JP5745385B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus.

  In an electrophotographic image forming apparatus, a recording sheet on which a toner image is transferred is conveyed to a fixing unit, and the recording sheet is heated and pressurized by the fixing unit to fix the toner image on the recording sheet (Patent Document 1 below). reference). Fluorine-based resin is generally used for the pressure member and heating member (member that contacts the recording paper) in the fixing unit, and this fluorine-based resin is a material that is negatively charged by friction with the recording paper. .

JP-A-10-31369

  By the way, the triboelectric chargeability of the pressure member and the heating member in the fixing unit is very high in the initial state (the state in which the fluororesin is not worn), and as the number of fixing processes (number of sheets) on the recording paper increases ( That is, as the number of recording paper passes increases, the surface gradually decreases as the fluororesin surface wears. For this reason, at the beginning of use of the fixing unit, static electricity accumulated in the pressure member and the heating member is transferred to the recording paper, and the recording paper is relatively strongly charged to negative polarity. Further, in the case of double-sided image formation in which one sheet of recording paper passes through the fixing unit twice, the negative charge amount on the recording sheet increases. Furthermore, when using positive toner, a negative transfer bias is used to transfer the toner image onto the recording paper, so the negative charge amount on the recording paper further increases.

  In order to eliminate the charging of the recording paper due to the transfer bias, the image forming apparatus is generally provided with a static eliminator that neutralizes the charge on the recording paper. The static eliminator is designed to eliminate static electricity transferred from the fixing unit to the recording paper. Since this is not a consideration, the charge on the recording paper cannot be sufficiently removed. When a charged recording sheet is transported along a predetermined transport path (passing path), for example, the sheet passing to the fixing unit becomes unstable due to adsorption to a metallic guide provided in the passing path. As a result, the recording paper is wrinkled or the recording paper is jammed.

  The present invention has been made in view of the above-described circumstances, and an object of the present invention is to effectively suppress the charging of the recording paper due to the fixing process and stabilize the conveyance of the recording paper.

  In order to achieve the above object, in the present invention, as a first solving means, an image forming means for forming a toner image on a recording paper, a fixing means for fixing the toner image on the recording paper, and a recording that has passed through the fixing means. An image forming apparatus comprising: a counting unit that counts the number of sheets; and a discharging unit that is provided in a passage path of the recording sheet and discharges the recording sheet by using a discharging bias. A means is provided that includes a control means for reducing the charge elimination bias as the number of sheets increases.

  In the present invention, as the second solving means, in the first solving means, the control means decreases the static elimination bias in steps each time the number of recording sheets counted by the counting means reaches a predetermined number. Is adopted.

  In the present invention, as a third solving means, in the first or second solving means, the image forming means forms a toner image on the image carrier using positive polarity toner, and the toner image is converted to negative polarity. The transfer bias is transferred to the recording paper, and the discharging means employs a means for supplying a positive discharging bias to the recording paper.

  In the present invention, as the fourth solving means, in any one of the first to third solving means, the fixing means adopts a means that a contact surface that contacts the recording paper is formed of a fluorine-based material. To do.

  In the present invention, as a fifth solution, in any one of the first to fourth solutions, a toner image is formed on the front surface, and a toner image is separately formed on the back surface of the recording paper that has passed through the fixing device. A means for providing a double-sided image forming function is employed.

  According to the present invention, the number of recording sheets that have passed through the fixing unit is counted, and the neutralization bias is decreased as the counted number of recording sheets increases. That is, according to the present invention, when the number of recording sheets that have passed through the fixing unit is small and the fixing unit is easily charged, the neutralizing bias for neutralizing the recording sheet is increased to improve the neutralizing capability, while the fixing unit is fixed. When the number of recording papers passing through the means is large and the fixing means is difficult to be charged, the static elimination bias for neutralizing the recording paper is reduced to lower the static elimination capability. According to the present invention, since the charge removal capability is changed by changing the magnitude of the charge removal bias in accordance with the chargeability of the fixing unit, it is possible to effectively suppress charging of the recording paper due to the fixing process. Therefore, it is possible to stabilize the conveyance of the recording paper.

1 is a functional block diagram illustrating an overall configuration of a multifunction peripheral A according to an embodiment of the present invention. In one embodiment of the present invention, a characteristic diagram (a) showing the current value of the static elimination bias according to the number of recording papers P that have passed through the fixing roller 51, and the transportability of the recording paper P according to changes in the fixing counts. It is an experimental result (b) which verified the relationship with the electric current value of static elimination bias.

Embodiments of the present invention will be described below with reference to the drawings.
The multifunction peripheral A according to the present embodiment is a color-type image forming apparatus that forms a color image based on an electrophotographic system. As shown in FIG. 1, an operation display unit 1, an image reading unit 2, an image data storage unit Unit 3, image forming unit 4, communication unit 5 and calculation control unit 6. The arithmetic control unit 6 is a control means in the present embodiment.

  The operation display unit 1 includes operation keys and a touch panel, and functions as a man-machine interface that associates the user with the multifunction peripheral A. The operation display unit 1 outputs a user operation instruction for an operation key or an operation button displayed on the touch panel to the calculation control unit 6 as an operation signal, and various operations are performed on the touch panel based on a control signal input from the calculation control unit 6. Display information of.

  The image reading unit 2 is a surface image of a document automatically fed by an ADF (Automatic document feeder) or a document placed on a platen glass based on a control signal input from the arithmetic control unit 6. The (original image) is read by the line sensor and converted into original image data, and the original image data is output to the image data storage unit 3.

  The image data storage unit 3 is a semiconductor memory, a hard disk device, or the like. Based on a control signal input from the arithmetic control unit 6, original image data, print image data and communication received by the communication unit 5 from an external client computer The unit 5 stores facsimile image data received from an external facsimile machine, reads out the image data based on a control signal input from the arithmetic control unit 6, and outputs it to the image forming unit 4.

  The image forming unit 4 forms a toner image based on the image data read from the image data storage unit 3 on the recording paper P taken out from the paper feed cassette 45 based on a control signal input from the arithmetic control unit 6. It is. The image forming unit 4 includes a belt roller 41, an intermediate transfer belt 42, four image forming units 43Y, 43C, 43M, 43K corresponding to toner colors (Y, M, C, K), primary transfer rollers 44Y, 44C, 44M, 44K, paper feed cassette 45, pick-up roller 46, transport roller 47, registration roller 48, secondary transfer roller 49, separation static elimination unit 50, fixing roller 51, paper discharge roller 52, paper discharge tray 53, reverse roller 54, a branch guide 55, three pairs of reversing paper conveyance rollers 56, and a recording paper sensor 57. Note that the belt roller 41 to the secondary transfer roller 49 constitute an image forming unit in the present embodiment. The fixing roller 51 is a fixing unit in the present embodiment. Further, the separation / elimination unit 50 is a neutralization unit in the present embodiment.

  As shown in the figure, the belt roller 41 includes three rollers that are spaced apart from each other, that is, a driving roller 41a, a driven roller 41b, and a tension roller 41c. That is, the driving roller 41a and the driven roller 41b are arranged at a certain distance in the horizontal direction, and the tension roller 41c is arranged at a position slightly displaced upward between the driving roller 41a and the driven roller 41b. ing. The intermediate transfer belt 42 is an endless belt stretched around such a belt roller 41 (drive roller 41a, driven roller 41b, tension roller 41c), and travels in a direction indicated by an arrow by the drive roller 41a.

  That is, the intermediate transfer belt 42 runs in the horizontal direction between the driving roller 41a and the driven roller 41b. The driving roller 41a described above is a roller in which a motor that generates a driving force is axially coupled, and causes the intermediate transfer belt 42 to travel in the direction of the arrow by the power of the motor. The driven roller 41b is a free roller provided so as to freely rotate, and guides the intermediate transfer belt 42 according to the power of the drive roller 41a. Further, the tension roller 41c is a roller that is provided with a rotating shaft so as to be movable, and applies a certain tension (tension) to the intermediate transfer belt 42 by pressing the intermediate transfer belt 42 with a predetermined adjusting force.

  As shown in the figure, the image forming units 43Y, 43C, 43M, and 43K are provided at predetermined intervals in the horizontal running portion of the intermediate transfer belt 42 described above. Of these image forming units 43Y, 43C, 43M, and 43K, the image forming unit 43Y is a unit that forms a yellow (Y) toner image, and is provided at a position closest to the driven roller 41b. The image forming unit 43C is a unit that forms a cyan (C) toner image, and is provided at a position close to the driven roller 41b next to the image forming unit 43Y. The image forming unit 43M is a unit for forming a magenta (M) toner image, and is provided at a position near the driven roller 41b next to the image forming unit 43C. The image forming unit 43K is a unit that forms a black (K) toner image, and is provided at a position closest to the drive roller 41a.

  Such image forming units 43Y, 43C, 43M, and 43K each include photosensitive drums ay, ac, am, and ak, charging portions by, bc, bm, and bk, laser scanning units cy, cc, cm, and ck, and development. The units dy, dc, dm, dk and the cleaners ey, ec, em, ek are constituent elements.

  That is, the image forming unit 43Y includes a photosensitive drum ay, a charging unit by, a laser scanning unit cy, a developing unit dy, and a cleaner ey. The image forming unit 43C includes a photosensitive drum ac, a charging unit bc, and a laser scanning unit. cc, a developing unit dc, and a cleaner ec. The image forming unit 43M includes a photosensitive drum am, a charging unit bm, a laser scanning unit cm, a developing unit dm, and a cleaner em. The image forming unit 43K is a photosensitive member. It comprises a drum ak, a charging unit bk, a laser scanning unit ck, a developing unit dk, and a cleaner ek.

  Each of the photosensitive drums ay, ac, am, and ak is a cylindrical member having a peripheral surface formed of a predetermined photosensitive material (for example, amorphous silicon). Each charging unit by, bc, bm, bk uniformly charges the peripheral surface (photosensitive surface) of each photosensitive drum ay, ac, am, ak. Each laser scanning unit cy, cc, cm, ck forms an electrostatic latent image on the photosensitive surface by irradiating the charged photosensitive surface with laser light.

  Each of the developing units dy, dc, dm, and dk contains a predetermined amount of toner (positive toner) inside and supplies the toner to the photosensitive surface, thereby generating an electrostatic latent image formed on the photosensitive surface. Develop as a toner image. Each of the cleaners ey, ec, em, and ek scrapes and removes toner (residual toner) remaining on the photosensitive surface after the toner image is transferred.

  As shown in the figure, four primary transfer rollers 44Y, 44C, 44M, and 44K are provided corresponding to the image forming units 43Y, 43C, 43M, and 43K, and each intermediate transfer belt 42 is sandwiched between each. Opposite to the photosensitive drums ay, ac, am, ak of the image forming units 43Y, 43C, 43M, 43K. A negative primary transfer bias (high voltage) is applied to each primary transfer roller 44Y, 44C, 44M, 44K, and each primary transfer roller 44Y, 44C, 44M, 44K The toner images of the respective colors respectively formed on the photosensitive drums ay, ac, am, and ak of the image forming units 43Y, 43C, 43M, and 43K are transferred (primary transfer) to the intermediate transfer belt 42 by the action of the transfer bias.

  The paper feed cassette 45 is a container for storing a plurality of recording papers P having a predetermined shape such as A4 size and B5 size. The pickup roller 46 is a roller that is provided in pressure contact with the recording paper P in the upper part of the paper feeding cassette 45, takes out the recording paper P in the paper feeding cassette 45 one by one, and sends it out to the transport roller 47. The transport roller 47 is a roller that transports the recording paper P fed from the pickup roller 46 toward the registration roller 48. The registration roller 48 is a roller that supplies the recording paper P supplied from the transport roller 47 to the secondary transfer roller 49 at a predetermined timing.

  The secondary transfer roller 49 is a roller disposed opposite to the driving roller 41a with the intermediate transfer belt 42 interposed therebetween, and transfers the toner image on the intermediate transfer belt 42 to the recording paper P (secondary transfer). A negative secondary transfer bias (high voltage) is applied to the secondary transfer roller 49, and the secondary transfer roller 49 applies the toner image on the intermediate transfer belt 42 by the action of the secondary transfer bias. Transfer (secondary transfer) to the recording paper P.

  The separation charge removal unit 50 supplies a positive charge removal bias toward the recording paper P based on a control signal input from the arithmetic control unit 6. This neutralizing bias is for neutralizing the charging of the recording paper P to make it non-charged, and for improving the separation of the recording paper P from the secondary transfer roller 49. The separation / neutralization unit 50 has a sawtooth electrode made of stainless steel, and an electric field is formed from the tip of the sawtooth electrode so that the recording paper P is discharged.

  The fixing roller 51 includes a heating roller 51a provided with a heater therein, and a pressure roller 51b that is in pressure contact with the heating roller 51a. The fixing roller 51 heats and presses the recording paper P by sandwiching the recording paper P onto which the toner image of each color is transferred by the heating roller 51a and the pressure roller 51b, and the toner image of each color is placed on the recording paper P. To settle. The heating roller 51a and the pressure roller 51b are formed of a fluorine-based material in which a contact surface (surface) that contacts the recording paper P is negatively charged by friction. That is, the surfaces of the heating roller 51a and the pressure roller 51b are negatively charged due to friction with the recording paper P.

  The paper discharge roller 52 is a roller that conveys the recording paper P conveyed from the fixing roller 51 and guided by the branch guide 55 toward the paper discharge tray 53. The paper discharge tray 53 is a storage unit that stores and holds the recording paper P supplied from the paper discharge roller 52. The reverse roller 54 is a roller for switchback transporting the recording paper P that is transported from the fixing roller 51 and guided by the branch guide 55. That is, the reversing roller 54 sandwiches the recording paper P supplied from the fixing roller 51 by rotating forward, and transports the recording paper P toward the reversing paper transporting roller 56 by reversing in the sandwiched state.

  The branch guide 55 selectively switches the transport destination of the recording paper P discharged from the fixing roller 51 to the paper discharge roller 52 or the reverse roller 54 based on a control signal input from the arithmetic control unit 6. In other words, when the recording paper P is discharged to the paper discharge tray 53, the branch guide 55 takes the transporting destination of the recording paper P as the discharge roller by adopting the first posture (the posture of the dotted line shown in FIG. 1). On the other hand, the conveyance destination of the recording paper P is switched to the reversing roller 54 by adopting the second posture (solid line posture shown in FIG. 1).

  The reverse paper transport roller 56 is a roller provided in a transport path (reverse path) for transporting the recording paper P supplied from the reverse roller 54 toward the registration roller 48. As shown in the figure, the reversing paper conveyance rollers 56 are provided at three locations separated in the reversing path. The recording paper sensor 57 is disposed between the fixing roller 51 and the branch guide 55, detects the number of recording papers P that have passed through the fixing roller 51, and outputs a detection signal indicating the number to the arithmetic control unit 6.

  Here, in the double-sided image formation in which the toner image is formed on the front surface and the back surface of the recording paper P, the reversing roller 54, the branch guide 55, and the reversing paper transport roller 56 function to fix the fixing roller in the front surface image formation. The recording paper P that has passed 51 is supplied again to the registration roller 48 in a state where the front surface and the back surface are reversed, and image formation on the back surface of the recording paper P is performed.

  The communication unit 5 communicates with an external multifunction peripheral or facsimile apparatus via a telephone line on the basis of a control signal input from the arithmetic control unit 6, and with a client computer or the like via a LAN (Local Area Network). It communicates. That is, the communication unit 5 has a communication function compliant with a facsimile standard such as G3 and a communication function compliant with a LAN standard such as Ethernet (registered trademark).

  The arithmetic control unit 6 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and an interface circuit that transmits / receives various signals to / from each electrically connected unit. . The arithmetic control unit 6 performs various arithmetic processes based on the control program stored in the ROM and controls the overall operation of the multifunction peripheral A by communicating with each unit.

  As will be described in detail later, the arithmetic control unit 6 drives the separation / neutralization unit 50 according to the number of recording papers P as a part of the above various arithmetic processings to determine the current value of the static elimination bias to be supplied to the recording papers P. adjust. That is, the arithmetic control unit 6 counts the number of recording sheets P that have passed through the fixing roller based on the detection signal input from the recording sheet sensor 57, and the neutralization bias increases as the counted number of recording sheets P increases. Decrease. Note that such an arithmetic control unit 6 constitutes the counting means in the present embodiment together with the recording paper sensor 57.

Next, the operation of the MFP A configured as described above will be described.
First, the overall operation of the multifunction machine A will be described. For example, when the user sets a document on the ADF and operates the operation display unit 1 to instruct copying of the document onto one side of the recording paper P, an instruction signal related to the instruction is arithmetically controlled from the operation display unit 1. Input to unit 6. As a result, the arithmetic control unit 6 causes the image reading unit 2 to sequentially read the document image for each page of the document and stores the document image data of the document image in the image data storage unit 3. Then, the arithmetic control unit 6 generates bitmap image data corresponding to each toner color based on the document image data, and performs image forming processing of the document image on the image forming unit 4 based on the bitmap image data. Let it run.

  In other words, the arithmetic control unit 6 drives the pickup roller 46 to take out the recording paper P in the paper feed cassette 45 one by one and sends it to the transport roller 47 and drives the transport roller 47 to register the recording paper P. It is conveyed toward the roller 50. The arithmetic control unit 6 drives the driving roller 41a to bring the intermediate transfer belt 42 into a running state and drives the image forming units 43Y, 43M, 43C, and 43K, based on the above-described bitmap image data. Thus, a toner image composed of positive polarity toner of each color is formed on the photosensitive surface (circumferential surface) of each photosensitive drum 43a. The arithmetic control unit 6 applies the negative primary transfer bias to the primary transfer rollers 44Y, 44M, 44C, and 44K, thereby transferring the toner images on the photosensitive drums 43a onto the intermediate transfer belt 42. Next transfer.

  The arithmetic control unit 6 drives the registration roller 50 in synchronization with the image formation processing timing of each color in the image forming units 43Y, 43M, 43C, and 43K, and causes the secondary transfer roller 51 to have a negative secondary transfer bias ( The toner value (original image) on the intermediate transfer belt 42 is secondarily transferred to a desired position on the recording paper P by applying a current value of 60 μA). Then, the arithmetic control unit 6 causes the separation / neutralization unit 50 to use a positive neutralization bias to neutralize the recording paper P, drive the fixing roller 52, and switch the branch guide 55 to the first posture. Then, the recording paper P is conveyed toward the paper discharge roller 53. Then, the arithmetic control unit 6 drives the paper discharge roller 53 to discharge the recording paper P to the paper discharge tray 53.

  On the other hand, when the user gives an instruction to copy (copy) the original on both sides of the recording paper P, the arithmetic control unit 6 proceeds with the processing until the fixing roller 52 is driven in the same manner as the above processing, and thereafter Different processing. In other words, the arithmetic control unit 6 drives the fixing roller 52 and transports the recording paper P toward the reversing roller 54 by switching the branch guide 55 to the second posture (solid line posture shown in FIG. 1). . The arithmetic control unit 6 rotates the reversing roller 54 forward for a predetermined time and then switches the branch guide 55 to the first posture (the dotted posture shown in FIG. 1) and reversely rotates the reversing roller 54. The recording paper P is transported toward the reverse paper transporting roller 56. Then, the arithmetic control unit 6 drives the reversal paper conveyance roller 56 to convey the recording paper P toward the registration roller 48.

  Further, the arithmetic control unit 6 forms a toner image composed of positive polarity toner of each color on the photosensitive surface of each photosensitive drum 43a. The arithmetic control unit 6 applies the negative primary transfer bias to the primary transfer rollers 44Y, 44M, 44C, and 44K, thereby transferring the toner images on the photosensitive drums 43a onto the intermediate transfer belt 42. Next transfer. The arithmetic control unit 6 applies the negative primary transfer bias to the primary transfer rollers 44Y, 44M, 44C, and 44K, thereby transferring the toner images on the photosensitive drums 43a onto the intermediate transfer belt 42. Next transfer.

  The arithmetic control unit 6 drives the registration roller 50 in synchronization with the image formation processing timing of each color in the image forming units 43Y, 43M, 43C, and 43K, and causes the secondary transfer roller 51 to have a negative secondary transfer bias ( The toner image on the intermediate transfer belt 42 is secondarily transferred to a desired position on the back surface of the recording paper P by applying a current value of 60 μA). Then, the arithmetic control unit 6 drives the fixing roller 52 while causing the separation and neutralization unit 50 to use the positive neutralization bias to supply the recording paper P while neutralizing it, and also brings the branch guide 55 into the first posture. By switching, the recording paper P is conveyed toward the paper discharge roller 53. Then, the arithmetic control unit 6 drives the paper discharge roller 53 to discharge the recording paper P to the paper discharge tray 54.

  Here, the arithmetic control unit 6 performs the following characteristic processing when the image forming unit 4 performs the image forming process. That is, the arithmetic control unit 6 reduces the static elimination bias in a stepwise manner every time the number of recording sheets P that have passed through the fixing roller 51 reaches a predetermined number. For example, as shown in FIG. 2A, the arithmetic control unit 6 sets the current value of the static elimination bias to 5 μA when the number of recording sheets P passing through the fixing roller 51 is 0 to 200, It is set to 4 μA between 201 and 400, 3 μA between 401 and 600, 2 μA between 601 and 800, and 801 and above. Set to 1 μA.

  That is, the arithmetic control unit 6 controls the separation / neutralization unit 50 so that the current value of the neutralization bias is decreased stepwise every time the number of recording sheets P that have passed through the fixing roller 51 increases by 200 sheets. In this way, by reducing the current value of the static elimination bias in accordance with the increase in the number of sheets of recording paper P that pass through the fixing roller 51, the charging of the recording paper P due to the charging of the fixing roller 51 can be effectively suppressed. Is possible.

  FIG. 2B shows an experimental result in which the relationship between the transportability of the recording paper P and the current value of the neutralization bias according to the change in the fixing count (the number of recording papers P that have passed through the fixing roller 51) is shown. Yes. As shown in FIG. 2B, when the fixing count is 0, JAM and wrinkles are generated when the current value is 1 μA and 2 μA, and the conveyance is performed when the current value is 3 μA and 10 μA. It is unstable but free of JAM and wrinkles, and when the current value is 4 μA, 5 μA, and 7 μA, the conveyance is good. When the fixing count is 1000 sheets, the conveyance is good when the current is 1 μA to 5 μA, and when the current value is 7 μA or 10 μA, the conveyance is unstable but there is no JAM or wrinkle.

  In addition, when the fixing count is 100,000 sheets, the conveyance is good when the current value is 1 μA to 3 μA, and when the current value is 4 μA, the conveyance is unstable but there is no JAM or wrinkle, When the current value is 5 μA, 7 μA, or 10 μA, JAM or wrinkles are generated. That is, the charge transferred from the fixing roller 51 during image formation on the recording paper P is eliminated from the recording paper P by reducing the neutralization bias as the number of recording papers P that have passed through the fixing roller 51 increases. The conveyance of the recording paper P can be stabilized.

  That is, the control calculation unit 6 counts the number of recording sheets P that have passed through the fixing roller 51, and decreases the neutralization bias as the counted number of recording sheets P increases. That is, when the number of recording sheets P that have passed through the fixing roller 51 is small and static electricity is likely to be generated in the fixing roller 51, the control calculation unit 6 increases the static elimination bias supplied to the recording sheet P, while fixing. When the number of recording papers P that have passed through the roller 51 is large and static electricity is unlikely to be generated in the fixing roller 51, the static elimination bias supplied to the recording paper P is reduced.

  According to the present embodiment, by changing the magnitude of the static elimination bias according to the charging property of the fixing roller 51, the charge transferred from the fixing roller 51 together with the charge charged during transfer is effectively transferred from the recording paper P. Since neutralization can be performed, the conveyance of the recording paper P can be stabilized.

As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment, For example, the following modifications can be considered.
(1) In the above embodiment, the neutralization bias is decreased step by step by 200 sheets, but the present invention is not limited to this. For example, the interval may be smaller than 200 sheets (for example, 100 sheets each), or may be larger than 200 sheets (for example, 300 sheets each). In the above embodiment, the current value of the secondary transfer bias is 60 μA. However, if the current value of the secondary transfer bias is lower than 60 μA, the current value of the static elimination bias is set lower than the set value. When the current value of the secondary transfer bias is higher than 60 μA, stable conveyance of the recording paper P may be realized by setting the current value of the static elimination bias higher than the set value.

(2) Although the roller-type fixing roller 51 is employed in the above embodiment, the present invention is not limited to this. For example, the present invention may be applied to an image forming apparatus in which a fixing belt method or an IH method is used instead of the roller method as a toner fixing method.

(3) In the above-described embodiment, the separation and neutralization unit 50 supplies the positive neutralization bias to the recording paper P, but the present invention is not limited to this. For example, the contact surface of the fixing roller 51 that is in contact with the recording paper P is formed of a positively charged material, and the toner images formed on the photosensitive drums ay, am, ac, and ak using the negative polarity toner are positive electrodes. In an image forming apparatus in which a toner image is transferred from the intermediate transfer belt 42 to the recording paper P using a positive secondary transfer bias and then transferred to the recording paper P using a positive primary transfer bias. The neutralization unit 50 may neutralize the positive charge charged on the recording paper P by using a negative neutralization bias.

(4) In the above embodiment, the fixing roller 51 has the contact surfaces of the heating roller 51a and the pressure roller 51b that are in contact with the recording paper P made of a fluorine-based material. The present invention may be applied to an image forming apparatus using a material that is electrically charged.

  A ... MFP (image forming apparatus), 1 ... operation display unit, 2 ... image reading unit, 3 ... image data storage unit, 4 ... image forming unit, 5 ... communication unit, 6 ... arithmetic control unit (control means, count) Means), 41a, 41b, 41c ... belt roller, 42 ... intermediate transfer belt, 43Y, 43C, 43M, 43K ... image forming unit, 44Y, 44M, 44C, 44K ... primary transfer roller, 45 ... paper feed cassette, 46 DESCRIPTION OF SYMBOLS ... Pick-up roller, 47 ... Conveyance roller, 48 ... Registration roller, 49 ... Secondary transfer roller, 50 ... Separation static elimination part (static elimination means), 51 ... Fixing roller (fixing means), 52 ... Discharge roller, 53 ... Discharge Tray, 54 ... reversing roller, 55 ... branch guide, 56 ... reversing paper transport roller, 57 ... recording paper sensor (counting means), ay, am, ac, ak ... photoconductor drum , By, bm, bc, bk ... charging unit, cy, cm, cc, ck ... laser scanning unit, dy, dm, dc, dk ... developing unit, ey, em, ec, ek ... cleaner, 51a ... heating roller, 51b ... Pressure roller, P ... Recording paper

Claims (4)

Image forming means for forming a toner image on a recording paper, a fixing roller for fixing the toner image on the recording paper, a counting means for counting the number of recording papers that have passed through the fixing roller , and a passage route for the recording paper An image forming apparatus comprising: a discharging unit that discharges the recording paper using a discharging bias.
Control means for decreasing the static elimination bias as the cumulative number from the initial state of the recording paper counted by the counting means increases,
The contact surface of the fixing roller with the recording paper is formed of a material that is negatively charged by friction,
The image forming unit forms a toner image on an image carrier using positive polarity toner, and transfers the toner image onto the recording paper using a negative polarity transfer bias.
The image forming apparatus according to claim 1, wherein the charge removing unit removes charge by supplying a positive charge removing bias to the recording paper .   2. The image forming apparatus according to claim 1, wherein the control unit reduces the static elimination bias in a stepwise manner every time the number of the recording sheets counted by the counting unit reaches a predetermined number. 3. The image forming apparatus according to claim 1 , wherein a contact surface of the fixing roller that contacts the recording paper is formed of a fluorine-based material . 4. The image forming apparatus according to claim 1 , further comprising a double-sided image forming function that separately forms a toner image on a back surface of the recording paper on which a toner image is formed on the front surface and passes through the fixing roller . Image forming apparatus.

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