JP3826565B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a copying machine, a printer, a FAX, etc., in which a charging unit, an image writing unit, and a developing unit are arranged around an image forming body to transfer and fix a toner image formed on the image forming body onto a transfer material. The present invention relates to an electrophotographic image forming apparatus.
[0002]
[Prior art]
Conventionally, in double-sided image formation, an image on one side formed on an image forming body is transferred and fixed onto a transfer material, which is once stored in a double-sided reversing paper feeding device and formed again on the image forming body. A method is adopted in which a transfer material is fed from a double-sided reversing paper feeding device in synchronization with the image, and the image is transferred and fixed on the other surface of the transfer material.
[0003]
In this double-sided image forming apparatus, as described above, the transfer material is conveyed such as feeding to the double-sided reversing paper feeding device and passing through the fixing device twice, so that the reliability of the transfer material conveyance is low, and jam and transfer It was a cause of wrinkling of the material. On the other hand, a toner image is formed on both surfaces of a transfer material according to Japanese Patent Publication Nos. 49-37538, 54-28740, JP-A-1-44457, and 4-214576, etc., and then fixed once. Something to do is proposed.
[0004]
Similarly, the inventors of the present application have arranged toner image forming means including charging means, image writing means, developing means, etc. around an image forming body (photosensitive drum), and a toner image formed on the photosensitive drum is obtained. The image is once transferred to a belt-like intermediate transfer member (toner image receiver) by the first transfer unit, and a toner image is formed again on the photosensitive drum, and the toner image receiver is conveyed on both sides of the transfer material. The toner image on the photosensitive drum is transferred as a front image by the first transfer unit, and the toner image on the toner image receiver is transferred as the back image by the second transfer unit and then transferred by the transfer material separating unit. An image forming apparatus for forming a double-sided image by forming the double-sided image by fixing the toner image on the transfer material by fixing the toner image from the toner image receiver and examining the double-sided image formation using the apparatus. Yes.
[0005]
[Problems to be solved by the invention]
However, in the image forming apparatus, when a toner image receiver having a low volume resistivity is used, the discharge from the second transfer unit or transfer material separating unit is generated on the toner image receiver before and after the transfer material or at both ends. There is a problem that lightning strikes and the toner image receiver is damaged to cause image defects on the back surface image or transfer defects on the front surface image. In addition, when separating the transfer material from the intermediate transfer body, the transfer material after being transferred by the second transfer means is strongly electrostatically adsorbed to the intermediate transfer body and is therefore very difficult to separate. The transfer material separating means is provided. When both the second transfer means and the transfer material separating means are provided facing the driving roller for conveying the toner image receiver, the second transfer means and the transfer material separating means are provided. Since it is necessary to make both small, the second transfer unit and the transfer material separating unit are insufficiently discharged, or the second transfer unit and the transfer material separating unit are arranged close to each other. In addition, the transfer of the toner image from the toner image receiver to the back surface of the transfer material and the separation of the transfer material from the toner image receiver are not performed stably due to interference from the discharge from the transfer material separating means. Problems arise.
[0006]
In particular, when the second transfer unit and the transfer material separating unit are arranged close to each other, the charge of the intermediate transfer member charged by the second transfer unit is not leaked until the separation position, and the separation is performed stably. The problem of not.
[0007]
The present invention improves the above-described problems and provides an image forming apparatus in which transfer of a toner image to the back surface of a transfer material and separation of the transfer material from the intermediate transfer member are stably performed without damage to the intermediate transfer member. The purpose is to provide.
[0008]
[Means for Solving the Problems]
The object is to form an image forming body, a toner image forming means for forming a toner image on the image forming body, and a belt-like shape capable of transferring the toner image on the image forming body and conveying a transfer material. An intermediate transfer member, first transfer means for transferring the toner image on the image forming member to the surface of the intermediate transfer member or the transfer material, and the toner image on the intermediate transfer member on the back surface of the transfer material. In the image forming apparatus having the second transfer means for transferring and the fixing means for fixing the toner image on the transfer material, the volume resistivity of the intermediate transfer member is set to 10 ¹² to 10 ¹⁵ Ω · cm, A conductive rotation roller is provided in contact with the second transfer means via the intermediate transfer member and a position where the transfer material is separated from the intermediate transfer member, and further separated. Of the rotating roller provided in The distance of the center position and the center position of the rotation rollers provided at a position opposite to the second transfer means and above 30 mm, it Ru is achieved by an image forming apparatus according to claim.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below. The description of the present application does not limit the technical scope of the claims or the meaning of the terms. In addition, the following assertive description in the embodiment of the present invention shows the best mode, and does not limit the meaning or technical scope of the terms of the present invention.
[0011]
In the description of the embodiments below, when transferring a color toner image to a transfer material, the surface of the transfer material facing the image forming body is the surface, and the other side of the transfer material, that is, an intermediate transfer body The surface of the transfer material facing the surface is called the back surface, the image transferred to the surface of the transfer material is called the front image, and the image transferred to the back surface of the transfer material is called the back image.
[0012]
An image forming process and each mechanism of an embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a sectional view of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention, FIG. 2 is a side sectional view of the image forming body of FIG. 1, and FIG. FIG. 3 is a diagram illustrating a toner image forming state on both sides of the image forming apparatus according to the invention, and FIG. 3A is a diagram for forming a back image by transferring the toner image formed on the image forming body onto the intermediate transfer member. FIG. 3B is a diagram in which a front surface image is formed on the image forming body in synchronization with the back surface image on the intermediate transfer member, and FIG. 3C is a diagram showing double-sided image formation on the transfer material. FIG. 4 shows the positional relationship between a rotation roller provided at a position facing the first transfer unit and the second transfer unit and a rotation roller provided at a transfer material separating position from the intermediate transfer member. FIG. 5 is a diagram showing guidance of the transfer material to the fixing means by a spur.
[0013]
In FIG. 1, 10 is a photosensitive drum as an image forming body, 11 is a scorotron charger as charging means for each color, 12 is an exposure optical system as image writing means for each color, and 13 is developing means for each color. 14a is a toner image receiver as an intermediate transfer member, 14c is a transfer device as a first transfer means, 14g is a back surface transfer device as a second transfer means, and 150 is a transfer material charging means. A paper charger, 14h is a paper separation AC static eliminator serving as a transfer material separating means, 160 is a transport unit having a spur 162, and 17 is a fixing device serving as a fixing means.
[0014]
The photosensitive drum 10 which is an image forming body has, for example, a transparent conductive layer, an a-Si layer or an organic photosensitive layer (OPC) on the outer periphery of a cylindrical base formed by a transparent member made of optical glass or transparent acrylic resin. 1 is formed, and is rotated clockwise as indicated by an arrow in FIG. 1 with the conductive layer grounded.
[0015]
As shown in FIG. 2, the photosensitive drum 10 has a bearing with respect to a drum shaft 30 that is installed and fixed to the apparatus main body by bearings B1 and B2 fitted into flange members 10a and 10b at both ends for engaging and fixing the photosensitive drum. The gear G, which is rotatably supported and integrated with the flange member 10b, is engaged with a drive gear (not shown) on the apparatus main body side and is driven at a constant speed in a predetermined direction.
[0016]
In the present embodiment, a scorotron charger 11 that is a charging unit for each color, an exposure optical system 12 that is an image writing unit for each color, and a developing unit 13 that is a developing unit for each color are set as one set. Four sets are provided for the image forming process of each color of yellow (Y), magenta (M), cyan (C), and black (K), and with respect to the rotation direction of the photosensitive drum 10 indicated by an arrow in FIG. Arranged in the order of Y, M, C, K.
[0017]
A scorotron charger 11 serving as a charging means for each color has a control grid held at a predetermined potential and a discharge electrode 11a made of, for example, a sawtooth electrode, and is mounted opposite to the photosensitive layer of the photosensitive drum 10. Then, a charging action (negative charging in the present embodiment) is performed by corona discharge having the same polarity as the toner, and a uniform potential is applied to the photosensitive drum 10. As the discharge electrode 11a, other wire electrodes or needle electrodes can be used.
[0018]
In the exposure optical system 12, which is an image writing unit for each color, the exposure position on the photosensitive drum 10 is located downstream in the rotation direction of the photosensitive drum 10 with respect to the aforementioned scorotron charger 11 for each color. In this way, it is arranged inside the photosensitive drum 10. As shown in FIG. 2, each exposure optical system 12 is a line in which a plurality of LEDs (light emitting diodes) as light emitting elements for image exposure light arranged in the main scanning direction in parallel with the drum shaft 30 are arranged in an array. Exposure unit 12a, a light focusing optical transmission body (trade name: Selfoc lens array) 12b as an imaging element, and a lens holder 12c, and is attached to the holding member 20. . In addition to the exposure optical system 12 for each color, a simultaneous transfer exposure device 12 d and a uniform exposure device 12 e are attached to the holding member 20, and are integrally accommodated inside the substrate of the photosensitive drum 10. The exposure optical system 12 for each color image-exposes the photosensitive layer of the photosensitive drum 10 from the back according to the image data of each color read by a separate image reading device and stored in the memory, and electrostatically is applied on the photosensitive drum 10. A latent image is formed. As the exposure element 12a, a plurality of light emitting elements such as FL (phosphor light emission), EL (electroluminescence), and PL (plasma discharge) arranged in an array can be used. Note that the emission wavelength of the image exposure light emitting element is usually in the range of 780 to 900 nm, which is highly transmissive to Y, M, and C toners. In this embodiment, image exposure is performed from the back side. Since it is a system, it may have a shorter wavelength of 400 to 780 nm, which is not sufficiently transmissive to the color toner. In FIG. 2, WA is a lead wire from a light emitting element (LED) of the image exposure means.
[0019]
The developing device 13 which is a developing unit for each color maintains a predetermined gap with respect to the peripheral surface of the photosensitive drum 10 and rotates in the forward direction and the rotating direction of the photosensitive drum 10, for example, a thickness of 0.5 to 1 mm, an outer diameter. A developing sleeve 131 made of 15-25 mm cylindrical non-magnetic stainless steel or aluminum material and a developing casing 138 are provided, and yellow (Y), magenta (M), cyan (C), and black (K) are contained therein. 1-component or 2-component developer). Each developing device 13 is kept in contact with the photosensitive drum 10 with a predetermined gap, for example, 100 to 500 μm, by an abutting roller (not shown), and a DC voltage and an AC voltage are superimposed on the developing sleeve 131. By applying the developed bias, non-contact reversal development is performed, and a toner image is formed on the photosensitive drum 10.
[0020]
The toner image receiver 14a, which is an intermediate transfer member, is an endless belt having a volume resistivity of 10 ¹⁰ to 10 ¹⁶ Ω · cm, preferably 10 ¹² to 10 ¹⁵ Ω · cm. For example, modified polyimide, thermosetting polyimide, ethylene tetrafluoro A conductive film is dispersed in an engineering plastic such as ethylene copolymer, polyvinylidene fluoride, nylon alloy, etc., and is preferably provided on the outside of a semiconductive film substrate having a thickness of 0.1 to 1.0 mm, preferably as a toner filming prevention layer. This is a seamless belt having a two-layer structure and having a fluorine coating of 5 to 50 μm. In addition to this, a semiconductive rubber belt having a thickness of 0.5 to 2.0 mm in which a conductive material is dispersed in silicon rubber, urethane rubber, or the like can also be used. The toner image receiver 14a is stretched in contact with a drive roller 14d, a support roller 14j, a driven roller 14e, a guide roller 14f, and a tension roller 14i, and is rotated counterclockwise as indicated by an arrow in FIG. The driven roller 14e, the support roller 14j, the drive roller 14d, the tension roller 14i, and the guide roller 14f are provided in this order according to the rotation direction of the toner image receiver 14a. The driven roller 14e, the support roller 14j, the drive roller 14d, and the guide roller 14f are fixed. Thus, the tension roller 14i is movable during rotation by the elasticity of the toner image receiver 14a. As will be described later, the driving roller 14d, the supporting roller 14j, and the driven roller 14e are all conductive rotating rollers that are grounded, and the driven roller 14e is charged with a transfer material via a toner image receiver 14a that is an intermediate transfer member. The sheet charging device 150 is opposed to the paper transfer device 14, the support roller 14 j is opposed to the back surface transfer device 14 g serving as the second transfer device, and the driving roller 14 d is opposed to the paper separation AC charge removal device 14 h serving as the transfer material separation device. Provided. The drive roller 14d is rotated by driving from a drive motor (not shown), and the toner image receiver 14a is driven and rotated. The support roller 14j, the driven roller 14e, the guide roller 14f, and the tension roller 14i are driven and rotated by the rotation of the toner image receiver 14a. The slack of the belt of the rotating toner image receiver 14a is tensioned by the tension roller 14i.
[0021]
The transfer device 14c, which is a first transfer means, is provided to face the photosensitive drum 10 with the toner image receiver 14a interposed therebetween, and forms a transfer area 14b between the toner image receiver 14a and the photosensitive drum 10. To do. A DC voltage having a polarity opposite to that of the toner (plus polarity in the present embodiment) is applied to the transfer device 14c to form a transfer electric field in the transfer area 14b, whereby the toner image on the photosensitive drum 10 is transferred to the toner image receiver. The image is transferred onto 14a or the surface of the recording paper P which is a transfer material.
[0022]
A back transfer device 14g as a second transfer means is provided to face a support roller 14j as a conductive rotating roller that is grounded with the toner image receiver 14a interposed therebetween, and has a polarity opposite to that of the toner (in this embodiment). Is applied with a positive polarity), and the toner image on the toner image receiver 14a is transferred to the back surface of the recording paper P.
[0023]
The paper charger 150 serving as a transfer material charging unit is provided to face the driven roller 14e that is grounded with the toner image receiver 14a interposed therebetween, and contacts and contacts the toner image receiver 14a with the support shaft 152 as a rotation fulcrum. The recording paper P is charged and attracted to the toner image receiver 14a.
[0024]
A paper separation AC static eliminator 14h, which is a transfer material separation means, is a drive that is a conductive rotating roller that is grounded with the toner image receiver 14a sandwiched between ends of the toner image receiver 14a on the fixing device 17 side as necessary. An AC voltage, which is provided opposite to the roller 14d and is superimposed with a DC voltage having the same or opposite polarity as that of the toner, is applied to neutralize the recording paper P conveyed by the toner image receiver 14a.
[0025]
The conveyance unit 160 is provided between the toner image receiver 14 a and the fixing device 17, and a spur 162 is provided on the upper surface of the conveyance unit 160. When the recording paper P is separated from the toner image receiver 14a, the spur 162 scoops up the recording paper P to be bent and conveyed toward the toner image receiver 14a, and also has the toner image on the back surface. Is conveyed to the fixing device 17 while preventing the backside toner image from being disturbed.
[0026]
The fixing device 17 serving as fixing means is composed of two rollers, a fixing roller 17a having a heater therein and a pressure roller 17b, and applies heat and pressure between the fixing roller 17a and the pressure roller 17b. The toner image on the recording paper P is fixed.
[0027]
Next, the image forming process will be described.
[0028]
The photosensitive drum 10 is rotated in the clockwise direction indicated by the arrow in FIG. 1 by starting the photosensitive member driving motor (not shown) by the start of image recording, and at the same time, the photosensitive drum 10 is charged by the yellow (Y) scorotron charger 11. Application of a potential is started.
[0029]
After the photosensitive drum 10 is applied with an electric potential, image writing by an electric signal corresponding to the first color signal, that is, Y image data is started by the Y exposure optical system 12, and a document is formed on the surface of the photosensitive drum 10. An electrostatic latent image corresponding to the Y image of the image is formed.
[0030]
The latent image is reversely developed in a non-contact state by the Y developing device 13 to form a yellow (Y) toner image on the photosensitive drum 10.
[0031]
Next, a potential is applied to the photosensitive drum 10 from above the Y toner image by the charging action of the magenta (M) scorotron charger 11, and the M exposure optical system 12 applies a second color signal, that is, M image data. Image writing is performed by a corresponding electric signal, and a magenta (M) toner image is formed on the yellow (Y) toner image by non-contact reversal development by the M developing unit 13. .
[0032]
By a similar process, a cyan (C) toner image corresponding to the third color signal is further superimposed by the cyan (C) scorotron charger 11, the C exposure optical system 12, and the C developing unit 13. Further, a black (K) toner image corresponding to the fourth color signal is successively superimposed on the black (K) scorotron charger 11, the K exposure optical system 12, and the K developing device 13. Then, a superposed color toner image of four colors of yellow (Y), magenta (M), cyan (C) and black (K) is formed on the peripheral surface within one rotation of the photosensitive drum 10 (toner image). Forming means).
[0033]
Image writing to the photosensitive layer of the photosensitive drum 10 by the Y, M, C, and K exposure optical systems 12 is performed from the inside of the drum through the above-described transparent substrate. Therefore, writing of the images corresponding to the second, third, and fourth color signals is performed without any influence of the toner image formed earlier, and is equivalent to the image corresponding to the first color signal. It is possible to form an electrostatic latent image.
[0034]
The superimposed color toner image, which is the back image formed on the photosensitive drum 10 as an image forming body by the above image forming process, is intermediately transferred by the transfer device 14c as the first transfer means in the transfer area 14b. The toner image receiver 14a, which is a body, is collectively transferred (FIG. 3A). At this time, uniform exposure may be performed by the simultaneous transfer exposure unit 12d provided inside the photosensitive drum 10 so that good transfer is performed.
[0035]
The toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the photosensitive drum AC static eliminator 16, and then enters the cleaning device 19 as the photosensitive drum cleaning means or comes into contact with the photosensitive drum 10. It is cleaned by a cleaning blade 19a made of a rubber material and collected by a screw 19b in a waste toner container (not shown). Further, the history of the photosensitive drum 10 in the previous image formation is eliminated on the peripheral surface of the photosensitive drum 10 by exposure by the uniform exposure device 12e before charging using, for example, a light emitting diode.
[0036]
After the superimposed color toner image to be the back image is formed on the photosensitive drum 10 as described above, the superimposed color toner image to be the front image is subsequently formed in the same manner as the above color image forming process. (FIG. 3B). At this time, the image data is changed so that the front surface image formed on the photoconductive drum 10 becomes a mirror image with respect to the back image formed on the photoconductive drum 10.
[0037]
Along with the surface image formation on the photosensitive drum 10, the recording paper P as a transfer material is sent out by a feed roller 15a from a paper feed cassette 15 as a transfer material storage means, and a timing roller 15b as a transfer material feed means. The color toner image of the front image carried on the photosensitive drum 10 and the color toner image of the back image carried on the toner image receiver 14a are synchronized by driving the timing roller 15b. To the transfer area 14b. At this time, the tip of the recording paper P that is brought into contact with the recording paper P and is applied with a DC voltage having the same polarity as the toner (negative polarity in this embodiment) is fed by the brush-shaped paper charger 150, and the recording paper P is the same as the toner. The paper is charged to the polarity, and is attracted to the toner image receiver 14a and fed to the transfer area 14b. By charging the paper with the same polarity as the toner, the toner image is prevented from being attracted by being attracted to the toner image on the toner image receiver 14a or the toner image on the photosensitive drum 10, thereby preventing the toner image from being disturbed. Simultaneously with the passage of the recording paper P, the paper charger 150 is separated from the toner image receiver 14a, and the contact is released.
[0038]
The paper charger 150 is released from contact with the toner image receiver 14 a immediately before or simultaneously with the passage of the trailing edge of the recording paper P and is separated from the recording paper P. Further, the voltage is applied to the paper charger 150 only when the recording paper P is being fed, and the voltage applied to the paper charger 150 is cut off simultaneously with the separation from the recording paper P.
[0039]
Further, as the transfer material charging means, a conductive roller, a semiconductive film member, or a blade member that can be contacted and released from the toner image receiver 14a and to which a DC voltage having the same polarity as the toner is applied is used. Is also possible.
[0040]
In the transfer area 14b, the surface image on the photosensitive drum 10 is collectively collected on the recording paper P by a transfer device 14c as a first transfer means to which a voltage having a polarity opposite to that of the toner (plus polarity in the present embodiment) is applied. Transferred to the surface. At this time, the back surface image on the toner image receiver 14a is not transferred to the recording paper P and exists on the toner image receiver 14a. Uniform exposure by a simultaneous transfer exposure device 12d using, for example, a light emitting diode provided inside the photosensitive drum 10 so as to face the transfer region 14b so that a good transfer can be performed at the time of transfer by the transfer device 14c. May be performed.
[0041]
The recording paper P on which the color toner image is transferred on the front surface is conveyed to a back surface transfer device 14g as a second transfer means to which a voltage having a polarity opposite to that of the toner (a positive polarity in the present embodiment) is applied. The back surface image on the peripheral surface of the toner image receiver 14a is collectively transferred to the back surface of the recording paper P by the container 14g (FIG. 3C).
[0042]
The recording paper P on which the color toner images are formed on both sides is then separated from the toner image receiver 14a by the curvature of the drive roller 14d or, if necessary, the charge removal action by the paper separation AC charge remover 14h as a transfer material separation means. Then, the toner image is conveyed to the fixing device 17 through the conveying unit 160 provided with a spur 162, and heat and pressure are applied between the fixing roller 17a and the pressure roller 17b so that the toner image on the recording paper P is formed. The recording paper P that has been fixed and on which double-sided image recording has been performed is sent with the front and back images reversed, and is discharged by a paper discharge roller 18 to a tray outside the apparatus.
[0043]
The toner remaining on the peripheral surface of the toner image receiver 14a after the transfer can be brought into and out of contact with the toner image receiver 14a provided opposite the guide roller 14f across the toner image receiver 14a. Cleaning is performed by a toner image receiver cleaning device 140 having a toner image receiver cleaning blade 141 and a cleaning roller 144.
[0044]
Further, the toner remaining on the peripheral surface of the photosensitive drum 10 after the transfer is subjected to static elimination by the photosensitive drum AC static eliminator 16, and then the residual toner is removed by the cleaning device 19. The history of the photosensitive drum 10 in the previous image formation is canceled by 12e, and the next image formation cycle is started.
[0045]
By using the above method, the superimposed color toner images are collectively transferred, so that color misregistration of the color image on the toner image receiver 14a, toner scattering and rubbing hardly occur, and good double-sided color with little image deterioration. Image formation is performed.
[0046]
In the above embodiment, as shown in FIG. 4, the drive roller 14 d and the support roller 14 j that are grounded together are conductive rotating rollers, and the support roller sandwiching the toner image receiver 14 a that is an intermediate transfer member. 14j faces the back surface transfer device 14g, the drive roller 14d faces the paper separation AC charge remover 14h, and the back surface transfer device 14g and the paper separation AC charge removal device 14h are arranged at a predetermined interval. A conductive rotating roller grounded to each of the back surface transfer device 14g and the paper separation AC static eliminator 14h is provided so that a discharge current flows through each rotating roller, thereby separating the paper from the back surface transfer device 14g and the paper. Interference of discharge with the AC static eliminator 14h is prevented, and each discharge is stabilized. Further, by separating the second transfer means and the separation position with a gap, the transfer material can be easily separated at the separation position. Further, the grounded conductive member facing the back surface transfer device 14g is a support roller 14j which is a conductive rotating roller, so that the toner image receiver 14a and the grounded conductive member are discharged when the back surface transfer device 14g is discharged. The problem that the electrostatic force acts and the toner image receiver 14a is in close contact with the grounded conductive member and the conveyance becomes unstable is eliminated.
[0047]
Back surface transfer as a second transfer means via the central position of a driving roller 14d as a rotation roller provided at a position where the recording paper P is separated from the toner image receiver 14a as an intermediate transfer member and the toner image receiver 14a. L1 is the distance between the center position of the support roller 14j, which is a rotation roller provided at a position facing the container 14g, and L2 is the distance between the center position of the support roller 14j and the position of the transfer device 14c, which is the first transfer means. The center of a follower roller 14e, which is a rotating roller, is provided in contact with the position of the transfer device 14c and the paper charger 150, which is a transfer material charging unit, via a toner image receiver 14a, which is an intermediate transfer member. When the distance from the position is L3, the distances L1, L2, and L3 are each preferably 20 mm or more. This prevents the interference of discharge between the paper separation AC neutralizer 14h and the back surface transfer device 14g, the interference of discharge between the back surface transfer device 14g and the transfer device 14c, and the interference of discharge between the transfer device 14c and the paper charger 150, respectively. Is done. In particular, when a non-contact corona discharger is used as the paper charger 150, the interference of discharge between the paper charger 150 and the transfer device 14c is prevented.
[0048]
Further, the interval L1 is set larger than the interval L2 (L1 ≧ L2), and the charge of the recording paper P that is strongly electrostatically attracted to the toner image receiver 14a during the transfer of the back surface transfer device 14g or the transfer of the back surface transfer device 14g. It is preferable to leak the charge of the toner image receiver 14a, which is charged at the time, to the separation position, and the distance L1 between the center position of the drive roller 14d and the center position of the support roller 14j is preferably 20 mm or more and 200 mm or less. . If the distance L1 is less than 20 mm, the recording paper P is not leaked until the charge on the toner image receiver 14a charged by the back surface transfer device 14g reaches the separation position where the paper separation AC neutralizer 14h is provided. However, when the distance L1 exceeds 200 mm, the leak is almost completely performed, but the adhesion between the recording paper P and the toner image receiver 14a is weakened, and the back surface image may be disturbed. In general, the outer diameter of the drive roller 14d is 10 to 40 mm, and the outer diameter of the support roller 14j is 6 to 20 mm.
[0049]
Further, in the volume resistivity range of the toner image receiver 14a described below, the distance L1 between the center position of the drive roller 14d and the center position of the support roller 14j is preferably 30 mm or more and 200 mm or less.
[0050]
As described above, the volume resistivity of the toner image receiver 14a as an intermediate transfer member is 10 ¹⁰ to 10 ¹⁶ Ω · cm, preferably 10 ¹² to 10 ¹⁵ Ω · cm. When the volume resistivity is less than 10 ¹² Ω · cm, particularly less than 10 ¹⁰ Ω · cm, the back surface transfer device 14g and the paper separation AC static eliminator 14h provided to face each other of the grounded conductive rotating roller. The discharge is a lightning strike on the toner image receiver 14a and damages the toner image receiver 14a. When the volume resistivity exceeds 10 ¹⁵ Ω · cm, particularly 10 ¹⁶ Ω · cm, the charge on the toner image receiver 14a charged by the back transfer device 14g is at the separation position where the paper separation AC neutralizer 14h is provided. It does not leak until it reaches, making it difficult to separate.
[0051]
The charge leakage is such that the volume resistivity of the toner image receiver 14a is 10 ¹⁰ to 10 ¹⁶ Ω · cm, preferably 10 ¹² to 10 ¹⁵ Ω · cm, and the moving speed of the toner image receiver 14a is 50 to 500 mm / cm. In the case of the range of sec, since the distance between the center position of the drive roller 14d and the center position of the support roller 14j is good when it is 30 mm or more, the outer diameter of the drive roller 14d is reduced to a small diameter of 10 to 20 mm. It is also possible to omit the separated AC static eliminator 14h. It is also possible to further promote charge leakage by installing a conductive brush or the like inscribed in the toner image receiver 14a and grounded between the drive roller 14d and the support roller 14j.
[0052]
By setting the volume resistivity value of the intermediate transfer member as described above, the intermediate transfer member is not damaged, and the charge on the intermediate transfer member by the second transfer unit is not transferred until the separation position. Leakage occurs and transfer material is easily separated.
[0053]
As described above, the volume resistance value of the toner image receiver 14a which is an intermediate transfer member is set to a predetermined value, and the conductive rotation roller is provided at each of the position facing the second transfer unit and the separation position. This stabilizes the separation of the recording paper P, which is a transfer material, but the recording paper P conveyed by the toner image receiver 14a is separated by the charge removal action by the paper separation AC discharger 14h or the curvature of the drive roller 14d. At this time, the recording paper P is slightly bent in the direction of the toner image receiver 14a due to the electrostatic adhesion between the toner image receiver 14a and the recording paper P. Therefore, as shown in FIG. 5, it is preferable to provide a conveyance unit 160 having a spur 162 and to scoop up the leading end of the recording paper P by the spur 162 and guide it to the fixing device 17.
[0054]
As described above, the transfer material separated from the intermediate transfer member is scooped up by a spur and guided to the fixing device, so that the transfer material can be conveyed to the fixing unit without disturbing the back surface toner image on the transfer material. Is done.
[0055]
Note that the paper separation AC static eliminator 14h, which is a transfer material separation means, is not necessarily provided as described in the description of the above embodiment, and the present invention is also applied to a method using curvature separation by the drive roller 14d as a separation method. Is what applies. Further, although the color image forming apparatus has been described as an embodiment of the above double-sided image forming apparatus, the present invention is not necessarily limited to this, and monochrome double-sided image formation by the same process as described in FIG. This also applies to the device.
[0056]
Furthermore, in the image forming apparatus of the present invention, in addition to the double-sided image formation for forming images on both sides of the transfer material as described in the above embodiment, one side for forming an image on only one side of the front or back surface of the transfer material. Of course, image formation can also be performed.
[0057]
【The invention's effect】
According to the first aspect, by setting the volume resistivity value of the intermediate transfer member within a predetermined range, and providing a conductive rotation roller at each of the position facing the second transfer unit and the separation position, The intermediate transfer member is not damaged, and the transfer of the back image by the second transfer unit and the separation at the separation position can be stabilized.
Further, the charge on the intermediate transfer member by the second transfer means leaks until the separation position, and the transfer material is reliably separated.
[0060]
According to the second aspect , the transfer material after being transported and separated by the intermediate transfer member is picked up by the spur and is favorably transported to the fixing unit without disturbing the toner image on the transfer material.
[0061]
According to the third aspect , the transfer material can be easily separated at the separation position.
[Brief description of the drawings]
FIG. 1 is a cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a side sectional view of the image forming body of FIG.
FIG. 3 is a diagram illustrating a toner image forming state on both sides of the image forming apparatus according to the present invention.
FIG. 4 is a diagram illustrating a positional relationship between a rotation roller provided at a position facing the first transfer unit and the second transfer unit and a rotation roller provided at a transfer material separation position from the intermediate transfer member. .
FIG. 5 is a diagram showing guidance of a transfer material to a fixing unit by a spur.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 Photosensitive drum 11 Scorotron charger 12 Exposure optical system 13 Developing device 14a Toner image receiver 14c Transfer device 14d Drive roller 14g Back surface transfer device 14h Paper separation AC neutralizer 14j Support roller 17 Fixing device 162 Spur

Claims (3)

An image forming member, a toner image forming unit that forms a toner image on the image forming member, an intermediate transfer member that can transfer the toner image on the image forming member and conveys a transfer material, A first transfer unit that transfers the toner image on the image forming body to the surface of the intermediate transfer member or the transfer material; and a second transfer unit that transfers the toner image on the intermediate transfer member to the back surface of the transfer material. And an image forming apparatus having fixing means for fixing the toner image on the transfer material.
The volume resistivity of the intermediate transfer member is 10 ¹² to 10 ¹⁵ Ω · cm,
A conductive rotation roller is provided in contact with the second transfer means via the intermediate transfer member and at a position where the transfer material is separated from the intermediate transfer member.
The interval between the center position of the rotation roller provided at the separating position and the center position of the rotation roller provided at a position facing the second transfer means is 30 mm or more.
An image forming apparatus. The image forming apparatus according to claim 1, wherein the transfer material and the intermediate transfer member and said Rukoto provided spur to convey the transfer material between the position and the fixing means for separating. The image forming apparatus according to claim 1, further comprising a transfer material separating unit that neutralizes the transfer material at a position where the transfer material and the intermediate transfer member are separated from each other .

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