JP2006301272A - Image transfer apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image transfer apparatus wherein a charge whose polarity is opposite to that of toner is prevented from being supplied from a destaticizing member to the rear side of a form by grounding the destaticizing member or interposing a rectifying means between the destaticizing member and a power source for the destaticizing member, and then, irregularities in an image such as "toner-scattering" due to the discharge of the opposite charge arising with a specified apparatus constitution when the form is electrified on a carrying path, and to provide an image forming apparatus. <P>SOLUTION: The destaticizing member 5 for destaticizing the rear side of a secondarily transferred recording paper is connected to the power source 7b for the destaticizing member. It is allowed to use a brush type destaticizing brush, a saw-tooth destaticizing needle or a conductive non-woven destaticizing cloth as the destaticizing member 5. The installation of the destaticizing member 5 is set near the downstream of the recording paper carrying path passing through a secondary transfer nip so as to face an intermediate transfer belt 1 constituting an image carrier together with a bias roller 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image transfer apparatus and an image forming apparatus such as an electrophotographic copying machine and a laser printer. More specifically, after electrostatically transferring a toner image onto a transfer material such as plain paper or an OHP sheet, the back surface of the transfer material is neutralized. The present invention relates to an image transfer apparatus including a charge eliminating unit and an image forming apparatus using the image transfer apparatus.

  Conventionally, in an image forming apparatus using an electrophotographic system, a charge-removing member such as a charge-removing needle or a charge-removing brush that removes the back surface of a sheet after transferring a toner image from an image carrier onto the sheet has been used.

  FIG. 7 is a diagram showing a schematic configuration around an image transfer unit in an image forming apparatus using a conventional electrophotographic system. In FIG. 7, reference numeral 30 denotes an image carrier composed of a photosensitive drum, an intermediate transfer belt, etc., which carries and conveys a toner image in the direction indicated by an arrow. The image carrier 30 is grounded. A sheet 31 is conveyed to a transfer nip described later in synchronization with a toner image on the image carrier 30.

  A transfer member 32 includes a transfer roller, a transfer brush, and the like. The transfer member 32 contacts the image carrier 30 to form a transfer nip. When the paper 31 is transported to the transfer nip, a voltage having a polarity opposite to that of the toner (positive voltage in FIG. 7) is applied to the transfer member 32 by the transfer power supply 34. Thereby, a transfer electric field is formed between the image carrier 30 and the transfer member 32. Coulomb force acts on the toner on the image carrier 30 by the transfer electric field and is transferred toward the paper 31. Due to the separation discharge after transfer, a charge having a polarity opposite to that of the toner, and a positive charge in FIG.

  Reference numeral 33 denotes a static elimination member composed of a static elimination brush, a static elimination needle, and the like, which is connected to the ground or the static elimination power source 35 shown in FIG. When the transferred paper 31 is conveyed to a position opposite to the charge removal member 33, a negative charge is induced at the tip of the charge removal member 33 due to the charge accumulated on the back surface of the paper 31. When the voltage between the front end of the charge removal member 33 and the back surface of the paper 31 exceeds the discharge voltage Vth, discharge starts from the front end of the charge removal member 33 toward the back surface of the paper 31, and the charge accumulated on the back surface of the paper 31 is Removed.

  As described above, the following effects can be obtained by removing the charge on the back surface of the paper 31. The first effect is prevention of poor paper separation from the image carrier 30. When excess charge accumulates on the back surface of the paper 31, a Coulomb suction force acts between the paper 31 and the image carrier 30. As a result, the paper 31 is electrostatically attracted to the image carrier 30 and cannot be separated. On the other hand, since the charge removal member 33 is provided to remove excess charges, the Coulomb suction force between the paper 31 after transfer and the image carrier 30 is weakened, and the paper 31 is easily separated from the image carrier 30. Become.

  The second effect is prevention of image defects due to abnormal discharge. If excessive charges are accumulated, abnormal discharge occurs between the paper 31 and the image carrier 30 when the paper 31 is separated from the image carrier 30. As a result, a scaly discharge pattern is formed on the halftone image. On the other hand, since the extra charge is removed by providing the charge eliminating member 33, the occurrence of abnormal discharge can be suppressed, and as a result, scaly image defects can be suppressed.

A configuration in which the image transfer unit of the image forming apparatus as shown in FIG.
JP-A-6-230681

  However, in the constituent elements of the conventional image transfer unit, a phenomenon has occurred in which charges having a polarity opposite to that of the toner are discharged from the charge eliminating member to the back side of the sheet. Hereinafter, problems when the charging polarity of the toner is negative will be described.

  As a first case in which the discharge phenomenon occurs, a paper guide made of an insulating resin member may be used. During conveyance, the sheet is rubbed against the sheet guide, and the sheet is easily charged. This is particularly noticeable when using high surface resistance paper, printing in low humidity environments, and duplex printing. In the case where the sheet is negatively charged, when the charged sheet is conveyed to a position opposite to the charge removal member, a positive charge is induced in the grounded charge removal member. When the voltage between the paper and the charge removal member exceeds the discharge start voltage Vth, the positive charge is discharged from the charge removal member to the back side of the paper.

  Even when the static eliminating member is connected to a negative voltage power source, if the absolute value | Vt−Vd | of the difference between the charging voltage Vp of the paper and the output voltage Vd of the static eliminating power source exceeds Vth, the static eliminating member is grounded. In the same manner as described above, the positive charge is discharged from the static elimination member to the back side of the paper.

  As a second case in which the discharge phenomenon occurs, a configuration in which a negative voltage is applied to the image carrier and the transfer member is grounded can be mentioned. In the case of the above configuration, since the neutralizing member is disposed opposite to the bias roller (not shown), | Vt−Vd | between the negative voltage Vt to the bias roller and the applied voltage Vd to the neutralizing member at the time of transfer. When> Vth is established, a positive charge is induced in the charge removal member. Similarly to the above, when the voltage between the bias roller and the charge removal member exceeds the discharge start voltage, the positive charge is discharged from the charge removal member and supplied to the back side of the sheet.

  As described above, even if a negative voltage power source (static power source) is connected to the static elimination member to supply negative charge from the static elimination member to the back side of the paper, if the paper is charged and the device configuration requirements are different, In some cases, a positive charge is induced and discharged toward the back side of the paper. When the positive charge is supplied to the back side of the paper, the negatively charged toner once transferred to the paper moves toward the positive charge on the back side of the paper, and as a result, the toner protrudes from the image area. There has been a problem that image disturbance occurs. A specific example of this “toner jump” is shown in FIG. As shown in FIG. 8, the phenomenon of “toner skipping” occurs in the paper transport direction.

  The present invention has been made in view of the above circumstances, and a rectifying means is interposed between the static elimination member and the ground or the power supply for the static elimination member, so that the polarity opposite to that of the toner from the static elimination member toward the back side of the sheet. An image transfer apparatus and an image forming apparatus that prevent image disturbance such as “toner jumping” due to discharge of a reverse charge generated by a specific apparatus configuration when a sheet is charged in a conveyance path are provided. For the purpose.

  The present invention provides a transfer unit that transfers an image formed on an image carrier to a recording material, a neutralizing unit that is disposed near a recording material conveyance path downstream of the transfer unit, and that neutralizes the recording material, In the image transfer apparatus, the neutralization unit includes a rectifying unit that supplies only the charge having the same polarity as the toner from the neutralization unit to the recording material.

  According to the present invention, the rectifying means is interposed between the static eliminating member and the ground or the power source for the static eliminating member to prevent the charge having the opposite polarity to the toner from being supplied from the static eliminating member toward the back surface of the paper. It is possible to provide an image transfer apparatus and an image forming apparatus that prevent image disturbance such as “toner jumping” due to discharge of a reverse charge generated by a specific apparatus configuration when a sheet is charged in a path.

  According to a first aspect of the present invention, a transfer unit that transfers an image formed on an image carrier to a recording material, and a recording material conveyance path downstream of the transfer unit are arranged in the vicinity of the recording material, An image transfer apparatus including a charge eliminating unit that performs a configuration in which the charge eliminating unit includes a rectifying unit that supplies only the charge having the same polarity as the toner from the charge eliminating unit to the recording material.

  According to this configuration, the rectifying means is interposed between the static elimination member and the ground or the power supply for the static elimination member to prevent the charge having the polarity opposite to that of the toner from being supplied from the static elimination member toward the back surface of the paper. It is possible to provide an image transfer apparatus that prevents image disturbance such as “toner jumping” due to discharge of a reverse charge generated by a specific apparatus configuration when a sheet is charged in a path.

  According to a second aspect of the present invention, in the image transfer apparatus according to the first aspect, a grounding unit that grounds the neutralizing unit or a neutralizing power source that supplies a charge for neutralizing to the neutralizing unit, wherein the rectifying unit includes: The structure which is a diode interposed between the grounding means or the power supply for static elimination and the static elimination means is adopted.

  According to this configuration, since the diode is merely interposed between the grounding means or the power supply for static elimination and the static elimination means, the image transfer performance of the image transfer apparatus can be improved at low cost.

  A third aspect of the present invention is the image transfer apparatus according to the first or second aspect, further comprising a transfer power supply for supplying a charge having the same polarity as the toner to the image carrier, wherein the charge eliminating unit is the image carrier. The structure which arrange | positions in the position facing a body is taken.

  According to this configuration, it is possible to reliably prevent the “toner jumping” phenomenon that appears in the transport direction on the back surface of the recording material after transfer.

  A fourth aspect of the present invention employs a configuration of an image forming apparatus including the image transfer apparatus according to any one of the first to third aspects.

  According to this configuration, the rectifying means is interposed between the static elimination member and the ground or the power supply for the static elimination member to prevent the charge having the polarity opposite to that of the toner from being supplied from the static elimination member toward the back surface of the paper. It is possible to provide an image forming apparatus that prevents image disturbance such as “toner jumping” due to discharge of a reverse charge generated by a specific apparatus configuration when a sheet is charged in a path.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a schematic sectional view showing a configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 100 is a tandem image forming apparatus. In the image forming apparatus 100, four color toner images contributing to the color development of the color image are individually formed on the four image carriers, sequentially superimposed on the intermediate transfer member, and primarily transferred, and then the primary transfer image. Are collectively transferred (secondary transfer) to the recording medium.

  In FIG. 1, symbols Y, M, C, and K at the end of the reference numerals assigned to the components of the image forming apparatus 100 are Y for a yellow image, M for a magenta image, C for a cyan image, and K for a black image. The constituent elements involved in each image formation are shown, and the constituent elements having the same reference numerals have a common configuration.

  The image forming apparatus 100 includes the photosensitive drums 11Y, 11M, 11C, and 11K as the four image carriers and the intermediate transfer belt 1. Around the photosensitive drums 11Y, 11M, 11C, and 11K, charging members 12Y, 12M, 12C, and 12K, developing devices 13Y, 13M, 13C, and 13K, primary transfer members 15Y, 15M, 15C, and 15K, and drum cleaning Members 18Y, 18M, 18C, and 18K are provided.

  Each of the photosensitive drums 11Y, 11M, 11C, and 11K is rotated in a predetermined direction. The surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K are uniformly charged to predetermined potentials by the charging members 12Y, 12M, 12C, and 12K, respectively. A scanning line of a laser beam corresponding to image data of a specific color is irradiated by the exposure device 10 onto the surface of each charged photoconductive drum 11Y, 11M, 11C, 11K. As a result, electrostatic latent images for the specific colors are formed on the surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K.

  The electrostatic latent images for the specific colors formed on the respective photosensitive drums 11Y, 11M, 11C, and 11K are thin layered yellow, magenta, cyan, and black from the developer bottles 14Y, 14M, 14C, and 14K. The developing devices 13Y, 13M, 13C, and 13K to which the color toner is supplied are visualized. As a result, unfixed images of four colors that contribute to color development of color images are formed on the respective photosensitive drums 11Y, 11M, 11C, and 11K.

  The four color toner images visualized on the photosensitive drums 11Y, 11M, 11C, and 11K are endless intermediate transfer belts as the intermediate transfer members by the primary transfer members 15Y, 15M, 15C, and 15K. 1 is primarily transferred. As a result, the four color toner images formed on the photosensitive drums 11Y, 11M, 11C, and 11K are sequentially superimposed to form a full-color image on the intermediate transfer belt 1.

  In each of the photosensitive drums 11Y, 11M, 11C, and 11K, after the toner image is transferred to the intermediate transfer belt 1, residual toner remaining on the surface is removed by the drum cleaning members 18Y, 18M, 18C, and 18K. .

  On the other hand, at the lower part of the image forming apparatus 100, a paper feed cassette 19 in which recording paper such as printing paper as a recording medium is stored is provided. The recording paper is fed upward from the paper feed cassette 19 by the pickup roller 20 and the paper guide 3 along a sheet path indicated by a broken line in the drawing.

  The recording paper fed to the sheet path is conveyed through the sheet path by a pair of conveyance rollers 21 and a registration roller 22 and is suspended between the bias roller 2 and the support roller 9 and the outer peripheral surface of the intermediate transfer belt 1 and the intermediate transfer belt 1. It passes through a transfer nip formed by the secondary transfer roller 4 in contact with the outer peripheral surface. The full color image (unfixed image) formed on the intermediate transfer belt 1 is collectively transferred to the recording paper by the secondary transfer roller 4 in the secondary transfer unit 25 when passing through the transfer nip portion. The intermediate transfer belt 1 is rotated in the arrow direction in the figure by a driving roller 16 driven at a predetermined timing by a driving system (not shown). After the toner image is transferred onto the recording paper, the transfer residual toner remaining on the intermediate transfer belt 1 is removed by the belt cleaning unit 17.

  The bias roller 2 may be made of a conductive material, and the material may be coated with a metal material such as aluminum or SUS, or conductive rubber or conductive elastomer.

The materials used for the intermediate transfer belt 1 are styrene-butadiene rubber, silicon rubber, fluorine rubber, urethane rubber, acrylic rubber, epichloro, which are resin materials such as polyimide, polycarbonate, polyester, polyamide, and polyvinylidene fluoride. Rubbers such as hydrin rubber and elastomer materials can be used. Further, the intermediate transfer belt 1 may use a laminated structure of the resin material and rubber or elastomer material. In order to adjust the resistance value of the intermediate transfer belt 1 used in the present embodiment, a conductive agent such as carbon, metal powder, metal oxide, or conductive polymer compound may be added. The electrical resistance of the intermediate transfer belt 1 is desirably about 10 ⁹ to 10 ¹² Ω / □, preferably 5 × 10 ^{10 to} 5 × 10 ¹¹ Ω / □.

  Next, the recording paper passes through the fixing nip portion formed by the pressure roller 24 that contacts the outer peripheral surface of the fixing roller 23 of the fixing device 200 along the sheet path. As a result, the unfixed full-color image that is collectively transferred at the transfer nip portion is heated and fixed on the recording paper.

  Further, the secondary transfer roller 4 in the secondary transfer unit 25 is brought into contact with the intermediate transfer belt 1 by a biasing member such as a spring (not shown) during a printing operation. At the time of rest, it is separated from the intermediate transfer belt 1 by a separation / contact motor (not shown). If the secondary transfer roller 4 is left in contact with the intermediate transfer belt 1 for a long time, the secondary transfer roller 4 is permanently deformed. In contrast, in the present embodiment, the intermediate transfer belt 1 and the secondary transfer roller can be separated from each other, so that even if the image forming apparatus 100 is left in a rest state for a long period of time, the secondary transfer roller 4. Can be prevented from permanent deformation.

  Further, in the secondary transfer unit 25, a charge eliminating member 5 for removing charges accumulated on the back surface of the recording paper is attached in the vicinity of the secondary transfer roller 4. The secondary transfer unit 25 is detachably mounted in an open / close door 26 that is opened and closed by a hinge 27.

  The open / close door 26 is an open / close door of the apparatus main body that opens and closes when the jammed paper remaining on the conveyance path is removed and when the secondary transfer unit 25 is attached / detached. As shown in FIG. 2, the opening / closing door 26 rotates around the hinge 27 along the direction of the arrow shown. The secondary transfer unit 25 can be replaced with the opening / closing door 26 opened as shown in FIG.

  By integrating the secondary transfer roller 4 and the charge removal member 5 as the secondary transfer unit 25, there are the following advantages. That is, since the positions of the secondary transfer roller 4 and the charge removal member 5 slightly change according to the thickness of the recording paper, the distance from the back surface of the recording paper to the charge removal member 5 is stabilized. As a result, the electric field strength between the back surface of the recording paper and the charge eliminating member 5 is stabilized, and a stable discharge is obtained at the tip of the charge eliminating member 5. Further, since the position of the static eliminating member 5 is movable, it is possible to prevent the recording paper from being caught by the static eliminating member 5 and causing a paper jam. In addition, when the secondary transfer roller 4 and the charge removal member 5 reach the end of their lives, the secondary transfer unit 25 can be replaced as a unit, so that replacement work is facilitated.

As a material of the secondary transfer roller 4, EPDM (ethylene propylene rubber), NBR (nitrile butadiene rubber), polyurethane, epichlorohydrin rubber, sponge, or the like can be used. In order to adjust the electrical resistance of the secondary transfer roller 4, a conductive agent such as carbon, metal powder, metal oxide, or conductive polymer compound may be added. The electrical resistance of the secondary transfer roller is 1 × 10 ⁶ to 1 × 10 ⁸ Ω, preferably 1 × 10 ^{7 to} 5 × 10 ⁷ Ω. The hardness is 20 to 50 degrees, preferably 30 to 40 degrees in Asker C.

  Next, a schematic configuration in the vicinity of the secondary transfer unit 25 will be described with reference to a schematic configuration cross-sectional view shown in FIG.

  In FIG. 4, the angle D between the center line connecting the centers of the bias roller 2 and the secondary transfer roller 4 (the one-dot chain line in the figure) and the intermediate transfer belt 1 suspended between the support roller 9 and the bias roller 2 is as follows. The secondary transfer roller 4 is arranged to be less than 90 degrees, preferably less than 85 degrees. Accordingly, only the secondary transfer roller 4 and the intermediate transfer belt 1 are formed on the upstream side in the sheet conveying direction in the contact portion between the secondary transfer roller 4 and the intermediate transfer belt 1 (hereinafter referred to as the secondary transfer nip). The nip N1 is formed on the downstream side in the sheet conveying direction with a nip N2 where the secondary transfer roller 4 and the bias roller 2 are in contact with each other via the intermediate transfer belt 1. Since the secondary transfer roller 4 is electrically grounded, the transfer electric field strength E1 between the intermediate transfer belt 1 and the secondary transfer roller 4 at the nip N1 is extremely low.

  On the other hand, in the nip N2, since the secondary transfer voltage is applied to the bias roller 2 from the secondary transfer power source 7a, a transfer electric field E2 having a high strength is formed. With such a configuration, the following effects can be obtained. That is, when the recording paper 8 enters the secondary transfer nip, the transfer electric field strength E1 is low in the nip N1, so that the toner on the intermediate transfer belt 1 is not discharged between the recording paper 8 and the intermediate transfer belt 1. Is gripped by the recording paper 8. As a result, toner scattering when the recording paper 8 enters is prevented. When the toner gripped by the recording paper 8 at the nip N1 enters the nip N2, the toner is electrostatically attracted toward the recording paper 8 by the transfer electric field strength E2, and as a result, is transferred onto the recording paper 8. Thereby, high-quality transfer without toner scattering is realized.

  The neutralizing member 5 for neutralizing the back surface of the recording paper 8 after the secondary transfer is connected to the neutralizing member power source 7b. The neutralization member 5 may be a brush-shaped neutralization brush, a sawtooth-shaped neutralization needle, a neutralization cloth made of a conductive nonwoven fabric, or the like. The neutralization member 5 is attached to a position facing the intermediate transfer belt 1 constituting the image carrier together with the bias roller 2 in the vicinity of the downstream side of the recording paper conveyance path that has passed through the secondary transfer nip.

  The neutralizing member power supply 7b outputs a voltage having the same polarity as the toner, and the output voltage value is variable depending on the basis weight and material of the recording paper 8, the operating environment of the image forming apparatus 100, and the like. The bias roller 2 is connected to a secondary transfer power source 7a. The secondary transfer power supply 7a outputs a voltage having the same polarity as the toner, and the output voltage value is variable depending on the basis weight and material of the recording paper 8, the operating environment of the image forming apparatus 100, and the like. The output voltage values of the secondary transfer power source 7a and the neutralization member power source 7b are controlled by a control unit (not shown) at each operation timing in the secondary transfer operation of FIG.

  Next, the operation of the image forming apparatus 100 of the present embodiment will be described with reference to the cross-sectional view of FIG. 1 and the timing chart shown in FIG.

  When a print start signal is transmitted from an external device such as a PC to the image forming apparatus 100, the image forming apparatus 100 receives the print start signal, and the photosensitive drums 11Y, 11M, 11C, 11K, and the developing devices 13Y, 13M, The rotation of 13C, 13K, the intermediate transfer belt 1 and the fixing device 200 is started. Next, a voltage is applied to the charging members 12Y, 12M, 12C, and 12K, and the photosensitive drums 11Y, 11M, 11C, and 11K are charged to a predetermined surface potential. Next, the light source of the exposure device 10 is turned on according to the image signal received from the external device, and the exposure device 10 converts the image data of a specific color onto the charged surfaces of the photosensitive drums 11Y, 11M, 11C, and 11K. The corresponding scanning line of the laser beam is irradiated. Thereby, an electrostatic latent image for each specific color is formed on the surface of each of the photosensitive drums 11Y, 11M, 11C, and 11K.

  Next, a predetermined voltage is applied to the developing devices 13Y, 13M, 13C, and 13K, and four color toners adhere to the electrostatic latent images on the photosensitive drums 11Y, 11M, 11C, and 11K, and the toner images of the respective colors are formed. It is formed. Next, a predetermined voltage is applied to the primary transfer members 15Y, 15M, 15C, and 15K, and the toner images of the respective colors on the photosensitive drums 11Y, 11M, 11C, and 11K are transferred to the same position on the intermediate transfer belt 1. A color toner image is formed. After this primary transfer, transfer residual toner remaining on the photosensitive drums 11Y, 11M, 11C, and 11K is removed by the drum cleaning members 18Y, 18M, 18C, and 18K.

  Next, the color toner image formed on the intermediate transfer belt 1 is carried on the intermediate transfer belt 1 and conveyed to the vicinity of the secondary transfer unit 25. On the other hand, the recording paper stored in the paper feed cassette 19 is picked up by the pickup roller 20 and conveyed to the registration roller 22 through the paper guide 3 and the conveying roller pair 21. In synchronization with the color toner image carried and conveyed on the intermediate transfer belt 1, the registration roller 22 rotates to a contact portion (hereinafter referred to as a secondary transfer nip) between the intermediate transfer belt 1 and the secondary transfer roller 4. Be transported. A predetermined voltage is applied to the bias roller 2 in advance.

  At the same time as the recording paper passes through the secondary transfer nip in the secondary transfer unit 25, the color toner image on the intermediate transfer belt 1 is transferred to the recording paper side by electrostatic repulsion. After this secondary transfer, the transfer residual toner remaining on the intermediate transfer belt 1 is carried and conveyed to the belt cleaning unit 17 and removed. The recording paper that has passed through the secondary transfer nip is conveyed to a position facing the charge removal member 5. A predetermined voltage is previously applied to the charge removal member 5 from the power supply 7b for the charge removal member. Thereby, the electric charge accumulated on the back side of the recording paper is removed.

  The recording paper that has passed through the position facing the neutralizing member 5 is guided to the fixing device 200 along the paper guide 3. Simultaneously with passing through the fixing device 200, the color toner image is fixed and fixed on the recording paper. Then, the fixed recording sheet is guided to the sheet guide 3 and the discharge roller pair 28 and is discharged out of the image forming apparatus 100.

  Next, a specific example of the secondary transfer operation in the secondary transfer unit 25 will be described with reference to a timing chart shown in FIG. The timing chart shown in FIG. 5 shows a case where two recording sheets are continuously fed.

  When the image forming apparatus 100 receives a print start signal from an external device such as a PC, the separation contact motor of the secondary transfer unit 25 rotates and the intermediate transfer belt 1 and the secondary transfer roller 4 are separated (OFF). ) To a state where both are in contact (ON). Next, after the separation motor completes the transition from OFF to ON, the secondary transfer unit 25 transitions to the cleaning period T1. In the secondary transfer unit cleaning period T1, a positive polarity voltage (Vc +) and a negative polarity voltage (Vc−) are alternately applied to the bias roller 2 from the secondary transfer power source 7a every rotation of the bias roller 2. Is done. As a result, even when positive and negative polarity toners adhere to the secondary transfer roller 4, the toner moves from the secondary transfer roller 4 to the intermediate transfer belt 1 and the surface of the secondary transfer roller 4 is cleaned. After the completion of the secondary transfer unit cleaning period T1, the process proceeds to the standby period T2 until the recording paper is conveyed to the secondary transfer nip.

  When conveyance of the recording paper is started from the registration roller 22 (paper passing period T3), predetermined voltages (Vt) and (Vd) are applied to the secondary transfer roller 4 and the charge removal member 5, respectively. In the case of continuous sheet passing, the voltage applied to the secondary transfer roller 4 and the charge removal member 5 is switched to (Vc−) and (0V), respectively, at the sheet interval T4. After the recording paper has completed passing through the position opposite to the charge removal member 5, the secondary transfer voltage and the charge removal member voltage are each switched to (0V) to complete the power supply. After the power supply is completed, the separation motor moves from ON to OFF, and the secondary transfer roller 4 is separated from the intermediate transfer belt 1. The secondary transfer process is completed by the above process.

  In the paper passing period T5 shown in FIG. 5, the output voltage values of the secondary transfer power supply 7a and the discharging member power supply 7b are controlled in the same manner as the operation shown in the paper passing period T3.

  Next, as a specific example of the secondary transfer operation described in the above embodiment, the configuration requirements of the secondary transfer unit and the test conditions for confirming the presence or absence of “toner skipping” are set and the test operation is executed. Examples 1 to 3 will be described below.

In Example 1, a single layer belt made of a conductive polyimide material having a surface resistivity of 1 × 10 ¹¹ Ω / □ and a thickness of 85 μm was used as the intermediate transfer belt 1. The bias roller 2 was a φ21 aluminum roller. As the secondary transfer roller 4, a roller having an outer diameter of φ28 in which a sponge layer of epichlorohydrin rubber and a solid rubber layer having a thickness of about 1 mm were laminated on a φ16 cored bar. The hardness of the sponge layer alone of the secondary transfer roller 4 was about 15 degrees Asker C, the hardness of the laminated structure was about 35 degrees Asker C, and the electric resistance was 2 × 10 ⁷ Ω. Further, the angle D between the center line connecting the centers of the bias roller 2 and the secondary transfer roller 4 shown in FIG. 4 and the intermediate transfer belt 1 suspended between the support roller 9 and the bias roller 2 is about 80 degrees. The secondary transfer roller 4 was arranged so as to be.

  Moreover, the static elimination member 5 used the static elimination needle made from stainless steel of W = 2mm, H = 3mm, and thickness t = 1.5mm shown in FIG. Further, the static elimination needle 5 was arranged so that the closest distance from the tip of the static elimination needle 5 to the bias roller 2 was about 7 mm and the closest distance from the tip of the static elimination needle 5 to the secondary transfer roller 4 was about 3 mm. As the rectifying means 6, a high voltage diode having a withstand voltage (VDDM) of 12 kV and a forward current (IF) of 1 mA was used.

  Furthermore, as test conditions, the process speed was set to 170 mm / s, and a black monochrome patch mark was printed on a recording sheet. When the toner image on the recording paper after fixing was observed, “X” was judged when “toner skipping” was visually confirmed, and “◯” was judged when it was not visually confirmed. In addition, an analog ammeter was connected between the static elimination needle 5 and the static elimination member power source 7b, and the static elimination current flowing when the paper was passed was visually read.

In Example 1, plain paper A having a surface resistivity of 0.7 × 10 ¹² to 4 × 10 ¹² Ω / □ and a basis weight of 70 g / m ² was passed as a recording paper on one side. The surface resistivity of the recording paper was measured by using a resistivity meter and measuring the resistance value after an applied voltage of 500 V and 10 seconds. The secondary transfer voltage was set to -1800V, and the charge removal voltage was set to 0V.

  The results of determining “toner skipping” based on the above constituent requirements and test conditions are shown in Table 1 described later.

  In the second embodiment, the configuration requirements are the same as those in the first embodiment, and the test conditions are set as follows. The process speed was set to 105 mm / s, and yellow, magenta, cyan, and black patch marks were printed on recording paper. When the toner image on the recording paper after fixing was observed, “X” was judged when “toner skipping” was visually confirmed, and “◯” was judged when it was not visually confirmed.

In Example 2, instead of plain paper A, plain paper B having a surface resistivity of 1 × 10 ^{11 to} 5 × 10 ¹¹ Ω / □ and a basis weight of 70 g / m ² was passed as a recording paper on one side. The surface resistivity of the recording paper was measured by using a resistivity meter similar to that in Example 1, and the resistance value after 10 seconds of applied voltage 500 V was measured.

  The results of determining “toner skipping” based on the above constituent requirements and test conditions are shown in Table 1 described later.

  In the third embodiment, the configuration requirements are the same as those in the first embodiment, and the test conditions are set as follows. The process speed was set to 105 mm / s, and yellow, magenta, cyan, and black patch marks were printed on both sides of the recording paper. When the toner image on the recording paper after fixing was observed, it was judged as “X” when the toner jump could be visually confirmed, and “◯” when the toner could not be visually confirmed.

  In Example 3, the same paper B as in Example 2 was passed. The secondary transfer voltage and static elimination voltage on the first recording sheet were set as described in Example 1. The secondary transfer voltage on the second surface of the recording paper was set to -2400V, and the charge removal voltage was set to -1500V.

  The results of determining “toner skipping” based on the above constituent requirements and test conditions are shown in Table 1 described later.

(Comparative Example 1)
In comparison with Example 1 above, the case where the high voltage diode is removed and printing is performed with the charge eliminating needle 5 and the charge removing member power supply 7b directly connected, and the presence or absence of toner jump in the acquired image is determined.
As shown in Table 1 below.

(Comparative Example 2)
As compared to Example 2 above, a case where the high-voltage diode is removed and printing is performed in a state where the static elimination needle 5 and the neutralization member power source 7b are directly connected, and the presence or absence of toner jump in the acquired image is determined as Comparative Example 2. It shows in Table 1 mentioned later.

(Comparative Example 3)
As compared to Example 3 above, a case where the high-voltage diode is removed and printing is performed in a state where the neutralization needle 5 and the neutralization member power source 7b are directly connected, and the presence or absence of toner jump in the acquired image is determined as Comparative Example 3. It is shown in Table 1 below.

  As described above, in the case of the recording sheet A with high resistance shown in Comparative Examples 1 and 3 and the recording sheet B on which double-sided printing was performed, “toner skipping” was noticeable. In Comparative Examples 1 and 3, it was found that the static elimination current showed a positive value, and the positive charge was moving from the static elimination needle 5 toward the recording paper.

  On the other hand, in Examples 1 and 3 in which the high voltage diode was inserted, the movement of the positive charge from the static elimination needle 5 toward the recording paper was blocked by the high voltage diode, and as a result, the static elimination current showed 0 μA. As a result, a high-quality toner image in which “toner skipping” was suppressed was obtained.

  As described above, in the image forming apparatus according to the present embodiment, the discharging member 5 that discharges the output terminal of the discharging member power source that applies a voltage having the same polarity as the toner to the discharging member and the back surface of the recording paper after the secondary transfer. A diode as a rectifying means is interposed between the two.

  For this reason, it is possible to prevent charge having a polarity opposite to that of the toner from being supplied to the back side of the sheet from the charge eliminating member, and “toner jumping” due to discharge of the reverse charge generated by a specific apparatus configuration due to charging of the sheet in the transport path. Image disturbance can be prevented. As a result, it is possible to record an image with higher image quality than before, and the recording performance of the image forming apparatus can be improved.

  Further, in the image forming apparatus according to the present embodiment, since a “toner jump” is prevented, a diode is merely interposed as a rectifier between the output terminal of the power supply for the static elimination member and the static elimination member. Thus, a high-quality toner image can be obtained, and the performance of the image forming apparatus can be improved at a low cost.

  Further, the image forming apparatus according to the present embodiment includes a secondary transfer power source that applies a voltage having the same polarity as that of the toner to the bias roller, and the charge removal member faces the intermediate transfer roller that forms the image carrier together with the bias roller. Therefore, the “toner skipping” phenomenon that appears in the transport direction on the back surface of the recording paper after the secondary transfer can be reliably prevented.

  In the present invention, a rectifying means is interposed between the static eliminating member and the ground or the power source for the static eliminating member to prevent the charge having a polarity opposite to that of the toner from being supplied from the static eliminating member toward the back surface of the paper. It is possible to prevent image disturbance such as “toner jumping” due to discharge of a reverse charge generated by a specific apparatus configuration when the sheet is charged, and can be applied to image forming apparatuses such as facsimiles and printers.

1 is a schematic cross-sectional view showing a configuration of an image forming apparatus according to an embodiment of the present invention. Schematic sectional view showing a configuration in which an opening / closing door of the image forming apparatus according to the present embodiment is opened Schematic sectional view showing a configuration for exchanging the secondary transfer unit of the image forming apparatus according to the present embodiment Schematic sectional view showing the configuration in the vicinity of the secondary transfer unit according to the present embodiment Timing chart showing an operation example of the secondary transfer operation according to the present embodiment The figure which shows an example of the static elimination needle which concerns on this Embodiment The figure which shows schematic structure around the conventional image transfer part Diagram showing toner skipping phenomenon that occurs on the backside of conventional recording paper

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt 2 Bias roller 3 Paper guide 4 Secondary transfer roller 5 Static elimination member 6 Rectification means (diode)
7a Power supply for secondary transfer 7b Power supply for discharging member 8 Recording paper 9 Support roller 10 Exposure device 11Y, 11M, 11C, 11K Photosensitive drum 12Y, 12M, 12C, 12K Charging member 13Y, 13M, 13C, 13K Developing device 14Y, 14M, 14C, 14K Developer bottles 15Y, 15M, 15C, 15K Primary transfer member 16 Drive roller 17 Belt cleaning unit 18Y, 18M, 18C, 18K Drum cleaning member 19 Paper feed cassette 20 Pickup roller 21 Conveying roller pair 22 Registration roller DESCRIPTION OF SYMBOLS 23 Fixing roller 24 Pressure roller 25 Secondary transfer unit 26 Opening / closing door 27 Hinge 28 Paper discharge roller pair 100 Image forming apparatus 200 Fixing apparatus

Claims (4)

Transfer means for transferring an image formed on the image carrier to a recording material;
An image transfer apparatus comprising: a discharging unit disposed near the recording material conveyance path downstream of the transfer unit, and discharging the recording material.
The image transfer apparatus according to claim 1, wherein the charge eliminating unit includes a rectifying unit that supplies only the charge having the same polarity as the toner from the charge eliminating unit to the recording material. A grounding means for grounding the static elimination means or a static elimination power source for supplying charge for static elimination to the static elimination means,
2. The image transfer apparatus according to claim 1, wherein the rectifying means is a diode interposed between the grounding means or the static elimination power source and the static elimination means. A transfer power supply for supplying the image carrier with a charge of the same polarity as the toner;
The image transfer apparatus according to claim 1, wherein the charge eliminating unit is disposed at a position facing the image carrier.   An image forming apparatus comprising the image transfer apparatus according to claim 1.

Images