt roller 18, a belt cleaning unit 28 for removing a toner image that has not been transferred to the paper P is disposed. The belt cleaning unit 28 is located between the transfer nip portion and the image forming portion 20 </ b> C when viewed in the rotational direction of the intermediate transfer belt 16.
The image forming apparatus 1 is provided with a control device 29 that performs integrated control of the entire image forming apparatus 1.

  Next, an image forming operation by the image forming apparatus 1 configured as described above will be described. When the start of image formation is input by the user, first, the photosensitive drums 21C to 21K are rotationally driven, whereby the surface of the photosensitive drums 21C to 21K is uniformly charged by the charger 22. Next, a light beam is irradiated by the optical scanning device 26 based on the input image signal, and electrostatic latent images corresponding to the image signal are formed on the photosensitive drums 21C to 21K.

  Then, cyan, magenta, yellow, and black developers filled from a replenishing device (not shown) are supplied to the photosensitive drums 21C to 21K to form a toner image corresponding to the electrostatic latent image. The After an electric field is applied to the intermediate transfer belt 16 at a predetermined transfer voltage, cyan, magenta, yellow, and black toner images on the photosensitive drums 21C to 21K are transferred onto the intermediate transfer belt 16 by the intermediate transfer roller 25. Is done.

  These four color images are formed with a predetermined positional relationship predetermined for forming a predetermined full-color image. Thereafter, the developer remaining on the surfaces of the photosensitive drums 21 </ b> C to 21 </ b> K is removed by the cleaning unit 24 in preparation for the subsequent formation of a new electrostatic latent image.

When the intermediate transfer belt 16 starts to rotate clockwise as the drive belt roller 17 is rotated by a drive motor (not shown), the paper P is conveyed from the registration roller pair 11 to the transfer nip portion at a predetermined timing. The full color image is transferred from the intermediate transfer belt 16 to the paper P at the transfer nip portion.
Then, the paper P onto which the toner image has been transferred is conveyed to the fixing roller pair 14 and heated and pressurized by the fixing roller pair 14 to fix the toner image on the surface of the paper P, thereby forming a predetermined full color image. . The paper P on which the full color image is formed is discharged to the discharge tray 4 by the discharge roller pair 15.

  Here, a portion surrounded by a broken line in FIG. The transport unit 30 is a unit in which the transport roller 7, the drive roller 9, the pre-transfer guide 12, and the transfer roller 13 described above are unitized.

  As shown in FIG. 2, the transport unit 30 has transport guide surfaces 31 a and 31 b that define a part of the paper transport path 5. The drive roller 9 and the transfer roller 13 are rotatably supported in order from the bottom above the conveyance guide surface 31b and below the conveyance guide surface 31a. The drive roller 9 and the transfer roller 13 are rotated by a driving force from the outside. Driven.

Further, a pre-transfer guide 12 made of, for example, resin is disposed in the transport unit 30 between the driving roller 9 and the transfer roller 13. The pre-transfer guide 12 is disposed so as to face the conveyance guide 32 with the paper conveyance path 5 interposed therebetween.
The pre-transfer guide 12 and the conveyance guide 32 guide the paper P conveyed from the registration roller pair 11 to the secondary transfer position to a better position. Specifically, the distance between the leading end of the pre-transfer guide 12 on the downstream side in the sheet conveyance direction and the intermediate transfer belt 16 is maintained at around 0.5 mm.

  Note that the pre-transfer guide 12 is swingably supported by the transport unit 30 so that an excessive load is not applied to the paper when a thick thick paper or the like is used as the paper P.

Next, a calibration operation in the image forming apparatus 1 will be described.
The calibration operation can be performed immediately after activation of the image forming apparatus 1, at the time of printing standby, before and after printing, and when printing is continuously performed on a plurality of sheets P, during printing. Further, the calibration operation is not limited to one time, and may be repeatedly executed regularly or irregularly.

  In the calibration operation, in the case of the tandem-type full-color image forming apparatus 1 as described above, a patchwork-like correction toner image (correction patch image) is formed on the intermediate transfer belt 16, and the correction toner image is formed. By detecting the amount and position of the toner, density correction and color misregistration correction are performed. That is, in FIGS. 1A and 1B, each of the image forming units 20C to 20K forms correction toner images of cyan, magenta, yellow, and black on the intermediate transfer belt 16, and is upstream of the secondary transfer position shown in FIG. A correction toner image is detected by the image detection device 19 disposed on the side, and density and color misregistration correction is performed.

  More specifically, the image detection device 19 includes, for example, a light source and a photodetector. The light source irradiates a predetermined position on the intermediate transfer belt 16 with measurement light, and the photodetector reflects the toner image on the intermediate transfer belt 16. Receives measurement light.

  When calibration is started, a correction toner image is formed on the photosensitive drums 21C to 21K by the same process as the image forming operation described above. The formed toner image is transferred to a predetermined position on the intermediate transfer belt 16 by the intermediate transfer roller 25, and cyan, magenta, yellow, and black correction toner images are formed.

  The image detecting device 19 detects the density of the correction toner image on the intermediate transfer belt 16 and compares the detected density with a predetermined reference density. Based on the comparison result, the developing bias of the charger 22 and the exposure amount of the optical scanning device 26 are adjusted, whereby density correction is performed for each color.

  The correction toner image includes a geometric pattern, and the image detection device 19 detects the position of the geometric pattern on the intermediate transfer belt 16. Then, the detected position is compared with a predetermined reference position, and the timing of the optical scanning device 26 is adjusted based on the comparison result. By this timing adjustment, color misregistration correction is performed for each color.

  Note that the sheet P is not passed through the transfer nip portion while the correction toner image passes through the transfer nip portion. For this reason, the correction toner image reaches the belt cleaning unit 28 without being secondarily transferred to the paper P. The correction toner image is removed from the intermediate transfer belt 16 by the belt cleaning unit 28, and a series of calibration operations is completed.

The above-described image forming operation and cleaning operation are controlled by the control device 29.
Therefore, from the viewpoint of function, the control device 29 has a transfer belt rotation speed control unit 291, a sheet conveyance speed control unit 292, a development bias control unit 293, a primary transfer bias control unit 294, a secondary transfer bias control unit 295, An optical scanning device control unit 296 and an image detection device control unit 297 are provided.

  Here, since the paper P is not passed to the transfer nip portion during the calibration operation, the interval between the front end of the pre-transfer guide 12 and the intermediate transfer belt 16 is set to be as small as about 0.5 mm. The toner of the correction toner image formed on the intermediate transfer belt 16 may be transferred to the pre-transfer guide 12. The toner transferred to the pre-transfer guide 12 then adheres to the back surface of the paper P that passes through the pre-transfer guide 12 and causes the back surface of the paper P to become dirty.

In particular, when performing a calibration operation during an image forming operation (printing operation) during continuous printing, when the previous paper P passes, the paper P and the pre-transfer guide 12 rub against each other for transfer. The front guide 12 is charged, and the correction toner image is easily transferred to the pre-transfer guide 12 due to static electricity. Therefore, in this case, the back stain is likely to occur on the paper P that passes next to the vicinity of the pre-transfer guide 12.
In order to avoid the occurrence of such back stains, in the present embodiment, the image forming apparatus 1 includes an electrical resistance measuring device 40 as means for measuring the electrical resistance of the paper P.

  The electrical resistance measuring device 40 uses the transport roller 6 and the transport roller 7 of the transport roller pair 8 as a pair of electrodes for measurement. In order to impart conductivity to the transport roller 6 and the transport roller 7, the transport roller 6 and the transport roller 7 are made of, for example, a metal or a conductive resin material containing a conductive agent.

  The control device 29 has an electrical resistance measurement device control unit 298 for controlling the electrical resistance measurement device 40. Under the control of the electrical resistance measuring device control unit 298, the electrical resistance measuring device 40 applies a voltage or current between the transport roller 6 and the transport roller 7 when the paper P passes through the transport roller pair 8. The electric resistance (volume resistance) in the thickness direction of the paper P is measured. The measured electrical resistance of the paper P is input to the electrical resistance device control unit 298.

  Based on the electrical resistance of the input paper P, the control device 29 determines the time for the correction toner image to reach the transfer nip portion, and operates the image forming apparatus 1 based on this determination. That is, the control device 29 adjusts the time when the correction toner image reaches the transfer nip portion based on the input electric resistance of the paper P.

  As a preferred aspect, in this embodiment, when the electric resistance of the paper P is higher than the threshold value, the calibration operation is stopped so that the correction toner image does not reach the transfer nip portion during continuous printing.

However, the threshold varies depending on the configuration of the image forming apparatus 1. For this reason, the threshold is preferably set for each image forming apparatus 1 as follows.
First, a paper P1 that easily causes back stain and a paper P2 that hardly causes back stain are prepared. These paper P1 and paper P2 are, for example, a high resistance resistivity meter (Hiresta UP MCP-HT450, manufactured by Mitsubishi Chemical Analytech Co., Ltd., UR, in an environment with a temperature of 26.6 degrees and a humidity of 53.6%. A volume resistance measured using a probe, a conductive table, and an applied voltage of 500 V) can be used as follows.
Volume resistance of paper P1: 2.2 × 10 ¹¹ [Ω · cm]
Volume resistance of paper P2: 6.3 × 10 ¹⁰ [Ω · cm]

Then, the electrical resistance of the paper P1 and the electrical resistance of the paper P2 are actually measured by the image forming apparatus 1. Then, a threshold value is set to an intermediate value between the electrical resistance of the paper P1 and the electrical resistance of the paper P2, and is stored in the control device 29.
According to the threshold value thus set, when printing is performed on the paper P1 in the image forming apparatus 1, the measured value of the electrical resistance of the paper P1 becomes higher than the threshold value, so the image forming apparatus 1 performs the calibration operation. No correction toner image is formed.
On the other hand, when printing is performed on the paper P2 in the image forming apparatus 1, the measured value of the electrical resistance of the paper P2 becomes lower than the threshold value, so that the image forming apparatus 1 appropriately performs the calibration operation.

  Here, in the case of continuous printing, the correction toner image passes through the vicinity of the pre-transfer guide 12 and the transfer nip portion between the previous paper P and the subsequent paper P. Therefore, in this specification, the calibration operation ( The correction toner image formed in the calibration mode) is also referred to as an inter-sheet toner image. On the other hand, the toner image transferred to the paper P is also referred to as a transfer toner image.

  In the image forming apparatus 1, in order to discharge the old developer in the developing unit 23, an unnecessary toner image is formed on the intermediate transfer belt 16 with the discharged developer, and unnecessary toner is formed in the belt cleaning unit 28. A refresh operation (refresh mode) for collecting an image may also be performed. The inter-paper toner image in this specification includes an unnecessary toner image during the refresh operation.

According to the image forming apparatus 1 of the embodiment described above, the control device 29 determines the time when the inter-sheet toner image reaches the transfer nip portion based on the electric resistance of the paper P.
The higher the electrical resistance of the paper P, the easier it is to charge the pre-transfer guide 12 by sliding contact with the pre-transfer guide 12. The charged pre-transfer guide 12 is easily contaminated with the inter-sheet toner image, and the pre-transfer guide 12 adheres to the back surface of the paper P, causing back stain.

  In this image forming apparatus 1, the timing at which the inter-sheet toner image reaches the transfer nip portion is determined according to the electric resistance of the paper P. Therefore, when the pre-transfer guide 12 is charged, or the pre-transfer guide When the toner 12 is easily charged, the toner image between the sheets is prevented from passing near the pre-transfer guide 12. As a result, the pre-transfer guide 12 is prevented from being soiled by the inter-paper donor image, so that the back surface of the paper P is prevented from being soiled.

  According to the image forming apparatus 1 of the embodiment described above, when the electric resistance of the paper P is higher than the threshold value, the calibration operation is not performed and the inter-paper toner image is not formed. The guide before transfer is reliably prevented from being stained, and the back side of the paper P is reliably prevented from being stained.

  Further, according to the image forming apparatus 1 of the above-described embodiment, the volume resistance as the electric resistance of the paper P is measured by a pair of electrodes that sandwich the paper P in the thickness direction. By using the volume resistance as the electric resistance, the charging of the pre-transfer guide 12 is reliably predicted, and therefore the time when the inter-paper toner image reaches the transfer nip portion is accurately determined. As a result, the pre-transfer guide 12 is reliably prevented from being stained, and the back side of the paper P is reliably prevented from being stained.

  Furthermore, according to the image forming apparatus 1 of the above-described embodiment, since the electrode for measuring the electrical resistance of the paper P includes the transport roller 6 and the transport roller 7, the electrical resistance of the paper P can be reduced with a simple configuration. Measured.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention.
According to the image forming apparatus 1 of the embodiment described above, when the electric resistance of the paper P is higher than the threshold value, the time when the inter-paper toner image is not formed and the inter-paper toner image reaches the transfer nip portion is as follows. Although it was postponed without limiting the time limit, it may be postponed with a limited time limit. That is, when the electrical resistance of the paper P is higher than the threshold value, the time interval from when the paper P passes through the transfer nip portion until the inter-paper toner image reaches the transfer nip portion is extended for a predetermined period. It's okay.

  By extending the time interval, even if the pre-transfer guide 12 is slidably charged with the paper P and charged, the time required for the pre-transfer guide 12 to discharge until the inter-paper toner image reaches the vicinity of the pre-transfer guide 12 is secured. Is done. As a result, while the inter-paper toner image is formed, the pre-transfer guide 12 is prevented from being stained and the back side of the paper P is prevented from being stained.

  In order to extend the time interval until the inter-paper toner image reaches the transfer nip portion by a predetermined period, for example, the rotational speed of the intermediate transfer belt 16 may be decreased. Alternatively, the spatial interval between the toner image transferred to the paper P and the inter-paper toner image on the intermediate transfer belt 16 may be increased. When the rotation speed of the intermediate transfer belt 16 is changed, the conveyance speed of the paper P is also changed.

  In the image forming apparatus 1 according to the embodiment described above, the transport roller 6 and the transport roller 7 of the transport roller pair 8 constitute electrodes. However, the pair of rollers of the feeding unit 3 or the pair of registration rollers 11 The drive roller 9 and the driven roller 10 may constitute an electrode. Alternatively, apart from the existing rollers, a roller pair as electrodes for sandwiching the paper P in the thickness direction may be further provided.

  In the above-described embodiment, the image forming apparatus 1 using the endless intermediate transfer belt 16 as the intermediate transfer member (image carrier) has been described. However, the present invention is not limited to the intermediate transfer belt. The present invention can also be applied to an image forming apparatus using a transfer drum. In addition, the image forming apparatus 1 using four color developers of yellow, magenta, cyan, and black has been described in order to obtain a full color image. However, the present invention forms an image having a color material having a different hue. It can also be used for an apparatus or an image forming apparatus having a different number of colors.

Finally, in the above-described embodiment, a color image forming apparatus is described as the image forming apparatus 1. However, the present invention can also be applied to an image forming apparatus such as a copying machine or a facsimile machine. is there.
The present invention has been described above with specific embodiments. However, the present invention is not limited to these descriptions, and a configuration obtained by appropriately combining configurations described as different embodiments is also a technique of the present invention. A configuration obtained by appropriately combining a conventionally known technique with the configuration obtained in this manner is also included in the technical scope of the present invention.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 6 Conveyance roller (electrical resistance measuring means)
7 Transport roller (electrical resistance measuring means)
8 Conveying roller pair 9 Driving roller 10 Driven roller 11 Registration roller pair 12 Pre-transfer guide 13 Transfer roller 16 Intermediate transfer belt (image carrier)
17 drive belt roller 18 driven belt roller 19 image detection device 29 control device 30 transport unit 40 electrical resistance measuring device (electrical resistance measuring means)
P paper

Claims (5)

An image carrier;
On the image carrier, an image forming unit that forms a transfer toner image transferred to a sheet and an inter-sheet toner image not transferred to the sheet;
A transfer member that is disposed so as to form a transfer nip portion together with the image carrier, and to which a transfer bias is applied so that the transfer toner image is transferred to the paper when the paper passes through the transfer nip portion. When,
A pre-transfer guide that is disposed in the vicinity of the transfer nip portion and guides the paper to the transfer nip portion;
Measuring means for measuring the electrical resistance of the paper;
An image forming apparatus comprising: a control device that adjusts a time at which the inter-paper toner image reaches the transfer nip portion based on an electric resistance of the paper measured by the measuring unit. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the controller does not form the inter-sheet toner image on the image forming unit when the electric resistance of the sheet measured by the measuring unit is higher than a threshold value. The image forming apparatus according to claim 1.
When the electrical resistance of the paper measured by the measuring unit is higher than a threshold value, the control unit reaches the transfer-to-paper toner image after the paper has passed through the transfer nip. An image forming apparatus characterized in that the time interval until is extended. The image forming apparatus according to any one of claims 1 to 3,
The image forming apparatus characterized in that the measuring means has a pair of volume resistance measuring electrodes for sandwiching the sheet in the thickness direction and measuring the volume resistance of the sheet. The image forming apparatus according to claim 4.
2. The image forming apparatus according to claim 1, wherein the pair of volume measuring electrodes is a pair of rollers that sandwich the sheet.

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